The tools for developing systems for NMR improve each year. Some firmware based designs based on Field Programmable Gate Arrays (FPGAs) have been developed to implement both the core and peripheral ...apparatus for NMR Relaxometers and NMR Cryoporometers. Hand held in size they are particularly suitable for desktop, mobile and field use.
Software tools now enable the writing of firmware that enable the rapid design of digital and digitised R.F. data and control systems. This firmware can then be loaded into and run on hardware that often is only the size of a credit-card. These devices can include a single-chip Linux computer with an FPGA capable of processing digital RF on the same chip. These can generate RF signals digitally, process RF signals for up- and down-conversion, and can provide an on chip NMR pulse sequencer.
An extremely well tested NMR digital transmitter has been upgraded to use the latest surface-mount Bipolar and Field Effect Transistors. The circuitry is now the size of a book of matches, and interfaces to credit-card sized FPGA modules for RF generation, phase shifting and drive signals. This NMR transmitter design uses digital logic principles rather than conventional tuned R.F. techniques Offering both active-damping and active-quench, a very square R.F. Pulse with fast turn off is achieved, with Mark 1 giving 2.6 μs π/2 and 4.8 μs π pulses into a 5 mm diameter NMR sample (2.7 mT B1) at 20 MHz for Protons. T1ρ pulses are stable and consistent.
The structural study of lanthanum sodium aluminoborosilicate (55SiO2-(25-x) Al2O3-xB2O3–15Na2O–5La2O3) glasses were investigated. The structural characterization by solid state Nuclear Magnetic ...Resonance have outlined the role of aluminum/boron substitution. This study has a particular interest for applications like the nuclear waste glass storage. Various types of matrices have been considered for containment: borosilicate, aluminosilicate and aluminoborosilicate, the latter with a high rare earth content ability is of particular interest. This system will be considered in our study from the point of view of a simple five-oxide glass, rich in TR2O3 (TR = La), in order to provide additional elements of understanding to the model glasses of containment for nuclear waste, lanthanum simulating, among other things, all lanthanides as well as minor actinides contained in the waste. In this paper, ourwork focused on the study of the influence of boron on the structure by solid state Nuclear Magnetic Resonance (NMR). In particular, we examine the impact of aluminum/boron substitution in a series of glasses in term of structural changes.
•We have investigated a composition of glasses with a high content of rare earth elements.•29Si,27Al, 23Na and 11B MAS NMR was used to describe the vitreous aluminoborosilicate network.•Glasses homogeneity is discussed according to the influence of boron/aluminum substitution.•NMR spectroscopy gave a better discerption to discuss the structure in term of Qn(mAl) and Qn species.
There are varieties of methods available for the exploration of solids using nuclear magnetic resonance (NMR) spectroscopy. Some of these methods are quite sophisticated, others require specialized ...equipment. This review is addressed to those for whom NMR is not the main research method. It discusses simple methods that can be applied to solids with little or no adaptation to a specific system. Despite their technical simplicity and ease of use, these methods are powerful analytical tools that provide unique insights into the structure, dynamics, and noncovalent interactions in homo- and heterogeneous systems. Particular attention is paid to the characterization of porous materials and solids containing phosphorus. 31P NMR of organometallic compounds has been used as an example of how theoretical calculations can help in deeper analysis of experimental data.
During acid attack on concrete structural components, a degraded layer develops whose properties as a protective barrier are decisive for durability. 29Si NMR spectroscopy and 27Al NMR spectroscopy ...were used with XRD to investigate the degraded layer on hardened cement paste exposed to HCl and H2SO4. The layer comprises an amorphous silica gel with framework silicates, geminate and single silanol groups in which Si is substituted by Al. Amorphous Al(OH)3 and Fe(OH)3 are present. The gel forms by polycondensation and cross-linking of C-A-S-H chains at AlO4 bridging tetrahedra. In the transition zone between the degraded layer and the undamaged material, portlandite dissolves and Ca is removed from the C-A-S-H phases maintaining their polymer structure at first. With HCl, monosulphate in the transition zone is converted into Friedel's salt and ettringite. With H2SO4, gypsum precipitates near the degradation front reducing the thickness of the transition zone and the rate of degradation.
The development of science has led to the emergence of many new modern materials, which also require more advanced tools for their characterization and analysis. NMR and MRI are certainly among such ...tools, also due to their continuous development, which has made them more powerful, versatile, and sensitive. With these advances, these two techniques have been able to address many open problems associated with the emergence of new materials.This reprint comprises a collection of advanced NMR and MRI techniques and methods, together with a demonstration of their application to the target materials for which they were designed and optimized. These are presented in 25 original, peer-reviewed articles for the Special Issue in the MDPI journal Molecules. The topics covered include MR methods in pharmaceutical research, NMR in cement research, MR methods in wood research, diffusion in materials, characterization of materials by NMR relaxometry, NMR spectroscopy of materials, and MRI of materials.
A variety of nuclear magnetic resonance (NMR) applications have been developed for structure-based drug discovery (SBDD). NMR provides many advantages over other methods, such as the ability to ...directly observe chemical compounds and target biomolecules, and to be used for ligand-based and protein-based approaches. NMR can also provide important information about the interactions in a protein-ligand complex, such as structure, dynamics, and affinity, even when the interaction is too weak to be detected by ELISA or fluorescence resonance energy transfer (FRET)-based high-throughput screening (HTS) or to be crystalized. In this study, we reviewed current NMR techniques. We focused on recent progress in NMR measurement and sample preparation techniques that have expanded the potential of NMR-based SBDD, such as fluorine NMR (
F-NMR) screening, structure modeling of weak complexes, and site-specific isotope labeling of challenging targets.
Lignin was isolated with subcritical water:ethanol:CO2 (Sub-CW) from biorefinery biomasses, such as giant reed (AD) and miscanthus (MG), with recovery yields about 30% on Klason lignin. Their ...structural composition assessed by IR and NMR techniques, as well as Derivatization Followed by Reductive Cleavage (DFRC/GC-MS). The 2D HSQC-NMR spectra elucidated that the Sub-CW extracts contained different lignin dimers and co-extracted carbohydrates. The DFRC/GC-MS revealed that syringyl molecules were more abundant in AD, while guaiacyl monomers were predominant in MG. Lignin residues were derivatized with phospholane to quantitatively estimate the amount of OH groups by 31P NMR, showing a marked predominance of aliphatic units for both lignins, due to the presence of either hydroxyls in lignin side-chain or residual carbohydrates. Lignin residues derivatized with phospholane allowed to record 31P-DOSY NMR spectra. AD-lignin showed a smaller diffusivity constant than for MG-substrate, possibly because of the larger content of disaccharides in MG lignin. We showed that the molecular composition of lignin isolated by the Sub-CW technique may differ depending on the type of biomass used for the extraction, suggesting a different industrial application of lignin from various biomass.
•Lignin from two energy crops by subcritical water was characterized at a molecular level.•2D HSQC NMR and GC/MS distinguished among phenolic monomers and dimers extracted.•Lignins showed different hydrodynamic radii, as assessed by 31P-DOSY NMR.•Lignins show similar amount of OH groups, except alkyl ones, as noted by 31P NMR.•Since their different composition, lignins may be used for different industrial applications.
The kraft process is the main process used for the production of chemical pulps. In this process, an efficient delignification is achieved, yielding bleachable grade pulps. In recent years, there has ...been interest in valorization of the dissolved lignins, prompted by the development of technically feasible processes to retrieve it from the black liquor. However, the structural-, functional-, and size-related heterogeneities of lignin present both analytical challenges and challenges in developing new applications. Hence, refining of the crude product is essential. Herein, advanced NMR characterization (13C NMR, APT/DEPT NMR, 31P NMR, HSQC, HMBC, HSQC-TOCSY) was applied to profile the detailed molecular structures of refined kraft lignins and unravel mechanistic insights on important lignin reactions during kraft pulping. From this structural analysis of the lignins, a model oligomer was synthesized and analyzed to provide support to the effect that a retro-aldol reaction in combination with radical recombination reactions play a significant role in the formation of the reconstituted fraction of kraft lignin. In this regard, a new type of linkage accounting for approximately 10% of the interunits in kraft lignin is reported.
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