Reading molecular structural Information of amino acids through an extended molecular pairing technique

We have recently reported the formation of developed nanofibers upon mixing ATP and certain cationic cyanine dyes. This combination is selected through the combinatorial mixing of ATP and many cationic molecules, allowing to develop nanofibers consisted of ATP and cyanine dye molecules¹⁾. In this work, the molecular pairing approach is applied to amino acids. As amino acids do not specifically interact with cationic dyes, they are first converted to anionic isoindole derivatives by the reaction with o-phthalaldehyde and 2-mercaptoethanesulfonic acid. When an isoindole product of gultamic acid was mixed with cationic cyanine dyes, immediate color change occurred from pink to orange. The blue-shifted absorption of cyanine dyes implies the formation of developed chiral assemblies with excitation energy delocalized among the parallel-aligned chromophores. Transmission electron microscopy revealed the formation of nanofibers with ca. 50 nm in width and several micrometers in length. These spectroscopic properties and nano structures of the mixtures changed depending on the chemical structures of amino acids.