We present a molecular model of the major “conformational substates” observed by infrared spectroscopy in carbonmonoxyhemoglobins, myoglobins, and peroxidases, in terms of an electrical perturbation of the CO fundamental vibrational frequencies due to the possibility of Hϵ2 ↔ Hδ1 tautomerism, and 180° Cβ–Cγ ring flips, of distal histidine residues. The model supports a previous interpretation of vibrational frequencies and nuclear magnetic resonance chemical shifts of CO ligands in heme proteins as originating in a weak electric field (dipole and quadrupole interactions with permanent dipole moments, dipole polarizabilities, and shielding polarizabilities), and opens up the possibility of future detailed molecular interpretations of both NMR chemical shifts (of 1H, l3C, and 15N), as well as IR data, on proteins and other macromolecules.
ASJC Scopus subject areas
- General Chemistry
- Colloid and Surface Chemistry