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101.
Heteronuclear multiple quantum (n=+/-0 and n=+/-2) correlated spectroscopy revamped by asymmetric z-gradient echo detection (CRAZED) experiments were performed on the spins 31P and 1H in a H3PO4 solution in order to determine the optimum flip angle for the read pulse. It has been shown that for the negative quantum signals, the maximum signals appear at beta=0, and for the positive quantum signals, the maximum signals appear at beta=pi. The CRAZED signals were compared to the single quantum signals in two-pulse two-gradient experiments. It is found that the CRAZED signals can also be distinguished into gradient echoes and spin echoes. The gradient-echo-type CRAZED signal requires beta=0 and the spin-echo-type CRAZED signal requires beta=pi for maximum echo intensities, in the same way as in single quantum experiments. 相似文献
102.
Zhou Z Lan W Zhang W Zhang X Xia S Zhu H Ye C Liu M 《Journal of chromatography. A》2007,1154(1-2):464-468
Directly coupled HPLC-NMR has become a powerful tool for separation and structural elucidation of unknown compounds. However, there are only a few reports on application of on-flow two-dimensional (2D) NMR in HPLC-NMR. Here we present an alternative method for recording real-time 2D-NMR spectrum (total correlation spectroscopy, TOCSY) on a commercial HPLC-NMR system. The method is based on well-established Hadamard matrix for 2D-NMR frequency encoding. In addition, a modified/improved solvent suppression approach is incorporated. This makes it possible to carry out the experiment with both polar and gradient eluents, the widely used chromatographic conditions. The method is example using a synthesized mixture of three amino acids (His, Phe and Try) and a human urine sample. The method demonstrated here may be utilized for high-throughput structural or unknown component identification and fast dynamic study in a variety of applications. 相似文献
103.
A target-catalyzed hairpin assembly (CHA) and graphene/Au-NPs hybrids-based platform has been developed for the determination of DNA. This new sensor not only avoided any labeling but also reduced the background signal. In the absence of target, the assembly of H1 and H2 couldn't be triggered. The catalytic activity of graphene/Au-NPs hybrids was inhibited by adsorption of H1 and H2, leading to the “inactive” hybrids unable to catalyze the oxidation reaction of 3,3′,5,5′-tetramethylbenzidine (TMB). However, with the addition of target DNA, the target-catalyzed hairpin assembly was initiated and produced plenty of H1–H2 duplex, which had a weak binding affinity with the graphene/Au-NPs. Thus, the protected interface of graphene/Au-NPs hybrids became active and catalyzed the oxidation reaction of TMB accompanied with a colorless to-blue color change. This approach exhibited good sensitivity and specificity for target DNA with a detection limit of 5.74 × 10−11 M, and realized the assay of target DNA in human serum samples. Besides, this sensor could be further expanded to detect viruses or proteins by adapting the corresponding aptamers, showing great potential in biochemical detections. 相似文献
104.
研究了原始凝胶3、3Na2O·Al2O3·10SiO2·200H2O在100℃NaY型沸石向NaPc型沸石转晶的晶化过程,应用电子显微镜、X-射线衍射、TMS-GC和固体高分辨Si29-NMR方法研究了沸石晶核的形成、晶体粒度和外貌的变化及液、固相中硅酸根离子存在状况及转晶中沸石结构的变化,并提出了转晶的液相传质机理。 相似文献
105.
1.IntroductionM.Obata[1]provedthefollowingcharacteristicofasphere:InorderforacompleteRiemanmanmanifoldMofdimensionntobeasphereofradiusa-1>0itisnecessaryandsulficientthatMadmitsaC2real-valuedfunction4withwheregisthetoemannianmetriconMandtheHessianof.T... 相似文献
106.
The spin-locking mechanism of the spin I=3/2 quadrupolar nuclei under magic angle spinning (MAS) has been theoretically and experimentally investigated, and the criterion of adiabatic passage around zero-crossings of the quadrupole splitting was inferred from the time-dependent Shrödinger equation in this article. The theory, numerical simulations, and experiments conducted in this work all indicated that second-order quadrupole interaction and off-resonance play important roles in the spin-locking of the quadrupolar nuclei, and they were responsible for the great loss of the spin-locking signals. The spin-locking for a spin I=3/2 nucleus might be achieved by minimizing the effect of the second-order quadrupole interaction by using a radio frequency (RF) offset. This offset was realized by setting the RF to the opposite position of the isotropic second-order quadrupolar shift of single quantum coherences. 相似文献
107.
108.
Bruker MSL系列核磁谱仪的数字化改造 总被引:1,自引:0,他引:1
提出并实现了对BrukerMSL系列核磁谱仪进行高技术低成本的数字化改造 ,该系统具有产生形状脉冲的2个全频段射频通道和一个数字接收机 ,有进行最新核磁实验的功能 相似文献
109.
110.
高阶ICCG误差阵模与条件数的估计 总被引:1,自引:0,他引:1
文[1]针对模型问题,应用高阶近似LU分解法给出了阶为0,1,2时ICCG法的预处理阵表达式,进而估计了误差阵的无穷模及条件数。针对更复杂的高阶问题给出了三阶和四阶ICCG法误差阵无穷模的估计以及相应的条件数上限。在不同节点数的条件下,对实际计算的条件数与文中所给出的上限作了比较。 相似文献