TRANSITION MOMENTS OF 2'-DEOXYADENOSINE

Polarized reflection spectra from two faces of single crystals of 2'-deoxyadenosine have been measured (600-140 nm). Absorption curves obtained by Kramers-Kronig analysis of the reflection spectra are consistent with the set of transition moments reported in a similar study of 9-methyladenine and 6-methylaminopurine. The present results for six observed transitions are as follows: I (f = 0.09, theta = 67 degrees, lambda = 274 nm); II (f = 0.18, theta = 35 degrees, lambda = 254 nm); III (f = 0.25, theta = -45 degrees, lambda = 213 nm); IV (f = 0.11, theta = 15 degrees, lambda = 202 nm); V(f = 0.33, theta = 64 degrees, lambda = 189 nm); VII (f = 0.28, theta = 6 degrees, lambda = 159 nm). [The in-plane angle, theta, is measured from the C-4-C-5 reference axis toward C-6. Transition VI of the earlier study was not observed.] The shifts in transition moment directions arising from crystal field induced exciton mixing in 2'-deoxyadenosine are calculated to be small (11 degrees or less), and therefore the results derived from the crystal spectra using an oriented gas approach appear to be fairly representative of the ''free'' adenine chromophore. Furthermore; it is concluded that the presence (or absence) of a deoxyribose group has little effect on the spectral parameters of the adenine chromophore.