Metabolite profiling of human amniotic fluid by hyphenated nuclear magnetic resonance spectroscopy

The metabolic profiling of human amniotic fluid (HAF) is of potential interest for the diagnosis of disorders in the mother or the fetus. In order to build a comprehensive metabolite database for HAF, hyphenated NMR has been used, for the first time, for systematic HAF profiling. Experiments were carried out using reverse-phase (RP) and ion-exchange liquid chromatography (LC), in order to detect less and more polar compounds, respectively. RP-LC conditions achieved good separation of amino acids, some sugars, and xanthines. Subsequent NMR and MS analysis enabled the rapid identification of 30 compounds, including 3-methyl-2-oxovalerate and 4-aminohippurate identified in HAF for the first time, to our knowledge. Under ion-exchange LC conditions, a different set of 30 compounds was detected, including sugars, organic acids, several derivatives of organic acids, and amino acids. In this experiment, five compounds were identified for the first time in HAF: D-xylitol, amino acid derivatives (N-acetylalanine, N-acetylglycine, 2-oxoleucine), and isovalerate. The nonendogenous nature of some metabolites (caffeine, paraxanthine, D-xylitol, sorbitol) is discussed. Hyphenated NMR has allowed the rapid detection of approximately 60 metabolites in HAF, some of which are not detectable by standard NMR due to low abundance (microM) and signal overlap thus enabling an extended metabolite database to be built for HAF.     

Protein structure determination in solution by two-dimensional and three-dimensional nuclear magnetic resonance spectroscopy

Over the last decade, nuclear magnetic resonance (NMR) spectroscopy has evolved into a powerful method for determining structures of biological macromolecules. This has opened a unique opportunity for obtaining high-resolution three-dimensional structures in solution, in contrast to the well-established methods of X-ray diffraction, which are applicable only to solids and in particular single crystals. This rapid development has been spurred by several key advances in the field, especially the introduction of two- and three-dimensional NMR experiments, high field spectrometers (500 and 600 MHz), and computational algorithms for converting NMR derived restraints into three-dimensional structures. This review outlines the methodology employed for solving protein structures in solution, describing the basic NMR experiments necessary as well as introducing the concepts upon which the computational algorithms are founded. A variety of examples is discussed, illustrating the present state of the art, and future possibilities are indicated.     

核磁共振技术在茶叶生化成分鉴定中的应用

核磁共振(NMR)在化合物结构鉴定中有着无可比拟的优势.文中就NMR技术在茶叶品质成分、有害成分及品质鉴定中的运用状况进行了阐述与分析,指出了NMR在茶叶鉴定中的技术特点及急待攻克的局限性,提出NMR与其他仪器的联用可为茶叶生化成分研究提供更加全面准确的信息.该文对从事茶叶生化组分鉴定及其生理活性机理研究的工作者有一定借鉴作用.     

Low-temperature synthesized aluminosilicate glasses

The reaction below 100 °C of a dehydroxylated clay (metakaolinite) suspended in an alkaline sodium silicate solution leads to an amorphous aluminosilicate, called in this work low-temperature inorganic polymer glass (LTIPG or IPG).Some Theological transformations during the isothermal hardening process are followed with dynamic mechanical analysis (DMA) and compared with differential scanning calorimetry (DSC) and modulated differential scanning calorimetry (MDSC). It can be concluded that the change in storage modulus (DMA) during the formation of the inorganic network can be characterized quantitatively with the evolution of the heat capacity (MDSC), and that the reaction rate is not decreased by the vitrification process. During the first heating after polymerization up to 1000 °C, the material shrinks due to the evaporation of residual water from the reaction mixture as illustrated by thermogravimetric analysis (TGA) and thermomechanical analysis (TMA). The low-temperature synthesized inorganic polymer glass is thermomechanically stable up to a temperature of at least 650 °C. In that temperature zone, the glass transition can be detected with TMA and DMA.     

17O quantitative nuclear magnetic resonance spectroscopy of gasoline and oxygenated additives

17O Nuclear magnetic resonance (NMR) spectroscopy allows exclusive detection and direct quantification of oxygenates in gasoline unaffected by its hydrocarbon content, using the internal standard quantitative NMR (QNMR) method. Chemical shifts of 24 oxygen-containing compounds as potential additives and contaminants have been measured in gasoline and corrected values of deltaO 18.1 and 3.9 determined for neat methyl tert-butyl ether (MTBE) and neat di-n-butyl ether, respectively. Quantification of ethanol in gasoline can be readily achieved by 17O QNMR with dimethyl sulfone as an internal standard reference material, at the levels currently used in retail gasolines (1-20%). In addition, the simultaneous detection and quantification of the oxygenates methanol, ethanol, 2-propanol, tert-butyl alcohol, and MTBE in gasoline has been established to further demonstrate the specificity of the method. 17O NMR has distinct advantages over 1H and 13C QNMR methods, and although it cannot reliably differentiate 1-propanol, 1-butanol, 1-pentanol, and isopentyl alcohol, 17O NMR does allow the rapid and unambiguous identification of unexpected oxygenates such as acetates and ketones found as contaminants in some retail gasoline.     

Hyphenation of gas chromatography to microcoil 1H nuclear magnetic resonance spectroscopy

Whereas the hyphenation of gas chromatography (GC) with mass spectrometry is of great importance, little is known about the coupling to nuclear magnetic resonance spectroscopy (NMR). The investigation of this technique is an attractive proposition because of the valuable information given by NMR on molecular structure. The experiments shown here are to our knowledge the first hyphenating capillary GC to microcoil NMR. In contrast to liquids, gases have rarely been investigated by NMR, mainly due to the experimental difficulties in handling gases and the low signal-to-noise-ratio (SNR) of the NMR signal obtained at atmospheric pressure. With advances in NMR sensitivity (higher magnetic fields and solenoidal microprobes), this limitation can be largely overcome. In this paper, we describe the use of a custom-built solenoidal NMR microprobe with an active volume of 2 microL for the NMR detection of several compounds at 400 MHz, first in a mixture, and then with full coupling to capillary GC to identify them separately. The injected amounts of each analyte in the hyphenated experiments are in the range of 15-50 micromol, resulting in reasonable SNR for sample masses of 1-2 microg.     

Pore structure and sorption properties of silica aerogels studied by magnetic resonance imaging and pulsed-field gradient spectroscopy

Magnetic resonance imaging (MRI) has provided direct visualization of gaseous xenon and methane in the void spaces of aerogels, offering unique information and insights into the pore structure and molecular diffusivities of occluded sorbates. Nuclear magnetic resonance (NMR) pulsed-field gradient (PFG) techniques were used to characterize exchange and diffusive motion of sorbed xenon gas at equilibrium. PFG measurements showed evidence of anisotropic diffusion; nominal self-diffusivity coefficients of xenon on the order of D = 10(-7) m2/s were determined. Based on a mathematical relationship for the restricted diffusion of gases in confined environments, an expression for estimating the mean free path was derived, from which the average pore size could be obtained from the extrapolated value of the diffusion coefficient to low xenon pressures.     

Structure of dispersion media by nuclear magnetic resonance

The change of the diamagnetic shielding constant of a benzene molecule interacting with the solid phase surface is calculated.Notation _d diamagnetic shielding constant - e, m_e electron charge and mass, respectively - c speed of light - _b ^o benzene wave function - _m ^o and _m ^o* eigenfunctions of benzene molecule and their conjugates - W_mo matrix elements of the perturbation operator - E _o ^o energy of the ground state of a benzene molecule - e _m ^o energy of the excited states of a benzene molecule - a ₀ Bohr radius Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 41, No. 3, pp. 476–482, September, 1981.     

Multiple solenoidal microcoil probes for high-sensitivity, high-throughput nuclear magnetic resonance spectroscopy

Two designs for incorporating multiple solenoidal microcoils into a single probe head are presented to increase the throughput of high-resolution NMR. Through a combination of radio frequency switches and low-noise amplifiers, multiple NMR spectra can be acquired in the same time as a single spectrum from a conventional probe consisting of one coil. Since this method does not compromise sensitivity with regard to the individual microcoils, throughput increases linearly with the number of coils. Only one receiver is needed, and data acquisition parameters can be optimized for each sample. Specifically, a four-coil system has been implemented for proton NMR at 250 MHz using a wide-bore magnet, with an observe volume of 28 nL for each microcoil. Signal cross-contamination was approximately 0.2% between individual coils, and simultaneous one- and two-dimensional spectra have been obtained from samples of fructose, galactose, adenosine triphosphate, and chloroquine (7 nmol of each compound). A more compact two-coil configuration has also been designed for operation at 500 MHz, with observe volumes of 5 and 31 nL for the two coils. One- and two-dimensional spectra were acquired from samples of 1-butanol (55 nmol) and ethylbenzene (250 nmol).     

Influence of pressure upon coupling pressurized capillary electrochromatography with nuclear magnetic resonance spectroscopy

In this work, the influence of supplementary pressure on the separation efficiency of pressurized capillary electrochromatography (pCEC) was examined. At low pressures of up to 30 bar, which is more than sufficient to prevent bubble formation, no significant loss in separation efficiency is observed. Even at 100 bar, the efficiency of pCEC is still significantly better than without application of an electric field. In addition, analysis times are drastically reduced compared to both capillary electrochromatography (CEC) and capillary HPLC. On the basis of these results, an improved interface for capillary NMR coupling is described and used for the separation and identification of a mixture of unsaturated fatty acid methyl esters. Under these conditions, the analysis time could be shortened by up to a factor of 10 when pCEC is coupled to NMR spectroscopy.     

The photomagnetic effect detected by nuclear magnetic resonance

The results of experiments with transparent easy-plane antiferromagnetic iron borate (FeBO₃) show that nuclear magnetic resonance (NMR) offers an effective tool for the study of photomagnetism in magnetically ordered materials. It is established that illumination of a FeBO₃ sample leads to a shift of the ⁵⁷Fe NMR frequency due to a change in the electron magnetization and significantly increases the nuclear induction signal intensity in the range of existence of the domain boundaries.     

Elastic properties of lanthanum aluminosilicate glasses

The elastic properties of two series of lanthanum aluminosilicate glasses (15La₂O₃-xAl₂O₃-(85−x)SiO₂ and 25La₂O₃-yAl₂O₃-(75−y)SiO₂, where x, y=15, 20, 25, 30, 35 mol%), were obtained by the ultrasonic pulse-echo technique, at room temperature. The correlation of elastic stiffness, the cross-link density, and the fractal bond connectivity of these glasses are discussed. The derived experimental values of Young’s modulus, bulk modulus, shear modulus and Poisson’s ratio for our glasses are compared with those theoretically calculated values in terms of the Makishima-Mackenzie model.