Perumal Subramaniam

Synthesis, structural elucidation, biological, antioxidant and nuclease activities of some 5-Fluorouracil-amino acid mixed ligand complexes.

Some biologically active mixed ligand complexes (1-9) have been synthesized from 5-Fluorouracil (5-FU; A) and amino acids (B) such as glycine (gly), L-alanine (ala) and L-valine (val) with Ni(II), Cu(II) and Zn(II) ions. The synthesized mixed ligand complexes (1-9) were characterized by various physico-chemical, spectral, thermal and morphological studies. 5-Fluorouracil and its mixed ligand complexes have been tested for their in vitro biological activities against some pathogenic bacterial and fungal species by the agar well diffusion method. The in vitro antioxidant activities of 5-Fluorouracil and its complexes have also been investigated by using the DPPH assay method. The results demonstrate that Cu(II) mixed ligand complexes (4-6) exhibit potent biological as well as antioxidant activities compared to 5-Fluorouracil and Ni(II) (1-3) and Zn(II) (7-9) mixed ligand complexes. Further, the cleaving activities of CT DNA under aerobic conditions show moderate activity with the synthesized Cu(II) and Ni(II) mixed ligand complexes (1-6) while no activity is seen with Zn(II) complexes (7-9). Binding studies of CT DNA with these complexes show a decrease in intensity of the charge transfer band to the extent of 5-15% along with a minor red shift. The free energy change values (Δ(‡)G) calculated from intrinsic binding constants indicate that the interaction between mixed ligand complex and DNA is spontaneous.

Spectroscopic investigation on kinetics, thermodynamics and mechanism for electron transfer reaction of iron(III) complex with sulphur centered radical in stimulated biological system

Electron transfer reactions of biological organic sulphides with several metal ions to generate sulphide radical cations are a great concern in biochemical process. To understand the mechanism, a stimulated biological system having model compounds, iron(III)-bipyridyl complex with thio-diglycolic acid (TDGA) was investigated. Spectroscopic study reveals the kinetics and thermodynamics of the reaction in aqueous perchloric acid medium. The reaction follows first and fractional order of 0.412 with respect to [Fe(bpy)3](3+) and TDGA, respectively. The oxidation is insensitive to variation in [H(+)] but slightly decreases with increase in ionic strength ([I]). Addition of acrylamide, a radical scavenger has no effect on the rate of the reaction. The high negative value of ΔS(#) (-74.3±1.09 J K(-1) mol(-1)) indicates the complex formed has a definite orientation higher than the reactants. Based on the above results, a suitable reaction mechanism for this reaction is proposed.

Morphological and pharmacological investigation on some biopotent materials derived from substituted pyrimidine and imidazole enzyme constituents

Coordinating behavior of novel N2O type mixed ligand complexes (1-6) have been synthesized from substituted fluoropyrimidine [5-Fluorouracil (5-FU; A)] with biopotent imidazole enzyme constituents (B) viz., imidazole(him) and benzimidazole(bim) in the presence of Ni(II), Cu(II) and Zn(II) ions. Synthesized complexes were characterized by chemical analysis, spectral studies, magnetic moment and conductivity measurements. The results of chemical analysis and the observed low molar conductance values propose their stoichiometry to be 1:1:1 (M:A:B) with non-electrolytic nature. From the spectral data, it is inferred that the ligands A & B coordinate with M(II) ions in bi and monodentate approach through C(4)=O, N(3) and imidazole ring N(3) atoms respectively. The thermogravimetric analysis shows the dehydration, decomposition and thermal stability of mixed ligand complexes. XRD and SEM patterns show sharp crystalline peaks with homogeneous morphology. In vitro antimicrobial activities of free ligands (A & B) and their metal complexes were screened against some pathogenic strains by well diffusion technique. Absorption and gel electrophoresis experiments on the interaction of mixed ligand complexes with DNA suggest that all the complexes can bind as well as cleave the DNA by intercalation between chromophores and DNA base pairs. In addition, in vitro antioxidant activities were tested by DPPH free radical scavenging model.

Electrophilic and nucleophilic pathways in ligand oxide mediated reactions of phenylsulfinylacetic acids with oxo(salen)chromium(V) complexes

Abstract The mechanism of oxidative decarboxylation of phenylsulfinylacetic acids (PSAA) by oxo(salen)Cr(V)+ ion in the presence of ligand oxides has been studied spectrophotometrically in acetonitrile medium. Addition of ligand oxides (LO) causes a red shift in the λ max values of oxo(salen) complexes and an increase in absorbance with the concentration of LO along with a clear isobestic point. The reaction shows first-order dependence on oxo(salen)-chromium(V)+ ion and fractional-order dependence on PSAA and ligand oxide. Michaelis–Menten kinetics without kinetic saturation was observed for the reaction. The order of reactivity among the ligand oxides is picoline N-oxide>pyridine N-oxide>triphenylphosphine oxide. The low catalytic activity of TPPO was rationalized. Both electron-withdrawing and electron-donating substituents in the phenyl ring of PSAA facilitate the reaction rate. The Hammett plots are non-linear upward type with negative ρ value for electron-donating substituents, (ρ − =−0.740 to −4.10) and positive ρ value for electron-withdrawing substituents (ρ + =+0.057 to +0.886). Non-linear Hammett plot is explained by two possible mechanistic scenarios, electrophilic and nucleophilic attack of oxo(salen)chromium(V)+-LO adduct on PSAA as the substituent in PSAA is changed from electron-donating to electron-withdrawing. The linearity in the log k vs. E ox plot confirms single-electron transfer (SET) mechanism for PSAAs with electron-donating substituents.

Stability and Structural Studies on Ni(II)–5-Fluorouracil Mixed Ligand Complex Systems

Binary and mixed ligand species formation and their distribution in the 5-fluorouracil (5-FU; A) and Ni(II) system in the presence of amino acids (B), namely glycine (gly), l-alanine (ala), l-valine (val) and l-phenylalanine (phe), were studied potentiometrically at different temperatures and pHs. The computer assisted analysis illustrates the existence of MAB and MAB2 species, where 5-fluorouracil and amino acids act as bidentates to form stable metal chelates. The distribution of different chemical species with temperature and pH was also studied. In addition, the coordination environments in the MAB system were determined by spectrophotometric measurements. The binding nature of both 5-FU (A) and amino acids (B) in MAB species of the Ni(II)–5-FU–amino acid systems reveal tetra coordination to the central Ni(II) ion. The fifth and sixth positions in MAB complexes are occupied by solvent water molecules/perchlorate ions and thus form a stable hexa coordinated environment. The calculated stabilization parameters indicate that the formed mixed ligand species have higher stabilities than their corresponding binary systems. Thermodynamic parameters were determined from the temperature dependent stability constant values. The mixed ligand complex systems show remarkable in vitro antimicrobial, antioxidant and nuclease activities.

Interaction of Pyridine-2,6-dicarboxylic Acid with Cr(VI) in the Oxidative Decarboxylation of Phenylsulfinyl Acetic Acid and Linear Free Energy Relationship

Aims: To investigate the catalytic activity of pyridine-2,6-dicarboxylic acid in the redox reaction of Cr(VI) and phenylsulfinyl acetic acid. Study Design: The mechanism of the reaction was designed on the basis of the observed results of kinetic, spectral and substituent effect studies. Place and Duration of Study: Laboratory of the Research Department of Chemistry, Aditanar College of Arts and Science, Tiruchendur, Tamil Nadu, India. September 2013 – January 2014. Methodology: Phenylsulfinyl acetic acid and ten metaand para-substituted phenylsulfinyl acetic acids essential for the present kinetic study were synthesized. The kinetic study was performed in 40% acetonitrile-60% H2O medium under pseudo-first-order conditions by maintaining [PSAA] >> Original Research Article Subramaniam and Thamil Selvi; ACSj, 6(2): 105-114, 2015; Article no.ACSj.2015.042 106 [Cr(VI)] throughout the experiment. The progress of the reaction was monitored by following the rate of disappearance of Cr(VI) spectrophotometrically at 351 nm. The effect of pyridine-2,6dicarboxylic acid on the rate of the reaction and the applicability of linear free energy relationship with different phenylsulfinyl acetic acids were tested. Results: The reaction shows unit order dependence on Cr(VI) but follows Michalis-Menten kinetics with respect to substrate as well as catalyst. The order with respect to [H] is between one and two. The thermodynamic parameters ∆ ‡ S (-93.2 JK -1 mol -1 ) and ∆ ‡ H (57.7 kJ mol -1 ) are evaluated respectively from the intercept and slope of the Eyring’s plot. The Hammett’s correlation affords a negative ρ value (-1.05). Conclusion: Pyridine-2,6-dicarboxylic acid catalyzes the reaction and Cr(VI)-PDA complex is assumed to be the oxidizing species of the reaction. The sulfur of PSAA undergoes nucleophilic attack on Cr(VI)-PDA complex forming a ternary complex, Cr(VI)-PDA-PSAA which experiences decarboxylation, ligand coupling and further decomposition giving methylphenyl sulfone as the product. The mechanism with the associated reaction kinetics is assigned in support of substituent effect.