Potentiometric pH Titrations Research Articles

Glycine and L-Tryptophan, a Comparative Investigation on Interactions in Cu(II) Binary and Ternary Complexes in Aqueous Solution

The acidity and stability constants of M(Trp) i M: Cu 2+ , Cu(Bpy ii ) 2+ , and Cu(Phen iii ) 2+ complexes, were de- termined by potentiometric pH titration. It is shown that the stability of the binary Cu(Trp) complex is determined by the basicity of the carboxylate group on one side and amino group on the other side. It is demonstrated that the equilibrium, Cu(Har iv ) 2+ + Cu(Trp) Cu(Har)(Trp) + Cu 2+ , is displacement due to the well known experience that mixed ligand complexes formed by a divalent 3d ion, a heteroaromatic N base and an O donor ligand possess increased stability. The other part of this displacement, which amount on average to an increased stability of the mixed ligand Cu(Bpy)(Trp) and Cu(Phen)(Trp) complexes of about 0.97 or 1.31 log unit. The stability constants of the 1:1 complexes formed between Cu 2+ , Cu(Bpy) 2+ or Cu(Phen) 2+ and Trp 2− , were determined by potentiometric pH titration in aqueous solution (I = 0.1 M, NaNO3, 25℃). The order of the stability constants was reported. The results show following order for Trp, Cu(Trp) Cu(Bpy)(Gly) ≤ Cu(Phen)(Gly). A comparative investigation between ternary com- plexes of Trp and Gly v is made. The comparison of stability constants of these ternary complexes show that Cu(Har)(Gly) exist in open form but Cu(Har)(Trp) is found near 100% in closed form. The differences between the above mentioned sta- bility constants based on stacked form of Cu(Har)(Trp). The stacked form provides for increased stability.

Characterizations of the Photocatalytically-Oxidized Cross-Linked Chitosan-Glutaraldehyde and its Application as a Sub-Layer in the TiO2/CS-GLA Bilayer Photocatalyst System

Photocatalytically-oxidized cross-linked chitosan-glutaraldehyde (CS-GLA) was obtained via irradiation of a simple assemblage of an immobilized layer-by-layer TiO2/CS-GLA system on a glass plate with a 45-W fluorescent lamp. The oxidation process was observed to occur only in the presence of oxygen and TiO2 within 5 cycles (10 h) of irradiation. Characterizations studies of the oxidized cross-linked polymer involving swelling index, pH-potentiometric titration and ionic conductivity measurements, as well as CHN, FTIR, 13C solid-state NMR,UV–Vis DRS and photoluminescence spectroscopy analyses generally indicated that the oxidation led to the formation of carbonyl groups, partial elimination of some un-reacted amino groups and change of visual color to be more brown without altering much of the whole molecular structure of the CS-GLA. This study also indicated that the photocatalytic performance of TiO2/oxidized CS-GLA system was higher than both TiO2/CS-GLA system and TiO2 single layer for the removal of phenol. Moreover, the adsorption effect was extremely negligible and the photodegradation of phenol was mainly due to the photocatalytic process.

Structural Basis for Bifunctional Zinc(II) Macrocyclic Complex Recognition of Thymine Bulges in DNA

The zinc(II) complex of 1-(4-quinoylyl)methyl-1,4,7,10-tetraazacyclododecane (cy4q) binds selectively to thymine bulges in DNA and to a uracil bulge in RNA. Binding constants are in the low-micromolar range for thymine bulges in the stems of hairpins, for a thymine bulge in a DNA duplex, and for a uracil bulge in an RNA hairpin. Binding studies of Zn(cy4q) to a series of hairpins containing thymine bulges with different flanking bases showed that the complex had a moderate selectivity for thymine bulges with neighboring purines. The dissociation constants of the most strongly bound Zn(cy4q)-DNA thymine bulge adducts were 100-fold tighter than similar sequences with fully complementary stems or than bulges containing cytosine, guanine, or adenine. In order to probe the role of the pendent group, three additional zinc(II) complexes containing 1,4,7,10-tetraazacyclododecane (cyclen) with aromatic pendent groups were studied for binding to DNA including 1-(2-quinolyl)methyl-1,4,7,10-tetraazacyclododecane (cy2q), 1-(4-biphenyl)methyl-1,4,7,10-tetraazacyclododecane (cybp), and 5-(1,4,7,10-tetraazacyclododecan-1-ylsulfonyl)-N,N-dimethylnaphthalen-1-amine (dsc). The Zn(cybp) complex binds with moderate affinity but little selectivity to DNA hairpins with thymine bulges and to DNA lacking bulges. Similarly, Zn(dsc) binds weakly both to thymine bulges and hairpins with fully complementary stems. The zinc(II) complex of cy2q has the 2-quinolyl moiety bound to the Zn(II) center, as shown by (1)H NMR spectroscopy and pH-potentiometric titrations. As a consequence, only weak (500 μM) binding is observed to DNA with no appreciable selectivity. An NMR structure of a thymine-bulge-containing hairpin shows that the thymine is extrahelical but rotated toward the major groove. NMR data for Zn(cy4q) bound to DNA containing a thymine bulge is consistent with binding of the zinc(II) complex to the thymine N3(-) and stacking of the quinoline on top of the thymine. The thymine-bulge bound zinc(II) complex is pointed into the major groove, and there are interactions with the guanine positioned 5' to the thymine bulge.

Synthesis, characterization, spectroscopic, crystal structures and solution studies of two coordination compounds of zinc(II) and iron(III) based on chelidamic acid and acridine

Two new proton transfer compounds, (acrH)2[Zn(hypydc)2]·10H2O 1 and (acrH)[Fe(hypydc)2]·4.5H2O 2 [where hypydcH2=4-hydroxypyridine-2,6-dicarboxylic acid (chelidamic acid) and acr=acridine] have been synthesized and characterized by elemental analysis, spectral (UV–Vis, IR), 1H NMR, 13C NMR spectroscopy and single crystal X-ray diffraction. The crystallographic analysis revealed that ZnII and FeIII atoms are coordinated by two N atoms and four O atoms from the carboxylate groups of (hypydc)2− ligands, forming a distorted octahedral geometry. In the anions two pyridine rings are inclined to one another by 88.10(5)° and 83.95(13)° for 1 and 2, respectively. The (H2O)n [n=3–6] cyclic–linear water clusters connected two layers of anionic complexes in 1. The crystal packing of 1 show a 3D network formed through H-bonds involving water molecules, NH groups of acridinium and carboxylate anions. In 2 two types of rubout O–H⋯O hydrogen bond synthons, R44 (16) and R44 (18) link the anions and water molecules to form two-dimensional network parallel to bc plane. In crystal structures of both complexes extensive O–H⋯O, N–H⋯O and C–H⋯O hydrogen bonds as well as electrostatic forces, C–O⋯π and π–π stacking play important roles in stabilizing structures. The protonation constants of hypydc and acr, in all of probability protonated forms, the equilibrium constants for the hypydc–acr proton transfer system and the stoichiometry and stability of complexation of this system with Zn2+ and Fe3+ ions in 50% dioxane–50% water (V/V) solvent were investigated by potentiometric pH titration method. The stoichiometries of the most complex species in solution were compared with corresponding crystalline metal ion complexes 1 and 2.

Characterization, crystal structures and solution studies of Zn(II), Cd(II) and Mg(II) complexes obtained from a proton transfer compound including pyridine-2-carboxylic acid and piperazine

The three complexes [Zn(pyc)2(H2O)2]·H2O (1), (pipH2)[Cd(pyc)3]·3H2O (2) and [Mg(pyc)2(H2O)2]·H2O (3) (pycH: pyridine-2-carboxylic acid, pip: piperazine) were prepared using a proton transfer compound (pipH2)(pyc)2 and corresponding metallic salts. The characterization was carried out using IR and NMR spectroscopies and single crystal X-ray diffraction. These complexes crystallize in the space group P21/n of the monoclinic system. Cell parameters of the complexes are a = 9.769(2)A, b = 5.157(1)A, c = 14.539(3)A and β = 90.205(3)° for (1); a = 8.436(2)A, b = 14.616(4)A, c = 19.050(6)A and β = 96.830(5)° for (2); a = 11.639(6)A, b = 8.796(5)A, c = 14.936(8)A and β = 107.221(1)° for (3). The crystal structures of (1) and (3) complexes illustrate that the metal ions are coordinated by two pyridine-2-carboxylate but in crystal structure (2) the metal ion is coordinated by three pyridine-2-carboxylate. The protonation constants of the building blocks of the pyridine-2-carboxylic acid–piperazine adduct and the equilibrium constants for the reaction of pyridine-2-carboxylate with piperazine and the stoichiometry and stability of the Zn2+, Cd2+ and Mg2+ complexes with pycH in aqueous solution were accomplished by potentiometric pH titration. The corresponding stability constants, stoichiometry and distribution of the species were determined with program BEST. The solution studies strongly support the self-association and stoichiometry similar to that observed for the isolated crystalline complexes.

Comparative study on two novel nine-coordinated supramolecular compounds of cerium(III) and yttrium(III): Solid and solution states studies

The solution chemistry and solid-state structures of two new metal–organic compounds of Ce(III) and Y(III) atoms, (4-apyH)3[Ce(pydc)3]·4H2O, 1, and (4-apyH)3[Y(pydc)3]·4H2O, 2 (pydc=pyridine-2,6-dicarboxylate, 4-apy=4-aminopyridine), have been investigated. These compounds were obtained via proton transfer methodology. On the basis of crystallographic data, each MIII is coordinated in a distorted tricapped trigonal prism geometry. Furthermore, [M(pydc)3]3− anions and (4-apyH)+ moieties form a three-dimensional structure by a variety of noncovalent interactions such as extensive O–H⋯O, N–H⋯O and C–H⋯O hydrogen bonds, ion pairing, C–H⋯π, π–π and carbonyl stacking interactions. The equilibrium constants for the binary pydc-4-apy proton transfer system, the stoichiometry and stability of complexation of this system with Ce3+ and Y3+ ions in aqueous solution were investigated by potentiometric pH titration method. In each case, the stoichiometry of the dominant metal complex species in solution was compared to that obtained from the crystal structure.

Thermodynamic dissociation constants of risedronate using spectrophotometric and potentiometric pH-titration

Abstract Risedronate inhibits bone resorption in diseases like osteoporosis, Paget’s disease, tumor bone diseases or the malfunction of phosphocalcium metabolism. The acid-base properties of risedronate in an aqueous solution have been studied in a pH range from 2 to 12 and can be described in terms of four dissociation steps: pK a,2, pK a,4, pK a,5 (related to the dissociation of POH groups) and pK a,3 related to the dissociation of protonated amino group NH3+. The mixed dissociation constants were determined at different ionic strengths I = 0.02 to 0.20 mol dm−3 KCl and of 25°C and 37°C using pH-spectrophotometric and pH-potentiometric titration methods. Determination of group parameters L 0, H T might lead to false estimates of common parameters p K a;therefore, the computational strategy employed is important. A comparison between the two programs ESAB and HYPERQUAD demonstrated that the ESAB program provides a better fit of potentiometric titration curve. The thermodynamic dissociation constants pK aT were estimated by a nonlinear regression of (pK a, I) data and a Debye-Hückel equation at 25°C and 37°C, pK a,2T = 2.37(1) and 2.44(1), pK a,3T = 6.29(3) and 6.26(1), pK a,4T = 7.48(1) and 7.46(2) and pK a,5T = 9.31(7) and 8.70(3) at 25°C and 37°C using pH-spectroscopic data and pK a,2T = 2.48(3) and 2.43(1), pK a,3T= 6.12(2) and 6.10(2), pK a,4T = 7.25(2) and 7.23(1) and pK a,5T = 12.04(5) and 11.81(2) at 25°C and 37°C. The ascertained estimates of three dissociation constants pK a,3, pK a,4, pK a,5 are in agreement with the predicted values obtained using PALLAS

Synthesis, characterization, solution study and crystal structure of complexes of Cr(III), Co(II), Ni(II) and Cu(II) with chelidamic acid and 2,9-dimethyl-1,10-phenanthroline

The title compounds, (dmpH)[Cr(chelH)2]·3H2O, 1, (dmpH)[Co(chelH2)(chelH)]·3H2O, 2, (dmpH)[Ni(chelH2)(chelH)]·2H2O, 3 and [Cu(chelH)(dmp)]·3H2O, 4 (dmp is 2,9-dimethyl-1,10-phenanthroline and chelH3 is chelidamic acid or 4-hydroxypyridine-2,6-dicarboxylic acid) were obtained by one-pot reaction of 2,9-dimethyl-1,10-phenanthroline and 4-hydroxypyridine-2,6-dicarboxylic acid with corresponding salts in aqueous solution. The compounds were identified by IR, MS, elemental analysis and single crystal X-ray crystallography; also they were studied in the solution phase. The compounds 1, 2 and 3 are similar in coordination sphere around the metal ions, with some differences between protonation sites of chelidamate ion and the charge of complex, but compound 4 is essentially different. The compounds 1, 2 and 3 are six coordinated, but 4 is five coordinated. There are various O–H···O, O–H···N and N–H···O hydrogen bonds found in the structures. In a solution study, the protonation constants of dmp and chel, the equilibrium constants of the chel–dmp proton-transfer system and the stoichiometry and stability of complexation of this system with Cr(III), Co(II), Ni(II) and Cu(II) ions in an aqueous solution were investigated by potentiometric pH titration method. The stoichiometry of the most complexes species in solution was found to be very similar to the crystalline cited metal ion complexes.

Synthesis and evaluation of oxovanadium(iv) complexes of Schiff-base condensates from 5-substituted-2-hydroxybenzaldehyde and 2-substituted-benzenamine as selective inhibitors of protein tyrosine phosphatase 1B

Five oxovanadium(IV) complexes, which were divided into two groups, [V(IV)O(bhbb, nhbb)(H(2)O)(2)] (tridentate ligands: H(2)bhbb = 2-(5-bromo-2-hydroxylbenzylideneamino)benzoic acid, 1; H(2)nhbb = 2-(5-nitro-2-hydroxylbenzylideneamino)benzoic acid, 2) and [V(IV)O(cpmp, bpmp, npmp)(2)] (bidentate ligands: Hcpmp = 4-chloro-2-((phenylimino)methyl)phenol, 3; Hbpmp = 4-bromo-2-((phenylimino)methyl)phenol, 4; Hnpmp = 4-nitro-2-((phenylimino)methyl) phenol, 5) have been prepared and characterized by elemental analysis, infrared, UV-visible and electrospray ionization mass spectrometry. The coordination in [V(IV)O(bhbb)(H(2)O)(2)] (1) was confirmed by X-ray crystal structure analysis. The oxidation state of V(IV) with d(1) configuration in 1-5 was confirmed by EPR. The speciation of VO/H(2)bhbb in methanol-aqueous solution was investigated by potentiometric pH titrations. The result indicated that the main species were [V(IV)O(bhbb)(OH)](-) and [V(IV)O(bhbb)(OH)(2)](2-) at the pH range 7.0-7.4. The structure-activity relationship of the vanadium complexes in inhibiting protein tyrosine phosphatases (protein tyrosine phosphatase 1B, PTP1B; T-cell protein tyrosine phosphatase, TCPTP; megakaryocyte protein-tyrosine phosphatase, PTP-MEG2; Src homology phosphatase 1, SHP-1 and Src homology phosphatase 2, SHP-2) was investigated. The oxovanadium(IV) complexes were potent inhibitors of PTP1B, TCPTP, PTP-MEG2, SHP-1 and SHP-2, but exhibited different inhibitory abilities over different PTPs. Complexes 2 and 4 displayed better selectivity to PTP1B over the other four PTPs. Kinetic data showed that complex 2 inhibited PTP1B, TCPTP and SHP-1 with a noncompetitive inhibition mode, but a classical competitive inhibition mode for PTP-MEG2 and SHP-2. The results demonstrated that both the structures of vanadium complexes and the conformations of PTPs influenced PTP inhibition activity. The proper modification of the organic ligand moieties may result in screening potent and selective vanadium-based PTP1B inhibitors.

Evaluation of humic and fulvic acid extracts of compost, oilcake, and soils on complex formation with arsenic

Fulvic acid (FA) and humic acid (HA) were extracted from compost, oilcake, and surface soils collected from arsenic-contaminated and uncontaminated sites of West Bengal. These HA/FA samples were characterised by pH–potentiometric titrations, viscometric measurements, visible spectrophotometry, and surface tension determinations. The results were correlated with coiling–decoiling behaviour, as well as aliphatic/aromatic balance of HA/FAs. The stability constant (logK) of the complexes formed by the natural HA/FA fractions of the given soils were quite stable, and the HA/FA fractions of the organic manures with arsenate in aqueous phases suggested the dependence of such complexation on the nature and properties of the humic polymers, which, in turn, would affect the retention/release of arsenate in soil. The release potential of arsenic from the arsenate–HA/FA complexes by soluble sulfate and nitrate salts was also examined in terms of the appropriate exchange isotherms. In general, sulfate demonstrated a moderately greater degree of exchangeability with arsenate than did nitrate, at higher concentrations.

EPR and speciation simulation study of Cu2+ complexes in an amine-based aqueous precursor system used for preparation of superconducting YBCO coatings

In this work, we investigate the chemistry for an aqueous acetate-triethanolamine-ammonia based YBa(2)Cu(3)O(7-δ) (YBCO) precursor system. These precursor solutions are suited for the chemical solution deposition of superconducting YBCO layers on top of single crystal SrTiO(3) or buffered NiW tapes. The development of this kind of precursor inks often involves trial-and-error experimenting and thus is very time-consuming. To reduce labwork to the minimum, the theoretical prediction of pH stability limits and the complexation behaviour of the different metal ions and complexants in the inks are very important. For this purpose, we simulated, based on literature values, the complexation behaviour of Cu(2+) in the aqueous precursor solutions as a function of pH. To validate the used model, we performed potentiometric pH titrations for solutions with similar composition and checked the correctness of fit between experiment and model. The generated complexometric results are coupled with X-band EPR spectra to further confirm the results. EPR spectra for fully prepared precursor solutions as well as for Cu(2+) reference solutions containing only one type of ligand (acetate, triethanolamine or ammonia) were investigated as a function of pH. We find that, in line with speciation simulation, only acetates are actively complexing the Cu(2+) ions at pH values below 7, while when reaching higher pH levels mainly triethanolamine complexes are formed. Over the entire pH range, no trace of free Cu(2+)or Cu(OH)(2), possibly creating precipitation during gelation and thus complicating further processing, could be found.

Comprehensive studies of non-covalent interactions within four new Cu(ii) supramolecules

This work investigates the supramolecular aggregation of Cu(II) complexes based on a combination of the heterocyclic N-donor ligand 2-aminopyrimidine (2-apym) and a variety of different carboxylate ligands, like salicylic acid (H2SAL), maleic acid (H2MAL), and glycine (HGLY). Four new Cu(II) complexes [Cu(HSAL)2(2-apym)2] (I), [Cu(HSAL)2(2-apym)2]·(H2SAL)2(2-apym) (I′), {(H2-apym)[Cu(GLY)(μ-Cl)2Cl]}n (II) and [Cu(μ-MAL)(2-apym)]n (III) have been synthesized and characterized by elemental analyses, FT-IR spectra, and X-ray structural analyses. I and I′ appear as molecular clusters whereas II is a 1-D coordination polymer with weak axial Cu–Cl interactions. However the last one shows a 2-D coordination polymer with trigonal bipyramidal geometry for Cu(II) ion. The two last cases have no molecular fragments packed with non-covalent interactions. In these new supramolecular compounds, existent species join together with the cooperation of multiple inter/intra-molecular classical O–H⋯O/N, N–H⋯O/N, and non-classical N–H⋯Cl hydrogen bonds (H-bonds), offset face to face π⋯π, edge to face C/N–H⋯π, and lp⋯π stacking interactions in the form of various homo/hetero-synthons leading to architecturally different structures. DFT calculations were used to estimate the binding energy of the involved non-covalent interactions and whole stabilization energy of related network of I, I′, and II. Theoretical calculations facilitate the comparison of intermolecular interactions, which demonstrate that for all of I–II, N–H⋯N and N–H⋯O H-bonds govern the network formation. The equilibrium constants for the three proton-transfer systems including SAL/2-apym, GLY/2-apym, MAL/2-apym, the stoichiometry and stability of complexation of these systems with Cu2+ ion in aqueous solution were investigated by potentiometric pH titration method. The stoichiometries of the most complex species in solution was compared to the crystalline Cu2+ ion complexes with the cited proton-transfer systems.

X-Ray, Crystal Structure and Solution Phase Studies of a Polymeric SrII Compound

In the crystal structure of the title polymeric compound, (C 42 H38 N6O33 Sr 5.2(H2O)) n, five independent metal atoms (Sr1-Sr5) have different coordination environments. The Sr1 and Sr5 atoms are nine coordinated and feature distorted tricapped trigonal-prismatic and capped square-antiprismatic geometries, respectively. The rest Sr II atoms have eight coordination numbers. These units are connected via the carboxylate O atoms of mono- and di anionic forms of pyridine- 2,6-dicarboxylic acid, (pydcH 2), and bridging water molecules that resulted in the formation of polymeric layers in 3-D. In the crystal structure, non-covalent interactions consisting of hydrogen bonds (O—H···O and C—H···O), �-� (interplanar distances of 3.413(2); 3.601(2) A) and CO···� (O···� distances of 3.249(3); 3.275(3) A) stacking interactions play an important roles in stabilizing the structure. The protonation constants of propane-1, 2-diamine (1, 2-pn) and pyridine-2,6-dicarboxylate ion (pydc) 2- , the equilibrium constants for the pydc-1,2-pn proton transfer system and the stoichiometry and stability of this system with Sr 2+ ion in aqueous solution were investigated by potentiometric pH titrations. The stoichiometry of one of the most abundant complexed species in solution was found to be the same as that of the crystalline Sr II complex.

Supramolecular structure of calcium(II) based on chelidamic acid: An agreement between theoretical and experimental studies

A novel supramolecular structure of an s-Block metal ion, Ca(II) atom, formulated as (pnH2)2au][Ca2(H2O)2(Hhypydc)4]·4H2O (1), was synthesized and characterized by elemental analysis, IR, 1H and 13C NMR spectroscopies and single crystal X-ray diffraction. Compound 1 is a member of a large family of supramolecular metallic compounds recently derived from a proton transfer ion pair, (pnH2)(Hhypydc), where pn is propane-1,3-diamine and (Hhypydc)2-is 4-hydroxypyridine-2,6-dicarboxylate ion. Based upon the molecular structure analysis of the binuclear anionic complex, the coordination environment around each Ca(II) atom is pentagonal bipyramidal with seven-coordination number. The strong hydrogen bonding between hydroxyl groups of two neighboring anionic complexes produce the nice tape as X-like supramolecular structure. Optimization was carried out using two standard basis sets of 6-31G (d,p) for the single anionic complex (S) and LanL2MB basis set for the double anionic complexes (D) which describe the electrons of all atoms. As an interesting finding from our theoretical calculations, when we reoptimized the double complexes in the presence of strong hydrogen bond interaction between two hydroxyl groups, O3-H3A…O8ii (ii = x-1, y, z-1), it was revealed that the parallel position of ligands to each other was exactly like that of the solid state. The complexation reaction of H3hypydc with Ca2+ in aqueous solution was investigated by potentiometric pH titrations, the equilibrium constants and species distribution in various pHs. The for major complexes formed are described.

A proton transfer and a nickel(II) compound including pyridine-2,6-dicarboxylate and Phenylhydrazinium ions: Synthesis, characterization, crystal structure and solution study

The new compounds, (phhyH)2(pydc), 1 and (phhyH)[Ni(pydc)(pydcH)].3H2O, 2, phhy: phenylhydrazine, pydcH2: pyridine-2,6-dicarboxylic acid, were synthesized and characterized by IR, 1H NMR, 13C NMR and UV spectroscopy. The structure of 2 was determined by X-ray crystallography. In the crystal structure, the metal ion was six coordinated by two tridentate (pydc)2− and (pydcH)− groups and each anionic complex unit, [Ni(pydc)(pydcH)]− was accompanied by one (phhyH)+ as counter ion and two water molecules. In compound 2, a large number of O-HOO, N-HO and C-HO hydrogen bonds were observed. These interactions as well as other noncovalent interactions such as ion pairing, C-Oπ and π-π stacking play an important role in the formation and stabilization of the crystal lattice. In the solution study, the equilibrium constants for the binary pydc-phhy proton transfer system, the stoichiometry and stability of complexation of this system with Ni2+ ion in aqueous solution were investigated using potentiometric pH titration method. The stoichiometry of the most abundant species in the solution was compared to the crystalline cited metal ion complexes.

Recognition and catalytic hydrolysis of adenosine 5′-triphosphate by cadmium(II) and L-glutamic acid

Interactions among Cd2+, glutamic acid (Glu), and adenosine 5′-triphosphate (ATP) have been studied by potentiometric pH titration, IR, Raman, fluorescence, and NMR methods. In the Cd2+–ATP binary system, the main interaction sites are the α-, β-, and γ-phosphate groups, N-1, and/or N-7. Cd2+ binds to the N-1 site at relatively low pH and binds to the N-7 site of adenosine ring of ATP with increasing pH. In the Cd2+–Glu–ATP ternary system, ATP mainly binds to Cd2+ by the triphosphate chain. Oxygens of Glu coordinate with Cd2+ to form a complex to catalyze ATP hydrolysis. Hydrolysis of ATP catalyzed by the CdGlu complex was studied at pH 7.0 and 80°C by 31P-NMR spectrometry. Kinetics studies showed that the rate constant of ATP hydrolysis was 0.0199 min−1 in the ternary system, which is 9.9-fold faster than that in the ATP solution (2.01 × 10−3 min−1). Hydrolysis occurs through an addition–elimination reaction mechanism with Cd2+ regulating the recognition and catalytic hydrolysis of ATP; water participates in the hydrolysis reaction of ATP at different steps with different functions in the ternary system.

Hydrothermal synthesis, X-Ray crystallography, TGA and SEM analyses and solution studies of a novel Nano-sized 1D zinc(II) coordination Polymer

A novel coordination polymer of zinc(II) atom, [(pipzH2)[Zn(pyzdc)2].6H2O]n (1) (H2pyzdc and pipz are pyrazine-2,3- dicarboxylic acid and piperazine, respectively), was successfully synthesized under hydrothermal conditions and structurally characterized by means of elemental analysis, FTIR, TGA and SEM. Polymer 1 was further structurally characterized by single crystal X-ray diffraction consisting of 1D-polymeric units. The crystal structure of the title polymer consisted of polymeric Zn complex anions and discrete piperazindiium cations. The Zn cation, located on the inversion center, was N,O-chelated by two (pyzdc)2− anions in the basal plane, and was further coordinated by two carboxyl O atoms from the adjacent pyzdc anions in the axial directions with a longer Zn-O bond distance of 2.1746(15) A, forming a distorted ZnN2O4 coordination geometry. The pyzdc anions bridged the Zn cations to the one-dimensional polymeric chains running along the crystalographic b axis. The (pipzH2)2+ linked with the complex chains via kinds of hydrogen bonds. The polymer 1 crystallized in the monoclinic space group P21/n with Z = 2. The cell parameters of the title polymer were a = 6.5318(16) A, b = 17.492(4) A, c = 10.688(3) A and β = 100.841(4)°. The polymer 1 bears ion-pairing interactions, O-HO, N-HO, and C-HO hydrogen bonds as main factors in the formation of its 1D supramolecular architecture. Obtained results from TGA showed that the title polymer was thermally quite stable, and so its framework possessed remarkable thermal stability up to 700 °C. The SEM analysis verified that layers present in 1 were formed in Nano-sized particle. The protonation constants of acridine (Acr), H2pyzdc, and pipz as the building blocks of the proton transfer systems including pyzdc-Acr in mixed 20% dioxane-80% water (V/V) solvent and pyzdc-pipz in aqueous solvent, and the corresponding stability constants of these systems were determined by potentiometric study. The stoichiometry and stability of complexation of these systems with Zn2+ ion were investigated by potentiometric pH titration method. The stoichiometry of the most complex species in the solution was compared with the corresponding crystalline metal ion complexes.

Two Zn(II) and Cd(II) compounds derived from 9-aminoacridine: Syntheses, characterizations, crystal structures and solution Studies

The aqueous reactions of zinc(II) and cadmium(II) nitrate and pyridine-2,6-dicarboxylic acid, (pydcH2), with 9-aminoacridine, (AAcr), resulted in the formation of two new proton transfer compounds, (AAcrH)2[Zn(pydc)2].3H2O (1) and (AAcrH)2[Cd(pydc)2].4H2O (2). The compounds were characterized using IR spectroscopy and single crystal X-ray diffraction. Both compounds crystallized in the triclinic crystal system, space group \(P\bar 1\), with two molecules per unit cell. The anions were six-coordinate complexes with distorted octahedral geometries around the Zn(II) and Cd(II) centers. The dihedral angles indicated that the two (pydc)2− ligands were almost perpendicular to each other. The complex anions of [M(pydc)2]2- were neutralized with (AAcrH)+ cations. These cations formed extended stacks throughout the structures. The water molecules clustered around cyclic tetramers, bridging the anions and forming a link to the aminoacridiunium stacks. A potentiometric pH titration method was used to investigate the protonation constants of AAcr and pydc, the pydc-AAcr proton transfer equilibrium constants, and the stoichiometries and stabilities of complex formation with Zn2+ and Cd2+ ions in 50% dioxane-50% water.

Carboxyethylated polyaminostyrene for selective copper removal

In order to prepare copper selective chelating resin, β-alanine functionality was introduced into polystyrene matrix by the aza-Michael addition of poly(4-aminostyrene) to acrylic acid. The resin was characterized by elemental analysis and pH potentiometric titration in terms of the degree of carboxyethylation (DS = 1.3) and protonation constant of the amine group (log K H = 7.48). The optimum pH for Cu2+ adsorption was found to be 7–8 (0.1 M ammonium acetate buffer) and the contact time required to achieve the equilibrium was about 1 h. The adsorption kinetics follows a pseudo-second order reaction rate, where the initial stage is governed by intraparticle diffusion. The adsorption isotherm data are in good agreement with the Langmuir model. The resin shows high adsorption capacity (1.26 mmol/g) and exhibits high selectivity toward Cu2+ ions with no affinity to Zn2+, Co2+, Cd2+ ions and only weak affinity to Ni2+ ions.

Ternary oxovanadium(IV) complexes with amino acid-Schiff base and polypyridyl derivatives: Synthesis, characterization, and protein tyrosine phosphatase 1B inhibition

To investigate the structure–activity relationship of vanadium complexes in inhibiting protein tyrosine phosphatase1B (PTP1B), eight mixed-ligand oxovanadium(IV) complexes, [V IVO(SalAla)(NN)] (H 2SalAla for salicylidene alanine, NN for N,N′-donor heterocyclic base, namely, 2,2′-bipyridine (bpy, 1 ), 1,10-phenanthroline (phen, 2 ), dipyrido[3,2-d:2′,3′-f]quinoxaline (dpq, 3), dipyrido[3,2-a:2′,3′-c]phenazine (dppz, 4 )), [V IVO(SalLys)(dpq)] ( 5 ), [V IVO(SalLys)(dppz)] ( 6 ), [V IVO(SalAsp)(dppz)], ( 7 ) and [V IVO(SalTrp)(dppz)] ( 8 )), of which 3– 8 are new, have been prepared and characterized by elemental analysis, infrared, UV–visible, electrospray ionization mass spectrometry and conductivity. The molar conductance data confirmed the non-electrolytic nature of the complexes in DMSO solution. The coordination in [V IVO (SalAla)(phen)] ( 2 ) was confirmed by X-ray crystal structure analysis. The oxidation state of V(IV) with d 1 configuration in 2 was confirmed by EPR. The speciation of VO–SalAla–phen in aqueous solution was investigated by potentiometric pH titrations. The results indicate that the main species are two ternary complexes at the pH range 7.0–7.4. Biochemical assays demonstrate that the mixed-ligand oxovanadium(IV) complexes are potent inhibitors of PTP1B with IC 50 values in the range of 62–597 nM, approximately 3–10 fold weaker in potency than those of similar mixed-ligand oxovanadium(IV) complexes of salicylidene anthranilic acid (SAA) derivative with polypyridyl ligands, except complex 8 , which exhibits comparable or better inhibition activity than those of the mixed-ligand oxovanadium(IV) complexes of SAA derivative with polypyridyl ligands. The results demonstrate that the structures of vanadium complexes influence the PTP1B inhibition activity. Kinetics assays reveal that complex 2 inhibits PTP1B in a competitive manner.