14N/15N ISOTOPE EFFECT ON THE ELECTRON TRANSFER PROCESS BETWEEN PHENOTHIAZINE AND ITS RADICAL CATION
✍ Scribed by Long-Min Wu; Jian-Ming Lü; Xiao-Lin Wen; Xue-Qing Jia; You-Cheng Liu; Zhong-Li Liu
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 181 KB
- Volume
- 10
- Category
- Article
- ISSN
- 0894-3230
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✦ Synopsis
An appreciable equilibrium isotope effect has been observed for electron transfer from phenothiazine (PT) to the radical cation of its 15 N-substituted analogue ([ 15 N]PT +• ), i.e.
PT+[
15 N]PT +• K PT +• +[ 15 N]PT via electron paramagnetic resonance analysis of the mixed radical cations formed from mixing the [ 15 N]phenothiazine radical cation hexachloroantimonate and phenothiazine in acetonitrile (K = 0•77 ؎ 0•10 at 25 °C), and by physical separation of the neutral phenothiazines from the radical cation salts in the equilibrium mixture (K = 0•83 ± 0•10 at 25 °C). Infrared and Raman spectra of [ 14 N]-and [ 15 N]phenothiazines and their radical cations were measured to assign the vibrational frequency shifts caused by the heavy-atom substitution and radical cation formation, which gave an estimate of the enthalpy change of 441•7 J mol Ϫ 1 for the electron transfer process. These results reveal that 15 N substitution of phenothiazine decreases appreciably the ionization potential of the molecule, making it easier to lose an electron to form the corresponding radical cation in solution.