Molecular and component volumes of saturated n-alkanols in DOPC+DOPS bilayers.
The volumetric properties of fluid bilayers consisting of dioleoylphosphatidylcholine (DOPC, 96wt%) and dioleoylphosphatidylserine (DOPS, 4wt%) with incorporated saturated n-alkanols (CnOH, n=10-16 is the even number of carbons in alkyl chain) were studied by vibrating tube densitometry. The mixing of DOPC and DOPS was found to be ideal and the molecular volumes of pure lipids V(DOPC) and V(DOPS) are additive in mixed bilayers. The increase of V(DOPS) with temperature was steeper than that of V(DOPC) as quantified by significantly higher coefficient of isobaric thermal expansivity gamma. This difference is supposed to be related to the high thermal expansivity of the serine headgroup. The molecular volumes of lipids and CnOH (V(CnOH)) in fluid DOPC+DOPS bilayers are constant and additive within error limits for n=12 and 16 and for the CnOH mole fractions in the lipid bilayer x(AL)<or=0.5 and x(AL)<or=0.3, respectively. In homologous series of CnOHs incorporated into DOPC+DOPS bilayer, the V(CnOH) volume increases linearly with the CnOH chain length n at x(AL)=0.29. From this dependence obtained at several temperatures, the component volume of the CnOH hydroxyl group V(OH) was calculated and found to decrease between 20 degrees C and 51 degrees C while the component volume of the CnOH methylene group V(CH2) increases with temperature. The excess molecular volume, DeltaV, for the transfer of CnOH into the DOPC+DOPS bilayers display a biphasic dependence on the alkyl length, n, with a minimum for n=12. When calculated with respect to the pure CnOH, DeltaV is negative for homologs with n>8.
Klacsová
Mária
M
Department of Nuclear Physics and Biophysics, Faculty of Mathematics, Physics and Informatics, Comenius University, SK-842 48 Bratislava, Slovakia. klacsova@fpharm.uniba.sk
Westh
Peter
P
Balgavý
Pavol
P
D000438:Alcohols / Q000737:chemistry*; D003720:Densitometry; D008051:Lipid Bilayers / Q000737:chemistry*; D056004:Molecular Dynamics Simulation; D010713:Phosphatidylcholines / Q000737:chemistry*; D010718:Phosphatidylserines / Q000737:chemistry*; D013696:Temperature
D000438:Alcohols; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D010718:Phosphatidylserines; C042511:1,2-dioleoylphosphatidylserine; C017251:1,2-oleoylphosphatidylcholine