Theoretical studies of chemical dynamics in complex systems Nanoconfined water microdroplets biomolecular hydration layer and water mediated protein association

Abstract

The thesis contains theoretical studies of the structure and dynamics in different complex systems. Depending on the systems and properties of interest we divide the thesis into five parts. In the first part, we study chemical dynamics in nanoconfined water. Here we primarily focus on the dielectric properties of dipolar fluids confined inside nano-containers of various sizes and shapes. We discover an extremely slow convergence of the static dielectric constant (and#949;) of water with the size of the nanospheres. Our studies reveal an ultrafast relaxation of the collective orientation of water which is absent in the Stockmayer fluid. We connect this anomaly to the substantially low value of the Kirkwood g-factor for spherically confined water. We extrapolate the values of and#949; to obtain its true value in the thermodynamic limit which corroborates well with the values in periodic systems. We perform molecular dynamics simulations with three different liquid-surface interactions to study the surface effects. The dielectric response of water under becomes anisotropic in non-spherical confinements, namely, cylindrical and slab geometries. Because of the difference in the dielectric boundary conditions along the different directions, the eigenvalues of the dielectric tensor becomes unequal. We derive the fluctuation formulae for the anisotropic dielectric constants. For the cylindrical geometry, we find that the axial component (and#949;z) and the perpendicular component (and#949;x/y) converge to the bulk value, with the diameter of the nanotube, in an opposite manner. and#949;x/y shows relatively slower convergence starting from a lower value whereas and#949;z shows faster convergence starting from a higher value. For the slab system, the parallel component (and#949;and#8741;) does not show much deviation from the bulk value. On the contrary, the perpendicular component (and#949;and#8869;) exhibits extremely low values for smaller systems and shows a slow convergence toward bulk...