title: Electronic structure of some adenosine receptor antagonists. III. Quantitative investigation of the electronic absorption spectra of alkyl xanthines.
abstract: Quantitative and comparative investigation of the electronic absorption spectra of theophylline, caffeine and their derivatives is reported. The spectra of theophylline, caffeine and theobromine were compared to establish the predominant tautomeric species in solution. This comparison, analysis of solvent effects and assignments of the observed transitions via MO computations indicate the exits of only one tautomeric species in solution that is the N7 form. A low-lying triplet state was identified which corresponds to a HOMO-LUMO transition. This relatively long-lived T1 state is always less polar than the ground state and may very well underlie the photochemical reactivity of alkyl xanthines. Substituents of different electron donating or withdrawing strengths and solvent effects are investigated and analyzed. The present analysis is facilitated via computer deconvolution of the observed spectra and MO computation.
authors.affiliation: Faculty of Science, Department of Chemistry, University of Cairo, Giza, Egypt.
authors.forename: H
authors.initials: H
authors.lastname: Moustafa
authors.forename: Samia H
authors.initials: SH
authors.lastname: Shalaby
authors.forename: K M
authors.initials: KM
authors.lastname: El-sawy
authors.forename: Rifaat
authors.initials: R
authors.lastname: Hilal
mesh_terms: D002110:Caffeine / Q000737:chemistry*; D058915:Purinergic P1 Receptor Antagonists; D013057:Spectrum Analysis; D013805:Theobromine / Q000737:chemistry*; D013806:Theophylline / Q000737:chemistry*
chemical_list: D058915:Purinergic P1 Receptor Antagonists; D002110:Caffeine; D013806:Theophylline; D013805:Theobromine