| 1. |
- Lomoth, R, et al.
(författare)
-
Genuine pyrimidine radical cations generated by radiation-induced electron transfer to butyl chloride or acetone parent ions
- 1999
-
Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 103:15, s. 2641-2648
-
Tidskriftsartikel (refereegranskat)abstract
- Radical cations of multiple methylated uracils and thymines were generated by electron transfer to parent ions of solvents of low polarity such as n-butyl chloride and acetone. Pulse radiolysis resulted in the transient optical absorption spectra of the pyrimidine radical cations (Py.+) which exhibit bands generally peaking around lambda = 400 nm and in acetone showing an additional band in the range of lambda(max) = 500-560 nm. The identification of the solute radical cations is based on the direct observation of the formation of Py.+ by electron transfer (k = (1-2) x 10(10) M(-1)s(-1)), the nucleophilic reaction with the counterion (e.g., Cl-), the relatively low reactivity with oxygen even for the fully methylated nitrogen groups (k < 2 x 10(8) M(-1)s(-1)), and the observation of a subsequent electron transfer from triphenylamine to the pyrimidine radical cations proceeding in a diffusion-controlled manner. The solvent dependence of the spectral shape of Py.+ was also studied in acetone/n-butyl chloride mixtures and was found to depend on the polarity of the surroundings. This phenomenon is explained in terms of a lactam-lactim-like tautomerism of the transient involving the whole plane molecule. Quantum chemical calculations support the experimental findings by explaining the spectral structure and enable the formulation of the lactims as either 1,4- or 3,4-localized.
|
|
| 2. |
- Lomoth, R, et al.
(författare)
-
Spectral and kinetic identification of radical cations of pyrimidine bases by stepwise electron transfer
- 1998
-
Ingår i: Chemical Physics Letters. - 0009-2614 .- 1873-4448. ; 288:1, s. 47-51
-
Tidskriftsartikel (refereegranskat)abstract
- Radical cations of methylated derivatives of uracil and thymine were generated by electron transfer to the parent radical cation, generated in acetone by nanosecond pulse radiolysis. The resulting transient absorption peaking around 400 and 550 nm is assigned to the radical cations of the pyrimidine bases. Direct kinetic and spectroscopic evidence for this assignment has been given by a subsequent electron transfer from triphenylamine to the pyrimidine radical cations yielding the characteristic absorption spectrum of the triphenylamine radical cation. (C) 1998 Elsevier Science B.V. All rights reserved.
|
|
| 3. |
- Lomoth, R, et al.
(författare)
-
Transients of the oxidation of pyrimidines with SO4•- : Structure and reactivity of the resulting radicals
- 1999
-
Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 103:33, s. 6571-6579
-
Tidskriftsartikel (refereegranskat)abstract
- Depending on the methylation pattern, the reaction of SO4.- with various methylated pyrimidines yields radicals deprotonated at N(1) and C(5)-OH or C(6)-OH adduct radicals and probably allyl radicals by subsequent deprotonation at the C(5)-methyl group of the thymines. All of these radicals are derived from the initial SO4.- adducts on the pyrimidines that have lifetimes of several microseconds in the case of N(1)-methylated thymines. These transients could be taken for long lived pyrimidine radical cations. However, spectral and kinetic comparison with the pyrimidine radical cations generated by electron transfer in nonpolar solvents (butyl chloride, acetone) reveals the adduct nature of these transients. In the course of sulfate adduct decay, pyrimidine radical cations could be formed as nondetectable short-lived (tau < 20ns) intermediates rapidly reacting to the above-mentioned radical products. The reactivity of the SO4.- adducts, as well as that of the other pyrimidinyl radicals observed, was characterized by the subsequent oxidation of triphenylamine and di- or trimethoxybenzene, which supports the mechanistic interpretation given above. Hence there is no indication of long-lived pyrimidine radical cations under the conditions of the SO4.- oxidation of pyrimidines in aqueous solution.
|
|
