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B3LYP/6-31++G** method was applied to investigate the mechanism of alanine isomerization.12 minima and 22 transition states were obtained after optimization and several paths of isomerization were found.It is found that intramolecular single-bond rotation and proton transfer might lead to isomerization.The energy barrier of C–N bond rotation was lower than 2.52 kcal·mol 1,while the energy barrier ranges of the rotation of C–C and C–O were separately 0.43~ 7.01 and 4.69~12.19 kcal·mol 1,and the minimum energy barrier of proton transfer was 30.76 kcal·mol 1.The most probable isomerization path and mechanism for the two most stable conformations was discussed to find that the highest energy barrier to be crossed in this path was 11.87 kcal·mol 1.In order to understand the microscopic nature why only 4 conformations were detected in the experiment,thermodynamic properties of all conformations at the experimental temperature of 391 K was calculated.It is found that conformations XII,XI,X and IX can only unidirectionally convert into conformations rapidly with low energy and vanish immediately.The other conformations were distributed according to Maxwell-Boltzman's law,and the distribution probabilities of conformations I,II,III,IV,V,VI,VII and VIII were respectively 27.2%,26.5%,25.8%,6.4%,5.2%,4.8%,2.5% and 1.6%.Conformations I,II and III with bigger probability and stronger absorption peak were easy to detect in the experiment.Conformation IV had a relatively smaller probability(6.4%) and weak absorption peak which,however,could also be identified.The other conformations had too small probability to identify in the spectrum. 相似文献
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腌菜试样用稀磷酸及过氧化氢置于PTFE罐中,在微波炉先后在400 W及500 W消解2 min及4 min,所得试样溶液于100 mL容量瓶中定容供光度测定.在稀磷酸介质中偶氮胂Ⅰ溶液与溴酸钾溶液的氧化褪色反应因亚硝酸根的存在而催化加速.有及没有亚硝酸根存在的两份相同试液的吸光度A及A0之差△A与亚硝酸根质量浓度在50 μg·L-1以内呈线性关系,其检出限为0.82 μg·L-1用此方法分析3件腌菜试样,测定结果的相对标准偏差(n=6)均小于2%.以此样品为基体,加入亚硝酸根标准溶液进行回收试验,测得的回收率在98.0%~102.0%之间. 相似文献
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在中国原子能科学研究院 HI- 1 3串列加速器上建立了用 Q3D磁谱仪动量分析和ΔE- E粒子分辨对材料表面进行高分辨的弹性反冲探测分析技术 .用 1 0 0 Me V12 7I对 C/Li F多层样品的深度分布分析表明 ,表面分辨达到 1 .2 nm.所建立的ΔE(气体 ) - E(半导体 )望远镜探测器可同时分析从轻至中重的所有元素 .实测了新光电材料 Ga N,La2 Sr Cu O4 超导膜和新超硬材料 C3N4 (Si)等样品. High resolution depth profiling technique with elastic recoil detection analysis has been developed at the HI 13 tandem accelerator of CIAE. A depth resolution of 1.2 nm was achieved at the surface of the samples with the Q3D magnetic spectrometer and the focal plane detector. From light to medium heavy elements were simultaneous analyzed with a small Δ E E telescope. The method was applied to depth profile analysis of C/LiF multilayers, La 2SrCuO 4 superconductor and GaN foil samples. 相似文献
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反相离子对色谱法同时测定水中的硝酸根和亚硝酸根 总被引:10,自引:0,他引:10
1 引 言NO-3 和NO-2 是环境、食品等许多方面要检测的对人体有害的离子。同时测定NO-3 和NO-2 的方法有光度分析法、极谱法、色谱法等。色谱法具有试样前处理简单 ,样品用量少 ,分离速度快的特点 ,所以在分析化学中被普遍使用。NO-3和NO-2 在 2 1 0nm处均有较强的吸收 ,且吸收光谱严重重叠 ,难以用一般的分光光度法同时进行检测。我们采用反相离子对色谱法 ,以甲醇 /水 ( 2 0 /80 ,V/V)为流动相 ,四乙基溴化铵为离子对试剂 ,在ODSC1 8反相键合色谱柱上将它们进行分离 ,紫外光度计 ( 2 1 0nm)同时检测水中的NO-3… 相似文献
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姜华 《数学的实践与认识》2010,40(12)
研究了关于对数和指数的两个函数:gα(x)=((ln(1+x))/x)~α及h_β(x)=((e~x-1)/x)~β.得到当x0时,g_α(x)+h_β(x)2及g_α(x)h_β(x)1这两个不等式成立的充分必要条件. 相似文献
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离心压缩机静叶间时序效应的实验研究 总被引:2,自引:0,他引:2
轴流压缩机中的时序(Clocking)效应已通过实验和数值模拟被证实存在,而离心压缩机中时序效应的研究还很少见报道.本文通过实验,研究了静叶间时序效应对压缩机性能的影响,并采用热膜传感器,测量了叶轮出口和扩压器进口流场.实验表明,Clocking效应对压缩机效率影响明显,影响幅值超过2%,最大达到3.6%,对压比也有相应的影响.不同Clocking位置,叶轮出口切向集平均速度改变达3.3%,径向达16.5%;对扩压器进口切向集平均速度的影响超过2%,径向达4%,且扩压器进口流动角改变1.5°. 相似文献
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