Xie X.,CAS Beijing National Laboratory for Molecular |
Zhang L.,CAS Beijing National Laboratory for Molecular |
He Q.,CAS Beijing National Laboratory for Molecular |
Hou J.,CAS Beijing National Laboratory for Molecular |
And 5 more authors.
Chemistry - A European Journal | Year: 2015
We present herein a mechanistic investigation by nanoelectrospray ionization mass spectrometry of copper-catalyzed aerobic oxidative processes involved in the N-nitrosocarbonyl aldol reaction of N-hydroxycarbamates. Protonated amine and copper as charge-tags aided the detection of reaction intermediates, which verified the enamine mechanism together with a competing enol process. Our experimental results reveal that the copper-catalyzed aerobic oxidation of N-hydroxycarbamates may proceed through an autoxidation catalytic mechanism in which a CbzNHO. radical abstracts a hydrogen from the bound N-hydroxycarbamate to release the nitroso intermediate through a bimolecular hydrogen-atom transfer. In this process, the chiral diamine also works as a ligand for copper to facilitate the aerobic oxidative step. The dual role of the chiral vicinal diamine as both an aminocatalyst and a bidentate ligand was finally uncovered. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source
Zhang N.,CAS Beijing National Laboratory for Molecular |
Zhu K.,Beijing Institute of Technology |
Xiong C.,CAS Beijing National Laboratory for Molecular |
Jiang Y.,Beijing Institute of Technology |
And 3 more authors.
Analytical Chemistry | Year: 2016
Accurate nanoparticle mass characterization is a challenging task, especially at a single particle level. To solve this problem, a strategy for the mass measurement of single intact nanoparticle was proposed. A microscopy-based ion trap mass spectrometer was built up. To improve the detection sensitivity, a cylindrical ion trap with transparent conductive end-caps was used to increase the transmission of scattered light, and a vacuum ultraviolet lamp was used to increase the charge state of the isolated nanoparticle. By detecting the scattered light of the isolated nanoparticle, a series of secular frequencies were obtained, from which the corresponding mass-to-charge ratio of the nanoparticle was calculated. Finally, a Labview program was used to help deduce the charge state and absolute mass of the individual nanoparticle. Masses of gold nanoparticles with different sizes were accurately examined, which are (5.08 ± 0.44) × 107 Da for 20 nm, (3.55 ± 0.34) × 108 Da for 40 nm, and (1.22 ± 0.14) × 109 Da for 60 nm, respectively. The mass of MOFs with irregular shapes was also determined, which is (6.48 ± 1.08) × 109 Da. This method can provide the mass information on nanomaterials, thus opens up new possibility of characterizing nanoparticles at the single particle level. © 2016 American Chemical Society. Source