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 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Equilibrium solubilities of the first four homologous alkyl p-aminobenzoate esters were determined in methanol, ethanol, and 1-propanol at 25, 33, and 40 degrees; the esters and the alcohols comprise separate homologous series. The solution process of a solute may be considered to be the summation of two sequential steps, melting and mixing, and the magnitude of solubility depends upon temperature and the extent of interactions between solute and solvent molecules. Quantitative solute concentrations, obtained from spectrophotometric analysis, were converted to mole fractions. Statistical analysis of the logarithmic mole fraction solubilities of the aminobenzoates, which were linear with respect to both reciprocal absolute temperature and the logarithm of absolute temperature, generated enthalpies and entropies of solution, respectively. The heats of fusion and the melting points of these aminobenzoates were determined to calculate their ideal solubilities. Excess free energies and partial molal free energies of each solution were calculated from the activity coefficients of the solutes; the thermodynamic elements for these systems are discussed.
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PMID:Solution thermodynamics of alkyl p-aminobenzoates. 125 58

We describe an abrupt increase (at 32 degrees ) in the energy of activation for the reaction of hepatic adenylyl cyclase in the presence of glucagon or epinephrine. This increase is not seen in the presence of fluoride, prostaglandin E(1), or 1-propanol, or in the absence of cyclase stimulators. The change in energy of activation found with hormones is abolished by 1-propanol. This change does not represent differences in hormone or substrate binding at different temperatures, but seems to reflect interactions among elements of the cyclase stimulation sequence. Similar changes in energy of activation were not observed for alkaline phosphatase, cyclic AMP-phosphodiesterase, 5'-nucleotidase, or ouabain-sensitive ATPase. Since the mole fraction of cholesterol in liver membranes is sufficiently high to preclude a phase change in bulk membrane lipids, our observation suggests either that cyclase is restricted to cholesterol-poor membrane regions or that the change in its energy of activation is largely restricted to protein components of the cyclase apparatus. The data are compatible with fundamental differences in the stimulation process(es) for the hormones (glucagon and epinephrine) as compared with those for fluoride and prostaglandin E(1).
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PMID:A temperature-sensitive change in the energy of activation of hormone-stimulated hepatic adenylyl cyclase. 435 55

A three-solvent system was used to determine the Hildebrand solubility parameters of organic nonelectrolytes. The experimental Hildebrand solubility parameter represents a weighted average of the mole fraction solubilities of the solute in these three individual solvents (ethyl acetate, 1-propanol, and 1,2-propanediol). The solvent system estimated the Hildebrand solubility parameters of solutes within a range from 8.9 to 14.8 (cal/cm3)2(1). Deviations ranged from 0.8 to 12.9%, with the highest value at the extreme and well within 10% at the median. Estimation of the Hildebrand solubility parameters of solutes within a wider range and with somewhat better accuracy was made with a five-solvent system (hexane, ethyl acetate, 1-propanol, 1,2-propanediol, and water).
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PMID:An experimental method for determining the Hildebrand solubility parameter of organic nonelectrolytes. 825 86

Several recent reports have provided evidence that interactions of small alcohols with lipid bilayer membranes are dominated by adsorption to the membrane-water interface. This mode of interaction is better modeled by binding models than solution theories. In the present study, alcohol-membrane interactions are examined by applying the 'solvent exchange model' [J.A. Schellmann, Biophys. Chem. 37 (1990) 121] to calorimetric measurements. Binding constants (in mole fraction units) for small alcohols to unilamellar liposomes of dimyristoyl phosphatidylcholine were found to be close to unity, and in contrast to partitioning coefficients they decrease through the sequence ethanol, 1-propanol, 1-butanol. Thus, the direct (intrinsic) affinity of the bilayer for these alcohols is lower the longer the acyl chain. A distinction between binding and partitioning is discussed, and it is demonstrated that a high concentration of solute in the bilayer (large partitioning coefficients) can be obtained even in cases of weak binding. Other results from the model suggest that the number of binding sites on the lipid bilayer interface is 1-3 times the number of lipid molecules and that the binding is endothermic with an enthalpy change of 10-15 kJ/mol. Close to the main phase transition of the lipid bilayer the results suggest the presence of two distinct classes of binding sites: 'normal' sites similar to those observed at higher temperatures, and a lower number of high-affinity sites with binding constants larger by one or two orders of magnitude. The occurrence of high-affinity sites is discussed with respect to fluctuating gel and fluid domains in bilayer membranes close to the main phase transition.
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PMID:Thermodynamics of alcohol-lipid bilayer interactions: application of a binding model. 1051 96

Using the reversed-phase bonded-phase HPLC packing Partisil-10 ODS-3, sorption isotherms have been measured for the alcohols 1-propanol (PrOH) and 1-hexanol (HexOH), and as well, a simultaneous sorption curve for the two alcohols has been measured from solutions containing a low and constant concentration of HexOH as sample with increasing concentrations of PrOH as organic modifier. The mobile-phase effect of PrOH is quantified by solution-phase activity coefficients obtained either from vapor/solution equilibrium measurements or from cloud point measurements. Since sorbed alcohols are located at the ODS/solution interface, the stationary-phase effect of PrOH is modeled in terms of three processes: (i) competition for space; (ii) decrease of space required per mole with increasing concentration of sorbed PrOH; and (iii) change of free energy of sorption with increasing concentration of sorbed PrOH. The model yields excellent fits to the isotherms and to the simultaneous sorption curve. Comparison of the model-fitting parameters for the simultaneous sorption curve with those for the PrOH isotherm confirms that the stationary-phase effect of PrOH on HexOH is due exclusively to processes i and ii. Sorbed PrOH causes rearrangement of the C18 chains of the ODS phase. For volume percent PrOH less than 15% in the mobile phase, the effect of PrOH on sample sorption is nearly exclusively in the stationary phase. Between 15 and 30%, both mobile- and stationary-phase effects are important.
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PMID:Stationary-phase contribution of 1-propanol organic modifier to changes in sorption of 1-hexanol on an ODS-bonded phase 1073 8

The total vapor pressures at 26 degreesC of binary (water-alcohol) and ternary (water-alcohol-vesicle) systems were measured for six short chain alcohols. The vesicles were unilamellar dipalmitoyl phosphatidylcholine (DMPC). The data was used to evaluate the effect of vesicles on the chemical potential of alcohols expressed as the preferential binding parameter of the alcohol-lipid interaction, gamma23. This quantity is a thermodynamic (model-free) measure of the net strength of membrane-alcohol interactions. For the smaller investigated alcohols (methanol, ethanol and 1-propanol) gamma23 was negative. This is indicative of so-called preferential hydration, a condition where the affinity of the membrane for water is higher than the affinity for the alcohol. For the longer alcohols (1-butanol, 1-pentanol, 1-hexanol) gamma23 was positive and increasing with increasing chain length. This demonstrates preferential binding, i.e. enrichment of alcohol in the membrane and a concomitant depletion of the solute in the aqueous bulk. The measured values of gamma23 were compared to the number of alcohol-membrane contacts specified by partitioning coefficients from the literature. It was found that for the small alcohols the number of alcohol-membrane contacts is much larger than the number of preferentially bound solutes. This discrepancy, which is theoretically expected in cases of very weak binding, becomes less pronounced with increasing alcohol chain length, and when the partitioning coefficient exceeds approximately 3 on the molal scale (10(2) in mole fraction units) it vanishes. Based on this, relationships between structural and thermodynamic interpretations of membrane partitioning are discussed.
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PMID:Binding of small alcohols to a lipid bilayer membrane: does the partitioning coefficient express the net affinity? 1124 45

Surface tensions (sigma) for [1,3-dioxolane+methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, and 1-pentanol] and excess molar volumes (v(E)) for [1,3-dioxolane+methanol, ethanol, 1-propanol, 2-propanol, and 2-butanol] at the temperature 298.15 K and normal atmospheric pressure have been determined as a function of mole fractions. The magnitude of these experimental quantities is discussed in terms of the nature and type of intermolecular interactions in binary mixtures. In order to analyze the surface tension behavior, the extended Langmuir (EL) model was used and the results obtained for the systems containing 1,3-dioxolane were compared with those of other formerly published series: [1,4-dioxane+alkanes] and [1,4-dioxane+alcohols].
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PMID:Surface tension and density of mixtures of 1,3-dioxolane+alkanols at 298.15 K: analysis under the extended Langmuir model. 1502 9

Mesoscale structure of 1-propanol aqueous solutions with propanol mole fraction xp ranging from 0.1 to 0.33 has been studied by means of small angle neutron scattering (SANS) and large-scale reverse Monte Carlo (RMC) technique. Analysis of the SANS intensities in terms of a fractal model shows that the fractal dimension df of mesoscale structure of the solution is about 1.8-1.9 for water-rich solution and about 1.5 for propanol-rich solution. Percolation analysis on the RMC results reveals that the water molecules and the propanol molecules cluster, respectively, as a mass fractal, the dimension dM of which is about 2.3-2.5 for both clusters for water-rich solution. Furthermore, the distribution of the cluster size is expressed by a simple power law with an exponent tau of about 1.35-1.5 for the propanol clusters and 1.05-1.2 for the water clusters. These results imply that the current solution is characterized by polydisperse mass fractals. In fact, a theoretical relation for polydisperse system of mass fractals, df = dM(2-tau), holds well in the current solution. The characteristic change in df from 1.8-1.9 to 1.5 described above is attributed to the crossover between the water-rich regime and the propanol-rich regime. Most of the water molecules and the propanol molecules are located on the interface between clusters, and the water molecules form thin layers of about 10 A thick irrespective of 1-propanol content studied.
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PMID:Mass-fractal clustering and power-law decay of cluster size in 1-propanol aqueous solution. 1533 5

The solubilization phenomenon was investigated in mixed surfactant systems. The solubilization power of a mixed surfactant reaches its maximum at a particular temperature at each mixing ratio of surfactants. When the mole fraction of C4E1 in the total surfactant (w1 value) was varied in a water/C12E5/C4E1/decane system, the minimum mole fraction of total surfactant in the system necessary to obtain a single microemulsion phase (xi value) was almost unchanged for w1<0.3, whereas it increased remarkably for w1>0.8. The molar solubilization capacity (Cs=(1-xi)/xi) of the mixed surfactant decreased remarkably for w1<0.3, whereas it decreased gradually for w1>0.8. The result [Formula: see text] is due largely to the characteristic of the function xi(Cs)=1/(1+Cs), specifically, [Formula: see text] , where dxi/dw1=(dxi/dCs)(dCs/dw1). The partial molar solubilization capacity (Cs) of C4E1 was negative at almost all w1, but the Cs value of C12E5 went through a maximum on the addition of C4E1. Propanol (a cosurfactant) has the same effect on the solubilization phenomenon in the water/C12E6/propanol/heptane system. In the water/C12E5/C12E7/decane system, the Cs value of each surfactant did not vary greatly as the mixing ratio of surfactants was varied. The Cs and xi values were close to molar additivity for each mixing ratio.
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PMID:Solubilization by different-sized surfactant mixtures. 1584 38

Glass-forming monohydroxy alcohols exhibit two dielectric relaxation signals with super-Arrhenius temperature dependence: a Debye peak and an asymmetrically broadened alpha-process. We explore the behavior of these distinct relaxation features in mixtures of such liquids by dielectric measurements. The study focuses on the viscous regime of two binary systems: 2-methyl-1-butanol with 2-ethyl-1-hexanol and 1-propanol with 3,7-dimethyl-1-octanol. We find that the logarithmic relaxation time, log(tau), of the Debye peak follows an ideal mixing law (linear change with mole fraction), even in the case of mixing structurally dissimilar components. By contrast, the log(tau) versus mole fraction curve for the alpha-process is nonlinear, indicative of slower structural relaxation relative to the expectation on the basis of ideal mixing behavior. The latter observation is analogous to the effect of composition on viscosity, heat of mixing, and glass-transition temperature, whereas the ideal mixing of log(tau) seen for the Debye peak is the exception. We conclude that the unusual ideal mixing behavior of dielectric relaxation in monohydroxy alcohols is not a result of structural similarity, but rather yet more evidence of the Debye process being decoupled from other dynamic and thermodynamic properties.
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PMID:Ideal mixing behavior of the debye process in supercooled monohydroxy alcohols. 1685 40


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