Shao-Mu Ma

Infrared spectra of phospholipid membranes: interfacial dehydration by volatile anesthetics and phase transition

Fourier-transform infrared attenuated total reflection (ATR) spectroscopy was used to study the effect of volatile anesthetics on fully hydrated dipalmitoylphosphatidylcholine (DPPC) vesicle membranes. The main phase transition was monitored by the change in the C-H2 asymmetric stretching frequencies of the lipid tails. The surface property was analyzed by the changes in the P = O stretching, (CH3)3-N+ stretching of the hydrophilic head, and C = O stretching of the glycerol skeleton. The partial pressures of those agents that decreased the transition temperature 1.0 C degree were halothane 0.75, enflurane 1.90 and CCl4 0.85 kPa. At a 2:1 lipid/anesthetic mole ratio, the polar anesthetics, halothane and enflurane, increased the ratio of (P = O stretching band area)/((CH3)3-N+ stretching band area) by 26.3% and 21.1%, respectively, whereas apolar CCl4 increased it 10.5%. The water molecules bound to the P = O moiety are apparently replaced by the anesthetic molecules. The deconvoluted C = O spectra showed two peaks: free sn-1 that is closer to the lipid core and hydrogen-bonded sn-2 that is closer to the polar head. Addition of halothane and enflurane, but not CCl4, increased the number of peaks to three. The third peak is free sn-2, formed by disrupting hydrogen-bonding to water. Because the temperature-induced spectral change was limited to C-H2 stretching at the main phase transition, the effects of anesthetics on the lipid membrane structure are not identical to temperature elevation. Among anesthetics, the effects of apolar and polar molecules on the interfacial properties are different.

Membrane-buffer partition coefficients of tetracaine for liquid-crystal and solid-gel membranes estimated by direct ultraviolet spectrophotometry

The membrane-buffer partition coefficient of tetracaine was measured by direct ultraviolet spectrophotometry in dimyristoylphosphatidylcholine unilamellar liposomes at temperatures above and below the main phase transition. The partition coefficients of uncharged tetracaine to solid-gel (18 degrees C) and liquid-crystal (30 degrees C) membranes were 6.9 x 10(4) and 1.2 x 10(5), respectively. Despite the general assumption that local anesthetic binding to the solid membrane is negligible, this study showed that the solid membrane binding amounts to 57.5% of the liquid membrane binding. Binding of the charged form to the liquid or solid membrane was not detectable under the present experimental condition of 0.03 mM tetracaine bulk concentration. The present method measures metachromasia of local anesthetics when bound to lipid membranes. Its advantage is that the separation of the vesicles from the solution is not required. A linearized equation is presented that estimates the partition coefficient or binding constant graphically from a linear plot of the absorbance data. The method is applicable for estimation of drug partition when a measurable spectral change occurs due to complex formation.

Significant‐Structure Theory of Binary Mixtures. II

The significant‐structure theory has been successfully applied to the three binary systems involving carbon tetrachloride, benzene, and cyclohexane. In the first paper, the system carbon tetrachloride—cyclohexane was discussed. In this paper the other two systems, carbon tetrachloride—benzene and cyclohexane—benzene, are considered. The excess properties have been calculated on mixing at constant pressure as well as on mixing at constant volume. By taking account of the fact that the parameters in our theory are concentration dependent, a partition function for mixtures can be formulated in a similar way to those for single liquids.

Temperature dependence of rate constants of thermal activated processes and vibrational relaxation in starvation kinetics

Abstract The purpose of this paper is to study the conditions under which the rate constant exhibits the Arrhenius type of temperature dependence and the damping effect on the rate constant. According to the starvation kinetics, the rate of reaction is determined by the rate of energy flow in the high temperature range. We shall show that the rate of energy flow (vibrational relaxation) reaches a finite limit in the high temperature condition.

Thermodynamic properties of solid C2H4

The significant structures procedure of liquids has been used to calculate the thermodynamic properties of solid C(2)H(4). Two degeneracy terms were used to describe the behavior in the vicinities of the two phase transitions. The calculated entropy and specific heat agree well with experimental results from a few kelvins to the melting point. Less satisfactory agreement is obtained for compressibility and thermal expansion coefficients. This simple model represents surprisingly well the phase transitions in the solid state.

Application of significant structure theory of liquids to critical phenomena. Calculation of critical-point exponents

Abstract Three critical-point exponents β, δ, γ and the corresponding coefficients B, D and G are calculated using significant structure theory. The results are compared with those obtained from the van der Waals equation, Berthelots equation and the Dieterici equation. The significant structure theory and the van der Waals equation behave similarly in the critical region. All these equations of state predict a finite Cν at the critical point.