Shiraz A. Markarian

Raman and FT IR ATR study of diethylsulfoxide/water mixtures

Abstract The Raman and FT IR ATR spectra of diethylsulfoxide (DESO)-water mixtures in the SO and C–H stretching vibration regions at different molar ratios are considered. Noticeable changes are observed in the ν SO region, suggesting the existence of strong H-bonds between DESO and water molecules; on the contrary the ν CH bands change only in a less extent, supporting the existence of SO⋯HC hydrogen bonds in pure DESO that gradually break in the presence of water. In addition, FT IR measurements confirm the existence of ‘free’ SO group at low concentrations of DESO. The results obtained are well explainable in frame of the cluster-structure model of liquid water.

Vibrational spectra of diethylsulfoxide

FT IR and Raman spectroscopic studies of pure diethylsulfoxide (DESO) in the liquid and in the solid states and its solutions in various solvents have been performed. Analysis of SO- and CH-stretching regions in a wide range of concentration shows that the bands may be fitted satisfactorily by considering seven components. In addition, fundamental frequencies have been assigned using ab initio calculations at the RHF/3-21G* levels. The results obtained confirm a viewpoint on a self-associative structure of DESO, and support the hypothesis of the existence of different types of intermolecular associates including both dipole-dipole and hydrogen bonding mechanisms.

Dielectric relaxation study of diethylsulfoxide/water mixtures

Complex dielectric spectra of diethylsulfoxide (DESO)/water mixtures at 25°C over the entire concentration range of DESO, in the frequency range 0.2 ≤ ν/GHz ≤ 89 have been measured. In general, a description of the complex permittivity spectra requires a consideration of different types of relaxation processes depending upon DESO concentration. For the lower DESO concentration range the relaxation contribution to the spectrum is described by two Debye terms, whereas for higher concentration three Debye terms are used. For both at mol fraction equals to 0.9 and pure DESO as well Cole–Davidson type is valid. In addition, the data on the dimethylsulfoxide (DMSO)/water system obtained in this work well agree with those known from literature. The concentration dependent excess dielectric constant, excess inverse relaxation time and Kirkwood correlation factor of the mixtures have been determined.

Ab initio and DFT study of hydrogen bond interactions between ascorbic acid and dimethylsulfoxide based on FT-IR and FT-Raman spectra

The hydrogen bonding of 1:1 complexes formed between l-ascorbic acid (LAA) and dimethylsulfoxide (DMSO) has been studied by means of ab initio and density functional theory (DFT) calculations. Solutions of l-ascorbic acid (AA) in dimethylsulfoxide (DMSO) have been studied by means of both FT-IR (4000-220 cm(-1)) and FT-Raman spectroscopy. Ab initio Hartree-Fock (HF) and DFT methods have been used to determine the structure and energies of stable conformers of various types of L-AA/DMSO complexes in gas phase and solution. The basis sets 6-31++G(**) and 6-311+G(*) were used to describe the structure, energy, charges and vibrational frequencies of interacting complexes in the gas phase. The optimized geometric parameters and interaction energies for various complexes at different theories have been estimated. Binding energies have been corrected for basis set superposition error (BSSE) and harmonic vibrational frequencies of the structures have been calculated to obtain the stable forms of the complexes. The self-consistent reaction field (SCRF) has been used to calculate the effect of DMSO as the solvent on the geometry, energy and charges of complexes. The solvent effect has been studied using the Onsager models. It is shown that the polarity of the solvent plays an important role on the structures and relative stabilities of different complexes. The results obtained show that there is a satisfactory correlation between experimental and theoretical predictions.

Low temperature dielectric relaxation study of aqueous solutions of diethylsulfoxide

In the present work, dielectric spectra of mixtures of diethylsulfoxide (DESO) and water are presented, covering a concentration range of 0.2-0.3 molar fraction of DESO. The measurements were performed at frequencies between 1Hz and 10MHz and for temperatures between 150 and 300K. It is shown that DESO/water mixtures have strong glass-forming abilities. The permittivity spectra in these mixtures reveal a single relaxation process. It can be described by the Havriliak-Negami relaxation function and its relaxation times follow the Vogel-Fulcher-Tammann law, thus showing the typical signatures of glassy dynamics. The concentration dependence of the relaxation parameters, like fragility, broadening, and glass temperature, are discussed in detail.

The effect of dimethylsulfoxide on absorption and fluorescence spectra of aqueous solutions of acridine orange base.

The photophysical properties of aqueous solutions of acridine orange base (AOB) in wide concentration range of dimethylsulfoxide (DMSO) were studied by using absorption and steady-state fluorescence spectroscopy techniques at room temperature. The absorption spectrum of acridine orange in water shows two bands at 468 and 490 nm which were attributed to the dimer ((AOBH)2(2+)) and monomer (AOBH(+)) species respectively. In DMSO solution for the same AOB concentration only the basic form was detected with the band at 428 nm. The addition of DMSO to AOB aqueous solution leads to the decrease of absorption band at 490 nm and the new absorption band increases at 428 nm due to deprotonated (basic) form of AO and the first isosbestic point occurs at 450 nm. The evolution of isosbestic point reveals that an other equilibrium, due to the self-association of DMSO molecules takes place. From the steady-state fluorescence spectra Stokes shifts were calculated for AOB in aqueous and DMSO solutions. The addition of DMSO into the aqueous solution induced the enhancement in the fluorescence intensity of the dye compared to those in water.

94 The investigation of Hoechst 33258 interaction with DNA in aqueous solutions of dimethylsulfoxide

The melting of DNA complexes with Hoechst 33258 (H33258) has been carried out in both presence and absence of dimethylsulfoxide (DMSO) to reveal the effect of the mentioned compound on melting parameters of DNA-H33258 complexes at r = 0.1, where r = [H33258]/[DNA] and at 0.02 M Na+ ion concentration. It is known that the structural–functional changes of macromolecules take place in aqueous solutions of DMSO (Markarian et al., 2006). It has been shown earlier that DNA hydration degree increase results in sharp changing of the binding mechanism of H33258 to DNA: AT-specific mode of binding disappears and ligand molecules start to intercalate into DNA at r ⩽ 0.1 (Vardevanyan et al., 2008). Moreover, the increase of T m of complexes is higher compared to the case of relatively low hydration degree of DNA. This is conditioned by the fact that at DNA hydration, increasing the intercalation becomes more preferable since in this case hydrophobic ligand molecules are shielded from water more effectively. The results obtained confirm that with the increasing of DMSO content in solution the melting temperature, T m, decreases. Moreover, denaturation of complexes leads to the decrease of the fluorescence intensity of ligand molecule. We suggest that the observed phenomenon happens due to the structural change of solution which promotes dissociation of ligand molecules bound to DNA, and hence a facilitated denaturation of DNA-H33258 complexes occurs.