Pyrene derivatives as fluorescent probes of conformation near the 3′ termini of polyribonucleotides

When pyrene butyric acid hydrazide or pyrene acetic acid hydrazide is attached to single-strand RNA 3′ termini a red shift in absorbance and substantial hypochromicity are observed. A strong induced CD is seen and the fluorescence intensity is quenched by an order of magnitude. In double-stranded samples, a further 10-fold quenching of fluorescence is seen. Several lines of evidence suggest that the residual fluorescence of pyrene butyric acid hydrazide-duplex conjugates arises from a minor species. The most likely possibility is dye reacted at a site other than the 3′ end. Some indication exists that 3′-attached pyrene may perturb the relative stability of nearby duplex. Within the limits of this reservation, it appears that 3′-pyrene conjugates may be rather useful for detecting the existence of duplex regions accessible to a dye at the 3′ end of complex RNAs.