title: Free energy and entropy of activation for phospholipid flip-flop in planar supported lipid bilayers.
abstract: Basic transition state theory is used to describe the activation thermodynamics for phospholipid flip-flop in planar-supported lipid bilayers (PSLBs) prepared by the Langmuir-Blodgett/Langmuir-Schaeffer method. The kinetics of 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) flip-flop were determined as a function of temperature and lateral surface pressure using sum-frequency vibrational spectroscopy (SFVS). From the temperature and lateral pressure dependent DSPC flip-flop kinetics, a complete description of the activation thermodynamics for flip-flop in the gel state, including free energy of activation (DeltaG(++)), area of activation (Deltaa(++)), and entropy of activation (DeltaS(++)), was obtained. The free energy barrier for flip-flop of DSPC was determined to be DeltaG(++) = 105 +/- 2 kJ/mol at 40 degrees C at a deposition surface pressure of 30 mN/m. The free energy barrier was found to consist of large opposing entropic and enthalpic contributions. The influence of alkyl chain length on the activation thermodynamics of flip-flop was also investigated. Decreasing the alkyl chain length led to a decrease in DeltaG(++) due primarily to an increase in DeltaS(++). The values obtained here are compared to previous studies investigating flip-flop by vesicle based methods.
authors.affiliation: University of Utah, Department of Chemistry, 315 South 1400 East, Salt Lake City, Utah 84112, USA.
authors.forename: Timothy C
authors.initials: TC
authors.lastname: Anglin
authors.forename: Michael P
authors.initials: MP
authors.lastname: Cooper
authors.forename: Hao
authors.initials: H
authors.lastname: Li
authors.forename: Katherine
authors.initials: K
authors.lastname: Chandler
authors.forename: John C
authors.initials: JC
authors.lastname: Conboy
mesh_terms: D000465:Algorithms; D019277:Entropy; D007700:Kinetics; D008051:Lipid Bilayers / Q000737:chemistry*; D010713:Phosphatidylcholines / Q000737:chemistry*; D013696:Temperature
chemical_list: D008051:Lipid Bilayers; D010713:Phosphatidylcholines; C010942:1,2-distearoyllecithin