Kinetic determination of ascorbic acid by the BZ oscillating chemical system

A new analytical method for the determination of ascorbic acid by the perturbation caused by different amounts of ascorbic acid on the BZ oscillating chemical system involving the Ce(IV)-catalyzed reaction between potassium bromate and malonic acid in a acidic medium is proposed. The method relies on the linear relationship between the change in the oscillation amplitude of the chemical system and the concentration of ascorbic acid, which is in this work exposed for the first time. The calibration curve is linearly proportional to the concentration of ascorbic acid over the range 3.5x10(-6)-4.7x10(-4) M, with the regression coefficient is 0.9975. Two different methodologies were used to address the determination. Some aspects of the potential mechanism of action of ascorbic acid on the BZ oscillating chemical system are discussed in detail.     

Synthesis and thermodynamic properties of a metal-organic framework: [LaCu6(μ-OH)3(Gly)6im6](ClO4)6

A metal-organic complex, which has the potential property of absorbing gases, [LaCu₆(μ-OH)₃(Gly)₆im₆](ClO₄)₆ was synthesized through the self-assembly of La³⁺, Cu²⁺, glycine (Gly) and imidazole (Im) in aqueous solution and characterized by IR, element analysis and powder XRD. The molar heat capacity, C_p,m, was measured from T = 80 to 390 K with an automated adiabatic calorimeter. The thermodynamic functions [H_T − H_298.15] and [S_T − S_298.15] were derived from the heat capacity data with temperature interval of 5 K. The thermal stability of the complex was investigated by differential scanning calorimetry (DSC).     

动物尿液中盐酸克伦特罗的分子印迹固相萃取-气相色谱-质谱法研究

采用分子印迹聚合物(MIP)固相萃取小柱提取、净化并富集猪尿液中的盐酸克伦特罗分子,用N,O-双三甲基硅基三氟乙酰胺(BSTFA)衍生化,毛细管气相色谱-质谱联用(选择离子模式,选择离子为277、262、243和86)对衍生物分析。优化了MIP固相萃取柱的淋洗条件,考察了MIP固相萃取柱的净化效果和消除基体干扰能力,建立了对动物尿液中盐酸克伦特罗的定性、定量分析的方法。在优化条件下,本法检出限(LOD)为0.51μg/L,定量限(LOQ)为1.00μg/L;不同盐酸克伦特罗加入量的回收率为71.0%~89.3%;相对标准偏差为3.2%~9.7%。将该方法与农业行业标准方法比较,结果吻合较好。但该方法灵敏度和精密度高,操作更为简单、快捷。     

三尖杉酯碱侧链酸的不对称合成及结构表征

以N-Boc苏氨醛为起始原料,经Wittig、Meisenheimer重排和催化氢化系列反应,不对称合成了天然产物三尖杉酯碱的侧链酸,中间体及目标产物结构经核磁共振(1 H NMR、13 C NMR)、红外光谱和质谱表征.结果表明,所用合成方法具有产率高、反应条件温和、操作简单等优点;目标化合物的总收率达30%.     

A sensitive DNA biosensor based on a facile sulfamide coupling reaction for capture probe immobilization

A novel DNA biosensor was fabricated through a facile sulfamide coupling reaction. First, the versatile sulfonic dye molecule of 1-amino-2-naphthol-4-sulfonate (AN-SO₃⁻) was electrodeposited on the surface of a glassy carbon electrode (GCE) to form a steady and ordered AN-SO₃⁻ layer. Then the amino-terminated capture probe was covalently grafted to the surface of SO₃⁻-AN deposited GCE through the sulfamide coupling reaction between the amino groups in the probe DNA and the sulfonic groups in the AN-SO₃⁻. The step-by-step modification process was characterized by electrochemistry and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy. Using Ru(NH₃)₆³⁺ as probe, the probe density and the hybridization efficiency of the biosensor were determined to be 3.18 × 10¹³ strands cm⁻² and 86.5%, respectively. The hybridization performance of the biosensor was examined by differential pulse voltammetry using Co(phen)₃^3+/2+ (phen = 1,10-phenanthroline) as the indicator. The selectivity experiments showed that the biosensor presented distinguishable response after hybridization with the three-base mismatched, non-complementary and complementary sequences. Under the optimal conditions, the oxidation peak currents of Co(phen)₃^3+/2+ increased linearly with the logarithm values of the concentration of the complementary sequences in the range from 1.0 × 10⁻¹³ M to 1.0 × 10⁻⁸ M with a regression coefficient of 0.9961. The detection limit was estimated to be 7.2 × 10⁻¹⁴ M based on 3σ.     

Low‐Background,Highly Sensitive DNA Biosensor by Using an Electrically Neutral Cobalt(II) Complex as the Redox Hybridization Indicator

An electrically neutral cobalt complex, [Co(GA)₂(phen)] (GA=glycollic acid, phen=1,10‐phenathroline), was synthesized and its interactions with double‐stranded DNA (dsDNA) were studied by using electrochemical methods on a glassy carbon electrode (GCE). We found that [Co(GA)₂(phen)] could intercalate into the DNA duplex through the planar phen ligand with a high binding constant of 6.2(±0.2)×10⁵ M ^?1. Surface studies showed that the cobalt complex could electrochemically accumulate within the modified dsDNA layer, rather than within the single‐stranded DNA (ssDNA) layer. Based on this feature, the complex was applied as a redox‐active hybridization indicator to detect 18‐base oligonucleotides from the CaMV35S promoter gene. This biosensor presented a very low background signal during hybridization detection and could realize the detection over a wide kinetic range from 1.0×10^?14 M to 1.0×10^?8 M , with a low detection limit of 2.0 fM towards the target sequences. The hybridization selectivity experiments further revealed that the complementary sequence, the one‐base‐mismatched sequence, and the non‐complementary sequence could be well‐distinguished by the cobalt‐complex‐based biosensor.     

Synthesis,Physical Properties,and Anion Recognition of Two Novel Larger Azaacenes: Benzannelated Hexazaheptacene and Benzannelated N,N′‐Dihydrohexazaheptacene

Two novel larger azaacenes with six or ten N atoms in their backbones, benzannelated 9,11,13,22,24,26‐hexazatetrabenzo[a,c,l,n]heptacene ( HATBH , 1 ) and benzannelated 9,26‐dihydro‐9,11,13,22,24,26‐hexaza‐tetrapyrido[3,2‐a: 2′,3′‐c: 3′′,2′′‐l: 2′′′,3′′′‐n]heptacene ( DHATPH, 2 ), have been successfully synthesized in two steps. The theoretical band gaps estimated through DFT calculations for HATBH ( 1 ) and DHATPH ( 2 ) are 1.949 eV and 2.278 eV, which are close to the experimentally obtained optical band gaps (2.14 eV and 2.39 eV). Interestingly, HATBH ( 1 ) can act as efficient anion sensor for F^? and H₂PO₄^?, while DHATPH ( 2 ) selectively responds to F^? among the ten different anions used (F^?, Cl^?, Br^?, I^?, PF₆^?, HSO₄^?, NO₃^?, BF₄^?, AcO^?, and H₂PO₄^?). Our synthetic strategy could offer a promising and easy way to obtain even larger azaacenes.     

Ultrasonic Preparation of Hierarchical Graphene‐Oxide/TiO2 Composite Microspheres for Efficient Photocatalytic Hydrogen Production

Hierarchical graphene oxide (GO)‐TiO₂ composite microspheres with different GO/TiO₂ mass ratios were successfully prepared by mixing GO and TiO₂ microspheres under ultrasonic conditions. Ultrasonication helped the GO and TiO₂ microsphere to uniformly mix on the microscale. The results showed that the GO‐TiO₂ composites that were prepared by ultrasonic mixing exhibited significantly higher hydrogen‐evolution rates than those that were synthesized by simple mechanical grinding, owing to synergetic effects, including enhanced light absorption and scattering, as well as improved interfacial charge transfer because of the excellent contact between the GO sheets and TiO₂ microspheres. In addition, GO‐TiO₂‐3 (3 wt. % GO) showed the highest hydrogen‐generation rate (305.6 μmol h^?), which was about 13 and 3.3‐times higher than those of TiO₂ microsphere and GO‐P25 (with 3 wt. % GO), respectively. Finally, a tentative mechanism for hydrogen production is proposed and supported by photoluminescence and transient photocurrent measurements. This work highlights the potential applications of GO‐TiO₂ composite microspheres in the field of clean‐energy production.     

Malathion detection method using microhotplate-based preconcentrator and ion mobility spectrometer

A simple and rapid method using a microhotplate-based preconcentrator and an ion mobility spectrometer (IMS) is proposed for the detection of malathion in water. The preconcentrator is prepared by micro-electro-mechanical system (MEMS) process. Coated with Polydimethylsiloxane (PDMS), it has the advantages of solvent-less, low energy cost, self-heating and ease to combine with IMS. The operating conditions of the preconcentrator-IMS system, such as extraction time, extraction temperature, agitation speed and desorption temperature, were optimised. Using the preconcentrator, the sampling procedure can be simplified and the detection limit of the system can be decreased. A linear relationship between the IMS response and the concentration of the analyte solution was verified. The malathion detection limit based on 3 times the baseline noise is 0.43?µg?L^?1 and the total analysis time is less than 30?minutes.     

双金属(Sn/Ni)掺杂多孔硅微球的液相合成与电化学储锂性能

使用廉价的硅铝合金前驱体,通过简单的化学沉积方法制备了新型双金属(Sn/Ni)掺杂多孔硅微球(pSi@SnNi)。pSi@SnNi复合材料的三维多孔结构可以缓冲硅在锂化过程中的巨大体积膨胀,增加储锂活性位点。双金属(Sn/Ni)的掺杂可以提高硅的电子导电性,改进pSi的结构稳定性。由于其独特的组成和微观结构,具有适当Sn/Ni含量的pSi@SnNi复合材料显示了较大的可逆储锂容量(0.1 A·g^-1下为2 651.7 mAh·g^-1)、较高的电化学循环稳定性(1 A·g^-1下400次循环后为1 139 mAh·g^-1)和优异的倍率性能(2.5 A·g^-1下为1 235.8 mAh·g^-1)。