13C- and 57Fe-NMR studies of the Fe-C-O unit of heme proteins and synthetic model compounds in solution: Comparison with IR vibrational frequencies and X-ray structural data

Charalampos G. Kalodimos, Ioannis P. Gerothanassis, Geoffrey E. Hawkes

Research output: Contribution to journalReview article

4 Scopus citations

Abstract

13C- and 57Fe-NMR spectra of several carbon monoxide hemoprotein models with varying polar and steric effects of the distal organic superstructure, constraints of the proximal side, and solvent polarity are reported. The 13C shieldings of heme models cover a 4.0 ppm range that is extended to 7.0 ppm when several hemoglobin CO and myoglobin CO species at different pHs are included. Both heme models and heme proteins obey a similar excellent linear δ(13C) versus ν(C-O) relationship that is primarily due to modulation of π backbonding from Fe dπ to the CO π* orbital by the distal pocket polar interactions. There is no direct correlation between δ(13C) and Fe-C-O geometry. The poor monotonic relation between δ(13C) and ν(Fe-C) indicates that the iron-carbon π bonding is not a primary factor influencing δ(13C) and δ(57Fe). The δ(57Fe) was found to be extremely sensitive to deformation of the porphyrin geometry, and increased shielding by more than 600 ppm with increased ruffling was observed for various heme models of known X-ray structures.

Original languageEnglish (US)
Pages (from-to)S57-S69
JournalBiospectroscopy
Volume4
Issue number5 SUPPL. 1
DOIs
StatePublished - 1998

Keywords

  • C-NMR
  • Fe-NMR
  • Heme models
  • Heme proteins
  • ν(C-O) stretching vibration
  • ν(Fe-C) stretching vibration

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