title: Evidence for a near-resonant charge transfer mechanism for double-stranded peptide nucleic acid.
abstract: We present evidence for a near-resonant mechanism of charge transfer in short peptide nucleic acid (PNA) duplexes obtained through electrochemical, STM break junction (STM-BJ), and computational studies. A seven base pair (7-bp) PNA duplex with the sequence (TA)(3)-(XY)-(TA)(3) was studied, in which XY is a complementary nucleobase pair. The experiments showed that the heterogeneous charge transfer rate constant (k(0)) and the single-molecule conductance (σ) correlate with the oxidation potential of the purine base in the XY base pair. The electrochemical measurements showed that the enhancement of k(0) is independent, within experimental error, of which of the two PNA strands contains the purine base of the XY base pair. 7-bp PNA duplexes with one or two GC base pairs had similar measured k(0) and conductance values. While a simple superexchange model, previously used to rationalize charge transfer in single stranded PNA (Paul et al. J. Am. Chem. Soc. 2009, 131, 6498-6507), describes some of the experimental observations, the model does not explain the absence of an enhancement in the experimental k(0) and σ upon increasing the G content in the duplexes from one to two. Moreover, the superexchange model is not consistent with other studies (Paul et al. J. Phys. Chem. B 2010, 114, 14140), that showed a hopping charge transport mechanism is likely important for PNA duplexes longer than seven base pairs. A quantitative computational analysis shows that a near-resonant charge transfer regime, wherein a mix of superexchange and hopping mechanisms are expected to coexist, can rationalize all of the experimental results.
authors.affiliation: Department of Chemistry, Duke University, Durham, North Carolina 27708, USA.
authors.forename: Ravindra
authors.initials: R
authors.lastname: Venkatramani
authors.forename: Kathryn L
authors.initials: KL
authors.lastname: Davis
authors.forename: Emil
authors.initials: E
authors.lastname: Wierzbinski
authors.forename: Silvia
authors.initials: S
authors.lastname: Bezer
authors.forename: Alexander
authors.initials: A
authors.lastname: Balaeff
authors.forename: Shahar
authors.initials: S
authors.lastname: Keinan
authors.forename: Amit
authors.initials: A
authors.lastname: Paul
authors.forename: Laura
authors.initials: L
authors.lastname: Kocsis
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: D020029:Base Pairing; D001483:Base Sequence; D004553:Electric Conductivity; D004563:Electrochemistry; D004579:Electron Transport; D008958:Models, Molecular; D020135:Peptide Nucleic Acids / Q000737:chemistry* / Q000235:genetics
chemical_list: D020135:Peptide Nucleic Acids