Louis George

Simultaneous first order derivative spectrophotometric determination of vanadium and zirconium in alloy steels and minerals.

A simple, selective and sensitive spectrophotometric method has been developed for the individual and simultaneous determination of trace amounts of vanadium(V) and zirconium(IV) in acetic acid medium using a newly synthesised reagent diacetylmonoxime salicyloylhydrazone (DMSH), without any prior separation. The molar absorptivity and Sandells sensitivity of the coloured species are 1.30 x 10(4) and 1.82 x 10(4) L mol(-1)cm(-1) and 3.9 and 2.5 ng cm(-2) for V(V) and Zr(IV), respectively. Beers law is obeyed between 0.26-2.80 and 0.30-3.20 μg mL(-1) concentration of vanadium (V) and zirconium (IV) at 405 and 380 nm respectively. The stoichiometry of the complex was found to be 1:1 (metal:ligand) for V(V) and 1:2 for Zr(IV) complexes. These metal ions interfere with the determination of each other in zero order spectrophotometry. The first derivative spectra of these complexes permitted a simultaneous determination of V(V) and Zr(IV) at zero crossing wavelengths of 445 nm and 405 nm, respectively. The optimum conditions for maximum colour development and other analytical parameters were evaluated. The proposed method has been successfully applied for the determination of zirconium and vanadium in standard alloy steel samples, mineral and soil samples.

Effect of solvent polarity on the photophysical properties of chalcone derivatives

The absorption and fluorescence characteristics of (E)-3-(furan-2-yl)-1-(4-nitrophenyl)prop-2-en-1-one (FNPO), (E)-1-(4-aminophenyl)-3-(furan-2-yl)prop-2-en-1-one (AFPO) and (E)-3-(furan-2-yl)-1-(2-hydroxyphenyl)prop-2-en-1-one (FHPO) were recorded in eighteen different solvents with increasing polarities at room temperature. The solvatochromic effects on absorption and fluorescence spectra have shown bathochromic shifts from non-polar to polar solvents for the reported molecules due to intramolecular charge transfer (ICT) interactions. It has indicated a large difference in dipole moment between electronically ground and excited states and the molecules were found to be more stabilized in singlet excited state than the ground state. The ground and excited state dipole moments of FNPO, AFPO and FHPO were determined experimentally by solvatochromic shift method using Bilot–Kawski, Lippert–Mataga, Bakhshiev, Kawski–Chamma–Viallet and Reichardts microscopic solvent polarity functions. HOMO–LUMO energy values of FNPO, AFPO and FHPO were determined using cyclic voltammetry and compared with those values obtained by TD-DFT (B3LYP/6-311G(d,p)) method.

Estimation of Ground-State and Singlet Excited-State Dipole Moments of Substituted Schiff Bases Containing Oxazolidin-2-one Moiety through Solvatochromic Methods.

Absorption and fluorescence studies on novel Schiff bases (E)-4-(4-(4-nitro benzylideneamino)benzyl)oxazolidin-2-one (NBOA) and (E)-4-(4-(4-chlorobenzylidene amino)benzyl)oxazolidin-2-one (CBOA) were recorded in a series of twelve solvents upon increasing polarity at room temperature. Large Stokes shift indicates bathochromic fluorescence band for both the molecules. The photoluminescence properties of Schiff bases containing electron withdrawing and donating substituents were analyzed. Intramolecular charge transfer behavior can be studied based on the influence of different substituents in Schiff bases. Changes in position and intensity of absorption and fluorescence spectra are responsible for the stabilization of singlet excited-states of Schiff base molecules with different substituents, in polar solvents. This is attributed to the Intramolecular charge transfer (ICT) mechanism. In case of electron donating (−Cl) substituent, ICT contributes largely to positive solvatochromism when compared to electron withdrawing (−NO2) substituent. Ground-state and singlet excited-state dipole moments of NBOA and CBOA were calculated experimentally using solvent polarity function approaches given by Lippert–Mataga, Bakhshiev, Kawskii-Chamma-Viallet and Reichardt. Due to considerable π- electron density redistribution, singlet excited-state dipole moment was found to be greater than ground-state dipole moment. Ground-state dipole moment value which was determined by quantum chemical method was used to estimate excited-state dipole moment using solvatochromic correlations. Kamlet-Abboud-Taft and Catalan multiple linear regression approaches were used to study non-specific solute-solvent interaction and hydrogen bonding interactions in detail. Optimized geometry and HOMO-LUMO energies of NBOA and CBOA have been determined by DFT and TD-DFT/PCM (B3LYP/6-311G (d, p)). Mulliken charges and molecular electrostatic potential have also been evaluated from DFT calculations.

Electrocatalytic oxidation of morin on electrodeposited Ir-PEDOT nanograins

Nanoclusters of Ir were electrochemically deposited on carbon fiber paper (CFP) substrate modified with poly(3,4-ethylenedioxythiophene) (PEDOT), a conducting polymer between the potential range 0.0 V and 0.6 V at 0.05 V/s scan rate. The electrocatalytic activity of Ir-PEDOT/CFP electrode towards oxidation of morin, a flavonoid was significantly greater than that of PEDOT/CFP and bare CFP electrodes. Factors affecting the anodic peak of morin namely, effect of pH, scan rate and number of cycles were optimized. The electrochemical route involved adsorption controlled and irreversible processes. Under optimal conditions, the linear dynamic range for the determination of morin was found to be 0.12 nM-2.80 nM. The significantly low detection limit (42.18 pM) demonstrates the ultrasensitivity of the proposed method. The reliability of the method was evaluated for the quantification of morin present in mulberry leaves, guava leaves and grape wine.

Fluorescence and solvatochromic studies of biologically important Schiff base derivatives

Schiff bases have extensive applications in therapeutic and optoelectronic fields. Schiff bases have shown significant optical properties and used as photochromic compound, light emitting diode, nonlinear optical materials, optical and electrochemical sensors. In the present investigation, we report detail study on photophysical properties of two Schiff base derivatives. Absorption and fluorescence studies on novel Schiff bases (E)-4-(4-(4-nitrobenzylideneamino)benzyl)oxazolidin-2-one (NBOA) and (E)-4-(4-(4chlorobenzylideneamino)benzyl)oxazolidin-2-one (CBOA) have been performed in a series of solvents of increasing polarity at room temperature. Large Stokes shift shows bathochromic red-shift for fluorescence band in both the ligands. The substituents in Schiff base help to understand the intramolecular charge transfer processes. Electron donating substituent contributes large extent of ICT and positive solvatochromism compared to electron withdrawing one. Ground-state and singlet excited-state dipole moments of NBOA and CBOA have been calculated experimentally using Lippert–Mataga, Bakhshiev, Kawskii-Chamma-Viallet, and Reichardt methods. The singlet excitedstate dipole moment was found to be greater than that of the ground-state. Kamlet-Abboud-Taft and Catalan multiple linear regression approaches were used to get detailed information of both non-specific solute-solvent interaction and hydrogen bonding interactions. Optimized geometry and HOMO-LUMO energies of NBOA and CBOA have been determined by TD-DFT (B3LYP/6-311G (d, p)). Mulliken charges and molecular electrostatic potential have also been evaluated from DFT calculations.