A series of 2-amino-6-(2-oxo-2H-chromen-3-yl)-4-pyridine-3-carbo-nitriles were synthesized by the one-pot, multicomponent reaction of 3-acetyl-coumarin, aromatic aldehydes, malononitrile, and ammonium acetate in acetic acid under microwave irradiation. The reactions were completed in 10–13 min with 61–86% yields, were environmental benign, and had easy workup. Their structures were confirmed by 1H NMR, IR, and MS spectra and elemental analysis. 相似文献
Glycine, as a kind of commercially available and inexpensive ligand, is used to prepare an air-stable and water-soluble catalyst used in Sonogashira reaction in our study. In the presence of 1% [PdCl2(NH2CH2COOH)2] as catalyst, excellent catalytic activity towards the Sonogashira coupling of aryl iodides with terminal alkynes without using any additive such as Cu(I)-cocatalyst is observed in a mixture of water and acetone (3/3 mL) under air at 60 °C with NaOH as a base, giving products in good to excellent yields. 相似文献
A strategy of ultra performance liquid chromatography-quadrupole-time of flight-mass spectrometry (UPLC-Q-TOF-MS) coupled to recycling preparative HPLC was utilized to sensitively detect the minor constituents and preparatively isolate coumarin isomers from the petroleum ether extract of Peucedanum praeruptorum roots. UPLC-Q-TOF-MS was achieved on an Agilent ZORBAX Extend C-18 analytical column (50 mm × 2.1 mm i.d. 1.8 μm) using methanol:H2O as the mobile phase, and three pairs of coumarin isomers with similar polarity were detected. Then recycling preparative HPLC was successfully used in one step for the isolation and purification of these six compounds with optimized mobile phases (methanol: H2O, 73:27, 81:19, 78:22, v/v). The structures of six coumarins including three new coumarins named praeruptorin (F–H) (1, 3 and 6) were identified by spectroscopic analysis. 相似文献
DFT calculations were performed for diphenyl sulfide and diphenyl sulfone. The electrochemistry of diphenyl sulfide on the gold electrode was investigated by cyclic voltammety and the results show that standard electrode potential for redox couple diphenyl sulfone/diphenyl sulfide is 1.058 V, which is consistent with that of 1.057 calculated at B3LYP/6-31++G(d,p)-IEFPCM level. The front orbit theory and Mulliken charges of molecular explain well on the oxidation of diphenyl sulfide in oxidative desulfurization. According to equilibrium theory the experimental equilibrium constant in the oxidative desulfurization of H2O2, is 1.17 × 1048, which is consistent with the theoretical equilibrium constant is 2.18 × 1048 at B3LYP/6-31++G(d,p)-IEFPCM level. 相似文献
Quantile regression is a powerful complement to the usual mean regression and becomes increasingly popular due to its desirable properties. In longitudinal studies, it is necessary to consider the intra-subject correlation among repeated measures over time to improve the estimation efficiency. In this paper, we focus on longitudinal single-index models. Firstly, we apply the modified Cholesky decomposition to parameterize the intra-subject covariance matrix and develop a regression approach to estimate the parameters of the covariance matrix. Secondly, we propose efficient quantile estimating equations for the index coefficients and the link function based on the estimated covariance matrix. Since the proposed estimating equations include a discrete indicator function, we propose smoothed estimating equations for fast and accurate computation of the index coefficients, as well as their asymptotic covariances. Thirdly, we establish the asymptotic properties of the proposed estimators. Finally, simulation studies and a real data analysis have illustrated the efficiency of the proposed approach.
In this paper, we establish an extension of the connections between an analytic generalization of the Busemann-Petty problem and the positive definite distributions. Our results show that the structure of the positive definite distributions in Rn is closely related to the analytic generalization of the Busemann-Petty problem which was posed by Koldobsky. 相似文献
We report a theoretical analysis and numerical simulation of bandwidth and stability enhancement in optical parametric amplification (OPA) when using chirped periodically poled KTiOPO4. Calculation results show that the bandwidth and stability are enhanced significantly by the use of a chirped grating. Temperature-gradient and fanned gratings are introduced and chirp factors of them are deduced and calculated. The use of a fanned grating flattens the Quasi-phase-matching response and improves the efficiency. Finally, we propose a method to reduce the instability induced by an unstable pump. 相似文献
Oscillation on the current-voltage curve measured by atomic force microscopy is observed when the distance between the tip and sample is large enough and beyond a critical value. The appearance of the oscillation is attributed to the excitation of electron standing waves between the tip and sample. From the first peak position and the voltage difference between the first two peaks on the current-voltage curve, the value of the work function at the detected point on silver film surface and the distance between the tip and the detected point can be calculated. 相似文献