Thermodynamic Quantities of Surface Formation of Aqueous Electrolyte Solutions.

The surface tensions of aqueous salt solutions of LiCl, KCl, and CsCl were measured as a function of concentration and temperature. By analyzing the results, the thermodynamic quantities of surface formation such as entropy (Deltas), Helmholtz free energy (Deltaf), and energy of surface formation (Deltau) were evaluated. Addition of salts into aqueous solution leads to an increase in Deltaf but decreases in Deltas and Deltau. The variations of Deltas, Deltaf, and Deltau with the change of salt concentration are almost the same for all alkali metal chlorides in spite of their large difference in hydration force. Copyright 1999 Academic Press.

Thermodynamic Quantities of Surface Formation of Aqueous Electrolyte Solutions.

The surface tensions of aqueous solutions of sodium, magnesium, and lanthanum chlorides were measured as a function of concentration and temperature. By analyzing the results, the concentration dependence of the thermodynamic quantities of surface formation such as entropy (Deltas), Helmholtz free energy (Deltaf), and energy of surface formation (Deltau) were evaluated. The Deltaf increased almost linearly with increasing concentration, and the degree of the increase is mainly determined by the net charges of the salts. The Deltas decreased with the addition of salt into the solution. It was found that the net charge of salts determines the degree of the decrease in Deltas. On the other hand, a slight change in the Deltau is observed because of the opposite contribution of Deltaf and TDeltas to the Deltau value. Copyright 1999 Academic Press.

Thermodynamic Quantities of Surface Formation of Aqueous Electrolyte Solutions.

The surface tensions of binary salt mixtures made up from NaCl and MgCl2 in aqueous solution were measured as a function of concentration and temperature. By analyzing the results, the thermodynamic quantities of surface formation such as entropy (Deltas), Helmholtz free energy (Deltaf), and energy of surface formation (Deltau) were evaluated. The Deltaf of the mixtures positively deviates from the straight line connecting those of NaCl and MgCl2 aqueous solutions. On the other hand, Deltas shows negative deviation from the linear relation. Copyright 1999 Academic Press.

Protein hydration and unfolding--insights from experimental partial specific volumes and unfolded protein models.

BACKGROUND: The partial specific volume of a protein is an experimental quantity containing information about solute-solvent interactions and protein hydration. We use a hydration-shell model to partition the partial specific volume into an intrinsic volume occupied by the protein and a change in the volume occupied by the solvent resulting from the solvent interactions with the protein. We seek to extract microscopic information about protein hydration and unfolding from experimental volume measurements without using computer simulations. We employ the idea that the protein-solvent interaction will be proportional to the surface area of the protein. RESULTS: A linear relationship is obtained when the difference between the experimental protein partial specific volume and its intrinsic volume is plotted as a function of the protein solvent-accessible surface area. The effect of using different protein volume definitions on the analysis of protein volumetric properties is discussed. Volumetric data are used to test a model for the unfolded state of proteins and to make predictions about the denatured state. CONCLUSIONS: The linear relationship between hydration-shell volume change and accessible surface area reflects the similar surface properties (fractional composition of nonpolar, polar and charged surface) among a diverse set of proteins. This linear relationship is found to be independent of how the solution is partitioned into solute and solvent components. The interpretation of hydration shell versus bulk water properties is found to be very model dependent, however. The maximally exposed unfolded protein model is found to be inconsistent with experimental volume changes of unfolding.

Thermodynamic Studies of the Adsorbed Films and Micelles of Sodium Taurodeoxycholate.

Surface tension of aqueous solutions was measured for sodium taurodeoxycholate, as a typical example of the bile salt compounds, in the temperature range 20 to 35 degreesC at 2.5 degreesC intervals and concentration range 0 to 7 mmol kg-1. We examined thermodynamic quantities obtainable from the surface tension measurements according to the thermodynamic relations given by K. Motomura [J. Colloid Interface Sci. 64, 348 (1978)]. Sodium taurodeoxycholate was strongly adsorbed and formed the saturated adsorbed film at low concentrations. However, the gaseous/expanded phase transition does not take place in the film. The thermodynamic quantities associated with adsorption did not change as markedly at the critical micelle concentration as those observed for typical surfactants. It was suggested that molecular interactions between sodium taurodeoxycholate molecules in aqueous solutions and adsorbed films are too weak to induce critical changes in the thermodynamic quantities. Copyright 1997 Academic Press.

Miscibility of phosphatidylcholine binary mixtures in unilamellar vesicles: phase equilibria.

Miscibility among phospholipids with different lipid chain-lengths or with different head groups has attracted a number of research efforts because of its significance in biological membrane structure and function. The general consensus about the miscibility of phosphatidylcholines with varying lipid chain-lengths appears to be that binary mixtures of phospholipids with a difference of two carbon atoms in the lipid chain mix well at the main phase transition. Miscibility between phosphatidylcholines with differences of four carbon atoms appears to be inconclusive. Previous reports on the phase transition of binary phospholipid mixtures are concerned mainly with multilamellar vesicles and are mostly limited to the main transition. In the present study, unilamellar vesicles were used and miscibility in binary systems between dimyristoyl-, dipalmitoyl- and distearoyl-phosphatidylcholines at pretransition as well as main transition temperatures was evaluated by constructing phase diagrams. Two methods were used to monitor the phase transitions: differential scanning microcalorimetry and optical absorbance methods. The optical method has the advantage that unilamellar vesicles of dilute phospholipid concentrations can be used. The liquidus and solidus phase boundaries were determined by the onset temperature of heating and cooling scans, respectively, because the completion temperature of a phase transition has no meaning in binary solutions. Dimyristoyl- and distearoyl-phosphatidylcholines, where the difference in the lipid chain-length is four carbon atoms, mixed well even at pretransition temperature.

Membrane expansion and inhalation anesthetics. Mean excess volume hypothesis.

High-precision solution densimetry was used to determine volume parameters for the interaction of inhalation anesthetics with water, nonpolar solvent, and phospholipid vesicles. The precision of the densimeter is mainly limited by the constancy of the temperature during measurement. Therefore, temperature stability was maintained within +/- 0.0005 degrees and monitored by a microprocessor-controlled Thermistor thermometer with 0.0001 degrees resolution. All values were obtained at 25 degrees. Because volatile anesthetics in liquid form usually contain water, they were purified by passage through activated aluminum oxide columns. The molal volumes of dried preparations at the pure liquid states were: halothane, 106.3(3); isoflurane, 123.6(6); and enflurane, 121.9(9) cm3 X mole-1 at 298.150 degrees K. The mean molal excess volumes of anesthetic-water mixtures were negative at dilute anesthetic concentrations in water and positive at dilute water concentrations in liquid anesthetics. These values were dependent on the mole fractions of each component and showed a minimum in the water-rich region and a maximum in the anesthetic-rich region. In water, the partial molal volumes were halothane 93.7, isoflurane 103.4, and enflurane 98.6 cm3 X mole-1 at infinite dilution, and increased as the anesthetic concentration was increased. The partial molal volumes of water in liquid anesthetics were in halothane 21.7, isoflurane 21.0, and enflurane 20.5 cm3 X mole-1 at infinite dilution, and decreased as the anesthetic concentration was decreased. The mean excess volumes of the anesthetic-decane mixture were positive in the entire mixing range. The partial molal volumes of anesthetics in n-decane at infinite dilution were halothane 114.9, isoflurane 135.3, and enflurane 135.2 cm3 X mole-1. The mean specific excess volumes of the mixture of anesthetics and dimyristoylphosphatidylcholine vesicle suspension showed positive values. The partial molal volume was not evaluated because of the theoretical difficulty in estimating it in a dispersed two-phase system. Because the mean excess volume of anesthetics dissolved in water is always negative and that incorporated into phospholipid suspension is positive, anesthetics expand the total volume of the model membrane system when translocated from water to the membrane. Anesthesia occurs when the mean excess volume of the total system exceeds a limiting value, and the bulk membrane size is irrelevant. Although the present result in no way disclaims alternative hypotheses, it demonstrates that the pressure reversal of anesthesia can be explained without assuming any specific receptors for these anesthetics.

Is membrane expansion relevant to anesthesia? Mean excess volume.

Recent disputes about the relevance of membrane expansion to the mechanism of anesthesia indicate that there is confusion about the concept of membrane expansion and stabilization. One theory suggests that the membrane is expanded when its size is increased by the size of the incorporated anesthetic molecules, whereas another theory contends that extra space must be created over the size of the incorporated anesthetic molecules in order for the membrane to be considered as expanded. This article is intended to clarify the discrepancies between these concepts. The volume theories of anesthesia are reviewed critically. The volume change of the membrane, induced by the interaction of anesthetics, is not a simple summation of membrane volume and anesthetic volume. There are a number of factors that affect the volume when anesthetic molecules interact with the membrane in water. The theories that envision membrane expansion as the increase of volume by the size of anesthetic molecules assume that there is no interaction between membrane and anesthetic molecules (if there is interaction, there is excess volume change) and are incompatible with the pressure reversal of anesthesia. The physical meaning of the pressure reversal of anesthesia is described, and the absolute necessity of the presence of excess volume for pressure to antagonize anesthesia is discussed. Excess volume expansion per se may not be the cause of anesthesia, but the mechanism by which the excess volume is created must be the key event that induces anesthesia. The mean excess volume hypothesis postulates that the size of the membrane is irrelevant to anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)