The excited states of adenine in different polynucleotides dissolved in ethylene glycol: H2O glasses have been studied by optical emission and ESR at 77deg;K. In singlehyphen;stranded poly A the optical properties were very similar to the constituent AMP monomers except for a red shift of the luminescence. The ESR Dgr;m=1 transitions were observed withD=0.116 cmminus;1andE=0.027 cmminus;1for poly A andD=0.119 cmminus;1andE=0.027 cmminus;1(all plusmn;0.002 cmminus;1) for AMP. This means that the triplet transfer time is longer than 2times;10minus;10sec since more rapid tripletmdash;triplet jumping would give a time averaging ofE.In the ordered doublehyphen;helix form of poly A the excited states are completely quenched when onehyphen;half of the bases are protonated. In poly (A+2U) and poly (A+2I) ordered copolymers the excited states are also quenched. However in random distributions of U, C, and I in single strands of poly A no quenching was observed. This leads to the conclusion that the hydrogen bonding rather than energy transfer is responsible for the quenching observed in the ordered polymers.
展开▼
