Our research focuses on theoretical studies of soft condensed matter. While it is clear that the short-range structure of complex fluids plays an important role in determining the physical and chemical propreties, the complexity of these systems precludes modeling them on an atomistic level. A judicious choice of coarse-grained models that hopefully capture the essential features without incorporating much of the detail is therefore a crucial step in the theoretical study of these systems. We are interested in constructing such models, and then employing theory and computer simulation to investigate their properties, with the final aim of predicting experimental observables. Our research has two components: the development of methods, and the application of these methods to understand the structure and dynamics of condensed phases. Some areas of current interest are:
Dynamics in complex media
The dynamics of in disordered materials is of importance in a number of phenomena including separation processes, drug delivery, electrophoresis, and transport in cells. Fascinating transport processes arise in many of these areas of nano-scale research. In living cells, for example, transport plays an important role in neurotransmission and protein secretion. We are studying the dynamics of macromolecules in complex environments via computer simulations. The goal is to obtain an understanding of the mechanism of molecular motion. It is hoped that we will obtain an understanding of these dynamic phenomena that will provide us with a theoretical standard against which experimental data, e.g., the diffusion of proteins in E. coli, may be compared.
The conformational properties and phase behavior of solutions of macromolecules is of interest from a basic scientific standpoint because they are extremely sensitive to the solution conditions. We are interested in two classes of macromolecules: polyelectrolytes and β-peptides. Our understanding of solutions of polyelectrolytes and peptides is in its infancy, and there are many issues that are far from resolved. These include the conformational properties, self-diffusion, viscosity, and adsorption behavior. We are using computer simulation and liquid state theory to establish the importance of solvent effects, counterion correlations, and polymer architecture on the behavior of polyelectrolytes in solution. The methods we develop and the knowledge we obtain should be useful in the study of other complex fluids including surfactants, biological macromolecules, and gels.
The cell membrane is a very heterogeneous environment with several types of lipids and peripheral and integral membrane proteins. We are using simple models to study three different aspects of membrane biophysics: the diffusion of membrane components, the self-assembly of lipids (rafts), and the self-assembly of proteins. The lateral diffusion of proteins and lipid molecules in cell membranes is essential to many physiological processes including diffusion-controlled reactions, such as in the electron transfer reactions involving cytochromes in the mitochondria, and the binding of hormones. We are using a combination of computer simulation, geometric analyses, and percolation theory to elucidate the effect of obstacles (integral membrane proteins) on the diffusion of lipids and GPI anchored proteins.
Effect of peptides on crystallization
The effect of peptides on the nucleation and growth of ice crystals under super-cooled conditions is important for a number of reasons including a fundamental understanding of the hardiness of plants in extreme conditions, the survival of artic fish, and the preservation of ice-cream. The freeze-thaw cycle in most freezers results in the nucleation of crystals in ice-cream with undesirable textural consquences. Peptide oligomers have been suggested as additives that might inhibit crystallization while not affecting the taste of the ice-cream. We are using atomistic simulations to study the crystallization of water with added salt and small peptides. We hope to learn the mechanism by which crystallization is affected by additives.