Fourier transform infrared studies of proteins using nonaqueous solvents. Effects of methanol and ethylene glycol on albumin and immunoglobulin G

An infrared/attenuated total reflection (ATR) technique has been utilized to study the structural changes in proteins induced by nonaqueous solvents, without the need of dissolving the protein in the nonaqueous solvent. For the two proteins studied, methanol and ethylene glycol caused similar changes in albumin, i.e., an increase in helix secondary structure. However, the two solvents had dissimilar effects on immunoglobulin G (IgG). Changes in the pH of aqueous solutions of IgG produced a third effect. By dissolving some IgG in ethylene glycol and then adsorbing IgG from this solution onto an ATR crystal, the time behavior of the adsorption process could be studied and a mechanism for the structural changes proposed.