822-12-8Relevant articles and documents
Revealing the Surface Structure of CdSe Nanocrystals by Dynamic Nuclear Polarization-Enhanced 77Se and 113Cd Solid-State NMR Spectroscopy
Adamson, Marquix A. S.,Blome-Fernández, Rafael,Chen, Yunhua,Dorn, Rick W.,Flintgruber, Anne H.,Hanrahan, Michael P.,Medina-Gonzalez, Alan M.,Rossini, Aaron J.,Vela, Javier,Wei, Lin
, p. 8747 - 8760 (2021/06/28)
Dynamic nuclear polarization (DNP) solid-state NMR (SSNMR) spectroscopy was used to obtain detailed surface structures of zinc blende CdSe nanocrystals (NCs) with plate or spheroidal morphologies which are capped by carboxylic acid ligands. 1D 113Cd and 77Se cross-polarization magic angle spinning (CPMAS) NMR spectra revealed distinct signals from Cd and Se atoms on the surface of the NCs, and those residing in bulk-like environments, below the surface. 113Cd cross-polarization magic-angle-turning (CP-MAT) experiments identified CdSe3O, CdSe2O2, and CdSeO3 Cd coordination environments on the surface of the NCs, where the oxygen atoms are presumably from coordinated carboxylate ligands. The sensitivity gain from DNP enabled natural isotopic abundance 2D homonuclear 113Cd-113Cd and 77Se-77Se and heteronuclear 113Cd-77Se scalar correlation solid-state NMR experiments which revealed the connectivity of the Cd and Se atoms. Importantly, 77Se{113Cd} scalar heteronuclear multiple quantum coherence (J-HMQC) experiments were used to selectively measure one-bond 77Se-113Cd scalar coupling constants (1J(77Se, 113Cd)). With knowledge of 1J(77Se, 113Cd), heteronuclear 77Se{113Cd} spin echo (J-resolved) NMR experiments were used to determine the number of Cd atoms bonded to Se atoms and vice versa. The J-resolved experiments directly confirmed that major Cd and Se surface species have CdSe2O2 and SeCd4 stoichiometries, respectively. Considering the crystal structure of zinc blende CdSe and the similarity of the solid-state NMR data for the platelets and spheroids, we conclude that the surface of the spheroidal CdSe NCs is primarily composed of {100} facets. The methods outlined here will generally be applicable to obtain detailed surface structures of various main group semiconductor nanoparticles.
Salt effects on solvolysis reactions of p-nitrophenyl alkanoates catalyzed by 4-(dialkylamino)pyridine-functionalized polymer in buffered water and aqueous methanol solutions
Wang, Guang-Jia,Ye, Donghao,Fife, Wilmer K.
, p. 12536 - 12540 (2007/10/03)
Specific salting-in effects that lead to striking substrate selectivity were observed for the hydrolysis of p-nitrophenyl alkanoates 2 (n = 2-16) catalyzed by 4-(dialkylamino)pyridine-functionalized polymer 1 in aqueous Tris buffer solution at pH 8.0 and 30°C. Macromolecule 1 was found to exhibit clear substrate preference for 2 (n = 6) in 0.05 M aqueous Tris buffer solution, as contrasted with the corresponding reaction in 0.05 M aqueous phosphate or borate buffer solutions where the substrate selectivity is absent. The formation of a reactive catalyst substrate complex, 1·2, appears to be promoted by the presence of tris(hydroxymethyl)methylammonium ion, an efficient salting-in agent, from the Tris buffer system. The salting-in effect on formation of 1·2 complex is presumed responsible for the substrate specificity. The salting-out effects of sodium chloride on the solvolysis of 2 catalyzed by 1 were also investigated in 1:1 (v/v) methanol-water solution at pH 8.0 and 30°C. The rate of 1-catalyzed solvolysis of 2 (n = 10-16) was found to vary inversely with NaCl concentration (0-1.0 M). The magnitude of the salting-out effects is dependent on the alkyl chain length in 2 and the concentrations of 1 and NaCl. At 7.5 x 10-5 unit mol L-1 1 and 0-1.0 M NaCl the order of reactivity for 2 (n = 10-16) was n = 10 > 12 > 14 > 16. However, at 5.0 x 10-6 unit mol L-1 1, a revised reactivity order, 2, n = 14 > 12 > 16, was obtained at [NaCl] 0.15 M. A significant decrease in the substrate preference for 1-catalyzed solvolysis of 2 (n = 10-16) was observed at higher NaCl concentrations. We suggest that the reduced catalytic efficiency and selectivity expressed by 1 in the presence of sodium chloride should be attributed to changes in the morphology and composition of aggregates containing 1 and 2 in aqueous methanol solution that lead to decreased dependence of aggregate formation on the hydrophobicity of the substrate.
Gel compositions and cosmetic/compositions containing the same
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, (2008/06/13)
A gel composition useful as a thickening agent, for example in cosmetic compositions, containing an aluminum-magnesium-hydroxy compound of the general formula where R represents the anion of a monocarboxylic acid having 2 to 22 carbon atoms and n, x, y and z are defined by and and also containing an organic, lipophilic compound which is liquid at 20° C.
