Probing hydration shell hydrogen bonding: Osmolyte and confinement effects

Abstract

Hydration shell waters are of fundamental importance for regulating protein properties. The influence of water is modulated by osmolytes and confinements. The detailed mechanism(s) remain uncertain due in part to the lack of probes that can expose osmolyte and confinement effects associated with hydration shell waters. This thesis sets out to understand the nature of hydration shell hydrogen bonding as a function of osmolytes and confinements with the aid of G&barbelow;adolinium V&barbelow;ibronic S&barbelow;ide B&barbelow;and L&barbelow;uminescence S&barbelow;pectroscopy (GVSBLS) that can directly probe the hydrogen bonding between first and second hydration shell waters surrounding Gd3+. This local environment specificity is used in probing how the hydrogen bonding pattern of waters within the hydration is influenced by: (i) coordination; (ii) osmolytes; (iii) confinements; and (iv) combination of osmolytes and confinements.;The results demonstrate that the hydrogen bonding pattern among hydration layer waters is a function of the local structure at the Gd3+ binding site while in contrast bulk water hydrogen bonding network is independent of protein.;The results suggest a mechanism of action for Hofmeister series ions in which high charge density cations sequester waters. Under such conditions anion-specific effects emerge as anions compete with the remaining free waters for hydrogen bonding sites.;The results provide support for the claim that the denaturant urea unfolds protein at least in part by weakening hydration shell water hydrogen bonding while leaving bulk water relatively unchanged and thereby initiating the penetration of water into the inner hydrophobic core of the protein. In contrast, osmolytes as polyols that are know to stabilize folded protein conformations are shown to strengthen both hydration shell and bulk water hydrogen bonding network.;The results indicate the extended hydrogen bonding network associated with bulk waters get enhanced under conditions of confinement where the degree of such enhancement is a function of the confinement protocol.;Finally the results illustrate that under certain conditions the combination of confinements and osmolytes can tune hydrogen bonding networks on hydration shell hydrogen bonding in a synergistic manner.