Hybrid Palladium Catalyst Assembled from Chiral Phosphoric Acid and Thioamide for Enantioselective ß-C(sp3 )-H Arylation.

A hybrid palladium catalyst assembled from a chiral phosphoric acid (CPA) and thioamide enables a highly efficient and enantioselective ß-C(sp3 )-H functionalization of thioamides (up to 99 % yield, 97 % ee). A kinetic resolution of unsymmetrical thioamides by intermolecular C(sp3 )-H arylation can be achieved with high s-factors. Mechanistic investigations have revealed that stereocontrol is achieved by embedding the substrate in a robust chiral cavity defined by the bulky CPA and a neutral thioamide ligand.

Mechanistic understanding of catalysis by combining mass spectrometry and computation.

Mechanistic studies are of great importance for the understanding, optimization, and design of chemical reactions, especially catalysis. In recent years, the combination of mass spectrometry and computational chemistry has been proven to be powerful and effective for the exploration of reaction mechanisms. The former provides information of possible reaction intermediates, which are difficult to obtain using other experimental methods, while the latter gives detailed structural information of reaction intermediates and explores reaction energy profiles. This review covers applications of the combined method and highlights its strengths in mechanistic studies. Representative works are discussed to demonstrate the complementarity and synergy of mass spectrometry and computational chemistry. Some challenges in mechanistic studies with these tools and their possible solutions, as well as the trend for future developments are also discussed.

Assembling a Hybrid Pd Catalyst from a Chiral Anionic CoIII Complex and Ligand for Asymmetric C(sp3 )-H Functionalization.

An unusual hybrid palladium catalyst containing an anionic chiral CoIII complex and a chiral phosphoramidite ligand shows a high capacity for catalyzing asymmetric thioamide-directed C(sp3 )-H arylation and delivers excellent yield and enantioselectivity (up to 99 % yield, 99 % ee). Significant synergy between the chiral ligand and the anion in terms of stereochemical control was observed. Mechanistic investigations have revealed both the nature of the C-H activation and the origin of the enantioselectivity.

Mechanistic Study on Pd/Mono-N-protected Amino Acid Catalyzed Vinyl-Vinyl Coupling Reactions: Reactivity and E/Z Selectivity.

A combined mass spectrometric and computational study of the Pd/mono-N-protected amino acid (MPAA)-catalyzed vinyl-vinyl coupling reactions is reported. Computational study reveals that the reaction is initiated by C-H activation of the styrene followed by the insertion of acrylate. This is supported by mass spectrometry. The MPAA ligand facilitates the cross-coupling reaction between monosubstituted alkenes by stabilizing the active palladium catalyst and offering the N-protecting group as a stronger base than acetate. The E/Z selectivity is attributed to the stronger d-π interaction between the catalyst and the substrate in the transition state leading to E product.

Burst of reactive oxygen species in pedicel-mediated fruit abscission after carbohydrate supply was cut off in longan (Dimocarpus longan).

Cutting off carbohydrate supply to longan (Dimocarpus longan Lour.) fruit by girdling and defoliation or by detachment induced 100% abscission within a few days. We used these treatments to study the involvement of reactive oxygen species (ROS) in fruit abscission. Girdling plus defoliation decreased sugar concentrations in the fruit and pedicel and depleted starch grains in the chloroplasts in the cells of abscission zone. Prior to the occurrence of intensive fruit abscission, there was a burst in ROS in the pedicel, which peaked at 1 day after treatment (DAT), when H2O2 in the abscission zone was found to be chiefly located along the plasma membrane (PM). H2O2 was found exclusively in the cell walls 2 DAT, almost disappeared 3 DAT, and reappeared in the mitochondria and cell walls 4 DAT. Signs of cell death such as cytoplasm breakdown were apparent from 3 DAT. The burst of ROS coincided with a sharp increase in the activity of PM-bound NADPH oxidase in the pedicel. At the same time, activities of antioxidant enzymes including superoxide dismutase (SOD), catalase, and peroxidase (POD) were all increased by the treatment and maintained higher than those in the control. Accompanying the reduction in H2O2 abundance, there was a sharp decrease in PM-bound NADPH oxidase activity after 1 DAT in the treated fruit. H2O2 scavenger dimethylthiourea (DMTU, 1 g L(-1)) significantly inhibited fruit abscission in detached fruit clusters and suppressed the increase in cellulase activity in the abscission zone. These results suggest that fruit abscission induced by carbohydrate stress is mediated by ROS. Roles of ROS in regulating fruit abscission were discussed in relation to its subcellular distribution.

[A bibliometric investigation to research fronts of major sub-specialties in internal medicine].

OBJECTIVE: To outline the research fronts of ten major sub-specialties in internal medicine. METHODS: Based on their impact factor scores and the proportion of the journals of 10 subspecialties (endocrinology & metabolism, cardiac & cardiovascular systems, hematology, infectious diseases, nephrology, gastroenterology & hepatology, respiratory system, rheumatology, critical care medicine, clinical neurology) in Journal Citation Report (JCR), and careful consulation of expert clinicians, we identified 50 journals. Their bibliographic records (including references) published in 2011 were downloaded, and the frequency of the references (citations) in each sub-specialty was counted and the highly cited records were extracted. We performed a clustering analysis according to the co-cited times among any pairs of the highly cited records. To tag each cluster of highly cited records, we browsed the titles and abstracts of all highly cited records in the same cluster, and concluded the main topics of each cluster. Finally, we extracted the current published papers devoted to particular cluster by some clustering analysis indicators. The clusters of highly cited records were considered as the intelligence base, and the main topics in current papers which citing these highly cited papers were considered as research fronts. RESULTS: Totally 50 journals on 10 sub-specialties in internal medicine were identified. A total of 202 highly cited papers, 38 clusters (knowledge bases) , and 152 corresponding current citing papers presenting the research fronts were selected. CONCLUSIONS: We confirm and present research fronts in 10 major sub-specialties of internal medicine. This study provides a synchronic structure of contemporary research activities in internal medicine sub-specialties.