State Nuclear Magnetic Resonance Spectroscopy Research Articles

A Spectroscopic Marker for Structural Transitions Associated with Amyloid-β Aggregation.

An amyloid aggregate evolves through a series of intermediates that have different secondary structures and intra- and intermolecular contacts. The structural parameters of these intermediates are important determinants of their toxicity. For example, the early oligomeric species of the amyloid-β (Aβ) peptide have been implicated as the most cytotoxic species in Alzheimer's disease but are difficult to identify because of their dynamic and transitory nature. Conventional aggregation monitors such as the fluorescent dye thioflavin T report on only the overall transition of the soluble species to the final amyloid fibrillar aggregated state. Here, we show that the fluorescent dye bis(triphenylphosphonium) tetraphenylethene (TPE-TPP) identifies at least three distinct aggregation intermediates of Aβ. Some atomic-level features of these intermediates are known from solid state nuclear magnetic resonance spectroscopy. Hence, the TPE-TPP fluorescence data may be interpreted in terms of these Aβ structural transitions. Steady state fluorescence and lifetime characteristics of TPE-TPP distinguish between the small oligomeric species (emission wavelength maximum, λmax = 465 nm; average fluorescence lifetime, τFl measured at 420 nm = 3.58 ± 0.04 ns), the intermediate species (λmax = 452 nm; τFl = 3.00 ± 0.03 ns), and the fibrils (λmax = 406 nm; τFl = 5.19 ± 0.08 ns). Thus, TPE-TPP provides a ready diagnostic for differentiating between the various, including the toxic, Aβ aggregates and potentially can be utilized to screen for amyloid aggregation inhibitors.

Preparation and characterization of glimepiride eutectic mixture with l-arginine for improvement of dissolution rate.

In this study, glimepiride and l-arginine (GA) binary mixtures at various molar ratios were prepared to evaluate whether they could improve the poor water solubility and dissolution characteristics of glimepiride. It was shown that glimepiride and arginine form a eutectic mixture, a type of crystalline solid dispersions, at a 1:1M ratio and eutectic temperature of 426.9K using a phase diagram constructed using differential scanning calorimetry (DSC) and thermo-microscopy. The preserved characteristic powder X-ray diffraction (PXRD) patterns and infrared (IR) spectra of each material in those of GA binary mixtures confirmed the formation of eutectic mixture without molecular interaction in solid state. The formation of GA eutectic mixture (GAEM) resulted in the improvement of solubility through pH modification and the intermolecular interaction of glimepiride and l-arginine in aqueous mediums, thereby wettability and dissolution rate of glimepiride were also enhanced. The intermolecular interaction between glimepiride and l-arginine at a 1:1 stoichiometry of the complex in solution state was identified by phase solubility, stoichiometric determination, and solution state nuclear magnetic resonance (NMR) spectroscopy. Specific molecular interactions such as hydrogen bonding and hydrophobic interaction were suggested as main mechanisms of GA complexation in solution. Therefore, this study concludes that the GAEM could be an effective way to improve the solubility and dissolution rate of glimepiride.

Construction of physically crosslinked chitosan/sodium alginate/calcium ion double-network hydrogel and its application to heavy metal ions removal

Abstract Chemical hydrogels have been extensively applied to the removal of heavy metal pollutants. However, most of chemical hydrogels inevitably contain toxic chemical crosslinker residues, which impose serious threats on the environment. Herein, a novel eco-friendly physically-crosslinked double-network hydrogel of chitosan/sodium alginate/calcium ion (CTS/SA/Ca2+ PCDNH) was prepared by the combination of the semi-dissolution acidification sol–gel transition method with the internal gelation method. The PCDNH is formed via the physical crosslinking of sustainable biopolymers, which avoids the excessive use of toxic chemical reagents. In addition, the PCDNH exhibits significantly better mechanical properties than the single-network physical hydrogel crosslinked via electrostatic interactions, which overcomes the weak mechanical properties of physical hydrogels. The formation mechanism and structure of the hydrogel were determined by Fourier-transform infrared spectroscopy (FTIR), 13C solid state nuclear magnetic resonance spectroscopy (13C-SSNMR) and scanning electron microscopy (SEM). The heavy metal ions adsorption mechanism was explored by X-ray photoelectron spectroscopy (XPS) analysis. The adsorption kinetics, isotherms and thermodynamics were further studied to understand the adsorption mechanism. Our work has provided a new method for the fabrication of natural polymers-based eco-friendly, low-cost and robust physical hydrogels for the heavy metal ions removal.

Amido-amine derivative of alginic acid (AmAA) for enhanced adsorption of Pb(II) from aqueous solution

The present work reports the alternate synthesis of amido-amine derivative of alginic acid (AmAA) with high degree of functionalization. The AmAA have been characterized for percentage functionalization, functional group change, surface morphology and thermal decomposition behavior. The results indicate that the amido-amine derivatisation of alginic acid (AA) with >95% functionalization, significantly improves its Pb(II) adsorption efficiency (395.72 mg/g to 535.87 mg/g) over the AA. The equilibrium and kinetic studies showed that Langmuir and Freundlich adsorption isotherm models fitted well to the experimental data, and these followed pseudo-second order kinetic model. The FTIR (Fourier transform infrared spectroscopy) and 13C CP-MAS NMR (Cross-polarization magic angle spinning carbon-13 solid state nuclear magnetic resonance spectroscopy) analysis revealed that Pb(II) binds to the carboxyl group in case of AA and to the carbonyl & amine group in case of AmAA, which leads to increase in its adsorption efficiency. The study concludes that the functionalization of amido-amine on AA improves its adsorptive efficiency for Pb(II) from aqueous medium.

Side Chain Hydrogen-Bonding Interactions within Amyloid-like Fibrils Formed by the Low-Complexity Domain of FUS: Evidence from Solid State Nuclear Magnetic Resonance Spectroscopy.

In aqueous solutions, the 214-residue low-complexity domain of the FUS protein (FUS-LC) is known to undergo liquid-liquid phase separation and also to self-assemble into amyloid-like fibrils. In previous work based on solid state nuclear magnetic resonance (ssNMR) methods, a structural model for the FUS-LC fibril core was developed, showing that residues 39-95 form the fibril core. Unlike fibrils formed by amyloid-β peptides, α-synuclein, and other amyloid-forming proteins, the FUS-LC core is largely devoid of purely hydrophobic amino acid side chains. Instead, the core-forming segment contains numerous hydroxyl-bearing residues, including 18 serines, six threonines, and eight tyrosines, suggesting that the FUS-LC fibril structure may be stabilized in part by inter-residue hydrogen bonds among side chain hydroxyl groups. Here we describe ssNMR measurements, performed on 2H,15N,13C-labeled FUS-LC fibrils, that provide new information about the interactions of hydroxyl-bearing residues with one another and with water. The ssNMR data support the involvement of specific serine, threonine, and tyrosine residues in hydrogen-bonding interactions. The data also reveal differences in hydrogen exchange rates with water for different side chain hydroxyl groups, providing information about solvent exposure and penetration of water into the FUS-LC fibril core.

Non thermal plasma in liquid media: Effect on inulin depolymerization and functionalization

We report the complete conversion of inulin in gas/liquid media by a dielectric barrier discharge plasma at atmospheric pressure. Depending on the plasma treatment time (from 1 to 30 min) and the chemical nature of the gases (air, oxygen, nitrogen), it was possible to depolymerize inulin into fructo-oligosaccharides with a degree of polymerization under 5 or to achieve a total conversion of inulin into its two monomeric constituents, fructose and glucose in 20 min, without any degradation products. Combined results from liquid chromatography (HPLC), solid state Nuclear Magnetic Resonance (ssNMR) and mass spectroscopy revealed that the breakage of the β 1-4-bridged oxygen occurs by an acidic attack, following the oxidation of the polymer. Infrared spectroscopy revealed the oxidation and breakage of the polymer and also adsorption of nitrate species. Non thermal plasma treatment appears as a promising technology for the efficient production of mono and oligosaccharides from various sources for the added value molecules in food and pharmaceutical application domains.

Nanostructural evolution of alkali-activated mineral wools

Mineral wools are the most widely used building insulation material worldwide. Annually, 2.5 million tonnes of mineral wool waste are generated in the EU alone, and this is a largely unutilised material that is landfilled or incinerated. However, mineral wool wastes are promising precursors for production of alkali-activated cementitious binders due to their favourable chemical and mineralogical composition and high surface area. Alkali-activation is therefore a valuable route for valorisation of large quantities of mineral wool waste. This study resolves the phase assemblage and nanostructure of reaction products formed upon alkali activation of stone wool and glass wool by sodium hydroxide and sodium silicate solutions with X-ray diffraction, electron microscopy and solid state nuclear magnetic resonance spectroscopy experiments probing 27Al and 29Si. The stone wool-based alkali-activated binder comprises an amorphous sodium- and aluminium-substituted calcium silicate hydrate (C-(N-)A-S-H) gel, an amorphous sodium aluminosilicate hydrate (N-A-S-H) gel and small amounts of the layered double hydroxide phase quintinite and zeolite F. The glass wool-based alkali-activated binder comprises an amorphous Ca- and Al-substituted sodium silicate (N-(C-)(A-)S–H) gel. Gel chemical composition and reaction kinetics of alkali-activated mineral wools are shown to be dependent on the activating solution chemistry, with reaction rate and extent promoted by inclusion of a source of soluble Si in the reaction mixture. This work provides the most advanced description of the chemistry and structure of alkali-activated mineral wools to date, yielding new insight that is essential in developing valorisation pathways for mineral wools by alkali activation and providing significant impetus for development of sustainable construction materials.

Bimetallic Mo-Co/ZSM-5 and Mo-Ni/ZSM-5 catalysts for methane dehydroaromatization: A study of the effect of pretreatment and metal loadings on the catalytic behavior

Methane dehydroaromatization is studied using different loadings (0.2 wt%, 0.6 and 1 wt%) of Co and Ni additives on a 6 wt% Mo/ZSM-5 catalyst to evaluate the promoting effect of Ni and Co on reactivity and stability of the catalysts. A synergy between Mo and the additives is observed when combining a reduction/carburization pretreatment with an optimum additive loading: benzene yield and catalytic stability are both improved. The fresh and spent samples were characterized by X-Ray Diffraction, 27Al Magic-Angle Spinning Solid State Nuclear Magnetic Resonance Spectroscopy, Temperature-Programmed Reduction and Thermogravimetric Analysis. The results suggest that catalytic enhancement in precarburized Mo-Co and Mo-Ni samples is due to a combination of effects: extraction of Al from the ZSM-5 framework to form inactive Al2(MoO4)3 is reduced, interaction of Mo with the additives enhances the retention of Mo species within the zeolite channels, prevents Mo aggregation in reaction and modifies the reducibility of the Mo sites.

A supramolecular interaction strategy enabling high-performance all solid state electrolyte of lithium metal batteries

In general, solid polymer electrolyte suffers from relatively low ionic conductivity and inferior oxidation stability. Herein, these issues can be effectively addressed by a supramolecular strategy based on the intermolecular interaction between a novel amorphous comb polymer of poly[propylene oxide-co-2-(2-methoxyethoxy)ethyl glycidyl ether] [P(PO/EM)] and highly fluorinated anion based lithium salt of lithium trifluoro(perfluoro-tert-butyloxyl)borate (LiTFPFB). The supramolecular solid state polymer electrolyte exhibits superior lithium ion transference number (0.59). It is noted that this polymer electrolyte presents enlarged electrochemical window up to 4.6 V (vs. Li/Li+ at 70 °C), which is resulted from the powerful supramolecular interaction between polymer skeleton and lithium salt. The supramolecular interaction was confirmed by Fourier transform infrared spectroscopy (FT-IR) analysis, solid state nuclear magnetic resonance (NMR) spectroscopy, stripping and self-healing tests. More bracingly, high voltage LiFe0.2Mn0.8PO4/Li cell based on this polymer electrolyte exhibits improved cycling performance (capacity retention is 88.7% after 100 cycles at 0.1C). Meanwhile, this well-designed electrolyte endows LiFe0.2Mn0.8PO4/Li cell pouch cell excellent safety characteristic even under deformation and truncation procedures. This supramolecular strategy paves a new way for boosting high energy density all solid state lithium metal batteries.

Understanding kinetics and thermodynamics of the interactions between amitriptyline or eosin yellow and aminosilane-modified cellulose

A new adsorbent matrix (Cel-SiN) for the adsorption of the dye eosin yellow (EY) and the drug amitriptyline (AMI) from aqueous media has been synthesized. The Cel-SiN matrix was obtained via chemical modification of cellulose with (3-aminopropyl)trimethoxysilane. Successful modification was confirmed using Fourier transform infrared (FTIR) and 13C and 29Si solid state nuclear magnetic resonance (SSNMR) spectroscopies, thermal analysis (TG/DTG), X-ray diffraction (XRD), and elemental analysis. The effects of pH, contact time, concentration, and temperature were evaluated in batch adsorption tests. Cel-SiN efficiently adsorbed AMI and EY in aqueous media, with maximum adsorption capacities of 92.28 ± 1.34 mg g−1 for AMI (pH = 7, time =240 min, and temperature = 318 K) and 61.0 ± 0.36 mg g−1 for EY (pH = 5, time =80 min, and temperature = 298 K). The adsorption process occurs mainly via hydrogen bonding interactions for AMI and electrostatic interactions for EY.

The Study of Composite Artificial-SEI for Lithium Metal Anodes

The strive for higher energy density for rechargeable lithium batteries has created a renaissance of interest in lithium-metal anodes. Yet, lithium metal secondary batteries are disadvantaged by multiple safety issues rendering this class of batteries potentially unsafe and impractical owing to the risk of thermal runaway. The Solid-Electrolyte-Interphase (SEI) is the key factor which determines the performance and safety of lithium metal battery. The layer, formed instantaneously upon contact of the metal with the electrolyte, consists of reduction products of electrolyte components. It serves as an interphase between the metal and the electrolyte and has the properties of a solid electrolyte. It was found that ionic migration through the SEI is the rate-determining step for many battery systems, including the lithium metal batteries. [1] It has been widely demonstrated in the literature that non-homogeneous SEI composition and morphology initiate uneven plating and stripping of lithium metal anode, resulting in dendritic short circuits. Moreover, the volume and morphology changes of the metal create stress in the SEI which increases the risk of capacity loss and safety issues due to formation of preferential sites for dendrite formation. The main goal of the formation of an artificial-SEI on the lithium-metal anode, is to overcome these risks. So far, most of the research on an artificial SEI was focused on preventing of the natural SEI formation and has used either single-component coating or sacrificial SEI-forming additive to the electrolyte. [1,2], Here we present an alternative approach – the formation of pre-designed composite artificial SEI to facilitate improved natural SEI. The increase of the homogeneity of the current distribution on the anode surface is expected to hinder the formation of dendrites. The study includes the effect of the chemical composition of the artificial SEI on the structure, composition and performance of the natural SEI, morphology of the plated lithium metal, faradaic efficiency, lithium ion conduction mechanisms and the performance of the modified lithium metal anode. The study is conducted via two major routes: Solid state Nuclear Magnetic Resonance (ssNMR) spectroscopy and electrochemical characterization. A combined investigation of 1H, 7Li, 19F, and 13C ssNMR is used for the study of the composition, formation and lithium conduction mechanisms of the SEI. [3,4] The combination of impedance spectroscopy, cyclic voltammetry, chronopotentiometry and battery cycling techniques facilitates the study of SEI formation, lithium metal cycling and the development artificial SEI for practical lithium metal batteries. The successful development of an artificial SEI on lithium metal will promote the safe operation of high energy and power lithium-anode batteries and facilitate the use of cleaner energy for transportation, grid leveling and mobile devices. [1] E. Peled and S. Menkin, SEI- Past, Present and Future, J. Electrochem. Soc. 2017 volume 164, issue 7, A1703-A1719 [2] S.Menkin, D.Golodnitsky, E.Peled, Artificial solid-electrolyte interphase (SEI) for improved cycleability and safety of lithium-ion cells for EV applications, Electrochemistry Communications, 2009 11, 9, 1789-1791 [3] R.Bhattacharyya, B.Key, H.Chen, A.S. Best, A. F. Hollenkamp, and C.P. Grey, In situ NMR Observation of the Formation of Metallic Lithium Microstructures in Lithium Batteries, NATURE MATERIALS VOL 9 JUNE 2010 [4] O.Pecher, J.Carretero-González, K.J. Griffith, and Clare P. Grey, Materials’ Methods: NMR in Battery Research, Chem. Mater. 2017, 29, 213−242

Eumelanin Graphene-Like Integration: The Impact on Physical Properties and Electrical Conductivity.

The recent development of eumelanin pigment-based blends integrating “classical” organic conducting materials is expanding the scope of eumelanin in bioelectronics. Beyond the achievement of high conductivity level, another major goal lays in the knowledge and feasible control of structure/properties relationship. We systematically investigated different hybrid materials prepared by in situ polymerization of the eumelanin precursor 5,6-dihydroxyindole (DHI) in presence of various amounts of graphene-like layers. Spectroscopic studies performed by solid state nuclear magnetic resonance (ss-NMR), x-ray photoemission, and absorption spectroscopies gave a strong indication of the direct impact that the integration of graphene-like layers into the nascent polymerized DHI-based eumelanin has on the structural organization of the pigment itself, while infrared, and photoemission spectroscopies indicated the occurrence of negligible changes as concerns the chemical units. A tighter packing of the constituent units could represent a strong factor responsible for the observed improved electrical conductivity of the hybrid materials, and could be possible exploited as a tool for electrical conductivity tuning.

High-Resolution 17O NMR Spectroscopy of Structural Water.

The importance of studying site-specific interactions of structurally similar water molecules in complex systems is well known. We demonstrate the ability to resolve four distinct bound water environments within the crystal structure of lanthanum magnesium nitrate hydrate via 17O solid state nuclear magnetic resonance (NMR) spectroscopy. Using high-resolution multidimensional experiments at high magnetic fields (18.8-35.2 T), each individual water environment was resolved. The quadrupole coupling constants and asymmetry parameters of the 17O of each water were determined to be between 6.6 and 7.1 MHz, 0.83 and 0.90, respectively. The resolution of the four unique, yet similar, structural waters within a hydrated crystal via 17O NMR spectroscopy demonstrates the ability to decipher the unique electronic environment of structural water within a single hydrated crystal structure.

Tunable ionization degree in cationic polyurethanes and effects on phase separation

A linear non-ionic hard-soft segmented polyurethane (PU0) was prepared by the prepolymer synthesis method. The isocyanate terminated prepolymer, formed by a short and rigid aromatic diisocyanate and a long flexible poly(tetramethylene oxide) (PTMO), was chain extended with a piperazine (PIP) diol derivative. The non-ionic polyurethane was then ionized by a post-modification method, i.e. alkylation of the piperazine nitrogen atoms, thus obtaining cationomers with three different ionization degrees, named PU10, PU50, PU80. The polymers were characterized by means of FT-IR spectroscopy, solution and solid state Nuclear Magnetic Resonance (NMR) spectroscopies, Differential Scanning Calorimetry (DSC) and ThermoGravimetric Analysis (TGA). The chemical structure of the obtained polymers and their cationic content was confirmed by solution state 1H NMR. It was found that the methylation occurs quantitatively up to 50% of the PIP nitrogen atoms and that, even if a large excess of methylating agent is used, in our operating conditions a maximum of 80% of the PIP nitrogen atoms are ionized. All the characterization techniques used suggested that an increasing ionization degree induces a better phase separation between hard and soft domains, with a lower amount of diisocyanate units dispersed in the soft phase. In particular, FT-IR showed that the introduction of ionic sites modifies the hydrogen bond network and induces a better aggregation of the rigid units. In addition, DSC showed that (i) the glass transition temperature values of the polymers decrease and tend to that measured for pure PTMO upon increasing ionization; (ii) a crystalline phase due to PTMO packing in ordered structures appears at the highest ionization degrees, similarly to pure PTMO. 1H Time-Domain NMR and 13C solid state NMR revealed an increase in PTMO mobility with increasing ionic content, in agreement with DSC results.The measurements of proton spin lattice relaxation times in both the laboratory (T1) and rotating (T1ρ) frames allowed limits on the size of the hard domains to be estimated. T1ρ data hint at a phase demixing effect upon increasing the ionization degree.

Alkyl chain length effects of hydroxyl-functionalized imidazolium ionic liquids in the ionothermal synthesis of LiFePO4

LiFePO4 is one of the most promising cathode materials for lithium ion batteries. To investigate the role of the cation in the ionothermal synthesis of LiFePO4, three imidazolium-based ionic liquids, containing hydroxyl-terminated alkyl chains of various lengths, were synthesized using microwave-assisted methods: 1-(3-hydroxypropyl)-3-methyl imidazolium bis(trifluoromethylsulfonyl)amide, 1-(6-hydroxyhexyl)-3-methyl imidazolium bis(trifluoromethylsulfonyl)amide, and 1-(9-hydroxynonyl)-3-methyl imidazolium bis(trifluoromethylsulfonyl)amide. An ionothermal synthesis was attempted with each ionic liquid, using various precursors. The resulting solid products were investigated using powder X-ray diffraction and solid state nuclear magnetic resonance spectroscopy. The yield of LiFePO4 increased with an increase in the hydroxyl-terminated alkyl chain length on the imidazolium.

Pyrolyzing Renewable Sugar and Taurine on the Surface of Multi-Walled Carbon Nanotubes as Heterogeneous Catalysts for Hydroxymethylfurfural Production

Conversion of biorenewable feedstocks into transportation fuels or chemicals likely necessitates the development of novel heterogeneous catalysts with good hydrothermal stability, due to the nature of highly oxygenated biomass compounds and the prevalence of water as a processing solvent. The use of carbon-based materials, derived from sugars as catalyst precursors, can achieve hydrothermal stability while simultaneously realizing the goal of sustainability. In this work, the simultaneous pyrolysis of glucose and taurine in the presence of multi-walled carbon nanotubes (MWCNTs), to obtain versatile solid acids, has been demonstrated. Structural and textural properties of the catalysts have been characterized by TEM, TGA, and XPS. Additionally, solid state nuclear magnetic resonance (ssNMR) spectroscopy has been exploited to elucidate the chemical nature of carbon species deposited on the surface of MWCNTs. Al(OTf)3, a model Lewis acidic metal salt, has been successfully supported on sulfonic groups tethered to MWCNTs. This catalyst has been tested for C6 sugar dehydration for the production of HMF in a tetrahydrofuran (THF)/water solvent system with good recyclability.

Enhanced pharmacological efficacy of sumatriptan due to modification of its physicochemical properties by inclusion in selected cyclodextrins

The study focused on the pharmacological action of sumatriptan, in particular its antiallodynic and antihyperalgesic properties, as an effect of cyclodextrinic inclusion of sumatriptan, resulting in changes of its physicochemical qualities such as dissolution and permeability through artificial biological membranes, which had previously been examined in vitro in a gastro-intestinal model. The inclusion of sumatriptan into β-cyclodextrin and 2-hydroxylpropylo-β-cyclodextrin by kneading was confirmed with the use of spectral (fourier-transform infrared spectroscopy (FT-IR); solid state nuclear magnetic resonance spectroscopy with magic angle spinning condition, 1H and 13C MAS NMR) and thermal (differential scanning calorimetry (DSC)) methods. A precise indication of the domains of sumatriptan responsible for its interaction with cyclodextrin cavities was possible due to a theoretical approach to the analysis of experimental spectra. A high-performance liquid chromatography with a diode-array detector method (HPLC-DAD) was employed to determine changes in the concentration of sumatriptan during dissolution and permeability experiments. The inclusion of sumatriptan in complex with cyclodextrins was found to significantly modify its dissolution profiles by increasing the concentration of sumatriptan in complexed form in an acceptor solution compared to in its free form. Following complexation, sumatriptan manifested an enhanced ability to permeate through artificial biological membranes in a gastro-intestinal model for both cyclodextrins at all pH values. As a consequence of the greater permeability of sumatriptan and its increased dissolution from the complexes, an improved pharmacological response was observed when cyclodextrin complexes were applied.

Phosphate glass matrix composites incorporating trisilanol phenyl polyhedral oligomeric silsesquioxane prepared by viscous flow sintering method with enhanced benefits

The effect of mixing and sintering processes to prepare tin fluorophosphate glass (Pglass) matrix composites incorporating trisilanol phenyl polyhedral oligomeric silsesquioxane (TSP-POSS) was investigated by comparing manual and suspension mixing, one-step and stepwise sintering processes to explore the structure dynamics and physical properties in the composites as a function of the different process conditions used. Energy Dispersive X-ray analysis confirmed optimal homogeneous dispersion of the TSP-POSS molecules in the composites prepared by the suspension method. The observed increase of glass transition temperature and the reduction of non-bridging bonds in the composites are believed to be the reason for the effective dispersion of TSP-POSS molecules in the composites. The chemical reaction between the TSP-POSS and Pglass was strongly influenced by the mixing/dispersion and sintering processes investigated. 13C cross polarized magic angle spinning (CP MAS) solid state nuclear magnetic resonance (NMR) spectroscopy confirmed the chemical stability of the TSP-POSS during the sintering process at elevated temperatures. In addition, a chemical reaction between the TSP-POSS and Pglass was evidenced by 29Si CP MAS NMR analysis. This study will provide a better fundamental understanding of the effective dispersion mechanism of the TSP-POSS molecules in the Pglass matrix that will facilitate tailoring the physicochemical properties of the composites with addition of various small concentrations of TSP-POSS for a number of applications where the pure Pglass is not applicable due to the intrinsic properties of the Pglass.

Synthesis, structural, optical and solid state NMR study of lead bismuth titanate borosilicate glasses

Various compositions (0.0 ≤ x ≤ 1.0) in the glassy system 55[(PbxBi1-x)TiO3]-44[2SiO2.B2O3] doped with one mol percent of graphene nanoplatlets (GNPs) have been synthesized using the conventional melt-quenching technique. X-ray diffraction (XRD) study revealed the formation of bulk and transparent lead bismuth titanate borosilicate glasses. Density and molar volume were determined using the liquid displacement method. Structural analyses were carried out in detail using different characterization techniques such as infrared spectroscopy, Raman spectroscopy, UV–vis spectroscopy and solid state nuclear magnetic resonance (SSNMR) spectroscopy. 29Si and 11B-MAS-NMR-spectral analysis for five glass samples with different fraction of PbO reveal that as increases the content of PbO, the silicate and borate network become more polymerized.

Computational Multinuclear NMR Characterization of Metal-Doped Amorphous Silica Catalysts

Metal-doped amorphous silica has shown strong catalytic activity in a number of industrial applications, including lignin depolymerization, ethanol dehydration, and olefin metathesis. The metal dopant is essential to the catalyst’s reactivity, and although an increased metal concentration typically results in increased reactivity, it is the structure of the metal site that determines the activity strength. However, the structure of the active site is difficult to characterize experimentally as it is influenced by the irregular, amorphous silica support. Insights from computational simulations can greatly aid the characterization of these materials, which in turn may lead to improved catalyst design. In this study, we focus on a primary technique for the experimental investigation of solid materials, i.e., solid state nuclear magnetic resonance spectroscopy. We use density functional theory simulations to obtain nuclear magnetic resonance (NMR) spectra and quadrupolar coupling constants of metal-doped amor...