Daniel Gezelter

Dynamics and Phase Transitions in Lipid Membranes

Lipids are one of the principal components of the membranes that encapsulate cellular structures. Lipid bilayers (the primary structural motif in membranes) also present physical barriers to molecules moving into and out of the cell. A drug molecule that has been perfectly tuned to a receptor site may be useless if it cannot get to that site before it is metabolized and removed from the body. Drugs and peptides therefore depend on how fast they can diffuse into and through a cell membrane to reach their targets. In our lab, we work on computational approaches to studying the physical behavior and dynamics of lipid bilayers, with a particular emphasis on transport properties like diffusion and permeability.

Biological membranes also operate at temperatures very close to some phase transitions in pure lipids. Phase transitions dramatically alter both the structure and dynamics of the bilayer. We are particularly interested in how features of the individual molecules and simple interactions between the molecules can alter the bulk and emergent properties of the membrane.

Although standard all-atom simulations are valuable, the time and length scales available are usually insufficient to study membrane phase transitions and transport. We develop coarse-grained models of lipids and have made predictions about the structure of the elusive (P_{ë_}‰Û÷) rippled phase of bilayers. Our molecular-scale models suggest a role for the head-group packing and orientational ordering in creating the nanometer-scale buckling of these important membranes.

Other areas of research which also impact membrane biophysics:

• Reverse non-equilibrium molecular dynamics (RNEMD) methods to study transport
• Real-space methods for calculating multipolar electrostatic interactions
• Lattice dipole models for membranes
• The interfaces between water and ice
• Vibrational spectroscopy of liquid crystals

Publications

1. "Nitrile vibrations as reporters of field-induced phase transitions in 4-cyano-4'-pentylbiphenyl (5CB)" Marr, J.M.; Gezelter, J.D. J. Phys. Chem. B 2014, 118 (28), 8441-8448.
2. "Velocity Shearing and Scaling RNEMD: a minimally perturbing method for simulating temperature and momentum gradients" Kuang, S.; Gezelter, J.D. Mol. Phys. 2012, 110, 691-701.
3. "Dipolar ordering in the ripple phases of molecular-scale models of lipid membranes" Sun, X.; Gezelter, J.D. J. Phys. Chem. B 2008, 112, 1968-1975.
4. "Spontaneous Corrugation of Dipolar Membranes" Sun, X.; Gezelter, J.D. Phys. Rev. E 2007, 75, 031602.