Applications of ferrocene-peptide conjugates : towards new biosensors and materials

Abstract

Ferrocene-peptide conjugates represent a hybrid area between organometallic chemistry and biochemistry. In these bioconjugates, the ferrocene (Fc) moiety can serve as molecular scaffold, chromophore, sensitive probe, biological marker, redox active site, etc. Disubstituted Fc systems, in which both cyclopentadienyl rings are substituted, provide influence over the supramolecular structure of the assemblies, and serve as starting materials for the design of electronic biomaterials. Recently, 1'-amino-ferrocene-1-carboxylic acid (Fca) and 1,1'-diaminoferrocene Fc[NH2]2 were recognized as useful tools in bioorganometallic chemistry. This work sketches some novel preparative and structural aspects of Fc-peptide conjugates and explores their applications as biosensors and as polymeric materials. First, I demonstrated that Fca invariably induces a turn-like structure, which is stable in solution and the solid state. The obtained results showed different behaviour for Fca peptides depending on the chirality and position of the attached amino acid. The axial chirality of the Fca is completely dependent on the chirality of the first amino acid attached to the amino terminal of the Fca group.Second, I was able to develop a surface based sensor for the electrochemical detection of papain based on Fc-peptide conjugates. The idea was to place a surface-bound redox probe in close proximity to the electrode surface. In addition, the redox-active Fca label will be part of the recognition site but will not interfere with the recognition process. My sensor provides an attractive alternative for the electrochemical detection of non-labelled non-redox active proteins, which under current detection schemes remains a significant challenge.This work represents a truly important proof of concept for establishing this novel bioorganometallic approach for the electrochemical detection of important biological targets.Last, I was successful in developing a very convenient method to synthesize 1,1'-bis(tert-butoxycarbonylamino)ferrocene as a stable derivative of Fc[NH2]2. This new synthetic approach has circumvented the problems encountered with the explosive diazide usually used as a precursor in the conventional synthons of Fc[NH2]2. Building on this achievement, a series of novel peptide-like oligomeric and polymeric ferrocenyl-amides were synthesized and fully characterized. The electrochemical investigations on these polymers suggested unresolved or no electronic interaction between the ferrocene groups in all systems. These results may reveal the influence of the amide groups on suppressing the electronic interaction between the iron centers in my polymers. Thus, my systematic work on Fc-peptide conjugates lays solid foundations in the fields of structural control, biosensors, and material science.