Investigation by NMR spectroscopy of the structural characteristics of modified oligo-nucleotides with pendant porphyrins

Abstract

During the past years, we focused on exerting control over the position and distance of porphyrins along our specifically designed oligonucleotidic scaffold. Indeed, in naturally occurring light-harvesting complexes, biopolymer scaffolds hold pigments at intermolecular distances that optimize photon capture, electronic coupling, and energy transfer. To this end, four uridine-porphyrin conjugates (a monomer, a dimer, a tetramer and an octamer) were subjected to a comprehensive conformational analysis by using NMR spectroscopy. The collected NOE NMR data highlighted characteristic and strong interactions indicating that the glycosidic angle between the ribose and uracil base is anti. In order to further investigate the conformation of this family of molecules, NMR experiments were carried out at variable temperatures. At low temperature, the signals of the porphyrinic protons decoalesce, showing two sets of [Formula: see text]-pyrrolic protons. Similar observations are made for signals corresponding to sugar moieties and especially the H1′ protons, indicating molecular motions within our porphyrin-uridin arrays. These results testify in favor of the existence of a dynamic process between C3′-endo and C2′-endo conformations.