Laser flash photolysis and magnetic field effect studies on the interaction of uracil and its derivatives with menadione and 9,10-anthraquinone

Laser flash photolysis and an external magnetic field have been used to study the interaction of two quinone molecules, namely, 9,10-anthraquinone (AQ) and 2-methyl-1,4-naphthoquinone, commonly known as menadione (MQ), with the RNA base uracil (U) and two of its derivatives, 1,3-dimethyluracil (dmU) and uridine (dU). We have conducted our studies in homogeneous organic and heterogeneous micellar media in order to investigate the effect of media on the molecules and any change in reactivity on account of substitution. In organic homogeneous medium, both the quinones have behaved similarly with the bases. Here U has undergone both electron transfer (ET) and hydrogen (H) transfer, while dU and dmU have failed to exhibit any ET. Failure to support ET has been attributed to keto-enol tautomerism, which has been found to have a significant role in determining the occurrence of ET from these pyrimidine bases. However, in SDS micelles some variations regarding the reactivity of these molecules have been discerned. The variations are 2-fold. Here ET from U has been found to get completely eclipsed by a dominant H abstraction with both the quinones, and AQ reveals a difference in the extent of H abstraction with the bases in SDS. With U and dU, the prevailing H abstraction with AQ has succeeded in formation of only AQH(*), while dmU has produced both AQH(*) and AQH(2), the latter being formed by two successive H abstraction. Explanations of this intriguing behavior with U and its derivatives with quinone molecules have been the main concern in this work.