Preferential solvation of lysozyme by dimethyl sulfoxide in binary solutions of water and dimethyl sulfoxide

To reveal the denaturation mechanism of lysozyme by dimethyl sulfoxide (DMSO), thermal stability of lysozyme and its preferential solvation by DMSO in binary solutions of water and DMSO was studied by differential scanning calorimetry (DSC) and using densities of ternary solutions of water (1), DMSO (2) and lysozyme (3) at 298.15 K. A significant endothermic peak was observed in binary solutions of water and DMSO except for a solution with a mole fraction of DMSO (x ₂) of 0.4. As x ₂ was increased, the thermal denaturation temperature T _m decreased, but significant increases in changes in enthalpy and heat capacity for denaturation, ΔH _cal and ΔC _p, were observed at low x ₂ before decreasing. The obtained amount of preferential solvation of lysozyme by DMSO (∂g ₂/∂g ₃) was about 0.09 g g⁻¹ at low x ₂, indicating that DMSO molecules preferentially solvate lysozyme at low x ₂. In solutions with high x ₂, the amount of preferential solvation (∂g ₂/∂g ₃) decreased to negative values when lysozyme was denatured. These results indicated that DMSO molecules do not interact directly with lysozyme as denaturants such as guanidine hydrochloride and urea do. The DMSO molecules interact indirectly with lysozyme leading to denaturation, probably due to a strong interaction between water and DMSO molecules.     

Rheological properties of cellulose solution in paraformaldehyde/dimethyl sulfoxide system (1)

The rheological properties of three cellulose samples are investigated, including the dependence of the non‐Newtonian Index, structural viscosity and zero shear viscosity on temperature and the concentration of their paraformaldehyde/dimethyl sulfoxide solutions; the values of viscous flow activation energy of them are higher than that of the viscose solution. With the increase of molecular weight, solution concentration and the decrease of temperature, the rheological properties become worse. The rheological properties of cotton linters Cotton 1 are better than those of wood pulp Wood 2 despite a similar degree of polymerization. Copyright © 1999 John Wiley & Sons, Ltd.     

Quenching of nucleotide-derived radicals by bis benzimidazole derivative Hoechst-33258 in aqueous solution

The pulse radiolysis technique has been employed to investigate the reaction of DNA-minor-groove ligand bisbenzimidazole Hoechst 33258 with pyrimidine and purine nucleotide-derived radicals. Formation of an N-centred Hoechst-33258 radical is observed. Bimolecular rate constants and the yields of Hoechst-33258 radical have been evaluated. While the rate constant for the reaction of pyrimidine-derived radicals with Hoechst-33258 remained the same (1–2) × 10⁹ dm³ mol⁻¹ s⁻¹, the yields of the Hoechst-33258 radical varied from 25% (5′-cytidine monophosphate) to 75% (5′-guanosine monophosphate) under anoxic conditions. The rate constant values for the reaction of purine-derived radicals with Hoechst-33258, under oxic and anoxic conditions, remained the same whereas with pyrimidine-derived radicals, the rate constant value under oxic conditions was about two orders of magnitude lower than under anoxic conditions. The difference in the yields of Hoechst-33258 radical with various nucleotide-derived radicals suggest the formation of different types of radicals and that the reaction mainly occurs by electron transfer from Hoechst-33258 to the nucleotide radicals.     

The oxysulfenylation of alkenes with dimethyl sulfoxide/oxalyl chloride

A convenient method for the oxysulfenylation of alkenes using dimethyl sulfoxide/oxalyl chloride is described. Cycloalkenes give trans-adducts stereospecifically. The reactions of styrene are highly regioselective for Markovnikov adducts, whereas aliphatic alkenes lead to anti-Markovnikov adducts mainly.     

Vapor pressure of dimethyl sulfoxide and water binary system

The total vapor pressures of dimethyl sulfoxide (DMSO) and water mixtures have been measured at 15, 20, 25 and 30°C. The activity coefficients and molar excess Gibbs energies of the system have been calculated. Possible association interaction in the system are discussed.     

Thermal hazards and safe scale-up of reactions containing dimethyl sulfoxide

Extensive thermal analysis has shown that DMSO-containing reaction mixtures can be more energetic and decompose at lower temperatures than pure DMSO. Several processes at Merck using DMSO as a solvent were found to have the onset temperatures of decompositions reduced to the point where it became a thermal and operational hazard. The onset temperature depended on the reagents in the reaction mixture and the thermal history of the mixture. The case studies presented in this paper will include discussion on what process hazards were identified, how the process hazards differ from the pure DMSO hazards, and how to scale up these processes safely.     

The mechanism and pathway of the ozonation of 4-chlorophenol in aqueous solution

Chlorophenols (CPs) have been widely used in dif- ferent formulations as preservatives, herbicides, insec- ticides, bactericides and solvents. Parts of chlorophe- nols were released to the natural environment during the usage. As a result, many water sources were con- taminated with CPs[1,2]. Furthermore, they also can be formed during the disinfection of phenol containing water by chlorination. Several CPs are recognized as the priority pollutants by the United States EPA (En- vironmenta…     

Thallium-205 NMR spectroscopy. Solvation of the Tl(l) ion in the binary solvent systems water/pyridine,water/dimethyl sulfoxide,and pyridine/dimethyl sulfoxide

Solvation of the Tl⁺ ion in 0.005M solutions of water/pyridine, water/dimethyl sulfoxide, and pyridine/dimethyl sulfoxide was studied with ²⁰⁵ Tl NMR spectroscopy as a function of solvent composition and anion (NO ₃ ^– and ClO ₄ ^t- ). Dimethyl sulfoxide solvated the Tl⁺ ion more strongly than did pyridine, despite the latter's greater electron-donating ability. This was explained in terms of structural effects, which were found to be large for all three binary solvent systems. Ion pairing was evident in the DMSO/pyridine and water/pyridine solvent systems in which the pyridine mole fraction was greater than 0.8.     

The solvation of the dioxouranium(VI) ion by dimethyl sulfoxide

The species UO₂(DMSO) ₅ ²⁺ is shown from¹H NMR studies to be the predominant dioxouranium(VI) species existing in dilute anhydrous acetonedimethyl sulfoxide (DMSO) solutions, and this result is compared with data reported for the analogous water-acetone-dimethyl sulfoxide system. Complete line-shape analyses of exchange-modified¹H NMR line shapes indicate that the mechanism for DMSO exchange on UO₂(DMSO) ₅ ²⁺ is probably of theD orI _D type. A typical set of rate parameters arek _ex (260°K) =273±14 sec^–1, H ^#=38.9±0.5 kJ-mole^–1, and S ^#=–47.5±1.8 J-^oK^–1-mole^–1 for a solution in which [UO₂(DMSO)₅ ²⁺], [DMSO], and [d ₆ acetone] are, respectively, 0.01155, 0.0875, and 13.00 moles-dm^–3.     

Investigations on the structure of dimethyl sulfoxide and acetone in aqueous solution

Aqueous solutions of dimethyl sulfoxide (DMSO) and acetone have been investigated using neutron diffraction augmented with isotopic substitution and empirical potential structure refinement computer simulations. Each solute has been measured at two concentrations-1:20 and 1:2 solute:water mole ratios. At both concentrations for each solute, the tetrahedral hydrogen bonding network of water is largely unperturbed, though the total water molecule coordination number is reduced in the higher 1:2 concentrations. With higher concentrations of acetone, water tends to segregate into clusters, while in higher concentrations of DMSO the present study reconfirms that the structure of the liquid is dominated by DMSO-water interactions. This result may have implications for the highly nonideal behavior observed in the thermodynamic functions for 1:2 DMSO-water solutions.     

Water effect on the gelation behavior of polyacrylonitrile/dimethyl sulfoxide solution

The gelation behavior of polyacrylonitrile (PAN)/dimethyl sulfoxide (DMSO) solution containing different amounts of water has been investigated using various methods. The ternary phase diagram of PAN/DMSO/water system indicated that water enhanced the temperature at which phase separation of PAN/DMSO solution occurred. Intrinsic viscosities [η] of dilute PAN/DMSO solution and PAN/DMSO/water solution at varied temperatures were measured to examine the influence of water on the phase behavior of PAN/DMSO solution. The presence of water in the solution gave rise to elevated critical temperature T_c. The gelation temperature T_g obtained by measuring the loss tangent tan δ at different oscillation frequencies in a cooling process was found to increase with increased water content in the solution. The critical relaxation exponent n value, however, changed little with varied concentration. During the aging process, the gelation rate of PAN/DMSO solution increases with the water level. The n values of the PAN/DMSO solutions with 2 wt% and 4 wt% water were a little larger than that of the solution without water, which may be explained by the turbid gel resulted from phase separation. The n values obtained in the aging process were larger than those obtained in the cooling process for the same three solutions, ascribed to the weaker gel with less cross-linking points formed in long time. Water led to the formation of denser gel structure. The coarser gel surface can also be attributed to the phase separation promoted by water.     

Permeability of atenolol and propranolol in the presence of dimethyl sulfoxide in rat single-pass intestinal perfusion assay with liquid chromatography/UV detection

A simple and sensitive RP-HPLC-UV method was developed and validated for simultaneous determination of atenolol and propranolol and subsequently applied to investigate the effect of dimethyl sulfoxide in rat in situ intestinal permeability studies. Atenolol (400 microm) and propranolol (100 microm) were perfused in the small intestine of anaesthetized (pentobarbitone sodium 60 mg/kg, i.p.) male Sprague-Dawley rats either in the presence (1, 3 and 5%) or in the absence of dimethyl sulfoxide. There was no significant alteration (p > 0.05) in the permeability of atenolol and propranolol, which indicated there was no effect of various concentrations of dimethyl sulfoxide (1-5%) on the membrane integrity of the rat intestinal tissues. The analytical method was validated on a C(4) column with a mobile phase comprising ammonium acetate buffer (pH 3.5, 0.02 m) and acetonitrile in the ratio of 30:70 (v/v) at a flow rate of 1.0 mL/min. The validated method was found to be accurate and precise and stability studies were carried out at different storage conditions and both analytes were found to be stable. These findings are applicable for determining the absorbability of water-insoluble drugs and new chemical entities for the purpose of classifying them in the biopharmaceutical classification system.     

Molecular weight and aggregation of Aeromonas gum treated with dimethyl sulfoxide in aqueous solution

Aeromonas (A) gum, an acidic hetero polysaccharide, in 0.2 M LiCl/dimethyl sulfoxide (DMSO) was fractionated satisfactorily according to the nonsolvent addition method. Eight fractions were chosen to examine their aggregation behavior in aqueous solution. The weight‐average molecular weight (M_w), radius of gyration 〈S²〉^1/2, and intrinsic viscosities [η] of the fractions in 0.2 M LiCl/DMSO and 0.5 M NaCl aqueous solution at 25 °C were measured by static light scattering and viscometry. The results indicated that the A gum was aggregated in 0.5 M NaCl aqueous solution at 25 °C, and the aggregates were broken in 0.2 M LiCl/DMSO. The apparent weight‐average aggregation number (N_ap) of the fractions increased with the process of fractionation, that is, N_ap increased from 1.1 to 15 with decreasing M_w of the single chain. The fractions obtained by treating with DMSO were more easily dissociated in the aqueous solution, and its N_ap was lower than that of the A gum fractions that were not treated with DMSO. Moreover, the A gum molecules with relatively low M_w aggregated easily to form a compact spherelike structure in the aqueous solution. Elemental analysis and ¹³C NMR spectroscopy indicated that DMSO was adsorbed on the A gum molecules caused by the fractionation program; DMSO not only prevented the polysaccharide aggregation but also increased the solubility. A model has been proposed to describe the aggregation behavior of the A gum chains with DMSO overcoat in the aqueous solution. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2269–2276, 2002     

Studies of the reaction of the hydroxyl radical with the oxalate ion in an acidic aqueous solution by pulse radiolysis

The reaction of the · OH radical with the oxalate ion in an acidic aqueous solution was studied by pulse radiolysis. The rate constant for the reaction of formation of the radical HOOC-COO·(λ_max = 250 nm, ɛ = 1800 L mol⁻¹ cm⁻¹) is (5.0±0.5)·107 L mol⁻¹ s⁻¹. In the reaction with the hydrogen ion (k = 1.1·10⁷ L mol⁻¹ s⁻¹), the radical HOOC-COO· is transformed into a nonidentified radical designated arbitrarily as H⁺(HOOC-COO)· (λ_max = 260 nm, ɛ = 4000 L mol⁻¹ cm⁻¹). Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1165–1167, June, 2008.     

Primary radicals in the photo-oxidation of aromatics — reactions of xylenols with OH, N3 and H radicals and formation and characterization of dimethylphenoxyl, dihydroxydimethylcyclohexadienyl and hydroxydimethylcyclohexadienyl radicals by pulse radiolysis

Photo-oxidations of environmental organics in illuminated TiO₂ dispersions have implicated surface-bound ^•OH radicals and/or valence band holes. To explore the implications of the former oxidizing entity, six isomeric xylenols (dimethylphenols) were examined by pulsed (nanoseconds to milliseconds) radiolysis methods. The spectral and kinetic characteristics of formation and decay of the transients formed by the reaction of N₃^•, ^•OH and H^• radicals with these xylenols were assessed in buffered (pH 4, 10⁻³ M phosphate) aqueous media, where the xylenols exist in their protonated form (pK ≈ 10.19–10.65). The products from the reaction of N₃^• with 2,6- and 3,4-xylenol were exclusively the corresponding dimethylphenoxyl radicals, formed via electron transfer followed by deprotonation. In contrast, except with 3,4-xylenol, the principal radical intermediates formed initially upon reaction with ^•OH were the corresponding ^•OH adducts, the dihydroxydimethylcyclohexadienyl radicals. 3,4-Xylenol was examined in the pH range 4–10. At pH 8 the initial ^•OH adduct (dihydroxy-3,4-dimethylcyclohexadienyl radical) was subsequently transformed (about 20%–40%) via water elimination into the dimethylphenoxyl radical. In contrast, at pH 9 and 10 the ^•OH adduct and the dimethylphenoxyl radical were formed concurrently (about 60% ^•OH adduct and about 40% dimethylphenoxyl species), the latter through an inner-sphere electron transfer pathway. The switch in behaviour from pH 8 to pH 9 suggests that the pK_a of the dihydroxy-3,4-dimethylcyclohexadienyl radical is about 8–9, about 2 pK units below the pK_a of the parent substrate (10.4). A mechanism for the conversion of the ^•OH adduct to the dimethylphenoxyl radical is proposed. Reaction of 2,6-xylenol with H^• radicals gave exclusively the H^• adduct (hydroxycyclohexadienyl radical), whose spectral characteristics are similar to those of the related ^•OH adduct.     

Determination of dimethyl sulfoxide and dimethyl sulfone in urine by gas chromatography–mass spectrometry after preparation using 2,2‐dimethoxypropane

A method for routinely determination of dimethyl sulfoxide (DMSO) and dimethyl sulfone (DMSO₂) in human urine was developed using gas chromatography–mass spectrometry. The urine sample was treated with 2,2‐dimethoxypropane (DMP) and hydrochloric acid for efficient removal of water, which causes degradation of the vacuum level in mass spectrometer and shortens the life‐time of the column. Experimental DMP reaction parameters, such as hydrochloric acid concentration, DMP–urine ratio, reaction temperature and reaction time, were optimized for urine. Hexadeuterated DMSO was used as an internal standard. The recoveries of DMSO and DMSO₂ from urine were 97–104 and 98–116%, respectively. The calibration curves showed linearity in the range of 0.15–54.45 mg/L for DMSO and 0.19–50.10 mg/L for DMSO₂. The limits of detection of DMSO and DMSO₂ were 0.04 and 0.06 mg/L, respectively. The relative standard deviations of intra‐day and inter‐day were 0.2–3.4% for DMSO and 0.4–2.4% for DMSO₂. The proposed method may be useful for the biological monitoring of workers exposed to DMSO in their occupational environment. Copyright © 2009 John Wiley & Sons, Ltd.     

Absorption,desorption and interaction of SO2 with the binary system tetraethylene glycol + dimethyl sulfoxide

The gas-liquid equilibrium (GLE) data were determined for the mixture SO₂ + N₂ in the binary system of tetraethylene glycol (TeEG) + dimethyl sulfoxide (DMSO) at T = 298.15–313.15 K and p = 123.15 kPa with the SO₂ partial pressures of 0.4–150 Pa. From GLE data, Henry’s law constants (HLCs) were obtained. When the SO₂ concentration in the gas phase was designed at y_SO2 = 500 ppmv, the SO₂ solubility in the binary system is located in a minimum of 9.36 mol m^?3 in TeEG and a maximum of 80.34 mol m^?3 in DMSO. The SO₂ absorption process was reversible from the five absorption–desorption cycles, and the solvents could repeat utilisation without obvious loss of absorption capacity and the homologous SO₂ desorption efficiency was nearby 98.7%. Furthermore, the spectral consequences illustrated that H-bonding was formed among TeEG, DMSO and SO₂.     

Kinetics and mechanism of oxidation of dimethyl sulfoxide by chloramine-T in aqueous solution

The kinetics of oxidation of dimethyl sulfoxide (DMSO) by chloramine-T (CAT) is studied in HClO₄ and NaOH media with OsO₄ as a catalyst in the latter medium. In acid medium, the rate law is -d [CAT]/dt = k [CAT][DMSO][H⁺]. Alkali retards the reaction and the rate law takes the form -d [CAT]/dt = k [CAT][DMSO][OsO₄]/[NaOH], but is reduced to -d [CAT]/dt = k [CAT][DMSO] at higher alkali concentrations. The reaction is subjected to changes in (a) ionic strength, (b) concentrations of added neutral salts, (c) concentrations of added reaction product, (d) dielectric constant, and (e) solvent isotope effect, and the subsequent effects on the reaction rate are studied. The reaction mechanism in acid medium assumes an electrophilic attack by the free acid RNHCl (CAT′) at the sulfur site in DMSO, forming a reaction intermediate which subsequently decomposes to dimethyl sulfone on hydrolysis. Formation of a cyclic complex between RNHCl and OsO₄ which interacts with the substrate in a slow step explains the observed results in alkaline medium. The simplification of the rate equation at higher alkali concentrations is attributed to a direct reaction between chloramine-T and the substrate.     

Deuterated dimethyl sulfoxide as a good NMR solvent for the characterization of alkali metal cyclopentadienides, amides, alkoxides and phenoxides

A series of alkali metal cyclopentadienides, amides, alkoxides and phenoxides was characterized using NMR spectroscopy in deuterated dimethyl sulfoxide. Deuterated dimethyl sulfoxide showed very good stability and solubility for these compounds. Very nice and well resolved spectra were obtained for most compounds tested. The low cost of the solvent makes it possible to use it for the routine characterization of these alkali salts as the ligands in organometallic synthesis.