Strong OH Research Articles

Intrinsic physicochemical interactions of calcium hydroxide-based medications.

To investigate intrinsic physicochemical properties and interactions of three different calcium hydroxide-based medications via means of different analytical methods. Two-commercial premixed medications: TempCanal(TCmx) and ProCalR(PCmx) and powder-form ProCal(PCpw) with glycerin were used. Vibrational modes were analyzed using Raman spectroscopy. Spectral mapping of samples was carried out using characteristic vibrational modes of calcium hydroxide and barium sulfate. Crystalline and amorphous phases were studied with X-rays powder diffraction analysis. Topographic features were examined by scanning electron microscope examination and quantitative analysis was determined using energy-dispersive X-ray spectroscopy analysis. Strong OH stretch of in Raman spectra were observed at 3,697 and 3,615 cm-1 for TCmx and reference, respectively. However, OH mode was not observed for PCmx and PCpw. Moreover, some peaks in the fingerprint areas of TCmx and PCpw overlapped with each other. The characteristic vibration bands of barium sulfate and calcium hydroxide were observed in all samples, and no new peak was observed in the Raman spectra of samples. Calcium hydroxide-based medications were seen as differed in their chemical composition. No new crystalline or amorphous phase peak was observed. Only calcium hydroxide and barium sulfate were matched in X-rays powder-diffraction analysis. Energy-dispersive X-ray spectroscopy analysis showed that amount of Ba and S elements in the PCpw were lower than TCmx and PCmx whereas, for Ca in the PCpw was higher than TCmx and PCmx. The present study revealed the structural difference among different forms of calcium hydroxide-based medications. The vehicle and substrates of the tested medications altered the physicochemical properties of the compound via electrostatic interactions.

Conformer selective monohydrated clusters of 1,2,3,4 –tetrahydroisoquinoline in S0: I-Potential energy surface studies, vibrational signatures and NBO analysis

The global minima in the potential energy surface of 1, 2, 3, 4-tetrahydroisoquinoline (THIQ):(H2O) prefer the twisted equatorial orientation of the NH group. It is characterized by a strong OH⋅⋅⋅N and a weak O-H⋅⋅⋅π hydrogen bonds. The computations at the ab initio level and DFT methods with M06–2X and ωB97X-D functionals generated consistent results. The monohydrate with the axial orientation of NH having a single OH⋅⋅⋅N bond in the twisted configuration of THIQ is higher by 240 ± 40 cm−1. The N⋅⋅⋅H bond length is smaller in the latter. All the clusters are located in the potential energy surface of THIQ :(H2O) drawn with the variation of the dihedral angles of the saturated ring of THIQ. Various kinds of hydrogen bonds are observed. Binding energy of each structure is computed incorporating BSSE corrections. Interestingly, the largest of them correspond to a conformer of THIQ, where it was a transition state in the bare molecule. The vibrational analysis of the clusters indicates the reassignment of a number of bands in the observed IR spectra. The red-shifts observed in the different stretching modes of water in the two lowest energy clusters are suitably explained. This is further verified from NBO computations. The changes in s-character, NBO energies and OH bond lengths with the variation of hydrogen bond distances clearly signify the dominant nature of hyperconjugation mechanism. The natures of each OH bonds of water are investigated thoroughly. The bond which is not taking part in hydrogen bonding shows some apparently unexpected behaviors. HOMO and LUMO plots and their energy differences are employed to qualitatively explain the experimental results observed earlier. Changes in Molecular Electrostatic Potentials (MEP) on cluster formation are explained and confirm our computations. Maximum hardness principle (MHP) is followed by the most stable monohydrate only. Hardness values display a certain arrangement depending on the type of hydrogen bonding sites. We suggest further experiments to confirm our key observations.

Effect of cobalt addition on platinum supported on multi-walled carbon nanotubes for water-gas shift

A series of cobalt-promoted Pt catalysts supported on multi-walled carbon nanotubes was synthesized, and their performance was evaluated for the water-gas shift (WGS) reaction. Compared to the monometallic Pt catalyst, the WGS turnover rate (TOR) at 300 °C was promoted by a factor of 10 at a Pt:Co molar ratio of 1:3. X-ray absorption spectroscopy and XRD showed the presence of a Pt3Co alloy along with a partially oxidized cobalt and a free cobalt metal phase after reduction pretreatment. In order to determine the dominant active site over the Co-promoted catalysts, selective leaching of partially oxidized Co (designated as CoOxHy) and Co metal was performed with a 5% wt. acetic acid solution, while preserving the Pt-rich phases. The WGS TOR at 300 °C for the Co-promoted catalysts after leaching was observed to be even lower than that of the monometallic Pt catalyst. Thus, the alloy formation was determined to be inconsequential towards promotion in the WGS TOR, while the dominant active site was determined to be a PtCo alloy in intimate contact with the CoOxHy phase. Combined Density Functional Theory (DFT) calculations and ab-initio thermodynamic phase diagrams point to a monolayer of CoOH being the most stable Co phase on Pt(111) under WGS conditions. Calculations of OH binding energies on Pt(111), Pt3Co(111), and at the interface between CoOH overlayers and Pt(111) show that trends in the WGS activity of these catalysts are linked to the strength of OH binding, with the strongest OH binding found at the interface between CoOH and Pt, supporting the conclusion that a similar interface is the source of enhanced WGS activity in the PtCo bimetallic system.

Electrocatalytic oxidation of PCP-Na by a novel nano-PbO2 anode: degradation mechanism and toxicity assessment

This study aims at investigating the electrocatalytic oxidation of sodium pentachlorophenate (PCP-Na) using a novel nano-PbO2 powder anode. The nano-PbO2 powder (marked as HL-PbO2) was prepared by a simple hydrolysis process, and hydrothermal treatment was followed to improve the activity of HL-PbO2. The HL-PbO2 treated for 24h by hydrothermal process (HL/HT-PbO2-24) was confirmed to possess higher crystallinity, higher oxygen evolution potential, and more active sites, resulting in stronger OH radical generation capacity and higher electrochemical activity. Compared with conventional electrodeposited PbO2 (ED-PbO2) anode, the HL/HT-PbO2-24 anode showed higher PCP-Na degradation rate. Under the same operating conditions, the mineralization current efficiency at HL/HT-PbO2-24 was 2.7 times than that at ED-PbO2. Five intermediates were detected in PCP-Na degradation solution and possible degradation mechanism of PCP-Na was discussed. In addition, the acute toxicity of PCP-Na degradation solution to zebrafish embryos and the oxidative stress induced in zebrafish embryos/larvae were studied to evaluate the ecological security of electrocatalytic oxidation of PCP-Na.

Switching a HO···π Interaction to a Nonconventional OH···π Hydrogen Bond: A Completed Crystallographic Puzzle.

In this article, we present crystallographic and spectroscopic evidence of a tunable system wherein a HO···π interaction switches incrementally to a nonconventional OH···π hydrogen bonding (HB) interaction. More specifically, we report the synthesis of substituted forms of model system 1 to study the effects of aryl ring electronic density on the qualitative characteristics of OH···π hydrogen bonds therein. The OH stretch in experimental infrared data, in agreement with density-functional theory (DFT) calculations, shows continuous red-shifts as the adjacent ring becomes more electron rich. For example, the OH stretch of an amino-substituted analogue is red-shifted by roughly 50 cm-1 compared to the same stretch in the CF3 analogue, indicating a significantly stronger HB interaction in the former. Moreover, DFT calculations (ωB97XD/6-311+G**) predict that increasing electronic density on the adjacent top ring reduces the aryl π-OH σ* energy gap with a concomitant enhancement of the OH n-π* energy gap. Consequently, a dominant π-σ* interaction in the amino substituted analogue locks the system in the in-form while a favorable n-π* interaction reverses the orientation of the oxygen-bound hydrogen in its protonated form. Additionally, the 1H NMR data of various analogues reveal that stronger OH···π interactions in systems with electron-rich aromatic rings slow exchange of the alcoholic proton, thereby revealing coupling with the geminal proton. Finally, X-ray crystallographic analyses of a spectrum of analogues clearly visualize the three distinct stages of "switch"-starting with exclusive HO···π, to partitioned HO···π/OH···π, and finally to achieving exclusive OH···π forms. Furthermore, the crystal structure of the amino analogue reveals an interesting feature in which an extended HB network, involving two conventional (NH···O) and two nonconventional (OH···π) HBs, dimerizes and anchors the molecule in the unit cell.

Zn-CNTs-Cu catalytic in-situ generation of H2O2 for efficient catalytic wet peroxide oxidation of high-concentration 4-chlorophenol

4-chlorophenol (4-CP) with high concentration is difficult to degrade thoroughly by traditional treatment methods due to its high biotoxicity and refractory to bio-degradation. A novel catalytic wet peroxide oxidation (CWPO) system based on Zn-CNTs-Cu catalysts through the in-situ generation of H2O2 was constructed and investigated for the degradation of high-concentration 4-CP for the first time. Zn-CNTs-Cu composite was prepared by the infiltration melting-chemical replacement method. The operational factors effect, mechanism, and pathways of Zn-CNTs-Cu/O2 system for high concentration of 4-CP degradation were systematically performed and discussed. At the optimal experimental conditions, the degradation efficiency of 4-CP through CWPO system with Zn-CNTs-Cu/O2 achieved 100 %, which was 689 % higher than that of wet oxidation system with O2 alone. According to the mainly in-situ generated H2O2, the strong oxidative OH radical and wet-oxidation effect of O2, high concentration of 4-CP degraded into small molecular organic matter, even been mineralized into carbon dioxide and water in the Zn-CNTs-Cu/O2 based CWPO system. Overall, Zn-CNTs-Cu/O2 CWPO system can efficiently degrade high-concentration 4-CP through the in-situ generation of H2O2 without extra replenishment, and it provides a novel method and strategy to the efficient treatment of refractory chlorophenols wastewater.

Probing molecular interactions of polysaccharides in the presence of water

Herein we report new dielectric relaxation processes at high frequency (ca. 1.2•108 Hz) in polysaccharides pellets (cellulose, chitin, chitosan, starch and amylopectin) that are traceable to strong OH–H2O interactions. Temperature dependence of high frequency dielectric relaxation behavior is investigated using dielectric spectroscopy. In situ temperature FTIR, XRD and TGA measurements are studied to assess relaxation processes related to vibration of OH groups. Upon heating below the glass transition there appears an Arrhenius-type dependence with negative activation energy; this is due to re-orientation of dipoles to lower energy. Upon further heating a glass transition is observed and then there appears another Arrhenius-type process with positive activation energy due to the increasing of random thermal motions of chains, water molecule evaporation and hydrogen bonding destruction. In dry samples the activation energies of this relaxation are practically zero because no exist water molecules and OH groups of polysaccharides are trapped in a potential well.

Rapid screening of antioxidant bioactive components in blue ginger (Dichorisandra thyrsiflora) essential oil by GC electronic-nose and radical scavenging mechanisms

In this study, a gas chromatography-type electronic nose (GC E-nose) was used to identify the chemical components of blue ginger (Dichorisandra thyrsiflora) essential oil (DTEO) and to rapidly screen the antioxidant and radical scavenging activities of these components through combined with the chemical methodology. The results showed that most of the compounds in DTEO had certain scavenging abilities to 1,1-diphenyl-2- picrylhydrazine (DPPH), 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulphonate) (ABTS) and hydroxyl (OH) radicals, but the radical scavenging abilities were quite different. α-Terpineol, eucalyptol, β-elemene, and epicurzerenone showed the strongest DPPH radical scavenging abilities and scavenging rates were 82.5%, 81.4%, 72.4%, and 60.4%, respectively. Eucalyptol, 2-nonanol, myrtenol, and α-terpineol showed the strongest ABTS radical scavenging abilities and scavenging rates were 82.9%, 81.7%, 81.7%, and 78.6%, respectively. Myrtenol and camphor showed the strongest OH radical scavenging abilities and scavenging rates were 55.0% and 53.2%, respectively. Furthermore, the mechanisms of radical scavenging and the structure-activity relationship between the structure and radical scavenging activity were elucidated.

Conformation and bonding of 2-methoxypyridine and its monohydrate from rotational spectra

Rotational spectra of 2-methoxypyridine and its monohydrate have been characterized by pulsed jet Fourier transform microwave spectroscopy and complementary ab initio calculations. Rotational spectra of the parent monomer and seven mono-substituted isotopologues (13C and 15N) were measured in natural abundance, which allow determining the accurate structure of the skeleton of 2-methyoxypyridine. The barrier to the methyl internal rotation was determined from the A/E torsional symmetry species of the rotational transitions. For the 2-methyoxypyridine⋯H2O complex, rotational spectra of the parent dimer and isotopologues formed with isotopically enriched water (H218O, HOD, DOH and D2O) indicate that the observed isomer is stabilized by a strong OH⋯N and a secondary bifurcated (CH)2⋯O weak hydrogen bonds. Bader's quantum theory of atoms in molecules and Johnson's non-covalent interaction analyses were applied and visualized to have a better understanding of the non-covalent interactions in 2-methyoxypyridine⋯H2O.

Large H2O solubility in dense silica and its implications for the interiors of water-rich planets

Sub-Neptunes are common among the discovered exoplanets. However, lack of knowledge on the state of matter in [Formula: see text]O-rich setting at high pressures and temperatures ([Formula: see text]) places important limitations on our understanding of this planet type. We have conducted experiments for reactions between [Formula: see text] and [Formula: see text]O as archetypal materials for rock and ice, respectively, at high [Formula: see text] We found anomalously expanded volumes of dense silica (up to 4%) recovered from hydrothermal synthesis above ∼24 GPa where the [Formula: see text]-type (Ct) structure appears at lower pressures than in the anhydrous system. Infrared spectroscopy identified strong OH modes from the dense silica samples. Both previous experiments and our density functional theory calculations support up to 0.48 hydrogen atoms per formula unit of ([Formula: see text])[Formula: see text] At pressures above 60 GPa, [Formula: see text]O further changes the structural behavior of silica, stabilizing a niccolite-type structure, which is unquenchable. From unit-cell volume and phase equilibrium considerations, we infer that the niccolite-type phase may contain H with an amount at least comparable with or higher than that of the Ct phase. Our results suggest that the phases containing both hydrogen and lithophile elements could be the dominant materials in the interiors of water-rich planets. Even for fully layered cases, the large mutual solubility could make the boundary between rock and ice layers fuzzy. Therefore, the physical properties of the new phases that we report here would be important for understanding dynamics, geochemical cycle, and dynamo generation in water-rich planets.

Sequential Synthesis and Active‐Site Coordination Principle of Precious Metal Single‐Atom Catalysts for Oxygen Reduction Reaction and PEM Fuel Cells

AbstractCarbon‐supported precious metal single‐atom catalysts (PM SACs) have shown promising application in proton exchange membrane fuel cells (PEMFCs). However, the coordination principle of the active site, consisting of one PM atom and several coordinating anions, is still unclear for PM SACs. Here, a sequential coordination method is developed to dope a large amount of PM atoms (Ir, Rh, Pt and Pd) into a zeolite imidazolate framework (ZIF), which are further pyrolyzed into nitrogen‐coordinated PM SACs. The PM loadings are as high as 1.2–4.5 wt%, achieving the highest PM loadings in ZIF‐derived SACs to date. In the acidic half‐cell, Ir1‐N/C and Rh1‐N/C exhibit much higher oxygen reduction reaction (ORR) activities than nanoparticle catalysts Ir/C and Rh/C. In the contrast, the activities of Pd1‐N/C and Pt1‐N/C are considerably lower than Pd/C and Pt/C. Density function theory (DFT) calculations reveal that the ORR activity of PM SAC depends on the match between the OH* adsorption on PM and the electronegativity of coordinating anions, and the stronger OH* adsorption is, the higher electronegativity is needed for the coordinating anions. PEMFC tests confirm the active‐site coordination principle and show the extremely high atomic efficiency of Ir1‐N/C. The revealed principle provides guidance for designing future PM SACs for PEMFCs.

Photochemical reactions of 1,3-butadiene with nitrogen oxide in different matrices: Kinetic behavior, humidity effect, product and mechanisms

Understanding the photochemical reaction process between VOCs and co-pollutants in the troposphere is crucial for controlling the haze. The photochemical reactions of 1,3-butadiene (1,3-BD) with NO were carried out at 308 K for up to 96 h in clean air with various relative humidity (RH) values, and actual haze atmosphere. In the haze, the representative pseudo-first-order kinetic rate constants of the 1,3-BD–NO system was 1.53 time higher than those in dry clean air. The effect of the RH (0%–80%) on the conversion behavior of the 1,3-BD–NO system in clean air was studied, revealing that increasing RH promoted the photochemical reaction in the low range of 0%–40% but retarded it in the high range of 40%–80%. Interestingly, OH radicals were directly detected under different RH values, and the strongest OH signal was obtained at an RH of 40%. Multiple macromolecular products with carbon numbers of 10–36 were identified. Unexpectedly, richer products and extended unsaturation range were detected at an RH of 40% than 0%. The photochemical products were also analyzed using ion chromatography. A reaction mechanism was proposed from the detected NO2, O3, OH, HNO2, HNO3, organic acids and macromolecular products.

New mechanism insights into methane steam reforming on Pt/Ni from DFT and experimental kinetic study

In this contribution, we combine density functional theory (DFT) calculations, experimental kinetic study and DFT-assisted analysis to elucidate the impact of the interface of monolayer Pt on the Ni surface on catalytic performance of steam methane reforming including carbon formation on core-shell (Ni@Pt) catalysts and compare it with Ni and Pt catalysts. We demonstrate that core-shell structured Ni@Pt significantly lowers the carbon formation without sacrificing much the activity. The DFT results demonstrate that the metal identity, core shell structure and support have significant impacts on the reaction mechanisms. The direct methane activation is energetically favorable reaction pathway on Ni, while the OH* assisted methane activation is the favorable pathway on Pt and Ni@Pt catalysts, where methane activation is the rate-determining step on all catalysts. We unambiguously reveal that the core-shell Ni@Pt catalyst modified the surface Pt electron density and shifted d-band center away from Fermi level compared to Ni(1 1 1) and Pt(1 1 1). It results in a strong basic surface OH* which actively reacts with CHx and thus enhances carbon formation resistance. Above all, Ni-core/Pt-shell particle could decouple the activity and carbon resistance to keep the activity and reduce carbon formation simultaneously in methane steam reforming. In addition, by taking into account the activation of steam on the support, the effective activation energy estimated from DFT-assisted analysis is well consistent with the experimental value on the both Ni and Ni@Pt catalysts, which could shed some light on building a bridge between experimental work and DFT-assisted kinetic study.

Protonation of Naphthalene-(Water)n Nanoclusters: Intracluster Proton Transfer to Hydration Shell Revealed by Infrared Photodissociation Spectroscopy.

Solvation-dependent intracluster proton transfer (ICPT) within bare and Ar-tagged protonated naphthalene-(water)n clusters, H+(Np-Wn) with n ≤ 3, is characterized by infrared photodissociation (IRPD) spectroscopy in a supersonic plasma expansion. IRPD spectra of size-selected clusters recorded in the CH and OH stretch range (2750-3800 cm-1) are analyzed with dispersion-corrected density functional theory (DFT) calculations (B3LYP-D3/aug-cc-pVTZ) to determine both the protonation site and the structure of the hydration network. Ar tagging of H+(Np-Wn) leads to colder spectra with higher spectral resolution. The position of the excess proton is controlled by a subtle balance between the difference in proton affinity (PA) of Np and Wn and the involved solvation energies. For n = 1, the excess proton is localized on the Np ring, leading to a H+Np-W structure with a bifurcated CH···O ionic H-bond, because of the large difference in PA of Np and W. For n = 2, ICPT occurs, and the cluster has a structure in which a symmetric Zundel ion is connected to Np via two strong OH···π ionic H-bonds. Because of the similar PA values of W2 and Np, the energetics of the ICPT is largely decided by the higher solvation energy in favor of Np-H+W2 as compared to H+Np-W2. For n ≥ 3, the PA of Wn substantially exceeds the one of Np, leading to ICPT. Attachment of the bulky planar Np ring to H+Wn causes an increasing perturbation of the bare H+Wn cluster with size by symmetry reduction and the strong OH···π H-bonds. Comparison of H+(Np-Wn) with the related H+(Bz-Wn) clusters (Bz = benzene) indicates the implications of extending the aromatic π-electron system on both the critical threshold size for ICPT (nc = 1 for Bz and nc = 2 for Np) and the structure of the hydration network.

High-Temperature Evolution of Point Defect Equilibria in Hydrous Forsterite Synthesized at 1100 °C and up to 4 GPa

Water distribution in the deep Earth represents one of the most important topics in the field of geodynamics due to its large impact on the physical and chemical properties of the Earth’s mantle, such as electrical conductivity, seismic anisotropy, diffusion, and rheology. In this study, we synthesized hydrous forsterite at 1100 °C and up to 4 GPa with either a piston-cylinder or multianvil apparatus. As a starting material, we used synthetic forsterite, unbuffered by SiO2, obtained by thermo-mechanical activation of talc and magnesium carbonate hydroxide. Hydration was carried out using liquid H2O as hydrogen source. Samples were polycrystalline in an effort to distribute H2O throughout the sample both rapidly and homogeneously. Using the Paterson calibration, we observed total water content concentrations ranging between 100 and 500 ppm wt H2O. Multiple absorption bands are found in the frequency range between 3400 and 3650 cm−1, identifying at least seven peaks in all samples. Vibrational bands were centered at 3476, 3535, 3550, 3566, 3578, 3605, and 3612 cm−1, in good agreement with experimental studies conducted on both hydrous forsterite and single crystals of olivine. The stronger OH stretching peaks can be attributed to vibrational modes associated with the hydrogarnet defect 4 H Si x in which four protons occupy a vacant tetrahedral site. None of the OH bands observed are found at frequencies associated with hydrogen occupying vacant octahedral sites. High-temperature FTIR spectroscopy was used to evaluate the evolution of IR spectra as a function of temperature, up to 500 °C. The complete reversibility of peak absorption vs. temperature in the OH stretching region confirms that no water loss occurred during heating. We observe an overall a decrease in total absorption with increasing temperature, and a prominent decrease in the relative intensities of the higher frequency bands (>3600 cm−1) with respect to lower frequency bands. We have assigned a series of equilibrium expressions based on the variation of relative peak areas with temperature and find that enthalpies of these processes range between 0.047–0.068 eV (4.5–6.5 kJ/mol), very low in comparison to activation energies observed for electrical conduction in hydrous olivine. Major changes in the vibrational spectrum are expected to be related to configurational changes of the same fully protonated hydrogarnet defect species. However, the complexity of the FTIR spectra may also be related to partially protonated defects, such as the associate defect 3 H Si ′ + H i • generated by a dissociation reaction of the hydrogarnet species.

Engineering Surface Structure of Spinel Oxides via High-Valent Vanadium Doping for Remarkably Enhanced Electrocatalytic Oxygen Evolution Reaction.

Spinel oxides (AB2O4) with unique crystal structures have been widely explored as promising alternative catalysts for efficient oxygen evolution reactions; however, developing novel methods to fabricate robust, cost-effective, and high-performance spinel oxide based electrocatalysts is still a great challenge. Here, utilizing a complementary experimental and theoretical approach, pentavalent vanadium doping in the spinel oxides (i.e., Co3O4 and NiFe2O4) has been thoroughly investigated to engineer their surface structures for the enhanced electrocatalytic oxygen evolution reaction. Specifically, when the optimal concentration of vanadium (ca. 7.7 at. %) is incorporated into Co3O4, the required overpotential to reach a certain jGEOM and jECSA decreases dramatically for oxygen evolution reactions in alkaline media. Even after 30 h of chronopotentiometry, the required potential for V-doped Co3O4 just increases by 16.3 mV, being much lower than that of the undoped one. It is observed that the pentavalent vanadium doping introduces lattice distortions and defects on the surface, which in turn exposes more active sites for reactions. DFT calculations further reveal the rate-determining step changing from the step of *-O to *-OOH to the step of *-OH to *-O, while the corresponding energy barriers decrease from 1.73 to 1.57 eV accordingly after high-valent V doping. Moreover, the oxygen intermediate probing method using methanol as a probing reagent also demonstrates a stronger OH* adsorption on the surface after V doping. When vanadium doping is performed in the inverse spinel matrix of NiFe2O4, impressive performance enhancement in the oxygen evolution reaction is as well witnessed. All these results clearly illustrate that the V doping process can not only efficiently improve the electrochemical properties of spinel transition metal oxides but also provide new insights into the design of high-performance water oxidation electrocatalysts.

Stable isotope analyses of the carbonate component of bones and teeth: The need for method standardization

In addition to the collagen and phosphate components of bones and teeth, the stable carbon and oxygen isotope compositions of skeletal carbonate are frequently measured to determine diet, environmental conditions, and populational or individual migration in bioarchaeological research. A standardized method for the stable isotopic analysis of skeletal carbonate has not yet been established, despite the importance of these data. In this study, significant differences in the stable oxygen isotope values of bones and dental enamel were observed, which arose due to instrument- and methodology-based differences. The same target archaeological samples were analyzed in three laboratories, and the stable isotope analyses were supplemented by Fourier Transformation Infrared Spectroscopy (FTIR) measurements, which detected a strong OH− concentration-dependence in the stable oxygen isotopic shifts measured between the three laboratories. Laboratory experiments were conducted to quantify the effects of reaction temperature and phosphoric acid (H3PO4) concentration on the oxygen isotopic composition of carbonate, both of which resulted in significant, though smaller δ18O changes than the OH-related δ18O change. As such, we suggest that the δ18O values of bone structural carbonate should not be included in anthropological interpretation and that the analysis of tooth enamel should be conducted at 70 °C using 102% H3PO4, in order to make the results comparable. Furthermore, carbonated hydroxylapatite (CHAP) reference materials with varied isotopic compositions should be developed in the near future.

A new type of Indium(III) fluoride complex containing In(III) atoms in both anion and cation: Crystal structure and vibrational spectra

A new type of fluoride complex of indium(III) [N(CH3)4]6[In(H2O)6][InF6]3·18H2O (1) containing In(III) atoms in the hexafluoride complex anion and the hexaaquacomplex cation has been synthesized and structurally studied. The structure of [N(CH3)4]6[In(H2O)6][InF6]3·18H2O is formed by isolated octahedral complex [In(1)F6]3– and [In(2)F6]3– anions, octahedral complex [In(3)(H2O)6]3+ cations, [N(CH3)4]+ cations, and crystallization H2O molecules. A formation in the structure of 1 of a rather strong OH···F hydrogen bond between the coordinated H2O molecules of the cation and F atoms of the complex anion with O···F distances of 2.472(1) Å has been established. The synthesized and structurally studied compound 1 is the obtained for the first time indium(III) fluoride complex containing a hexaaquacomplex [In(3)(H2O)6]3+ cation having the configuration of a practically ideal octahedron. The vibrational spectra of the synthesized compound have been discussed with taking into account the results of crystal structure studies.

The mechanism of electrophilic addition of singlet oxygen to pyrrolic ring

Pyrrolic compounds assume an important role in the chemistry of living organisms, coal surrogates and novel drugs. However, literature reports a few studies on their reactivity towards prominent oxidising agents. This contribution presents a comprehensive mechanistic study of the oxidation of unsubstituted pyrrole with singlet oxygen (O2 1∆g) by deploying a quantum chemical framework leading to the production of succinimide, as the major products, through a Diels–Alder addition of O2 1∆g to the aromatic ring. Other products such as maleimide, hydroperoxide, formamide and epoxide adducts appear to form via insignificant channels. The primary Diels–Alder channel encompasses a barrier of 41 kJ/mol with a fitted rate constant of k(T) = 1.87 × 10−13 exp(− 48,000/RT) cm3 mol−1 s−1. Furthermore, a kinetic study has been undertaken to investigate the influence of substituents on reaction rate of the Diels–Alder addition of singlet oxygen to a pyrrolic ring. The results clarify that electropositive substituents such as BeH and BH2 operate as π-acceptors and thus deactivate the ring towards electrophilic attack of singlet oxygen. However, substituents comprising of strong π-donors, e.g., NH2 and OH, destabilise the ring structure, increasing its oxidation reactivity.

New insights into CO2 methanation mechanisms on Ni/MgO catalysts by DFT calculations: Elucidating Ni and MgO roles and support effects

CO2 methanation mechanisms were investigated by DFT calculations on pure Ni(111), hydrogen-assisted MgO(110) and Ni/MgO surfaces to get insights into Ni and MgO roles and support effects on the mechanisms. For Ni/MgO catalysts, Ni is the active site and MgO acts as the promoter for CO2 methanation reaction. The role of Ni on the reaction is not only to decompose H2 to H atom but also the active site for CO2 hydrogenation. Compared with the pure Ni surface, Bader charge analysis has demonstrated strong metal–support interactions between Ni and MgO distinctly improve Ni reducibility of the Ni/MgO surface. This leads to that the C terminal of CO2 gains more electrons from the Ni/MgO surface, thus promoting the process of C-terminal hydrogenation on the surface. Consequently, CO2 methanation follows the formate pathway via the H2COO* intermediate on the Ni/MgO surface, differing from the formate pathway via the HCOOH* intermediate on the Ni(111) surface. In addition, the presence of MgO support is beneficial for the OH removal and then the H2O formation during CO2 methanation, due to the H-spillover effect and the strong OH adsorption on the MgO support.