FLUORESCENCE AND ABSORPTION SPECTROSCOPIC PROPERTIES OF RNA 5'-CAP ANALOGS DERIVED FROM 7-METHYL-GUANOSINES, N-2,7-DIMETHYL-GUANOSINES AND N-2,N-2,7-TRIMETHYL-GUANOSINES

Absorption and fluorescence properties of several cap analogues, namel y nucleosides, nucleoside 5'-monophosphates and P-1,P-3-dinucleoside t riphosphates derived from 7-methylguanine, N-2,7-dimethylguanine and N -2,N-2,7-trimethylguanine, have been studied. The data obtained includ e the absorption and fluorescence spectra of the cationic (N1-protonat ed) and zwitterionic (N1-deprotonated) species, the pK(a) values of th e ground and excited states of the methylated base moiety and the effe ct of temperature and solvent composition (mixtures of water and 1,4-d ioxane) on the fluorescence intensity. Furthermore, the fluorescence l ifetimes of N-2,N-2,7-trimethylguanosine 5'-triphosphate and anosine(5 ')-P-3-[N-2,N-2,7-trimethylguanosine(5')] triphosphate have been deter mined as a function of temperature. These data dearly indicate that dy namic quenching must be taken into account when the extent of the intr amolecular stacking of the latter compound is estimated by fluorescenc e spectroscopy.