Equilibria In Aqueous Solutions Research Articles

Adsorption Equilibrium, Kinetics, and Column Breakthrough Data for Aqueous Solutions of Binary-Acid and Ternary-Acid Mixtures of Acetic Acid, Butyric Acid, and Lactic Acid on IRN-78 Ion-Exchange Resin at Initial pH Levels of ∼3–7 and at 25–55 °C

Adsorption Equilibrium, Kinetics, and Column Breakthrough Data for Aqueous Solutions of Binary-Acid and Ternary-Acid Mixtures of Acetic Acid, Butyric Acid, and Lactic Acid on IRN-78 Ion-Exchange Resin at Initial pH Levels of ∼3–7 and at 25–55 °C

(Invited) Electrolyte Engineering for Disruptive Cost Reduction of Electrolyzer: Hydrogen Generation from Dense Carbonate Buffer Solution

Water electrolysis using renewable electricity is a key process for generating green hydrogen, a crucial element in the pursuit of a sustainable society. To make substantial strides in lowering the cost of green hydrogen, it is imperative to address not only the expense of the electricity involved but also the cost associated with the electrolyzer itself [1]. The current challenge lies in the materials chosen for electrolyzers operating under extreme acidic or alkaline conditions, which necessitate the use of costly corrosion-resistant components. A viable solution involves considering non-extreme pH water as an electrolyte, allowing for the utilization of affordable and readily available materials, such as iron or stainless steel, in key electrolyzer components like the frame or bipolar plate [2]. Despite the reported inferior performance of non-extreme pH electrolysis compared to extreme pH conditions, primarily due to inevitable pH shifts (resulting in concentration overpotential) and elevated solution resistance, advancements in technology and research hold the potential to overcome these challenges.Our research group has been actively engaged in the exploration of electrolyte engineering, a concept centered on optimizing the diffusion flux of buffer ions to mitigate the previously mentioned challenges in non-extreme pH conditions [3,4]. Our approach involves leveraging a dense buffer solution to maximize the flux of buffer ions, resulting in a significant reduction in concentration overpotential. This strategy becomes even more impactful when the operating temperature is elevated to the commercially viable range of 80-100 °C [5]. The synergistic effect of employing a dense buffer solution, combined with elevated temperatures, proves to be a promising avenue for advancing electrolyte engineering and optimizing the performance of electrolysis systems in non-extreme pH conditions. In this presentation, we will delve into our discoveries concerning non-noble metal electrocatalysts, specifically focusing on their efficacy in both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER).Our research has led us to identify transition metal-based electrocatalysts that demonstrate exceptional efficiency in catalyzing OER within a carbonate buffer electrolyte at near-neutral pH [6]. Among the diverse materials we explored, the iron-nickel composite, coupled with copper or gold on electrochemically activated Ni (ECA-Ni) substrates [7], stands out as a superior performance. Notably, these electrodes exhibited a remarkable OER catalysis rate of 1 A cm−2 and an overpotential of approximately 330 mV, becoming competitive with highly alkaline counterpart.Next, our research has uncovered noteworthy electrocatalysts based on copper and molybdenum, demonstrating exceptional efficiency in catalyzing the hydrogen evolution reaction (HER) within a carbonate buffer electrolyte at pH 10.5 [8]. The most promising sample achieved a current density of 1 A cm−2 at an overpotential of approximately 0.2 V, a performance comparable to previously reported HER results in highly alkaline conditions. Detailed characterization of these electrocatalysts unveiled that the addition of copper resulted in a rougher surface structure, contributing to the largest double-layer capacitance. These characteristics are indicative of an enlarged active surface area, which is pivotal for enhanced catalytic activity. Furthermore, the introduction of copper element correlated with a decreased apparent Tafel slope, suggesting a tailored nature of the active sites. These insights not only shed light on the structural modifications induced by copper but also underscore its role in optimizing the electrocatalytic performance.Finally, we integrated the previously developed HER and OER catalysts with a carefully selected polyether sulfone (PES) diaphragm [8]. This strategic combination resulted in a notable enhancement of overall cell performance within a 3.0 mol kg− 1 K-carbonate solution at pH 10.5 and a temperature of 353 K. The resultant cell performance, factoring in the series resistance, achieved a 1 A cm− 2 at a voltage of approximately 2.0 V. This achievement stands competitively against the top-class commercial alkaline electrolyzers. These findings not only highlight the feasibility of non-extreme pH electrochemical electrolyzers in industrial applications but also underscore the potential for further advancements and optimizations. The demonstrated success serves as a compelling indicator of the viability of our approach and opens avenues for refining non-extreme pH electrolysis for even greater efficiency and applicability in industrial settings.Reference[1] M. Chatenet, et al., Chem. Soc. Rev. 2022, 51, 4583.[2] M. Pourbaix, “Atlas of Electrochemical Equilibria in Aqueous solutions”, 1974.[3] T. Shinagawa and K. Takanabe, ChemSusChem 2017, 10, 1318.[4] T. Shinagawa et al., ChemCatChem 2019, 11, 5961.[5] T. Naito, et al., ChemSusChem 2022, 8, e202102294.[6] T. Nishimoto, et al., ChemSusChem 2022, e202201808.[7] T. Shinagawa, et al., Angew. Chem. Int. Ed. 2017, 56, 5061.[8] T. Nishimoto, et al., ACS Catal. 2023, 13, 14725.

Quantum chemical package Jaguar: A survey of recent developments and unique features.

This paper is dedicated to the quantum chemical package Jaguar, which is commercial software developed and distributed by Schrödinger, Inc. We discuss Jaguar's scientific features that are relevant to chemical research as well as describe those aspects of the program that are pertinent to the user interface, the organization of the computer code, and its maintenance and testing. Among the scientific topics that feature prominently in this paper are the quantum chemical methods grounded in the pseudospectral approach. A number of multistep workflows dependent on Jaguar are covered: prediction of protonation equilibria in aqueous solutions (particularly calculations of tautomeric stability and pKa), reactivity predictions based on automated transition state search, assembly of Boltzmann-averaged spectra such as vibrational and electronic circular dichroism, as well as nuclear magnetic resonance. Discussed also are quantum chemical calculations that are oriented toward materials science applications, in particular, prediction of properties of optoelectronic materials and organic semiconductors, and molecular catalyst design. The topic of treatment of conformations inevitably comes up in real world research projects and is considered as part of all the workflows mentioned above. In addition, we examine the role of machine learning methods in quantum chemical calculations performed by Jaguar, from auxiliary functions that return the approximate calculation runtime in a user interface, to prediction of actual molecular properties. The current work is second in a series of reviews of Jaguar, the first having been published more than ten years ago. Thus, this paper serves as a rare milestone on the path that is being traversed by Jaguar's development in more than thirty years of its existence.

ALIGNMENT BETWEEN CURRICULUM STANDARDS AND ASSESSMENT IN UNDERSTANDING CHEMICAL REACTION PRINCIPLES AT UPPER-SECONDARY SCHOOLS

This study utilized the SEC (Survey of Enacted Curriculum) method to examine the alignment between Chinese high school chemistry curriculum standards (HSCCS) and the assessment of ‘Chemical Reaction Principles’ in the National College Entrance Examinations (NCEEs). The HSCCS and NCEEs were coded into two-dimensional matrices separately using SPSS, MATLAB, and EXCEL. The alignment coefficients were analyzed both macroscopically and specifically based on two dimensions: themes and cognitive levels. The findings indicated a generally low alignment between NCEEs and HSCCS in the ‘Chemical Reaction Principles’ domain, and no statistically significant alignment was observed. Comparing Porter alignment coefficients revealed a gradual increase in the overall alignment level between 2018–2022 NCEEs and HSCCS due to curricular reforms. Further specific analyses and comparisons highlighted significant discrepancies between NCEEs and HSCCS concerning themes and cognitive levels. Regarding themes, ‘Ionic Reactions and Equilibrium in Aqueous Solutions’ showed substantial alignment between NCEEs and HSCCS. However, for ‘Application of Ionic Reactions and Equilibrium’ and ‘Systems and Energy,’ NCEEs diverged significantly from or exceeded HSCCS requirements. Concerning cognitive levels, NCEEs demanded higher levels of student cognition compared to HSCCS. Keywords: alignment, chemical reaction principles, content analysis, curriculum standards, upper-secondary schools

Specific Amino Acid Residues in the Three Loops of Snake Cytotoxins Determine Their Membrane Activity and Provide a Rationale for a New Classification of These Toxins.

Cytotoxins (CTs) are three-finger membrane-active toxins present mainly in cobra venom. Our analysis of the available CT amino acid sequences, literature data on their membrane activity, and conformational equilibria in aqueous solution and detergent micelles allowed us to identify specific amino acid residues which interfere with CT incorporation into membranes. They include Pro9, Ser28, and Asn/Asp45 within the N-terminal, central, and C-terminal loops, respectively. There is a hierarchy in the effect of these residues on membrane activity: Pro9 > Ser28 > Asn/Asp45. Taking into account all the possible combinations of special residues, we propose to divide CTs into eight groups. Group 1 includes toxins containing all of the above residues. Their representatives demonstrated the lowest membrane activity. Group 8 combines CTs that lack these residues. For the toxins from this group, the greatest membrane activity was observed. We predict that when solely membrane activity determines the cytotoxic effects, the activity of CTs from a group with a higher number should exceed that of CTs from a group with a lower number. This classification is supported by the available data on the cytotoxicity and membranotropic properties of CTs. We hypothesize that the special amino acid residues within the loops of the CT molecule may indicate their involvement in the interaction with non-lipid targets.

Thermal stability and vapor-liquid equilibrium of aqueous solutions of choline and tetramethylammonium taurate

The thermal degradation of tetramethylammonium taurate and choline taurate and aqueous solutions of these compounds were examined. The thermal degradation products for each of the solid compounds are identified and the data show that the compounds lose less than 1 % of their mass when heating is below 85 °C for 10 h. However, it is difficult to distinguish between the degradation of the compounds and the loss of strongly retained water. The degradation products of the compounds in aqueous solution are also identified and a degradation pathway is proposed. Additionally, the vapor–liquid equilibrium of the compounds in aqueous solutions was measured and the data was fit to the non-random two-liquid (NRTL) model. The data indicate significant deviations from ideality as described by the activity coefficients of the solutions. The results provide insight into the selection of absorber stripping temperatures, the modeling of absorber columns that utilize aqueous ionic absorber fluids, and how these properties are impacted by different cations.

Development of environmentally-friendly modified bioadsorbents for water treatment

As a result of scientific research, it was found that synthesized pure sorbents based on a composite of Fe3O4 nanoparticles and AlgBT have an increased adsorption capacity due to the inclusion of double hydroxides and an alginate matrix. The processes of complex formation occur according to the principle of maximum inheritance of the structural features of the original coordination compounds, which make it possible to predict and implement the hypothetical structures of new compounds. All this significantly improves the adsorption capacity of the developed adsorbents with respect to phosphate ions. Modified sorbents with a clay basis are therefore a particularly intriguing field. The current research constructed and described modified sorbents, and then conducted tests in the laboratory to determine how well they absorbed phosphate. This study used spectroscopic techniques (SEM, FTIR, X-ray diffraction, and XRD analytical methods) to examine the structure and physicochemical characteristics of improved ecologically friendly sorbents based on alginates, bentonite, and nanoparticles. The alginate core may be physically and chemically modified and can take part in a variety of phosphate anion adsorption methods thanks to the active COOH and OH groups that are present there. The sorption efficiency was established for a modified Fe3O4NPs@AlgBT. Equilibrium in the system sorbent-an aqueous solution of Na2HPO4 is established in 10 hours after the start of sorption, while two-thirds of all sobbed anions pass into the solid phase during the first two hours. The limiting sorption of phosphate ions on modified Fe3O4NPs@AlgBT reaches 410 mg/g, which makes it possible to offer it as an effective sorbent for industrial wastewater treatment

Electrochemical Activation of NiFe2O4 for the Oxygen Evolution Reaction in Alkaline Media

Electrochemical H2 production via low temperature H2O electrolysis is a promising strategy to facilitate decarbonization across sectors;1 however, current high-performing proton exchange membrane (PEM) electrolyzers require the use of expensive and rare platinum-group metals (PGMs) for catalysts and hardware, limiting scale up feasibility.2 More recently, anion exchange membrane (AEM) electrolyzers have emerged as an alternative strategy, combining the zero-gap approach employed by PEM with operation in an alkaline environment where many non-PGMs are thermodynamically stable.3 In fact, oxides of first row transition metals including Ni, Fe, and Co have been proposed as promising anode catalyst alternatives to IrO2 in AEM electrolyzers.4–7 However, these materials suffer from high overpotentials (> 300 mV @ 10 mA/cm2)8 and kinetic improvements are needed to facilitate the deployment of this technology.Ni-Fe oxides have gained particular attention due to their high ex-situ activities and typically low material criticality compared to IrO2 or other non-PGMs such as Co.9 Ni and Fe are known to have a synergistic effect, with trace amounts of Fe in Ni catalysts leading to increased OER activity.10 However, the mechanism behind the improved performance and the optimal Fe content is heavily debated in the literature;11 for example, this activity enhancement has been attributed to increased electrical conductivity with increasing Fe content,10 stabilization of the Ni4+ state,12 and a shift of the Ni (II/III) redox couple.13 Furthermore, these studies have evaluated Ni-Fe catalysts in their metallic or oxy(hydroxide) forms, although device-level conditioning may passivate near-surfaces and minimize performance differences between catalysts with difference ex-situ oxide content.14 Uncovering how Fe content changes over time-on-stream for nanoparticle oxides and correlating this to changes in activity is needed to facilitate optimization of these materials at the device level. To this end, this work evaluated the stability of NiFe2O4 nanoparticles (30 nm) in alkaline environments, correlating changes in Fe composition to changes in activity. All tests were performed in a rotating disc electrode cell with Au working electrode (0.193 cm2), Au counter electrode, and reversible hydrogen reference electrode. Tests were performed in 0.1 M NaOH electrolyte at room temperature with a catalyst loading of 17.8 μgM/cm2.We found that the activity of NiFe2O4 improved over time-on-stream (+ 80 % in current at 1.65 V after 13.5 h) concurrent with a dissolution of Fe (2 – 8 wt% Fe loss). We hypothesize that the Fe content in NiFe2O4 (48 wt% Fe) was prohibitively high, and that dissolution of Fe shifted this value closer to optimum, resulting in higher activity. For NiFe (oxy)hydroxide materials, optimal Fe content has been reported at 15 - 25 wt% Fe.10 However, this value likely changes depending on the structure of the material and, relatedly, the relative abundances of Ni and Fe on the surface. We further looked at the effect of longer time on stream at 1.8 V (13.5 h – 27 h) and potentiodynamic cycling (1.4 - 1.8 V, 1.4 – 2.0 V, 0.0 – 2.0 V; 13.5 h) on NiFe2O4 stability. The results, in turn, showed that catalyst reactivity for OER improved over time-on-stream by 50 – 80% for potentiostatic holds and by upwards 500% for cycling tests (Fig. 1). This activity improvement was found to be concurrent with Fe dissolution (determined from ICP-MS), which ranged from 2 – 8 wt% Fe loss for the potentiostatic stress test to upwards of 40 wt% Fe loss for the cycling tests. Increased time on stream (13.5 – 27 h) was found to not significantly impact the activity enhancement. These results show a correlation between Fe dissolution and activity improvement and suggest that the activity of nanoparticle NiFe2O4 oxides may be electrochemical activated via this method, providing new insights into the viability of NiFe oxides as alternatives to IrO2 for OER.[1] Borup et al., Electrochem. Soc. Interface 2021, [2] IRENA Green Hydrogen Cost Reduction - Scaling up Electrolyzers to Meet the 1.5C Climate Goal 2020, [3] Pourbaix, Atlas of Electrochemical Equilibria in Aqueous Solutions, 1974, [4] Suen et al., Chem. Soc. Rev. 2017, [5] Plevová et al., J. Power Sources 2021, [6] Burke et al., Chem. Mater. 2015, [7] Anderson et al., J. Electrochem. Soc. 2020, [8] McCrory et al., J. Am. Chem. Soc 2015, [9] European Commission, Report on Critical Raw Materials for the EU 2018, [10] Trotochaud et al., J. Am. Chem. Soc. 2014, [11] Anantharaj et al., Nano Energy 2021, [12] Li et al., Proc. Natl. Acad. Sci. 2017, [13] Görlin et al., J. Am. Chem. Soc. 2016, [14] Alia et al., J. Electrochem. Soc. 2019 Figure 1

Activating Nickel-Molybdenum Electrocatalyst Via Copper-Element Modification Toward 1 A cm−2 Hydrogen Evolution in Non-Extreme pH Carbonate Buffer Electrolyte

Water electrolysis driven by renewable electricity produces green hydrogen, which will play a pivotal role in realizing a sustainable society. However, the production cost of green hydrogen is currently $5.3/kg, nearly four times higher than $1.4/kg of grey hydrogen,[1] which necessitates the reduction of green hydrogen cost toward its large-scale deployment. While reducing electrolyzer cost is one of the key interventions,[2] extremely acidic or alkaline conditions in currently commercialized electrolyzers require expensive corrosion-tolerant materials as the components, which hinders further reduction of electrolyzer cost. In this sense, non-extreme pH water electrolyzer can be innovative technology because its milder conditions than those in currently commercialized electrolyzers potentially enable the use of cheap and abundant materials (such as Fe or stainless steel) as electrolyzer components (such as frame or bipolar plate),[3] which can reduce the electrolyzer cost and, in the end, production cost of green hydrogen. Non-extreme pH electrolysis was reported to suffer inferior performance compared to those in extreme pH conditions.[4] However, our previous study using nickel and iron-based anode in potassium carbonate buffer solution at pH 10.5 achieved high oxygen evolution reaction (OER) performances comparable to those of highly alkaline OER,[5] which should be followed by the development of highly effective cathode for hydrogen evolution reaction (HER) to realize the highly efficient non-extreme pH electrolyzer.The present study reports on our discovery of the nickel and molybdenum-based electrocatalysts that efficiently catalyze HER in carbonate buffer electrolyte at pH 10.5. First of all, visibly flat films of nickel (Ni), molybdenum oxide (MoOx), and nickel molybdenum oxide (NiMoOx) were prepared by cathodic electrodeposition on rotating disk electrodes. Their electrocatalytic testing revealed that, as in alkaline conditions, the coexistence of Ni and Mo is required to achieve high catalytic activity even in K-carbonate solution at pH 10.5. Subsequently, a variety of transition metal elements (manganese, cobalt, copper, and tungsten) were introduced into NiMoOx via co-electrodeposition onto Ni foam substrate to further enhance the HER performance. Among the developed electrodes, NiMoOx modified with copper element (NiMoOx(Cu)) was the best and achieved 1 A cm−2 at an overpotential of ca. 0.2 V, which is comparable to those of previously reported HER in highly alkaline conditions (Figure 1). Our characterization revealed that Cu addition into NiMoOx made the surface structure to be rougher and led to the largest double-layer capacitance, both of which indicate the enlarged active surface area. Besides, the presence of Cu element decreased the apparent Tafel slope, suggesting the tailored nature of active site, which was consistent with the shift of Ni and Mo peaks in ex situ X-ray photoelectron spectroscopy (XPS) analysis. Finally, combined with previously developed nickel and iron-based anode[5] and carefully selected polyether sulfone (PES) diaphragm, overall cell performance was elevated in 3.0 mol kg−1 K-carbonate solution at pH 10.5 and 353 K. The resultant cell performance including the series resistance achieved 1 A cm−2 at a voltage of merely ca. 2.0 V, competitive to those of top-class commercial alkaline electrolyzers. These findings demonstrate the potential of non-extreme pH electrochemical electrolyzers in industrial applications.Reference[1] “Finding the sea of green”, EDISON, 2021.[2] M. Chatenet, et al., Chem. Soc. Rev. 2022, 51, 4583.[3] M. Pourbaix, “Atlas of Electrochemical Equilibria in Aqueous solutions”, 1974.[4] T. Naito, et al., ChemSusChem 2022, 8, e202102294.[5] T. Nishimoto, et al., ChemSusChem 2022, e202201808. Figure 1

Growth rate of CO2 and CH4 hydrates by means of molecular dynamics simulations.

CO2 and CH4 hydrates are of great importance both from an energetic and from an environmental point of view. It is therefore highly relevant to quantify and understand the rate with which they grow. We use molecular dynamics simulations to shed light on the growth rate of these hydrates. We put the solid hydrate phase in contact with a guest aqueous solution in equilibrium with the pure guest phase and study the growth of both hydrates at 400 bars with temperature. We compare our results with previous calculations of the ice growth rate. We find a growth rate maximum as a function of the supercooling in all cases. The incorporation of guest molecules into the solid structure strongly decelerates hydrate growth. Consistently, ice grows faster than either hydrate and the CO2 hydrate grows faster than the CH4 one because of the higher solubility of CO2. We also quantify the molecular motion required to build the solids under study and find that the distance traveled by liquid molecules exceeds by orders of magnitude that advanced by any solid. Less molecular motion is needed in order for ice to grow as compared to the hydrates. Moreover, when temperature increases, more motion is needed for solid growth. Finally, we find a good agreement between our growth rate calculations and experiments of hydrate growth along the guest-solution interface. However, more work is needed to reconcile experiments of hydrate growth toward the solution among each other and with simulations.

Experimental Study and Modeling of the Liquid–Liquid and Solid–Liquid–Liquid Equilibrium of Aqueous Solutions Involving 1-Butanol and Xylitol at Different Temperatures

Experimental Study and Modeling of the Liquid–Liquid and Solid–Liquid–Liquid Equilibrium of Aqueous Solutions Involving 1-Butanol and Xylitol at Different Temperatures

Modeling phase equilibria and speciation in aqueous solutions of rare earth elements with hydroxide and organic ligands

A thermodynamic model has been developed for calculating speciation and phase equilibria in aqueous solutions of rare earth elements (REEs) with hydroxide, acetate, citrate, and oxalate anions. The computational framework is based on the Mixed-Solvent Electrolyte (MSE) framework, which has been previously used to establish a systematic treatment of binary and multicomponent systems containing REE sulfates and chlorides up to solid–liquid saturation at temperatures up to 300 °C. The model has been parametrized by performing a multi-property analysis of critically evaluated speciation and solubility data. For rare earth hydroxides, a comprehensive model has been developed for fourteen REEs (i.e., for yttrium and all lanthanides except promethium). The effect of the crystallinity of rare earth hydroxides on their solubility has been analyzed. Model parameters have been determined for two limiting cases, i.e., for crystalline and amorphous hydroxides, while recognizing that the hydroxides may span a range of degrees of crystallinity. For the organic ligands, the model has been established for neodymium with additional analysis for other selected REEs. The model accurately reproduces the effects of pH, temperature, and complexation with organic ligands on the behavior of rare earth elements in aqueous solutions. When coupled with previously developed models for inorganic rare earth salts, it provides a thermodynamic tool for the design and optimization of separation processes for the production and recycling of REEs and for predicting the properties of REEs in geological and biological settings.

Computational investigation on the antioxidant activities and on the Mpro SARS-CoV-2 non-covalent inhibition of isorhamnetin.

In the present work, we report a computational study on some important chemical properties of the flavonoid isorhamnetin, used in traditional medicine in many countries. In the course of the study we determined the acid-base equilibria in aqueous solution, the possible reaction pathways with the •OOH radical and the corresponding kinetic constants, the complexing capacity of copper ions, and the reduction of these complexes by reducing agents such as superoxide and ascorbic anion by using density functional level of theory Density Functional Theory. Finally, the non-covalent inhibition ability of the SARS-CoV-2 main protease enzyme by isorhamnetin was examined by molecular dynamics (MD) and docking investigation.

DMSO-Induced Unfolding of the Antifungal Disulfide Protein PAF and Its Inactive Variant: A Combined NMR and DSC Study.

PAF and related antifungal proteins are promising antimicrobial agents. They have highly stable folds around room temperature due to the presence of 3-4 disulfide bonds. However, unfolded states persist and contribute to the thermal equilibrium in aqueous solution, and low-populated states might influence their biological impact. To explore such equilibria during dimethyl sulfoxide (DMSO)-induced chemical unfolding, we studied PAF and its inactive variant PAFD19S using nuclear magnetic resonance (NMR) and differential scanning calorimetry (DSC). According to the NMR monitoring at 310 K, the folded structures disappear above 80 v/v% DMSO concentration, while the unfolding is completely reversible. Evaluation of a few resolved peaks from viscosity-compensated 15N-1H HSQC spectra of PAF yielded ∆G = 23 ± 7 kJ/M as the average value for NMR unfolding enthalpy. The NMR-based structures of PAF and the mutant in 50 v/v% DMSO/H2O mixtures were more similar in the mixed solvents then they were in water. The 15N NMR relaxation dynamics in the same mixtures verified the rigid backbones of the NMR-visible fractions of the proteins; still, enhanced dynamics around the termini and some loops were observed. DSC monitoring of the Tm melting point showed parabolic dependence on the DMSO molar fraction and suggested that PAF is more stable than the inactive PAFD19S. The DSC experiments were irreversible due to the applied broad temperature range, but still suggestive of the endothermic unfolding of PAF.

Study on vapor-liquid equilibrium and microscopic properties of DL-proline, L-glutamic acid, and L-serine aqueous solutions.

The vapor–liquid equilibrium (VLE) in aqueous amino acid solutions is essential in chemical production, such as purification, isolation, or crystallization of amino acid intermediates. In this work, VLE of DL-proline, L-glutamic acid, and L-serine aqueous solutions was measured at pressures ranging from 4.82 to 102.58 kPa. The developed model was successfully applied to correlate experimental data with temperatures in the range of 298.15–382.75 K. Model parameters (h, , , , and ) were given. Moreover, the amino acid aqueous solution was investigated by Fourier transform infrared spectroscopy (FTIR). By analyzing infrared spectra, the strength of intermolecular interactions was obtained, and the structure–activity relationship between the microscopic interactions and the VLE was established.

Steam Activation of Acid-Chars for Enhanced Textural Properties and Pharmaceuticals Removal.

The present work aims to explore steam activation of sisal or glucose-derived acid-chars as an alternative to KOH activation to prepare superactivated carbons, and to assess the adsorption performance of acid-chars and derived activated carbons for pharmaceuticals removal. Acid-chars were prepared from two biomass precursors (sisal and glucose) using various H2SO4 concentrations (13.5 M, 12 M, and 9 M) and further steam-activated at increasing burn-off degrees. Selected materials were tested for the removal of ibuprofen and iopamidol from aqueous solution (kinetic and equilibrium assays) in single-solute conditions. Activated carbons prepared from acid-char carbonized with 13.5 M and 12 M H2SO4 are mainly microporous solids composed of compact rough particles, yielding a maximum surface area and a total pore volume of 1987 m2 g−1 and 0.96 cm3 g−1, respectively. Solid state NMR reveals that steam activation increased the aromaticity degree and amount of C=O functionalities. Steam activation improved the acid-chars adsorption capacity for ibuprofen from 20-65 mg g−1 to higher than 280 mg g−1, leading to fast adsorption kinetics (15–20 min). The maximum adsorption capacities of selected activated samples for ibuprofen and iopamidol were 323 and 1111 mg g−1, respectively.

Modeling Micellar Growth and Branching in Mixtures of Zwitterionic with Ionic Surfactants.

Zwitterionic surfactants are widely applied as drag-reducing or thickening agents because their aggregation patterns may drastically change in response to variations of the system composition or external stimuli, which provides controllable viscoelasticity. For predicting aggregation behavior of surfactant mixtures, classical molecular thermodynamic models have been widely used. Particularly, the results of modeling have been reported for zwitterionic/ionic surfactant mixtures. However, for solutions containing a zwitterionic surfactant, no molecular thermodynamic model has been proposed for a micellar branch. In this work we extend the classical molecular thermodynamic aggregation model to describe aggregation in the aqueous mixtures that contain a zwitterionic and an ionic surfactant. We derive analytical expressions (1) for the contribution of dipoles to the electrostatic term of the standard free energy of aggregation into micellar branches and (2) for the dipolar contribution to the persistence length of wormlike micelles. The dependence of micellar branching on the surfactant concentration is taken into account by including the population of micellar branches in the material balance equations. This model is applied to predict aggregation equilibrium in aqueous salt solutions of betaine (oleoylamidopropyl-N,N-dimethylbetaine) mixed with sodium dodecyl sulfate (SDS) and the longer tail sodium n-alkyl sulfates. We discuss the predicted properties of the aggregates and micellar networks and compare our predictions with available experimental data.

Aggregates of cationic calix[4]arenes in aqueous solution as media for governing protolytic equilibrium, fluorescence, and kinetics

Many water-soluble ionic calixarenes readily form micelle-like aggregates in aqueous solution. Presently, it is firmly proved that such aggregates tend to shift the state of the acid-base equilibrium of indicator dyes just in the same manner as cationic surfactant micelles do. In this paper, we further the corresponding studies and report the peculiarities of several kinds of solvatochromic effects, fluorescence, acid-base equilibrium and kinetic processes in aqueous solutions of four cationic amphiphilic calix[4]arenes bearing hydrophilic choline groups at the upper rim: 5,11,17,23-tetra(N,N-dimethyl-N-hydroxyethylammonium)methylene-25,26,27,28-tetraalkyl-oxycalix[4]arene tetrachlorides. n-Propyl, n-hexyl, n-octyl, and n-dodecyl were used as alkyls, and the calixarenes were designated as of Cn-C4A-Ch, where n = 3, 6, 8, and 12, respectively. The principal colloidal properties, i.e., particle size and electrophoretic mobility of aggregates were characterized via dynamic light scattering. In parallel, the results were compared with those obtained in the presence of micelles of the common cationic surfactant cetyltrimethylammonium bromide and of large-sized aggregates of the calix[6]arene with six methoxy groups at the lower rim. As tools, molecular probes of triphenylmethine and fluorescein series, as well as the solvatochromic Reichardt’s dye were used. The obtained block of data sheds light upon the properties of calixarene aggregates as tools for governing chemical processes.

Minimum Thickness of Continuous Cu Layers on Mo from Fluoride Free Electrolytes

Mo as a refractory metal has physical properties which are of interest for applications in CIGS photovoltaic cells fabrication and for next generation of liners for Cu interconnects[1]. Therefore it is of fundamental and practical interest to develop a process for Cu metallization of Mo surfaces where contiguity and high coverage is achieved at minimum thickness. However, one of the obstacles that prevent readily use of Mo as substrate for Cu electrodeposition is tendency of its surface to form a high quality oxide[2] ,[3].The surface energy of Mo-oxide is much lower than Cu which results in sporadic 3D nucleation and low adhesion of Cu deposit[2]. The presented work addresses this fundamental problem by combining the knowledge/breakthroughs demonstrated in the field of electro-polishing of refractory metals such as Nb[4] with common pulse electrodeposition practice[1] ,[5]. A design of deposition pulse reverse potential/current function for Cu is presented which converts a Mo-oxide/Cu to a Mo/Cu interface. Elaborate measurements of the thin film impedance during the Cu growth complemented with Pb UPD decoration studies and AFM surface morphology analysis are presented. These data indicate that Cu layers reach full contiguity and coverage of the Mo substrate at the thickness level of 3-5 nm. Considering that common Cu electrodeposition bath chemistry for interconnects contains additives whose incorporation makes Cu deposit somewhat incompatible with photovoltaic layers[1], this work presents the Cu solution chemistry which is additive free and can serve as a base for further improvement of the specific Cu deposition processes depending on its application.[1] . J. Bi et al, Journal of Power Sources, 326, (2011) 211.[2] . D. Mercier et al, Journal of the Electrochemical Society, 160 (2013) 3103.[3] . M. Pourbaix, Atlas of electrochemical equilibria in aqueous solutions. 2d English ed. 1974, Houston, Tex.: National Association of Corrosion Engineers.[4] . Journal of The Electrochemical Society, 160 (9) E94-E98 (2013).[5] . J.C. Puippe and F. Leaman, Theory and Practice of Pulse Plating, AESF, (1986).

UPPER SECONDARY SCHOOL STUDENTS’ CONCEPTIONS OF CHEMICAL EQUILIBRIUM IN AQUEOUS SOLUTIONS: DEVELOPMENT AND VALIDATION OF A TWO-TIER DIAGNOSTIC INSTRUMENT

Student understanding of chemical equilibrium in aqueous solutions (CEAS) plays a vital role in their upper secondary school chemistry learning and everyday life. Diagnosis of students’ alternative conceptions (ACs) of the CEAS will provide teachers with valuable information to make instructional decisions on student learning. This study aims to develop and validate an instrument to diagnose students’ ACs about the CEAS, including ionization equilibrium, water self-ionization equilibrium, the equilibrium of salt hydrolysis, and precipitation and dissolution equilibrium. Using Treagust (1998)’s development framework, we have developed 25 two-tier multiple-choice items for the CEAS diagnostic test. After completing the corresponding courses, 750 Grade 11 students from five public schools responded to the CEAS diagnostic test. Rasch modeling approach was employed to provide psychometric properties of the CEAS diagnostic test consisting of one-dimensionality, reliability, and validity. This study identified 15 ACs toward the CEAS. This study found that most students performed better on concept tiers rather than reasoning tiers. In addition, students have difficulties in connecting acidity, solubility, ionization, and chemical reaction and in using mathematical thinking to do transformation between concentration, equilibrium constant, and pH value. Keywords: chemical equilibrium in aqueous solutions, alternative conceptions, two-tier multiple-choice items, Rasch modeling