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A new fluorescence sensor (QDs-IIP), based on ion-imprinted polymers (IIP) as recognition element and Mn-doped ZnS quantum dots (QDs) as fluorophore, was synthesized for the selective and sensitive determination of hexavalent chromium (Cr(VI)) ions. The QD was first coated by SiO2 layer, and then modified with Cr(VI)-imprinted polymer. Several parameters affecting fluorescence intensity such as tetraethylorthosilicate (TEOS) volume, ZnS:Mn@SiO2 amount, and radiation time were investigated and optimized. The QDs-IIP was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), transmission electron microscope (TEM), and scanning electron microscope (SEM). Furthermore, the fluorescence quenching mechanism was investigated by using UV-VIS and fluorescence spectrophotometer, and it was found that internal filtration effect was the main fluorescence quenching mechanism. The relative fluorescence intensity (F0/F) increased linearly with the increase of Cr(VI) concentration in the range of 20 μg L−1–1.0 mg L−1. The QDs-IIP sensor showed high recognition selectivity for Cr(VI) in comparison with the QDs-NIP sensor with an imprinting factor (IF) of 2.53, and it could be reused 5 times. In addition, an analytical method of Cr(VI) based on the QDs-IIP sensor was established with a limit of detection of 5.48 μg L−1, and was then applied to actual water samples with satisfactory results. Therefore, QDs-IIP can be deemed as a practicable fluorescent sensor for trace Cr(VI) detection. [ABSTRACT FROM AUTHOR]

The multiple electronic state mechanisms of the reaction of carboryne with benzene were investigated by M11 calculations. Mechanisms leading to [412] cycloaddition product P412, [212] cycloaddition product P212, C-C insert product PC-Cins and CAH insert product PC-Hins were considered. The barrier/stability to structural characteristics correlations revealed that, 1) [212] addition is a two-step mechanism which exhibits three electronic state reactivity, and both the addition steps are controlled by the barriers on open-shell singlet (OSS) potential energy surface (PES); 2) [4+2] product P412 is a kinetic product on the experimental condition, and other products should be obtained under more harsher condition. The theoretical results well explain the experimental facts. [ABSTRACT FROM AUTHOR]

Aminoglycosides are a class of antibiotics commonly used in animal husbandry. If the antibiotics cannot be used legitimately, they would remain in animal foods and environment, even causing damage to human health. The effective detection to these residues is an important part of the protection of human health. In this review, the methodology studies about the detection of aminoglycoside residues are summarized for the related researchers to conveniently understand the progress of this field. These methodology studies involve multi-residue and single residue detection methods. The former includes high-performance liquid chromatography, liquid chromatography-mass spectrometry, and capillary electrophoresis, which are about 40 % of the literature we can access to. Developing the new fluorescent probe is a possible direction for these studies. The latter is about 50 % of the amount of literature, in which most are various immunoassays. The development of highly selective antibodies or aptamers is a possible direction for these assays. Since aminoglycosides have no useful absorption, their derivatization becomes an important part of the sample pretreatment. The presentations related to derivatization are about 30 % of the listed literature, and most of the rest are the purification of the samples. The development of solid-phase extraction adsorbent material which is high selectivity to this class of antibiotics and can be used repeatedly is a possible development direction. [ABSTRACT FROM AUTHOR]

In this paper, a three-parameter family of self-similar and weak solutions are constructed rigorously in two space dimensions for all positive time to the Euler equations with axisymmetric and radial negative initial velocity for the Chaplygin gas. Under the axisymmetry and self-similar assumptions, the equations are reduced to a system of three ordinary differential equations, from which we obtain structures of solutions besides their existence. The solutions exhibit some phenomena, such as formation and evolution of black hole, expansion and explosive expansion, in the evolution of universe. [ABSTRACT FROM AUTHOR]