Insights into C-C Bond Cleavage Mechanisms in Dichloroacetonitrile Formation during Chlorination of Long-Chain Primary Amines, Amino Acids, and Dipeptides.

Dichloroacetonitrile (DCAN) as one of the potentially prioritized regulated DBPs has drawn great attention; however, understanding its formation, especially the C-C bond cleavage mechanisms, is limited. In this study, DCAN formation mechanisms from long-chain primary amines, amino acids, and dipeptides during chlorination were investigated by a combined computational and experimental approach. The results indicate that nitriles initially generate for all of the above precursors, then they undergo ß-C-hydroxylation or/and α-C-chlorination processes, and finally, DCAN is produced through the Cα-Cß bond cleavage. For the first time, the underlying mechanism of the C-C bond cleavage was unraveled to be electron transfer from the O- anion into its attached C atom in the chlorinated nitriles, leading to the strongly polarized Cα-Cß bond heterocleavage and DCAN- formation. Moreover, DCAN molar yields of precursors studied in the present work were found to be determined by their groups at the γ-site of the amino group, where the carbonyl group including -CO2-, -COR, and -CONHR, the aromatic group, and the -OH group can all dramatically facilitate DCAN formation by skipping over or promoting the time-consuming ß-C-hydroxylation process and featuring relatively lower activation free energies in the C-C bond cleavage. Importantly, 4-amino-2-hydroxybutyric acid was revealed to possess the highest DCAN yield among all the known aliphatic long-chain precursors to date during chlorination. Additionally, enonitriles, (chloro-)isocyanates, and nitriles can be generated during DCAN formation and should be of concern due to their high toxicities.

Biostable L-DNA-Templated Aptamer-Silver Nanoclusters for Cell-Type-Specific Imaging at Physiological Temperature.

The high susceptibility of the natural D-conformation of DNA (D-DNA) to nucleases greatly limits the application of DNA-templated silver nanoclusters (Ag NCs) in biological matrixes. Here we demonstrate that the L-conformation of DNA (L-DNA), the enantiomer of D-DNA, can also be used for the preparation of aptamer-Ag NCs. The extraordinary resistance of L-DNA to nuclease digestion confers much higher biostability to these NCs than those templated by D-DNA, thus making cell-type-specific imaging possible at physiological temperatures, using at least 100-times lower Ag NC concentration than reported D-DNA-templated ones. The L-DNA-templated metal NC probes with enhanced biostability might promote the applications of metal nanocluster probes in complex biological systems.