| This thesis presents experimental studies of thermal stability of DNA at low hydration levels and solid-state stabilization of proteins with carbohydrates, a computational investigation of hydration, solution structure and dynamics in dilute carbohydrate solutions, and a development of microscopic theory and equation of state for liquid water.; In the DNA work, we studied the thermal and structural properties of salmon DNA as a function of water content up to 12 wpn (water molecules per nucleotide). The DSC and IR results indicate a two-step thermal denaturation process for DNA with hydration levels less than 12 wpn.; In the study of protein stability in a carbohydrate matrix, we examined the effects of carbohydrates (fructose, sucrose, trehalose, maltotriose, and dextran), freeze-drying and subsequent heating on the structure and enzymatic activity of alpha-chymotrypsin and catalase. It is shown that an inverse relationship exists between the molecular weight of the carbohydrate and its efficacy on preserving the structure and activity of catalase during lyophilization. It is also shown that the Maillard reaction between carbohydrates and proteins, which causes significant loss of enzymatic activity at elevated temperatures, is successfully suppressed in glassy systems with less than 1% (w/w) water content.; In the computational work, we used molecular dynamics to investigate the effects of carbohydrates on water structure and dynamics. Glucose, sucrose, and trehalose disrupt the tetrahedral arrangement of their surrounding water molecules and restrict their translational and rotational mobility. They also induce a pronounced decoupling between translational and rotational motions of these water molecules.; In the development of the liquid water microscopic model, we formulated the extension of the single-bond model of associating fluids [J. Chem. Phys. 111, 2647 (1999)] to account for the formation of multiple hydrogen bonds in liquid water.{09}This model is capable of reproducing many anomalies of liquid water, such as density maxima, compressibility and heat capacity minima, and a dramatic increase in the response functions upon supercooling. It is also able to generate two thermodynamically consistent phase behaviors which are consistent with the two-critical-point and singularity-free interpretations for the unusual behavior of water at low temperatures. |
