Mr. Ali Hassanali
Department of Chemistry
The Ohio State University
Columbus, OH

Monday, February 15, 2010
3:00 pm (CT)
3269 Beckman Institute

Abstract

Water, the fundamental constituent of life, has been found to have a critical role at both organic and inorganic surfaces. The properties of water near surfaces, is known to be different from water far away from surfaces. This talk will explore the degree to which inorganic materials such as amorphous silica (glass) and biomolecular surfaces change the properties of water, and the role of these interfaces in biological function. In the first part of the talk I will examine the mobility of water near protein surfaces which has been of considerable recent interest. Some theories postulate that interfacial water is incapable of undergoing rapid rotational motions due to the strong attraction from the protein surface. This has led to confusing and conflicting interpretations on the molecular origin of the slow features observed in time dependent fluorescence Stokes shift experiments that probe the environment of protein surfaces. Our theoretical studies resolve the conflicts and show that the slow dynamics observed originates from the protein and water jostling in a concerted fashion. Our studies support a change in the paradigm for the function of proteins to include both the protein and the surrounding water as active participants in biological function. In the second part of the talk, I will discuss the water-amorphous silica interface. For 80 years scientists have employed models in which ions and water near the silica surface form a stagnant layer called the Stern layer. To account for all experimental features, these models invoke puzzling properties such as the transport of ions through immobile water. We have successfully constructed and validated a model for the water-amorphous silica interface. Our simulations challenge the classical textbook Stern layer model. Both ions and water exhibit a substantial degree of mobility, yet the phenomena the Stern layer was originally invoked to explain are reproduced by our calculations. Preliminary results showing the binding properties of tri-peptides to the silica surface will also be discussed briefly. Finally, I will illustrate the repair of damaged DNA bases in a pocket of water molecules using ab initio MD simulations. Theoretical studies for the repair of DNA bases damaged by sunlight demonstrate that fast water motions are critical in ensuring the rapid repair of the bases on the ps timescale. We also find a significant amount of charge delocalization from the anionic thymine dimers to the surrounding solvent throughout the splitting process. We have constructed a simple analytical theory using our ground state calculations that suggests new insights into the mechanisms of efficient DNA repair that might be deployed in the active site of the DNA repair protein.