MOLECULAR ORDER AND DYNAMICS OF DIPHYTANYLGLYCEROL PHOSPHOLIPIDS - A H-2-NMR AND P-31-NMR STUDY

2H NMR and 31P-NMR have been applied to study the conformational and organizational properties of synthetically deuterated dihexadecylglycerol phosphate and diphytanylglycerol phosphate, and of biosynthetically deuterated diphytanylglycerol lipid analogues, predominantly phosphatidylglycerol phosphate (PGP) and sulfated triglycosyl diphytanylglycerol (GLS from the extreme halophile, Halobacterium cutirubrum. Comparison of the 2H-NMR data derived from phytanylglycerol lipids and n-alkylglycerol lipids, with data previously reported for n-acylglycerol lipids, indicated that both the hydrocarbon-glycerol ether linkage and the presence of the branch methyl groups have a marked effect on the physical properties (both conformation and dynamics) of the hydrocarbon chains. The branched chains in the diphytanylglycerol lipids are more disordered than the n-alkyl or n-acyl chains of conventional lipids, as evidenced by narrower quadrupolar splittings (< 25 kHz), and the rates of motion responsible for relaxation are much slower (spin lattice relaxation time, Tl, values of 4.8 to 10.3 ms; correlation time for segmental reorientation, τc = 2.1 × 10-9 s at 8°C). Over the temperature range - 10 to 50°C there is no evidence from the NMR data for a phase transition. The thermal response is weak, suggesting that the branched phytanyl chains of theHalobacteria lipids perform a regulatory function on the fluidity of the membranes, as does cholesterol in mammalian systems. © 1990.