The nature of active sites in Pt–ReO_X/TiO_2 catalysts for selective hydrogenation of carboxylic acids to alcohols

The highly dispersed Pt–Re OX(x ≤ 1) sites ca. 0.5 nm in size were formed via a successive and strong interaction of the Re precursor with titania and then of the Pt complex with deposited low-valent rhenium oxide clusters. The size, charge and chemical composition were characterized by means of HRTEM/STEM with EDX mapping, XPS, and FTIRS. These sites with Re/Pt = 2 were shown to be highly active and selective in the hydrogenation of carboxylic acid to alcohol under very mild conditions(T = 130 °C, P = 50 bar). The reaction rate constant for the hydrogenation of hexanoic acid increased linearly with the Pt content. As for the homogeneous pincer-type Ru-organic complexes, the active Pt–Re OXsites can dissociate heterolytically the molecular hydrogen with the formation of hydroxyl groups and Pt hydride for hydrogenation of the carboxylic group. Indeed, TOF of 20 h-1 and selectivity of 98%–99% are approaching the values typical of homogeneous catalysts. The first order kinetics described well the experimental data obtained in a wide range of reaction conditions.     

A novel hybrid electrode of zeolitic imidazolate framework–derived carbon encapsulated in reduced-TiO2 nanotube arrays: Fabrication and photoelectrocatalytic activity

Constructing high-efficient photoelectrodes is one of the promising tasks in photoelectrocatalytic (PEC) technology. Al-reduced TiO₂ nanotube arrays (R-TNTAs) exhibit distinct improved visible-light response ability in comparison with traditional TiO₂ nanomaterials. In addition, metal–organic framework (MOF)-derived porous carbon materials possess versatile advantages partly due to preserved geometry configuration of MOF. Inspired by these characteristics, in this work, we synthesized the novel hybrid electrodes of C–N (Zn)@R-TNTAs through the pyrolysis of ZIF-8@R-TNTAs at controlled temperatures, which were pre-synthesized by coating zeolitic imidazolate frameworks (ZIF-8) onto R-TNTAs. The resulting hybrid electrodes were characterized using field-emission scanning electron microscopy, powder X-ray diffraction, X-ray photoelectron spectra, and Fourier-transform infrared techniques. The EC property and PEC activity of the composite electrodes were also analyzed, and the dependence of these on the pyrolysis temperature was also explored. The results showed that the pyrolyzed carbon materials were uniformly deposited in the inner TiO₂ nanotubes and thus effectively enhanced their EC and PEC activities. The best EC and PEC capacities were obtained by C–N (Zn)@R-TNTAs (600); the maximum photocurrent density was 0.85 mA cm⁻², which is ~1.5 times that of single R-TNTAs; and the maximum H₂ evolution rate was 58.83 μmol h⁻¹ cm⁻², being ~2.3 times that of R-TNTAs. In addition, C–N (Zn)@R-TNTAs (600) exhibited the best PEC activity in the degradation of rhodamine B with excellent catalytic stability. Based on EC analyses, a possible band structure and enhanced PEC mechanism for C–N (Zn)@R-TNTAs were proposed. There are only a few reports related to reduced TiO₂ nanotubes, and this work highlights the ideas of designing the hybrid electrodes based on reduced TNTAs and MOF-derived carbon materials, which may find broad applications in PC and PEC processes.     

Heat-treated Fe/N/C catalysts for O2 electroreduction: are active sites hosted in micropores?

Limited availability of platinum is a potential threat to fuel cell commercialization. Since the 1970s, alternative catalysts to the electrochemical reduction of oxygen have been obtained from heat treatment at T > 600 degrees C of carbon with a non-noble metal and a source of nitrogen atoms. However, the process by which the heat treatment activates these materials remains an open question. Here, we report that the activation process of carbon black and iron acetate heat-treated in NH(3) comprises three consecutive steps: (i) incorporation of nitrogen atoms in the carbon, (ii) micropore formation through reaction between carbon and ammonia, and (iii) completion of active sites in the micropores by reaction of iron with ammonia. Step (ii) is the slowest. Moreover, the microporous surface per mass of catalyst controls the macroscopic activity when enough nitrogen atoms are incorporated in the structure of the carbon support. These facts should help in determining the structure of the active sites and in identifying methods to increase the site density of such catalysts.     

2-methylterrylene in hexadecane: do we see single rotational quantum jumps of methyl groups?

We performed comparative low temperature (2-30 K) hole-burning and single molecule experiments with 2-methylterrylene with the goal to detect single rotational tunneling jumps of methyl groups. The hole-burned spectrum with its sharply structured side features which are perfectly symmetrically arranged with respect to the central hole supports the assignment to rotational tunneling transitions. However, instead of one, three clearly distinguishable methyl groups show up in the spectrum. Based on molecular mechanics simulations we attribute them to different, nearly degenerate orientations of guest molecules in one specific site of the hexadecane lattice. The frequency distribution of spontaneous jumps of single molecules reflects the features of the hole-burned spectra, although the distribution in the single molecule experiments is significantly broader. The photoinduced frequency transformation of single molecules ("single molecule photobleaching experiments") fits to the features of the hole-burned spectra, except that, surprisingly, no significant number of spectral jumps could be generated in the frequency range where the prominent narrow antiholes are observed in the hole-burned spectra.     

Brønsted acid sites in metal-containing solid acids: from quantification to molecular design of new catalysts/silver(I)-polyoxometalates

Based on H/D isotope exchange studies devoted to the quantification of the number of Br?nsted acid sites in solid acids, we report herein an innovative approach to determine the amount of silver cations present in Keggin-type polyoxometalates (POM). The molecular design of these bifunctional heteropolyacids can therefore be achieved by varying the Ag(+)versus H(+) exchange ratio in the starting mixture. Consequently, the stoichiometries of Ag(x)H(4-x)SiW??O?? POM were ascertained for 0 < x < 4 by the H/D exchange technique.     

Orientational effect of aryl groups in aryl selenides: how can 1h and 13c NMR chemical shifts clarify the effect?

Two sets of delta(H) and delta(C) are proposed by employing 9-(arylselanyl)anthracenes [9-(p-YC6H4Se)Atc: 1] and 1-(arylselanyl)anthraquinones [1-(p-YC6H4Se)Atq: 2] with various Y's. Structures of 1 and 2 are (A: pl) and (B: pd), respectively, for all Y examined in chloroform-d. After elucidation of the behavior of delta(H, C: 1) and delta(H, C: 2), they are applied to determine the structures in chloroform-d solutions for 1-(arylselanyl)naphthalenes (3), 1-(arylselanyl)-2-methylnaphthalenes (4), and 1-(arylselanyl)-8-bromonaphthalenes (5). Although the structure of 4 remains in (A: pl) in the solutions for all Y examined, that of 5 is (B: pd), except for Y = CN and NO2. On the other hand, 3 is shown to equilibrate between (A: pl) and (B: pd). Although the contributions of (B: pd) and (A: pl) are predominant for Y = NMe2 and NO2, respectively, the equilibrium constants change from Y to Y in the solutions. The results are supported by the quantum chemical calculations, containing the solvent effect of chloroform. These results demonstrate that delta(H, C: 1) and delta(H, C: 2), as well as delta(Se), serve as the practical standards for pl and pd, respectively, to analyze the structures of p-YC6H4ZR (Z = Se) in solutions.     

An updated review of metal–organic framework materials in photo(electro)catalytic applications: From CO2 reduction to wastewater treatments

This review summarizes recent advances in the development of metal–organic framework (MOF) materials, focusing on their photocatalytic and photoelectrocatalytic activities for different applications, such as CO₂ reduction, water splitting, elimination of inorganic contaminants, and degradation of organic pollutants. In each section, the first applications described focus on the photocatalysts developed using MOF materials. Meanwhile, the latest are centered on photoelectrode applications using these materials. The last advances in the synthesis process are discussed in terms of improvement in electron transfer and charge separation, which enhance the activity of the photo (electro)catalysts. Finally, some insights about the upcoming applications of MOF materials are provided.     

Identification and Characterization of Monomeric,Volatile SiCl3NH2 as Product of the Reaction between SiCl4 and NH3: An Important Intermediate on the Way to Silicon Nitride?

We studied the reaction of SiCl(4) with NH(3) by mass spectrometry and IR spectroscopy. By means of mass spectrometry, SiCl(3)NH(2) was for the first time identified as an intermediate generated in significant amounts in the course of the reaction. In additional experiments, SiCl(3)NH(2) was formed as a stable gaseous product of the ammonolysis of SiCl(4), and the product was identified and characterized in detail by IR spectroscopic methods (gas phase and matrix isolation) in combination with quantum-chemical calculations. The calculations also gave access to important thermodynamical data.     

Zn2+'s ability to alter the distribution of Cu2+ among the available binding sites of Aβ(1-16)-polyethylenglycol-ylated peptide: implications in Alzheimer's disease

The formation of mixed copper(II) and zinc(II) complexes with Aβ(1-16)-PEG has been investigated. The peptide fragment forms stable mixed metal complexes at physiological pH in which the His13/His14 dyad is the zinc(II)'s preferred binding site, while copper(II) coordination occurs at the N-terminus also involving the His6 imidazole. Copper(II) is prevented by zinc(II) excess from the binding to the two His residues, His13 and His14. As the latter binding mode has been recently invoked to explain the redox activity of the copper-Aβ complex, the formation of ternary metal complexes may justify the recently proposed protective role of zinc(II) in Alzheimer's disease. Therefore, the reported results suggest that zinc(II) competes with copper for Aβ binding and inhibits copper-mediated Aβ redox chemistry.     

Three structural modifications in the series of layered solids T(H2O)2[Ni(CN)4]·xH2O with T = Mn,Co, Ni: Their nature and crystal structures

In the studied series of layered solids, the available coordination sites at T metal centers are occupied by water molecules which serve to stabilize additional water molecules in the interlayer region through hydrogen bonding interactions. The stability of these 2D solids results from these interactions between coordinated and weakly bonded water molecules. In this contribution, the crystal structures and related properties of the titled compounds are reported. Three different structural modifications for a given T metal were found. The refined crystal structures were supported by the recorded infrared, Raman, and UV–vis spectra and thermogravimetric data. Two of these modifications were found to be room and high temperature thermodynamic products and the remaining one a room temperature kinetic product.     

The internal link of serum steroid hormones levels in insomnia,depression, and Alzheimer's disease rats: Is there an effective way to distinguish among these three diseases based on potential biomarkers?

Insomnia, depression, and Alzheimer's disease are all neurodegenerative diseases and are associated with the levels of steroid hormones. To investigate the internal connection and difference of steroid hormones among these three diseases and distinguish them from the perspective of biomarkers, an easy, quick, and efficient high‐performance liquid chromatography with tandem mass spectrometry method was established and validated to determine six steroid hormones simultaneously in rat serum. The separation was accomplished on a SHIM‐PACK XR‐ODS chromatographic column with 0.1% v/v formic acid and methanol as the mobile phase and the detection was performed with electrospray ionization source in the positive ion mode. Based on the concentrations of steroid hormones, all the groups could be distinguished obviously from each other by using partial least square discriminant analysis. Meanwhile, 11‐deoxycortisol, corticosterone, and cortisol were identified as potential biomarkers and 100% of samples were classified correctly by Bayes’ discriminant function. These biomarkers were further screened by one‐way analysis of variance and cortisol was significantly different among all these groups. Bayes’ discriminant function was also built by cortisol and the classification accuracy was 87.2%. This workflow including determination of steroid hormones and discrimination among three neurological diseases would provide a basis for further clinical studies.     

Rücktitelbild: Phosphine‐Catalyzed Remote β‐C?H Functionalization of Amines Triggered by Trifluoromethylation of Alkenes: One‐Pot Synthesis of Bistrifluoromethylated Enamides and Oxazoles (Angew. Chem. 13/2015)

An unprecedented phosphine‐catalyzed remote β‐C H functionalization of amine derivatives triggered by trifluoromethylation of an alkene with Togni’s reagent was disclosed. This reaction proceeded through the highly selective and concomitant activation of an unactivated alkene and the β‐C H bond of an amine derivative, providing bistrifluoromethylated enamides in excellent yields with good regio‐, chemo‐, and stereoselectivity. Furthermore, the newly developed one‐pot protocol provides a facile and step‐economical access to valuable trisubstituted 5‐(trifluoromethyl)oxazoles. Mechanistic studies showed that this reaction may initiate with a novel phosphine‐catalyzed radical trifluoromethylation of unactivated alkene via a phosphorus radical cation.     

Metal‐Free Radical [2+2+1] Carbocyclization of Benzene‐Linked 1,n‐Enynes: Dual C(sp3)?H Functionalization Adjacent to a Heteroatom

A new metal‐free oxidative radical [2+2+1] carbocyclization of benzene‐linked 1,n‐enynes with two C(sp³) H bonds adjacent to the same heteroatom is described. This method achieves two C(sp³) H oxidative functionalizations and an annulation, thus providing efficient and general access to a variety of fused five‐membered carbocyclic hydrocarbons.     

{Bis[N,N′-(2-alkyl-6-para-methylphenyl)phenyl)imino]acenaphthene}dibromonickel catalysts bearing bulky methylphenyl groups: synthesis,characterization, crystal structures and application in catalytic polymerization of ethylene and styrene

Two new Ni(II) complexes containing methylphenyl groups, {bis[N,N′-(2,6-dimethyl-4-p-methylphenylphenyl)imino]acenaphthene}dibromonickel 4a and {bis[N,N′-(2-ethyl-4,6-di(p-methylphenyl)phenyl)imino]acenaphthene}dibromonickel 4b, were synthesized and characterized. The molecular structures of both complexes were determined by single-crystal X-ray diffraction. Both complexes have pseudo-tetrahedral geometry about the nickel center, showing pseudo C _2v and C ₂ molecular symmetry, respectively. Complex 4c, {bis[N,N′-(2,4,6-trimethylphenyl)imino]acenaphthene}dibromonickel, was also synthesized for comparison. These complexes were tested as catalysts for the polymerization of ethylene and styrene under mild conditions using diethylaluminum chloride. The precatalyst 4b bearing one ortho-ethyl group and two bulky p-methylphenyl groups in the ortho- and para-aryl position of the ligand, displayed highly catalytic activity for the polymerization of ethylene [4.70 × 10⁶ g PE/(mol Ni h bar)], and produced branched polyethylene (76 methyl, 8 ethyl, 5 propyl and 22 butyl or longer branches/1,000 C at 60 °C). Interestingly, complex 4b also displays high catalytic activity [5.46 × 10⁵ g polystyrene/(mol Ni·h)] for styrene polymerization and produces nearly atactic polystyrene at 70 °C (stereo-triad distributions: rr, 39.9 %; mr, 30.4 %; mm, 29.8 %; stereo-diad distributions: r, 55.1 %; m, 44.9 %).     

New Insights into Factors Influencing B?N Bonding in X:BH3−nFn and X:BH3−nCln for X=N2, HCN,LiCN, H2CNH,NF3, NH3 and n=0–3: The Importance of Deformation

Understanding the bonding in complexes X:BH_3?nF_n and X:BH_3?nCl_n, for X=N₂, HCN, LiCN, H₂CNH, NF₃, NH₃ with n=0–3, is a challenging task. The trends in calculated binding energies cannot be explained in terms of any of the usual indexes, including π donation from the halogen lone pairs to the p(π) empty orbital on B, deformation energies, charge capacities, or LUMO energies, which are normally invoked to explain the higher Lewis acidity of BCl₃ relative to BF₃. The results of the high‐level G3B3 ab initio calculations reported in this study suggest that the interaction energies of these complexes are determined by a combination of at least three factors. These include the decrease in the electron‐accepting ability of B as a result of π donation by the halogen atom, the increase in the electron‐acceptor capacity of B due to deformation of the acid, and the large increase in the deformation energy of the acid with increasing halogen substitution. The dominant effects are those derived from the electronic effects of acid deformation. Deformation not only has direct energetic consequences, which are reflected in the large differences between dissociation (D₀) and interaction (E_int) energies, but also leads to an enhancement of the intrinsic acidities of BH_3?nF_n and BH_3?nCl_n moieties by lowering the LUMO energies to very different extents, consistent with the frontier orbital model of chemical reactivity. Although this lowering depends on both the number and the nature of the halogen substituents, binding energies do not systematically increase or decrease as the number of halogen atoms increases.     

Neurotoxin (N-Oxalyl-L-α,β-Diamino Propionic Acid) Content in Different Plant Parts of Grass Pea (Lathyrus sativus L.) Spanning Seedling to Maturity Stage: Does It Increase over Time?

ODAP (N-oxalyl-L-2,3-diaminopropionic acid) is present in the seeds of grass pea. In this study, variation of total ODAP accumulation in leaves throughout the crop growth starting from 40 days after sowing to maturity, and the distribution pattern of ODAP in different plant parts including the seeds at the mature stage was analyzed. Five grass pea accessions were evaluated for two subsequent growing seasons in one location of ICARDA, Aleppo (Syria). The results found that the rate of accumulation of total ODAP varied during plant development. Increased rates of synthesis were noticed in young leaves of grass pea. The highest total ODAP content in leaves was noted in the early growth stage (40–50 days after sowing). Mean total ODAP content in leaves ranged from 0.17 to 0.96 percent during 2010–2011 and from 0.19 to 1.28 percent during 2011–2012. During maturity, the total ODAP content was lowest in the seeds than in leaves, stems, pod cover, seed coat, and cotyledons. The ranges of total ODAP content were 0.13 (seed)–0.34 (stem), 0.20 (seed)–1.01 (leaf), 0.22 (seed)–0.62 (leaf), 0.21 (seed)–0.66 (leaf), and 0.21 (seed)–0.78 (leaf) percent in B387, B222, B390, Bio-520, and B587 accessions, respectively, during maturity. The results indicated that the rate of accumulation and synthesis of total ODAP varied during the plant lifespan. The lowest total ODAP content of leaves was observed after 130 days of sowing. The lower total ODAP content after the early vegetative stage of grass pea plants makes them suitable as a feed.     

Simultaneous LC?CMS?CMS Determination of HM30181A, [2-(2-{4-[2-(6,7-Dimethoxy-3,4-dihydro-1H-isoquinolin-2-yl)-ethyl]-phenyl}-2H-tetrazol-5-yl)-4,5-dimethoxyphenyl]amide, as a new P-Glycoprotein Inhibitor and Its Two Metabolites, M1 and M2, in Human Plasma: Application to a Pharmacokinetic Study

A simultaneous simple, rapid, and sensitive LC?CMS?CMS method was developed and validated for the determination of HM30181A, [2-(2-{4-[2-(6,7-dimethoxy-3,4-dihydro-1H-isoquinolin-2-yl)-ethyl]-phenyl}-2H-tetrazol-5-yl]-4,5-dimethoxy-phenyl]amide, as a P-glycoprotein inhibitor and its two metabolites, M1 and M2, in human plasma using docetaxel as an internal standard (IS). The analytes were extracted from 200???L of biological sample by liquid?Cliquid extraction using 1?mL of methyl-t-butyl ether. Chromatographic separation was carried on a Luna C8 column at 30???C with mobile phase consisting of distilled water with 0.1% formic acid and acetonitrile (75:25, v/v) at a flow rate of 0.7?mL?min^?1 for human plasma samples. The method was linear over concentration ranges of 0.5?C50, 0.1?C10, and 0.1?C10?ng?mL^?1 for HM30181A, M1, and M2, respectively, in human plasma. The values of coefficient variation for the assay precision were <12.5, <9.10, and <9.96% for HM30181A, M1, and M2, respectively, in human plasma. The values of accuracy were 93.0?C108, 94.7?C104%, and 95.7?C105% for HM30181A, M1, and M2, respectively, in human plasma. This method is simple, sensitive, and applicable for the pharmacokinetic studies of HM30181A and its metabolites in humans.