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Dr. Andre Sutrisno Dr. Victor V. Terskikh Qi Shi Zhengwei Song Prof. Jinxiang Dong San Yuan Ding Prof. Wei Wang Bianca R. Provost Dr. Thomas D. Daff Prof. Tom K. Woo Prof. Yining Huang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(39):12251-12259
Metal–organic frameworks (MOFs) are an extremely important class of porous materials with many applications. The metal centers in many important MOFs are zinc cations. However, their Zn environments have not been characterized directly by 67Zn solid‐state NMR (SSNMR) spectroscopy. This is because 67Zn (I=5/2) is unreceptive with many unfavorable NMR characteristics, leading to very low sensitivity. In this work, we report, for the first time, a 67Zn natural abundance SSNMR spectroscopic study of several representative zeolitic imidazolate frameworks (ZIFs) and MOFs at an ultrahigh magnetic field of 21.1 T. Our work demonstrates that 67Zn magic‐angle spinning (MAS) NMR spectra are highly sensitive to the local Zn environment and can differentiate non‐equivalent Zn sites. The 67Zn NMR parameters can be predicted by theoretical calculations. Through the study of MOF‐5 desolvation, we show that with the aid of computational modeling, 67Zn NMR spectroscopy can provide valuable structural information on the MOF systems with structures that are not well described. Using ZIF‐8 as an example, we further demonstrate that 67Zn NMR spectroscopy is highly sensitive to the guest molecules present inside the cavities. Our work also shows that a combination of 67Zn NMR data and molecular dynamics simulation can reveal detailed information on the distribution and the dynamics of the guest species. The present work establishes 67Zn SSNMR spectroscopy as a new tool complementary to X‐ray diffraction for solving outstanding structural problems and for determining the structures of many new MOFs yet to come. 相似文献
33.
Novel Microstrip Photonic Bandgap Cell Structures 总被引:2,自引:0,他引:2
Zhengwei Du Ke Gong Jeffrey S. Fu Baoxin Gao 《International Journal of Infrared and Millimeter Waves》2001,22(7):1075-1086
In general, a planar microstrip photonic bandgap (PBG) structure os a periodic array of holes etched in the ground plane of a microstrip line. To use a circuit with a PBG, the PBG structure cannot be fixed on a metal base and needs to be shielded. In this paper, two kinds of novel microstrip PBG unit cells with special patterns etched in the strip line, which can be used as the conventional microstrip circuits, are proposed and analyzed in detail. The results show that the transmission line theory is valid for the theoretic analysis of PBG circuits. 相似文献
34.
掺Nd3+氟化物玻璃中的绿色上转换发光研究 总被引:3,自引:1,他引:2
本文报道了掺钕氟化物玻璃在858nm半导体激光激发下的上转换发光。在观测到的各条条谱线中,与三光子过程相联系的绿光发射在强度上占绝对优势,表明钕离子在合适的氟化物玻璃有可能成为有效的绿光发射的上转换材料。 相似文献
35.
Bai Jingzhi Bian Jianguo Chai Zhengwei Chen HongfangChen Jiangchuan Chen Shaomin Chen Yaqing Chen YuanboCheng Baosen Cheng Baosen cui Xiangzong Ding Huiliang Du Zhizhen Fan XiaolingFang Jian Gao Cuishan Gao Meili Gao Shuqi Gu Jianhui Gu ShudiGu. Wei 《中国物理 C》1997,(5)
分析J/ψ衰变终态为三个光子的衰变道,测量得到了衰变道J/ψ→γπ0和J/ψ→γη’的分支比分别为Br(J/ψ→γπ0)=(4.6±1.1)×10-5和Br(J/ψ→ッη')=(4.12±0.82)×10-3;相对分支比F(J/ψ→γη’)/F(J/ψ→γη)=4.79±0.85,在实验误差范围内与两个理论模型的预言都能一致。 相似文献
36.
本文用气液色谱(GLC)法的保留值方法测定作为Lewis碱的脂肪醇和脂肪胺在固定液角鲨烷中的溶解平衡常数K_R~+、碱与作为Lewis酸的辣Ni[CF_3COCHC(C_4H_4S)=NCH_2]_2配合物的表观平衡常数K_R以及碱的真实加合常数K_1,以LnK_1对1/T作图求出了加合作用的热力学函数△H和△S值.它们和醇及胺中碳数n间存在线性关系。K_R~+和K_R值随碳数的增加而增大,K_1值随碳数的增加而减小。所有加合反应都是热的,熵值随着碳数的增加而减小。 相似文献
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38.
The lateral organization of membrane proteins and lipids domains has a direct impact on many cellular processes, but generally these domains are too small to be resolved by diffraction-limited resolution of fluorescence microscopy. Here, we use quantum dot (QD) labeling based on near-field optical imaging, to study the nanoscale organization of hyaluronan receptor CD44 molecules of fixed mesenchymal stem cells (MSCs) in air, with a optical resolution down to 50 nm. The photostability and high luminance of QD evidently improve the signal-to-noise ratio and reproducibility of near-field optical data. Importantly, the blinking-intensity analysis was proposed to identify single QD, providing a calibration to relate intensity to numbers of antibody for the first time. Additionally, the fluorescence-topographic imaging enables us to investigate the topographic location pattern. Our results demonstrate that CD44 molecules on MSCs are enriched into nanosized domain and they predominantly locate on the peak of the membrane protrusions, which may contribute to clarify the underlying mechanism of functions ascribed to these molecules. 相似文献
39.
High-frequency
electropulse deposition of microcrystallized MGH754 ODS alloy coatings 总被引:2,自引:0,他引:2
A simple but more efficient technique——high-frequency electropulse deposition——wasdeveloped to produce microcrystallized MGH754 ODS alloy coatings on the 1Cr18Ni9Ti stainless steel substrate. The coating has a very fine grain size of 30—300 nm and metallurgical bonding with the substrate. Isothermal oxidation in air at 1 000℃ for 100 h shows that micro-crystallisation and dispersed oxide particles promote the selective oxidation of Cr greatly to form a protective and continuous Cr2O3 scale and also improve the scale spallation resistance dramatically, thus increasing the oxidation resistance of 1Cr18Ni9Ti. 相似文献
40.
Highly ordered mesoporous silica materials have been synthesized under mildly acidic conditions by templating with a nonionic triblock copolymer (Pluronic P104) in a two-step process. It was found that a transformation from the SBA-15 type 2-dimensional (2D) hexagonal channel mesostructure (p6mm symmetry) to the MSU-X type 3-dimensional (3D) worm-like mesostructure could be induced by varying the pH whilst keeping all other conditions constant. The transformation between two types of mesoporous silica materials can be attributed to the effect of varying proton concentration on the interaction between organic micelles and inorganic species. Both types of mesoporous materials have high surface areas, large pore volumes, thick pore walls, large mean pore sizes, and narrow pore size distribution. 相似文献