Models of DNA C1‘ Radicals. Structural, Spectral, and Chemical Properties of the Thyminylmethyl Radical and the 2‘-Deoxyuridin-1‘-yl Radical

Abstract

The thyminylmethyl radical and the 2′-deoxyuridin-1′-yl radical were studied. The former radical was produced in laser flash photolysis (LFP) studies from two precursors derived from thyminylacetic acid, the N-hydroxypyridine-2-thione ester (PTOC ester), and the phenylselenyl ester. The thyminylmethyl radical has an absorbance in the range 315-340 nm. The rate constant for its reaction with octadecanethiol in THF at ambient temperature determined by LFP methods is (3.1 ( 0.6) × 10 7 M -1 s -1 . The 2′-deoxyuridin-1′-yl radical was produced in bulk photolyses from both diastereomers of the corresponding C1′ tert-butyl ketone, 1′-pivaloyl-2′-deoxyuridine, and in LFP studies from one diastereomer. Trapping of this C1′ radical with 2-mercaptoethanol, cysteine, or glutathione gave both anomers of 2′-deoxyuridine; the product ratios were similar in each case and insensitive to precursor identity or thiol concentrations. Rate constants for reactions of the 2′-deoxyuridin-1′-yl radical with thiols and metal ions were determined by LFP methods; the respective rate constants for reactions with 2-mercaptoethanol, cysteine, glutathione, CuCl 2 , and FeCl 3 in water at ambient temperature are (2.3 ( 0.5) × 10 6 , (2.9 ( 0.4) × 10 6 , (4.4 ( 0.3) × 10 6 , (7.9 ( 0.3) × 10 7 , and ca. 1 × 10 8 M -1 s -1 . The 2′-deoxyuridin-1′-yl radical was addressed computationally. The radical center is not planar, and an energy profile for interconversion of the two anomeric forms of the radical was produced. Computed vertical transitions for the thyminylmethyl radical and one anomer of the 2′-deoxyuridin-1′-yl radical are in good agreement with the experimentally measured UV-visible spectra.

The Release of 5-Methylene-2-Furanone from Irradiated DNA Catalyzed by Cationic Polyamines and Divalent Metal Cations

“…This is surprising since the formation of dL, a tentative precursor to 5-MF, requires one-electron oxidation of the intermediate C1′ radical. As has been demonstrated previously (35)(36)(37), in the presence of oxygen this step proceeds through the formation and decomposition of an intermediate peroxyl radical through elimination of superoxide O 2 •-. In our experiments, the absence of oxygen only partially suppressed formation of 5-MF; therefore, another oxidant must play the role of oxygen in this anoxic system.…”

Radical Ions from 3,3′′′,3′′′″‐Tris(butylsulfanyl)‐2,2′:5′,2″:5″,2′′′,5′′′,2′′′′:5′′′′,2′′′″‐sexithiophene: An Experimental and Theoretical Study of the p‐ and n‐Doped Oligomer

“…Time-dependent DFT calculations [39] were performed to assign the absorption bands observed above 400 nm, since they reproduce well optical transitions not only in diamagnetic systems, [39] but also in radical species. [40,41] Table 2 shows that there is good agreement between theory and experimental results on going from the title compound to the positively charged species. However, the assignment of the two main peaks in the optical spectrum of the radical cation deserves some comments.…”

Selective Generation and Reactivity of 5′‐Adenosinyl and 2′‐Adenosinyl Radicals

“…The rates of H-transfer from alkanethiols to alkyl radicals depend strongly upon the radical substituents. [21,22] For example, the a,b-dialkoxyalkyl radical reacts about 10 times slower than the analogous unsubstituted alkyl radical. A reasonable assumption for the reaction of C2' radical 11 with GSH is a rate constant of about 10 6 m À1 s…”