Isotope effect on the solubility of amino acids in water

The solubilities of glycine, alanine, phenylalanine, and proline in H₂O and D₂O from 283 K to 335 K were determined. It was found that glycine and alanine are less soluble in heavy water than in light water but proline is more soluble in heavy water over the whole temperature range studied. Phenylalanine is more soluble in H₂O than D₂O below 310 K but above that temperature heavy water becomes a better solvent. An influence of H/D isotope substitution on the enthalpies of solution is also observed. In the case of glycine and alanine enthalpies of solution in heavy water increase by a small amount and in the same time the solution enthalpy for phenylalanine in D₂O increases markedly. No change in the solution enthalpy for proline was observed. The isotope effects on solubility and the solution enthalpy are qualitatively discussed.     

Preparation and characterization of bis(acetonitrile)bis(acetylacetonato)technetium(III)

A new chemical species of bis(acetonitrile)bis(acetylacetonato)technetium(III), [Tc(acac)₂(CH₃CN)₂]⁺, has been prepared by the reaction of tris(acetylacetonato)technetium(III) with acetonitrile in the presence of a strong acid, perchloric or hydrochloric acid. The reaction kinetics were followed by observing spectral change of Tc(acac)₃ in the UV-visible region. The complex has been characterized by combination of elemental analyses, IR and UV-visible spectrophotometry, ion-exchange chromatography, and paper electrophoresis. Applicability of this substance to synthesize mixed-ligand technetium(III) complexes was discussed based on the solubility of this complex and the ease of substitution of the acetonitrile ligand.     

Water Activity and Solubility Measurements and Pitzer Model Simulation of the MgCl<Subscript>2</Subscript>–RbCl–H<Subscript>2</Subscript>O Ternary System at 298.15 K

Water activities for the MgCl₂–RbCl–H₂O ternary system and its sub-binary MgCl₂–H₂O and RbCl–H₂O systems at 298.15 K have been measured using the isopiestic method. The measured results for the binary systems agree well with literature data. The measured equal water activity lines for the MgCl₂–RbCl–H₂O ternary system deviate from Zdanovskii’s rule. The solubilities for the MgCl₂–RbCl–H₂O ternary system also have been measured using a isothermal visual first/last crystal method, and the results are consistent with one reported set of solubility data. Pitzer’s model was selected to correlate the measured water activity and solubility data and the parameters reported in the literature are re-examined by comparing the model-calculated equal water activity lines and solubilities with experimental values measured in this work. New and reasonable parameters are obtained by fitting the water activity and solubility data measured in this work and those reported in the literature. The water activities and solubilities were simulated with the new parameters and the results show that the Pitzer model can successfully represent the thermodynamic properties and be used to calculate the solubility isotherms.     

Study of equilibrium solution and thermodynamic models in correlation with solubility data of rivastigmine tartrate in (H2O + isopropanol), (H2O + ethanol), and (H2O + acetonitrile) binary solvent mixtures

Millions of people around the world have been suffering from Alzheimer’s disease (AD) everyday. Rivastigmine tartrate is a potential AD drug. A crystallization process can enhance purities of rivastigmine tartrate properly. Predictive models for solubilities of rivastigmine tartrate will improve subsequent industrial crystallization process design. In this work, the solubility of rivastigmine tartrate in (H₂O?+?isopropanol), (H₂O?+?ethanol), and (H₂O?+?acetonitrile) binary solvent systems in the temperature range of 278.15–333.15 K under atmospheric pressure was measured and investigated by employing the analytical stirred-flask method. Binary solvent systems of rivastigmine tartrate overcame drawbacks of mono-solvent crystallization systems, such as high viscosity. Three thermodynamic models, including modified Apelblat equation, the general cosolvency model, and the Jouyban–Acree model, were employed to correlate with the obtained experimental solubility data. Moreover, the calculations of apparent thermodynamic properties of rivastigmine tartrate dissolution process involving the Gibbs free energy, enthalpy, and entropy were accomplished by using the van’t Hoff analysis. Among the three models, the modified Apelblat equation is the most suitable one for predicting the solubility behavior of rivastigmine tartrate in binary solvent systems. Based on the data from modified Apelblat equation, a crystallization process of (H₂O?+?ethanol) binary solvent mixture was developed.

     

Effect of temperature on the solubility of carnallite type double salts

A method based on Pitzer's model has been used for calculation of the solubilities of carnallite type double salts crystallizing in the systems MeX–MgX₂–H₂O (Me=Li, NH₄, K, Rb, Cs; X=Cl, Br). The solubility of congruently soluble double salts was also determined experimentally at 25–75°C. The results from studies of the solubility diagrams of ternary carnallite type water-salt systems over a wide temperature range are summarized. It is found that the width of the crystallization region for each of the salts can be explained by the relative differences in the solubilities of the ternary solution components (MeX, MgX₂·6H₂O and MeX·MgX₂·6H₂O) and by a change of temperature, and by the effect of temperature on the solubility. A method is proposed for calculating Pitzer's ternary parameters of interionic interaction (_MN and _MNX) on the basis of experimental data for the solubility in water of the double salts crystallizing in the corresponding ternary water-salt systems.     

Solubility of rare earth metal bromides and iodides in aqueous systems

Abstract  

The International Union of Pure and Applied Chemistry (IUPAC) project of collection, compilation, and critical evaluation of solubility data of bromides and iodides of the scandium group and all lanthanides in water and aqueous systems containing either halide acids, halide salts, or organic compounds is under preparation. As a result of their similarity to the chlorides, which were recently evaluated, the bromides and iodides in the lanthanide series should show some regularities in their solubility data. Unfortunately, the corresponding results show a large scatter when ordered according to the atomic number. Thus, it is complicated to select the best data for recommendation. Reasons for the inaccuracy of solubility measurements are outlined. In fact some solubility values of bromides predicted by correlation with chlorides seem to be more reliable than the experimental ones. As sufficient experimental data at various temperatures were available, the water-rich fragment of the LaBr₃–H₂O equilibrium phase diagram has been formed and depicted. It seems to be similar to the well-known LaCl₃–H₂O diagram. Several regularities, with respect to stoichiometry and solubility of compounds formed, were observed during investigations of the aqueous ternary systems. The complex iodides of various lanthanides display more regularities in their properties than the bromides do.     

Self‐Assembled Amphiphilic Water Oxidation Catalysts: Control of O−O Bond Formation Pathways by Different Aggregation Patterns

The oxidation of water to molecular oxygen is the key step to realize water splitting from both biological and chemical perspective. In an effort to understand how water oxidation occurs on a molecular level, a large number of molecular catalysts have been synthesized to find an easy access to higher oxidation states as well as their capacity to make O?O bond. However, most of them function in a mixture of organic solvent and water and the O?O bond formation pathway is still a subject of intense debate. Herein, we design the first amphiphilic Ru‐bda (H₂bda=2,2′‐bipyridine‐6,6′‐dicarboxylic acid) water oxidation catalysts (WOCs) of formula [Ru^II(bda)(4‐OTEG‐pyridine)₂] ( 1 , OTEG=OCH₂CH₂OCH₂CH₂OCH₃) and [Ru^II(bda)(PySO₃Na)₂] ( 2 , PySO₃^?=pyridine‐3‐sulfonate), which possess good solubility in water. Dynamic light scattering (DLS), scanning electron microscope (SEM), critical aggregation concentration (CAC) experiments and product analysis demonstrate that they enable to self‐assemble in water and form the O?O bond through different routes even though they have the same bda^2? backbone. This work illustrates for the first time that the O?O bond formation pathway can be regulated by the interaction of ancillary ligands at supramolecular level.     

NMR.-Investigation of the Formaldehyde Addition and Oligomerisation Equilibria in the System Formaldehyde/Water/Acetic Acid/Hydrochloric Acid

An NMR. investigation of the state of formaldehyde in acidic solutions has been carried out. Solutions of DCl/D₂O/CD₃COOD containing two sources of formaldehyde, i.e. paraformaldehyde (I) and trioxane (II), were used for this purpose. In systems I and II the effect of various D₂O/CD₃COOD ratios, at a constant DCl concentration, was studied, while for II the effect of changing DCl concentration was also investigated. The results show that in aqueous solution, formaldehyde exists primarily as the monomeric and linear oligomeric forms of methylene glycol. Reducing the amount of D₂O (at constant DCl concentration), while increasing the CD₃COOD content, results in an increase in the polymeric species and in trioxane. In addition, substitution of water by acetic acid results in systems that are catalytically more active than aqueous solutions of the same hydrochloric acid concentration. Along with the usual polymer-monomer equilibria which exist in such solutions, side reactions of methylene glycol with the hydrochloric acid present also occur to a small extent, e.g. acetylation, substitution of OH by Cl and the Cannizzaro reaction. It is suggested that these findings will result in a better understanding of the formaldehyde crosslinking reactions in cotton cellulose.     

Study of Complex Formation Between 18-Crown-6 and Pb2+, Tl+ and Cd2+ Cations in Binary Aqueous/Non-aqueous Solvents Using Polarographic Techniques (DPP and SWP)

The complexation of Pb²⁺, Tl⁺ and Cd²⁺ cationsby 18-crown-6 was studied in water/propanol (H₂O/PrOH),water/acetonitrile (H₂O/AN) and water/dimethylformamide(H₂O/DMF) binary systems at 20 °C using squarewave polarography (SWP) and differential pulse polarography (DPP).It was confirmed that the stoichiometry of each of the complexes formed between 18C6 and the respective cations is 1 : 1. The formation constants of the complexes were found to increase with increasing concentration of the non-aqueous solvent. In all cases, a stability order of Pb²⁺ > Tl⁺ > Cd²⁺ was observed. In general,the stabilities of individual complexes were found to decrease as the binary solvent mixture varied from H₂O/AN to H₂O/PrOH to H₂O/DMF.     

A thermodynamic study of complexation process between <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>′-dipyridoxylidene(1,4-butanediamine) and Cd<Superscript>2+</Superscript> in some binary mixed solvents using conductometry

Complexation of the Cd²⁺ ion with N,N′-dipyridoxylidene(1,4-butanediamine) Schiff base was studied in pure solvents including acetonitrile (AN), ethanol (EtOH), methanol (MeOH), tetrahydrofuran (THF), dimethylformamide (DMF), water (H₂O), and various binary solvent mixtures of acetonitrile–ethanol (AN–EtOH), acetonitrile–methanol (AN–MeOH), acetonitrile–tetrahydrofuran (AN–THF), acetonitrile–dimethylformamide (AN–DMF), and acetonitrile–water (AN–H₂O) systems at different temperatures using the conductometric method. The conductance data show that the stoichiometry of complex is 1: 1 [ML] in all solvent systems. A non-linear behavior was observed for changes of log K_f of [Cd(N,N′-dipyridoxylidene(1,4-butanediamine)] complex versus the composition of the binary mixed solvents, which was explained in terms of solvent–solvent interactions. The results show that the thermodynamics of complexation reaction is affected by the nature and composition of the mixed solvents.     

Isotope Effects in Plasmonic Photosynthesis

The photoexcitation of plasmonic nanoparticles has been shown to drive multistep, multicarrier transformations, such as the conversion of CO₂ into hydrocarbons. But for such plasmon-driven chemistry to be precisely understood and modeled, the critical photoinitiation step in the reaction cascade must be identified. We meet this goal by measuring H/D and ¹²C/¹³C kinetic isotope effects (KIEs) in plasmonic photosynthesis. In particular, we found that the substitution of H₂O with D₂O slows hydrocarbon production by a factor of 5–8. This primary H/D KIE leads to the inference that hole-driven scission of the O−H bond in H₂O is a critical, limiting step in plasmonic photosynthesis. This study advances mechanistic understanding of light-driven chemical reactions on plasmonic nanoparticles.     

Measurement of mineral solubilities in the ternary systems NaCl−ZnCl<Subscript>2</Subscript>−H<Subscript>2</Subscript>O and MgCl<Subscript>2</Subscript>−ZnCl<Subscript>2</Subscript>−H<Subscript>2</Subscript>O at 373 K

In this work, the solubilities of the salt minerals and the densities of solution in two ternary systems sodium chloride–zinc chloride–water and magnesium chloride–zinc chloride–water were measured at 373 K using an isothermal solution saturation method. Based on the determined equilibrium solubility data and the corresponding equilibrium solid phase, the phase diagrams and density diagrams of the two systems were plotted. The results show that the two ternary systems are complex and the eutectic points, the univariant solubility curves and the solid crystalline phase regions are shown and discussed. The phase diagram of the ternary system NaCl?ZnCl₂?H₂O at 373 K is constituted of two eutectic points, three univariant solubility curves and three solid crystalline phase regions corresponding to NaCl, ZnCl₂ and 2NaCl · ZnCl₂. And the phase diagram of the ternary system MgCl₂?ZnCl₂?H₂O at 373 K includes two eutectic points, three univariant solubility curves and three solid crystalline phase regions corresponding to MgCl₂ · 6H₂O, MgCl₂ · ZnCl₂ · 5H₂O and ZnCl₂. The experimental results were simply discussed.     

The solubility of CO2 and N2O in olive oil

The solubility of CO₂ and N₂O in olive oil has been measured at temperatures of about 298, 310, and 323 K with a gravimetric microbalance under pressures up to 2 MPa. The molecular weight of olive oil has been analyzed and found to be about 882 g mol⁻¹ as a mixed oil compound. The observed solubility data have been correlated with a cubic equation of state (EOS) model. N₂O has a larger solubility than CO₂ in olive oil based on either the mole or mass fraction. The present results clarify some ambiguities from the previous N₂O solubility data in the literature.     

Die Berechnung komplexer Absorptionsgleichgewichte ionogener Substanzen in wäßrigen Lösungsmitteln mit Hilfe eines Reaktionsmodells

The solubility of ionogen substances in water and aqueous ionic solutions is important for calculation of absorption processes. Aqueous solutions with complex reaction systems behave themselves extremely nonideal. In simple cases equilibria can be determined with the concept of nonideal thermodynamics. The model used in this work is based on ideal calculation of reaction equilibria and gas solubility. The model parameters (equilibrium constants andHenry constants) for the systems SO₂-H₂O,MEA-H₂S-H₂O,DEA-H₂S-H₂O andMEA-CO₂-H₂O are computed by regression of experimental data. Equilibrium reactions are selected according toBrinkley's method. The selection of the reacting species has decisive influence on the accuracy of the data fitting. Data regression is done numerically and leads to the formulation of nonlinear systems of equations, which have to be solved for each data point. This solutions are performed in an inner loop. By using the maximum-likelihood-principle the model parameters are optimized in the superior regression loop. Experimental data for the regression are the partial pressure and the total concentration of gas in the liquid phase. The used model is able to fit these data satisfactoryly. The model parameters, which are calculated from simultaneous data regression for different temperatures, ensure a simple correlation ofvan't Hoff. However, for similar reactions equilibria in different reaction systems, it is impossible to compute the same values for the equilibrium constants.     

Density Functional Theory Study on Hydrogen Bonding Interaction of Catechin-(H2O)n

Density functional theory B3LYP method with 6‐31G* basis set has been used to optimize the geometries of the catechin, water and catechin‐(H₂O)_n complexes. The vibrational frequencies have been studied at the same level to analyze these complexes. Six and eleven stable structures for the catechin‐H₂O and catechin‐(H₂O)₂ have been found, respectively. Theories of atoms in molecules (AIM) and natural bond orbital (NBO) have been utilized to investigate the hydrogen bonds involved in all the systems. The interaction energies of all the complexes corrected by basis set superposition error, are from ?13.27 to ?83.56 kJ/mol. All calculations also indicate that there are strong hydrogen‐bonding interactions in catechin‐water complexes. The strong hydrogen‐bonding contributes to the interaction energies dominantly. The O–H stretching motions in all the complexes are red‐shifted relative to that of the monomer.     

Effect of the orientation of coordinated water molecules on the electronic structure of trans halo-aquo complexes: application to TiCl2(H2O) 4 + and VCl2(H2O) 4 +

The X method has been utilized to calculate the electronic structure of trans-TiCl₂(H₂O) ₄ ⁺ and trans VCl₂(H₂O) ₄ ⁺ ions. Different conformations of coordinated water molecules have been considered. It has been found that the most stable configuration in both cases is the one with the plane of the water molecules parallel to the Cl-metal-Cl axis. The nature of the tetragonally distorted ground state has been found to depend on the orientation of the water molecules in these systems.     

Substitution Patterns of Cellulose Ethers - Influence of the Synthetic Pathway

Commercial cellulose ethers are usually prepared under heterogeneous reaction conditions. In contrast, this contribution also describes the derivatization under homogeneous conditions in N-methylmorpholine-N-oxide monohydrate (NMMNO*H₂O) and under heterogeneous conditions after converting native cellulose to amorphous cellulose. Amorphous cellulose is prepared by dissolving cellulose in NMMNO*H₂O followed by precipitation in different media. The degree of order and the porosity of the regenerated cellulose is significantly influenced by the content of water in the precipitating agent. The differences are described by measurements using wide angle X-ray scattering, solid-state ¹³C-NMR, mercury porosimetry, and water/liquid retention values. Three synthetic pathways (heterogeneous, heterogeneous with amorphous cellulose and homogeneous) are compared regarding the structure-property relationship of the cellulose ethers formed. Carboxymethylation, hydroxyethylation, hydroxypropylation and sulfoethylation are considered in detail. The choice of synthetic pathway has a significant influence on the degree of substitution (DS), the distribution of substituents on the level of the anhydroglucose unit (AGU), solubility behavior, and the viscosity of aqueous solutions. In general an increasing solubility and an increasing viscosity are observed from heterogeneous to heterogeneous with amorphous cellulose to homogeneous reaction conditions. There is a remarkable difference between the heterogeneously produced cellulose ethers with a DS distribution C2 ≥ C6 > C3 and the strictly homogeneous etherification in NMMNO*H₂O/organic solvent systems with a DS distribution of C3 > C2 ≫ C6. This high regioselectivity at the secondary OH-groups of the AGU may be caused by the strong solvation behavior of NMMNO*H₂O and thereby a protecting function at the C6-OH-group.     

Applcation of the Pitzer equations to the solubility of ternary aqueous nitrate solutions at 25°C

The solubilities of the ternary systems Cu(NO₃)₂–Ca(NO₃)₂–H₂O and Cu(NO₃)₂–Mg(NO₃)₂–H₂O at 25°C were calculated from the solubility data for the binary systems by using the Pitzer equations. The calculated solubility isotherms were confirmed experimentally. The activity coefficients of the components, the osmotic coefficient, and the activity of water were calculated from the experimental isotherms.     

Saponification of ethyl acetate in 2,6-lutidine + water near its critical point

We have measured the rate of saponification of ethyl acetate (CH₃COOC₂H₅) in 2,6-lutidine (2,6-DMP)?+?water (H₂O) near and far away from its critical point by electrical conductivity experiment. We found that the rate of saponification slowed in the one-phase region at temperatures near the critical point. This behaviour is evidence in support of critical slowing down. Moreover, the experimental results were compared with those of the same reaction in a different critical mixture of 2-butoxyethanol?+?H₂O [Y.W. Kim, Int. J. Thermophys. 25, 1025 (2004)].     

An isotopic effect in the dielectric spectra of Ark. 9/water systems

Dielectric spectra of H₂O and D₂O molecules in the L_α liquid crystalline phase of nonylphenoxy-poly(ethylenoxy)ethanol(Ark. 9)/water lyotropic systems have been investigated by dielectric time domain spectroscopy in the frequency range from 10 MHz to 10 GHz. By fitting the Cole-Cole formula to the dielectric spectra, obtained at different temperatures the dielectric increments, the relaxation times and the distribution parameters have been calculated. A strong retardation of water molecules has been found for the lamellar phase with low water content, i.e. 10 water molecules (H₂O or D₂O) per one Ark. 9 molecule. The relaxation times obtained at room temperature for the light and heavy water are 63 and 93 ps, respectively. It means that the retardation factor for D₂O molecules in the L_α phase is close to 1.5 and higher than that found for pure heavy water (1.25). Any decomposition of the dielectric spectra obtained seems to be unsubstantiated. The temperature dependences of the relaxation times acquired for both kinds of water obey the Arrhenius behaviour.