Mössbauer spectroscopy of hemoglobin model compounds: Evidence for conformational excitation

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Abstract
Zero-field Mössbauer spectra of a model compound for hemoglobin, capable of undergoing reversible oxygenation, were recorded at various temperatures. A pair of peaks with temperature-dependent quadrupole splitting and linewidth were observed. The results have been interpreted in terms of a model which is consistent with previous x-ray studies and which provides for relaxation effects as the molecule assumes two possible conformational states. In terms of the proposed model, the two conformational states have been characterized by their energy separation and their respective electric field gradient tensors. The relaxation rate at each temperature has also been determined.