Solvent, nonaqueous refractive index

In view of these results, two observations may be made (a) as a corollary to studies of protein ultraviolet spectra in any particular nonaqueous solvent, the spectral properties of relevant simple compounds in that solvent must be investigated and (5) any changes in protein spectra produced as a result of modification of the native protein conformation in a particular nonaqueous solvent must be superimposed on changes resulting simply from the replacement of the aqueous environment by the nonaqueous one of generally different polarizability and refractive index. In the extreme case, for example, it may make little or no difference spectrally whether the aromatic chromophores remain internally bound within the protein molecule, or whether they become exposed to the solvent, and hence no useful information about protein conformations can be expected. More studies have to be made to clarify to what extent spectral changes can be useful in the investigation of proteins in nonaqueous solvents. 

The relative PLMA MW was determined by using nonaqueous SEC with THF as solvent and an HP1037A refractive index detector from Hewlett-Packard. A solid-phase extraction cartridge (Waters Sep-Pak) was used to take the PLMA and surfactants from the water phase to THF and to adjust the concentration for SEC. Sodium sulfate was used to dry the THF extract before injection into the SEC columns. For some samples there was too much surfactant present, and it overloaded the cartridge in such cases ion-exchange beads were used to reduce the concentration of the ionic surfactants in the aqueous phase before extraction. The advantage of this extraction procedure is its simplicity. The overall separation scheme is shown in Scheme I. 

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