A γ-turn mimetic for selective sensing of Cu(ii) and a combinatorial multiple logic gate

Abstract

We have designed and synthesized a γ-turn mimetic using fenamic acid and α-aminoisobutyricacid (Aib), the conformation and optoelectronic properties of which can be changed by appropriate external stimuli. From single-crystal X-ray diffraction analysis, the compound has a kink-like conformation that is stabilized by a six-membered intramolecular N–H⋯OC hydrogen bond. The γ-turn mimetic 1 molecules self-assemble via intermolecular N–H⋯O hydrogen bonds to form chains extending in the c-direction. The γ-turn mimetic 1 further assembled to form a complex sheet-like structure through multiple π–π stacking interactions along the crystallographic a and c directions. The γ-turn mimetic compound selectively recognizes Cu(II) over Cu(I) and others like Ni(II), Pb(II), Mg(II), Zn(II), Mn(II), Co(II), Fe(III), and As(III), with a distinct colour change. In situ oxidation of Cu(I) with an oxidizing agent such as H₂O₂ exhibits the same effect as that of Cu(II). Interestingly, the brown colour of the complex turned colourless by elimination of Cu(II) via reduction to Cu(I) using ascorbic acid. Based on this reversible selective Cu(II) sensing event, we have developed a combinatorial multiple logic gate.