-
[show abstract]
[hide abstract]
ABSTRACT: A diradical-platinum(ii) complex was able to recognize the subtle difference in cavity size between β- and γ-cyclodextrin with on-off switching of intense near-infrared absorption. This provides a new probe for identifying the size of hydrophobic cavities, which has been successfully applied here to differentiate human serum albumin from α-chymotrypsin.
Chemical Communications 04/2013; · 6.17 Impact Factor
-
Inorganica Chimica Acta. 01/2013; 397:42-47.
-
[show abstract]
[hide abstract]
ABSTRACT: Dissociation kinetic analysis of a complex of Ce(3+) 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. Dissociation rate constants, kd, of Ce(3+)-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 Ce(3+)-Quin2 complex in alkaline conditions. The solvolytic dissociation rate constant, and the hydroxide ion-assisted dissociation rate constant of Ce(3+)-Quin2 complex were determined to be 1.55 × 10(-3) and 3.24 × 10(2) s(-1) in the analysis of the dependence of kd with the concentration of hydroxide ion, respectively.
Analytical Sciences 01/2013; 29(5):553-7. · 1.25 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: 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,
\textAg4 + \textTb 3+ \textTCAS 2 {\text{Ag}}_{4}^{ + } \cdot{\text{Tb}}^{ 3+ } \cdot{\text{TCAS}}_{ 2} , at the center of which an octa-oxygen cube encapsulated the Tb3+ center to completely shield it from solvent molecules.
Journal of Inclusion Phenomena 04/2012; 64(3):379-383. · 1.89 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: 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(I)(4)·Nd(III)·TCAS(2) in a wide pH range of 6-12. In contrast, the Ag(I)-Yb(III)-TCAS system gave Ag(I)(2)·Yb(III)(2)·TCAS(2) at a pH of around 6 and Ag(I)(2)·Yb(III)·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(I)(2)·Yb(III)(2)·TCAS(2), two TCAS ligands sandwiched a cyclic array of a Ag(I)-Ag(I)-Yb(III)-Yb(III) core. In Ag(I)(2)·Yb(III)·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(I)(4)·Nd(III)·TCAS(2) revealed that the structure was similar to Ag(I)(2)·Yb(III)·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(I)(4)·Nd(III)·TCAS(2), 0; Ag(I)(2)·Yb(III)(2)·TCAS(2), 2.4; and Ag(I)(2)·Yb(III)·TCAS(2), 0. These findings were compatible with the solution-state structures. The luminescent quantum yield (Φ) for Ag(I)(4)·Nd(III)·TCAS(2) was 4.9 × 10(-4), which is the second largest value ever reported in H(2)O. These findings suggest that the O(8) cube is an ideal environment to circumvent deactivation via O-H oscillation of coordinating water. The Φ values for Ag(I)(2)·Yb(III)(2)·TCAS(2) and Ag(I)(2)·Yb(III)·TCAS(2) were found to be 3.8 × 10(-4) and 3.3 × 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.
Inorganic Chemistry 02/2012; 51(3):1648-56. · 4.60 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: 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·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.
European Journal of Inorganic Chemistry. 01/2012; 2012(22):3541-3545.
-
Berichte der deutschen chemischen Gesellschaft 06/2010; 2010(22):3458 - 3465. · 2.94 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The effect of urea as an electrophoretic buffer solution modifier on the ion-association (IA) capillary electrophoresis (CE) separation of four anionic metal complexes of Al(III), Co(III), Cr(III), and Fe(III) with 2,2'-dihydroxyazobenezene-5,5'-disulfonate (DHABS) using a hydrophobic ion-association agent, tetrapentylammonium bromide, was studied. The mutual separation of the four anionic metal-DHABS complexes was not achieved without the addition of urea in the electrophoretic buffer solution. However, the addition of 1.5 M urea in the electrophoretic buffer solution brought about a complete separation of the four metal complexes. The ion-association constants between all metal-DHABS complexes and tetrapentylammonium in an aqueous urea solution were smaller than those in a neat aqueous solution. This indicates the hydrophobic interaction contributing to the ion-association between analytes and ion-association agent during IA-CE separation processes can be controlled with the addition of urea to the electrophoretic buffer solution. Another advantage of adding urea was a substantial enhancement of separation efficiency with a reduction of the half-bandwidth of the peaks. Also, a reduction of the electrophoretic mobility of the electroosmotic flow when urea was added was much less than when organic solvents were used.
Analytical Sciences 01/2010; 26(11):1151-6. · 1.25 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: 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 identical with 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 5D4 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.
Analytica chimica acta 10/2009; 650(2):258-63. · 4.31 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: CE reactor (CER), which was developed as a tool for direct measurement of the dissociation kinetics of metal complexes, was successfully applied to the complexes of Escherichia coli ssDNA-binding protein (SSB) with ssDNA. The basic concept of CER is the application of CE separation process as a dissociation kinetic reactor for the complex, and the observation of the on-capillary dissociation reaction profile of the complex as the decrease of the peak height of the complex with increase of the migration time. The peak height of [SSB-ssDNA] decreases as the migration time increases since the degree of the decrease of [SSB-ssDNA] through the on-capillary dissociation reaction is proportional to the degree of the decrease of the peak height of [SSB-ssDNA]. The dissociation degree-time profiles for the complexes are quantitatively described by analyzing a set of electropherograms with different migration times. Dissociation rate constants of [SSB-ssDNA] consisting of 20-mer, 25-mer and 31-mer ssDNA were directly determined to be 3.99x10(-4), 4.82x10(-4) and 1.50x10(-3)/s, respectively. CER is a concise and effective tool for dissociation kinetic analysis of biomolecular complexes.
Electrophoresis 09/2009; 30(17):3079-85. · 3.30 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: 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(IV) 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.
Analytical Chemistry 09/2009; 81(18):7849-54. · 5.86 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A unique tactic for the separation of single-base sequential isomers of oligomeric single-stranded DNA by a CE separation system employing the specific interaction of metal ion with nucleotide was demonstrated, enabling the separation of the mixture of a 12-mer oligonucleotide and its single-base mutants, as well as their positional isomers.
The Analyst 08/2009; 134(7):1299-301. · 4.23 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We have developed a concise tool for the investigation of the transition of humic substances in environmental water. The separation of water-soluble humic substances was achieved rapidly and effectively by capillary electrophoresis using a polyacrylamide-coated capillary and a phosphate electrophoretic buffer solution (pH 7.0) containing hydroxyethyl cellulose. The separation mechanism was assessed using the ultrafiltration technique. The effect of the complexation of humic substances with metal ions was studied by using the proposed method. When Fe(III) ions or EDTA was added to the sample solution of fulvic acid, a distinct change in the electropherogram pattern based on the conformational change of fulvic acid was observed. The successful application of the proposed method to the characterization of humic substances in a river water sample was also demonstrated.
Analytical and Bioanalytical Chemistry 12/2008; 393(2):761-6. · 3.78 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A new method for the highly sensitive and selective determination of boron at nanograms per cubic decimeter levels has been developed based on the derivatization reaction of boron using salicylaldehyde and 1-amino-8-naphtol-3,6-disulfonate with reversed-phase partition high-performance liquid chromatography. A detection limit as low as 2.0 nmol/dm(3) (22 ng/dm(3)) was achieved without any preconcentration. No significant interference was observed in the determination of 16 micromol/dm(3) of boron with the addition of nine metal ions (Al(III), Cu(II), Co(II), Fe(II), Fe(III), Ni(II), Mn(II), V(V), Zn(II)) at concentrations 100 times greater than that of boron without any masking procedure. The proposed method was successfully applied to the determination of boron in river water, tap water, doubly distilled water, and highly purified water.
Analytical and Bioanalytical Chemistry 07/2008; 391(3):1101-6. · 3.78 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The compositions and photophysical properties of luminescent ternary complexes of thiacalix[4]arene-p-sulfonate (TCAS), Tb(III), and Ag(I) ions were determined. At pH 6, Ag(I) (2)Tb(III) (2)TCAS(2) formed. Moreover, at pH 10, in the presence of a 20-fold excess of Ag(I) and a 50-fold excess of TCAS with respect to Tb(III), Ag(I) (2)Tb(III)TCAS(2) formed as the main luminescent species. The structure of these complexes was proposed: two TCAS 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(I) (2)Tb(III) (2)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(I) (2)Tb(III)TCAS(2), the yield Phi (=0.11) was small, which is attributed to the low efficiency of photosensitization (eta=0.11). However, the tau 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.
Chemistry - An Asian Journal 06/2008; 3(5):849-53. · 4.50 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: 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.
The Analyst 11/2005; 130(10):1337-9. · 4.23 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: An aromatic polyaminocarboxylate ligand, 1-(4-aminobenzyl)ethylenediamine-N,N,N',N'-tetraacetate (ABEDTA), is proposed as a complexing reagent in the pre-capillary mode so as to form kinetically inert Ln(III) complexes, meaning that no added ligand is necessary in alkaline carrier buffer solutions. In addition, highly-sensitive detection is possible through a light-absorbing moiety of an aminobenzyl group in the ligand. The fine-tuning of the electrophoretic mobilities of the Ln-abedta complexes is successfully achieved by adding an auxiliary carbonate ion ligand which alters the charge-to-size ratio of the complexes through fast exchange equilibria in a carrier buffer. In fact, all of the complexes are detectable with very similar analytical sensitivity and acceptable resolution (except for Ln=Sm, Eu, Gd) by using NaOH-borate carrier buffer solution at pH 12.35 with 20 mM of Na2CO3. A typical detection limit for Tb(III) ion (to 3sigma) is as low as 0.94 microM, which translates to an absolute amount of 9.4 fmol in a 1.0 x 10(-8) dm(-3) (10 nL) injection.
Analytical and Bioanalytical Chemistry 04/2004; 378(6):1644-7. · 3.78 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A highly sensitive and selective method for the determination of the Be(II) ion has been developed by the use of reversed-phase high-performance liquid chromatography (HPLC) with fluorometric detection using 2-(2'-hydroxyphenyl)-10-hydroxybenzo[h]quinoline (HPHBQ) as a precolumn (off-line) chelating reagent. The reagent HPHBQ has been designed to form the kinetically inert Be chelate compatible with high fluorescence yield, which is appropriate to the HPLC-fluorometric detection system. The Be-HPHBQ chelate is efficiently separated on a LiChrospher 100 RP-18(e) column with a methanol (58.3 wt %)-water eluent containing 20 mmol kg(-1) of tartaric acid and is fluorometrically detected at 520 nm with the excitation at 420 nm. Under the conditions used, the concentration range of 20-8,000 pmol dm(-3) of Be(II) ion can be determined without interferences from 10 micromol dm(-3) each of common metal ions, typically Al(III), Cu(II), Fe(III), and Zn(II), and still more coexistence of Ca(II) and Mg(II) ions at 0.50 mmol dm(-3) and 5.0 mmol dm(-3), respectively, is tolerated. The detection limit (3a baseline fluctuation) is 4.3 pmol dm(-3) (39 fg cm(-3)). The extraordinarily high sensitivity with toughness toward the matrix influence was demonstrated with the successful application to environmental Be analyses, such as determination of Be in rainwater and tap water.
Analytical Chemistry 03/2003; 75(3):413-9. · 5.86 Impact Factor
-
Bunseki kagaku 01/2001; 50(2):113-117. · 0.43 Impact Factor
-
Chemistry Letters - CHEM LETT. 01/1996;
