Cucurbit[7]uril-Styryl Dye Complexes for Fluorescent Recognition of DNA and Cell Imaging

This paper focused on the DNA-binding properties of novel dicationic cyanine dyes, in which pyridinium centers are linked by bridges of different functionalities. We found that dye 1, bearing a flexible butyl-4-methylpyridinium terminal fragment, has the ability to bind to the DNA groove. The attachment of a quite rigid para-xylylene-4-methylpyridinium unit as a terminal group in dye 2 contributed to dual DNA-binding modes: intercalation and groove binding. We tested the encapsulation ability and the effect on the dye-DNA binding mode by using a synthetic molecular container such as CB[7]. Unexpectedly, monitoring dye-DNA interaction in the presence of CB[7] revealed that dye molecules partially remain in DNA frameworks, even though they had a higher affinity towards CB[7]. In the case of dye 1, the transformation of dimeric forms to the left-handed aggregates to yield a ternary system CB[7]-dye-DNA occurred. As for dye 2, reversibility of intercalation and a slight right-handed aggregation templated by DNA are observed. A cytotoxicity and ability of dyes to stain the living cells in their free and encapsulated forms have been investigated. These findings provide useful information about ligand-DNA interactions, which are valuable for the rational design of drug delivery systems and platforms for cellular imaging and therapy.