Solution Equilibria Research Articles

Real-time Raman analysis of the hydrolysis of formaldehyde oligomers for enhanced collagen fixation

Formaldehyde (FA) is widely applied as a fixative for proteins such as collagen. Current studies have confirmed that the reversible oligomer-to-monomer equilibrium of FA in aqueous solution and the proportion of FA monomer is a significant factor affecting tissue fixation. Since the hydrolysis of FA oligomers is a dynamic process affected jointly by different factors, its real time monitoring has proved to be challenging. In this work, by utilizing the well-established Raman technique as an analytical platform, we identified the factors affecting the hydrolysis of FA oligomers by rationally examining the νs (OCO) and νas (OCO) modes with varying conditions, such as time, pH, temperature, and FA concentration. The optimized conditions of the highest hydrolysis rate of oligomers into monomers for fixation on collagen and tissues have been found to be relatively low FA concentration (≤5%) in phosphate-buffered saline at pH 9.0 in room temperature. In order to compare the fixation quality of the optimized conditions to that of the conventional conditions used by current medical practices (4% FA concentration in tap water under room temperature), Raman spectroscopy and chemical derivatization methods with o-phthalaldehyde and fluorescent probe FAP-1 have been investigated, and our results revealed that the FA molecules under our optimized conditions have reacted with at least 15% more amino groups within collagen compared to those under the conventional conditions mentioned above. This study provides direct evidence of the FA equilibrium in solution by Raman spectroscopy, which could be applied for the optimal use of FA in medicine, even at an industrial scale.

Solvent extraction equilibrium modeling for the separation of ammonia, nickel(II), and copper(II) from the loaded LIX84-I

A novel solvent extraction equilibrium model has been developed to separate nickel and copper from the loaded LIX84-I (active component: 2-hydroxy-5-nonylacetophenone oxime dissolved in a nonpolar diluent, ShellSol D70) formed by the extraction from ammoniacal alkaline solutions. The targeted process consists of the scrubbing of ammonia and subsequent selective stripping of nickel(II) followed by stripping of copper(II), in which sulfuric acid is used in each step. The present model considers the equilibria of extraction of copper, nickel, and ammonia; distribution of metal-extractant complexes; and solution equilibria in aqueous and organic phases and was compared with the experimental results under varying sulfuric acid concentrations and phase ratios. As a result, this model was shown to accurately predict the equilibria after scrubbing and stripping from the initial operational conditions. This model is also applicable to the extraction of copper and nickel from an ammoniacal solution and thus facilitates the design, optimization, and control of the ammoniacal process for the separation of copper and nickel.

NEED ANALYSIS OF STUDENT WORKSHEET (LKS) OF IONIC EQUILIBRIUM AND pH OF THE SALT SOLUTION BASED ON PROBLEM SOLVING

Problem solving skills are one of the skills needed by students in the era of the industrial revolution 4.0, so it becomes a challenge for a teacher to design creative learning. One of the media that supports students' problem solving skills is to use worksheets. Meanwhile, the worksheets used so far are general in nature. Suitable worksheets are developed that support students in solving problems, namely problem solving-based worksheets. This study aims to analyze the need for problem solving-based student worksheets. This type of research is a qualitative descriptive study. This needs analysis is part of the research and development of the 4D model, specifically the Define stage. The subjects in this study were students of class XII in SMA Negeri 3 Cirebon City and chemistry teachers as informants. The results showed that students needed worksheets that were more attractive and easy to understand. The worksheets available are in accordance with KD, KI and the 2013 curriculum, but not yet according to student needs. Based on data obtained from several analyzes including analysis of student perceptions, teacher perceptions, student characteristics, curriculum, assignments, concepts and analysis of learning objectives. So it is necessary to develop problem solving worksheets, especially in the matter of ionic equilibrium and pH of salt solutions which can train students to solve problems and relate theory to facts in everyday life.

Aggregates of Ethoxylated Surfactant with Added n-Octanol: Details of Corona Structure from a Molecular-Thermodynamic Model

Polar heads of many nonionic surfactants have complex chemical structure. In the micellar aggregates these heads are engaged in specific and nonspecific interactions with one another and with the hydration water. We present here a molecular-thermodynamic aggregation model that takes into account explicitly the hydrogen bonding and other specific interactions within the hydrated corona of a mixed nonionic aggregate. Apart from the aggregation characteristics that are usually obtained from the classical aggregation models – critical micelle concentration (CMC), the distribution of the aggregates over the size and shape and their composition - our model helps to establish a number of likely details of structure, including the corona thickness, hydration, and the partial penetration of the micelle components in the corona region. In this work the model is applied to describe the aggregation equilibrium in aqueous solutions of nonionic surfactants of the polyoxyethylene-p-(1,1,3,3-tetramethylbutyl)phenyl ether family that is closely related to Tritons, the commercial surfactants of an extensive practical use. The model gives reasonable estimates of the CMCs and predicts correctly the trends in CMC and in the aggregation numbers vs the number of oxyethylene groups in the surfactant molecule. The hydration numbers and the fraction of water engaged in hydrogen bonds are calculated. For the hydration of the aggregate coronae, the predicted trend is in line with that found for other ethoxylated nonionic surfactants: poly(ethylene oxide) alkyl ethers and neonols. For surfactant solutions with added n-octanol, the model suggests that the tails of the octanol molecules are deeply buried in the cores of the mixed micelles with only one methylene group penetrating the coronae. We predict co-surfactant effect of added n-octanol: the depression of the CMCs is progressively stronger for more hydrophilic surfactants with larger EO heads.

Studies on stable phase equilibria of quaternary system LiBr-NaBr-SrBr2-H2O at 308.15 and 323.15 K

The stable phase equilibria of LiBr–NaBr–SrBr2–H2O were studied at 323.15 K and 308.15 K by the isothermal solution equilibrium method. The isothermal phase diagram of the quaternary system was drawn by using solubilities of salts and solid phase identification. The X-ray powder diffraction method was used to identify the corresponding equilibrium solid phases of the invariant points in the quaternary system. The quaternary system LiBr–NaBr–SrBr2–H2O at 323.15 K has no double salts or solid solution. There are two invariant points, five univariant curves, and four crystallization fields corresponding to LiBr•H2O, NaBr, SrBr2•2H2O, and SrBr2•6H2O respectively, of which NaBr has the largest crystallization field, indicating that its solubility is the smallest and it is the easiest to be precipitated from the saturated solution. The phase diagram of quaternary system LiBr-NaBr-SrBr2-H2O at 308.15 K has three invariant points, seven univariant curves, and five crystallization fields corresponding to LiBr•2H2O, NaBr, NaBr•2H2O, SrBr2•2H2O, and SrBr2•6H2O, respectively. Among them, the crystallization field of LiBr•2H2O is the smallest, indicating that the solubility of LiBr•2H2O in this system is the largest.

Unlocking Phase Diagrams for Molybdenum and Tungsten Nanoclusters and Prediction of their Formation Constants.

Understanding and controlling aqueous speciation of metal oxides are key for the discovery and development of novel materials, and challenge both experimental and computational approaches. Here we present a computational method, called POMSimulator, which is able to predict speciation phase diagrams (Conc. vs pH) for multispecies chemical equilibria in solution, and which we apply to molybdenum and tungsten isopolyoxoanions (IPAs). Starting from the MO4 monomers, and considering dimers, trimers, and larger species, the chemical reaction networks involved in the formation of [H32Mo36O128]8- and [W12O42]12- are sampled in an automatic manner. This information is used for setting up ∼105 speciation models, and from there, we generate the speciation phase diagrams, which show an insightful picture of the behavior of IPAs in aqueous solution. Furthermore, we predict the values of 107 formation constants for a diversity of molybdenum and tungsten molecular oxides. Among these species, we could include several pentagonal-shaped species and very reactive tungsten intermediates as well. Last but not least, the calibration employed for correcting the density functional theory (DFT) Gibbs energies is remarkably similar for both metals, which suggests that a general rule might exist for correcting computed free energies for other metals.

REGULARITY AND CONVERGENCE TO EQUILIBRIUM FOR A CLASS OF NONLOCAL EVOLUTION EQUATIONS

We study a class of semilinear nonlocal partial differential equations, which model different problems related to processes in materials with memory. Our aim is to derive sufficient conditions ensuring the global solvability, regularity, and convergence to equilibrium of solutions

Deep Learning of Binary Solution Phase Behavior of Polystyrene.

Predicting binary solution phase behavior of polymers has remained a challenge since the early theory of Flory-Huggins, hindering the processing, synthesis, and design of polymeric materials. Herein, we take a complementary data-driven approach by building a machine learning framework to make fast and accurate predictions of polymer solution cloud point temperatures. Using polystyrene, both upper and lower critical solution temperatures are predicted within experimental uncertainty (1-2 °C) with a deep neural network, Gaussian process regression (GPR) model, and a combination of polymer, solvent, and state features. The GPR model also enables intelligent exploration of solution phase space, where as little as 25 cloud points are required to make predictions within 2 °C for polystyrene of arbitrary molecular weight in cyclohexane. This study demonstrates the effectiveness of machine learning for the prediction of liquid-liquid equilibrium of polymer solutions and establishes a framework to incorporate other polymers and complex macromolecular architectures.

Deferoxamine B: A Natural, Excellent and Versatile Metal Chelator.

Deferoxamine B is an outstanding molecule which has been widely studied in the past decade for its ability to bind iron and many other metal ions. The versatility of this metal chelator makes it suitable for a number of medicinal and analytical applications, from the well-known iron chelation therapy to the most recent use in sensor devices. The three bidentate hydroxamic functional groups of deferoxamine B are the centerpiece of its metal binding ability, which allows the formation of stable complexes with many transition, lanthanoid and actinoid metal ions. In addition to the ferric ion, in fact, more than 20 different metal complexes of deferoxamine b have been characterized in terms of their chemical speciation in solution. In addition, the availability of a terminal amino group, most often not involved in complexation, opens the way to deferoxamine B modification and functionalization. This review aims to collect and summarize the available data concerning the complex-formation equilibria in solutions of deferoxamine B with different metal ions. A general overview of the progress of its applications over the past decade is also discussed, including the treatment of iron overload-associated diseases, its clinical use against cancer and neurodegenerative disorders and its role as a diagnostic tool.

PRECIPITATION OF METAL HYDROXIDES FROM AQUEOUS SOLUTIONS AS A RESULT OF SPONTANEOUS CONDENSATION OF POLYNUCLEAR HYDROXOCOMPLEXES

Background. Generally, it is assumed that the formation of a solid phase (precipitate) happens when the activities of the involved ions would exceed those defined by the thermodynamic solubility product. However, in case of precipitation of metal hydroxides, this is a simplification, and the real pattern is more complicated, since metal ions form strong mono- and polynuclear hydroxocomplexes in a solution. Formation of such complexes, especially those with zero charge, should result in the deviation from the common solubility product rule. Objective. The aim of this paper is to develop a precipitation model, which takes into account the effect of the formation of the hydroxocomplexes on the solubility of a metal hydroxide. Eventually, this solubility includes the sum of the concentrations of metal ions, and all neutral, positively and negatively charged hydroxocomplexes involved in all equilibria in aqueous solution. Methods. We assume that formation of the solid precipitate is the result of spontaneous condensation of polynuclear neutral hydroxocomplexes when their concentrations in a solution exceed a certain critical value. These critical concentrations can be estimated from the consideration of all equilibria with the assumption that the equilibrium constants for the formation of neutral polynuclear complexes when their nuclearity increases by one are approximately equal and do not significantly depend on the size of the particle. Results. Using this approach, we developed the model, which predicts spontaneous condensation with formation of a precipitate. Also, we calculated the dependencies of pH-logCM for precipitation of various divalent cation hydroxides. It was shown that there exist minimal concentrations, below which no precipitates are formed at any pH value. Conclusions. Such approach also explains the nature of linear correlations between logarithms of solubility products and stability constants of neutral complexes described in literature. These results are important for the development and optimization of industrial wastewater treatment processes.

PENGARUH PENGGUNAAN BLENDED LEARNING BERBASIS SCHOOLOGY TERHADAP HASIL BELAJAR PESERTA DIDIK PADA MATERI HIDROLISIS GARAM

This research aimed at increasing student learning achievement on Ion and pH Saline Solution Equilibrium lesson by using Schoology blanded Learninglearning model. Qualitative method was used in this research with quasi- experimental research design. All the eleventh-grade students of Natural Science of State Senior High School 1 TapungHilir in the Academic Year of 2018/2019 were the population of this research, and the samples were the eleventh-grade students of Natural Science 1 as the experimental group and the students of Natural Science 2 as the control group. Pretest-posttest control group design was used in this research. Sampling was done by using random technique. Analyzing the data was using one-way ANOVA. The data were analyzed by using inferential statistic with the help of SPSS 16.0 software. The results of calculating the data showed that the score of Sig. was lower than α, the significance score was 0.003. It showed that the learning achievement mean on Ion and pH Saline Solution Equilibrium lesson was increasing through the use of Schoology based Blended Learning. It could be concluded that there was an effect of using Schoology- based Blended Learning toward student learning achievement on Ion and pH Saline Solution Equilibrium lesson.

PENERAPAN MODEL PEMBELAJARAN KOOPERATIF TIPE JIGSAW UNTUK MENINGKATKAN HASIL BELAJAR KOGNITIF

Abstract The used of the jigsaw-type cooperative learning model can improve the cognitive learning outcomes of students, especially on ionic equilibrium material in salt solution. This study aims to improve students' cognitive chemistry learning outcomes on ion equilibrium in salt solution by applying the jigsaw-type cooperative learning model. This research is a classroom action research with the Kemmis and MC models. Taggart, which included the stages of planning, implementing, observing / collecting data and reflecting, which were carried out in 2 (two) cycles. This research was conducted in class XI IPA at public high school Christian YABT Manokwari with a sample of 17 students. The data collection techniques used were tests and observation sheets. The results showed that the increase in the average value of learning outcomes chemistry from cycle I was 56.18 with classical completeness of 29% to 85.29 with classical completeness of 82% in cycle II. The results of observations on learning using the jigsaw type cooperative model have good responses from students. This proves that the type of jigsaw cooperative learning has a positive impact on students in the teaching and learning process. Keywords : Jigsaw Model, learning outcomes cognitive, Ion Balance, Salt Solution

Complex formation of an estrone-salicylaldehyde semicarbazone hybrid with copper(II) and gallium(III): Solution equilibria and biological activity

The solution chemical properties such as proton dissociation, complex formation with copper(II) and gallium(III) ions in addition to antibacterial and antitumor activity of a novel tridentate salicyaldehyde semicarbazone-estrone hybrid (estrone-SC) and a related bicyclic compound (thn-SC) were investigated. The crystal structure of complex [Cu(thn-SCH−1)Cl] was studied by single crystal X-ray diffraction method. Estrone-SC and thn-SC form mono-ligand complexes with Cu(II) characterized by relatively high stability, however, they are much less stable than their thiosemicarbazone analogues. The neutral Cu(II) complexes with (O−,N,O−)(H2O) coordination mode predominate at physiological pH. Estrone-SC and thn-SC are more efficient Ga(III) binders in comparison with thiosemicarbazones, although the complexes also suffer dissociation at pH 7.4. The Cu(II) complex of estrone-SC displayed significant cytotoxicity in A549, SW480 and CH1/PA cancer cells, and moderate apoptosis induction and ROS formation. The semicarbazone compounds did not exhibit antibacterial effect; unlike the related Cu(II)-thiosemicarbazone complexes represented by the fairly low MIC values (3–50 μM) obtained on the Gram-positive Staphylococcus aureus and Enterococcus faecalis bacteria.

Factors Determining the Metal Ion Binding Ability and Selectivity of Hydroxamate-Based Compounds

There has been a long tradition for a broad spectrum of applications of both natural and synthetic hydroxamic acids and derivatives. Even nowadays, a huge number of newly designed representatives (from different monohydroxamate-based compounds to siderophore conjugates) are used to develop potential drug candidates with desired activities. Since these compounds are effective metal-chelating agents, their biological roles and actions as well as their various applications, e.g., in the medicinal practice, are all in direct correlation with their metal complexation. Consequently, the knowledge of the stoichiometry and binding modes of metal complexes with hydroxamic acid-based ligands, their thermodynamic parameters, and speciation profiles in solution are crucial for scientists working in any of the above-mentioned fields. This review, in addition to presenting a few factors, which might affect the metal-binding capabilities of these organic ligands, displays and summarizes the different parameters typically used to give the stoichiometry, composition, and stability of the species formed in a solution equilibrium system in measurable concentration. Discussion of the possibilities for quantitative comparison of metal-binding effectivity and selectivity of various hydroxamic acids with each other by using solution equilibrium data is also the focus of this publication.

Conformational Heterogeneity and Cooperative Effects of Mammalian ALOX15.

Arachidonic acid lipoxygenases (ALOXs) have been suggested to function as monomeric enzymes, but more recent data on rabbit ALOX15 indicated that there is a dynamic monomer-dimer equilibrium in aqueous solution. In the presence of an active site ligand (the ALOX15 inhibitor RS7) rabbit ALOX15 was crystalized as heterodimer and the X-ray coordinates of the two monomers within the dimer exhibit subtle structural differences. Using native polyacrylamide electrophoresis, we here observed that highly purified and predominantly monomeric rabbit ALOX15 and human ALOX15B are present in two conformers with distinct electrophoretic mobilities. In silico docking studies, molecular dynamics simulations, site directed mutagenesis experiments and kinetic measurements suggested that in aqueous solutions the two enzymes exhibit motional flexibility, which may impact the enzymatic properties.

Stability analysis of nontrivial stationary solution and constant equilibrium point of reaction–diffusion neural networks with time delays under Dirichlet zero boundary value

In this paper, Lyapunov-Razumikhin technique, design of state-dependent switching laws, a fixed point theorem and variational methods are employed to derive the existence and the unique existence results of globally exponentially stable (positive) stationary solution of delayed reaction–diffusion cell neural networks under Dirichlet zero boundary value, including the global stability criteria in the classical meaning. Next, sufficient conditions are proposed to guarantee the global stability invariance of ordinary differential systems under the influence of diffusions. New theorems show that the diffusion is a double-edged sword in judging the stability of diffusion systems. Besides, an example is constructed to illuminate that any non-zero constant equilibrium point must be not in the phase plane of dynamic system under Dirichlet zero boundary value, or it must lead to a contradiction. Next, under Lipschitz assumptions on active function, another example is designed to prove that the small diffusion effect will cause the essential change of the phase plane structure of the dynamic behavior of the delayed neural networks via a Saddle point theorem. Finally, a numerical example illustrates the feasibility of the proposed methods. It is worth mentioning that some interesting mathematical problems are originally put forward in the last chapter.

Chemical stability diagrams as a powerful tool to the synthesis of Cu2SnS3 thin films by chemical bath deposition

Cu2SnS3 films are produced by chemical bath method employing low toxicity citrate precursor taking advantage of the strong complexes formed with Cu(II) and Sn(II). The deposition conditions for Cu2SnS3 thin films were obtained through a thermodynamic analysis of the effect of tin concentration on Cu(II)–Sn(II)-Citrate complexes and Cu(II)–Sn(II)-Citrate-Thiourea system using a species distribution and potential–pH (Eh-pH) analysis. Theoretical analysis of the speciation fraction of Cu(II) and Sn(II) shown that the predominant species at pH equal to 4.5 at 90 °C are [Cu2(Cit)2OH]3− and [Sn2(Cit)2]2−. For the Cu(II)–Sn(II)-Citrate-Thiourea system at 90 °C, the Eh-pH diagrams established that binary precursors, Cu2S and SnS2, would be obtained under basic pH conditions. Subsequently, Cu2SnS3 films were synthetized at 90 °C at pH equal to 8 by keeping fixed the molar relationships complexing agent-metal and sulfur-metal. The redox potentials were measured in solution and chemical equilibrium diagrams were constructed, confirming the existence of binary precursors under reductive conditions. Characterization of structural, electronic and transport properties indicated that Cu2SnS3 fabricated by chemical bath deposition have monoclinic crystal structure, a direct band gap energy of 1.70 eV and p-type conductivity.

Determination of the binding mechanism of cobalt(II) meso-tetraphenyl porphyrin with plant-esterase

Abstract Plant-esterase (EC 3.1.1.X) has received much attention because plant esterase and acetylcholinesterase (AChE) share a similar sensitivity towards organophosphorus (OP) pesticides detection with the same inhibition mechanism. To improve the analytical performance, tetraphenyl metal porphyrin, as an indicator was introduced to combine with plant-esterase. The time of reach equilibrium in PBS solution was shortened after adding plant-esterase by assaying the intensify change of the porphyrin spectrum. Meanwhile, intensify of porphyrin spectrum with plant-esterase was increased compared with that of only the porphyrin spectrum in solution. Tetraphenyl metal porphyrin, such as cobalt(II) meso-tetraphenyl porphyrin, is a mixed reversible inhibitor of plant-esterase from kinetic parameters. The combination ratio of plant-esterase and porphyrin is 2:1. On the other hand, the interaction between CoTPPCl and plant-esterase is the strongest among all tested tetraphenyl metal porphyrin. And the mixed system (CoTPPCl-plant-esterase) showed the best sensitivity towards the tested pesticide. All these results indicated that a complex system composed of tetraphenyl metal porphyrin and plant-esterase was fit for detecting pesticides. They make meaningful guidance on the further design of sensing material in monitoring pesticides.

Preparation of hydroxyapatite by aqueous precipitation from calcium carbonate and phosphoric acid

Hydroxyapatite (Ca10(PO4)6(OH)2, HAp) is the representative biological mineral which is hard to attain the solution equilibrium and difficult to produce by solution synthesis. HAp finds new application fields to remove harmful elements from polluted wastewater in industrial scales. The low-cost manufacturing process should be developed using abundant available CaCO3 materials. Calcium carbonate (CaCO3), as an economically feasible and abundant precursor, has been used in calcium source for the HAp synthesis. The synthesis was conducted by reacting CaCO3 with phosphoric acid (H3PO4) in aqueous solution with aid of citric acid and sodium hydroxide under moderate synthesis conditions. Compositionally pure HAp has been prepared. The process offered a relatively fast, convenient and economical route for the synthesis of HAp.

A study of the micellar aggregation of aqueous N,N,N-decyltrimethyl ammonium chloride via extended microsecond-time atomistic molecular dynamics simulation and realistic potential models

We report on the micellization behavior of the cationic surfactant N,N,N-decyltrimethyl ammonium chloride in water, studied via an explicit-solvent, very long atomistic molecular dynamics simulation. We aim at systematically exploring the related properties of the surfactant solution, focusing at first on their accurate prediction via simulations long enough to allow their precise calculation based on phase space trajectories that fall within the “true thermodynamic equilibrium”. To accomplish this goal, explicit-solvent, atomistic molecular dynamics runs were performed attaining, for the first time, simulation time scales of ≈1.2 μs. According to the results obtained, these novel simulations led to a rigorous estimation and detailed analysis of the properties related to the aggregation process such as the average number of free monomers, the average size and shape of formed micelles, the critical micelle concentration of the solution, the temporal evolution of cluster size distribution and others. It turns out from the analysis of the principal moments of inertia of the micelles that their average shape is oblate ellipsoidal. Also, from the pair radial distribution functions the average cross-sectional structure of the micelles reveals a hydrophobic core composed of the surfactant tail groups, while their outer shell consists from the hydrophilic heads. Moreover, it is found that the chloride counterions form a Stern layer around the micelles and close to the hydrophilic heads, while water molecules were also identified very close to the micelles. The results obtained are in good agreement with quite recent experimental data (previously not available) but differ from those of previous atomistic simulations of similar systems, covering time scales between a few tens and hundreds of ns for the most recent of them. Our results clearly indicate that the required system equilibrium is achieved at about 800 ns and beyond. This key result is in agreement with previous considerations that, reaching true equilibrium of surfactant solutions with respect to their aggregate properties and specifically the cluster size distribution of micelles is extremely time-demanding. It is also shown that self-assembly takes place in three temporal phases, starting from aggregation of monomers into small oligomers, through micellar growth at the expense of monomers and smaller oligomers, to the final formation of stable micelles, with sizes fluctuating slightly around certain values.In this context, the present systematic study of the micellar formation properties aims at providing a stepping stone for a further rigorous computational investigation of several related and interesting molecular processes, such as the encapsulation of specific molecules within micelles; the desalination of water; and even usage of micelles as fundamental chemical reaction intermediates (e.g. micellar reactor catalysts) to mention but a few, all of them falling well within our theoretical-computational research interests.