Model-free estimation of the effective correlation time for C-H bond reorientation in amphiphilic bilayers: 1H-13C solid-state NMR and MD simulations

被引:26
作者
Ferreira, Tiago Mendes [1 ,2 ]
Ollila, O. H. Samuli [2 ,3 ]
Pigliapochi, Roberta [2 ,4 ]
Dabkowska, Aleksandra P. [2 ]
Topgaard, Daniel [2 ]
机构
[1] Univ Paderborn, Dept Chem, D-33098 Paderborn, Germany
[2] Lund Univ, SE-22100 Lund, Sweden
[3] Aalto Univ, Dept Biomed Engn & Computat Sci, Helsinki Biophys & Biomembrane Grp, Espoo, Finland
[4] Univ Cambridge, Dept Chem, Cambridge CB2 1EW, England
基金
瑞典研究理事会;
关键词
MOLECULAR-DYNAMICS SIMULATION; MAGNETIC-RESONANCE RELAXATION; LIPID-BILAYER; PHOSPHOLIPID-MEMBRANES; CONSTANT-PRESSURE; ORDER; EFFICIENT; LIQUID; MOTION; RANGE;
D O I
10.1063/1.4906274
中图分类号
O64 [物理化学(理论化学)、化学物理学];
学科分类号
070304 ; 081704 ;
摘要
Molecular dynamics (MD) simulations give atomically detailed information on structure and dynamics in amphiphilic bilayer systems on timescales up to about 1 mu s. The reorientational dynamics of the C-H bonds is conventionally verified by measurements of C-13 or H-2 nuclear magnetic resonance (NMR) longitudinal relaxation rates R-1, which are more sensitive to motional processes with correlation times close to the inverse Larmor frequency, typically around 1-10 ns on standard NMR instrumentation, and are thus less sensitive to the 10-1000 ns timescale motion that can be observed in the MD simulations. We propose an experimental procedure for atomically resolved model-free estimation of the C-H bond effective reorientational correlation time tau(e), which includes contributions from the entire range of all-atom MD timescales and that can be calculated directly from the MD trajectories. The approach is based on measurements of C-13 R-1 and R-1 rho relaxation rates, as well as H-1-C-13 dipolar couplings, and is applicable to anisotropic liquid crystalline lipid or surfactant systems using a conventional solid-state NMR spectrometer and samples with natural isotopic composition. The procedure is demonstrated on a fully hydrated lamellar phase of 1-palmitoyl-2-oleoyl-phosphatidylcholine, yielding values of tau(e) from 0.1 ns for the methyl groups in the choline moiety and at the end of the acyl chains to 3 ns for the g(1) methylene group of the glycerol backbone. MD simulations performed with a widely used united-atom force-field reproduce the tau(e)-profile of the major part of the acyl chains but underestimate the dynamics of the glycerol backbone and adjacent molecular segments. The measurement of experimental tau(e)-profiles can be used to study subtle effects on C-H bond reorientational motions in anisotropic liquid crystals, as well as to validate the C-H bond reorientation dynamics predicted in MD simulations of amphiphilic bilayers such as lipid membranes. (C) 2015 AIP Publishing LLC.
引用
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页数:10
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