Carbon dioxide in the liquid and supercritical fluid states is useful
as a replacement for toxic organic solvents. However, nonvolatile hydr
ophilic substances such as proteins, ions, and most catalysts are inso
luble. This limitation was overcome by the formation of aqueous microe
mulsion droplets in a carbon dioxide-continuous phase with a nontoxic
ammonium carboxylate perfluoropolyether surfactant. Several spectrosco
pic techniques consistently indicated that the properties of the dropl
ets approach those of bulk water. The protein bovine serum albumin (BS
A) with a molecular weight of 67,000 is soluble in this microemulsion
and experiences an environment similar to that of native BSA in buffer
.