Shift In Equilibrium Research Articles

Evaluation of mass transfer behaviour of sulfamethoxazole species at ion–exchange membranes by chronopotentiometry for electrodialytic processes

In recent years, electrodialysis has been often considered as an appropriate method to treat industrial and/or municipal wastewater containing pharmaceutically active compounds. However, the scarcity of information on the ion transport mechanisms through the membranes, especially concerning occurrence of possible sorption phenomena, has limited the process implementation in practice. The present work aims to evaluate, by chronopotentiometry, the transport of sulfamethoxazole (SMX) through a cation- (CEM) and anion-exchange membrane (AEM) using synthetic solutions at different concentrations (0.001–0.1 g/L) and pH conditions (1.6 for CEM and 9 for AEM). The dominant mechanism of mass transfer under overlimiting current conditions at each membrane/solution system was determined. The potential drop profile measured during and after application of current pulses, as well as the transition times obtained from the curves, showed that sorption occurs at/in both membranes, especially for the AEM. Besides, this phenomenon was reversible for the CEM and irreversible for the AEM under the conditions evaluated herein. The chronopotentiograms of the AEM showed that the intense occurrence of water dissociation with the most diluted solution caused chemical equilibrium shifts in the membrane/electrolyte system, leading to formation of neutral SMX species that can impair the electrodialysis performance. The results obtained are useful for optimizing the electrodialytic treatment of SMX-containing solutions as well as of other compounds with similar physicochemical properties.

Delineating the conformational landscape of cannabinoid receptor 1 (CB1R) using gaussian accelerated molecular dynamics and network analysis.

The cannabinoid receptor 1, CB1R, is a class A GPCR implicated in various disease states, including pain and inflammation. Interestingly, both the agonists, which can alleviate pain, and the antagonists, which can lead to appetite suppression in obese patients, have substantial therapeutic benefits. Crystal structures for the CB1R have also been determined in the inactive and active states. However, the role of these ligands in stabilizing these different states and how they contribute to this shift in equilibria is relatively unknown. The free energy surface for these transitions has also not been determined. Using Gaussian Accelerated MD, we have explored the different conformational states of the CB1R, exploring both the effects of orthosteric and allosteric ligands on the free energy landscape. Furthermore, we have analyzed the residue contacts and performed network analysis to determine the information flow pertinent to the transition between states. The results provide unprecedented insights into the activation of CB1R, and the critical residues involved in this process. These results can help to guide structure-based drug design where potential drugs can be evaluated on their ability to stabilize a preferred conformation of the receptor of focus.

Promoting Molecular Exchange on Rare-Earth Oxycarbonate Surfaces to Catalyze the Water–Gas Shift Reaction

It is highly desirable to fabricate an accessible catalyst surface that can efficiently activate reactants and desorb products to promote the local surface reaction equilibrium in heterogeneous catalysis. Herein, rare-earth oxycarbonates (Ln2O2CO3, where Ln = La and Sm), which have molecular-exchangeable (H2O and CO2) surface structures according to the ordered layered arrangement of Ln2O22+ and CO32- ions, are unearthed. On this basis, a series of Ln2O2CO3-supported Cu catalysts are prepared through the deposition precipitation method, which provides excellent catalytic activity and stability for the water-gas shift (WGS) reaction. Density functional theory calculations combined with systematic experimental characterizations verify that H2O spontaneously dissociates on the surface of Ln2O2CO3 to form hydroxyl by eliminating the carbonate through the release of CO2. This interchange efficiently promotes the WGS reaction equilibrium shift on the local surface and prevents the carbonate accumulation from hindering the active sites. The discovery of the unique layered structure provides a so-called "self-cleaning" active surface for the WGS reaction and opens new perspectives about the application of rare-earth oxycarbonate nanomaterials in C1 chemistry.

The Impact of Nε-Acryloyllysine Piperazides on the Conformational Dynamics of Transglutaminase 2

In addition to the classic functions of proteins, such as acting as a biocatalyst or binding partner, the conformational states of proteins and their remodeling upon stimulation need to be considered. A prominent example of a protein that undergoes comprehensive conformational remodeling is transglutaminase 2 (TGase 2), the distinct conformational states of which are closely related to particular functions. Its involvement in various pathophysiological processes, including fibrosis and cancer, motivates the development of theranostic agents, particularly based on inhibitors that are directed toward the transamidase activity. In this context, the ability of such inhibitors to control the conformational dynamics of TGase 2 emerges as an important parameter, and methods to assess this property are in great demand. Herein, we describe the application of the switchSENSE® principle to detect conformational changes caused by three irreversibly binding Nε-acryloyllysine piperazides, which are suitable radiotracer candidates of TGase 2. The switchSENSE® technique is based on DNA levers actuated by alternating electric fields. These levers are immobilized on gold electrodes with one end, and at the other end of the lever, the TGase 2 is covalently bound. A novel computational method is introduced for describing the resulting lever motion to quantify the extent of stimulated conformational TGase 2 changes. Moreover, as a complementary biophysical method, native polyacrylamide gel electrophoresis was performed under similar conditions to validate the results. Both methods prove the occurrence of an irreversible shift in the conformational equilibrium of TGase 2, caused by the binding of the three studied Nε-acryloyllysine piperazides.

Calculation of thermodynamic properties and transport coefficients of Ar-C-Si plasma

The compositions, thermodynamic properties and transport coefficients of the argon-carbon-silicon plasma at local thermodynamic equilibrium and local chemical equilibrium in temperatures range of 300－30000 K and pressure range of 0.1 to 10 atm and are different mixture ratios are investigated in this work. The condensed phases and Debye-Hückel corrections are both taken into account. The equilibrium component in gas phase is calculated by mass action law (Saha’s law and Gulberg-Waage’s law), Dalton’s partial pressure law, conservation of the elements and charge quasi-neutral equation, and at the same time the condensed species is calculated under the assumption of local phase equilibrium. Thermodynamic properties including density, enthalpy and specific heat are evaluated through a classical statistical mechanics approach. The transport coefficient calculations including viscosity, electrical conductivity, and thermal conductivity are carried out by using a third-order approximation (second-order for viscosity) of the Chapman-Enskog method. Collision integrals are obtained by using the relatively new data. The results show that the concentration and ratio of blend of C vapor and Si vapor can greatly affect the properties of the Ar plasma owing to the introduced C and Si vapor’ s own properties and their new reactions. While the pressure influences those properties through the shift of chemical equilibrium and the change of total number density. In addition, the introduction of condensed species leads the thermodynamic properties and transport coefficients of the lower temperature plasma to become almost the same as those of pure argon, and causes discontinuous points at phase-transition temperature. The final calculation results are in good agreement with those in the literature, and the slight difference in transport coefficient between them can be explained by the different selection of interaction potentials. The results are expected to provide reliable basic data for the numerical simulation of argon-carbon-silicon plasma.

RGB-LED-PHOTOMETER AND THE DIGITAL IMAGE-BASED METHOD USING A SMARTPHONE FOR CHEMISTRY AND PHYSICS TEACHING

This work describes the analysis of molecular spectroscopy in the UV/Vis region, as well as the study of transmittance, absorption, and reflectance phenomena in an undergraduate class using an LED (light emitting diodes)-photometer and digital image-based (DIB) method using a smartphone to compare with a benchtop spectrophotometer and literature data employing paired T-test for 95% confidence. The novelties of this work are focused on the use of simple, low-cost, and portable analytical instrumentation, based on an RGB-LED photometer and DIB using a smartphone, for teaching Chemistry to undergraduate classes. Moreover, discussions were held on concepts related to the Beer-Lambert law, spectroscopy, pH, equilibrium shift, and calculation for determining the equilibrium constant and pKa of bromothymol blue, which was used as proof of concept. The advantages are the use of low-cost instrumentation for teaching Chemistry, students’ access to concepts, such as radiation source, photodetector, transmittance calculation from analog data, regulation of the power of the light emitted by the LED, and details to understand the interaction between matter and light were described by undergraduate students in Physics and Chemistry throughout the course of Experiments in Thermodynamic and Chemical Equilibrium. The better understanding of theoretical concepts and the possibility of taking the RGB-LED-photometer and DIB instrumentation to schools, exhibitions, science fairs, and Chemistry teaching meetings were pointed out by students as the main advantages of the instrumentation and methods described.

Изучение реакции ионов Cu(II) с N-(бензоил)-N'-(фенилсульфонил)гидразином в аммиачных средах спектрофотометрическим методом

The reaction of complexation of N-(benzoyl)-N'-(phenylsulfonyl)hydrazine with Cu(II) ions in an ammonia medium has been studied. The absorption spectra of the reagent and its complex with Cu(II) ions have been recorded and analyzed. The optimal conditions for the formation of the complex compound were found: the pH range of complex formation; optimal time for color development; amount of photometric reagent. Under optimal conditions for the complex formation of BPSH with Cu(II) ions, a calibration graph was constructed. The Bouguer-Lambert-Beer law is fulfilled in the range from 0,5 to 1,75 mg Cu(II) in 25 ml of solution. The true (19389) and apparent (4708) molar light absorption coefficients were calculated. The methods of saturation, equilibrium shift, curve intersection, isomolar series, and conductometric titration were used to determine the molar ratios in a solution of a complex compound – [Сu(II)]:[BFSH] = 1:1 and 1:2. According to the Babko method, the conditional stability constant of the complex was calculated – 2,45∙1013. The convergence and correctness of the spectrophotometric technique were determined by the method of mathematical statistics.

Zwitterion-neutral form equilibria and binding selectivity of pyridineboronic acids.

A 11B NMR study of 3-pyridineboronic acid at variable pH in water and 50 vol% aqueous dioxane confirms that the tautomeric equilibrium of the acid is shifted to the zwitterionic form in water, but to the molecular form in the mixed organic solvent. Interactions of 3- and 4-pyridineboronic acids with sialic acid, fructose and several other diols were studied by potentiometric titrations in a wide range of pH in water and water-organic mixtures. In all reaction media the stability of boronate complexes increases upon an increase in pH for neutral low acidic diols such as fructose and glucose but has the opposite trend for highly acidic sialic and lactic acids occurring as anionic species. The selectivity of pyridineboronic acids to sialate anions in an acidic medium is interpreted quantitatively by combining the pH-profiles with Brønsted type correlations for binding constants. In addition, mathematical expressions allowing one to predict the optimum pKa value of a boronic acid for the strongest binding of a given diol (sialic acid or fructose) at a given pH are suggested. The shifts in the tautomeric equilibrium induced by changing the solvent polarity in aqueous-organic mixtures are manifested in the magnitude of relative shifts of pKa of pyridineboronic acids induced by diol complexation.

PROCESS INTENSIFICATION FOR HYDROGEN PRODUCTION FROM AMMONIA

Ammonia is presented as one of the main carriers for the transport and storage of hydrogen under mild conditions. In this context, the present work introduces the integration and intensification of an ultrapure hydrogen production process from ammonia as a feedstock. A production scale is set to satisfy the requirements of a typical hydrogen refueling station (200 kgH2/day). A multifunctional shell-and-tube reactor is designed to carry out the ammonia cracking reaction. The system operates at a moderate pressure (8 bar) and in a temperature range for the ammonia decomposition reaction between 300 °C and 650 °C. Total ammonia conversion is achieved due to the chemical equilibrium shift by H2 extraction through the incorporation of 100 % selective membranes. The Pd-Ag membranes provide a recovery of about 86 % of the hydrogen produced. The remaining hydrogen (i.e., the non-permeated stream) is catalytically combusted representing the only source of heat of the entire process.

A novel analytical, bioanalytical and theoretical approach to the platinum(II)-3-hydroxy-2-(4-methoxyphenyl)-4H-chromen-4-one complex

A concise, ingenious and expedite extractive spectrophotometric procedure for the micro-level analysis of Pt(II) using the novel synthesized Ligand of flavonoids family, 3-hydroxy-2-(4-methoxyphenyl)-4H-chromen-4-one was elucidated by employing chelation as the basis of reaction between the two. The impetuous complexation and hence the chelation under basic conditions was revealed by the formation of dark brown coloured complex at an ambient pH of 8.79. The resulting brown coloured complex was extractable in non-aqueous organic solvents, the effectual and sensitive extraction and hence maximal colour intensity being exhibited in dichloromethane in the wavelength range 500–514 nm. The formed complex retained its adherence to the same colour intensity up to 5 days, thus validating its stability. The stoichiometric ratio as deduced by Job’s continuous variations, mole ratio and equilibrium shift methods of the formed Pt(II)-3-hydroxy-2-(4-methoxyphenyl)-4H-chromen-4-one complex was ascertained to be 1:2 (M:L).The coherence to linearity was meticulously discerned in the concentration range 0.42–1.48 ppm of platinum(II). The corresponding ocular and statistical parameters of the resultant stable Pt(II)- 3-hydroxy-2-(4-methoxyphenyl)-4H-chromen-4-one complex comprising of molar attenuation coefficient, Sandell’s sensitivity, %RSD, regression coefficient and limit of detection were evaluated as 7.1206×104 L/mol cm−1, 0.0027 µg cm−2,0.302 %, 0.9948 and 0.011 µg mL−1, respectively at 507 nm. To acquire a deeper knowledge of the complex's structural characteristics, theoretical investigations including Quantum theory of atoms in molecules and Natural bond orbital analysis were employed using Density functional theory calculations. The compound had been successfully used in therapeutic applications as an antibacterial, antioxidant and antineoplastic agent, in addition to its commercial analytical applicability.

On the concentration polarisation in molten Li salts and borate-based Li ionic liquids.

Electrolytes that transport only Li ions play a crucial role in improving rapid charge and discharge properties in Li secondary batteries. Single Li-ion conduction can be achieved via liquid materials such as Li ionic liquids containing Li+ as the only cations because solvent-free fused Li salts do not polarise in electrochemical cells, owing to the absence of neutral solvents that allow polarisation in the salt concentration and the inevitably homogeneous density in the cells under anion-blocking conditions. However, we found that borate-based Li ionic liquids induce concentration polarisation in a Li/Li symmetric cell, which results in their transference (transport) numbers under anion-blocking conditions (tabcLi) being well below unity. The electrochemical polarisation of the borate-based Li ionic liquids was attributed to an equilibrium shift caused by exchangeable B-O coordination bonds in the anions to generate Li salts and borate-ester solvents at the electrode/electrolyte interface. By comparing borate-based Li ionic liquids containing different ligands, the B-O bond strength and extent of ligand exchange were found to be directly linked to the tabcLi values. This study confirms that the presence of dynamic exchangeable bonds causes electrochemical polarisation and provides a reference for the rational molecular design of Li ionic liquids aimed at achieving single-ion conducting liquid electrolytes.

Designing Small-scale Chemistry for General Chemistry Practical Work Course

Hands-on chemistry activity or practical work is an important aspect of teaching at the high school and college level as part of the science education curriculum. This study aims to design Small-scale Chemistry (SSC) for general chemistry practical work. The product are laboratory work manual and practical kit. The development model used is ADDIE model (Analysis, Design, Development, Implementation, and Evaluation). At the analysis stage, five experiment will be designed to become SSC. There are five experiments, namely determining the order of the reaction, observation the shift in chemical equilibrium, identification acid-base with indicators, determining the strength of the acid and water electrolysis. The feasibility of the manual and practical kit in content feasibility (0.84), language feasibility (0.90), presentation feasibility (0.84), graphic feasibility (0.90), and kit feasibility (0.94). All are categorized as valid based on the validity criteria of Aiken's V. The results of the implementation show that the SSC design can be implemented and the results can be observed for General Chemistry experiment learning activities. The chemicals used for the experiment are far less than the macro-scale practical work. This is in accordance with the SSC principle.

Probing the Size Limit of Dispersion Energy Donors with a Bifluorenylidene Balance: Magic Cyclohexyl.

We report the synthesis of 14 2,2'-disubstituted 9,9'-bifluorenylidenes as molecular balances for the quantification of London dispersion interactions between various dispersion energy donors. For all balances, we measured ΔGZ/E at 333 K using 1H NMR in seven organic solvents. For various alkyl and aryl substituents, we generally observe a preference for the "folded" Z-isomer due to attractive London dispersion interactions. The cyclohexyl-substituted system shows the largest Z-preference in this study with ΔGZ/E = -0.6 ± 0.05 kcal mol-1 in all solvents, owing to the rotational freedom of cyclohexyl groups paired with their large polarizability that maximizes London dispersion interactions. On the other hand, rigid and sterically more demanding substituents like tert-butyl unexpectedly favor the unfolded E-isomer. This is a result of the close relative position in which the functional groups are positioned in this molecular balance. This close proximity is the reason for the increase of Pauli repulsion in the Z-isomers with large rigid substituents (tert-butyl, adamantyl, and diamantyl) which leads to an equilibrium shift toward the unfolded E-form. While we were able to reproduce most of our experimental trends qualitatively using contemporary computational chemistry methods, quantitative accuracy of the employed methods still needs further improvement.

Preparation and characterization of oriented hydroxyapatite bundles in supersaturated solution: ionic interference and charge balance

Hydroxyapatite (HA), an artificial bioceramic with high similarity to the mineral constituent of vertebrate bones and teeth, has attracted extensive attention due to its excellent bioactivity and biocompatibility. The micro-nano structure of HA is a vital factor in expanding its application in biomedicine as well as in many other industrial fields. What's more, HA nanofiber exhibits outstanding properties among its various morphologies. In this work, HA bundles with the same oriented nanofibers are successfully synthesized in a solvothermal reaction system by controlling the amount of carbonate addition and using oleic acid as a template. Under the synergistic effect of different molar ratios of hydroxide ion to carbanion ([OH−]/[CO32−]), HA nanofibers gradually increase their aspect ratio and tend to grow into oriented bundles. This product has admirable flexibility and good mechanical strength, as well as great application potential. Based on the characterization and analysis results, we take a further exploration of the effects of ionic interference ([OH−]/[CO32−]) and charge balance (CO32− vs PO43, Na + vs Ca2+) on the microstructure, phase composition and thermal stability of HA nanofibers bundles (HANBs) in the solvothermal system during the chemical reaction process. And then, the formation and assembly mechanism of HANBs is proposed, and the role of van der Waals forces in this process is also discussed. Furthermore, the generation of this clustered state may be influenced by the shift in the dissolution equilibrium of insoluble carbonates during synthesis. This research provides a new direction for controlling the micro-nano morphology of HA to further obtain products with desirable properties.

Concurrent production and purification of glycolic acid from mixed esters via selective hydrolysis reactions catalyzed and thermodynamically promoted by MgO

Methyl glycolate (MG) in the presence of methyl levulinate (MLE) was selectively converted into magnesium glycolate via MgO-mediated hydrolysis reactions under mild conditions. The conversion of MG reached 95.2% while that of MLE was 15.1%, with reaction selectivity of 100%. After facile isolation procedures, the magnesium glycolate was readily transformed into glycolic acid, monomer of biodegradable plastic, with recovery rate of 90.2%. The basic sites with medium strength on MgO dominated the catalytic activity. The precipitation of magnesium glycolate led to the shift of chemical equilibrium for MG hydrolysis. DFT calculation results showed that the energy barriers for MG hydrolysis were smaller than those for MLE hydrolysis by 46–47 kJ/mol. Both the shift of chemical equilibrium and lower energy barriers contributed to the much higher reactivity of MG compared to MLE. This paper sheds light on the selective hydrolysis of esters and complete hydrolysis of an ester.

The Effect of Terminal Bromoalkoxy Substituents on the Photochromism of Functionalized 2H‐Chromenes

AbstractA series of 2,2‐diphenyl‐2H‐chromene derivatives bearing electron‐donating groups at the benzopyran ring have been synthesized. A significant effect of the bromoalkoxy chain length and the concentration of chromenes on the conversion of closed (CF) into open forms under UV irradiation and the equilibrium between TC (transoid‐cis) and TT (transoid‐trans) isomers in the photostationary state was found. For chromene derivatives, a sequential (CF→TC→TT) or parallel (CF→TC; CF→TT) mechanism of transformation of the closed form into an open one is possible. A high solution concentration contributes to a significant shift of the photochromic equilibrium towards the TT isomer. The proposed scheme of the ring‐opening reaction was confirmed by the analysis of the NMR spectra of acetonitrile solutions of chromene derivatives obtained by gradual irradiation. The results obtained are important for a deeper understanding of the nature of photochromic reactions.

EXTRACTION AND ATOMIC-ABSORPTION DETERMINATION OF TUNGSTEN (VI) WITH 2-HYDROXY-5-T-BUTYLPHENOL-4'-NITROAZOBENZENE

The complexation of tungsten (VI) with an azo compound synthesized from para-tret-butylphenol (2-hydroxy-5-Tr-butylphenol-4-nitro-asobenzene) has been studied spectrophoto¬metrically. The optimum pH values of the solution are 2.0-3.0. The maximum light absorption of the complexes in n-butanol is in the range 460-470nm, and that of the reagent at 360-370; complex formation is accompanied by a bathochromic shift. The spectrophotometric characteristics of the complex have been calculated and the composition of the complex was determined by various methods. Using the equilibrium shift and isomolar series methods it has been found that the W:R ratio is 1:2. By the Sommer method it has been found that during complex formation one proton is released from each reagent molecule. The complex stability constant βk = 9.04·108 and the complex formation reaction equilibrium constant (4.2·104) have been calculated by the method of Komar. The molar absorption coefficient is (3.44.2).104. The graduation diagram is linear at a tungsten concentration of 1.0-10 µg/ml, n-butanol has been used as an extractant. A single extraction with n-butanol 97% of tungsten as a complex is extracted. Methods of extraction-atomic-absorption and extraction-photometric determination of tungsten have been developed and the influence of a number of extraneous ions on the determination of tungsten has been revealed. The correctness of the results obtained has been controlled by analysing the State Standard Alloy Reference Materials

EMReact: a tool for modelling electromagnetic field induced effects in chemical reactions by solving the discrete stochastic master equation

The effects of electromagnetic fields (EMF) have been widely debated concerning their role in chemical reactions. Reactions, usually took hours or days to complete, have been shown to happen a thousand times faster using EMF radiations. This work develops a formalism and a computer program to evaluate and quantify the EMF effects in chemical reactions. The master equation employed in this program solves the internal energy of the reaction under EMFs while including collisional effects. Multiphoton absorption and emission are made possible with the transitioning energy close to the EMF and are influenced by the dielectric properties of the system. Dimethyl Sulfoxide and Benzyl Chloride are simulated under different EMF intensities. The results show that EMF absorption is closely related to the collisional redistribution of energy in molecules. The EMF effect can be interpreted as a shift of the thermodynamic equilibrium. Under such nonequilibrium energy distribution, the ‘temperature’ is not a reliable quantity for defining the state of the system.

Approach for the Description of Chemical Equilibrium Shifts in the Systems with Free and Connected Chemical Reactions

Approach for the description of chemical equilibrium shifts in the systems with free and connected chemical reactions was elaborated. Driving forces of chemical equilibrium shifts were temperature change (at P = const), pressure change (at T = const), and input or output of reagents or products (at T, P = const). It was demonstrated how the conditions for passing through the extremes of the state parameters (T, P, and components molar numbers) in one of the reactions transmitted to other reactions, connected with the first one by reagents or products.

Advancement of Electrochemical Thermoelectric Conversion with Molecular Technology

AbstractThermocells are a thermoelectric conversion technology that utilizes the shift in an electrochemical equilibrium arising from a temperature difference. This technology has a long history; however, its low conversion efficiency impedes its practical usage. Recently, an increasing number of reports have shown drastic improvements in thermoelectric conversion efficiency, and thermocells could arguably represent an alternative to solid thermoelectric devices. In this Minireview, we regard thermocells as molecular systems consisting of successive molecular processes responding to a temperature change to achieve energy generation. Various molecular technologies have been applied to thermocells in recent years, and could stimulate diverse research fields, including supramolecular chemistry, physical chemistry, electrochemistry, and solid‐state ionics. These research approaches will also provide novel methods for achieving a sustainable society in the future.