Poster abstracts

Poster number 111 submitted by Ali Hassanali

A model for the water-amorphous silica interface: structure, dynamics and applications to biology.

Ali Hassanali (Biophysics The Ohio State University), Hui Zhang (Chemistry The Ohio State University), Christopher Knight (Chemistry The Ohio State University), Yun Kyung Shin (Chemistry The Ohio State University), Sherwin Singer (Chemistry The Ohio State University)

Abstract:
Amorphous silica-water interfaces are found ubiquitously in nanoscale devices, including devices fabricated from silica as well as from silicon that acquire a surface oxide layer. The surface silanol groups serve as hydrogen-bonding sites for a variety of chemical species, and their reactivity enables convenient chemical modification, making silica surface strategic in bio-sensing applications. We have extended the popular BKS and SPC/E models for bulk silica and water to describe the hydrated, hydroxylated amorphous silica surface. The parameters of our model were determined using ab initio quantum chemical studies on small fragments. Our model will be useful in empirical potential studies, and as a starting point for ab initio molecular dynamics calculations. At this stage, we present a model for the undissociated surface. Our calculated value for the heat of immersion, 0.6 J m², falls within the range of reported experimental values of 0.2-0.8 Jm². We also study the perturbation of water properties near the silica-water. The disordered surface is characterized by regions that are hydrophilic and hydrophobic, depending on the statistical variations in silanol group density.

Recently we have extended our model to include dissociated silanol groups and we are in the process of inserting biomolecules such as KWK (Lys-Trp-Lys) which has been studied previously in our group. We also demonstrate the validity of the hydrophilic and hydrophobic patches on our silica surface using ab initio molecular dynamics simulations. We also discuss applications of our model in understanding electroosmotic flow in nano-devices which is critical in the transport of biomolecules.

Keywords: amorphous, silica, water