Oleic acid phase transition temperature

The perturbation of the intercellular lipid bilayers in the stratum corneum seems to be the most important reason for the enhancing activity of fatty acids such as oleic acid. Oleic acid has been described to decrease the phase transition temperatures of the skin lipids... 

Several years ago, Chakrabarti et al. " described for the first time such a polymerization of RNA inside DMPC vesicles by polynucleotide phosphorylase. In these experiments, ADP was added externally to the enzyme-containing vesicles (this enzymatic reaction does not require template nucleic acids for initiation) and incubated at 23°C, the main phase transition temperature of DMPC. Because of these gel-to-liquid crystalline transitions of the bilayer, the vesicles could take up ADP from the external milieu, and the enzyme could produce poly (A). On the other hand, the enzyme could not leak out because of its size. Similar experiments were also carried out in our group by Walde et al. Here, the vesicles consisted of a single-chain amphiphile (oleic acid/oleate) that forms vesicles at a pH of about 8.0. ADP was shown to permeate across the oleic acid/oleate membrane and was incorporated inside the vesicles by polynucleotide phosphorylase to poly(A). 

The results presented here show that electrical pulsation causes reversible enhancement of peptide transport through human skin in vitro. In all cases, only intact peptide was measured. Moreover, the enhanced flux cannot be accounted for by increased current, and it is most likely due to increased ionic mobility of the peptide within the skin. Thus, electrical pulsation reversibly alters the ion-transport properties of skin. The rate-limiting barrier to skin transport of ionized compounds is the lipids of the stratum comeum. Alteration of stratum comeum lipids results in a significant increase in skin transport (Golden et al, 1987 Potts and Francoeur, 1990). For example, heating the skin to temperatures just above the stratum comeum lipid phase-transition temperature results in a 100-fold increase in sodium-ion conductivity. The sodium-ion conductivity returns to pretreatment values when the skin is cooled (Oh et al, 1993). Similarly, alteration of stratum comeum lipid stmcture with chemical perturbants such as oleic acid increases ion conductivity (Potts et al, 1992). The application of a transient electrical pulse to other lipid-based membranes creates a high-permeability state associated with the reversible formation of pores within the membrane (electroporation). Thus, it seems likely that electrical pulsation of human skin results in the formation of transient pores within stratum comeum lipids. 

Danger and Sekwen (20) investigated the effect of free fatty acids on the permeability of the 1,2-dimyristoyl-5 >72-glycero-3-phosphotidylcholine (DMPC) bilayer at the main phase transition. When vesicles were formed between DMPC and oleic acid, the phase transition temperature was reduced drastically, but at the phase transition from the gel to liquid crystalline phase, membrane permeability reaches a maximum. Saturated fatty acids did not have the same effect on the bilayer as unsaturated fatty acids, in that there was a reduced effect on the phase transition temperature. They also concluded that -bilayer flip-flop is at a maximum at the phase transition temperature of DMPC being in the millisecond range for oleic acid. DMPC was found to have a flip-flop rate of 4 h at the phase transition and even longer rates at other temperatures. 

Figure 9. NMR spectra of the plasma membranes of Acholeplasma laidlawii enriched in palmitic acid labeled at the 13-position (I3-Ai 16 0) and in oleic acid labeled at the 12-position (12-d2 18 1). Spectra were obtained at the growth temperature, 37°C. The temperatures of optimal growth, To, and the calorimetric gel to liquid crystal phase transition of the lipids in the membranes, T, are indicated. Details of sample preparation and spectral acquisition are given in Ref. 23 and 24.

Two glass transition temperatures are ascribed due to soft and hard segments in the case of PUs synthesized from oleic acid. Thus, a phase-separated morphology is suggested (17). 

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