Purines from spectral study

Information on tautomerism, and sites of protonation of purines has been derived from NMR spectral studies. Thus protonation of adenine is first suggested to occur at N-1 with no evidence for protonation of the amino group (65JOC1110) although protonation of the substituted amino group does occur in 6-dimethylamino-3-methylpurine (68CC1002). 

NMR spectral studies of purine nucleosides have been much concerned with assignment of anomeric structure. The dihedral angle between vicinal protons in the cis H(l )-H(2 ) configuration, as with a-D-ribofuranosyl derivatives, and the trans H(l )-H(2 ) configuration, as with )3-D-ribofuranosyl derivatives, may vary from 0-45° and 75-165°, respectively (62JA62). 

The fluorescence polarization excitation spectrum has been measured for thymine in aqueous solution. " The depolarization at the red edge is attributed to the hidden n, ir transition. Ionization of the lowest excited singlet and triplet states have been determined by the effect of pH on the absorption, fluorescence, and phosphorescence spectra of purines and pyrimidines. " Spectral, polarization, and quantum yield studies of cytidylyl-(3, 5 )-adenosine have also been published. Intermediates in the room-temperature flash photolysis of adenine and some of its derivatives have been identified hydrated electron, radical cations and anions, and neutral radicals resulting from their reactions have been assigned. Photoionization occurs via the triplet state. FMN encapsulated in surfactant-entrapped water pools interacts with polar head groups, entrapped water molecules, and outer apolar solvent. ... 

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