417 Emerging Lessons On Aromatic Interactions: Molecular Recognition of Cationic Dyes with π-Extended 2'-Deoxyadenosine Nucleotides

Friday, November 6, 2009: 10:40 AM
Rio Grande (Camino Real Hotel)
Hugo Morales-Rojas , Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos, Cuernavaca, Mexico
Karina Mondragón-Vásquez , Centro de Investigaciones Químicas, Universidad Autónoma del Estado de Morelos, Cuernavaca, Mexico

Non-covalent interactions between aromatic species play a prominent role in molecular recognition phenomena in chemistry, biology and material sciences. Despite the large number of supramolecular host developed for the recognition of molecules and ions, relatively few of them are designed to target aromatic guest in aqueous environments. Compounds like N6-(N'-arylcarbamoyl)-2'-deoxyadenosine (1) are synthetically accessible starting from the natural nucleoside 2'-deoxyadenosine, and its water solubility can be enhanced by incorporation of one or two anionic H-phosphonate groups (PO2H-) at the positions 3'-OH or 5'-OH. Our research group has synthesized several derivatives of 1 that incorporate aromatic residues with different size (phenyl, 1-naphthyl, 9H-fluoren-2-yl), shape (2-naphthyl) and electronic properties (fluorophenyls, 4-nitrophenyl), with the goal of examine the inter-molecular association between aromatic species in solution.

Titration studies by UV-vis absorption spectroscopy have shown that these p-extended 2'-deoxyadenosine nucleotides have large association constants (105-107 M-1) in the binding of cationic phenothiazinium and phenoxazinium salts in aqueous buffer solutions. Studies employing 1H, 19F and 31P NMR spectroscopy, and molecular modeling indicated that size and shape-complementarity of the aromatic rings in host and guest provides selectivity. Remarkably, the observed free binding energies can be explained by constant free energy increments attributed mainly to dispersive interactions. In the light of the recent theoretical studies claiming that dispersion rather than electrostatics is the driving force in the recognition between aromatic groups in gas phase, our findings provide experimental evidence that dispersion interactions also contribute more significantly to aromatic recognition in aqueous solution.