Spinning Nuclear Magnetic Resonance Spectroscopy Research Articles

Interactions of boron released from surface pre-reacted glass ionomer with enamel/dentin and its effect on pH

This study investigated the interaction of borate ions released from surface pre-reacted glass ionomer (S-PRG) fillers with the biological apatites of enamel and dentin using solid-state (SS) magic-angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy analysis. We further evaluated the effect of borate ions on the pH change. Bovine enamel and dentin powder were submerged in S-PRG eluate (with borate ion concentration of 100 mM) for 3 h, then washed with deionized water (DW). The dried enamel and dentin specimens were used for 11B SS-NMR and Fourier transform infrared spectroscopy (FT-IR) analysis. Enamel and dentin blocks were treated with three solutions: DW (control), S-PRG eluent and borate solution (100 mM). The treated samples were submerged in the demineralization solution and the pH was measured using a pH meter daily for 6 days. The surfaces of the enamel and dentin blocks were then observed using field emission scanning electron microscopy (FE-SEM). SS-NMR analysis revealed the presence of adsorbed borate ions in the enamel and dentin samples in a tetra-coordinated form. The pH results demonstrated an increase in pH values in the S-PRG and borate groups. SEM images showed that the surfaces of the control group were demineralized, whereas the surfaces of the S-PRG and borate groups were intact. These results concluded that borate ions could be adsorbed to enamel and dentin in the tetra-coordinated form. Borate ions possess a buffer capacity which may help to protect the tooth structure against acid attacks and promote remineralization.

Dysregulated Alanine as a Potential Predictive Marker of Glioma-An Insight from Untargeted HRMAS-NMR and Machine Learning Data.

Metabolic alterations play a crucial role in glioma development and progression and can be detected even before the appearance of the fatal phenotype. We have compared the circulating metabolic fingerprints of glioma patients versus healthy controls, for the first time, in a quest to identify a panel of small, dysregulated metabolites with potential to serve as a predictive and/or diagnostic marker in the clinical settings. High-resolution magic angle spinning nuclear magnetic resonance spectroscopy (HRMAS-NMR) was used for untargeted metabolomics and data acquisition followed by a machine learning (ML) approach for the analyses of large metabolic datasets. Cross-validation of ML predicted NMR spectral features was done by statistical methods (Wilcoxon-test) using JMP-pro16 software. Alanine was identified as the most critical metabolite with potential to detect glioma with precision of 1.0, recall of 0.96, and F1 measure of 0.98. The top 10 metabolites identified for glioma detection included alanine, glutamine, valine, methionine, N-acetylaspartate (NAA), γ-aminobutyric acid (GABA), serine, α-glucose, lactate, and arginine. We achieved 100% accuracy for the detection of glioma using ML algorithms, extra tree classifier, and random forest, and 98% accuracy with logistic regression. Classification of glioma in low and high grades was done with 86% accuracy using logistic regression model, and with 83% and 79% accuracy using extra tree classifier and random forest, respectively. The predictive accuracy of our ML model is superior to any of the previously reported algorithms, used in tissue- or liquid biopsy-based metabolic studies. The identified top metabolites can be targeted to develop early diagnostic methods as well as to plan personalized treatment strategies.

Synthesis and properties of phosphate cancrinite (PO4‐CAN) a synthetic counterpart of depmeierite

AbstractPhosphate cancrinite (PO4‐CAN) has been synthesized under mild hydrothermal conditions at 473 K using kaolin, sodium orthophosphate‐dodecahydrate and strong alkaline conditions (8 M NaOH solution). Cancrinite crystals of rod‐like habit and maximum lengths up to 2 μm were observed and characterized by X‐ray powder diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDXS) and Fourier transform infrared spectroscopy (FTIR). Magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR) of the nucleus 31P, thermogravimetry (TG/DTG) and heating experiments under open conditions in a furnace were additionally performed. The empirical formula Na8[SiAlO4]6(PO4)0.58(CO3)0.13(H2O)4.6 was calculated from EDXS analyses and TG data under consideration of a minor carbonate content, detected by FTIR spectroscopy. PO4‐CAN is stable up to 800 °C before thermal destruction rapidly occurs at 825 °C. The final product of TG analyses at 1000 °C is a mixture of a nepheline‐like phase and the phosphate content of the initial cancrinite sample. XRD and FTIR results of the synthesis product are in good agreement with literature data of the rare mineral depmeierite.

Dinuclear Copper Complex Immobilized on a Janus-Type Material as an Interfacial Heterogeneous Catalyst for Green Synthesis.

We herein describe a rational design of a heterogeneous catalyst composed of a dinuclear cuprate anion being immobilized electrostatically on one surface of Janus-type nanosheets while the other surface is decorated with highly hydrophobic octyl groups. The catalyst was found to be well dispersible in the organic phase of a biphasic aqueous/organic mixture. It was characterized by means of elemental analysis, atomic absorption spectroscopy, mass spectrometry, N2 absorption-desorption analysis, thermogravimetric analysis, scanning electron microscopy (SEM), and solid-state 13C and 29Si cross-polarization magic-angle spinning nuclear magnetic resonance spectroscopy. The Janus nature of the catalyst was investigated by employing a selective surface labeling method and by means of SEM. The catalyst shows higher activity compared to a non-Janus analogue in a biphasic synthesis. It was successfully used for the azide-alkyne cycloaddition and the Chan-Lam C-N coupling reaction. In addition, new and simple ways have been established for the production of a coumarin-triazole derivative and for the synthesis of the biologically active compound Monastrol via a solvent-free Biginelli reaction. The role of the dinuclear copper centers is discussed mechanistically.

One pot synthesis of new cross-linked chitosan-Schiff' base: Characterization, and anti-proliferative activities

Four novel chitosan hydrogels were successfully synthesized through the cross-linking reaction of chitosan with different concentrations of ethyl 5-(3,5-dihydroxy-1,4-dioxan-2-yl)-2-methylfuran-3-carboxylate. Their structures were confirmed by Fourier transform infrared spectroscopy (FT-IR), 13C Cross polarization magic angle spinning nuclear magnetic resonance spectroscopy (CP/MAS 13C NMR), ultraviolet-visible spectroscopy, thermogravimetric analysis (TGA, DTA), and X-ray diffraction (XRD). Cytotoxicity on hepatocellular carcinoma (HepG-2) cell line and a normal African green monkey kidney (Vero) cell line were studied using the MTT assay. The resultant hydrogels showed a good inhibitory effect comparing to the un-modified parent; the hydrogels with the lowest degree cross-linking (0.125 and 0.25 mol cross-linker per one chitosan residue) showed potent anticancer activity in the HepG2 cells with IC50 of 57.9 and 80.9 μg/ml, respectively. These results show that the newly synthesized cross-linked chitosan derivatives demonstrated more selectivity to the HepG2 than the Vero cells, indicating its potential for Investigation in the cure of hepatocellular carcinoma.

Structure and viscosity of CaO–Al2O3–B2O3–BaO slags with varying mass ratio of BaO to CaO

AbstractThe structure of CaO–Al2O3–B2O3–BaO glassy slags with varying mass ratio of BaO to CaO has been investigated by Raman spectroscopy, 11B and 27Al magic angle spinning nuclear magnetic resonance (MAS‐NMR) spectroscopy and atomic pair distribution function (PDF). 11B MAS‐NMR spectra reveal the dominant coordination of boron as trigonal. Both simulations on 11B MAS‐NMR spectra and Raman spectroscopy indicate the presence of orthoborate as the primary borate group with a few borate groups with one bridging oxygen and minor four‐coordinated boron sites. 27Al MAS‐NMR and PDF show the Al coordination as tetrahedral. Raman spectral study shows that the transverse vibration of AlIV–O–AlIV and AlIV–O–BIII, stretching vibration of aluminate structural units and vibration of orthoborate and pyroborate structural groups. A broader distribution of Al–O bond lengths in PDF also supports the enhanced network connectivity. Viscosity measurements show the increase in viscosity of molten slags with increasing mass ratio of BaO to CaO, which further attributes to the enhanced degree of polymerization of the aluminate network.

Multiple templating strategy for the control of aluminum and phosphorus distributions in AFX zeolite

A multiple templating strategy using both bulky and small organic structure-directing agents (SDAs) was adapted for AFX zeolite synthesis in order to control the distribution of aluminum and phosphorus. An AFX zeolite with an Si/Al ratio of 4.8 was obtained in the presence of a bulky and rigid SDA, N,N,N',N'-tetraethylbicyclo[2.2.2]oct-7-ene-2,3:5,6-dipyrrolidinium cation (TEBOP2+), and co-existing Na+ cations. The use of a tetramethylammonium cation (Me4N+) as the SDA instead of Na+ provided AFX zeolite with a middle Si/Al ratio of 7.9. Elemental analysis and 13C and 29Si magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy suggested that TEBOP2+ existed in the wide aft cage in both AFX zeolites, while the higher Si/Al ratio was derived from the lower charge density of Me4N+ occupying the narrow gme cage. We also attempted to control the distribution of phosphorus in phosphorus-modified AFX zeolite. The large tetraethylphosphonium cation (Et4P+) and small tetramethylphosphonium cation (Me4P+) were selectively incorporated into aft and gme cages during the hydrothermal synthesis, respectively. As a result, phosphorus oxide with different polymerization degrees were formed by calcination treatment according to the size of the cage occupied by the phosphorus-modifying agents (P-MAs). This direct phosphorus modification using alkylphosphonium was characterized by elemental analysis and 13C, 27Al, and 31P MAS NMR and two-dimensional (2D) 31P–27Al heteronuclear correlation NMR spectroscopies.

Physicochemical properties and structural dynamics of organic\u2013inorganic hybrid [NH3(CH2)3NH3]ZnX4 (X\u2009=\u2009Cl and Br) crystals

The physical properties of the organic–inorganic hybrid crystals having the formula [NH3(CH2)3NH3]ZnX4 (X = Cl, Br) were investigated. The phase transition temperatures (TC; 268K for Cl and 272K for Br) of the two crystals bearing different halogen atoms in their skeletons were determined through differential scanning calorimetry. The thermodynamic properties of the two crystals were investigated through thermogravimetric analysis. The structural dynamics, particularly the role of the [NH3(CH2)3NH3] cation, were probed through 1H and 13C magic-angle spinning nuclear magnetic resonance spectroscopy as a function of temperature. The 1H and 13C NMR chemical shifts did not show any changes near TC. In addition, the 1H spin–lattice relaxation time (T1ρ) varied with temperature, whereas the 13C T1ρ values remained nearly constant at different temperatures. The T1ρ values of the atoms in [NH3(CH2)3NH3]ZnCl4 were higher than those in [NH3(CH2)3NH3]ZnBr4. The observed differences in the structural dynamics obtained from the chemical shifts and T1ρ values of the two compounds can be attributed to the differences in the bond lengths and halogen atoms. These findings can provide important insights or potential applications of these crystals.

Cs absorption capacity and selectivity of crystalline and amorphous Hf and Zr phosphates

Removal of radioactive Cs from sodium-rich solutions is a technical challenge that goes back to post World War II nuclear waste storage and treatment; and interest in this topic was reinvigorated by the Fukushima-Daiichi nuclear power plant disaster, 10 years ago. Since the 1960′s there has been considerable focus on layered Zr phosphates as robust inorganic sorbents for separation of radionuclides such as Cs. Here we present synthesis and characterization, and direct comparison of Cs sorption capacity and selectivity of four related materials: 1) crystalline α-Zr phosphate and α-Hf phosphate, and 2) amorphous analogues of these. Powder X-ray diffraction, thermogravimetry, solid-state 31P magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy, and compositional analysis (inductively coupled plasma optical emission spectroscopy and mass spectroscopy, ICP OES and ICP MS) provided formulae; respectively M(HPO4)2⋅1H2O and M(HPO4)2⋅4H2O (M = Hf, Zr) for crystalline and amorphous analogues. Maximum Cs loading, competitive Cs-Na selectivity and maximum Cs-Na loading followed by the above characterizations plus 133Cs MAS-NMR spectroscopy revealed that amorphous analogues are considerably better Cs-sorbents (based on maximum Cs-loading and selectivity over Na) than the well-studied crystalline Zr-analogue. Additionally, crystalline α-Hf phosphate is better Cs-sorbent than crystalline α-Zr phosphate. All these studies consistently show that Hf phosphate is less crystallize than Zr phosphate, when obtained under similar or identical synthesis conditions. We attribute this to lower solubility of Hf phosphate compared to Zr phosphate, preventing ‘defect healing’ during the synthesis process.

Preparation of Li3PS4–Li3PO4 Solid Electrolytes by Liquid-Phase Shaking for All-Solid-State Batteries

A solid solution of a 100Li3PS4·xLi3PO4 solid electrolyte was easily prepared by liquid-phase synthesis. Instead of the conventional solid-state synthesis methods, ethyl propionate was used as the reaction medium. The initial stage of the reaction among Li2S, P2S5 and Li3PO4 was proved by ultraviolet-visible spectroscopy. The powder X-ray diffraction (XRD) results showed that the solid solution was formed up to x = 6. At x = 20, XRD peaks of Li3PO4 were detected in the prepared sample after heat treatment at 170 °C. However, the samples obtained at room temperature showed no evidence of Li3PO4 remaining for x = 20. Solid phosphorus-31 magic angle spinning nuclear magnetic resonance spectroscopy results proved the formation of a POS33− unit in the sample with x = 6. Improvements of ionic conductivity at room temperature and activation energy were obtained with the formation of the solid solution. The sample with x = 6 exhibited a better stability against Li metal than that with x = 0. The all-solid-state half-cell employing the sample with x = 6 at the positive electrode exhibited a better charge–discharge capacity than that employing the sample with x = 0.

Hydrothermal conversion of zeolite omega from magadiite with assistance of seed crystals

In this work, we report a rapid and sustainable synthetic strategy of zeolite omega with the addition of omega seeds via the transformation of magadiite with an initial chemical recipe of 0.76 NaOH: SiO2: 0.01 Al2O3: 7–14H2O, and the crystallization time was shortened to 5 h at 80 °C. The effect of experiment parameters has been discussed in details. In addition, the conversion behavior and the changes of secondary building units were characterized and studied by X-ray diffraction (XRD), scanning electron microscopy, Fourier Transform infrared (FT-IR), and Raman spectroscopy and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. During the conversion process, omega seeds would be partially destroyed and residual seeds supplied substrate for the growth of zeolite omega, most parts of five-membered rings and six-membered rings in magadiite were remained as building units to promote the formation of zeolite omega, and Al species preferred to enter T2 position which was located in six-membered rings. The toluene adsorption property of final product was also measured.

Role of cations on the dissolution mechanism of kaolinite in high alkaline media

Kaolinite and its dehydroxylated forms are widely used in industry, including the growing field of geopolymers. Until now, a deep understanding of the dissolution mechanism of kaolinite particles in alkaline media is still lacking. This work aims to investigate the dissolution mechanisms through aluminum and silicon leaching of two references kaolinites (KGa-1b and KGa-2) regarding various 2 M alkali treatment (KOH, NaOH and 50/50 NaOH + KOH) as a function of time and at 80 °C. For this, a wide range of methods have been used, from the determination of [Si] and [Al] in solution to the analysis of solids by combining X-ray diffraction (XRD), Fourier Transformed Infrared (FTIR), X-ray Absorption Near Edge Structure (XANES) and Magic Angle Spinning Nuclear Magnetic Resonance (MAS-NMR) spectroscopies and Transmission Electronic Microscopy (TEM) observations. The results evidence a higher dissolution rate with poorly crystallized kaolinites, confirming the role of the crystallinity of the samples toward reactivity in an alkaline media. In addition, the nature of the cation significantly affect the degree of dissolution following the sequence KOH < NaOH + KOH < NaOH. This process is combined with a change in Al speciation from 6-coordinated to 4-coordinated sites, as evidenced by XAS and MAS-NMR experiments. Altogether, these results allow to propose different dissolution mechanisms at the particle scale depending on the cations. The dissolution in presence of KOH proceeds uniformly from the edges, starting from the edges of the octahedral sheet, whereas in the case of NaOH, the edges dissolution is oriented with respect to areas of less coherence starting from the tetrahedral sheet.

Stability and solubility of members of tin perovskites in the schoenfliesite subgroup, [formula omitted](BSn[formula omitted])(OH,O)[formula omitted] (B = Ca, Fe[formula omitted], Mg, Mn[formula omitted], Zn, Cu)

In this work, we determined thermodynamic properties of a suite of tin perovskites □2(BSn4+)(OH,O)6 that correspond to the minerals burtite (B = Ca), jeanbandyite (Fe3+), schoenfliesite (Mg), wickmanite (Mn), vismirnovite (Zn), and mushistonite (Cu). Purity of the samples was verified by powder X-ray diffraction, chemical analysis (ICP-OES), solid state 119Sn magic-angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy, 57Fe Mössbauer spectroscopy, thermogravimetry (TG), and Karl-Fischer titration. Enthalpies of formation (ΔfHo) were determined by acid-solution calorimetry (in 5 N HCl at T = 298 K, with SnCl4 as the reference phase), that for jeanbandyite also in high-temperature oxide-melt calorimetry (in sodium molybdate at T = 973 K, with SnO2 as the reference phase). For the two methods, the difference for the ΔfHo values is 10.7 kJ·mol−1, a fair agreement. Because of the high H2O content of the studied phases, acid-solution calorimetry was given preference as it is less sensitive to errors in H2O determination. Entropy was estimated, including configurational or magnetic contribution. The resulting ΔfGo (kJ·mol−1) and logKsp values are: CaSn(OH)6−1885.8±7.6, 7.7; FeSn(OH)5O −1425.4±7.6, −5.8; MgSn(OH)6−1812.4±7.5, 3.3; ZnSn(OH)6−1519.6±7.6, 0.7; MnSn(OH)6−1598.7±7.7, 1.0; CuSn(OH)6−1311.2±7.9, 0.0. The logKsp value relate to reaction MSn(OH)6 + 6H+→ M2+ + Sn4+ + 6H2O or FeSn(OH)5O + 7H+→ Fe3+ + Sn4+ + 6H2O. The solid solution between vismirnovite and mushistonite was found to be thermodynamically non-ideal, with a mixing parameters W=−15.38 kJ·mol−1. Calculations of Gibbs free energies of selected reactions show that the tin perovskites are stabilized at basic pH. For example, burtite becomes stable with respect to cassiterite (SnO2) in systems buffered by calcite, gypsum or the C-S-H phase from cement at pH > 9–10.5. Similarly, jeanbandyite is stabilized in systems buffered by ferrihydrite [Fe(OH)3] but not in those buffered by goethite (FeOOH). Saturation indices calculated from polluted water in field settings show the same trend; the tin perovskites are stable under alkaline conditions and the solutions become supersaturated with respect to the tin perovskites. Hence, under alkaline conditions, such phases could take up and retain tin in the environment.

Bizeolite Pt/ZSM-5:ZSM-12/Al2O3 catalyst for hydroisomerization of C-8 fraction with various ethylbenzene content

A bizeolite catalyst based on ZSM-5 and ZSM-12 was designed to maximize the yield of valuable aromatics from ethylbenzene (EB) rich feedstocks for the first time. The catalyst Pt/ZSM-5:ZSM-12/Al2O3 was characterized by X-ray diffraction (XRD), nitrogen physisorption, temperature-programmed desorption of ammonia (TPD-NH3), transmission and scanning electron microscopy (TEM and SEM), X-ray fluorescence analysis (XRF), Fourier-transformed infrared spectroscopy (FTIR) and 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. The catalyst and its components were tested in isomerization of an industrial C-8 aromatic cut (C8-Ar) and feedstocks with high EB content. The catalyst demonstrated higher conversion of EB and m-xylene (MX) compared with an industrial catalyst and higher selectivity to dealkylation products.

An advanced solid polymer electrolyte composed of poly(propylene carbonate) and mesoporous silica nanoparticles for use in all-solid-state lithium-ion batteries

Composite solid polymer electrolytes (CSPEs) are promising candidates for replacing potentially hazardous organic liquid electrolytes used in Li ion batteries (LIBs). CSPEs are easy to process, have the ability to form films, and make better interfacial contact. However, their poor mechanical strength, low ionic conductivity, and long cycling stability limit their practical applications. Here, we demonstrate the fabrication of a cost-effective, flexible, self-standing, and highly stable CSPE using poly(propylene carbonate) (PPC) as the host matrix and highly mesoporous silica nanoparticles (MSNs) as the filler. The fabricated CSPE had a high ionic conductivity of approximately 8.5 × 10−4 S cm−1 at 60°C, electrochemical potential stability up to approximately 4.8 V vs. Li/Li+, an ultra-high lithium transference number of approximately 0.86, impressive stability over 1000 h of Li stripping/plating, and an excellent electrode compatibility. With cyclability over 200 cycles and a negligible overpotential, the Li/CSPE/LFP cell delivered a reversible capacity of 171 and 103 mAh g−1 at 0.1 C and 1 C, respectively, with a good rate capability up to 5 C. The interaction of Li+ with PPC and the MSNs is demonstrated by solid-state magic angle spinning nuclear magnetic resonance (MAS-NMR) and X-ray photoelectron spectroscopy (XPS) studies. The enhanced physico-electrochemical properties of the CSPE were attributed to the large MSNs-related surface area, which enables firm interaction with the PPC matrix and provides a less-tortuous polymer-ceramic phase for fast lithium ion transportation. The proposed MSNs-reinforced CSPE thus opens new possibilities for the fabrication and engineering of solid-state batteries.

Comparison of the composition and structure for coal-derived and petroleum heavy subfraction by an improved separation method

The property of coal-derived asphaltene and resin shows remarkable differences from petroleum one, such as the molecular aggregation and thermal cracking characteristics. It is significant to make deep-level analysis of their composition and structure to provide detailed molecule information for coal tar deep processing. In this paper, an improved separation method, which innovatively developed two-stage asphaltene extraction and two-stage silica gel separation coupling process, was built to obtain the purified asphaltene and resin components derived from coal tar (C-asp and C-res) and petroleum (P-asp and P-res). All samples were analyzed comparatively through Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), solid state cross polarization/magic angle spinning nuclear magnetic resonance spectroscopy (13C-CP/MAS-NMR), thermogravimetric analysis (TG) and scanning electron microscopy (SEM). It is found that C-asp and C-res contain more OH groups resulting in stronger aggregate effect and OH-OH and OH-ether O are the main hydrogen bond. C-asp and C-res have more C-O of phenols and C = O of COOH group. C-asp and C-res have fewer and shorter alkyl side chains. The aromatic ring substitutive degree (σ) of C-asp and C-res is higher while the alkyl branching degree of P-asp and P-res is higher. Besides, asphaltene has higher σ, alkyl substituents number (n), average stack height of aromatic sheet (Lc), average number of aromatic sheets associated in per stacked cluster (M) and shorter average substituted alkyl chain length (L) compared with resin. Finally, the average molecular structure models of C-asp, P-asp, C-res and P-res are obtained.

Microbiota modulation of allelopathy depends on litter chemistry: Mitigation or exacerbation?

Having a pivotal role in biogeochemical cycles, litter decomposition affects plant growth and regeneration by inducing the release of allelochemicals. The aim of this study was to assess the role of the microbiota in modulating the allelopathic effects of freshly fallen and decomposed leaf litter. To disentangle the chemical and microbial effects, bioassays were carried out on four target plants in sterile and non-sterile conditions. All litter types were characterized by carbon-13 cross polarization magic-angle spinning nuclear magnetic resonance (13C-CPMAS NMR) spectroscopy, and the associated fungal and bacterial microbiota were described by next-generation sequencing. When the litter extract was sterilized, freshly fallen litter severely inhibited the plant root growth, but during decomposition, the allelopathic effect rapidly decreased. Root growth was negatively correlated with extractable carbon and positively correlated with parameters associated with tissue lignification. In non-sterile conditions, the living microbiota modulated the leaf litter allelopathic effects of mitigation (26.5% of cases) and exacerbation (26.6% of cases). The mitigation effect was more frequent and intense in stressful conditions, i.e., highly phytotoxic freshly fallen litter, than in benign environments, i.e., decomposed litter. Finally, we identified specific bacterial and fungal operational taxonomic units (OTUs) that could be involved in the mediation of the litter allelopathic effect. This study highlights the importance of studying allelopathy in both sterile conditions and in the presence of a living microbiota to assess the role of litter chemistry and the potential impact of plant detritus on the agro-ecosystem and natural plant communities.

Internalization of Fluoride in Hydroxyapatite Nanoparticles.

Hydroxyapatite (HAP) is a cost-effective material to remove excess levels of fluoride from water. Historically, HAP has been considered a fluoride adsorbent in the environmental engineering community. This paper substantiates an uptake paradigm that has recently gained disparate support: assimilation of fluoride to bulk apatite lattice sites in addition to surface lattice sites. Pellets of HAP nanoparticles (NPs) were packed into a fixed-bed media filter to treat solutions containing 30 mg-F/L (1.58 mM) at pH 8, yielding an uptake of 15.97 ± 0.03 mg-F/g-HAP after 864 h. Solid-state 19F and 13C magic-angle spinning nuclear magnetic resonance spectroscopy demonstrated that all removed fluoride is apatitic. A transmission electron microscopy analysis of particle size distribution, morphology, and crystal habit resulted in the development of a model to quantify adsorption and total fluoride capacity. Low- and high-estimate median adsorption capacities were 2.40 and 6.90 mg-F/g-HAP, respectively. Discrepancies between experimental uptake and adsorption capacity indicate the range of F- that internalizes to satisfy conservation of mass. The model was developed to demonstrate that F- internalization in HAP NPs occurs under environmentally relevant conditions and as a tool to understand the extent of F- internalization in HAP NPs of any kind.

Structure of a retinal chromophore of dark-adapted middle rhodopsin as studied by solid-state nuclear magnetic resonance spectroscopy.

Middle rhodopsin (MR) found from the archaeon Haloquadratum walsbyi is evolutionarily located between two different types of rhodopsins, bacteriorhodopsin (BR) and sensory rhodopsin II (SRII). Some isomers of the chromophore retinal and the photochemical reaction of MR are markedly different from those of BR and SRII. In this study, to obtain the structural information regarding its active center (i.e., retinal), we subjected MR embedded in lipid bilayers to solid-state magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy. The analysis of the isotropic 13C chemical shifts of the retinal chromophore revealed the presence of three types of retinal configurations of dark-adapted MR: (13-trans, 15-anti (all-trans)), (13-cis, 15-syn), and 11-cis isomers. The higher field resonance of the 20-C methyl carbon in the all-trans retinal suggested that Trp182 in MR has an orientation that is different from that in other microbial rhodopsins, owing to the changes in steric hindrance associated with the 20-C methyl group in retinal. 13Cζ signals of Tyr185 in MR for all-trans and 13-cis, 15-syn isomers were discretely observed, representing the difference in the hydrogen bond strength of Tyr185. Further, 15N NMR analysis of the protonated Schiff base corresponding to the all-trans and 13-cis, 15-syn isomers in MR showed a strong electrostatic interaction with the counter ion. Therefore, the resulting structural information exhibited the property of stable retinal conformations of dark-adapted MR.

Bipyridine-silica nanotubes with high bipyridine contents in the framework

Abstract Bipyridine-silica nanotubes (BPy-NTs) represent a solid chelate ligand for the formation of efficient heterogeneous metal complex catalysts. BPy-NTs are typically synthesized by the co-condensation of bipyridine (BPy)- and benzene (Ph)-bridged organosilane precursors. However, the amount of BPy in the framework has been limited to a maximum of 1.22 mmol g−1 owing to the difficulty in the formation of the NT structure. In this study, BPy-NTs with a large amount of BPy ligands (2.43 mmol g−1) were prepared from a reaction mixture with a high molar ratio of BPy precursor (up to 80 mol%) via the optimization of synthesis conditions. Stable nanotube structures with inner diameters in the range of 6.1–7.0 nm and lengths of tens to hundreds of nanometers were characterized using scanning transmission electron microscopy, N2 adsorption, and 29Si magic angle spinning nuclear magnetic resonance spectroscopy analyses. A large amount of Pt(bpy)Cl2 complexes were homogeneously immobilized on the NT walls (PtCl2@BPy-NTs), which was confirmed by high-angle annular dark-field scanning transmission electron microscopy, UV–vis absorption, and X-ray photoelectron spectroscopy analyses. PtCl2@BPy-NTs exhibited efficient photocatalysis for H2 evolution under visible light irradiation. The photocatalytic activity increased as the amount of Pt complexes loaded on the BPy-NTs increased. A small amount of Pt metal particles was formed on the BPy-NTs during the photoreaction, which promoted the H2 evolution reaction, as a catalyst with higher activity than only the Pt complex.