Photo- and Radiation-Chemical Formation and Electrophilic and Electron Transfer Reactivities of Enolether Radical Cations in Aqueous Solution

• Published in: Chemistry : a European journal Vol. 7; no. 21; pp. 4640 - 4650
• Main Authors: Bernhard, Klaus, Geimer, Judith, Canle-Lopez, Moises, Reynisson, Johannes, Beckert, Dieter, Gleiter, Rolf, Steenken, Steen
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag GmbH 05.11.2001; WILEY‐VCH Verlag GmbH
• Subjects: density functional calculations; DNA; electron paramagnetic resonance; ionization potential; photoionization; redox potential
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/1521-3765(20011105)7:21<4640::AID-CHEM4640>3.0.CO;2-E

In aqueous solution, enolether radical cations (EE.+) were generated by photoionization (λ≤222 nm) or by electron transfer to radiation‐chemically produced oxidizing radicals. Like other radical cations, the EE.+ exhibit electrophilic reactivity with respect to nucleophiles such as water or phosphate as well as electron transfer reactivity, for example, towards one‐electron reductants such as phenols, amines, vitamins C and E, and guanine nucleosides. The reactivity of these electron donors with the radical cation of cis‐1,2‐dimethoxyethene.+ (DME.+) can be described by the Marcus equation with the reorganization energy λ=16.5 kcal mol−1. By equilibrating DME.+ with the redox standard 1,2,4‐trimethoxybenzene, the reduction potential of DME.+ is determined to be 1.08±0.02 V/NHE. The oxidizing power of the radical cation of 2,3‐dihydrofuran, which can be considered a model for the enolether formed on strand breakage of DNA, is estimated to be in the range 1.27–1.44 V/NHE. In aqueous solution, enolether radical cations were generated by photoionization (λ≤222 nm) or by electron transfer to radiation‐chemically produced oxidizing radicals. The radical cations exhibit electrophilic reactivity with respect to nucleophiles such as water or phosphate as well as electron transfer reactivity towards one‐electron reductants such as phenols, amines, vitamins C and E, and guanine nucleosides. The oxidizing power of the radical cation of 2,3‐dihydrofuran, which can be considered as a model for the enolether formed on strand breakage of DNA, is estimated as 1.27–1.44 V/NHE.