C-13 shieldings, O-18 isotope effects on C-13 shieldings, and Fe-57-C-13 spin couplings of the Fe-C-O unit in superstructured hemoprotein models: Comparison with hemoproteins, C-O vibrational frequencies, and X-ray structural data
Φόρτωση...
Ημερομηνία
Τίτλος Εφημερίδας
Περιοδικό ISSN
Τίτλος τόμου
Εκδότης
Springer Verlag (Germany)
Περίληψη
Τύπος
Είδος δημοσίευσης σε συνέδριο
Είδος περιοδικού
peer reviewed
Είδος εκπαιδευτικού υλικού
Όνομα συνεδρίου
Όνομα περιοδικού
J Biomol NMR
Όνομα βιβλίου
Σειρά βιβλίου
Έκδοση βιβλίου
Συμπληρωματικός/δευτερεύων τίτλος
Περιγραφή
C-13 NMR spectra of several carbon monoxide (99.7% C-13 and 11.8% O-18 enriched) hemoprotein models with varying polar and steric effects of the distal organic superstructure and constraints of the proximal side are reported. This enables the Fe-57-C-13(O) coupling constants ((1)J(57Fe-13C)), C-13 shieldings (delta(C-13)), and O-18 isotope effects on C-13 shieldings ((1) Delta(13)C(O-18/O-16)) to be measured and hence comparisons with hemoproteins, C-O vibrational frequencies and X-ray structural data to be made. Negative polar interactions in the binding pocket and inhibition of Fe-->CO back-donation or positive distal polar interactions with amide NH groups appear to have little direct effect on (1)J(57Fe-13C) couplings. Similarly, the axial hindered base 1,2-dimethylimidazole has a minor effect on the (1)J(57Fe-13C) values despite higher rates of CO desorption being observed for such complexes. On the contrary, C-13 shieldings vary widely and an excellent correlation was found between the infrared C-O vibrational frequencies (nu(C-O)) and C-13 shieldings and a reasonable correlation with O-18 isotope effects on C-13 shieldings. This suggests that delta(C-13), nu(C-O) and (1) Delta(13)C(O-18/O-16) are accurate monitors of the multiple mechanisms by which steric and electronic interactions are released in superstructured heme model compounds. The C-13 shieldings of heme models cover a 4.0 ppm range which is extended to 7.0 ppm when several HbCO and MbCO species at different pH values are included. The latter were found to obey a similar linear delta(C-13) versus nu(C-O) relationship, which proves that both heme models and heme proteins are homogeneous from the structural and electronic viewpoint. Our results suggest that nu(C-O), delta(C-13) and (1) Delta(13)C(O-18/O-16) measurements reflect similar interaction which is primarily the modulation of pi back-bonding from the Fe d(x) to the CO pi* orbital by the distal pocket polar interactions. The lack of correlation between (1) Delta(13)C(O-18/O-16) and crystallographic CO bond lengths (r(C-O)) reflects significant uncertainties in the X-ray determination of the carbon and oxygen positions.
Περιγραφή
Λέξεις-κλειδιά
c-13 shieldings, hemoproteins, isotope effects, model compounds, free-energy relationships, carbon-monoxide, heme-proteins, resonance raman, pocket porphyrins, capped porphyrin, binding, ligand, nmr, complex
Θεματική κατηγορία
Παραπομπή
Σύνδεσμος
<Go to ISI>://000074811500006
http://download.springer.com/static/pdf/783/art%253A10.1023%252FA%253A1008253901009.pdf?auth66=1381649571_dae7fb51c5201bc0bb90a10ad4c8bda7&ext=.pdf
http://download.springer.com/static/pdf/783/art%253A10.1023%252FA%253A1008253901009.pdf?auth66=1381649571_dae7fb51c5201bc0bb90a10ad4c8bda7&ext=.pdf
Γλώσσα
en
Εκδίδον τμήμα/τομέας
Όνομα επιβλέποντος
Εξεταστική επιτροπή
Γενική Περιγραφή / Σχόλια
Ίδρυμα και Σχολή/Τμήμα του υποβάλλοντος
Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Χημείας