Human hemoglobin, modified with poly(ethylene oxide) with average molecular weight of 3500 (PEO-Hb) was dissolved in PEO200 (molecular weight of 200) containing 0.5 M KCl. A quasi-reversible redox reaction of the PEO-Hb was found in PEO oligomers by alternatingly changing the potential polarity (+/- 1.2 V vs Ag). The PEO-Hb showed redox reactions in PEO200 even at 120 degrees C. PEO modification was concluded to give the thermal stability in some extent. In phosphate buffer at 70 degrees C, the electrochemical redox reaction of native Hb was not observed spectroscopically, but that of PEO-Hb was detected. The most effective factor was, however, concluded to be the use of PEO oligomers as a solvent. The molecular motion of PEO oligomers should be milder than that of water at higher temperature. This lower molecular motion was suggested to keep the redox activity of PEO-Hb in the PEO oligomer at 120 degrees C. However, the PEO-Hb in PEO200 was stable in the oxidized form at 30 degrees C; it was reduced without giving potential at 120 degrees C. Cyclic voltammetry revealed that this autoreduction was attributed to the shift of redox potential with elevating temperature.

Hemoglobin (Hb) was chemically modified with poly-(ethylene oxide) (PEO) to prepare PEO-Hb. This PEO-Hb was cast onto the I T 0 (Indium Tin Oxide) electrode, and the modified electrode was then soaked in PEO oligomer solution containing 0.2 M KCI. PEO-Hb was electrochemically reduced by applying a negative potential (ranging from -0.5 to -1.2 V us. Ag). Electron transfer between adjacent PEO-Hbs in the cast layer was considered to be slow. Higher salt concentration and more negative potential gave an effective reduction of PEO-Hb in PEO oligomers. Re-oxidation of the reduced PEO-Hb was also carried out by giving positive potential. This redox reaction was confirmed as reversible by potential polarity charge. A similar redox reaction was carried out in d y poly(oligo(oxyethy1ene) methac y l a t e ) containing KCl. Polymer electrolytes were revealed to be effective polymer solvents for the redox reaction of PEO-modified hemoglobin cast on the I T 0 electrode.

Horse-heart myoglobin (Mb) was modified with poly(ethylene oxide) (PEO) to solubilize it in PEO oligomers. PEO-modified Mb (PEO-Mb) showed a quasi-reversible electrochemical redox reaction in PE0200 (molar mass of 200 g). PEO-Mbs, modified with lower molecular weight of PEO chains, were soluble in PEO oligomers with wider range of molecular weight. A conformation of PEO-Mb was studied with circular dichroism spectroscopy in phosphate buffer solution (PBS) or PEO oligomers. The a-helix content of PEO-Mb, determined by the molar ellipticity at 222 nm, decreased from 71 % to about 58% after PEO modification. However, the degree of PEO modification did not affect the a-helix content of PEO-Mbs. On the other hand, the a-helix content of PEO-Mbs was reduced by lowering the molecular weight of the modified PEO chains. Since the a-helix content of PEO-Mb in PBS and that in the PEO oligomers were almost identical, the conformation of PEO-Mb in PBS was considered to be maintained even in PEO oligomers. Although the reduction rate constant of PEO-Mb in PEO oligomers depended on the total molecular weight of the PEO-Mbs, their relation did not obey the Stokes-Einstein equation. The reduction of the PEO-Mb was probably affected by the interfacial electron transfer process at the electrode surface rather than by diffusion in the PEO oligomer.

Lithium perchlorate (LiClO4) was dissolved in dehydrated chloroform with polyethylene oxides (PEO) having different molecular weights. The mixing ratio of ether oxygen unit (O) of PEO to cation (Li+) was set to 20:1. The solution viscosity of the PEO/LiClO4 mixtures was measured using an Ubbelohde viscometer at 30.0°C. The concentration dependence of the reduced viscosity was analyzed by diluting the initial PEO/LiClO4 mixed solution with pure chloroform to keep the ratio of Oto Li+ constant. The increase in the reduced viscosity for a dilute solution was found in every mixture system, but not in the PEO solution without salt. Similar experiments were also carried out in chloroform/dimethylformamide (DMF) mixed solvent (4:1 by volume). These results were analyzed using the Fuoss equation, which was applied for the analysis of a polyelectrolyte aqueous solution. Linear relations are depicted in the Fuoss plots, suggesting that the PEO/LiClO4 mixture shows polyelectrolyte‐like behavior in chloroform or in chloroform/DMF mixed solvent. This is attributed to the intramolecular electrostatic repulsion of lithium cations which are trapped by the PEO chains through ion–dipole interaction.