Nature of the thermal pretransition of synthetic phospholipids: dimyristoyl- and dipalmitoyllecithin

Abstract

The hydrated synthetic lecithins, dimyristoyl and dipalmitoyllecithins, undergo two thermal transitions, a broad low enthalpy "pretransition" prior to the sharp first-order "chain-melting" transition. Both phospholipids exhibit the same temperature-dependent structural changes associated with the thermal pretransition. At low temperatures, below the pretransition, a one-dimensional lamellar lattice is observed. The hydrocarbon chains are fully extended and tilted with respect to the plane of the lipid bilayer. The hydrocarbon chain packing displays a temperature dependence and the angle of tilt of the hydrocarbon chains decreases with increasing temperature, reaching a minimum value of 30 degrees at the pretransition temperature of both lecithins. The pretransition is associated with a structural transformation from a one-dimensional lamellar to a two-dimensional monoclinic lattice consisting of lipid lamellae distorted by a periodic ripple. The hydrocarbon chains remain tilted in the temperature range intermediate between the pretransition and chain-melting transition. The cell parameters of this two-dimensional lattice exhibit a compositional dependence. The a parameter (proportional to the lamellar repeat distance) increases with increasing water content, while the b parameter (a measure of the ripple periodicity) decreases with increasing water content. At the chain-melting transition, the hydrocarbon chains of the phospholipid melt and assume a liquid-like conformation and the lattice reverts to one-dimensional lamellar. These structural changes observed for dimyristoyl- and dipalmitoyllecithins may be a common feature of all synthetic lecithins exhibiting a thermal pretransition. The appearance of the pretransition and accompanying two-dimensional may arise from specific interactions between the choline moiety of the polar head group and the structured water matrix surrounding it.

The effects of cholesterol and β-sitosterol on the structure of saturated diacylphosphatidylcholine bilayers

“…3b), the values of t p & 11-13°C and t m & 23-24°C being in good agreement with data from the literature (Cevc 1993;Janiak et al 1976). In the fluid phase at 33°C, d = 6.26 nm, similar to 6.27 nm at 30°C reported by Nagle and TristramNagle (2000).…”

“…In the disordered fluid L d phase, the repeat distance diminishes slowly. This temperature dependence of d is typical of DPPC in excess water (Janiak et al 1976;Tenchov et al 1989). At 50°C, d = 6.77 nm, a value similar to that (6.70 nm) mentioned by Nagle and TristramNagle (2000).…”

Interaction of a human plasma lipid transfer protein complex with lipid monolayers

“…The assumption that neutral lipids are miscible with phospholipids is consistent with the fact that cholesteryl esters can be dispersed in either monolayer [6][7][8][9] or bulk phospholipid systems [10][11][12][13]. Smaby et al [7] demonstrated that cholesteryl oleate and dioleoylphosphatidylcholine form stable monolayers with a solubility limit of 43 tool% for the cholesteryl ester.…”

“…Smaby et al [7] demonstrated that cholesteryl oleate and dioleoylphosphatidylcholine form stable monolayers with a solubility limit of 43 tool% for the cholesteryl ester. According to Janiak et al [11], a bulk lipid system of hydrated dimyristoylphosphatidylcholine accommodates less cholesteryl ester; the ternary system was completely miscible to approx. 5 mol% of cholesteryl myristate.…”

Coexisting Stripe- and Patch-Shaped Domains in Giant Unilamellar Vesicles

“…It is established that DPPC bilayers undergo two thermal transitions above room temperature (24). One is a low-enthalpy pretransition and the other is a high-enthalpy chain melting transition (29). Below the pretransition temperature, DPPC forms a two-dimension lamellar structure in which the hydrocarbon chains are fully extended in an all-trans conformation and tilted with respect to the plane of the bilayer.…”