Relative Equilibrium Constants Research Articles

A Note on Stability of a Dopant for Perovskite Solar Cells: Dimerization of 2,2′-bis(trifluoromethyl)-[1,1′-biphenyl]-4,4′-diamine Iodine

The note continues with the density-functional theory (DFT) quantum-chemical understanding of perovskite solar cells at molecular level. In particular, 2,2′-bis(trifluoromethyl)-[1,1′-biphenyl]-4,4′-diamine iodine (or BFBAI2, stoichiometry C14H12F6I2N2) is further calculated—the species is known to improve the power conversion efficiency and device stability. The thermodynamic-stability calculations are performed at the M06-2X/3-21G level with anharmonic vibrational analysis (including vibrational-rotational coupling) for construction of the vibrational-rotational partition functions. The dimerization is shown to be an essential feature of BFBAI2 (it is based on the formation of two hydrogen bonds). The BFBAI2 dimerization is described in the terms of the standard Gibbs energy and the related dimerization equilibrium constant. Comparisons are made with the water dimer, commonly used as a model system for hydrogen-bond formation. The equilibrium constants for the water dimerization are consistently lower than for the dimerization of BFBAI2 - as the presence of two hydrogen bonds in the BFBAI2 dimer contributes to the larger stabilization. The dimerization of BFBAI2 upon higher surface coverages represents an additional factor for the layer stabilization as there is decrease in the standard Gibbs energy at moderate temperatures. The dimerization also brings additional features for modulation of surface conditions.

Mechanistic aspect for the atom transfer radical polymerization of itaconimide monomers with methyl methacrylate: a computational study

Abstract Atom transfer radical polymerization (ATRP) is a versatile & famous technique for the synthesis of well defined molecular architectures. In ATRP, there is a dynamic equilibrium exists between active & dormant species. Therefore, ATRP progress through a sequence of activation & deactivation cycles, ending upon complete monomer consumption & termination reactions are minimized. This paper presents a systematic computational study on kinetics & thermodynamics associates in the ATRP of itaconimide monomers & methyl methacrylate (MMA). For this, the copolymerization system is modeled as a unimer, dimer & trimer of various itaconimides & MMA monomer. The density functional theory with B3LYP functional & 6–31 + G(d)/LanL2DZ basis sets is used in the prediction of geometries & energetics associated with the dissociation of terminal R–X bond present in the unimer, dimer & trimer. The relative equilibrium constant (K ATRP) for the ATRP activation/deactivation steps is calculated from the free energy values associated with dissociation of R–X bond. The relative K ATRP values of dimer & trimer of selected monomers is compared with their respective unimer. From the transition state geometries of the dimeric propagating radical, activation energy is calculated. The gas phase rate coefficients for propagation (k p) (of itaconimides & MMA copolymerization) are calculated using the standard transition state theory. The effect of system parameters such as solvent, temperature & substituent on K ATRP & k p values of dimer is investigated systematically. The change in the initiating system & temperature has significant effect on k p values as compared to solvent & various substituent. The K ATRP values of dimer & trimer dormant species are higher as compared to their respective monomeric species. The neighboring monomer & penultimate monomer plays vital role in kinetics & thermodynamics associated with copolymerization. The obtained initial results show that the mechanism of copolymerization of itaconimide monomers & MMA follows penultimate model.

Active Thermochemical Tables: the thermophysical and thermochemical properties of methyl, CH3, and methylene, CH2, corrected for nonrigid rotor and anharmonic oscillator effects

The thermophysical properties (isobaric heat capacity, entropy, enthalpy increment) of two prominent radicals, methyl, CH3, and methylene, CH2, were computed using the Nonrigid Rotor Anharmonic Oscillator (NRRAO) approach and compared to their RRHO counterparts, demonstrating significant differences between the results from the two approaches. Methylene presents a typical case in which the NRRAO thermophysical properties have significantly higher values than their RRHO counterparts at higher temperatures. In the case of methyl, the positive anharmonicity of the umbrella motion causes an opposite effect, and the NRRAO corrected thermophysical properties have lower values than their RRHO counterparts. The NRRAO corrected thermophysical properties, in turn, affect the resulting thermochemical properties. Two reactions important in combustion modelling were tested: the recombination of methyl radical with hydrogen atoms to form methane, and the recombination of two methyl radicals to form ethane. The related NRRAO equilibrium constants differ significantly from their RRHO analogs, and the consequences for chemical modelling are discussed. Also reported are the most current ATcT enthalpies of formation for CHn (n = 4-0) species and for C2H6, together with the tightly related sequential bond dissociation enthalpies along with the CHn series.

Mechanistic investigation in ultrasound‐assisted interesterification using non‐edible oil blends and heterogeneous catalyst

AbstractThis study explores the mechanistic issues of ultrasound‐assisted interesterification through identification of links between physics and chemistry of the process. Notably, the interesterification reactions have been carried out using blended feedstock of non‐edible oils—keeping in view requirements for large‐scale processes. The reaction system consisted of blended non‐edible oils, methyl acetate and a solid (Cu2O) catalyst. Initial optimization of the process parameters was done using statistical design. To get insight into physical mechanism of interesterification process, reactants/products profiles in control (mechanical agitation) and test (sonication) experiments were analysed using the Langmuir–Hinshelwood–Hougen–Watson type kinetic model. The relative adsorption equilibrium constants required (to fit the kinetic model) were obtained using binary composite isotherm coupled with the non‐random two‐liquid (NRTL) model for activity coefficients. Kinetic constants of interesterification showed two times rise with sonication, while the adsorption equilibrium constants reduced slightly. Activation energy of reaction reduced from 89.04 to 66.97 kJ/mol, which is attributed to reduction in mass transfer barriers due to intense microconvection generated by sonication.

Probing Substrate/Catalyst Effects Using QSPR Analysis on Friedel-Crafts Acylation Reactions over Hierarchical BEA Zeolites.

Attempts to optimize heterogeneous catalysis often lack quantitative comparative analysis. The use of kinetic modelling leads to rate (k) and relative sorption equilibrium constants (K), which can be further rationalized using Quantitative Structure-Property Relationships (QSPR) based on Multiple Linear Regressions (MLR). Friedel-Crafts acylation using commercial and hierarchical BEA zeolites as heterogeneous catalysts, acetic anhydride as the acylating agent, and a set of seven substrates with different sizes and chemical functionalities were herein studied. Catalytic results were correlated with the physicochemical properties of substrates and catalysts. From this analysis, a robust set of equations was obtained allowing inferences about the dominant factors governing the processes. Not entirely surprising, the rate and sorption equilibrium constants were found to be explained in part by common factors but of opposite signs: higher and stronger adsorption forces increase reaction rates, but they also make the zeolite active sites less accessible to new reactant molecules. The most relevant parameters are related to the substrates’ molecular size, which can be associated with different reaction steps, namely accessibility to micropores, diffusion capacity, and polarizability of molecules. The relatively large set of substrates used here reinforces previous findings and brings further insights into the factors that hamper/speed up Friedel-Crafts reactions in heterogeneous media.

A systematic framework for assessing the applicability of reactive distillation for quaternary mixtures using a mapping method

Reactive distillation (RD) is a useful process intensification technique used in the chemical process industries as it offers important advantages such as energy and cost savings, relative to conventional technologies. However, industrial application of RD is still limited by the complexity of designing and understanding such a complex process. While simple, robust shortcut design methods that require only basic information (such as the relative volatility of components) exist for conventional distillation, such methods for evaluating the applicability of RD are not yet established.This work fills this gap by presenting a new systematic framework for assessing the RD applicability based on a mapping method. The method enables RD designs to be screened using only relative volatilities and chemical equilibrium constant as input data. The evaluation focuses on reactions involving four components (A + B ⇌ C + D) with various boiling point orders, which are of most industrial importance. The proposed systematic framework is validated through its application to five case studies, (trans-)esterifications presenting various separation challenges due to the formation of azeotropes. This novel approach offers a valuable aid for engineers in taking an educated go/no-go decision in the very initial stages of conceptual design, before performing any rigorous simulations of RD flowsheets.

Effect of boiling point rankings and feed locations on the applicability of reactive distillation to quaternary systems

Reactive distillation (RD) offers major benefits such as costs reduction and energy saving, but the understanding and design of RD processes usually demand complex tasks that include extensive studies and rigorous simulations. To reduce this complexity and the time required, this study applies a novel mapping method to quickly provide insights into the RD applicability to reversible quaternary systems (A + B ⇌ C + D). Generic cases are used to produce applicability graphs (i.e. plots of reflux ratio vs number of theoretical stages) and multiple RD column configurations. The systems are assumed to have ideal properties and fixed key parameters (i.e. relative volatilities and chemical equilibrium constants). This study focuses on quaternary reactions considering different boiling point rankings and feed locations. Using the mapping method, quick results are achievable regarding the preliminary economic ranking of RD processes and the optimal feed locations with reduced energy requirement (i.e. lower reflux ratio). Ultimately, this study provides a much better understanding of the effect of boiling point orders and feed locations on the RD applicability and conceptual design, being a valuable tool in early techno-economic evaluations.

Scanning Single-Molecule Fluorescence Correlation Spectroscopy Enables Kinetics Study of DNA Hairpin Folding with a Time Window from Microseconds to Seconds.

Single-molecule fluorescence measurements have been widely used to explore kinetics and dynamics of biological systems. Among them, single-molecule imaging (SMI) is good at tracking processes slower than tens of milliseconds, whereas fluorescence correlation spectroscopy (FCS) is good at probing processes faster than submilliseconds. However, there is still shortage of simple yet effective single-molecule fluorescence method to cover the time-scale between submilliseconds and tens of milliseconds. To effectively bridge this millisecond gap, we developed a single-molecule fluorescence correlation spectroscopy (smFCS) method that works on surface-immobilized single molecules through surface scanning. We validated it by monitoring the classical DNA hairpin folding process. With a wide time window from microseconds to seconds, the experimental data are well fitted to the two-state folding model. All relevant molecular parameters, including the relative fluorescence brightness, equilibrium constant, and reaction rate constants, were uniquely determined.

Addition of halogens and interhalogens on palladacyclopentadienyl complexes stabilized by pyridyl−thioether N−S spectator ligands

We have studied from the experimental and theoretical point of view the oxidative addition of halogens (I2 and Br2) and interhalogens (ICl and IBr) on palladiumcyclopentadienyl complexes bearing heteroditopic pyridyl−thioether spectator ligands.Addition of I2 or of a stoichiometric amount of Br2 to a CDCl3 solution of the starting palladacyclopentadienyl complexes yields the expected palladium−σ−butadienyl derivatives. The bromide derivative in the presence of a further excess of Br2 gives the wanted dibromo−(E, E)−σ−butadienyl and the pyridylthioether palladium(II) dibromide species. The rates of these reactions have been determined.When the interhalogens are used as oxidizing agents the thermodynamically hampered species is formed at first. Only in the case of the reaction of IBr is the formation of the energetically hampered derivative followed by partial isomerization to the most stable complex. The rate of isomerization and the related equilibrium constant between isomers have been measured. On the basis of the experimental evidence and the computational approach we have proposed a plausible energetic path yielding the first formed unexpected species.Finally, the solid state structures of two reaction products were resolved and reported.

Adsorptive removal of fluoride from aqueous solution using single- and multi-walled carbon nanotubes

In the present study, defluoridation study of liquid phase with the help of multi-walled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) were well investigated and elucidated. The impact of different experimental conditions such as solution pH, initial fluoride concentration, adsorbent dose, and contact time was well studied and optimized for the maximum fluoride removal from water. The experimental data were fitted by the Freundlich, Langmuir and Dubinin–Radushkevich (D–R) isotherm models and the related equilibrium constants were calculated. The results of the isotherm studies showed that fluoride removal by both adsorbents followed the Freundlich isotherm model. Kinetic studies were conducted and the results demonstrated that the experimental data were fitted well with the pseudo-second order kinetic model. Furthermore, two multiple regression-based equations were also derived to model the removal of fluoride from aqueous solutions by the carbon nanotubes. This study demonstrated that the polynomial equations satisfactorily described the behavior of the present defluoridation process for both MWCNTs (R2=0.913) and SWCNTs (R2=0.941).

A Thermodynamic Model for the Solubility Prediction of Barite, Calcite, Gypsum, and Anhydrite, and the Association Constant Estimation of CaSO4(0) Ion Pair up to 250 °C and 22000 psi

Mineral solubility predictions are critical for estimating scaling risks at conditions of high temperature, pressure, and ionic strength (IS) in mixed electrolytes which occur in various industrial processes. On the basis of the Pitzer theory, this study establishes a thermodynamic model to predict the solubilities and scaling risks of barite, calcite, gypsum, and anhydrite under these extreme conditions. This study combines the related equilibrium constants, virial coefficients, and the solubilities of these minerals from 0 °C to 250 °C, from 14.7 psi to 22000 psi, with up to 6 mol NaCl/kg H2O with or without mixed electrolytes to determine the temperature and pressure dependences of the following virial coefficients for Ca2+–SO42–, Ba2+–SO42–, Ba2+–Cl–, Na+–SO42–, and Ca2+–Br– binary interactions used in the Pitzer theory. Using these virial coefficients, the solubilities of these four minerals can be accurately predicted with no apparent temperature, pressure, or IS bias in solutions under the extreme ...

GATES as the Unique Tool for Simulation of Electrolytic Redox and Non-Redox Systems

The Generalized Approach to Electrolytic Systems (GATES), based on physical (charge conservation), physicochemical (conservation of elements) and chemical (mass action) laws is the best theory applicable for computer simulation of equilibrium, non-equilibrium and metastable, mono- and polyphase electrolytic redox and non-redox systems. The Generalized Electron Balance (GEB) concept, related to electrolytic redox systems, is put in context with the principle of conservation of all elements in electrolytic redox systems, with aqueous, non-aqueous or mixedsolvent media. Two equivalent approaches to GEB are presented, and termed as the Approach I and Approach II to GEB. The GEB, that enters GATES as GATES/GEB, is fully compatible with charge and concentration balances and completes the set of equations necessary for thermodynamic resolution of redox systems. Computer simulation of such systems is based on all attainable physicochemical knowledge involved in the related algorithm, solvable with use of an iterative computer program, and then presented graphically. This paper is referred mainly to dynamic redox systems, realized according to titrimetric mode. The speciation diagrams for dynamic redox systems are perceived as a reasonable alternative to (static) Pourbaix diagrams. The GEB concept, unknown before 1992, is perceived as the law of the matter conservation, as the general law of Nature. From the GATES viewpoint, the stoichiometric reactions are only the basis to formulate the related equilibrium constants. GATES is also the basis for Generalized Equivalence Mass (GEM) concept, formulated with none relevance to the stoichiometry of chemical reaction notation. From the GATES viewpoint, the stoichiometry is a superfluous concept.

Dipalladium(I) terphenyl diphosphine complexes as models for two-site adsorption and activation of organic molecules.

A para-terphenyl diphosphine was employed to support a dipalladium(I) moiety. Unlike previously reported dipalladium(I) species, the present system provides a single molecular hemisphere for binding of ligands across two metal centers, enabling the characterization and comparison of the binding of a wide variety of saturated and unsaturated organic molecules. The dipalladium(I) terphenyl diphosphine toluene-capped complex was synthesized from a dipalladium(I) hexaacetonitrile precursor in the presence of toluene. The palladium centers display interactions with the π-systems of the central ring of the terphenyl unit and that of the toluene. Exchange of toluene for anisole, 1,3-butadiene, 1,3-cyclohexadiene, thiophenes, pyrroles, or furans resulted in well-defined π-bound complexes which were studied by crystallography, nuclear magnetic resonance (NMR) spectroscopy, and density functional theory. Structural characterization shows that the interactions of the dipalladium unit with the central arene of the diphosphine does not vary significantly in this series allowing for a systematic comparison of the binding of the incoming ligands to the dipalladium moiety. Several of the complexes exhibit rare μ-η(2):η(2) or μ-η(2):η(1)(O or S) bridging motifs. Hydrogenation of the thiophene and benzothiophene adducts was demonstrated to proceed at room temperature. The relative binding strength of the neutral ligands was determined by competition experiments monitored by NMR spectroscopy. The relative equilibrium constants for ligand substitution span over 13 orders of magnitude. This represents the most comprehensive analysis to date of the relative binding of heterocycles and unsaturated ligands to bimetallic sites. Binding interactions were computationally studied with electrostatic potentials and molecular orbital analysis. Anionic ligands were also demonstrated to form π-bound complexes.

Study of Vitamin-B1 Interaction with Dihydroxyanthraquinone Dye and its Thermodynamic Elucidation

Interaction of Alizarin Red-S dye with thiamin (vitaminB1) was studied using spectrophotometric method at room temperature and neutral pH. The yellowish color appeared due to the Alizarin Red-S interaction with vitamin B1. According to the Benesi-Hildebrand equation, the related equilibrium constant, Kb, for the interaction has been determined and the Gibbs free energy of interaction has been calculated. Also the Benesi-Hildebrand equation has been used for assay of vitamin B1 in tablets. Results show that the method has good sensitivity for vitamin B1 and is in good agreement with HPLC method.

The Mechanism of the Porphyrin Spectral Shift on Inorganic Nanosheets: The Molecular Flattening Induced by the Strong Host–Guest Interaction due to the “Size-Matching Rule”

The mechanism inducing the unique absorption spectral shifts of porphyrin molecules upon adsorption on the clay surface was experimentally confirmed to be the flattening of the meso substituent with respect to the plane of the porphyrin ring. We investigated the spectral shift systematically by using seven types of porphyrin derivatives, differing in their center metal, meso substituent, and number of cationic sites. The aggregation, which usually induces the spectral shift, is suppressed in our clay/porphyrin systems. The adsorption strengths of porphyrin molecules on the clay surface were estimated as the relative adsorption equilibrium constants Krel. The seven types of porphyrins studied had different values of Krel, which can be explained by the steric effect and the Coulomb interaction due to the differences in the molecular structure. The obtained Krel values have interesting information of the photochemical property of the clay/porphyrin complexes. The absorption spectral shifts of the porphyrin Soret bands between those in the bulk solution and those on the clay surface are well related to Krel values. Like this, by the systematic experiments using the series of porphyrin derivatives, it was directly confirmed that the flattening of the molecule is the dominant mechanism for the spectral shift on the surface of inorganic nanosheets.

Intermolecular Migratory Insertion of Unactivated Olefins into Palladium–Nitrogen Bonds. Steric and Electronic Effects on the Rate of Migratory Insertion

We report a detailed examination of the effect of the steric and electronic properties of the ancillary ligand and the alkene reactant on the rate of migratory insertion of unactivated alkenes into the palladium-nitrogen bond of isolated palladium amido complexes. A series of THF-bound and THF-free amidopalladium complexes ligated by cyclometalated benzylphosphine ligands possessing varied steric and electronic properties were synthesized. The THF-free complexes react with ethylene at -50 °C to form olefin-amido complexes that were observed directly and that undergo migratory insertion, followed by β-hydride elimination to generate enamine products. The effect of the steric properties of the ancillary ligand on the binding of the alkene and the rate of migratory insertion were evaluated individually. The relative binding affinity of ethylene vs THF is larger for the less sterically hindered complex than for the more hindered complex, but the less hindered complex undergoes the insertion of ethylene more slowly than does the more hindered complex. These two changes in relative equilibrium and rate constants cause the rates of reaction of ethylene with the two THF-ligated species having different steric properties to be similar to each other. Reactions of the complexes containing electronically varied ancillary ligands showed that the more electron-poor complexes underwent the migratory insertion step faster than the more electron-rich complexes. Reactions of a THF-ligated palladium-amide with substituted vinylarenes showed that electron-poor vinylarenes reacted with the amido complex slightly faster than electron-rich vinylarenes. Separation of the energetics of binding and insertion indicate that the complex of an electron-rich vinylarene is more stable in this system than the complex of a more electron-poor vinylarene but that the insertion step of the bound, electron-rich vinylarene is slower than the insertion step with the bound, electron-poor vinylarene.

Expression and Characterization of Full-LengthAmpullaria crosseanEndoglucanase EG65s and Their Two Functional Modules

Three endoglucanase cDNAs, eg65a, eg65b, and eg65c, were cloned from the mollusk Ampullaria crossean in previous work. To characterize the full-length enzymes as well as their individual functional modules via heterologous expression analysis, the three full-length putative endoglucanases (rEG65a, rEG65b, and rEG65c) and the corresponding catalytic modules (EG65a-CM, EG65b-CM, and EG65c-CM) were expressed in Pichia pastoris GS115, and the three corresponding carbohydrate-binding modules (EG65a-CBM, EG65b-CBM, and EG65c-CBM) were expressed in Escherichia coli BL21 (DE3). The properties of recombinant rEG65b, EG65a-CM, EG65b-CM, and EG65c-CM were characterized. Binding assays of CBMs with insoluble polysaccharides indicated that both EG65b-CBM and EG65c-CBM bound to phosphoric-acid swollen cellulose (PASC), Avicel, and oat-spelt xylan, while EG65a-CBM did not. The relative equilibrium constants (K(r)) of EG65b-CBM and EG65c-CBM were determined by absorption isotherm measurements. In this study, the CBMs of animal cellulases were expressed and characterized for the first time.

Carboxylic groups in mesoporous silica and ethane-bridged organosilica: effect of the surface on the reactivity

Proton-donor ability of carboxylic groups incorporated by co-condensation into SBA-15 and ethane-bridged periodic mesoporous organosilica (PMO) has been studied through IR spectroscopy by dosing ammonia, which forms reversibly COO(-) groups and NH(4)(+) ions. The related equilibrium constants, determined by elaboration of IR data, reveal a lower reactivity of -COOH groups at the surface of PMO than on SBA-15, when the two samples have been outgassed at the same temperature. This finding is interpreted in terms of different dielectric constants and intermolecular interactions engaged with the surface species. Carboxylic groups on ethane-bridged organosilica react with silanols upon thermal treatment at 473 K to form a mixed anhydride species Si-O-C(O)-, at variance with the same groups on SBA-15.

High-Precision Measurement of Isotope Effects on Noncovalent Host−Guest Interactions

The self-assembled supramolecular host [Ga(4)L(6)](12-) can bind cationic guest molecules to both the interior and exterior of the host assembly through noncovalent interactions. Very small equilibrium isotope effects (EIEs) have been precisely measured for the association of benzyltrimethylphosphonium isotopologues to the host exterior surface by adapting an NMR titration method originally developed by the Perrin group for measuring isotope effects on acidity constants. Deuteration of the phosphonium methyl groups was found to have a larger EIE than deuteration at the ring and benzyl positions, suggesting subtle differences in the noncovalent interactions between the host exterior and different guest C-H/D bonds. The application of this method to the measurement of EIEs on noncovalent host-guest interactions demonstrates the generality of this NMR technique in precisely measuring relative equilibrium constants.

Dual Effect of Amino Modified Polystyrene Nanoparticles on Amyloid β Protein Fibrillation

The fibrillation kinetics of the amyloid β peptide is analyzed in presence of cationic polystyrene nanoparticles of different size. The results highlight the importance of the ratio between the peptide and particle concentration. Depending on the specific ratio, the kinetic effects vary from acceleration of the fibrillation process by reducing the lag phase at low particle surface area in solution to inhibition of the fibrillation process at high particle surface area. The kinetic behavior can be explained if we assume a balance between two different pathways: first fibrillation of free monomer in solution and second nucleation and fibrillation promoted at the particle surface. The overall rate of fibrillation will depend on the interplay between these two pathways, and the predominance of one mechanism over the other will be determined by the relative equilibrium and rate constants.