Homochiral MOF as Circular Dichroism Sensor for Enantioselective Recognition on Nature and Chirality of Unmodified Amino Acids

Self-assembly of zinc salt with rationally designed chiral ligand, (1 R,2 R )-2-(pyridine-4-ylcarbamoyl) cyclohexanecarboxylic acid (RR-PCCHC) generated 2D homochiral metal–organic framework [Zn(RR-PCCHC) 2 ] (HMOF- 1 ) that is composed of DNA-like right-handed double-helix structure. HMOF- 1 shows high solvent and thermal stability and is also stable in neutral, weak acidic and weak basic aqueous solution. Emulsified HMOF- 1 shows strong inherent circular dichroism (CD) signal in aqueous solution, which can show regular intensity change by induction of amino acids. On the basis of the measuring of CD signal intensity, a chemosensor for unmodified amino acids is fabricated, which differ from reported those in which CD signal is amplified by a complicated chemical reaction of originally CD-silent molecule with probed amino acids. This chemosensor can be used for rapid, convenient and sensitive detection of micro amount of amino acids. Most remarkably, 3 × 10 –8 mol of l -aspartic acid and 4 × 10 –8 mol of d -aspartic acid in aqueous solution can completely quench CD signal of emulsified HMOF- 1 in H 2 O. It is found that the difference of recognition ability between d - and l -proline is the largest in all probed amino acids. The LOD (limit of detection) of the proposed sensor for the determination of aspartic acid is 13.31 ppm. The recognition efficiency η = × 100% for l -aspartic acid is as high as 92.1%. The interacting mechanism of DNA-like HMOF-1 with probed amino acids is similar to that of groove binding of targeting drug with DNA.