Untitled

Abstract

Molecular dynamics simulations of three model lipid monolayers of 2,3-diacyl-D-glycerolipids, that contained stearoyl (18:0) in the position 3 and oleoyl (18:ω9cis), linoleoyl (18:2ω6cis), or linolenoyl (18:3ω3cis) in the position 2, have been carried out. The simulation systems consisted of 24 lipid molecules arranged in a rectangular simulation cell, with periodic boundary conditions in the surface plane. 1 nanosecond simulations were performed at T = 295 K. C-C and C-H bond order parameter profiles and the bond orientation distributions about the monolayer normal have been calculated. The relation of the distributions to the order parameters was analyzed in terms of maxima and widths of the distributions. The cis double bond order parameter is found to be higher than those of adjacent single C-C bonds. The widths of the two distributions of C-H bonds of the cis double bond segment in di- and triunsaturated molecules are much smaller than that obtained for methylene group located between the double bonds. The bond orientation distribution function widths depend on both the segment location in the chain and the segment chemical structure.

Computer simulation study of intermolecular voids in unsaturated phosphatidylcholine lipid bilayers

“…However, with increasing lipid unsaturation the fraction of the free volume is found to increase in the middle of the membrane and decrease in the outer part of the apolar phase. This finding is consistent both with our previous results 59, [73][74][75] and with experimental data, 76,77 and can be explained by the fact that due to the increasing flexibility of the hydrocarbon tails when containing more methylene-interrupted C v C double bonds [73][74][75] these unsaturated tails do not extend to the middle of the membrane. 59 The analysis of the percolation of the voids has revealed that the preformed cross-membrane channels are not broad enough to let small molecules, such as water, go readily through them, however, they are likely to facilitate the permeation of such molecules across the membrane.…”

“…This result indicates that the central part of the bilayer is rather compact, i.e., there are considerably less voids among the CH 3 groups than among the chains of CH 2 groups. However, the central part of the membrane becomes more loosely packed with increasing unsaturation of the lipid molecules, in accordance with our previous finding that polyunsaturated sn-2 chains are characterized by very high equilibrium flexibility, [73][74][75] and hence do not penetrate as deep into the bilayer as the saturated sn-1 chains even if they consist of more carbon atoms. 59 This high flexibility of the chains consisting of methylene-interrupted C v C double bonds can also explain the deepening of the minimum of the profiles at the outer part of zone 1 with increasing lipid unsaturation.…”

“…This result is in agreement with our findings above, and can again be explained by the increasing flexibility of the increasingly unsaturated chains consisting of methyleneinterrupted C v C double bonds. [73][74][75] It is also in accordance with experimental results obtained for membranes of similar lipid molecules, indicating that the water permeability of fluid bilayers increases with increasing unsaturation of the hydrocarbon chains. 76,77…”

Computer simulation of lipid membranes: Methodology and achievements

“…The PU FA tails of lipids are of great importance for the structure and functioning of biomembranes [179][180][181][182][183][184][185][186]. Docosahexaenoic acid, 22 : 6(n 3)cis, is the longest and most unsaturated FA commonly found in nature.…”

“…Many theoretical investigations (during the period of last 7 years) were devoted to the various properties of unsaturated and PU FA chains of different lipid molecules in bilayers; several FA chains most fre quently studied by molecular simulations and corre sponding references are enumerated below: 22 : 6(n 3)cis [181,[192][193][194][195][196][197][198][199][200][201][202][203][204], 22 : 5(n 3)cis [192], 20 : 4(n 6)cis [64, 195, 198, 200-203, 205, 206], 18 : 3(n 3)cis [195,198,200,201,203], 18 : 2(n 6)cis [64,195,198,[200][201][202][203]207], 18 : 1(n 9)cis [54, 55, 59, 64, 74, 88, 181, 194-196, 198, 200-203, 205, 208-231].…”