Examining the origins of the hydration force between lipid bilayers using all-atom simulations.
Using 237 all-atom double bilayer simulations, we examined the thermodynamic and structural changes that occur as a phosphatidylcholine lipid bilayer stack is dehydrated. The simulated system represents a micropatch of lipid multilayer systems that are studied experimentally using surface force apparatus, atomic force microscopy and osmotic pressure studies. In these experiments, the hydration level of the system is varied, changing the separation between the bilayers, in order to understand the forces that the bilayers feel as they are brought together. These studies have found a curious, strongly repulsive force when the bilayers are very close to each other, which has been termed the "hydration force," though the origins of this force are not clearly understood. We computationally reproduce this repulsive, relatively free energy change as bilayers come together and make qualitative conclusions as to the enthalpic and entropic origins of the free energy change. This analysis is supported by data showing structural changes in the waters, lipids and salts that have also been seen in experimental work. Increases in solvent ordering as the bilayers are dehydrated are found to be essential in causing the repulsion as the bilayers come together.
Gentilcore
Anastasia N
AN
Department of Physiology, Johns Hopkins University, School of Medicine, Baltimore, MD, USA.
Michaud-Agrawal
Naveen
N
Crozier
Paul S
PS
Stevens
Mark J
MJ
Woolf
Thomas B
TB
D008051:Lipid Bilayers / Q000737:chemistry*; D008560:Membrane Fluidity; D008956:Models, Chemical; D008958:Models, Molecular; D008962:Models, Theoretical; D056004:Molecular Dynamics Simulation; D010713:Phosphatidylcholines / Q000737:chemistry; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D014867:Water
J Am Chem Soc. 2002 Jan 16;124(2):318-26
11782184
Nature. 1996 Jan 18;379(6562):219-25
8538786
J Chem Phys. 2005 Jun 22;122(24):244902
16035811
J Phys Chem B. 2005 Apr 7;109(13):6422-9
16851715
J Chem Phys. 2005 Dec 8;123(22):224702
16375490
J Chem Phys. 2006 Sep 7;125(9):094713
16965111
Biophys J. 2003 Sep;85(3):1647-55
12944279
Biophys J. 2003 Sep;85(3):1734-40
12944288
Biophys J. 1999 Apr;76(4):2081-9
10096903
Biophys J. 1977 May;18(2):209-30
861359
Biophys J. 2007 Jun 15;92(12):4369-78
17400691
J Mol Graph. 1996 Feb;14(1):33-8, 27-8
8744570
Chem Phys Lipids. 1991 May-Jun;58(1-2):1-5
1934192
Biophys J. 1994 May;66(5):1441-9
8061193
J Colloid Interface Sci. 1999 Dec 15;220(2):235-249
10607439
Biophys J. 2004 Jun;86(6):3772-82
15189873
Chem Phys Lipids. 1994 Apr 19;70(2):121-31
8033284
J Chem Phys. 2006 Jan 28;124(4):044709
16460202
Proc Natl Acad Sci U S A. 1979 Jun;76(6):2750-4
288063
Annu Rev Phys Chem. 1993;44:369-95
8257560
Biochemistry. 1985 Aug 13;24(17):4608-18
4063343
J Chem Phys. 2004 Dec 8;121(22):10847-51
15634036
Biophys J. 2001 Dec;81(6):3005-15
11720971
J Membr Biol. 2005 Dec;208(3):193-202
16604469
Phys Rev Lett. 2003 Oct 31;91(18):188102
14611319
Biophys J. 2004 Oct;87(4):2446-55
15454442
Langmuir. 2007 Jan 30;23(3):1388-93
17241063