DNA ionic liquids: Transport characteristics and photo-induced electron transfer

Ionic liquids are described that contain duplex DNA as the anion and polyether-decorated transition metal complexes based on M(bpy₃₅₀) ₃2+ as the cation (M = Co, Ni, Ru; bpy₃₅₀ = 4,4′-(CH₃(OCH₂CH₂) ₇OCO)₂-2,2′-bipyridine). The pure Co(bpy ₃₅₀)₃DNA melt does not exhibit recognizable voltammetric waves. Analysis of voltammetry and chronoamperometry of mixtures of these phases with complexes having ClO₄− counterions (Co(bpy₃₅₀)₃(ClO₄)₂) and no other diluent provides charge transport rates from the oxidation and reduction currents for the complexes. As the mole fraction of the Co(bpy₃₅₀) ₃(ClO₄)₂ complex in the mixture is varied from ca. 0.25 to 1, the physical diffusion constants derived from the Co 3+/2+ wave increase from 1 × 10−11 cm 2/s to 5 × 10−10 cm2/s, and apparent diffusion constants dominated by the Co2+/1+ electron self-exchange increase from 1 × 10−11 cm 2/s to 2 × 10−8 cm2/s. DNA suppresses the Co2+/1+ electron transfer reactions of Co complexes for which it is counterion.; Undiluted voltammetry of DNA molten salts containing the powerful oxidizers Fe(bpy₃₅₀)₃(ClO₄)₂ and Ru(bpy ₃₅₀)₃(ClO₄)₂ exhibit electrocatalytic waves. Independent experiments show that Fe(bpy₃₅₀)₃ 3+ and Ru(bpy₃₅₀)₃3+ selectively oxidize guanine and adenine in duplex DNA. Digital simulations are used to study the DNA oxidation.; Several independent models show that electron hopping among the bases of DNA is necessary to explain the measured current responses and that the relative timescale of the processes occurring are: D_PHYS > DNA D_APP > M₃₅₀3+-DNA electron transfer.; Molten salts of Ni(bpy₃₅₀)₃2+ and single stranded oligonucleotides were prepared. Photo-induced electron transfer was observed between small amounts of Ru(bpz)₃2+ _* (E2+*/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. A linear relationship was observed between the fraction of Ru(bpz)₃2+ _* that was quenched and the mole fraction of guanine-containing oligonucleotides. 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).