Ground and excited-state interactions of coumarin and nucleotide base

Abstract

GRAZYNA WENSKA and STEFAN PASZYC. Can. J . Chem. 66, 5 13 (1988).Steady-state and time-resolved fluorescence measurements for a series of bichromophoric con~pounds containing 7-methoxycoumarin and nucleotide base residues have been performed in water and in organic solvents. The data from these studies have been used to calculate the relative proportion of folded and extended conformations of bichromophores. Ground-state stacking interactions of coumarin and nucleotide base have been found to be limited to aqueous solution. ' The contribution of the dynamic quenching mechanism to the total fluorescence quenching in water has been estimated. The absence of dynamic quenching in organic solvents isexplained on the basis of the very short lifetime of the fluorophore in methanol.GRAZYNA WENSKA et STEFAN PASZYC. Can. J. Chem. 66, 513 (1988).Operant dans I'eau et dans des solvants organiques, on a mesurC la fluorescence a I'Ctat stationnaire ainsi que celle rCsolue en fonction du temps d'une sCrie de composCs bichromophoriques contenant des rtsidus mCthoxy-7 coumarine et une base nuclCotide. On a utilisC les donntes ainsi obtenues pour calculer les proportions relatives des conformations replite et Ctendue des bichromophores. On a trouve que les interactions d'empilement dans 1'Ctat fondamental de la coumarine et de la base nuclCotide sont IimitCes aux solutions aqueuses. On a t v a l d la contribution du mecanisme de piegeage dynamique au pitgeage total de la fluorescence dans I'eau. On explique l'absence de pitgeage dynamique dans les solvants organiques par le temps de vie tres court du fluorophore dans le methanol.[Traduit par la revue] Introduction It is well known that heteroaromatic compounds from the psoralen family form noncovalent complexes with nucleic acids (1, 2). The formation of the complex by weak forces, i.e., aromatic ring stacking due to hydrophobic and van der Waals forces, is one of several parameters contributing to the overall photobiological activity of psoralens (furocoumarins). The complexation is usually described in terms of the "intercalation model", which predicts that the psoralen molecule is placed between two adjacent nucleotide base pairs. Both ultraviolet absorption and fluorescence spectroscopy can be used to detect the intercalation complex. Its formation is generally accompanied by the bathochromic shift and hypochromicity of the near ultraviolet (uv) absorption band of the psoralen derivative. The fluorescence properties of psoralens also vary upon intercalation. The ability of nucleic acid bases to form such complexes with psoralen has been tested using model compounds in which both interacting molecules were connected with a hydrocarbon chain. The percentage of stacked or folded conformation, as opposed to extended, was determined by the study of the variation of the hypochromic effect with temperature (3, 4).Recently we synthesized a series of compounds containing 7-methoxycoumarin and nucleic acid base: adenine, thymine, and uracil, linked together with a polymethylene chain. ...

Solution and Fluorescence Properties of Symmetric Dipicolylamine-Containing Dichlorofluorescein-Based Zn2+ Sensors

“…The low Φ value for DBA-DCF in basic solution also suggests that its phenyl units play a role in the quenching process. It seems more likely, however, that the greater hydrophobicity of the aromatic rings in this latter compound promotes π-stacking interactions that disrupt the fluorescence …”

Incorporation of Coumarin-Based Fluorescent Monomers into Co-Oligomeric Molecules

“…The fluorescence quantum yields of the co-oligomers 2a , 2b and 3a , derived from monomers 2 and 3 , are close to those of the model coumarins lacking the vinyl group: 7-hydroxycoumarin has Ф f = 0.11 in ethanol [ 29 ] and 7-methoxycoumarin has Ф f = 0.05 in methanol [ 30 ], which are significantly lower than those of the original vinylcoumarins 2 and 3 .…”