Calcium Bis[bis(trimethylsilyl)amino‐triethylgallate] — A Molecule with Ca‐C‐Ga Three‐Center Bonds

The reaction of calcium‐bis[bis(trimethylsilyl)amide] with two equivalents triethylgallium yields nearly quantitatively the addition product. In the solid state the calcium atoms are coordinated by two nitrogen atoms and two ethyl groups, whereas in solution all ethyl substituents are magnetically equivalent even at low temperatures. The Ca‐C‐Ga two‐electron three‐center bonds show mean Ca‐N and Ca‐C distances of 243 and 268 pm, respectively.     

酒石酸亚铁分光光度法测定茶多酚

采用没食子酸丙酯为基准物质酒石酸亚铁作为显色剂，光度法测定茶多酚制品中茶多酚的含量。最大吸收波长５４０ｎｍ摩尔吸光系数２．６５×１０＾３回收率为９８％－１０１％，相对标准偏差为０．９０％。方法简便，结果令人满意。     

Sensitized photoluminescent properties of manganese-activated magnesium gallate phosphor

The vaccum-ultra-violet (VUV)- and UV-excited luminescent properties of MgGa₂O₄:Mn²⁺ phosphor with various co-dopants were investigated. Spinel-structured manganese-activated magnesium gallate exhibited intense green emission with the spectrum centered at 503 nm under 147 and 254 nm excitation induced by the transition from the lowest excited state to the ground state, ⁴T₁-⁶A₁, of the tetrahedral-sited Mn²⁺. With optimized incorporation ranges, Eu³⁺, Ce³⁺ and Al³⁺ co-doping, enhanced the overall fluorescence efficiency under 147 nm and these could be tentatively interpreted in terms of optical properties of host compounds and co-doped ions.     

New difluoro-boradiazaindacene shaped with gallate platforms

The present account describes the synthesis of difluoro-boradiazaindacenes (F-Bodipy) functionalized at the central 8-position by phenylamino or phenyldiamino moieties conveniently transformable into phenyl amide scaffoldings. Molecules carrying three linear or branched chains, or six linear chains were prepared and fully characterized. Four X-ray crystal structures were determined and the packing is discussed in terms of molecular interactions, a key feature for the formation of aggregates or thin films. With the exception of nitro derivatives quenched by a photo-induced reductive electron transfer and the amino-derivatives partially quenched, all dyes are highly fluorescent with quantum yields lying between 50 and 90%. The few nanosecond excited-state lifetimes and the weak Stokes shifts are in keeping with singlet excited states. Reversible reduction and oxidation processes occur around −1.34 and +0.97 V in solution and the electroactivity and photoluminescence are maintained in thin films. Interestingly, two distinct emissions are observed at 550 and 635 nm by electroluminescence of the trimethoxyphenyl-Bodipy derivative, corresponding, respectively, to the luminescence of isolated molecules and aggregates. Dispersion of the Bodipy into a fluorescent poly(N-vinylcarbazole) polymer (PVK) (approximately 3 mol% per repeating unit of PVK) by solution processing exclusively produces yellow emission due to isolated Bodipy fluorophore.     

高效液相色谱法测定饲料中的没食子酸丙酯

建立了饲料中抗氧化剂没食子酸丙酯的高效液相测定方法,优化了实验条件:流动相采用甲醇-0.2%乙酸(60∶40),检测波长为275.2nm,柱温为30℃.结果表明,在0.5-100μg/mL范围内,没食子酸丙酯浓度与峰面积呈良好的线性关系,相对标准偏差(RSD)为0.11%,回收率在90.1%-101.3%之间.方法简便...     

Transmission Electron Microscopy Study of Polymorphism in Barium Gallate BaGa2O4

Polymorphism in barium gallate BaGa₂O₄ was studied using electron diffraction and high resolution electron microscopy. Three modifications of BaGa₂O₄ with structures closely related to the high-temperature α-form were observed. The phase transitions from γ-BaGa₂O₄ (a _γ = 18.6143(2) Å = 2<formula><radical><radicand>3</radicand></radical></formula>a _α, c _γ = 8.6544(1) Å = c _α, S.G. P6₃) to β-BaGa₂O₄ (a _β = 2a _α, c _β = c _α S.G. P6₃) and to the new δ-polymorph having a monoclinic structure (a _δ = c _α, b _δ = 2a _α + b _α, c _δ = 2b _α and β ≈ 92°, S.G. P2₁/c) were induced by electron beam irradiation. High resolution electron microscopy (HREM) observations allow to establish the close similarity between the structures of δ-BaGa₂O₄ and β-SrGa₂O₄. The γ→β and β→δ transitions involve a rearrangement of oxygen atoms in the BaO layers together with a tilting distortion of the tetrahedral framework. The microstructure of the δ-phase is characterised by the presence of numerous translation and orientation domains.     

Development, validation and application of Micellar Electrokinetic Capillary Chromatography method for routine analysis of catechins, quercetin and thymol in natural samples

Natural matrices such as several vegetables, fruits or beverages are the origin of different natural antioxidants with great interest to be used instead of synthetic antioxidants in several applications, as a result of their health-promoting and disease-preventing properties. In this work, a capillary electrophoresis method capable of separating and quantifying some of these antioxidants (seven catechins with the same or similar molecular weight and relation q/z) is showed. Short analysis time and precision parameters equivalent to those obtained by liquid chromatography were obtained. This method was developed using the micellar electrokinetic chromatography (MEKC) mode with ultraviolet–visible detection. Quality parameters were established, obtaining low instrumental detection and quantification limits (0.6–2.0 mg L^{− 1} and 2.0–6.5 mg L^{− 1}, respectively), good precision (relative standard deviation in the intermediate repeatability lower than 7% for every compound) and short analysis time. The developed method also showed good performance for the determination of two more natural antioxidants, quercetin and thymol. The applicability of the method to the analysis of catechins in several natural samples was tested.     

Silver-ion redox sensing based on colloid formation by gallate ester derivatives

Plasmon absorption of silver colloid, which was formed by reduction of silver ion with compounds bearing gallate ester groups in ethanol, was observed by absorption spectroscopy. The time-dependent absorption of silver colloid was found, which shows that the silver colloid is unstable and easy to aggregate. It seemed that a calixarene derivative bearing two gallate ester groups was the most suitable for determining silver ion. In order to prevent the silver colloid aggregation, poly(N-vinylpyrrolidone) (PVP) was added into the solution at a constant time after the preparation of sample solutions. In the calibration graph, the absorbance increased with increasing silver ion concentration, especially in the concentration range of 2.00 × 10⁻⁶ to 1.00 × 10⁻⁵ M. It is possible to determine silver ion concentrations using this method.