Scheme 1.

The synthetic routes and structures of CPDs. TPAs (blue) are synthesized by reacting citric acid with β or γ-aminothiols such as cysteine, cysteamine, 2-aminothiolphenol, etc. DPRs (red) are synthesized from citric acid and other primary amines/anilines that do not contain a thiol group, e.g. alanine, γ-Aminobutyric acid, propylamine, ethylenediamine, ethanolamine, phenylenediamine, and others. All chiral molecules used were L-isomers unless specifically stated otherwise.