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Report Narrative

We have continued our work on understanding the effect of cosolvents on the physicochemical behavior of hydrophilic molecules in water and on the aggregates of macromolecules with potential catalytic activity. This work has involved one graduate students and one undergraduate student. PRF funds have significantly contributed to the completion of two PhD dissertations and the start of two new PhD projects. PRF funds have also allowed the PI to publish several papers and successfully apply for tenure at his institution. The PI reports below the specific results obtained for the September 2009-September 2010 period.

Diffusion of hydrophilic molecules in multicomponent aqueous mixtures. Transport properties of saccharide-salt aqueous mixtures are important for basic research and applications in the biotechnological fields. We have experimentally determined the nine multicomponent diffusion coefficients for the Sucrose(0.25M)+NaCl(0.50M)+KCl(0.50M)+H2O quaternary system at 25 °C. A simple excluded-volume model can be used to successfully predict the effect of sucrose on salt cross-term diffusion coefficients for ternary and quaternary systems. We have found that the ternary cross-term diffusion coefficients can be used to make reasonable estimates of the corresponding quaternary coefficients.  These estimates can replace the corresponding experimental data when they cannot be measured with satisfactory precision. This work has been published in J. Mol. Liq. 156, 2010, 33-37.

Polymeric aggregates with potential catalytic activity. We have previously shown that the morphology of protein aggregates is controlled by the presence/absence of phase transitions such as liquid-liquid phase separation (LLPS). Phase transitions are related to the nature and concentration of cosolvents. This concept was extended to hydrophilic polymers such as polyvinyl alcohol (PVA). For PVA (100 kg/mol) in water in the presence of polyethylene glycol (8 kg/mol), LLPS was observed. However, in the presence of salts, PVA formed amorphous aggregates. Strong kosmotropic salts lead to the formation of PVA macroscopic aggregation in relatively short time. On the other hand, our dynamic-light-scattering measurements revealed that milder kosmotropic salts lead to the formation of PVA mesoscopic aggregates with tunable size (from 20 nm to 500 nm). Our objective is to use these PVA aggregates as scaffold for catalytically active molecules. In order to obtain catalytically active aggregates, we have experimentally investigated PVA binding to several molecules chosen for their catalytic relevance. We have found that a few porphyrin molecules bind to PVA by performing spectrophotometric measurements and partitioning studies in the presence of PVA hydrogel. We believe that our investigation will lead to the preparation of catalytically active polymeric aggregates with properties similar to that of redox proteins such as cytochromes. This work is currently in progress.