NMR study of heterogeneity in pyridine-N-oxide...HCl crystal

An origin of narrow ¹H NMR signals in pyridine-N-oxide (PyO)...HCl crystal has been investigated by means of MAS, SPEDAS, NOESY and COSY techniques. Spectra of crystalline samples are compared with those of solid phase obtained from liquid PyO...HCl solutions (in acetonitile/H₂O) after the heterogeneous phase separation. It has been concluded that partially resolved peaks in ¹H NMR spectra of solids are related with heterogeneity of spin system and presence of different H-bond clusters of water molecules. NOESY spectra show no cross-peaks even at very long mixing time (500 ms). This indicates there is no exchange process between spins causing different peaks, and thus the corresponding molecular aggregates are captured in “islands of mobility8 without any channels sufficient for exchange. Appearance of MAS side bands as “pseudo8 cross-peaks in 2D NMR spectra using MAS/COSY technique is reported. In the case of accidental coincidence of spinning frequency (ω _MAS ) with spectral distances between some diagonal signals, intensive non-diagonal peaks are observed at the corresponding cross-positions. A misleading conclusion concerning spin coupling is easy to avoid using various ω _MAS . This work is dedicated to Professor Robert Blinc on the occasion of his 70^th birthday.     

Multi-dimensional 1H-13C HETCOR and FSLG-HETCOR NMR study of sphingomyelin bilayers containing cholesterol in the gel and liquid crystalline states

(13)C cross polarization magic angle spinning (CP-MAS) and (1)H MAS NMR spectra were collected on egg sphingomyelin (SM) bilayers containing cholesterol above and below the liquid crystalline phase transition temperature (T(m)). Two-dimensional (2D) dipolar heteronuclear correlation (HETCOR) spectra were obtained on SM bilayers in the liquid crystalline (L(alpha)) state for the first time and display improved resolution and chemical shift dispersion compared to the individual (1)H and (13)C spectra and significantly aid in spectral assignment. In the gel (L(beta)) state, the (1)H dimension suffers from line broadening due to the (1)H-(1)H homonuclear dipolar coupling that is not completely averaged by the combination of lipid mobility and MAS. This line broadening is significantly suppressed by implementing frequency switched Lee-Goldburg (FSLG) homonuclear (1)H decoupling during the evolution period. In the liquid crystalline (L(alpha)) phase, no improvement in line width is observed when FSLG is employed. All of the observed resonances are assignable to cholesterol and SM environments. This study demonstrates the ability to obtain 2D heteronuclear correlation experiments in the gel state for biomembranes, expands on previous SM assignments, and presents a comprehensive (1)H/(13)C NMR assignment of SM bilayers containing cholesterol. Comparisons are made to a previous report on cholesterol chemical shifts in dimyristoylphosphatidylcholine (DMPC) bilayers. A number of similarities and some differences are observed and discussed.     

HR/MAS高分辨魔角微量探头用于天然橡胶固体1H、13C NMR测试及其与液体BBO探头、固体CP/MAS探头测试的比较

采用BRUKER高分辨魔角微量探头（HR/MAS），液相宽带BBO探头和固体CP/MAS探头，对天然橡胶固体、乳液以及天然橡胶溶于氘代苯的溶液进行了¹H、¹³C 1D和2D NMR谱的测试和比较. 发现HR/MAS探头用于天然橡胶固体和乳液时可以得到高分辨的¹H、¹³C谱，克服了CP/MAS探头测试固体¹³C NMR谱或者是固体¹H NMR谱时，谱图存在S/N值可能较小、谱峰可能宽化的弱点.     

Two-dimensional ENDOR-ESEEM correlation spectroscopy

A two-dimensional (2D) experiment that correlates electron-nuclear double resonance (ENDOR) and electron spin-echo envelope modulation (ESEEM) frequencies, useful for unraveling and assigning ENDOR and ESEEM spectra from different paramagnetic centers with overlapping EPR spectra, is presented. The pulse sequence employed is similar to the Davies ENDOR experiment with the exception that the two-pulse echo detection is replaced by a stimulated echo detection in order to enhance the resolution in the ESEEM dimension. The two-dimensional data set is acquired by measuring the ENDOR spectrum as a function of the time interval T between the last two microwave pulses of the stimulated echo detection scheme. This produces a series of ENDOR spectra with amplitudes that are modulated with T. Fourier transformation (FT) with respect to T then generates a 2D spectrum with cross peaks connecting spectral lines of the ESEEM and ENDOR spectra that belong to the same paramagnetic center. Projections along the vertical and horizontal axes give the three-pulse FT-ESEEM and ENDOR spectra, respectively. The feasibility of the experiment was tested by simulating 2D ENDOR-ESEEM correlation spectra of a system consisting of an electron spin (S = (1/2)) coupled to two nuclei (I(1) = I(2) = (1/2)), taking into account experimental conditions such as pulse durations and off-resonance irradiation frequencies. The experiment is demonstrated on a single crystal of Cu(2+) doped l-histidine (Cu-His), containing two symmetrically related Cu(2+) sites that at an arbitrary orientation exhibit overlapping ESEEM and ENDOR spectra. While the ESEEM spectrum is relatively simple and arises primarily from one weakly coupled (14)N, the ENDOR spectrum is very crowded due to contributions from two nonequivalent nitrogens, two chlorides, and a relatively large number of protons. The simple ESEEM projection of the 2D ENDOR-ESEEM correlation spectrum is then used to disentangle the ENDOR spectrum and resolve two sets of lines corresponding to the different sites. Copyright 2000 Academic Press.     

Very fast magic angle spinning (1)H-(14)N 2D solid-state NMR: sub-micro-liter sample data collection in a few minutes

Substantial resolution and sensitivity enhancements of solid-state (1)H detected (14)N HMQC NMR spectra at very fast MAS rates up to 80 kHz, in a 1mm MAS rotor, are presented. Very fast MAS enhances the (1)H transverse relaxation time and efficiently decouples the (1)H-(14)N interactions, both effects leading to resolution enhancement. The micro-coil contributes to the sensitivity increase via strong (14)N rf fields and high sensitivity per unit volume. (1)H-(14)N HMQC 2D spectra of glycine and glycyl-L-alanine at 70 kHz MAS at 11.7 T are observed in a few minutes with a sample volume of 0.8 μL.     

二维相关光谱探测荧光能量转移现象

以EuCl₃和NdCl₃混合水溶液为研究对象,按正交浓度序列以浓度为外部扰动构建紫外可见-荧光二维相关光谱。在混合溶液的二维相关光谱中,观察到了Eu3+的荧光发射谱峰与Nd^{3+的吸收谱峰之间存在交叉峰。交叉峰的出现表明Eu3+和Nd3+的荧光发射与吸收之间存在能量传递。二维相关光谱中交叉峰的产生并非由于溶剂水分子与溶质(Eu3+或Nd3+)之间相互作用;若以单一溶质的EuCl₃和NdCl₃的水溶液构造模拟的“混合溶液”的拟合光谱构建二维紫外可见-荧光相关光谱,由于Eu3+和Nd3+在空间上相互分离,无相互作用发生,交叉峰并不存在。二维相关光谱的交叉峰可为从光谱学角度探测复杂体系能量传递及其相关机制提供一条新思路。}     

Photo-CIDNP MAS NMR beyond the T1 limit by fast cycles of polarization extinction and polarization generation

In nanosecond-laser flash photo-CIDNP MAS NMR, polarization generation (PG) proceeds much faster than longitudinal spin relaxation. With a nanosecond-laser setup linked to the NMR console the repetition time of the experiment is then limited by the minimum recycle delay of the NMR spectrometer and the maximum repetition rate of laser flashes. These limits can only be reached if polarization left after the NMR experiment is completely canceled before the next laser flash. We introduce a presaturation pulse sequence, based on three (pi/2) (13)C pulses and optimized timing and phase cycling that allows for such efficient polarization extinction (PE). The technique is demonstrated on selectively isotope labeled bacterial reaction centers (RCs) of Rhodobacter (Rb.) sphaeroides wildtype (WT). High-quality (13)C photo-CIDNP MAS NMR spectra are obtained using cycle rates up to 4 Hz. The PE-PG strategy proposed here provides a general experimental scheme for reduction of measurement time in magnetic resonance experiments based on fast PG.     

Unusual "AB" Spectra in High-Resolution Magic-Angle-Spinning NMR-Studies of Solids

Phosphorus-31CP-MAS spectra of Cd(NO₃)₂(PPh₃)₂ have been obtained as a function of spinning frequency. Although the two ³¹P nuclei are crystallographically equivalent and have the same isotropic chemical shifts in the solid state, they exhibit spinning-rate-dependent MAS spectra which have been analyzed to obtain the value of ²J(P, P). At high spinning rates, the spectra are analogous to "A₂" spectra in isotropic solutions, while at slower spinning rates, the spectra are more characteristic of strongly coupled "AB" solution spectra. The AB spectra are unusual in that δ_A = δ_B and J(A, B) is given by the splitting between the alternate peaks in the four-peak multiplet as opposed to the splitting between the outer and adjacent inner lines. This assignment was confirmed by a 2D CP-MAS J-resolved experiment. The unusual spinning-rate-dependent MAS lineshapes result from recoupling of the J interaction between the two crystallographically equivalent nuclei via anisotropic interactions, i.e., weak homonuclear dipolar coupling and differences in the orientation dependence of the chemical-shift tensors. Such spinning-rate-dependent MAS lineshapes are predicted to be a more frequent observation at higher applied magnetic fields.     

Very high-resolution 1H MAS NMR of a natural polymeric material

The use of ultrafast magic angle spinning (> 30 kHz) in tandem with delayed echo acquisition is shown to yield very high-resolution lH MAS NMR spectra of complex natural organic materials. For the first time, very high-resolution 1H MAS NMR spectra are reported for cork and wood components, two natural materials with great economic importance. The effect of the spinning rate on the 1H NMR spectra was evaluated with single-pulse acquisition and delayed-echo acquisition. The delayed-echo acquisition spectra presented linewidths as sharp as 67 and 25 Hz. The narrow peaks, characterised by proton spin-spin and spin-lattice relaxation, were assigned to the isotropic chemical shifts and the general spectral features were shown to correlate with the sample chemical structure. The tentative assignments of cork 1H MAS NMR signals were presented.     

基于二维相关荧光谱土壤中PAHs检测方法研究

传统荧光光谱技术已被用于土壤中多环芳烃(PAHs)的检测,但由于土壤体系的复杂性、PAHs污染物的多样化和微量化,传统的荧光光谱技术无法有效提取土壤中PAHs的特征信息。为了解决上述问题,提出并建立一种基于二维相关荧光谱土壤中多环芳烃的检测方法。以土壤中典型的多环芳烃蒽和菲为研究对象,配置38个蒽菲混合标准土壤样品(蒽和菲的浓度范围均为0.000 5～0.01 g·g-1),在激发波长265～340 nm,发射波长350～500 nm范围内采集了所有样品的三维荧光谱。以激发波长为外扰,对外扰变化的动态一维荧光谱进行相关计算,得到每一样品的同步二维相关荧光谱。研究了浓度均为0.005 g·g-1蒽菲混合土壤样品的三维荧光谱和同步二维相关荧光谱特性,在同步谱主对角线398,419,444和484 nm处存在自相关峰,其中,398和484 nm荧光峰来自土壤中的菲,419和444 nm荧光峰来自土壤中的蒽;在主对角线外侧,蒽和菲两组荧光峰之间存在负的交叉峰,进一步验证了其来源不同;同时,在(408,434) nm和(434,467) nm处出现交叉峰,其中408和434 nm荧光峰来自土壤中的菲,467 nm荧光峰来自土壤中的蒽。指出与三维荧光谱表征的信息相比,二维相关荧光谱不仅能提取更多的特征信息(408和467 nm的特征峰在三维荧光谱中未被表征),而且还能提供荧光峰之间的相互关系,对其来源进行有效解析。在上述研究二维相关荧光谱特性的基础上,基于同步相关谱矩阵(38×151×151)建立了定量分析土壤中蒽和菲污染物浓度的多维偏最小二乘(N-PLS)模型,对蒽的校正和预测相关系数分别为0.986和0.985,校正均方根误差(RMSEC)和预测均方根误差(RMSEP)分别为4.33×10-4和5.55×10-4 g·g-1;对菲的校正和预测相关系数分别为0.981和0.984,RMSEC和RMSEP分别为5.20×10-4和4.80×10-4 g·g-1。为了比较,基于三维荧光光谱矩阵(38×16×151)建立了定量了分析土壤中蒽和菲的N-PLS模型,对蒽的校正和预测相关系数分别为0.981和0.972,RMSEC和RMSEP分别为5.09×10-4和6.74×10-4 g·g-1;对菲的校正和预测相关系数分别为0.957和0.956,RMSEC和RMSEP分别为7.36×10-4和7.77×10-4 g·g-1。指出,对于土壤中的蒽和菲检测,基于二维相关荧光谱的N-PLS模型的相关系数r,RMSEC和RMSEP都要优于基于三维荧光谱的N-PLS模型。研究结果表明：所提出和建立的方法-二维相关荧光谱直接检测土壤中PAHs污染物不仅可行,而且能提供更好的分析结果。该研究为激光诱导荧光结合相关谱技术现场直接检测土壤中多环芳烃污染物提供了理论和实验基础,具有较好的应用前景。     

A solid-state NMR application of the anomeric effect in carbohydrates: galactosamine, glucosamine, and N-acetyl-glucosamine

Simple 2D 13C/15N heteronuclear correlation solid-state NMR spectroscopy was implemented to resolve the 15N resonances of the alpha and beta anomers of three amino monosaccharides: galactosamine (GalN), glucosamine hydrochloride (GlcN), and N-acetyl-glucosamine (GlcNAc) labeled specifically with 13C1/15N spin pairs. Although the 15N resonances could not be distinguished in normal 1D spectra, they were well resolved in 2D double CP/MAS correlation spectra by taking advantage of the 13C spectral resolution. The alpha and beta resonances shifted apart by 3-5 ppm in their 13C chemical shifts, and differed by 1-2 ppm in the extended 15N dimension. Aside from this, the detection of other 13C/15N correlations over short distances was also achieved arising from the C2, C3 and CO carbons present in natural abundance. 2D double CP/MAS chemical shift correlation NMR spectroscopy is a simple and powerful technique to characterize the anomeric effect of amino monosaccharides. Applications of the 2D method reveal well-resolved 15N and 13C chemical shifts might be useful for structural determination on carbohydrates of biological significance, such as glycopeptide or glycolipids.     

Photoacoustic Spectroscopy Studies on DL-β-Phenylalanine and Pd(Phe)2·H2O Complex

The complex crystal of Pd(Phe)2·H20 was synthesized and its PA spectra (with DL-β-Phenylalanine) were also determined in the range of 280–780nm at room temperature and explained. A method used to resolve the PA amplitude spectrum was suggested. With the phase spectrum of complex, the PA absorption peaks were resolved by this method, and the nonradiative relaxation time of all absorption bands were calculated.     

Raman spectra of the lattice vibrations of solid nitrogen near room temperture

Abstract

Low-frequency peaks begin to appear in Raman spectra of solid N₂ when δ-N₂ transforms to either the ?- or η-N₂ phase and orientational order develops in δ-N₂. These same peaks are known at 15 K but are very much broader at the higher temperatures. Near the phase boundaries, these peaks are extremely weak and remain weak even under the best of conditions. We have used Raman spectra of these modes to map the δ-? and δ-? phase boundaries.     

Inverse detection and heteronuclear editing in 1H-15N correlation and 1H-1H double-quantum NMR spectroscopy in the solid state under fast MAS

Signal enhancement in heteronuclear correlation spectra as well as signal selection in 1H experiments can be achieved through inverse, i.e., 1H, detection in the solid state under fast MAS conditions. Using recoupled polarization transfer (REPT), a heteronuclear 1H-15N single-quantum correlation (HSQC) experiment is presented whose symmetrical design allows the frequency dimensions to be easily interchanged. By observing the 15N dimension indirectly and detecting on 1H, the sensitivity is experimentally found to be increased by factors between 5 and 10 relative to conventional 15N detection. In addition, the inverse 1H-15N REPT-HSQC scheme can be readily used as a filter for the 1H signal. As an example, we present the combination of such a heteronuclear filter with a subsequent 1H-1H DQ experiment, yielding two-dimensional 15N-edited 1H-1H DQ MAS spectra. In this way, specific selection or suppression of 1H resonances is possible in solid-state MAS experiments, by use of which the resolution can be improved and information can be unravelled in 1H spectra.     

用多核固体核磁共振研究CsH2PO4 和CsH5(PO4)2的制备

探讨可能用作燃料电池固体酸电解质的化合物CsH₂PO₄ (CDP)和CsH₅(PO₄)₂(CPDP)的制备. CDP和CPDP混合物由摩尔比1∶4的Cs₂CO₃∶H₃PO₄水溶液结晶而成,而CDP和Cs₂HPO₄·1.5H₂O (H-DCHP)混合物依其摩尔比1∶2的水溶液制备. 甲醇清洗能最有效地将CDP从其混合物中分离出来. CDP、CPDP以及H-DCHP的¹³³Cs 和³¹P 魔角旋转谱以及CPDP和H-DCHP的¹H魔角旋转谱均为首次报道,对各化合物的谱峰做了指认. 说明,透过确认合成的电解质以及合成过程所产生的副产物,多核固体核磁共振对于控制固体酸电解质合成的品质是一个非常有用的工具.     

时间和相位混合编码的量子密钥分发方案

提出了一种在双马赫-曾德尔干涉仪量子保密通信系统上同时实现时间编码和相位编码的混合量子密钥分发方案.提出的方案将原来相位编码方案中丢弃的脉冲进行时间编码,因此成码率是原方案的二倍.系统同时获得时间编码密钥和相位编码密钥,既可以一组用于通信,另一组用于监视窃听,又可以将两组密钥组合成新密钥.系统具有良好的应用前景. 关键词： 量子保密通信 量子密钥分发 相位编码 时间编码     

用TPPI方法消除2D COSY和MQSY实验中与辐射阻尼有关的谐波峰

在二维相关(COSY)和多量子(MQSY)实验中,TPPI(Time-proportional-phase-in-crement)方法被用于消除与辐射阻尼相关的谐波峰.二维实验中,^c/2混合脉冲常常非线性地改变磁化强度的进动相位.这一非线性变化和辐射阻尼一起导致依赖于化学位移偏置的谐波.然而,如果混合脉冲的相位正比于演化时间t₁,谐波消失,但水峰保持不变.     

Dual processing of two-dimensional exchange data in magic angle spinning NMR of solids.

We discuss procedures for processing data in rotor-synchronized two-dimensional magic angle spinning (2D MAS) NMR exchange measurements for both structural and dynamical studies. We show, both mathematically and experimentally, that there are two distinct data processing procedures that lead to 2D MAS exchange spectra with purely absorptive crosspeaks. One procedure is that described previously by Hagemeyer, Schmidt-Rohr, and Spiess (HSS). The other procedure is related, but different, and leads to crosspeak intensities given by the formulae of Herzfeld, Roberts, and Griffin (HRG). In 2D MAS exchange experiments on doubly (13)C-labeled l-alanylglycylglycine, we demonstrate that the HSS and HRG crosspeak intensities can be extracted separately from the same data set and contain independent information. Processing and analysis of 2D MAS exchange data with both the HSS and the HRG procedures may enhance utilization of the information content of 2D MAS exchange measurements.     

Eu3+摩尔浓度对Y2O2S:Eu3+,Mg2+,Ti4+红色长余辉材料光谱的影响

用高温固相法制备了Y2O2S：Eu^3 ,Mg^2 ,Ti^4 红色长余辉材料。测量了该材料的余辉曲线,余辉时间为1h以上;由X射线衍射得到晶体结构为Y2O2S.测量了不同Eu^3 摩尔浓度下的激发光谱和发射光谱,得到从^5DJ(J=0,1,2,3)^-7FJ(J=0,1,2,3,4,5)的发射谱线,并得到位于260,345,468和540nm激发峰。由于激活剂饱和效应,Y2O2S：Eu^3 ,Mg^2 ,Ti^4 发射光谱中513．6,540．1,556．4,587．3和589．3nm属于从^5D2,^5D1到^7FJ(J=0,1,2,3,4)跃迁的发射峰随Eu^3 摩尔浓度的增加相对削弱;激发谱包括位于350nm左右属于电荷转移态吸收(Eu^3 -O^2-,Eu^3 -S^2 )的激发主峰和在可见光区位于468,520和540nm属于Eu^3 离子4f-4厂吸收的激发峰。随着Eu^3 摩尔浓度的增加,位于468,520和540nm的激发峰相对增强。     

Presentation of sideband envelopes by two-dimensional one-pulse (TOP) spectroscopy.

A novel way of representing 1D MAS spinning sideband spectra in a 2D-resolved fashion is explained. The method is illustrated with 2H MAS data of deuterated polycarbonate. From the resulting 2D spectrum, the isotropic shifts can be identified on one axis and the rotary echo decay spectra along the other axis.