Nipamanjari Deb

Use of Fluorescence Probes for Studying Kamlet-Taft Solvatochromic Parameters of Micellar System Formed by Binary Mixture of Sodium Dodecyl Sulfate and Triton-X 100

Fluorescence probes have been used to estimate Kamlet-Taft solvatochromic parameters alpha and pi* representing hydrogen-bond donation ability and dipolarity/polarizability, respectively, of sodium dodecyl sulfate (SDS)-Triton X 100 (TX100) mixed aggregates with varying compositions. The hydrogen-bond donation ability of the mixed aggregate has been found to increase with SDS composition, whereas the dipolarity/polarizability parameter decreases. The relative contribution of electrostatic and steric effect toward the total free energy of micellization have been calculated for the mixture. The solvatochromic parameters alpha and pi* depend linearly on the total free energy of micellization, indicating a correlation between aggregational and solvatochromic properties.

Inclusion of riboflavin in β-cyclodextrin: A fluorimetric and absorption spectrometric study

Formation of inclusion complexes between riboflavin and beta-cyclodextrin (beta-CD) with both 1:1 and 1:2 stoichiometry has been established by fluorimetric titration. However, in absorption spectrometric experiment, spectral change of riboflavin in the visible range could be observed only by taking beta-CD at a much higher concentration (about 100 times) than riboflavin and under such condition only 1:2 complexes could be detected. Its formation constant (K) was determined by a multiple linear regression analysis of the absorption data. The reliability of the K value was confirmed by the consistency achieved on analyzing the data at two different wavelengths.

Determination of individual proton affinities of reserpine from its UV-vis and charge-transfer spectra.

Proton affinities of the two N atoms of reserpine (methyl-11,17alpha-dimethoxy-18beta-[(3,4,5-trimethoxybenzoyl)oxy]-3beta,20alpha-yohimban-16beta-carboxylate) have been determined in two ways from the pH-dependent variation of the UV-vis absorption spectra (i) of reserpine itself and (ii) of the charge-transfer (CT) spectra of its complexes with o-chloranil, p-chloranil, and DDQ in aqueous medium (containing 0.1% ethanol v/v). For the second method, the CT absorption bands of the complexes were determined, their formation constants were estimated by a modified Benesi-Hildebrand equation, and variation of CT absorption spectra with a change in pH was noted. A necessary working formula for the second method was derived and utilized with the experimental data. The pKa values obtained by the two methods are well in agreement with each other within the limits of experimental error. To our knowledge, so far, this is the first report on determination of pKa from charge-transfer complex formation in aqueous solution using simple absorption spectroscopy in the UV-vis region. The results obtained were further checked by noting the variation of fluorescence intensity of reserpine upon addition of o-chloranil, acid, and base, and almost complete agreement with the absorption spectrometric result was observed.

Charge transfer complex formation between TX-100/CCl4 reverse micelle and a series of π-electron acceptors: determination of cmc and aggregation number

Electron donor–acceptor interaction of the reverse micelle (RM) of TX-100 in CCl4 medium with a number of π-acceptors has been established by analysing the charge transfer (CT) absorption bands in the light of Mullikens theory. Aggregation number (n) and operational critical micellisation concentration of the RM and formation constants of the RM–p-chloranil and RM-o-chloranil complexes have been determined by UV-visible spectrophotometry. Values of n thus obtained (20–30) are close to that of TX-100/cyclohexane dry reverse micelles determined by other methods and also to a theoretically calculated value of n for AOT/CCl4 dry RM.

Calculation of the Kirkwood–Frohlich correlation factor and dielectric constant of methanol using a statistical model and density functional theory

The geometries of methanol monomer and methanol clusters, (CH3OH) m , m = 2–10, were optimized using the DFT/B3LYP/6-31++G(d,p) method. For each m > 2, a number of conformers were found to satisfy the optimization condition, showing no imaginary frequency in their calculated IR spectra. With increasing m, five- and six-membered rings begin to appear with open chain branches and the calculated IR spectra approach the experimentally observed IR spectrum of liquid methanol. Using the average energy of formation of one hydrogen bond and a statistical model, the Kirkwood–Frohlich (K–F) correlation factor (g) and dielectric constant (ε) were calculated for each methanol cluster. From a plot of ε versus cluster size (m), the bulk dielectric constant was obtained by extrapolation to m→∞. The value of g averaged over all conformers is in almost complete agreement with the g value obtained in an earlier molecular dynamics simulation study by Fonseca and Ladanyi [J. Chem. Phys. 93, 8148 (1990)]. Using this value of g in the K–F equation, the dielectric constant (ε) of methanol was calculated and found to be in fair agreement with (∼17% lower than) the experimental value and also with an earlier molecular dynamics simulation [Mol. Phys. 94, 435 (1998)]. The calculated ε follows the same trend in variation with temperature as the experimental ε in the range 288–318 K.

Fluorimetric study of water–ethanol interaction and its effect on the micellisation of sodium dodecyl sulphate in the presence of bovine serum albumin

The model for self-association of ethanol in water which was established earlier by compressibility and infrared absorption measurements, has been further supported in the present work by monitoring fluorimetrically the variation of the solvatochromic Kamlet-Taft pi* parameter of ethanol-water mixtures over the entire mole fraction range. This model has been used to interpret the variation of the critical micellisation concentration (cmc) of sodium dodecyl sulphate in the presence of bovine serum albumin (BSA) in aqueous ethanol mixtures (as obtained from the tryptophan fluorescence intensity of BSA) in low ethanol mole fraction range.

Graph-theoretical parameters for π-MO calculation of a series of aromatic amines in the light of DFT theory: comparison with experimental CT transition energies

Expressions for the energies of the highest occupied π-molecular orbitals of a series of aromatic amines have been derived in terms of the vertex weight h N (for amine nitrogen) and edge weight k C–N (for the C–N bond) by representing the amine molecule in terms of vertex- and edge-weighted graphs. Graph-theoretical methods have been used to evaluate the quantities involved in such expressions. The HOMO energies of the amines calculated by density functional theory using the 6-31++G** basis set have been correlated with these expressions to estimate the perturbational parameter h N and the Coulomb integral α. The acceptability of the estimated values of α and h N has been tested by their ability to explain the experimentally observed trends in the CT transition energies of a series of charge-transfer complexes of amines with tetracyanoethylene. An important structural feature, namely rotation of the –NH2 group about the C–N bond due to steric repulsion with the nearest H-atom in the case of 1-amino compounds, has been observed by such a correlation. The result agrees well with the DFT-optimized geometries of the structures.