| This dissertation reports studies of photoinduced electron transfer (ET) in anthraquinone (AQ)-substituted nucleosides with three different types of linker between the 2-position of AQ and either the N 6 or the C8 position of dA: AQCdA, linker is C=O to N6; AQ1dA, linker is -CH2- to N6; and AQ2dA, linker is -CH2CH2- to C8. AQCdA was studied using femtosecond transient absorbance (TA) spectroscopy with 400-nm excitation by 200-fs duration pulses. AQ1dA and AQ2dA were studied using nanosecond TA spectroscopy using 341-nm excitation by 6-ns duration pulses. Additionally, anthraquinone-2,6-disulfonate (AQ26DS2− ) was quenched by NO2− via bimolecular reaction. The resulting ET photoproduct (AQ26DS(D)·2− ) was observed with 250-ns time resolution step-scan FTIR. The lifetime for this ET product was 1.1 μs in oxygen-saturated D2O. Other AQ compounds were also studied under bimolecular conditions using nanosecond TA spectroscopy. Photoinduced ET product (AQ·−/dA ·+) was observed for AQCdA in polar organic solvents. However, no photoinduced ET product was observed in McOH for AQ1dA or AQ2dA. None of these nucleosides was soluble in water.; Steady state FTIR studies for AQUA and model substituted AQ compounds showed that the linker behaved as a carbonyl attached to N 6 rather than as an amide. This finding was reproduced computationally by RHF 6-31G type of calculation. To understand the lack of photoinduced ET in AQ1dA and AQ2dA, anthraquinone-2-sulfonate (AQ2S−) was studied in the presence of 2′-deoxyadenosine (dA) in both methanol and water. In the former solvent, excited AQ2S− was not reductively quenched by dA, while formation of ET product was successful in water. This result proves that, unsubstituted (or alkyl substituted) AQ undergoes photoinduced ET from the reaction with dA only because of protonation (or deprotonation) of the ET products. In polar organic solvents, protonation cannot occur so ET from dA is not observed. |
