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Proceedings of the 31 st European Peptide SymposiumMichal Lebl, Morten Meldal, Knud J. Jensen, Thomas Hoeg-Jensen (Editors)European Peptide Society, 2010Mapping Charge Delocalization in a Peptide Chain Triggeredby Oxidation of a Terminal Ferrocene MoietyVanessa Marcuzzo, Alessandro Donoli, Roberta Cardena,Alessandro Moretto, Claudio Toniolo, and Saverio SantiDepartment of Chemical Sciences, University of Padova, Padova, 35131, ItalyIntroductionElectron transfer is one of the most relevant processes in chemistry and biology. Longrangeelectron transfer (ET) through proteins and enzymes is a fundamental step for allliving organisms. The spatial organization of the electron donor and electron acceptor inpeptides and proteins, as well as the dynamics of the ET between them, critically dependson the structure-directing and charge-transmitting properties of hydrogen bonds. ETthrough peptide helices has attracted much attention because their assemblies are universalmotifs found in biological ET systems.Results and DiscussionTwo series of peptides of different length and rigidity, based on the strongly helicogenicα-aminoisobutyric acid (Aib) residue and containing a terminal ferrocene (Fc) unit,Fc−CO-(Aib) n −OMe (A n , n = 1−5, OMe, methoxy) and Z−(Aib) n −NH−Fc (B n , n = 1−5, Z,benzyloxycarbonyl), were prepared and investigated. We utilized the oxidation-statesensitive, spectroscopic tags of peptides, the CO and NH groups, to map chargedelocalization triggered by oxidation of the terminal ferrocene, induced and monitored byVis-IR-NIR spectroelectrochemistry. The rigid and well-defined 3 10 -helical structure of(Aib) n homo-peptides [1,2] is advantageous for the study of the distance dependence ofcharge delocalization. The orientation of the carbonyl groups in the 3 10 -helix produces adipole with the positive end at the N-terminus and the negative end at the C-terminus.Thus, the A n and B n peptides series are characterized by an opposite-direction macrodipoletowards the redox Fc/Fc + probe.0,720,68E 1/2(V vs SCE)0,640,600,560,520,480,441 2 3 4 5n-AibFig. 1. Redox potentials vs saturated calomel electrode (SCE) of the Z-(Aib) n -NHFc(n=1-5) peptide series recorded at a 0.5 mm diameter gold disk electrode in CH 2 Cl 2 with0.1 M nBu 4 NPF 6 as supporting electrolyte.584