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Variation in hydration forces between neutral phospholipid bilayers: evidence for hydration attraction.
R P Rand1, N Fuller, V A Parsegian
1Department of Biological Sciences, Brock University, St. Catharines, Ontario, Canada.
Biochemistry
|October 4, 1988
Summary
Hydration forces in lipid bilayers show diverse behaviors, with phosphatidylethanolamine (PE) and phosphatidylcholine (PC) exhibiting distinct interactions. This study reveals that variable attractive and repulsive hydration components explain the range of interbilayer spacings observed in neutral bilayers.
Area of Science:
- Biophysics
- Lipid bilayer dynamics
- Intermolecular forces
Background:
- Hydration forces are recognized as dominant in lipid hydrophilic surface interactions.
- Existing models of hydration and van der Waals forces do not fully explain observed differences in bilayer repulsion, particularly between phosphatidylethanolamine (PE) and phosphatidylcholine (PC).
Purpose of the Study:
- To investigate the structural parameters, hydration levels, and interbilayer forces of various neutral lipid lamellar phases.
- To understand the basis for diverse hydration behaviors observed in different lipid bilayers.
Main Methods:
- Analysis of structural parameters, hydration degrees, and interbilayer repulsive forces for 1-palmitoyl-2-oleoyl-PE (POPE), egg PE, transphosphatidylated egg PE (egg PE-T), methylated egg PE-T variants (MMPE, DMPE), 1-stearoyl-2-oleoyl-PC (SOPC), and their mixtures.
- Application of the Marcelja and Radic formalism to estimate both repulsive and attractive components of hydration forces.
Main Results:
- Significant differences in hydration levels, hydration force coefficients, and decay lengths were observed between POPE and SOPC bilayers.
- Mixing SOPC with POPE led to disproportionate increases in hydration.
- Methylation of egg PE-T progressively altered its hydration and repulsive properties towards those of egg PC, with a single methylation having a substantial effect.
Conclusions:
- The conventional model requires modification to account for the diverse hydration behaviors of neutral bilayers.
- Hydration forces may possess an attractive component, potentially arising from interbilayer hydrogen-bonded water bridges.
- Variable contributions of attractive and repulsive hydration components likely explain the range of hydration degrees and interbilayer spacings in different neutral bilayers.