Hydroxyl Proton Research Articles

Non-Classical Deactivation Mechanism in a Supported Intermetallic Catalyst for Propane Dehydrogenation.

Platinum-based supported intermetallic alloys (IMAs) demonstrate exceptional performance in catalytic propane dehydrogenation (PDH) primarily because of their remarkable resistance to coke formation. However, these IMAs still encounter a significant hurdle in the form of catalyst deactivation. Understanding the complex deactivation mechanism of supported IMAs, which goes beyond conventional coke deposition, requires meticulous microscopic structural elucidation. In this study, we unravel a nonclassical deactivation mechanism over a PtZn/γ-Al2O3 PDH catalyst, dictated by the PtZn to Pt3Zn nanophase transformation accompanied with dezincification. The physical origin lies in the metal support interaction (MSI) that enables strong chemical bonding between hydroxyl groups on the support and Zn sites on the PtZn phase to selectively remove Zn species followed by the reconstruction towards Pt3Zn phase. Building on these insights, we have devised a solution to circumvent the deactivation by passivating the MSI through surface modification of γ-Al2O3 support. By exchanging protons of hydroxyl groups with potassium ions (K) on the γ-Al2O3 support, such a strategy significantly minimizes the dezincification of PtZn IMA via diminished metal-support bonding, which dramatically reduces the deactivation rate from 0.2044 to 0.0587 h-1. These findings decode the nonclassical PDH deactivation mechanism over supported IMA catalysts and elaborate a new logic for the design of high-performance IMA based PDH catalysts with long-term stability.

Improved thermal stability and electrical conductivity of dysprosium doped barium zirconium cerate electrolyte

Acceptor-doped perovskites based on the BaCeO3 have been extensively investigated as promising candidates for proton-conducting electrolyte at intermediate temperatures. This operational regime is characterized by proton conduction facilitated via hydroxyl protons that effectively occupy vacancies of oxide ions within the perovskite crystal lattice structure. While the trade-off parameters (proton conductivity and chemical stability) concern the utility of cerium-based electrolytes, acceptor doped compounds hinder the mobility of protons due to dopant-charge and dopant-host interactions. However, Dy-doped compounds reveal a promising behavior relative to most acceptor substituents with marginal constraints at higher doping concentration. As a result, a threshold doping range is essential to combat material inconsistencies such as cationic disorder to proton trapping effect. Therefore in the present study we synthesize the single-phase dysprosium and zirconium co-doped barium cerate at different doping concentrations (BaCe0.8-xZr0.2DyxO3-δ (x = 0.0–0.20)) to showcase the chemical inertness of the compound against oxidizing and reducing atmospheres preserving high ionic conductivity. According to our experimental outcomes, higher ionic conductivity among wet atmospheric conditions suggests the role of moisture to contribute additional charge carriers among the Dy-doped samples via explicitly generated oxygen vacancies. As a result, BaCe0.65Zr0.2Dy0.15O3-δ demonstrates a highest total conductivity, reaching 2.44 x 10-2 S cm−1 at 575 °C, with an associated activation energy of 0.61 eV within the temperature range of 300–600 °C. The study also reveals the optimal operating temperature of the proton conducting electrolyte to avoid mixed ionic (H+ and O2–) conduction.

Adsorption of 2-4-6.trichlorophenol on montmorillonite surface: ONIOM study

The wastewater contains several chemicals, organic and inorganic molecules, among themolecules, 2.4.6-trichlorophenol, which is a source of contamination. The main aim of this work is to distinguish the process of 2.4.6-trichlorophenol retention with montmorillonite using QM: MM-ONIOM approach and applying local and global reactivity parametersthatare an excellent key for identifying adsorption sites. A weak hydrogen bond between the hydroxyl proton of 2,4,6-trichlorophenol molecule and oxygen atom on the montmorillonite surface, with a specific distance, Hb = 2.66 Å using M06-2X functional) has proved the physical adsorption. Thermochemical analysis reveals the exothermic nature of adsorption process. Negative ΔH values signify heat release and negative ΔG values indicating spontaneity under standard conditions.Theobtained results have proved an agreement with other experimental and theoretical data.

Alkaline modified Zr-loading on nanosheet zeolite towards production of γ-valerolactone from levulinic acid through catalytic transfer hydrogenation

A self-pillared nanosheet ZSM-5 zeolite (SP) loading Zr catalyst is prepared for conversion of levulinic acid (LA) to produce γ-valerolactone (GVL). The hierarchical pore by nanosheet aggregates promotes Zr dispersion with establishment of strong interaction between Zr and zeolite. Moreover, Na ions are introduced to modify the chemical environment of Zr on nanosheet zeolite (Zr/NaSP). In catalytic transfer hydrogenation of LA using isopropanol as H-donor, uniformly dispersed Zr species on SP zeolite is conducive for both conversion of LA as well as production of GVL, in comparison with samples using conventional microporous ZSM-5 as supports (Zr/CZ). More importantly, different from protonated zeolite sample (Zr/HSP), the introduction of alkali sites could attract protons in hydroxyl groups of isopropanol, which accelerates the generation rates of GVL. The as-designed Zr/NaSP catalyst delivers GVL generation rates of 31.9 mmol·g-1·h-1, which provides a potential catalyst for GVL production.

Unveiling the therapeutic potential of organotellurium(IV) Schiff base complexes through structural elucidation, antimalarial, antioxidant and antimicrobial studies

Infectious diseases have long been a formidable adversary to human health and well-being, presenting a persistent global challenge with far-reaching implication for individuals, communities and societies at large. Thus, with the aim of a combating agent against malarial and oxidant causing ailments, the newly synthesized Organotellurium(IV) complexes with a hydroxynaphthaldehyde Schiff base ligand are proposed in the present research. The structures of the complexes were established through various physical and spectral analysis. The weak electrolytic (8.77 to 35.08 ohm−1 cm2 mol−1) and crystalline nature of the compounds were demonstrated by molar conductivity and TGA, respectively. The ligand and complexes (7a-7f) shows molecular ion peaks at m/z 458.3563, 726.1039, 713.6978, 727.6179, 799.4780, 771.3178 and 799.3978 amu which were well consistent with their formula, revealing formation of compounds. The shifting of ligand's azomethine peak (7.74 ppm) and disappearance of naphthyl hydroxyl proton (12.28 ppm) in 1H NMR spectra confirmed the chelation of ligand with metal ion in proposed manner. In the FT-IR spectra, the complexation of ligand with metal ion was confirmed by disappearance of hydroxyl group (3355 cm−1) band and shifting of C = N (1245 cm−1) and CO (1632 cm−1) band whereas appearance of Te-O (of 285–293 cm−1) and Te-N (458–467 cm−1) bands, revealed the bonding of metal with metal and octahedral nature of the complexes. Optimized structures, HOMO-LUMO energies and associated chemical reactivity descriptors of the compounds were computed by DFT calculations. The in vitro studies demonstrate that the complexes 7c (1.06 ± 0.11 μM) and 7f (1.22 ± 0.05 μM) exhibited moderate inhibition of the Plasmodium falciparum 3D7 strain, complexes 7a (100.96 ± 0.32 μg/mL) and 7d (96.32 ± 0.40 μg/mL) demonstrated the highest free radical quenching ability. Complex 7c displayed the highest antibacterial actions, whereas 7f exhibited the highest antifungal actions against the tested pathogens. Molecular docking and ADMET studies demonstrated enhanced binding affinity of the complexes compared to the Schiff base and their drug-like qualities.

Electron transfer in MOF-derived cobalt-magnesium oxide–carbon microsphere composite catalytic ozonation of thiamphenicol

Cobalt-magnesium oxide–carbon microsphere composite (Co-MgO-CMS), Cobalt-carbon nanosheet composite (Co-CNS), and magnesium oxide–carbon nanorod composite (MgO-CNR) were synthesized by the MOFs self-sacrificing template method. And they were used as the catalysts for catalytic ozonation of thiamphenicol (20 mg/L) in water at an initial pH of 7.0. The phase of Co-MgO-CMS is mainly composed of metallic cobalt, magnesium oxide and carbon according to X-ray diffraction and transmission electron microscopy analyses. Thiamphenicol removal efficiency is enhanced through Co-MgO-CMS catalytic ozonation (75.4 %, in 6 min), compared with those in ozonation alone (39.8 %), Co-CNS catalytic ozonation (43.2 %), MgO-CNR catalytic ozonation (65.1 %) and Mg-Co binary oxide (Mg2CoOy) catalytic ozonation (69.0 %). Self-increasing of solution pH, protonated hydroxyl groups and electron transfer on metallic Co and lattice Co2+ are advantageous for the ozone decomposition into reactive oxygen species in Co-MgO-CMS catalytic ozonation. Owing to the metallic Co in Co-MgO-CMS, the electron transfer ability of Co-MgO-CMS is better than that of Mg2CoOy according to the in situ electrochemical test. Moreover, electron transfers directly from metallic Co to ozone. While protonated hydroxyl groups are the key for electron transfer on lattice Co2+. A possible degradation pathway for thiamphenicol in Co-MgO-CMS catalytic ozonation is proposed according to the detected intermediates. This work provides insight into improvement on electron transfer ability of concerted acid-base catalyst in heterogeneous catalytic ozonation.

Removal of Congo red dye from industrial effluents using metal oxide-clay nanocomposites: Insight into adsorption and precipitation mechanisms

The efficacy of magnesium oxide (MgO)-bentonite clay nanocomposite particles (MgO nanoparticles embedded in powdered bentonite clay) for water and wastewater treatment applications is examined herein. Congo red (CR), a widely used azo dye, was used as the model contaminant. For CR concentrations ≤120 mg/L, the optimum nanocomposite dosage was ≤1 g/L, achieving CR removal ≥99% for contact times (mixing durations) ≤10 min, whereas temperature and pH had no significant effect on the treatment process. The removal of CR dye followed the pseudo-second-order model than the first order model. Furthermore, adsorption isotherms followed the Langmuir adsorption isotherm rather than the Freundlich adsorption isotherm (R2 ≥ 0.99), hence confirming monolayer homogenous adsorption. The surface morphological and physicochemical characteristics of the nanocomposite were also identified, and results suggest that CR removal was governed by electrostatic attraction between the protonated hydroxyl groups (i.e., -OH2+), embedded on the nanocomposite surface, and the negatively charged –SO3-groups of the CR dye. When used for the treatment of real printing ink wastewater, CR was practically removed (⁓100%), whereas for real printing and dyeing wastewater (PDW), a more challenging effluent that also contains salts and other contaminants, CR removal was ≥80%. Overall, the produced MgO-bentonite clay nanocomposite hold great promise for sustainable CR removal, a typical contaminant that is released by many industries including printing, tannery and textile, paper, plastic, and paint and coatings.

Characteristic and mechanism of efficient phosphate removal by Portland cement/slag powder/coal ash-hydrate (PC/SP/CA-H)

The excessive presence of phosphate in water leads to eutrophication, prompting us to develop a novel material named PC/SP/CA-H (Portland cement/slag powder/coal ash-hydrate). The experimental data accorded with the pseudo-second-order kinetics and Langmuir model, suggesting that chemical interactions predominated in the adsorption process. Within 4 hours, PC/SP/CA-H rapidly removed phosphate at a rate of 65%, which exceeded 90% after 12 hours with a material dosage of 30 g/L and a phosphate concentration of 30 mg/L. The maximum phosphate adsorption capacity of PC/SP/CA-H was 8.84 mg/g. The material exhibited effective phosphate removal capabilities across a wide pH range of 3.0–11.0. It demonstrated remarkable selectivity to phosphate in the presence of competitive anions, such as CO32-, HCO3-, NO3-, SO42-, and Cl-. Characterization analyses including SEM, BET, XRD, XRF, FTIR, and XPS were conducted to investigate the performance of PC/SP/CA-H and mechanisms of phosphate removal. The findings indicated that phosphate replaced hydroxyl groups on the material to form inner-sphere complexes through ligand exchange. Besides, phosphate was adsorbed onto the positively charged material via electrostatic attraction with protonated hydroxyl groups (-OH2+). It also reacted with metal cations (Ca2+) released by the material to form insoluble crystalline substances (Ca-P) through surface precipitation. This material holds promising prospects for efficiently removing phosphate from water or wastewater, while simultaneously enhancing the resource utilization of coal ash and slag powder.

Comparative Conformational Analysis of Acyclic Sugar Alcohols Ribitol, Xylitol and d-Arabitol by Solution NMR and Molecular Dynamics Simulations.

Ribitol (C5H12O5) is an acyclic sugar alcohol that was recently identified in O-mannose glycan on mammalian α-dystroglycan. The conformation and dynamics of acyclic sugar alcohols such as ribitol are dependent on the stereochemistry of the hydroxyl groups; however, the dynamics are not fully understood. To gain insights into the conformation and dynamics of sugar alcohols, we carried out comparative analyses of ribitol, d-arabitol and xylitol by a crystal structure database search, solution NMR analysis and molecular dynamics (MD) simulations. The crystal structures of the sugar alcohols showed a limited number of conformations, suggesting that only certain stable conformations are prevalent among all possible conformations. The three-bond scholar coupling constants and exchange rates of hydroxyl protons were measured to obtain information on the backbone torsion angle and possible hydrogen bonding of each hydroxyl group. The 100 ns MD simulations indicate that the ribitol backbone has frequent conformational transitions with torsion angles between 180∘ and ±60∘, while d-arabitol and xylitol showed fewer conformational transitions. Taking our experimental and computational data together, it can be concluded that ribitol is more flexible than d-arabitol or xylitol, and the flexibility is at least in part defined by the configuration of the OH groups, which may form intramolecular hydrogen bonds.

Differentiation of isomeric chalcone and dihydroflavone using liquid chromatography coupled with hydrogen-deuterium exchange tandem mass spectrometry (HDX-MS/MS): An application for flavonoids-focused characterization of Snow chrysanthemum

Although the co-occurrences of isomeric chalcones and dihydroflavones widely appear in medicinal plants, the differentiation of such isomerism seldom succeeds using MS/MS, attributing to totally identical MS/MS spectra. Here, efforts were paid to pursue an eligible tool allowing to address the technical challenge. Being inspired by that one more proton signal is observed in 1H NMR spectrum of isoliquiritigenin than liquiritigenin when employing DMSO‑d6 as solvent, hydrogen-deuterium exchange (HDX)-MS/MS was evaluated towards differentiating isomeric chalcones and dihydroflavones through replacing H2O with D2O to prepare the mobile phase. As a result, differences were observed for either MS1 or MS2 spectrum when comparing two pairs of isomers, such as liquiritigenin vs. isoliquiritigenin and liquiritin vs. isoliquiritin, because the isomeric precursor and fragment ion species owned different amounts of hydroxyl protons and those reactive protons could be partially or completely substituted by deuterium protons at the exposure in D2O to result in n × 1.006 mass increments. Moreover, utmost four hydrogen/deuterium exchanges occurred for a single glucosyl moiety. Thereafter, HDX-MS/MS was applied to characterize the flavonoids of Snow chrysanthemum, a precious edible herbal medicine that is rich in isomeric chalcones and dihydroflavones. Through paying special attention to the deuterium labeling styles of (de)protonated molecules as well as those featured fragment ions, five pairs of isomeric chalcones and dihydroflavones were confirmatively differentiated, in addition to that 28 flavonoids were structurally annotated by applying those well-defined mass fragmentation rules. Hence, this study offered an in-depth insight towards the flavonoids-focused characterization of Snow chrysanthemum, and more importantly, HDX-MS/MS is a superior tool to differentiate, but not limited to, isomeric chalcones and dihydroflavones.

Initial-site characterization of hydrogen migration following strong-field double-ionization of ethanol.

An essential problem in photochemistry is understanding the coupling of electronic and nuclear dynamics in molecules, which manifests in processes such as hydrogen migration. Measurements of hydrogen migration in molecules that have more than two equivalent hydrogen sites, however, produce data that is difficult to compare with calculations because the initial hydrogen site is unknown. We demonstrate that coincidence ion-imaging measurements of a few deuterium-tagged isotopologues of ethanol can determine the contribution of each initial-site composition to hydrogen-rich fragments following strong-field double ionization. These site-specific probabilities produce benchmarks for calculations and answer outstanding questions about photofragmentation of ethanol dications; e.g., establishing that the central two hydrogen atoms are 15 times more likely to abstract the hydroxyl proton than a methyl-group proton to form H[Formula: see text] and that hydrogen scrambling, involving the exchange of hydrogen between different sites, is important in H2O+ formation. The technique extends to dynamic variables and could, in principle, be applied to larger non-cyclic hydrocarbons.

Photoacid-macroion assemblies: how photo-excitation switches the size of nano-objects.

Electrostatic self-assembly of photoacids with oppositely charged macroions yields supramolecular nano-objects in aqueous solutions, whose size is controlled through light irradiation. Nano-assemblies are formed due to electrostatic attractions and mutual hydrogen bonding of the photoacids. Irradiation with UV light leads to the deprotonation of the photoacid and, consequently, a change in particle size. Overall, the hydrodynamic radii of the well-defined photoacid-macroion nano-objects lie between 130 and 370 nm. For a set of photoacids, we determine the acidity constants in the ground and excited state, discuss the sizes of photoacid-macroion nano-objects (by dynamic and static light scattering), their composition and the particle shapes (by small-angle neutron scattering), and relate their charge characteristics to size, structure and shape. We investigate the association thermodynamics and relate nanoscale structures to thermodynamics and, in turn, thermodynamics to molecular features, particularly the ionization energy of the photoacid hydroxyl group proton. Structure-directing effects completely differ from those for previously investigated systems, with hydrogen bonding and entropic effects playing a major role herein. This combined approach allows developing a comprehensive understanding of assembly formation and photo-response, anchored in molecular parameters (pKa, ionization energy, substituent group location), charge characteristics, and the association enthalpy and entropy. This fundamental understanding again paves the way for tailoring application solutions with novel photoresponsive materials.

SYNTHESIS AND STUDY OF SOME NOVEL β-ARYLAMINO-2-OXY-5- METHYLPROPIOPHENONES AS POLYETHYLENE STABILIZERS

The number of -arylamino-2-oxy-5-methylpropiophenones has been synthesized by reacting of - dimethylamino-2-oxy-5-methylpropiophenone hydrochloric acid salt with aniline derivatives in order to use these compounds as stabilizers for polyethylene. It was shown that the thermal stability of the compounds, depending on the nature of the substituent in the aniline fragment of the molecule was observed in a temperature range between 165 and 213°C. All studied compounds, introduced into polyethylene, increased its resistance to temperature effects. It was revealed that -arylamino-2-oxy-5-methylpropiophenones had a stabilizing effect due to the suppression of thermo-oxidative degradation of polyethylene. They multiplied the oxidation induction period of polyethylene and reduced the rate of oxidation. Among the compounds studied -phenoxybenzylamino-2-oxy-5-methylpropiophenone showed the highest stabilizing effect. All studied compounds had sufficient light-stabilizing activity, substantially due the presence in their molecules of a strong intramolecular hydrogen bond IHB (OH ... O = C) of the chelate type between the phenolic hydroxyl proton and the carbonyl oxygen of the acyl group.

Promoting C-F bond activation via proton donor for CF4 decomposition.

Tetrafluoromethane (CF4), the simplest perfluorocarbons, is a permanently potent greenhouse gas due to its powerful infrared radiation adsorption capacity. The highly symmetric and robust C-F bond structure makes its activation a great challenge. Herein, we presented an innovated approach that efficiently activates C-F bond utilizing protonated sulfate (-HSO4) modified Al2O3@ZrO2 (S-Al2O3@ZrO2) catalyst, resulting in highly efficient CF4 decomposition. By combining in situ infrared spectroscopy tests and density function theory simulations, we demonstrate that the introduced -HSO4 proton donor has a stronger interaction on the C-F bond than the hydroxyl (-OH) proton donor, which can effectively stretch the C-F bond for its activation. Consequently, the obtained S-Al2O3@ZrO2 catalyst achieved a stable 100% CF4 decomposition at a record low temperature of 580 °C with a turnover frequency value of ~8.3 times higher than the Al2O3@ZrO2 catalyst without -HSO4 modification, outperforming the previously reported results. This work paves a new way for achieving efficient C-F bond activation to decompose CF4 at a low temperature.

Low-field NMR with multilayer Halbach magnet and NMR selective excitation

This study introduces a low-field NMR spectrometer (LF-NMR) featuring a multilayer Halbach magnet supported by a combined mechanical and electrical shimming system. This setup offers improved field homogeneity and sensitivity compared to spectrometers relying on typical Halbach and dipole magnets. The multilayer Halbach magnet was designed and assembled using three nested cylindrical magnets, with an additional inner Halbach layer that can be rotated for mechanical shimming. The coils and shim-kernel of the electrical shimming system were constructed and coated with layers of zirconia, thermal epoxy, and silver-paste resin to facilitate passive heat dissipation and ensure mechanical and thermal stability. Furthermore, the 7-channel shim coils were divided into two parts connected in parallel, resulting in a reduction of joule heating temperatures from 96.2 to 32.6 °C. Without the shimming system, the Halbach magnet exhibits a field inhomogeneity of approximately 140 ppm over the sample volume. The probehead was designed to incorporate a solenoidal mini coil, integrated into a single planar board. This design choice aimed to enhance sensitivity, minimize B1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${B}_{1}$$\\end{document} inhomogeneity, and reduce impedance discrepancies, transmission loss, and signal reflections. Consequently, the resulting linewidth of water within a 3 mm length and 2.4 mm inner diameter sample volume was 4.5 Hz. To demonstrate the effectiveness of spectral editing in LF-NMR applications at 29.934 MHz, we selectively excited hydroxyl and/or methyl protons in neat acetic acid using optimal control pulses calculated through the Krotov algorithm.

In vivo lymph node CEST-Dixon MRI in breast cancer patients with metastatic lymph node involvement.

Axillary lymph nodes (LNs) often present a reservoir for metastatic breast cancer, yet metastatic LN involvement cannot be discerned definitively using diagnostic imaging. This study investigated whether in vivo CEST may discriminate LNs with versus without metastatic involvement. 3T MRI was performed in patients with breast cancer before clinically-indicated mastectomy or lumpectomy with LN removal, after which LN metastasic involvement was determined using histological evaluation. Non-contrast anatomical imaging, as well as B0 and B1 field maps, were acquired in sequence with three-point CEST-Dixon (3D turbo-gradient-echo; factor = 25; TR/TE1/ΔTE = 851/1.35/1.1 ms; spatial-resolution = 2.5 × 2.5 × 6 mm; slices = 10; four sinc-gauss pulses with duty-cycle = 0.5, total saturation duration = 701.7 ms; B1 = 1.5 μT; saturation offsets = -5.5 to +5.5 ppm; stepsize = 0.2 ppm; scan duration = 6 min 30 s). The mean z-spectrum from LNs with (n = 20) versus without (n = 22) metastatic involvement were analyzed and a Wilcoxon rank-sum test (significance: p < 0.05) was applied to evaluate differences in B0, B1 , and magnetization transfer ratio (MTR) in differing spectral regions of known proton exchange (nuclear Overhauser effect [NOE], amide, amine, and hydroxyl) between cohorts. No difference in axillary B1 (p = 0.634) or B0 (p = 0.689) was observed between cohorts. Elevated MTR was observed for the NOE (-1.7 ppm; MTR = 0.285 ± 0.075 vs. 0.248 ± 0.039; p = 0.048), amine (+2.5 ppm; MTR = 0.284 ± 0.067 vs. 0.234 ± 0.31; p = 0.005), and hydroxyl (+1 ppm; MTR = 0.394 ± 0.075 vs. 0.329 ± 0.055; p = 0.002) protons in LNs from participants with versus without metastatic involvement. Findings are consistent with a unique metastatic LN microenvironment detectable by CEST-Dixon and suggest that CEST MRI may have potential for mapping LN metastasis non-invasively in vivo.

Effective assignment of positional isomers in dimeric shikonin and its analogs by 1H NMR spectroscopy

An approach for distinguishing two types of positional isomers of dimeric shikonin and its analogs was explored with 4JC,H long-range correlation by prolonging the acquisition time at 2,3JC,H values of 2.0 and 8.0 Hz. Furthermore, the 1H (proton) nuclear magnetic resonance (NMR) pattern of phenolic hydroxyl protons was developed as a “diagnosis signal” to ascertain the relative location of each side chain in DMSO‑d6 at sample concentrations of 0.022–0.034 mol/L. The chemical shift differences of 0.6 ppm between OH-5′ and OH-1 and between OH-8′ and OH-4 are assigned to Type A and Type B, respectively. All reported ambiguous structures were corrected by this pattern. Additionally, the steric structures of isolated compounds were elucidated by quantum chemical calculations of electronic circular dichroism (ECD) spectra.

Low-density preference of the ambient and high-pressure polymorphs of DL-menthol.

Lower-density polymorphs of DL-menthol were nucleated and crystallized in their high-pressure stability regions. Up to 0.30 GPa, the triclinic DL-menthol polymorph α, which is stable at atmospheric pressure, is less dense than a new β polymorph, which becomes stable above 0.40 GPa, but is less dense than the α polymorph at this pressure. The compression of polymorph α to at least 3.37 GPa is monotonic, with no signs of phase transitions. However, recrystallizations of DL-menthol above 0.40 GPa yield the β polymorph, which is less compressible and becomes less dense than α-DL-menthol. At 0.10 MPa, the melting point of the β polymorph is 14°C, much lower compared with those of α-DL-menthol (42-43°C) and L-menthol (36-38°C). The structures of both DL-menthol polymorphs α and β are very similar with respect to the lattice dimensions, the aggregation of OH...O molecules bonded into Ci symmetric chains, the presence of three symmetry-independent molecules (Z' = 3), their sequence ABCC'B'A', the disorder of the hydroxyl protons and the parallel arrangement of the chains. However, the different symmetries relating the chains constitute a high kinetic barrier for the solid-solid transition between polymorphs α and β, hence their crystallizations below or above 0.40 GPa, respectively, are required. In the structure of polymorph α, the directional OH...O bonds are shorter and the voids are larger compared with those in polymorph β, which leads to the reverse density relation of the polymorphs in their stability regions. This low-density preference reduces the Gibbs free-energy difference between the polymorphs: when polymorph α is compressed to above 0.40 GPa, the work component pΔV counteracts the transition to the less dense polymorph β, and on reducing the pressure of polymorph β to below 0.40 GPa, its transition to the less dense polymorph α is also hampered by the work contribution.

Preparation of a ternary amorphous solid dispersion using hot-melt extrusion for obtaining a stable colloidal dispersion of amorphous probucol nanoparticles

In our previous reports, ternary amorphous solid dispersions (ASDs) of probucol (PBC)/polymer/surfactant were prepared by spray-drying and cryo-grinding, and colloidal dispersions of amorphous PBC nanoparticles were obtained by dispersing the ternary ASD into water. In this study, hot-melt extrusion, which is a practical method for preparing ASD formulations, was utilized to obtain ternary ASDs and colloidal dispersions of amorphous PBC nanoparticles. Polyvinylpyrrolidone K12 (PVP) with a relatively low Tg (below 100 °C) was used as a polymer, while poloxamer P407 (P407), which is chemically stable during the hot-melt extrusion process, was utilized as a surfactant. Ternary ASDs were successfully produced with high weight ratios of PVP and P407. A hydrogen bond between the PBC hydroxyl proton and PVP carbonyl oxygen in the ternary ASD was detected using solid-state NMR spectroscopy, suggesting that amorphous PBC was stabilized mainly by PVP. Stable colloidal dispersions of amorphous PBC nanoparticles were obtained from the PBC/PVP/P407 ASD at a weight ratio of 1:4:2. The mean particle size was below 200 nm and the amorphous state of PBC remained stable upon storage at 25 °C for 14 d. Solution-state 1H NMR and zeta-potential measurements suggested that P407 mainly stabilized the colloidal dispersion of amorphous PBC nanoparticles by steric hindrance at the solid/liquid interface. The findings of this study demonstrate that hot-melt extrusion can form practical ternary ASDs that provide colloidal dispersion of amorphous drug nanoparticles. Thus, this study advocates for the use of hot-melt extrusion in the design of an amorphous formulation for a variety of poorly water-soluble drugs.

First‐Principles Modeling of the Adsorption Mechanism of Carboxylic and Phosphonic Acids onto Pristine and Defective Delafossite CuAlO2 Surfaces

In order to provide atomistic insights on the mechanism and stability of dye grafting to delafossite surfaces, the authors study, using density‐functional theory calculations in vacuo and in implicit solvent, the adsorption of carboxylic and phosphonic anchoring groups onto stoichiometric and defective slabs exposing the most stable (012) termination. A remarkable increase of the adsorption energies is found on the reduced surfaces when the vacancy is on the top surface layer, in proximity to the molecule. While on the pristine substrate, the monodentate anchoring is the most stable one, and on the reduced interface, a strong bidentate bridging anchoring mode is favored, after the transfer of the hydroxyl proton to the oxygen surface atom adjacent to the copper vacancy. Identification of a largely stable bidentate coordination suggests a possible long‐term device stability, as well as a larger efficiency of the interfacial hole injection, indicating that may be a good alternative to NiO in p‐type photocathodes.