Preparation and X-ray Analysis of Crystals of Azido- and Chlorocobalamin Containing LiCl: A Structural Model for the Interactions of the Corrin Ring with Ionic Species
| Autor: | Silvano Geremia, Miroslav Slouf, Lucio Randaccio, Michela Furlan |
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| Přispěvatelé: | Randaccio, Lucio, Furlan, M., Geremia, Silvano, Slouf, M. |
| Rok vydání: | 1998 |
| Předmět: | |
| Zdroj: | Scopus-Elsevier |
| ISSN: | 1520-510X 0020-1669 |
| Popis: | Recently, the reactions of adenosylcobalamin (AdoCbl) and methylcobalamin (MeCbl) (for XCbl see Chart 1) with cyanide have been reinvestigated.1,2 The AdoCbl has been shown1 to react by attack of the cyanide ion on the â-adenosyl side. On the contrary, no cyanation reaction between MeCbl and cyanide has been observed under the same conditions. 1H NMR results2 suggested the formation of an ion-pair species MeCbl‚CN-, with the potentially π-interacting cyanide ion located close to the corrin ring, on the side of dimethylbenzimidazole ligand. Association between MeCbl and charged species, particularly anions such as PtX4 or AuCl4, has been reported in a few cases3 and ion-pair formation, prior to substitution, has been suggested4 in the displacement of the â-H2O ligand in aquocobalamin. NMR studies on the dimerization of RCbl, with several R groups, indicated that all the RCbl, whether forming dimers (R ) Me, Et) or not (R ) n-Pr, Ado, CN, H2O), showed NaCl specific (although not easily interpretable) shifts of some resonances.5 All these results suggest the existence of weak bonding interactions between corrinoids and charged species, which influence the corrinoid solution behavior. The interest in the study of the interactions, involving corrinoids and charged species, resides in the possible role that they could play in determining the organo-group transfer and electron-transfer reactions of B12 compounds.2,5,6 Furthermore, such interactions are potentially important in the binding of corrinoids to B12 proteins, via charged amino acid residues. With the aim to obtain, at least in the solid state, a structural picture of the interactions between corrinoids and charged species, we have tried to crystallize cobalamins in the presence of highly concentrated salts, using the well-known hanging-drop technique, usually employed for obtaining protein single crystals. We report here the preparation and the X-ray analysis, based on synchrotron data, of crystals of chloroand azidocobalamin containing LiCl, 1 and 2, respectively. |
| Databáze: | OpenAIRE |
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