M. I. S. Sastry

Bio: M. I. S. Sastry is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Raman spectroscopy & Hydrogen bond. The author has an hindex of 3, co-authored 4 publications receiving 101 citations.

Self-association of dimethyl sulphoxide and its dipolar interactions with water: Raman spectral studies

Abstract: Raman spectra of solutions of dimethyl sulphoxide (DMSO) in carbon tetrachloride (CCl 4 ) and water are reported for both parallel and perpendicular polarizations in the S=O stretching region. The various bands obtained were subjected to Gaussian band fittings. It was observed that the bands for solutions in CCl 4 may be fitted satisfactorily by considering four components and those for solutions in water may be fitted by considering five components. It is inferred that the band at ca 1070 cm -1 observed in the spectra of DMSO in CCl 4 belongs to the S=O stretching mode of free DMSO, whereas the two bands observed at ca 1058 cm -1 and ca 1040 cm -1 belong to out-of-phase and in-phase S=O stretchings of the cyclic dimer. The low-frequency band at ca 1025 cm -1 is assigned to linear dimer/higher polymers. Aqueous solutions of DMSO show an additional band at ca 1010 cm -1 due to DMSO hydrogen-bonded with water.

Raman spectral studies of solutions of alkali metal perchlorates in dimethyl sulfoxide and water

Abstract: Raman spectra of solutions of alkali metal perchlorates in dimethyl sulfoxide (DMSO) in the Cl—O, C—S, and S=O stretching regions, as well as of perchlorates in aqueous solutions in the Cl—O stretc...

Second derivative analysis of S=O stretching band in Raman spectra of dimethyl sulphoxide in carbon tetrachloride and water

Abstract: Raman spectra of solutions ofdmso (dimethyl sulphoxide) are studied in the S=O stretching region by second derivative analysis. Broad bands observed in the normal Raman spectra show well resolved components in the derivative plots. On the basis of the various components obtained in these plots for solutions ofdmso in carbon tetrachloride and water, existence of equilibria between various associated species, involving dipolar and hydrogen bonding interactions, is suggested. It is concluded that solutions ofdmso in CCl4 may have monomers, cyclic and linear dimers and polymers, whereas its aqueous solutions show the existence of 1:1 and 1:2 hydrogen bonded complexes of water withdmso in addition to smaller concentrations of monomers, dimers and polymers.

Water dynamics in water/DMSO binary mixtures.

Abstract: The dynamics of dimethyl sulfoxide (DMSO)/water solutions with a wide range of water concentrations are studied using polarization selective infrared pump-probe experiments, two-dimensional infrared (2D IR) vibrational echo spectroscopy, optical heterodyne detected optical Kerr effect (OHD-OKE) experiments, and IR absorption spectroscopy. Vibrational population relaxation of the OD stretch of dilute HOD in H(2)O displays two vibrational lifetimes even at very low water concentrations that are associated with water-water and water-DMSO hydrogen bonds. The IR absorption spectra also show characteristics of both water-DMSO and water-water hydrogen bonding. Although two populations are observed, water anisotropy decays (orientational relaxation) exhibit single ensemble behavior, indicative of concerted reorientation involving water and DMSO molecules. OHD-OKE experiments, which measure the orientational relaxation of DMSO, reveal that the DMSO orientational relaxation times are the same as orientational relaxation times found for water over a wide range of water concentrations within experimental error. The fact that the reorientation times of water and DMSO are basically the same shows that the reorientation of water is coupled to the reorientation of DMSO itself. These observations are discussed in terms of a jump reorientation model. Frequency-frequency correlation functions determined from the 2D IR experiments on the OD stretch show both fast and slow spectral diffusion. In analogy to bulk water, the fast component is assigned to very local hydrogen bond fluctuations. The slow component, which is similar to the slow water reorientation time at each water concentration, is associated with global hydrogen bond structural randomization.

ATR-FTIR spectroscopic studies on aqueous LiClO4, NaClO4, and Mg(ClO4)2 solutions

Abstract: The ATR-FTIR spectra of aqueous LiClO4, NaClO4, and Mg(ClO4)2 solutions with ClO4− concentrations ranging from 0 to 3.00 mol dm−3 were obtained. After subtracting the spectra of pure water, positive peaks on the high wavenumber side and negative peaks on the low wavenumber side of the O–H stretching bands are observed in the difference spectra. The positive peaks appear constantly at about 3580 cm−1 independent of cation, which are assigned to the water molecules weakly hydrogen-bonded with ClO4−. However, the negative peaks appear at 3203, 3196, and 3254 cm−1 for LiClO4, NaClO4, and Mg(ClO4)2 solutions, respectively, and the peak areas show significant difference with increasing the concentration of perchlorate anions and are dependent on cations. The negative peaks are attributed to the “structure breaking” effect of perchlorate ions on the hydrogen bond network of water, which is in agreement with Raman spectroscopic studies. Besides the “structure breaking” effect of ClO4− on destroying the strong hydrogen bonds of the water molecules with fully hydrogen-bonded five-molecule tetrahedral nearest neighbor structure, the difference of the negative peaks are the results of the different “structure making” effect of the three cations, which is consistent with the ability of the polarization and hydration, in the order of Na+ < Li+ ≪ Mg2+. The overall shifting of the v3 band of perchlorate ions towards low wavenumber with increasing the concentration of perchlorates is attributed to the presence of solvent separated ion pairs, i.e., M⋯(H2O)n⋯ClO4−. The symmetric stretching vibration (v1) of perchlorate ions, which is an infrared inactive mode for free perchlorate ions, shows a weak band at ∼930 cm−1 in a wide concentration range of the three systems. The appearance of the weak band is considered as the perturbation of the ZnSe/water interface on perchlorate ions.

Dielectric relaxation in dimethyl sulfoxide/water mixtures studied by microwave dielectric relaxation spectroscopy.

Abstract: Dielectric spectra of dimethyl sulfoxide (DMSO)/water mixtures, over the entire concentration range, have been measured using the transmission line method at frequencies from 45 MHz to 26 GHz and at temperatures of 298−318 K. The relaxation times of the mixtures show a maximum at an intermediate molar fraction of DMSO. The specific structure of mixtures in different concentration regions was determined by the dielectric relaxation dynamics, obtained from the effect of temperature on the relaxation time. A water structure “breaking effect” is observed in dilute aqueous solutions. The average number of hydrogen bonds per water molecule in these mixtures is found to be reduced compared to pure water. The increase in the dielectric relaxation time in DMSO/water mixtures is attributed to the spatial (steric) constraints of DMSO molecules on the hydrogen-bond network, rather than being due to hydrophobic hydration of the methyl groups. The interaction between water and DMSO by hydrogen bonding reaches a maximum...

Molecular Structure of Dimethyl Sulfoxide Intercalated Kaolinites

Abstract: Upon the intercalation of kaolinite with DMSO, new Raman bands at 3660, 3536, and 3501 cm are observed for the low-defect kaolinite and at 3664, 3543, and 3509 cm for the high-defect kaolinite. An additional band at 3598 cm was observed for the high-defect kaolinite. The band at 3660 cm was assigned to the inner-surface hydroxyls hydrogen bonded to the S=O group. The other three bands are attributed to the hydroxyl stretching frequencies of water in the intercalation complex. The hydroxyl deformation region is characterized by one intense band in both the FTIR and Raman spectra at 905 cm. Significant changes in the Raman spectra of the intercalating molecule are observed. Splitting of the C-H symmetric and antisymmetric stretching vibrations occurs. Two Raman bands at 2917 and 2935 cm and four bands at 2999, 3015, 3021, and 3029 cm are observed. The in-plane methyl bending region shows two Raman bands at 1411 and 1430 cm. The DRIFT spectra show complexity in these regions. The S=O stretching region shows bands at 1066, 1023, and 1010 cm upon intercalation with DMSO for the low-defect kaolinite and 1058, 1028, and 1004 cm for the high-defect kaolinite. The 1058 cm band is signed to the free monomeric S=O group and the 1023 and 1010 cm bands to two different polymeric S=O groups. Bands attributed to the C-S stretching vibrations, the in-plane and out-of-plane S=O bending and the CSC symmetric bends all move to higher frequencies upon intercalation. It is proposed that intercalation with DMSO depends on the presence of water and that the additional bands at 3536 and 3501 cm are due to the presence of water in the intercalate.