Change in Effective pH of Salt Solutions on Freezing, as Evidenced by Altered Reactivities of Heme a towards Carbonyl Reagents

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Abstract
Addition of NaHSO3 or HCN to the formyl group of heme a was greatly accelerated by freezing reaction mixtures prepared in aq. Na2CO3, and freezing resulted in characteristic color and spectral changes of the solutions. Similar changes were observed on decreasing the pH of alkaline reaction mixtures with HCl at room temperature, indicating that the effective pH of certain salt solutions is greatly lowered by freezing. The reactivity of the formyl group changed depending on the redox state of the heme iron and the species of ligand.