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      Molecular dynamics of anhydrous glycolipid self-assembly in lamellar and hexagonal phases

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          Abstract

          The molecular dynamics of a synthetic branched chain glycolipid, 2-decyl-tetradecyl-β- d-maltoside (C 14-10G 2), in smectic and columnar liquid crystal phases.

          Abstract

          The molecular dynamics of a synthetic branched chain glycolipid, 2-decyl-tetradecyl-β- d-maltoside (C 14-10G 2), in the dry assemblage of smectic and columnar liquid crystal phases has been studied by dielectric spectroscopy as a function of frequency and temperature during the cooling process. Strong relaxation modes were observed corresponding to the tilted smectic and columnar phases, respectively. At low frequency (∼900 Hz to 1 kHz) in the smectic phase, Process I* was observed due to the tilted sugar bilayer structure. The process continued in the columnar phase (Process I) with an abrupt dynamic change due to phase transition in the frequency range of ∼1.3 kHz to 22 kHz. An additional process (Process II) was observed in the columnar phase with a broader relaxation in the frequency range of ∼10 Hz to 1 kHz. A bias field dependence study was performed in the columnar phase and we found that the relaxation strength rapidly decreased with increased applied dc bias field. This relaxation originates from a collective motion of polar groups within the columns. The results of dielectric spectroscopy were supported by a molecular dynamics simulation study to identify the origin of the relaxation processes, which could be related to the chirality and hydrogen bonds of the sugar lipid.

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          Natural surfactants

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            Is Open Access

            Anomalous diffusion of phospholipids and cholesterols in a lipid bilayer and its origins

            Combining extensive molecular dynamics simulations of lipid bilayer systems of varying chemical composition with single-trajectory analyses we systematically elucidate the stochastic nature of the lipid motion. We observe subdiffusion over more than four orders of magnitude in time, clearly stretching into the sub-microsecond domain. The lipid motion delicately depends on the lipid chemistry, the lipid phase, and especially on the presence of cholesterol. We demonstrate that fractional Langevin equation motion universally describes the lipid motion in all phases including the gel phase, and in the presence of cholesterol. The results underline the relevance of anomalous diffusion in lipid bilayers and the strong effects of the membrane composition.
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              Molecular mechanism for lipid flip-flops.

              Transmembrane lipid translocation (flip-flop) processes are involved in a variety of properties and functions of cell membranes, such as membrane asymmetry and programmed cell death. Yet, flip-flops are one of the least understood dynamical processes in membranes. In this work, we elucidate the molecular mechanism of pore-mediated transmembrane lipid translocation (flip-flop) acquired from extensive atomistic molecular dynamics simulations. On the basis of 50 successful flip-flop events resolved in atomic detail, we demonstrate that lipid flip-flops may spontaneously occur in protein-free phospholipid membranes under physiological conditions through transient water pores on a time scale of tens of nanoseconds. While the formation of a water pore is induced here by a transmembrane ion density gradient, the particular way by which the pore is formed is irrelevant for the reported flip-flop mechanism: the appearance of a transient pore (defect) in the membrane inevitably leads to diffusive translocation of lipids through the pore, which is driven by thermal fluctuations. Our findings strongly support the idea that the formation of membrane defects in terms of water pores is the rate-limiting step in the process of transmembrane lipid flip-flop, which, on average, requires several hours. The findings are consistent with available experimental and computational data and provide a view to interpret experimental observations. For example, the simulation results provide a molecular-level explanation in terms of pores for the experimentally observed fact that the exposure of lipid membranes to electric field pulses considerably reduces the time required for lipid flip-flops.
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                Author and article information

                Journal
                PPCPFQ
                Physical Chemistry Chemical Physics
                Phys. Chem. Chem. Phys.
                Royal Society of Chemistry (RSC)
                1463-9076
                1463-9084
                2016
                2016
                : 18
                : 22
                : 15182-15190
                Affiliations
                [1 ]Low Dimensional Materials Research Center
                [2 ]Faculty of Science
                [3 ]University Malaya
                [4 ]50603 Kuala Lumpur
                [5 ]Malaysia
                [6 ]Fundamental and Frontier Science of Self-Assembly Center
                [7 ]Dipartimento di Chimica Industriale “Toso Montanari” viale Risorgimento 4 Universita' di Bologna
                [8 ]40136 Bologna
                [9 ]Italy
                Article
                10.1039/C6CP00583G
                e9bec50e-b3a5-4129-9fdb-22f57a213f14
                © 2016
                History

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