Novel Electrochemical Chiral Sensors Based On Chiral Organic Small Molecules

Graphene quantum dots(GQDs)and tartaric acid(TA)were successively electrodeposited onto the surface of a glassy carbon electrode(GCE).Due to the intrinsic chirality of L-(+)-TA and D-(–)-TA and the signal amplification function of GQDs,the GQDs-TA hybrid modified GCE could be regarded as an efficient electrochemical chiral sensor and used for chiral recognition of tryptophan(Trp)isomers.The recognition efficiency with the proposed GQDs-TA is significantly higher than that with TA alone.Of particular interest,GQDs-L-(+)-TA and GQDs-D-(–)-TA exhibit completely opposite selectivity toward L-Trp and D-Trp.Also in this work,the pH-sensitive enantiorecognition of the GQDs-TA hybrids was investigated.A quinine(QN)-based chiral sensor with alterable enantioselectivity is constructed for electrochemical chiral recognition of Trp isomers.The electrochemical signals of L-and D-Trp on the QN modified electrode depend closely on temperature,and more particularly are reversed at certain temperatures,which could be attributed to the temperature-sensitive H-bonds and?-?interactions between QN and the Trp isomers.The mechanisms of the reverse chiral recognition are investigated by density functional theory(DFT),variable-temperature UV spectra,and variable-temperature ~1H NMR spectra.In addition,the chiral recognition is highly specific to the isomers of Trp compared with other chiral amino acids.Polypyrrole(PPy)was synthesized by galvanostatic method using(1S)-(+)-10-camphorsulfonic acid((+)-CSA)as the chiral dopant,and the produced PPy was further overoxidized in the solution of(+)-CSA.Conformational change of the overoxidized PPy(OPPy)induced with(+)-CSA occurred,resulting in a twisted helical architecture of the OPPy chains.The as-prepared OPPy was highly optical active,which could be used in the construction of chiral sensors for Trp isomers.