State Nuclear Magnetic Resonance Spectroscopy Research Articles

Spectroscopic and theoretical investigation of Brønsted acid sites in amorphous mixed Zr-Si oxide nanoparticles

Mixed Zr-Si oxide nanoparticles were investigated to disclose the relation between the Brønsted acidity of these materials and the atomic composition of the particles. To this aim, we combined experimental structural characterizations via X-ray absorption and Solid State Nuclear Magnetic Resonance spectroscopies with Reactive Molecular Dynamics simulations and Quantum Chemistry calculations. Despite the materials’ complexity, we identified the surface hydrogens responsible for the Brønsted acidity by estimating the adsorption energy of pyridine on several topologically distinct hydroxyl groups. Among the investigated sites, the hydrogens connected to the oxygen atoms bridging surface Zr and Si atoms (i.e., Zr-O(H)-Si) exhibited the most marked Brønsted acidity. The agreement of all the employed techniques demonstrates how the proposed concerted characterization effectively elucidates these complex amorphous materials’ structure/properties relationships. These new insights allowed us to develop a material with exceptionally high Brønsted acid character that outperformed benchmark silica-alumina and sulfonated zirconia in the dehydrogenation reaction of 1-octanol to produce olefins.

Probing the Effect of Environments on the Stability of Ni2P Nanoparticle Electrocatalysts

Ni2P has been shown to be an effective catalyst for the hydrogen evolution reaction (HER), making it a promising replacement for Pt which is the current state of the art HER catalyst.1,2 H2 is a clean-energy critical fuel and chemical highlighted by the US Department of Energy’s “Hydrogen Shot,” which seeks to reduce “the cost of carbon-neutral hydrogen by 80% to $1 per 1 kg in 1 decade, highlighting the key role of hydrogen in implementing carbon-neutral solutions.”3 Ni2P is also a good or promising catalyst for other reactions, such as alcohol oxidation, hydrodesulfurization,4,5 nitrate reduction, and oxygen evolution reaction.6 However, Ni2P and other TMPs are susceptible to oxidation, which can lead to catalyst degradation and loss in certain conditions.7,8 Stability is an important part of catalysis, especially for achieving the goals of the Hydrogen Shot. Therefore, it is important to understand complex degradation mechanisms in order to better understand structure-activity relationships in these materials. In the present work, in situ Ni K-edge X-ray absorption spectroscopy (XAS) and ex situ P Kα and Kβ X-ray emission spectroscopy (XES) couple together to understand the degradation of Ni2P and show the effects of electrolyte pH, ligands, and air on Ni2P nanoparticles.5 nm Ni2P nanoparticles were synthesized by heating NiCl2 and tris(diethylamino)phosphine in oleylamine. The nanoparticles were drop cast onto carbon fiber paper electrodes and Si wafers or Au-coated wafers for P Kα and Kβ XES. Oleylamine ligands are removed by thermal annealing. Electrochemical experiments were conducted with a three-electrode cell using carbon fiber paper or Au-coated wafers deposited with Ni2P nanoparticles as working electrode, Ag/AgCl calibrated to the H2 redox couple as reference electrode, and graphite rod as counter electrode. P Kα and Kβ XES experiments were conducted inside a N2 glovebox to prevent unintentional air oxidation. Transmission-mode Ni K-edge XAS was conducted on a benchtop spectrometer.Upon exposure to air, as-synthesized Ni2P nanoparticles were studied via P Kα and Kβ XES. Results showed that the phosphide species converted to phosphate with analysis of intermediates well fit by a simple two-phase mixture. Phosphide:phosphate ratios were quantified using linear combination analysis, providing a powerful tool to analyze P speciation on various samples in an inert environment and with minimal loss of material, both advantages of this system over 31P magic angle spinning solid state nuclear magnetic resonance spectroscopy and X-ray photoelectron spectroscopy. Continued work looks at analyzing the effects of the ligand environment on the stability of nanoparticles in electrolytes spanning from acidic to basic pH. We hypothesize that ligands will significantly stabilize the nanoparticles against corrosion and that without ligands Ni2P readily converts to a nickel phosphate species upon exposure to electrolyte.References(1) Popczun, E. J.; McKone, J. R.; Read, C. G.; Biacchi, A. J.; Wiltrout, A. M.; Lewis, N. S.; Schaak, R. E. Nanostructured Nickel Phosphide as an Electrocatalyst for the Hydrogen Evolution Reaction. J. Am. Chem. Soc. 2013, 135 (25), 9267–9270. https://doi.org/10.1021/ja403440e.(2) Liu, P.; Rodriguez, J. A. Catalysts for Hydrogen Evolution from the [NiFe] Hydrogenase to the Ni2P(001) Surface: The Importance of Ensemble Effect. J. Am. Chem. Soc. 2005, 127 (42), 14871–14878. https://doi.org/10.1021/ja0540019.(3) Bullock, M.; More, K. Basic Energy Sciences Roundtable: Foundational Science for Carbon-Neutral Hydrogen Technologies (Report); DOESC Office of Basic Energy Sciences, 2022. https://doi.org/10.2172/1834317.(4) Layan Savithra, G. H.; Muthuswamy, E.; Bowker, R. H.; Carrillo, B. A.; Bussell, M. E.; Brock, S. L. Rational Design of Nickel Phosphide Hydrodesulfurization Catalysts: Controlling Particle Size and Preventing Sintering. Chem. Mater. 2013, 25 (6), 825–833. https://doi.org/10.1021/cm302680j.(5) Rodriguez, J. A.; Kim, J.-Y.; Hanson, J. C.; Sawhill, S. J.; Bussell, M. E. Physical and Chemical Properties of MoP, Ni2P, and MoNiP Hydrodesulfurization Catalysts: Time-Resolved X-Ray Diffraction, Density Functional, and Hydrodesulfurization Activity Studies. J. Phys. Chem. B 2003, 107 (26), 6276–6285. https://doi.org/10.1021/jp022639q.(6) Menezes, P. W.; Indra, A.; Das, C.; Walter, C.; Göbel, C.; Gutkin, V.; Schmeiβer, D.; Driess, M. Uncovering the Nature of Active Species of Nickel Phosphide Catalysts in High-Performance Electrochemical Overall Water Splitting. ACS Catal. 2017, 7 (1), 103–109. https://doi.org/10.1021/acscatal.6b02666.(7) Ha, D.-H.; Han, B.; Risch, M.; Giordano, L.; Yao, K. P. C.; Karayaylali, P.; Shao-Horn, Y. Activity and Stability of Cobalt Phosphides for Hydrogen Evolution upon Water Splitting. Nano Energy 2016, 29, 37–45. https://doi.org/10.1016/j.nanoen.2016.04.034.(8) Parra-Puerto, A.; Ng, K. L.; Fahy, K.; Goode, A. E.; Ryan, M. P.; Kucernak, A. Supported Transition Metal Phosphides: Activity Survey for HER, ORR, OER, and Corrosion Resistance in Acid and Alkaline Electrolytes. ACS Catal. 2019, 11515–11529. https://doi.org/10.1021/acscatal.9b03359.

Probing the Nature of Surface Hydrides by Deuterium Quadrupolar Parameters: A Case Study on Silica‐Supported Zirconium Hydrides

AbstractSupported metal hydrides are key reactive intermediates in various catalytic processes, such as hydrogenation and dehydrogenation, but are often challenging to characterize spectroscopically. Here, deuterium solid state nuclear magnetic resonance spectroscopy is used to understand the structure of the corresponding silica‐supported zirconium hydrides after H/D exchange as an illustrative example of supported metal hydrides, which have been shown to display notable reactivity towards small molecules (e. g., CO2 and N2O) and to activate both C−H and C−C bonds, hence their use in to the conversion of hydrocarbons (alkanes, polyolefins etc.)

Construction mechanism of gellan gum/chitosan/calcium ion multiple‐network hydrogel by self‐assembly strategy and its regulation

AbstractRecently, double‐network or multiple‐network hydrogel constructed by physical methods has been considered a green method to improve the comprehensive properties of biomass hydrogel. Herein, a novel physically cross‐linked hydrogel with multiple network of gellan gum/chitosan/calcium ion (GG–CS–Ca) was constructed by self‐assembly to accomplish the synergistic improvement of mechanical strength and uranium adsorption property compared to adsorbents GG–Ca and carboxymethyl konjac glucomannan/GG–Al originated from gellan gum previously prepared. Moreover, the driving mechanism of self‐assembly of GG–CS–Ca was deduced by 13C solid state nuclear magnetic resonance spectroscopy (13C‐SSNMR), rheological analysis, and phase transition analysis. The results indicated electrostatic interaction was dominant during the self‐assembly of GG–CS–Ca. The self‐assembly mechanism was also illustrated by investigating the x‐ray photoelectron spectrometer (XPS) combined with the analysis of the phase transition process. Comprehensively, the self‐assembly constructed GG–CS–Ca hydrogel network contained three kinds of network including the GG–CS network constructed by electrostatic action of protonated CS with negative charged GG, the GG–Ca network constructed by ionic cross‐linking of COO− in GG and Ca2+, and the GG network formed after the phase transformation of GG hot sol by cooling. It explored a new method for constructing biomass‐based physical hydrogels with both favorable mechanical strength and uranium adsorption capacity in uranium removal.Highlights A novel physically cross‐linked hydrogel (GG–CS–Ca) with multiple network was constructed by self‐assembly. The GG–CS–Ca hydrogel accomplished the synergistic improvement of mechanical strength and uranium adsorption properties. The self‐assembly mechanism of constructing the GG–CS–Ca hydrogel network contained three aspects. The electrostatic interaction was the dominant action during the self‐assembly of GG–CS–Ca.

Synthesis, characterization, and dissolution properties of Aceclofenac-isobutabolammonium salt

The solubility issues of Biological Classification System Class II drugs are a challenge for formulation, and salt formation is a potential solution. In this study, we report the synthesis and solid-state characterization of aceclofenac-isobutanolammonium (IBA) salt using 2-Amino-2-methyl propanol (AMP) as the potential counterion. Various techniques, including X-ray powder diffractometry, differential scanning calorimetry, thermogravimetry, solution state nuclear magnetic resonance spectroscopy and, infrared Fourier transform spectroscopy, were used for characterization. The in vitro dissolution study showed a significant increase in solubility and dissolution profile of the salt. The results suggest that aceclofenac-IBA salt has potential as a formulation strategy for enhancing the solubility and bioavailability of Class II drugs.

Ex vivo exposure to calcitonin or raloxifene improves mechanical properties of diseased bone through non-cell mediated mechanisms

Raloxifene (RAL) reduces clinical fracture risk despite modest effects on bone mass and density. This reduction in fracture risk may be due to improved material level-mechanical properties through a non-cell mediated increase in bone hydration. Synthetic salmon calcitonin (CAL) has also demonstrated efficacy in reducing fracture risk with only modest bone mass and density improvements. This study aimed to determine if CAL could modify healthy and diseased bone through cell-independent mechanisms that alter hydration similar to RAL.26-week-old male C57BL/6 mice induced with chronic kidney disease (CKD) beginning at 16 weeks of age via 0.2 % adenine-laced casein-based (0.9 % P, 0.6 % C) chow, and their non-CKD control littermates (Con), were utilized. Upon sacrifice, right femora were randomly assigned to the following ex vivo experimental groups: RAL (2 μM, n = 10 CKD, n = 10 Con), CAL (100 nM, n = 10 CKD, n = 10 Con), or Vehicle (VEH; n = 9 CKD, n = 9 Con). Bones were incubated in PBS + drug solution at 37 °C for 14 days using an established ex vivo soaking methodology. Cortical geometry (μCT) was used to confirm a CKD bone phenotype, including porosity and cortical thinning, at sacrifice. Femora were assessed for mechanical properties (3-point bending) and bone hydration (via solid state nuclear magnetic resonance spectroscopy with magic angle spinning (ssNMR)). Data were analyzed by two-tailed t-tests (μCT) or 2-way ANOVA for main effects of disease, treatment, and their interaction. Tukey's post hoc analyses followed a significant main effect of treatment to determine the source of the effect.Imaging confirmed a cortical phenotype reflective of CKD, including lower cortical thickness (p < 0.0001) and increased cortical porosity (p = 0.02) compared to Con. In addition, CKD resulted in weaker, less deformable bones. In CKD bones, ex vivo exposure to RAL or CAL improved total work (+120 % and +107 %, respectively; p < 0.05), post-yield work (+143 % and +133 %), total displacement (+197 % and +229 %), total strain (+225 % and +243 %), and toughness (+158 % and +119 %) vs. CKD VEH soaked bones. Ex vivo exposure to RAL or CAL did not impact any mechanical properties in Con bone. Matrix-bound water by ssNMR showed CAL treated bones had significantly higher bound water compared to VEH treated bones in both CKD and Con cohorts (p = 0.001 and p = 0.01, respectively). RAL positively modulated bound water in CKD bone compared to VEH (p = 0.002) but not in Con bone. There were no significant differences between bones soaked with CAL vs. RAL for any outcomes measured.RAL and CAL improve important post-yield properties and toughness in a non-cell mediated manner in CKD bone but not in Con bones. While RAL treated CKD bones had higher matrix-bound water content in line with previous reports, both Con and CKD bones exposed to CAL had higher matrix-bound water. Therapeutic modulation of water, specifically the bound water fraction, represents a novel approach to improving mechanical properties and potentially reducing fracture risk.

Thermal Stability of Na3–xV2(PO4)2F3–yOy: Influence of F– for O2– Substitution and Degradation Mechanisms

The Na-ion battery technology appears as a reliable, sustainable, and environmentally friendly alternative to the Li-ion one, especially for stationary energy storage. As for the Li-ion technology, the safety aspect is of high importance to ensure large-scale development. In this work, we studied the thermal stability and decomposition mechanisms of carbon-coated Na3V2(PO4)2F3 and two fluorine-rich phases belonging to the solid-solution Na3V3+2–yV4+y(PO4)2F3–yOy (y = 0.07 and y = 0.12), that family of compounds being often considered among the most promising positive electrode materials for Na-ion batteries. This study shows the good thermal stability of these polyanionic materials and reveals that a low O2– for F– substitution has a very limited effect on the thermal stability of fully reintercalated materials recovered in the discharged state of the battery, whereas it has a beneficial impact for highly deintercalated ones, obtained by in-depth charges. Furthermore, whatever the state of charge and the oxygen content in NaxV2(PO4)2F3–yOy (1 ≤ x ≤ 3 and y = 0, 0.07 and 0.12), the thermal degradation leads, quite unexpectedly, to the formation of crystalline Na3V3+2(PO4)2F3 in addition to an amorphous phase. The fluorination of the partial oxygen for fluorine substituted material was clearly demonstrated by X-ray diffraction (XRD) and solid state nuclear magnetic resonance spectroscopy (NMR) on materials recovered after differential scanning calorimetry (DSC) analyses. The formation of a fully sodiated crystalline phase from the thermal degradation of the material obtained in charged states of the battery, with or without the presence of electrolyte, was never reported before.

Mechanochemical synthesis of LAGP/PEG hybrid solid electrolyte: Investigation of surface structure and chemistry

The drive towards all solid state lithium ion batteries requires discovery of new methods for synthesis of true hybrid solid electrolytes in which organic and inorganic components are chemically associated to simultaneously maximize lithium ion conductivity and processability. Herein, the first mechanochemical milling synthesis of an ambient processable hybrid lithium aluminum germanium phosphate (Li1.5Al0.5Ge1.5(PO4)3)/polyethylene glycol (PEG) solid electrolyte is presented. Fourier transform infrared (FTIR) spectroscopy and thermogravimetric analysis (TGA) provide evidence that the mechanochemical milling procedure impels a condensation reaction between the ceramic and organic phases which produces a surface product, water. Solid state nuclear magnetic resonance (NMR) spectroscopy confirms that protons from the polymer or associated surface water product are in bonding proximity to the Q2 metaphosphate sites of the glassy phase of the ceramic. This work thus establishes the viability of mechanochemical milling as a synthetic pathway for a class of promising ambient processable hybrid electrolytes.

Effect of phosphorylation on the assembly of Hippo signaling regulatory complexes.

The Hippo pathway is an evolutionarily conserved signaling network that plays a crucial role in maintaining tissue homeostasis by regulating cell growth/proliferation, differentiation, and apoptosis in response to environmental stimuli. The Hippo pathway integrates a variety of cellular cues including cell contact/density, growth factors, oxidative stress, hormones, and metabolic conditions, to regulate the function of the transcriptional co-activator protein YAP (yes-associated protein) in humans, and its orthologue Yki (yorkie) in Drosophila. Many upstream signals regulate YAP activity by influencing YAP phosphorylation at S127 (S168 in Yki). Although it is understood that phosphorylation of YAP at S127 induces YAP-14-3-3 binding and subsequent cytoplasmic retention, little is known about how phosphorylation at S127 impacts YAP local structure or the assembly of Hippo signaling regulatory complexes. Here we use traditional biophysical techniques such as solution state nuclear magnetic resonance spectroscopy, circular dichroism spectroscopy, fluorescence spectroscopy, isothermal titration calorimetry, and size-exclusion chromatography multi-angle light scattering, to determine the structure, map the binding interface, and characterize the binding thermodynamics of pS127 YAP and Hippo pathway binding partner LATS1 (large tumor suppressor kinase 1).

Biophysical investigations of antimicrobial peptide mimics for mechanistic studies.

With a relentless rise in the growth of antimicrobial resistance, much attention is being focused on Antimicrobial peptides (AMP) and the development of AMP mimicking agents to combat this nefarious issue. However lesser reports come up with adequate reasoning behind the driving force of the membrane perturbing nature. Here, we shall be discussing the two branches of AMP mimics, peptoids and small molecules. Further, we explore the mode of action behind the antimicrobial properties displayed by the library of peptoids and small molecule mimics. To address this big challenge of understanding how the membrane active compound behaves, each of the compounds were introduced to the liposomes, mimicking the bacterial model membranes, and their interactions was recorded using solid state nuclear magnetic resonance spectroscopy. We observe that each of the mimics interact with the liposome as the global shape of the vesicles gets deformed. Also we observed a definite interaction with the fatty acyl chain as changes in order parameters were observed with respect to that of pure lipids. To develop a thorough understanding of the pore forming abilities of these compounds, a fluorescent dye release studies was executed using both bacterial and mammalian model membranes. The calcein dye release test revealed that the small molecule mimics undergo a cooperative effect. For the peptoids investigated, the extent of release could be correlated with their antimicrobial activity as well as the toxicity data.

Structural Studies of Expressed tIK, Anti-Inflammatory Peptide

Cytokine imbalance is one of the causes of inflammation. Inflammation has yet to be adequately treated without side effects. Therefore, we tried to develop a peptide drug with minimal side effects. Peptide drugs have the advantage of being bio-friendly and bio-specific. In a previous study, three peptides with anti-inflammatory activity were derived based on a truncated IK (tIK) protein, which was a fragment of the IK protein with anti-inflammatory effects. The objective of this study was to optimize the process of expressing, isolating, and purifying the three peptides using bacterial strains and describe the process. Circular dichroism and solution state nuclear magnetic resonance spectroscopy were performed on the final purified high-purity peptide and its secondary structure was also identified.

Synthesis, characterisation and optimisation of bulk molecularly imprinted polymers from nonsteroidal anti-inflammatory drugs

The scope of this study was to synthesise and characterise the multi-template molecularly imprinted polymer (MIP) and to use target compounds, naproxen, ibuprofen, diclofenac, fenoprofen and gemfibrozil as templates so as to achieve all maximum extraction efficiency for all compounds. These compounds are a class of nonsteroidal anti-inflammatory drugs (NSAIDs) generally used by humans, as they have pain-relieving activities. MlPs are cross-linked polymeric materials that display high binding capacity and selectivity towards templates of interest. The synthesis consisted of a bulk polymerisation process at 60 °C by using NSAIDs as multi-templates, ethylene glycol dimethacrylate (EGDMA), 2-vinyl pyridine (2VP) and toluene as cross-linker, functional monomer and porogen, respectively. Nonimprinted polymer (NIP) was synthesised in a similar manner with the omission of the templates. Characteristics of the polymers were analysed using Scanning Electron Microscopy (SEM), Fourier Transformed Infrared Spectroscopy (FTIR), Solid State Nuclear Magnetic Resonance Spectroscopy (NMR) and Thermal Gravimetric Analysis (TGA). An adsorption method of NSAIDs using the bulk polymerised MIP was investigated under various pH, mass, concentration and time conditions. Other parameters included adsorption kinetics and adsorption isotherms. Uptake of NSAIDs from an aqueous medium was achieved with 40 mg of MIP at pH 4.0 within 10 min of contact time. The extraction efficiencies achieved for NSAIDs in aqueous solutions ranged from 90-98% for all compounds tested. The adsorption capacity obtained for MIP ranged from 1.230-1.249 mg g-1 and 0.90-1.136 mg g-1 for NIP, whereas the selectivity values ranged from 1.12-2.4. A kinetic study revealed that adsorption obeys a second-order rate, and the Langmuir model explains adsorption isotherm data. This work showed that the multi-template approach for all the target compounds has the potential to give maximum extraction efficiencies in MIP extraction systems from aqueous samples.

Physicochemical characterisation of barley straw treated with sodium hydroxide or urea and its digestibility and in vitro fermentability in ruminants

The development of strategies to overcome the shortage of forage due to persistently low rainfall is becoming a central task for animal nutrition in research and practice. In this study, it was investigated how the treatment of straw with NaOH or feed urea in a practicable procedure for modern farms affects rumen fermentation (gas production and greenhouse gas concentration) as well as the digestibility of feed energy and nutrients. For this purpose, the treatments were tested individually and in different proportions in a total mixed ration (TMR) in ruminal batch cultures in vitro and in a digestibility trial with sheep. In order to explain the observed effects at the molecular level, descriptive data from 13C solid state nuclear magnetic resonance (NMR) and Fourier-transform infrared (FTIR) spectroscopy were obtained. NaOH treatment of straw increased crude ash (CA), non-fibrous carbohydrates, digestible energy (DE), and metabolizable energy (ME) concentration, whereas the proportion of neutral detergent fibre (aNDFom) and hemicellulose decreased. In urea treated straw, NH3–N and crude protein increased, whereas acid detergent lignin (ADL), DE, and ME decreased. The physically effective fibre (peNDF8) concentration increased in TMR containing 18% of NaOH or urea treated straw (p < 0.01). The application of straw treatments as pure substrates (not as part of a TMR) increased gas production and decelerated ruminal fermentation (p < 0.05). In vitro organic matter digestibility (IVOMD) of the straw (0.31) increased after NaOH (0.51; p < 0.05) and urea treatment (0.41; p > 0.05). As part of a TMR, straw treatments had no distinct effect on gas production or IVOMD. Concentrations of CH4 and CO2 were likewise not affected. Apparent total tract digestibility of aNDFom, acid detergent fibre (ADFom), hemicellulose, and cellulose increased in the TMR by approximately 10% points following NaOH treatment (p < 0.05). The inclusion of urea treated straw did not affect apparent digestibility. Calculated true digestibility of aNDFom was 0.68, 0.74, and 0.79, of ADFom 0.58, 0.57, and 0.65, and of ADL 0.02, 0.13, and 0.08 in TMR including untreated, NaOH treated, and urea treated straw, respectively. 13C NMR and FTIR analyses consistently revealed that the global structure and crystallinity of the carbohydrates (cellulose and hemicellulose) was not altered by treatment and the concentration of lignin was likewise not affected. Depolymerisation of lignin did not occur. However, NMR signals assigned to acetyl groups were significantly altered indicating that straw treatments disrupted linkages between hemicelluloses and lignin. Moreover, the acetates signal was affected. This signal can be assigned to linkages between ferulic acids and hemicelluloses (arabinoxylans). FTIR spectra of straw treatments mainly differed at a wavelength of 1730 cm−1 and 1240 cm−1. Disappearance of the 1730 cm−1 peak suggests removal of hemicelluloses or lignin related compounds by treatment. The disappearance of the lignin peak at 1240 cm−1 could be due to conjugated ketone (phenyl-carbonyl) removal or the removal of ferulic and p-coumaric acid acetyl groups. Both treatments are supposed to release fermentable cell wall components (hemicelluloses) from lignin-associated bonds and as a result, straw fibre can be better fermented in the rumen. This contributes to energy supply and increased fibre digestibility at least in the TMR that contained NaOH treated straw. The alkaline straw treatments probably induced a release of phenolics such as ferulic acid and p-coumaric acid, which can be metabolised in the gut and the liver and metabolites might be excreted with the urine. This could notably contribute to metabolic energy losses.

Transfer of phase coherence by the dipolar field in total correlation liquid state nuclear magnetic resonance spectroscopy.

In this work, it is shown that radio-frequency pulse trains designed for total correlation nuclear magnetic resonance spectroscopy can mediate inter-molecular transfer of phase coherence from one spin species to another by the dipolar field. In contrast to previous studies (where short pulses interleaved with long free precession delays were used), here the transverse component of the dipolar field plays an important role. The transfer is so efficient that signal intensities close to those of a single pulse experiment can be achieved. The results are rationalized by numerical simulations that take into account relaxation and diffusion.

Structure identification of binary (cyclic alcohol guests + methane) clathrate hydrates using Rietveld analysis with the direct space method

Herein, the alcohol inclusion and interactions occurring in binary (cyclobutanol + CH4), (cyclopentanol + CH4), and (cyclohexanol + CH4) clathrate hydrates were investigated using Rietveld analysis with the direct space method. The alcohol geometry in the hydrate cages of the binary-hydrates was examined using 13C solid–state nuclear magnetic resonance spectroscopy and density function theory calculations. Structural characterization of the binary-hydrates indicated that OH groups of the alcohols may interact with the host-framework via hydrogen-bonding. Additionally, the possibility of OH group incorporation of cyclic alcohols into the host framework should be conducted in the future.

Investigations on the Spin States of Two Mononuclear Iron(II) Complexes Based on N-Donor Tridentate Schiff Base Ligands Derived from Pyridine-2,6-Dicarboxaldehyde

Iron(II)-Schiff base complexes are a well-studied class of spin-crossover (SCO) active species due to their ability to interconvert between a paramagnetic high spin-state (HS, S = 2, 5T2) and a diamagnetic low spin-state (LS, S = 0, 1A1) by external stimuli under an appropriate ligand field. We have synthesized two mononuclear FeII complexes, viz., [Fe(L1)2](ClO4)2.CH3OH (1) and [Fe(L2)2](ClO4)2.2CH3CN (2), from two N6–coordinating tridentate Schiff bases derived from 2,6-bis[(benzylimino)methyl]pyridine. The complexes have been characterized by elemental analysis, electrospray ionization–mass spectrometry (ESI-MS), Fourier-transform infrared spectroscopy (FTIR), solution state nuclear magnetic resonance spectroscopy, 1H and 13C NMR (both theoretically and experimentally), single-crystal diffraction and magnetic susceptibility studies. The structural, spectroscopic and magnetic investigations revealed that 1 and 2 are with Fe–N6 distorted octahedral coordination geometry and remain locked in LS state throughout the measured temperature range from 5–350 K.

Dynamic heterogeneity and nanophase separation in rubber-toughened amine-cured highly cross-linked polymer networks

Solid state nuclear magnetic resonance (NMR) spectroscopy and small-to wide-angle X-ray scattering (SWAXS) methods were used to characterize the heterogeneous dynamics and polymer domain structure in rubber modified thermoset materials containing the diglycidyl ether of bisphenol A (DGEBA) epoxy resin and a mixture of Jeffamine reactive rubber and 4,4-diaminodicyclohexylmethane (PACM) amine curing agent. The polymer chain dynamics and morphologies as a function of the PACM/Jeffamine ratio were determined. Using dipolar-filtered NMR experiments, the resulting networks are shown to be composed of mobile and rigid regions that are separated on nanometer length scales, along with a dynamically immobilized interface region. Proton NMR spin diffusion experiments measured the dimensions of the mobile phase to range between 9 and 66 nm and varied with the relative PACM concentration. Solid state 13C magic angle spinning NMR experiments show that the highly mobile phase is composed entirely of the dynamically flexible polyether chains of the Jeffamine rubber, the immobilized interface region is a mixture of DGEBA, PACM, and the Jeffamine rubber, with the PACM cross-linked to DGEBA predominantly residing in the rigid phase. The SWAXS results showed compositional nanophase separation spanning the 11–77 nm range. These measurements of the nanoscale compositional and dynamic heterogeneity provide molecular level insight into the very broad and controllable glass transition temperature distributions observed for these highly cross-linked polymer networks.

The influence of poly(allylamine hydrochloride) hydrogel crosslinking density on its thermal and phosphate binding properties

Sevelamer hydrochloride (SH) or Renagel® is an effective phosphate binder prescribed to prevent the absorption of phosphate in end stage renal disease (ESRD) patients. The relationship between SH structure and binding capacity and affinity is very important and can be used in characterising the sensitivity of the hydrogel to binding conditions. Thus, a series of hydrogels were prepared by varying the amount of crosslinker, whilst the other hydrogel components were kept constant. Variation of this parameter influenced the hydrogel structure as shown by swelling data, differential scanning calorimetry and solid state nuclear magnetic resonance spectroscopy. The hydrogels’ physical characteristics were found to correlate with the number of phosphate binding sites and affinity obtained from the Langmuir–Freundlich Isotherm (L–FI) and affinity distribution spectra (AD). The hydrogels formed using lower amounts of crosslinker showed a slight increase in binding capacity but with lower affinity. However, the influence of the pH of the binding media on the binding parameters of sevelamer hydrochloride was significant. This is the first report on the use of AD spectra generated from L-FI binding parameters in hydrogels, which demonstrates the sensitivity of the affinity and binding site numbers to changes in hydrogel physical properties and the pH of the binding media.

Quantitative analysis of the strength generating C-S-H-phase in concrete by IR-spectroscopy

The C-S-H-phase is the most important strength generating phase in concrete and other cementitious materials. The analysis of C-S-H is therefore an important instrument of innovations in the field of concrete and its durability and sustainability. The quantification and insights in C-S-H are hindered by the predominantly amorphous structure of C-S-H. Only the time consuming and expensive solid state nuclear magnetic resonance spectroscopy (NMR) gives a chance to get results, but is restricted to model substances. A new technique, based on the cheap and widespread infrared-spectroscopy (IR) was developed. The quantitative analysis is based on the silicon content in the different structural units of C-S-H and a calibration with natural and synthetic materials with known silicon content in these units. The technique allows to investigate specimens from real structures. Specimens with quartz or limestone aggregate can be analyzed directly. In other cases the aggregates must be separated, for example with heavy liquid separation. Tests with different mortars showed a good correspondence of measured and expected values of C-S-H concentration.

Structure Determination of Microtubules and Pili: Past, Present, and Future Directions.

Historically proteins that form highly polymeric and filamentous assemblies have been notoriously difficult to study using high resolution structural techniques. This has been due to several factors that include structural heterogeneity, their large molecular mass, and available yields. However, over the past decade we are now seeing a major shift towards atomic resolution insight and the study of more complex heterogenous samples and in situ/ex vivo examination of multi-subunit complexes. Although supported by developments in solid state nuclear magnetic resonance spectroscopy (ssNMR) and computational approaches, this has primarily been due to advances in cryogenic electron microscopy (cryo-EM). The study of eukaryotic microtubules and bacterial pili are good examples, and in this review, we will give an overview of the technical innovations that have enabled this transition and highlight the advancements that have been made for these two systems. Looking to the future we will also describe systems that remain difficult to study and where further technical breakthroughs are required.