X-ray structural investigation of gossypol and its derivatives XXII. Structure of the H-clathrate of gossypol with dimethyl sulfoxide

In crystals obtained from solutions in DMSO, gossypol molecules are again present in the aldehyde tautomeric form. These crystals are H-clathrates with the channel type of structure which has much in common with the structure of the complexes of gossypol with methanol and with formic acid.Institute of Bioorganic Chemistry, Uzbekistan Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, Nos. 3,4, pp. 330–334, May–August, 1992.     

Cyclopolymerization of diallylamine derivatives in dimethyl sulfoxide

Diallyl quaternary ammonium chlorides, bromides and N-alkyldiallylamine hydrochlorides were polymerized with ammonium persulfate (APS) in dimethyl sulfoxide (DMSO). The dependences of yield and molecular weight of polymers on polymerization conditions were examined and quaternary ammonium chlorides were found to have better polymerizability than bromides. The poly(diallyl quaternary ammonium chlorides) obtained with APS—DMSO system are expected to have quite high molecular weights, as determined from the measurement of limiting viscosity numbers of the polymers in NaCl aqueous solution.     

Electrochemical reduction of 4-aminopyrimidine and cytosine in dimethyl sulfoxide

The electrochemical reduction in dimethyl sulfoxide of cytosine (4-amino-2-hydroxypyrimidine) and one of its model compounds (4-aminopyrimidine) has been examined. Initially, each pyrimidine (RH) undergoes a reversible, diffusion-controlled one-electron reduction of the 3,4 N=C double bond to the radical anion (RH⁻, which can dimerize or can react with the parent compound (father-son reaction) to form the neutral free radical (RH₂) and the pyrimidine anion (R⁻); the radical can dimerize or be further reduced, perhaps after effectve protonation; the anion forms a redox couple with Hg(1)−Hg(0). Other coupled reactions, which may occur under suitable conditions, include reaction between anionic dimer (⁻RH−RH⁻) and RH, proton-assisted decomposition of dimer to form reducible RH₃⁺, and deamination of the two-electron reduction product (RH₃), which is a gem diamine, to generate 2-hydroxypyrimidine or pyrimidine itself. The effects on the electrochemical redox pattern of added water, strong acid (HClO₄), weak acid (chloroacetic and benzoic acids), and strong base (Et₄NOH) are described.     

Electrochemical determination of the superoxide ion concentration from KO2 dissolved in dimethyl sulfoxide.

An electrochemical determination of the O2- concentration from KO2 in DMSO solution using steady state microelectrode voltammetry shows that the KO2/DMSO method with the combined use of a crown compound or sonication is a reliable and simple technique for introduction of O2- to the biomimitic reaction system.     

Electrochemical reduction of uracil in dimethyl sulfoxide: Autoprotonation of the anion radical

The electrochemical reduction of uracil in dimethyl sulfoxide was investigated, using d.c.and a.c. polarography, cyclic voltammetry, and controlled potential electrolysis. Uracil is reduced in a one-electron step (E_1/2=?2.3 V); the apparent number of electrons transferred (n) decreases from one at infinite dilution to one-half at concentrations above 1mM. The concentration dependent n-value is due to proton transfer by the parent compound to the radical anion formed on reduction. Such a proton transfer, which has been observed for 2-hydroxypyrimidine, deactivates part of the uracil, which would otherwise be available for reduction, by formation of the more difficultly reducible conjugate base. The uracil anion forms insoluble mercury salts, producing two oxidation waves (E_1/2 of ?0.1 and ?0.3 V); the latter wave is due to formation of a passivating film on the electrode. Digital simulations indicate that the protonation rate exceeds 10⁵M^?1 s^?1 and that, at low uracil concentration, some of the free radical formed on protonation is further reduced. At concentrations exceeding 1 mM, all of the free radical dimerizes. The effect of added acids and base on the electrochemical behavior is described.     

An investigation of water dynamics in binary mixtures of water and dimethyl sulfoxide

The motion of water molecules in mixtures of water and d6-dimethyl sulfoxide (DMSO) has been explored through molecular dynamics (MD) simulations using the SPC/E water model (J. Chem. Phys. 1987, 91, 6269) and the P2 DMSO model (J. Chem. Phys. 1993, 98, 8160). We evaluate the self-intermediate scattering functions, FS(Q,t), which are related by a Fourier transform to the incoherent structure factors, S(Q,omega), measured in quasielastic neutron scattering (QNS) experiments. We compare our results to recent QNS experiments on these mixtures reported by Bordallo et al. (J. Chem. Phys. 2004, 121, 12457). In addition to comparing the MD data to the experimental signals, which correspond to a convolution of S(Q,omega) with a resolution function, we examine the rotational and translational components of FS(Q,t) and investigate to what extent simulation results for the single-molecule dynamics follow the dynamical models that are used in the analysis of the experimental data. We find that the agreement between the experimental signal and the MD data is quite good and that the portion of FS(Q,t) due to translational dynamics is well represented by the jump-diffusion model. The model parameters and their composition dependence are in reasonable agreement with experiment, exhibiting similar trends in water mobility with composition. Specifically, we find that water motion is less hindered in water-rich and water-poor mixtures than it is near equimolar composition. We find that the extent of coupling between rotational and translational motion contributing to FS(Q,t) increases as the equimolar composition of the mixture is approached. Thus, the decoupling approximation, which is used to extract information on rotational relaxation from QNS spectra at higher momentum transfer (Q) values, becomes less accurate than that in water-rich or DMSO-rich mixtures. We also find that rotational relaxation deviates quite strongly from the isotropic rotational diffusion model. We explore this issue further by investigating the behavior of orientational time correlations for different unit vectors and corresponding to Legendre polynomials of orders 1-4. We find that the rotational time correlations of water molecules behave in a way that is more consistent with the extended jump rotation model recently proposed by Laage and Hynes (Science 2006, 311, 832).     

X-ray crystallographic investigation of the adduct of decachloro-o-carborane with dimethyl sulfoxide

Conclusions The structure of the 11 adduct of decachloro-o-carborane with DMSO was determined by x-ray crystallography. It was established that the structure contains cyclic associates of two DMSO molecules and two decachloro-o-carborane molecules linked by hydrogen bonds of the C-H...O type.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2257–2261, October, 1982.     

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.     

Thermolysis of dimethyl sulfoxide

The thermal decomposition of dimethyl sulfoxide at small extent of reaction has been studied at temperatures of 297-350°C and pressures of 10–400 Torr. The major products CH₄, C₂H₄, and SO₂ were shown to follow first-order kinetics. The activation energies for production of each was about 48 kcal·mole^?1. A chain mechanism has been postulated in the light of the results of isotopic substitution experiments.     

Ion exchange in dimethyl sulfoxide media. IV

Summary Selective separations of beryllium from other metal ions (Cu, Cd, Zn, Ni, Fe, Co, Mg, Ca, Sr, Ba, Al, and Pb) were achieved by means of cation exchange in an aqueous 20% v/v DMSO medium containing 0.25 mol/l of thiocyanate. The observed improvements of separation factors in the presence of DMSO were attributed mainly to enhanced complex formation with thiocyanate for a number of heavy metal ions, and for increased differentiation of solvation tendencies in the binary medium. From a semi-quantitative study of species distribution it was concluded that strongly solvated BeSCN⁺ and Be⁺⁺ species predominate under conditions of the described column elutions, although traces of Be(SCN)₂ may be present. The simplicity and convenience of the described procedure suggest wide applicability for isolation or separation ofg to mg amounts of beryllium from concomitant cations, particularly in the presence of large quantities of aluminum and the alkaline earth metals.

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Zusammenfassung Die selektive Trennung des Berylliums von anderen Metallionen (Cu, Cd, Zn, Ni, Fe, Co, Mg, Ca, Sr, Ba, Al und Pb) wurde erreicht durch Kationenaustausch in 20% iger wäßriger Dimethylsulfoxidlösung, die 0,25-molar an Thiocyanat war. Die Verbesserung der Trennungsfaktoren in Gegenwart von DMSO beruht hauptsächlich auf der verstärkten Komplexbildung einiger Schwermetallionen mit Thiocyanat und auf dem größeren Unterschied der Solvatationsneigung in dem binären Medium. Aus einer semiquantitativen Untersuchung der Verteilungsverhältnisse ergab sich, daß stark solvatierte BeSCN⁺- und Be²⁺-Ionen unter den angegebenen Elutionsbedingungen vorherrschen, wenn auch Spuren von Be(SCN)₂ anwesend sein können. Die Einfachheit des beschriebenen Verfahrens legt dessen Anwendung zur Isolierung oder Trennung von Mikrogramm- bis Milligrammengen Be von Begleitkationen nahe, besonders bei Gegenwart großer Mengen Aluminium und alkalischer Erdmetalle.

     

Acidity of di- and triprotected hydrazine derivatives in dimethyl sulfoxide and aspects of their alkylation

The pK(a) values in DMSO for 22 di- and triprotected hydrazine NH acids and two monosubstituted hydrazines have been determined using potentiometric titration. The results of density functional theory calculations at the B3LYP/6-311+G level of gas-phase acidities of a representative selection of mono-, di-, and trisubstituted hydrazines are compared with both the relevant published and novel experimental titration data. In the course of this work, a rough estimation of the pK(a) value of hydrazine in DMSO (ca. 38.0) has been deduced. For typical triprotected compounds of this kind containing moderately electron-withdrawing carbamate and imidodicarbonate or arenesulfonylcarbamate functions the pK(a) values fall in the range 15.1-17.3, whereas for N,N'-diprotected hydrazines with a carbamate and an aromatic sulfonyl group the corresponding values are 12.7-14.5. Several of these triprotected derivatives have recently been applied preparatively in stepwise synthesis of substituted hydrazines using alkyl halides as electrophiles in the presence of a phase transfer catalyst, and a few of them, with varying success, have been examined in model experiments with benzyl alcohol, triphenylphosphine, and diethyl azodicarboxylate in the Mitsunobu reaction. The dependence of the reactivity on the intrinsic acidity of the hydrazines in this reaction is highlighted. Furthermore, the regioselective alkylation of an N,N'-diprotected hydrazine can be rationalized on the basis of the presented data.     

Carbocation-forming reactions in dimethyl sulfoxide

Mesylate derivatives of 3-aryl-3-hydroxy-beta-lactams and thiolactams react in DMSO-d(6) by first-order processes to give alcohol products. Substituent effect studies implicate carbocation intermediates (ion-pairs) that are captured by DMSO-d(6) to give transient oxosulfonium ions. Rapid reaction of the oxosulfonium ions with trace amounts of water leads to the alcohol product and regenerates DMSO-d(6). H(2)(17)O labeling studies show that (17)O is incorporated into the DMSO. The mesylate derivatives of endo- and exo-2-hydroxy-2-phenylbicyclo[2.2.1]heptan-3-one also react in DMSO-d(6) to give the alcohol products. Ion-pair intermediates that capture DMSO giving unstable oxosulfonium ions are again proposed. Exo-2-phenyl-endo-bicyclo[2.2.1]heptyl trifluoroacetate readily eliminates trifluoroacetic acid in DMSO-d(6) via a cationic mechanism involving loss of the endo-trifluoroacetate leaving group as well as an exo-hydrogen. The O-methyl oxime derivative of alpha-chloro-alpha,alpha-diphenylacetophenone reacts in DMSO-d(6) to give 1-methoxy-2,3-diphenylindole, a product derived from cyclization of a cationic intermediate. A common ion rate suppression provides further evidence for a cationic mechanism. The triflate derivative of pivaloin reacts by a cationic mechanism in DMSO-d(6) to give rearranged products. The rate is even faster than in highly ionizing solvents such as trifluoroethanol or trifluoroacetic acid. 1-Adamantyl mesylate reacts in DMSO-d(6) by a first-order process (Y(OMs) = -4.00) to give a long-lived oxosulfonium ion, 1-Ad-OS(CD(3))(2)(+), which can be characterized spectroscopically. This oxosulfonium ion reacts only slowly with water at elevated temperatures to give 1-adamantanol. DMSO is therefore a viable solvent for k(s), k(C), and k(Delta) cationic processes.     

Structure and dynamics of water confined in dimethyl sulfoxide.

We study the structure and dynamics of hydrogen-bonded complexes of H2O/D2O and dimethyl sulfoxide (DMSO) by infrared spectroscopy, NMR spectroscopy and ab initio calculations. We find that single water molecules occur in two configurations. For one half of the water monomers both OH/OD groups form strong hydrogen bonds to DMSO molecules, whereas for the other half only one of the two OH/OD groups is hydrogen-bonded to a solvent molecule. The H-bond strength between water and DMSO is in the order of that in bulk water. NMR deuteron relaxation rates and calculated deuteron quadrupole coupling constants yield rotational correlation times of water. The molecular reorientation of water monomers in DMSO is two-and-a-half times slower than in bulk water. This result can be explained by local structure behavior.     

Dehydrogenation of 4-aryl(hetaryl) spinacine derivatives with dimethyl sulfoxide

Aromatization of 4-aryl(hetaryl)tetrahydroimidazo[4,5-c]pyridine-6-carboxylic acids and their lithium salts by the action of dimethyl sulfoxide has been revealed for the first time. Heating of these compounds in DMSO for 5–7 h at 90–95°C leads to the formation of 4-aryl(hetaryl)imidazo[4,5-c]pyridine derivatives as a result of dehydrogenation and decarboxylation. Heating of the corresponding lithium salts generated in situ (DMSO, 90–95°C, 3–5 h) affords difficultly accessible 4-aryl(hetaryl)imidazo[4,5-c]pyridine-6-carboxylic acids.