NMR of biomolecules in low viscosity, liquid CO2

We demonstrate that hetero- and homonuclear NMR spectra of cyclosporin A and pancreatic trypsin inhibitor (BPTI) can be recorded at room temperature in liquid CO2, a medium of very low viscosity, which has been reported to have no adverse effect on molecular structure or activity of several proteins. Rotational diffusion of cyclosporin A in a CO2/methanol mixture is approximately three-fold faster than in chloroform. Translational diffusion for BPTI, dissolved in liquid CO2 by co-adding detergent and trifluoroethanol, is measured to be faster than in water, but rotational diffusion is not. Development of improved detergents is anticipated to make feasible the encapsulation of most biological macromolecules in water-containing reverse micelles, which can be suspended in a wide array of apolar, supercritical or near-critical solvents.