Solubility, diffusion coefficient and ionic conductivity of alkyl viologens in poly(ethylene oxide) and its derivatives

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 (PEO 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, PEO-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 PEO. 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 PEO-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 PEO-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.

Effect of cast solvent on the electron transfer reaction for poly(ethylene oxide)-modified myoglobin on the electrode in poly(ethylene oxide) oligomers

Myoglobin from horse skeletal muscle was modified with poly(ethylene oxide) (PEO) with an average molecular weight of 2000 or 5000. Myoglobin was soluble after this modification in several organic solvents and PEO oligomers. The electron transfer reactions of PEO-modified myoglobin cast on the indium tin oxide (ITO) glass electrode were investigated by cyclic voltammetry. The PEO-modified myoglobin, cast on the electrode from water or a methanol solution, showed quasi-reversible redox reactions in PEO (average MW of 400). On the other hand, no redox response was seen in PEO-modified myoglobin cast on it using chloroform or benzene as a casting solvent. A clear redox response of the PEO-modified myoglobin was observed after methanol treatment of these layers cast from chloroform or a benzene solution. This suggests that the conformational change of the adsorbed PEO-modified myoglobin layer on the ITO electrode cast from chloroform or a benzene solution was not irreversible. The cast condition of PEO-modified myoglobin on the ITO glass electrode was revealed to affect the electron transfer reaction for protein considerably in PEO oligomers.