Heteronuclear NMR studies of cobalamins. 10. sup 15 N NMR studies of ( sup 15 N)cyanocobalt corrins

Journal Article · Wed Sep 19 00:00:00 EDT 1990 · Inorganic Chemistry; (USA)

DOI:https://doi.org/10.1021/ic00344a040· OSTI ID:6010606

Brown, K L; Gupta, B D ^[1]

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1. Univ. of Texas, Arlington (USA)

{sup 15}N NMR chemical shifts and {sup 15}N-{sup 13}C coupling constants have been determined for cyanocobalamin (CNCbl) and several other monocyano and dicyanocobalt corrins enriched in {sup 15}N or in {sup 15}N and {sup 13}C in the axial cyanide ligands(s). The {sup 15}N chemical shift is found to be nearly as sensitive (ca. 75%) to changes in trans axial ligation as the {sup 13}C chemical shift of {sup 13}CN cyanocobalt corrins. All alternations in the cobalt coordination sphere have opposite effects on the {sup 13}C and {sup 15}N chemical shifts; i.e. there is a strictly inverse relationship between {delta}{sub 15{sub N}} and {delta}{sub 13{sub C}}. This suggests that the resonance structure Co{sup +}{double bond}C{double bond}N{sup {minus}} indicative of d{pi}-p{pi} metal-to-ligand back-bonding is important in these cobalt-cyanide complexes and that its contribution to the overall bonding is highly sensitive to trans axial ligation effects. {sup 15}N chemical shifts and {sup 15}N-{sup 13}C coupling constants of enriched, base-off CNCbl have also been studied as a function of acidity in sulfuric acid/water mixtures and have permitted an assignment of the previously demonstrated protonation of the axial cyanide ligand in such media. The results are only consistent with a conjugate acid species that is N-bound (rather than the normal C-bound) and protonated at the cyanide carbon. 82 refs., 3 figs., 2 tabs.

• OSTI ID: 6010606
• Journal Information: Inorganic Chemistry; (USA), Journal Name: Inorganic Chemistry; (USA) Vol. 29:19; ISSN 0020-1669; ISSN INOCA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
400202 -- Isotope Effects
Isotope Exchange
& Isotope Separation
AMINES
CHEMICAL SHIFT
COBALT COMPLEXES
COMPLEXES
DATA
EXPERIMENTAL DATA
INFORMATION
ISOTOPES
LIGHT NUCLEI
NITROGEN 15
NITROGEN ISOTOPES
NMR SPECTRA
NUCLEI
NUMERICAL DATA
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
SPECTRA
STABLE ISOTOPES
TRANSITION ELEMENT COMPLEXES