G. C. Hayward, H. Hill, J. M. Pratt, ROBERT J. P. Williams
{"title":"The chemistry of vitamin B12. Part XII. The co-ordination of nitrogenous bases","authors":"G. C. Hayward, H. Hill, J. M. Pratt, ROBERT J. P. Williams","doi":"10.1039/J19710000196","DOIUrl":null,"url":null,"abstract":"Formation constants have been determined for the substitution of co-ordinated water in diaquocobinamide by ammonia and imidazole, in aquocobalamin by ammonia, and in cyanoaquocobinamide by ammonia, pyridine, imidazole, benzimidazole, and adenine; the last three bases can co-ordinate in the conjugate anion form. It is shown that the formation constants for the binding of ammonia are more sensitive to the nature of the trans-ligand than those for the binding of imidazole, and that the relative order of their formation constants can change as the trans-ligand is varied. Pseudo-first-order rate constants for the substitution of co-ordinated ammonia by water at 30° have been obtained for corrinoids with the following trans-ligands: H2O, 1·4 × 10-5 s–1; 5,6-dimethylbenzimidazole, 8·6 × 10-5 s–1; CN–, SO32–, and CH3–, 3 × 10–1 s–1. The order of ligands observed in the kinetic trans-effect parallels that for the thermodynamic trans-effect.","PeriodicalId":17321,"journal":{"name":"Journal of The Chemical Society A: Inorganic, Physical, Theoretical","volume":null,"pages":null},"PeriodicalIF":0.0000,"publicationDate":"1971-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"12","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of The Chemical Society A: Inorganic, Physical, Theoretical","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.1039/J19710000196","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 12
Abstract
Formation constants have been determined for the substitution of co-ordinated water in diaquocobinamide by ammonia and imidazole, in aquocobalamin by ammonia, and in cyanoaquocobinamide by ammonia, pyridine, imidazole, benzimidazole, and adenine; the last three bases can co-ordinate in the conjugate anion form. It is shown that the formation constants for the binding of ammonia are more sensitive to the nature of the trans-ligand than those for the binding of imidazole, and that the relative order of their formation constants can change as the trans-ligand is varied. Pseudo-first-order rate constants for the substitution of co-ordinated ammonia by water at 30° have been obtained for corrinoids with the following trans-ligands: H2O, 1·4 × 10-5 s–1; 5,6-dimethylbenzimidazole, 8·6 × 10-5 s–1; CN–, SO32–, and CH3–, 3 × 10–1 s–1. The order of ligands observed in the kinetic trans-effect parallels that for the thermodynamic trans-effect.