Molecular motion of Hb S in gel: study of dipolar orientation

Although the configuration of Hb S molecules in gel is now well known, there are still many unsolved problems with regard to the rotational freedom of individual molecules in the gel. Dielectric relaxation technique provides the information as to the orientation of polar molecules in solution and even in solid state if orientational freedom is not completely suppressed. Using this technique, the dipole moment of Hb S and its rotational characteristics were investigated in solution as well as in gel. It was found that gelation does not have profound effects on the dipole moment and orientation of the Hb S molecule. This result indicates that Hb S molecules are still rotational in gel. Furthermore, temperature dependence of the characteristic frequency of rotation was determined. Using Eyring's theory of rate processes, the activation enthalpy of Hb S rotation was calculated. We found the values of delta H to be 2.5 kcal/mol for solution and 6.0 kcal/mol for gel respectively. Based on these results, we conclude that the orientation of Hb S does not require large activation energy even in gel.