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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Thermodynamic quantities of the self-association of 6-methylpurine in water (1)-dimethylsulfoxide (DMSO) (2) mole fraction, x2 less than 0.1) and water (1) - N,N-dimethylformamide (DMF) (2) (x2 less than or equal to 1.0) mixed solvents have been obtained through heat of dilution measurements, at 25 degrees C. In the water-DMSO solvent system, the standard enthalpy and entropy changes, delta Ho and delta So, of the association exhibited an abrupt behavior. They decreased remarkbly with the the mole fraction of DMSO until about x2 = 0.012 and after that, they increased steeply. In the case of water-DMF solvent system, the values of delta Ho and delta So didn't show the abrupt behavior. They decreased steeply until about x2 = 0.1 and, at higher mole fractions, became relatively constant. These behaviors are rationalized on the basis of solvent structural effects and solvation in these association systems.
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PMID:Self-association of purine base, 6-methylpurine, in water - organic component mixtures. 54 24

Adenosine aminohydrolase from calf intestinal mucosa is sensitive to changes in its environment produced by small mole fractions of dimethylsulfoxide (DMSO). At a mole fraction of 0.1 where the dielectric constant is lowered from that of 78 of neat water to about 76.5, Vmax was reduced by 65% and affinity for substrate (adenosine) and the two competitive inhibitors, insine and N6-benzyladenosine, was decreased markedly. However, this decreased affinity was such that Ki/Km remained virtually constant for both inhibitors. DMSO itself showed the kinetics of a mixed inhibitor with Ki decreasing with increasing mole fraction. This cosolvent also decreased the heat stability of the enzyme which suggests that enzyme conformation is altered by DMSO. Comparison of data in the presence of DMSO with previously obtained data with dioxane shows that heat stability as well as Vmax, at a given value of dielectric constant, is independent of the amount or nature of cosolvent used to achieve that dielectric constant. However, cosolvent induced changes in Ki indicate that colligative as well as dielectric constant effects contribute to the observed changes in kinetic behavior. These experiments may be considered as models for the behavior of enzymes in the medium of lowered dielectric constant expected in the vicinity of cytoplasmic membranes. The results indicate that in such an environment, adenosine aminohydrolase would be expected to be less efficient a catalyst, but equally susceptible to product inhibition, as compared to media of dielectric constant approaching that of water.
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PMID:Cosolvent-buffer mixtures as models for the cytoplasmic mileu: the enzymology of adenosine aminohydrolase. 98 42

Dimethylsulfoxide-water-Dowex 50W-X8 systems are characterized by measurements of solvent selectively and proton magnetic resonance spectra. The H+-, Li+-, NH4+-, NHe4+-, NBu4+-, Mg2+-, Zn2+-, and La3+- forms are studied over a wide range of binary-solvent mole fractions. The relative selectivities for water by the ion exchanger, based on an integrated Kipling parameter, are Zn2+-form (reference) --1.00, Mg2+ --0.43, La3+ --0.38, Li+ +0.17, NMe4+ 0.20, NH4+ 0.31, NBU4+ 0.33, and H+ 0.68, the polyvalent counterions preferring DMSO. All of the ionic forms except the NH4+-form exhibit over much of the mole fraction range separations between the external water and the internal water peaks exceeding 50 Hz, the magnitude of the separation varying with the counter-ion. Comparison of results is facilitated by maintaining a constant ratio between the total number of moles of solvent and the number of equivalents of ions exchanger.
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PMID:Models for biological ion exchangers. II. Solvent selectivity in DMSO-water-Dowex 50W. 102 18

Tri-n-butyltin(TBT) compounds having the chemical formula (C4H9)3SnX are broad-spectrum biocidal agents whose toxic effect is primarily at the membrane level. Red blood cells (RBC) exposed to micromolar concentrations of tributyltin compounds (TBTX) undergo morphological changes and hemolysis. Determination of the mechanism of action whereby TBT elicits membrane damage continues to be a challenging endeavor. Because xenobiotic TBT+ and endogenous O2.- have been found to penetrate and alter RBC membrane function, it is hypothesized that they may combine chemically within the RBC hydrophobic lipid bilayer during TBT insult to initiate lipid peroxidative processes. The present study has been designed (1) to determine if TBT+ and O2.- combine chemically in aprotic media and, if so, (2) to characterize any free-radical complex(es) generated. The reactions of the membrane-active TBTX compounds (X = OCH3, Cl, Br, or I) with O2.- have been investigated in the aprotic solvent system cis-dicyclohexano-18-crown-6 ether/DMSO using EPR techniques. When incremental amounts of each TBT halide were added to O2.- solutions at room temperature, the EPR signal characteristic of O2.- diminished in intensity and disappeared when a 1:1 O2.-/TBT+ mole ratio was attained. Although the same phenomenon was observed for all TBT halides used, only the KO2/TBTI reaction produced detectable amounts of a new oxygen-centered free-radical complex. The EPR spectral parameters calculated from the product anisotropic frozen glass spectra were gx = 2.054, a(x) = 31.7 G, gy = 2.021, gz = 2.002, gav = 2.026.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:In vitro activation of lipophilic tributyltins by superoxide produces tributylstannyl superoxo radicals, proposed initiators of lipid peroxidation: an EPR model study. 133 86

The reason for the differences in phototoxic potential between the 5 quinolone antibacterial agents lomefloxacin, enoxacin, ciprofloxacin, ofloxacin and DR-3355 (the s-isomer of ofloxacin) in mice was investigated. Superoxide anion, hydrogen peroxide (H2O2), and bleaching of p-nitrosodimethylaniline (B-NDMA) were detected in quinolone solutions during irradiation with ultraviolet-A (UVA). Apparent levels of H2O2 and the B-NDMA per mole of quinolone paralled the phototoxic potentials in the mice. The N-NDMA induced by quinolones and UVA was inhibited partially by treatment with D-mannitol and dimethylsulfoxide, and also with diethylenetriamine-pentaaceticacid (DTPA), suggesting that Haber-Weiss and Fenton reactions occurred. UVA concentration-dependently increased the level of the B-NMDA in H2O2 solution and the swelling in the ear pretreated by intra-auricular injection of H2O2. Both augmentations were inhibited by DTPA or DMSO. The swelling induced by the 5 quinolones and UVA was completely inhibited by pretreatment with dimethylsulfoxide. Oxygen consumption was detectable during the photodegradation, and increased with time. These results showed that the phototoxic potentials of the 5 quinolones were probably related to the amounts of toxic oxygens generated in the target cells during irradiation.
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PMID:Possible reasons for differences in phototoxic potential of a 5 quinolone antibacterial agents: generation of toxic oxygen. 133 37

The administration of dimethyl sulfoxide with cisplatin at a mole ratio of 200:1 results in a considerable reduction in the nephrotoxicity produced when cisplatin alone is administered to Sprague-Dawley rats at 7.5 mg/kg. Observed measures of nephrotoxicity which were significantly improved by the coadministration of cisplatin and DMSO over the values found for cisplatin alone include BUN, serum creatinine, creatinine clearance and histopathological evidence of renal damage. The weight loss associated with cisplatin administration was also significantly reduced by DMSO coadministration. The use of DMSO did not result in any observable loss in antitumor activity of cisplatin against the Walker 256 carcinosarcoma.
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PMID:Coadministration of dimethyl sulfoxide reduces cisplatin nephrotoxicity. 176 65

The synthesis and properties of an amide isostere of the antibiotic distamycin, thioformyldistamycin 3 is described. Compound 3 exists predominantly in the E conformation of the thioamide group in freshly prepared DMSO solution but is converted into the Z form, predicted by molecular mechanics to be more stable, on standing for 24 h. The coalescence temperature in DMSO is 110 degrees C by 1H-NMR. The thioformyl moiety of 3 is resistant to both peptidase action and acid treatment. Complementary strand MPE footprinting on a EcoRI/Hind III restriction fragment of pBR322 DNA demonstrated that either E or Z forms of 3 give a single set of footprints very similar to that of the parent antibiotic with strongest protection at TAAG and TATTAT with moderately strong protection at ATTT and AAAA. The strength of binding of 3 and distamycin from delta Tm measurements to either poly.d(AT) or calf thymus DNA is comparable. Molecular modeling predicted a preferred conformation for 3 wherein the C = S bond has a torsional angle of 110 degrees with the pyrrole ring. The energy difference between this conformation and the E form is less than 1 kcal/mole. In contrast the E-form has an energy 17.3 kcal/mole greater than the Z and a value of 26.3 kcal/mole was calculated for the energy barrier between the two isomers.
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PMID:Amide isosteres of lexitropsins: synthesis, DNA binding characteristics and sequence selectivity of thioformyldistamycin. 181 46

The question of whether nonhydrolyzable nucleotide analogues and other nucleoside triphosphates support tubulin assembly was addressed. Tubulin which contained residual GTP at the exchangeable site polymerized in the absence of added GTP in the presence of DMSO or glycerol. After maximum absorbance was reached, disassembly occurred at a slow rate. When 0.5 mM GMPPCP, GMPPNP, or ATP was included in the assembly reaction, disassembly did not occur, and about 0.1 mol of these nucleotides per mole of tubulin was incorporated into the protein. When 5 mM nucleotide was used or alkaline phosphatase was included in the case of the nonhydrolyzable analogues, a greater amount of assembly occurred and about 0.7-0.8 mol of analogue was incorporated. The products of the assembly reaction were cold-labile microtubules and protofilament ribbons. After cold-depolymerization of the microtubules and ribbons, a second cycle of assembly produced some microtubules, but cold-stable amorphous polymers were the major product. In addition, when GTP at the exchangeable site was first removed by a cycle of assembly, followed by depolymerization, assembly in the presence of GMPPCP, GMPPNP, or ATP produced a mixture of microtubules and cold-stable polymers, both of which contained bound analogue. Incorporation of GMPPCP, GMPPNP, or ATP into polymerized tubulin always occurred at the expense of GDP at the exchangeable site, the content of which decreased correspondingly. Incubation of tubulin with 5 mM GMPPCP, GMPPNP, or ATP under nonassembly conditions also displaced GDP.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:GTP analogues interact with the tubulin exchangeable site during assembly and upon binding. 210 23

Met5-enkephalin was studied in 1 mM solutions in 2H2O at room temperature and in a cryoprotective mixture (DMSOd6/2H2O, mole fraction of DMSO 0.49) in the temperature range 265-298 K. Small positive effects were observed between the ortho and meta protons of Tyr in aqueous solution at room temperature. Intraresidue effects can be made strong and negative by increasing the viscosity of the medium with a combination of cryoprotective mixtures and low temperatures. The use of mixtures with properties very close to water is very promising for conformational studies of enkephalins and of other small linear peptides.
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PMID:Nuclear Overhauser effects in linear peptides. A low-temperature 500 MHz study of Met-enkephalin. 358 48

1. The diffusion of the cryoprotective non-electrolyte dimethyl sulphoxide (DMSO) in the isolated guinea-pig taenia coli at 37, 25 and 0 degrees C has been studied using [(35)S]DMSO.2. Within 1 hr after immersion at 37 degrees C in Krebs solution containing 20% (w/v) DMSO and trace amounts of [(35)S]DMSO, the non-electrolyte was distributed uniformly throughout a volume equivalent to the total initial water content of the muscle.3. The kinetics of efflux of [(35)S]DMSO from muscles at constant volume were analysed on the basis of two models: one incorporated radial diffusion in extracellular fluid with simultaneous permeation into the cells, the other involved only radial diffusion in homogeneous cylinders of tissue having no internal barriers to diffusion; the former was found to give a better representation of the efflux kinetics.4. If it was assumed that the rate of diffusion of DMSO in the extracellular space of taenia coli was the same as that in the bathing medium, the values of the extracellular space and the permeability of smooth muscle to DMSO, obtained from the analysis of the efflux kinetics, were 454 +/- 19 ml./kg and 2.36 +/- 0.05 x 10(-6) cm sec(-1) at 37 degrees C.5. The activation energy for the transfer of DMSO across the surface of the cell was estimated to be 6.0 kcal/mole at 37 degrees C, 6.6 kcal/mole at 25 degrees C and 11.6 kcal/mole at 0 degrees C, indicating either that the equivalent pore radius of the cells decreased with temperature or that the cell permeability represented the sum of two fluxes, one through the aqueous pores of the cell and the other through the lipid phase of the cell membrane, each with a different energy of activation.6. A net flux of water across the surface of the cells, superimposed on the efflux of DMSO, markedly affected the rate of diffusion of the non-electrolyte out of the whole tissue; however, it was considered that an analysis of the efflux kinetics was not possible under these conditions.7. These results provide a basis for methods which will be used to investigate the possibility of preserving tissue in unfrozen aqueous media at sub-zero temperatures.
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PMID:Diffusion and distribution of dimethyl sulphoxide in the isolated guinea-pig taenia coli. 549 41


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