PHOTOCHEMISTRY AND PHOTOPHYSICS OF GUANINE-CONTAINING DINUCLEOSIDES

Yields and action spectra are reported for photochemistry, fluorescence and total luminescence at 405 nm due to UV excitation (240-300 nm) of dilute (.apprx. 0.1 mM) solutions of GMP and the dinucleosides linking guanine with adenine (ApG and GpA), cytosine (CpG) and uracil (GpU) in neutral ethylene glycol-water (7:3) glasses at 140-165.degree. K. Phosphorescence lifetimes were determined at 140.degree. K. Less complete data are presented for GpC, UpG and dpGpT. Quantum yields for all 3 processes usually increased as the excitation wavelength increased. Intramolecular exciplex formation was not dominant under these conditions but interactions were strong enough to frustrate attempts at interpretation of results within the Forster very weak coupling framework. The GMP photochemistry may proceed from the triplet state. This photochemistry is not quenched in ApG, GpA and dpGpT at 163.degree. K although the adenine and thymine moieties have lower triplet states. At 140.degree. K the phosphorescence from ApG and GpA was entirely characteristic of A but both G and T components were observed from dpGpT.