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水汽系统氢电导率监测用氢交换柱附加误差超标是造成氢电导率测量不准确的主要原因,而氢交换柱附加误差超标主要源于阳树脂的再生度低。理论分析和研究结果表明,氢交换柱附加误差与阳树脂再生度及水样Cl-浓度均有关系,再生度越低,Cl-浓度越高,氢交换柱附加误差就越大。对于超临界水汽系统氢电导率测量用氢交换柱,为了保证附加误差满足不大于5%的标准要求,建议控制树脂再生度在85%以上。阳树脂再生度取决于再生工艺,动态再生和电再生的效果要比静态浸泡再生好,可以保证树脂的再生度和氢交换柱的附加误差满足要求。 相似文献
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用质谱学方法测定分子的氢氘交换反应过程和结果是研究蛋白质分子等生物体系的分子构象,如蛋白质折叠状态的常用方法之一.本文利用线型离子阱.飞行时间质谱技术,在气相中测定了由不同个数钠离子所取代的简单多肽分子——五联丙氨酸(5Ala-nH+nNa).H^+,,n=2,3,4,5的氢氘交换反应情况,得到了由不同个数钠离子取代的分子离子的氢氘交换反应速度以及交换的氢氘数量等,并研究了钠离子个数对分子氢氘交换反应的影响.结果表明,在本工作的实验条件下,钠离子的取代将影响分子离子的氢氚交换反应.当钠离子数为2时,(5Ala-2H+2Na).H^+分子离子很难发生氢氘交换反应;当钠离子数增加时,对于(5Ala-3H+3Na).H^+,(5Ala-4H+4Na).H^+,和(5Ala-5H+5Na).H^+等,分子的氢氘交换反应速度会加快.这可能是由于钠离子的取代导致了分子离子的构型以及分子的质子亲和势发生了显著的改变,因此影响它们的氢氘交换反应.此外,我们还研究了线型四极场的q值对离子氢氘交换反应的影响,发现对于某种离子,当其对应的四极场q值低于0.8时,对各种离子的交换反应速度影响不大,但当q值接近第一稳定区图的边界点,即当q接近0.908时,对某些离子的交换反应速度影响很明显.q值对离子的交换反应速度影响可以用离子的运动速度加快而导致碰撞反应能量增加来解释. 相似文献
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电阻型湿敏材料的核磁共振研究 总被引:1,自引:0,他引:1
利用核磁共振氢谱研究了不同湿度和温度条件下聚乙烯亚胺,聚乙烯铵盐及环氧乙烷3种电阻型湿敏材料,通过化学位移变化分析了感湿机理,指出3种材料中的活泼氢和水作用后能形成新的活泼氢,新旧活泼氢可发生快速交换现象,并产生带电离子,因而材料的电阻值随湿度的增加而大幅度地降低。 相似文献
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本文采用UCCSD(T)/aug-cc-pVTZ方法研究了H NH3反应势能面,获得了夺氢反应和交换反应过渡态的的几何结构和振动频率。夺氢反应的过渡态具有Cs对称性,其能垒为61.92 kJ/mol。交换反应的过渡态具有C3v对称性,其能垒为39.69 kJ/mol。H NH3发生形成Td对称性的反应中间体NH4里德堡自由基。与夺氢反应相比,交换反应具有更低的反应能垒,并且NH4自由基在反应中可形成长寿命的共振态,和夺氢反应形成竞争关系,因此在H NH3反应的量子动力学研究中必须同时考虑这两类反应。本文还采用更大的基组aug-cc-pVQZ和aug-cc-pV5Z研究了势能面对基组的收敛行为。 相似文献
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磷钼酸四氢三铵的制备及其交换性能臧二乐,梁树权(北京农业大学应用化学系北京100094)(中国院学院化学研究所北京)关键词磷钼酸四氢三铵,制备,离子交换性能通式为M_nXY_(12)O_(40)·pH_2O(其中M为一价阳离子;X为P、As、Si、G... 相似文献
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Jaime Fernández Rico Rafael López Ignacio Ema Guillermo Ramírez 《International journal of quantum chemistry》2010,110(6):1137-1141
Exchange energy of molecules at equilibrium geometries is shown to be highly independent of the basis set and nearly equal to the sum of the exchange energies of isolated atoms. Furthermore, molecular exchange can be predicted along a chemical series with high accuracy in terms of empirical exchange contributions associated to the constituent atoms, whose values, obtained by fitting, are similar to those of the isolated atoms. It is concluded that molecular exchange is essentially a sum of atomic contributions whose differences from those of the isolated atoms are small and characteristic of the neighboring atoms. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 相似文献
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Shen K. Yang 《中国化学会会志》1997,44(4):401-406
The hydrogens at 3-position of diazepam, a frequently prescribed anxiolytic drug worldwide, undergo an efficient exchange with deuterium atoms in alkaline deuterated methanol. The position of deuterium exchange is confirmed by proton nuclear magnetic resonance and mass spectral analyses. A base-catalyzed keto-enol tautomerism is proposed to be responsible for the observed deuterium exchange. This finding has been applied to the preparation of tritium-labeled diazepam in which only aromatic protons are labeled with tritium atoms. A tritium-labeled diazepam lacking tritium atoms at 1 and 3 positions is valuable as a substrate for quantitative metabolism studies. 相似文献
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Magnetic susceptibility of solid solutions of multicomponent bismuth niobates with pyrochlore structure containing chromium atoms was studied. The parameters determining the state of chromium atoms and the exchange coupling between the paramagnetic atoms were calculated. The best agreement between the experimental and theoretically calculated magnetic moments of the chromium atoms is observed on the condition that all the chromium atoms in the Bi2MgNb2O9 structure are in the form of ferromagnetic exchange-coupled dimers with an exchange parameter J 18 cm-
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Does the Sign of the Cu–Gd Magnetic Interaction Depend on the Number of Atoms in the Bridge?
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Dr. Jean‐Pierre Costes Dr. Carine Duhayon Dr. Sonia Mallet‐Ladeira Prof. Sergiu Shova Dr. Laure Vendier 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(6):2171-2180
Several theoretical investigations with CASSCF methods confirm that the magnetic behavior of Cu–Gd complexes can only be reproduced if the 5d Gd orbitals are included in the active space. These orbitals, expected to be unoccupied, do present a low spin density, which is mainly due to a spin polarization effect. This theory is strengthened by the experimental results reported herein. We demonstrate that Cu–Gd complexes characterized by Cu–Gd interactions through single‐oxygen and three‐atom bridges consisting of oxygen, carbon, and nitrogen atoms, present weak ferromagnetic exchange interactions, whereas complexes with bridges made of two atoms, such as the nitrogen–oxygen oximato bridge, are subject to weak antiferromagnetic exchange interactions. Therefore, a bridge with an odd number of atoms induces a weak ferromagnetic exchange interaction, whereas a bridge with an even number of atoms supports a weak antiferromagnetic exchange interaction, as observed in pure organic compounds and also, as in this case, in metal–organic compounds with an active spin polarization effect. 相似文献
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A natural CXN zeolite (stilbite, type code-STI) discovered in China was modified with NH4^ exchange by using ammonium salt and calcinations (procedure Ⅰ), or with NH4 exchange followed by treatment with acid (procedure Ⅱ). The coordination state of Si and A1 atoms in the framework, the property of ion exchange, and the adsorption of the H-STI zeolite samples prepared by different modification procedure were investigated with XRD,EDX,^29Si and ^27Al MAS NMR, Ag^ ion exchange and Ne adsorption. The results of the investigations indicate that different procedure of the modification made variety on the distribution of the framework Si atoms and A1 atoms,the content of non-framework aluminum, and the blocking channels and the shielding effect to the positions of the exchangeable cations. The H-STI zeolite prepared by the procedure Ⅱ possesses high ion exchange capacity, open and perfect pore system, and high thermal stability. 相似文献
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The quantum chemical simulation of exchange interaction according to the broken symmetry approach was performed for a series of binuclear CuII complexes containing the asymmetric exchange moiety based on bis-hydrazones of 2,6-diformylphenol. The calculated values were compared between themselves and with the experimental values of the exchange parameter 2J for the binuclear copper(II) complexes with bis-hydrazones based on 2,6-diformylphenol in order to reveal the influence pattern of the nature of nonbridging donor atoms X (O, N, S, and Se) onto the exchange interaction. The strength of exchange interaction of the antiferromagnetic type depends significantly on the nature of nonbridging donor atoms, increasing in the series of X = O, NH, S, and Se. 相似文献
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通过粉状白钨酸和黄钨酸的离子交换性能的测定,比较了它们之间化学活性的相对大小。用动态法(交换柱法)测得了它们的离子交换容量,计算了与钨原子相联的羟基数目。并用静态法(振荡平衡法)测定了白钨酸对不同阳离子的交换情况及各种鸽酸的pH滴定曲线。 相似文献
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One- and two-dimensional 129Xe NMR spectroscopy has been employed to study the porosity of cocrystallized MCM-49/ZSM-35 zeolites under the continuous flow of hyperpolarized xenon gas. It is found by variable-temperature experiments that Xe atoms can be adsorbed in different domains of MCM-49/ZSM-35 cocrystallized zeolites and the mechanically mixed counterparts. The exchange of Xe atoms in different types of pores is very fast at ambient temperatures. Even at very low temperature two-dimensional exchange spectra (EXSY) show that Xe atoms still undergo much faster exchange between MCM-49 and ZSM-35 analogues in the cocrystallized zeolites than in the mechanical mixture. This demonstrates that the MCM-49 and ZSM-35 analogues in cocrystallized zeolites may be stacked much closer than in the physical mixture, and some parts of intergrowth may be formed due to the partially similar basic structure of MCM-49 and ZSM-35. 相似文献
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A long-range corrected (LC) time-dependent density functional theory (TDDFT) incorporating relativistic effects with spin-orbit couplings is presented. The relativistic effects are based on the two-component zeroth-order regular approximation Hamiltonian. Before calculating the electronic excitations, we calculated the ionization potentials (IPs) of alkaline metal, alkaline-earth metal, group 12 transition metal, and rare gas atoms as the minus orbital (spinor) energies on the basis of Koopmans' theorem. We found that both long-range exchange and spin-orbit coupling effects are required to obtain Koopmans' IPs, i.e., the orbital (spinor) energies, quantitatively in DFT calculations even for first-row transition metals and systems containing large short-range exchange effects. We then calculated the valence excitations of group 12 transition metal atoms and the Rydberg excitations of rare gas atoms using spin-orbit relativistic LC-TDDFT. We found that the long-range exchange and spin-orbit coupling effects significantly contribute to the electronic spectra of even light atoms if the atoms have low-lying excitations between orbital spinors of quite different electron distributions. 相似文献
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Jinsong Ni Alex G. Harrison 《Journal of the American Society for Mass Spectrometry》1992,3(8):853-858
The H/D exchange reactions of enolate ions with CH3OD and C2H5OD at low collision energies in the quadrupole collision cell of a hybrid tandem BEqQ mass spectrometer have been studied. The optimum parameters for exchange were elucidated using the enolate ion of acetone as a test reactant ion. With the exception of the enolate ions of 2,4-pentanedione and dimethylmalonate, all the enolate ions studied underwent exchange with CH3OD and C2H5OD. Ion signals were observed corresponding to exchange of from one to all of the enolic hydrogen atoms. The H/D exchange reaction was more facile with C2H5OD as the reagent gas, and the results with this gas clearly permit a count of the number of enolic hydrogen atoms present in the molecule. 相似文献