High Reactant Concentrations Research Articles

Some remarks on the Langmuir–Hinshelwood kinetics

This work considered the Langmuir–Hinshelwood (LH) scheme for a single reactant. In a first step, the validity of the quasi-steady state approximation (QSSA) was revised in terms of nonlinear relaxation processes. It was found that the LH equation obtained from the QSSA is not valid most of the times, except for example in the case of high reactant concentrations when the relaxation time is small enough to reduce the order of the underlying system of differential equations. Subsequently, the observability properties of the LH equations were studied in order to find that the dynamical behavior of the adsorption complex can be reconstructed from measurements of the reactant trajectory. Finally, the estimation problem of the kinetic parameters based solely on the reactant concentration behavior was considered. It is then shown that the full set of kinetic parameters can be estimated from a single reactant depletion curve by solving a least-squares problem for the complete LH scheme. Numerical results were used to illustrate the findings of this work.

Isopolymolybdate adsorption as related to inhibition and self-inhibition of electrode processes

Abstract Electrochemical behavior of aqueous isopolymolybdates at various pH (0.1–8.7) is addressed in dropping mercury electrode experiments. Formation of compact adlayers is found to be responsible for decreased current of molybdate reduction (self-inhibition), especially at higher reactant concentrations. Correlation of the observed self-inhibition degree with the decrease of the surface tension is observed in the overall pH range. The difference in adsorption behavior of oxocations, neutral species and oxoanions is illustrated experimentally. Self-inhibition in acidic solutions is accented, as a previously known complication for electroanalysis. This phenomenon is assigned to adsorption of the neutral oxomolybdate species. Inhibition of the outer-sphere electron transfer processes is studied for two model reactions, and the role of pH-affected speciation is found to be the same as for self-inhibition. Similarities with speciation effect in corrosion protection are discussed on the basis of these findings.

Mask-Like Symmetrical Microclusters through a Diffusion-Limited Assembly Approach.

A diffusion-limited assembly approach was explored to fabricate symmetrical [Cu(Succinate)]n microclusters with a different shape and size for the first time. The molecular structure of succinate and its coordination reaction capability towards copper(II) ions governed the one-dimensional growth of the nanofibers and the concomitant formation of the microclusters. In detail, a symmetrical concentration gradient was formed around the endpoints of the nanofibers caused by the diffusion-limited process at high reactant concentrations. The concentration gradient forced the nanofibers to grow divergently and further aggregate into open microcluster structure. The shape and size of the microclusters could be tuned by altering the concentration of the reactants. Particularly, mask-like double-hole symmetrical microclusters (MDHSMs) were obtained when the concentration of both reactants was as high as 140 mM. The resultant MDHSMs showed high selectivity in adsorption of dyes and proteins, and may find potential applications in water treatment, bioseparation, and immobilization of biomacromolecules.

Hydride transfer between a phenolic surface pool and reactant paraffins in the catalytic cracking of m-cresol/hexanes mixtures over an HY zeolite

The effect of the presence of m-cresol on the monomolecular and bimolecular pathways of paraffin conversion has been studied over the bare surface of an HY zeolite in a micropulse reactor. The influence of m-cresol is interpreted in terms of the two types of sites present in pristine HY zeolites pretreated at high temperatures. These two types of sites are described as normal Brønsted acid sites and synergistic sites. The latter have higher activity and favor the monomolecular path. They are more severely deactivated than the former by the presence of m-cresol, especially at low reactant concentrations, where the monomolecular reaction is the dominating path. At higher reactant concentrations, hydride transfer from paraffins becomes important and promotes desorption of the phenolic compounds, which hinders the deactivating effect of m-cresol and the growth of a surface phenolic pool, typically formed by condensation reactions of phenolics. Hydride transfer between the paraffinic feed and the surface carbenium ions is also reduced by the presence of m-cresol.

Micelle-Enhanced Bioorthogonal Labeling of Genetically Encoded Azido Groups on the Lipid-Embedded Surface of a GPCR.

Genetically encoded p-azido-phenylalanine (azF) residues in G protein-coupled receptors (GPCRs) can be targeted with dibenzocyclooctyne-modified (DIBO-modified) fluorescent probes by means of strain-promoted [3+2] azide-alkyne cycloaddition (SpAAC). Here we show that azF residues situated on the transmembrane surfaces of detergent-solubilized receptors exhibit up to 1000-fold rate enhancement relative to azF residues on water-exposed surfaces. We show that the amphipathic moment of the labeling reagent, consisting of hydrophobic DIBO coupled to hydrophilic Alexa dye, results in strong partitioning of the DIBO group into the hydrocarbon core of the detergent micelle and consequently high local reactant concentrations. The observed rate constant for the micelleenhanced SpAAC is comparable with those of the fastest bioorthogonal labeling reactions known. Targeting hydrophobic regions of membrane proteins by use of micelle-enhanced SpAAC should expand the utility of bioorthogonal labeling strategies.

Chain, ladder and self-penetrated cobalt and nickel coordination polymers containing sterically bulky isophthalate and long-spanning dipyridylamide ligands

Hydrothermal reaction of cobalt or nickel nitrate with 5-tert-butylisophthalic acid (H2tbip) and bis(4-pyridylformyl)piperazine (bpfp) under varying synthetic conditions afforded four coordination polymers that were subsequently structurally characterized via single-crystal X-ray diffraction. {[Co(Htbip)2(H2O)2(bpfp)]·H2O}n (1), prepared with a lower concentration of added base, exhibits a 1D sawtooth chain structure. {[Co2(tbip)2(H2O)4(bpfp)]·2H2O}n (2), prepared under higher base conditions, and its analog {[Ni2(tbip)2(H2O)4(bpfp)]·2H2O}n (3), show isostructural 1D ladder topologies. {[Ni(tbip)(H2O)2(bpfp)]·2.25H2O}n (4), prepared using a higher concentration of reactants than for 3, manifests an extremely rare 658 4T10 4-connected self-penetrated topology and represents the first metal dicarboxylate coordination polymer to possess this network. Thermal decomposition behavior of these materials is also discussed.

Spatial confinement of a Co3O4 catalyst in hollow metal-organic frameworks as a nanoreactor for improved degradation of organic pollutants.

We here first proposed a yolk-shell Co3O4@metal-organic frameworks (MOFs) nanoreactor via a facile method to accommodate sulfate radical-based advanced oxidation processes (SR-AOPs) into its interior cavity. The mesoporous and adsorptive MOFs shells allow the rapid diffusion of reactant molecules to the encapsulated Co3O4 active sites, and the confined high instantaneous concentration of reactants in the local void space is anticipated to facilitate the SR-AOPs. As a proof of concept, the nanoreactor was fully characterized and applied for catalytic degradation of 4-chlorophenol (4-CP) in the presence of peroxymonosulfate (PMS). The enhancement of SR-AOPs in the nanoreactor is demonstrated by the result that degradation efficiency of 4-CP reached almost 100% within 60 min by using the yolk-shell Co3O4@MOFs catalysts as compared to only 59.6% under the same conditions for bare Co3O4 NPs. Furthermore, the applicability of this nanoreactor used in SR-AOPs was systematically investigated in terms of effect of reaction parameters and identification of intermediates and primary radical as well as mineralization of the reaction and stability of the composite. The findings of this study elucidated a new opportunity for improved environmental remediation.

Pervaporation Membrane Reactor for Producing Hydroxylamine Chloride via an Oxime Hydrolysis Reaction

A cost-effective route for the synthesis of hydroxylamine chloride (NH2OH·HCl) was proposed by combining ammoximation and oxime hydrolysis reactions (A–O–H route). This route is limited by low equilibrium conversion of oxime hydrolysis, which is a reversible reaction that produces ketone and NH2OH·HCl. A pervaporation membrane reactor (PVMR) was recommended in this route for improving butanoxime hydrolysis conversion by in situ removal of byproduct butanone. Using a PDMS membrane, the effects of feed composition, temperature, and reactant concentration on the PVMR performance were investigated. An enhancement of conversion from about 20% to 84% was achieved. When using a high reactant concentration, NH2OH·HCl can be crystallized in the PVMR. The longtime experiment demonstrated that the membrane was stable in acidic and ionic environments in the reaction mixture.

Solution photochemistry of [p-(dimethylamino)phenyl]pentazole (DMAPP) at 193 and 300 nm.

The photochemistry of [p-(dimethylamino)phenyl]pentazole (DMAPP) at 193 nm and in the near UV is reported, with emphasis on the nature of the final stable products. The (dimethylamino)phenyl azide (DMAPA) is found as a major product in MeCN, but not in dichloromethane (DCM). (In this paper the acronyms DMAPP and DMAPA refer to the para isomers.) The photochemistry of DMAPA is also explored for comparison. The data obtained in MeCN solutions are consistent with the initial formation of the corresponding nitrene, but in DCM, different products are found, on the basis of NMR data. In the case of high reactant concentration in DCM (10(-2) M), quantitative conversion of DMAPP and DMAPA is observed, indicating a high quantum yield. In contrast, MeCN solutions react much more slowly. A radical-type chain reaction mechanism is proposed to account for this observation. At high dilution, DMAPP is completely converted to products in both solvents. Possible mechanisms accounting for these results are discussed.

Influence of the solvent and of the reaction concentration for palladium-catalysed direct arylation of heteroaromatics with 4-bromoacetophenone

The solvent is certainly one of the main sources of wastes during palladium-catalysed direct arylation reactions. We found that such direct arylations of heteroaromatics can be performed using very high concentrations of reactants (0.5 M–5 M). However, the Pd catalyst precursor used must be adapted to both the solvent nature and the concentration of reactants. The reactions performed in DMA, NMP or DMF can be carried out in very concentrated reaction mixtures using 0.1 mol% Pd(OAc)2 catalyst without phosphine ligand. On the other hand, the reactions in CPME, pentan-1-ol or diethylcarbonate should be performed with a palladium catalyst associated with a phosphine ligand. These reaction conditions allow us to reduce the amount of wastes formed in the course of these couplings.

Electrostatic immobilization of substrate and polyoxotungstate catalyst at the surface of micelles for enhanced reaction efficiency in water

Polyoxometalate (POM)-based micellar catalysts were prepared by assembling the Keggin tri-anion [PW12O40]3− and (L)-N-acetylmethioninate salts of Gemini surfactants in water. Contrary to conventional catalytic systems, we propose a new approach in which the POM catalyst and the substrate to be oxidized ((L)-N-acetylmethioninate) are both localized at the surface of micelles by electrostatic interaction before the reaction. The high local concentration of reactants due to their confinement at the surface of micelles enhances the reaction kinetics. Catalyst recovery experiments showed that, after two cycles of reactions, the activity of the catalysts was not changed.

Fabrication and Physical Properties of Thin Films TiNx for Infrared Absorption

Infrared absorptivity of pixel arrays plays a pivotal role in bolometer performance. There are a series reports focusing on improving the absorptivity in last two decades [1, 2]. Many materials have been examined as suitable infrared light absorbers, such as thin films MoSix and TiNx. In general, the optimized sheet resistance is ~ 377Ω/square related to the absorption [3-4]. However, there are fewer reports on the investigation of synergetic effects from ultrathin substrate SiNx, which is a desirable material during microfabrication process of the bolometers. In this paper, we present the experimental and optical analysis for construction of the film TiNx on SiNxsubstrates. The thin films TiNx were prepared by reactive magnetron sputtering technique under Ar/N2 atmosphere. The RF sputtering power is 350 W and the total gas flux is about 25 sccm. The amount (N2%) of nitrogen as a function of Ohm-square at the temperature (25, 200 oC) are summarized in fig 1. It shows that the sheet resistance is sensitive to the substrates temperature. The logarithmic value of sheet resistance is approximately proportional to N2 ratio at the substrate temperature from 25 oC to 200 oC. The reaction rate is rather slow at low temperature (25 oC) even with a high reactant gas concentration for TiNx growth. The relatively high substrate temperature (200 oC) is desirable for the TiNx growth. The resistivity with 13% N2 at 200 oC is close to the value 377Ω/square in literature [3-4]. The light absorptivity of multilayer structure (TiNx/SiNx/Al, SiNx/Al) has been recorded by Fourier Transform Infrared Spectroscopy, as shown in Fig. 2. It can be seen that the infrared absorptivity of the sandwich-type structure (TiNx/SiNx/Al) shows higher IR absorption than that of the structure SiNx/Al. The structure TiNx/SiNx/Al shows obviously enhanced resonant peak in 1/4 of 3/4 wavelength optical thickness due to the existence of Fabry-Perot resonator, which related to the Peak A and C of the recorded spectra. The intrinsic absorption of SiNx can be indexed to Peak B and D. As compared with the pristine SiNx, it can be seen that the absorption dramatically increases at the wavelength 8 um (peak C). In summary, we report preparation of thin film TiNx through reactive magnetron sputtering technique. The optimized resistivity of the films is applied to build a resonant structure for enhancing infrared absorptivity. A drastically increases has been obtained as compared with the pristine SiNx.

A Comprehensive Electrochemical Solution to Climate Change: STEP, the Solar Thermal Electrochemical Pressure Process for the Production of Societal Staples

The solar thermal electrochemical pressure process is capable of the production of societal staples with little or no carbon footprint, and can directly capture & convert carbon dioxide from the air that can be stored as useful graphite.In STEP the efficient formation of metals, fuels, cement, chlorine, and carbon capture is driven by solar thermal heated endothermic electrolyses of concentrated reactants occurring at voltage below that of the room temperature energy stored in the products. As one example, CO2 is reduced to either fuels, or storable carbon, at solar efficiency higher than the best photovoltaics. This is due to a synergy of efficient solar thermal absorption and electrochemical conversion at high temperature and reactant concentration. CO2-free STEP iron production, from iron ore, occurs via Fe(III) in molten carbonate. Water is efficiently split to H2 by molten hydroxide electrolysis, and chlorine, sodium and magnesium from molten chlorides. STEP cement uses a novel molten electrochemistry for the production of calcium oxide (lime from limestone).1-7 The solar electrochemical generation of societal staples and fuels decreases society's dependence on grid-based electricity. A pathway is provided for the STEP decrease of atmospheric carbon dioxide levels to pre-industrial age levels in 10 years.Selected STEP references:(1) S. Licht, "STEP generation of energetic molecules: A solar chemical process to end anthropogenic global warming," J. Phys. Chem., C, 2009, 113, 16283-16292.(2) S. Licht, B. Wang, S. Ghosh, H. Ayub, D. Jiang, J. Ganley, "A New Solar Carbon Capture Process: STEP Carbon Capture," J. Phys. Chem. Lett., 2010, 1, 2363-2368, with online 2 page supplement.(3) S. Licht, "Efficient Solar-Driven Synthesis, Carbon Capture, and Desalinization, STEP: Electrochemical Production of Fuels, Metals, Bleach," Advanced Materials, 2011, 47, 5592-5612.(4) S. Licht, H. Wu, C. Hettige, B. Wang, J. Lau, J. Asercion, J. Stuart, " STEP Cement: solar thermal electrochemical production of CaO without CO2 emission " Chem. Comm., 2012, 48, 6019-6021, with online 20 page supplement.(5) B. Wang, Y. Hu, H. Wu, S. Licht, "STEP Pollutant to Solar Hydrogen: Solar driven thermal electrochemical wastewater treatment with synergetic production of hydrogen," Electrochemical Science Letters, 2013, 2, H34-H36.(6) B. Cui, S. Licht, ”Critical STEP advances for sustainable iron production,” Green Chemistry , 2013, 15(4), 881-884, with 16 page online supplementary information(7) S. Licht, B. Cui, B. Wang, ”STEP Carbon Capture: the barium advantage,” Journal of CO2 Utilization, 2013, 2, 58-63.

Recyclable 1,2‐bis[3,5‐bis(trifluoromethyl)phenyl]diselane‐catalyzed oxidation of cyclohexene with H2O2: a practical access to trans‐1,2‐cyclohexanediol

1,2‐Bis[3,5‐bis(trifluoromethyl)phenyl]diselane‐catalyzed oxidation of cyclohexene by hydrogen peroxide affords a quick, clean and practical access to the important compound trans‐1,2‐cyclohexanediol under mild conditions. The highly atom‐economic properties, clean procedures, high reaction concentration, short reaction time, mild conditions and eco‐friendly, recyclable and low loading catalysts facilitate this methodology for possible future practical industrial production. Copyright © 2014 John Wiley & Sons, Ltd.

Gallium(III) complexes of NOTA-bis (phosphonate) conjugates as PET radiotracers for bone imaging.

Ligands with geminal bis(phosphonic acid) appended to 1,4,7-triazacyclonone-1,4-diacetic acid fragment through acetamide (NOTAM(BP) ) or methylenephosphinate (NO2AP(BP) ) spacers designed for (68) Ga were prepared. Ga(III) complexation is much faster for ligand with methylenephosphinate spacer than that with acetamide one, in both chemical (high reactant concentrations) and radiolabeling studies with no-carrier-added (68) Ga. For both ligands, formation of Ga(III) complex was slower than that with NOTA owing to the strong out-of-cage binding of bis(phosphonate) group. Radiolabeling was efficient and fast only above 60 °C and in a narrow acidity region (pH ~3). At higher temperature, hydrolysis of amide bond of the carboxamide-bis(phosphonate) conjugate was observed during complexation reaction leading to Ga-NOTA complex. In vitro sorption studies confirmed effective binding of the (68) Ga complexes to hydroxyapatite being comparable with that found for common bis(phosphonate) drugs such as pamindronate. Selective bone uptake was confirmed in healthy rats by biodistribution studies ex vivo and by positron emission tomography imaging in vivo. Bone uptake was very high, with SUV (standardized uptake value) of 6.19 ± 1.27 for [(68) Ga]NO2AP(BP) ) at 60 min p.i., which is superior to uptake of (68) Ga-DOTA-based bis(phosphonates) and [(18) F]NaF reported earlier (SUV of 4.63 ± 0.38 and SUV of 4.87 ± 0.32 for [(68) Ga]DO3AP(BP) and [(18) F]NaF, respectively, at 60 min p.i.). Coincidently, accumulation in soft tissue is generally low (e.g. for kidneys SUV of 0.26 ± 0.09 for [(68) Ga]NO2AP(BP) at 60 min p.i.), revealing the new (68) Ga complexes as ideal tracers for noninvasive, fast and quantitative imaging of calcified tissue and for metastatic lesions using PET or PET/CT.

Influence of CVD Parameter on Structure of Graded SiC-C Coating

The influence of chemical vapor deposition process parameters including carrier gas composition, deposition temperature, and content of reactants on the structure of graded SiC-C coating is discussed on the basis of thermodynamic calculation in this paper. The addition of enough hydrogen into carrier gas is necessary for the fabrication graded SiC-C coating. The increase of deposition temperature benefits the control of composition in graded coating but the concentration of free Si and free C becomes high at a too high deposition temperature. A high concentration of reactants is preferred while more defects are apt to exist in coatings if the concentration of reactants is too high. The optimum CVD process parameters for graded SiC-C coating are: gradually changing the molar ratio of SiCl4 and CH4 from 0 to 1 when the concentration of CH4 in hydrogen is 1-2 vol%, and the deposition temperature is 1200-1500 °C.

Violation of the mass-action law in dilute chemical systems

The mass-action law, which predicts the rates of chemical reactions, is widely used for modeling the kinetics of the chemical reactions and their stationary states, also for complex chemical reaction networks. However, violations of the mass-action equations have been reported in various cases: in confined systems with a small number of molecules, in non-ideally-stirred systems, when the reactions are limited by the diffusion, at high concentrations of reactants, or in chemical reaction networks with marginally stable mass-action equations. In this paper, I describe a new mechanism, leading to the violation of the mass-action equations, that takes place at a low concentration of at least one of the reactants; in this limit, the reaction rates can be easily inferred from the chemical reaction network. I propose that this mechanism underlies the replication stability of the hypercycles, a class of chemical reaction networks hypothetically connected with abiogenesis. I provide two simple examples of chemical reaction networks in which the mechanism leading to the violation of the mass-action law is present. I study the two chemical reaction networks by means of a simulation performed with a cellular automaton model. The results have a general validity and represent a limitation of the validity of the mass-action law, which has been overlooked up to now in the studies about the chemical reaction networks.

Interaction of pressure wave and propagating flame during knock

To determine the mechanism of interaction between a pressure wave and a propagating flame during knock, normal combustion and knock are numerically modeled in a simplified one-dimensional hydrogen-fueled spark ignition engine. The heat release rate of the flame front during knock abruptly increases when the pressure wave propagates through the reaction zone. The pressure wave in the diffusion zone perturbs temperature and thus causes thermal runaway at positions with low temperature and high reactant concentrations. Analysis of the Damköhler number (the ratio of gas dynamic time to chemical reaction time) and the estimated overpressure revealed that abruptly raised heat release rate during knock facilitates the amplification of the pressure wave and reinforces the interaction between pressure wave and chemical heat release.

The role of carbohydrates at the origin of homochirality in biosystems.

Pasteur has demonstrated that the chiral components in a racemic mixture can separate in homochiral crystals. But with a strong chiral discrimination the chiral components in a concentrated mixture can also phase separate into homochiral fluid domains, and the isomerization kinetics can then perform a symmetry breaking into one thermodynamical stable homochiral system. Glyceraldehyde has a sufficient chiral discrimination to perform such a symmetry breaking. The requirement of a high concentration of the chiral reactant(s) in an aqueous solution in order to perform and maintain homochirality; the appearance of phosphorylation of almost all carbohydrates in the central machinery of life; the basic ideas that the biochemistry and the glycolysis and gluconeogenesis contain the trace of the biochemical evolution, all point in the direction of that homochirality was obtained just after- or at a phosphorylation of the very first products of the formose reaction, at high concentrations of the reactants in phosphate rich compartments in submarine hydrothermal vents. A racemic solution of D,L-glyceraldehyde-3-phosphate could be the template for obtaining homochiral D-glyceraldehyde-3-phosphate(aq) as well as L-amino acids.

Synthesis of novel chiral tetra-(hydrazinecarboxamide) cyclophane macrocycles

Abstract A novel class of chiral enantiomerically pure C 2 -symmetric polyamide macrocycles has been synthesized from the reaction of chiral dioxolane dicarbohydrazides, obtained from commercially available tartaric acid, and aromatic diisocyanates. The novel macrocycles form in almost quantitative yields in a chemoselective [2+2]-cyclocondensation reaction under conformational bias of the dicarbohydrazides. The reaction takes place in anhydrous THF at a relatively high concentration of reactants without addition of external templates or application of high dilution conditions. The structures of the novel polyamide macrocycles were verified and fully assigned by 1 H NMR, 13 C NMR, 2D ROESY NMR, 2D HMBC, 2D HMQC, DEPT 135, FT IR, and CD spectroscopy.