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The present study investigating the experimental equilibrium solubility of 2-chloro-4-amino-6,7-dimethoxyquinazoline (CADQ) dissolved in 12 kinds of neat organic solvents, including methanol, ethan...

Zonisamide is moderately soluble in water with a reported solubility of 0.8 mg·mol–1 (6.78 × 10–5 in mole fraction). The objective is to study the solubility of zonisamide in methanol, ethanol, n-p...

Intermetallic compounds are atomically ordered inorganic materials containing two or more transition metals and main-group elements in unique crystal structures. Intermetallics based on group 10 an...

The solid–liquid solubility of indole-3-acetic acid in pure methanol, ethanol, n-propanol, isopropanol, acetone, n-butanol, acetonitrile, chloroform, ethyl acetate, 1,4-dioxane, N,N-dimethylformamide (DMF), and dimethyl sulfoxide (DMSO) was measured by using a isothermal saturation method. The determination temperature range is from 278.15 to 323.15 K. The order of solubility data from high to low was ethyl acetate > DMSO > DMF > n-butanol > acetone > isopropanol > 1,4-dioxane > n-propanol > ethanol > methanol > acetonitrile > chloroform. Two thermodynamic models (modified Apelblat equation and λh equation) were used to correlate the solubility values of indole-3-acetic acid in different monosolvents, and the two equations can correlate the experimental values very well. The values of root-mean-square deviations (RMSDs) and relative average deviations (RADs) between the experimental and calculated solubility values were not exceeding 0.27 × 10–6 and 0.75 × 10–2, respectively. In order to study the effect ...

Modified and stabilized palladium nanoparticles were prepared successfully by using an ionic liquid, 1-butyl-3-methylimidazolium trifluoroacetate. Activated carbon was used as a support for the palladium catalyst. Instead of using hydrogen gas, the Pd-catalyzed hydrodechlorination (HDC) reaction in this study used aqueous formic acid–formate buffer solutions as a hydrogen source due to its non-flammability. The results showed that both the ionic liquid and active carbon support facilitate the Pd active center to effectively carry out the catalytic HDC reaction of 4-chlorophenol (4-CP). The ionic liquid (IL) played a dual role as both a solvent and co-factor to facilitate the reaction. The IL would stabilize, better disperse, and prevent the congregation of palladium nanoparticles. On the other hand, active carbon provides a stronger binding site for stabilizing the active Pd centers. The catalytic HDC reaction indicated that the turn over frequency (TOF) of ionic liquid with a reduced catalyst was about 5–6 times higher than that of the non-ionic liquid mediated catalyst. This excellent catalytic activity suggested that the ionic liquid is dispersing nanoparticles effectively, preventing the creation of Pd nanoparticle clusters through the strong interaction of Pd species with the ionic liquid (IL). This IL-Pd interaction helped to form a protection layer to stabilize the Pd active centers. This study also confirmed that both the Pd0 and Pdn+ states were required for the catalytic HDC reaction. Furthermore, the Pd-catalyst was characterized by different techniques such as Brunauer–Emmett–Teller (BET) surface area analysis, X-ray photoelectron spectroscopy, transmission electron microscopy (TEM) and Fourier-transform infrared spectroscopy (FT-IR).

The global need for improved fuels has promoted the development of the renewable photovoltaic industry. However, a significant amount of diamond wire saw silicon powder (DWSSP, ∼300,000 t/a) is produced during the process of solar cell manufacturing. Thus, there is a significant need for strategies to recycle and utilize DWSSP for increased sustainability and protection of the environment. Here, nano-porous silicon composites materials derived from silicon cutting waste were used to fabricate lithium-ion anodes with high capacity and stable cycling performance. DWSSP was chemically crushed using nano-copper-assisted etching. Next, porous silicon/Ag composites (PSi/Ag) were prepared by nano-silver-assisted etching, using dopamine as a source of organic for surface coating. Carbon-coated porous silicon/Ag nanocomposites (PSi/Ag/C) exhibited excellent cycling performance with retained discharge capacity of 1092.9 mAh g-1 after 300 cycles at 1000 mA/g, with a capacity retention rate of 80%. These results indicate that PSi/Ag/C from DWSSP can be used to prepare functional lithium-ion battery anodes. This work describes the high-value utilization of an abundant waste material produced in the solar industry and provides an effective strategy to produce porous materials for energy storage.

A green and biodegradable carbohydrate-derived alkylamine was designed and employed as ligand for Ullmann type C–N coupling catalyzed by copper in water. The coupling of aryl iodide and N-nucleophiles were examined and moderate to excellent yields were obtained. In addition, the in-water coupling strategy was expanded successfully to the reaction of indoles with 4-iodoanisole. By measuring the solubility, it is speculated that carbohydrate-derived alkylamine plays the role of chelating copper and promoting the dissolution of 4-iodoanisole in water. Remarkably, this methodology was environmentally friendly and economical because of the use of aqueous media in place of organic solvents.

To improve the photocatalytic property and recovery rate of existing ZnO materials, a magnetically separable heterostructure photocatalytic composed of GO sheets and nanohybrid Fe 3 O 4 /ZnO material was synthesized by a simple low-temperature chemical synthesis process. This synthesis enables simultaneous decoration of Fe 3 O 4 /ZnO spheres on both sides of the GO sheets. As a result, the Tauc's plot revealed the band gap of Fe 3 O 4 /ZnO-GO sample decreases to 2.07 eV from 3.38 eV of ZnO. This smaller energy band gap and slower recombination rate of electron-hole pairs greatly improve the photocatalytic activity of the Fe 3 O 4 /ZnO-GO complex through the wider visible light absorption range. The photocatalytic reaction rate of the pure ZnO photocatalyst is 4.84 × 10 −3 min −1 , for Fe 3 O 4 /ZnO composite is 1.564 × 10 −2 min −1 and for Fe 3 O 4 /ZnO-GO composite is 5.558 × 10 −2 min −1 . The stability and recovery rate and photocatalytic property retention also greatly improved from ZnO-only photocatalyst. The photocatalytic reactivity of Fe 3 O 4 /ZnO-GO nanocomposite structure reaches 92.8% efficiency on the first run and was at 75% efficiency after the four cycling.

The growing photovoltaic industry produces a mass of silicon cutting waste each year. How to effectively manage the resulting silicon cutting waste is essential from an environmental and an economic perspective. In this study, a new strategy was developed to utilize silicon cutting waste and fabricate high-performance lithium-ion battery anode materials . This study combines nanocopper-assisted chemical etching technology with graphite and carbon nanotubes (CNTs) coating technology . The resulting Si/nano-Cu/CNTs/C composite show an excellent reversible capacity of 1750 mAh/g and 64% capacity retention rate after 100 cycles at 200 mA/g. Different current charging and discharging tests were applied, and good rate performance achieved. When the current was switched from 2000 mA/g to 100 mA/g, the discharge capacity returned to the original 1750 mAh/g, demonstrating excellent rate performance. Furthermore, the higher ion diffusion coefficient improved the conductivity of the electrode, and the combination of silicon and carbon is beneficial to the electrode stability, which was verified by simulation calculation. Our work indicates that the silicon waste can be a cost-effective silicon source in the preparation of high-performance Si/C anode material by the simple and economical manufacturing method.

Hollow microcapsules are of great interest to the biotechnology and pharmaceutical industries, especially in the field of drug delivery and personalized drug. However, the microcapsules made by polyelectrolytes are soft and unstable in the harsh environment. An improved layer-by-layer (LbL) method is reported here to fabricate hard-shell microcapsules cross-linked by Ca2+. The zeta potential measurement confirms the coverage and LbL intact structure. The additional antibacterial property is introduced via dispersed silver nanoparticles (Ag NPs). The SEM and TEM confirm the dispersion of the metal nanoparticles uniformly on the microcapsules. The antibacterial property is confirmed via the inhibition zone test on Escherichia coli and Staphylococcus aureus. The in vitro controlled-release of ibuprofen (IBU) embedded in the microcapsules exhibits a two-stage release behavior: a fast release at the initial bust phase within the first hour and a subsequent prolonged release of 10 h for 80 wt% and complete release needs ca. 20 h. The success synthesis of this bifunctional microcapsule opens a new channel’s applications of microcapsules in the food, agriculture, biotechnology, pharmaceutical industries, drug delivery and novel material design.

The two-dimensional thin film, as an effective interface modification layer to improve the power conversion efficiency (PCE) of graphene/silicon (Gr/Si) heterojunction solar cells has attracted extensive attention recently. However, the complicated manufacturing process and specialized equipment requirements impede its broad application. Herein, carbon quantum dots (CQDs) fabricated under the mild reaction condition was first time used to modify Gr/Si devices interface structure. The effects of CQDs size distributions and coating thickness on J-V characteristics and the energy band structure of Gr/CQDs/Si solar cells were systematically analyzed. The results indicate that the PCE of resulting Gr/CQDs/Si solar cells could reach 9.97% when the thickness and sizes of CQDs interlayer are ∼26 nm and 4–7 nm, without any chemical doping, which is 6.8-times PCE than that of virgin Gr/Si solar cells. The CQDs interlayer serves as both an electron blocking layer and hole transport layer to reduce the carrier recombination, leading to a lower reverse saturation current as well as a larger VOC then improved the device performance. The enhanced PCE shows that the CQDs species have the potential applications in a cost-effective photovoltaic device.

A better understanding of the chemistry of molecular precursors is useful in achieving more predictable and reproducible nanocrystal preparations. Recently, an efficient approach was introduced that consists of fine-tuning the chemical reactivity of the synthetic molecular precursors used, while keeping all other reaction conditions constant. Using nickel phosphides as a research platform, we have studied how the chemical structure and reactivity of a family of commercially available organophosphite precursors (P(OR)3, R = alkyl or aryl) alter the preparation of metallic and metal phosphide nanocrystals. Organophosphites are a versatile addition to the pnictide synthetic toolbox, nicely complementing other available precursors such as elemental phosphorus or trioctylphosphine (TOP). Experimental and computational data show that different organophosphite precursors selectively yield Ni, Ni12P5, and Ni2P and that these phases evolve over time through separate mechanistic pathways. Based on our observations,...

Phosphine chalcogenides are useful reagents in chalcogen atom transfer reactions and nanocrystal syntheses. Understanding the strength and electronic structure of these bonds is key to optimizing their use, but a limited number of experimental and computational studies probe these issues. Using density functional theory (DFT), we computationally screen multiple series of trisubstituted phosphine chalcogenide molecules with a variety of phosphorus substituents and examine how these affect the strength of the phosphorus–chalcogen bond. DFT provides valuable data on these compounds including P–E bond dissociation energies, P–E bond order, Lowdin charge on phosphorus and chalcogen atoms, and molecular geometries. Experimentally monitoring the 31P and 77Se NMR chemical shifts and published Hammett constants provides good estimates and confirmation of the relative magnitude of electronic shielding around these nuclei and confirms the predictive value of the computational results.

A new carboxylate rich asymmetric tripodal ligand, N-[2-carboxybenzomethyl]-N-[carboxymethyl]-β-alanine (H3camb), and its di-copper(II), (NH4)2[1]2, and di-zinc(II), ((CH3)4N)2[2]2, complexes have been synthesized as carbohydrate binding models in aqueous solutions. The ligand and complexes have been fully characterized using several techniques, including single crystal X-ray diffraction. The interactions of (NH4)2[1]2 and ((CH3)4N)2[2]2 with D-glucose, D-mannose, D-xylose and xylitol in aqueous alkaline media were investigated using UV-Vis and (13)C-NMR spectroscopic techniques, respectively. The molar conductance, NMR and ESI-MS studies indicate that the complexes dissociate in solution to produce the respective complex anions, 1(-) and 2(-). Complexes 1(-) and 2(-) showed chelating ability towards the naturally abundant and biologically relevant sugars, D-glucose, D-mannose, D-xylose, and xylitol. The complex ions bind to one molar equivalent of the sugars, even in the presence of stoichiometric excess of the substrates, in solution. Experimentally obtained spectroscopic data and computational results suggest that the substrates bind to the metal center in a bidentate fashion. Apparent binding constant values, pK(app), between the complexes and the substrates were determined and a specific mode of substrate binding is proposed. The pK(app) and relativistic density functional theory (DFT) calculated Gibbs free energy values indicate that D-mannose displayed the strongest interaction with the complexes. Syntheses, characterizations, detailed substrate binding studies using spectroscopic techniques, single crystal X-ray diffraction and geometry optimizations of the complex-substrates with DFT calculations are also reported.

The geometric and electronic structures of calixarene bismuth(III) complexes have been investigated by ab initio method in this study. Three conformations (cone shape conformation with C2v symmetry, 1,2-alternative conformation with C2h symmetry and 1,3-alternative conformation) are investigated as possible binding modes between bismuth fragment and calixarene fragment. The optimized geometries are then compared with the recent reported crystal structure. Two bis-muth(III) fragments are needed to bind with calixarene ligand due to the inert-pair effect. Co-crystalized LiCl-DMSO fragment plays a crucial role in stabilizing the bismuth calixarene crystal, where the binding energy ΔH is estimated to be 55.3 kcal/mol or 56.1 kcal/mol with zero-point energy correction. The estimated ΔG is -28.2 kcal/mol for the complex, which is consistent with the strong HC4Bi-ClLi interactions. The trans effect is evidenced by two slight longer Bi-O bond lengths.

Introduction In clinical practice, Nao An Capsule (NAC), a traditional Chinese medicine (TCM) prescription, is regarded as having good therapeutic effect on ischemic stroke (IS). A network pharmacology based method was used to uncover the active substances and mechanism of NAC in treatment of IS. Methods The components of NAC, in addition to their interacting targets, were searched from the TCMSP database. The components were filtered by the metrics of oral bioavailability and drug likeness, and the targets were compared to the disease associated ones searched from the CTD and TTD databases. After that, the components and targets were fed into the Cytoscape software to build a component-target-disease network. Afterwards, the protein-protein interactions among the identical targets were visualized by the STRING database, and the GO and pathway enrichment analysis were performed by the Metascape database. Finally, the potential active substances and targets were validated by molecular docking simulation. Results 51 compounds, 325 interacting targets in addition to 54 disease-related targets were obtained, in which 16 identical targets were observed, and analyzed to be enriched in 18 pathways. 13 of those identical targets had compact relationships with each other in STRING analysis. The compounds interacting with the 13 targets had stronger affinities than the native ligands in molecular docking simulation. Conclusion The present method did not only preliminarily reveal the active substances and mechanism of NAC in treatment of IS from the perspective of network pharmacology, but show its potential application for research and development of other TCM prescriptions.

Our previous work demonstrated that hydroxide ion (OH-) was able to catalyze aldol condensation reaction at room temperature between 5-hydroxymethylfurfural (HMF) and levulinic acid (LA). This work identified three primary reaction steps in this condensation reaction using density functional theory (DFT): (1) deprotonation of LA to generate LA ions, (2) LA ions addition at hydroxymethyl site of HMF, and (3) internal dehydration to form the condensation product. The reaction pathway through the C5 of LA forms a linear product that is favored with respect to both energy and configuration in all three elementary reaction steps. This is qualitatively consistent with the phenomenon observed in our previous experiment where the linear form is a main product. Further confirmation comes from the frontier orbital analysis of the transition states in the linear reaction route and explains the regioselectivity of product formation.

We demonstrate molecular control of nanoscale composition, alloying, and morphology (aspect ratio) in CdS-CdSe nanocrystal dots and rods by modulating the chemical reactivity of phosphine-chalcogenide precursors. Specific molecular precursors studied were sulfides and selenides of triphenylphosphite (TPP), diphenylpropylphosphine (DPP), tributylphosphine (TBP), trioctylphosphine (TOP), and hexaethylphosphorustriamide (HPT). Computational (DFT), NMR ((31)P and (77)Se), and high-temperature crossover studies unambiguously confirm a chemical bonding interaction between phosphorus and chalcogen atoms in all precursors. Phosphine−chalcogenide precursor reactivity increases in the order: HPTETOPETBPEDPPETPPE (E = SSe). For a given phosphine, the selenide is always more reactive than the sulfide. CdS(1-x)Se(x) quantum dots were synthesized via single injection of a R(3)PS-R(3)PSe mixture to cadmium oleate at 250 °C. X-ray diffraction (XRD), transmission electron microscopy (TEM), and UV/Vis and PL optical spectroscopy reveal that relative R(3)PS and R(3)PSe reactivity dictates CdS(1-x)Se(x) dot chalcogen content and the extent of radial alloying (alloys vs core/shells). CdS, CdSe, and CdS(1-x)Se(x) quantum rods were synthesized by injection of a single R(3)PE (E = S or Se) precursor or a R(3)PS-R(3)PSe mixture to cadmium-phosphonate at 320 or 250 °C. XRD and TEM reveal that the length-to-diameter aspect ratio of CdS and CdSe nanorods is inversely proportional to R(3)PE precursor reactivity. Purposely matching or mismatching R(3)PS-R(3)PSe precursor reactivity leads to CdS(1-x)Se(x) nanorods without or with axial composition gradients, respectively. We expect these observations will lead to scalable and highly predictable "bottom-up" programmed syntheses of finely heterostructured nanomaterials with well-defined architectures and properties that are tailored for precise applications [corrected].

A better understanding of the chemistry of molecular precursors is useful in achieving more predictable and reproducible nanocrystal preparations. Recently, an efficient approach was introduced that consists of fine-tuning the chemical reactivity of the synthetic molecular precursors used, while keeping all other reaction conditions constant. Using nickel phosphides as a research platform, we have studied how the chemical structure and reactivity of a family of commercially available organophosphite precursors (P(OR)3, R = alkyl or aryl) alter the preparation of metallic and metal phosphide nanocrystals. Organophosphites are a versatile addition to the pnictide synthetic toolbox, nicely complementing other available precursors such as elemental phosphorus or trioctylphosphine (TOP). Experimental and computational data show that different organophosphite precursors selectively yield Ni, Ni12P5, and Ni2P and that these phases evolve over time through separate mechanistic pathways. Based on our observations,...

In light of recent experiments suggesting high-spin (HS) Ni(II) species in the catalytic cycle of [NiFe] hydrogenase, a series of models of the Ni(II) forms Ni-SI(I,II), SI-CO and Ni-R(I,II,III) were examined in their high-spin states via density functional calculations. Because of its importance in the catalytic cycle, the Ni-C form was also included in this study. Unlike the Ni(II) forms in previous studies, in which a low-spin (LS) state was assumed and a square-planar structure found, the optimized geometries of these HS Ni(II) forms resemble those observed in the crystal structures: a distorted tetrahedral to distorted pyramidal coordination for the NiS4. This resemblance is particularly significant because the LS state is 20-30 kcal/mol less stable than the HS state for the geometry of the crystal structure. If these Ni(II) forms in the enzyme are not high spin, a large change in geometry at the active site is required during the catalytic cycle. Furthermore, only the HS state for the CO-inhibited form SI-CO has CO stretching frequencies that match the experimental results. As in the previous work, these new results show that the heterolytic cleavage reaction of dihydrogen (where H2 is cleaved with the metal acting as a hydride acceptor and a cysteine as the proton acceptor) has a lower energy barrier and is more exothermic when the active site is oxidized to Ni(III). The enzyme models described here are supported by a calibrated correlation of the calculated and measured CO stretching frequencies of the forms of the enzyme. The correlation coefficient for the final set of models of the forms of [NiFe] hydrogenase is 0.8.

Gas-phase photoelectron spectroscopy is used to investigate metal–metal interactions and the mixed-valence positive ion states of biferrocene and bis(μ-fulvalenediyl)diiron. The spectra of phenylferrocene and 1,1′-diphenylferrocene are used to show that, in comparison to ferrocene, the extension of the ligand π system and the reduced ligand symmetry do not have an appreciable effect on the band profile of the metal-based ionizations. In contrast, the initial ionization bands of both bimetallic molecules, which derive from the metal-based 2 E 2g ionizations of ferrocene, are spread over a wide energy range, indicating delocalization across the two metal halves of the molecule and formal oxidation states of +2 1 / 2 for each metal atom in these cation states. The broadening and splitting of this ionization band for bis(μ-fulvalenediyl)diiron is twice that observed for biferrocene, consistent with a through-bond ligand-mediated mechanism of interaction. Ionizations of the bimetallic molecules that derive from the metal-based 2 A 1g ionizations of ferrocene occur in a single narrow band, indicating that both through-space and through-ligand interactions are not appreciable for the d z 2 -based orbitals. The difference between the metal–metal interactions in these positive ion states follows from the different overlap and energy match of the metal orbitals with fulvalendiyl orbitals of the appropriate symmetry. Most important to the metal–metal interaction in the ground ion state are empty fulvalendiyl orbitals with two nodes perpendicular to the C 5 planes and gerade and ungerade symmetries with respect to the inversion centers of the molecules. In the gas phase, both species are found to be strongly interacting, delocalized mixed-valence compounds in their ground ion states.

Density functional calculations (B3LYP) of the associative reaction of (η5-C5H4X)M(CO)2 with PR3 (X = H, Me, Cl; M = Co, Rh, Ir) show that transition-state (TS) effects dominate the reaction rate. ...

Gas-phase photoelectron spectroscopy is used to investigate the bonding between early transition metals and carbonyl and cyclopentadienyl ligands for the molecules (η5-C5H4R)M(CO)4 (R = H, M = V, Nb, Ta; R = SiMe3, M = Nb, Ta; R = COCH3, M = Nb). The lowest ionization energy region contains two overlapping ionizations that arise from the two orbitals that are occupied according to the formal d4 metal configuration. However, the character of these ionizations is dominated by the carbonyls rather than by the metals, as evidenced by the extensive C−O stretching vibrational progressions observed with these ionizations, by the trends in the ionization cross sections between the molecules and with different ionization sources, and by the relative lack of shifts of these ionizations with metal substitution from vanadium to niobium to tantalum or with trimethylsilyl and acetyl substitutions on the cyclopentadienyl. The second group of ionizations for these molecules corresponds to orbitals with predominantly cycl...

The teaching of chemistry to non-chemistry engineering majors has proven to be a challenge, not only because it needs to prepare these students for the new standards and requirements outlined by the U.S. Accreditation Board of Engineering & Technology (ABET), but also because these students have different interests and preferences than chemistry. Further complicating the situation, these engineering majors often take only one semester of chemistry at the general chemistry level and do not consider chemistry as a significant contribution to their knowledge and/or to their major. In order to remedy the current deficiency in students’ interest and meet the requirements from ABET, a new chemistry course with specially designed pedagogy was formulated and implemented for engineering majors. A team of undergraduate students and an instructor were assembled to introduce the essential chemistry concepts and skills to freshmen engineering majors. Several approaches were used to assist students with learning chemistry: hands-on demonstration, technology-concentrated online learning tools, and Process Oriented Guided Inquiry Learning setup. The combination of these approaches allows students to construct, visualize, and correlate the chemical concepts into engineering applications. The results and students’ responses are reported in this study.

To explore reaction dynamic of hydroxyl radical (*OH) and salicylic acid,and to determine the elimination ratios of TCM polysaccharide to *OH by kinetic fluorescent analysis.The impact dynamics factors of this reaction were studied by fluorescent, such as the reaction of concentration, reaction time and temperature. The dynamical equation was built, a kinetic fluorescent spectrophotometry based on the reaction was developed to determine the elimination ratio. Repetitiveness and reliability of this method were tested by vitamin C.The dynamical equation of reaction rate to salicylic acid was gamma = 0. 9818x -1. 1801 under the condition of lambda ex = 295 nm, lambda em = 411 nm at room temperature, r approximately 1. The 50% elimination ratio (IC50) of TCM polysaccharide of Tangerine peel and Ganoderma lucidum to *OH was 78.01 mg/L and 232.5 mg/L, respectively. The IC50 of vitamin C was 24.52 microg/L, RSD was 0.23% (n = 5).The method is sensitive and reliable, it can be used to determine the elimination ratio of TCM polysaccharide to *OH.

Flow risk of a hot waxy crude pipeline mainly comes from restart failure, i.e. oil gelation resulted from prolonged pipeline shutdown, and unstable operation at low flow rate. Once the unstable operation happens, the friction loss of the pipeline increases with decreasing flow rate and finally flow may cease if treated improperly. To avoid these flow risks, the pumping temperature of the crude is generally required to be kept above a minimum allowable temperature, and conventionally the pour point temperature is taken. This practice is effective but quite rough. Obviously, to control the inlet temperature of a heating station at the pour point temperature implies different safety margin for winter and summer operation. For large throughput hot oil pipelines, reduction of the heating temperature even by a little bit may save a great amount of fuel. Therefore, how to save fuel while ensuring safe operation has been a valuable topic for long time. On the other hand, many factors impacting the flow safety are stochastic and with uncertainty, so analysis without considering this feature can hardly yield convincible results, though this has been the common case for many years. In this paper, by taking the stochastic feature into account, a Stable Operation Index (SOI) and a Pipeline Restartability Index (PRI) were proposed to assess the flow safety of a pipeline concerning the low-flowrate stable operation and restartability after shutdown. Combining these two indexes, a Pipeline Flow Safety Index (PFSI) was adopted to assess the flow risks of hot waxy crude pipelines. On this basis a new approach to quantitatively determining the safe pumping temperature was developed and illustrated by a case study. Encouraging results show that this new approach has the potential to replace the simple rule of pour point as a guide to determining the safe pumping temperature of waxy crude pipelines.Copyright © 2006 by ASME

A new method using microwave digestion technique was developed for the determination of cadmium, chromium and lead in Lycoris radiata by graphite furnace atomic absorption spectrometry (GFAAS). Digestion solvents were discussed for sample preparation by microwave digestion technique. The optimum condition of determination by GFAAS was studied in the presence of NH4H2PO4 matrix modifier. The detection limits of Cd, Cr and Pb are 0.066 7, 1.22 and 0.810 microg x L(-1), respectively. The method was applied to the determination of Cd, Cr and Pb in Lycoris radiata samples with satisfactory results. The RSD of determination were lower than 3.1%. The recoveries were from 83.8% to 118%.

Publisher Summary There are three mechanisms proposed for the acceptorless reaction: the dissociative pathway (D), associative pathway (A) and interchange pathway (I), whose importance may depend on the temperature, concentration of reactive species (alkane, alkene, and dihydrogen), and phosphine substituents. This chapter discusses the elementary reaction steps of these mechanisms focusing primarily on the anthraphos systems. The chapter describes the impact of different methods (coupled cluster, configuration–interaction and various DFT functionals), different basis sets, and phosphine substituents on the oxidative addition of methane to related Iridium (Ir) systems. The chapter compares the elementary reaction steps, including the effect of reaction conditions such as temperature, hydrogen pressure, alkane and alkene concentration, phosphine substituents and alternative metals (Rh). The chapter describes how these elementary steps constitute the reaction mechanisms.

Density functional calculations have been applied to models of both transfer and acceptorless alkane dehydrogenation for the iridium(III) pincer complex, ( R PCP )IrH2 ( R PCP  η 3 -C6H3(CH2PR2)2-1,3). The iridium pincer complex is the first efficient homogeneous catalyst that does not require photons or sacrificial hydrogen acceptors to drive the reaction, although with the latter the transfer reaction can accomplished under mild conditions. There are four essential steps for the catalytic cycle in both transfer and acceptorless reactions: oxidative addition of alkane, reductive elimination, β-hydrogen (β-H) transfer, and loss of olefin. The transfer reaction can utilize a hydrogen acceptor to produce a 14-electron intermediate, ( R PCP )Ir(I), and the acceptorless reaction can produce an 18-electron intermediate, ( R PCP )Ir(V)(H)3(alkyl) species. Because the critical barriers are well-balanced in the Ir(V) catalytic cycle for acceptorless alkane dehydrogenation, no transition state (TS) is higher in energy than the products and no intermediate is lower in energy than the reactant. This balance could explain why pincer complexes are more efficient catalysts for alkane dehydrogenation than the corresponding Cp–Ir(III) complex. Entropy contributions, which play a larger role at high temperature, open new pathways for the acceptorless reaction. Free energies of activation suggest that the dynamics of the acceptorless reaction might be sampling the entire range of pathways and Ir oxidation states from Ir(I) to Ir(V).

Publisher Summary There are three mechanisms proposed for the acceptorless reaction: the dissociative pathway (D), associative pathway (A) and interchange pathway (I), whose importance may depend on the temperature, concentration of reactive species (alkane, alkene, and dihydrogen), and phosphine substituents. This chapter discusses the elementary reaction steps of these mechanisms focusing primarily on the anthraphos systems. The chapter describes the impact of different methods (coupled cluster, configuration–interaction and various DFT functionals), different basis sets, and phosphine substituents on the oxidative addition of methane to related Iridium (Ir) systems. The chapter compares the elementary reaction steps, including the effect of reaction conditions such as temperature, hydrogen pressure, alkane and alkene concentration, phosphine substituents and alternative metals (Rh). The chapter describes how these elementary steps constitute the reaction mechanisms.

25 páginas, 9 figuras y 2 tablas, The binding of carbon monoxide a competitive inhibitor of many hydrogenases, to the active site of Desulfovibrio fructosovorans hydrogenase has been studied by infrared spectroscopy in a spectroelectrochemical cell. Direct evidence has been obtained of which redox states of the enzyme can bind extrinsic CO. Redox states A, B and SU do not bind extrinsic CO. only after reductive activation of the hydrogenase can CO bind to the active site. Two states with bound extrinsic CO can be distinguished by FTIR. These two states are in redox equilibrium and are most probably due to different oxidation states of the proximal 4Fe-4S cluster. Vibrational frequencies and theoretical quantum mechanics studies (DFT) of this process preclude the possibility of strong bonding of extrinsic CO to the Fe or Ni atoms or the site. We propose that CO inhibition is caused by weak interaction of the extrinsic ligand with the Ni atom, blocking electron and proton transfer at the active site. A calculated structure with a weakly bound extrinsic CO at Ni has relative CO frequencies in excellent agreement with the experimental ones., The Spanish Ministry of Science and Technology (project BQU2000-0991) and the European Union BIOTECH program (grant BIO-98-0280) supported this work. We thank Prof. Siem Albracht for useful discussions, Dr. Arturo Martinez-Arias for doing the EPR measurements, the Autonomous Community of Madrid (CAM) for the postdoctoral fellowship of A. L. De Lacey and the German Academic Exchange Service (DAAD) for the postdoctoral fellowship of C. Stadler. MBH thanks NSF (CHE-9800184) for financial support.

The first density functional calculations on high-spin (HS) Ni(II) models for the active site of the [NiFe] hydrogenases predict a ligand arrangement about Ni that is in better agreement with the crystal structures than previous predictions for low-spin (LS) Ni(II) models. With the crystal structures' geometry, the HS form is approximately 20 kcal/mol lower in energy than the LS one.

Various states or forms of the active site in Ni-Fe hydrogenase, both catalytically active and inactive forms, have been identified and investigated experimentally. Until recently, the geometric structure of each form remained an open question. Several recent theoretical studies with density functional theory have attempted to redress this deficiency. In this commentary, the similarities and differences among the structures proposed by these studies will be addressed.