高转速下采用S-RESIDOR方法测量1H-27Al偶极偶合常数

提出利用S-RESIDOR(Symmetry-based Resonance Echo Saturation Irradiation DOuble Resonance)方法测量¹H-²⁷Al偶极偶合常数. 通过理论模拟,讨论了四极作用常数、饱和照射脉冲功率、照射时间对¹H/²7Al S-RESIDOR实验的影响. 发现四极作用常数对¹H/²⁷Al S-RESIDOR偶极去相曲线影响较小,中等强度的饱和照射功率即能满足实验要求. 高转速下,在氢型丝光沸石上进行了¹H/²⁷Al S-RESIDOR实验,测量得到Br-nsted酸位上的 ¹H与骨架上²⁷Al的偶极偶合常数为874 Hz.     

含硼分子筛的11B VAS NMR和1H MAS NMR研究

以变角旋转(VAS) NMR方法考察了三配位硼的存在状态,得到其四极作用常数C_q为2.4MHz,电场梯度不对称系数η为0.0.硼引入骨架形成的酸性羟基质子的信号位于2.3ppm,¹H{¹¹B}双共振实验证实其与硼原子的关联很弱.与6.5ppm分子筛吸水峰同时出现的2.7ppm的信号也被认为是吸水的信号,与非骨架铝羟基质子的信号在同一位置,但可通过¹H{²⁷Al}双共振实验加以判别.     

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。     

煅烧高岭土的NMR研究

采用²⁹Si、²⁷Al MAS NMR谱对不同产地高岭在同一煅烧温度及同一产地高岭土在不同煅烧温度的煅烧产物进行了研究. 实验结果表明：不同产地高岭土在同一煅烧温度煅烧产物的²⁹Si MAS NMR相似,²⁷Al MAS NMR谱有所区别,煅烧温度对煅烧产物的²⁹Si、²⁷Al MAS NMR有一定影响.     

南海海绵Dysidea fragilis中两个倍半萜内酯的NMR研究

用一维¹H、¹³C NMR谱、DEPT ¹³C NMR谱、选择性远程DEPT ¹³C NMR、¹H-¹H COSY和¹³C-¹H COSY二维核磁共振技术研究了南海海绵Dysidea fragilis中的两个倍半萜herbadysidolide(1)和furodysinin lactone(2),确认了化学结构,并对其¹³C NMR和¹H NMR谱进行了归属.药理活性试验表明:1和2具有一定的心血管活性.     

SSZ-13分子筛上甲醇转化过程中甲氧基物种的生成与活性研究

本文使用固体核磁共振（NMR）技术研究了SSZ-13分子筛上甲醇制烯烃反应过程中表面甲氧基物种的生成以及反应活性.通过二维¹³C-²⁷Al HMQC NMR方法确证了甲醇在分子筛骨架Brønsted酸位上生成的甲氧基物种,以及在Lewis酸位上生成的另外一种表面甲氧基物种.¹³C NMR结合气相色谱-质谱（GC-MS）实验结果表明,这两种甲氧基物种在甲醇制烯烃反应中均具有较高的反应活性,既可以导致烃池物种的生成,也可以参与烃池反应生成碳氢化合物.     

几种N-取代马来酰胺酸辅酶模型的核磁共振研究

我们对8种N-取代马来酰胺酸辅酶模型与不同类型的亲核试剂反应后生成的产物进行了¹H、¹³C NMR的研究, 测得¹H、¹³C谱化学位移,研 究探讨其规律性, 并测试了IR谱和元素分析.     

3'(,3")-(二)甲酰基(二)苯并冠醚的2D NMR研究

测定了3'(,3")-(二)甲酰基(二)苯并冠醚(1~7)的¹H、¹³C谱,首次结合¹H-¹H COSY、¹³C-¹H COSY、COLOC二维谱对这些化合物的¹H、¹³C化学位移进行了归属。用NOESY谱确定了合成产物冠4、冠5的结构,并对溶液中的构象异构体及其溶剂影响进行了初探。作者以冠1~8的¹H、¹³C谱的归属为参照,提出了正确归属冠醚醚环上次甲基¹H、¹³C化学位移的一般规则。     

低聚核苷酸d(GGTATACC)2的1H和13C NMR研究

通过综合分析2D ¹H NOE谱(混合时间100ms),¹³C-¹H异核多量子化学位移相关谱和¹H双量子滤波化学位移相关谱归属了低聚脱氧核糖核酸片断d(GGTATACC)₂ ¹H和¹³C的化学位移.该8聚核苷酸在溶液中为双螺旋B型结构,各碱基相对于糖环呈反式构象,糖环本身则均以C2'-endo构象为主.     

1,2-二氢-4-苯基(2H)二氮杂萘酮的NMR谱研究

报道了1,2-二氢-2-(4-氨基苯基)-4-[4-(4-氨基苯氧基)苯基](2H)二氮杂萘-1-酮的合成,并用2D同核化学位移相关谱(¹H,¹H-COSY),2DROESY谱,2D异核¹³C-¹H相关谱和2D异核¹³C-¹H多键相关谱(HMBC)对该化合物的¹H和¹³C NMR谱进行了完整归属,证明了此化合物是含二氮杂萘酮结构,而不是二氮杂萘醚结构.     

Multinuclear (27Al, 29Si, 47,49Ti) solid-state NMR of titanium substituted zeolite USY

Multinuclear solid-state NMR spectroscopy, employing 29Si MAS,27Al MAS/3Q-MAS and (47,49)Ti wide-line experiments, has been used for the structural characterization of titanium substituted ultra-stable zeolite Y (Ti-USY). 27Al MAS experiments show the presence of aluminum in four (Al(IV)), five (Al(V)), and six (Al(VI)) coordination, whereas the multiplicity within Al(IV) and Al(VI) is revealed by 27Al 3Q-MAS experiments. Two different tetrahedral and octahedral Al environments are resolved and their isotropic chemical shifts (delta(CS)) and second-order quadrupole interaction parameters (P(Q)) have been determined by a graphical analysis of the 3Q-MAS spectra. The emergence of signal with higher intensity at -101 ppm in the 29Si MAS spectrum of Ti-USY samples indicates the possible occurrence of Q4(3Si,1Ti) type silicon environments due to titanium substitution in the faujasite framework. High-field (11.74T) operation, using a probehead specially designed to handle a large sample volume, has enabled the acquisition of 47,49Ti static spectra and identification of the titanium environment in the zeolite. The chemical shielding and electric field gradient tensors for the titanium environment in the zeolite have been determined by a computer simulation of the quadrupolar broadened static 47,49Ti NMR spectra.     

27Al multiple-quantum MAS NMR of mechanically treated bayerite (alpha-Al(OH)3) and silica mixtures

Two-dimensional 27Al multiple-quantum magic angle spinning (MQMAS) NMR experiments are used to study mixtures of bayerite (alpha-Al(OH)3) with either silicic acid (SiO2.nH2O) or silica gel (SiO2) that have been ground together for varying lengths of time. This mechanical treatment produces changes in the 27Al MAS and MQMAS NMR spectra that correspond to the formation of new Al species. Mean values of the quadrupolar interaction (PQ) and isotropic chemical shift (deltacs) are extracted from the two-dimensional 27Al NMR spectra for each of these species. The presence of significant distributions of both 27Al quadrupolar and chemical shift parameters is demonstrated and the effect of grinding duration on the magnitudes of these distributions is discussed.     

Unambiguously distinguishing Si[3Si,1Al] and Si[3Si,1OH] stuctural units in zeolite by 1H/29Si/27Al triple resonance solid state NMR spectroscopy

We present an experimentally feasible triple-resonance NMR method that establishes the correlation among three different nuclei, avoiding the difficulty to directly explore the weak coupling between two NMR nuclei, such as (29)Si and (27)Al. Using this method, we are able to give an unambiguous assignment to the various peaks in (29)Si CP NMR spectrum of MCM-22 zeolite and discriminate (29)Si signals from SiOHAl and SiOH groups. In addition, in combination with (1)H/(27)Al double-resonance technique, the (1)H/(27)Al/(29)Si triple-resonance experiment suggests the presence of two different kinds of Br?nsted acid sites in H-MCM-22 zeolite.     

27Al satellite transition spectroscopy (SATRAS) of polycrystalline aluminum borate 9Al2O3.2B2O3.

27Al NMR spectra of polycrystalline aluminum borate 9Al2O3.2B2O3 have been measured at 104, 130 and 156 MHz. The parameters of the quadrupole interaction and the isotropic chemical shifts have been obtained by fitting the CT/MAS pattern and consideration of the inner satellite transitions m = 3/2<-->1/2 and m = - 1/2<-->- 3/2. The gain in spectral resolution concerned with the observation of the MAS lines of the inner satellites leads to complete separation of the signals of AlO6, AlO5 and AlO4 polyhedra. Also signals of structural groups of one and the same coordination number can be distinguished. Experimental and theoretical lineshape calculations are compared.     

Procedures for labeling the high-resolution axis of two-dimensional MQ-MAS NMR spectra of half-integer quadrupole spins

The increasing development and application of the multiple-quantum MAS NMR for half-integer quadrupole spins has led to various RF pulse sequences for improving the excitation of multiple-quantum coherences and their conversion to single-quantum coherences. As a result, several conventions for labeling the Fl dimension of a 2D MQ-MAS spectrum appear in the literature. The corresponding relations for extracting the isotropic chemical shift, the quadrupole coupling constant, and the asymmetry parameter from experimental data are not always provided. We analyze these various conventions systematically and propose a new one, similar to that introduced by J.-P. Amoureux and C. Fernandez (2000, Solid State NMR 10, 339-343). These various conventions are illustrated with 27Al (I = 5/2) nuclei in aluminum acetylacetonate Al(CH3COCHCOCH3)3. Another experimental problem often met, the aliasing of peaks in the 2D spectrum, is analyzed and illustrated with 27Al (I = 5/2) in NH4Y zeolite and 23Na (I = 3/2) in sodium pyrophosphate Na4P2O7.     

High-field 19.6T 27Al solid-state MAS NMR of in vitro aluminated brain tissue

The combination of (27)Al high-field solid-state NMR (19.6T) with rapid spinning speeds (17.8 kHz) is used to acquire (27)Al NMR spectra of total RNA human brain temporal lobe tissues exposed to 0.10 mM Al(3+) (as AlCl(3)) and of human retinal pigment epithelial cells (ARPE-19), grown in 0.10 mM AlCl(3). The spectra of these model systems show multiple Al(3+) binding sites, good signal/noise ratios and apparent chemical shift dispersions. A single broad peak (-3 to 11 ppm) is seen for the aluminated ARPE-19 cells, consistent with reported solution-state NMR chemical shifts of Al-transferrin. The aluminated brain tissue has a considerably different (27)Al MAS NMR spectrum. In addition to the transferrin-type resonance, additional peaks are seen. Tentative assignments include: -9 to -3 ppm, octahedral AlO(6) (phosphate and water); 9 ppm, condensed AlO(6) units (Al-O-Al bridges); 24 ppm, tetrahedral AlO(3)N and/or octahedral Al-carbonate; and 35 ppm, more N-substituted aluminum and /or tetrahedral AlO(4). Thus, brain tissue is susceptible to a broad range of coordination by aluminum. Furthermore, the moderate (27)Al C(Q) values (all less than 10 MHz) suggest future NMR studies may be performed at 9.4T and a spin rate of 20 kHz.     

Fourier transform microwave spectroscopy of aluminum hydrosulfide, AlSH

Pure rotational transitions of three isotopic species of aluminum hydrosulfide, AlSH, have been measured with a cavity pulsed jet Fourier transform microwave spectrometer. AlSH was prepared by the reaction of laser ablated Al metal with H₂S, and was stabilized in pulsed supersonic free jets of Ar. For each species the transition 1₀₁-0₀₀ was measured; hyperfine structure due to the nuclear spin of ²⁷Al was observed for the first time and analyzed. For Al³²SH and Al³²SD, the rotational constants are in excellent agreement with published values. For the third species, Al³⁴SH, this is the first observation, and its rotational constants are consistent with the published geometry. Information on the electronic structure of the molecule has been obtained using the ²⁷Al nuclear quadrupole coupling constants and nuclear spin-rotation constants. The latter have been used to evaluate ²⁷Al NMR shielding parameters, which are compared with those of other ²⁷Al compounds. These shieldings have been found to be in excellent agreement with theoretical predictions. The results should also help facilitate astrophysical searches for the molecule.     

Perturbed Al photon echo ENDOR double resonance in Pr:YAlO3 and Eu:YAlO3

Aluminum pure quadrupole spectra measured by photon echo ENDOR double resonance (PENDOR) are reported for crystals of YAlO₃ doped with Pr³⁺ and for crystals doped with Eu³⁺. These spectra, which correspond to aluminum nuclei adjacent to a rare earth impurity, are compared to the results of a conventional NMR study of ²⁷ Al in YAlO₃.     

Al and Si MAS NMR investigations of cordierite glass, μ- and α-cordierite

²⁷Al and ²⁹Si Magic-Angle Spinning NMR results are reported for conventionally prepared glass of cordierite stoichiometry (2MgO · 2Al₂O₃ · 5SiO₂), the metastable high-quartz solid solution (μ-cordierite) and the high-temperature polymorph of cordierite (α-cordierite). Both, ²⁷Al two-dimensional (2D) quadrupole nutation experiments and ²⁷Al satellite transition spectroscopy (SATRAS) have been applied to identify two different tetrahedrally-coordinated aluminium sites (AlO₄). SATRAS has been used to extract the quadrupole interaction parameters and their distribution, the isotropic chemical shifts and the relative populations of the different Al sites. Both, the ²⁷Al and ²⁹Si NMR results, lead to the conclusion that a perfect Si/Al disorder does not exist in these investigated cordierite samples.     

Al Multiple-Quantum MAS NMR of Mechanically Treated Bayerite (α-Al(OH)3) and Silica Mixtures

Two-dimensional ²⁷Al multiple-quantum magic angle spinning (MQMAS) NMR experiments are used to study mixtures of bayerite (α-Al(OH)₃) with either silicic acid (SiO₂.nH₂O) or silica gel (SiO₂) that have been ground together for varying lengths of time. This mechanical treatment produces changes in the ²⁷Al MAS and MQMAS NMR spectra that correspond to the formation of new Al species. Mean values of the quadrupolar interaction (P_Q) and isotropic chemical shift (δ_CS) are extracted from the two-dimensional ²⁷Al NMR spectra for each of these species. The presence of significant distributions of both ²⁷Al quadrupolar and chemical shift parameters is demonstrated and the effect of grinding duration on the magnitudes of these distributions is discussed.