Hydrogen bonding between liganded CO and heme-proteins

Perturbations of the CO bond in carbon monoxide bound to iron in different heme-proteins are discussed. Properties evaluated from Hartree-Fock-Slater electronic structure calculations are correlated with experimental observations. The net charge on oxygen (HFS) is related to the Fe(III)/Fe(II) reduction potential (EMF). Consequently, proteins with low EMF, e.g. peroxidases, have more ability to form FeCOH…H. protein hydrogen bonds than, for example, oxidases with higher EMF. This can explain anomalous vibrational frequencies, ν CO, observed for acidified peroxidases. Calculations reveal that direct interaction between CO and polar groups on the protein can cause peturbations of the CO π-bond order similar to those from EMF shifts. Dioxygen and carbon monoxide are compared in regard to hydrogen bonding to heme-proteins.