Nankai University

About: Nankai University is a education organization based out in Tianjin, China. It is known for research contribution in the topics: Catalysis & Adsorption. The organization has 42964 authors who have published 51866 publications receiving 1127896 citations. The organization is also known as: Nánkāi Dàxué.

Cross-Dehydrogenative Coupling Reactions by Transition-Metal and Aminocatalysis for the Synthesis of Amino Acid Derivatives

Abstract: The direct cross-dehydrogenative coupling (CDC) of C H bonds has become a potent strategy for C C bond formation. As CDC reactions avoid prefunctionalization of the substrates, they are more atom-economical and environmentally friendly than other cross-coupling reactions. Several research groups have reported CDC reactions of various sp C H bonds, such as benzylic and allylic C H bonds, a-C H bonds of tertiary amines and ethers, and C H bonds of alkanes, with other C H bonds. As far as we know, there are only two successful examples of CDC reactions for the synthesis of amino acid derivatives, although these compounds are so important in terms of their biological activity. Li and co-workers developed CDC reactions of N-acetylglycine esters and N-aryl glycine amides with malonates and alkynes in the presence of Cu(OAc)2 (2.0 equiv) and catalyzed by CuBr, respectively. 8] However, they reported that N-aryl glycine esters, unlike N-aryl glycine amides, could not undergo a CDC reaction. Owing to the importance of amino acid derivatives and the lack of successful CDC reactions of glycine derivatives with ketones, we embarked on a study of CDC reactions of N-substituted glycine esters with unmodified ketones for the synthesis of amino acid derivatives. In recent years, cooperative metal and organocatalysis has received considerable attention, since it can potentially enable unprecedented transformations currently impossible with a metal catalyst or an organocatalyst alone. Owing to their significance and in continuation of our recent investigation on cooperative metal and organocatalysis, we planned to carry out the investigation on CDC reactions by cooperative catalysis. In the last decade, a lot of interest has been paid to C H activation with metal catalysts and subsequent C C bond formation with nucleophiles. At the same time, enamines have become crucial reactive intermediates in organocatalysis as elegant nucleophiles for C C bond formation. However, there have been only a few reports on the application of aminocatalysis to C C bond formation after C H activation by transition-metal catalysis. In 2009, Klussmann and co-workers developed a CDC reaction of tertiary amines with methyl ketones by dual catalysis by a vanadium complex and proline. Almost all tertiary-amine substrates that underwent the CDC reaction efficiently were tetrahydroisoquinoline derivatives. To the best of our knowledge, there is no successful and disclosed example of a CDC reaction of secondary amines with ketones. Herein, we present our preliminary results on the synthesis of amino acid derivatives by CDC reactions of N-substituted glycine esters with unmodified ketones by cooperative transitionmetal and aminocatalysis. Initially, we screened different N substituents on glycine esters and various organocatalysts, transition-metal catalysts, ligands, solvents, oxidants, and additives (see the Supporting Information). The experiments demonstrated that for optimal results, the reaction should be performed by the cooperative catalysis of Cu(OAc)2·H2O (10 mol %) and pyrrolidine (30 mol %) with tert-butyl hydroperoxide (TBHP; 1.5 equiv) at ambient temperature under neat conditions in air. Under the optimized conditions, acetone reacted with the N-4methylphenylglycine ester 2a smoothly to give the desired coupling product 3a in 73% yield (Table 1, entry 1). If either pyrrolidine or Cu(OAc)2·H2O was present, no coupling product 3a was obtained. A series of N-aryl glycine esters 2a–f were then examined in the CDC reaction. The reaction

Diatomic Metasurface for Vectorial Holography.

Abstract: The emerging metasurfaces with the exceptional capability of manipulating an arbitrary wavefront have revived the holography with unprecedented prospects. However, most of the reported metaholograms suffer from limited polarization controls for a restrained bandwidth in addition to their complicated meta-atom designs with spatially variant dimensions. Here, we demonstrate a new concept of vectorial holography based on diatomic metasurfaces consisting of metamolecules formed by two orthogonal meta-atoms. On the basis of a simply linear relationship between phase and polarization modulations with displacements and orientations of identical meta-atoms, active diffraction of multiple polarization states and reconstruction of holographic images are simultaneously achieved, which is robust against both incident angles and wavelengths. Leveraging this appealing feature, broadband vectorial holographic images with spatially varying polarization states and dual-way polarization switching functionalities have been ...

Efficient NH3-SCR removal of NOx with highly ordered mesoporous WO3(χ)-CeO2 at low temperatures

Abstract: To eliminate nitrogen oxides (NOx), a series of highly ordered mesoporous WO3(χ)-CeO2 nanomaterials (χ represents the mole ratio of W/Ce) were synthesized by using KIT-6 as a hard template, which was used for selective catalytic reduction (SCR) to remove NOx with NH3 at low temperatures. Moreover, the nanomaterials were characterized by TEM, XRD, Raman, XPS, BET, H2-TPR, NH3-TPD and in situ DRIFTS. It can be found that all of the prepared mesoporous WO3(χ)-CeO2 (χ = 0, 0.5, 0.75, 1 and 1.25) showed highly ordered mesoporous channels. Furthermore, mesoporous WO3(1)-CeO2 exhibited the best removal efficiency of NOx, and its NOx conversion ratio could reach 100% from 225 ° C to 350 ° C with a gas hourly space velocity of 30 000 h-1, which was due to higher Ce3+ concentrations, abundant active surface oxygen species and Lewis acid sites based on XPS, H2-TPR, NH3-TPD and in situ DRIFTS. In addition, several key performance parameters of mesoporous WO3(1)-CeO2, such as superior water resistance, better alkali metal resistance, higher thermal stability and N2 selectivity, were systematically studied, indicating that the synthesized mesoporous WO3(1)-CeO2 has great potential for industrial applications.

Semiconducting Oligomer Nanoparticles as an Activatable Photoacoustic Probe with Amplified Brightness for In Vivo Imaging of pH

Abstract: An activatable photoacoustic nanoprobe based on a semiconducting oligomer with amplified brightness and pH-sensing capability is developed by taking advantage of nanodoping to simultaneously create both intraparticle photoinduced electron transfer and intramolecular protonation within a single particle. This organic nanoprobe permits noninvasive real-time ratiometric photoacoustic imaging of pH in tumors in living mice through systemic administration at a relatively low dosage.