Biological and chemical Sciences
University of south pacific
Surendra Prasad is working as professor in department of school of biological and chemical sciences in University of South Pacific in Fiji.
My research group and I are interested in understanding the kinetics of ligand substitution reactions of transition metal compounds with particular emphasis on their application as analytical tool. Our investigations are aimed at building mechanistic understanding of ligand substitution as well as oxidation reactions that can advance our knowledge of catalytic kinetic methods (CKMs). We determine catalysed and uncatalysed reaction mechanisms by studying chemical kinetics and apply such reactions for the development of inexpensive analytical methods for trace determination of toxicants, environmental pollutants and species of biological interest. The development of methods for determination of toxic species, environmental pollutants and species of biological interest at trace level is challenging analytical expertise especially for complex samples. The specialized instrumentation needed for trace analysis and the associated procedures involved are often very expensive. The “Kinetic Methods of Analysis” (also called Reaction Rate Methods) utilising spectrophotometric monitoring is an inexpensive analytical method. The CKM continues to be the most popular method in the literature of Kinetic Methods of Analysis. My research group is involved in the developments of CKMs for trace determination of toxicants, environmental pollutants and species of biological interest. It has been demonstrated that it is possible to determine catalytic or inhibitor species (environmental pollutants, toxicants or species of biological interest) by measuring their effects on reaction rates, down to ppm/ppb levels. The cost effective CKMs for the determination of Hg2+, Cu2+, Se2+, Se4+, Ru3+, cysteine, thiosulphate, MNDT (S2C2(CN)22-), NO3-, NO2- etc. in environmental and vegetables samples have been developed using different indicator reactions. The methods are simple, sensitive, selective and economical compared to AAS, radio-istope techniques, mass spectrometry, activation analysis, etc. The undertaken research projects are intended to study regional environmental problems and to develop professional manpower in the area of development of cost-effective analytical techniques. Hence we have been working on the following research projects: i. Development of catalytic kinetic method for trace determination of mercury(II). Along with understanding the kinetics and mechanism of ligand substitution/oxidation reactions a CKM is being proposed for ascertaining the trace levels of toxic mercury(II). The method being developed is to be tested for determination of mercury(II) in the real water samples like waters of Fiji. ii. Chemical and biological monitoring of selective heavy metal species in inland, coastal waters and soils samples in Viti Levu (Fiji). This is a collaborative research project with Dr. Rajendra Prasad (Chemistry Division) and Mr. Waisea Votadroka (Institute of Applied Sciences) of the University of the South Pacific and Prof. P.K. Dasgupta, Chairman, Department of Chemistry and Biochemistry, University of Texas, Arlington (UTA), TX, USA. iii. Studies on adsorptive removal of nephrotoxic heavy metals from aqueous solutions and contaminated natural waters. This is a collaborative study in which senior chemistry staff member, Dr. Rajendra Prasad, of the University of the South Pacific is involved. Multi-step Ligand Exchange/Oxidation Reactions I have made significant contributions towards enhancing understanding the mechanism of ligand exchange reactions. I have succeeded in studying the reaction dynamics of relatively slow as well as fast (t½ = m sec.) reactions and in unraveling the mechanistic features of the reactions occurring in four, five and six steps. The kinetics and mechanism of ligand exchange reactions involving polydentate ligands viz. aminopolycarboxylates, polyamines, polychromics coordinated to Mn(III), Fe(III), Zn(II) and Ni(II) centres by cyanide ions and PAR have been investigated. All these reactions follow variable order dependence in cyanide. The reverse rate is first order in M(CN)x [x = 4, 5, 6; M = metal] and first order in L [L = ligand] and exhibit an inverse first order dependence in [CN-]. These results led us to postulate a multi-step mechanistic scheme in which cyanide ions add one by one to the vacant sites generated by the progressive unwrapping of the ligand coordinated to the metal centres. Besides, the kinetics of catalysed and uncatalysed monodentate ligand exchange reactions of hexacyanoferrate(II) complex with N-methylpyrazinium ion (Mpz+), α-nitroso β-naphthol, pyrazine, 2-methyl pyrazine (2Mepz), etc. are being investigated followed by their application as analytical tool. Food Chemistry In addition to above areas of research, we have been working on the following projects: i. Exposure to cadmium and arsenic via leafy vegetables in Fiji. This is a collaborative study in which senior chemists of the University of the South Pacific, Dr. Rajendra Prasad. ii. Study of the effects of cooking and deep-freezing on the nitrate concentration in Fiji’s vegetables using flow injection analysis (FIA). iii. Application of catalytic kinetic method to ascertain the contents of nitrite in water and vegetables samples in Fiji. The flow injection analysis (FIA) and spectrophotometeric techniques have been developed to determine NO3- and NO2- respectively in vegetables and water samples. The methods are being applied to the determination of NO3- in commonly consumed leafy, fruit and root vegetables of Fiji. Synthesis, Characterization, Antibacterial and Antifungal Studies of Inorganic Complexes To discover the antibacterial and antifungal properties of inorganic complexes, we have been working on the following research projects: i. Synthesis of new molecular receptors based on polypyridyl-ruthenium(II) linked metallo-macrocycles. This is a collaborative study in which senior chemists of the University of the South Pacific, Dr. Rajendra Prasad. ii. An Investigation on Chelating Behavior of Heterocyclic Semicarbazones toward Bioactive Metal ions. iii. An Investigation on Structure and Bonding in Some High Coordinated Complexes of Thorium(IV) and Dioxouranium(VI) Derived from Heterocyclic Semicarbazones as Primary Ligand and Diphenyl Sulfoxide as Secondary Ligand. A series of mono- and binuclear ruthenium complexes of the type [Cp(EPh3)RuL]-/+, [(bipy)2RuL]0/2+, [Ru2Cp2(EPh3)4L], [Ru2Cp2(EPh3)3L] 2+ and [Ru2Cp(EPh3)2(bipy)2]+/3+ [E = P, As, Sb; L = S2C2(CN)22- or (C6H5CH2)S2C2(CN)2] have been synthesized exploiting the nucleophilicity of S and N in L. The complexes have been characterized by microanalysis, conductance, IR, 1H and 31P NMR and UV-visible spectral data. Also synthesis magneto-spectral and thermal characteristics of some lanthanide(III) chloro complexes derived from 4[N-(4’-hydroxy-3’-methoxybenzalidene)amino]antipyrine semicarbazone; 4[N-(3’,4’,5’trimethoxy-benzalidene)amino]antipyrinesemicarbazone; 4[(furan-2-ylmethylene)amino]-1,5-dimethyl-2-phenylpyrazol-3-one; isonicotinic acid(3’,4’,5’-trimethoxybenzylidene)hydrazide and some mixed ligand complexes of thorium(IV) and dioxouranium(VI) with semicarbazones as primary ligand and sulfoxide as secondary ligand and penta-coordinated complexes of oxovanadium(IV) derived from thiosemicarbazones of 4-aminoantipyrine have been carried out. Besides these, synthesis and spectral investigations of some platinum metals ions coordination compounds of 4[N-(furan-2-carboxalidene)-amino]antipyrine thiosemicarbazone and 4[N-(3’,4’,5’-trimethoxybenzalidene)amino]antipyrine thiosemicarbazone has been carried out. Also, synthesis, magneto-spectral, biological and thermal investigations of cobalt(II) and nickel(II) coordination compounds of thiosemicarbazones derived from 4-aminoantipyrine and hydrazones of isonicotinic acid hydrazide has been done. It has been established that many of the complexes studied have potent antibacterial and antifungal properties/activities.