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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 15, Number 8
BKCSDE 15(8)
August 20, 1994 

1H NMR Study of Imidazole, L-Histidine, and Their Derivatives Coordinated to the Paramagnetic Undecatungstocobalto(Ⅱ)silicate and -nickelo(Ⅱ)silicate Anions
Moonhee Ko, Gyung Ihm Rhyu, Hyunsoo So*
1H NMR spectra of imidazole, 2-and 4(5)-methylimidazole, histamine, L-histidine, L-histidine methyl ester, Nα-acetyl-L-histidine, and L-carnosine coordinated to the paramagnetic undecatungstocobalto(Ⅱ)silicate (SiW11Co) and undecatungstonickelo(Ⅱ)silicate (SiW11Ni) anions are reported. For these complexes the ligand exchange is slow on the NMR time scale and the pure resonance lines of the free ligand and the complexes have been observed separately at room temperature. Two different complexes are formed, depending upon which nitrogen atom of the imidazole ring is coordinated to the cobalt or nickel ion of SiW11M. Thus the NMR spectrum of a D2O solution containing a ligand and SiW11M consists of three sets of lines originating from the free ligand and two complexes. All NMR lines of the SiW11Co complexes have been assigned unequivocally using the saturation transfer technique. The temperature dependence of some spectra are also reported. The NMR spectra of some complexes show that the internal rotation of the substituent on the imidazole ring is hampered by the heteropolyanion moiety even at room temperature.
673 - 679
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