Stabilizing effect of water/alcohol solvents towards autoxidation of human haemoglobin.

The stabilization of haemoglobin (Hb) in water/alcohol solvents (ethanol, butan-1-ol, ethylene glycol and glycerol) against autoxidation, a major barrier to the successful use of Hb in biological and medical engineering was studied, with these solvents, a large decrease in the autoxidation rate is observed over a range of concentrations. Studies on the effect of Hb concentration on autoxidation showed that, irrespective of the Hb concentration, oxyHb is more stabilized in water/alcohol solvents than in water. In these solvents, at the concentration exhibiting the maximal stabilizing effect, the oxygen affinity of Hb was little disturbed, but the changes in enthalpy and entropy of activation increased with the stabilization effect of alcohol. The impact of alcohols on the thermal denaturation of metHb was studied. We observed that metHb is less stable in ethanol and butan-1-ol than in water, whereas the opposite is observed with glycerol and ethylene glycol. The strong stability of oxyHb observed with these solvents could result both from an increase in water structure and an increase of viscosity. Finally, e.p.r. has shown that alcohols lead to an increase of the global distance between the nitrogens of proximal histidine (F8) and nitric oxide in the nitrosyl Hb.