The Contrasting Role of Water and Acid Within Organic Phase Amphiphile Aggregation

Hypothesis: Amphiphile self-assembly in non-polar media is often enhanced by polar co-solutes, as observed upon amphiphile mediated transport of water and acid into organic solution. Such co-extraction precludes understanding the individual roles of polar solutes upon self-assembly. Using this liquid-liquid extraction (LLE) system as a test-bed, we hypothesize that co-solute competition and hydrogen bond (HB) characteristics cause different size/shape distributions of assembled amphiphiles and alter self-assembly mechanisms in non-polar solvents. Experiments: Concentration dependent classical molecular dynamics simulation and intermolecular network analyses identified the correlating relationships between HB properties of H2O and HNO3 upon the aggregation of N,N,N,N-tetraoctyl-3-oxapentanediamide (TODGA), a prevalent LLE amphiphile extractant. Findings: Concentration dependent competition of hydrogen bonding fundamentally impacts amphiphile self-assembly in non-polar media. H2O bridges TODGA and enhances self-assembly, however as [H2O]org increases, preferential self-solvation leads to large (H2O)n clusters that cause TODGA clusters to sorb to the (H2O)n periphery and form extended aggregation. HNO3 restricts the (H2O)n size by disrupting the HB network. At large [H2O]org, HNO3 modulates TODGA self-assembly from extended to local aggregation. We attribute prior experimental observations to the role of water rather than co-extracted HNO3, thus providing valuable new insight into the means by which extractant aggregation can be tuned.

Development and Validation of Retention Models in Supercritical Fluid Chromatography for Impregnation Process Design

The retention factor is the key quantity for the thermodynamic analysis of the retention mechanism in chromatographic experiments. In this work, we measure retention factors for moderately polar solutes on four silica-based porous matrices as stationary phases by supercritical fluid chromatography. Elution of the solutes is only possible with binary mixtures of supercritical carbon dioxide (sc-CO2) and modifier (methanol) due to the low polarity of pure sc-CO2. The addition of modifiers makes the retention mechanism more complex and masks interactions between solute and stationary phase. In this work, we develop and validate several retention models that allow the obtaining of retention factors in modifier-free sc-CO2. Such models pave the way for quantifying adsorption interactions between polar solutes and non-swellable porous matrices in pure sc-CO2 based on retention data obtained in sc-CO2/modifier mixtures. The obtained information will thereby facilitate the understanding and design of impregnation processes, which are often performed in modifier-free conditions.

Comparison of the Fitting Performance of Retention Models and Elution Strength Behaviour in Hydrophilic-Interaction and Reversed-Phase Liquid Chromatography

Hydrophilic interaction liquid chromatography (HILIC) is able to separate from polar to highly polar solutes, using similar eluents to those in the reversed-phase mode (RPLC) and a polar stationary phase, where water is adsorbed onto its surface. It is widely accepted that multiple modes of interaction take place in the HILIC environment, which can be far more complex than the interactions in an RPLC column. The behaviour in HILIC should be adequately modelled to predict the retention with optimisation purposes and improve the understanding on retention mechanisms, as is the case for RPLC. In this work, the prediction performance of several retention models is studied for seven HILIC columns (underivatised silica, and silica containing diol, amino and sulfobetaine functional groups, together with three columns recently manufactured with neutral, anionic, and cationic character), using uracil and six polar nucleosides (adenosine, cytidine, guanosine, thymidine, uridine, and xanthosine) as probe compounds. The results in HILIC are compared with those that were offered by the elution of several polar sulphonamides and diuretics analysed with two C18 columns (Chromolith Speed ROD and Zorbax Eclipse XDB). It is shown that eight retention models, which only consider partitioning or both partitioning and adsorption, give similar good accuracy in predictions for both HILIC and RPLC columns. However, the study on the elution strength behaviour, at varying mobile phase composition, reveals similarities (or differences) between RPLC and HILIC columns of diverse nature. The particular behaviour for the HILIC and RPLC columns was also revealed when the retention, in both modes, was fitted to a model that describes the change in the elution strength with the modifier concentration.

Fungal X-Intrinsic Protein Aquaporin from Trichoderma atroviride: Structural and Functional Considerations

The major intrinsic protein (MIP) superfamily is a key part of the fungal transmembrane transport network. It facilitates the transport of water and low molecular weight solutes across biomembranes. The fungal uncharacterized X-Intrinsic Protein (XIP) subfamily includes the full protein diversity of MIP. Their biological functions still remain fully hypothetical. The aim of this study is still to deepen the diversity and the structure of the XIP subfamily in light of the MIP counterparts—the aquaporins (AQPs) and aquaglyceroporins (AQGPs)—and to describe for the first time their function in the development, biomass accumulation, and mycoparasitic aptitudes of the fungal bioagent Trichoderma atroviride. The fungus-XIP clade, with one member (TriatXIP), is one of the three clades of MIPs that make up the diversity of T. atroviride MIPs, along with the AQPs (three members) and the AQGPs (three members). TriatXIP resembles those of strict aquaporins, predicting water diffusion and possibly other small polar solutes due to particularly wider ar/R constriction with a Lysine substitution at the LE2 position. The XIP loss of function in ∆TriatXIP mutants slightly delays biomass accumulation but does not impact mycoparasitic activities. ∆TriatMIP forms colonies similar to wild type; however, the hyphae are slightly thinner and colonies produce rare chlamydospores in PDA and specific media, most of which are relatively small and exhibit abnormal morphologies. To better understand the molecular causes of these deviant phenotypes, a wide-metabolic survey of the ∆TriatXIPs demonstrates that the delayed growth kinetic, correlated to a decrease in respiration rate, is caused by perturbations in the pentose phosphate pathway. Furthermore, the null expression of the XIP gene strongly impacts the expression of four expressed MIP-encoding genes of T. atroviride, a plausible compensating effect which safeguards the physiological integrity and life cycle of the fungus. This paper offers an overview of the fungal XIP family in the biocontrol agent T. atroviride which will be useful for further functional analysis of this particular MIP subfamily in vegetative growth and the environmental stress response in fungi. Ultimately, these findings have implications for the ecophysiology of Trichoderma spp. in natural, agronomic, and industrial systems.

Water as a tuneable solvent: a perspective

Water is the most sustainable solvent, but its polarity limits the solubility of non-polar solutes. Confining water in hydrophobic nanopores could be a way to modulate water solvent properties and enable using water as tuneable solvent (WaTuSo).

Selecting ultrafiltration membranes for fractionation of high added value compounds from grape pomace extracts

The purpose of the current study is to investigate the use of ultrafiltration membrane for the fractionation of phenolic compounds from subcritical water grape pomace extract and the separation of these compounds from other co-extracted components. The extract was assayed in a cross-flow apparatus against eleven membranes with molecular weight ranging from 100 to 2 kDa. Monitoring of the process was executed by determining performance parameters and retention coefficients of proteins, polysaccharides, sugars, phenolic and anthocyanin classes. Results indicated that retention of solutes was affected, not by size exclusion, but primarily by severe fouling phenomena due to polar solutes adsorption on the membrane surface. With the exception of the separation obtained between polymeric and monomeric proanthocyanidins, polysulfone membranes were not able to fractionate phenolic classes. Membranes starting of 20 kDa and over retained high percentages (>60%) of polysaccharides and proteins.

Solubility of Polar and Non-Polar Aromatic Molecules in Subcritical Water: The Role of the Dielectric Constant

Liquid water at temperatures above the boiling point and high pressures, also known as pressurized hot water, or subcritical water (SBCW), is an effective solvent for both polar and non-polar organic solutes. This is often associated to the decrease of water's dielectric constant at high temperatures, apparently allowing water to behave like an organic solvent. The decrease of the solubility at high pressures, in turn, is explained by a mild increase of the dielectric constant of water. Nevertheless, the relationship between the dielectric constant of water, hydration, and the solubility of polar and non-polar molecules in SBCW, remains poorly understood. Here, we study through molecular dynamics, the hydration thermodynamic parameters and the solubility of non-polar and polar aromatic model systems, for which a solubility increase in SBCW is observed. We show that the temperature dependence of the hydration free energy of the model non-polar solutes is nonmonotonic, exhibiting a solute size independent maximum at ~475 K, above which hydration becomes entropically favorable and enthalpically unfavorable. The monotonic increase of the solubility, separated here in hydration and vaporization or sublimation components of the pure liquid or solid solute, respectively, is, in turn, related to the temperature increase of the latter, and only to a minor extent with the decrease of the hydration free energy above ~475 K, via the hydration entropy. A solubility increase or decrease is also found at high pressures for different solutes, explained by the relative magnitude of the hydration and the vaporization or sublimation components of the solubility. For the model solid polar system studied, the hydration free energy increases monotonically with the temperature, instead, and the solubility increase is caused by the decrease of the sublimation component of the solubility. Thus, despite of the observed increase of the hydration free energy with pressure, related to the entropic component decrease, our results indicate that the dielectric constant plays no significant role on the solubility increase of non-polar and polar solutes in SBCW, opposite to the dielectric constant picture. The structure of water next to the solutes is also investigated and a structural enhancement at room temperature is observed, resulting in significantly stronger pair interactions between a water molecule and its third and fourth nearest water neighbors. This structural and energetic enhancement nearly vanishes, however, at high temperatures, contributing to a positive hydration entropy. <br>

Solubility of Polar and Non-Polar Aromatic Molecules in Subcritical Water: The Role of the Dielectric Constant

Liquid water at temperatures above the boiling point and high pressures, also known as pressurized hot water, or subcritical water (SBCW), is an effective solvent for both polar and non-polar organic solutes. This is often associated to the decrease of water's dielectric constant at high temperatures, apparently allowing water to behave like an organic solvent. The decrease of the solubility at high pressures, in turn, is explained by a mild increase of the dielectric constant of water. Nevertheless, the relationship between the dielectric constant of water, hydration, and the solubility of polar and non-polar molecules in SBCW, remains poorly understood. Here, we study through molecular dynamics, the hydration thermodynamic parameters and the solubility of non-polar and polar aromatic model systems, for which a solubility increase in SBCW is observed. We show that the temperature dependence of the hydration free energy of the model non-polar solutes is nonmonotonic, exhibiting a solute size independent maximum at ~475 K, above which hydration becomes entropically favorable and enthalpically unfavorable. The monotonic increase of the solubility, separated here in hydration and vaporization or sublimation components of the pure liquid or solid solute, respectively, is, in turn, related to the temperature increase of the latter, and only to a minor extent with the decrease of the hydration free energy above ~475 K, via the hydration entropy. A solubility increase or decrease is also found at high pressures for different solutes, explained by the relative magnitude of the hydration and the vaporization or sublimation components of the solubility. For the model solid polar system studied, the hydration free energy increases monotonically with the temperature, instead, and the solubility increase is caused by the decrease of the sublimation component of the solubility. Thus, despite of the observed increase of the hydration free energy with pressure, related to the entropic component decrease, our results indicate that the dielectric constant plays no significant role on the solubility increase of non-polar and polar solutes in SBCW, opposite to the dielectric constant picture. The structure of water next to the solutes is also investigated and a structural enhancement at room temperature is observed, resulting in significantly stronger pair interactions between a water molecule and its third and fourth nearest water neighbors. This structural and energetic enhancement nearly vanishes, however, at high temperatures, contributing to a positive hydration entropy. <br>

Hydration Thermodynamics of Non-Polar Aromatic Hydrocarbons: Comparison of Implicit and Explicit Solvation Models

The precise description of solute-water interactions is essential to understand the chemo-physical nature in hydration processes. Such a hydration thermodynamics for various solutes has been explored by means of explicit or implicit solvation methods. Using the Poisson-Boltzmann solvation model, the implicit models are well designed to reasonably predict the hydration free energies of polar solutes. The implicit model, however, is known to have shortcomings in estimating those for non-polar aromatic compounds. To investigate a cause of error, we employed a novel systematic framework of quantum-mechanical/molecular-mechanical (QM/MM) coupling protocol in explicit solvation manner, termed DFT-CES, based on the grid-based mean-field treatment. With the aid of DFT-CES, we delved into multiple energy parts, thereby comparing DFT-CES and PB models component-by-component. By applying the modified PB model to estimate the hydration free energies of non-polar solutes, we find a possibility to improve the predictability of PB models. We expect that this study could shed light on providing an accurate route to study the hydration thermodynamics for various solute compounds.