ELECTRONIC-SPECTRUM OF THE ADENINE CHROMOPHORE

Electronic transition moment information for the adenine chromophore is obtained by examining polarized spectra of single crystals of two different methylated adenines. Polarized reflection spectra of the a, b, and c axes from the (100) and (001) crystal faces of 6-(methylamino)purine and of the b and c axes from the (100) face of 9-methyladenine have been measured from 370 to 135 nm. Corresponding absorption curves are obtained by Kramers-Kronig analysis. These spectra are analyzed so as to assign eight different transitions as follows: I (f = 0.10, θ = +83°, λ = 275 nm), II (f = 0.20, θ = 25°, λ = 265 nm), III (f = 0.25, θ = -45°, λ = 213 nm), IV (f = 0.11, θ = 15°, λ = 204 nm), V (f = 0.30, θ = 72°, λ = 187 nm), VI (f ≈ 0.1, θ = ∼-45°, λ = 175 nm), VII (f = 0.23, θ = 6°, λ = 160 nm), VIII (f ≈ 0.1, θ = ∼-45°, λ = 147 nm). [The in-plane angle, θ, is measured from the C4-C5 reference axis toward C6.] Absorption curves for both crystal systems are reasonably well reproduced with this model spectrum. The results of various previous work are considered in light of the above assignments. © 1990 American Chemical Society.