Effect of backbone flexibility on charge transfer rates in peptide nucleic acid duplexes |
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Authors: | Wierzbinski Emil de Leon Arnie Yin Xing Balaeff Alexander Davis Kathryn L Reppireddy Srinivas Venkatramani Ravindra Keinan Shahar Ly Danith H Madrid Marcela Beratan David N Achim Catalina Waldeck David H |
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Institution: | Department of Chemistry, University of Pittsburgh, Pennsylvania 15260, United States. |
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Abstract: | Charge transfer (CT) properties are compared between peptide nucleic acid structures with an aminoethylglycine backbone (aeg-PNA) and those with a γ-methylated backbone (γ-PNA). The common aeg-PNA is an achiral molecule with a flexible structure, whereas γ-PNA is a chiral molecule with a significantly more rigid structure than aeg-PNA. Electrochemical measurements show that the CT rate constant through an aeg-PNA bridging unit is twice the CT rate constant through a γ-PNA bridging unit. Theoretical calculations of PNA electronic properties, which are based on a molecular dynamics structural ensemble, reveal that the difference in the CT rate constant results from the difference in the extent of backbone fluctuations of aeg- and γ-PNA. In particular, fluctuations of the backbone affect the local electric field that broadens the energy levels of the PNA nucleobases. The greater flexibility of the aeg-PNA gives rise to more broadening, and a more frequent appearance of high-CT rate conformations than in γ-PNA. |
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