Synthesis and characterization of Co(II), Ni(II), Cu(II) and Zn(II) complexes of tridentate Schiff base derived from vanillin and DL-alpha-aminobutyric acid

Co(II), Ni(II), Cu(II) and Zn(II) complexes of the Schiff base derived from vanillin and dl-alpha-aminobutyric acid were synthesized and characterized by elemental analysis, IR, electronic spectra, conductance measurements, magnetic measurements, powder XRD and biological activity. The analytical data show the composition of the metal complex to be [ML(H(2)O)], where L is the Schiff base ligand. The conductance data indicate that all the complexes are non-electrolytes. IR results demonstrate the tridentate binding of the Schiff base ligand involving azomethine nitrogen, phenolic oxygen and carboxylato oxygen atoms. The IR data also indicate the coordination of a water molecule with the metal ion in the complex. The electronic spectral measurements show that Co(II) and Ni(II) complexes have tetrahedral geometry, while Cu(II) complex has square planar geometry. The powder XRD studies indicate that Co(II) and Cu(II) complexes are amorphous, whereas Ni(II) and Zn(II) complexes are crystalline in nature. Magnetic measurements show that Co(II), Ni(II) and Cu(II) complexes have paramagnetic behaviour. Antibacterial results indicated that the metal complexes are more active than the ligand.     

Dissociation of gas-phase dimeric complexes of lactic acid and transition-metal ions formed under electrospray ionization conditions; the role of reduction of the metal ion

Dimeric complex ions of the type [M(A-H)A]+, where M=metal ion (Co, Ni, Cu, and Zn) and A=ligand (lactic acid, methyl lactate or ethyl lactate), were generated in the gas phase under electrospray ionization conditions. The collision-induced dissociation spectra of [M(A-H)A]+ ions were recorded to study the behaviour of ligand and metal ions in decomposition of these dimeric complex ions. Based on the fragmentation pathways observed for complex ions of lactic acid, it is found that both the carboxylic and hydroxyl groups of lactic acid are involved in the complex formation following displacement of a proton by the metal ion. The dimeric complex ions of Co, Ni, and Zn dissociated to yield similar types of ions, whereas that of Cu behaved differently. The dissociations of Co-, Ni-, and Zn-bound dimeric complexes involved losses of neutral molecules while keeping the oxidation state of the metal ion unchanged. However, elimination of radicals is found in the dissociation of dimeric complex ions of Cu, and the oxidation state of copper is reduced from Cu(II) to Cu(I) in the resulting fragment ions. The deprotonated ligand is involved in the fragmentation pathway of Cu complexes, whereas it is intact in other complexes. The oxidation state of the metal ion, nature of the ligand, and site of attachment to the metal ion are found to control the dissociation of these dimeric complex ions.     

BINDING ABILITY OF OXINE-LIKE LIGANDS. POTENTIOMETRIC AND POLAROGRAPHIC STUDY ON Ni(II), Co(II), Zn(II) AND Cd(II) COMPLEXES OF 9-HYDROXYPYRIDO(1,2,-α)PYRIMIDIN-4-ONE

Abstract

Potentiometric and polarographic studies of metal ion coordination with 9-hydroxypyrido[1,2-α]pyrimidin-4-one (HPP) with Ni(II), Zn(II), Co(II) and Cd(II) ions have been carried out. For comparison, stability constants with 8-hydroxy-imidazo[1,2-α]pyridine (HIP) were also measured. Due to the low solubility of the latter ligand complexes, measurements were made also in dioxan/water solutions. In the case of both ligands the coordination mode is the same. The oxine-like binding via {N, O^?} donor set leads to formation of stable ML and ML₂ complexes. Stability constants clearly indicate that both ligands are very effective and the HPP, having a more favourable position of the electron pair on nitrogen, forms stronger complexes with smaller metal ions i.e., Ni(II), Zn(II) and Co(II). Cd(II) is better fitted to the HIP donor set.     

Synthesis and spectroscopic studies of novel Cu(II), Co(II), Ni(II) and Zn(II) mixed ligand complexes with saccharin and nicotinamide

Four novel mixed ligand complexes of Cu(II), Co(II), Ni(II) and Zn(II) with saccharin and nicotinamide were synthesised and characterised on the basis of elemental analysis, FT-IR spectroscopic study, UV–Vis spectrometric and magnetic susceptibility data. The structure of the Cu (II) complex is completely different from those of the Co(II), Ni(II) and Zn(II) complexes. From the frequencies of the saccharinato CO and SO₂ modes, it has been proven that the saccharinato ligands in the structure of the Cu complex are coordinated to the metal ion ([Cu(NA)₂(Sac)₂(H₂O)], where NA — nicotinamide, Sac — saccharinato ligand or ion), whilst in the Co(II), Ni(II) and Zn(II) complexes are uncoordinated and exist as ions ([M(NA)₂(H₂O)₄](Sac)₂).     

Synthesis,Characterization and Spectral Studies of Triethanolamine Complexes of Metal Saccharinates. Crystal Structures of [Co(TEA)2](SAC)2 AND [Cu2(μ-TEA)2(SAC)2]·2(CH3OH)

The novel transition metal saccharinate complexes of triethanolamine (TEA) have been synthesized and characterized by elemental analyses, magnetic moments, UV-Vis and IR spectra. Mn(II), Co(II), Ni(II), Zn(II), Cd(II) and Hg(II) form mononuclear complexes of [M(TEA)₂](SAC)₂, where SAC is the saccharinate ion, while the Cu(II) complex is dimeric. The TEA ligand acts as a tridentate N,O,O'-donor ligand and one ethanol group is not involved in coordination. The SAC ion does not coordinate to the metal ions and is present as the counter-ion in the Mn(II), Co(II), Ni(II), Zn(II), Cd(II) and Hg(II) complexes, but coordinates to the Cu(II) ion as a monodentate ligand. The crystal structures of the [Co(TEA)₂](SAC)₂ and [Cu₂(μ-TEA)₂(SAC)₂]·2(CH₃OH) complexes were determined by single crystal x-ray diffraction. The Co(II) ion has a distorted octahedral coordination by two TEA ligands. The Cu(II) complex crystallizes as a dimethanol solvate and has doubly alkoxo-bridged centrosymmetric dimeric molecules involving two tridentate triethanolaminate (deprotonated TEA) and two monodentate SAC ligands. The geometry of each Cu(II) ion is a distorted square pyramid. Both crystal structures are stabilized by hydrogen bonds to form a three-dimensional network.     

Salisaldehyde-2-aminobenzimidazole schiff base complexes of Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II)

New metal complexes of Fe(III), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) with salicylidine-2-aminobenzimidazole (SABI) are synthesized and their physicochemical properties are investigated using elemental and thermal analyses, IR, conductometric, solid reflectance and magnetic susceptibility measurements. The base reacts with these metal ions to give 1:1 (Metal:SABI) complexes; in cases of Fe(III), Co(II), Cu(II), Zn(II) and Cd(II) ions; and 1:2 (Metal:SABI) complexes; in case of Ni(II) ion. The conductance data reveal that Fe(III) complex is 2:1 electrolyte, Co(II) is 1:2 electrolyte, Cu(II), Zn(II) and Cd(II) complexes are 1:1 electrolytes while Ni(II) is non-electrolyte. IR spectra showed that the ligand is coordinated to the metal ions in a terdentate mannar with O, N, N donor sites of the phenloic -OH, azomethine -N and benzimidazole -N3. Magnetic and solid reflectance spectra are used to infer the coordinating capacity of the ligand and the geometrical structure of these complexes. The thermal decomposition of the complexes is studied and indicates that not only the coordinated and/or crystallization water is lost but also that the decomposition of the ligand from the complexes is necessary to interpret the successive mass loss. Different thermodynamic activation parameters are also reported, using Coats-Redfern method. This revised version was published online in July 2006 with corrections to the Cover Date.     

Metal complexes of bridging neutral radical ligands: pymDTDA and pymDSDA

Metal complexes of the 4-(2'-pyrimidyl)-1,2,3,5-dithiadiazolyl (pymDTDA) neutral radical ligand and its selenium analogue (pymDSDA) are presented. The following series of metal ions has been studied using M(hfac)(2) as the coordination fragment of choice (hfac = 1,1,1,5,5,5-hexafluoroacetylacetonato): Mn(II), Co(II), Ni(II), and Zn(II). The binuclear cobalt and nickel complexes of pymDTDA both exhibit ferromagnetic (FM) coupling between the unpaired electrons on the ligand and the metal ion, while the binuclear zinc complex of pymDTDA is presented as a comparative example incorporating a diamagnetic metal ion. The binuclear manganese complex of pymDTDA, reported in a preliminary communication, is compared to the pymDSDA analogue, and new insight into the magnetic behavior reveals that intermolecular magnetic coupling, mediated by chalcogen-oxygen contacts, gives rise to a significant increase in the χT product at low temperature. Surprisingly, the binuclear nickel complex of pymDSDA forms dimers in the solid state, as do the mononuclear complexes of cobalt and nickel with pymDTDA. In addition, mixed mononuclear/binuclear complexes of Mn- and Zn(pymDTDA) have been identified.     

Chelating Polymers. II. Amino Acetic Acid Chelating Polymers Derived from Hydroxyarylamino Acetic Acids

The prototype dimeric chelating compounds 3,3′-methylenebis-[N(4-hydroxyphenyl) iminodiacetic acid] and 3,3′-methylenebis-[N(4-methoxyphenyl) iminodiacetic acid] were synthesized and characterized by composition analysis, infrared spectroscopy, and potentiometric titration data. Their chelating characteristics with Cu(II), Ni(II), Co(II), and Zn(l1) ions were established by composition analysis and comparative infrared spectroscopy.

The results suggest chelation and structures of the usual iminodiacetatometal complex type for the Ni(II), Co(II), and Zn(I1) compounds of 3,3′methylenebis-[N-(4-hydroxyphenyl) iminodiacetic acid] and for the Cu(I1, Ni(II), and Co(I1) compounds of 3,3′-methylenebis-[N-(4-methoxyphenyl) iminodiacetic acid]. The composition analysis of each of these compounds indicates 1:2:2 mole ratios of ligand to metal ion to water. Square planar structures are proposed wherein the two iminodiacetatometal chelate moieties are essentially independent of each other.

The composition analysis of the Cu(II) compound of 3,3′-methylenebis-[N-(4-hydroxyphenyl) iminodiacetic acid] indicates a 1:2:1 mole ratio of ligand to metal ion to water. Structures are proposed in which some of the carboxylate groups are bridges between two metal coordination centers.

The composition analysis of the Zn(II) compound of 3,3′-methylenebis-[N-(4-methoxyphenyl) iminodiacetic acid] indicates a 1:1 mole ratio of ligand to metal ion. A structure is proposed in which both nitrogen atoms and two of the four carboxylate groups of the dimeric ligand are coordinated to the same metal ion.

A preliminary investigation was made of oligomeric compounds analogous to the prototype dimeric compounds.     

Bioactivity of some divalent M(II) complexes of penicillin based Schiff base ligand: Synthesis,spectroscopic characterization,and thermal study

A series of four novel metal complexes of Co(II), Ni(II), Cu(II) and Zn(II) were synthesized from Schiff base derived from amoxicillin (AMX) and picolinaldehyde (PC2). The ligand and metal complexes were fully characterized by physical and spectral techniques such as elemental microanalysis, conductivity, FT-IR, ¹H & ¹³C NMR, UV–vis, mass spectra, EPR, magnetic moment measurement, TGA/DTA, PXRD and antibacterial activity study. The spectroscopic study revealed 1:2 metal ligand ratio and coordination sites in the ligand for metal ions were evaluated by analysis of the spectral results. The surface morphology of the complexes was evaluated by SEM analysis. Molar conductivity implies non-electrolytic nature of the complexes. UV–vis. spectral study nicely supports octahedral geometry for Co(II) and Zn(II) complexes and tetrahedral geometry for Cu(II) complex. The kinetic parameters were extracted from Coats-Redfern equation. The PXRD study revealed nano-crystalline nature of Co(II), Ni(II) & Cu(II) complexes and amorphous nature of Zn(II) complex. The proposed geometry of the complexes was optimized by MM2 calculation supported in Cs-ChemOffice Ultra-11 program. The ligand and metal complexes were screened for antibacterial potency against four human pathogenic clinical strains of bacteria and the data revealed their promising antibacterial activity.     

On the mechanism of electroreduction of sulphur-containing ligands induced by the electroreduction of transition metal cations

The large scale electrolysis of Zn(II), Cd(II), Hg(II), Cu(II), Ni(II), Co(II), Co(III), Fe(II), Mn(II), Cr(II), Cr(III), Bi(III), In(III) and Sb(III) at mercury electrodes in presence of mercaptoacetic acid, 3-mercaptopropionic acid, cysteine and thiourea was carried out and the products were investigated. In case of transition metal ions the catalytic reduction of organic compounds resulting in the formation of sulphide ions was found. There are two possible ways of the production of these ions: (i) consisting in the formation of a complex between transition metal ion and organic ligand which is subsequently, reduced, and (ii) direct electroreduction of organic compound on the electrode modifiied by the deposition of metal and metal sulphide. For both cases the mechanism of electroreduction was discussed.     

Parafac decomposition of three-way kinetic-spectrophotometric spectral matrices corresponding to mixtures of heavy metal ions

Binary and ternary mixtures of some of the following heavy metal ions Zn(II), Ni(II), Pb(II), Co(II) and Cd(II) were analyzed by a ligand substitution kinetic method. Three-way data matrices were generated by acquisition of UV-Vis spectra (332-580 nm) as a function of the time of a substitution reaction observed between the complex of the heavy metal ions with the non selective metallochromic indicator 4-(2-pyridylazo) resorcinol (PAR) and EDTA, and of different relative concentration of the metal ions (1-6 mM). The PARAFAC trilinear model, without restrictions, was used in the data analysis. A full decomposition of the data matrices was obtained (spectra, concentration and time profiles). It was shown that ligand substitution kinetic methods coupled to three-way chemometric analytical methods can be used for the development of robust sensors for the analysis of binary [Zn(II)+Ni(II), Pb(II)+Cd(II), Zn(II)+Pb(II)] or ternary [Zn(II)+Pb(II)+Co(II)] mixtures of metal ions in the micromolar concentration range.     

Di- and trinuclear complexes derived from hexakis(2-pyridyloxy)cyclotriphosphazene. Unusual P-O bond cleavage in the formation of [{(L'CuCl)2(Co(NO3)}Cl] (L' = N3P3(OC5H4N)5(O))

Hexakis(2-pyridyloxy)cyclotriphosphazene (L) is an efficient multisite coordination ligand which binds with transition metal ions to produce dinuclear (homo- and heterometallic) complexes [L(CuCl)(CoCl3)], [L(CuCl)(ZnCl3)], [L(CoCl)(ZnCl3)], and [L(ZnCl2)2]. In these dinuclear derivatives the cyclophosphazene ligand utilizes from five to six nitrogen coordination sites out of the maximum of nine available sites. Further, the spacer oxygen that separates the pyridyl moiety from the cyclophosphazene ring ensures minimum steric strain to the cyclophosphazene ring upon coordination. This is reflected in the near planarity of the cyclophosphazene ring in all the dinuclear derivatives. In the dinuclear heterobimetallic derivatives one of the metal ions [Cu(II) or Co(II)] is hexacoordinate and is bound by the cyclophosphazene in a eta5-gem-N5 mode. The other metal ion in these heterobimetallic derivatives [Co(II) or Zn(II)] is tetracoordinate and is bound in an eta(1)-N(1) fashion. In the homobimetallic derivative, [L(ZnCl2)2], one of the zinc ions is five-coordinate (eta3-nongem-N3), while the other zinc ion is tetracoordinate(eta2-gem-N2). The reaction of L with CuCl2 followed by Co(NO3)2.6H2O yields a trinuclear heterobimetallic complex [{(L'CuCl)2Co(NO3)}Cl] [L' = N3P3(OC5H4N)5(O)]. In the formation of this compound an unusual P-O bond cleavage involving one of the phosphorus-pyridyloxy bonds is observed. The molecular structure of [{(L'CuCl)2Co(NO3)}Cl] [L' = N3P3(OC5H4N)5(O)] reveals that each of the two the P-O-cleaved L' ligands is involved in binding to Cu(II) to generate the motif L'CuCl. Two such units are bridged by a Co(II) ion. The coordination environment around the bridging Co(II) ion contains four oxygen (two P-O units, one chelating nitrate) and two nitrogen atoms (pyridyloxy nitrogens).     

Understanding ion sensing in Zn(II) porphyrins: spectroscopic and computational studies of nitrite/nitrate binding

The development of effective sensor elements relies on the ability of a chromophore to bind an analyte selectively and then study the binding through changes in spectroscopic signals. In this report the ability of Zn(II) Tetraphenyl Porphyrin (ZnTPP) to selectively bind nitrite over nitrate ions is examined. The results of Benesi-Hildebrand analysis reveals that ZnTPP binds NO(2)(-) and NO(3)(-) ions with association constants of 739 ± 70 M(-1) and 134 ± 15 M(-1), respectively. Interestingly, addition of a pyridine ligand to the fifth coordination site of the Zn(II) center enhances ion binding with the association constants increasing to 71,300 ± 8,000 M(-1) and 18,900 ± 3,000 M(-1) for nitrite and nitrate, respectively. Density functional theory calculations suggest a binding mechanism through which Zn(II)-porphyrin interactions are disrupted by ligand and base coordination to Zn(II), with Zn(II) having more favorable overlap with nitrite orbitals, which are less delocalized than nitrate orbitals. Overall, these provide new insights into the ability to tune the affinity and selectivity of porphyrin based sensors utilizing electronic factors associated with the central Zn(II) ion.     

Coordination properties of hydralazine Schiff base Synthesis and equilibrium studies of some metal ion complexes

In the present study, a new ligand is prepared by condensation of hydralazine (1-Hydralazinophthalazine) with 2-butanon-3-oxime. The acid-base equilibria of the schiff-base and the complex formation equilibria with the metal ions as Cu(II), Ni(II), Co(II), Cd(II), Mn(II) and Zn(II) are investigated potentiometrically. The stability constants of the complexes are determined and the concentration distribution diagrams of the complexes are evaluated. The effect of metal ion properties as atomic number, ionic radius, electronegativity and ionization potential are investigated. The isolated solid complexes are characterized by conventional chemical and physical methods. The potential coordination sites are assigned using the i.r. and (1)H NMR spectra. The structures of the isolated solid complexes are proposed on the basis of the spectral and magnetic studies.     

Symposium on Biomedical Polymers

ABSTRACT

Glycine functions were incorporated into 2–20 mol% N,N′-methylene-bis-acrylamide (NNMBA)-crosslinked polyacrylamides by transamidation with excess sodium salt of glycine. Complexation characteristics of glycine functions in different structural environments were investigated towards Co(II), Ni(II), Cu(II) and Zn(II) ions. The observed trend in complexation was found to be: Cu(II) > Ni(II) > Co(II) > Zn(II). The polymeric ligands and metal complexes were characterized by various spectral techniques. The polymeric ligands could be recycled several times and the metal ion desorbed resins showed specificity to the desorbed metal ion than other metal ions. This originates from the development of certain ‘pockets’ left by the desorbed metal ion or the ‘memory’ of the polymeric ligands for the desorbed metal ion. This lightly crosslinked systems showed much faster rebinding kinetics. The conditions of metal ion binding and rebinding were optimized to exploit the specific and selective separation of metal ions using metal ion desorbed systems. The specificity and selectivity characteristics depend on the degree of NNMBA crosslinking.     

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.     

Metal-binding properties of an Hpn-like histidine-rich protein

The Hpn-like protein (Hpnl), a histidine- and glutamine-rich protein, is critical for Helicobacter pylori colonization in human gastric muscosa. In this study, the thermodynamic properties of Ni(II), Cu(II), Co(II), and Zn(II) toward Hpnl were studied by isothermal titration calorimetry (ITC). We found that Hpnl exhibits two independent binding sites for Ni(II) as opposed to one site for Cu(II), Co(II), and Zn(II). Protease digestion and chemical denaturation analysis further revealed that Ni(II) confers a higher stability upon Hpnl than other divalent metal ions. The potential Ni(II) binding sites are localized in the His-rich domain of Hpnl as confirmed by mutagenesis in combination with modification of histidine residues of the protein. We also demonstrated that the single mutants (H29A and H31A) and tetrameric mutant (H29-32A) cut nearly half of the binding capacity of Hpnl towards nickel ions, whereas other histidine residues (His30, 32, 38, 39, 40, and 41) are nonessential for nickel coordination. Escherichia coli cells that harbored H29A, H31A, and H29-32A mutant genes exhibited less tolerance toward high concentrations of extracellular nickel ions than those with the wild-type gene. Our combined data indicated that the conserved histidine residues, His29 and His31 in the His-rich domain of Hpnl, are critical for nickel binding, and such a binding is important for Hpnl protein to fulfill its biological functions.     

Matrix-assisted laser desorption/ionization studies on transition metal complexes of benzimidazole thiosemicarbazones

The transition metal (M=Fe, Co, Ni, Cu, Zn, Cd and Hg) complexes of 2- acetylbenzimidazolethiosemicarbazone (L(1)) and 1-methyl 2-acetylbenzimidazole-thiosemicarbazone (L(2)) are analyzed by MALDI using HCCA, THP, MMNPD and DMN as the matrices. All the MALDI spectra are clean without any contribution from the complex ions resulted by multiple proton addition/removal. All the complexes, except Cu, irrespective of the matrix used, show 1:2 complex ions wherein two ligands (neutral or deprotonated) complex with the metal ion depending on the nature and stable oxidation state of the central metal ion viz., [M + 2L - 2H](+) ion for Fe and Co complexes (+3 oxidation state) and [M + 2L - H](+) ion for Ni, Zn, Cd and Hg (+2 oxidation state). The Cu complex show 1:1 complex ion corresponding to [2M + 2L - 2H](+) ions. When HCCA is used as a matrix, the complex ions due to ligand exchange by matrix are also found, and this process is relatively more if a neutral ligand is bound to the metal ion in the original complex ion. The type of complex ions found under MALDI experiments are similar to those found under ESI experiments. However, the complex ions due to reduction of Cu are found only in the MALDI analysis of Cu complexes.