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1.
The surface silanol groups on faujasite type zeolites, which were formed by hydrothermal and acid treatments and considered to be lattice defect, were characterized. IR measurements of silanol groups were made in situ and thermogravimetic analysis was conducted under vacuum so as to quantify their content. It was thus possible to quantify separately the concentration of silanol groups forming hydroxy nests and the concentration of terminal silanol groups present on the secondary pores and crystal external surfaces. As the evacuation temperature increased, silanol groups forming hydroxy nests were found to decrease as a result of dehydroxylation condensation. The number of terminal silanol groups on the secondary pores and external surface remained virtually unchanged. The concentration of terminal silanol groups agreed well with the value calculated according to the proposed destruction model of the zeolite framework. This justified the model that there remained the double 6-ring structure on the secondary pore surfaces after the sodalite cage was collapsed as a result of the treatments. The effect of silanol groups forming hydroxy nests on the zeolite surface polarity was examined by measuring immersional heats in various solvents. It turned out that the extremely localized silanol groups forming hydroxy nests in the framework were linked via hydrogen bond to each other and showed nonpolar behavior. Copyright 1999 Academic Press. 相似文献
2.
The chemical interaction between dimethylchlorosilane and silica of varied degree of hydroxylation was subjected to a systematic study. The optimal conditions for complete substitution of isolated silanol groups with dimethyl hydride silyl groups were found. It is suggested that the reaction of dimethylchlorosilane with the surface of silicon dioxide can be used to determine the concentration of free silanol groups in the surface layer of silica. 相似文献
3.
Homogeneity and structure of organically modified polysiloxane networks prepared by sol-gel co-condensation, as well as location and nature of water molecules and silanol groups were studied by 1D and 2D solid-state NMR. 1H–29Si and 1H–1H interatomic distances were estimated from variable contact-time CP/MAS experiments, 1H NMR chemical shifts and off-resonance WISE NMR. A structure model of these networks is proposed and discussed. The fraction of proton-inaccessible units Q4 in the networks decreases with increasing amounts of dimethylsiloxane (D) and methylsiloxane (T) units. In contrast to systems prepared by co-condensation of tetraethoxysilane (TEOS) with dimethyl(diethoxy)silane (DMDEOS), proton-inaccessible units form essential fraction in networks prepared by co-condensation of TEOS with methyl(triethoxy)silane (MTEOS). The proton-accessible part of the networks with high O/Si ratios is nano-heterogeneous phase, which is composed of water containing Q
i
particles separated by copolymer domains. The overall homogeneity and uniformity of binding sites around silanol groups increases by co-condensation TEOS with DMDEOS or MTEOS, while the amount of physisorbed water as well as the hydrogen bond strength decreases, as compared with neat silica gel prepared by polycondensation of TEOS. 相似文献
4.
A. Özbay S. Sağlam T.R. Sertbakan E. Kasap S. Özçelik 《Journal of inclusion phenomena and macrocyclic chemistry》2007,58(1-2):49-54
Infrared spectra of M(1,10-diaminodecane)Ni(CN)4 · 1,5 G (M=Co, Ni or Cd; G=o-xylene, m-xylene, p-xylene) and Cd(l,6-diaminohexane)M(CN)4 · C6H6 (M=Cd or Hg) clathrates are reported. The 1,10-diaminodecane and 1,6-diaminohexane molecules in the host permit the inclusion
of bulky guest molecules. The spectral data of clathrates were compared with those of the corresponding host. The spectral
features suggest that these compounds are similar in structure to other Hofmann-type and Hofmann-Td type clathrates, respectively. 相似文献
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Jareerat Samran Pranee Phinyocheep Philippe Daniel Daniel Derouet Jean-Yves Buzare 《Macromolecular Symposia》2004,216(1):131-144
The diimide hydrogenation of natural rubber (NR) was studied by using p-toluenesulfonylhydrazide (TSH) as a diimide-releasing agent. The microstructure and the percentage of hydrogenation were studied by Raman, 1H-NMR and 13C-NMR spectroscopic techniques. Quantitative measurements on fraction of hydrogenated part gave the results in good agreement by using these techniques. The results indicated that percent hydrogenation increased with increasing of reaction time and about 80-85 % hydrogenation was achieved when a two-fold excess of TSH was used. The vibrational characteristic of C=C bond of NR is strongly Raman active and noted at 1663 cm−1. The decrease of this signal was clearly observed during the progress of hydrogenation but the vibrational frequency of the cis and trans structures of the trisubstituted olefin unit of NR can not be differentiated by this technique. While 1H- and 13C-NMR analysis showed that cis-trans isomerization of carbon-carbon unsaturation of NR occurred during hydrogenation. 相似文献
7.
Using the surface charge density/surface potential relationship for a spherical colloidal particle with high surface potential, a simple expression for the relationship of the apparent acid constant with the degree of dissociation of surface silanol groups of silica with different sizes is derived. The present formula has good agreement with literature values and is quite simple for practical use. 相似文献
8.
为理解Pt 纳米晶(NCs)表面上吸附与反应的结构效应, 本文利用电化学衰减全反射-表面增强红外吸收光谱(ATR-SEIRAS)初步研究了{100}优先取向的Pt 纳米晶表面CO电吸附和电氧化. 合成并清洗过的Pt 纳米晶在硫酸溶液中的循环伏安图出现了四对氧化还原峰, 其中位于0.26和0.36 V的峰分别对应于短程有序和长程有序Pt{100}上的氢吸脱附. 利用Bi、Ge 不可逆吸附法估算出Pt{100}和Pt{111}纳米晶筹分别占34% 和17%. 在原位红外光谱研究中, 首次分辨出线性吸附的CO (COL)物种在Pt 纳米晶的三个基础小晶面上的振动谱峰. 动电位光谱分析结果表明Pt{110}上吸附的COL优先电氧化, 其次{111}上的COL发生氧化, 而Pt{100}上COL氧化过电位最高. 相似文献
9.
Synthetic Control of Spectroscopic and Photophysical Properties of Triarylborane Derivatives Having Peripheral Electron‐Donating Groups
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Dr. Akitaka Ito Kazuyoshi Kawanishi Dr. Eri Sakuda Prof. Dr. Noboru Kitamura 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(14):3940-3953
The spectroscopic and photophysical properties of triarylborane derivatives were controlled by the nature of the triarylborane core (trixylyl‐ or trianthrylborane) and peripheral electron‐donating groups (N,N‐diphenylamino or 9H‐carbazolyl groups). The triarylborane derivatives with and without the electron‐donating groups showed intramolecular charge‐transfer absorption/fluorescence transitions between the π orbital of the aryl group (π(aryl)) and the vacant p orbital on the boron atom (p(B), π(aryl)–p(B) CT), and the fluorescence color was tunable from blue to red by the combination of peripheral electron‐donating groups and a triarylborane core. Detailed electrochemical, spectroscopic, and photophysical studies of the derivatives, including solvent dependences of the spectroscopic and photophysical properties, demonstrated that the HOMO and LUMO of each derivative were determined primarily by the nature of the peripheral electron‐donating group and the triarylborane core, respectively. The effects of solvent polarity on the fluorescence quantum yield and lifetime of the derivatives were also tunable by the choice of the triarylborane core. 相似文献
10.
Amount, properties, state of silica siloxane, silanol surface structures can be expedientlyregulated by varying the regime of thermal dehydroxylation and the amount of chemisorbed water. The obtained data can be used in the development of the procedures for the synthesis and stabilization of nanostructures and layers of chemical modifiers on the silica surface. 相似文献
11.
Lisa A. Bischoff Jarno Riefer Raphael Wirthensohn Tobias Bischof Rüdiger Bertermann Dr. Nikolai V. Ignat'ev Prof. Dr. Maik Finze 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(60):13615-13620
Salts of the tetrakis(pentafluoroethyl)aluminate anion [Al(C2F5)4]− were obtained from AlCl3 and LiC2F5. They were isolated with different counter-cations and characterized by NMR and vibrational spectroscopy and mass spectrometry. Degradation of the [Al(C2F5)4]− ion was found to proceed via 1,2-fluorine shifts and stepwise loss of CF(CF3) under formation of [(C2F5)4−nAlFn]− (n=1–4) as assessed by NMR spectroscopy and mass spectrometry and supported by results of DFT calculations. In addition, the [(C2F5)AlF3]− ion was structurally characterized. 相似文献
12.
四氯合锌酸二(正十二烷基铵)晶体相变机理的付里叶变换红外光谱研究 总被引:1,自引:0,他引:1
采用变温红外光谱研究了层结构标题配合物的固。固相变机理;相变主要与烷烃链和-NH_3极性端基结构变化有关,主要来源于烷烃链的堆积结构和构象的有序。无序变化,同时伴有N-H…Cl氢键强度的降低,由于在高温烃链产生GTG+GTG'和临近端基的TG构象以及GG链段,链大量扭曲,形成了烷烃链的“熔化”态,发现同相和异相C-C伸缩振动频率对烷烃“链熔化”相变很敏感,可用于表征烷烃链的链长变化。 相似文献
13.
K.J. Rao H. Benqlilou-MouddenB. Desbat P. VinatierA. Levasseur 《Journal of solid state chemistry》2002,165(1):42-47
Site disorder of Co3+ ions in sputtered films of lithium cobaltite has been examined using infrared spectroscopy. Both transmission and reflectance modes have been used to characterize the nature of IR absorption. It is found that Co3+ in the sputtered films occupy two types of octahedral sites that differ in the nature of second-neighbor environment. Li+ ions exhibit two bands, which may arise from tetrahedral and octahedral site occupancies or from the presence of disordered regions in the films. 相似文献
14.
Polymorphs α, β, and γ of Ga2O3 having hexagonal (corundum‐type), monoclinic and cubic (spinel‐type) structure, respectively, were prepared in a high‐surface‐area form, and characterized by powder X‐ray diffraction. Nitrogen adsorption at 77 K showed these gallia samples to have specific surface areas of 77 (α‐Ga2O3), 40 (β‐Ga2O3) and 120 m2 g?1 (γ‐Ga2O3). Fourier transform infrared spectroscopy of adsorbed carbon monoxide (at 77 K) and pyridine (at room temperature) showed that the three gallia polymorphs have a very similar surface Lewis acidity, regardless of their different crystal structures. This Lewis acidity was assigned, mainly, to coordinatively unsaturated tetrahedral Ga3+ ions situated on the surface of the small crystallites which constitute the different metal oxide varieties. Ga3+···CO adducts formed after CO adsorption gave (in all cases) a characteristic C–O stretching band at 2195–2200 cm?1, while Lewis‐type adducts formed with adsorbed pyridine were characterized by IR absorption bands at 1610–1612 and 1446–1450 cm?1. The three (partially hydroxylated) gallia polymorphs showed also a very weak Brønsted acidity, which they manifested by forming hydrogen‐bonded adducts with both CO and pyridine; however no protonation of adsorbed pyridine occurred. 相似文献
15.
基质金属蛋白酶与天然黄酮醇类药物抑制剂识别机理的光谱学研究 总被引:1,自引:1,他引:0
基质金属蛋白酶(Matrix metalloproteiriases, MMPs)是肿瘤细胞对正常组织的侵袭和转移过程中重要的调节因子, 可以水解多种细胞内、细胞外及细胞膜上的底物, 因而影响着多种细胞的行为.当MMPs表达异常时, 很多种病理会改变甚至恶化, 因此, MMPs已成为近年来备受关注的一类抗肿瘤药物靶标蛋白酶. 选用MMPs的几种天然黄酮醇类药物小分子抑制剂,利用荧光滴定光谱和紫外-可见(UV-Vis)吸收光谱相结合, 研究了它们与MMPs家族成员之一MMP-16之间的分子识别和作用机理. 研究结果表明, 这几种黄酮醇化合物不但对MMP-16显示出了较强的结合能力, 而且在结合模式、结合比和抗氧化性能等多方面都表现出了很强的结构-性能差异. 相似文献
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17.
Structural and Infrared Spectroscopic Study on Solvation of Acetylene by Protonated Water Molecules
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Xiang-tao Kong Xin Lei Qin-qin Yuan Bing-bing Zhang Zhi Zhao Dong Yang Shu-kang Jiang Dong-xu Dai Ling Jiang 《化学物理学报(中文版)》2016,29(1):31-37
The effect of solvation on the conformation of acetylene has been studied by adding one water molecule at a time. Quantum chemical calculations of the H+(C2H2)(H2O)n (n=1-5) clusters indicate that the H2O molecules prefer to form the OH…π interaction rather than the CH…O interaction. This solvation motif is different from that of neutral (C2H2)(H2O)n (n=1-4) clusters, in which the H2O molecules prefer to form the CH…O and OH…C H-bonds. For the H+(C2H2)(H2O)n cationic clusters, the first solvation shell consists of one ring structure with two OH…π H-bonds and three water molecules, which is completed at n=4. Simulated infrared spectra reveal that vibrational frequencies of OH…π H-bonded O-H stretching afford a sensitive probe for exploring the solvation of acetylene by protonated water molecules. Infrared spectra of the H+(C2H2)(H2O)n(n=1-5) clusters could be readily measured by the infrared photodissociation technique and thus provide useful information for the understanding of solvation processes. 相似文献
18.
G. Rezaei Behbehani Marie Dillon Jennifer Smyth W. Earle Waghorne 《Journal of solution chemistry》2002,31(10):811-822
The infrared spectra of tetramethylurea have been measured in mixtures of dimethylsulfoxide or acetonitrile with D2O or deuterated methanol (CH3OD). Marked solvatochroism is observed for bands associated with the C=O and C–N stretches of tetramethylurea, with the former moving to lower wavenumber, and the latter to higher, as the concentration of the protic component is increased. The C=O band shows four distinct absorbances, which are attributed to non-, mono, di-, and trihydrogen bonded tetramethylurea. The relative populations of the different hydrogen bonded species were determined from analyses of the C=O band shapes. It is found that the variations in the populations of the different hydrogen bonded species can be accounted for by a simple mass action treatment. 相似文献
19.
通过红外光谱在线监测1,5-二乙酰基-3,7-二硝基-1,3,5,7-四氮杂环辛烷(简写DADN)合成奥克托今(HMX)的反应过程,利用渐进因子分析(EFA)、多元曲线分辨 交替最小二乘法(MCR-ALS)和直观推导式演进特征投影法(HELP)等化学计量学方法对反应过程获得的光谱信息进行解析,得到了各组分浓度变化曲线和对应的红外光谱,并将MCR-ALS和HELP两种方法的分析结果进行比较,得出可相互验证的一致结论,从而推测出该反应合理的反应机理。 所得结果与文献报道吻合,表明化学计量学方法结合在线红外光谱是研究奥克托今合成机理的有效手段。 相似文献