title: Synthesis, X-ray structure of ferrocene bearing bis(Zn-cyclen) complexes and the selective electrochemical sensing of TpT.
abstract: The new ligand, [Fc(cyclen)(2)] (5) (Fc=ferrocene, cyclen=1,4,7,10-tetraazacyclododecane), and corresponding Zn(II) complex receptor, [Fc{Zn(cyclen)(CH(3)OH)}(2)](ClO(4))(4) (1), consisting of a ferrocene moiety bearing one Zn(II)-cyclen complex on each cyclopentadienyl ring, have been designed and prepared through a multi-step synthesis. Significant shifts in the (1)H NMR signals of the ferrocenyl group, cf. ferrocene and a previously reported [Fc{Zn(cyclen)}](2+) derivative, indicated that the two Zn(II)-cyclen units in 1 significantly affect the electronic properties of the cyclopentadienyl rings. The X-ray crystal structure shows that the two positively charged Zn(II)-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 CH(2)Cl(2)/CH(3)CN and Tris-HCl aqueous buffer solution under conditions of cyclic voltammetry to give a well defined ferrocene-centred (Fc(0/+)) 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 Fc(0/+) component, is postulated to result from a change in the configuration of bis(Zn(II)-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 Zn(II) 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+/-0.10x10(6) M(-1) at pH 7.4.
authors.affiliation: School of Chemistry, Monash University, Clayton, Victoria, Australia.
authors.forename: Zhanghua
authors.initials: Z
authors.lastname: Zeng
authors.forename: Angel A J
authors.initials: AA
authors.lastname: Torriero
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Belousoff
authors.forename: Alan M
authors.initials: AM
authors.lastname: Bond
authors.forename: Leone
authors.initials: L
authors.lastname: Spiccia
mesh_terms: D018360:Crystallography, X-Ray; D000080027:Cyclams; D005296:Ferrous Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D006571:Heterocyclic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D000075163:Metallocenes; D008968:Molecular Conformation; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D015032:Zinc / Q000737:chemistry*
chemical_list: D000080027:Cyclams; D005296:Ferrous Compounds; D006571:Heterocyclic Compounds; D000075163:Metallocenes; D009942:Organometallic Compounds; C038072:cyclen; D015032:Zinc; C004998:ferrocene