Deuterium exchange of PnT was carried out by the dissolution
of PnT in CD3OD.
Quartz EPR tubes (4 mm i.d., Suprasil) containing weighed
powder samples were evacuated and sealed. EPR samples were
γ-irradiated with a 60Co source at 77 K for 3 h at a dose rate of
0.96 kGy minϪ1. EPR measurements were carried out with an
FE-1X JEOL spectrometer with 100 kHz field modulation at 77
K unless otherwise noted. EPR signals obtained at an interval
of (50/8191) mT were digitized by a 12-bit A/D converter and
fed to an NEC PC-9801 microcomputer. To monitor changes in
EPR sensitivity and field spacing a capillary tube containing
Mn2ϩ dispersed in MgO was inserted into an EPR cavity and
fixed. All of the spectra in the text are shown as those elimin-
ated Mn2ϩ signals from observed spectra. Difference spectra
and double integrals of the spectra were taken by the micro-
computer at the standardization of the peak heights of the
second peak of Mn2ϩ. EPR spectral simulation was performed
by use of the Lefebvre and Maruani program.23 Component
line shape was taken to be Lorentzian unless otherwise
indicated.
References
1 For reviews see: (a) J. N. Herak, in Physico-chemical Properties
of Nucleic Acids, ed. J. Duchesne, Academic Press, London, 1973,
p. 197; (b) W. A. Bernhard, Adv. Radiat. Biol., 1981, 9, 199; (c) J.
Hüttermann, in Radical Ionic Systems, ed. A. Lund and M.
Shiotani, Kluwer Academic Publ., Dordrecht, 1991, p. 435; (d)
W. Flossmann, H. Zehner and A. Müller, Z. Naturforsch., 1980,
35c, 20.
Fig. 6 EPR spectra of ET (a) and PrT (b) γ-irradiated at 77 K. The
peaks indicated by arrows are due to signals of color centers produced
in quartz EPR tubes.
2 B. Pruden, W. Snipes and W. Gordy, Proc. Natl. Acad. Sci., 1965, 53,
917.
3 J. Hüttermann, Int. J. Radiat. Biol., 1970, 17, 249.
4 T. Henriksen and W. Snipes, J. Chem. Phys., 1970, 52, 1997.
5 A. Dulcˇic´ and J. N. Herak, J. Chem. Phys., 1972, 57, 2537.
6 H. C. Box and E. E. Budzinski, J. Chem. Phys., 1975, 62, 197.
7 E. Sagstuen, E. O. Hole, W. H. Nelson and D. M. Close, J. Phys.
Chem., 1989, 93, 5974.
Conclusion
Ionized irradiation of pentylthymines at 77 K efficiently pro-
duces the 5-thymyl radical and secondary radicals of the type
RRЈCHCHCH in addition to the hydrogen-abstraction radical
˙
3
2 and possibly the hydrogen-addition radical 3. The efficient
production of 5-thymyl radicals in pentylthymines is discussed
and concluded to be related to the formation of secondary alkyl
radicals.
8 M. Iwasaki, K. Toriyama, M. Fukaya, H. Muto and K. Nunome,
J. Phys. Chem., 1985, 89, 5278.
9 D. J. Henderson and J. E. Willard, J. Am. Chem. Soc., 1969, 91,
3014; T. Ichikawa and N. Ohta, J. Phys. Chem., 1977, 81, 560.
10 T. Ichikawa and N. Ohta, Radiat. Phys. Chem., 1987, 29, 429.
11 For examples see: Y. Inaki, N. Matsumura, K. Kanbara and
K. Takemoto, in Polymers for Microelectronics—Science and Tech-
nology, ed. Y. Tabata, I. Mita, S. Nonogaki, K. Horie and S. Tagawa,
Kondansha-VCH, Tokyo, 1990, p. 91; Y. Inaki, N. Matsumura and
K. Takemoto, ACS Symp. Ser., 1994, 537, 142.
12 Color centers produced in quartz sample tubes gave intense signals
in narrow regions of the observed spectra and hence the presence of
the signals from color centers could not cause serious errors in the
identification of produced radicals. The contributions of the color
centers in the radical yields of pentylthymines at 77 K were
estimated to be about 2% and those of MT and thymine at 77 K
were about 4%. These contributions would not affect greatly the
estimation of the radical yields.
Experimental
Thymine was supplied by Aldrich Chemicals and recrystallized
from water. 1-Methylthymine from Sigma Chemicals was
used as received. The other alkylthymines were synthesized
from thymine by the procedure22 adopted in the preparation
of bromoalkylthymines; thymine was converted to its bis(tri-
methylsilyl) ether derivative 7 and 7 was alkylated with the
appropriate bromoalkane to afford the alkylthymines (Scheme
1). The reagents used in the syntheses of the alkylthymines were
13 P. B. Ayscough and C. Thomson, Trans. Faraday Soc., 1962, 58,
1477.
14 T. Henriksen, Radiat. Res., 1969, 40, 11.
15 J. Schmidt, J. Chem. Phys., 1975, 62, 370.
16 W. Snipes and J. Schmidt, J. Chem. Phys., 1968, 49, 1443.
17 W. Bernhard and W. Snipes, J. Chem. Phys., 1967, 46, 2848.
18 M. D. Sevilla, J. Phys. Chem., 1971, 75, 626.
19 R. Bergene and T. B. Melø, Int. J. Radiat. Biol., 1973, 23, 263.
20 W. Flossmann, J. Hüttermann, A. Müller and E. Westhof,
Z. Naturforsch., Teil C, 1973, 28, 523; W. Flossmann, A. Müller and
E. Westhof, Mol. Phys., 1975, 29, 703.
Scheme 1
21 A. Dulcˇic´ and J. N. Herak, Mol. Phys., 1973, 26, 605.
22 J. S. Nowick, J. S. Chen and G. Noronha, J. Am. Chem. Soc., 1993,
115, 7636.
all commercially available from Aldrich Chemicals, Shinetsu
Silicone and Tokyo Kasei except for 2- and 3-bromopentanes
which were prepared by bromination of the corresponding alco-
hols. The synthesized alkylthymines were purified by repeated
recrystallizations from n-hexane–methanol or –ethanol.
23 R. Lefebvre and J. Maruani, J. Chem. Phys., 1965, 42, 1480.
Paper 9/03253C
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J. Chem. Soc., Perkin Trans. 2, 1999, 2597–2602