Heme Release in Myoglobin-DDAB Films and Its Role in Electrochemical NO Reduction

摘要

Electrochemical nitric oxide (NO) reduction by heme groups incorporated in films of didodec-yldimethylammonium bromide (DDAB) on pyrolitic graphite was investigated.It is shown that DDAB most likely induces the release of the heme group from myoglobin and therefore myoglobin-DDAB and heme-DDAB films give the same voltammetric responses.This is confirmed by UV/vis spectroscopy showing a clear shift in the Soret band of myoglobin in a DDAB solution.The electrochemical NO reduction on a heme-DDAB film at different pH values reveals the presence of pH-dependent and pH-independent NO reduction pathways.The selectivity of these pathways is probed by combining the rotating ring-disk electrode technique with online electrochemical mass spectroscopy showing that the product of the pH-independent pathway is N_2O and the product of the pH-dependent pathway is NH_2OH.The preference for one or the other pathway seems to depend on whether a proton or a NO molecule is transferred to a Fe~(II)-NO~- reaction intermediate and is influenced by pH,NO concentration,and potential.