Liquid N2 Temperature Research Articles

Copper-assisted anticancer activity of hydroxycinnamic acid terpyridine conjugates on triple-negative breast cancer.

The development of active therapeutic agents to treat highly metastatic cancer while minimizing damage to healthy cells is of utmost importance. Due to potential antioxidant properties, hydroxycinnamic acid derivatives (caffeic acid and p-coumaric acids) were found to inhibit highly metastatic breast cancer cell growth both in vitro and in vivo without much effect on normal cells. Especially due to the structure-activity relationships, ester and amide derivatives of hydroxycinnamic acids are reported to gain much higher radical scavenging ability than their naked hydroxycinnamic acid analogs like caffeic acid and p-coumaric acid. These results prompted us to design a set of ligands by incorporating an amide moiety on caffeic acid and p-coumaric acid to achieve the least toxicity towards healthy cell lines. Further, the Cu(II) complexes of amide-coupled caffeic acid and p-coumaric acid ligands have been explored for their therapeutic activity on triple-negative breast cancer and other cancer cells like colon, and prostate cancer. The Cu(II) complexes (4 & 5) were characterized by UV-Vis spectroscopy, FTIR, and X-band EPR spectroscopy. The trigonal bipyramidal geometry of complexes was confirmed by the X-band EPR spectra recorded in solution state at liquid N2 temperature. The purity of the complexes was determined by elemental analysis and HPLC traces. Initially, Calf thymus DNA (ct-DNA) binding studies with the complexes were explored. The results suggested the complexes (4 & 5) bind majorly through an intercalative mode of binding with ct-DNA, whereas no significant binding was observed for the bare organic ligands (2 & 3). The intercalation binding modes of 4 and 5 were further supported by UV-visible spectroscopy, ct-DNA melting point analysis, and CD spectroscopy. Moreover, these complexes showed better activity towards cisplatin-resistant TNBC cell lines (4T1, a TNBC cell line derived from the mammary gland tissue of a mouse). The combination of antioxidants and Cu(II) as the metal center made the complexes more cytotoxic toward cancer cell lines (4T1) (IC50 ∼ 3.5 ± 2.5 μM) and the least toxic toward healthy cells (L929) (IC50 ∼ 15 ± 5 μM). Finally, the mechanism of cell death was studied using JC-1 staining and a cell colony formation assay. These studies might help in designing safer anticancer drugs for treating more aggressive types of cancer.

Analysis of red-luminescence lifetime components of non-bridging oxygen hole centers in γ-ray irradiated silica glasses

The relation between 1.9 eV red-luminescence intensity of non-bridging oxygen hole centers (NBOHCs) in silica and incident laser shot number was proved to be important to predict the occurrence of laser damage, in which a more precise prediction will benefit from a deeply understanding of the red-luminescence of NBOHCs. This study focuses on analyzing NBOHCs in silica glasses irradiated by gamma rays, including the electron paramagnetic resonance spectra in the main g2 factor range, excitation spectra in the UV range, emission spectra and emission lifetimes in the red range, as well as their relations with hydroxyl and temperature. At 53 K, the main g2-factor of NBOHCs in high-hydroxyl (high-OH) and low-hydroxyl (low-OH) silica differs by only ∼1.5 × 10−4. Whereas in the higher g-value side of the main g2-factor band, low-OH silica exhibited a little broadened resonance absorption bandwidth. At room temperature, the 5.64-3.44 eV excitation spectra monitoring at 1.9 eV and the 2.16-1.65 eV emission spectra exciting at 4.8 eV exhibit the same excitation peak of 4.54 eV and emission peak of 1.907 eV for both high-OH and low-OH silica. Whereas at liquid-N2 temperature, high-OH silica exhibits a broader emission bandwidth in the higher energy side of the red-luminescence band. At room temperature, the average emission lifetime of NBOHC in high-OH silica is 14.5 µs, whereas that in low-OH silica is 13.4 µs. However, at liquid-N2 temperature, their average lifetimes respectively increased and decreased greatly to 22.3 and 9.7 µs, showing a quite obvious variation. In high-OH silica, the large number of hydroxyl attract the hydrogen ions that are released with the temperature decrease, forming metastable hydrogen-bonded hydroxyl. Finally, only NBOHCs corresponding to longer lifetime components, without neighboring hydrogen and its interaction, remain in the high-OH silica at lower temperature. In low-OH silica, there is few hydroxyl, so that the hydrogen released with the temperature decrease can only act on NBOHCs without neighboring hydrogen. Finally, those NBOHCs that correspond to shorter lifetime components and interact with neighboring hydrogen remain in the low-OH silica at lower temperature. The results on the characteristics of this red luminescence provides new ideas and ways for the future prediction about the laser damage of silica. Especially, the component analysis on the emission lifetime decay curves that can reflect the characteristics of NBOHCs and their neighboring environment can not only be used to distinguish between contributions to the red-luminescence from different types of NBOHCs, but also to analyze the relations between other ions or defects around NBOHCs and laser damage initiation, for a more precise prediction.

Hydrophobic coating using sustainable sol-gel process doped with carboxylic acids to protect heritage copper artefacts

Metal corrosion and its mitigation using alkoxysilane based sol-gel coatings presenting specific properties are a matter of interest in many areas of applications, from industrial to cultural heritage materials. Thanks to their adhesive and coupling nature with different molecules and substrates, they show excellent results against aggressive environments. This study focuses on the protection of historical copper-based alloys. A tetramethyl orthosilicate-based (TMOS-based) sol-gel coating was doped with carboxylic acid compounds (heptanoic, octanoic and decanoic acids) recognized for their non-toxicity and their interesting corrosion inhibition properties on ancient corroded copper. The development of the coating and the basic understanding of the fundamental chemistry as well as the protection mechanism on the historical samples were studied. Contact angle measurements allowed to show that the resulting coating displayed a hydrophobic protection at the surface of the samples while its chemical composition was evaluated using thermogravimetric analysis, SEM-EDS and Raman spectroscopy. The porosity of the sol-gel matrix and the distribution of the acids in the porous silica network were then investigated by establishing nitrogen adsorption/desorption isotherms at liquid N2 temperature. Examination of the sample's cross-section by SEM-EDS showed that the TMOS-based coatings doped with carboxylic acids penetrated up to 60 % in depth in the corrosion layer of the ancient copper, while the Raman analyses showed that the acids formed organometallic complexes both at the surface and in the corrosion layer, leading to the protection of the metallic substrate against further corrosion.

Solvent‐free synthesized zeolites as compatibility agents in FKM rubber

AbstractDry hybrid synthesized zeolite was added to a fluoroelastomer (FKM). Carbon black filler was also evaluated. The resulting systems were evaluated in terms of rheological, physicochemical and morphological characteristics. Replacing carbon black with zeolites decreased the torque maximum (125–144 nM) for all samples. The type of filler has a significant influence on the thermal stability of FKM compounds. The use of x‐ray microtomography (IMX for) on the investigated samples (fluorinated polymers) was shown to be a potential and powerful tool for fractioning the components of the resulting composite material. According to microtomography images, increasing the filler content increases the number of pores, probably due to the greater difficulty in dispersing larger volumes of fillers, which are shown as interconnected conglomerates. The SodC8.5 filler showed a considerable increase in stress at rupture (11 MPa) with only 1 phr, maintaining stability up to 10 phr, while elongation at break increased. The use of Sod and SodC8.5 loads showed an improvement of 15% and 30% in relation to the base compound. Finally, in a thermal stability test at the temperature of liquid N2, the SodC8.5 sample showed the best dimensional stability (approx. 7%), verifying the good compatibility between the filler and the fluorinated polymeric matrix.

Oxide dispersion-strengthened silver: manufacturing and properties

Abstract Novel oxide dispersion-strengthened (ODS) silver alloys were synthesised by mechanical alloying and subsequent consolidation via hot pressing in protective atmosphere. The effect of dispersoid size and volume fraction on the electrical and mechanical properties is exemplified with Cr2O3, CaO and Y2O3 as model candidates for a systematic study of the principles of particle selection. The results for the development of the microstructure under different processing conditions show that control of the impurity level is of primary importance for achieving high-quality, fully dense material. Hence, a modified cryo-milling technique at liquid-N2 temperature was applied. Data at ambient temperature are presented, revealing that the mechanical and electrical properties can be tailored within a wide range as a function of the microstructure. These results are explained by microstructural concepts for room temperature yielding and electrical conductivity.

Chemical reactions in the Fe2SiO4-D2 system with a variable deuterium content at 7.5 GPa

Abstract Hydrogen-induced decomposition of fayalite (Fe2SiO4) at high pressure is of considerable interest for a better understanding of the chemical processes occurring in the cores and mantles of icy satellites. At pressures up to 10 GPa and temperatures 250–300 °C (typical of the cores and mantles of Jupiter’s and Saturn’s satellites), a variable amount of hydrogen can react with fayalite contained in their rocks. Volatile compounds that can form via these reactions are usually identified by mass spectroscopy. In our experiments, we used compressed deuterium gas instead of hydrogen to ensure that the volatiles analyzed by mass spectroscopy could only result from the decomposition of fayalite. To study the effect of the amount of deuterium present in the system, the fayalite (Fa) samples were deuterated at P = 7.5 GPa and T = 280 °C with the preset molar ratios D2/Fa = 1, 1.5, 2.2, and 5 in the reaction cell. The deuterated samples were further quenched to the liquid N2 temperature and, after releasing the pressure, removed from the reaction cell and studied by quadrupole mass-spectroscopy, X-ray diffraction, and Raman spectroscopy. Our results showed that the high-pressure deuteration invariably led to the chemical decomposition of fayalite. The solid products of the reaction varied from a mixture of ferrosilite (FeSiO3) and iron at D2/Fa = 1 to a mixture of silica and iron at D2/Fa = 2.2. The decomposition occurred via breaking the Fe-O bonds and was always accompanied by the formation of water. Applying the observed reactions to the natural conditions of, e.g., the center of Titan or Ganymede, one may infer that fayalite can be dissolved in the hydrogen fluid or replaced by iron, ferrosilite, or silica depending on the molar ratio H2/Fa.

Attaining record-high magnetic exchange, magnetic anisotropy and blocking barriers in dilanthanofullerenes.

While the blocking barrier (Ueff) and blocking temperature (TB) for “Dysprocenium” SIMs have been increased beyond liquid N2 temperature, device fabrication of these molecules remains a challenge as low-coordinate Ln3+ complexes are very unstable. Encapsulating the lanthanide ion inside a cage such as a fullerene (called endohedral metallofullerene or EMF) opens up a new avenue leading to several Ln@EMF SMMs. The ab initio CASSCF calculations play a pivotal role in identifying target metal ions and suitable cages in this area. Encouraged by our earlier prediction on Ln2@C79N, which was verified by experiments, here we have undertaken a search to enhance the exchange coupling in this class of molecules beyond the highest reported value. Using DFT and ab initio calculations, we have studied a series of Gd2@C2n (30 ≤ 2n ≤ 80), where an antiferromagnetic JGd⋯Gd of −43 cm−1 was found for a stable Gd2@C38-D3h cage. This extremely large and exceptionally rare 4f⋯4f interaction results from a direct overlap of 4f orbitals due to the confinement effect. In larger cages such as Gd2@C60 and Gd2@C80, the formation of two centre-one-electron (2c-1e−) Gd–Gd bonds is perceived. This results in a radical formation in the fullerene cage leading to its instability. To avoid this, we have studied heterofullerenes where one of the carbon atoms is replaced by a nitrogen atom. Specifically, we have studied Ln2@C59N and Ln2@C79N, where strong delocalisation of the electron yields a mixed valence-like behaviour. This suggests a double-exchange (B) is operational, and CASSCF calculations yield a B value of 434.8 cm−1 and resultant JGd–rad of 869.5 cm−1 for the Gd2@C59N complex. These parameters are found to be two times larger than the world-record J reported for Gd2@C79N. Further ab initio calculations reveal an unprecedented Ucal of 1183 and 1501 cm−1 for Dy2@C59N and Tb2@C59N, respectively. Thus, this study offers strong exchange coupling as criteria for new generation SMMs as the existing idea of enhancing the blocking barrier via crystal field modulation has reached its saturation point.

The Effect of Severe Plastic Deformation on the Corrosion Resistance of AISI Type 304L Stainless Steel

The AISI type 304L stainless steel (SS) was solution annealed at 1050 °C and cryo-rolled at liquid nitrogen (L-N2) temperature (77 K) under severe plastic deformation (SPD). The thickness reduction through cryo-rolling plastic deformation was carried out up to 90% (designated as CR-90) of initial thickness. The cryo-rolling during rolling at liquid N2 temperature (77 K), resulted in transformation induced plastic deformation of the austenite γ-phase into α’- martensite phase. The phase transformation was characterized by x-ray diffraction (XRD) and saturation magnetization (Ms) measurement. The microstructure was measured by using optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD peak positions confirmed the martensite (α’) phase formation. Saturation magnetization (Ms) value of the cryo-rolled specimens shows increasing linearity with cryo-rolling, and transformed to bct martensite (α’). The measured corrosion rate of the cryo-rolled specimens as per ASTM A-262 practice-C test (Huey test) ranges from 6.6 mpy or 0.167 mm/yr (CR 0) to 12.9 mpy or 0.328 mm/yr (CR 90), indicating the effects of severe deformation of strain-induced martensite with the cryo-rolling. Further, the role of severe deformation of strain-induced martensite with the cryo-rolling on AISI type 304L SS and also influence on the corrosion resistance are investigated in detail. The deformation microstructure roles, i.e., the phases and volume percentage induced by the different percentage of the cryo-rolling that influences the corrosion resistance properties and corresponding corrosion resistance in nitric acid have been investigated.

NMR of petrochemical-type chemical reactions

A simple technique is presented for NMR of chemically reacting systems at conditions of high temperature and pressure. The method can follow reactions that are typical of refinery operations – hydrogenation, transfer dehydrogenation, methanol synthesis, and isomerization. All of the reacting materials are flame-sealed into a glass capillary. Gaseous agents such as O2 and CO are loaded into the capillary by condensation at liquid N2 temperature. H2 is provided by loading LiAlH4. The capillary holds the high pressure, up to 7 MPa, so the NMR probe can be a simple design with hot air flowing over the sample tube, up to 350 °C. Example reaction results are presented, including hydrogenation of benzene, hydrogenation/dehydrogenation of cyclohexene to benzene and cyclohexane (a disproportionation), and synthesis of methane, methanol and dimethyl ether from CO and H2. In this work we present a simple, inexpensive method with rapid temperature response for tracking chemical reactions in real-time at high temperature and high pressure.

In silico design of pseudo D5h actinide based molecular magnets: role of covalency in magnetic anisotropy

Actinide molecular magnets are of great interest in the area molecular magnetism as they possess strong covalency and spin-orbit coupling that their 4f congeners lack. Despite these known advantages, the actinide based molecular magnets have not been explored in detail due to the limited availability of actinide salts. While theoretical tools are proven to be useful in lanthanide chemistry towards prediction, they are still at an infant stage in actinide chemistry. In this manuscript, we have attempted to utilise CASSCF/RASSI-SO calculations to predict suitable pseudo D5h molecules possessing attractive magnetic properties. To begin with, we have undertaken an extensive benchmarking of the methodology employed by studying two sets of isostructural, [NdTp3], [UTp3], [Nd(COT″)2]-, [U(COT″)2]- {Tp− = trispyrazolylborate, COT″ = bis(trimethylsilyl)cyclooctatetraenyl dianion} complexes. The method assessment reveals that the methodology employed is reliable as this has reproduced the experimental observables. With this, we have moved forward with prediction where pseudo-D5h symmetric [L2M(H2O)5][I]3L2.(H2O) {M = Nd, U, Pu; L = tBuPO(NHiPr)2} systems are modelled from their Nd(III) X-ray structure. Our calculations reveal that the Uranium complex studied possess superior SIM characteristics compared to its lanthanide analogue. Plutonium complex has prolate electron density at the ground state, and hence the ligand environment is unsuitable for yielding SIM behaviour. The role of solvent molecules, counter anions and equatorial and axial ligand are explored and tantalizing prediction with a barrier height of 1403.3 and 989.5 cm−1 are obtained for [tBuPO(NHiPr)2-U-tBuPO(NHiPr)2]3+ and [Pu(H2O)5]3+ models, respectively and this paves the way for synthetic chemist to target such geometries in actinide based SIMs. Is pseudo D5h geometry suitable for Actinide SIMs? In this article, we have extensively studied uranium complex and compared it with its lanthanide analogue. The pseudo D5h symmetric uranium complex possesses oblate electron density which is favourable in the axial ligand field and henceforth it is predicted to have attractive SIM behaviour. Studies on models suggest the low-coordinate actinide chemistry may hold the key to further the blocking temperature beyond liquid N2 temperatures.

Transmission behaviors of metallic ATR mid-infrared hollow waveguide at low temperature and performance improvement

With the rapid development of infrared fibers and their applications, there is an increasing demand for applications at low temperature. In this paper, the CO2 laser transmission performances are investigated based on metallic GeO2 ATR hollow waveguide, showing the abnormal phenomenon of decreased transmission power at liquid N2 temperature (77 K). In addition, the influences of liquid N2 environment on the properties of GeO2 reflective film and hollow core gas medium have been investigated. The optical constants n and k of GeO2 are measured at low temperature, and the impacts of different fiber core gas media (dry air, Ar and N2) on low-temperature transmission performances are studied in detail. The results indicate that the decrease of transmission power is mainly due to the absorbance and scattering of solidified water vapor and liquefied air in hollow waveguide at low temperature. The transmission performance can be improved by filling the hollow fiber core with N2 gas. Specifically, the output power of fiber with appropriate N2 gas flow rate at low temperature could remain at a high level all the time, which is similar to the value of sample under room temperature. The present works could pave the way for the future transmission applications of mid-infrared hollow waveguide in cryogenic-temperature environments.

Optical properties of the Eu2+-ion immersed as a doping impurity into a KCl:KBr:RbBr solid solution: Influence of the different aggregation-precipitation states of the doping ions

The optical properties of the Eu2+-ion immersed as a doping impurity in mixed KCl–KBr–RbBr crystals were investigated together with the changes that these properties suffer by thermal quenching at liquid-N2 temperature and, also, during thermal annealing at 523 K. The crystal matrix, as characterised by X-ray diffraction, consists of a strongly-textured F-type cubic ternary KCl:KBr:RbBr solid solution (a0 = 6.59 ± 0.02 Å). The absorption spectrum of freshly-quenched samples shows two broad absorption bands peaking at about 328 and 247 nm (10Dq = 9998 ± 143 cm−1) whereas the fluorescence spectrum of these samples shows a single nearly-symmetric emission band peaking at about 420 nm. These spectra, being similar in general to the corresponding ones of freshly-quenched single crystals of KCl:Eu2+, KBr:Eu2+ and RbBr:Eu2+, change during the annealing treatment so that, for well-annealed samples, the absorption bands peak at 277 and 333 nm (10Dq = 6689 ± 91 cm−1) whereas the fluorescence spectrum consists of four emission bands peaking at about 420, 427, 449 and 480 nm. These changes, indicating that the doping ion environment evolves during annealing, are discussed to be due to the occurrence of different precipitation states of the doping ions. The structural nature of these states, and, also, an aggregation-precipitation kinetics, is proposed.

Analysis of Losses in High-Purity Neon Production Technology. Part 2.* Processing of a Ne–He Mixture to Obtain Pure Products

Inert gases are valuable products that are widely used in industry. Their processing scheme includes several enrichment, purification, and separation stages of a Ne–He mixture (NHM). Primary enrichment of the NHM occurs in air-separation plants. Secondary enrichment uses a reflux condenser at liquid N2 temperature (~78 K). The impurity concentration at the reflux condenser outlet can be decreased by reducing the operating temperature. However, the specific energy consumption increases whereas the extraction coefficient is practically not affected if a vacuum pump is applied. A promising trend for reducing the cooling temperature is to use non-machine cold sources. The Ne extraction coefficient during rectification depends on the impurity (He) content in the waste gases. The main method for increasing the efficiency of Ne production installations is to use additional non-machine cooling of the rectification input stream. The adsorption installation for recycling Ne from He concentrate can be chilled using two coolants, i.e., Ne and liquid N2. The research showed that the specific energy consumption of the separation is 5–7 times greater to reach Ne temperature (28 K) than liquid N2 temperature (78 K).

Microstructural origins for a strong and ductile Al0.1CoCrFeNi high-entropy alloy with ultrafine grains

A single-phase Al0.1CoCrFeNi high-entropy alloy (HEA) with face-centered cubic structure was subjected to cryo-rolling at the liquid N2 temperature and subsequent annealing. Microstructural characterization of post-annealed samples by electron backscattered diffraction and transmission electron microscopy revealed that, the dominant grain boundaries (GBs) are of Σ3 type low energy twin boundaries owing to the low stacking fault energy of the HEA. The resulting ultrafine-grained single-phase HEA with abundant Σ3 twin boundaries shows a high strength above 1.0 GPa and a tensile strain larger than 20%. The quantitative analysis on the grain size dependence of strength suggests that a high lattice friction stress and a high GB strengthening via low energy Σ3 twin boundaries are two major contributions for the excellent strength-ductility balance of the ultra-fine grained HEA.

Synthesis and properties of 1D manganese-doped hematite particles

The properties of Mn-doped hematites and their Mn-doped precursors were investigated using the 57Fe Mössbauer spectroscopy, XRD, FT-IR, UV/Vis/NIR and FE SEM. Mn-doped goethite precursors were synthesized in a high alkaline pH medium starting with iron choline citrate. The XRD analysis of all Mn-doped goethites and Mn-doped hematites showed only the presence of a goethite or hematite crystal structure. The RT Mössbauer spectrum of reference goethite showed typical features of precipitated goethite. With increased Mn-doping the spectral lines of the goethite precursor were broadening, the hyperfine magnetic field decreased and the relative intensity of central quadrupole doublets increased. The RT Mössbauer spectra of Mn-doped hematite showed features of the hematite phase and increased relative intensity of a central quadrupole doublet which disappeared in the spectra recorded at liquid N2 temperature. The presence of this superparamagnetic component in the RT Mössbauer spectra is a direct consequence of Mn-doping. In the FT-IR spectra the characteristic IR bands sensitive to Mn-doping were identified. The UV/Vis/NIR spectra showed shifts of optical absorption bands and a strong absorption increase in the visible part of the spectrum. FE SEM images of Mn-doped goethite precursor showed a change in shape from rod to star-like particles. Upon heating at 300 °C for 4 h in air, the obtained Mn-doped hematite particles preserved the original morphologies of Mn-doped goethite precursors. Taking into account the superparamagnetic spectra (RT and liquid N2 temperature), XRD and the corresponding FE SEM images of Mn-doped hematite particles it can be concluded that these particles contained substructure. In this substructure of Mn-doped hematites the fraction of superparamagnetic crystallites (domains) is given by calculated value for the superparamagnetic doublet present.

Composition in the Interface between Clay Mineral Surfaces and Divalent Cation Electrolytes.

The interfacial free energy of a solid, which determines its adsorption properties, depends on interactions between the surface and the fluid. A change in surface composition can completely change the behavior of the solid. Decades of work have explored adsorption and its effects at solid-fluid interfaces from the macroscopic perspective and using molecular modeling, so the concept of the electric double layer (EDL) is well established in the community. However, direct, molecular level, experimental observations of the composition within the interface region, and its change with time and conditions, are not abundant. We used cryogenic X-ray photoelectron spectroscopy (cryoXPS) to observe the composition in the clay mineral-solution interface region as a function of bulk solution composition, on illite and chlorite in MgCl2 and CaCl2 electrolytes, over a range of concentrations (1-125 mM), in situ, on vitrified samples. These samples were prepared from very thin smears of centrifuged wet paste that were instantaneously chilled to liquid N2 temperature. They preserved the adsorbed solution in its amorphous state, maintaining the location of the ions and water with respect to the solid, without the disruption that occurs during drying or the rearrangement that results as water crystallizes during freezing. With decreasing ionic strength, we could directly monitor the loss of negative charge in the interface region, producing an anion deficiency, as predicted by theory. The Cl-/Me2+ ratio dropped below 1 for chlorite at 12-25 mM MeCl2 and for illite at 75-100 mM. In addition to better understanding of clay mineral behavior in solution, this work demonstrates that only those clay minerals where surface charge density is the same or lower than that for chlorite contribute to a low salinity enhanced oil recovery response (LS EOR). This explains many of the contradictory results from studies about the role of clay minerals in LS EOR.

Magnetic Characterization of Chromium Intermediates in the Reduction of Chromium (VI) by Glutathione in Acidic Solutions

Chromium (VI) is carcinogenic through intermediates formed in the cellular milieu by reduction with small reductants like glutathione (GSH), ascorbate, cysteine, and NADPH. Although the reduction of chromate by thiols has been investigated, the participation of Cr(IV) intermediates has been inferred only indirectly due to the Cr(IV) refractive behavior towards EPR spectroscopy. Biological data from numerous reports indicate that Cr(IV) is the species most likely responsible for the carcinogenicity of Cr(VI). Our kinetic studies suggested that in acidic solutions, glycine buffer at pH 2.8, the reduction of chromate with GSH involves mostly a chromium(IV) intermediate. As a step towards the full characterization of the paramagnetic species involved in the reduction of chromate by thiols at neutral pH, we embarked on an investigation of the reduction of chromate with GSH in glycine buffer at pH 2.8 using a Superconducting QUantum Interference Device (SQUID) magnetometer. Our results indicate a strong influence of temperature and confirm the presence of Cr(IV). At 2 K, the saturation magnetization method was applied to the frozen reaction when it reached the peak of formation of intermediates and the contributions were calculated to be 30% of Cr(IV) and 69% of Cr(V). When the Curie–Weiss method was applied to determine the effective magnetic moment, the use of the linear portion of the curve, 100–200 K, yielded 58% Cr(IV) and 42% Cr(V); when data from the region below the temperature of liquid N2 (77 K) is employed, the intermediate is exclusively Cr(IV).

Water Interaction with Sputter-Deposited Nickel Oxide on n-Si Photoanode: Cryo Photoelectron Spectroscopy on Adsorbed Water in the Frozen Electrolyte Approach

The interaction of water with a magnetron-sputtered nickel oxide thin film on an n-type silicon photoanode is investigated in perspective to oxygen evolution. The substrate was exposed in-situ stepwise to gas phase water up to 10 L at liquid N2 temperature and analyzed via X-ray and UV photoelectron spectroscopy in the so called frozen electrolyte approach. Photoemission of the pristine NiOx layer shows the presence of stoichiometric NiO and Ni2O3 as well as of non-stoichiometric phases. In the monolayer range, molecular and dissociative adsorption is detected assigned to the NiO respective Ni2O3 phase. Initially, the emission of the molecular adsorbed water species interacting with NiO is found at 0.8 eV lower binding energies as compared to water related emission for higher coverages with binding energies commonly assigned to H2O-H2O interaction. In addition to the chemical analysis, the electronic structure of the n-Si/SiOx/NiOx/H2O photoanode is measured and discussed.

An international multi-laboratory investigation of carbon-based hydrogen sorbent materials

New materials are needed to achieve the hydrogen storage targets set out by the US Department of Energy for fuel cell vehicular applications. In order to enable the pathway toward this discovery, precise and accurate characterization of the hydrogen storage performance of these materials is needed. Determining the precise and accurate hydrogen storage capacity of materials requires rigorous attention to detailed experimental parameters and methodology. Slight errors in even small experimental details can result in a large deviation in the determination of the material’s true characteristics. Here, we compare measurements of the gravimetric excess hydrogen uptake capacities for two different carbon sorbent materials measured by different laboratories at ambient and liquid N2 temperatures. The participants for this study consist of research laboratories led by experienced scientists in the hydrogen storage field. This collaborative evaluation of standard sorbents illustrated considerable reproducibility over a broad range of materials’ hydrogen sorption gravimetric capacities.

Hydrogen solubility in cristobalite at high pressure.

Powder samples of cristobalite-I are loaded with hydrogen at pressures up to 90 kbar and T = 250 °C and quenched under pressure to the liquid N2 temperature. The quenched samples are examined at ambient pressure by X-ray diffraction, Raman spectroscopy, and thermal desorption analysis. The hydrogen content of the samples is found to increase with pressure and reach a molecular ratio of H2/SiO2 ∼ 0.10 at P = 90 kbar. At ambient pressure, the samples consist of a mixture of approximately 80% cristobalite-I phase and 20% cristobalite-II-like phase, the crystal lattices of both phases being slightly expanded due to the hydrogen uptake. According to Raman spectroscopy, the hydrogen is dissolved in these phases in the form of H2 molecules.