Structural Insights into the Recognition of N2‐Aryl‐ and C8‐Aryl DNA Lesions by the Repair Protein XPA/Rad14

Aromatic amines are strongly carcinogenic. They are activated in the liver to give reactive nitrenium ions that react with nucleobases within the DNA duplex. The reaction occurs predominantly at the C8 position of the dG base, thereby giving C8‐acetyl‐aryl‐ or C8‐aryl‐dG adducts in an electrophilic aromatic substitution reaction. Alternatively, reaction with the exocyclic 2‐NH₂ group is observed. Although the C8 adducts retain base‐pairing properties, base pairing is strongly compromised in the case of the N² adducts. Here we show crystal structures of two DNA lesions, N²‐acetylnaphthyl‐dG and C8‐fluorenyl‐dG, within a DNA duplex recognized by the repair protein Rad14. The structures confirm that two molecules of the repair protein recognize the lesion and induce a 72 or 78° kink at the site of the damage. Importantly, the same overall kinked structure is induced by binding of the repair proteins, although the structurally different lesions result in distinct stacking interactions of the lesions within the duplex. The results suggest that the repair protein XPA/Rad14 is a sensor that recognizes flexibility. The protein converts the information that structurally different lesions are present in the duplex into a unifying sharply kinked recognition motif.     

Growth inhibition in calcium sulfate crystal using a copolymer in oil fields: theoretical study and experimental evaluations

A poly(itaconic acid-co-sodium vinylsulphonate) (PIASVS) was theoretically studied and experimentally evaluated as an inhibitory agent against the growth of calcium sulfate (CaSO₄) crystals, in both non-saline and saline solutions. Density functional theory revealed that the CaSO₄ crystal precipitation could be precluded through the effective pairing of Ca²⁺ and SO₄^2? ions by carboxylic group polymer heads and that, moreover, the Na⁺ cations of the sulphonate polymer heads could be easily replaced by Ca²⁺. With PIASVS concentration of 50 ppm, lower than what is required in oil recovery processes, the polymer inhibited 33% in CaSO₄ crystals growth in non-saline solution, but the salt increased the inhibitory performance of PIASVS up to 54%. Thermogravimetric analysis, scanning electron microscopy and X-ray diffractometry techniques showed that PIASVS changed the CaSO₄ crystal morphology from a bassanite phase in non-saline solution to a bassanite/gypsum mix. The crystal morphology observations along with the conductivity measurements confirmed the pairing of ions from dissolved CaSO₄ by NaCl and PIASVS. Dynamic light scattering revealed that, the PIASVS cluster size increased in non-saline solution but decreased in saline solutions, suggesting that NaCl increases the PIASVS solubility in aqueous solution. The performance of PIASVS as anti-scaling agent was found to be suitable for the conditions found in the Mexican oil reservoirs.     

Doping dependence of low-energy quasiparticle excitations in superconducting Bi2212

The doping-dependent evolution of the d-wave superconducting state is studied from the perspective of the angle-resolved photoemission spectra of a high-T_c cuprate, Bi₂Sr₂CaCu₂ O_8+δ (Bi2212). The anisotropic evolution of the energy gap for Bogoliubov quasiparticles is parametrized by critical temperature and superfluid density. The renormalization of nodal quasiparticles is evaluated in terms of mass enhancement spectra. These quantities shed light on the strong coupling nature of electron pairing and the impact of forward elastic or inelastic scatterings. We suggest that the quasiparticle excitations in the superconducting cuprates are profoundly affected by doping-dependent screening.     

PRELIMINARY STUDY ON PORTIONS OF SYSTEMS Na2O-CaO-AI2O3-Fe2O3 AND Na2O-CaO-Fe2O3-SiO2*

Portions of the quaternary system Na₂O-CaO-Al₂O₃-Fe₂O₃ have been studied by the exploration of (1) the plane CaO-4CaO.Al₂O₃°Fe₂O₃-(Na₂O + 3Al₂O₃) and (2) planes above the base system CaO.5CaO.3Al₂O3–2CaO.Fe₂O₃ which contain successively increasing amounts of Na₂O up to 6%. A portion of the quaternary system Na₂O-CaO-Fe₂O₃-SiO₂ has been studied by the exploration of a plane containing 5% of Na₂O above the base system CaO-2CaO.SiO₂-CaO.Fe₂O₃. In the pseudosystem CaO-4CaO.Al₂O₃.Fe₂O₃-(Na₂O + 3A1₂O₃) the compound Na₂O.-8CaO.3A1₂O₈ was found to exist as a primary phase, and the area in which the plane cuts the Na₂O.8CaO.3A1₂O₃ primary-phase volume was established. Three points on uni-variant curves were located. The iron phase (4CaO.A1₂O₃.Fe₂O₃ solid solution) was observed to exist in a solid-solution series. In the system Na₂O-CaO-5CaO.3Al₂O_3--2CaO.Fe₂O₃ it was found that the compound Na₂O.8CaO.3Al₂O3 appears at an Na₂O concentration of 4.2%. As soda, however, is taken into solid solution by other phases, it was not feasible at this time to determine the invariant point for Na₂O.8CaO.3A1₂O₃, 3CaO.Al₂O₃, 5CaO.3A1₂O₃, and 4CaO.Al₂O₃.-Fe₂O_a solid solution. In the system Na₂O-CaO-2CaO.SiO₂-CaO.Fe₂O₃ no ternary compounds were observed up to the 5% limit of Na₂O employed. A soda-containing phase occurred in solid solution with α-2CaO.SiO₂, which may precipitate on cooling, forming inclusions in the ß-2CaO.SiO₂, or enter into reaction with the glassy phase.     

SELECTIVE CARBON MONOXIDE OXIDATION IN H2-RICH GAS STREAM OVER Co3O4/CeO2/ZrO2, Ag/CeO2/ZrO2, AND MnO2/CeO2/ZrO2 CATALYSTS

Activity and selectivity of selective CO oxidation in an H₂-rich gas stream over Co₃O₄/CeO₂/ZrO₂, Ag/CeO₂/ZrO₂, and MnO₂/CeO₂/ZrO₂ catalysts were studied. Effects of the metaloxide types and metaloxide molar ratios were investigated. XRD, SEM, and N₂ physisorption techniques were used to characterize the catalysts. All catalysts showed mesoporous structure. The best activity was obtained from 80/10/10 Co₃O₄/CeO₂/ZrO₂ catalyst, which resulted in 90% CO conversion at 200°C and selectivity greater than 80% at 125°C. Activity of the Co₃O₄/CeO₂/ZrO₂ catalyst increased with increase in Co₃O₄ molar ratio.     

Circular dichroism study of poly(l-tyrosine), poly(l-glutamic acid) and of random and sequential copolymers of l-glutamic acid and l-tyrosine in trimethylphosphate

Random and sequential copolypeptides containing l-glutamic acid and l-tyrosine, as well as poly(l-tyrosine) and poly(l-glutamic acid) were investigated by means of c.d. spectroscopy in trimethylphosphate as solvent. In random copolymers, variation of ellipticities at 202.5 and 230 nm versus tyrosyl content follows a smooth curve, without any sharp change. This led to the conclusion that poly(l-tyrosine) α-helix is right-handed. From c.d. studies on sequential copolymers we were able to recognize that the 230 nm contribution of tyrosyl side chains is closely related to the array in which tyrosyl residues are arranged in the chain. For instance, it was found that (n, n + 2) and (n, n + 3) pairings of tyrosyl side-chains in (Tyr-Glu)_n and (Glu-Tyr-Glu)_n respectively, were poorly effective, while the (n, n + 4) pairing in (Glu-Glu-Tyr-Glu)_n is more. However, the strongest contribution at 230 nm was observed on the alternating-páirs copolymer (Glu-Tyr-Tyr-Glu)_n. This result suggests a new conformational arrangement of tyrosyl side chains in sequential copolymers, as well as in poly(l-tyrosine) and other aromatic polypeptides, based on a regular pairing of the aromatic groups, arranged in two contiguous superhelices.     

Structural-chemical mechanism of formation of solid solutions in the La2SrAl2O2-Ho2SrAl2O7 system

The processes of phase formation in the La₂O₃-Ho₂O₃-SrO-Al₂O₃ system are investigated in the temperature range 1200–1500°C. The structural characteristics of the compounds described in the studied system are presented. It is established that the formation of (La_1?x Ho_x)₂SrAl₂O₇ solid solutions proceeds through the formation of LaAlO₃, LaSrAlO₄, SrAl₂O₄, and SrHo₂O₄ compounds. An increase in the holmium content and the temperature leads to a crossover from the mechanism in which the interaction of LaAlO₃ and LaSrAlO₄ is a limiting stage to the mechanism in which the decisive role is played by the interactions of SrAl₂O₄ with Ho₂O₃ and SrHo₂O₄ with Al₂O₃.     

Thermal routes to metal complexed polyimines; facile conversion of CoX2(NH2CH2CH{OEt}2)2 to CoX2{=NCH2CH=}2

Cobalt(II) complexes of the form CoX₂(NH₂CH₂CH{OEt}₂)₂ [X=Cl, Br, I] react hydrolytically in solution to convert hemiacetal moieties to aldehydes, the latter undergoing Schiff base condensation. Complex decomposition and the separation of metal salt and organic material occur concomitantly. In contrast, thermal reactions afford metal complexed polyimines of the form CoX₂{=NCH₂CH=}₂. Analyses are consistent with the liberation of four equivalents of ethanol per mole of CoX₂(NH₂CH₂CH{OEt}₂)₂ via an autocatalytic cycle of hemiacetal hydrolysis and Schiff base condensation. Such thermal routes offer facile access to metal complexed polyimines.     

The promotion of Argon and water molecule on direct synthesis of H2O2 from H2 and O2

Direct synthesis of hydrogen peroxide (H₂O₂) from H₂ and O₂ is an ideal route. H₂/O₂ plasma has a great potential for direct synthesis of high purity H₂O₂ without purification operations. However, low yield and high energy consumption limits the application of H₂/O₂ plasma in industry. This article reports that gas state Ar and H₂O molecule serving as molecular catalysts promoted the synthesis of H₂O₂ from H₂/O₂/Ar/H₂O plasma dramatically: the H₂O₂ yield was enhanced by 244% and the energy consumption was reduced by 70.9%. Ar not only increased the electron density, but also selectively accelerated the dissociation of H₂ toward the formation of ?HO₂, a key intermediate species in H₂O₂ synthesis. While H₂O facilitated the formation of ?HO₂ radical and stabilized it by forming a HO₂?H₂O complex, resulting in enhancing the H₂O₂ production. This single molecular catalysis reduced the cost of H₂O₂ synthesis more than 50%. © 2017 American Institute of Chemical Engineers AIChE J, 64: 981–992, 2018     

Enhanced one-step purification of C2H4 from C2H2/C2H4/C2H6 mixtures by fluorinated Zr-MOF

The extraction of C₂H₄ from C₂H₆/C₂H₄/C₂H₂ mixtures is of great significance in the chemical industry for C₂H₄ production but the process remains challenging due to the similarity of these C₂ hydrocarbon species in their molecular size and physical properties. Here, we report the fluorination of a stable Zr-MOF, UiO-66, to fine-tune the pore dimensions and pore functionality. In particular, UiO-66-CF₃ shows notably preferential adsorption of C₂H₆ and C₂H₂ over C₂H₄, with C₂H₂/C₂H₄ and C₂H₆/C₂H₄ selectivities of 1.4 and 1.9, respectively. Theoretical calculations provide insight into the binding sites of UiO-66-CF₃ for C₂ hydrocarbon adsorption. Breakthrough experiments further confirmed the capability of the material for purification of C₂H₄ from C₂H₂/C₂H₄/C₂H₆ ternary mixtures, evidenced by the high purity C₂H₄ (99.9%+) obtained directly from outlet gas.     

Avoiding the intermediate phase Zr2WP2O12 to develop a larger-negative-thermal-expansion-coefficient material Zr2W2P2O15

Zr₂W₂P₂O₁₅ with larger-negative-thermal-expansion-coefficient (NTEC, −4.01×10⁻⁶ K⁻¹, 143–673 K) is developed by controlling reaction process to avoid the intermediate phase of Zr₂WP₂O₁₂, whose smaller NTEC limits its application. From 1473 K to1573 K, Zr₂WP₂O₁₂ forms easily but the reaction between Zr₂WP₂O₁₂ and WO₃ to generate Zr₂W₂P₂O₁₅ is difficult even followed by heating up to 1673 K. However, putting raw materials of ZrO₂, WO₃ and NH₄H₂PO₄ into a pipe furnace at sintering temperature 1673 K directly, the Zr₂W₂P₂O₁₅ is formed avoiding the intermediate phase of Zr₂WP₂O₁₂.     

Dehydrogenation of ethylbenzene over TiO2-Fe2O3 and ZrO2-Fe2O3 mixed oxide catalysts

The mixed metal oxides TiO₂-Fe₂O₃ and ZrO₂-Fe₂O₃ were examined as potential catalysts for the dehydrogenation reaction of ethylbenzene. The acidic and basic properties and surface area, pore volume and pore size distribution of these catalysts were measured. The catalytic activities can be correlated very well with the surface area and the acidity and basicity of ZrO₂-Fe₂O₃ catalysts. However, for TiO₂-Fe₂O₃ catalysts, the surface area, the amount of acidic and basic sites and TiFe₂O₅ crystallinity are all important factors affecting the catalytic activities for ethylbenzene dehydrogenation. A synergistic effect was found for the TiO₂-Fe₂O₃ and ZrO₂-Fe₂O₃ catalyst system and also for the TiO₂-Fe₂O₃-ZrO₂ system, i.e. the activities of these catalysts can be ranked in the following order: TiO₂-Fe₂O₃-ZrO₂>TiO₂-Fe₂O₃ >ZrO₂>Fe₂O₃>TiO₂. Meanwhile, all of these catalysts showed higher activities than the conventional potassium-promoted iron catalysts.     

An update on the mechanism of the graphene–NO reaction

Cognizant of the key experimental facts from studies of carbonaceous solids ranging from soot to graphite, we performed a quantum chemistry study of the interaction of NO monomer or dimer with one or more zigzag sites. Thermodynamic and kinetic results were used to examine two alternative mechanisms proposed in the literature, and to compare them with the graphene–O₂ reaction mechanism. The chemisorption stoichiometry similarities are striking; but the differences, especially regarding the intermediate role of N₂O, have important practical implications. Monomer chemisorption on an isolated site is a dead-end and temporarily inhibiting process, similar to that of formation of a stable C–O surface complex in the graphene–O₂ reaction. When two sites are available, successive monomer adsorption eventually leads to N₂O formation subsequent to parallel reorientation of the first NO molecule. If three contiguous sites are available, N₂ and CO are the principal products. Chemisorption of the dimer provides a straightforward path to N₂ and CO₂ when one site is available and to N₂ and CO when two sites are available. The formation of N₂O is also feasible in this case, both during adsorption and desorption; in the adsorption phase it is very sensitive to the details of the electron pairing processes.     

A coupled phase diagram experimental study and thermodynamic optimization of the Li2O-CaO-Al2O3 and Li2O-CaO-SiO2 systems,and prediction of the phase diagrams of the Li2O-CaO-Al2O3-SiO2 system

A coupled experimental phase diagram study and thermodynamic modeling of the Li₂O-CaO-Al₂O₃ and Li₂O-CaO-SiO₂ systems was conducted at 1 atm total pressure. Differential scanning calorimetry (DSC) measurements were performed in the Li₂O-CaO-Al₂O₃ and Li₂O-CaO-SiO₂ systems. In addition, the phase relations in the Li₂O-CaO-Al₂O₃ system were determined by equilibration/quenching experiments at 1643 and 1743 K, and the phases were characterized with X-ray diffraction (XRD) and Electron-probe micro analysis-wavelength dispersive spectroscopy (EPMA-WDS). The absence of ternary compounds or solid solutions was confirmed. Congruent melting of Li₂CaSiO₄ compound in the Li₂O-CaO-SiO₂ system was determined at 1350 ± 5 K. Thermodynamic optimization of the Li₂O-CaO-Al₂O₃ and Li₂O-CaO-SiO₂ systems was carried out based on new phase diagram experiments and critically evaluated literature data. The phase diagrams of the quaternary Li₂O-CaO-Al₂O₃-SiO₂ system were predicted using the thermodynamic models with optimized model parameters.     

Coating Titania Aerosol Particles with ZrO2, Al2O3/ZrO2 and SiO2/ZrO2 in a Gas-Phase Process

The formation of ZrO₂, Al₂O₃/ZrO₂, and SiO₂/ZrO₂ coatings on TiO₂ particles by a continuous gas-phase process was studied. Titania particles were formed by the reaction of TiCl₄ vapor with O₂ in a hot-wall tubular reactor at 1300°C and were mixed with ZrCl₄ and AlCl₃ or SiCl₄ vapors near the end of the reactor. The ZrCl₄/TiCl₄ molar ratio was varied from 6.7 x 10^-4 to 5 x 10^-3 while the AlCl₃/TiCl₄and SiCl₄/TiCl₄ molar ratios varied in the ranges 8 x 10^-3-8 x 10^-2 and 2 x 10^-2-8 x 10^-2, respectively. Discrete tetragonal ZrO₂ nanoparticles of average diameter 20 nm were formed on the surfaces of the titania particles at a surface concentration that increased with the ZrCl₄ gas-phase concentration. The sequential introduction of AlCl₃ and ZrCl₄ vapors resulted in composite coatings. These consisted of dense, coherent, amorphous, and smooth Al₂O₃ layers approximately 10 nm thick, on top of which ZrO₂ nanocrystalline particles were dispersed in a similar pattern as in the absence of Al₂O₃. Concentration depth profiles of these powders were obtained by Auger Electron Spectroscopy and supported the TEM observations. Particles coated by sequentially introducing SiCl₄ and ZrCl₄ vapors had amorphous rough SiO₂ coatings, 5-10 nm thick, and ZrO₂ particles sporadically dispersed on their surfaces. Increasing the SiCl₄/ZrCl₄ molar ratio from 5 to 19 increased the thickness and roughness of the silica layers and resulted in encapsulation of the ZrO₂particles inside the silica coatings. The different coating morphologies obtained were attributed to different coating formation mechanisms for the metal oxides used in this study.     

The phase system CaO-CO(NH2)2-N2O5-H2O at 25°C

Isotherms in the acidic region of the phase system CaO-CO(NH)₂-N₂O₅-H₂O at 25°C were determined. In this region, CO(NH₂) · HNO₃ occupies the largest field of the diagram with small encompassing fields for CO(NH₂)₂, Ca(NO₃)₂ · 4CO(NH₂)₂, Ca(NO₃)₂ · 4H₂O, Ca(NO₃)₂ · 2H₂O, and Ca(NO₃)₂.     

Direct Oxidation of H2 to H2O2 and Decomposition of H2O2 Over Oxidized and Reduced Pd-Containing Zeolite Catalysts in Acidic Medium

Both the conversion and H₂O₂ selectivity (or yield) in direct oxidation of H₂-to-H₂O₂ (using 1.7 mol% H₂ in O₂ as a feed) and also the H₂O₂ decomposition over zeolite (viz. H-ZSM-5, H-GaAlMFI and H- ) supported palladium catalysts (at 22 °C and atmospheric pressure) are strongly influenced by the zeolite support and its fluorination, the reaction medium (viz. pure water, 0.016 M or 1.0 M NaCl solution or 0.016 M H₂SO₄, HCl, HNO₃, H₃PO₄ and HClO₄), and also by the form of palladium (Pd⁰ or PdO). The oxidized (PdO-containing) catalysts are active for the H₂-to-H₂O₂ conversion and show very poor activity for the H₂O₂ decomposition. However, the reduced (Pd⁰-containing) catalysts show higher H₂ conversion activity but with no selectivity for H₂O₂, and also show much higher H₂O₂ decomposition activity. No direct correlation is observed between the H₂-to-H₂O₂ conversion activity (or H₂O₂ selectivity) and the Pd dispersion or surface acidity of the catalysts. Higher H₂O₂ yield and lower H₂O₂ decomposition activity are, however, obtained when the non-acidic reaction medium (water with or without NaCl) is replaced by the acidic one.     

SO2-Assisted Simultaneous Reduction of SO2 and NO by CO on SnO2-TiO2 Solid Solution

Sn_0.5Ti_0.5O₂ shows excellent catalytic performance both for the CO-SO₂ reaction and the CO-SO₂-NO reaction. At 350 ° C, 525 ppm SO₂/520 ppm NO/2085 ppm CO, SV = 3000 h^-1, the conversion of SO₂ is nearly complete in the CO-SO₂ reaction and above 89% in the CO-SO₂-NO reaction; NO conversion is above 98% in the latter reaction. The selectivities of S and N₂ are both close to 100%. SO₂ shows a significant promoting effect on the activity of the Sn_0.5Ti_0.5O₂ catalyst for NO reduction by CO. Combining transient response experiments, catalytic tests and TPD results, we propose a SO₂-assisted NO-CO reaction concept. The existence of a surface sulfur species, which was formed during the CO-SO₂ or CO-SO₂-NO reaction, is proved by XPS analysis. It is the active site for NO reduction in the CO-SO₂-NO reaction, and through which SO₂ accomplishes its promoter role. On the basis of the results obtained, the SO₂-assisted redox mechanism of simultaneous reduction of SO₂ and NO by CO is proposed.     

Dual effect of ZrO2 on phase separation and crystallization in Li2O–Al2O3–SiO2–P2O5 glasses

ZrO₂ is an effective nucleation agent for low-expansion lithium–aluminum silicate (LAS) glass–ceramic (GC) with high Al₂O₃ content. However, the effect of ZrO₂ is still not fully understood in LAS glasses with low contents of Al₂O₃ and P₂O₅. In this work, the effect of ZrO₂ on the phase separation and crystallization of Li₂O–Al₂O₃–SiO₂–P₂O₅ glasses were investigated. The results revealed that ZrO₂ significantly increased T_g and the crystallization temperature of Li₂SiO₃ and Li₂Si₂O₅ crystals. Li₃PO₄ crystals precipitated preferentially in the glass containing 3.6-mol% ZrO₂, wherein Zr was stable in the network and no precipitation of ZrO₂ nanocrystals was observed. Moreover, the separation of phosphate-rich phases in the as-quenched glasses increased with the addition of ZrO₂. The findings of the study revealed a dual role of ZrO₂. First, ZrO₂ acted as a glass network former rather than a nucleation agent, increasing glass viscosity and the nucleation barrier of Li₂SiO₃ through its strong network connectivity. Second, as Zr preferentially combined with non-bridging oxygen to form Si–O–Zr linkages, a sufficient amount of charge-balancing Li⁺ ions existed in the network, which promoted the separation of phosphate-rich phases. It indicated that the incorporation of ZrO₂ contributes to the activation of the nucleation role of P₂O₅, thus contributing to the formation of nanocrystals and fine microstructure of GCs.     

Study of CO2 permeation in Zn2+-modified Al2O3-carbonate membrane

Molten carbonate-based membranes for CO₂ capture have received attentions because of their high CO₂ selectivity, potential energy-saving capability and environmental friendliness. Zn²⁺-modified Al₂O₃/carbonates membranes with the enhanced CO₂ permeability have been developed in this work. Interfaces of LiAlO₂ were formed on the surface of Al₂O₃ due to the carbonates incorporation. Microstructural and interfacial characterisation of the membrane revealed that the outermost LiAlO₂ layer was due to the reactions between Li₂CO₃ and ZnAl₂O₄, resulting in the dissolution of ZnO in the molten carbonate. CO₂ permeability of 0.5% ZnAl₂O₄/Al₂O₃/carbonates reached 9.12 × 10⁻¹² mol.m⁻¹s⁻¹ Pa⁻¹ at 700°C, higher than that of Al₂O₃/carbonates, because of the dissolved ZnO. With the increase of ZnAl₂O₄, CO₂ permeability was decreased. The dissolved ZnO in the molten carbonates could enhance the ionic conductivity, whereas a higher amount of ZnO than its solubility will attenuate its effects on CO₂ permeation.