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Synthesis and phase purity of the negative thermal expansion material ZrV2O7
No full textSynthesis of pure, homogeneous, and reproducible materials is key for the comprehensive understanding, design, and tailoring of material properties. In this study, we focus on the synthesis of ZrV2O7, a material known for its negative thermal expansion properties. We investigate the influence of solid-state and wet chemistry synthesis methods on the purity and homogeneity of ZrV2O7 samples. Our findings indicate that different synthesis methods significantly impact the material\u27s characteristics. The solid-state reaction provided high-purity material through extended milling time and repeated calcination cycles, while the sol-gel reaction enabled a “near-atomic” level of mixing and, therefore, homogenous phase-pure ZrV2O7. We confirmed purity via X-ray diffraction and Raman spectroscopy, highlighting differences between phase-pure and multiphase ceramics. These analytical
techniques allowed us to distinguish subtle differences in the structure of the material. Based on ab initio simulated phonon data, we were able to interpret the Raman spectra and visualise Raman active atom vibrations. We show that phase purity enables the unbiased characterisation of material properties such as negative thermal expansion
Point Sensor Network Detects Short Releases Under Favorable Wind Conditions
No full textIn this study, we apply a recursive Bayesian state updater algorithm to assimilate meteorological data with point-sensor measurements of methane concentrations to infer timeseries of methane emission rates at three operating oil and gas facilities. These calculations are performed over a timeframe with known numerous short (~ 30 minute) controlled releases, allowing for "ground truth\u27\u27 data to compare our emission estimates against. The highly-varying and unknown operational emissions pose challenges in analyzing quantification results when trying to determine whether there is evidence in the emission estimates of a given controlled release. Ultimately, we find that despite the non-ideal conditions at these sites (poor sensor placement and the presence of large obstructions that the quantification model does not account for) that the site-level emission estimates show evidence for 31 out of the 60 controlled releases and that the majority of nondetections were due to the wind simply not pointing from the source to any sensor in the network during a short release event
A New Time-resolved Luminescent Sensor
No full textWe present a new time-resolved chemosensor for the detection of Ba2+ ions. Our sensor is based on
an iridium(III) compound with dual (fluorescent and phosphorescent) emission. The nature of the
luminescent response of the sensor depends on its state; specifically, the phosphorescent emission of
the free state at long wavelengths is strongly suppressed, while that of the Ba2+-chelated compound
is strongly enhanced. Furthermore, the residual phosphorescent emission of the free compound
decays with two short decay constants, τ 1
free ∼ 3.5 ns (88%) and τ 2
free ∼ 209 ns (12%), while the
chelated compound decays with two long decay constants, τ 1ch ∼ 429 ns (21%) and τ 2 ch ∼ 1128 ns
(76%). This exceptional behaviour, supported by quantum chemical calculations, allows a time-
based separation between the signal of the free and the chelated species. Among other applications,
our sensor could be the basis of a Ba2+ tagging detector for neutrinoless double beta decay searches
in xenon
Raman Broad Scans of Glasses with Rare Earth Element (REE) Oxides and their Decomposition with q-BWF Line Shapes
No full textRRUFF database is proposing the Raman broad scans of glasses CaO-Al2O3-SiO2 with rare earth element (REE) oxides, that is of CaO-RE2O3-Al2O3-SiO2 glasses. Raman data are courtesy of E. Cairns, University of Edinburgh. Here we show how we can use the q-BWF functions to decompose these spectra. The q-BWF functions are generalizing the Breit-Wigner-Fano line shape in the framework of the q-exponential function proposed by Constantino Tsallis and his statistics. Besides asymmetry, the decompositions with q-BWF line shapes are stressing Gaussian and non-Gaussian behaviors of components. The data analysis of CaO-RE2O3-Al2O3-SiO2 glasses is highlighting the presence of photoluminescence regular patterns in the Raman broad scans
Tailored anharmonic potential energy surfaces for infrared signatures
No full textAccurately calculated infrared spectra are essential for supporting experimental interpretation, yet full-space anharmonic vibrational structure calculations are only feasible for a limited number of degrees of freedom. Fortunately, characteristic spectroscopic signatures are often dominated by a few key vibrations. We propose a computational protocol specifically tailoring high dimensional anharmonic potential energy surfaces for the accurate and efficient calculation of such spectral signatures with vibrational coupled cluster response theory. Our protocol focuses on the selection of appropriate coordinates for the relevant degrees of freedom and the identification of specific mode-coupling terms for the potential energy surface that require more thorough treatment. This includes applying different levels of electronic structure theory and selecting a restricted set of higher mode-coupling terms (> mode pairs). We validate this protocol on two spectral regions: the fundamental C=O stretching vibrations in uracil and the fundamental OH stretchings in catechol. Our findings indicate that the convergence behaviour towards harmonic frequencies in the so-called FALCON algorithm is an effective indicator for the locality character of the relevant degrees of freedom. We find that the C=O stretchings in uracil are better described using normal coordinates, while the description with local FALCON coordinates of the OH stretching vibrations in catechol showed superior performances in VCC spectra calculations. Overall, our protocol offers valuable guidelines for accurate and efficient anharmonic calculation of vibrational spectral signatures
Electronic response and charge inversion at polarized gold electrode
No full textWe have studied polarized Au(100) and Au(111) electrodes immersed in electrolyte solution by implementing finite-field methods in density functional theory-based molecular dynamics (DFTMD) simulations. This allows us to directly compute the Helmholtz capacitance of electric double layer by including both electronic and ionic degrees of freedom, and the results turn out to be in excellent agreement with experiments. It is found that the electronic response of Au electrode makes a crucial contribution to the high Helmholtz capacitance and the instantaneous adsorption of Cl can lead to a charge inversion on the anodic polarized Au(100) surface. These findings point out ways to improve popular semi-classical models for simulating electrified solid-liquid interfaces and to identify the nature of surface charges therein which are difficult to access in experiments
Strategic Fluorination to Achieve a Potent, Selective, Metabolically-Stable, and Orally-Bioavailable Inhibitor of CSNK2.
No full textThe host kinase casein kinase 2 (CSNK2) has been proposed to be an antiviral target against β-coronaviral infection. To pharmacologically validate CSNK2 as a drug target in vivo, potent and selective CSNK2 inhibitors with good pharmacokinetic properties are required. Inhibitors based on the pyrazolo[1,5-a]pyrimidine scaffold possess outstanding potency and selectivity for CSNK2, but bioavailability and metabolic stability were often challenging. By strategically installing a fluorine atom on an electron-rich phenyl ring of a previously characterized inhibitor 1, we discovered compound 2 as a promising lead compound with improved in vivo metabolic stability. Compound 2 maintained excellent cellular potency against CSNK2, submicromolar antiviral potency, favorable solubility, and was remarkably selective for CSNK2 when screened against 192 kinases across the human kinome. We additionally present a co-crystal structure to support its on-target binding mode. In vivo, compound 2 was orally bioavailable, and demonstrated modest and transient inhibition of CSNK2, although antiviral activity was not observed, possibly attributed to its lack of prolonged CSNK2 inhibition
Spectroscopic Signatures of Phonon Character in Molecular Electron Spin Relaxation
No full textSpin-lattice relaxation constitutes a key challenge for the development of quantum technologies, as it destroys superpositions in molecular quantum bits (qubits) and magnetic memory in single molecule magnets (SMMs). Gaining mechanistic insight into the spin relaxation process has proven challenging owing to a lack of spectroscopic observables relative to the many degrees of freedom involved. Here, we use pulse electron paramagnetic resonance (EPR) to profile systematic changes in the spin relaxation anisotropy as a function of temperature for two Cu(II) coordination compounds. For randomly-oriented powder samples, large anisotropy changes arise between 20 and 50 K that delineate multiple regimes of relaxation for each molecule studied. Local mode fitting of the average T1 value fails to consistently extract the anisotropy regime crossover. Single-crystal T1 anisotropy experiments reveal a surprising difference between the symmetry of the spin relaxation tensor in these two regimes. In the high-temperature regime, spin relaxation is fastest and slowest along the principal axes of the molecular g-tensor, which obeys the symmetry of the molecular point group. In the low-temperature regime, spin relaxation is fastest and slowest along arbitrary directions of the g-tensor, instead responding to the crystal packing. We interpret this switch as arising from a change in the localization of the phonons driving spin relaxation at different temperatures, consistent with delocalized lattice phonons in the low-temperature regime and localized molecular vibrations in the high-temperature regime. Variable-temperature T1 anisotropy thus provides a unique method of interrogating the character of nuclear motions causing the spin relaxation process
Development and application of an advanced percolation model for pore network characterization by physical adsorption
No full textPhysical adsorption is one of the most widely used techniques to characterize porous materials because of being reliable and able to assess micro- and mesopores within one approach. However, challenges and open questions persist in characterizing disordered and hierarchically structured porous materials. This study introduces a pore network model aiming to enhance the textural characterization of nanoporous materials. Our model, based on percolation theory on a finite sized Bethe lattice, includes all mechanisms known to contribute to adsorption hysteresis in mesoporous pore networks during capillary condensation and evaporation. The model accounts for delayed and initiated condensation during adsorption as well as equilibrium evaporation, pore blocking and cavitation during desorption. Coupled with dedicated non-local-density functional theory (NLDFT) kernels, the proposed method provides a unified framework for modeling the entire experimental adsorption-desorption isotherm, including desorption hysteresis scans. The applicability of the method is demonstrated on a selected set of nanoporous silica materials exhibiting distinct types of hysteresis loops (types H1, H2a, H1/H2a and H5), including ordered mesoporous silica networks, i.e, KIT-6 silica, hybrid SBA-15/MCM-41 silica with plugged pores, but also two disordered silica pore networks, i.e., a hierarchical meso-macroporous monolith and porous Vycor glass. For all materials, good correlation is found between calculated and experimental primary adsorption and desorption isotherms as well as desorption scans. The model allows to determine key pore network characteristics such as pore connectivity and pore size distributions as well as a parameter correlated with the impact of pore network disorder and corresponding effects on the adsorption behavior. The versatility and enriched textural insights provided by the proposed novel network model allow for a comprehensive characterization previously inaccessible, and hence will contribute to a further advancement in the textural characterization of novel nanoporous materials. It has the potential to provide important guidance for the design and selection of porous materials for optimising various applications, including separation processes (such as chromatography), heterogeneous catalysis, gas- and energy storage
Exploring Potential Coplanar Chiral Bipyridine Ligands for Asymmetric Catalysis
No full textBipyridines represent a class of ligands renowned for their versatility and efficacy in numerous transition metal-catalyzed reactions. Chiral bipyridine ligands are noted for their distinctive reactivity and stereoselectivity. In this work, we have designed and synthesized a class of bipyridine ligands endowed with an axially chiral scaffold. These ligands feature: (a) a precisely aligned coplanar bipyridine framework that is beneficial for metal chelation; (b) a spacious environment around the metal-bipyridine complexes, capable of hosting substrates with substantial steric bulk; (c) a chiral pocket induced by the axially chiral architecture. These atropochiral planar bipyridine ligands were successfully applied in copper-catalyzed ring-opening reactions of cyclic diaryliodoniums with bulky secondary amines, achieving high efficiency and stereoselectivity that were unsuccessful in our previous efforts