Spectroscopic and Electrochemical Investigations into the Interactions of Metal Ions with a Ferrocenoyl–Histidine Peptide Conjugate

Abstract

A new ferrocene-peptide conjugate Fc-[His(DNP)-GlyOMe] 2 (2) was synthesized and characterized spectroscopically. The conjugate displays the familiar 1,2Ј-P helical Herrick conformation in solution and exhibits a reversible oneelectron oxidation at 380 mV versus Fc/Fc + . , Zn 2+ , and Cd 2+ with conjugate 2 were probed by using a range of techniques, including cyclic voltammetry, and NMR and CD spectroscopies. Electrochemical studies showed that the system exhibits a rare cathodic potential shift upon the addition of metal ions, which followed the order Cu 2+ (-436 mV) Ͼ Fe 2+ (-284 mV) Ͼ Zn 2+ (-270 mV) Ͼ Cd 2+ (-238 mV) Ͼ Mg 2+ (-

Metal Coordination to Unsymmetric 1,n′‐Disubstituted Ferrocene Histidine Peptides

“…This suggests that metal complexation occurs with the imidazole rings. Similar changes have been reported formerly in which the addition of metal to Fc‐peptides containing His resulted in metal binding to His residues as was observed based on the 1 H NMR results , . Conversely, there has been a report in which metal titration with several bis(histidine) derivatives of 1, n′ ‐ferrocenedicarboxylic acid that were synthesized for potential as ligands to build a small peptidic model systems of zinc structural sites that showed a slow exchange process revealing the lifetime of two states: bound and unbound metal to ligand evidenced by distinguishable resonances for both conditions.…”

“…In some cases when carrying out 1 H NMR titration experiments the chiral protons and diastereotopic protons will shift as the side‐chain rotation will not be constrained as metal complexation takes place. [21c], , After metal addition each of the α‐ and diastereotopic β‐proton resonances were not observed to change significantly beyond 1:1 stoichiometry. This offers strong evidence that each peptide ligand offers only its imidazole donors for ligation.…”

“…Metal coordination was expected to involve the imidazole groups of the His residues (Scheme ). [21c], , Such metal coordination to the imidazole groups is expected to influence the redox properties of the Fc group and, in addition, should further be detectable by a shift in the resonance of the imidazole protons in the 1 H NMR spectrum. The fast exchange process for Fc‐peptide conjugates 3 and 4 were monitored in the absence and presence of metal ions Zn 2+ , Co 2+ and Cd 2+ as shown in Figure and Figures S14–S18 of the Supporting Information.…”

“…A striking quality of these divalent metal ions is that each one of them are capable of accommodating tetrahedral coordination environment , . As an increasing amount of metal ions were added to Fc‐peptide conjugates 3 and 4 , it became visible that there was no substantial changes in the CD spectra were observed after 1 mol equivalent of metal ion.…”

Helically Chiral Peptides That Contain Ferrocene‐1,1′‐diamine Scaffolds as a Turn Inducer

“…The metal complexes show the Cotton effects of the same sign as the corresponding precursors 22 and 24 in the region of the ferrocene group. This suggests that these metal ions do not alter the conformation of the ferrocene group, as we have previously found for the Fn−[CO−His(DNP)−Gly−OMe] 2 metal complexes . Presumably, the differences are due to the proximity of the metal coordination site to the ferrocene group.…”