An Electrochemical Study of the Interactions Between Trace Metals and Humic Substances in Freshwaters by Anodic Stripping Voltammetry with a Thin Mercury Film Rotating Disk Electrode

An improved theoretical approach to Anodic Stripping Voltammetry with a Thin Mercury Film Rotating Disk Electrode for elucidating the nature of the interactions of Pb(II), Cd(II) and Zn(II) with humic substances in model solutions of Laurentian fulvic acid, and of Pb(II), Cd(II), Zn(II) and Cu(II) in freshwaters, is presented. Conditional stability constants of Pb(II), Cd(II) and Zn(II) complexes decreased with the ionic potential (z²/r) and increased with softness of the metal ion, indicating strong affinity of soft, polarizable donor ligands on humic substances for softer metal ions, resulting in an appreciable covalent character in electrostatic bonding between the metals and humic substances.     

Chemistry of a Ni(II) acetohydroxamic acid complex: formation, reactivity with water, and attempted preparation of zinc and cobalt analogues

Mononuclear Ni(II), Co(II), and Zn(II) complexes of the bppppa (N,N-bis[(6-phenyl-2-pyridyl)methyl]-N-[(6-pivaloylamido-2-pyridyl)methyl]amine) ligand have been synthesized and characterized by X-ray crystallography, 1H NMR, UV-vis (Ni(II) and Co(II)) and infrared spectroscopy, and elemental analysis. Each complex has the empirical formula [(bppppa)M](ClO4)2 (M = Ni(II), 2; Zn(II), 3; Co(II), 4) and in the solid state exhibits a metal center having a coordination number of five; albeit, the cation of 2 also has a sixth weak interaction involving a perchlorate anion. Treatment of [(bppppa)Ni](ClO4)2 (2) with 1 equiv of acetohydroxamic acid results in the formation of [(bppppa)Ni(HONHC(O)CH3)](ClO4)2 (1), a novel Ni(II) complex having a coordinated neutral acetohydroxamic acid ligand. In 1, one phenyl-appended pyridyl donor of the bppppa chelate ligand is dissociated from the metal center and acts as a hydrogen bond acceptor for the hydroxyl group of the bound acetohydroxamic acid ligand. Treatment of 1 with excess water results in the formation of 2 and free acetohydroxamic acid. We hypothesize that this reaction occurs due to disruption of the intramolecular hydrogen bonding interaction involving the bound acid. In this series of reactions, the bppppa ligand exhibits behavior reminiscent of a type III hemilabile ligand in terms of one phenylpyridyl donor. Treatment of 3 or 4 with acetohydroxamic acid results in no reaction, indicating that the bppppa-ligated Ni(II) derivative 2 exhibits unique coordination chemistry with respect to reaction with acetohydroxamic acid within this series of complexes. We attribute this reactivity to the ability of the bppppa-ligated Ni(II) center to adopt a pseudo-octahedral geometry, whereas the Zn(II) and Co(II) complexes retain five coordinate metal centers.     

QZ1 and QZ2: rapid, reversible quinoline-derivatized fluoresceins for sensing biological Zn(II)

QZ1, 2-[2-chloro-6-hydroxy-3-oxo-5-(quinolin-8-ylaminomethyl)-3H-xanthen-9-yl]benzoic acid, and QZ2, 2-[6-hydroxy-3-oxo-4,5-bis-(quinolin-8-ylaminomethyl)-3H-xanthen-9-yl]benzoic acid, two fluorescein-based dyes derivatized with 8-aminoquinoline, have been prepared and their photophysical, thermodynamic, and zinc-binding kinetic properties determined. Because of their low background fluorescence and highly emissive Zn(II) complexes, QZ1 and QZ2 have a large dynamic range, with approximately 42- and approximately 150-fold fluorescence enhancements upon Zn(II) coordination, respectively. These dyes have micromolar K(d) values for Zn(II) and are selective for Zn(II) over biologically relevant concentrations of the alkali and alkaline earth metals. The Zn(II) complexes also fluoresce brightly in the presence of excess Mn(II), Fe(II), Co(II), Cd(II), and Hg(II), offering improved specificity for Zn(II) over di(2-picolyl)amine-based Zn(II) sensors. Stopped-flow kinetic investigations indicate that QZ1 and QZ2 bind Zn(II) with k(on) values of (3-4) x 10(6) M(-1) s(-1), compared to (6-8) x 10(5) M(-1) s(-1) for select ZP (Zinpyr) dyes, at 4.3 degrees C. Dissociation of Zn(II) from QZ1 and QZ2 occurs with k(off) values of 150 and 160 s(-1), over 5 orders of magnitude larger than those for ZP probes, achieving reversibility on the biological (millisecond) time scale. Laser scanning confocal and two-photon microscopy studies reveal that QZ2 is cell-permeable and Zn(II)-responsive in vivo. Because of its weaker affinity for Zn(II), QZ2 responds to higher concentrations of intracellular Zn(II) than members of the ZP family, illustrating that binding affinity is an important parameter for Zn(II) detection in vivo.     

Three novel zinc(II) sulfonate-phosphonates with tetranuclear or hexanuclear cluster units

Hydrothermal reactions of zinc(II) carbonate with m-sulfophenylphosphonic acid (m-HO3S-Ph-PO3H2) and 1,10-phenanthroline (phen) or 4,4'-bipyridine (bipy) lead to three novel zinc(II) sulfonate-phosphonates, namely, [Zn(phen)3]2[Zn4(m-O3S-Ph-PO3)4(phen)4].20H2O (1), [Zn6(m-O3S-Ph-PO3)4(phen)8].11H2O (2), and [Zn6(m-O3S-Ph-PO3)4(bipy)6(H2O)4].18H2O (3). Compound 1 contains a tetranuclear zinc(II) cluster anion in which four Zn(II) ions are bridged by two tetradentate and two bidentate phosphonate groups, and the four negative charges of the cluster are compensated by two [Zn(phen)3]2+ cations. Compound 2 features a hexanuclear zinc(II) cluster in which the same tetranuclear cluster of 1 is bridged with two additional Zn(II) ions. The structure of 3 features a porous 3D network based on hexanuclear zinc(II) units of [Zn6(m-O3S-Ph-PO3)4] interconnected by 4,4'-bipy ligands. The hexanuclear cluster in 3 is different from that in 2 in that all four phosphonate groups in 3 are tridentate bridging. Compounds 1, 2, and 3 exhibit broad blue fluorescent emission bands at 378, 409, and 381 nm, respectively.     

Complexation and Thermal Studies of Uric Acid with Some Divalent and Trivalent Metal Ions of Biological Interest in the Solid State

Nine new [metal uric acid] complexes [M(Ua) n ]°·XH 2 O have been synthesized. These complexes have been characterized by elemental analysis, X-ray diffraction (XRD), magnetic susceptibility ( w eff. ), FTIR spectra, thermal analysis (TG & DTA), and electronic spectra (UV/visible). Uric acid (HUa) coordinates as a bidentate ligand to Mn(II), Fe(II), Co(II), Ni(II), Cu(II), Zn(II), Al(III), Cr(III) and Fe(III) through the protonated N-7 within the imidazole ring and O-6 within the pyrimidine ring. Uric acid forms neutral metal urate complexes with all the above metal ions. The quantitative compositions were determined as [M(Ua) 2 ·(H 2 O) 2 ]°·XH 2 O where M(II)=Mn, Fe, Co, Ni, Cu, Zn and X=2, 4, 2, 4, 2, 2, respectively. The M(II) complexes exhibit an isostructural octahedral coordination with N-7, O-6 of two uric acid ligand molecules, and O of two water molecules. Compositions were also determined as [M(Ua) 3 ]°·YH 2 O where M(III)=Al, Cr, Fe and Y=6, 3, 3 respectively. All the M(III) complexes form an isostructural octahedral coordination with N-7 and O-6 of three uric acid ligand molecules. Iron(III) complexes prepared with N 1 , N 3 and N 9 -methyl uric acid yielded brown complexes with a metal ligand ratio of 1 3, while N 7 -methyl uric acid did not yield a complex due to blockage of N-7 with a methyl group.     

Amino acid and peptide bioconjugates of copper(II) and zinc(II) complexes with a modified N,N-bis(2-picolyl)amine ligand

Four chelating nitrogen ligands 2-5 derived from N,N-bis(2-picolyl)amine (bpa, 1) were synthesized, namely, (PyCH(2))(2)N-CH(2)-p-C(6)H(4)-CO(2)R (R = Me, 2, and R = H, 3) and (PyCH(2))(2)N-(CH(2))(n)-CO(2)H (n = 2, 4, and n = 5, 5). Amino acid conjugates 6 and 7 were formed by condensation of 3 with H-Phe-OMe and H-betaAla-OMe, respectively. Cu(II) and Zn(II) complexes of 1-7 were prepared and fully characterized. The X-ray structures of 1(Zn), 2(Zn), 4(Cu), and 7(Cu) were determined. The Zn complexes 1(Zn) and 2(Zn) as well as 7(Cu) show a distorted trigonal bipyramidal coordination environment in the solid state. An octahedral complex is observed for 4(Cu) which forms chains along the crystallographic b axis by intermolecular coordination of the carboxylic acid to the metal ion of a neighboring complex. Ligand 3 was used to prepare the peptide bioconjugate 8 (3-Ahx-Pro-Lys-Lys-Lys-Arg-Lys-Phe-NH(2)) with a nuclear localization signal (nls) heptapeptide by solid phase synthesis. Cu(II) and Zn(II) complexes of 8 were synthesized in situ and studied by FAB-MS, ESI-MS, UV/vis, and EPR (for 8(Cu)), and FAB-MS, ESI-MS, and NMR (for 8(Zn)). All spectroscopic results clearly support metal coordination to the bpa ligand in the bioconjugates 8(M), even in the presence of other potential ligands from amino acid side chains of the peptide. We suggest metal-peptide conjugates like 8(M) as artificial metallochaperones because they have the potential to deliver metal ions to specific compartments in the cell as determined by the peptide moieties.     

Zinspy sensors with enhanced dynamic range for imaging neuronal cell zinc uptake and mobilization

Thiophene moieties were incorporated into previously described Zinspy (ZS) fluorescent Zn(II) sensor motifs (Nolan, E. M.; Lippard, S. J. Inorg. Chem. 2004, 43, 8310-8317) to provide enhanced fluorescence properties, low-micromolar dissociation constants for Zn(II), and improved Zn(II) selectivity. Halogenation of the xanthenone and benzoate moieties of the fluorescein platform systematically modulates the excitation and emission profiles, pH-dependent fluorescence, Zn(II) affinity, and Zn(II) complexation rates, offering a general strategy for tuning multiple properties of xanthenone-based metal ion sensors. Extensive biological studies in cultured cells and primary neuronal cultures demonstrate 2-{6-hydroxy-3-oxo-4,5-bis[(pyridin-2-ylmethylthiophen-2-ylmethylamino)methyl]-3H-xanthen-9-yl}benzoic acid (ZS5) to be a versatile imaging tool for detecting Zn(II) in vivo. ZS5 localizes to the mitochondria of HeLa cells and allows visualization of glutamate-mediated Zn(II) uptake in dendrites and Zn(II) release resulting from nitrosative stress in neurons.     

Heterodinuclear metal arrangement in a flat macrocycle with two chemically-equivalent metal chelating sites

A phenanthroline-based macrocycle 1 has been newly developed which has two chemically equivalent metal chelating sites within the spatially restricted cavity for dinuclear metal arrangement. The macrocycle 1 reacts with Zn(CF(3)CO(2))(2) or ZnCl(2) to form homodinuclear Zn(II)-complexes. A single-crystal X-ray structural analysis of the resulting Zn(2)1(CF(3)CO(2))(4) determined the complex structure in which two Zn(II) ions are bound by two phenanthroline sites and two CF(3)CO(2)(-) ions bind to each Zn(II) ion in a tetrahedral geometry. Similarly, a homodinuclear Cu(I)-macrocycle was formed from 1 and Cu(CH(3)CN)(4)BF(4). Notably, from 1 and an equimolar mixture of Cu(CH(3)CN)(4)BF(4) and Zn(CF(3)CO(2))(2), a heterodinuclear Cu(I)-Zn(II)-macrocycle was exclusively formed in high yield (>90%) because of the relatively low stability of the dinuclear Cu(I)-macrocycle. A heterodinuclear Ag(I)-Zn(II)-macrocycle was similarly formed with fairly high selectivity from a mixture of Ag(I) and Zn(II) ions. Such selective heterodinuclear metal arrangement was not observed with other combinations of M-Zn(II) (M = Li(I), Mg(II), Pd(II), Hg(II), La(III), and Tb(III)).     

Protonation Equilibria of Carminic Acid and Stability Constants of Its Complexes with Some Divalent Metal Ions in Aqueous Solution

The dissociation constants of carminic acid (7-D-glucopyronosyl-3,5,6,8-tetra- hydroxy-1-methyl-9,10-dioxo-anthracene-2-carboxylic acid) (CA), together with the stability constants of its Cu(II), Zn(II), Ni(II), Co(II) and Hg(II) complexes, were studied potentiometrically in aqueous medium at 25.0?(1)?°C, and at the ionic background of 0.1?mol?dm^?3 of NaCl, and determined with the SUPERQUAD computer program. It has been observed that carminic acid has five dissociation constants, and for H₅L their values are 3.39?(7), 5.78?(7), 8.35?(7), 10.27?(7), and 11.51?(7). This ligand behaves as a bi-dentate ligand, and the carboxyl and the ortho hydroxy groups of the ligand coordinate to the metal ions. Various metal complexes were produced in solution under the experimental conditions, for each metal ion used, including hydrolyzed species. The species distribution curves of the complexes formed in the solution were calculated and reviewed. The stability of the complexes was found to follow the order: Cu(II) > Zn(II) > Ni(II) > Co(II) > Hg(II).     

Group II B Metal Complexes with N-Benzoylglycine (Hippuric Acid) and their Amine Adducts

Zn(II), Cd(II) and Hg(II) complexes with N-benzoylglycine (Hippuric acid) (abbreviation HHippu) and their amine adducts are of the type M(Hippu)₂. H₂O, M(Hippu)₂, M(Hippu)₂. B (M = Zn, Cd and Hg, and B = piperazine, 1, 10-phenantroline; M = Zn and B = Pyridine; M = Hg and B = ethylenediamine), M(Hippu)₂? 2B (B = N-methylpiperazine, piperidine, morpholine and pyridine) and M(Hippu)₂?3B (M = Zn, Cd and B = ethylenediamine). The amine and amino-acid coordination are investigated with the infrared spectra. The monohydrate and anhydrous bis(hippurate)metal(II) have identical i.r. spectra, indicating that the water molecule is not coordinated to the metal ions. A monodentate coordination of the amino acid is found in the amine adducts of Zinc(II), while in those of Cadmium(II) and Mercury(II)a symmetrical or asymmetrical bidentate coordination through the (COO^?) group is suggested and a pseudooctahedral configuration proposed. Only in monohydrate, anhydrous and monopyridine bis(hippurate) Zinc(II) (with the lowering of the ν (NH) of the ? NH-group of the N-benzoylglycine) does this group appear to be involved in the metal coordination.     

The New Complexes of Selected Transition Metal Ions with a Ligand Formed by Condensation of Isatin with Amino Acid: Spectral,Thermal, and Magnetic Properties

The new complexes of 2-[(2-oxo-1,2-dihydroindol-3-ylidene)amino]butanoic acid, LH (where L = C₁₂H₁₁N₂O₃), with Mn(II), Co(II), Ni(II), Cu(II), and Zn(II) of general formulae MLCl·nH₂O, for Co(II), Ni(II) and Cu(II), and ML₂·H₂O for Mn(II) and Zn(II), where n = 1, 2 depending on M(II) ions, are synthesized. The complexes crystallize in a monoclinic system, and upon heating in the air (293–1173 K) decompose in three steps forming eventually the corresponding oxides of the metals(II). In the course of this process the organic ligand decomposes releasing the molecules of H₂O, CO₂, NH₃, CO, hydrocarbons, and additionally HCl for Co(II), Ni(II) and Cu(II) complexes. Magnetic moments of compounds are determined in the ranges of 76–303 and 2–300 K. All analyzed compounds, except that of Zn(II), demonstrate the paramagnetic properties with the ferro- and antiferromagnetic interactions between molecular centres.

     

Study on the synergistic extraction of cobalt(II) with lower fatty acids in the presence of heterocyclic amines and some metal ion separations

The synergistic extraction of cobalt(II) with a chloroform solution of propionic, butyric or valeric acid in the presence of beta-picoline, pyridine or quinoline has been investigated. The effect of different variables, such as pH of the aqueous phase, and concentration of metal ion, acid and amine, is reported. On the basis of slope analysis the species extracted were generally found to be CoA(2).2HA.2B where HA is the acid and B the base, but CoA(2).HA.2B.H(2)O for the butyric acid-quinoline system. The extraction constants were used to assess the relative effectiveness of the amines as synergists. From the extraction data, methods for separation of Co(II) from Mn(II), Cr(III), Fe(III), Zn(II), Cd(II) and Hg(II), with fairly high separation factors, have been worked out.     

Synthesis of isoreticular zinc(II)-phosphonocarboxylate frameworks and their application in the Friedel-Crafts benzylation reaction

Three isoreticular zinc(II)-phosphonocarboxylate frameworks, namely {[Zn(3)(pbdc)(2)]·2H(3)O}(n) (ZnPC-2), {[Zn(3)(pbdc)(2)]·Hpd·H(3)O·4H(2)O}(n) (Hpd@ZnPC-2) and {[Co(1.5)Zn(1.5)(pbdc)(2)]·2H(3)O}(n) (CoZnPC-2) (H(4)pbdc=5-phosphonobenzene-1,3-dicarboxylic acid, pd=pyrrolidine), were solvothermally synthesized. ZnPC-2 has a 3D structure based on trinuclear Zn(II) clusters (Zn(3)-SBU) showing 3D interconnected channels. Hpd@ZnPC-2 contains an isoreticular framework of ZnPC-2 with small channels blocked by Hpd molecules. In CoZnPC-2, Zn(II) ions in ZnPC-2 are partially substituted by Co(II) ions. The Friedel-Crafts benzylation reactions were carried out over these isoreticular porous materials. The catalytic results reveal that ZnPC-2 is an excellent heterogeneous Lewis acid catalyst with a high selectivity (>90%) towards less bulky para-oriented products. The catalytic reaction has been proved to occur inside the pore of ZnPC-2, and the immobilized Zn(3)-SBUs are the active sites.     

Crystal structures and spectroscopic properties of zinc(II) ternary complexes of vitamin L, H' and their isomer m-aminobenzoic acid with bipyridine

The crystal structures of the three Zn(II) complexes, [Zn(bpy)(o-AB)2] (1) (bpy=2,2'-bipyridine, o-AB=o-aminobenzoic acid=Vitamin L), [Zn(bpy)(m-AB)Cl]2 (2) (m-AB=m-aminobenzoic acid), [Zn(bpy)(p-AB)Cl]*p-AB*H2O (3) (p-AB=p-aminobenzoic acid=Vitamin H'), have been determined and the basic coordination geometries and architectures organized by hydrogen-bonds and pi-pi interactions also characterized. The substitute amine group at ortho-, meta-, and para-position of AB plays an important role to produce completely different coordination motif of these complexes, further, in all complexes, aromatic amines are not coordinated to Zn(II) atom. While two different types of coordination modes of the carboxylate O atoms are present in these complexes: one mode consists of the usual Zn-O bond lengths (2.009(2)-2.251(2) A) in complex 1, 2 and 3; another consists of a very long Zn-O bond lengths (2.422(2) A) in complex 1. Each of the complexes has the characteristic UV absorption bands around 250-310 nm region, and the intense fluorescence band at near 325 nm.     

Mononuclear Cu(II), Zn(II), and Co(II) Complexes with 2-Furoate Anions and 2,2'-Bpy: Synthesis,Structure, and Biological Activity

Russian Journal of Coordination Chemistry - The mononuclear complexes [M(Fur)2(Bpy)(H2O)] (M = Cu (I), Zn (II)) were prepared by the reactions of copper(II) and zinc(II) acetates with 2-furoic acid...     

Assembly of zinc metallacrowns with an a-amino hydroxamic acid ligand

In the assembly of metallacrowns for molecular recognition,luminescence,and molecular magnetism[1_TD$IF]applications,substituting the ring ion can have profound effects on the structure,stability,and physical properties of the inorganic macrocycle.The assembly of Zn(II) metallacrowns with an a-amino hydroxamic acid ligand(phe HA) was investigated to compare the assembly behavior with the well studied metallacrowns containing Cu(II) and Ni(II).Electrospray ionization mass spectrometry reveals that the benchmark species Zn5(phe HA)42+and Ln Zn5(phe HA)53+assemble in pyridine,which is consistent with the behavior of Cu(II) and Ni(II).A Ln Zn4(phe HA)43+species is also observed in a 1:1DMF-pyridine mixture.An unprecedented La(III)[16-MCZn(II),phe HA,Hphe HA-6]5+complex was crystallographically characterized that possesses unusual C2 symmetry.These results provide insights into the design of functional metallacrowns through ring ion substitution.     

Reactivity of M(II) metal-substituted derivatives of pig purple acid phosphatase (uteroferrin) with phosphate

The Fe(II) of the binuclear Fe(II)Fe(III) active site of pig purple acid phosphatase (uteroferrin) has been replaced in turn by five M(II) ions (Mn(II), Co(II), Ni(II), Cu(II), and Zn(II)). An uptake of 1 equiv of M(II) is observed in all cases except that of Cu(II), when a second more loosely bound Cu(II) is removed by treatment with edta. The products have been characterized by different analytical procedures and by UV-vis spectrophotometry. At 25 degrees C, I = 0.100 M (NaCl), the nonenzymatic reactions with H(2)PO(4)(-) give the mu-phosphato product, and formation constants K/M(-1) show an 8-fold spread at pH 4.9 of 740 (Mn), 165 (Fe), 190 (Co), 90 (Ni), 800 (Cu), 380 (Zn). The variations in K correlate well with stability constants for the complexing of H(2)PO(4)(-) and (CH(3)O)HPO(3)(-) with M(II) hexaaqua ions. At pH 4.9 with [H(2)PO(4)(-)] > or = 3.5 mM rate constants k(obs) decrease, and an inhibition process in which a second [H(2)PO(4)(-)] coordinates to the dinuclear center is proposed. The mechanism considered accounts for most but not all of the features displayed. Thus K(1) values for the coordination of phosphate to M(II) are in the range10-60 M(-1), whereas K(2) values for the bridging of the phosphate to Fe(III) are in the narrower range 7.8-12.4. From the fits described K(i) approximately 10(3) M(-1) for the inhibition step, which is independent of the identity of M(II). Values of k(obs) decrease with increasing pH, giving pK(a) values which are close to 3.8 and independent of M(II) (Fe(II), Zn(II), Mn(II)). The acid dissociation process is assigned to Fe(III)-OH(2) to Fe(III)-OH(-), where OH(-) is less readily displaced by phosphate.     

Pharmacological and Pharmacokinetic Studies of Anti-diabetic Tropolonato-Zn(II) Complexes with Zn(S(2)O(2)) Coordination Mode

Zn(II) complexes are expected to be useful in the treatment of diabetes mellitus because of the hypoglycemic effect produced by its insulin-mimetic activity. Previous reports indicated that Zn(II) complexes with coordinating sulfur exhibit higher insulin-mimetic activity. In this study, we investigated the pharmacological and pharmacokinetic differences between Zn(O(4)) and Zn(S(2)O(2)) coordination modes of tropolonato-Zn(II) complexes with insulin-mimetic activity. Among the tropolonato-Zn(II) complexes with various coordination modes, di(2-mercaptotropolonato)zinc(II) (ZT2) with the Zn(S(2)O(2)) coordination mode was found to exhibit the highest in vitro insulin-mimetic activity with respect to inhibition of free fatty acid (FFA) release and enhancement of glucose uptake in isolated rat adipocytes treated with adrenaline. On comparing investigations of the antidiabetic effect in vivo, ZT2 was found to exhibit potent hypoglycemic activity and improve insulin resistance in type 2 diabetic KKA(y) mice at a low orally administered daily dose. Di(tropolonato)zinc(II) (ZT1), which has the Zn(O(4)) coordination mode, had a lesser effect at the same dose. In a pharmacokinetic analysis based on the (65)Zn tracer method, ZT2 was found to be absorbed at a significantly slower rate with a longer half-life than was ZT1. These results suggest that the potent hypoglycemic activity of ZT2 might be attributed to its long half-life.     

Determination of cadmium, zinc, nickel and cobalt in tobacco by reversed-phase high-performance liquid chromatography with 2-(8-quinolylazo)-4,5-diphenylimidazole as a chelating reagent.

A sensitive and selective method has been developed for the simultaneous determination of cadmium, zinc, nickel and cobalt. The method is based on the chelation of metal ions with 2-(8-quinolylazo)-4,5-diphenylimidazole (QAI) and the subsequent reversed-phase (RP) high-performance liquid chromatographic separation and spectrophotometric detection of the metal chelates. The chelates were separated on an RP column with acetonitrile-water containing ethylenediamine tetraacetic acid and sodium acetate (pH 7.5). Though Zn(II) and Cd(II) chelates with azo compounds were generally labile in the RP column, these chelates with QAI were successfully detected. When analyses were carried out at 575 nm and at 0.001 absorbance unit full scale, the peak height calibration curves were linear up to 2.0 ng for Cd(II), 2.4 ng for Zn(II), 0.14 ng for Ni(II) and 0.72 ng for Co(II) in 100-microL injections, respectively; the detection limits (3sigma, three times of the standard deviation for the blank signal) for Cd(II), Zn(II), Ni(II) and Co(II) were 4.8, 24, 2.4 and 7.2 pg in 100 microL of injected solution, respectively. The proposed method was successfully applied to the analysis of tobacco without any preliminary concentration or separation.     

Spectrophotometric study of the complex formation of 3-(2-hydroxyphenyl)-2-mercaptopropenoic acid with Ni(II) and Zn(II)

The dissociation and complex formation equilibria between Ni(II) and Zn(II) with 3-(2-hydroxyphenyl)-2-mercaptopropenoic acid, at 25 degrees in aqueous 0.1 and 1.0M sodium perchlorate solutions, containing about 1% ethanol, have been studied spectrophotometrically. The data were connected directly from the spectrophotometer to an IBM-PC via a serial interface, using the DUMOD program (written in BASIC), described in the paper. The obtained spectra were treated by the factor analysis program NIPALS in order to determine the number of absorbing species and the experimental error. Dissociation constants of ligand (H(3)L), and formation constants for the complexes Ni(HL), Ni(HL)(2), Zn(HL) and Zn(HL)(2) at 0.1 and 1.0M ionic strengths, refined by the SQUAD program, are reported.