title: Role of nucleobase energetics and nucleobase interactions in single-stranded peptide nucleic acid charge transfer.
abstract: Self-assembled monolayers of single-stranded (ss) peptide nucleic acids (PNAs) containing seven nucleotides (TTTXTTT), a C-terminus cysteine, and an N-terminus ferrocene redox group were formed on gold electrodes. The PNA monomer group (X) was selected to be either cytosine (C), thymine (T), adenine (A), guanine (G), or a methyl group (Bk). The charge transfer rate through the oligonucleotides was found to correlate with the oxidation potential of X. Kinetic measurements and computational studies of the ss-PNA fragments show that a nucleobase mediated charge transport mechanism in the deep tunneling superexchange regime can explain the observed dependence of the kinetics of charge transfer on the PNA sequence. Theoretical analysis suggests that the charge transport is dominantly hole-mediated and takes place through the filled bridge orbitals. The strongest contribution to conductance comes from the highest filled orbitals (HOMO, HOMO-1, and HOMO-2) of individual bases, with a rapid drop off in contributions from lower lying filled orbitals. Our studies further suggest that the linear correlation observed between the experimental charge transfer rates and the oxidation potential of base X arises from weak average interbase couplings and similar stacking geometries for the four TTTXTTT systems.
authors.affiliation: Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA.
authors.forename: Amit
authors.initials: A
authors.lastname: Paul
authors.forename: Silvia
authors.initials: S
authors.lastname: Bezer
authors.forename: Ravindra
authors.initials: R
authors.lastname: Venkatramani
authors.forename: Laura
authors.initials: L
authors.lastname: Kocsis
authors.forename: Emil
authors.initials: E
authors.lastname: Wierzbinski
authors.forename: Alexander
authors.initials: A
authors.lastname: Balaeff
authors.forename: Shahar
authors.initials: S
authors.lastname: Keinan
authors.forename: David N
authors.initials: DN
authors.lastname: Beratan
authors.forename: Catalina
authors.initials: C
authors.lastname: Achim
authors.forename: David H
authors.initials: DH
authors.lastname: Waldeck
mesh_terms: D001483:Base Sequence; D055664:Electrochemical Techniques; D009690:Nucleic Acid Conformation; D009841:Oligonucleotides / Q000737:chemistry; D010084:Oxidation-Reduction; D020135:Peptide Nucleic Acids / Q000737:chemistry*; D055672:Static Electricity
chemical_list: D009841:Oligonucleotides; D020135:Peptide Nucleic Acids