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.