Liquid-state Nuclear Magnetic Resonance Research Articles

Solid Effect DNP in a Rapid-melt setup

Dynamic Nuclear Polarization (DNP) has become a key element in nuclear magnetic resonance (NMR). Recently, we developed a novel approach to DNP enhanced liquid-state NMR based on rapid melting of a solid hyperpolarized sample followed by ‘in situ’ liquid-state NMR detection. This method allows 1H detection with fast cycling options for signal averaging. In nonpolar solvents, doped with BDPA radicals, proton enhancement factors were achieved of up to 400. A short recycling delay of about 5s allows for a fast determination of the hyper-polarization dynamics as function of the microwave frequency and power. Here, we use the rapid melt dnp method to study the mechanisms for DNP in the solid phase in more detail. Solid Effect, Cross Effect, Solid Overhauser and Liquid-state (supercritical) Overhauser DNP enhancement can be observed in the same setup. In this paper, we concentrate on Solid Effect DNP observed with both homogeneous narrow line radicals such as BDPA and with wide line anisotropic nitroxide radicals such as TEMPOL. We find indications that BDPA protons play an important role in Solid Effect DNP with this radical. A simplified spin diffusion model for BDPA can give a semi-quantitative description of the enhancements as function of the microwave power and as function of the proton concentration in the solid solution. For aqueous frozen samples we observe a similar Solid Effect DNP enhancement, which is analyzed within the simplified spin diffusion model.

Multinuclear NMR spectroscopy for differentiation of molecular configurations and solvent properties between acetone and dimethyl sulfoxide

The differences in molecular configuration and solvent properties between acetone and dimethyl sulfoxide (DMSO) were investigated using the developed technique of 1H, 13C, 17O, and 1H self-diffusion liquid state nuclear magnetic resonance (NMR) spectroscopy. Acetone and DMSO samples in the forms of pure solution, ionic salt-added solution were used to deduce their active sites, relative dipole moments, dielectric constants, and charge separations. The NMR results suggest that acetone is a trigonal planar molecule with a polarized carbonyl double bond, whereas DMSO is a trigonal pyramidal-like molecule with a highly polarized S–O single bond. Both molecules use their oxygen atoms as the active sites to interact other molecules. These different molecular models explain the differences their physical and chemical properties between the two molecules and explain why DMSO is classified as an aprotic but highly dipolar solvent. The results are also in agreement with data obtained using X-ray diffraction, neutron diffraction, and theoretical calculations.

Characterizing mixed phosphonic acid ligand capping on CdSe/ZnS quantum dots using ligand exchange and NMR spectroscopy

The ligand capping of phosphonic acid functionalized CdSe/ZnS core-shell quantum dots (QDs) was investigated with a combination of solution and solid-state (31) P nuclear magnetic resonance (NMR) spectroscopy. Two phosphonic acid ligands were used in the synthesis of the QDs, tetradecylphosphonic acid and ethylphosphonic acid. Both alkyl phosphonic acids showed broad liquid and solid-state (31) P NMR resonances for the bound ligands, indicative of heterogeneous binding to the QD surface. In order to quantify the two ligand populations on the surface, ligand exchange facilitated by phenylphosphonic acid resulted in the displacement of the ethylphosphonic acid and tetradecylphosphonic acid and allowed for quantification of the free ligands using (31) P liquid-state NMR. After washing away the free ligand, two broad resonances were observed in the liquids' (31) P NMR corresponding to the alkyl and aromatic phosphonic acids. The washed samples were analyzed via solid-state (31) P NMR, which confirmed the ligand populations on the surface following the ligand exchange process. Copyright © 2015 John Wiley & Sons, Ltd.

(R)‐α‐trifluoromethylalanine containing short peptide in the inhibition of amyloid peptide fibrillation

The extracellular deposition of insoluble amyloid fibrils resulting from the aggregation of the amyloid-β (Aβ) is a pathological feature of neuronal loss in Alzheimer's disease (AD). Numerous small molecules have been reported to interfere with the process of Aβ aggregation. Compounds containing aromatic structures, hydrophobic amino acids and/or the α-aminoisobutyric acid (Aib) as β-sheet breaker elements have been reported to be effective inhibitors of Aβ aggregation. We synthesized two peptides, one containing the Aib amino acid and the other including its trifluoromethylated analog (R)-α-Trifluoromethylalanine ((R)-Tfm-Alanine) and we evaluated the impact of these peptides on Aβ amyloid formation. The compounds were tested by standard methods such as thioflavin-T fluorescence spectroscopy and transmission electron microscopy but also by circular dichroism, liquid state nuclear magnetic resonance (NMR) and NMR saturation transfer difference (STD) experiments to further characterize the effect of the two molecules on Aβ structure and on the kinetics of depletion of monomeric, soluble Aβ. Our results demonstrate that the peptide containing Aib reduces the quantity of aggregates containing β-sheet structure but slightly inhibits Aβ fibril formation, while the molecule including the trifluoromethyl (Tfm) group slows down the kinetics of Aβ fibril formation, delays the random coil to β-sheet structure transition and induces a change in the oligomerization pathway. These results suggest that the hydrophobic Tfm group has a better affinity with Aβ than the methyl groups of the Aib and that this Tfm group is effective and important in preventing the Aβ aggregation.

Rapid-melt Dynamic Nuclear Polarization

In recent years, Dynamic Nuclear Polarization (DNP) has re-emerged as a means to ameliorate the inherent problem of low sensitivity in nuclear magnetic resonance (NMR). Here, we present a novel approach to DNP enhanced liquid-state NMR based on rapid melting of a solid hyperpolarized sample followed by ‘in situ’ NMR detection. This method is applicable to small (10nl to 1μl) sized samples in a microfluidic setup. The method combines generic DNP enhancement in the solid state with the high sensitivity of stripline 1H NMR detection in the liquid state. Fast cycling facilitates options for signal averaging or 2D structural analysis. Preliminary tests show solid-state 1H enhancement factors of up to 500 for H2O/D2O/d6-glycerol samples doped with TEMPOL radicals. Fast paramagnetic relaxation with nitroxide radicals, In nonpolar solvents such as toluene, we find proton enhancement factors up to 400 with negligible relaxation losses in the liquid state, using commercially available BDPA radicals. A total recycling delay (including sample freezing, DNP polarization and melting) of about 5s can be used. The present setup allows for a fast determination of the hyper-polarization as function of the microwave frequency and power.Even at the relatively low field of 3.4T, the method of rapid melting DNP can facilitate the detection of small quantities of molecules in the picomole regime.

A new approach for molecular characterisation of sediments with Fourier transform ion cyclotron resonance mass spectrometry: Extraction optimisation

Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) can begin to tease apart the molecular character of sedimentary organic matter (SOM). We therefore tested five different solvents (aqueous base, CHCl3, MeOH, pyridine and water) for their ability to extract a representative fraction from two organic rich lacustrine sediments, Mangrove Lake, Bermuda (MLB) and Mud Lake, Florida (MLF). Following comparison using liquid state nuclear magnetic resonance spectroscopy (NMR) and negative ion mode electrospray ionization mass spectrometry (FTICRMS) we found that pyridine was the optimal solvent, extracting a more diverse (10–100× greater integration for carbonyl, amide and amine groups) and a larger number of peaks on average (1375–1450 vs. 380–1450). Comparison of the pyridine extracts between MLB, MLF and two organic poor sediments from the Mississippi River Delta and Bayou Grande (Pensacola, FL) showed that only 4.9% of the molecular formulae were common to all four and that unique formulae made up the highest proportion of the assignments. The use of pyridine for extracting immature (Holocene) SOM for FTICRMS analysis can therefore be widely applied to immature sediments and produce representative spectra.

Simultaneous recovery of organic and inorganic content of paper deinking residue through low-temperature microwave-assisted pyrolysis.

Significant amounts of paper deinking residue (DIR) has been and is still being generated from paper deinking processes, representing both an economic and environmental burden for recycled paper mills. Our research on low-temperature (<200 °C) microwave-assisted (MW-assisted) pyrolysis of DIR allows for simultaneously efficient fast separation and recovery of the organic and inorganic content of DIR at relatively low temperature and within 15 min. Our study is the first highly detailed account of the use low-temperature MW-assisted pyrolysis to effect this change. The obtained liquid and solid products were characterized by a variety of analytical techniques (e.g., attenuated total reflection infrared, gas chromatography-mass spectrometry, liquid-state nuclear magnetic resonance (NMR), X-ray diffraction, solid-state cross-polarization/magic-angle spinning (13)C NMR, and Bloch-decay (13)C NMR). The results reveal that the process efficiently separates the inorganic minerals as microwave residue (mainly calcite and kaolinite) from organic matter, and hence the microwave residue could be reused to produce new paper/cardboard products. The organic fraction bio-oil generated is energy-densified and rich in carbohydrates and is a potential source for valuable aromatic compounds.

Characterization of Alginates by Nuclear Magnetic Resonance (NMR) and Vibrational Spectroscopy (IR, NIR, Raman) in Combination with Chemometrics.

This chapter describes three different spectroscopic methods for structural characterization of the commercial important hydrocolloid alginate extracted from brown seaweed. The "golden" reference method for characterization of the alginate structure is (1)H liquid-state NMR of depolymerized alginate polymers using a stepwise hydrolysis. Having implemented this method, predictive and rapid non-destructive methods using vibrational spectroscopy and chemometrics can be developed. These methods can predict the M/G-ratio of the intact alginate powder with at least the same precision and accuracy as the reference method in a fraction of the time that is required to measure the alginate using the reference method. The chapter also demonstrates how solid-state (13)C CP/MAS NMR can be used to determine the M/G ratio on the intact sample by the use of multivariate chemometrics and how this method shares the characteristics of the solid-state non-destructive IR method rather than its liquid-state counterpart.

Experimental heat-bath cooling of spins

Algorithmic cooling (AC) is a method to purify quantum systems, such as ensembles of nuclear spins, or cold atoms in an optical lattice. When applied to spins, AC produces ensembles of highly polarized spins, which enhance the signal strength in nuclear magnetic resonance (NMR). According to this cooling approach, spin-half nuclei in a constant magnetic field are considered as bits, or more precisely quantum bits, in a known probability distribution. Algorithmic steps on these bits are then translated into specially designed NMR pulse sequences using common NMR quantum computation tools. The algorithmic cooling of spins is achieved by alternately combining reversible, entropy-preserving manipulations (borrowed from data compression algorithms) with selective reset, the transfer of entropy from selected spins to the environment. In theory, applying algorithmic cooling to sufficiently large spin systems may produce polarizations far beyond the limits due to conservation of Shannon entropy. Here, only selective reset steps are performed, hence we prefer to call this process “heat-bath” cooling, rather than algorithmic cooling. We experimentally implemented two consecutive steps of selective reset, thus transferring entropy from two selected spins to the environment. We performed such cooling experiments, with commercially available labeled molecules, on standard liquid-state NMR spectrometers. We report in particular on our original experiment, unpublished until now except on the arXiv (quant-ph/0511156) in 2005, which was, to the best of our knowledge, the world’s first experiment that yielded polarizations results that bypassed Shannon’s entropy-conservation bound, so that the entire spin-system was cooled.

Membrane lipids protected from oxidation by red wine tannins: a proton NMR study.

Dietary polyphenols widespread in vegetables and beverages like red wine and tea have been reported to possess antioxidant properties that could have positive effects on human health. In this study, we propose a new in situ and non-invasive method based on proton liquid-state nuclear magnetic resonance (NMR) to determine the antioxidant efficiency of red wine tannins on a twice-unsaturated phospholipid, 1,2-dilinoleoyl-sn-glycero-3-phosphocholine (DLiPC), embedded in a membrane model. Four tannins were studied: (+)-catechin (C), (-)-epicatechin (EC), (-)-epicatechin gallate (ECG), and (-)-epigallocatechin gallate (EGCG). The lipid degradation kinetics was determined by measuring the loss of the bis-allylic protons during oxidation induced by a radical initiator, 2,2'-Azobis(2-methylpropionamidine) dihydrochloride (AAPH). The antioxidant efficiency, i.e. the ability of tannins to slow down the lipid oxidation rate, was shown to be higher for galloylated tannins, ECG and EGCG. Furthermore, the mixture of four tannins was more efficient than the most effective tannin, EGCG, demonstrating a synergistic effect. To better understand the antioxidant action mechanism of polyphenols on lipid membranes, the tannin location was investigated by NMR and molecular dynamics. A correlation between antioxidant action of tannins and their location at the membrane interface (inserted at the glycerol backbone level) could thus be established.

Thermolytic Decomposition of Ethane 1,2-Diamineborane Investigated by Thermoanalytical Methods and in Situ Vibrational Spectroscopy

Ethane 1,2-diamineborane (BH3NH2CH2CH2NH2BH3, EDAB hereafter) samples have been synthesized by reacting ethylenediamine dihydrochloride with sodium borohydride in tetrahydrofuran solution. Structural and bonding properties of EDAB have been characterized by liquid-state nuclear magnetic resonance, X-ray powder diffraction, and vibrational spectroscopy (infrared and Raman). The thermolytic decomposition of EDAB has been investigated by means of combined thermogravimetry, differential thermal analysis, and mass spectrometry measurements, both under vacuum and inert gas flow conditions. These experiments allow the determination of the enthalpies and activation energies of two hydrogen desorption stages below 520 K as well as the yields and purity of the released gases. These results show that EDAB presents a thermal stability, both under vacuum and under inert gas flow, higher than that of its parent counterparts methylamine borane (BH3NH2CH3) and ammonia borane (BH3NH3). Contrary to those compounds, EDAB re...

Water-extractable organic matter and enzyme activity in three forest soils of the Mediterranean area

Soil enzyme activities mediate key ecosystem functions of degradation, transformation and carbon mineralization. The study of microbial activity and its relations with water-extractable organic matter (WEOM) can be crucial to understand the dynamics of soil organic carbon pool. We investigated FDA-hydrolytic, β-glucosidase, cellulase, o-diphenol oxidase activities in soils under Fagus sylvatica (beech), Quercus ilex (holm-oak) and Quercus cerris (turkey-oak) stands. We investigated WEOM by liquid-state nuclear magnetic resonance (NMR) spectroscopy, useful to highlight the major functionalities in this fraction of soil organic matter. The highest enzyme activities, on mass basis, were recorded in soil under beech, with the highest organic carbon content. Reporting enzyme activities on organic carbon basis, it was possible to reveal enzyme enrichment for β-glucosidase and diphenol oxidase activities in soil under turkey-oak, with low organic matter. The 1H NMR spectra of WEOM highlighted a great richness of soluble organic compounds in soils with high organic carbon content, such as beech and holm-oak soils. All spectra are dominated by carbohydrate resonances. Spectra of WEOM from each stand exhibited specific signals. In WEOM from holm-oak, signals from substituted aliphatics account for up 28% of the total spectrum; in this sample signals from acetic and formic acids predominate, likely relating to the lower microbial utilization, according to the low heterotrophic (FDA-hydrolytic) activity. Only in WEOM from beech, signals from aromatics were detected probably related to the lower lignin degradation in soil, as expressed by the low phenol oxidase activity. However, the relationships among WEOM quality, tree species and microbial activity need further investigations.

Efficient entanglement operator for a multi-qubit system

In liquid-state nuclear magnetic resonance quantum computation, a selective entanglement operator between qubits 2 and 3 of a three-qubit molecule is conventionally realized by applying a pair of short π-pulses to qubit 1. This method, called refocusing, is well suited to heteronuclear molecules. When the molecule is homonuclear, however, the π-pulses applied to qubit 1 often induce unwanted z-rotations on qubits 2 and 3, even if the z-components of qubits 2 and 3 are left unchanged. This phenomenon is known as the transient Bloch-Siegert effect, and compensation thereof is required for precise gate operation. We propose an alternative refocusing method, in which a weak square pulse is applied to qubit 1. This technique has the advantage of curbing the Bloch-Siegert effect, making it suitable for both hetero- and homonuclear molecules.

Sargassum filipendula alginate from Brazil: Seasonal influence and characteristics

The aim of this work is focused on the extraction and characterization of the Brazilian seaweed Sargassum filipendula alginate. Alginates obtained at different seasons were characterized by liquid state nuclear magnetic resonance spectroscopy and scanning electron microscopy. The alginate extraction efficiency was about 20%. Different seasons of the year and different stages in the life cycle of Sargassum sp. in southeastern Brazil influenced the M/G and, consequently, the technological properties of extracted alginates.

New challenges in structural biology: catching the complexity of dynamic nanomachines.

New challenges in structural biology: catching the complexity of dynamic nanomachines.

Thermoresponsive xylan hydrogels via copper-catalyzed azide-alkyne cycloaddition

In the present work, hydrogels of birch wood xylan and thermoresponsive poly(ethylene glycol)-b-poly(propylene glycol)-b-poly(ethylene glycol) (PEG-PPG-PEG) were prepared using copper catalyzed alkyne-azide cycloaddition (CuAAC) in aqueous reaction conditions. First, reactive azide groups were introduced on the backbone of xylan by etherification of 1-azido-2,3-epoxypropane in alkaline water/isopropanol-mixture at ambient temperature, providing degree of substitution (DS) values up to 0.28. On the second step, the azide groups were reacted with propargyl bifunctional PEG-PPG-PEG utilizing CuAAC, leading to formation of crosslinked hydrogels. The novel xylan derivatives were characterized with liquid and solid state nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared spectroscopy (FT-IR) and elemental analysis (EA). The temperature controlled swelling behavior of the developed hydrogels was evaluated in the range of 7–70°C by water absorption and compressive stress–strain measurements, which showed a reduction in water content and change in stiffness with increasing temperature. The morphology of the hydrogels at different temperatures was studied by scanning electron microscopy (SEM), which showed a reduction in pore size with increasing temperature.

Solid-state evaluation and polymorphic quantification of venlafaxine hydrochloride raw materials using the Rietveld method

Venlafaxine hydrochloride (VEN) is an antidepressant drug widely used for the treatment of depression. The purpose of this study was to carry out the preparation and solid state characterization of the pure polymorphs (Forms 1 and 2) and the polymorphic identification and quantification of four commercially-available VEN raw materials. These two polymorphic forms were obtained from different crystallization methods and characterized by X-ray Powder Diffraction (XRPD), Diffuse Reflectance Infrared Fourier Transform (DRIFT), Raman Spectroscopy (RS), liquid and solid state Nuclear Magnetic Resonance (NMR and ssNMR) spectroscopies, Differential Scanning Calorimetry (DSC), and Scanning Electron Microscopy (SEM) techniques. The main differences were observed by DSC and XRPD and the latter was chosen as the standard technique for the identification and quantification studies in combination with the Rietveld method for the commercial raw materials (VEN1-VEN4) acquired from different manufacturers. Additionally Form 1 and Form 2 can be clearly distinguished from their (13)C ssNMR spectra. Through the analysis, it was possible to conclude that VEN1 and VEN2 were composed only of Form 1, while VEN3 and VEN4 were a mixture of Forms 1 and 2. Additionally, the Rietveld refinement was successfully applied to quantify the polymorphic ratio for VEN3 and VEN4.

Multidiagnostic analysis of silicate speciation in clear solutions/sols for zeolite synthesis

The formation of zeolites in presence of tetraalkylammonium cations from so-called clear solutions using silicon alkoxides is a highly complex process which challenges experimental chemistry. Most clear solutions are better described as clear sols as they contain nanosized silicate particles, which are formed during hydrolysis of the Si source before self-assembly into the zeolite framework. This process spans multiple time- and length-scales and only a combination of different analysis methods allows revelation of molecular level zeolite formation mechanisms. On the example of the early stages of the formation of zeolite beta from clear solutions/sols the different windows of observation of liquid-state 29Si and 27Al nuclear magnetic resonance (NMR) spectroscopy, small angle X-ray scattering (SAXS), dynamic light scattering (DLS) and mass spectrometry (MS) are demonstrated. Each diagnostic means by itself needs to be carefully assessed for its window of temporal and spatial resolution which can be achieved by exploiting the overlapping information available from their combination.

Identification of a New Interaction Mode between the Src Homology 2 Domain of C-terminal Src Kinase (Csk) and Csk-binding Protein/Phosphoprotein Associated with Glycosphingolipid Microdomains

Proteins with Src homology 2 (SH2) domains play major roles in tyrosine kinase signaling. Structures of many SH2 domains have been studied, and the regions involved in their interactions with ligands have been elucidated. However, these analyses have been performed using short peptides consisting of phosphotyrosine followed by a few amino acids, which are described as the canonical recognition sites. Here, we report the solution structure of the SH2 domain of C-terminal Src kinase (Csk) in complex with a longer phosphopeptide from the Csk-binding protein (Cbp). This structure, together with biochemical experiments, revealed the existence of a novel binding region in addition to the canonical phosphotyrosine 314-binding site of Cbp. Mutational analysis of this second region in cells showed that both canonical and novel binding sites are required for tumor suppression through the Cbp-Csk interaction. Furthermore, the data indicate an allosteric connection between Cbp binding and Csk activation that arises from residues in the βB/βC loop of the SH2 domain.

Measuring bipartite quantum correlations of an unknown state.

We report the experimental measurement of bipartite quantum correlations of an unknown two-qubit state. Using a liquid state Nuclear Magnetic Resonance setup and employing geometric discord, we evaluate the quantum correlations of a state without resorting to prior knowledge of its density matrix. The method is applicable to any 2 ⊗ d system and provides, in terms of number of measurements required, an advantage over full state tomography scaling with the dimension d of the unmeasured subsystem. The negativity of quantumness is measured as well for reference. We also observe the phenomenon of sudden transition of quantum correlations when local phase and amplitude damping channels are applied to the state.