Design and synthesis of flavin-conjugated peptides and assembly on a gold electrode

Flavin-conjugated peptides composed of one or two amphiphilic α-helix segments have been designed and synthesized. 7-Acetyl-10-methylisoalloxazine (Fla) as a model flavin has been introduced on the side chain of Cys at the 6th, 7th or 8th position of each α-helical 14-peptide. A CD study in aqueous solution revealed that the position of Fla on the peptide strongly influenced the peptide secondary structure. Additionally, CD spectra indicated that the Fla in the peptides was oriented in a different manner depending on the position when the peptide took on the α-helix structure. Furthermore, the flavin-conjugated peptides have been adsorbed on a gold surface through the sulfide linkage, as a basic study for peptidyl devices in the future. By the use of Fla as an electrochemical probe, we examined properties of the peptide assembled on the gold electrode. The cyclic voltammetry measurements revealed that the functional group, Fla, was redox-active on the electrode and the peptide bound on the surface in a monolayer. Moreover, the flavin-conjugated peptide could mediate the electron transfer from the electrode to Fe(CN)₆^3- ion or cytochrome c in a vector manner. The redox-active probe, Fla, has been demonstrated to provide significant information about the assembly and function of the α-helix peptides on the gold electrode surface by electrochemical measurements.