Biphasic effect of long-chain n-alkanols on the main-phase transition of phospholipid vesicle membranes

Abstract

The action of n-alkanols upon the transition temperature of phospholipid membranes between liquid-crystalline and solid-gel phases was not a monotonic function of alkanol concentrations. All n-alkanols tested (1 -nonanol, 1 -decanol, 1 -undecanol, 1 -dodecanol, and 1-tridecanol) depressed the transition temperature at low concentrations and elevated it at high concentrations. There were no n-alkanols that exclusively depressed or elevated the transition temperature. The observed phase equilibria were interpreted according to phase diagrams. The diagrams expressed a minimum point, suggesting that the mixing was not ideal. Although a possibility cannot be entirely ruled out that the minimum point has a finite width to form a eutectic mixture in a narrow concentration range, it appears that all n-alkanols form uniform membranes with the phospholipids under the present experimental conditions. The shape of these phase diagrams was similar to that of liquid-gas equilibria, which form azeotropes. The position of the minimum in phase diagrams was shifted to lower alkanol concentrations when longer alkanols were used; when the chain length exceeded 10-12 carbon atoms, the effect appeared to be predominantly temperature elevation.

Miscibility of phosphatidylcholine binary mixtures in unilamellar vesicles: Phase equilibria

“…For this reason, the optical method was mainly used to analyze the phase behavior. The agreement between differential scanning microcalorimetry and the optical method was excellent as previously reported (Kamaya et al, 1984), when compared at 100 mM phospholipid suspensions.…”

“…After adding an appropriate amount of water to make the phospholipid concentration about 1 mM for a dilute solution, phospholipids were suspended by a Vortex Mixer (Fisher, Pittsburgh, Pa.). Unilamellar vesicles were prepared from the vortex suspension by ultrasonic irradiation in a cup-horn of a Branson Sonifier W185 (Danbury, Conn.I at above the phase-transition temperature as previously reported (Kamaya et al, 1984). The preparation was aged at 4~ for one week to obtain relatively homogeneous size distribution by fusing vesicles, as described by Wong et al (1982).…”

Dose-dependent nonlinear response of the main phase-transition temperature of phospholipid membranes to alcohols

“…We found (Kamaya et al, 1984), however, that elevation and depression of the transition temperature were not a simple function of the alkanol alkyl chain-length; the transition temperature was nonlinearly related to the alkanol concentrations and the effect was biphasic. As an example, 1-decanol decreased the transition temperature of dipalmitoylphosphatidylcholine membranes at low concentrations but elevated it when the alkanol/lipid mole ratio exceeded about 0.3.…”

“…It has been reported (Eliasz et al, 1976;Lee, 1976;Jain & Wu, 1977;Pringle & Miller, 1979;Kamaya et al, 1984) that shorter alkyl-chain l-alkanols depressed whereas longer ones elevated the main transition temperature of phospholipid membranes. The crossover from depression to elevation of the transition temperature occurred at about the chainlength of 10 to 12 carbon atoms.…”

Molecular and component volumes of saturated n-alkanols in DOPC+DOPS bilayers

“…Amphiphilic molecules, including n-alkanols, partitioning into phospholipid bilayers affect their physico-chemical properties, such as phase transition temperature (Lee, 1976;Pringle and Miller, 1979;Gallová et al, 1992;Kamaya et al, 2002), structural polymorphism (Hornby and Cullis, 1981;Klacsová et al, 2009), bilayer structural parameters (Uhríková et al, 2002;Karlovská et al, 2004;Griepernau et al, 2007), ordering of acyl chains (Westerman et al, Abbreviations: DOPC, 1,2-dioleoyl-sn-glycero-3-phosphocholine; DOPS, 1,2-dioleoyl-sn-glycero-3-phosphoserine; DOPC + DOPS, homogeneous mixture of DOPC (96%, w/w) and DOPS (4%, w/w); DMPC, 1,2-dimyristoyl-sn-glycero-3-phosphocholine; DPPC, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine; POPC, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine; PC, phosphatidylcholine; EYPC, egg yolk phosphatidylcholine; CnOH, alkan-1-ol (n is the number of carbons in the aliphatic chain); SAXD, small-angle X-ray diffraction; WAXD, wide-angle X-ray diffraction; SANS, small-angle neutron scattering; MD, molecular dynamics.…”