Discriminating three biothiols by using one fluorescent probe

A 1,1′-bi-2-naphthol (BINOL) based dialdehyde (R)-1 is found to exhibit selective fluorescent response towards cellular thiols, l-Cys, l-Hcy, and GSH. (R)-1 reacts with l-Trp to form a Schiff base 2 which quenches the emission of l-Trp at λ = 340. Coordination of 2 with Zn(ll) leads to greatly enhanced emission at λ = 530 nm. When the in situ generated 2 from the combination of the solution of (R)-1 (1.0 × 10−5 M) + Trp (2 equiv) +Zn(OAc)2 (2 equiv) is treated with l-Cys, l-Hcy, and GSH, different fluorescent responses at three emission wavelengths, including 340, 421 and 530 nm, are observed. This allows the in situ generated 2 to be used as a ratiometric fluorescent probe to discriminate these three biothiols. NMR study of (R)-1 with D- or l-Cys in the presence of Zn(II) shows that the unique reactivity of Cys provides basis for the selective ratiometric fluorescent response. (R)-1 + Zn(II) also exhibits enantioselective fluorescent response toward D- and l-Cys.