Equilibrium investigation of complex formation reactions involving copper(II), nitrilo-tris(methyl phosphonic acid) and amino acids,peptides or DNA constitutents. The kinetics,mechanism and correlation of rates with complex stability for metal ion promoted hydrolysis of glycine methyl ester

The complex formation reactions of [Cu(NTP)(OH₂)]^4? (NTP?=?nitrilo-tris(methyl phosphonic acid)) with some selected bio-relevant ligands containing different functional groups, are investigated. Stoichiometry and stability constants for the complexes formed are reported. The results show that the ternary complexes are formed in a stepwise mechanism whereby NTP binds to copper(II), followed by coordination of amino acid, peptide or DNA. Copper(II) is found to form Cu(NTP)H _n species with n?=?0, 1, 2 or 3. The concentration distribution of the various complex species has been evaluated. The kinetics of base hydrolysis of glycine methyl ester in the presence of copper(II)-NTP complex is studied in aqueous solution at different temperatures. It is proposed that the catalysis of GlyOMe ester occurs by attack of OH^? ion on the uncoordinated carbonyl carbon atom of the ester group. Activation parameters for the base hydrolysis of the complex [Cu(NTP)NH₂CH₂CO₂Me]^4? are, ΔH^±?=?9.5?±?0.3?kJ?mol^?1 and ΔS^±?=??179.3?±?0.9?J?K^?1?mol^?1. These show that catalysis is due to a substantial lowering of ΔH^±.     

Studies of copper (Ⅱ) complexes as catalysts for the hydrolysis of DNA

Hydrolysis of DNA is an important enzymatic reaction , but it is exceedingly difficult to mimic in the laboratory because of the stability of hydrolysis of DNA. In this paper, the cleavage activity of complexes formed between Cu(Ⅱ) and four different amino acid or amino acid methyl ester on DNA is studied by gel elec-trophoresis. It is found that DNA could be cleaved by Cu(Ⅱ)-L-His and Cu(Ⅱ)-L-His methyl ester complexes and the efficiency of cleavage is largely dependent on the metal ion-to-ligand ratio. Further experiments show that the cleavage of DNA mediated by Cu(Ⅱ)-L-His complexes occurs via a hydrolytic mechanism and the active chemical species that affects DNA cleavage is proposed to be MI2H and ML2H22 .     

Binary and Ternary Complexes of Copper(II) Involving N,N,N′,N′-Tetramethylethylenediamine (Me4en) and Various Biologically Relevant Ligands

Binary and ternary complexes of copper(II) involving N,N,N′,N′-tetramethylethylene-diamine (Me₄en) and various biologically relevant ligands containing different functional groups are investigated. The ligands (L) used are dicarboxylic acids, amino acids, peptides and DNA unit constituents. The ternary complexes of amino acids, dicarboxylic acids or peptides are formed by simultaneous reactions. The results showed the formation of Cu(Me₄en)(L) complexes with amino acids and dicarboxylic acids. The effect of chelate ring size of the dicarboxylic acid complexes on their stability constants was examined. Peptides form both Cu(Me₄en)(L) complexes and the corresponding deprotonated amide species Cu(Me₄en)(LH₋₁). The ternary complexes of copper(II) with (Me₄en) and DNA are formed in a stepwise process, whereby binding of copper(II) to (Me₄en) is followed by ligation of the DNA components. DNA constituents form both 1:1 and 1:2 complexes with Cu(Me₄en)²⁺. The concentration distribution of the complexes in solution was evaluated. [Cu(Me₄en)(CBDCA)] and [Cu(Me₄en)(malonate)] are isolated and characterized by elemental analysis and infrared measurements.     

Synthesis,characterization and biological activities of homo-binuclear Cu(II) and Zn(II) complexes derived from 2-hydroxy-5-methyl-1,3-benzenedicarboxaldehyde derivatives

Few novel binuclear Schiff base metal complexes [M₂LCl₃], where M = Cu(II) and Zn(II); L= 2,6-bis-({2-[(3-hydroxy-4-nitrobenzylidene)amino]ethylimino}methyl)-4-methylphenol (BHEM), 2,6-bis-({2-[(3,4-dimethoxybenzylidene)amino]ethylimino} methyl)-4-methylphenol (BDEM) and 2,6-bis-({2-[(2,3,5-trichlorobenzylidene)amino]ethylimino}methyl)-4-methylphenol (BTEM), have been synthesized and characterized by analytical and spectral data. The data suggest that BHEM/BDEM/BTEM ligands afford square-pyramidal/distorted square-pyramidal geometry on metalation with Zn(II)/Cu(II). The binding behaviour of these complexes with DNA has been investigated using electronic absorption spectroscopy as well as viscosity and voltammetric measurements; the results show that they interact with DNA through intercalating way. From the DNA cleavage study of these complexes, investigated by gel electrophoresis, we found that they efficiently cleave supercoiled pUC19 DNA in the presence of a reducing agent (3-mercaptopropionic acid) and on irradiation with UV light of 360 nm wavelength. The mechanism reveals that singlet oxygen (¹O₂) plays a significant role in the photo cleavage. The superoxide dismutase (SOD) mimetic activity of the synthesized complexes demonstrates that most of the complexes have promising SOD-mimetic activity. The antimicrobial study indicates that the complexes inhibit the growth of bacteria and fungi more than the free ligands.     

Ternary complexes involving copper(II) and amino acids,peptides and DNA constituents. The kinetics of hydrolysis of α-amino acid esters

Binary and ternary complexes of copper(II) involving picolylamine (Pic) and amino acids, peptides (HL) or DNA constituents have been investigated. Ternary complexes of amino acids or peptides are formed by simultaneous reactions. Amino acids form the Cu(Pic)L complex, whereas peptides form Cu(Pic)L and Cu(Pic)(LH_–1). The ternary complexes of copper(II) with picolylamine and DNA are formed in a stepwise process, whereby binding of copper(II) to picolylamine is followed by ligation of the DNA components. The stability of the ternary complexes is compared with the stabilities of the corresponding binary complexes. The hydrolysis of glycine methyl ester (MeGly) is catalysed by the Cu(pic)²⁺ complex. The kinetic data is fitted assuming that the hydrolysis proceeds in two steps. The first step, involving coordination of the amino acid ester by the amino and carbonyl groups, is followed by rate-determining attack by the OH^– ion. The second step involves equilibrium formation of the hydroxo-complex, Cu(pic)(MeGly)(OH), followed by intramolecular attack.     

Cu (II) tyrosinate complexes containing methyl substituted phenanthrolines: Synthesis,X‐ray crystal structures,biomolecular interactions,antioxidant activity,ROS generation and cytotoxicity

In this paper, three new copper (II) complexes, [Cu(4‐mphen)(tyr)(H₂O)]ClO₄ (1) , [Cu(5‐mphen)(tyr)(H₂O)]ClO₄·1.5H₂O (2) and [Cu (tmphen)(tyr)(NO₃)]0.5H₂O (3) (4‐mphen: 4‐methyl‐1,10‐phenanthroline, 5‐mphen: 5‐methyl‐1,10‐phenanthroline, tmphen: 3,4,7,8‐tetramethyl‐1,10‐phenanthroline and tyr: L‐tyrosine), were synthesized and characterized using elemental analyses, FT‐IR, ESI‐MS, cyclic voltammetry and single‐crystal X‐ray diffraction. It was found that the complexes adopt a distorted five‐coordinate square pyramidal geometry. The interaction of the three complexes with calf thymus DNA was also investigated using UV–visible absorption spectra, ethidium bromide and Hoechst 33258 displacement assay and thermal denaturation. The DNA cleavage activity of the complexes, monitored using gel electrophoresis, showed significant damage of the pUC19 plasmid DNA. Binding activity of bovine serum albumin (BSA) reveals that these complexes can strongly quench the fluorescence of BSA through a static quenching mechanism. The results suggested that interaction of the complexes with DNA occurred through a partial intercalation into the minor grooves of DNA. In addition, interaction of the complexes with bovine serum albumin quenched the fluorescence emission of the tryptophan residues of the protein binding constants and thermodynamic parameters were obtained from the fluorescence quenching experiments at different temperatures. Free radical scavenging activities of the complexes were determined by various in vitro assays such as 1,1‐diphenyl‐2‐picryl‐hydrazyl free radicals (DPPH˙) and H₂O₂ scavenging methods. In addition, the cytotoxicity of these complexes in vitro on tumor cell lines (Caco‐2 and MCF‐7) was examined by XTT and showed better antitumor effect on the tested cells. ROS (reactive oxygen species) and comet experiments are consistent with each other and these complexes lead to DNA damage via the production of ROS. The effect of the hydrophobic properties of the synthesized complexes on DNA and BSA binding activities were discussed.     

Complex Formation Reactions of Promethazine Copper(II) and Various Biologically Relevant Ligands. Synthesis,Equilibrium Constants,Spectroscopic Characterization and Biological Activity

Binary and ternary complexes of copper(II) involving promethazine, N,N-dimethyl-3-(phenothiazin-10-yl)propylamine (Prom) and various biologically relevant ligands containing different functional groups, were investigated. The ligands (L) are dicarboxylic acids, amino acids, amides and DNA constituents. The ternary complexes of amino acids, dicarboxylic acids or amides are formed by simultaneous reactions. The results showed the formation of Cu(Prom)(L) complexes with amino acids and dicarboxylic acids. The effect of chelate ring size of the dicarboxylic acid complexes on their stability constants was examined. Amides form both Cu(Prom)(L) complexes and the corresponding deprotonated species Cu(Prom)(LH₋₁). The ternary complexes of copper(II) with (Prom) and DNA are formed in a stepwise process, whereby binding of copper(II) to (Prom) is followed by ligation of the DNA components. DNA constituents form both 1:1 and 1:2 complexes with Cu(Prom)²⁺. The stability of these ternary complexes was quantitatively compared with their corresponding binary complexes in terms of the parameters Δlog₁₀ K. The values of Δlog₁₀ K indicate that the ternary complexes containing aromatic amino acids were significantly more stable than the complexes containing alkyl- and hydroxyalkyl-substituted amino acids. The concentration distribution of various complex species formed in solution was also evaluated as a function of pH. The solid complexes [Cu(Prom)L)] where L=1,1-cyclobutanedicarboxylic acid (CBDCA), oxalic and malonic acid were isolated and characterized by elemental analysis, infrared, TGA, and magnetic susceptibility measurements. Spectroscopic studies of the complexes revealed that the complexes exhibits square planar coordination with copper(II). The isolated solid complexes have been screened for their antimicrobial activities using the disc diffusion method against some selected bacteria and fungi. The activity data show that the metal complexes are found to have antibacterial and antifungal activity.     

Photopolymerization reactions initiated by copper (II)–amino acid chelates: Investigation of the initiating species by flash photolysis. I

Flash photolysis of copper (II)–bis(amino acid) complexes (amino acids: glutamic acid, serine, or valine) in deaerated aqueous solution produces transient species having absorption maxima at around 350 nm. The transient species are identified as copper (II)–alkyl complexes. In the case of Cu(valine)₂ at pH > 6.5 formation of Cu(II)-alkyl complex is not observed; this is interpreted to be due to the presence of two bulky methyl groups of the coordinated valine ligand, which hinders the rearrangement. Pseudo-first-order rate constants for the decay of the transients are determined at different pH with varying concentration of amino acid ligand. The free-radical species of the complexes responsible for the initiation of the vinyl polymerization reactions are identified as Cu(I)-coordinated amino acid radicals which are formed in the primary photochemical reaction of the complex. A mechanism for the secondary reactions involving the initiating species consistent with the nature of the product formed and the pH dependence of the decay of the transients is proposed.     

Synthesis and spectral studies of new N2S2 and N2O2 Mannich base ligands and their metal complexes

New Mannich bases bis(thiosemicarbazide methyl) phosphinic acid H₃L¹ and bis(1-phenylsemicarbazide methyl) phosphinic acid H₃L² were synthesized from condensation of phosphinic acid and formaldehyde with thiosemicarbazide and 1-phenylsemicarbazide, respectively. Monomeric complexes of these ligands, of general formula K₂[Cr^III(L ⁿ )Cl₂], K₃[Fe^II(L¹)Cl₂], K₃[Mn^II(L²)Cl₂], and K[M(L ⁿ )] (M = Co(II), Ni(II), Cu(II), Zn(II) or Cd(II); n = 1, 2) are reported. The mode of bonding and overall geometry of the complexes were determined through IR, UV-Vis, NMR, and mass spectral studies, magnetic moment measurements, elemental analysis, metal content, and conductance. These studies revealed octahedral geometries for the Cr(III), Mn(II), and Fe(II) complexes, square planar for Co(II), Ni(II), and Cu(II) complexes and tetrahedral for the Zn(II) and Cd(II) complexes. Complex formation via molar ratio in DMF solution has been investigated and results were consistent to those found in the solid complexes with a ratio of (M : L) as (1 : 1).     

Synthesis and characterization of cobalt(II), nickel(II), copper(II) and zinc(II) complexes of 2-nitrobenzoic acid with methyl carbazate as ancillary ligand. Crystal structure of the copper(II) complex

Divalent metal complexes of general formula [M(2-nb)₂(mc)₂].2(2-nbH), where M = Co(II), Ni(II), Cu(II) or Zn(II), 2-nbH = 2-nitrobenzoic acid and mc = methyl carbazate (NH₂NHCOOCH₃), have been prepared and characterized by physicochemical and spectroscopic methods. Single-crystal X-ray study of the Cu(II) complex revealed that the molecule is centrosymmetric, with two N,O-chelating mc ligands in equatorial positions and a pair of monodentate 2-nb anions in the axial positions. The lattice 2-nbH molecules help to establish the packing of monomers through hydrogen-bonding interactions. Thermal stability and reactivity of the complexes were studied by TG–DTA. Emission studies show that these complexes are fluorescent.     

Synthesis and characterization of two Cu(II) complexes with a new pyrazole-based Schiff base ligand: crystallography,DNA interaction and antimicrobial activity of Ni(II) and Cu(II) complexes

Reaction of Cu(II) nitrate with a new pyrazole-based Schiff base ligand, 5-methyl-3-formylpyrazole-N-(2′-methylphenoxy)methyleneimine (MPzOA), afforded two types of Cu(II) complexes at different reaction temperatures, [Cu(MP_zOA)(NO₃)]₂ (1) and [Cu(3,7,11,15-tetramethylporphyrin)(H₂O)](NO₃)₂ (2), reported together with a Ni(II) complex, [Ni(MPzOA)₂(H₂O)₂]Br₂ (3). The compounds are characterized by single crystal X-ray structure analyses along with several physico-chemical and spectral parameters. Complex 1 is authenticated as a bis(μ-pyrazolato)dicopper(II), while 2 is a porphyrinogen and 3 is a distorted octahedral complex. Structural analyses of the complexes reveal that 1 crystallized in monoclinic P2₁/n space group while 2 and 3 crystallized in monoclinic C2/c space group. DNA-binding studies of the complexes have shown that the complexes interact with CT-DNA. DNA-cleavage studies with plasmid DNA have shown that 1 and 2 induce extensive DNA cleavage in the presence of H₂O₂ as an additive, whereas there is no change in degradation of super-coiled DNA by 3 in the presence of additive. The antimicrobial studies of the complexes against Escherichia coli DH5α bacteria strain indicated that all the complexes were capable of killing E. coli with different LD50 values.     

Atom transfer radical polymerization of methyl methacrylate at ambient temperature using soluble Cu(I) complex catalysts formed with mixed ligands of multidentate amines and halide ions

An Erratum has been published for this article in J Polym Sci Part A: Polym Chem (2004) 42(19) 5030 . The addition of soluble quaternaryammonium halides (QX) in catalytic amounts takes into solution CuX/pentamethyldiethylenetriamine (PMDETA) complex (X = Cl, Br) in methyl methacrylate (MMA). The soluble catalyst complex provided much better control of the polymerization of MMA at ambient temperature than did the insoluble catalyst formed in the absence of QX, with CuCl/PMDETA/Aliquat® 336 (AQCl) proving to be superior to the CuBr/PMDETA/Bu₄NBr catalyst system. The effect was independent of the size of the quaternaryammonium ion. Also, the presence of Cl in the catalyst–QX combination either as CuCl or as QCl was enough to give much better control than that provided by a wholly Br‐based system. Among the various initiators used, that is, ethyl 2‐bromoisobutyrate (EBiB), methyl 2‐bromopropionate (MBP), 1‐phenylethyl bromide (PEBr), and p‐toluenesulfonyl chloride (pTsCl), only EBiB gave a satisfactory result. With MBP and PEBr the initiation was slower than the propagation, whereas with pTsCl the initiation was very fast, so that instantaneous termination occurred. The living nature of the polymers was shown by block copolymer preparation. It has been suggested that some of the added halide ions entered into the coordination spheres of Cu(I) and Cu(II), leading to their improved solubility and stronger deactivation by the Cu(II) complex. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4132–4142, 2004     

Poly(propylene imine) dendrimer complexes of Cu(II), Zn(II), and Co(III) as catalysts of hydrolysis of p-nitrophenyl diphenyl phosphate

Poly(propylene imine) dendrimers having 8, 32, and 64 primary amine end groups form diamino Cu(II), diamino Zn(II), and tetramino Co(III) complexes that are identified spectrophotometrically and titrimetrically. The dendrimer–metal ion complexes catalyze the hydrolysis of p-nitrophenyl diphenyl phosphate in zwitterionic buffer solutions at pH ≤ 8.1 with relative activities Cu(II) > Zn(II) > Co(III). The rates of hydrolysis are faster with sodium perchlorate than with sodium chloride to control ionic strength. In sodium perchlorate solutions with Cu(II) the rates increase with increasing size of the dendrimer. In sodium chloride solutions with Cu(II) the rates decrease with increasing size of the dendrimer. Rate constants in buffered sodium chloride solutions of dendrimers and 1.0mM Cu(II) are 1.3–6.3 times faster than in the absence of Cu(II). The fastest hydrolyses occurred at a dendrimer primary amine to Cu(II) ratio NH₂/Cu ≤ 2. At NH₂/Cu = 4 and with the 1,4,7,10-tetraazacyclodecane complex of Cu(II) hydrolysis rates were much slower. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2727–2736, 1999     

Synthesis and characterization of cobalt(II), nickel(II) and copper(II) perchlorate complexes with bis [(diphenylphosphinyl)methyl] phenylphosphine oxide,bis [(disphenylphosphinyl)methyl]ethyl phosphinate,and bis [(diphenylphosphinyl)methyl] phosphinic acid

The synthesis and characterization of cobalt(II), nickel(II) and copper(II) perchlorate complexes containing bis [(diphenylphosphinyl)methyl] [phenylphosphine oxide (RPPH), bis [(diphenylphosphinyl)methyl] ethyl phosphinate (RPOEt), and bis [(diphenylphosphinyl)methyl] phosphinic acid (RPOH) have been studied. The substituent at the central phosphorus atom of the ligand is responsible for the types of complexes formed. The new complexes [M(RPPh)₂(ClO₄)₂.nH₂O, [M(RPPh)₃](ClO₄)₂.4H₂O, [M(RPOEt)₂](ClO₄)₂.2H₂O, and [M(RPOH)₃] (ClO₄)₂.nH₂O are characterized as high spin and most of them have an octahedral or distorted octahedral geometry [M = Co(II), Ni(II), or Cu(II); n = 2?5]. The coordination of two P = O groups from one ligand to the metal has been proposed for most of the complexes formed. The coordination of all three P = O groups has been assumed for complexes [M(RPPh)₂](ClO₄)₂.nH₂O and [M(RPOEt)₂](ClO₄)₂.2H₂O.     

Synthesis and Magnetic Studies of Copper (II)‐Manganese (II) Heterobinuclear Complexes with an Oxamido Bridge

Four new copper (II)‐manganese (II) heterobinuclear complexes bridged byN, N'‐bis[2‐(dimethylamino)ethyl)]oxamido dianion (dmoxæ) and end‐capped with 1, 10‐phenanthroline (phen), 5‐methyl‐1, 10‐phenanthroline (Mephen), diaminoethane (en) or 1,3‐di‐aminopropane (pn). respectively, namely, [Cu(dmoxae)MnL₂] (CIO₄)₂ (L=phen, Mephen, en, pn), have been synthesized and characterized by elemental analyses, IR, electronic spectral studies, and molar conductivity measurements. The electronic reflectance spectrum indicates the presence of spin exchange‐coupling interaction between bridged copper(II) and manganese (II) ions. The cryomagnetic measurements (4.2‐300 K) of [Cu(dmoxae)Mn(phen)₂](CIO₄)₂ (1) and [Cu(dmoxae)Mn(Mephen)₂](CIO₄)₂(2) complexes demonstrated an antiferromagnetic interaction between the adjacent manganese(II) and copper (II) ions through the oxamido‐bridge within each molecule. On the basis of spin Hamiltonian, H= ‐ 2JS₁. S₂. the magnetic analysis was carried out for the two complexes and the spin‐coupling constant (J) was evaluated as ?35.9 cm^?1 for 1 and ‐ 32.6 cm^?1 for 2. The influence of methyl substitutions in the amine groups of the bridging ligand on magnetic interactions between the metal ions of this kind of complexes is also discussed.     

Magnetic and spectral studies on nickel(II) and copper(II) dithiocarbazates derived from isoniazid

Some isonicotinoyldithiocarbazate complexes of nickel(II) and copper(II), of general formulae M(IN-Dtcz)₂, [M(IN-DtczH)₂]Cl₂, and [M(IN-DtczH-Sal)₂]Cl₂ (M?=?Ni(II), Cu(II); INDtcz?=?isonicotinoyldithiocarbazate; IN-DtczH?=?isonicotinoyldithiocarbazic acid; IN-DtczH-Sal?=?salicylaldehyde Schiff base of isonicotinoyldithiocarbazic acid), have been synthesized. These complexes have been investigated by elemental analyses, mass, room temperature infrared and electronic spectra, and variable temperature magnetic susceptibility measurements. The three nickel(II) dithiocarbazates and [Cu(IN-DtczH-Sal)₂]Cl₂ exhibit NS linkage of the ligands, while Cu(IN-Dtcz)₂ and [Cu(IN-DtczH)₂]Cl₂ have ONS binding of the ligands. The nickel(II) dithiocarbazates have [NiN₂S₂] chromophore. Magnetic and solution electronic absorption spectral data reveal square-planar geometry for Ni(IN-Dtcz)₂ and the existence of square-planar–tetrahedral equilibrium for [Ni(IN-DtczH)₂]Cl₂ and [Ni(IN-DtczH-Sal)₂]Cl₂. Copper(II) dithiocarbazates, namely Cu(IN-Dtcz)₂, [Cu(IN-DtczH)₂]Cl₂, with ONS ligands having dimeric or polymeric octahedral structures, and [Cu(IN-DtczH-Sal)₂]Cl₂, with NS binding having dimeric square-planar structure, exhibit antiferromagnetism. Superexchange pathway involving the bridging nitrogen and sulfur of the isonicotinoyldithiocarbazate ligands rather than direct metal–metal exchange is suggested for antiferromagnetic interactions. The spin exchange parameter, ?2J?=?202.14 and 29.26?cm^?1, has been evaluated for [Cu(IN-DtczH)₂]Cl₂ and [Cu(IN-DtczH-Sal)₂]Cl₂, respectively, while it could not be evaluated for Cu(IN-Dtcz)₂ because the slope was negative due to the non-variation of its magnetic moment with temperature. The difference in antiferromagnetic behavior and inconsistency of 2J for [Cu(IN-DtczH-Sal)₂]Cl₂ has been attributed to different electronic and steric factors of the three ligands, that is, isonicotinoyldithiocarbazate, its acid, and salicylaldehyde Schiff-base derivative.     

Complex Formation Reactions of (2,2′-dipyridylamine)copper(II) with Various Biologically Relevant Ligands. The Kinetics of Hydrolysis of Amino Acid Esters

Binary and ternary copper(II) complexes involving 2,2′-dipyridylamine (DPA) and various biologically relevant ligands containing different functional groups are investigated. The ligands used are dicarboxylic acids, amino acids, peptides and DNA unit constituents. The ternary complexes of amino acids, dicarboxylic acids or peptides are formed by simultaneous reactions. The results showed the formation of 1:1 complexes with amino acids and dicarboxylic acids. The effect of chelate ring size of the dicarboxylic acid complexes on their stability constants was examined. Peptides form both 1:1 complexes and the corresponding deprotonated amide species. The ternary complexes of copper(II) with DPA and DNA are formed in a stepwise process, whereby binding of copper(II) to DPA is followed by ligation of the DNA components. DNA constituents form both 1:1 and 1:2 complexes with Cu(DPA)²⁺. The concentration distribution of the complexes in solution was evaluated. [Cu(DPA)(CBDCA)], [Cu(DPA)(malonate)] and [Cu(DPA)(oxalate)] were isolated and characterized by elemental analysis, i.r. and magnetic measurements. Spectroscopic studies of [Cu(DPA)(malonate)] revealed that the complex exhibits square planner coordination with copper(II). The hydrolysis of glycine methyl ester (MeGly) is catalyzed by the Cu(DPA)²⁺ complex. The reaction has been studied by a pH-state technique over the pH range 5.8–6.8 at 25 °C and I=0.1 mol dm⁻¹. The kinetic data fits assuming that the hydrolysis proceeds in two steps. The first step, involving coordination of the amino acid ester by the amino and carboxylic group, is followed by the rate-determining attack by the OH⁻ ion. The second step involves equilibrium formation of the hydroxo-complex, Cu(DPA)(MeGly)(OH), followed by intramolecular attack.     

Synthesis and characterization of two acetato-bridged dinuclear copper(II) complexes with 4-bromo-2-((4 or 6-methylpyridin-2-ylimino)methyl)phenol as ligand

The synthesis and characterization of two new acetato-bridged dinuclear copper(II) complexes are described. Both compounds have the general formula [Cu(L)(µ-O₂C–CH₃)]₂, in which L = 4-bromo-2-((4-methylpyridin-2-ylimino)methyl)phenol or 4-bromo-2-((6-methylpyridin-2-ylimino)methyl)phenol. The title compounds consist of dinuclear units with bridging acetato groups and a ligand linked to each copper via the phenol oxygen and nitrogen. Both compounds were synthesized in a one-step reaction and characterized by elemental analysis, Fourier transform infrared (FTIR), electron spin resonance (ESR), and electronic spectra and by room temperature magnetic moments. The compounds exhibit antiferromagnetic interactions at room temperature. UV-Vis spectra show four absorptions attributed to d–d transitions of copper, ligand → metal charge transfer and π → π* or n → π* transitions of ligand. The FTIR spectra indicate a Cu₂O₄C₂ ring vibration. Both complexes show room temperature magnetic moments of about 1.6 B.M. per copper. The X-band ESR studies indicate a weak half-field band, characteristic of the Cu(II)–Cu(II) dimer, observed at 1552 and 1558 G for the complexes, strongly suggesting that the hyperfine structure arises from a spin triplet species. The spectra of frozen samples in DMSO or DMF at liquid nitrogen temperature show a typical Δm = 1 transition.     

Potentiometric studies of binary and ternary complexes involving cadmium(II) and nitrilo-tris(methyl phosphonic acid) with amino acids, peptides and DNA constituents

The complexing properties of nitrilo-tris(methylphosphonic acid) (NTP) with cadmium(II) were investigated pH-metrically at 25 degrees C and at ionic strength of 0.1 mol dm(-3) (NaNO3). Stoichiometry and stability constants for the complexes formed are reported. Cadmium (II) forms Cd(NTP)(4-) and the corresponding hydroxy complexes. The ternary complexes are formed in a stepwise mechanism whereby NTP binds to cadmium(II), followed by coordination of amino acids, peptides or DNA. The concentration distribution of the various complex species has been evaluated.     

Synthesis of a heterodinuclear ruthenium(II)–platinum(II) complex linked by l-cysteine methyl ester

A potential anticancer heterodinuclear ruthenium(II)–platinum(II) complex, [ruthenium(II)(4,4′-dimethyl-2,2′-bipyridine)₂(5-(l-cysteine-methyl ester)-1,10-phenanthroline)-trans-chlorodiammineplatinum(II)] chloride, [Ru(Me₂bipy)₂(5-(l-cysteine-Me)-phen)-trans-Pt(NH₃)₂Cl]Cl₃, was synthesised. l-Cysteine methyl ester was used to link the two metal centres, as more conventional straight chain diaminoalkanes and 2-mercaptoethylamine failed to couple to the phenanthroline ligand. From the precursor mononuclear ruthenium(II) complexes, which were separated into their Δ- and Λ-isomers by column chromatography, the dinuclear complex was synthesised and characterised by ¹H and ¹³C NMR, UV–Vis, circular dichroism, fluorescence and electrospray ionisation mass spectrometry.