M. N. Kumara

Anodically generated manganese(III) sulphate for the oxidation of dipeptides in aqueous sulphuric acid medium: A kinetic study

The kinetic of oxidation of dipeptides (DP) namely valyl-glycine (Val-Gly), alanyl-glycine (Ala-Gly) and glycyl-glycine (Gly-Gly), by Mn(III) have been studied in the presence of sulphate ions in acid medium at 26°C. The reaction was followed spectrophotometrically at λmax = 500 nm. A first-order dependence of the rate on both [Mn(III)]o and [DP]o was observed. The rate is independent of the concentration of reduction product, Mn(II) and hydrogen ions. The effects of varying the dielectric constant of the medium and addition of anions such as sulphate, chloride and perchlorate were studied. The activation parameters have been evaluated using Arrhenius and Eyring plots. The oxidation products were isolated and characterized. A mechanism involving the reaction of DP with Mn(III) in the rate-limiting step is suggested. An apparent correlation was noted between the rate of oxidation and the hydrophobicity of these dimers, where increased hyphobicity results in increased rate of oxidation

Crystal structure of ethyl 6-bromo-2-[(E)-2-phenyl-ethen-yl]quinoline-4-carboxyl-ate.

In the title compound, C20H16BrNO2, the dihedral angle between the quinolone ring system mean plane (r.m.s. deviation = 0.018 Å) and the phenyl ring bridged by the ethynyl group, is 25.44 (14)°. There is an intramolecular C—H⋯O hydrogen bond forming an S(6) ring motif. In the crystal, molecules are linked via C—H⋯O hydrogen bonds forming chains propagating along the b-axis direction.

Crystal structure of 8-eth­­oxy-3-(4-nitro­phen­yl)-2H-chromen-2-one

In the title compound, C17H13NO5, the coumarin ring system is essentially planar (r.m.s. deviation = 0.008 Å). The nitrophenyl ring makes a dihedral angle of 25.27 (9)° with the coumarin ring plane. The nitro group is almost coplanar with the phenyl ring to which it is attached, making a dihedral angle of 4.3 (3)°. The ethoxy group is inclined to the coumarin ring plane by 4.1 (2)°. Electron delocalization was found at the short bridging C—C bond with a bond length of 1.354 (2) Å. In the crystal, molecules are linked via C—H⋯O hydrogen bonds, forming sheets in the bc plane. The sheets are linked via π–π stacking [centroid–centroid distances = 3.5688 (13) and 3.7514 (13) Å], forming a three-dimensional structure.

Synthesis and Fluorescence Study of Some New Blue Light Emitting 3-(1,3-benzothiazol/benzoxazol-2-yl)-2H- chromen-2-ones

The synthesis and fluorescence efficiency of 3-(1, 3-benzothiazol/benzoxazol-2-yl)-2H-chromen2-one derivatives 4a-j have been described. To improve the fluorescence characteristics especially emission wavelength, the substitution like diethylamino, fluoro, bromo, chloro, trifluoromethyloxy, methyloxy and methyl groups on 7th position of salicyladehydes 1a-j and substitutions such as fluoro, methyl and nitro groups on 5th and 6th position of ethyl-1,3benzothiazol/benzoxazole-2yl-acetates were selected as donor and acceptor groups. The fluorescence property was investigated spectrophotometrically in chloroform at 1⇥10 6 M concentration with Rhodamine B as standard dye. All the compounds were found to emit blue light in the region between 450 to 495 nm. The quantum yield of all the compounds 4a-j were found to be moderate when compared to Rhodamine B as standard.

Crystal structure of ethyl 2-(2,4,5-tri-meth-oxy-phen-yl)quinoline-4-carboxyl-ate.

In the title compound, C21H21NO5, the dihedral angle between the quinoline ring system (r.m.s. deviation = 0.028 Å) and the trimethoxybenzene ring is 43.38 (5)°. The C atoms of the methoxy groups deviate from their attached benzene ring by −0.396 (2), −0.049 (2) and 0.192 (2) Å for the ortho-, meta- and para-substituents, respectively. The pendant ethyl chain is disordered over two orientations in a 0.527 (5):0.473 (5) ratio. A short intramolecular C—H⋯O contact closes an S(6) ring. In the crystal, inversion dimers linked by pairs of weak C—H⋯O interactions generate R 2 2(6) loops. The dimers are linked by further C—H⋯O interactions to generate [1-10] chains.

SYNTHESIS AND KINETICS OF OXIDATION OF PHENYLALANYL-GLYCINE, ISOLEUCYL-GLYCINE, AND LEUCYL-GLYCINE WITH ANODICALLY GENERATED MANGANESE(III) SULFATE. A MECHANISTIC STUDY

The kinetics of oxidation of dipeptides (DP), namely phenylalanyl-glycine (Phe-Gly), isoleucyl-glycine (Ile-Gly) and leucyl-glycine (Leu-Gly), by Mn(III) have been studied in the presence of sulfate ions in acidic solution at 26 °C. The reaction was followed spectrophotometrically at λmax = 500 nm. A first-order dependence of the rate on both [Mn(III)] and [DP] was observed. The rate is independent of the concentration of reduction product, Mn(II) and hydrogen ions. The effects of varying the dielectric constant of the medium and addition of anions such as sulfate, chloride and perchlorate were studied. The activation parameters have been evaluated using Arrhenius and Eyring plots. The oxidation products were isolated and characterized. A mechanism involving the reaction of DP with Mn(III) in the rate limiting step is suggested.

Oxidation Of Di-Peptides With Mn(III): Synthesis, Characterization And Mechanistic Study

Synthesis and characterization of the dipeptides(DP) namely Glycyl-Proline (Gly-Pro), Alanyl-Proline (Ala-Pro) and Valyl-Proline (Val-Pro), were made. Kinetics of oxidation of these DP by Mn(III) have been studied in the presence of sulfate ions in acidic medium at 26∘C. The reaction was followed spectrophotometrically at λmax = 500 nm. A first order dependence of rate on both Mn(III) and DP was observed. The rate is independent of the concentration of reduction product, Mn(II) and hydrogen ions. Effects of varying dielectric constant of the medium and addition of anions such as sulfate, chloride and perchlorate were studied. Activation parameters have been evaluated using Arrhenius and Eyring plots. The oxidation products were isolated and characterized. A mechanism involving the reaction of DP with Mn(III) in the rate limiting step is suggested.