Carbon-13 and Oxygen-17 Chemical Shifts, (16O/18O) Isotope Effects on13C Chemical Shifts, and Vibrational Frequencies of Carbon Monoxide in Various Solvents and of the Fe−C−O Unit in Carbonmonoxy Heme Proteins and Synthetic Model Compounds

Abstract

13C shieldings, δ(13C), 17O shieldings, δ(17O), and 18O isotope effects on 13C shieldings, 1Δ13C(18O/16O), of carbon monoxide (99.7% 13C, 0.9% 17O, and 11.8% 18O enriched) in a variety of solvents and of the Fe−C−O unit of several carbonmonoxy hemoprotein models with varying polar and steric effects of the distal organic superstructure and constraints of the proximal side are reported. This enables, first, comparisons with hemoproteins, C−O vibrational frequencies, ν(C−O), and X-ray structural data to be made; second, to investigate whether polarizable CO is an adequate model for distal ligand effects in carbonmonoxy heme proteins and synthetic model compounds; third, to investigate the effect of electronic perturbation within the heme pocket and pocket deformation on δ(13C), δ(17O), 1Δ13C(18O/16O), and ν(C−O). A variety of solvents with varying dielectric constants and solvation abilities appears to have negligible effect on δ(17O), δ(13C), and 1Δ13C(18O/16O) and little direct effect on ν(C−O) of dissolv...