Hydrodynamic interaction effects on local motions of chain molecules

The librational motions of a butane molecule in water are simulated by Brownian dynamics with and without inclusion of hydrodynamic interactions. Inclusion of the hydrodynamic interactions is found to increase the torsional correlation times by 35% to 46%, depending on the isomeric state of the butane molecule, and to decrease the rate constants for gauche–trans isomerization by about 28%. A critical discussion of the approximations involved in such simulations is presented.