Gel-liquid-crystalline phase transition

An increase indicates a broadening lifetime distribution. Gel-liquid-crystalline phase transition. 

Koynova R, Wang L, MacDonald RC (2007) Synergy in lipofection by cationic lipid mixtures superior activity at the gel-liquid crystalline phase transition. J Phys Chem B 111 7786-7795... 

A later publication from the same group [153] reporting on 31P- and 2H-NMR and DSC studies on zwitterionic and anionic phospholipids in the absence and presence of doxombicin (adriamycin) described different results [152], Doxorubicin had a stronger disordering effect on the membrane of lipid mixtures enriched with anionic lipids. However, extensive segregation of DOPE and DOPA or DPS was not observed even under conditions of Hlrphase formation . According to the authors, the reason for this discrepancy was that in the earlier paper the phase separation was obtained with membranes subject to gel-liquid crystalline phase transition , which was, however, discounted in the first paper. 

Kariel N, Davidson E, Keough KM. Cholesterol does not remove the gel-liquid crystalline phase transition of phosphatidylcholines containing two polyenoic acyl chains. Biochim Biophys Acta 1991 1062 70-76. 

Calorimetry and Raman spectroscopy were used to measured the gel state of cerebrosides from bovine brain.The enthalpy of the gel-liquid crystalline phase transition for kerasin (15.8 kcal moF ) was markedly higher than that for phrenosin and unfractionated bovine brain cerebrosides ca. 7 kcal moF ). 

Small unilamellar vesicles (SUV)(hydrodynamic diameter, Dft < 50 nm) are not adequate for the purpose of site dissection. With total internal volumes seldom exceeding 11/mole of amphiphile in the bilayer, SUV s do not permit the entrapment of analytically convenient amounts of substrate. Larger (DODA)C and DCP vesicles (Dh > 300 nm), LUV, were first obtained by chloroform vaporization at 70 °C [36]. (DODA)C LUV have a sharp gel-liquid crystalline phase transition temperature (Tc), an internal volume of 9 + 11/mole and exhibit ideal osmotic behavior towards KCl (0-0.050 M) and sucrose [36b]. LUV of comparable properties, obtained by dichloro-methane vaporization, at 40 °C and membrane extrusion. 

J Suurkuusk, BR Lentz, Y Barenholz, RL Biltonen, TE Thompson. A calorimetric and fluorescent probe study of the gel-liquid crystalline phase transition in small, single-lamellar dipahnitoylphosphatidylcholine vesicles. Biochemistry 75 1393-1401 (1976). 

Very interesting shapes can be observed in nonphospholipid diacyl surfactant systems [66]. In polymerizable lipids, for instance, tubular (with either circular or spiral cross-section) structures are often observed in the gel phase, which reversibly transform into liposomes above T. (the main gel-liquid crystalline phase transition temperature). Upon electrical pulses or the addition of polymers novel structures with novel morphologies, such a helices and strings-of-pearl, can be observed [67]. 

Computer simulations of both equilibrium and dynamic properties of small solutes indicate that the solubility-diffusion model is not an accurate approximation to the behavior of small, neutral solutes in membranes. This conclusion is supported experimentally [57]. Clearly, packing and ordering effects, as well as electrostatic solute-solvent interactions need to be included. One extreme example are changes in membrane permeability near the gel-liquid crystalline phase transition temperature [56]. Another example is unassisted ion transport across membranes, discussed in the following section. 

A reduction in the chain length of the sn-2 fatty acid has a greater effect in this respect than does a comparable reduction at the sn-1 position. The gel— liquid crystalline phase transition temperature of the two positional isomers of PC containing C-14 and C-16 fatty acyl chains compared to DPPC is (DPPC) 41°C > T, (MPPC) 34°C > (PMPC) 27°C (22). 

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