W R Rudnicki | PubMed Health

PubMed1997

Modeling the DNA-solvent interface.

We extend the technique of using perpendicular distribution functions to salt solutions around nucleic acids. Both solute density averaged and nonaveraged reference frames are considered and compared. Using a previous simulation of DNA in salt water of over a nanosecond in duration, the aqueous distribution functions were found to be well coveraged, whereas the salt perpendicular distribution functions were less well determined. Three-dimensional density reconstructions reliably showed the prominent solvation features with transferable functions. The number of solute atom types needed for reconstructions of a given precision was determined in the context of the reference simulation data set with the goal of achieving a required level of reconstruction quality.

Computer Simulation↗

PubMed1994

Lagrangian molecular dynamics using selected conformational degrees of freedom, with application to the pseudorotation dynamics of furanose rings.

Using internal conformational degrees of freedom for biopolymers as natural variables, and introducing a Lagrangian dynamics approach, one can simulate time-dependent processes over a much longer time scale than in classical Newtonian molecular dynamics (MD) techniques. Two factors contribute to this: a substantial reduction in the number of degrees of freedom and a very large increase in the size of the time step. We present the Lagrangian equations of motion for repuckering transitions in model furanose (F), ribose (R), and 2'-deoxyribose (dR) ring systems using the pseudorotation phase angle as the single dynamic variable. As in most Lagrangian analyses, the effective masses for the R and dR models are dependent on conformation, and we test the behavior of this variable mass (VM) model. Since the variation in effective mass is small, the VM model is compared with a simplified constant mass (CM) model, which is shown to be an excellent approximation. The equations of motion for the CM and VM models are integrated with the leapfrog and the iterative leapfrog algorithms, respectively. The Lagrangian dynamics approach reduces the number of degrees of freedom from about 40 to 1, and allows the use of time steps on the order of 20 fs, about an order of magnitude greater than is used in conventional MD simulations.

Biopolymers↗