Determination of the (Na) Sternheimer antishielding factor by Na NMR spectroscopy on sodium oxide chloride, Na3OCl

The (Na⁺) Sternheimer antishielding factor γ_∞ (Na⁺) was determined by ²³Na NMR spectroscopy on sodium oxide chloride, Na₃OCl. The quadrupolar coupling constant of the sodium ion in Na₃OCl was determined to QCC=11.34 MHz, which presents the largest coupling constant of a sodium nucleus observed so far. Applying a simple point charge model, the largest principal value of the electric field gradient at the sodium site was calculated to V_zz=−6.76762·10²⁰ V/m². From these values we calculated the (Na⁺) Sternheimer antishielding factor to γ_∞ (Na⁺)=−5.36. In sodium oxide, Na₂O, we observed an isotropic chemical shift of δ_CS=55.1 ppm, referenced to 1 M aqueous NaCl (δ=0 ppm).     

垂直场中稀土离子Dy3+对23Na NMR的影响

在用电磁铁NMR谱仪研究细胞内外Na⁺浓度的实验中,发现了一些与超导谱仪实验相异的现象,对这些现象进行理论分析,且认为可以由此测得稀土金属原子的磁矩。     

Influence of sodium ion dynamics on the 23Na quadrupolar interaction in sodalite: a high-temperature 23Na MAS NMR study

High-temperature ²³Na MAS NMR experiments up to 873 K for a number of different sodalites (Na₈[AlSiO₄]₆(NO₃)₂, Na₈[AlSiO₄]₆(NO₂)₂, Na₈[AlSiO₄]₆I₂, Na_7.9[AlSiO₄]₆(SCN)_7.9 · 0.5H₂O, Na₈[AlGeO₄]₆(NO₃)₂, and Na₇[AlSiO₄]₆(H₃O₂) · 4H₂O) were carried out. The spectra of the first five sodalites consist of a quadrupolar MAS pattern with different quadrupolar coupling constants. The quadrupolar interaction for the thiocyanate sodalite, the nitrate aluminosilicate, and germanate sodalite decreases strongly passing a coalescence state on heating, while the quadrupolar interaction of the iodide and nitrite sample shows nearly no change. The basic hydrosodalite shows an asymmetric lineshape at room temperature and, between 350 and 370 K, a second line due to the evaporation of cage-water emerges. The linewidth increases with rising temperature. The temperature dependence of the quadrupolar interaction seems to be a function of the sodalite β-cage expansion. Two conceivable jump mechanisms are proposed for a tetrahedral two-site jump between occupied and unoccupied tetrahedral sites.     

A multiple-field (23)Na NMR study of sodium species in porous carbons

The sodium environments in porous carbon materials prepared from NaOH activation of a char were investigated by means of multiple-field solid-state ²³Na NMR measurements, carried out at magnetic fields of 4.7, 8.45 and 14.1 T, with single-pulse excitation and magic angle spinning (MAS). The recorded spectra showed a relatively featureless resonance with linewidth and peak shift strongly dependent on the magnetic field strength and on the hydration level of the samples. The existence of second-order quadrupolar effects was inferred, although the structural disorder and the mobile character associated with the Na environment precluded the direct observation of typical quadrupolar features in the MAS NMR spectra. The analysis of the spectra collected at multiple magnetic fields yielded the values of −2.8 ppm for the isotropic chemical shift and 1.8 MHz for the quadrupole coupling constant, which were interpreted as due to Na⁺ ions bonded to oxygenated groups at the edges of the graphene planes within the carbon pore network.     

Two-dimensional triple-quantum Na MAS NMR spectroscopy of sodium cations in dehydrated zeolites

Two-dimensional triple-quantum (2D-3Q) ²³Na MAS NMR spectroscopy has been applied for the investigation of sodium cations in dehydrated zeolites NaY, NaEMT, NaZSM-5 and NaMOR. The experiments have shown that the new 2D-3Q technique allows the determination of the isotropic chemical shifts and quadrupolar couplings of sodium cations with SOQE (second-order quadrupolar effect) parameters of up to ca. 4 MHz. In the present work, SOQE parameters of 1.0–1.2 MHz were found for sodium cations located at positions SI in the hexagonal prisms of dehydrated zeolites NaY and NaEMT. The sodium cations located in the 10-ring and 12-ring channels of dehydrated zeolites NaZSM-5 and NaMOR, respectively, are characterized by a SOQE parameter of 2.0 MHz while a value of 3.1 MHz was determined for sodium cations in the sidepockets of the channels in dehydrated NaMOR.     

Adsorption of Na onto γ-alumina studied by solid-state Na and Al nuclear magnetic resonance spectroscopy

The adsorption of Na⁺ on γ-alumina surfaces at four coverages of Na₂CO₃ [5, 10, 15 and 20% (w/w)] was characterized by solid-state ²³Na and ²⁷Al nuclear magnetic resonance (NMR) spectroscopy. The experimental results suggest that two distinct adsorbed species are present on the alumina surface: surface species and surface salts. At the lower coverages of Na₂CO₃ (5 and 10%), the surface species is predominant, in which the Na⁺ cations are associated with the oxygen atoms of γ-alumina. Increasing the loading level to 15% results in the appearance of a second adsorbed species that is attributed to the surface salt, Na₂CO₃, deposited on the solid surface. Further adsorption of Na₂CO₃ leads to an increase in the amount of surface salt while the amount of surface species remains unchanged. ¹H---²⁷Al Cross-polarization magic angle spinning (CP-MAS) experiments give the evidence that some Na⁺ cations in the form of surface species are coordinated with the Brönsted acid sites of γ-alumina. This may be the main driving force that improves appreciably the catalytic efficiency of an Na₂CO₃---Al₂O₃ catalyst.     

Na solid state MAS NMR of sodium halides occluded in zeolites

Occlusion of sodium chloride and sodium bromide in zeolitic pores was performed by heating mixtures of the salts with zeolites NaY and NaA under high vacuum conditions. The obtained samples were subjected to various further pretreatments like washing with water and zinc-exchange, and were investigated spectroscopically with the ²³Na MAS NMR technique at various Zeeman field strengths. In the case of NaY, the halides are occluded in both types of cages of the faujasite structure. About 90% of the sodalite cages are shown to have incorporated salt which is concluded to be part of [Na₄Hal]³⁺ clusters as in the case of sodalite type materials.     

H MAS and H[Na] double resonance NMR studies on the modification of surface hydroxyl groups of γ-alumina by sodium

The modification of surface hydroxyl groups with sodium in a series of Na₂CO₃-γ-Al₂O₃ catalysts was investigated as a function of both the Na₂CO₃ loading and the calcination temperature by means of ¹H magic angle spinning (MAS) and ¹H[²³Na] spin-echo double resonance NMR techniques. The ¹H NMR experiments revealed that sodium ions are homogeneously distributed over the alumina surface and closely coordinated with the surface hydroxyl groups. In the catalysts calcined at 250 °C, the acidic hydroxyl groups (with a chemical shift of 2.0 ppm) are preferentially associated with sodium ions at low Na₂CO₃ coverages (5 and 10%), while both the acidic and the basic (0 ppm) hydroxyl groups are accessible for sodium ions at high coverages (15 and 20%). The coordination causes a low-field shift of about 2 ppm in the ¹H MAS spectra, and a broad signal at 4.5 ppm appears. It is interesting that the 4.5 ppm signal is completely suppressed in the ¹H[²³Na] MAS experiments, providing direct evidence that a strong interaction exists between adsorbed sodium ions and the surface hydroxyl groups. Increasing the calcination temperature to 450 °C results in preferential removal of the acidic hydroxyl groups, and only the most basic hydroxyl groups remain when the calcination temperature is raised to 600 °C. This is attributed to the formation of the coordinated species which enhances the acidity of the surface hydroxyl groups and prompts their dehydroxylation, especially at high calcination temperature. Correlation of the ¹H MAS NMR results and catalytic activity measurements indicates that the basic hydroxyl groups are essential for the carbonyl sulfide hydrolysis reaction.     

Radially dependent antishielding factor γ(r) of the Sc3+ ion in the solid state

We report the results of our calculation of γ(r), the radially dependent antishielding factor of Sc³⁺ ion in the crytalline environment. Watson sphere model is used to approximately represent the crystal potential. Differential equations resulting from non-orthogonal Hartree-Fock perturbation theory are solved to obtain perturbations to core electron states. Contribution to γ(r) from electron self-consistency effect has been evaluated by using the latter wave-functions in the many-body expression of Schmidtet al.     

Na and H NMR Microimaging of Intact Plants

²³Na NMR microimaging is described to map, for the first time, the sodium distribution in living plants. As an example, the response of 6-day-old seedlings of Ricinus communis to exposure to sodium chloride concentrations from 5 to 300 mM was observed in vivo using ²³Na as well as ¹H NMR microimaging. Experiments were performed at 11.75 T with a double resonant ²³Na–¹H probehead. The probehead was homebuilt and equipped with a climate chamber. T₁ and T₂ of ²³Na were measured in the cross section of the hypocotyl. Within 85 min ²³Na images with an in-plane resolution of 156 × 156 μm were acquired. With this spatial information, the different types of tissue in the hypocotyl can be discerned. The measurement time appears to be short compared to the time scale of sodium uptake and accumulation in the plant so that the kinetics of salt stress can be followed. In conclusion, ²³Na NMR microimaging promises great potential for physiological studies of the consequences of salt stress on the macroscopic level and thus may become a unique tool for characterizing plants with respect to salt tolerance and salt sensitivity.     

Characterization of sodium cations in zeolite omega by solid-state23Na NMR spectroscopy

Sodium cations localized at crystallographically distinct cation sites in the hydrated zeolite omega were characterized by various solid-state²³Na NMR techniques, such as²³Na MAS,¹H-²³Na CP/MAS,²³Na quadrupolar nutation and variable temperature NMR spectroscopy. In the²³Na NMR spectrum of zeolite omega two signals were identified, a low-field Gaussian line at ca. ?3 ppm (its quadrupole coupling constant was estimated approximately on the order of magnitude of 0.2 MHz) and a high-field quadrupole pattern with an isotropic chemical shift of ?8 ppm and a quadrupole coupling constant of 2.3 MHz. The former signal is attributed to sodium cations in the 12-ring channels and the latter one to sodium cations in gmelinite cages of zeolite omega. The variable temperature NMR experiments reveal the interactions between the sodium cation and the adsorbed water molecules in zeolite omega. The sodium cations in the 12-ring channels are highly hydrated and so mobile as to average the¹H-²³Na dipole interaction. Hence, these sodium cations give no contribution to the¹H-²³Na cross polarization process. By contrast, the sodium cations in the gmelinite cages are less hydrated and more rigid. They are closely bonded not only to the adsorbed water molecules but also to the lattice oxygen of the gmelinite cages, which leads to an effective¹H-²³Na polarization transfer.     

A new method for suppressing the central transition in I=3/2 NMR spectra with a demonstration for 23Na in bovine articular cartilage

The splitting and the lineshape of the satellite transitions of 23Na are measures of the residual quadrupolar interaction and its distribution, which are related to the degrees of order and binding of sodium in biological tissues. However, these transitions are often masked by the stronger signals of the central transition and the isotropic sodium ions. A way to suppress the central signals, while preserving the lineshape and the intensity of the satellites, is suggested and tested on a liquid crystal and on bovine articular cartilage.     

Solid state NMR study of sodium thiocyanate/poly(ethylene oxide) electrolytes

¹H-, ¹³C-, ²³Na-solid state NMR measurements have been used to characterise the morphology and the dynamics of several NaSCN-PEO mixtures. Selective ¹³C-MAS experiments allowed to determine the composition of the (PEO)_nNaSCN samples in terms of the different phases present, as well as the real stoichiometry of the crystalline complex. ¹H- and ¹³C-spin-lattice relaxation times provided estimates of the dimensions of the different domains and gave information on the dynamics of the polymer chains. ²³Na-MAS spectra and 2D nutation experiments allowed to individuate the presence of different environments for the sodium cations on the basis of their quadrupolar interactions.     

Noninvasive (1)H and (23)Na nuclear magnetic resonance imaging of ancient Egyptian human mummified tissue

Historic mummies are a unique example of the human desire for immortality. Therefore, it is not surprising that modern diagnostic imaging has been widely applied to study them. Yet, magnetic resonance imaging (MRI) of such old remains has never been successfully achieved in a noninvasive way without rehydration. Furthermore, the impact of artificial mummification as done in ancient Egypt by natron (a blend of NaCl, Na(2)CO(3), NaHCO(3) and NaP(2)SO(4)) on human tissue with a particular focus on the sodium spatial distribution has never been addressed. Here, we show for the very first time completely noninvasive (1)H and (23)Na imaging of an ancient Egyptian mummified finger by nuclear magnetic resonance (NMR). Protons could be visualized by NMR only in the tissue close to surface and sodium primarily in the bone, while computer tomography images both, soft tissue and bone but does not distinguish between different chemical elements. The selective enrichment of sodium in the bone may by due to postmortem incorporation of (23)Na into the tissue by natron-based mummification because our reference measurement of a historical finger not subjected to artificial mummification showed no sodium signal at all. Our results demonstrate not only the general feasibility of nonclinical MRI to visualize historic dry human tissues but also shows the specific (1)H and (23)Na spatial distributions in such mummy tissue, which is particularly interesting for archeology and may open up a new application for MRI.     

Studies on the structures and interactions of glutathione in aqueous solution by molecular dynamics simulations and NMR spectroscopy

All-atom molecular simulations and temperature-dependent NMR have been used to investigate the conformations and hydrogen bonds of glutathione (GSH) in aqueous solution. The simulations start from three different initial conformations. The properties are characterized by intramolecular distances, radius of gyration, root-mean-square deviation, and solvent-accessible surface. GSH is highly flexible in aqueous solutions in the simulations. Moreover, conformations can covert between “extended” and “folded” states. Interestingly, the two different hydrogen atoms in cysteine (H_N2) and glycin (H_N3) show different capabilities in forming NH?OW hydrogen bonds. The temperature-dependent NMR results of the different amide hydrogen atoms also show agreements with the MD simulations. Competing formation of GSH hydrogen-bonding interactions in aqueous solutions leads to hydrogen-bonding networks and the distribution of conformations. These changes will affect the activity of GSH under physiological conditions.     

Na3La2(BO3)3:Sm3+的合成及其光谱特性

本文采用固相反应法,合成了一系列掺Sm^3 的Na3La2(BO3)2[Na3(La1-xSmx)2(BO3)3]发光,X－射线粉末衍射数据分析表明它们属于正交晶系,空间群为Amm2,测量了红外光谱,荧光光谱,观察到在599nm,645nm处有较强的荧光发射,并研究了发光强度与Sm^3 离子浓度（x)的关系,确定了Sm^3 离子在Na3La2(BO3)3基质中发光的适宜浓度。     

荧光光度法测定饮料中糖精钠含量

糖精钠在碳酸钠介质中可形成具有强荧光特性的荧光配合物,据此可在荧光光度计上测定饮料中糖精钠含量,同时对分析最佳条件进行了探讨。其结果为：汇源苹果汗中糖精钠含量为0.046μg/mL,方法的线性范围为0－50μg/mL,平均回收率为87.5％,相对标准偏差≤3.68%。     

结晶紫-紫外分光光度法测定食品中糖精钠的含量

pH7.0的Britton-Robinson(B-R)缓冲溶液中,结晶紫在250nm波长处有最大吸收,少量糖精钠的存在可使结晶紫在该波长处的吸收峰显著增强。在0.008-44μg/mL范围内,体系的吸光度的增强与糖精钠浓度呈良好的线性关系(r=0.9994),检出限为0.004μg/mL,回收率在98.1%-108.3%之间,该法用于食品中糖精钠含量的测定,与国标法(高效液相色谱法)对照,结果满意。     

980 nm激发下Tm~(3+)诱导的Gd~(3+)上转换发光性质研究

通过简单温和水热法,制备了系列Tm3+/Yb3+共掺GdF3粉末。用X射线衍射仪和场发射扫描电镜对样品进行了结构和形貌表征。在980 nm半导体连续激光二极管激发下,用荧光光谱仪对氩气保护下退火后的粉末样品进行了上转换发射光谱表征。粉末上转换发光动力学过程是在脉冲(脉宽10 ns,重复频率10 Hz)YAG∶Nd激光器激发光参量振荡器至980 nm激发下研究的,发光信号由单色仪和示波器记录。文章主要讨论了Gd3+的311.6 nm(6P7/2→8S7/2)的发光动力学行为。发光动力学分析结果表明:在980 nm激发下,Gd3+,作为一种基质离子,其发光是由Yb3+作为一级敏化离子通过多步能量传递把能量传递给Tm3+使其布居至3P2能级;然后Tm3+作为二级敏化离子通过能量传递过程3P2→3H6(Tm3+):8S7/2→6IJ(Gd3+)把能量传给Gd3+;进一步,Gd3+与Yb3+或Tm3+之间通过能量传递过程布居至高激发多重态6DJ能级;最后,可观察到Gd3+的激发态6D9/2,6IJ,6P5/2及6P7/2至基态8S7/2的发射。同时,Tm3+在其自身发光过程中也充当激活剂,除了3P2及1I6至3H6的发射外,其他发射不作研究。文章还研究了基质Gd3+依赖于Yb3+浓度、Tm3+浓度、退火温度及激发功率密度的紫外上转换发光性质。     

Li ion mobility in TeO2---LiO0.5---LiX (X = F, Cl) glasses determined by Li NMR and impedance spectroscopy

NMR and impedance spectroscopies have been used to study the Li⁺ ion mobility in the TeO₂---LiO_0.5---LiX (X = F, Cl) glasses. Activation energies determined from the temperature dependence of dc conductivity data decrease as the lithium or halogen content increases. Activation energies deduced from the analysis of the ac conductivity data in the complex modulus formalism and corresponding to the true one-particle energy barrier of ionic motion according to the coupling model, have been compared to those deduced from NMR data (T₁⁻¹ relaxation time): a good agreement is obtained. Finally, the influence of the glass composition and ion distribution on Li⁺ ion mobility has been discussed.