金属调控蛋白的结构、性质及应用

金属调控蛋白是微生物体内通过转录抑制或激活机制严格控制金属离子摄入、外排和储存的特异性金属离子结合蛋白,对维持体内适宜的金属离子浓度和平衡起着举足轻重的作用。本文综述了目前主要的七大家族金属调控蛋白的调控机制和拓扑结构,详细介绍了金属离子结合区域的结构特征和金属-配体的配位构型。基于金属-配体的配位构型,重点讨论了每类金属调控蛋白对目标金属离子特异性选择的机理。此外,本文还介绍了金属调控蛋白在重金属离子检测和吸附方面的应用,拓展了金属调控蛋白的研究和应用领域,同时为生物无机化学的研究方向开辟了新的思路。     

基于MnO2/石墨烯纳米材料的表面辅助激光解吸电离质谱在内毒素快速鉴定中的应用

利用大肠埃希菌（E.coli O111：B4）中提取精制的内毒素（Control standard endotoxin,CSE）为研究对象,以MnO₂/石墨烯（MnO₂/G）纳米复合材料为基质,建立了一种基于MnO₂/G纳米材料的表面辅助激光解吸电离质谱（Surface-assisted laser desorption ionization mass spectrometry,SALDI-MS）的内毒素检测新方法.利用SALDI-MS方法可实现对不同注射液和饮用水中内毒素的快速鉴定与定量分析.与传统的鲎试剂检测方法相比,基于MnO₂/G纳米复合材料的SALDI-MS方法具有操作简便、灵敏度高、分辨率高、检测速度快、高通量和耐盐性好等优点,有望应用于更多食品和药品中细菌内毒素的高通量快速筛查.     

Dehydrogenative Silylation of Alkenes for the Synthesis of Substituted Allylsilanes by Photoredox,Hydrogen‐Atom Transfer,and Cobalt Catalysis

A synergistic catalytic method combining photoredox catalysis, hydrogen‐atom transfer, and proton‐reduction catalysis for the dehydrogenative silylation of alkenes was developed. With this approach, a highly concise route to substituted allylsilanes has been achieved under very mild reaction conditions without using oxidants. This transformation features good to excellent yields, operational simplicity, and high atom economy. Based on control experiments, a possible reaction mechanism is proposed.     

Tetra‐proline‐modified calix[4]arene‐bonded silica stationary phase for simultaneous reversed‐phase/hydrophilic interaction mixed‐mode chromatography

A new water‐soluble tetra‐proline‐modified calix[4]arene‐bonded silica stationary phase was prepared straightforwardly by an indirect method and characterized by elemental analysis, energy dispersive Spectrometry, solid‐state ¹³C NMR spectroscopy, Fourier‐transform infrared spectroscopy, and thermogravimetric analysis. Due to the simultaneous introduction of polar tetra‐proline and nonpolar calix[4]arene, the developed column possessing a double retention mode of reverse‐phase liquid chromatography and hydrophilic interaction liquid chromatography. A series of hydrophobic and hydrophilic test samples, including nucleosides and nucleotides, amines, monosubstituted benzenes, chiral compounds, and phenols, were used to evaluate the developed stationary phase. A rapid separation capability, high separation efficiency, and selectivity were achieved based on the multiple interactions between solutes and tetra‐proline‐modified calix[4]arene‐bonded silica stationary phase. Moreover, the developed stationary phase was further used to detect and separate hexamethylenetetramine in rice flour. All the results indicated the potential merits of the developed stationary phase for simultaneous separation of complex hydrophobic and hydrophilic samples with high selectivity.     

Analysis of Chuanxiong Rhizoma substrate on production of ligustrazine in endophytic Bacillus subtilis by ultra high performance liquid chromatography with quadrupole time‐of‐flight mass spectrometry

Ligustrazine was the active ingredient of the traditional Chinese medicine Chuanxiong Rhizoma. However, the content of ligustrazine is very low. We proposed a hypothesis that ligustrazine was produced by the mutual effects between endophytic Bacillus subtilis and the Ligusticum chuanxiong Hort. This study aimed to explore whether the endophytic B. subtilis LB5 could make use of Chuanxiong Rhizoma fermentation matrix to produce ligustrazine and clarify the mechanisms of action preliminarily. Ultra high performance liquid chromatography with quadrupole time‐of‐flight mass spectrometry analysis showed the content of ligustrazine in Chuanxiong Rhizoma was below the detection limit (0.1 ng/mL), while B. subtilis LB5 produced ligustrazine at the yield of 1.0268 mg/mL in the Chuanxiong Rhizoma‐ammonium sulfate fermentation medium. In the fermented matrix, the reducing sugar had a significant reduction from 12.034 to 2.424 mg/mL, and rough protein content increased from 2.239 to 4.361 mg/mL. Acetoin, the biosynthetic precursor of ligustrazine, was generated in the Chuanxiong Rhizoma‐Ammonium sulfate (151.2 mg/mL) fermentation medium. This result showed that the endophytic bacteria B. subtilis LB5 metabolized Chuanxiong Rhizoma via secreted protein to consume the sugar in Chuanxiong Rhizoma to produce a considerable amount of ligustrazine. Collectively, our preliminary research suggested that ligustrazine was the interaction product of endophyte, but not the secondary metabolite of Chuanxiong Rhizoma itself.     

A rapid,sensitive, and widely applicable method for quantitative analysis of underivatized amino acids in different biological matrices by UHPLC‐MS/MS

A rapid, sensitive, and widely applicable method for the simultaneous quantitative analysis of 20 underivatized amino acids in different biological matrices, including serum, plasma, and tissue homogenates, using ultra high performance liquid chromatography with tandem mass spectrometry was developed and validated. Only 4 µL of serum, plasma, or tissue homogenate was extracted with 996 µL of solution (1.7 mM ammonium formate in 85% acetonitrile containing 0.1% formic acid) containing 100 ng/mL phenylalanine‐d5 as an internal standard without any further derivatization step. In addition, the matrix effects were small because a large volume of extraction solution was used. The total run time including reequilibration was 13 min. The results of linearity, accuracy, repeatability, precision, limits of detection, limits of quantification, and sample stability were sufficient to allow the measurement of the amino acids in different biological matrices. We conclude that our method is rapid, sensitive, and widely applicable and represents an improvement over other currently available technologies.     

Determination of vitamin A in blood serum based on solid‐phase extraction using cetyltrimethyl ammonium bromide‐modified attapulgite

Cetyltrimethyl ammonium bromide‐modified attapulgite was prepared and utilized as a novel sorbent in a simple solid‐phase extraction method for the determination of vitamin A in blood serum. Several factors affecting extraction efficiency were systematically optimized, including the sampling solvent and its volume, as well as the elution solvent and its volume. Under the optimal solid‐phase extraction conditions, the adsorption capacity of vitamin A was as high as 28 mg/g according to the Langmuir isotherm model. Based on the developed solid‐phase extraction method, the level of vitamin A in 200 µL blood serum sample could be accurately determined by high‐performance liquid chromatography. The recoveries of vitamin A spiked in 10% v/v methanol aqueous solutions were in the range of 86.9–92.8%, with the relative standard deviations not more than 8.1%. The method was applied to the determination of vitamin A in serum samples from 20 pregnant women. Compared with the previously reported solid‐phase extraction methods for determination of vitamin A in serum, our developed cetyltrimethyl ammonium bromide‐modified attapulgite‐based solid‐phase extraction method used lower serum volume, omitted extra steps (i.e. evaporation and re‐dissolution), and eliminated internal standard. The results were promising for it to be used in routine monitoring during pregnancy.     

Bragg grating writing through the polyimide coating of high NA optical fibres with femtosecond IR radiation

Bragg gratings are written with ultrafast 800 nm radiation and a phase mask through the polyimide polymer coatings of commercially available high NA fibres that are both unloaded and loaded with high pressure hydrogen gas. For polyimide coated fibres with very high germanium core concentrations, index modulations greater than 1 × 10⁻⁴ are induced. Stable core index modulations 60% of their original value were present after 115 h at 500 °C.     

Highly enhanced luminescence of ZnO green phosphors by calcining ZnS with NH4Br as additive

Zinc oxide (ZnO) phosphors with highly efficient green emission have been prepared by calcining ZnS with NH₄Br as additive in air atmosphere. The luminescent properties of as-prepared ZnO phosphors were characterized by X-ray photoelectron spectroscopy and photoluminescence. Our results reveal that the green emission is ascribed to a transition of a photo-generated electron from the localized defect centers (V_o⁺) to a deeply trapped hole (V_Zn⁻) within the band gap. The addition of NH₄Br enhances the luminescent emission of ZnO by promoting the formation of vacancies of both oxygen and zinc.     

Long-range electronic-to-vibrational energy transfer from nanocrystals to their surrounding matrix environment

A radiationless transition process of long-range, resonance interconversion of electronic-to-vibrational energy transfer (EVET) is discovered between the band-gap excitation of nanocrystal quantum dots to matrix vibrational overtone modes using fluorescence lifetime measurements. A theoretical analysis based on long-range dipole-dipole nonadiabatic couplings, being distinct from the traditional adiabatic or "static-coupling" pictures, is given and is in qualitative agreement with experiments. EVET should be considered in matrix choices for near-infrared optoelectronic applications of nanocrystals.