The electrochemical incorporation of carbon dioxide into epoxides catalyzed by nickel(II) complexes afforded cyclic carbonates in good yields under very mild conditions (p CO 2 = 1 atm, room temperature). Mechanistic and electrochemical studies revealed the cooperative role of reduced nickel species in the activation of CO 2 and the influence of magnesium ions as Lewis acids in the activation of the oxirane ring. Both the presence of nickel catalysts and Mg 2 ions were necessary for the electrocarboxylation of epoxides under mild conditions.

In an attempt to directly approach the postulated toxic domain of Clostridium difficile's TcdB-10463, eight subclones of different size and locations in the N-terminal third of the toxin were generated. Expression of these toxin fragments was checked in Western blots and the enzymatic activity of the expressed proteins was analyzed by glucosylating Ras related small GTP-binding proteins. Two polypeptides of 875 aa (TcdBc1-3) and 557 aa (TcdBc1-H) glucosylated their targets Rho, Rac and Cdc42 with the same activity and specificity as the holotoxin. In comparison 516 aa (TcdBc1-N) and 467 aa (TcdBc1-A) protein fragments exhibited highly reduced activity, while Tcdc1 and TcdB2-3 (aa 1-243 and 244-890, respectively) were enzymatically inactive. Our results indicate that all structures involved in the catalysis are located at several different sites within the 557 aa fully active fragment. The shortest enzymatically still active protein covers aa 1-467 and obviously fulfils all minimal requirements for glucosylation. The data support the postulated three domain model of 'large clostridial cytotoxins'.

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