Preparation of ß-lactoglobulin/gum arabic complex nanoparticles for encapsulation and controlled release of EGCG in simulated gastrointestinal digestion model.

In this work, the ß-lactoglobulin/gum arabic (ß-Lg-GA) complexes were prepared to encapsulate epigallocatechin gallate (EGCG), forming ß-Lg-GA-EGCG complex nanoparticles with an average particle size of 133 nm. The ß-Lg-GA complexes exhibited excellent encapsulation efficiency (84.5%), and the antioxidant performance of EGCG in vitro was improved after encapsulation. It was recorded that 86% of EGCG could be released in simulated intestinal fluid after 3 h of digestion, much faster than that in simulated gastric fluid, indicating that the ß-Lg-GA complexes were effective in enhancing EGCG stability, which was confirmed using SDS-PAGE and SEM. Further spectrum results demonstrated that various intramolecular interactions including electrostatic, hydrophobic and hydrogen bonding interactions contribute to the formation of ß-Lg-GA-EGCG complex nanoparticles. Also, XRDexperiments indicated that EGCG was successfully encapsulated by ß-Lg-GA complexes. Therefore, the ß-Lg-GA complexes hold great potentials in the protective delivery of sensitive bioactives.

Key Mechanistic Features in Palladium-Catalyzed Methylcyclopropanation of Norbornenes With Vinyl Bromides: Insights From DFT Calculations.

DFT calculations were performed to elucidate mechanistic details of an unusual palladium-catalyzed methylcyclopropanation from [2 + 1] cycloadditions of (Z)-2-bromovinylbenzene and endo-N-(p-tolyl)-norbornenesuccinimide. The reaction proceeds via oxidative addition (OA), intermolecular alkene insertion, deprotonation/protonation, intramolecular alkene insertion, ß-H elimination and reductive elimination (RE). Protonation is the rate-limiting step and requires an overall barrier of 28.5 kcal/mol. The sources of two protons for protonation and exchange have also been clarified and the calculations agree with experimental observations.

DFT studies on mechanistic origins of ligand-controlled selectivity in Pd-catalyzed non-decarbonylative and decarbonylative reductive conversion of acyl fluoride.

The mechanisms and origins for ligand-controlled non-decarbonylative and decarbonylative conversions of acyl fluorides catalyzed by palladium catalysts with different ligands tricyclohexylphosphine (PCy3) and 1,2-bis(dicyclohexylphosphino)ethane (DCPE) have been investigated by density functional theory (DFT) calculations. In the case of the DCPE ligand, the favorable catalytic cycle contains four steps, oxidative addition, decarbonylation, transmetallation and reductive elimination. In the case of the PCy3 ligand, the favorable catalytic cycle proceeds by three steps, oxidative addition, transmetallation and reductive elimination. Distortion/interaction analysis indicated that decarbonylation does not occur for PCy3 owing to the repulsive interaction between PCy3 and substrates. Present calculations agree with the experimental observations and understanding these surprising ligand-controlled non-decarbonylative and decarbonylative selectivity reactions could provide important insights into the development of selective catalyst systems.

Non-innocent PNN ligand is important for CO oxidation by N2O catalyzed by a (PNN)Ru-H pincer complex: insights from DFT calculations.

Milstein et al. developed an efficient and mild method for CO oxidation by N2O to give CO2 and N2 catalyzed by a (PNN)Ru-H pincer complex. To gain mechanistic information on this catalytic transformation, the reaction mechanism has been studied using density functional theory (DFT) calculations. It was found that the catalytic cycle for CO oxidation by N2O proceeds in three stages: N2O activation to form a (PNN)Ru-OH intermediate, CO insertion into the Ru-OH bond to form a (PNN)Ru-COOH intermediate and CO2 release from (PNN)Ru-COOH. In the CO2 release stage, CO2 is not released via a ß-H elimination mechanism as proposed in experiments, instead it is released via a deprotonation mechanism. The calculations demonstrated that the Ru-H bond of the catalyst plays an important role in facilitating the activation of N2O, which is the rate-determining step for the whole catalytic cycle, and the non-innocent PNN ligand is very important for CO oxidation by N2O. Our theoretical results are consistent with the experimental observations and could help design highly efficient catalysts for N2O activation.