EFFECT OF GLYCEROL ON THE TRANSLATIONAL AND ROTATIONAL MOTIONS IN LIPID BILAYERS STUDIED BY PULSED-FIELD GRADIENT H-1-NMR, EPR AND TIME-RESOLVED FLUORESCENCE SPECTROSCOPY

Glycerol can replace water in both lipid vesicles and lyotropic liquid -crystalline phases. 1,2-Dioleoyl-sn-glycero(3)phosphocholine (DOPC) f orms a lamellar (L(a)lpha) liquid-crystalline phase in arbitrary mixtu res of glycerol and water (Biochim. Biophys. Acta, 1993, 1149, 285.). Monoolein (MO) forms L(alpha) and also cubic liquid-crystalline phases in glycerol-water mixtures. The present study is focussed on characte rizing the influence of glycerol on the molecular dynamics in the lipi d bilayer. By EPR and time-resolved fluorescence spectroscopy we measu re the rotational mobility of spin-labelled fatty acids propyl)-4,4-di methyl-2-tridecyloxazolidin-3-yloxyl (5-DS) and etradecyl)-2-ethyl-4,4 -dimethyloxazolidin-3-yloxyl (16-DS)] and a hydrophobic fluorophore, 2 ,5,8,11-tetra-tert-butylperylene (TBPe), respectively. The translation al diffusion of MO in the cubic phase is obtained by pulsed-field grad ient H-1 FT NMR experiments. The rotational rate of 16-DS and TBPe dec reases continuously with increasing glycerol concentration, being a fa ctor of 2-3 lower at 100% glycerol. A continuous decrease in the lipid translational diffusion coefficient, D, is also found with increasing glycerol content, so that D = 12.6 x 10(-12) m(2) s(-1) at 0% and D = 1.9 x 10(-12) m(2) s(-1) at 100% glycerol. The effects of glycerol on both the translational diffusion of the lipid in the bilayers and the rotational dynamics of the probe molecules residing in the interior o f the hydrophobic regions are ascribed to changes of the viscosity in the interbilayer regions.