A cyclic Fc-histidine conjugate: Synthesis and properties - Interactions with alkali metal ions

The synthesis of the novel N,N-pi-(ferrocenophane-1,1'-diyldicarbonyl)-bridged histidine methyl ester 1 and of the acyclic bis(histidine methyl ester) derivative 3 are reported. The structure of 1 was studied in the solid state and in solution. The single-crystal structure of 1 shows that both proximal ferrocenyl (Fc) carbonyl groups are syn with respect to each other, which is a new structural motif for Fc-amino acid conjugates. This new syn conformation allows effective binding to alkali metal cations. Binding is evaluated by cyclic voltammetry monitoring the halfwave potential of the Fc group. Cation binding causes a shift to lower potential (Na+ > Li+ > K+, Cs+). Upon binding, compound 1 shows selectivity towards Na+ ions. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006).