NMR study of the structure of poly(N-benzoyl-8-octanelactam)

The structure of a polymer prepared by the polymerization of N-benzoyl-8-octanelactam initiated with benzoic acid was studied by ¹H and ¹³C NMR, using S-INEPT, COSY, COLOC, and ROSEY methods, with the aid of model oligomers. Beside the expected N-benzoylated segments, the polymer also contained deacylated segments and about 50% of branching units. The polymer can be characterized as a statistical, highly branched copolymer of N-benzoyl-8-octanelactam and 8-octanelactam. © 1993 John Wiley & Sons, Inc.     

脑部磁共振结合静息态fMRI方法在卒中患者认知障碍中的应用

本研究主要探讨脑部磁共振结合静息态fMRI方法在卒中患者认知障碍中的应用。本研究将符合卒中认知障碍患者25例设为患者组,将25例健康者设为对照组。采用脑部静息态核磁共振对实验者进行扫描,以脑部双侧海马为种子点进行功能连接分析,并通过软件分析两组实验者静息态双侧海马差异。结果发现,与对照组相比,患者组右侧海马与左右侧额中回、左侧额下回等的连接减少;右侧海马与左侧颞上中回、双侧丘脑的连接增加;左侧海马与左侧颞额中回、右侧颞额上回、右侧额下回的连接减少;左侧海马与右侧顶下回连接增加。总之,本研究发现卒中患者海马脑区与颞叶皮层、额叶皮层之间的连接减少,可能是由卒中患者脑损害导致。     

Quantification of the velocity acceleration factor for colloidal transport in porous media using NMR

Nuclear magnetic resonance (NMR) techniques were used to quantify the transport of colloids through porous media. This was achieved via the application of chemically-resolved pulsed field gradient (PFG) methods, hence probing the displacement (probability distribution) propagators of both the colloidal and continuous liquid phase. A dilute decane-in-water emulsion was used with flow through a random glass sphere packing being considered. The acquired propagators allowed for quantification of both colloidal entrapment and the velocities of both the continuous phase and the flowing colloids. The flowing colloids were found to experience a velocity acceleration factor (VAF) increase of 1.08 relative to the continuous phase. This was found to be independent of displacement observation time or flowrate. It was speculated to be a consequence of radial exclusion due to the finite size of the colloids. Simulations of the colloidal transport were also performed using a lattice Boltzmann platform and a Lagrangian particle-tracking algorithm which incorporated colloidal radial exclusion. Reasonable agreement was observed between the simulation and the experimental data.     

等级孔分子筛的可控合成、扩散研究及催化应用

等级孔分子筛是一类具有两种或多种以特定形式排布的孔结构的分子筛材料. 多层等级的孔结构使得分子筛孔道内的分子扩散得到显著改善, 进而提升了其在吸附和非均相催化等领域的应用性能. 等级孔分子筛的制备策略通常有两种, 即“自上而下”后处理法(如对母样分子筛进行脱铝、 脱硅产生介孔)和“自下而上”合成法(如软模板、 硬模板法). 本文主要对近20年来等级孔分子筛的合成方法进行了梳理, 并着重介绍了具有较高应用潜力的“自上而下”制备法. 鉴于合成等级孔分子筛的主要目的是提高分子的晶内扩散, 对近年来客体分子在等级孔分子筛内扩散的实验研究也进行了简要综述. 此外, 本文还综合评述了等级孔分子筛与传统分子筛在催化应用中的对比, 以展示前者在提升催化性能方面(如活性、 选择性等)的独特优势.     

A comparison of magnetic resonance imaging methods for fluid content imaging in porous media

Quantitative measurements are important for imaging fluid content in porous media. Conventional MRI methods suffer from contrast because of relaxation times in porous media, resulting in measurements of apparent fluid content, not the true fluid content. We compare four magnetic resonance imaging methods for fluid content imaging in several water‐saturated reservoir core plugs: frequency‐encoded spin echo, single point ramped imaging with T₁ enhancement, hybrid spin echo single point imaging (SE‐SPI), and T₂ mapping SE‐SPI. 1‐D profiles obtained with each method were compared in terms of image quality, image sensitivity, and quantification of water content. The image quality of short T₂ lifetime samples suffered from blurring in hybrid SE‐SPI images. Image sensitivity was the highest in the profiles obtained with frequency‐encoded spin echo. The quantification of frequency‐encoded spin echo, T₂ mapping SE‐SPI, and hybrid SE‐SPI suffered in core plugs with a significant population of short T₂ components because of T₂ attenuation. Overall, single point ramped imaging with T₁ enhancement was found to be the most general method for fluid content imaging. Copyright © 2013 John Wiley & Sons, Ltd.     

Comparison of Five Conductivity Tensor Models and Image Reconstruction Methods Using MRI

Imaging of the electrical conductivity distribution inside the human body has been investigated for numerous clinical applications. The conductivity tensors of biological tissue have been obtained from water diffusion tensors by applying several models, which may not cover the entire phenomenon. Recently, a new conductivity tensor imaging (CTI) method was developed through a combination of B1 mapping, and multi-b diffusion weighted imaging. In this study, we compared the most recent CTI method with the four existing models of conductivity tensors reconstruction. Two conductivity phantoms were designed to evaluate the accuracy of the models. Applied to five human brains, the conductivity tensors using the four existing models and CTI were imaged and compared with the values from the literature. The conductivity image of the phantoms by the CTI method showed relative errors between 1.10% and 5.26%. The images by the four models using DTI could not measure the effects of different ion concentrations subsequently due to prior information of the mean conductivity values. The conductivity tensor images obtained from five human brains through the CTI method were comparable to previously reported literature values. The images by the four methods using DTI were highly correlated with the diffusion tensor images, showing a coefficient of determination (R2) value of 0.65 to 1.00. However, the images by the CTI method were less correlated with the diffusion tensor images and exhibited an averaged R2 value of 0.51. The CTI method could handle the effects of different ion concentrations as well as mobilities and extracellular volume fractions by collecting and processing additional B1 map data. It is necessary to select an application-specific model taking into account the pros and cons of each model. Future studies are essential to confirm the usefulness of these conductivity tensor imaging methods in clinical applications, such as tumor characterization, EEG source imaging, and treatment planning for electrical stimulation.     

Molecular motion in nanocomposites of poly(ethylene oxide) and montmorillonite

Motion of chains of poly(ethylene oxide) within the interlayer spacing of 2:1 phyllosilicate/montmorillonite was studied with ¹H and ¹³C NMR spectroscopy. Measurements of the ¹H NMR line widths and relaxation times across a large temperature range were used to determine the effect of bulk thermal transitions on polymer chain motion within the nanocomposites. The results were consistent with previous reports of low apparent activation energies of motion. Details of the frequency and geometry of motion were obtained from a comparison of the ¹³C cross‐polarity/magic‐angle spinning spectra and relaxation times of the nanocomposite with those of the pure polymer. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1678–1685, 2001     

Preparation and characterization of amino-functionalized magnetic nanogels via photopolymerization for MRI applications

To design peptide-targeted iron oxide as magnetic resonance imaging (MRI) contrast agents, amino-functionalized magnetic nanogels were prepared by using N-(2-aminoethyl) methacrylamide hydrochloride (AEM·HCl) as monomer via new photochemical approach. Their chemical structure and composition were characterized by Fourier transform infrared spectra (FTIR) and thermogravimetric analyses (TGA). The core–shell structure of magnetic nanogels was confirmed by high-resolution transmission electron microscopy (HRTEM). The good storage stability, high magnetic content (88.7%), high saturation magnetizations and superparamagnetic behavior suggested their great potentials as MRI contrast agents, which were confirmed by their measurements of r₂ and coronal image of the crossing of mouse kidney.     

NMR Characterization of Lanthanide(3+) Complexes of Tetraazatetrakisphosphinato and Tetraazatetra­kisphosphonato Ligands

The three‐dimensional structures in aqueous solution of the entire series of the Ln³⁺ complexes [Ln(DOTP*‐Et)]^? (formed from the free ligand P,P′,P″,P′′′‐[1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetrayltetrakis(methylene)]tetrakis[P‐ethylphosphinic acid] (H₄DOTP*‐Et) were studied by NMR techniques to rationalize the parameters governing the relaxivity of the Gd³⁺ complex and evaluate its potential as MRI contrast agent. From the ¹H‐ and ³¹P‐NMR lanthanide‐induced‐shift (LIS) values, especially of the [Yb(DOTP*‐Et)]^? complex, it was concluded that the [Ln(DOTP*‐Et)]^? complexes adopt in solution twisted square antiprismatic coordination geometries which change gradually their coordination‐cage structure along the lanthanide series. These complexes have no inner‐sphere‐H₂O coordination, and preferentially have the (R,R,R,R) configuration of the P‐atoms in the pendant arms. Self‐association was observed in aqueous solution for the tetraazatetrakisphosphonic acid ester complexes [Ln(DOTP*‐OEt)]^? (=[Ln(DOTP‐Et)]^?) and [Ln(DOTP*‐OBu)]^? (=[Ln(DOTP‐Bu)]^?) at and above 5 mM concentration, through analysis of ³¹P‐NMR, EPR, vapor‐pressure‐osmometry, and luminescence‐spectroscopic data. The presence of the cationic detergent cetylpyridinium chloride (CPC; but not of neutral surfactants) shifts the isomer equilibrium of [Eu(DOTP*‐OBu)]^? to the (S,S,S,S) form which selectively binds to the cationic micelle surface.     

Permanent Polymer Coating for in vivo MRI Visualization of Tissue Reinforcement Prostheses

The clinical advantage of MRI visualization of prostheses in soft tissue prolapses is very appealing as over 1 000 000 MRI‐transparent synthetic meshes are implanted annually, and postoperative complications such as mesh shrinkage and migration are frequent. Here, the synthesis of a new material composed of a DTPA‐Gd complex grafted onto a backbone of PMA via a covalent bond is described (DTPA‐Gd‐PMA). This new polymer is sprayed onto meshes and gives an MR signal for a long period without any significant release of Gd. In vitro cytocompatibility tests on fibroblasts show limited cytotoxicity. Microscopic investigations indicate that vital cells rapidly colonize the material. Finally, coated meshes implanted in rats are easily recognizable using an MR imaging system.

     

A comparison of the pseudo-steady-state and shrinking-core model for the reduction of titanium dioxide to titanium

A multistage shrinking-core model is proposed for the electrodeoxidation of titanium dioxide to titanium. This takes place through a series of steps from TiO₂ to Ti₃O₅ to Ti₂O₃ to TiO to Ti. Ideally, the model would incorporate a number of shells of the above lower oxide phases with the shrinking core of TiO₂ in the center but this would be mathematically intractable. A simpler method would be to use the shrinking-core model for each of the individual reductions. Taking the experimental parameters and diffusion coefficient of oxygen in the different phases into account, an analytical solution is developed for the transient differential equation. The first ten eigenvalues are taken into account for the computation of the series solution. This is then compared with a solution based on a pseudo-steady-state approximation to the transient equations. Based on the results, for higher values (>0.01) of dimensionless applied current density, I _d , both the solutions disagree in terms of the time it takes for the core to shrink completely. The difference appears to be decreasing with lower values of I _d but for larger values of I _d the pseudo-steady-state approximation fails to yield results close to the analytical solution.     

MR Study of Water Distribution in a Beech (Fagus sylvatica) Branch Using Relaxometry Methods

Wood is a widely used material because it is environmentally sustainable, renewable and relatively inexpensive. Due to the hygroscopic nature of wood, its physical and mechanical properties as well as the susceptibility to fungal decay are strongly influenced by its moisture content, constantly changing in the course of everyday use. Therefore, the understanding of the water state (free or bound) and its distribution at different moisture contents is of great importance. In this study, changes of the water state and its distribution in a beech sample while drying from the green (fresh cut) to the absolutely dry state were monitored by 1D and 2D ¹H NMR relaxometry as well as by spatial mapping of the relaxation times T₁ and T₂. The relaxometry results are consistent with the model of homogeneously emptying pores in the bioporous system with connected pores. This was also confirmed by the relaxation time mapping results which revealed the moisture transport in the course of drying from an axially oriented early- and latewood system to radial rays through which it evaporates from the branch. The results of this study confirmed that MRI is an efficient tool to study the pathways of water transport in wood in the course of drying and is capable of determining the state of water and its distribution in wood.     

Multiple‐Frequency and Variable‐Temperature EPR Study of Gadolinium(III) Complexes with Polyaminocarboxylates: Analysis and Comparison of the Magnetically Dilute Powder and the Frozen‐Solution Spectra

An electron paramagnetic resonance (EPR) study of glasses and magnetically dilute powders of [Gd(DTPA)(H₂O)]^2?, [Gd(DOTA)(H₂O)]^?, and macromolecular gadolinate(1?) complexes P792 was carried out at the X‐ and Q‐bands and at 240 GHz (DTPA=diethylenetriaminepentaacetato; DOTA=1,4,7,10‐tetraazacyclododecane‐1,4,7,10‐tetraacetato). The results show that the zero‐field splitting (ZFS) parameters for these complexes are quite different in a powder as compared to the frozen aqueous solution. In several complexes, an inversion of the sign of the axial component D of the zero field splitting is observed, indicating a significant structural change. In contrary to what was expected, powder samples obtained by lyophilization do not allow a more precise determination of the static ZFS parameters. The results obtained in glasses are more relevant to the problem of electron spin relaxation in aqueous solution than those obtained from powders.     

Fast inspection of fruits using nuclear magnetic resonance spectroscopy

High-resolution nuclear magnetic resonance (NMR) spectroscopy is an indispensable technique for obtaining chemical structure information. Its quantitative and noninvasive properties have led to its growing popularity as an analytical tool in many fields, including biology, chemistry, medicine, and food science. During transportation and storage, chemical reactions among the many nutrients lead to a loss of food quality. In these circumstances, portable NMR spectrometers can readily be used for food inspection and quality control. Because of the heterogeneous tissue distribution in food, a high-resolution NMR method is required for detailed food inspection. Therefore, in this study, we demonstrated the feasibility of using an intermolecular double-quantum coherence signal to obtain high-resolution metabolic profiles of several fruits, including grape, cantaloupe, tomato, and watermelon. The resulting high-resolution NMR spectra facilitate the identification of important metabolites, which can be used as biomarkers for food quality control. The method established here may be adapted for food inspection using portable NMR equipment.     

Pyruvate cellular uptake and enzymatic conversion probed by dissolution DNP‐NMR: the impact of overexpressed membrane transporters

Pyruvate membrane crossing and its lactate dehydrogenase‐mediated conversion to lactate in cells featuring different levels of expression of membrane monocarboxylate transporters (MCT4) were probed by dissolution dynamic nuclear polarization‐enhanced NMR. Hyperpolarized ¹³C‐1‐labeled pyruvate was transferred to suspensions of rodent tumor cell carcinoma, cell line 39. The pyruvate‐to‐lactate conversion rate monitored by dissolution dynamic nuclear polarization‐NMR in carcinoma cells featuring native MCT4 expression level was lower than the rate observed for cells in which the human MCT4 gene was overexpressed. The enzymatic activity of lactate dehydrogenase was also assessed in buffer solutions, following the real‐time pyruvate‐to‐lactate conversion speeds at different enzyme concentrations. Copyright © 2016 John Wiley & Sons, Ltd.     

A Use of Modified Cyclodextrins as a Transporter for a Radiolabeled Tracer NMR Investigation

Cyclodextrins (D. Duchêne (ed.): New Trends in Cyclodextrins and Derivatives (1991)) have long been shown to be capable of modifying the water solubility of a number of hydrophobic guests through the formation of inclusion complexes. Among the three natural cyclodextrins (α, β and γ-cyclodextrins containing 6, 7 and 8 d-glucopyranose units, respectively), β-cyclodextrin is by far the most commonly used although it exhibits a weaker solubility in water (and therefore a weaker solubilization power). This specific feature has encouraged the synthesis of derivatives exhibiting an increased solubility in water. Methylated cyclodextrins are amongst the simplest derivatives, and their properties regarding the solubility and the solubilization power for hydrophobic guests are well documented especially concerning Heptakis (2,6-di-Omethyl)-cyclodextrin (DIMEB) and Heptakis (2,3,6-tri-Omethyl)-cyclodextrin (TRIMEB) K. Koizumi et al.:J. Chromatogr. 368, 329–337 (1986). In order to avoid the use of human serum albumin (HSA), this property has been applied here to the solubilization of a very sparingly water-soluble fatty acid derivative (16-iodo-3-methylhexadecanoic acid), which is known to localise in viable myocardial cells, allowing the generation of functional images reflecting the viability of the cardiac tissue through the use of radiolabeled analog (Demaison et al.: J. Nucl-Med. 29, 1230–1236 (1998)). Nuclear magnetic resonance (NMR) was used throughout this study to evidence that the observed solubilization and stabilisation (under conditions required for sterilisation) induced by cyclodextrins are due to the formation of a true inclusion complex and not to non-specific interactions; This technique further allows to derive thermodynamic as well as structural informations for this complex. On one hand, the inclusion complex prevents thermal degradation during sterilisation process compared to HSA. On the other hand, NMR displacement experiments against HSA showed that the complex likely dissociates in vivo.     

Assessment of the Extent of Starch Dissolution in Dimethyl Sulfoxide by 1H NMR Spectroscopy

Complete dissolution is needed for the separation, characterization, or homogeneous labeling of whole starch molecules. A method is presented to quantify the extent of starch dissolution in DMSO for the first time; it is validated on a commercial rice starch. It is used directly on starch dispersions containing possible undissolved or co‐dissolved species. High‐amylose maize starches, known to be digested slowly in vivo, only quantitatively dissolve in the presence of high concentrations of an H‐bond disrupter, LiBr, although they form clear dispersions at low LiBr concentrations. Starch quantitatively dissolves from waxy rice flours; non‐starch components partially co‐dissolve but do not interfere with the dissolution quantification.

     

Structure determinations of nitrogen compounds with the aid of NQR, NMR, and ESCA spectroscopy

Since it is often necessary or desirable to determine the structures of compounds containing nitrogen directly via the nitrogen atoms, the nuclear quadrupole resonance (NQR) and the nuclear magnetic resonance (NMR) as well as the photoelectron and the Auger-electron spectroscopy (ESCA) of nitrogen are becoming increasingly important. A comparative review of these three methods on the basis of measurement effect, information obtainable, applications, and limitations forms the subject of this article.     

NMR study of the propagation center in cationic polymerization of N-benzoyl-8-octanelactam. I. The structure of model living oligomers

Model living oligomers of N-benzoyl-8-octanelactam initiated by the model octanoylium hexachloroantimonate, SbCl₅, and by Ph₃C⁺ AsF₆^?, were studied by ¹H and ¹³C one- and two-dimensional nuclear magnetic resonance using the COSY, S-INEPT, COLOC, and ROESY methods. If prepared in the more solvating mixture of 1,1,2,2-tetrachloroethane (TCE) with 1,2-dichlorobenzene, the oligomers were found to be linear with the acylium ion as a living group on one end; in TCE only, the oligomers are highly branched. In both cases, the propagation center appears to be strongly coordinated to the nearest benzoylamide chain group. © 1993 John Wiley & Sons, Inc.