Synthesis, x-ray structure of ferrocene bearing Bis(Zn-cyclen) complexes and the selective electrochemical sensing of TpT
Zeng, Zhanghua, Torriero, Angel A. J., Belousoff, Matthew J., Bond, Alan M. and Spiccia, Leone 2009, Synthesis, x-ray structure of ferrocene bearing Bis(Zn-cyclen) complexes and the selective electrochemical sensing of TpT, Chemistry : a European journal, vol. 15, no. 41, pp. 10988-10996, doi: 10.1002/chem.200901639.
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Synthesis, x-ray structure of ferrocene bearing Bis(Zn-cyclen) complexes and the selective electrochemical sensing of TpT
The new ligand, [Fc(cyclen)2] (5) (Fc=ferrocene, cyclen=1,4,7,10-tetraazacyclododecane), and corresponding ZnII complex receptor, [Fc{Zn(cyclen)(CH3OH)}2](ClO4)4 (1), consisting of a ferrocene moiety bearing one ZnII-cyclen complex on each cyclopentadienyl ring, have been designed and prepared through a multi-step synthesis. Significant shifts in the 1H NMR signals of the ferrocenyl group, cf. ferrocene and a previously reported [Fc{Zn(cyclen)}]2+ derivative, indicated that the two ZnII-cyclen units in 1 significantly affect the electronic properties of the cyclopentadienyl rings. The X-ray crystal structure shows that the two positively charged ZnII-cyclen complexes are arranged in a trans like configuration, with respect to the ferrocene bridging unit, presumably to minimise electrostatic repulsion. Both 5 and 1 can be oxidized in 1:4 CH2Cl2/CH3CN and Tris-HCl aqueous buffer solution under conditions of cyclic voltammetry to give a well defined ferrocene-centred (Fc0/+) process. Importantly, 1 is a highly selective electrochemical sensor of thymidilyl(3′-5′)thymidine (TpT) relative to other nucleobases and nucleotides in Tris-HCl buffer solution (pH 7.4). The electrochemical selectivity, detected as a shift in reversible potential of the Fc0/+ component, is postulated to result from a change in the configuration of bis(ZnII-cyclen) units from a trans to a cis state. This is caused by the strong 1:1 binding of the two deprotonated thymine groups in TpT to different ZnII centres of receptor 1. UV-visible spectrophotometric titrations confirmed the 1:1 stoichiometry for the 1:TpT adduct and allowed the determination of the apparent formation constant of 0.89±0.10×106 M−1 at pH 7.4.
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