ISSN:
1075-4261
Keywords:
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Biology
,
Physics
Notes:
Effects of α-tocopherol (α-T) and α-tocopheryl acetate (α-TA) on dipalmiroyl-ph-phatidylcholine (DPPC) multilayers have been investigated by Fourier transform infrared and Raman spectroscopies. Earlier results have been confirmed by the temperature profiles built with the Raman intensity height ratios R = I2880/I2850 and r = I2935/I2880; both α-T and α-TA broaden the main phase transition, and the onset of the transition temperature Tc decreases as the concentration of α-T and α-TA increases. Effects are weaker in the case of α-TA. It has been shown that the chain packing is diminished in the gel phase and that gauche rotamer formation is promoted by α-T, and to a smaller extent by α-TA. The number of gauche bonds introduced by α-T and α-TA has been estimated by the measure of the intensity of the CH2 wagging progression modes. It seems also, that in the gel phase, α-T slightly increases the methyl end chain mobility, while α-TA decreases it. Moreover, α-T perturbs the infrared (IR) carbonyl stretching vibration (vC=0) of DPPC, whereas α-TA does not. This perturbation, which can explain the thermotropic behavior of DPPC/α-T multilayers, may have three origins: H-bonds between α-T and DPPC, conformational changes of the interfacial region, or increase of the hydration (possibility of dihydrates). For comparison, IR vC=0 spectra of palmiroyl-oleyl-phosphatidylcholine (POPC) have been recorded as well. POPC certainly has a different conformation of the glycerol backbone than DPPC, with a larger molecular area. The example of POPC proves that H-bonds, which certainly occur in a DPPC/α-T mixture, are not the single explanation for changes appearing in the interfacial region of DPPC multilayers, on incorporation of α-T. In any case, α-T seems to locate nearer the polar region of the membrane than α-TA, as seen by IR and Raman spectroscopy. © 1996 John Wiley & Sons, Inc.
Additional Material:
13 Ill.
Type of Medium:
Electronic Resource
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