Metal coordination of ferrocene–histidine conjugates12. Issue 14 (28th March 2017)

• Record Type: Journal Article
• Authors: Ferranco, Annaleizle; Basak, Shibaji; Lough, Alan; Kraatz, Heinz-Bernhard
• Is Part Of: Dalton transactions. Volume 46:Issue 14(2017)
• Page Start: 4844
• Page End: 4859
• Publication Date: 2017-03-28
• Subjects: Chemistry, Inorganic -- Periodicals; Chemistry, Physical and theoretical -- Periodicals; Chemistry, Inorganic -- Periodicals; 546.05
• DOI: 10.1039/c7dt00456g
• Languages: English
• ISSNs: 1477-9226

Abstract

Abstract : Synthesis and complete structural characterization of ferrocene–histidine dipeptides including detailed analysis of the ligand–metal complexation. Abstract : This study presents a few bis(histidine) ligands working to build a small peptidic model system of zinc structural sites. Ferrocene–peptide conjugates Fc[CO-His(Trt)-His(Trt)-OMe]2 (3 ), Fc[CO-His(Trt)-Asp(OMe)-OMe]2 (4 ), and Fc[CO-His(Trt)-Glu(OMe)-OMe]2 (5 ) were synthesized and characterized spectroscopically. 1 H-NMR and IR spectroscopic studies reveal hydrogen bonding interactions and while more detailed circular dichroism studies show a 1, 2′- P helical "Herrick conformation" for Fc-conjugates4 and5, we discovered M -helical chirality in Fc–peptide3 . The half-wave potentials ( E 1/2 ) of ferrocene–peptides follow the sequence3 <5 <4 which is rationalized by the capability of the peptide side chains to stabilize the oxidized ferrocene–peptide form. The diffusion coefficient ( D ) and electron transfer rate constant ( k sh ) values for all Fc-conjugates were determined by their resultant cyclic voltammetry data. The interactions for all Fc-conjugates were probed with metal ions Zn 2+, Cd 2+, Ni 2+, Cu 2+, Mn 2+, and Mg 2+ which were detected to interact at 1 : 1 ratio between the ligand and metal ion verified by 1 H-NMR and UV titration studies, electrochemical investigations, and ESI-MS experiments. Electrochemical studies for all Fc-conjugates exhibit anodic potential shifts upon the addition of metal ions, which follow the order Cu 2+ > Zn 2+ > Ni 2+ > Cd 2+ > Mn 2+ > Mg 2+ . NMR spectroscopic experiments show that the two nitrogen atoms present on each imidazole ring of His residues are the site of metal coordination. There is a strong indication that peptide conjugates4 and5 in the presence of Zn 2+ enforce a coordination number of four as the CD spectra of Fc-conjugates4 and5 exhibited a red shift which corresponds to the third and fourth coordination sites occupied by neutral carbonyl oxygen donor atoms, in addition, carbonyl amide appears downward shifted in wavenumber upon metal addition.