Aqueous Organic Solvent Mixtures Research Articles

Simulation and practical investigation of carbonic anhydrase stability in an industrial solvent system of methyl diethanolamine for carbon dioxide capture

Carbonic anhydrase owing to its potential as an industrial biocatalyst for carbon dioxide sequestration from flue gas has attracted considerable attention in solving global warming problems. A large body of research has been conducted to increase the thermal stability of carbonic anhydrase from different sources against the harsh operational conditions of CO2 capture systems. In contrast to cost-intensive protein engineering methods, solvation with aqueous-organic binary mixtures offers a convenient and economical alternative strategy for retention of protein structure and stability. This study aimed to examine the stabilizing effect of methyl diethanolamine (MDEA) as a component of an aqueous-organic solvent mixture on human carbonic anhydrase II (HCA II) at extreme temperatures. Computational and also spectroscopic examinations were employed for tracking conformational changes and stability evaluation of HCA II in 50:50 (vol %) water: MDEA binary mixture at high temperature. Molecular dynamic (MD) simulation studies predicted the high thermal stability of HCA II in the presence of MDEA. UV absorbance spectra confirmed the thermo-stabilizing effect of the binary solvent mixture on HCA II. While the enzymatic activity of HCA II at 25 °C in the presence of 10, 25, and 50 (vol%) of MDEA was substantially increased, no obvious effect on retention of HCA II activity in the water-MDEA binary solvent mixture at 85 °C was seen. It is shown that the solvation of HCA II in the presence of MDEA could result in the prevention of aggregate formation in high temperatures but not functional stability. Communicated by Ramaswamy H. Sarma

The Solvation Shell of Small Solutes in Aqueous-Organic Solvent Mixtures and Its Implications for Reversed-Phase Liquid Chromatography.

Reversed-phase liquid chromatography (RPLC) operates with water-organic solvent (W-OS) mobile phases where preferential solvation (PS) of solutes is likely. To investigate the relevance of the solute solvation shell in the mobile phase for RPLC retention, we combine data from molecular dynamics simulations of small, neutral solutes (six analytes and two dead time markers) in W-methanol (MeOH) and W-acetonitrile (ACN) mixtures with corresponding retention data obtained on an RPLC column over a wide range of W/OS ratios. Data derived from Kirkwood-Buff integrals show PS by the OS for analytes vs low or negative PS for dead time markers. W-ACN mixtures generate a higher amount of PS than W-MeOH mixtures, which contributes to the higher eluent strength of ACN in RPLC. Difference spatial distribution functions reveal anisotropic solvation shells with OS excess at hydrocarbon elements and W excess at functional groups, predicting that retention by the hydrophobic stationary phase is favored by hydrocarbon elements and limited by functional groups. Analysis of solute-solvent hydrogen bonds pinpoints the hydrogen-bond requirements toward W as the retention-limiting factor. The relation between the solute solvation shell and retention confirms the importance of W-OS and solute-W hydrogen bonding for RPLC retention.

Measurement of the pKa Values of Organic Molecules in Aqueous-Organic Solvent Mixtures by 1H NMR without External Calibrants.

Aqueous-organic solvent mixtures are commonly used for reactions or analyses, where the components of a system are insoluble in pure water. The acid dissociation constant is an important property to measure in these media as it determines the charge state, solubility, and reactivity of a molecule. While NMR spectroscopy is an established tool for the measurement of pKa in water, its use in aqueous-organic solvents is greatly hindered by the requirement for external calibrants on which a working pH scale is set. Such calibrants include buffer solutions, "anchor" molecules with known pKa values, and pH electrodes that have undergone lengthy calibration procedures in the solvent mixture of interest. However, such calibrations are often inconvenient to perform, while literature pKa data covering the required range may not be available at the solvent composition or the temperature of interest. Here, we present a method to determine pKa in aqueous-organic solvents directly by NMR. We first determine pKa of an organic acid such as 2,6-dihydroxybenzoic acid (2,6-DHB) by measuring its 1H chemical shift as a function of concentration along a concentration gradient using chemical shift imaging (CSI). Using 2,6-DHB as a reference, we then determine pKa of less acidic molecules in single CSI experiments via the variation of their 1H chemical shifts along pH gradients. As proof of concept, we determine the pKa values of organic acids and bases up to pKa 10 in 50% (v/v) 1-propanol/water, 50% (v/v) dimethyl sulfoxide/water, and 30% (v/v) acetonitrile/water and obtain good agreement with the literature values.

Comments on “Study on 2-amino-4-chloro-6-methoxypyrimidine in four binary solvent mixtures: Solubility measurement, calculation, preferential solvation and extended Hildebrand solubility parameter approach analysis”

A polemic is given regarding the apparent Gibbs energies of dissolution reported by Huang and Yao for 2-amino-4-chloro-6-methoxypyrimidine dissolved in four binary aqueous-organic solvent mixtures at the harmonic mean temperature. Our reanalysis of the authors’ experimental mole fraction solubility data yielded positive values, rather than negative values, for the apparent Gibbs energies of dissolution.

IUPAC-NIST Solubility Data Series. 105. Solubility of Solid Alkanoic Acids, Alkenoic Acids, Alkanedioic Acids, and Alkenedioic Acids Dissolved in Neat Organic Solvents, Organic Solvent Mixtures, and Aqueous–Organic Solvent Mixtures. III. Alkanedioic Acids and Alkenedioic Acids

Solubility data are compiled and reviewed for 19 alkanedioc and alkenedioic acids dissolved in neat organic solvents and well-defined binary organic and aqueous–organic solvent mixtures. The compiled solubility data were retrieved from the published chemical, engineering, and pharmaceutical literature covering the period between 1910 and the beginning of 2021.

Engineered Binding Microenvironments in Halogen Bonding Polymers for Enhanced Anion Sensing.

Mimicking Nature's polymeric protein architectures by designing hosts with binding cavities screened from bulk solvent is a promising approach to achieving anion recognition in competitive media. Accomplishing this, however, can be synthetically demanding. Herein we present a synthetically tractable approach, by directly incorporating potent supramolecular anion-receptive motifs into a polymeric scaffold, tuneable through a judicious selection of the co-monomer. A comprehensive analysis of anion recognition and sensing is demonstrated with redox-active, halogen bonding polymeric hosts. Notably, the polymeric hosts consistently outperform their monomeric analogues, with especially large halide binding enhancements of ca. 50-fold observed in aqueous-organic solvent mixtures. These binding enhancements are rationalised by the generation and presentation of low dielectric constant binding microenvironments from which there is appreciable solvent exclusion.

Engineering intraporous solvent environments: effects of aqueous-organic solvent mixtures on competition between zeolite-catalyzed epoxidation and H2O2 decomposition pathways.

Solvent molecules alter the free energies of liquid phase species and adsorbed intermediates during catalytic reactions, thereby impacting rates and selectivities. Here, we examine these effects through the epoxidation of 1-hexene (C6H12) with hydrogen peroxide (H2O2) over hydrophilic and hydrophobic Ti-BEA zeolites immersed in aqueous solvent mixtures (acetonitrile, methanol, and γ-butyrolactone). Greater H2O mole fractions provide greater epoxidation rates, lower H2O2 decomposition rates, and hence improved H2O2 selectivities to the desired epoxide product in each combination of solvent and zeolite. The mechanisms for epoxidation and H2O2 decomposition remain constant across solvent compositions; however, H2O2 activates reversibly in protic solutions. Differences in rates and selectivities reflect the disproportionate stabilization of transition states within zeolite pores with respect to surface intermediates and fluid phase reactants, as evinced by turnover rates normalized by the activity coefficients of C6H12 and H2O2. Opposing trends in activation barriers suggest that the hydrophobic epoxidation transition state disrupts hydrogen bonds with solvent molecules, while the hydrophilic decomposition transition state forms hydrogen bonds with surrounding solvent molecules. Solvent compositions and adsorption volumes within pores, from 1H NMR spectroscopy and vapor adsorption, depend on the composition of the bulk solution and the density of silanol defects within pores. Strong correlations between epoxidation activation enthalpies and epoxide adsorption enthalpies from isothermal titration calorimetry indicate that the reorganization of solvent molecules (and associated entropy gains) required to accommodate transition states provides the most significant contribution to the stability of transition states that determine rates and selectivities. These results demonstrate that replacing a portion of organic solvents with H2O offers opportunities to increase rates and selectivities for zeolite-catalyzed reactions while reducing usage of organic solvents for chemical manufacturing.

Effect of the aqueous-organic solvent mixtures upon super-aggregation of chitosan

Effect of the aqueous-organic solvent mixtures upon super-aggregation of chitosan

Estimating evaporation rates and contaminant air concentrations due to small spills of non-ideal aqueous organic solvent mixtures in a controlled environment

Although small spills of non-ideal organic solvent mixtures are ubiquitous undesirable events in occupational settings, the potential risk of exposure associated with such scenarios remains insufficiently investigated. This study aimed to examine the impact of non-ideality on evaporation rates and contaminant air concentrations resulting from small spills of organic solvent mixtures. Evaporation rate constants alphas (α) were experimentally measured for five pure solvents using a gravimetric approach during solvent evaporation tests designed to simulate small spills of solvents. Two equations were used for estimating contaminants’ evaporation rates from aqueous mixtures assuming either ideal or non-ideal behavior based on the pure-chemical alpha values. A spill model also known as the well-mixed room model with exponentially decreasing emission rate was used to predict air concentrations during various spill scenarios based on the two sets of estimated evaporation rates. Model predictive performance was evaluated by comparing the estimates against real-time concentrations measured for the same scenarios. Evaluations for 12 binary non-ideal aqueous mixtures found that the estimated evaporation rates accounting for the correction by the activity coefficients of the solvents (median = 0.0318 min−1) were higher than the evaporation rates estimated without the correction factor (median = 0.00632 min−1). Model estimates using the corrected evaporation rates reasonably agreed with the measured values, with a median predicted peak concentrations-to-measured peak concentrations ratio of 0.92 (0.81 to 1.32) and a median difference between the predicted and the measured peak times of −5 min. By contrast, when the non-corrected evaporation rates were used, the median predicted peak concentrations-to-measured peak concentrations ratio was 0.31 (0.08 to 0.75) and the median difference between the predicted and the measured peak times was +33 min. Results from this study demonstrate the importance of considering the non-ideality effect for accurately estimating evaporation rates and contaminant air concentrations generated by solvent mixtures. Moreover, this study is a step further in improving knowledge of modeling exposures related to small spills of organic solvent mixtures.

A Horseradish Peroxidase-Mediator System for Benzylic C-H Activation.

Enzyme-mediator systems generate radical intermediates that abstract hydrogen atoms under mild conditions. These systems have been employed extensively for alcohol oxidation, primarily in biomass degradation, but they are underexplored for direct activation of C(sp3)-H bonds in alkyl groups. Here, we combine horseradish peroxidase (HRP), H2O2, and redox mediator N-hydroxyphthalimide (NHPI) for C(sp3)-H functionalization of alkylbenzene-type substrates. The HRP-NHPI system is >10-fold more active than existing enzyme-mediator systems in converting alkylbenzenes to ketones and aldehydes under air, and it operates from 0-50 °C and in numerous aqueous-organic solvent mixtures. The benzylic substrate radical can be trapped through a reaction with NHPI, demonstrating the formation of benzylic products beyond ketones. Furthermore, we demonstrate a one-pot, two-step enzymatic cascade for converting alkylbenzenes to benzylic amines. Overall, the HRP-NHPI system enables the selective benzylic C-H functionalization of diverse substrates under mild conditions using a straightforward procedure.

Development of an Automatable Affinity Purification Process for DNA-Encoded Chemistry

DNA-encoded library technologies require high-throughput, compatible, and well automatable platforms for chemistry development, building block rehearsal, and library synthesis. An affinity-based process using Watson–Crick interactions was developed that enables purification of DNA-tagged compounds from complex reaction mixtures. The purification relies on a single-stranded DNA-oligonucleotide, called capture strand, which was covalently coupled to an agarose matrix and to which a DNA-compound conjugate from a DNA-encoded library (DEL) reaction can be reversibly annealed to. The thus-formed DNA duplex tolerated surprisingly stringent washing conditions with multiple solvents to remove excess reactants and reagents. The tolerated solvents included aqueous buffers, aqueous EDTA solutions to remove metal ions, aqueous mixtures of organic solvents, and even pure organic solvents. The purified DNA-conjugate was eluted with aqueous ammonia and could be used for reaction analysis or for instance in DNA-encoded library synthesis. The lab equipment for purification was tailored for automation with open-source hardware and constructed by 3D printing.

Membrane fouling mechanisms by BSA in aqueous-organic solvent mixtures

To exploit the benefits of membrane-based separation for the pharmaceutical and chemical industries, the understanding of membrane fouling in organic solvents is crucial. Specifically for the separation of biocatalysts in the manufacture of pharmaceuticals, this study investigated membrane fouling by bovine serum albumin (BSA) in 10% v/v isopropanol (IPA), 10% v/v dimethyl sulfoxide (DMSO), 30% v/v IPA, and 30% v/v DMSO, benchmarked against that in water. The presence of either IPA or DMSO worsened fouling, with the latter comparatively worse. To understand the fouling mechanisms, Field Emission Scanning Electron Microscopy (FESEM) images were taken to assess external fouling, Evapoporometry (EP) was used to measure the pore-size distributions of the fouled membranes to examine internal fouling, a fouling model was applied to extract the fouling parameters, and the interfacial interaction energies were derived. Results indicate that the worst fouling in 30% v/v DMSO was due to both significant external fouling and internal fouling, whereas the second-worst fouling by 30% v/v IPA was caused predominantly by internal fouling. The magnitudes of the total DLVO- and XDLVO-based interaction energies were found to be poorly related to the relative flux declines. This study provides valuable insights into membrane fouling in different solvent environments.

Formulation of Rosemary Extracts through Spray-Drying Encapsulation or Emulsification

Natural, plant-derived antioxidants can be used to prolong the shelf life of food or cosmetics, or as health-promoting additives. Although their extraction from plants has been extensively studied, purification and formulation processes need further research to allow their exploitation. In the present work, rosemary extracts were obtained by successive extractions with acetone and water or single extraction by either an acetone:water or ethanol:water mixture. The extracts were analyzed by HPLC-DAD, and rosmarinic acid, carnosic acid, carnosol, and several flavonoids were identified and quantified. The extracts obtained by water or aqueous mixtures of organic solvents were encapsulated in maltodextrin combined with gum arabic with a high encapsulation yield (90–100%) and efficiency (97%) for rosmarinic acid and flavonoids. The acetone extract, rich in carnosic acid, was transformed to oil solution and either encapsulated or formulated in emulsion. The shelf life of encapsulated products was tested over a period of six months, and the results showed high retention of rosmarinic acid (88%) and lower of flavonoids (54–80%). Carnosic acid presented lower retention either encapsulated in solid powder (65–70% after one month at ambient temperature) or in emulsion (48% after 20 days of storage at 15 °C), while it was partially transformed to carnosol.

Smart supramolecular photoresponsive gelator with long-alkyl chain azobenzene incorporated sugar derivatives for recycling aromatic solvents and sequestration of cationic dyes.

Phase-selective gelation of low molecular-weight photoresponsive organogelator possessing long aliphatic chain azobenzene sugar derivatives and its applications in the recycling of aromatic solvents and also the removal of cationic dyes is reported. Very low critical gelation concentration (CGC) in aromatic solvents implies that it acts as a very good gelator. The photoinduced gel-to-sol transition was attained by irradiation with UV light at 350 nm. These organogels work as a selective adsorbent for efficiently removing cationic dyes from individual aqueous dye solutions and in a mixture of cationic and anionic dye solutions show more than 95% removal within 12 h. These insights indicate that these sugar derivatives could be exploited in implementing smart materials for environmental remediation.

IUPAC–NIST Solubility Data Series. 105. Solubility of Solid Alkanoic Acids, Alkenoic Acids, Alkanedioic Acids, and Alkenedioic Acids Dissolved in Neat Organic Solvents, Organic Solvent Mixtures, and Aqueous–Organic Solvent Mixtures. II. Alkenoic and Alkynoic Acids

Solubility data are compiled and reviewed for ten alkenoic acids and one alkynoic acid dissolved in neat organic mono-solvents. The compiled solubility data were retrieved from the published chemical, engineering, and pharmaceutical literature covering the period from 1910 to the beginning of 2021.

IUPAC–NIST Solubility Data Series. 105. Solubility of Solid Alkanoic Acids, Alkenoic Acids, Alkanedioic Acids, and Alkenedioic Acids Dissolved in Neat Organic Solvents, Organic Solvent Mixtures, and Aqueous–Organic Solvent Mixtures. I. Alkanoic Acids

Solubility data are compiled and reviewed for 15 alkanoic acids dissolved in neat organic solvents and well-defined binary organic and aqueous–organic solvent mixtures. The compiled solubility data were retrieved from the published chemical, engineering, and pharmaceutical literature covering the period between 1910 and the beginning of 2021.

Effect of solution nonideality on cholesterol supersaturation for liquid antisolvent crystallization

The present work aims to analyze the effect of solution non-ideality on the magnitude of supersaturation of cholesterol (3) for crystallization from its solution in organic solvent (2) using water (1) as antisolvent. Real supersaturation (S) has been computed as the ratio of activities (a 3/a 3*) at the supersaturated (x 3) and saturated (x 3*) mole fractions respectively, by multiplying the ideal solution supersaturation (Sx = x 3/x 3*) with the activity coefficient ratio [γ3/γ3*]. The values of [γ3/γ3*] are estimated using the Pharma Modified UNIFAC model. The x 3* data have been measured experimentally in aqueous organic-solvent mixtures at different values of x 1 in ethanol at three temperatures (T) in the range of 290.5 to 299.5 K, and in acetone and acetonitrile at 299.5 K. These data have been correlated in terms of x 1 and T separately for computation of Sx , [γ3/γ3*], and S. The quantitative impact of solution non-ideality on the sensitivity of S to the variations of x 1, x 3, [x 3/x 3*], T and nature of solvent are investigated computationally. It is observed that [γ3/γ3*] is less than 1.0 and is relatively more significant at lower x 1 and higher Sx , though it is almost invariant with T and solvent. The value of Sx at 299.5 K is found higher than S by 15% at Sx = 2 and by 162% at Sx = 10. The results clearly establish that it is necessary to include the solution non-ideality in the estimation of solute supersaturation, as otherwise significant errors may result in computing nucleation and growth rates.

Anion recognition by halogen bonding and hydrogen bonding bis(triazole)-imidazolium [2]rotaxanes.

A novel halogen bonding (XB) bis(iodotriazole)-imidazolium motif is incorporated into the axle component of a [2]rotaxane via a discrete chloride anion template directed clipping methodology. 1H NMR anion titration experiments reveal the interlocked host is capable of strong halide and sulfate oxoanion binding in competitive aqueous-organic CDCl3/CD3OD/D2O (45 : 45 : 10 v/v) solvent mixtures. In comparison to a hydrogen bonding rotaxane analogue, which exhibited no pronounced selectivity between Cl-, I- and SO42-, the axle iodo-triazole donor motifs of the XB rotaxane modulate the anion recognition preference towards the lighter halides Cl- ≈ Br- > SO42- > I-.

Current perspectives on supercharging reagents in electrospray ionization mass spectrometry

In electrospray ionization mass spectrometry (ESI-MS), analytes are introduced into the mass spectrometer in typically aqueous-organic solvent mixtures, including pH modifiers. One mechanism for improving the signal intensity and simultaneously increasing the generation of higher charge-state ions is the inclusion of small amounts (approx. <0.5% v/v mobile phase solution) of charge-inducing or supercharging reagents, such as m-nitrobenzyl alcohol, o-nitrobenzyl alcohol, m-nitrobenzonitrile, m-(trifluoromethyl)-benzyl alcohol and sulfolane. We explore the direct and indirect (colligative properties) that have been proposed as responsible for their modes of action during ESI. Of the many theorized mechanisms of ESI, we re-visit the three most popular and highlight how they are impacted by supercharging observations on small ions to large molecules including proteins. We then provide a comprehensive list of 34 supercharging reagents that have been demonstrated in ESI experiments. We include an additional 19 potential candidate isomers as supercharging reagents and comment on their broad physico-chemical properties. It is becoming increasingly obvious that advances in technology and improved ion source design, analyzers e.g. the use of ion mobility, ion trap, circular dichroism (CD) spectroscopy, together with computer modeling are increasing the knowledge base and, together with the untested isomers and yet-to-be unearthed ones, offer opportunities for further research and application in other areas of polymer research.

Conductometric Study of Complexation of Macrocyclic Compounds with Zinc(II) and Copper(II) Ions in Aqueous-Organic Solvent Mixtures

The conductance behavior of Zn2+ and Cu2+ and their complexes with two ligands (crown ethers) have been inspected in 10, 20, 30, and 40% DMF–water mixed solvent at 298.15, 308.15, 318.15, and 328.15 K. The conductance study indicates a 1 : 1 complexation mode amongst the metal ions and ligands hereby studied. The order of stability constants with crown ethers was found to be Cu(II) > Zn(II). The stability constant for Zn2+ ion with crown ether complexes in 10 and 40 wt % solvent composition varies in the order of benzo-18-crown-6 > benzo-15-crown-5. The stability constant for Cu2+ ion with crown ether complexes in 10% solvent composition varies in the order of benzo-18-crown-6 > benzo-15-crown-5, and for 40% solvent composition, it is benzo-18-crown-6 > benzo-15-crown-5. The enthalpy and the entropy of complexation were estimated from the variation of stability constants with respect to the variation of temperature. The observed results elicit that the complexation is enthalpy stabilized, but entropy destabilized.