Two-dimensional correlation analysis of nuclear magnetic resonance metabonomics data

Two-dimensional (2D) correlation analysis has been used in this study to identify changes in complex nuclear magnetic resonance (NMR) metabonomics spectra of rat urine samples obtained during a study in which vasculitis (vascular injury), an important safety element in preclinical trials, was induced. Two types of correlation analysis were performed, along the variables and along the samples, and both 2D covariance and correlation coefficient maps were calculated. The binned and 'raw' NMR spectra were analyzed (0.04 and 0.001 ppm resolution, respectively). Good correlation was found among the major peaks of the binned spectra, and two groups of samples were identified using sample-sample 2D correlation maps. Much more complex correlation features were obtained from the 'raw' spectra, in which the specific, butterfly-like patterns were obtained in the covariance map but with only a few significant correlation coefficients in the corresponding 2D correlation maps. In terms of classification, the same group of the last nine spectra that indicated the end of the process and clustered in the 2D sample-sample covariance map of the binned data was also found in the 2D sample-sample covariance map of the raw NMR spectra but, again, not in the 2D correlation coefficient map. A discussion is given on the details of the application of the correlation analysis with regard to spectral data resolution, alignment, the effect of actual intensities of the NMR signal, and reference to various results from 2D correlation analysis of vibrational spectra.     

Heteronuclear 19F-1H statistical total correlation spectroscopy as a tool in drug metabolism: study of flucloxacillin biotransformation

We present a novel application of the heteronuclear statistical total correlation spectroscopy (HET-STOCSY) approach utilizing statistical correlation between one-dimensional 19F/1H NMR spectroscopic data sets collected in parallel to study drug metabolism. Parallel one-dimensional (1D) 800 MHz 1H and 753 MHz 19F{1H} spectra (n = 21) were obtained on urine samples collected from volunteers (n = 6) at various intervals up to 24 h after oral dosing with 500 mg of flucloxacillin. A variety of statistical relationships between and within the spectroscopic datasets were explored without significant loss of the typically high 1D spectral resolution, generating 1H-1H STOCSY plots, and novel 19F-1H HET-STOCSY, 19F-19F STOCSY, and 19F-edited 1H-1H STOCSY (X-STOCSY) spectroscopic maps, with a resolution of approximately 0.8 Hz/pt for both nuclei. The efficient statistical editing provided by these methods readily allowed the collection of drug metabolic data and assisted structure elucidation. This approach is of general applicability for studying the metabolism of other fluorine-containing drugs, including important anticancer agents such as 5-fluorouracil and flutamide, and is extendable to any drug metabolism study where there is a spin-active X-nucleus (e.g., 13C, 15N, 31P) label present.     

Polymerization of alkaline-calcium-silicate hydrates obtained by interaction between alkali–silica solutions and calcium compounds. A 29Si nuclear magnetic resonance study

Alkali–silica solutions containing varying amounts of silica and alkali ions have been prepared. Solids were obtained by interaction of these solutions with calcium hydroxide, calcium chloride or calcium sulphate. A 29Si nuclear magnetic resonance study has been carried out on these products during the initial and final stages of the synthesis. Three major kinds of solids appear in the CaO–Na2O(K2O)–SiO2 phase diagram; a chain-like nanocrystalline solid, a plate-like amorphous solid, and a three-dimensional amorphous network solid. A relationship between the initial system (i.e., the initial solution) and the final system (i.e., the solid plus the residual solution) is established. The solid is found to have a higher degree of polymerization than the initial solution while the residual solution is mearly an alkali–silica solution without calcium ions.     

Reduction of the Shoenberg magnetic interaction by magnetic feedback

It is demonstrated that the oft-times severe waveform distortion arising from the Shoenberg magnetic interaction in the de Haas-van Alphen effect can be very effectively suppressed when measurements are made on spherical samples in the presence of a uniform magnetic feedback field. A digital spectrum analyzer is used in conjunction with a large ramping modulation field (1 kG peak-to-peak) to obtain a Fourier transform of a portion of the dHvA waveform roughly every second, and the dHvA effect itself is used to provide criteria for setting the correct gain in the magnetic feedback loop. Examples drawn from a study of the [110] orientation in Pb serve to illustrate the advantages and improvements in waveform studies which accrue from the use of magnetic feedback. The improvement is particularly impressive in the three-harmonic method for determining the spin-splitting factor g _c for extremal orbits on the Fermi surface, and the value g _c = 0.704 is found for the [110] orbit in Pb ( oscillations). A careful search has been made for low-frequency dHvA oscillations in Pb corresponding to those reported in ultrasonic attenuation and magnetoresistance experiments, but no such oscillations could be found in the magnetization.This research was supported by the Natural Sciences and Engineering Research Council of Canada.     

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.     

Magic angle spinning NMR and 1H-31P heteronuclear statistical total correlation spectroscopy of intact human gut biopsies

Previously we have demonstrated the use of 1H magic angle spinning (MAS) NMR spectroscopy for the topographical variations in functional metabolic signatures of intact human intestinal biopsy samples. Here we have analyzed a series of MAS 1H NMR spectra (spin-echo, one-dimensional, and diffusion-edited) and 31P-{1H} spectra and focused on analyzing the enhancement of information recovery by use of the statistical total correlation spectroscopy (STOCSY) method. We have applied a heterospectroscopic cross-examination performed on the same samples and between 1H and 31P-{1H} spectra (heteronuclear STOCSY) to recover latent metabolic information. We show that heterospectroscopic correlation can give new information on the molecular compartmentation of metabolites in intact tissues, including the statistical "isolation" of a phospholipid/triglyceride vesicle pool in intact tissue. The application of 31P-1H HET-STOCSY allowed the cross-assignment of major 31P signals to their equivalent 1H NMR spectra, e.g., for phosphorylcholine and phosphorylethanolamine. We also show pathway correlations, e.g., the ascorbate-glutathione pathway, in the STOCSY analysis of intact tissue spectra. These 31P-1H HET-STOCSY spectra also showed different topographical regions, particular for minor signals in different tissue microenvironments. This approach could be extended to allow the detection of altered distributions within metabolic subcompartments as well as conventional metabonomics concentration-based diagnostics.     

De Haas-van Alphen effect study of magnetic interaction in lead

Frequency and amplitude modulation (FM and AM) of a high-frequency (HF) de Haas-van Alphen oscillation due to magnetic interaction (MI) with a low-frequency (LF) oscillation in lead has been examined for field directions parallel to and close to 110, in the light of the old and of a new treatment of MI based on uniform and inhomogeneous inductions over the sample, respectively. The de Haas-van Alphen signals have been measured by the standard low-frequency field modulation method. The strength of AM and the sideband around HF have been examined as a function of the strength of FM and it is found that the experimental data deviate significantly from the prediction by the old treatment. Moreover, the deviation depends not only on the particular sample chosen to study, but also on the orientation, suggesting that the MI effect is influenced by the microscopic inhomogeneity of the sample. The absolute amplitude of LF also has been measured and is found again to deviate significantly from the prediction by the old treatment. However, the measured amplitude shows a satisfactory agreement with the prediction by the new treatment. In conclusion, the new treatment is a plausible theory which can describe all our experimental results, not only qualitatively but also quantitatively.     

A study of the oxidation curing mechanism of polycarbosilane fibre by solid-state high-resolution nuclear magnetic resonance

The chemical structure of oxidation-cured polycarbosilane fibres has been studied by IR and chemical analysis, but its structure has not been identified in detail. In this work, the molecular structure was examined by chemical analysis, and solid state¹³C and²⁹Si nuclear magnetic resonance (NMR) spectroscopy. Si-O-Si, Si-O-C(I) and Si-O-C(II) bonds were formed by the oxidation curing process. The six chemical bonds (Si-C, Si-H, Si-Si, Si-O-Si, Si-O-C(I) and Si-O-C(II)) in oxidation-cured polycarbosilane were determined quantitatively, and the chemical structural model was shown. Solid state²⁹Si resolution NMR spectroscopy has proved to be a powerful tool for investigating the curing mechanism of oxidation-cured polycarbosilane fibres.     

Characterization of attenuated total reflection infrared spectral intensity variations of immature and mature cotton fibers by two-dimensional correlation analysis

Two-dimensional (2D) correlation analysis was applied to characterize the attenuated total reflection (ATR) spectral intensity fluctuations of immature and mature cotton fibers. Prior to 2D analysis, the spectra were leveled to zero at the peak intensity of 1800 cm(-1) and then were normalized at the peak intensity of 660 cm(-1) to subjectively correct the variations resulting from ATR sampling. Next, normalized spectra were subjected to principal component analysis (PCA), and two clusters of immature and mature fibers were confirmed on the basis of the first principal component (PC1) negative and positive scores, respectively. The normalized spectra clearly demonstrated the intensity increase or decrease of the bands ascribed to different C-O confirmations of primary alcohols in the 1050-950 cm(-1) region, which was not apparent from raw ATR spectra. The PC1 increasing-induced 2D correlation analysis revealed remarkable differences between the immature and mature fibers. Of interest were that: (1) Both intensity increase of two bands at 968 and 956 cm(-1) and the shifting of 968 cm(-1) in immature fibers to 956 cm(-1) in mature fibers, together with the intensity decreasing and shifting of the 1048 and 1042 cm(-1) bands, are the characteristics of cotton fiber development and maturation. (2) Intensities of most bands in the 1800-1200 cm(-1) region decreased with the fiber growth, suggesting they are from either noncellulosic components or CH and OH fractions in amorphous celluloses. (3) The reverse sequence of intensity variations of the bands in the 1100-1000 cm(-1) and 1000-900 cm(-1) region of asynchronous spectra indicated a different mechanism of compositional and structural changes in developing cotton fibers at different growth stages.     

On the interaction of magnetic fields and magnetic shields

Some general mathematical expressions have been derived for the induced self and mutual inductances of the wires inside a cylindrical ferromagnetic shell. An application of these results is given. It is shown that the effect of the ferromagnetic shell on the inductances of the multiconducting wires is strongly geometry dependent; the closer the wires to the magnetic shell, the stronger the effect. For wires in the center of the cylinder, no significant result will be caused by the presence of the magnetic shell.     

Alignment of SWNTs by protein-ligand interaction of functionalized magnetic particles under low magnetic fields

Carbon nanotubes (CNTs) have attracted considerable attention for applications using their superior mechanical, thermal and electrical properties. A simple method to controllably align single-walled CNTs (SWNTs) by using magnetic particles embedded with superparamagnetic iron oxide as an accelerator under the magnetic field was developed. The functionalization of SWNTs using biotin, interacted with streptavidin-coupled magnetic particles (micro-to-nano in diameter), and layer-by-layer assembly were performed for the alignment of a particular direction onto the clean silicon and the gold substrate at very low magnetic forces (0.02-0.89 T) at room temperature. The successful alignment of the SWNTs with multi-layer film was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). By changing the orientation and location of the substrates, crossed-networks of SWNTs-magnetic particle complex could easily be fabricated. We suggest that this approach, which consists of a combination of biological interaction among streptavidin-biotin and magnetite particles, should be useful for lateral orientation of individual SWNTs with controllable direction.     

A study of the pozzolanic reaction by solid-state 29Si nuclear magnetic resonance using selective isotopic enrichment

The hydration of a mixture of tricalcium silicate and silica has been studied by ²⁹Si solid-state nuclear magnetic resonance, using selective enrichment of the reactants with ²⁹Si in order to follow and compare the behaviour of the silicon nuclei originating from either source. This approach shows for the first time that the silicon atoms from the two components are not equilibrated throughout the hydration products but are preferentially located in distinct species. In particular, from the distinctive spectra observed when the silica only is enriched, it is concluded that the part of the calcium silicate hydrate gel formed which incorporates silicon from this source has a longer chain length and a slightly better-ordered structure than the remainder. The spectra obtained with selective enrichment are interpreted in terms of a model based on a dreierkette chain structure for C-S-H.     

In situ nuclear magnetic resonance study of defect dynamics during deformation of materials

Nuclear magnetic resonance techniques can be used to monitor in situ the dynamical behaviour of point and line defects in materials during deformation. These techniques are non-destructive and non-invasive. We report here the atomic transport, in particular the enhanced diffusion during deformation by evaluating the spin lattice relaxation time in the rotating frame, T ₁,in pure NaCl single crystals as a function of temperature (from ambient to about 900K) and strain-rate (to 1.0s^–1) in situ during deformation. The strain-induced excess vacancy concentration increased with the strain-rate while in situ annealing of these excess defects is noted at high temperatures. Contributions due to phonons or paramagnetic impurities dominated at lower temperatures in the undeformed material. During deformation, however, the dislocation contribution became predominant at these low temperatures. The dislocation jump distances were noted to decrease with increase in temperature leading to a reduced contribution to the overall spin relaxation as temperature is increased. Similar tests with an improved pulse sequence (CUT-sequence), performed on ultra-pure NaCl and NaF single crystals revealed slightly different results; however, strain-enhanced vacancy concentrations were observed. The applicability of these techniques to metallic systems will be outlined taking thin aluminium foils as an example.     

Characterization of absorbed water in aramid fibre by nuclear magnetic resonance

While many studies have focused on the mechanical degradation of aramid/epoxy composites by water absorption, little work has been done to gain a deeper understanding of the interaction between absorbed water and aramid fibres. In this study, ¹³C, ¹H, and ²³Na nuclear magnetic resonance was used to show that the absorbed water in Twaron fibre is located in small pores in the skin region of the fibres, and in larger core defects. The absorbed water partially dissolves sodium salts, consisting mainly of sodium carbonate, which are present in the pores. No evidence of chemical breakdown of the aramid polymer, or of water ingress within the polymer lattice, was observed.     

Microinhomogeneity of high-alkali aluminosilicate glasses studied by nuclear magnetic resonance spectroscopy

The structure of quenched aluminosilicate glasses with Na₂O/Al₂O₃ > 1 has been studied by high-resolution nuclear magnetic resonance spectroscopy. The aluminum in the structure of the glasses is shown to be in fourfold coordination. Increasing the sodium oxide content of the glasses reduces the degree of polymerization in their structure and leads to a nonuniform nonbridging oxygen distribution over the aluminosilicate glass network. The glasses have a locally microinhomogeneous structure due to the presence of both highly polymerized aluminosilicate anion groups and relatively depolymerized silicate anions.     

Characterization of hydrogenated amorphous carbon films by nuclear magnetic resonance techniques

Different nuclear magnetic resonance (NMR) methods have been used to investigate the structure of hydrogenated amorphous carbon films. Besides measuring the sp²-to-sp³ ratio by means of ¹³C cross-polarization magic-angle spinning total suppression of spinning sidebands NMR we studied the distribution of covalently bound hydrogen over sp²- and sp³-type carbon atoms using dipolar dephasing techniques. The reliability of the dipolar dephasing measurements is discussed and the results are compared with the data derived from a simple statistical model. Moreover they are compared with previous IR spectroscopy measurements. ¹H combined rotation-and-multipulse NMR spectra are presented which do not show resolved proton resonances in the case of as-deposited films but correspond in their line shape to the proton distribution measured with dipolar dephasing. Finally a few considerations concerning a refined structural model are presented.     

Electrical conductance of molecular junctions by a robust statistical analysis

We propose an objective and robust method to extract the electrical conductance of single molecules connected to metal electrodes from a set of measured conductance data. Our method roots in the physics of tunneling and is tested on octanedithiol using mechanically controllable break junctions. The single molecule conductance values can be deduced without the need for data selection.