Distance Dependence of the Charge Transfer Rate for Peptide Nucleic Acid Monolayers

Abstract

Charge transfer studies have been performed for self-assembled monolayers of single-stranded and double-stranded peptide nucleic acids (PNAs) having a C-terminus cysteine and an N-terminus ferrocene group as a redox reporter. The decay of the charge transfer rate with distance was strong for short single-stranded PNA molecules and weak for long single-stranded and double-stranded PNAs. Possible mechanisms for this "softening" of the distance dependence are discussed. The nature of the mechanism change can be explained by a transition of the charge transport mechanism from superexchange-mediated tunneling for short PNAs to a "hopping" mechanism for long PNAs.

Metal-containing peptide nucleic acid conjugates

“…[184][185][186] For charge transfer studies, the tunnelling decay constant was measured in SAMs of PNA sequences with varying numbers of thymines (from 3 to 7 thymines) by cyclic voltammetry. 186 According to the superexchange/tunnelling mechanism, decreases rapidly with increasing PNA length. For more than 7 thymines, the charge transfer rate is less distance dependent, which is consistent with the hopping theory.…”

Mechanistic Studies of Fc‐PNA(⋅DNA) Surface Dynamics Based on the Kinetics of Electron‐Transfer Processes

“…This is coherent with the MD simulations of Nilsson et al, according to which a base-stacked structure was predicted for single-stranded PNA in aqueous solution at room temperature. [40] Taking this into account, the contour lengths L could be calculated (L P12 = 6.08 nm and L P12·D12 = 5.72 nm; for the data for P3 to P16 see the Supporting Information) by adding the characteristic values for the lengths of the different molecule fragments (per nucleobase: 3.5 for the ssPNA species P3 to P16, [45] and 3.2 for the dsPNA·DNA species P12·D12; [51] 5 for the ferrocene unit, [45] and 13.8 for the peptidic Lys-Ahx-Cys linker [52] ).…”

“…The "standing-up" conformation revealed a significantly slower ET process. [44,45] However, until now no attempt has been made to rationalize this behavior quantitatively.…”

“…The determined k 0 is between the value of k 0 = 6 10 8 s À1 extrapolated for Fc moieties located close to the surface [44,57] and the values reported for the charge transport through 10-mer Fc-PNA strands (k 0 = 0.7 10 À2 s À1 for ssPNA and k 0 = 9.0 10 À2 s À1 for dsPNA·PNA). [45] . From this, we conclude that the ET at the loosely packed P12/Au and P12·D12/Au surfaces occurs over an average distance x that is between x min = d H (d H : outer Helmholtz plane) and x max = L (L: contour length of the strand).…”

Nucleic Acid Electronics: from Chemistry to Circuits

“…PNA is achiral so Using what we know, if the backbone is electrically neutral, we may guess that the base-pair sequence governs electron transport and its mechanism. And these notions have been confirmed in self-assembled monolayers of PNA: the hopping mechanism between the guanine residues predominates, resulting in insulative behavior [65]. By itself, PNA, coordinated with CNTs, can exhibit diode-like behavior, which is promising [66].…”