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401.
The chemoselectivity in the palladium‐catalyzed intramolecular cyclization of 2‐(o‐bromoaryl)‐alkenenitriles depends on the nature of α‐substitutents. 2‐(o‐Bromoanilino)alkenenitriles attacked the cyano group, followed by the cyano group transposition and hydrolysis, to give o‐(methylamino)benzonitrile. 2‐(o‐Bromobenzyl)alkenenitriles, 2‐(o‐bromophenylthio)alkenenitriles and 2‐(o‐bromophenoxy)‐alkenenitriles attacked the olefinic double bonds and led to l‐vinyl‐2‐indancecarbonitrile, 1,2,3,4‐tetrahydronaphthalene‐2‐carbonitriles, 3,4‐dihydro‐2H‐benzo[b]thiine‐2‐carbonitriles, and 3,4‐dihydro‐2H‐benzo[b]oxine‐2‐carbonitriles. A general mechanism for the palladium‐catalyzed arylations is proposed. 相似文献
402.
We study spectral properties of a quantum Hamiltonian with a complex-valued energy-dependent potential related to a model introduced in physics of nuclear reactions[30]and we prove that the principle of limiting absorption holds at any point of a large subset of the essential spectrum.When an additional dissipative or smallness hypothesis is assumed on the potential,we show that the principle of limiting absorption holds at any point of the essential spectrum. 相似文献
403.
404.
405.
Joris Chau Hernando Ombao Rainer von Sachs 《Journal of computational and graphical statistics》2019,28(2):427-439
Nondegenerate covariance, correlation, and spectral density matrices are necessarily symmetric or Hermitian and positive definite. This article develops statistical data depths for collections of Hermitian positive definite matrices by exploiting the geometric structure of the space as a Riemannian manifold. The depth functions allow one to naturally characterize most central or outlying matrices, but also provide a practical framework for inference in the context of samples of positive definite matrices. First, the desired properties of an intrinsic data depth function acting on the space of Hermitian positive definite matrices are presented. Second, we propose two pointwise and integrated data depth functions that satisfy each of these requirements and investigate several robustness and efficiency aspects. As an application, we construct depth-based confidence regions for the intrinsic mean of a sample of positive definite matrices, which is applied to the exploratory analysis of a collection of covariance matrices in a multicenter clinical trial. Supplementary materials and an accompanying R-package are available online. 相似文献
406.
An ion exchange sample probe using Ammonium Pyrrolidine Dithiocarbamate (APDC)-Polystyrene (PS) film for trace metal pre-concentration has been developed. The polymer-ligand mixture is coated onto glass plates and air-dried to form films with 10 to 20μm thick. The sample probe is immersed in the sample solution to preconcentrate metal ions onto the film. The film is then laser sampled for quantitative elemental analysis using ICP-AES. Using the ion exchange sample probe, sensitivity is enhanced. 相似文献
407.
V. E. Shishkin E. V. Mednikov Yu. V. Popov M. A. Shevchenko O. V. Anishchenko E. V. Gurba Chau Nhat Bang B. D. Emenka 《Russian Journal of General Chemistry》2011,81(4):639-641
The reactions of the C-phosphorylated acetamidines sodium derivatives with dialkylchlorophosphates were studied. They occur
selectively to afford N
1,N
1-dialkyl-N
2-benzoylbis(dialkoxyphosphoryl)-acetamidines. Based on the CH-acid properties of C-phosphorylated acetamidines, we developed
a convenient method for the synthesis of new diphosphorylated amidines. 相似文献
408.
409.
Sabrina Groth Christoph Budke Timo Weber Susanne Neugart Sven Brockmann Martina Holz Bao Chau Sawadski Diemo Daum Sascha Rohn 《Molecules (Basel, Switzerland)》2021,26(9)
Notable parts of the population in Europe suffer from allergies towards apples. To address this health problem, the analysis of the interactions of relevant allergens with other substances such as phenolic compounds is of particular importance. The aim of this study was to evaluate the correlations between the total phenolic content (TPC), polyphenol oxidase (PPO) activity, antioxidant activity (AOA), and the phenolic compound profile and the content of the allergenic protein Mal d 1 in six apple cultivars. It was found that the PPO activity and the content of individual phenolic compounds had an influence on the Mal d 1 content. With regard to the important constituents, flavan-3-ols and phenolic acids, it was found that apples with a higher content of chlorogenic acid and a low content of procyanidin trimers and/or epicatechin had a lower allergenic potential. This is probably based on the reaction of phenolic compounds (when oxidized by the endogenous PPO) with proteins, thus being able to change the conformation of the (allergenic) proteins, which further corresponds to a loss of antibody recognition. When apples were additionally biofortified with selenium, the composition of the apples, with regard to TPC, phenolic profile, AOA, and PPO, was significantly affected. Consequently, this innovative agronomic practice seems to be promising for reducing the allergenic potential of apples. 相似文献
410.
Two analogous multipolar chromophores ( 1 and 2 ) that contained 2,3,8‐trisubstituted indenoquinoxaline moieties have been synthesized and characterized for their two‐photon absorption properties, both in the femtosecond and nanosecond time regimes. We demonstrated that their multi‐branched framework structures, which incorporated appropriately functionalized indenoquinoxaline units, afforded large molecular nonlinear absorptivities within the studied spectroscopic range. Effective optical‐power‐limiting and stabilization behaviors in the nanosecond regime of dye molecule ( 2 ) were also investigated and the results indicated that such a structural motif could be a useful approach to the molecular design of highly active two‐photon systems for quick‐response and related broadband optical‐suppressing applications, in particular for confronting laser pulses of a long duration. 相似文献