γ-Irradiated DNA and DNA-Tl3+ ice samples were annealed to 130 K to remove the ESR signal of •OH (35 (link),36 (link)); since the •OH is in the separate ice phase, annealing does not result in additional DNA radicals (35 (link),36 (link)). These samples were then illuminated with light at two different temperatures. At 77 K, either of the two sources was used: (i) a 200 W high pressure Xe lamp (Oriel Corporation), with cut-off filters which cut off light ≤310 nm, ≤480 nm, or ≤540 nm, or band-pass filters (340–370 nm and 380–480 nm), (ii) a Nd-yag laser at 521 nm, with 40 J/pulse and a 10 Hz repetition rate. At 143 K, a 250 W tungsten lamp was used with and without a variety of cut-off filters.
Glassy guanine model compound samples were annealed to 150 K for 10–12 min (see Results) which resulted in the loss of (light yellow) Cl2•− and the concomitant formation of G•+ as evidenced by the ESR spectrum and color development in the sample: red–violet at pH ≤ 9, and blue at pH ≥ 11. The samples of deoxyribonucleosides/tides were illuminated at a variety of temperatures using a 250 W tungsten lamp with and without cut-off or band-pass filters. The phrase ‘visible light illumination’ used throughout this paper refers to illumination with this lamp with wavelengths ≤310 nm cut-off; because of the small size of the sample and small solid angle it subtends, only a small fraction of the 250 W impinges on the sample.
Glassy guanine model compound samples were annealed to 150 K for 10–12 min (see Results) which resulted in the loss of (light yellow) Cl2•− and the concomitant formation of G•+ as evidenced by the ESR spectrum and color development in the sample: red–violet at pH ≤ 9, and blue at pH ≥ 11. The samples of deoxyribonucleosides/tides were illuminated at a variety of temperatures using a 250 W tungsten lamp with and without cut-off or band-pass filters. The phrase ‘visible light illumination’ used throughout this paper refers to illumination with this lamp with wavelengths ≤310 nm cut-off; because of the small size of the sample and small solid angle it subtends, only a small fraction of the 250 W impinges on the sample.
