Molecular structural requirements, dye specificity, and application of anionic peptide amphiphiles that induce intense fluorescence in cationic dyes

We have previously reported that a double-chain anionic amphiphile capable of intermolecular triple hydrogen bonds could form extremely hydrophobic sites in water and specifically incorporated stilbazolium-based compact hemicyanine dyes as monomeric species, resulting in induction of intense fluorescence emission in the dyes. In this paper, the structural requirements of the intense fluorescence-inducing amphiphiles were investigated. It is noted that the introduction of beta-Ala residues into two long-chain alkyl group moieties was most effective for the amphiphiles derived from L-glutamic acid with relatively shorter side-chain methylenes. The dye specificity in terms of induction of the intense fluorescence was also investigated using hemicyanines (stilbazolium etc.), cyanine, carbocyanine, thiacarbocyanines, and azo dye. The amphiphile with the shortest octanoyl-beta-alanyl double-chain alkyl groups, longer side-chain, and shorter spacer was found to show increased sensitivity to alkali metal ions, especially Li+. This could be a potential OFF-ON type fluorescence sensor for Li+.