Deuterium-substitution effects on relaxation times and interligand nuclear Overhauser effects for assignment of ligand resonances and isomer identification in cobalt(III) complexes

Storm, Carlyle B.; Turner, A.; Rowan, Nancy S.

doi:10.1021/ic00202a033

Cited by 9 publications

(1 citation statement)

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“…Preparation of complexes [Co(NH3),imidazole](C104) and [Co(NH&-1 -methylimidazole](ClO,) were prepared according to literature procedures (14,26; 27) and their identities and purity checked by comparing their uv-visible and 'H nmr spectroscopic characteristics with published data (26)(27)(28)(29). ),imidazole](C104) (17.4 mg) placed in a heavywalled glass ampoule.…”

Section: Methodsmentioning

confidence: 99%

Metal ion – biomolecule interactions. Part 16. C(2)-H isotopic exchange in Co(III)-coordinated imidazoles

Buncel¹,

Yang²,

Moir³

et al. 1995

Can. J. Chem.

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Transition-metal-bound imidazoles are suitable models for evaluating the roles of metal ions in biomolecules having the imidazole moiety and similar heterocyclic residues as part of their structure. Such studies provide useful insights into metal-biomolecule interactions in biological systems, especially when the lability of the metal-ligand bond is substantially reduced, such that the identity of the metal-ligand complex is preserved during the course of the reaction under investigation. The present paper reports on a kinetic study of tritium exchange from the C(2) position of the imidazole moiety in the substitution-inert complex cations been determined in aqueous solution at 60°C. Both substrates are believed to react through rate-determining attack of hydroxide ion (kM+ pathway) at C(2)-T. Dissection of the kinetic data reveals an additional pathway for 1 consequent upon deprotonation of its pyrrole-like N-H(T) to yield 3, which is then attacked by hydroxide at C(2) (kM pathway). The ratio kM+/kN = lo3 that is obtained is in accord with the expected reduced reactivity of 3. Comparison of the present data with those reported for a variety of heterocyclic substrates shows that the order of reactivity, protonated >> metal ion coordinated >> neutral form of substrates, prevails. The superiority of the proton over metal ions in catalyzing isotopic hydrogen exchange is attributed to its larger ground state acidifying effect coupled with the greater transition state stabilization it affords, relative to metal ions. The exchange reaction of 3 via the kN pathway is the first example of a reactive anionic species in which the negative charge is located a to the exchanging C-H.Received January 17, 1995.Key words: tritium exchange, cobalt (111)-coordinated imidazoles.Resume : Les imidazoles lits a des mttaux de transition sont des modkles approprits pour tvaluer les rBles des ions mttalliques dans des biomoltcules dont une partie de la structure contient de l'imidazole ou des rCsidus htttrocycliques semblables. De telles Ctudes fournissent des donntes utiles sur les interactions mCtalbiomoltcule des systbmes biologiques, en particulier lorsque la labilitt du complexe mttal-coordinat est grandement rtduite alors que I'identitt du complexe mttal-coordinat est prtservte durant la reaction ttudite. Dans ce travail on rapporte les donntes obtenues au cours d'une ttude cinttique de l'tchange du tritium de la position C(2) de la portion imidazole lors de substitutions des cations complexes inertes [ C O ( N H~) , {~-~H } - imidazole13+ (1) et [~o(~~~),-l-mtth~l-(2-~~~-imidazole]~+ (2).On a dttermint les profils vitesse-pH en solutions aqueuses 60°C. On croit que les deux substrats rtagissent par le biais d'une attaque de la position C(2)-T par I'ion hydroxyde (voie kM+) qui dttermine la vitesse de la rtaction. La dissection des donntes cinttiques rtvkle l'existence d'une autre voie rtactionnelle du compost 1 qui suit la dCprotonation de son N-H(T), qui resemble h un pyrrole, en compost 3 qui est alors attaqut par l'h...

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Section: Methodsmentioning

confidence: 99%