Magic-angle Nuclear Magnetic Resonance Research Articles

A Metabolomics Study by 1H HRMAS NMR: From Sheep Milk to a Pressed-Curd Cheese: A Proof of Concept

For the first time, High-Resolution Magic Angle Nuclear Magnetic Resonance spectroscopy (NMR-HRMAS) was applied to directly identify specific metabolites from a Spanish raw ewe’s milk and enzymatic coagulation pressed-curd cheese (Protected Geographical Indication: Castellano) manufactured by two procedures (traditional/artisanal vs. industrial) and including the ewe’s raw milk. The NMR parameters were optimized to study the complex matrixes of this type of cheese. In addition, conventional overcrowded 1H-NMR-HRMAS spectra were selectively simplified by a Carr–Purcell–Meiboom–Gill (CPMG) sequence or a stimulated echo pulse sequence by bipolar gradients (DIFF), thus modulating spin–spin relaxation times and diffusion of molecular components, respectively. 1H-NMR-HRMAS spectroscopy displayed important information about cheese metabolites, which can be associated with different manufacturing processes (industrial vs. traditional) and ripening times (from 2 to 90 days). These results support that this spectroscopy is a useful technique to monitor the ripening process, from raw milk to commercial ripened cheese, using a minimum intact sample, implying the absence of time-consuming sample pretreatments.

Intercalation of p-toluenesulfonic acid into Mg-Al layered double hydroxide

Layered double hydroxide represents a class of materials for selective adsorption and catalysis. In the present work, anionic p-toluenesulfonic acid (PTSA) was successfully incorporated into the interlayer domain of Mg-Al layered double hydroxide (LDH), synthesized by the co-precipitation route. Materials were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, magic angle nuclear magnetic resonance (13C MAS-NMR) spectroscopy and UV-Visible diffuse reflectance (UV-VIS/DR). All samples supported PTSA intercalation at room temperature in the basal space, the interlayer distance increased by the intercalations of the above mentioned according to the arrangement of PTSA molecules in the interlayer. The LDH-PTSA structure collapsed at 400 °C and the organic portion of those materials occurred by partial combustion, which in turn gives rise to reduced species, such as carbon and sulfide anions.

From a plant secretion to the promising bone grafts: Cryogels of silicon-integrated quince seed mucilage by microwave-assisted sol–gel reaction

Design and fabrication of biologically active cryogels using novel biopolymer(s) are still of great importance at regenerating bone defects such as traumatic bone injuries, maxillofacial surgery, osteomyelitis, and osteoporosis. Nowadays, plant mucilage, an herbal biomaterial, has been drawn attention by scientists due to their marvelous potential to fabricate 3-dimensional (3D) physical constructs for the field of regenerative medicine. Herein, a 3D cryogel from silicon-integrated quince seed mucilage (QSM) is constructed using microwave-assisted sol-gel reaction, characterized in-depth by attenuated total reflectance Fourier transform-infrared spectroscopy (ATR-FTIR), solid-state silicon cross-polarization magic-angle nuclear magnetic resonance (29Si-CP-MAS NMR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimeter (DSC), micro-mechanical testing, porosity, and swelling tests, contact angle measurements, Brunauer-Emmet-Teller and Barret-Joyner-Halenda (BET-BJH) analysis, enzymatic biodegradation test, and field emission-scanning electron microscopy-energy dispersive X-ray spectroscopy (FE-SEM-EDX) mapping. The osteobiologic capacity of the cryogels is determined using human adipose-derived mesenchymal stem cells (hAMSCs) under invitro conditions. Osteogenic differentiation of hAMSCs on both QSM and silica-modified QSM (Si-QSM) cryogels is analyzed by histochemistry, immunohistochemistry, and quantitative-real time (q-RT) PCR techniques. The results obtained from invitro experiments demonstrate that the upregulation of osteogenesis-related genes in Si-QSM cryogels presents a stronger and earlier development over QSM cryogels throughout the culture period, which in turn reveals the great potential of this novel Si-incorporated QSM cryogels for bone tissue engineering applications.

Lanthanide (=Ce, Pr, Nd and Tb) ions substitution at calcium sites of hydroxyl apatite nanoparticles as fluorescent bio probes: Experimental and density functional theory study

Abstract An interesting property of hydroxyl apatite is the ability to undergo cationic and anionic substitution. In this study, nano hydroxyl apatite(nHAp) substituted with four different lanthanide ions(LnO)(Cerium,Praseodymium,Neodymium and Terbium) is prepared by co-precipitation method and characterized by X-Ray Diffraction, Fourier Transform Infrared, Fluorescence and UV‐Visible Spectroscopy and Transmission Electron Microscopy, and Magic Angle Nuclear Magnetic Resonance techniques. Rietveld refinement and computational study using Density Functional Theory has provided information about the effect of LnO substitution on nHAp phase. These studies reveal changes in lattice parameters and preferential calcium sites for LnO substitution in apatite structure. Experimental results have shown that LnO substituted particles have shown an intense fluorescent emission under UV‐Visible excitation. The ability of prepared LnO substituted nHAp particles to inhibit oxidative stress in terms of reduction of hydrogen peroxide is also demonstrated. In- vitro biocompatibility has been assessed via adsorption of human plasma/serum proteins on the surface of nHAp. Adsorption of the protein on nHAp also leads to passivation against corrosion. Particles have shown excellent cell viability and better proliferation of MG-63 cell lines. These results may open new avenues for the development of bioactive materials for bone regeneration and smart fluorescent probes for bio imaging applications.

Towards a full understanding of the nature of Ni(II) species and hydroxyl groups over highly siliceous HZSM-5 zeolite supported nickel catalysts prepared by a deposition-precipitation method.

Highly siliceous HZSM-5 zeolite supported nickel catalysts prepared by a deposition-precipitation (D-P) method were characterized by Fourier transform infrared (FT-IR), hydrogen temperature programmed reduction (H2-TPR), X-ray diffraction (XRD), N2-absorption/desorption, field emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and (27)Al magic-angle nuclear magnetic resonance (MAS NMR) techniques. The results showed that the D-P of nickel species occurred predominantly on the internal surface of highly siliceous HZSM-5 zeolite, in which the internal silanol groups located on the hydroxylated mesopores or nanocavities played a key role. During the D-P process, nickel hydroxide was first deposited-precipitated via olation/polymerization of neutral hydroxoaqua nickel species over the HZSM-5 zeolite. With the progress of the D-P process, 1 : 1 nickel phyllosilicate was formed over the HZSM-5 via the hetero-condensation/polymerization between charged hydroxoaqua nickel species and monomer silicic species generated due to the partial dissolution of the HZSM-5 framework. The 1 : 1 nickel phyllosilicate could also be generated via the hydrolytic adsorption of hydroxoaqua nickel species and their subsequent olation condensation. After calcination, the deposited-precipitated nickel hydroxide was decomposed into nickel oxide, while the 1 : 1 nickel phyllosilicate was transformed into 2 : 1 nickel phyllosilicate. According to the above mechanism, Ni(ii) species were present both in the form of nickel oxide and 2 : 1 nickel phyllosilicate, which were mutually separated from each other, being highly dispersed over HZSM-5 zeolite.

Ladder-Like Aromatic Imide-Functionalized Poly(silsesquioxane): Preparation and Characterization via the Sol-Gel Route

A ladder-like polysilsesquioxane (PSSQ) has been synthesized by reacting pyromellitic acid anhydride (PMDA) with (3-aminopropyl)triethoxysilane (APTES), yielding the corresponding poly(amic acid) (PAA). The as-prepared PAA was converted to an imide-functionalized PSSQ by thermal treatment at 220°C. The material was characterized by means of Fourier transform infrared spectroscopy, 13C and 29Si solid-state magic angle nuclear magnetic resonance spectroscopy, X-ray powder diffraction, thermogravimetric analysis, and differential thermogravimetric analysis. The findings give evidence that a ladder-like PSSQ is formed when PMDA reacts with APTES in a molar ratio of 1:1. Kinetic studies of the adsorption of methylene blue (MB) reveal that PMDA/APTES (molar ratio = 1:1) is capable of adsorbing MB whereas PMDA/APTES (molar ratio = 1:2) shows almost no MB adsorption capacity.

Ha‐ras and β‐catenin oncoproteins orchestrate metabolic programs in mouse liver tumors

The process of hepatocarcinogenesis in the diethylnitrosamine (DEN) initiation/phenobarbital (PB) promotion mouse model involves the selective clonal outgrowth of cells harboring oncogene mutations in Ctnnb1, while spontaneous or DEN-only-induced tumors are often Ha-ras- or B-raf-mutated. The molecular mechanisms and pathways underlying these different tumor sub-types are not well characterized. Their identification may help identify markers for xenobiotic promoted versus spontaneously occurring liver tumors. Here, we have characterized mouse liver tumors harboring either Ctnnb1 or Ha-ras mutations via integrated molecular profiling at the transcriptional, translational and post-translational levels. In addition, metabolites of the intermediary metabolism were quantified by high resolution (1)H magic angle nuclear magnetic resonance. We have identified tumor genotype-specific differences in mRNA and miRNA expression, protein levels, post-translational modifications, and metabolite levels that facilitate the molecular and biochemical stratification of tumor phenotypes. Bioinformatic integration of these data at the pathway level led to novel insights into tumor genotype-specific aberrant cell signaling and in particular to a better understanding of alterations in pathways of the cell intermediary metabolism, which are driven by the constitutive activation of the β-Catenin and Ha-ras oncoproteins in tumors of the two genotypes.

Insights into silicate carbonation processes in water-bearing supercritical CO2 fluids

Subsurface injection of CO2 is commonplace in certain industries, yet deployment at the scale required for emission reduction is unprecedented and therefore requires a high degree of predictability. Accurate modeling of subsurface geochemical processes related to geologic carbon sequestration requires experimentally derived data for mineral reactions. Most work in this area has focused on aqueous-dominated systems in which dissolved CO2 reacts to form crystalline carbonate minerals. Comparatively little laboratory research has been conducted on reactions occurring between minerals in the host rock and the wet supercritical fluid phase. We studied the carbonation of wollastonite [CaSiO3] exposed to variably hydrated supercritical CO2 (scCO2) at 50, 55 and 70°C and 90, 120 and 160bar. Reactions were followed by three novel in situ high pressure techniques, which demonstrated increased dissolved water concentrations in the scCO2 resulted in increased wollastonite carbonation approaching ∼50wt.%. Overall, the X-ray diffraction and infrared and magic angle nuclear magnetic resonance spectroscopies experiments conducted in this study allow detailed examination of mechanisms impacting carbonation rates. These include the development of amorphous passivating layers, thin liquid water films, and amorphous hydrated carbonate phases. Collectively, these results emphasize the importance of understanding geochemical processes occurring in wet scCO2 fluids.

Effects of afforestation on soil organic matter characteristics under subtropical forests with low elevation

We selected sites of natural broad-leaved forests and adjacent coniferous plantations (Cunninghamia konishii and Calocedrus formosana of 30 and 80 years old, respectively) in central Taiwan to evaluate the effects of plantations on soil organic matter (SOM) characteristics and composition. SOM was characterized by chemical analyses, solid-state 13C cross-polarization magic-angle nuclear magnetic resonance (CPMAS 13C NMR), and optical measurements. Semiquantitative analysis of CPMAS 13C NMR spectra showed the litter of broad-leaved forests to be less resistant to decomposition than that of coniferous forests. The humification degree of SOM was higher under broad-leaved than coniferous forests because of the relatively high percentage of aromatic C and carboxyl C in the humic acids (HAs) of A horizons under broad-leaved forests. Additionally, the E4/E6 ratio of HAs was lower in the A horizon under broad-leaved than coniferous forests, which reflected more condensation of SOM. High alkyl C content under coniferous forests could be attributed to needle litter quality, which has a high content of waxes or lipids. Afforestation with conifers induced accumulation of the litterfall layer, gradually increased SOM concentrations, and changed the composition structures of SOM in the topsoils.

Further studies into the feasibility of using aqueous alum solutions in the destruction of VX

The destruction of phosphorus based chemical warfare agents using aqueous buffer mixtures of aluminum sul- fate (alum) and sodium aluminate is pursued. The production of VX (O-ethyl-S-(2-(diisopropylamino)ethyl)-methylphos- phonothiolate) hydrolysis products ethyl methyl phosphonic acid (EMPA), an aluminum complex of EMPA, and S-(2- (diisopropylamino)ethyl)methylphosphonothiolate (EA-2192) is characterized in acidic and basic alum buffers. The study employs 31 P high resolution magic angle nuclear magnetic resonance spectroscopy (HRMAS NMR) for both quantitative and qualitative analysis. The acidic buffer results in a slower reaction rate and is less effective than the basic buffer.

Study of the alkaline environment in mixed alkali compositions by multiple-quantum magic angle nuclear magnetic resonance (MQ–MAS NMR)

45S5 Bioglasses of the composition 46.1 SiO2–2.6 P2O5–26.9 CaO–(24.4−x) Na2O–xMe2O (Me=Li or K) have been investigated using MAS NMR and MQ–MAS NMR methods. The analysis of the 29Si MAS NMR spectrum revealed two lineshapes whose chemical shift is consistent with two silica Qn=2,3 species. The 31P MAS NMR spectrum reveals the effect of both Na and Ca ions. The chemical shift of the observed 31P signal is intermediate between those of Na3PO4 (near 10ppm) and Ca3(PO4)2 (near 3–0ppm) species. The 23Na MAS NMR spectra were observed in the alkali oxide composition: 24.4 Na2O, 12.2 Na2O–12.2 K2O and 12.2 Na2O–12.2 Li2O. The substitution of Na with Li or K was done to determine the extend of alteration of the glass structure. This goal was best accomplished by 23Na MQ–MAS NMR. The two-dimensional spectra revealed three sites in the 24.4mol% Na2O glass. These sites were not resolved in the 1D MAS NMR spectroscopy. In the mixed glasses, only two sites were obtained.

C60with complete pentagon orientational ordering: A dielectric and13CNMR study of solidC60charged with NO

Solid ${\mathrm{C}}_{60}$ was stored in NO under high pressure and the gas molecules NO were found to diffuse into the octahedral interstitial sites in its fcc crystal lattice. Its ${}^{13}\mathrm{C}$ nuclear magnetic resonance magic angle spinning spectra composed of a primary resonance at 143.7 ppm, accompanied by two minor peaks shifted 0.4 and 0.8 ppm downfield, respectively. The dopant was found to depress its phase-transition temperature at 260 K in pure ${\mathrm{C}}_{60},$ and to reduce substantially the drop $\ensuremath{\Delta}{\ensuremath{\varepsilon}}^{\ensuremath{'}}$ at the phase-transition temperature. Furthermore, the spectral features associated with relaxation during glass transition at lower temperature, as observed in impedance spectra, were smeared. The fraction of P orientation below ${T}_{c}$ has been calculated from the impedance data. These results show that a nearly completely P oriented phase had occurred in $(\mathrm{NO}{)}_{0.1}{\mathrm{C}}_{60},$ and this phase is favored by a negative pressure on ${\mathrm{C}}_{60}$ lattice exerted by NO, as well as the electrostatic interaction between the two.

Synthesis of calcium silicate hydrate/polymer complexes: Part I. Anionic and nonionic polymers

High molecular weight anionic polymers have been incorporated into the calcium silicate hydrate (C–S–H) structure during precipitation of quasicrystalline C–S–H from aqueous solution. The anionic polymers studied were poly(methacrylic acid), poly(acrylic acid), and the sodium salt of poly(vinyl sulfonic acid). Expansion of the interlayer spacing coupled with high-carbon contents confirmed that the polymers intercalated between the layers. D-gluconic acid behaves similarly. Intercalation characteristics strongly depended on both the type of polymer and Ca/Si molar ratio of C–S–H; intercalation reached a maximum at an initial Ca/Si = 1.3 in all cases. Poly(vinyl alcohol) was the only nonionic polymer among those studied that was incorporated into C–S–H. Evidence for interlayer intercalation is less definite. The C–S–H/polymer complexes were examined by Fourier transform infrared spectroscopy, 29Si nuclear magnetic resonance magic angle spinning, and 13C cross-polarization, magic angle spinning nuclear magnetic resonance spectroscopy.

Synthesis of calcium silicate hydrate/polymer complexes: Part II. Cationic polymers and complex formation with different polymers

Some high molecular weight cationic polymers, poly(diallyldimethylammonium chloride) (PDC) and poly(4-vinylbenzyltrimethylammonium chloride) (PVC), have been incorporated into the calcium silicate hydrate (C–S–H) structure during precipitation of quasicrystalline C–S–H from aqueous solution. Expansion of the interlayer spacing [0.9 nm (PDC), 1.5 nm (PVC)] and a high-carbon content provided evidence that these polymers were intercalated between layers of C–S–H when Ca/Si <1.0. Intercalation characteristic properties strongly depended on both of the type of polymer and Ca/Si ratio in C–S–H. Poly(4-vinyl-1-methylpyridinium bromide) and methyl glycol chitosan (iodide) also interacted with C–S–H, probably by surface adsorption. The C–S–H/polymer complexes were examined by Fourier transform infrared spectroscopy, 29Si nuclear magnetic resonance magic angle spinning, and 13C cross-polarization, magic angle spinning nuclear magnetic resonance spectroscopy. Mechanisms of intercalation of different kinds of polymers between the C–S–H layers are discussed.

Multiple-Quantum MAS NMR Spectroscopy of Spin-[formula omitted]Quadrupolar Spin Systems Using Shaped Pulses

An investigation of the effect of shaping the pulses in multiple-quantum magic-angle nuclear magnetic resonance experiments was carried out on polycrystalline samples containing spin-32quadrupolar nuclear spins. Both theoretical analysis and numerical simulations show that there exist types of shaped pulses that are more advantageous than the usual rectangular pulses in exciting multiple-quantum coherences and converting these into single-quantum coherences or zero-quantum coherences (inz-filtering cases). The sensitivities can be enhanced without loss of resolution or increasing the RF offset dependences. Moreover, properly shaped pulses can moderate the requirements on the RF power and sample spinning speeds. Especially important for application purposes is the finding that lattice site quantification can also be improved by the use of certain shaped pulses.

29Si and 27Al MASNMR Study of Stratlingite

Strätlingite (2CaO·Al2O3·SiO2·8H2O) is a complex calcium aluminosilicate hydrate commonly associated with the hydration of slag‐containing cements or other cements enriched in alumina. Strätlingite can coexist with the hydrogarnet solid solution [hydrogarnet (3CaO·Al2O3·6H2O)‐katoite (3CaO·Al2O3·SiO2·4H2O)] and calcium silicate hydrate (C‐S‐H). Since Strätlingite is present in many blended cements, the knowledge of strätlingite's characteristic silicate anion structure and how aluminum is accommodated by the structure is important. Phase pure Strätlingite samples have been synthesized from oxides in the presence of excess water and from metakaolinite, calcium aluminate cement, CaO, NaOH, and water. The samples were characterized using X‐ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA) and then further examined using 29Si, with and without cross‐polarization (CP), and 27Al solid‐state magic angle nuclear magnetic resonance spectroscopy (MASNMR). For the most part, NMR data for these strätlingites corroborate structural information available in the literature. The aluminum atoms are both tetrahedrally and octahedrally coordinated, and the silicon atoms exist predominantly as Q2, Q2(1Al), and Q2(2Al) species. The presence of alkali affects the structure of strätlingite in subtle ways, significantly reducing the AlIV/A1VI ratio.

Applications of high resolution solid state nuclear magnetic resonance spectroscopy to surface studies

Surface properties have important effects on materials such as polymer composites, and technologies such as catalysis. The influences of surface properties arise on both macroscopic and microscopic scales. Therefore there is a need to characterize surfaces on a molecular level. A range of spectroscopic techniques are utilized for surface characterization. Recently, high resolution solid state nuclear magnetic resonance (NMR) Spectroscopy has proven to be a significant analytical technique for surface analysis. Solid state NMR is a particularly advantageous method for surface studies because there is no sample preparation necessary which could alter the molecular structure of the material as in other spectroscopic analyses. This technique allows for the detection of subtle molecular changes in the systems under study both qualitatively and quantitatively. With the range of information that can be obtained. Including: chemical structure, interactions, and molecular motion, solid state NMR promises to be a powerful addition to the established methods for the study of surfaces. This review focuses on surface characterization using the techniques developed for solid state magic-angle NMR where the observe nucleus is chosen to suit the surface system. The NMR studies of surfaces carried out to date can be divided primarily into 2 areas: the characterization of chemically modified silica surfaces and the study of the nature of molecular adsorption on catalytic surfaces. The solid state NMR studies of these systems have demonstrated that high resolution spectra are attainable and that this method of characterization, with its capabilities and relative ease of interpretation, is a valid and useful one.

Thermal Isomerization of Polyacetylene Films

Abstract Isomerization of the as-formed (-78°C) cis-polyacetylene to the trans isomer is relevant to the electronic structure, the crystal structure and the electrical properties of this prototypical conductive polymer. We have studied the process using Fourier transform infrared (FTIR) and 13C magic angle nuclear magnetic resonance (NMR) spectroscopies at temperatures between 80 and 110°C. The observed kinetics will be discussed in terms of three basic processes: a second order process which randomly converts cis-cis-cis (CCC) sequences to trans-cis-trans (TCT) sequences via a pair of biradicals, a fourth order process that converts CTCC sequences to TCTT sequences via four biradicals, and two fourth order processes which allow sequential migration along the chain. The correlation of observed electron spin resonance and x-ray results, among others, with these mechanisms will be shown.