In mixed crystals of Yb and Lu complexes, the Lu complex acts as a light-harvesting antenna for the Yb luminescence.

Cooperation between the coordination and crystallization processes enables a one-step selective crystallization of a Dy³⁺ complex from a Nd³⁺/Dy³⁺ mixture.

<p>A near-infrared (NIR) absorbing diradical-platinum(<sc>ii</sc>) complex solubilized in PBS by albumin can kill MCF-7 cells by the photothermal effect.</p>

Upon mixing with metal ions such as Cd-II, Tb-II, Cu-II, Ni-II, Pb-II, Zn-II, and Co-II at pH 10.0, solutions of silver nanoparticles (AgNPs) coated with calix[4]arene-p-tetrasulfonate (CAS-AgNP) exhibited multi-coloration from yellow to orange, violet, and green, depending on the metal elements present, which allowed for visual discrimination of the ions. This is contrary to the AgNP sensors exhibiting a uniform color change from yellow to red upon binding of a receptor molecules at the surface of AgNPs to an analyte. The TEM images of the samples obtained from the resultant solution showed two regions. First, a region where CAS-AgNPs assembled on the surface of the metal hydroxides. The size of the hydroxide crystals varied from 50 to 200 nm with the type of metal element present, and roughly correlated with the extinction band of the aggregated AgNPs. Second, the amorphous region in which CAS-AgNPs dispersed randomly. The difference in the amount of the crystal region and the area seemed to lead to the multi-coloration.

New bis-1,3-diketone derivatives of calix[4] arene (3-5) have been synthesized with good yields by the addition of a sodium salt of acetylacetone, 1-benzoylacetone and dibenzoylmethane to 5,17-bis-(bromomethyl)25,26,27,28- tetrahydroxycalix[4] arenes. The structural properties of the obtained compounds and their complexes have been established by means of IR, UV-Vis, NMR spectroscopy and quantum-chemical calculations. The complex ability of bis-1,3-diketones towards Al3+, Ni2+, Cu2+ and lanthanide ions (Nd3+, Eu3+, Tb3+) has been investigated by using a liquid-liquid extraction method. The UV-Vis data indicate thermodynamically favorable 1 : 1 complex formation of the ligands with Tb3+ in alkaline DMF, although the time required for the equilibration reveals the difference between calix[4] arenes bearing acetylaceton-, benzoylaceton-and dibenzoylmethane-substituents. The steric hindrance effect on ketoenol transformation is the reason for the difference. The ligand-centered emissions of Gd3+ complexes with benzoylaceton- and acetylaceton-substituted calix[4] arenes reveal them both as more convenient antennae for red and infra-red than for green lanthanide luminescence. Indeed, the benzoylaceton-substituted counterpart sensitizes Yb3+-centered luminescence to a good extent. Nevertheless, the luminescence of Tb3+ is sensitized by the acetylaceton-substituted counterpart to a better extent than that of Yb3+, while only poor red Eu3+ emission is observed under sensitization by both the ligands.

Thiacalix[4]arene-p-tetrasulfonate (TCAS) incorporated a trilanthanide(III) core to form a 3:2 Ln(3)TCAS(2) complex in aqueous solution. The self-assembly process was monitored at pH 9.5 and 7.4 by HPLC for all lanthanides except Pm-III. Self-assembly took place in three steps. First, TCAS and Ln(III) formed a 1: 1 Ln(1)TCAS(1) complex. Second, two molecules of Ln(1)TCAS(1) condensed to form Ln(2)TCAS(2). Finally, Ln(2)TCAS(2) reacted with additional Ln(III) to form Ln(3)TCAS(2). This self-assembly exhibited extremely slow kinetics and required 1-4 d to reach completion. Small amounts of minor species, including Ln(1)TCAS(1), Ln(2)TCAS(2), and Ln(4)TCAS(2), were observed depending on the Ln(III) species and pH. The generation of these species is controlled by factors such as the stability of the Ln-TCAS species, effect of coordinated water, and size of Ln(III). XAFS spectra of aqueous Gd(3)TCAS(2) solutions established the solution structure of the tri-Ln(III) cluster sandwiched by two TCAS ligands.

Solvolytic dissociation rate constants (k(d)) of bovine carbonic anhydrase II (CA) and its metallovariants (M-CAs, M = Co-II, Ni-II, Cu-II, Zn-II, and Cd-II) were estimated by a ligand substitution reaction, which was monitored by affinity capillary electrophoresis to selectively detect the undissociated CAs in the reaction mixture. Using EDTA as the competing ligand for Zn-CA, the dissociation followed the unimolecular nucleophilic substitution (S(N)1) mechanism with k(d) = 1.0 x 10(-7) s(-1) (pH 7.4, 25 degrees C). The corresponding solvolysis half-life (t(1/2)) was 80 days, showing the exceptionally high kinetic stability oft Zn-CA, in contrast to the highly labile [Zn-II(H2O)(6)](2+), where the water exchange rate (k(ex)) is high. This behavior is attributed to the tetrahedral coordination geometry supported by the tris(histidine) unit (His(3)) of CA. In the case of Co-CA, it showed a somewhat larger k(d) value (5.7 x 10(-7) s(-1), pH 7.4, 25 degrees C) even though it shares the same tetrahedral coordination environment with Zn-CA, suggesting that the d(7) electronic configuration of Co-II in the transition state of the dissociation is stabilized by the ligand field. Among M-CAs, only Ni-CA showed a bimolecular nucleophilic substitution (S(N)2) reaction path in its reaction with EDTA, implying that the large coordination number (6) of Ni-II in Ni-CA allows EDTA to form an EDTA-Ni-CA intermediate. Overall, k(d) values roughly correlated with kex values among M-CAs, with the kd value of Zn-CA deviating strongly from the trend and highlighting the exceptionally high kinetic stabilization of Zn-CA by the His(3) unit. (C) 2016 Elsevier Inc. All rights reserved.

In aqueous solution, Gd3+ and thiacalix[4]arene-p-tetrasulfonate (TCAS) form the complex [Gd(3)TCAS(2)](7-), in which a trinuclear Gd3+ core is sandwiched by two TCAS ligands. Acid-catalyzed dissociation reactions, as well as transmetalation and ligand exchange with physiological concentrations of Zn2+ and phosphate, showed [Gd(3)TCAS(2)](7-) to be extremely inert compared to other Gd complexes. Luminescence lifetime measurements of the Tb analogue Tb(3)TCAS(2) allowed estimation of the mean hydration number q to be 2.4 per Tb ion. The longitudinal relaxivity of [Gd(3)TCAS(2)](7-) (per Gd3+) was r(1) = 5.83 mM(-1) s(-1) at 20 Hz (37 degrees C, pH 7.4); however, this relaxivity was limited by an extremely slow water exchange rate that was 5 orders of magnitude slower than the Gd3+ aqua ion. Binding to serum albumin resulted in no relaxivity increase owing to the extremely slow water exchange kinetics. The slow dissociation and water exchange kinetics of [Gd(3)TCAS(2)](7-) can be attributed to the very rigid coordination geometry.

By affinity capillary electrophoresis (ACE), the thermodynamic binding constants of a sulfonamide (SA) inhibitor to bovine carbonic anhydrase II (CA) and metal mutated variants (M-CAs) were evaluated. 1-(4-Aminosulfonylphenylazo)-2-naphthol-6,8-disulfonate was used as the SA in the electrophoretic buffer for ACE. The Scatchard analysis of the dependence of the electrophoretic mobility of native CA on the SA concentration provided the binding constant to be K-b = (2.29 +/- 0.05) x 10(6) M-1 (at pH 8.4, 25 degrees C). On the other hand, apoCA showed far smaller value [K-b = (3.76 +/- 0.14) x 10(2) M-1], suggesting that the coordination of SA to the Zn-II center controlled the binding thermodynamics. The ACE of M-CAs showed the same behaviors as native CA but with different K-b values. For example, Co-CA adopting the same tetrahedral coordination geometry as native CA exhibited the largest K-b value [(2.55 +/- 0.05) x 10(6) M-1] among the M-CAs. In contrast, Mn- and Ni-CA, which adopted the octahedral coordination geometry, had K-b values that were about two orders of magnitude lower. Because the hydrophobic cavity of CA around the active center pre-organized the orientation of SA, thereby fixing the ligating NH- moiety to the apex of the tetrahedron supported by three basal His(3) of CA, metals such as Zn and Co at the center of M-CA gave the most stable CA-SA complex. However, pre-organization was not favored for octahedral geometry. Thus, pre-organization of SA was the key to facilitating the tetrahedral coordination geometry of the Zn-II active center of CA. (C) 2015 Elsevier Inc. All rights reserved.

A novel Tb(III) coordination polymer and discrete complexes have been synthesized by one-pot reaction utilising flexible tripodal Schiff base ligands, tris[2-(salicylideneamino)ethyl]amine (H3L) derivatives. Condensation of 5-methylsalicylaldehyde (5-MeSal) with tris(2-aminoethyl)amine (tren) in the presence of Tb(CF3SO3)(3) in a 3:2:1 (=5-MeSaktren:Tb(III)) molar ratio gives (TbL)-L-1, and the deprotonated ligand encapsulates the Tb(III) in its N4O3 cavity in endo-coordination. Here, the excess tren acts as a base to dissociate the proton of the ligand. Decreasing the amount of tren to a 3:1:1 ratio gives [Tb((H3L)-L-1)(2)](CF3SO3)(3). H2O. In this compound, the Tb(III) centre is coordinated by two (H3L)-L-1 ligands adopting the exo-capping mode to provide three O atoms outside the cavity of (H3L)-L-1. Replacing Tb(CF3SO3)(3) with Tb(NO3)3 in the above reaction induced a substantial structural change to coordination polymer [Tb((H3L)-L-1)(NO3)(3)DMF.1/6H(2)O](n). In this polymer, the ligand adopts an unprecedented exo-bridging coordination mode, which is the first bridging mode observed for this tripodal Schiff base ligands. Three aromatic rings of the exo-bridging ligand are close to each other by CH center dot center dot center dot pi interactions and each O atom coordinates to three different Tb(III) ions to construct a three-dimensional polymeric connection. The 3D framework has the nano-pore structure with inner walls that consisted of alternately appearing hydrophilic and hydrophobic regions. The present study shows that the tripodal Schiff base ligand can be a novel class of flexible building block to construct the Ln(III) coordination polymer. (C) 2014 Published by Elsevier Ltd.

Thiacalix[4]arenes bearing two amino groups instead of two hydroxy groups of p-tert-butylthiacalix[4]arene (2) at the distal 1,3- (5b) and proximal 1,2- positions (5c) are regioselectively synthesized via the nucleophilic aromatic substitution (SNAr) reaction of lithium benzylamide with tetra-O-methylsulfinylcalix[4]arenes 4(rctt) and 4(rcct), respectively. The SNAr reaction selectively proceeds at the benzene rings between two neighboring sulfinyl groups of a trans conformation. This is rationalized by the cooperative coordination of a methoxy group with a neighboring sulfinyl oxygen atom toward the metal ion to form a six-membered chelate, through which the amide ion attacks the aromatic nucleus. The N,O-hybrid thiacalixarenes 5b and 5c adopt cone conformations in their acetonitrile inclusion crystals. The distances between adjacent N and/or O atoms of their narrow-rim substituents indicate that the four substituents form a circular hydrogen-bond network but it is weaker than that of original thiacalixarene 2. Compound 5c also adopts a cone conformation in the guest-free crystal. This, combined with the fact that tetraaminated p-tert-butylthiacalix[4]arene 5a adopts a 1,3-alternate conformation in its guest-free crystal, indicates that the intramolecular O...N hydrogen bonds, not to mention the O...O hydrogen bond, in compound 5c play a crucial role in maintaining a cone conformation in the crystal.

Tetraaminothiacalixarene 3, bearing fouramino groups instead of the hydroxy groups of p-tert-butylthiacalix[4]arene 2, exhibits inclusion properties different fromthose of compound 2 towards small organicmolecules upon crystallisation fromneat solvents or guest solutions. X-ray crystallographic analyses reveal that nitromethane and acetonitrile are included into the cone-shaped cavity of compound 3, as is often seen in inclusion crystals of compound 2, whereas dichloromethane occupies a space between two distal benzene rings of compound 3, adopting a 1,3-alternate conformation. Acetic acid, which forms a dimer, fills a pore surrounded by four host molecules with a pinched cone conformation. Furthermore, guest-free crystals of compound 3 with a 1,3-alternate conformation absorb acetonitrile to give inclusion crystals with the same crystal structure as that obtained by the crystallisation. Thus, compound 3 flexibly changes its conformation according to the structures of guest compounds. © 2013 Taylor &amp Francis.

A capillary electrophoresis (CE)-based unique methodology for the dissociation kinetic analysis of metal complexes, capillary electrophoretic reactor (CER), is described. The basic idea of CER is using the following CE separation process as a kind of reactor for the dissociation reaction of metal complexes. In the precapillary derivatization CE of the metal complex employing an electrophoretic buffer solution without chelating reagent, the metal complex, which migrates in its isolated bands along a capillary from those of free ligand and metal ions, is exposed to an overwhelming force causing dissociation by CE resolution because of the absence of the free ligand in the electrophoretic buffer solution. This on-capillary dissociation reaction follows first-order kinetics. In order to determine the dissociation rate constant (kd) of the metal complex, it is therefore necessary to analyze the decay of the residual ratio of the complex with the increase in reaction time as first-order decay reaction. In CER, the migration time of the metal complex is considered to be equal to the reaction time of the on-capillary dissociation reaction, and the residual ratio of the metal complex can be evaluated from the peak height. The dissociation degree-time profiles for the complexes are quantitatively described as the decay of the peak height absorbance of the metal complex with the increase in migration time using the data of a series of electropherograms with different migration times. The kd of the metal complex can be estimated by analyzing it directly, readily, and accurately. An application of CER to the dissociation kinetic analysis of biomolecular complexes was also described. CER proposed here also serves as an experimental approach for such moderately slow decay kinetics with a half-life of "min." CER-related methods for faster dissociation reactions with a half-life of "sec" and slower dissociation reactions with a half-life of "hour," microchip capillary electrophoretic reactor (μCER) and ligand substitution mode CER (LS-CER) are also described. © 2013 John Wiley &amp Sons, Inc.

Dissociation kinetic analysis of a complex of Ce3+ with a polyaminocarboxylic ligand, 8-amino-2-[(2-amino-5- methylphenoxyl)methyl]-6-methoxyquinoline-N,N,N',N',-tetraacetic acid (Quin2), was studied by microchip capillary electrophoretic reactor. Dissociationrate constants, kd, of Ce3+-Quin2 complex in alkaline conditions at pH 8.3 . 9.8 were determined. The linear relationship of kd with the concentration of hydroxide ion indicates the existence of a hydroxide ion-assisted path in the dissociation reaction of Ce3+-Quin2complex in alkaline conditions. The solvolytic dissociationrate constant, and the hydroxide ion-assisted dissociation rate constant of Ce3+-Quin2 complex were determined to be 1.55 × 10.3 and 3.24 × 102 s-1 in the analysis of the dependence of kd with the concentration of hydroxide ion, respectively. © 2013 The Japan Society for Analytical Chemistry.

In aqueous solutions, thiacalixarene (TCAS) and LnIII (= NdIII, YbIII) self-assembled over a long period of time (1 d) to form 3:2 complexes LnIII3.TCAS2 in which the LnIII3 core is sandwiched between two TCAS ligands, which results in a high kinetic stability. This was not expected from the exo-coordination fashion of TCAS with the O,S,O donors found in the 1:1 complex LnIII center dot TCAS, and thus this feature was attributed to the multiple bonds between the LnIII3 core and TCAS. Our observations open an exciting possibility of designing kinetically stable LnIII complexes by using exo-type ligands as scaffolds to sandwich a multi-LnIII core rather than endo-type ones to encapsulate a LnIII core.

Heterogeneous self-assembly of thiacalix[4]arene-p-tetrasulfonate (TCAS), Ag-I, and Ln(III) (= Nd-III, Yb-III) in aqueous solutions conveniently afforded ternary complexes emitting Ln(III)-centered luminescence in the near-infrared (NIR) region. A solution-state study revealed that the Ag-I-Nd-III-TCAS system gave a complex Ag-4(I)center dot Nd-III center dot TCAS(2) in a wide pH range of 6-12. In contrast, the Ag-I-Yb-III-TCAS system gave Ag-2(I)center dot Yb-2(III)center dot TCAS(2) at a pH of around 6 and Ag-2(I)center dot Yb-III center dot TCAS(2) at a pH of approximately 9.5. The structures of the Yb-III complexes were proposed based on comparison with known Ag-I-Tb-III-TCAS complexes that show the same self-assembly behavior. In Ag-2(I)center dot Yb-2(III)center dot TCAS(2), two TCAS ligands sandwiched a cyclic array of a Ag-I-Ag-I-Yb-III-Yb-III core. In Ag-2(I)center dot Yb-III center dot TCAS(2), Yb-III was accommodated in an O-8 cube consisting of eight phenolate O- groups from two TCAS ligands linked by two S-Ag-S linkages. Crystallographic analysis of Ag-4(I)center dot Nd-III center dot TCAS(2) revealed that the structure was similar to Ag-2(I)center dot Yb-III center dot TCAS(2) but that it had four instead of two S-Ag-S linkages. The number of water molecules coordinating to Ln(III) (q) estimated on the basis of the luminescent lifetimes was as follows: Ag-4(I)center dot Nd-III center dot TCAS(2), 0; Ag-2(I)center dot Yb-2(III)center dot TCAS(2), 2.4; and Ag-2(I)center dot Yb-III center dot TCAS(2), 0. These findings were compatible with the solution-state structures. The luminescent quantum yield (Phi) for Ag-4(I)center dot Nd-III center dot TCAS(2) was 4.9 X 10(-4), which is the second largest value ever reported in H2O. These findings suggest that the O-8 cube is an ideal environment to circumvent deactivation via O-H oscillation of coordinating water. The Phi values for Ag-2(I)center dot Yb-2(III)center dot TCAS(2) and Ag-2(I)center dot Yb-III center dot TCAS(2) were found to be 3.8 X 10(-4) and 3.3 X 10(-3), respectively, reflecting the q value. Overall, these results indicate that the ternary systems have the potential for a noncovalent strategy via self-assembly of the multidentate ligand, Ln(III), and an auxiliary metal ion to obtain a highly efficient NIR-emissive Ln(III) complex that usually relies on elaborate covalent linkage of a chromophore and multidentate ligands to expel coordinating water.

We have demonstrated a facile synthesis of functionalized indocyanine green (ICG) derivatives. Heteroatom-substituted indolenine was synthesized via SNAr reaction of 5-chloro-2,4-dinitroanisole with 1,2-dimethyl-1-propenyl trimethylsilyl ether followed by reduction of the nitro groups. After the introduction of hydrophilic butanesulfonate moieties, homo-and heterocondensations with glutaconaldehyde dianilide provided symmetrical and unsymmetrical ICG derivatives, which exhibit near infrared (NIR) absorption and fluorescence emission similar to those of ICG. NIR fluorescence labeling reagent was synthesized using the amino group in the ICG derivative. The 1,3-dipolar cycloaddition with benzyl azide was performed utilizing copper nanoparticles toward a versatile method for the synthesis of NIR molecular imaging probes.

In alkaline aqueous solutions, 3,4-diaminobenzoate (H-2(L-2(PDA))) reacts with Pt-II to form a 1:2 (Pt:L) complex that intensely absorbs near-infrared (NIR) light at 713 nm (epsilon = 8.0 x 10(4) M (1) cm (1)). The absorption disappeared at pH &lt; 3 (in DMSO), showing pH-responsive switching of the NIR absorption. By comparing the NIR-absorbing behavior of this complex to that of a complex, [Pt-II(L-1(ISQ))(2)](2), containing the analogous phenylenediamine ligand [(L-1(ISQ))(2) = o-diiminobenzosemiquinonate radical], the complex can be formulated as [Pt-II(L-2(ISQ))(2)](2). The assignment of the entity was consistent with the redox and spectro-electrochemical behaviors and electronic spin resonance (ESR) spectroscopy. First, one-electron oxidation of [Pt-II(L-2(ISQ))(2)](2) formed an ESR-silent complex assignable to the dimeric complex [{Pt-II(L-2(ISQ))(L-2(IBQ))}(2)](2) [(L-2(IBQ)) = o-iminobenzoquinone form] in which the two radical centers at (L-2(ISQ))(2)(-) were antiferromagnetically coupled. Second, the one-electron reduced complex of [Pt-II(L-2(ISQ))(2)](2) exhibited an ESR signal attributed to [Pt-II(L-2(ISQ))(L-2(PDA))](3) ; 34% of the electronic spin was located at the Pt-II center rather than on the (L-2(ISQ))(2)(-) moiety. The pH-responsive switching-off of the NIR absorption was thus rationally explained by oxidation of [Pt-II(L-2(ISQ))(2)](2) to [{Pt-II(L-2(ISQ))(L-2(IBQ))}(2)](2) by the increase of the rest potential of the solution in the lower pH region. (C) 2011 Elsevier B.V. All rights reserved.

The electronic structure of a water-soluble near-infrared (NIR)-absorbing complex was determined to be singlet diradical [Pt(II)(L(ISQ))(2)](2-) [(L(ISQ))(2-) = o-diiminosulfobenzosemiquinonate radical] by X-ray diffraction and (1)H NMR spectroscopy. Cyclic voltammetry (CV) showed redox reactions of [Pt(II)(L(ISQ))(2)](2-) to give [Pt(II)(L(ISQ))(L(ISQ))(L(IBQ))](-) (E(1/2)(1) = -0.26 V vs. Fc(+)/Fc) and [Pt(II)(L(ISQ))(L(PDI))(13-) (E(1/2)(2) = -1.46 V) [(L(IBQ) = o-diiminosulfobenzoquinonate, (L(PDI))(3-) = o-phenylenediiminesulfonate]. The monoradical structure of the latter was confirmed by electron paramagnetic resonance (EPR) spectroscopy. Splitting of the reduction wave of [Pt(II)(L(ISQ))(L(IBQ))](-) in CV and the weak EPR signal suggested the formation of a dimer. Because the rest potential of the solution exceeds E(pa)(1) at pH 4.0, the decrease in the NIR absorption at pH &lt; 4.0 can be attributed to the oxidation of [Pt(II)(L(ISQ))(2)](2-) followed by dimerization.

By self-assembly in aqueous solution, calix- (CAS) and thiacalix[4]arene-p-tetrasulfonate (TCAS) formed luminescent complexes Tb(III).(CAS)(2) and Tb(III).TCAS, respectively, which were utilized as a host for cationic guests. Addition of 1-ethylpyridinium guest quenched luminescence of Tb(III).(CAS)2 in accordance with the Stern-Volmer (SV) relation with a low detection limit (D.L.) of 5.94 x 10(-8) M (S/N=3, M equivalent to mol dm(-3)). On the other hand, 1-ethylquinolinium quenched luminescence of Tb(III).TCAS most efficiently, affording a very low D.L. (6.71 x 10(-10) M). The agreement of the SV coefficients obtained with luminescent intensity (K(SV.all) = 6.74 x 10(6) M(-1)) and lifetime (K(SV.Tb) = 6.50 x 10(6) M(-1)) implied that dynamic quenching of (5)D(4) excited state of Tb(III) was predominant in the quenching processes. The quenching rate was estimated to be k(q.Tb) = 9.94 x 10(9) M(-1) s(-1), which was as fast as diffusion-limited rate. Quenching of Tb(III).(CAS)(2) was also applied to detection of NAD*, with a D.L. of 2.78 x 10(-7) M. (C) 2009 Elsevier B.V. All rights reserved.

A method employing capillary electrophoresis (CE) was developed to determine the rate constant of the very slow spontaneous dissociation of a complex species. The method uses a CE reactor (CER) to electrophoretically separate components from a complex zone and, thus, spontaneously dissociate a complex. The dissociation is accelerated by ligand substitution (LS) involving a competing ligand added to the electrophoretic buffer. The LS-CER method is validated using the dissociation of a Ti(IV)-catechin complex and EDTA as a competing ligand. There is good agreement between the spontaneous dissociation rate constant (k(d) = (1.64 +/- 0.63) x 10(-4) s(-1)) and the rate constant obtained by a conventional batchwise LS reaction (k(d) = (1.43 +/- 0.04) x 10(-4) s(-1)). Furthermore, the usefulness of the method is demonstrated using a Ti(IV)-tiron complex, for which k(d) = (0.51 +/- 0.43) x 10(-4) s(-1), corresponding to a half-life t(1/2)) of 3.8 h. Notably, a single run of LS-CER for the Ti(M complex is completed within 40 min, implying that LS-CER requires a considerably shorter measurement time (roughly equal to t(1/2)) than conventional CER. LS-CER can be widely applied to determine the spontaneous dissociation rates of inorganic diagnostic and therapeutic reagents as well as of biomolecular complexes.

A heterogeneous one-step self-assembly of Ag+, Tb3+, and thiacalix[4]arene (TCAS), of which the donor atoms S and O showed high selectivity toward Ag+ and Tb3+ ions, respectively, afforded a supramolecular cage compound, Ag-4(+)center dot Tb3+center dot TCAS(2), at the center of which an octa-oxygen cube encapsulated the Tb3+ center to completely shield it from solvent molecules.

This review article proposes a non-covalent strategy for activating separation and detection functionality; this strategy acts not through extensive organic synthesis to a covalently constructed molecular receptor, but by combining a simple molecular platform with a chemical "field" or functional component. For such a platform, we employed thiacalixarenes-calixarenes in which the bridging methylene groups are replaced with sulfur-to demonstrate usefulness of the non-covalent strategy and the multifunctionality of thiacalixarene. Thiacalixarene exhibits inherent abilities to recognize metal ions by coordinating with the bridging sulfur and adjacent phenol oxygen, as well as to include organic guest molecules in the cavity. Moreover, the non-covalent coupling of thiacalixarene provides systems with functions higher than thiacalixarene by itself. The functions described in this paper are as follows: (1) a 200-fold pre-concentration of heavy metal ions such as Cu-II, Cd-II, and Pb-II; (2) a pre-column derivatization reagent for the highly selective and sensitive determination of Ni-II, Al-III, Fe-III, and Ti-IV at sub-ppb levels with reversed-phase HPLC; (3) the self-assembled formation of a luminescence receptor with Tb-III ions for the detection of 10(-10) M levels of 1-ethylquinolinium guest; and (4) a sensing system for 10(-9) M levels of Ag-I ions by the formation of the Ag-I-Tb-III-thiacalixarene ternary supramolecular complex. These examples support the non-covalent strategy as a highly promising way to obtain functions beyond that of a molecular platform. In addition, these diverse functions indicate the multifunctionality of thiacalixarene as well as its suitability to the non-covalent strategy, since the inherent functional groups-such as the bridging sulfur, phenol oxygen, p-substituent, aromatic ring, and hydrophobic cavity-synergistically perform the functions.

A heterogeneous one-step self-assembly of Ag+, Tb3+, and thiacalix[4]arene (TCAS), of which the donor atoms S and O showed high selectivity toward Ag+ and Tb3+ ions, respectively, afforded a supramolecular cage compound, Ag+ Tb3+, at the center of which an octa-oxygen cube encapsulated the Tb3+ center to completely shield it from solvent molecules. © Springer Science+Business Media B.V. 2009.

A diterbium(III) complex was synthesized by using p-tert-butylsulfonylcalix[4]arene, which adopts a 1,2-alternate conformation, acts as a sensitive optical-antenna chromophore for UV and near-UV light and causes easy-axis magnetic anisotropy in the Tb(III) ions. The complex showed efficient If emission with a corrected quantum yield of ca. 85% even at room temperature. In addition, it showed superparamagnetic behaviour due to slow magnetic relaxation at low temperatures. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

http://www.jstage.jst.go.jp/article/bunsekikagaku/57/4/57_257/_article/-char/ja/

The compositions and photo-physical properties of luminescent ternary complexes of thiacalix[4]-arene-p-sulfonate (TCAS), Tb-III, and Ag-I ions were determined. At pH 6, Ag-2(I)center dot Tb-2(III)center dot TCAS(2) formed. Moreover, at pH 10, in the presence of a 20-fold excess of Ag-I and a 50-fold excess of WAS with respect to Tb-III, Ag-2(I)center dot Tb-III center dot TCAS(2) formed as the main luminescent species. The structure of these complexes was proposed: two WAS ligands are linked by two S-Ag-I-S linkages to adopt a double-cone supramolecular structure. Furthermore, each Tb-III. ion in the former complex accepts O-, S, O- donation, whereas in the latter, the Tb-III. center accepts eightfold O- donation. The luminescence quantum yield (phi) of Ag-2(I)center dot Tb-2(III)center dot TCAS(2) (0.16) was almost equal to that of Tb-III.TCAS, but the luminescence lifetime tau of the former (= 1.09 ms) was larger than that of the latter. For Ag-2(I)center dot Tb(III center dot)TCAS(2), the yield phi (=0.11.) was small, which is attributed to the low efficiency of photosensitization (eta=0.11). However, the T value (4.61 ms) was exceptionally large and almost equal to the natural luminescence lifetime of Tb-III. (4.7 ms), which is due to the absence of coordinating water molecules (q=0.1). This is compatible with the proposed structure in which the Tb-III. ion is shielded by a supramolecular cage that expels coordinated water molecules responsible for luminescence quenching.

Inclusion behavior of negatively charged host molecules, tiliacalix[4]arene-p-tetrasulfonate (TC4AS) and [6]arene-p-hexasulfonate (TC6AS), toward (ferrocenylmethyl)trimethylammonium (FcCH(2)NMe(3)(+)), hydroxymethylferroceiie (FcCH(2)OH), ferrocenecarboxylic acid (FcCOOH), and 1,1'-ferrocenedicarboxylic acid (Fc(COOH)(2)) was studied in aqueous solutions (pH 7.0) with cyclic voltammetry. Upon increasing the concentration of TC4AS to 4-fold of each guest, the anodic peak current density (j(p,a)) decreased, suggesting inclusion of the ferrocenyl guests in TC4AS. Also oxidation half-wave potential (E-1/2) of FcCH(2)N Me-3(+), FcCH(2)OH, and FcCOOH was shifted to cathodic direction, showing preferential inclusion of the oxidative state. Inclusion of neutral guests such as FcCH(2)OH and Fc(+)COO(-) implies that hydrophobic interaction between TC4AS and the guests is the chief driving force for formation of host-guest assembly. The decrease of E-1/2 for each guest was in the order: FcCH(2)NMe(3)(+) &gt; FcCH(2)OH &gt; FcCOOH, suggesting that electrostatic interaction con trols the preference toward oxidative form of the guest. Dicarboxylic Fc(COOH)(2) showed decrease of j(p.a) but increase of E-1/2 upon inclusion, suggesting TC4AS preferred reduced form Fc(COOH)(2) to oxidized form Fc(+)(COO-)(2). TC6AS behaved similarly to TC4AS but with larger decrease in of E-1/2 and j(p,a). The larger shift of E-1/2 for inclusion of FcCOOH, the oxidative form of which is also neutral (Fc(+)COO(-)), than that attained with TC4AS endorses main role of hydrophobic interaction between TCnAS (n = 4, 6) and ferrocenyl guest molecules. Having the most preferential electrostatic interaction, kinetically stable complex was formed between TC6AS and FcCH(2)NMe(3)(+). (C) 2007 Elsevier B.V. All rights reserved.

The conformational behaviors of all four stereoisomers [5(rctt), 5(rcct), 5(rtct), and 5(rccc)] of tetra-O-methylsulfinylcalix[4]arene were studied by the H-1 NMR spectroscopic method. Variable-temperature (VT) NMR experiments of 5(rctt), 5(rcct), and 5(rtct) revealed that each compound adopted the same conformation as that in the crystals at low temperatures and exhibited a self-exchange between the two equivalent species of this conformation at elevated temperatures. The values of the activation enthalpy Delta H-double dagger for the self-exchange were similar (similar to 70 kJ mol(-1)). Further, the activation entropy Delta S-c was more important for 5(rtct) (-40 J mol(-1) K-1) than for 5(rctt) (-5 J mol(-1) K-1) and 5(rcct) (-7 J mol(-1) K-1); consequently, the exchange rate of 5(rtct) was 150-180 times less than that of the other isomers at 273 K. On the other hand, 5(rccc) was in an equilibrium state between cone and partial-cone conformers at 253 K with the molar ratio being 85:15, which was in reasonable agreement with the relative stability between the two conformers calculated by the ab initio molecular orbital method.

This review deals with the formations, structures, and properties of transition metal and lanthanide clusters supported by thiacalix[n]arene and its oxidized derivatives, sulfinylcalix[4]arene and sulfonylcalix[4]arene. Each thiacalix[n]arene possesses donor atoms both on the lower rim position (phenol oxygen atoms) and on the cyclic framework itself (-S-, -SO-, or -SO2-), and behaves as a multidentate multi-nucleating ligand to support the formation of a phenoxo-bridged cluster core. For first row transition metals, calix[4]arenes offer a platform for assembling the metal ions via four fac-tridentate coordination sites, and planar tri- and tetra-nuclear clusters are formed. A larger and more flexible thiacalix[6]arene could bind up to five metal ions inside the coordination cavity formed when it adopts the pinched cone conformation. Sulfonylcalix[4]arene shows a strong affinity to lanthanide ions through phenoxo and sulfonyl oxygen donors, and yields a variety of cluster compounds involving di-, tetra-, octa-, and dodeca-nuclear cores, achieved by controlled synthetic conditions. (C) 2007 Elsevier B.V. All rights reserved.

A systematic investigation was conducted on the structures of tetra- and di-nuclear copper(II) complexes with three stereoisomers of sulfinylcalix[4]arenes (H4L), the isomerism of which is determined by the disposition of the sulfinyl oxygen with respect to a reference oxygen from the mean plane containing four sulfur atoms. The sulfinylcalix[4]arene with a trans-cis-trans S = O orientation (H4Lrtct) reacted with Cu(OAc)(2) to form [Cu(II)4(L-rtct)(OAc)(3)(mu-MeO)(MeOH)] (1), in which Lrtct4- adopts a cone conformation to afford tetrakis fac-tridentate coordination through four phenoxo oxygens and four sulfinyl groups giving a square Cu-4(II) core. Ligands H4Lrccc and H4Lrctt having cis-cis-cis and cis-trans-trans configurations formed [Cu-4(II)(L-rccc)(OAc)(3)(mu-OH)] (2) and [Cu-4(II)(L-rctt)(OAC)(3)(mu-OH)] (3), respectively, which have common features, such as a cone-type conformation of L4-, tetrakis fac-tridentate coordination fashion, and tetra-copper(II) core in a square-pyramidal geometry. The similarities among 1-3 clearly show that sulfinylcalix[4]arenes can coordinate to Cu-II in a fac-tridentate fashion via a donor atom X (O or S) from a sulfinyl group and two flanking phenoxo O-s(-) and that X is simply determined by the X-Cu distance. Using [Cu(acac)(2)] as a copper(II) source, H4L(rctt) formed [Cu-2(II)(H2Lrctt)(2)] (4), suggesting the significance of auxiliary ligand for bridging copper(II) centers to assemble the core, that is, the acetato ligands in complexes 1-3 are needed to form the core structure. Metal-metal interactions were investigated by means of magnetic susceptibility, and it was found that both ferro- and antiferromagnetic interactions occur in tetracopper(II) complex 3. In contrast, antiferromagnetic interaction is present in dicopper(II) complex 4.

New di- (2) and tetracarboxylate ligands (4) were prepared on a sulfonylcalix[4]arene platform by O-alkylation of thiacalix[4]arene with ethyl bromoacetate, followed by hydrolysis of the ester function and oxidation of the sulfide bridges. The sulfonyl-based ligands 2 and 4 formed luminescent 1:1 complexes with terbium(III) ion having higher luminescent quantum yield (Phi = 0.29, and 0.28(7), respectively) than 1:1 complexes of the corresponding thiacalix[4]arene-based di- (1) and tetracarboxylate ligands (3) (Phi = 0.03(8) and 0.00(3), respectively), implying higher efficiency of sulfonyl ligands (2 and 4) than those of thia ligands (1 and 3) in the energy transfer process. (c) 2006 Elsevier Ltd. All rights reserved.

A dodecaholmium wheel of [Ho-12(L)(6)(mal)(4)(AcO)(4)(H2O)(14)] (1; mal=malonate) was synthesized by using p-tert-butylsulfonylcalix[4]arene (H4L) as a cluster-forming ligand. The wheel consists of three fragments of mononuclear A(3-) ([Ho(L)(mal)(H2O)](3-)), trinuclear B3- ([Ho(H2O)(2) (mal)(Ho(L)(AcO))(2)](3-)), and C3+ ([Ho(H2O)(2)](3+)), and an alternate arrangement of these fragments (A(3-)-C3+-B3--C3+-A(3-)-C3+-B3--C3+-) results in a wheel structure. The longest and shortest diameters of the core were estimated to be 17.7562(16) and 13.6810(13) angstrom, respectively, and the saddle-shaped molecule possesses a pocketlike cavity inside.

Dinuclear and cubane-shaped lanthanide cluster complexes containing Eu-III and Tb-III were synthesized by step-by-step construction using p-tert-butylsulfonylcalix[4]arene as a cluster-forming ligand. The sulfonylcalixarene adopts a pinched-cone conformation in the dinuclear complexes and a cone conformation in the cubane complexes. Because the calixarene has a large pi-conjugate system expanding over the entire molecule, it behaves as a good antenna chromophore for UV and near-UV light, and a slight conformational change of the calixarene ( from cone to pinched-cone and vice versa) has an effect on the energy levels of excited S-1 and T-1 states. As a result, selectivity is observed in the luminescent properties of dinuclear and cubane-shaped systems of Eu-III and Tb-III.

Square-planar tetranuclear clusters [M-4(L)(AcO)(4)(mu(4)-OH)](-) (M = Mn-II, Co-II, and Ni-II) are synthesized using tetra-anionic p-tert-butylsulfonylcalix[4]arene (L4-) as a cluster-forming ligand. Three complexes are crystallographically isostructural, being crystallized in the triclinic crystal system with space group Pi. The calix[4]arene acts as a tetrakis fac-tridentate ligand through four phenoxo and four sulfonyl oxygen atoms to form square arrangement of four metal ions, which are further bridged by four chelating acetate ions and one hydroxo ion in a mu(4) manner to complete the hexacoordination of each metal center. Although the whole molecule of each complex is crystallographically independent, the molecule is highly symmetrical with a pseudo-four-fold axis lying on the mu(4)-OH- group. The tetranuclear clusters are stable enough to maintain the core structures even in highly dilute solution (approximate to 10 mu m), which was confirmed by mass spectroscopic study, however, bridging acetates were easily exchanged by other carboxylate chelates to form derivatives such as [M-4(L)(BzO)(4)(OH)](-). Metal-metal interactions were investigated by means of magnetic susceptibility, and it was revealed that both ferro- and antiferromagnetic interactions occur in the Ni-II complex depending on the bridging angles of Ni-O-Ni. (c) Wiley-VCH Verlag GmbH & Co.

Contrary to hexathiacalix [6] arene (H6L6S) forming [Cu-10(L-6S)(2)]-type spherical decacopper(II) complex, trithiacalix[6]arene (H6L3S), in which three sulfur bridges of H6L6S are replaced with methylenes in an alternate manner, affords nanosized wheel-shaped octanuclear complex [Cu-8(H2L3S)(4)] consisting of four [Cu2H2L3S] units.

Amberlite XAD-7 resin was impregnated with p-tert-butylsulfinylcalix[4]arene. Niobium(V) was collected on the impregnated resin in yields of more than 90% around pH 5.4, whereas tantalum(V) was negligibly collected. The collected niobium(V) was desorbed with 9 M sulfuric acid nearly quantitatively, hence the separation of niobium(V) from tantalum(V) was successfully achieved. (c) 2005 Elsevier B.V. All rights reserved.

Even though it was obtained in poor yield, p-tert-butylthiacalix[8]arene (TC8A) has been synthesized as a new member of thiacalix[n]arenes by the terephthalate-induced cyclization of a mixture of acyclic oligomers, which was obtained by the reaction between p-tert-butylphenol and sulfur with CaO in ethylene glycol/diphenyl ether system. Slow evaporation of the chloroform solution of TC8A afforded guest-free crystals consisting of TC8A itself. The close-packed crystal structure of TC8A resembles that of p-tert-butylcalix[8] arene (C8A) closely, containing a plated loop molecular structure. © Springer 2005.

Even though it was obtained in poor yield, p-tert-butylthiacalix[8]arene (TC8A) has been synthesized as a new member of thiacalix[n]arenes by the terephthalate-induced cyclization of a mixture of acyclic oligomers, which was obtained by the reaction between p-tert-butylphenol and sulfur with CaO in ethylene glycol/diphenyl ether system. Slow evaporation of the chloroform solution of TC8A afforded guest-free crystals consisting of TC8A itself. The close-packed crystal structure of TC8A resembles that of p-tert-butylcalix[8]arene (C8A) closely, containing a plated loop molecular structure.

A microchip capillary electrophoretic reactor has been proposed and successfully demonstrated in the direct evaluation of the solvolytic dissociation rate constant of the complex of Ce3+ with a polyaminocarboxylic ligand, 8-amino-2-[(2-amino- 5-methylphenoxyl) methyl]-6-methoxyquinoline-N, N, N', N'-tetraacetic acid.

X-ray diffraction revealed a single crystal of a Cu(II) complex of p-tert-butyldithiacalix[4]arene 5 (H4L) to be [CU3(HL)(H2L)(AcO)], in which three Cu(II) ions are sandwiched by two calixarene ligands including different guest molecules, CHCl3 and hexane, in each cone-shaped cavity.

A rapid column-adsorption method has been developed for concentrating traces of copper, cadmium, and lead in water prior to their determinations by graphite-furnace atomic-absorption spectrometry. The adsorbent used was prepared by loading a strongly basic anion-exchanger QAE-Sephadex A-25 (50 mg) with thiacalix[4]arenetetrasulfonate (20 mumol). Two-hundredfold preconcentration of the analyte elements was achieved by passing 100 mL of sample solution (pH 8.0) through a column packed with the adsorbent (6 min i.d.x7 min high) at a flow rate of 10 mL min(-1) and by the subsequent elution with 500 muL of aqueous nitric acid solution (1 mol L-1). The practical applicability of the proposed method was evaluated by analyzing certified reference seawater samples.

Sulfonylcalix[4]arenetetrasulfonate (SO(2)CAS) has been examined as a pre-column chelating reagent for ultratrace determination of metal ions by ion-pair reversed-phase high-performance liquid chromatography with spectrophotometric detection. Metal ions were converted into the SO(2)CAS chelates in an acetic buffer solution (pH 4.7). The chelates were injected onto a n-octadecylsilanized silica-type Chromolith(TM) Performance RP-18e column and were eluted using a methanol (50 wt.%)-water eluent (pH 5.6) containing tetra-n-butylammonium bromide (7.0 mmol kg(-1)), acetate buffer (5.0 mmol kg(-1)), and disodium ethylendiamine-N,N,N',N'-tetraacetate (0.10 mmol kg(-1)). Under the conditions used, Al(III), Fe(III), and Ti(IV) were selectively detected among 21 kinds of metal ions [AI(III), Ba(11), Be(II), Ca(II), Cd(II), Co(II), Cr(III), Cu(11), Fe(111), Ga(III), Hf(IV), In(III), Mg(II), Mn(II), Mo(VI), Ni(II), Pb(11), Ti(IV), V(V), Zn(II), and Zr(IV)]. The detection limits on a 3sigma blank basis were 8.8 nmol dm(-3) (0.24 ng cm(-3)) for Al(III), 7.6 nmol dm(-3) (0.42 ng cm(-3)) for Fe(III), and 17 nmol dm(-3) (0.80 ng cm(-3)) for Ti(IV). The practical applicability of the proposed method was checked using river and tap water samples. (C) 2003 Elsevier B.V. All rights reserved.

2,14-Dithiacalix[4]arene 34 was conveniently prepared in 16% yield by acid-catalyzed cyclocondensation of 2,2'-thiobis[4-tert-butylphenol] with formaldehyde. The present method also afforded the first isolation of the analogues with six and eight phenol units, 3(6) (10%) and 3(8) (5%), respectively. Solvent extraction showed that 34 had high selectivity toward Cu2+ ion at pH 5.5 by coordination of the bridging sulfur with cooperative donation of the adjacent phenolate oxygens. (C) 2003 Elsevier Ltd. All rights reserved.

Inclusion abilities of water-soluble thiacalix[4]arenetetrasulfonate (3) and mono-O-carboxy-methylated derivatives 5 and 6 toward water-miscible organic molecules such as alcohols, ketones, and nitriles in water were investigated by H-1 NMR. The limit chemical shift change of the guest upon inclusion in the host suggested that the hosts regioselectively encapsulate the guests from the side of aliphatic moiety. Large guests such as pentan-1-ol showed folding of the alkyl chain to be included inside the cavity. On the other hand, mono-O-substituted 6 included a guest molecule less deep in the cavity than 3 did. Binding constants ( K) of 3 toward guest molecules increased with hydrophobicity of the guest, suggesting that hydrophobic effect plays a main role for the complexation. On the contrary, mono-O-carboxymethyl derivatives 5 and 6 showed the opposite dependency of stability on hydrophobicity; higher affinities toward less hydrophobic guests. Among the guests examined, the smallest entities such as CH3OH and CH3CN were best included in 5 with the highest binding constant ever reported (K &gt; 10(2) M-1). It was concluded that introduction of the carboxymethyl group into one of the phenolic OH of thiacalix[4] arene led to tuning of the cavity shape for stereospecific inclusion of small guests. The tuning of cavity by the O-alkylation was actually confirmed by X-ray crystal analysis of a complex of 5 with diethyl ketone.

Using p-tert-butylthiacalix[6]arene (H6L) as a clustering ligand, five cluster complexes having Co-5(II) (2), Ni-4(II) (3) and (MNi4II)-Ni-II (M = COII (4), Mn-II (5), and Cu-II (6) cores were synthesized. In all the complexes except for 3, a pinched conic L6- acts as a pentanucleating ligand that involves a similar pyramidally arranged cluster core. Each mixed metal complex 4-6 involves four tetragonally arranged Ni-II ions occupying the basal plane of the pyramid and a M-II ion placed at the apex position. In 3, H2L4- is in a cone conformation and the four Ni-II ions are arranged on the donor surface of H2L4- in a zigzag manner. The mixed metal complexes 4-6 are synthesized by reacting 3 and the appropriate M(AcO)(2) in a 1: 1 ratio with a novel metal-induced core rearrangement occurring. In this reaction, the insertion of a M-II ion at the apex position forces the calixarene to take a cone conformation and the Ni-4(II) array rearranges to form a tetragonal cluster.

The solvent-extraction behavior of 2,8,14,20-tetrathiacalix[4]arene 2 was compared with those of 2-monothiacalix[4]arene 3 as well as linear tetramer (4) and dimer (5) of p-tert-butylphenol linked by sulfide bonds at the ortho positions in order to clarify the effect of the cyclic and acyclic structure and the number Of Sulfide bonds. The linear tetramer 4 showed almost the same extraction behavior as that of the cyclic counterpart 2, showing the dependence oil the pH for the extraction of Co(II), Ni(II), Cu(11), and Zn(II) ions. On the other hand, monothiacalix[4]arene 3 and acyclic dimer 5 showed far inferior extractability as compared to the former two, suggesting that the number of sulfide linkages, rather than the cyclic/acyclic structure, is predominant to determine the extractability. An equilibrium study on the extraction behavior of open-chain 4 (H4L) toward Co(H), Cu(II), and Zn(II) ions revealed that the composition of the extracted species can be written as [M-i(H2L)(i)] (i; integer), as was the case obtained by cyclic 2. Furthermore, the extraction constants of 4 for those metal ions were almost the same as those obtained by 2. The similarity of the extraction behavior between 2 and 4 suggests that the acyclic tetramer 4 may act as a pseudo-thiacalix[4]arene to have the same complexation manner as cyclic 2 by the O-,S,O--donor set, in which the presence of a phenol unit flanked by sulfide bonds at the both ortho positions is essential. In other words, the effect of the bridging sulfide in the phenol oligomers may be reasonably explained by the electron-withdrawing effect of the sulfide moiety to provide the phenol unit with a higher acidity to form [M-2(H2L)(2)]-type complexes having a double-cone structure stabilized by two sets of O-,S,O--ligated metal bridges.

All four stereoisomers of p-tert-butylsulfinylcalix[4]arene [4(rccc), 4(rcct), 4(rctt), and 4(rtct)], arising from the disposition of the four sulfinyl groups with respect to the mean plane of the four bridging sulfur atoms, have been prepared via oxidation of p-tert-butylthiacalix[4]arene (2) or its tetra-O-benzyl ethers 5 of defined conformations. Thus, treatment of 2 with 4.4 molar equiv of NaBO3.4H(2)O gave the rtct and rctt isomers in 27% and 17% yields, respectively, while oxidation of cone 5 (5(C)) and partial cone 5 (5(PC)) proceeded stereoselectively to give, after debenzylation of the resulting tetrasulfoxides 12 and 15, the rccc and rcct isomers in 56% and 28% yields, respectively, based on 5. The sulfinylcalix[4]arenes 4 were treated with iodomethane in the presence of a base to give the corresponding tetramethyl ethers 16, the structures of which in regard to the disposition of the sulfinyl groups and the conformation of the phenol units were determined by X-ray crystallography. Also reported is the synthesis of all four conformational isomers of tetra-O-benzyl ether of 2 (5(C), 5(PC), 5(1,2-A), and 5(1,3-A)).

Thiacalix[4]arenetetrasulfonate (TCAS) has been examined as a pre-column chelating reagent for the determination of trace metal ions by kinetic differentiation mode (KD) ion-pair reversed-phase high-performance liquid chromatography (HPLC) with spectrophotometric detection. Among 14 kinds of common metal ions tested here, viz. Al(III), Ca(II), Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Hg(II), Mg(II), Mn(II), Ni(II), Pb(II), V(V), and Zn(II) ion, only Ni(II) ion was detected as the WAS chelate in the HPLC separation stage in spite of TCAS forming the chelates with various metal ions except for Al(III), Ca(II), and Mg(II) at the pre-column chelation stage. The undetected metal-TCAS chelates seemed to be dissociated on an HPLC column where no added TCAS was present in the mobile phase because of their kinetic unstability. The calibration graph for Ni(II) ion gave a wide linear dynamic range (40-20,000 nM) with the very low detection limit (DL) (3sigma base-line fluctuation) to be 5.4 nM (0.32 ng ml(-1)). The practical applicability of the KD-HPLC method with TCAS was demonstrated with the determination of trace Ni in coal fly ash. (C) 2002 Elsevier Science B.V. All rights reserved.

A chelating adsorbent for heavy metal ions has been prepared by loading an anion-exchange resin with thiacalix[4]arenetetrasulfonate (TCAS). Batchwise extraction studies have revealed a high adsorption ability of the TCAS-loaded resin toward heavy metal ions with high selectivity. The present resin strongly retained the heavy metal ions tested here [CO(II), Ni(II), Cu(II), Zn(II), Cd(II), Hg(II), and Pb(II)] in a slightly acidic to neutral pH region, while no adsorption was observed for alkaline earth metal ions, Mg(II) and Ca(II), in this pH region. These adsorption characteristics of the present resin should be ascribed to the contribution of the bridging sulfur of the loaded WAS to selectively coordinate to metal ions categorized to be soft to intermediate Lewis acids by the Hard and Soft Acids and Bases (HSAB) rule. A continuous column adsorption system with the present resin allowed the selective and almost quantitative (more than 99.98%) removal of heavy metal ions.

The Pd(II) complexes of thiacalix[4] aniline (TCAn) and thiacalix[4] arene (TCAr), in which four aniline and phenol units are linked by four sulfides at the o,o'-positions, respectively, were prepared by simply heating the ligands with Pd(II)(OAc)(2) in CHCl3 or benzene at reflux and structurally characterized by X-ray diffraction methods. In TCAn, two thiacalix ligands adopting a pinched-cone conformation are fused at the narrower rims to coordinate to two Pd(II) ions by amide NH- and the adjacent S atoms. In contrast for TCAr, two ligands coordinate to two Pd(II) ions with phenolate O- and thioether S atoms at the narrower rims. Four sets of hydrogen bonding between the O- and free OH cause a deviation of the Pd(II) centers from the square coordination plane and also lead the conformation of the calix to be more cone-like to provide enough space to accommodate guest CH3CN molecules.

The energy-transfer luminescence of complexes of Tb3+ with calix- (CAS), thiacalix- (TCAS), and sulfonyl-calix[4]arene-p-tetrasulfonates (SO(2)CAS), in which four p-phenolsulfonates are jointed by -CH2-, -S-, and -SO2-, respectively, was applied to an ultratrace determination of the Tb3+ ion. Based on the complexation behavior of each calix ligand, a determination procedure was established. A time-resolved measurement was conveniently employed to separate the background fluorescence from the luminescence of the calix-Tb3+ complexes. An improved sensitivity was attained by sulfur-bridged calixes, WAS and SO(2)CAS, as compared to CAS, owing to the photophysical properties of the Tb3+-complexes. The detection limits for Tb3+ ion by CAS, TCAS, and SO(2)CAS ligands were estimated to be 8.2 X 10(-10) mol dm(-3) (131 ppt), 2.0 x 10(-10) mol dm(-3) (32 ppt), and 2.3 X 10(-10) mol dm(-3) (37 ppt) at S/N = 3, respectively. In terms of the selectivity, the effect of diverse coexisting ions on the luminescence intensity of the Tb3+ Complexes was studied. The luminescence of the WAS complex was interfered by the presence of a 5-fold amount of other lanthanide ions, while that of the SO(2)CAS complex was more tolerant for those metal ions, allowing the presence of as much as 50 to 100-fold amounts. Also, 10 to 1500-fold amounts of other common ions were tolerated by using SO(2)CAS. Thus, SO(2)CAS was proved to be a practical reagent for determining the Tb3+ ion at the sub-ppb level.

p-tert-Butylthiacalix[6]arene extracted soft to intermediate metal ions to the same extent as the [4] counterpart did, indicating that the O- S,O--tridentate binding manner rather than the effect of ring extension is critical to determine the complexing ability.

The one-step method for the synthesis of p-tert-butylthiacalix[n]arenes TCnAs (n=4 and 6) by reacting p-tert-butylphenol I with elemental sulfur in the presence of a base was advantageously replaced by a two-step procedure in which a sulfur-bridged linear dimer of I was prepared first to use as the starting material for the cyclo-condensation with sulfur to greatly improve the yields of TC4A (83%.) and TC6A (5.3%). The present dimer method allowed the isolation of TC8A in an appreciable amount (4.3%) for the first time. (C) 2002 Elsevier Science Ltd. All rights reserved.

X-Ray crystal structures of the mono-, di-, and tri(p-tert-butyl)-substituted thiacalix[4]arenes (TC4As; 1, 2, and 3, respectively) have been determined. TC4As 1-3 adopt a cone conformation and form dimeric self-inclusion units in such a manner that phenol moieties are inserted into the cavity of each molecule. In all the crystal structures of 1-3, lateral face-to-face interactions exist between the phenol rings that do not bear a tert-butyl substituent, and seemingly, this molecular assembly stabilizes the formation of self-inclusion. TC4As 1 and 2 adopt a cone conformation with C-2 symmetry, leading to the formation of rim-to-rim intermolecular hydrogen bonds so as to link the dimeric units up and down. On the other hand, 3 adopts a regular cone conformation with C-4 symmetry to form cyclic hydrogen bonds within the rim part of TC4A.

Inclusion ability of thiacalix[4]arenetetrasulfonate (TCAS) toward water-miscible organic molecules such as alcohols, ketones, cyclic ethers, and so on was studied by salting-out of the inclusion complex. NMR spectra of the recovered precipitates showed size selectivity to include the guest molecules. X-ray crystallographic analyses of TCAS salts including acetone and 1,4-dioxane suggested that guests are retained with the aid of cation coordination and H-bonding.

X-Ray crystal structures of the mono-, di-, and tri(p-tert-butyl)-substituted thiacalix[4]arenes (TC4As 1, 2, and 3, respectively) have been determined. TC4As 1-3 adopt a cone conformation and form dimeric self-inclusion units in such a manner that phenol moieties are inserted into the cavity of each molecule. In all the crystal structures of 1-3, lateral face-to-face interactions exist between the phenol rings that do not bear a tert-butyl substituent, and seemingly, this molecular assembly stabilizes the formation of self-inclusion. TC4As 1 and 2 adopt a cone conformation with C2 symmetry, leading to the formation of rim-to-rim intermolecular hydrogen bonds so as to link the dimeric units up and down. On the other hand, 3 adopts a regular cone conformation with C 4 symmetry to form cyclic hydrogen bonds within the rim part of TC4A.

The acid-base properties of sulfur-bridged calixarenes, thiacalix[4]arenetetrasulfonate (4) and its sulfonyl analogue (5), have been investigated via potentio- and spectrophoto-metric studies, comparing them with the conventional methylene-bridged calix[ 4] arenetetrasulfonate (3). The titration curves revealed the acidity of the phenolic OH groups in the calix[4]arenes 3-5 to be in the order: 3 &lt; 4 &lt;&lt; 5. In particular, the oxidation of the bridging sulfur to sulfone strongly enhanced the acidity of the sulfur-bridged calix[ 4] arene; the pK(a,n) values (n = 2-4) of the sulfone-bridged 5 were lower by 7 pK units than those of the sulfide-bridged 4. The effects of the linkage groups on the acidity of the calix[4]arenes are discussed from the structural and electronic viewpoints, such as the macrocyclic ring size, the hydrogen bonding manner, and the resonance of the linkage moiety.

Treatment of calix[4]arenes with 1,3-dichloro-1,1,3,3-tetraisopropyldisiloxane using imidazole as a base yielded O,O'-bridged calixarenes in excellent yields, which were subsequently treated with an alkyl halide/base to give O",O'''-dialkylated products in high yields. These were, in turn, amenable to fluoride-promoted quantitative desilylation, thus providing an efficient method for the net proximal dialkylation of calix[4]arenes at the lower rim. (C) 2002 Elsevier Science Ltd. All rights reserved.

Thiacalix[4]aniline (4), a cyclic tetramer of p-tent-butylaniline bridged with four sulfides, extracted Au(III) and Pd(II) ions specifically from acidic solutions among 41 metal ions including soft metal ions such as Hg(II), Cd(II), Zn(II), Pb(II), and Cu(II).

Heteroatom-bridged calixarenes have been confined into the unexplored frontier of the vast realm of the calixarene chemistry because of their synthetic difficulty. Since we found facile one-step synthesis of thiacalix[4]arene, in which four methylene bridges of calix[4]arene are replaced by four sulfides, we have been engaged in the study on this new molecular platform regarding the improvements for the synthetic procedures, structural analyses, chemical modifications, and functional developments. In this review are described the results of our own study to demonstrate the potentials over the limits of the conventional calixarenes, putting emphasis on the indispensable role of the bridging sulfur. Highlighted examples are (1) enlargement of the calix skeleton to provide larger cavity, (2) ready oxidizability to sulfoxide and sulfone for providing new members of S bridged calixarenes, and (3) coordination to specific metal ions controlled by the oxidation state of S. These indicate a hopeful future for the thiacalixarene platform in the forthcoming applications to functional molecular devices.

Heteroatom-bridged calixarenes have been confined into the unexplored frontier of the vast realm of the calixarene chemistry because of their synthetic difficulty. Since we found facile one-step synthesis of thiacalix[4]arene, in which four methylene bridges of calix[4]arene are replaced by four sulfides, we have been engaged in the study on this new molecular platform regarding the improvements for the synthetic procedures, structural analyses, chemical modifications, and functional developments. In this review are described the results of our own study to demonstrate the potentials over the limits of the conventional calixarenes, putting emphasis on the indispensable role of the bridging sulfur. Highlighted examples are (1) enlargement of the calix skeleton to provide larger cavity, (2) ready oxidizability to sulfoxide and sulfone for providing new members of S bridged calixarenes, and (3) coordination to specific metal ions controlled by the oxidation state of S. These indicate a hopeful future for the thiacalixarene platform in the forthcoming applications to functional molecular devices.

New analogues of calix[4]arenetetrasulfonate (1) were prepared, in which the methylene bridges are replaced by S (2) and SO2 (3). The complexation ability of these calixarene ligands 1-3 toward Tb3+ ion and luminescence properties of the resulting complexes were examined. All the ligands formed complexes with lanthanide ions (Pr3+, Sm3-. Eu3+, Tb3+ and Dy3+), among which the Tb3+ complex exhibited strong energy transfer luminescence. The pH dependence of the luminescence intensity suggested that the analogues 2 and 3 possess higher complexation ability towards Tb3+ than the parent 1, which should be ascribed to the higher acidity of the phenolic OH groups as well as the coordinating ability of the bridging groups S and SO2. The composition of the complexes of 2 and 3 was determined to be Tb(3+.)2 and Tb(3+.)3 by a molar ratio method. The photophysical properties such as emission lifetimes (tau) and quantum yields (Phi) of the complexes were estimated. Both Tb(3+.)2 and Tb(3-.)3 gave comparable tau values (0.7 ms), which are larger than that of Tb3+.(1)(2) (0.6 ms). Comparison of their lifetimes in D2O solution suggested that Tb(3+.)2 and Tb(3+.)3 have four to five coordinated water molecules responsible for quenching. On the other hand, complex Tb(3+.)2 gave the largest Phi value (0.15), whereas Tb3+.(1)(2) and Tb(3+.)3 gave very close Phi values (0.12 and 0.13, respectively). The results of this study showed that thiacalix[4]arenctetrasulfonate 2 and the sulfonyl analogue 3 are promising candidates for the scaffold to construct luminescence devices from the viewpoint of the higher complexation ability and luminescent performance.

Practical methods for the synthesis of sulfinyl-(5,6) and sulfonylcalix[4]arenes (7,8) were provided by the selective oxidation of thiacalix[4]arenes (3,4) with controlled amounts of an oxidant such as NaBO3 or hydrogen peroxide under mild conditions. The coordination ability of thiacalix[4]arene 4 and the sulfinyl and sulfonyl analogs (6,8) toward a wide variety of metal ions was investigated by solvent extraction and compared to that of the conventional methylene-bridged calix[4]arene 2. It was shown that the metal-ion selectivities of the sulfur-containing ligands 4, 6, and 8 were controlled by the oxidation state of the bridging sulfur moiety, which was best understood based on the hard and soft acid-base (HSAB) principle by assuming the critical role of the bridging groups in coordination to the metal center. Thus, 4 preferred soft metal ions by binding with S, while 8 did hard ones by ligating with sulfonyl O in addition to the adjacent two phenoxide oxygens, respectively. In good accordance with this hypothesis, 6 could bind to both hard and soft metal ions by using sulfinyl O and S, respectively. These made sharp contrast to the parent methylene-bridged 2, which could not essentially extract any metal ions at all, lacking lone pair electrons on the methylene bridge for coordination. (C) 2001 Elsevier Science Ltd. All rights reserved.

Single-crystal X-ray analysis has shown that p-tert-butyl-sulfinylcalix[4]arene (H4L) can bind Pd2+ ion by using either S or O atoms of bridging S=O groups in addition to phenolic oxy gen atoms to form in [Pd-2(H2L)(H3L)(2)] complex.

Cobalt(II) and nickel(II) complexes with a tetraanionic ligand of p-tert-butylsulfonylcalix[4]arene were synthesized and their X-ray structures show that the calixarene acts as a bis-tridentate dinucleating ligand with the 1.2-alternate conformation.

A new synthetic strategy for the construction of an inherently chiral, sulfur-bridged calix[4]arene molecular framework was presented by oxidation of one of the four epithio bonds of a tetrathiacalix[4]arene derivative of 1,3-alternate conformation: Tetra(carboxymethyl) ether of p-tert-butyltetrathiacalix[4]arene of 1,3-alternate conformation (7) was converted to the tetra(l-menthoxycarbonylmethyl) ether (8). Oxidation of the tetra 1-menthyl ester 8 by treatment with NaBO3 (1.1 molar equiv.) afforded a pair of diastereomers of the monosulfinyl derivatives (9) in 58% yield, which were readily separable by silica-gel column chromatography. Removal of the 1-menthyl moieties followed by methyl esterification gave enantiomerically pure samples of inherently chiral (-)- and (+)-monosulfinyltrithiacalix[4]arene derivatives ((-)-10 and (+)-10) in 62 and 56% yield, respectively.

The solvolytic dissociation rate constants of 1:2 complexes of Al3+ and Ga3+ with an azo dye ligand, 2,2'-dihydroxyazobenzene-5,5'-disulfonate (DHABS, H2L2-), have been evaluated with a capillary electrophoretic reactor (CER) system. This CER system is based on the fact that metal complexes encounter an overwhelming force to dissociate when apart from the ligand by CE resolution, Treatment of a capillary with a slightly acidic buffer solution, e.g,, pH 5, reduces the double-layer potential (zeta) of the inner silica wall, Owing to slow relaxation of the deprotonation equilibria of superficial silanol groups known as the pH hysteresis, this zeta potential can be actually retained during the electrophoresis of the metal complexes in question with a neutral buffer at pH 7.0. This method enables one to manipulate migration times, namely, residence times in a capillary tube, from 5 to 90 min, depending on the prescribed conditioning pH, without changing any other operation conditions such as buffer composition and electric field strength. The excellent performance of the CER is exemplified by the accurate estimation of the dissociation degree of the complexes. The dissociation degree-time profiles for the complexes are quantitatively described using both internal and external standards; the very inert complex of [(CoL2)-L-III](5-) for the peak signal standardization and methyl orange for the injection volume correction. The solvolytic dissociation rate constants of the 1:2 complexes of Al3+ and Ga3+ ions with DHABS [AlL2](5-) and [GaL2](5-) into the 1:1 ones have been determined as (4.9 +/- 1.0) x 10(-4) and (3.7 +/- 0.3) x 10(-3) s(-1) at 303 K, respectively.

The selective de-tert-butylation of p-tert-butyl thiacalix[4]arene (p-tert-butyl TCA) with AlCl3 at 80 degrees C has been investigated. Mono-, di-, and tri-p-tert-butyl thiacalix[4]arene (mono-, di- and tri-TCA, respectively) were obtained in yields of 6.5, 20 and 21%, respectively, when p-tert-butyl TCA was treated with 7.1 equiv. of AlCl3 for 30 min. De-tert-butyl TCA (TCA) was exclusively obtained when 10.5 equiv. of AlCl3 was used. These derivatives are converted to fluorescent active derivatives by modification with dansyl moiety at the lower rim, which are used as metal sensors in aqueous solution. The extent of the fluorescent variations with the metal cations was used to display the sensing factors, Delta I/I-0. These hosts show much higher sensitivity for transition metal cations such as Co2+, Ni2+, and Cd2+ than those of alkali metal cations such as Li+, Na+, and K+. The effect of p-tert-butyl groups on metal sensing ability of these hosts was studied. It was found that p-tert-butyl, groups decrease the sensing ability of these hosts. It is the first example to show that water soluble TCA derivatives can detect metal cations directly in aqueous solution by variation of fluorescence intensity upon addition of a metal cation. (C) 2000 Elsevier Science Ltd. All rights reserved.

The first chiral disulfinyldithiacalix[4]arenes have been obtained by oxidation of two adjacent epithio groups of the tetramethyl ether of tetra(p-tert-butyl)tetrathiacalix[4]arene. The chiral resolution was achieved by HPLC using Chiralpak AD as a stationary phase. Furthermore, the absolute configuration of these compounds was determined by X-ray crystallography, (C) 2000 Elsevier Science Ltd. All rights reserved.

Although the reaction of p-tert-butylphenol with elemental sulfur in the presence of CsOH as a base catalyst yielded a complex mixture comprised of sulfur-bridged phenol oligomers, p-tert-butylthiacalix[6]arene (TC6A) could be isolated in an appreciable yield (0.8%). The X-ray analysis revealed that TC6A adopted a distorted cone conformation stabilized by two sets of hydrogen bondings comprising three phenolic OH groups. The recrystallization from various solvents showed that TC6A had higher inclusion ability toward more guests than TC4A did, suggesting that the expanded central cavity and/or the crystal lattice of the former allowed a more comfortable accommodation of the guest molecules. (C) 2000 Elsevier Science Ltd.

Treatment of p-tert-butylthiacalix[4]arene (1) with benzyl bromide in THF-DMF using NaH as the base catalyst afforded the tetrabenzyl ether of cone conformation (4(c)) as the major product, oxidation of which, with NaBO3 in CHCl3-acetic acid, proceeded readily to give the corresponding sulfinyl compound (5) with the four S=O groups disposed on the same side of the plane defined by the macrocyclic ring probably to avoid the steric hindrance imposed by the benzyllic moieties. Cleavage of the ether bonds gave a new stereoisomer of p-tert-butylsulfinylcalix[4]arene (2(ccc)) with the four S=O groups arranged in a cis-cis-cis configuration. (C) 2000 Elsevier Science Ltd. All rights reserved.

A practical method for the synthesis of p-tert-butylthiacalix[4]arene (TC4A), in which the methylene bridges of p-tert-butyl-calix[4]arene (C4A) are replaced by epithio groups, is presented by heating a mixture of p-tert-butylphenol, elemental sulfur S-8, and NaOH as a base catalyst in tetraethylene glycol dimethyl ether. The inclusion behavior of TC4A for a wide range of solvent molecules is examined by recrystallization, showing preference for the guests depending upon the size and/or the substituent of the guests. The X-ray structure of a 1:2 host-guest complex of TC4A with 1,2-dichloroethane reveals that one guest molecule is included in the cavity of TC4A, while the other is included in the crystal lattice to form a clathrate-type complex. It is shown that the inclusion in the cavity is attained by a cooperative deformation of both the host and the guest. (C) 2000 Elsevier Science Ltd. All rights reserved.

New chirally modified p-tert-butylthiacalix[4]arenes were synthesized via conformation- and/or regioselective etherification with ethyl bromoacetate followed by hydrolysis of the ester moiety and then subsequent amidation with (S)-1-phenyl-ethylamine or (S)-1-(1-naphthyl)ethylamine. These chiral selectors were coated with OV-17 on capillary columns to examine their ability as chiral stationary phases (CSPs) for discrimination of enantiomeric amino acid, amine and alcohol derivatives. It was found that CSP-(S)-4 prepared from cone-shaped tetra-(S)-1-phenylethylamide (S)-4 showed good to fair separations for all the samples examined. On the contrary, the corresponding CSP-(S)-14 prepared from the cone-shaped tetraamide (S)-14 of the parent p-tert-butylcalix[4]arene did not indicate any enantioseparation at all for the same samples, showing that the bridging group of the calix[4]arene ring is critical for the advent of enantioselectivity. The effect of the types and the numbers of the chiral amide groups in the chiral selectors on enantioselectivity was also discussed.

Novel molecular receptors, cone- and 1,3-alternate-tetracarboxylic acid (3) and syn-A,C-dicarboxylic acid (5), were prepared by hydrolysis of the ester moiety of the tetra- (2) and di-ethers (4), which had been synthesized by regio- and conformation-selective O-alkylation of the phenolic oxygens of thiacalix[4]arene (1) with ethyl bromoacetate. The binding ability of cone- and 1,3-alternate-3, syn-5, as well as cone-shaped, methylene-bridged tetracarboxylic acid (9) toward transition metal ions was investigated by solvent extraction to show that the selectivity for the ions depends upon the bridging sulfur, carboxylate group, and the conformation. (C) 1999 Elsevier Science Ltd. All rights reserved.

Two removal methods of small halogenated organic substances in water are proposed by formation of ternary complexes between the halides, thiacalix[4]arenetetrasulfonate (TCAS), and anion exchange resins, among which treatment of the polluted water with TCAS to form TCAS-guest complexes followed by trapping them onto the resin enables almost complete (more than 99.99%) removal of halogenated organic compounds such as CH2Cl2 and CHCl3.

Single-crystal X-ray analysis has shown that p-tert-butylthiacalix[4]arene (H4L) binds to Zn2+ ion by bridging sulfur atoms in addition to phenolic oxygen atoms to form [Zn4L(H2L)(2)].

5,11,17,23-Tetra-tert-butyl-2,8,14,20-tetrathiacalix[4]arene-25,26,27,28-tetrol (TCA) underwent facile tetra-O-alkylation by treatment with ethyl bromoacetate in the presence of an alkali carbonate as base catalyst in DMF or acetone to provide a mixture of conformational isomers (cone, partial cone, and 1,3-alternate) of 5,1 1,17,23-tetra-tert-butyl-25,26,27,28-tetrakis[(ethoxycarbonyl)methoxy]-2,8,14,20-tetrathiacalix[4]arene (1), the stereochemistries of which were unambiguously assigned by H-1 NMR and X-ray analysis. The isomer distribution depended significantly on the base used, thus providing a facile route for the preparation of a particular conformer; Na2CO3, K2CO3, and Cs2CO3 gave cone- (77% yield), partial-cone- (58% yield), and 1,3-alternate-1 (78% yield) in acetone, respectively. Cone- and partial-cone-1, in turn, showed preference for Na+ and K+, respectively, in an ion-pair extraction study, while 1,3-alternate-1 preferred most Rb+ ion, followed by K+ and then Cs+. These results imply that the size of the cavities provided by the (ethoxycarbonyl)methoxy groups arranged on the periphery of the thiacalix[4]arene skeleton is in the order cone- &lt; partial-cone- &lt; 1,3-alternate-1. The ion selectivity of cone-1 was rather better than that of the methylene-bridged counterpart, 5,11,17,23-tetra-tert-butyl-25,26,27,28-tetrakis[(ethoxycarbonyl)methoxy]calix [4]arene (2). The stoichiometry of the complex of cone-1 with Na+ ion was determined to be 1 : 1 with the stability constant of 10(2.85) mol(-1) dm(3) in 50 (v/v)% CDCl3-CD3OD.

Thiacalix[4]arenes in which the four methylene bridges of calix[4]arenes are replaced by sulfide linkages, were selectively oxidized to sulfinyl- or sulfonylcalix[4]arene under mild conditions with control of the stoichiometry of the oxidant. Solvent extraction of the transition and alkaline earth metal ions with these hosts showed that the metal binding ability was governed by the oxidation state of the sulfur functionalities. (C) 1998 Elsevier Science Ltd: All rights reserved.

A new chiral stationary phase far capillary gas chromatography based on a chirally modified p-tert-butylthiacalix[4]arene with (S)-1-phenylethylamine was prepared to show good separations of enantiomeric amino acid, amine and alcohol derivatives, while the corresponding p-tert-butylcalix[4]arene counterpart did not differentiate the enantiomers.

A new water soluble host molecule, thiacalix[4]arene-tetrasulfonate (TCAS), was obtained by direct sulfonation of p-tert-butylthiacalix[4]arene. TCAS showed size- and shape selectivity to bind small chlorinated organic molecules in its hydrophobic cavity by a 1:1 or 1:2 manner in aqueous solution.

The ability of tetra(p-t-butyl)tetrathiacalix [4]arenetetrol (TCA, H4L), a cyclic tetramer of p-(t-butyl)phenol bridged with four epithio groups, to bind metal ions was investigated via a solvent extraction study. Although tetra(p-t-butyl)calix[4]arenetetrol (CA) has very poor affinity for transition metal ions (M2+), TCA is an excellent extractant of these metal ions. The chemical formulae of the extracted TCA metal complexes were found by slope analysis to be neutral 1:1 complexes [MH2L]. The origin of the high affinity of TCA for transition metal ions is discussed, in which it is suggested that Ligation of the epithio group is important as evidenced by an NMR study of the [ZnH2L] complex.

In order to develop the municipal air surveillance systems, Ni and V in airborne particulates, which are emitted by combustion of fossil fuel, can be employed as suitable index species. The ultra-trace determinations of these elements down to subnanograms per cubic meter of air in airborne particulate matrices have been successfully achieved with a coupled scheme of reversed-phase liquid chromatography and a spectrophotometric detection. The precolumn (off-line) chelation reagents, aroylhydrazones having O,N,O and N,N,O donor sets are appropriate to V and Ni, respectively, in terms of the specificity for these ions, which assures extraordinary suitability to the airborne particulate matrices being free from the interferences notably by Al and Fe. The detection limits (3 sigma basis) of the methods reach down to 10 pg for V and 30 pg for Ni in 0.1-mL injections. The monitoring data of these elements in air samples collected in Sendai City, Japan, are reported. Even in less polluted air, V is accurately detected in the range of 1.5-3.5 ng/m(3) with a short sampling period for only 24 h (ca. 30 m(3) air). The very low detection limit of 0.3 ng of V/m(3) is demonstrated for the continuous monitoring with such small sampling volume.

Two separation mechanisms are demonstrated for DNA fragments in free solution inside narrow capillary tubes. No sieving medium or huller additive is needed. in the electromigration mode, a likely model is that dissociated silanol groups on the capillary waits create an excess of positive charges in the diffuse layer near the surface. These provide electrostatic shielding of the negatively charged DNA fragments to lower their electrophoretic mobility against electroosmotic flow Small fragments can access the diffuse layer more readily because of lower steric hindrance and larger diffusion coefficients and are therefore eluted earlier than the large fragments. in the hydrodynamic mode, the Poisseuille flow profile causes molecules near the surface to move slower. So, the smaller DNA fragments are eluted later than the larger fragments.

A simple method to coat a non-ionic hydrophilic polymer onto the inner wall of a bare fused-silica capillary is established. The capillary is first filled with 1 M HCl solution, then flushed with 0.2% poly(ethylene oxide) solution containing 0.1 M HCl, and finally rinsed with the electrophoretic buffer. Each step takes only 5 min. For regeneration of the coating, this procedure is repeated. Four basic proteins were separated by this method around pH 3-7 with phosphate buffer. The separation efficiency in terms of peak shape was excellent compared to bare fused-silica capillaries and comparable to many other more sophisticated column-treatment methods. The reproducibility of migration times of proteins was less than 3% R.S.D. at pH 6 by manual operation of the coating process. Titration of the fused-silica surface with acid and the structure of poly(ethylene oxide) are important factors to form a stable coating via hydrogen bonding to the surface silanol groups.

2-Pyridylaldehydearoylhydrazones have been examined as reagents for precolumn derivatization of metal ions in the HPLC-spectrophotometry system. With the simplest analog, 2-pyridylaldehydebenzoylhydrazone (PAB), among 11 metal ions only Ni(II) ion gives the peak while the other metal chelates seem to be dissociated on an HPLC column where no added PAB is present in the eluent solutions. All other PAB analogs exhibit the peak for Ni(II) ion as well as Co(III) ion. In one reagent system, V(V) and Fe(II) chelates also appear in the chromatograms. It has been stressed that the selectivity principle is the kinetic differentiation (KD) towards metal chelates associated with the HPLC processes. The specificity for Ni(II) ion is in close relation to a key structure of the ligand molecules which provides an N,N,O coplanar coordination environment to form two five-membered chelate rings. An extremely selective and sensitive KD-HPLC method for the quantitation of Ni(II) ion at the ultra-trace levels was assessed; the detection limit (3 sigma)Blank) for Ni(II) ion was down to 5.34 x 10(-9) mol l-1 (31.5 pg in a 100 mul injection) and the excellent applicability was checked using coal fly ash samples.

A new separation method for highly charged metal chelates based on ion association in capillary zone electrophoresis (CZE) has been developed. Metal chelates of Al(III), Co(III), Cr(III) and Fe(III) ions with 2,2'-dihydroxyazobenzene-5,5'-disulphonate could not be separated by a conventional CZE system (electrophoretic buffer: [NaH2PO4](tau) = 0.02 M, pH 7.0, V = 21.7 kV, i = 20 mu A, l = 50 cm), because they have fixed and identical (-5) charges. However, when 25 mM tetrabutylammonium bromide was added to the same electrophoretic buffer, each of the four chelates was well resolved and migrated in the order Fe(III), Co(III), Cr(III) and AI(III) with theoretical plate numbers of 210 000-250 000 per 50 cm within 11 min (V = 21.3 kV, I = 40 mu A). The detection limits (S/N = 3) as determined by spectrophotometric detection (lambda = 494 nm, I.D. = 50 mu m) were 1.00, 1.89 and 3.11 fmol for Al, Co and Fe, respectively, in 6.0 10(-9) dm(3) of sample solution injected. The effect on the separation of the sizes, types and the concentrations of quaternary ammonium ions added to the electrophoretic buffer was also investigated. As a result, some evidence was obtained that the ion-association reaction between the chelates and ammonium ions probably took the major role in the separation mechanism.

Separation of 4-(2-pyridylazo)resorcinol (PAR) and its chelates of Co(III), Fc(II), Ni(II), and V(V) was accomplished within 6 min by simple capillary electrophoresis (CE) with a spectrophotometric detection. The detection limits, defined as 3sigma of base-line noise were 1.80 x 10(-7) mol dm-3 for Co(III) and 1.41 x 10(-7) mol dm-3 for Ni(II) chelates, and those on a mass basis were 1.08 fmol (63.6 fg) and 0.84 fmol (49.3 fg) in 6.0 x 10(-9) dm3 sample, respectively. A guideline on the ligand design for the CE system is also obtained from the pH dependence of the separation behavior of PAR chelates.

Proton n.m.r. spectra are reported for complexes of Al(III), Ga(III), and In(III) with a variety of 5,5'-disulphonated 2,2'-dihydroxyazobenzenes in D2O solution. Ligand exchange is slow on an n.m.r. time-scale, and both 1:1 and 1:2 complexes have been characterized. The spectra of the complexes of Al(III) and Ga(III) show that the metal ions are bound to only one of the nitrogens of the azo groups. In contrast, the 1:2 indium(III) complexes of the two symmetric ligands studied are fluxional, and values of DELTA-G double-ended-dagger are given for the process which 'flips' the metal ions between the two nitrogen atoms. For the 1:1 and 1:2 aluminium(III) and the 1:2 gallium(III) complexes of asymmetric ligands, the expected isomers have been observed, and the equilibrium isomer ratios are reported. Assignments based on H-1 n.m.r. spectra have been confirmed by the 15N n.m.r. spectrum of a 1:2 gallium(III) complex with a ligand enriched in N-15. The isomer ratios can be largely rationalized by considering the effect substituents in the 4 and 4' positions have on the electron density of the remote nitrogen atom in the azo groups. The effect of changes in pD on the isomer ratios and the H-1 chemical shifts has also been studied for the 1:2 gallium(III) complexes of a ligand with an ionizable 4'-OH group.