Studies of silicophosphate derivatives by 31P-->29Si CP MAS NMR

We show that it is possible to efficiently transfer magnetization from ³¹P to ²⁹Si, using variable amplitude CP MAS experiment. This experiment is demonstrated by using Si₅O(PO₄)₆, the synthesis protocol of which is described. From the obtained results, we show that the experiment allows the spectral edition of ²⁹Si spectra from ³¹P→²⁹Si CP, enabling the studies of derivatives involving Si–O–P linkages, such as phosphosilicate glasses, microporous silicoaluminophosphates (SAPO) and bioactive phosphosilicates.     

The crystallization kinetics of sodalites grown by the hydrothermal transformation of kaolinite studied by Si MAS NMR

The hydrothermal transformation of kaolinite to basic sodalite Na₈[AlSiO₄]₆ (OH · H₂O)₂ and hydroxoborate sodalite Na₈[AlSiO₄]₆ [B(OH)₄]₂ has been investigated at different temperatures (353 and 473 K). In the early stage of the reactions, the crystallization kinetics was studied by X-ray powder diffraction, thermogravimetry, IR spectroscopy and ²⁹Si MAS NMR spectroscopy. Besides the crystallization of the sodalites, no further intermediate phases were formed. MAS NMR of the ²⁹Si nucleus has been found to be a versatile tool to follow the progress of reactions from the signal ratio of the initial material and the crystallization product because the differences in chemical shifts result in well-separated signals. From these measurements, the growth rates of the sodalites could be determined quantitatively even for the very early stages of crystallization. It was found that sodium carbonate impurities in the NaOH solution used for the synthesis has an important influence on the reaction kinetics.     

Si CP/MAS NMR of phosphorus-bearing organosilicon compounds

While liquid-state ²⁹Si NMR of phosphorus-bearing organosilicon compounds with more than one phosphorus per molecule can take advantage of the presence of J-coupling ⁿJ(³¹P²⁹Si) for purposes of structural assignment from J-coupling patterns, conventional ²⁹Si CP/MAS spectra of such molecular solids do not reveal structural details in a straightforward manner. For such compounds it is necessary to obtain ²⁹Si CP/MAS spectra under conditions of simultaneous ¹H- and ³¹P-high power decoupling in order to derive reliable ²⁹Si chemical shift information. ²⁹Si CP/MAS NMR spectra, obtained with and without ³¹P high power decoupling during the acquisition time, of several organosilicon compounds containing Si_xP_y (x = 1 −10, y = 1 −10) moieties are reported.     

19F NMR技术在蛋白质研究中的应用

因为¹⁹F核自身的特性,如自旋为1/2;丰度高(100%),具有与¹H相当的灵敏度;化学位移分布广且对环境敏感;绝大部分生物体内都不含¹⁹F因而无背景干扰等;¹⁹F NMR自诞生以来就成为非常有吸引力的研究手段. 现在,¹⁹F NMR已被广泛用于核磁共振成像、药物化学及生物大分子的研究,各个方面均有较多的相关文献综述. 该综述将集中讨论¹⁹F NMR在蛋白质研究中的应用,包括蛋白质¹⁹F标记方法,¹⁹F NMR在蛋白质结构、 动力学、蛋白质折叠、蛋白质与药物的相互作用及In-cell NMR中的应用.     

F/Si distance determination in fluoride-containing octadecasil by Hartmann–Hahn cross-polarization under fast magic-angle spinning

¹⁹F/²⁹Si Hartmann–Hahn continuous wave cross-polarization (CP) has been applied under fast magic-angle spinning (MAS) to a powder sample of octadecasil. Strong oscillations occur during CP on a sideband matching condition between the isolated ²⁹Si–¹⁹F spin pairs formed by the silicons in the D4R units and the fluoride anions. The magnitude of the dipolar coupling constant was deduced directly from the line-splitting between the intense singularities of the Pake-like patterns obtained by Fourier transformation of the oscillatory polarization transfer. The corresponding Si–F internuclear distance, r=2.62±0.05 Å, is found to be in very good agreement with the X-ray crystal structure and the value of 2.69±0.04 Å recently reported from rotational echo double resonance (REDOR) and transferred echo double resonance (TEDOR) nuclear magnetic resonance (NMR) experiments. Furthermore, the CP technique is still reliable under fast MAS where both REDOR and TEDOR sequences suffer from severe artefacts due to finite pulse lengths. In octadecasil, a spinning frequency of 14 kHz is shown to be necessary for an effective suppression of ¹⁹F–¹⁹F spin diffusion. The influences of experimental missettings and radiofrequency (RF) field inhomogeneity are taken into account.     

AlL3-L'及AlL3-AlL3'(L=噻吩甲酰三氟丙酮,L'=乙酰丙酮)体系分子间配体交换的19F NMR研究

本文用¹⁹F NMR研究了Al(Ttfac)₃-aeac、Al(Ttfac)₃-Al(aeac)₃体系分子间配体交换反应,其中Ttfac为非对称二齿配体噻吩甲酰三氟丙酮),acac为对称二齿配体乙酰丙酮(反应的平衡常数、自由能,发现这一非对称二齿配体金属络合物与对称二齿配体金属络合物体系的配体交换反应平衡时各物种的摩尔分数服从随机统计分布,并讨论了结构与能量及交换反应平衡程度的关系。     

One- and two-dimensional solid-state magic angle spinning NMR studies on the hydration process of layered sodium disilicate SKS-6

Three different kinds of silanols, which include isolated silanol, silanol I (with the hydroxyl proton bonded to an oxygen atom in the adjacent layer) and silanol II (with the hydroxyl proton bonded to the non-bridging oxygen at the same silicon atom), are generated during the hydration process of SKS-6 (δ-Na₂Si₂O₅). ¹H–¹H nuclear Overhauser enhancement spectroscopy reveals that the proton of silanol I has an effective chemical exchange or spin diffusion with the proton of hydrogen-bonded water, while the proton of silanol II is likely far away from the other proton-containing species. ²⁹Si magic angle spinning, ¹H→²⁹Si CP/MAS NMR and ¹H–²⁹Si phase-modulated Lee–Goldburg decoupled correlation experiments demonstrate that the local environments of the silicon sites in the final hydrated sample are mainly composed of Q² [(SiO)₂Si(OH)O⁻Na⁺], Q³ [(SiO)₃Si(OH) and (SiO)₃SiO⁻Na⁺] and Q⁴ [Si(OSi)₄] groups.     

丝光沸石催化剂的固体高分辨核磁共振研究

利用²⁹Si MAS NMR及²⁷Al MAS NMR技术研究了丝光沸石催化剂制备过程中的结构变化,并利用Al的四极作用大小来区分重叠在一起的不同的Al物种.     

The surface structure of catalysts activated with hydrogen donors as elucidated by multinuclear solid-state NMR

¹H, ²⁷Al and ³¹P MAS, and ¹³C and ²⁹Si CP/MAS NMR spectroscopies, were used to characterize catalysts of Pd supported on various solids including SiO₂, AlPO₄ and Mg₃(PO₄)₂ that were activated with the chiral hydrogen-donor limonene. The above-mentioned techniques were used to check for the formation of an organopalladium complex between Pd²⁺ atoms and the olefin bonds in the limonene molecule on the catalyst surface. The results are compared with those obtained for catalysts activated in a hydrogen stream.     

A method for detection of spectral spin diffusion from minor peaks, and its application to F MAS NMR of antimony(III)-doped fluorapatite

A new technique for detecting spectral spin diffusion in solids under MAS NMR conditions that is particularly well suited for accurately measuring cross-relaxation from minor spectral components is presented. The pulse sequence, SINK (Saturation Inter-Nuclear Kinetics), selectively saturates the magnetization of a minor spectral component with a series of rotor-synchronized DANTE pulse trains and monitors spin diffusion to other peaks with a non-selective 90° pulse. We have used SINK with ¹⁹F MAS NMR on samples of calcium fluorapatite doped with Sb³⁺ to measure spin diffusion between a weak peak at 68.6 ppm due to fluoride ions associated with Sb³⁺ and other peaks in the spectrum. The SINK experiment clearly demonstrates that spin diffusion from the former peak to the main resonance of fluorapatite at 64.0 ppm is faster than spin diffusion to a second antimony-related peak at 65.6 ppm. These results strengthen our previous conclusion that antimony(III) occupies a phosphate site in the apatite lattice, with an SbO₃³⁻ group replacing a PO₄³⁻ group. The SINK experiment also enables the detection of a “hidden” peak at approximately 62.9 ppm that is otherwise obscured by the intense main peak at 64.0 ppm.     

19F固体核磁共振技术研究膜蛋白相互作用的进展

固体核磁共振技术因其可实现细胞膜环境中的蛋白质结构研究而广受关注.¹⁹F元素由于灵敏度高、天然丰度高,无生物背景等优点,被广泛应用于生物核磁共振技术中.氟标固体核磁共振技术常被用于细胞膜中蛋白质的相互作用研究,如：抗菌肽与细胞膜的相互作用、聚合膜蛋白结构分析等.此篇综述介绍了常用的蛋白质氟标修饰的实验方法,总结了常用的¹⁹F生物固体核磁共振实验技术,以及介绍了应用¹⁹F固体核磁共振研究膜蛋白的成功案例.此外,此篇综述讨论了¹⁹F固体核磁共振技术在蛋白质研究中的局限性.     

Y型沸石脱铝机制和铝状态的NMR研究

对Y型沸石原粉及几种不同脱铝样品进行了几种不同NMR方法的测量,确定了不同处理过程的脱铝机制和骨架内外铝状态的变化,²⁹Si MAS NMR谱给出了骨架Si、Al分布的信息,反映了不同方法处理样品其脱铝机制的差异,据此可以控制Y沸石脱铝过程获得更高的硅铝比,²⁷Al MAS NMR谱、二维章动NMR及¹H-²⁷Al CP/MAS NMR测量表明:水热处理的Y沸石中存在4种不同的铝状态。综合²⁹Si和²⁷Al MAS NMR观测,可相当程度地推断Y型沸石分子筛脱铝改性所发生的内部过程。     

表面活性剂全氟庚酸和全氟辛酸的19F NMR研究

测定了全氟庚酸(PFHA)和全氟辛酸(PFOA)在三氟三氯乙烷或正戊醇溶液中的不同浓度的¹⁹F NMR 化学位移并归属了谱图. 研究了活性剂浓度对化学位移影响的机理和对不同核的不同影响. 由化学位移δ值对浓度倒数作图,可求得活性剂的临界胶束浓度（cmc）：全氟庚酸：0.0195 mol/L (戊醇溶剂)和0.0406 mol/L（三氟三氯乙烷溶剂）;全氟辛酸：0.0547 mol/L（戊醇溶剂）. 用计算模拟法使δ对浓度倒数作图同实验数据作图相比较,可推测得全氟辛酸戊醇溶液的单体分子与胶束大分子的平衡常数为K=21（mol/L）^-(n-1)和胶束聚集数n=3.9.     

19F NMR化学位移经验公式的影响因素

化学位移是核磁共振技术的重要参数,目前对¹H NMR、¹³C NMR已提出一系列估算化学位移的经验公式,但¹⁹F NMR化学位移规律研究报道则较少,以δ=B+∑△i+C化学位移通式为基础,分析屏蔽常数对化学位移的作用,并针对¹⁹F原子,分析了氟的电子云密度、立体效应、溶剂效应、氢键、标准、浓度和温度等影响因素,对¹⁹F NMR化学位移经验公式的提出提供理论依据。     

Proton dynamics in letovicite, (NH4)3H(SO4)2: a 1H and 14N NMR spectroscopic study

The improper ferroelastic phase letovicite (NH₄)₃H(SO₄)₂ has been studied by ¹H MAS NMR as well as by static ¹⁴N NMR experiments in the temperature range of 296–425 K. The ¹H MAS NMR resonance from ammonium protons can be well distinguished from that of acidic protons. A third resonance appears just below the phase transition temperature which is due to the acidic protons in the paraelastic phase. The lowering of the second moment M₂ for the ammonium protons takes place in the same temperature range as the formation of domain boundaries, while the signals of the acidic protons suffer a line narrowing in the area of T_c. The static ¹⁴N NMR spectra confirm the temperature of the motional changes of the ammonium tetrahedra. Two-dimensional ¹H NOESY spectra indicate a chemical exchange between ammonium protons and the acidic protons of the paraphase.     

CO吸附和加氢反应过程的原位高压MAS NMR研究

应用原位变温高压MAS核磁共振技术,对比研究了CO在不同Rh基催化剂上的吸附和加氢反应过程. ²⁹Si MAS NMR研究结果表明：Rh基催化剂中加入金属助剂后,载体Silicate-1上的表面硅羟基减少,助剂金属与硅羟基作用锚锭在载体表面.¹³C MAS NMR研究结果表明：当引入CO/H2混合气后,在Rh/Silicate-1催化剂上只能观测到气相CO、线式吸附CO和孪式吸附CO的快速交换信号;而在Rh-Mn/Silicate-1和Rh-Mn-Li/Silicate-1催化剂上,还观测到了倾斜式吸附的CO共振信号,表明助剂Mn或Mn-Li的加入促进了CO的吸附. 随着反应温度升高,CO/H₂在Rh/Silicate-1催化剂上转化生成CO_²,进一步升高温度会有CH₄生成;而CO/H₂在RhMnLi/Silicate-1催化剂上反应活性更高,在较低的温度下就会转化生成CO₂,但未观测到甲烷的生成. ¹H MAS NMR 谱显示,反应后载体Silicate-1上硅羟基的量会减少,表明CO与载体部分表面硅羟基反应生成了CO₂.     

金属络合物分子间交换反应的核磁共振研究Ⅲ.噻吩甲酰三氟丙酮铝与苯甲酰丙酮铝体系分子间配体交换的19F NMR研究

用¹⁹F NMR研究了噻吩甲酰三氟丙酮铝与苯甲酰丙酮铝体系分子间的团体交换反应,求得了交换反应的平衡常数及自由能,结果表明交换反应有利于混合配体络合物生成,平衡时混和溶液中各组分分布偏离统计分布。     

Solid-state 29Si, 113Cd, 119Sn, and 31P NMR studies of II-IV-P2 semiconductors

Solid-state ²⁹Si, ¹¹³Cd, ¹¹⁹Sn, and ³¹P MAS NMR spectra are reported on a series of II-IV-P₂ compounds. In favorable cases (e.g., high degree of crystallinity, low concentration of unpaired electrons), well-defined spectra, with sharp lines for each specific nearest-neighbor configuration, are observed; in such cases, expected J coupling patterns are also seen. High-resolution solid-state NMR studies of this type provide useful information on structure (disorder), doping, and electron-mediated coupling in semiconductor systems.     

Si chemical shift tensors of silyl silicate cages

Static and ²⁹Si CP MAS spectra (spinning rates of 2000 and 500 Hz) of six silyl silicate cages are analyzed by deconvolution and simulation. The principal values of the various ²⁹Si chemical shift tensors provide information about the point symmetry of the Si sites. The intensities of the signals correspond sufficiently well with the stoichiometries.     

Multiple-quantum magic-angle spinning NMR with cross-polarization: Spectral editing of high-resolution spectra of quadrupolar nuclei

An experiment is presented that combines the multiple-quantum magic-angle spinning (MQMAS) technique with cross-polarization (CP). As a preliminary test of this new method, we measured and compared the ²⁷Al 3QMAS and ¹⁹F → ²⁷A1 CP 3QMAS spectra of a fluorinated AlPO₄ aluminophosphate. Complete discrimination between the fluorinated and nonfluorinated Al sites was easily achieved, which demonstrates the usefulness of CP MQMAS for spectral editing. Future applications of this experiment will include other spin pairs and heteronuclear correlation NMR spectroscopy.