Oxidative cyclopalladation triggers the hydroalkylation of alkynes

This report describes the oxidative cyclopalladation activation of a C≡C bond during the Pd-catalyzed hydroalkylation of alkynes and analyzes potential reaction pathways based on density functional theory calculations. The more favorable pathway in-volves an oxidative cyclopalladation to generate a palladacyclopropene intermediate, which is rarely examined in Pd-catalyzed alkyne transformations. The reaction pathway proposed herein is kinetically favorable relative to the commonly proposed alkyne insertion mode. Furthermore, the Laplacians of the electron density, interaction region indicators, Mayer bond orders, and localized orbital bonding are evaluated to determine the reaction processes and characterize the key intermediates. Theoretical calculations indicate covalent bonding between a Pd(II) center and the two C-atoms in three-membered palladacycle species. Finally, electrostatic potential analysis reveals that the regioselectivity is governed by the charge distribution on the palladacycle moiety during the protonation step.

Influence of lactic acid bacteria on physicochemical indexes,sensory and flavor characteristics of fermented sea buckthorn juice

Sea buckthorn has been proved to be a good substrate for lactic acid bacteria(LAB),but the research on the fermentation of sea buckthorn juice(SBJ)by LAB is still rare.This study was designed to determine the performance of fermented SBJ(FSBJ)in four LAB and investigate the sensory aspects of FSBJ.The results showed that the utilization rates of reducing sugar,titratable acid,and malic acid of SBJ fermented by Lactobacillus casei(SBJLc)were the highest and that lactic acid content was the greatest.The organic acid compositions of the four kinds of FSBJs were also different.The viable counts of all FSBJs was greater than 7 log CFU/mL,and that the viable count of SBJ fermented by SBJLc was the highest.In this study,the Electronic tongue combined with Electronic nose was used for the first time to study SBJ.Results showed that compared with the control,the response value of Sourness was significantly increased,while Bitterness and Astringency were significantly decreased.There was a significant difference in four FSBJs.The results of the electronic nose showed that SBJ fermented by Lactobacillus plantarum LP56(SBJLp)could be well identified by sensors sensitive to aromatic substances.The volatile compound contents before and after fermentation were significantly different,the highest being SBJLp.Finally,the results of sensory evaluation experiments showed that SBJLp was the most acceptable to consumers in terms of sensory evaluation.