Nicotinamide solvation state in aqueous dimethyl sulfoxide

The solvation state of biologically active compound vitamin B₃, viz., 3-pyridinecarboxamide, in an aqueous-dimethyl sulfoxide solvent of a variable composition was studied by ¹H and ¹³C NMR and IR spectroscopy. Below X _DMSO ?0.65 molar fraction, the solvation of the N heteroatom due to hydrogen bonds with water molecules weakens. At X _DMSO > 0.65 molar fraction, almost no changes are observed in the solvate state of the N heteroatom. The ¹H NMR spectra indicate that the degree of conjugation of the carbamide group with the heterocycle increases with an increase in the DMSO concentration. The structures of the dimethyl sulfoxide and mixed aqueous-dimethyl sulfoxide solvates of nicotinamide were optimized by the B3LYP/6311++(DP) method, and their ¹³C chemical shifts (GIAO) and IR spectra were obtained. According to the IR spectroscopic data, the number of hydrogen bonds involving the carbamide group decreases on going from H₂O to DMSO.     

Dielectric spectrum and structure of aqueous solutions of dimethyl sulfoxide

Russian Chemical Bulletin - Frequency measurements of aqueous solutions of dimethyl sulfoxide (DMSO) were carried out in the range of 0.5-36.5 GHz at temperatures 293-323 K. Relaxation spectra were...     

Features of light scattering in aqueous solutions of dimethyl sulfoxide

The water-dimethyl sulfoxide (DMSO) system was studied by means of static light scattering in the concentration range of 0 to 60 mol % DMSO at 20 and 50°C. In the concentration range of 10 mol % DMSO, an abnormal maximum of scattered light was detected, the intensity of which decreases with an increase of temperature. The formation of this maximum is related to hydrophobic effects in the system under study and the existence of an unattainable critical point of delayering. Temperature inversion of light scattering intensity was detected at ∼14 mol % DMSO; at higher concentrations of DMSO, the intensity at 50°C is notably higher than at 20°C (due to the increase in the concentration’s degree of fluctuation upon an increase in temperature); at 60 mol % DMSO, intensities of scattered light at 20 and 50°C almost coincide. The apparent molar volumes of DMSO in solutions were calculated from the published data on density in the temperature range of 5 to 50°C. The minima of these values from 10 to 15 mol % DMSO (i.e., in the range of the abnormal maximum of scattered light) were obtained. The manifestation of hydrophobic effects in aqueous solutions of amphiphilic molecules is explained using the example of the DMSO-H₂O 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     

Mechanism of the reaction of radicals with peroxides and dimethyl sulfoxide in aqueous solution

The reactions of methyl and methylperoxyl radicals derived from dimethyl sulfoxide (DMSO) with hydrogen peroxide, peroxymonocarbonate (HCO4 (-)), and persulfate were studied. The major reaction observed for the hydroperoxides was the abstraction of the hydrogen atom by the radicals. The radicals interact with a lone pair of electrons on the peroxide to produce methanol and formaldehyde. Furthermore, the results indicate that in RO2H and RO2R', electron-withdrawing groups cause a considerable increase in the reactivity of the peroxides towards the radicals and not only towards nucleophiles. The HO2 (.)/O2 (.-) and CO3 (.-) radicals react with DMSO to produce methyl radicals. Thus, the formation of the (.)CH3 radicals in the presence of DMSO is not proof of the formation of the (.)OH radicals in the system. These reactions must be considered when radical processes, such as in biological and catalytic systems, are studied. Especially, the plausible role of HCO4 (-) ions in biological systems as a source of oxidative stress cannot be overlooked.     

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.     

Molecular dynamics simulations of angiotensin II in aqueous and dimethyl sulfoxide environments

Angiotensin II (Ang II) is an octapeptidic hormone, which plays an important role in the mechanisms of blood pressure control. In this work, extensive molecular dynamics (MD) simulations have been carried out on this peptide, both in aqueous and in dimethyl sulfoxide (DMSO) environments. Experimentally proposed models for the structure of angiotensin II in both environments are not consensual and the results obtained have provided some further insight about the structural properties of this hormone. In these simulations, the N-terminus of Ang II in the aqueous environment has been associated with a considerable larger flexibility than the correspondent C-terminus, but this was not found in the case of the DMSO environment. This is consistent with the assumption that the biological activity of Ang II is associated with its C-terminal residues embedded in a hydrophobic environment of its AT1 receptor. Other features detected in DMSO environment were an H(His6 imidazole)-O(Phe8 carboxylate) hydrogen bond and a salt-bridge structure involving the Asp1 and Arg2 side chains. An additional important conformational feature is the spatial proximity between Tyr4 and His6 in both water and DMSO environments. This molecular feature may trigger the interest for the synthetic chemists to apply rational design for the synthesis of novel AT1 antagonists.     

Metal exchange reactions between cadmium protoporphyrin and cobalt and zinc chlorides in acetonitrile and dimethyl sulfoxide

Metal exchange between cadmium protoporphyrin CdPP and zinc and cobalt chlorides in dimethyl sulfoxide (DMSO) and acetonitrile (AN) was studied by spectrophotometry. Comparative analysis of the data on metal exchange between CdPP and ZnCl₂ in DMSO and between CdPP and CoCl₂ in AN was performed. The possible exchange mechanisms were considered. The results were compared with the data on cadmium mesoporphyrin exchange with zinc and cobalt.     

Complexation between iron(III) and nicotinamide in aqueous dimethyl sulfoxide

The stability constants of iron(III) complexes with nicotinamide in water-DMSO mixtures (X _DMSO = 0–0.75) were determined by potentiometric titration at 25.0 ± 0.1°C and an ionic strength of 0.25 (NaClO₄). The contributions from the solvation of the reagents to the Gibbs energy of complexation transfer were analyzed. The stabilities of iron(III), copper(II), and silver(I) complexes with nicotinamide were compared. The observed decrease in the stability constants was attributed to the stabilization of iron(III) solvate complexes as the DMSO content increases.     

FT-IR Investigation of Rare-Earth and Metal-Ion Solvation. Part 14. Interaction between uranyl perchlorate and dimethyl sulfoxide in anhydrous acetonitrile

The interaction between the uranyl ion and perchlorate in anhydrous acetonitrile has been investigated by FT-IR and Raman spectroscopy. Vibrations assigned to uncoordinated (u), monodentate (m), and bidentate (b) perchlorate anions were identified in 0.075M solutions. Quantitative data indicate that perchlorate is distributed as follows: 37 ± 2% are uncoordinated, 36 ± 7% are monodentate, and 27 ± 7% are bidentate. This is in agreement with the conductivity of the solutions which is at the lower end of the range accepted for 1:1 electrolytes. The splittings v₄–v₁(m) and v₈–v₁(b) of 147 and 246 cm^?1, respectively, point to a large inner-sphere interaction. An equilibrium occurs between two differently coordinated species. Various amounts of DMSO were added to 0.05M perchlorate solutions (R′ = [DMSO]_t/[UO]_t = 1–10). The v₇ (SO) and v₂₂ (CS) vibrations of DMSO were used to determine the average number of coordinated DMSO molecules per uranyl ion, which is close to 4. Some bidentate perchlorate ions are still present in these solutions, but all the MeCN molecules (2.6 on average) are expelled out of the inner coordination sphere. The data can again be interpreted in terms of an equilibrium between differently coordinated species. The average coordination number of the uranyl ion is 4.4, as the perchlorate salt in MeCN solution, and may be somewhat smaller in the presence of DMSO. The possible presence of dimeric species is also discussed.     

Spectropotentiometric and calorimetric study of the thermodynamics of protonation of protoporphyrin ligands in acetonitrile and dimethyl sulfoxide

Spectropotentiometric titration and direct calorimetry were used to study the thermodynamics of protonation of protoporphyrins in acetonitrile and dimethyl sulfoxide. Comparative analysis of the resulting data was performed.     

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.     

FTIR study of hydrogen bonding of stearic acid with ethanol, dimethyl sulfoxide,and acetonitrile in supercritical CO_2

FTIR spectroscopy was used to study the hydrogen bonding of stearic acid with ethanol, dimethyl sulfoxide (DMSO),and acetonitrile in supercritical CO_2 at 318.15 K, and 12.5 and 16.5 MPa. The concentrations of the cosolvents range from 0—0.6 mol·L~(-1). The area percentage of absorption bands for hydrogen-bonded and nonhydrogen-bonded species was obtained from the IR spectra. The acid and the cosolvents can form hydrogen bond even when their concentrations are very low. At fixed solute concentration, the extent of hydrogenbonding increases with cosolvent concentration. At higher ethanol concentrations, it seems that one stearic acid molecule can hydrogen bond with more than one ethanol molecules simultaneously. It is seen that the strength of the hydrogen bond formed by the acid and the cosolvents is in the order: DMSO>ethanol>acetonitrile.     

Complexation of nickel (II) ion with B3 vitamin in aqueous dimethyl sulfoxide

The stability change of nickel(II) ion complexes including one and two nicotinamide (B₃ vitamin) molecules in aqueous dimethyl sulfoxide (X_DMSO = 0–0.85 m.f.) was studied at 298.2±0.1 K and 0.25 ionic strength value (NaClO₄) using the potentiometric method. The first stage constant of complexation increased until organic solvent concentration was 0.5 m.f. and reduced at higher DMSO content. The difference between complex and central ions solvation is a dominating contribution into the Gibbs energy change of mononicotinamide complex formation reaction. When the second ligand molecule was bonded into the coordination compound, the nicotinamide contribution to Δ_trG_r rose and became prevailing at X_DMSO = 0.7–0.85. The ligand was found to replace a water molecule in the coordination sphere of the cation according to spectrophotometric study results.      

Multibubble sonoluminescence of Tb3+ ion in aqueous solutions of dimethyl sulfoxide

The intensity and spectra of multibubble sonoluminescence of TbCl₃ solutions in water-DMSO mixtures saturated with air and argon are studied. The spectra represent the superposition of the characteristic glow of Tb³⁺ ions and the continuum of emission of electronically excited products of solvent sonolysis (with H₂O*, OH*, and SO₂* as main emitters). Abnormal action of DMSO and sulfur dioxide on the characteristic luminescence of Tb³⁺ ions during sonolysis of aqueous solutions is revealed. These additives enhance the sonoluminescence of water to different extent, quench the sonoluminescence of Tb³⁺, and differently influence the photoluminescence quantum yield of this ion (DMSO acts as activator, whereas SO₂ acts as quencher). Sulfur dioxide quenches the sonoluminescence of Tb3+ much more efficiently than the photoluminescence of Tb³⁺. The abnormal effect of DMSO on sonoluminescence is most probably due to the quenching action of sulfur dioxide formed during sonolysis of DMSO on Tb³⁺* ions in cavitation bubbles.