Photoinduced Electron Transfer in Nucleic Acid Molten Salts

• Published in: The journal of physical chemistry. B Vol. 107; no. 26; pp. 6469 - 6473
• Main Authors: Leone, Anthony M, Brennaman, Matthew K, Tibodeau, Jennifer D, Papanikolas, John M, Murray, Royce W, Thorp, H. Holden
• Format: Journal Article
• Language: English
• Published: American Chemical Society 03.07.2003
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp022586c

Molten salts of Ni(bpy350)3 2+ and single stranded oligonucleotides were prepared (bpy350 = 4,4‘-(CH3(OCH2CH2)7.24OCO)2-2,2‘-bipyridine). Photoinduced electron transfer was observed between small amounts of Ru(bpz)3 2+* (E 2+*/1+ = 1.35 V vs SCE, bpz = 2,2‘-bipyrazine) added to the melt and guanine in the nucleic acid, by measuring the emission lifetime of the ruthenium complex in melts containing varying amounts of guanine-containing nucleic acid. Electrochemically determined diffusion coefficients in these media were <1 × 10-11 cm2/s, showing that the Ru(bpz)3 2+* diffuses less than 0.4 Å during the measured excited-state lifetime. A linear relationship was observed between the fraction of Ru(bpz)3 2+* that was quenched (calculated as (τ° − τ)/τ) and the mole fraction of guanine-containing oligonucleotides. This relationship supports a quenching mechanism that does not involve diffusion of the ruthenium complex. The average electron-transfer rate constant at full guanine loading was 7 × 106 s-1, which implies an average electron-transfer distance of 12.5 Å (center-to-center).