Beulah J.M. Rajkumar

Infrared and laser Raman studies of L-phenylalanine L-phenylalaninium perchlorate and bis(DL-phenylalaninium) sulphate monohydrate

Both crystals under study have two phenylalanine groups in the cationic part of the complex. In the L-phenylalanine L-phenylalaninium perchlorate crystal, two phenylalanine groups share one proton and become monoprotonated. In the bis(DL-phenylalaninium) sulphate monohydrate crystal, on the other hand, both the phenylalanine groups are protonated. This leads to several differences in the infrared and Raman spectra of these two crystals. The presence of both the carbonyl and the ionized carboxylic groups has been identified in the perchlorate crystal, while the sulphate crystal has only the carbonyl group. Extensive hydrogen bonding further leads to the shifting of bands due to several stretching and bending modes. It also reduces the Td symmetry of the anions to C2v symmetry causing the degeneracies of several modes to be removed.

Infrared and Raman spectra of L‐valine nitrate and L‐leucine nitrate

A comparative study of the infrared and Raman spectra of L-valine nitrate and L-leucine nitrate helps in determining the role of hydrogen bonds in these crystals. Both compounds have carboxylic and protonated amino groups in the cation while the nitrate ion forms the anion. The wavenumbers of several modes of vibrations were shifted from the expected values in both crystals. The removal of degeneracy of certain modes of vibration of the methyl group suggests that the two methyl groups attached to the same carbon atom are not identical and the symmetry of both of these groups was affected in their respective environments. Copyright

Infrared and Raman spectra of dl-aspartic acid nitrate monohydrate

Abstract Infrared and Raman spectral studies of dl -aspartic acid nitrate monohydrate help to determine the influence of extensive intermolecular hydrogen bonding in the aspartic acid crystal. The presence of the carbonyl rather than the carboxylic group indicates that the molecule is ionic. The shifting of several group frequencies in the molecule confirms extensive hydrogen bonding. The anion fundamentals however continue to be degenerate. This indicates that its symmetry is unaffected in the molecule.

Vibrational spectroscopic study of DL-methionine dihydrogen phosphate.

The two methionine cations in the asymmetric part of the unit cell of bis(DL-methionine dihydrogen phosphate) have different conformations. This, together with the different environments seen by the two -CH2- groups in each skeleton cause several of the group wavenumbers to occur as doublets or as broad bands. The anion contains two dissimilar P-O bonds, which distorts the phosphate tetrahedron. Due to this, the stretching wavenumbers appear as doublets. There is extensive hydrogen bonding in the system in all three crystallographic directions and this is responsible for the changes in the position and intensity of several bands. Fermi resonance has also been observed.

Spectral Investigations of Solvatochromism and Preferential Solvation on 1,4-Dihydroxy-2,3-Dimethyl-9,10-Anthraquinone

AbstractSolvatochromic and preferential solvation of 1,4-dihydroxy-2,3-dimethyl-9,10-anthraquinone (DHDMAQ) have been investigated using optical absorption and fluorescence emission techniques. Optical absorption spectra of DHDMAQ in different solvents show the intra molecular charge transfer band in the region 400–550nm. The observed blue shift with solvent polarity indicates the delocalisation of the excited state, owing to reduction in quasiaromaticity of the chelate rings formed by intra molecular hydrogen bonds, due to electrostatic or hydrogen bonding interaction. This is also confirmed by the observed low oscillator strength and the transition dipole moment. The observed quantum yield of DHDMAQ in different solvents is due to the inter molecular hydrogen bond in the excited state in addition to the intra molecular hydrogen bond. It also reveals from the low oscillator strength, which indicates that the radiative decay is low. Excited state dipole moment of DHDMAQ is calculated by solvatochromic data and it shows a lower value than ground state dipole moment. The preferential solvation parameter shows that in dimethyl formamide (DMF) + ethanol mixture, the DHDMAQ is preferentially solvated by ethanol in DMF rich region and by DMF in ethanol rich region. In the case of DMF + dichloromethane mixture DHDMAQ is preferentially solvated by DMF.

Fluorescence Quenching of 1,4-Dihydroxy-2,3-Dimethyl-9,10-Anthraquinone by Silver Nanoparticles: Size Effect

Size effect of silver nano particles on the photophysical properties of 1,4-dihydroxy-2,3-dimethyl-9,10-anthraquinone (DHDMAQ) have been investigated using optical absorption and fluorescence emission techniques. Silver nanoparticles of different sizes have been prepared by Creighton method using magnetic stirrer and ultrasonic field. Quenching of fluorescence of DHDMAQ has been found to increase with decrease in the size of the silver nanoparticles. Stern–Volmer quenching constants have also been calculated.

Structural, morphological and optical studies of l-cysteine modified silver nanoparticles and its application as a probe for the selective colorimetric detection of Hg2+

We report an extensive study on the evolution of a highly facile, selective colorimetric probe for Hg(2+) detection using cysteine modified silver nanoparticles. The nanoparticles are stable in a basic medium and the Surface Enhanced Raman Spectrum (SERS) reveal that the cysteine is bound to the Ag surface through the thiolate moiety with the charged carboxylate group pointing outwards in a morphology that lends itself to sensor applications. In the presence of Hg(2+), the absorption peak is quenched resulting in a drastic colour change. The sensor displays high selectivity to Hg(2+) over other metallic ions.

Influence of Silver Nanoparticles on 2,3-Bis(Chloromethyl)Anthracene-1,4,9,10-Tetraone

Size effect of silver nano particles on the photophysical properties of 2,3-bis(chloromethyl)anthracene-1,4,9,10-tetraone (BCMAT) have been investigated using optical absorption and fluorescence emission techniques. Silver NPs of different sizes have been prepared by two different methods. Quenching of fluorescence of BCMAT has been found to increase with decrease in the size of the silver NPs. Stern–Volmer quenching constants have also been calculated.

Conformational, vibrational spectroscopic, nonlinear optical activity, and structure–activity studies on 2-hydroxy-3,5-dinitropyridine: Combined experimental and density functional theory approach

ABSTRACT The conformational analysis was carried out to predict the most stable, optimized structure of 2-hydroxy-3,5-dinitropyridine among various conformers. The most stable, optimized structure of the molecule was predicted by the density functional theory (DFT) using the B3LYP method with the cc-pVQZ basis set. The vibrational frequencies, natural atomic charge distribution, and thermodynamic properties were calculated. The molecular electrostatic potential surface and contour map were simulated. The experimental and theoretical vibrational frequencies were assigned on the basis of potential energy distribution calculation. The density of states (DOS) spectrum was simulated. The frontier molecular orbital analysis was carried out. The natural bond orbital (NBO) analysis was performed to evaluate the donor–acceptor interactions in the molecule. The structure–activity descriptors were determined by Fukui functions and local reactivity descriptor calculations. The nonlinear optical (NLO) activity of the molecule was studied. The second harmonic generation test confirms the NLO activity of the title molecule.

Preferential solvation of acridine in binary mixtures

Preferential solvation studies of acridine have been investigated using optical absorption technique. The preferential solvation parameter shows that in dimethyl formamide (DMF)+ethanol mixture, the acridine is preferentially solvated by ethanol in DMF rich region and by DMF in ethanol rich region. In the case of DMF+Carbon tetrachloride mixture acridine is preferentially solvated by DMF.