著名苏联化学家H.H.谢苗诺夫

尼古拉依·尼古拉耶维奇·谢苗诺夫是著名的苏联化学家,他是苏联建国以后第一个荣获诺贝尔奖金的苏联学者。     

H?moglobinbestimmung

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H?O

光电化学分解水可将太阳能转换为绿色的氢能,为目前的能源危机和环境问题提供了一种理想的解决方案.在分解水反应中,涉及四空穴过程的产氧半反应是制约性能的关键步骤,往往需要在半导体表面沉积电催化剂以加速产氧反应动力学.因此,全面理解电催化剂在光电化学分解水体系中的作用至关重要.在目前的产氧电催化剂中,过渡金属羟基氧化物电催化剂(MOOH, M=Fe, Co, Ni)因其环保、廉价、高效以及稳定的特性,已被广泛用于半导体光阳极分解水器件中.而且, MOOH可用简单的电沉积方法沉积在光电极表面,易于大面积制备.然而,电沉积法制备的MOOH具有复杂的结构,对其作用机制的全面理解更加困难.因此,本文以电沉积MOOH修饰的硅基光阳极(n+p-Si/SiOx/Fe/FeOx/MOOH)作为模型,研究了不同电催化剂对硅光阳极光电化学产氧性能的影响.实验发现电催化剂的界面优化在电催化剂修饰的光电极中发挥着重要作用,这是因为优化的界面可以提升界面电荷传输,提供更多的催化反应活性位点以及更高的本征催化活性,从而更有利于光解水性能的提升.该项研究揭示了电催化剂在光解水器件中的作用,并为今后高效光解水器件的设计提供了一定指导.首先在多晶n+p-Si基底上热蒸镀了一层30 nm的金属Fe膜,并通过电化学活化将Fe膜表面转换为FeOx得到Fe/FeOx (记作a Fe)界面层,然后利用电沉积方法制备MOOH表面修饰层,最终得到n+p-Si/SiOx/a Fe:MOOH光阳极.X射线光电子能谱、拉曼光谱以及扫描电子显微镜表面元素成像的表征结果均证实电极表面由于界面层金属Fe元素的掺杂而形成了Fe1-xNixOOH.在模拟太阳光下用于光解水产氧时, n+p-Si/SiOx/aFe:NiOOH电极的起始电位为～1.01 VRHE (相对于可逆氢电极的电势),在1.23 VRHE下的光电流为38.82 mAcm–2,显著优于n+p-Si/SiOx/aFe、 n+p-Si/SiOx/aFe:FeOOH以及n+p-Si/SiOx/aFe:CoOOH三个对比样品,且其稳定性达到75 h.另外,我们发现n+p-Si/SiOx/aFe:MOOH电极的光电化学产氧性能均显著高于n+p-Si/SiOx/aFe电极,且p++-Si/SiOx/aFe:MOOH的电催化产氧性能也高于p++-Si/SiOx/MOOH,不仅证明了aFe界面层对Si与MOOH层之间的界面接触作用的有效调控,而且表明双电催化剂体系(aFe:MOOH)的电催化产氧活性高于单电催化剂(MOOH).热力学分析表明, n+p-Si/SiOx/a Fe:MOOH光阳极的光电压大小与其光解水产氧性能并不一致,从而排除了热力学因素对性能的关键影响.进一步从塔菲尔斜率、电化学活性表面积和电化学阻抗谱对各电极的动力学进行了分析,证明了动力学因素在上述光阳极产氧性能中的主导作用.同时发现,由于a Fe:NiOOH双电催化剂具有更高的本征电催化产氧性能,提供了更多的表面活性位点以及更有效地促进了光生载流子的传输,对动力学的提升效果更显著,从而使n+p-Si/SiOx/aFe:NiOOH光阳极表现出最高的光解水产氧性能.     

H?moglobin

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H?moglobin

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H?matoxylin

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Hämoglobinbestimmung

Analytical and Bioanalytical Chemistry -     

用离子阱经H2++H2碰撞反应碰撞反应制备H4+

用Penning型离子阱经碰撞反应H2++H2→H4+产生稳定的H4+。主要的反应产物是H3+,但十分明显地观测到H4+信号。H4+在阱中稳定存在时间长达0.1s量级。远比Kirchner等人测量的10-6s量级长。最后讨论了生成H4+的反应过程机制。     

State-selected ion-molecule reactions: H+2(ν) + He → HeH+ + H and He + H+ + H

Total cross sections for production of HeH⁺ and H⁺ in the reaction of state-selected H⁺₂ (v = 0 to 6) with He at 3.1 eV c.m. collision energy are measured by means of the threshold-photoelectron/photoion coincidence method, using pulsed synchrotron radiation. Both reaction cross sections are observed to rise with vibrational energy. The H⁺/HeH⁺ branching ratio, which is determined directly, remains approximately constant at about 0.3 for v ⩽ 3 and rises gradually for higher levels to reach the value 1.3 for v = 6. For v ⩽ 3 both reactions involve hard-type collisions and result in large-angle scattering. In contrast, at higher v levels, the HeH⁺ becomes essentially forward scattered with respect to the incident He direction, but with a velocity greater than that expected from the spectator stripping model. The H⁺ products are backward scattered with respect to the incident H⁺₂ for v ⩽ 1 and receed faster from the He atom than the H products. This observation directly leads to the conclusion that collision-induced dissociation from v = 0 and 1 involves transitions to the first excited potential-energy surface.     

Reactivity of the Ge–H,Sn–H,P–H,and Se–H Bonds in Radical Abstraction Reactions

The experimental data for the liquid- and gas-phase reactions of atoms and radicals with organoelement compounds R _{n – 1}E–H

H+H2(v=0,1)→H2(v′)+H反应截面的电子非绝热三维量子散射近似计算

本文把电子非绝热一维量子散射反应几率和三维量子散射反应截面的近似公式结合起来, 对于反应物分子(H_2)不同的量子振动态(v=0, 1) 分别计算了H+H_2(v=0)→H_2(v′=0, 1)+H和H+H_2(v=1)→H_2(v′=0, 1)+H的平均反应截面σ_0和σ_1, 并同文献上用电子绝热理论计算的结果作了比较, 表明对这类中性原予-分子反应碰撞的过程, 特别是当反应物分子处于振动激发态时, 电子非绝热效应是存在的。     

H?here Fettaldehyde

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C―H Activation

<正>Conventional syntheses of organic chemicals rely mostly on reactions between various reactive functional groups and reagents. Mechanistically, they are dominated by the involvement of highly reactive intermediates such as carbocations, carbanions, radicals and carbenes. Due to the high dissociation energy and low acidity of common C―H bonds,     

Zur H?moglobinbestimmung

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Structures and cytotoxic properties of cucumariosides H₂, H₃ and H₄ from the sea cucumber Eupentacta fraudatrix

New triterpene glycosides, cucumariosides H? (1), H? (2) and H? (3), have been isolated from the Far Eastern sea cucumber Eupentacta fraudatrix. The structures of 1-3 were elucidated using extensive NMR spectroscopy (1H- and 13C-NMR, DEPT, 1H-1H COSY, 1D TOCSY, H2BC, HMBC, heteronuclear single-quantum coherence, and NOESY) and ESI-MS. Glycosides 1-3 are monosulphated branched pentaosides having rare 3-O-methyl-D-xylose as a terminal monosaccharide. Glycosides 1 and 3 contain holostane aglycones, whereas 2 has a 23,24,25,26,27-pentanorlanostane aglycone with an 18(16)-lactone, which is also uncommon for the sea cucumbers. Glycoside 3 contains a very rare ethoxyl radical at C-25 of the aglycone side chain, and it is most probably an artefact that was formed during long storage of the ethanolic extract. Cytotoxic activities of 1-3 against mouse spleen lymphocytes, haemolytic activity against mouse erythrocytes and Ehrlich carcinoma cells have been studied. The presence of 25-hydroxy group in aglycone moiety significantly decreased the activities.     

H3PO→H2POH异构化反应的LMO研究

The localized molecular orbital (LMO) theory is used to study the reaction mechanism of the isomerization reaction: H_3PO→H_2POH. The energy transition state (TS) of the reaction is also obtained by Powell's mehtod using 6-31G basis set. The resluts show that the lone pair electrons of oxygen atom play an forortant role in this reaction.