Vibrational Raman Spectroscopy Research Articles

Co-Crystal Formation of Antibiotic Nitrofurantoin Drug and Melamine Co-Former Based on a Vibrational Spectroscopic Study.

The co-crystallization of active pharmaceutical ingredients (APIs) has received increasing attention due to the modulation of the relative physicochemical properties of APIs such as low solubility, weak permeability and relatively inferior oral bioavailability. Crystal engineering plays a decisive role in the systematic design and synthesis of co-crystals by means of exerting control on the inter-molecular interactions. The characterization and detection of such co-crystal formations plays an essential role in the field of pharmaceutical research and development. In this work, nitrofurantoin (NF), melamine (MELA) and their hydrated co-crystal form were characterized and analyzed by using terahertz time-domain spectroscopy (THz-TDS) and Raman vibrational spectroscopy. According to the experimental THz spectra, the hydrated co-crystal form has characteristic absorption peaks at 0.67, 1.05, 1.50 and 1.73 THz, while the THz spectra for the two raw parent materials (NF and MELA) are quite different within this spectral region. Similar observations were made from the experimental Raman vibrational spectra results. Density functional theory (DFT) calculation was performed to help determine the major vibrational modes of the hydrated co-crystal between nitrofurantoin and melamine, as well as identify the structural changes due to inter- and/or intra-molecular hydrogen bonding motifs between NF and MELA. The results of the theoretical frequency calculations corroborate the THz and Raman experimental spectra. The characteristic bands of the NF–MELA-hydrated co-crystal between nitrofurantoin and melamine were also determined based on the DFT simulated calculation. The reported results in this work provide us with a wealth of structural information and a unique vibrational spectroscopic method for characterizing the composition of specific co-crystals and inter-molecular hydrogen bonding interactions upon pharmaceutical co-crystallization.

A hydrogen-bonded assembly of cucurbit[6]uril and [MoO2Cl2(H2O)2] with catalytic efficacy for the one-pot conversion of olefins to alkoxy products

The reaction of the macrocyclic cavitand cucurbit[6]uril (CB[6]) and the diaqua complex [MoO2Cl2(H2O)2] in hydrochloric acid solution gave a water insoluble supramolecular compound with the general composition 2[MoO2Cl2(H2O)2]·CB[6]·xH2O·yHCl·z(CH3COCH3) (2). Single crystal X-ray diffraction (XRD) analysis revealed the presence of barrel-shape supramolecular entities, {CB[6]·10(H2O)}, aligned in layers which are shifted relative to adjacent layers to form a brick-like pattern. The CB[6]/water hydrogen-bonded entities further engage in intermolecular interactions with water, HCl and [MoO2Cl2(H2O)2] molecules to form a three-dimensional (3D) framework. Compound 2 was characterised by thermogravimetric analysis (TGA), IR and Raman vibrational spectroscopy, and 13C{1H} CP MAS NMR. The reference complex [MoO2Cl2(H2O)2]·(diglyme)2 (1) and compound 2 were studied for the oxidative catalytic conversion of olefins (cis-cyclooctene, cyclohexene and styrene) with aqueous H2O2 as oxidant. Using alcohols as solvents, 2 was employed in a one-pot two-stage strategy for converting olefins to alkoxy products, which involves oxidation (with H2O2) and acid chemistry. Mechanistic studies were carried out using different intermediates as substrates, and the type of solvent and substrate scope were investigated. The results demonstrated the ability of the CB[6]/MoVI supramolecular adduct to function as an acid-oxidation multifunctional catalyst, and its recovery and reuse via relatively simple procedures.

Enhancing Ni-YSZ Anode Resilience to Environmental Redox Stress with Aluminum Titanate Secondary Phases

Voltammetry, impedance spectroscopy, and operando vibrational Raman spectroscopy were used to examine the resilience of traditional and modified Ni-based SOFC anodes to environmental reduction/oxidation (redox) cycling. Traditional anodes were fabricated from Ni yttrium stabilized zirconia (YSZ) cermets while modified anodes consisted of the Ni-YSZ cermet containing 4 wt % Al2TiO5 (ALT). Anodes were part of full membrane electrode assemblies that included a YSZ electrolyte support and a LSM cathode. Experiments were performed at 800 °C. To examine anode resilience to redox cycling, cells operated with hydrogen under galvanostatic conditions for 20 min prior to oxidation at OCV using either H2O or O2. While H2O only partially oxidized anodes, O2 exposure fully oxidized anodes and rapidly accelerated degradation in undoped cells. Undoped cells typically suffered a 50% loss in conversion efficiency after approximately 15–20 redox cycles with O2. Under equivalent conditions, cells with ALT doped anodes degraded on average only 13 ± 3%. EIS modeling and ex situ FE-SEM measurements provide further insight into the mechanisms responsible for enhanced resilience shown by Ni-YSZ cermet anodes doped with ALT.

MODERN ASPECTS OF HOMEOPATHIC MEDICINES STANDARDISATION

The article describes the status of homeopathic medicines standardisation in the leading world pharmacopoeias. It reviews main requirements for raw materials of plant, animal, and mineral origin, which are used in the production of homeopathic medicines. It also considers requirements for homeopathic pharmaceutical substances, including technologies of obtaining homeopathic mother tinctures, homeopathic dilutions, triturations, etc., mono- and multi-component homeopathic medicines, as well as quality control of homeopathic substances and homeopathic medicines. The article analyses the nomenclature of homeopathic raw materials and homeopathic substances used by the leading world pharmacopoeias. It dwells upon the results of work devoted to the development of requirements for the following homeopathic dosage forms: homeopathic granules, homeopathic eye drops, homeopathic ointments, homeopathic infusions and decoctions, homeopathic mother tinctures, homeopathic solutions for injection, homeopathic solutions and liquid dilutions, homeopathic syrups, homeopathic mixtures, homeopathic suppositories, homeopathic tablets, homeopathic triturations. The article illustrates significant potential of using vibrational spectroscopy and Raman spectroscopy for the detection of distinctive features of homeopathic medicines at ultra-high dilutions. The article presents methodology for structuring pharmacopoeial standards for raw materials used in the production of pharmaceutical substances, for pharmaceutical substances that are used in homeopathic medicines, and for dosage forms, including specific aspects of production and standardisation of homeopathic medicines, which was implemented during preparation of draft monographs for the State Pharmacopoeia of the Russian Federation.

Geochemical characterization of W, Cu and F skarn tailings at Yxsjöberg, Sweden

Little attention has been paid to tailings from skarn ore deposits and their environmental impact, even though they can contain elevated concentrations of elements of potential concern together with sulfides and fluorite. Historical skarn tailings at Yxsjöberg, Sweden, containing e.g. Be, Bi, Cu, F, Sn, S, W, and Zn were geochemically characterized as a first step to evaluate the environmental impact and the potential to re-mine the tailings. The tailings were deposited between 1897 and 1963 in the Smaltjärnen Repository without dams or a complete cover, and have been in contact with the atmosphere for >30 years. Four vertical cores throughout the tailings were taken and divided into 134 subsamples, which were analyzed for total concentrations and paste pH. Selected samples from different depths were mineralogically characterized using optical microscopy, scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), Raman vibrational spectroscopy, and X-ray diffraction (XRD). Minerals, hand-picked from drilled rock cores, were analyzed for the element content, and a modified Element to Mineral Conversion (EMC) that pinpoints the quantitative distribution of elements between the minerals in the tailings was carried out. The average concentrations of Be, Bi, Cu, Sn, Zn, W, F and S in the tailings were 284, 495, 946, 559, 301, and 960 ppm, and 1.9 and 1.2 wt%, respectively. The tailings has reached a late stage development due to pyrrhotite oxidation resulting in low pH (<4) in the uppermost tailings, and formations of secondary minerals such as gypsum, hydrous ferric oxides (HFO) and orthogonal calcite. Secondary pyrite and magnetite, formed from monoclinic pyrrhotite was detected, and different weathering rates of secondary pyrite, hexagonal and monoclinic pyrrhotite was indicated, with secondary pyrite as the most stable and monoclinic pyrrhotite as the least. The rare and easily-weathered mineral danalite (Fe4Be3(SiO4)3S) was found in the drilled rock cores and by XRD in the tailings. However, the mineral could not be found by optical microscopy or SEM-EDS. This suggests that the mineral has been weathered to a great extent, which poses a high risk of releasing elements of potential concern to the groundwater since danalite contains approximately 40% of the total Be and Zn concentrations in the tailings. Fluorine was mainly found in fluorite, Cu in chalcopyrite, and Bi in bismuthinite; which all showed signs of weathering in acidic condition in the uppermost part, subsequent with decreased concentrations, followed by accumulation peaks deeper down in the tailings correlated with Al. Tungsten was mainly found in scheelite; most grains were unweathered, but a few grains had altered rims or HFO on the mineral surfaces. Tin was mainly found in ferrohornblende, hedenbergite and grossular. Beryllium, Cu, F, and Zn has high potential to be released to the surrounding environment from the Smaltjärnen Repository, while W, Bi and Sn are relatively stable in the tailings. Most of the scheelite is intact and re-mining could, therefore, be a suitable remediation method that would both reduce the environmental impact and simultaneously support the supply of critical raw materials in the EU.

Thieno[3,4-c]pyrrole-4,6-dione Oligothiophenes Have Two Crossed Paths for Electron Delocalization.

A new series of electron-deficient oligothiophenes, thieno[3,4-c]pyrrole-4,6-dione oligothiophenes (OTPDn ), from the monomer to hexamer, is reported. The optical and structural properties in the neutral states have been analyzed by absorption and emission spectroscopy together with vibrational Raman spectroscopy. In their reduced forms, these molecules could stabilize both anions and dianions in similar ways. For the dianions, two independent modes of electron conjugation of the charge excess were observed: the interdione path and the interthiophene path. The interference of these two paths highlighted the existence of a singlet diradical ground electronic state and the appearance of low-energy, thermally accessible triplet states. These results provide valuable insights into the device performance of TPD-based materials and for the rational design of new high-performance organic semiconductors.

Hyper‐Raman investigation of intermolecular vibrations of water and ice

AbstractWe have constructed a hyper‐Raman optimized spectrometer using a high repetition rate (200 kHz) picosecond‐pulsed Nd:YAG laser. This system has been applied to measure liquid water and ice (H2O and D2O) to obtain their hyper‐Raman spectra with high signal‐to‐noise ratios. Unique vibrational spectra of water and ice, distinct either from infrared absorption and Raman scattering, have been obtained. The intermolecular bands in the low‐wavenumber region are observed in the hyper‐Raman spectra with intensities higher than those of the intramolecular ones. They show H/D isotope shifts fully consistent with their assignments to the librational and translational motions of assembled water. The librational bands are found to shift to higher wavenumber on going from liquid water to ice, indicating a more confining environment in ice than in water. Hyper‐Raman spectroscopy will shed new light, complementary to the traditional infrared and Raman vibrational spectroscopies, on intermolecular interactions in liquid water and ice.

Characterization of the Action of Antibiotics and Essential Oils against Bacteria by Surface-Enhanced Raman Spectroscopy and Scanning Electron Microscopy

ABSTRACTThe description of the main structural alterations generated by the interaction between pathogenic microorganisms and antibiotic agents, either standard antibiotics or volatile plant derived oils, is an essential topic in understanding drug action mechanisms at the molecular level. To investigate this effect, an original approach based on ultrasensitive vibrational surface-enhanced Raman spectroscopy (SERS) and scanning electron microscopy (SEM) was used. Single-bacteria SERS spectra, recorded in the 600–1800 cm−1 wavenumber interval are reported for two bacterial strains: Enterococcus durans and Aeromonas media. Spectra-structure correlations for all types of localized vibrations, including bands assigned to proteins, saturated lipids, glycosidic linkages, and nitrogenous bases, are also discussed. SEM images revealed that the mechanism of action of antibiotic agents against the pathogenic microorganisms involves a complete denaturation of the bacterial membrane, which induces bacterial cells apoptosis.

Raman Spectroscopy as an ortho-para diagnostic of liquid hydrogen moderators

The intense radiation environment of a neutron moderator provides a mechanism for significant up-conversion of parahydrogen to orthohydrogen inside the moderator, as well as intrinsically catalyzing relaxation of orthohydrogen to parahydrogen. It is plausible that the steady-state orthohydrogen fraction of a moderator in a radiation environment such as at the Spallation Neutron Source (SNS) or the European Spallation Source (ESS) is as high as 30 % without supplemental catalysis. Direct measurement of the orthohydrogen fraction in the liquid hydrogen flow itself is essential to predict and monitor moderator performance, especially for thick or flat moderator concepts such as the ones that have been proposed for the ESS and for upgrades to the SNS. Raman spectroscopy provides a well-known method for directly measuring the hydrogen make-up in an unambiguous way. We describe our tests of Raman spectroscopy for application to the measurement of the orthohydrogen fraction of the hydrogen moderators at SNS and at the ESS. As part of this work, we have additionally developed a sample holder that has been used to perform simultaneous Raman and neutron vibrational spectroscopy on the VISION spectrometer at SNS. We discuss our plans to incorporate such a system as a diagnostic for liquid hydrogen moderators at SNS and at the ESS.

Adsorption of arsenite and arsenate on binary and ternary magnetic nanocomposites with high iron oxide content

Bare maghemite nanoparticles (Nps), binary, and ternary magnetic nanocomposites prepared with titanium dioxide (TiO2) and graphene oxide (GO) were synthesized by a facile and cheap co-precipitation chemical route, and used as magnetic nanoadsorbents to remove arsenite (As(III)) and arsenate (As(V)) from water. The structural, morphological, magnetic and surface properties were analyzed by XRD, TEM microscopy, FTIR and Raman vibrational spectroscopy, Mössbauer technique and N2 adsorption-desorption measurements. It was found that materials were composed of maghemite nanoparticles with crystallites diameters varying from 9 to 13 nm for bare Nps, binary and ternary nanocomposites, these nanocomposites contain a high percentage of maghemite phase (80%). The presence of TiO2 and GO in the binary and ternary materials was also confirmed. All the samples were found to show magnetic properties and a slight porosity, with a specific surface area that increases up to 82 m2/g when the metal oxides Nps were supported on GO. The aqueous arsenic adsorption performance was studied from kinetic and equilibrium point of view, and the pH adsorption capacity dependence was evaluated aiming to explain the adsorption mechanism. The three nanocomposites prepared in this work exhibit high adsorption capacity for arsenic species, with values of maximum adsorption capacity ranging from 83.1 to 110.4 mg/g for As(III) and from 90.2 to 127.2 mg/g for As(V) from bare to ternary nanocomposites, being possible to be separated with a permanent magnet of neodymium (Nd) in less than 10 min. Therefore, these nanosystems can be proposed as good adsorbents for both arsenic species from water.

Investigation of Protective Coatings for Bronze Using Combined Techniques

Bronze is a metal alloy that is commonly used for statuary, but also as decorative element in architecture. Naturally, the surface of bronze monuments tends to passivation and formation of patina. This acts as protection, but can also have a decorative value. Anyhow, in certain conditions an artificial protection of bronze sculptures is also desired. Waxes and polymeric protection (Incralac, Sotter, …), also in combinations of layers, are mostly used nowadays. However, in order to prepare more effective solutions for protection, there have been performed some studies on possibilities for application of organic coatings (benzotriazole [1,2]) and various polymeric protective coatings like acrylate/methacrylate [3], fluoropolymers [1], polyurethanes [4] and sol-gel [5,6]. Since conservators demand that the coatings have to be removable, sol-gel coatings are often overlooked. Various strippers, for example on the basis of benzyl alcohol, can be applied to remove polymeric coatings from bronze surfaces. From environmental point of view, the studies of polymeric coatings are not prepared only from solvent-born formulations, but are shifted also to water-born formulations and comparison of both types of coatings [3]. Herein is reported the investigation of fluoropolymer and polyurethane protective coatings for bronze. The characterization of these coatings was made by using different analytical techniques. For structural determination, infrared (IR) and Raman vibrational spectroscopies were applied. Surface characteristics were determined by scanning electron microscopy (SEM), atomic force microscopy (AFM) and contact angle measurements. Protective efficiency was analyzed using electrochemical techniques like potentiodynamic polarization and electrochemical impedance spectroscopy. As more advanced analytical techniques, there were applied ex situ IR reflection-absorption (IR RA) and in situ Raman spectroelectrochemistry. The analyzed coating is in both spectroelectrochemical techniques gradually chronocoulometrically charged at more and more positive anodic potentials to follow the eventual degradation processes that are analyzed spectroscopically after each charging. IR RA spectra are measured in near grazing incidence angle assembly using an angle of 80° and P polarized IR radiation. In such spectra longithudinal optical (LO) modes appear that are commonly shifted towards higher wavenumbers compared to usual transversal optical (TO) modes from absorbance IR spectra. The disadvantage is the contact of electrochemically treated protective coating with atmosphere. This circumstance is overcome in in situ Raman spectroelectrochemical technique. The coating on bronze is mounted in a custom-made Tephlon in situ three-electrode cell. The counter electrode is platinum grid and the reference electrode Ag/AgCl. All electrochemical experiments are performed in 0.5 M sodium chloride. Fluoropolymer coatings are prepared from resins on the basis of fluoroethylene/vinyl ether (FEVE) alternating copolymers (Asahi Glass Company, Japan). The building unit of FEVE compounds is -CF2-CFX-. Solvent- and water- born formulations are made from appropriate resins, by applying corresponding poly(isocyanate) hardener, defoamer, light stabilizers, surfactants and co-solvents. Results confirm that the higher contact angles for water are achieved for solvent-born coatings (> 100°) than for water-born coatings (< 80°). Potentiodynamic polarization measurements are in accordance with these values, suggesting higher protective effectivity of solvent-born coatings. The use of water-born coatings for outside long-term protection of bronze is questionable, since the ex situ IR RA measurements showed that after treatment at high anodic potential the coating becomes much thinner. Consequently, the band at 565 cm-1 appeared in the IR RA spectrum and can be assigned to Cu2O of the bronze substrate. Similarly, also the in situ Raman spectra showed that after application of long anodic chronocoulometric pulse the coating burned and detached from the bronze substrate. Solvent-born coatings reveal more stable behavior through in situ Raman spectroelectrochemical measurements. Solvent-born polyurethane protective coatings show hydrophobic properties and the contact angle of 110°. Relatively good protective properties are confirmed through potentiodynamic polarization curves, impedance spectroscopy and ex situ IR RA measurements. The latter technique shows quite stable response during forced degradation at high anodic potentials. The activity is carried out within the framework of the NANORESTART project which has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 646063.

Masking Contaminant-Induced SOFC Anode Degradation with H2

Common contaminants in solid oxide fuel cell (SOFC) fuels, including chlorine and sulfur, are believed to induce anode degradation through one of several, temperature-dependent mechanisms. At relatively low operating temperatures, mechanisms propose that contaminants adsorb to the Ni electrocatalyst, blocking active sites and reducing conversion efficiency. This effect is largely reversible and anodes recover performance when the contaminant is removed from the fuel feed. At higher temperatures, contaminants react with Ni to form non-conducting or volatile materials, thus impeding electrochemical oxidation and destroying anode microstructure. Using both electrochemical measurements and operando vibrational Raman spectroscopy in SOFCs operating at 700°C, we have discovered that small amounts of excess molecular hydrogen added to both methane contaminated with chlorine and a biogas simulant contaminated with chlorine masks, but does not prevent, Cl-induced anode degradation. Once the hydrogen is removed from the incident fuel feed, anodes fail abruptly and irreversibly, implying that Cl-induced degradation proceeded while the hydrogen was present despite impedance and voltammetry data showing no apparent signs of performance loss. Effects are more pronounced and occur more rapidly in SOFCs operating with the biogas simulant (a 50-50 mixture (by mole fraction) of CH4 and CO2) than for methane. These results are discussed in terms of a new high-temperature degradation mechanism that considers site specific catalytic activity on Ni surfaces and steric requirements for –CH and H2 bond activation.

Temperature measurements in confined swirling spray flames by vibrational coherent anti-stokes Raman spectroscopy

A gas turbine model combustor for swirling spray flames has been operated at atmospheric pressure with n-hexane, n-dodecane and kerosene Jet A-1. Temperature measurements were performed using single-shot broadband shifted vibrational coherent anti-Stokes Raman spectroscopy (SV-CARS). Series of 1200 single-shot measurements were performed at different radial and vertical locations in the flames from which the temperature distributions were deduced. In regions with high droplet load a significant number of CARS spectra were discarded due to large signal background from laser-induced breakdown effects. Results from the flames burning different fuels were compared and revealed considerable differences in the temperature profiles. The temperature measurements are part of a comprehensive research program that aims at the design of alternative fuels for aero engines and stationary gas turbines. In addition to the experimental characterization of the spray flames, the datasets are used for the validation and improvement of computational models.

Synthesis, Structure, and Vibrational Properties of [Ph4P]2NpO2Cl4 and [Ph4P]2PuO2Cl4 Complexes

The synthesis, structure, and vibrational properties are presented for an isostructural series of Np(VI) and Pu(VI) complexes of the form [Ph4P]2AnO2Cl4, where An = Np(VI) or Pu(VI). The reported complexes are readily synthesized in ambient laboratory conditions, and their molecular structures were determined using single crystal X-ray diffraction. Their vibrational spectra were studied using a combination of Raman and FT-IR vibrational spectroscopies. Analysis of the vibrational spectra and force constants highlight the periodic properties associated with the actinide contraction and filling of the 5f electronic shells. Additionally, we have assessed the utility of these complexes as conveniently synthesized starting materials for non-aqueous synthesis of transuranium molecules and materials.

The Interplay of Structure and Dynamics in the Raman Spectrum of Liquid Water over the Full Frequency and Temperature Range.

While many vibrational Raman spectroscopy studies of liquid water have investigated the temperature dependence of the high-frequency O-H stretching region, few have analyzed the changes in the Raman spectrum as a function of temperature over the entire spectral range. Here, we obtain the Raman spectra of water from its melting to boiling point, both experimentally and from simulations using an ab initio-trained machine learning potential. We use these to assign the Raman bands and show that the entire spectrum can be well described as a combination of two temperature-independent spectra. We then assess which spectral regions exhibit strong dependence on the local tetrahedral order in the liquid. Further, this work demonstrates that changes in this structural parameter can be used to elucidate the temperature dependence of the Raman spectrum of liquid water and provides a guide to the Raman features that signal water ordering in more complex aqueous systems.

A sample holder for simultaneous Raman and neutron vibrational spectroscopy.

We have built a sample holder (called a center stick or sample stick) for performing simultaneous Raman and neutron vibrational spectroscopy on samples of material at the VISION neutron vibrational spectrometer of the Spallation Neutron Source at Oak Ridge National Laboratory. This equipment holds material samples in the neutron beam within the cryogenic environment of the VISION spectrometer, allowing for samples to be studied at temperatures as low as 5 K. It also provides the capability for gas to be loaded to or evacuated from the sample while it is loaded at VISION. The optical components for directing and filtering light are located within the cryogenic volume, in physical proximity to the sample. We describe the construction of this sample holder and discuss our first measurements of simultaneous Raman and neutron vibrational spectra. The samples that we report on were of 4-nitrophenol at a temperature of 20 K and of cryogenic hydrogen of a number of different orthohydrogen fractions.

Determination of Processed Salmon Components Sticking to Polyethylene Terephthalate Coatings of Containers by FT-IR and Raman Vibrational Spectroscopy

Earlier studies determined that portions of salmon were strongly sticking to the polymer coating of the container walls after emptying the cans. In this sense, this work performed high- and low-frequency spectral characterizations of fresh salmon muscle, fat, and skin by Fourier-transform infrared (FT-IR) and Raman spectroscopy analyses to elucidate which components were effectively sticking to the underlying coating. The spectral analyses evidenced that the bands of skin and muscle were clearly distinctive. However, less perceptible contrasts were observed between fat and muscle until band 1700 cm−1, but above this limit, the minor spectral changes detected were sufficient to characterize both salmon components. The new spectral bands for skin occurred at 1030, 1202, and 1336 cm−1. Differences in intensity were also observed for band ν(C=O) at 1744 cm−1, even though it appeared in all components of the salmon. The bands for the ν(C–H) and ν(O–H) vibrations in the high-frequency region were the same, but the intensities and profiles were different. The similarities between the spectra of fresh salmon muscle and residues sticking to the polymer layers were substantial, corroborating that this is in fact the main component sticking to the polymer surface coating of industrial food cans.

Operando Studies of Redox Resilience in ALT Enhanced NiO-YSZ SOFC Anodes

This work explores the effects of aluminum titanate (ALT) as a dopant in standard NiO-YSZ SOFC anodes on cell resilience under reduction and oxidation (redox) cycling. Cells operated galvanostatically (50% Imax) at 800°C for the duration of a single redox cycle with hydrogen exposure lasting for 20 minutes prior to electrochemical oxidation. Observable reduction and oxidation of the Ni anode was monitored using operando vibrational Raman spectroscopy and electrochemical potential measurements, while electrochemical impedance spectroscopy (EIS) and linear sweep voltammetry (LSV) measurements were performed to determine cell condition and performance following each redox cycle. Repeated electrochemical redox cycling led to irreversible cell degradation for both ALT doped and standard anodes, but ALT conferred significantly more resilience to the doped anodes. Increased stability of Ni catalyst microstructure resulting from ALT addition was shown to slow degradation rates and increase average cell tolerance to redox cycles by a factor of two.

High-Pressure Chemistry and the Mechanochemical Polymerization of [5]-Cyclo-p-phenylene.

Evidence for the surprising formation of polymeric phases under high pressure for conjugated nanohoop molecules was found. This paper represents one of the unique cases, in which the molecular-level effects of pressure in crystalline organic solids is addressed, and provides a general approach based on vibrational Raman spectroscopy combining experiments and computations. In particular, we studied the structural and supramolecular chemistry of the cyclic conjugated nanohoop molecule [5]cyclo-para-phenylene ([5]CPP) under high pressures up to 10 GPa experimentally and up to 20 GPa computationally. The theoretical modeling for periodic crystals predicts good agreements with the experimentally obtained Raman spectra in the molecular phase. In addition, we have discovered two stable polymeric phases that arise in the simulation. The critical pressures in the simulation are too high, but the formation of polymeric phases at high pressures provides a natural explanation for the observed irreversibility of the Raman spectra upon pressure release between 6 and 7 GPa. The geometric parameters show a deformation toward quinonoid structures at high pressures accompanied by other deformations of the [5]CPP nanohoops. The quinonoidization of the benzene rings is linked to the systematic change of the bond length alternation as a function of the pressure, providing a qualitative interpretation of the observed spectral shifts of the molecular phase.

Ab-initio molecular dynamics and vibrational Raman spectroscopy investigations of quartz polymorph at high temperature

Quartz has found a wide range of applications over the past years. In the present work, the temperature dependence of microcrystalline quartz is investigated with Raman spectroscopy and DFT-based molecular dynamics simulations. We aimed to determine the structure at short and medium range distances as a function of the increasing temperature. The dynamics and the structural changes are analysed in terms of time-dependent properties, and the vibrational analysis obtained from calculated dipole trajectory and vibrational density of states (VDOS). The computed data is compared to Raman and infrared spectroscopic measurements. The approach is of a particularly great interest when we focus on the structural behaviour, and the dynamical disorder observed and characterised through geometric and thermodynamic data. The calculations confirm that the infrared and Raman signature as a function of temperature provide a sensitive analysis of the structural behaviour of quartz.