Induced thermostability of poly(ethylene oxide)-modified hemoglobin in glycols

The thermostability and redox activity of poly(ethylene oxide) (PEO)-modified human hemoglobin in PEO200 (PEG containing KCl, average MW of 200, <0.3% H2O) were investigated by UV-vis spectroscopy, by circular dichroism spectroscopy, and by cyclic voltammetry. Using PEO oligomers as a solvent, PEG-modified hemoglobin was reduced and oxidized at an indium tin oxide glass electrode in the temperature range of -10 to 120 degrees C. The thermostability of PEO-modified hemoglobin was affected by the molecular weight of the solvent PEG. In lower-molecular weight glycols (MW of <150), PEO-modified hemoglobin was denatured within a few minutes at 80 degrees C. On the other hand, the absorbance at the Soret band for PEG-modified hemoglobin was unchanged for 2 h at 80 degrees C in PEO200. A decrease in the water content of solvent PEO200 also improved the thermostability of PEG-modified hemoglobin. Improvement in the thermostability was attributed to physicochemical characteristics such as the relatively low molecular motion of PEO oligomers used as a solvent.