Unravelingthe Interplay of Backbone Rigidity andElectron Rich Side-Chains on Electron Transfer in Peptides: The Realizationof Tunable Molecular Wires

摘要

Electrochemical studies are reported on a series of peptides constrained into either a 310-helix (>1–>6) or β-strand (>7–>9) conformation, with variable numbers of electron rich alkene containing side chains. Peptides (>1 and >2) and (>7 and >8) are further constrained into these geometries with a suitable side chain tether introduced by ring closing metathesis (RCM). Peptides >1, >4 and >5, each containing a single alkene side chain reveal a direct link between backbone rigidity and electron transfer, in isolation from any effects due to the electronic properties of the electron rich side-chains. Further studies on the linear peptides >3–>6 confirm the ability of the alkene to facilitate electron transfer through the peptide. A comparison of the electrochemical data for the unsaturated tethered peptides (>1 and >7) and saturated tethered peptides (>2 and >8) reveals an interplay between backbone rigidity and effects arising from the electron rich alkene side-chains on electron transfer. Theoretical calculations on β-strand models analogous to >7, >8 and >9 provide further insights into the relative rolesof backbone rigidity and electron rich side-chains on intramolecularelectron transfer. Furthermore, electron population analysis confirmsthe role of the alkene as a “stepping stone” for electrontransfer. These findings provide a new approach for fine-tuning theelectronic properties of peptides by controlling backbone rigidity,and through the inclusion of electron rich side-chains. This allowsfor manipulation of energy barriers and hence conductance in peptides,a crucial step in the design and fabrication of molecular-based electronicdevices.