title: Non-covalent versus covalent control of self-assembly and chirality of Nile red-modified nucleoside and DNA.
abstract: A DNA-based covalent versus a non-covalent approach is demonstrated to control the optical, chirooptical and higher order structures of Nile red (Nr) aggregation. Dynamic light scattering and TEM studies revealed that in aqueous media Nr-modified 2'-deoxyuridine aggregates through the co-operative effect of various non-covalent interactions including the hydrogen bonding ability of the nucleoside and sugar moieties and the pi-stacking tendency of the highly hydrophobic dye. This results in the formation of optically active nanovesicles. A left-handed helically twisted H-type packing of the dye is observed in the bilayer of the vesicle as evidenced from the optical and chirooptical studies. On the other hand, a left-handed helically twisted J-type packing in vesicles was obtained from a non-polar solvent (toluene). Even though the primary stacking interaction of the dye aggregates transformed from H-->J while going from aqueous to non-polar media, the induced supramolecular chirality of the aggregates remained the same (left-handed). Circular dichroism studies of DNA that contained several synthetically incorporated and covalently attached Nr-modified nucleosides revealed the formation of helically stacked H-aggregates of Nr but--in comparison to the noncovalent aggregates--an inversed chirality (right-handed). This self-assembly propensity difference can, in principle, be applied to other hydrophobic dyes and chromophores and thus open a DNA-based approach to modulate the primary stacking interactions and supramolecular chirality of dye aggregates.
authors.affiliation: Institute for Organic Chemistry, University of Regensburg, 93040 Regensburg, Germany.
authors.forename: Reji
authors.initials: R
authors.lastname: Varghese
authors.forename: Hans-Achim
authors.initials: HA
authors.lastname: Wagenknecht
mesh_terms: D020029:Base Pairing; D002942:Circular Dichroism; D004396:Coloring Agents / Q000737:chemistry; D004247:DNA / Q000737:chemistry*; D006860:Hydrogen Bonding; D015394:Molecular Structure; D009705:Nucleosides / Q000138:chemical synthesis / Q000737:chemistry*; D010078:Oxazines / Q000737:chemistry*; D012689:Sequence Homology, Nucleic Acid; D013237:Stereoisomerism
chemical_list: D004396:Coloring Agents; D009705:Nucleosides; D010078:Oxazines; D004247:DNA; C044808:nile red