Thangarasu Pandiyan

Simultaneous and sensitive determination of ascorbic acid, dopamine, uric acid, and tryptophan with silver nanoparticles-decorated reduced graphene oxide modified electrode.

In this paper, we report the synthesis of silver nanoparticle-decorated reduced graphene oxide composite (AgNPs/rGO) by heating the mixture of graphene oxide and silver nitrate aqueous solution in the presence of sodium hydroxide. This material was characterized by means of X-ray diffraction, UV-vis spectroscopy, and transmission electron microscopy. AgNPs/rGO based electrochemical sensor was fabricated for the simultaneous determination of ascorbic acid, dopamine, uric acid, and tryptophan. Electrochemical studies were carried out by using cyclic voltammetry, linear sweep voltammetry, and chronoamperometry. AgNPs/rGO modified electrode exhibited excellent electrocatalytic activity, stability, sensitivity, and selectivity with well-separated oxidation peaks toward ascorbic acid, dopamine, uric acid, and tryptophan in the simultaneous determination of their quaternary mixture. The analytical performance of this material as a chemical sensor was demonstrated for the determination of ascorbic acid and dopamine in commercial pharmaceutical samples such as vitamin C tablets and dopamine injections, respectively. The applicability of this sensor was also extended in the determination of uric acid in human urine samples.

STRUCTURE, SPECTRA AND REDOX STUDIES OF NICKEL(II) BIS(BENZIMIDAZOLE-2-YLMETHYL)AMINES WITH COENZYME M REDUCTASE

Abstract The 1 : 1 and 1 : 2 nickel(II) complexes with the tridentate ligand bis(benzimidazol-2-ylmethyl)amine (bbma) and its amine (bbmma) and benzimidazole (bmbma) N-methyl-substituted derivatives have been prepared and their spectroscopic and redox properties studied. While the 1 : 1 complexes are of the type NiLX2·nH2O (X = ClO4−, Cl− or NO3−), the 1 : 2 complexes are of the type NiL2(ClO2)·nH2O (L = bbma, bbmma or bmbma, n = 0–4). The purple complex Ni(bbma)2(ClO4)2MeOH·H2O has been characterized by X ray crystallography. The NiII ion has an octahedral geometry with one nitrogen from the amine and one nitrogen atom of the benzimidazole in axial positions and the remaining three benzimidazole and amine nitrogen atoms coordinated in an equatorial fashion. A red shift was observed in the electronic spectra and an elevation of the redox potential was detected during the addition of the sodium salt of 2-mercaptoethanesulfonic acid (CoM) to the NiII complexes. The effects of methylation on the amine and also on the benzimidazole was observed in the electronic spectra and redox behaviour.

Cu nanoparticles supported mesoporous polyaniline and its applications towards non-enzymatic sensing of glucose and electrocatalytic oxidation of methanol

Cu nanoparticles supported on mesoporous polyaniline (Cu/Meso-PANI) was synthesized by the self assembly of dual surfactants followed by the in-situ reduction of CuCl2 in aqueous solution. Materials were characterized by X-ray diffraction, Scanning electron microscopy, Transmission electron microscopy, and UV-visible spectroscopic method. Cu/Meso-PANI based non-enzymatic electrochemical sensor was fabricated for glucose detection. The Cu/Meso-PANI modified electrode showed high electrocatalytic activity towards the oxidation of glucose compared to Cu/PANI (Cu nanoparticles supported on conventional polyaniline), which is due the highly dispersed copper in the high surface area Meso-PANI matrix. The Cu/Meso-PANI modified electrode exhibited high selectivity towards glucose against several common interfering species. Cu/Meso-PANI modified electrode was also explored for the electrochemical oxidation of methanol, which finds application in direct methanol fuel cell. The electrochemical oxidation of methanol was investigated at the surface of Cu/Meso-PANI modified electrode in alkaline medium using cyclic voltammetry and chronoamperometry methods. Various reaction parameters such as effect of scan rate and concentration of methanol were investigated. Furthermore, the rate constant (k) for the electrocatalytic oxidation of methanol was also calculated. The promising electrocatalytic activity of Cu/Meso-PANI modified electrode provides a new platform for the fabrication of polyaniline based high-performance sensors.

Mercaptoethanesulfonic acid studies with nickel(II) complexes of tetra- and hexadentate ligands containing pyridyl groups: synthesis, structure, spectra and redox behavior

Abstract Nickel(II)complexes of N,N,N′N′-tetrakis(2-pyridylmethyl)ethylenediamine (L1), N,N,N′N′-tetrakis(2-pyridylmethyl)-1,2-diaminopropane (L2), N,N,N′N′-tetrakis(2-pyridylmethyl)-1,3-diaminopropane (L3), N,N′-bis(2-pyridylmethyl)ethylenediamine (L4), N,N′-bis(2-pyridylmethyl)-1,2-diaminopropane (L5) and N,N′-bis(2-pyridylmethyl)-1,3-diaminopropane (L6) were prepared and their spectroscopic and redox behaviors studied. The distorted octahedral geometry was determined for [NiL2](ClO4)2 by using X-ray crystallography. The electronic spectral bands (3A2g→3T2g and 3A2g→1Eg transitions) of NiN6 and NiN4O2 were analyzed; it shows that the former complexes possess well-resolved bands compared to the latter compounds. In addition, the ligand field parameter Dq found for NiN4O2 complexes was much lower than that of NiN6 compounds; thereby, a more positive redox potential was detected for NiN4O2 complexes in electrochemistry over the NiN6 compounds. Further, the coordination studies of 2-mercaptoethanesulfonic acid as a simulator of coenzyme M reductase (CoM) with NiN4 or NiN6 chromophores were discussed.

Coenzyme M studies with nickel(II) compounds: Synthesis, structure, spectra and redox behaviors

Abstract Nickel(II) complexes of 1,6-bis(pyridyl)-2,5-dithiahexane (L1), 1,7-bis(2′-pyridyl)-2,6-dithiaheptane (L2) and 1,9-bis(2′-pyridyl)-2,5,8-trithianonane (L3) have been prepared and their spectroscopic and redox behaviors were studied. [Ni(II)L1(H2O)2](ClO4)2, and [Ni(II)L3(H2O)](ClO4)2 were crystallized in single crystal form; their structures were solved by X-ray crystallography. The structures of the complexes are of distorted octahedral geometry. A red shift in the electronic spectra and a positive potential shift in electrochemical studies were detected during the addition of the sodium salt of 2-mercaptoethanesulfonic acid (CoM) to Ni(II) complexes containing L1 and L2. The high redox potential shifting difference (PSD) was observed with the addition of CoM to [NiL1]2+, which accounts for the axial coordination of CoM with the nickel ion. However, [Ni(II)L3]2+ does not respond well with CoM addition due to the structural limitation around the Ni(II) ion. A destabilization of [Ni(II)L1]2+ and [Ni(II)L2]2+ complexes and stabilization for [Ni(II)L3]2+ were noticed in their redox studies and these trends were inversely changed during anaerobic CoM addition to Ni(II) complexes. A nephelauxetic effect (β values) has been shown to establish a good relation with PSD.

Dichloro[2,2'‐(2,5‐dithiahexamethylene)dipyridine‐N,N',S,S']nickel(II)

The title complex, cis-[NiCl 2 (C 14 H 16 N 2 S 2 )], has twofold crystallographic symmetry and the Ni atom has an octahedral coordination with two cis thioether S atoms, two trans pyridyl N atoms and two cis chloride ions. The main dimensions are Ni-N 2.1078 (16), Ni-S 2.4316 (7) and Ni-Cl 2.3855 (6) A.

Photochemical oxidation of chlorinated phenols in comparison with electro-oxidation

Photooxidation of chlorophenols was studied and the results were analyzed. It has been found that 4-chlorophenol is oxidized faster than other chlorinated phenols, indicating that higher chlorinated phenols are hard to decompose and the order of the decomposition was as follows: 4-CP > 2,4-DCP > 2,4,6-TCP > PCP.

Bis[bis(2-benzimidazol-2-ylethyl) sulfide]nickel(II) Dinitrate

The structure of the title compound, [Ni(C 18 H 18 N 4 S) 2 ](NO 3 ) 2 , consists of an octahedral nickel complex with the central Ni atom coordinated to four N atoms of the benzimidazole moieties and two S atoms. The nitrate ion lies in a well defined position in the lattice and plays an important role in the crystal packing. All four benzimidazole rings are nearly planar. The crystal structure is stabilized by a three-dimensional network of N-H...O and C-H...O hydrogen bonds.

Synthesis of imidazole-based NHC–Au(I) complexes and their application in non-enzymatic glucose sensing

In this study, imidazole-based NHC–Au(I) complexes were prepared. Geometrically optimized structures and molecular orbital energy diagrams were computed using density functional theory. Cyclic voltammetry and amperometric methods were used to evaluate the catalytic activity of the NHC–Au(I)-modified electrodes toward glucose oxidation. The mechanism of electrocatalytic oxidation at NHC–Au(I)-modified electrodes is explained on the basis of the oxidation and reduction potentials in the presence of glucose. Applicability of NHC–Au(I)-modified electrode was extended to determine the glucose level in the blood serum and the precision of the method was found to be satisfactory. The non-enzymatic sensor exhibited excellent reproducibility, repeatability, antifouling, and anti-interference characteristics.

[N,N'‐Bis(benzimidazol‐2‐ylethyl)‐1,2‐ethanediamine](nitrato‐O,O')nickel(II) Nitrate

The structure of the title compound, [Ni(C 20 H 24 N 6 )(NO 3 )](NO 3 ), consists of a distorted octahedral nickel complex with the central Ni atom coordinated to two N atoms of the benzimidazole moieties, two ethylenediamine N atoms and two O atoms of one of the nitrate ions ; the other nitrate ion lies in a well defined position in the lattice and plays an important role in crystal packing. The dihedral angle between the two benzimidazole rings is 85.1(1)°. The crystal structure is stabilized by a three-dimensional network of N-H...O and C-H...O interactions, and N-H...O intermolecular hydrogen bonds.