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Carbon dots (CDs) are versatile nanomaterials with tunable luminescent properties. We used a natural plant kaempferol as a carbon source to synthesize multicolor CDs by reacting it with various nitrogen sources. Blue, green, and red CDs (B-CDs, G-CDs, and R-CDs) with emission wavelengths of 445 nm, 510 nm, and 600 nm respectively were successfully synthesized. Their photoluminescence quantum yields of are up to 37.4%, 20.1%, and 30.8%, respectively. Surface analysis revealed abundant nitrogen groups influencing luminescence. B-CDs and G-CDs show excitation-dependent emissions, indicating a potential correlation between their luminescence and particle sizes, while R-CDs exhibit excitation-independent emission, suggesting they belong to molecular state CDs. All three CDs exhibit stable luminescent performance, as well as good salt resistance and photobleaching resistance. The practical application of multicolored CDs in anti-counterfeiting fluorescent inks was further explored. This work offers a straightforward, eco-friendly route to synthesize multicolor CDs.

Density functional theory calculations have been performed to gain insights into the catalytic mechanism of the N-quaternized pyridoxal (i.e., 1a)-mediated biomimetic asymmetric Mannich reaction of tert-butyl glycinate 3with N-diphenylphosphinyl imine 2ato give the diamino acid ester 4ain high yield with excellent enantiomeric and diastereomeric selectivity (Science2018, 360, 1438). The study reveals that the whole catalysis can be characterized via three stages: (i) the catalyst 1areacts with the tert-butyl glycinate 3to generate the active carbanion complex IM3. (ii) IM3then reacts with the N-diphenylphosphinyl imine 2agiving the imine intermediate IM8. (iii) IM8undergoes hydrolysis to give the final product anti-4aand regenerate the catalyst 1afor the next catalytic cycle. Each stage is kinetically and thermodynamically feasible for experimental realization. The hydrolysis step in the stage III is predicted to be the rate-determining step during the whole catalytic cycle. Furthermore, the origins of the enantioselectivity and diastereoselectivity for the target reaction, as well as the deactivation of the catalyst 1b, are also discussed.

A novel chiral stationary phase (C16-(S)-THIQCA) for ligand exchange high-performance liquid chromatography was prepared by synthesizing 2-(2-hydroxyl) hexadecyl-(S)-1,2,3,4-tetrahydro-3-isoquinolinecarboxylic acid as a chiral selector and coating it on ODS-bonded stationary phase. The enantiomeric resolutions of 16 D,L-amino acids were achieved on C16-(S)-THIQCA by using cupric acetate aqueous solution as mobile phase, column temperature 25°C, and detection at UV 254 nm. The enantioselectivities α of the D,L-amino acids separated were found to be in the range from 1.09 to 1.67 with the resolution Rsranging from 1.0 to 4.8. The elution order of D-isomer before L-isomer was observed for all D,L-amino acids used. The effects of chromatographic conditions including flow rate, column temperature, pH, and the concentration of Cu2+and NH4+on the resolutions of D,L-amino acid enantiomers were discussed.