▼ Optical tweezer-based experiments on molecular motors and trackways allow the kinetics of the interactions to be measured. This information helps us to understand the motors’ motion, which could be a first step in developing nanomachines. We set out to study the interactions between the commercially available molecular motor, chromokinesin, and its associated trackway, the microtubule, through bead assays using an Optical Tweezer system. We developed an optimal protocol and concentration for microtubule reconstitution and coating of the viewing chamber surface. We subsequently developed a protocol for coating polystyrene beads with chromokinesin and for introducing the beads into a chamber with sedimented microtubules (necessary for a bead assay). A study of the alignment of the optical tweezer system was conducted in an effort to develop the ability to move the trap in the z-direction, which is crucial for these experiments and has not been achieved hitherto with our trapping system. We suggest a course of action in order to continue the study of chromokinesin-microtubule interactions using the optical tweezer system. Advisors/Committee Members: Tees, David.

▼ A recent analysis of experimental results for viscosity and diffusion coefficients as functions of the volume fraction in colloidal systems near the glass transition has uncovered a substantial discrepancy with the predictions of Mode Coupling Theory (MCT). Considering the degree of difficulty of the experiments, and in particular the difficulty in precisely determining the volume fraction for the systems under study, it hasn't been clear to what degree the discrepancy comes from inaccurate experimental values and to what degree it comes from failure of Mode Coupling Theory. The goal of this project was to shed light on this question by using computer simulations. We have used molecular dynamics to simulate a binary hard sphere colloidal system consisting of 8000 particles interacting via a Weeks-Chandler-Andersen (WCA) pair potential. Our simulations covered temperatures of 0.1 and 0.01 in LJ units and volume fractions between 0.006 and 0.69. We found that as the volume fraction increased, there was a sharp decrease in the product of diffusion coefficient and viscosity. Our results are in qualitative agreement with the available experimental data, but differ significantly from the Mode Coupling Theory predictions. We suggest a possible interpretation of these results in that they provide evidence for the presence of dynamical heterogeneities - strong spatial fluctuations in the relaxation rate in glass forming liquids. Advisors/Committee Members: Castillo, Horacio.