Thermal behavior of collagen crosslinked with tannic acid under microwave heating

Journal of Thermal Analysis and Calorimetry - With the aim at assessment of thermal stabilities of collagen crosslinked with tannic acid under microwave, some thermo-analysis methods have been...     

A DFT study of the enantioselective reduction of oxime ethers promoted by chiral spiroborate esters

Mechanisms of borane reduction of the (E)‐acetophenone O‐methyl oxime catalyzed by the easily prepared and stable spiroborate ester 1, derived from diphenylvalinol has been reported for the first time using density functional theory. Two reaction pathways are investigated at the B3LYP/6‐31G(d,p) level of theory. The calculated results reveal that this reaction is accomplished via four steps. All the reactants, products, transition states, and intermediates have been optimized at the B3LYP/6‐31G (d,p) level. The analysis of these results reveals that one pathway is more energetically favorable than the other, and its associated product is in good agreement with the experimental result. The solvent effect has been further considered at the B3LYP/6‐31G(d,p) level in the solvent THF using the PCM model, and the results indicate that it has no great influence on the enantioselectivity of this reduction. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Copolymer-supported heterogeneous organocatalyst for asymmetric aldol addition in aqueous medium

In the current study, a convenient and simple way is presented to synthesize a novel type of supported heterogeneous organocatalyst in 21-81% yield by the copolymerization of 9-amino-9-deoxy-epi-cinchonine organocatalyst with acrylonitrile using AIBN as radical initiator. The chemical compositions (x/y) and weight-average molecular weights of copolymers 1a-d were determined by (1)H NMR and GPC analysis respectively. Their porous and layered structure, and surface morphology were characterized by nitrogen adsorption-desorption, XRD and TEM. In the asymmetric aldol addition of p-nitrobenzaldehyde to cyclohexanone and 1-hydroxy-2-propanone in water, all the supported organocatalysts 1a-d afforded excellent isolated yields (90.2-94.7%) and stereoselectivities (96.8-97.8%ee anti, anti/syn = 91/9). The highest catalytic property (96% yield, anti/syn = 90/10 and 99%ee anti) in water as the sole solvent was achieved under the optimized conditions. Compared with cyclohexanone, cyclopentanone and acetone showed the less desired enantioselectivities in the same aldol reactions. At the end of the aldol reaction, the copolymer-supported organocatalyst 1a was readily recovered in 95-98% yield from reaction mixture by simple filtration using an organic membrane. Even in the fifth run, there was no significant loss in catalytic activity and stereocontrol (94.3% yield, 97.2%ee anti, anti/syn = 90/10). After continuous reuse five times, there was some drop in catalytic activity and stereoselectivity.     

冷原子荧光光谱法测定含朱砂中成药中痕量汞的样品消解溶剂选择

目的为了测定紫金锭、复方牛黄消炎胶囊等含朱砂中成药样品中痕量汞的含量,方法比较并确定了高压密封消解法适用的消解溶剂体系。结果以y（王水）＋V（H2O2）=5＋1为消解溶剂,高压密封消解-冷原子荧光法测得紫金锭和复方牛黄消炎胶囊样品的总汞含量分别为7．22％和2．66％,样品的加标回收率为96．2％-97．8％,RSD小于2％（n=3）;结论实验表明,y（王水）＋y（H2O2）=5＋1混合溶剂适用于紫金锭、复方牛黄消炎胶囊等含朱砂中成药样品的消化,获得的样品汞含量测定结果令人满意。     

THERMAL BOUNDARY LAYER IN CFB BOILER RISER

Measurement of temperature profiles of gas-solid two-phase flow at different heights in commercial-scale circulating fluidized bed （CFB） boilers was carried out. Experimental results showed that the thickness of thermal boundary layer was generally independent of the distance from the air distributor, except when close to the riser outlet. Through analysis of flow and combustion characteristics in the riser, it was found that the main reasons for the phenomena were： 1 ） the hydrodynamic boundary layer was thinner than the thermal layer and hardly changed along the CFB boiler height, and 2） both radial and axial mass and heat exchanges were strong in the CFB boiler. Numerical simulation of gas flow in the outlet zone confirmed that the distribution of the thermal boundary layer was dominated by the flow field characteristics.     

受拉区带缺口钢筋混凝土梁弯曲极限承载力的近似计算

进行受拉区带缺口钢筋混凝土梁和无缺口梁的对比实验，分析带缺口梁的承载机理，提出一种近似计算弯曲极限承载力的方法。     

热挤压铸造新型镁合金微观组织及细胞生物活性分析

采用热挤压铸造工艺制造新型镁合金, Mg-Nd-Zn-Zr-Mn (平衡-3-0.2-0.4-0.2%)基, 研究了新型镁合金表面特征、力学性能及细胞生物活性. 选择NZ30K添加Mn元素制成新镁合金, 挤压前通过均匀化热处理, 减少挤压过程中铸态合金中的粗大析出相以及树枝晶形成的带状组织. 光谱测试分析合金成分; 显微观察合金铸态、横纵截面; 扫描电镜扫描; X射线衍射分析. 将合金制成金属棒、螺钉、接骨板等形状, 测试力学性能. 进行体外细胞培养, 利用DMEM完全培养基制作镁合金浸提液, 滤膜过滤后4℃保存; 大鼠骨髓间充质干细胞提取培养, 待细胞生长至70%~80%传代于24孔板种板, 添加浸提液培养12、24、36h, 利用线粒体膜电位检测试剂盒检测细胞凋亡活性. 以纯镁作为对照组, 进行力学性能测试及细胞活性凋亡测试. 热挤压后合金的组织由细小的再结晶晶粒与变形晶粒组成, 与铸态合金相比, 其组织明显细化. 经挤压加工后, Mg-3Nd-0.2Zn-0.4Zr-0.2Mn合金横截面为细小的等轴晶组织, 组织均匀性好; 纵截面出现了晶粒尺寸相对较大的长条状组织, 组织均匀性稍差. 扫描电镜图显示Mg-3Nd-0.2Zn-0.4Zr-0.2Mn合金中第二相颗粒沿挤压方向被碾碎成更细小的颗粒, 只有非常少量的弥散分布的颗粒状析出相, 而在该合金中有较多被碾碎的第二相, 发生了明显的动态再结晶, 挤压后获得的组织不均匀, 大晶粒被发生再结晶的小晶粒包围. 从X射线衍射图中可以看出该合金铸态组织主要由α-Mg、Mn、Mg12Nd和Y相等这几相组成. 力学性能测试表明, 新型镁合金综合力学性能明显优于纯镁金属. 短期细胞培养中, 新型镁合金无明显细胞毒性, 对细胞生长有积极促进作用. 新型镁合金热挤压后的横截面为细小等轴晶组织, 组织明显细化且均匀性好, 力学性能有极大提升; 在短期细胞培养过程中新型镁合金与纯镁都表现出无细胞毒性, 新型镁合金对细胞活性的提升优于纯镁组.     

极弱散射结构中的随机激光器

提出了一种基于空间散斑的极弱散射随机激光系统,并用该系统在不同抽运条件下分别实现了相干反馈输出和非相干反馈输出.结果表明,两种反馈机制存在内在的联系.提出了随机腔耦合的概念,对弱散射随机激光器的模式特性给出了合理的解释.     

[2 + 2 + 1] Cycloaddition of N-tosylhydrazones,tert-butyl nitrite and alkenes: a general and practical access to isoxazolines

N-Tosylhydrazones have proven to be versatile synthons over the past several decades. However, to our knowledge, the construction of isoxazolines based on N-tosylhydrazones has not been examined. Herein, we report the first demonstrations of [2 + 2 + 1] cycloaddition reactions that allow the facile synthesis of isoxazolines, employing N-tosylhydrazones, tert-butyl nitrite (TBN) and alkenes as reactants. This process represents a new type of cycloaddition reaction with a distinct mechanism that does not involve the participation of nitrile oxides. This approach is both general and practical and exhibits a wide substrate scope, nearly universal functional group compatibility, tolerance of moisture and air, the potential for functionalization of complex bioactive molecules and is readily scaled up. Both control experiments and theoretical calculations indicate that this transformation proceeds via the in situ generation of a nitronate from the coupling of N-tosylhydrazone and TBN, followed by cycloaddition with an alkene and subsequent elimination of a tert-butyloxy group to give the desired isoxazoline.

A novel [2 + 2 + 1] cycloaddition of N-tosylhydrazones, tert-butyl nitrite and alkenes was successfully established, which allowed facile construction of a wide range of isoxazolines.