Clathrate hydrate formation and protein solubilization in reversed micelles
Description
The thermodynamic conditions for the nucleation of clathrate hydrates in a new environment, that constituting the microaqueous pools of reversed micellar solutions containing empty reversed micelles, are described. Hydrate formation is highly dependent on the water-to-surfactant molar ratio, w$\sb0,$ which defines the size of the reversed micelles and influences the state of the microaqueous phase. Hydrate formation behavior approaches that in pure water, as the microaqueous droplets approach pure water properties The formation of clathrate hydrates in single phase reversed micellar systems containing proteins, and its effects on the stability of the encapsulated proteins, are discussed. The formation of methane hydrates essentially removes water from the reversed micelles, decreasing the mean micellar size. Proteins, once encapsulated in the micelles, remains solubilized as the average micellar water content is decreased. The observation appears valid both for proteins encapsulated in relatively small single-occupancy micelles and for proteins encapsulated as large aggregates. In contrast, when ethylene is used as the hydrate-forming gas species, pressurization beyond a critical pressure results in the destabilization and precipitation of the solubilized proteins The formation of clathrate hydrates in two-phase reversed micellar systems enhances the transfer of proteins from a bulk aqueous phase into a reversed micellar phase under specific conditions. However, increased ionic strength of the aqueous phase through hydrate formation retards the transfer of proteins into the reversed micellar phase A thermodynamic model for predicting clathrate hydrate formation in empty reversed micellar solutions is developed. The method is based on the thermodynamic models for hydrate formation in pure water and for the activity of water in reversed micelles. A computational scheme for predicting the dissociation/formation pressure at a given temperature is presented. The sensitivity of the activity of water in the reversed micelles to dissociation pressure is also discussed. Predictions are made for both hydrates of methane and ethylene, whose experimental data are available. The method gives reasonably good results by comparing the predicted values with the experimental data Potential applications and areas for further research are noted