Membrane pretransition temperature

The effect of halo thane (CF3CHBrCl) on the lateral surface conductance and membrane hydration has been studied by Yoshida and coworkers [41]. Below the pretransition temperature, the activation energy of the ion movement (H30++0FT) was 18.1 kj/mol, which corresponds to that of the spin-lattice relaxation time of water (18kJ/mol) above pretransition the activation energy increased to 51.3 kj/mol. Halothane did not show any effect on the ion movement when the temperature was below the pretransition temperature. When the temperature exceeded the pretransition temperature, the authors observed at 0.35 mM halothane (equilibrium concen-... 

The rote of cholesterol in the fluidity of biological membranes is characterized as essential. Cholesterol is a silent molecule and in the case of lipid bilayers and liposomes it is included into bilayers to control the rate of the release of encapsulated molecules or to influence the stability of liposomes. The addition of cholesterol in lipid bilayers composed of DPPC, at concentrations more than 20%, results in the decrease of the Tin and elimination of the pretransition temperature. 

Furthermore, DSC can be useful for modeling the toxic effects of xenobiotics such as phenols and especially chlorinated phenols. A detailed study was performed by Smejtek et al. [44]. Among other observations, it was found that pentachlorophenol induces changes in the -potential and the gel to fluid transition temperature in model lecithin membranes. The ionized form was more potent in abolishing pretransition. The unionized species induced an increase in melting transition width (Figure 3.8). 

Polar carotenoids decrease cooperativity of the main thermotropic phase transition and the pretransition of synthetic phosphatidylcholines while incorporated to membranes at low concentrations. This effect is realized by increasing motional freedom of lipid molecules in the ordered phase and decreasing the rate of lipid motion in the fluid phase at temperatures above the phase transition. The decrease of the cooperativity of the phase transition is a concentration-dependent process and leads to a complete removal of the phase transition at concentrations as high as 10 mol% carotenoid with respect to lipid (Subczynski et al. 1992, 1993 Strzalka and Gruszecki, 1994). Eigure 6 presents the effect ofviolaxanthin on the phase transition of the series of PC membranes monitored by 5-SASL ESR technique. 

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