IR and Raman study on the interactions of the 5′-GMP and 5′-CMP phosphate groups with Mg(II), Ca(II), Sr(II), Ba(II), Cr(III), Co(II), Cu(II), Zn(II), Cd(II), Al(III) and Ga(III)

The chief motive behind this research is the interest provoked by the presence of metal ions as necessary stabilizers of the negative charges of phosphate groups in nucleic acids. The effect that the presence of different metal ions produces on the band principally assigned to the nu(s) PO(3)(2-) mode has been studied using FT-IR and FT-Raman spectroscopy. The results obtained reveal the diagnostic capacity of these techniques in determining the type of metal ion interaction with respect to the mononucleotides that form DNA and RNA, providing a tool for improving the knowledge of the stabilizing or destabilizing effects of these ions on such macromolecules. The metal complexes of the ribonucleotides 5'-CMP and 5'-GMP with Mg(II), Ca(II), Sr(II), Ba(II), Cr(III), Co(II), Cu(II), Zn(II), Cd(II), Al(III) and Ga(III) were obtained in this study. After studying and analyzing the IR and Raman spectra of all these complexes and comparing them with the spectra of the corresponding disodium salts, it was verified that, independently of the type of nucleotide involved, the presence of the metal in the vicinity of the phosphate group produces an alteration in the aforementioned nu(s) PO(3)(2-) band. This effect is related to the type of interaction that the phosphate group has with the metal. Three components are observed: (1) one near 983-975 cm(-1) (detectable in IR and Raman), associated with phosphate groups in an electrostatic type of interaction with the metal ion, separated by two or more water molecules; (2) another near 989-985 cm(-1) (only in IR), associated with phosphate groups in indirect interaction through the water molecules of the coordination sphere of the metal ions; and (3) the IR and Raman bands near 1014-1001 cm(-1), which represent phosphate groups directly bonded to the metal ion. These results are supported by the behavior of 5'-CMP in aqueous solution in the presence of Mg(II) ions.     

Synthesis, characterization and antitumor studies of N-aroyl-N′-thioaroylhydrazines and their Co(II), Ni(II), Cu(II) and Zn(II) complexes

N-Salicyloyl-N-p-hydroxythiobenzohydrazide (H₂STPH) and N-benzoyl-N-thiobenzohydrazide (H₂BTBH) and their Co(II), Ni(II), Cu(II) and Zn(II) complexes were prepared and characterized by physicochemical studies. IR and NMR spectral studies imply dibasic tetradentate behaviour of the ligands bonding through `thiolato' sulfur, enolic oxygen and the two hydrazinic nitrogens in a polymeric fashion. The electronic spectra indicate [Ni(STPH)(H₂O)₂], [Co(STPH)(H₂O)₂] to be distorted octahedral while [Cu(BTBH)] has a square-planar geometry. In vitro antitumor results of the ligand and the complexes on P-815 (murine mastocytoma) and L-929 (murine fibroblast) indicate that these compounds show significant inhibition of ³H-thymidine and ³H-uridine incorporation in DNA and RNA, respectively, in these tumor cells at dose levels of 1, 2.5 and 5 g cm^–3. Antitumor studies suggest that [Cu(BTBH)] has significant dose dependent inhibitory effect on DNA synthesis. In vivo administration of [Cu(BTBH)] and [Ni(STPH)(H₂O)₂] resulted into prolongation of life span of Dalton's Lymphoma (DL) bearing mice.     

Free metal ion depletion by “good's” buffers: II. N-(2-acetamido)-2-aminoethanesulfonic acid (ACESH): Complexes with Calcium(II), Magnesium(II), Manganese(II), Cobalt(II), Zinc(II), Nickel(II), and Cooper(II)

Potentiometric, visible, and infrared studies of the complexation of N-(2-acetamido)-2-aminoethanesulfonic acid (ACESH) by Ca(II), Mg(II), Mn(II), Co(II), Zn(II), Ni(II), and Cu(II) are reported. Ca(II), Mg(II), and Mn(II) were found not to complex with ACES^?, while Co(II), Zn(II), Ni(II), and Cu(II) were found to form 2:1, ACES^? to M²⁺, complexes, and [Cu(ACES)₂] was found to undergo stepwise deprotonation of the amide groups to form [Cu(H_?1ACES)₂^2?]. Formation (affinity) constants for the various metal complexes are reported, and the probable structures of the various metal chelates in solution are discussed.     

Interaction of Adenosine 5′-Triphosphate with Metal Ions X-ray Structure of Ternary Complexes Containing Mg(II), Ca(II), Mn(II), Co(II), ATP and 2,2′ -Dipyridylamine

Abstract

The X-ray structures of the isomorphous Mg²⁺, Ca²⁺, Mn²⁺ and Co²⁺ complexes of ATP have been determined. The metal ions are wrapped in hexa-coordination by the α, β and γ phosphate groups of two ATP molecules thus blocking the interaction of the metal ions with the adenine base. A second metal ion which is fully hydrated, M(H₂O)²⁺ ₆, is engaged in a strong hydrogen bond with the γ phosphate group of ATP and suggests a possible step in facilitating the cleavage between the β and γ phosphates in phosphoryl transfer reactions.     

Speciation of binary complexes of Co(II), Ni(II) and Cu(II) with L-aspartic acid in propylene glycol–water mixtures

Abstract

Speciation of binary complexes of Co(II), Ni(II) and Cu(II) with L-aspartic acid in (0-60% v/v) propylene glycol-water mixtures was studied pH metrically at 303.0±0.1 K and at an ionic strength of 0.16 mol L^-1. The binary species refined were ML, ML₂, ML₂H₂, ML₂H₃ and ML₂H₄. The stabilities of the complexes followed the Irving-Williams order i.e.Co(II) <Ni(II) < Cu(II). The linear variation of stability constants as a function of dielectric constant of the medium indicated the dominance of electrostatic forces over non-electrostatic forces. Some species were stabilised due to electrostatic interactions and some were destabilised due to the decreased dielectric constant. The order of ingredients influencing the magnitudes of stability constants due to incorporation of errors in their concentrations was alkali > acid > ligand > metal. Equilibria for the formation of binary complexes were proposed based on the forms of the ligand and their existence at different pH values.     

Synthesis and characterization of β-diketiminate germanium(II) and tin(II) bromides

The equimolar reaction of a β-diketiminate lithium salt LLi(OEt₂) [L = HC(CMeNAr)₂; Ar = 2,6-iPr₂C₆H₃] with either GeBr₂ or SnBr₂ in diethyl ether affords the synthetically useful monomeric β-diketiminate-element halides LGeBr (1) and LSnBr (2), respectively. Both are soluble in hydrocarbon solvents, stable in inert atmosphere, and have been characterized by elemental analysis, NMR spectroscopy, and single-crystal X-ray diffraction analysis.     

Synthesis and antimicrobial activity of copper(II) and manganese(II) α,ω-dicarboxylate complexes

Copper(II) ,-dicarboxylate complexes of general formulae, [Cu(O₂C(CH₂)_nCO₂)]·xH₂O, [Cu(O₂C(CH₂)_nCO₂) (phen)₂]·xH₂O and [Cu(O₂C(CH₂)_nCO₂)(bipy)_y]·xH₂O (n=1–8; y=1, 2; phen = 1,10-phenanthroline; bipy = 2,2-bipyridine) were synthesised. These copper complexes, some related manganese(II) complexes and the metal-free ligands were screened in vitro for their ability to inhibit the growth of Candida albicans. Metal-free 1,10-phenanthroline and all of the copper(II) and manganese(II) phenanthroline complexes were potent growth inhibitors, with only one bipyridine complex, [Cu(O₂C(CH₂)CO₂)(bipy)₂]·2H₂O, having moderate activity. The remaining substances were effectively inactive. Complexes which were active against C. albicans also proved effective against C. glabrata, C. tropicalis and C. kreusi with the manganese complexes retaining superior activity. For the phenanthroline complexes the active drug species is thought to be the dication [M(phen)₂(H₂O)_n]²⁺ (M = Cu, Mn). Escherichia coli and Staphylococcus aureus were resistant to all of the metal complexes and also to metal-free 1,10-phenanthroline. Only the copper phenanthroline complexes showed intermediate activity against Pseudomonas aeruginosa.     

Antioxidant and Cytoprotective Activity of Oxydiacetate Complexes of Cobalt(II) and Nickel(II) with 1,10-Phenantroline and 2,2′-Bipyridine

Biological Trace Element Research - The antioxidant properties of oxydiacetate complexes of cobalt(II) and nickel(II) with 1,10-phenantroline and 2,2′-bipyridine have been investigated...     

Co (II), Ni(II) and Cu(II) complexes with a new pendant armed macrocyclic ligand showing several π,π-interactions

A new ligand, L, bearing four cyanoethyl pendant groups has been synthesized by reaction of the precursor ligand L¹ with acrylonitrile. The X-ray crystal structure of ligand L reveals the presence of a nanotubular structure in the solid state connected by intermolecular π,π-stacking interactions between adjacent pyridine rings. The coordination capability towards transition metal ions [Co(II), Ni(II) and Cu(II)] has been investigated starting from the hydrated nitrate and perchlorate salts of the metals. The new ligand L and the metal complexes obtained were characterized by elemental analysis, FAB MS, conductivity measurements, magnetic studies, IR and UV-vis spectroscopy. Furthermore, the crystal structure of ligand L and of the complexes [CoL][Co(NO₃)₄] · CH₃CN (1), [NiL](NO₃)₂ (3), [NiL](ClO₄)₂ · CH₃CN · 3H₂O (4), [CuL][Cu(NO₃)₃(H₂O)₂](NO₃) · H₂O (5) and [CuL](ClO₄)₂ · 2CH₃CN (6) were determined. The nitrate ions in the complexes are located near the pyridine rings and π,π-stacking interactions between pyridine rings, nitrate ions and nitrile groups have been found.     

pH-dependence of the specific binding of Cu(II) and Zn(II) ions to the amyloid-β peptide

Metal ions like Cu(II) and Zn(II) are accumulated in Alzheimer's disease amyloid plaques. The amyloid-β (Aβ) peptide involved in the disease interacts with these metal ions at neutral pH via ligands provided by the N-terminal histidines and the N-terminus. The present study uses high-resolution NMR spectroscopy to monitor the residue-specific interactions of Cu(II) and Zn(II) with (15)N- and (13)C,(15)N-labeled Aβ(1-40) peptides at varying pH levels. At pH 7.4 both ions bind to the specific ligands, competing with one another. At pH 5.5 Cu(II) retains its specific histidine ligands, while Zn(II) seems to lack residue-specific interactions. The low pH mimics acidosis which is linked to inflammatory processes in vivo. The results suggest that the cell toxic effects of redox active Cu(II) binding to Aβ may be reversed by the protective activity of non-redox active Zn(II) binding to the same major binding site under non-acidic conditions. Under acidic conditions, the protective effect of Zn(II) may be decreased or changed, since Zn(II) is less able to compete with Cu(II) for the specific binding site on the Aβ peptide under these conditions.     

X-ray absorption spectroscopic analysis of Fe(II) and Cu(II) forms of a herbicide-degrading α-ketoglutarate dioxygenase

 The first step in the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) by Ralstonia eutropha JMP134 is catalyzed by the α-ketoglutarate (α-KG)-dependent dioxygenase TfdA. Previously, EPR and ESEEM studies on inactive Cu(II)-substituted TfdA suggested a mixture of nitrogen/oxygen coordination with two imidazole-like ligands. Differences between the spectra for Cu TfdA and α-KG- and 2,4-D-treated samples were interpreted as a rearrangement of the g–tensor principal axis system. Herein, we report the use of X-ray absorption spectroscopy (XAS) to further characterize the metal coordination environment of Cu TfdA as well as that in the active, wild-type Fe(II) enzyme. The EXAFS data are interpreted in terms of four N/O ligands (two imidazole-like) in the Cu TfdA sample and six N/O ligands (one or two imidazole-like) in the Fe TfdA sample. Addition of α-KG results in no significant structural change in coordination for Cu or Fe TfdA. However, addition of 2,4-D results in a decrease in the number of imidazole ligands in both Cu and Fe TfdA. Since this change is seen both in the Fe and Cu EXAFS, loss of one histidine ligand upon 2,4-D addition best describes the phenomenon. These XAS data clearly demonstrate that changes occur in the atomic environment of the metallocenter upon substrate binding. Received: 3 July 1998 / Accepted: 13 October 1998     

Synthesis and structural investigations of Ni(II)- and Pd(II)-coordinated α-diimines with chlorinated backbones

Novel square planar Pd(II) α-diimines [PdX₂{ArNC(Cl)}₂], where Ar = C₆H₅, (2,6-Me₂C₆H₃), (2,6-ⁱPr₂C₆H₃) and X = Cl or Br, and the octahedral Ni(II) complex [NiBr₂{(C₆H₅)NC(Cl)}₂(THF)₂] have been prepared and characterised by spectroscopic methods. For two of the Pd(II) complexes and the Ni(II) complex the crystal structures were determined by X-ray crystallography. A further insight into the geometry and electronic structure of [PdBr₂{(2,6-Me₂C₆H₃)NC(Cl)}₂] was gained using density functional theoretical calculations (DFT). This compound resembles structurally and electronically typical olefin polymerisation pre-catalysts supported by α-diimines incorporating methyl- and 1,8-naphtalenyl substituents at the ligand backbone. The chlorine-substituted backbone of the free ligand [2,6-Me₂C₆H₃NC(Cl)]₂ can be employed in further alkylation reactions to generate new multifunctional ligand prototypes with potential uses as ansa-metallocene/diimines building blocks for catalytic applications of heterobimetallic complexes.     

Synthesis, structure and magnetic properties of two μ-oxo and thiocyanato-bridged manganese(II)-mercury(II) coordination polymers

Mixed-metal thiocyanate complexes [MnHg(SCN)₄(NOP)] (1) and [MnHg(SCN)₄(DMSO)] (2) (NOP = 3-methyl-4-nitropyridine-N-oxide, DMSO = dimethylsulfoxide) have been synthesized and structurally characterized by single crystal X-ray analysis. Complex 1 and 2 both contain a [Mn₂(μ₂-O)₂] lozenge, which is bridged to Hg(II) ions by end-to-end thiocyanate groups to form a 2-D and 3-D polymeric network, respectively. Magnetic studies indicate that both complexes are anti-ferromagnets, with 1 showing anti-ferrimagnetic ordering below 8.0 K.     

Synthesis,cytotoxicity and DNA-binding properties of Pd(II), Cu(II) and Zn(II) complexes with 4′-(4-(2-(piperidin-1-yl)ethoxy)phenyl)-2,2′:6′,2″-terpyridine

Pd(II), Cu(II) and Zn(II) complexes (1–3) based on 4′-(4-(2-(piperidin-1-yl)ethoxy)phenyl)-2,2′:6′,2″-terpyridine were synthesized and characterized by UV, IR, NMR, EPR, HRMS, elemental analyses, and molar conductivity measurements. The cytotoxicity of these complexes against HL-60, BGC-823, KB, Bel-7402, A549, Hela, K562 and MCF-7 cell lines in vitro was measured by MTT method. The DNA binding property of the complexes was evaluated by UV, fluorescence, CD spectroscopies and thermal denaturation. The cytotoxicity of complexes 1 and 3 against all the tested cell lines is better than that of cisplatin. Complexes 1 and 2 exhibit 7- and 4-folds higher cytotoxicity than cisplatin against Bel-7402 cell line. Complex 3 displays the highest cytotoxicity against all the cell lines tested, and shows 7-, 14-, 8-, 11- and 8-folds higher cytotoxicity than cisplatin against Bel-7402, A549, Hela, K562 and MCF-7 cell lines. The complexes bind to DNA via intercalation mode and complex 3 stabilizes the G-quadruplex. The results reveal that all the complexes display high cytotoxicity against all the tested cancer cell lines, and complex 3 is selective for G-quadruplex over duplex DNA.     

Biosorption of Cd(II) and Pb(II) onto brown seaweed, Lobophora variegata (Lamouroux): kinetic and equilibrium studies

The present work deals with the biosorption performance of raw and chemically modified biomass of the brown seaweed Lobophora variegata for removal of Cd(II) and Pb(II) from aqueous solution. The biosorption capacity was significantly altered by pH of the solution delineating that the higher the pH, the higher the Cd(II) and Pb(II) removal. Kinetic and isotherm experiments were carried out at the optimal pH 5.0. The metal removal rates were conspicuously rapid wherein 90% of the total sorption occurred within 90 min. Biomass treated with CaCl₂ demonstrated the highest potential for the sorption of the metal ions with the maximum uptake capacities i.e. 1.71 and 1.79 mmol g⁻¹ for Cd(II) and Pb(II), respectively. Kinetic data were satisfactorily manifested by a pseudo-second order chemical sorption process. The process mechanism consisting of both surface adsorption and pore diffusion was found to be complex. The sorption data have been analyzed and fitted to sorption isotherm of the Freundlich, Langmuir, and Redlich–Peterson models. The regression coefficient for both Langmuir and Redlich–Peterson isotherms were higher than those secured for Freundlich isotherm implying that the biosorption system is possibly monolayer coverage of the L. variegata surface by the cadmium and lead ions. FT-IR studies revealed that Cd(II) and Pb(II) binding to L. variegata occurred primarily through biomass carboxyl groups accompanied by momentous interactions of the biomass amino and amide groups. In this study, we have observed that L. variegata had maximum biosorption capacity for Cd(II) and Pb(II) reported so far for any marine algae. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Zinc(II) and cadmium(II) metal complexes of thiamine pyrophosphate and 2-(α-hydroxyethyl)thiamine pyrophosphate: models for activation of pyruvate decarboxylase

Metal complexes of thiamine pyrophosphate (TPP) of the general formula [M₂(TPPH)₂Cl₂].4H₂O (M =Zn²⁺, Cd²⁺) were isolated from methanolic solutions and characterized by elemental analysis, FT-IR, and multinuclear NMR spectroscopies. The data provide evidence for the bonding of the metals to the N(1') atom of the pyrimidine ring and to the pyrophosphate group. The stability constant measurements of TPP and 2-(α-hydroxyethyl)thiamine pyrophosphate (HETPP) metal complexes in aqueous solution imply the formation of dimeric complex species similar to the isolated solid products. They indicate also that HETPP forms more stable metal complexes than does TPP. To evaluate the coenzyme action of TPP and HETPP metal complexes, enzymic studies have been done using pyruvate decarboxylase apoenzyme. TPP metal complexes do not bind to the apoenzyme, unlike the Zn(II)-HETPP complex which can act as coenzyme. Considering these results, possible functional implications for thiamine involvement in catalysis are discussed. Received 13 September 1999 / Accepted 4 January 2000     

Electronic coupling and photochemical stability of O,N bound mononuclear Ru(II) and Os(II) – Hydroquinone complexes

The synthesis, spectroscopic and electrochemical characterisation of a series of optically tuneable, ruthenium (II) and osmium (II) polypyridyl complexes, O,N coordinated to electroactive donor ligand, bis-2,5-(2-benzoxazolyl)-hydroquinone (bbhq) is described. The complexes exhibit a rich optical spectroscopy which can be controlled through the redox state of the metal and bbhq ligand. The influence of both the metal and counter-ligand identity on the optical properties of these hydroquinone-based complexes is addressed.Regardless of the identity of metal or counter-ligand, it is the bbhq which is the site of the most facile oxidation and hydroquinone, semiquinone (bbsq) and quinone (bbq) can be generated electrochemically. In each instance, the semiquinone is strongly stabilised with respect to disproportionation, reflected in large stability constants for this moiety. The levels of orbital mixing between metal and ligand are discussed on the basis of the optical properties of the complex and the nature of the metal and counter-ligand. In addition, we address, for the first time, the effect of metal and counter-ligand on the photostability, of Ru(II) and Os(II) hydroquinone bound complexes. We find that like other ruthenium (II) complexes containing strong σ-bonding ligands, the M(bpy)₂ containing complexes are photostable, but the [Ru(biq)₂(bbhq)]⁺ complex is relatively photolabile.     

Binding of α-synuclein with Fe(III) and with Fe(II) and biological implications of the resultant complexes

Parkinson’s disease (PD) is hallmarked by the abnormal intracellular inclusions (Lewy bodies or LBs) in dopaminergic cells. Amyloidogenic protein α-synuclein (α-syn) and iron (including both Fe(III) and Fe(II)) are both found to be present in LBs. The interaction between iron and α-syn might have important biological relevance to PD etiology. Previously, a moderate binding affinity between α-syn and Fe(II) (5.8 × 10³ M⁻¹) has been measured, but studies on the binding between α-syn and Fe(III) have not been reported. In this work, electrospray mass spectrometry (ES-MS), cyclic voltammetry (CV), and fluorescence spectroscopy were used to study the binding between α-syn and Fe(II) and the redox property of the resultant α-syn-Fe(II) complex. The complex is of a 1:1 stoichiometry and can be readily oxidized electrochemically and chemically (by O₂) to the putative α-syn-Fe(III) complex, with H₂O₂ as a co-product. The reduction potential was estimated to be 0.025 V vs. Ag/AgCl, which represents a shift by −0.550 V vs. the standard reduction potential of the free Fe(III)/Fe(II) couple. Such a shift allows a binding constant between α-syn and Fe(III), 1.2 × 10¹³ M⁻¹, to be deduced. Despite the relatively high binding affinity, α-syn-Fe(III) generated from the oxidation of α-syn-Fe(II) still dissociates due to the stronger tendency of Fe(III) to hydrolyze to Fe(OH)₃ and/or ferrihydrite gel. The roles of α-syn and its interaction with Fe(III) and/or Fe(II) are discussed in the context of oxidative stress, metal-catalyzed α-syn aggregation, and iron transfer processes.     

Dicyanamido-metal(II) complexes. Part 4: Synthesis, structure and magnetic characterization of polynuclear Cu(II) and Ni(II) complexes bridged by μ-1,5-dicyanamide

The one pot aqueous reaction of M(ClO₄)₂ (M = Cu²⁺ or Ni²⁺) with N-methylbis[2-(2-pyridylethyl)]amine (MeDEPA) and N,N′-dimethyl-N,N′-bis(2-pyridylmethyl)ethylenediamine (bpmen) and 1,4,7,10-tetraazacyclododecane (cyclen) in presence of sodium dicyanamide (Nadca) yielded dicyanamido-bridged polynuclear complex {[Cu(MeDEPA)(μ-1,5-dca)]ClO₄}_n (1), and two dinuclear complexes [Cu₂(bpmen)₂(μ-1,5-dca)]₂(ClO₄)₅dca (2) and [Ni(cyclen)(μ-1,5-dca)]₂(ClO₄)₂ (3). These complexes were characterized by IR and UV-Vis spectroscopy. Room temperature single-crystal X-ray studies have confirmed that the Cu(II) centers in 1 and 2 adopt geometries that are more close to trigonal bipyramidal (TBP) in 1 and close to square pyramidal (SP) in 2, whereas in 3, the Ni(II) centers are located in octahedral environment with doubly bridged μ-1,5-dca bonding mode. The intermolecular M···M distances in these complexes are in the range of 7.3-8.6 Å. Variable temperature magnetic susceptibility studies have confirmed that the dca-bridges mediate very weak antiferromagnetic interaction between the M(II) centers with J values of −0.35, −0.18 and −0.43 cm⁻¹ for 1, 2 and 3, respectively. The results are compared and discussed in the light of other related bridged μ-1,5-dca Cu(II) and Ni(II) complexes.     

The many faces (and phases) of ceramide and sphingomyelin II – binary mixtures

A rather widespread idea on the functional importance of sphingolipids in cell membranes refers to the occurrence of ordered domains enriched in sphingomyelin and ceramide that are largely assumed to exist irrespective of the type of N-acyl chain in the sphingolipid. Ceramides and sphingomyelins are the simplest kind of two-chained sphingolipids and show a variety of species, depending on the fatty acyl chain length, hydroxylation, and unsaturation. Abundant evidences have shown that variations of the N-acyl chain length in ceramides and sphingomyelins markedly affect their phase state, interfacial elasticity, surface topography, electrostatics, and miscibility, and that even the usually conceived “condensed” sphingolipids and many of their mixtures may exhibit liquid-like expanded states. Their lateral miscibility properties are subtlety regulated by those chemical differences. Even between ceramides with different acyl chain length, their partial miscibility is responsible for a rich two-dimensional structural variety that impacts on the membrane properties at the mesoscale level. In this review, we will discuss the miscibility properties of ceramide, sphingomyelin, and glycosphingolipids that differ in their N-acyl or oligosaccharide chains. This work is a second part that accompanies a previous overview of the properties of membranes formed by pure ceramides or sphingomyelins, which is also included in this Special Issue.