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Schiff bases (SBs) are aldehyde- or ketone-like compounds in which the carbonyl group is replaced by an imine or azomethine. In spite of the large interest always shown in the coordination properties of Schiff base ligands and the attention paid in recent years to the possible variable biological activities of their metal complexes, studies dealing with protonation and formation equilibria of Schiff bases and their complexes are still very rare. Thus, the importance of the determination of the equilibrium constants of Schiff bases and their complex formation equilibria is of paramount importance to understand the complicated biological reactions like transamination, racemization and decarboxylation. The 33 ligands considered herein include salicylaldehyde/substituted salicylaldehyde SBs and salicylaldehyde/substituted salicylaldehyde amino acid SBs. This article is focused on protonation and complex-formation equilibria of salicylaldehyde or substituted salicylaldehyde SBs and salicylaldehyde amino acid SBs in aqueous and nonaqueous solutions, taking into account also the structure-activity correlation of SBs and their metal(II) complexes based on their stability constants. Activity of SBs enhances upon complexation and the order of activity is nearly in accord with the order of the formation constants of metal ions. The few enthalpy and entropy changes available for such protonation and complex-formation reactions are reported and discussed. [ABSTRACT FROM AUTHOR]

The complex formation reactions of [Cu(NTP)(OH 2 )] 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)NH 2 CH 2 CO 2 Me] 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 ± . [ABSTRACT FROM AUTHOR]

Binary and ternary complexes of Cu(II) involving imino-bis(methyl phosphonic acid) (IdP) abbreviated as H4A and some selected bio-ligands, amino acids, peptides and DNA constituents (L), were examined. Cu(II) forms CuA and CuAH complexes with IdP. Ternary complexes are formed in a stepwise mechanism whereby iminodiphosphonic acid binds to Cu(II), followed by coordination of amino acid, peptide or DNA. The concentration distribution of the various complex species has been evaluated. The kinetics of base hydrolysis of glycine methyl ester in the presence of Cu(II)-IdP was studied in aqueous solution at different temperatures, and in dioxane-water solutions of different compositions at 25°C. The activation parameters are evaluated and discussed. [ABSTRACT FROM AUTHOR]

Ternary complexes of copper(II) with 2-aminomethylthiophenyl-4-bromosalicylaldehyde (ATS) and some amino acids have been isolated and characterized by elemental analyses, IR, magnetic moment, molar conductance, UV–vis, mass spectra, and ESR. The proposed general formulas of the prepared complexes are [Cu(ATS)(AA)]·nH2O (where AA?=?glycine, alanine, and valine). The low molar conductance values suggest the non-electrolytic nature of the complexes. IR spectra show that ATS is coordinated to copper in a bidentate manner through azomethine-N and phenolic-OH. The amino acids also are monobasic bidentate ligands via amino and ionized carboxylate groups. The magnetic and spectral data indicate the square-planar geometry of Cu(II) complexes. The geometry of the Cu(II) complexes has been fully optimized using parameterized PM3 semiempirical method. The Cu–N bond length is longer than that of Cu–O in the isolated complexes. Also, information is obtained from calculations of molecular parameters for all complexes including net dipole moment of the metal complexes, values of binding energy, and lipophilicity value (logP). The antimicrobial activity studies indicate significant inhibitory activity of complex3against the selected types of bacteria. The mixed ligand complexes have also been studied in solution state. Protonation constants of ATS and amino acids were determined by potentiometric titration in 50% (v/v) DMSO–water solution at ionic strength of 0.1?M NaCl. ATS has two protonation constants. The binary and ternary complexes of copper(II) involving ATS and some selected amino acids (glycine, alanine, and valine) were examined. Copper(II) forms [Cu(ATS)], [Cu(ATS)2], [Cu(AA)], [Cu(AA)2], and [Cu(ATS)(AA)] complexes. The ternary complexes are formed in a simultaneous mechanism. The present paper reports on the synthesis, characterization, and the electronic absorption spectra of Cu(II) ternary complexes involving ATS-Schiff base, and some selected amino acids. The antibacterial, antifungal, and antitumor activities were investigated. The geometry of the studied Cu(II) complexes has been fully optimized using parameterized PM3 semiempirical method. Protonation and complex formation equilibria were investigated. [ABSTRACT FROM PUBLISHER]

Mononuclear cobalt(II), nickel(II), and copper(II) complexes of cetirizine·2HCl (CTZ = 2-[2-[4-[(4-chlorophenyl)phenyl methyl]piperazine-1-yl]-ethoxy]acetic acid) in the presence of alanine (Ala) as a representative example of amino acids were synthesized and elucidated by different physical techniques. All complexes have been characterized with the help of elemental analyses, molecular weights, molar conductance values, magnetic moments, and spectroscopic data. The measured molar conductance values in DMSO indicate that the complexes are nonelectrolytes. Quantum chemical calculations were performed with semi-empirical method to find the optimum geometry of complexes. The metal–oxygen bond length in the synthesized complexes obeys the order M–OH2 > M–OCTZ > M–OAla. Formation equilibria of the ternary complexes have been investigated. Ternary complexes are formed by a simultaneous mechanism. Stoichiometry and stability constants for the complexes formed are reported. The concentration distributions of various species formed in solution were also evaluated as a function of pH. CTZ and its metal chelates have been screened for their antimicrobial activities against some selected types of gram-positive (G+) and gram-negative (G−) bacteria. They were more active against (G+) than (G−) bacteria. The present article reports on the synthesis, characterization, and their electronic absorption spectra of M(II)–ternary complexes involving CTZ as antihistamine drug and alanine as a representative example of amino acids. The geometry of the studied M(II) complexes has been fully optimized using parameterized PM3 semi-empirical method. Protonation and complex formation equilibria were investigated. The antimicrobial activities were investigated. [ABSTRACT FROM PUBLISHER]