Gas solubility and permeability in MFA

An experimental analysis has been performed in this work, aimed to the characterization of thermodynamic and mass transport properties of a semicrystalline fluoro polymer (MFA) obtained from the copolymerization of tetrafluoroethylene (TFE) and perfluoromethylvinylether. Sorption and permeation experiments for two alkanes and corresponding perfluorinated compounds in MFA were performed at two different temperatures and solubility coefficients, as well as diffusivity and permeability, were determined. Experimental data were analyzed through different thermodynamic models to draw general conclusions about properties of MFA polymeric phases. Special attention was devoted to the glassy nature of MFA polymeric mixtures around room temperature. Indeed, analysis of experimental sorption data was performed through the use of specific models for glassy polymeric phases as well as by means of classical equilibrium models for fluid mixtures. Conclusions have been drawn from the aforementioned analysis, which significantly contributes to the discussion of correct location of glass‐transition temperature for PTFE and its copolymers. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1637–1652, 2007     

Effect of sugars on the solubility of hydrophobic solutes in water

It was found that the cosolvent effect of sugars on the solubilities of n-octanol, n-heptanol, and sodium dodecyl sulfate monomer in water depended on a set of factors that included molecular weight and concentration ofthe sugars, the kind of monosaccharides, the type of glycosidic linkages involved, and the temperature. All hexoses examined, D-glucose, D-galactose, and D-mannose, caused solubility depression of the hydrophobic solutes at low concentrations but to widely different extents. As the molecular weight of the sugar increased, the solubility depression was considerably lessened and further, as the concentration of the sugars increased, the solubility-increasing effect predominated leading to increased solubilities of the hydrophobic solutes relative of their solubility in pure water. The solubility-increasing effect was markedly enhanced at high temperatures. The free energy of the spontaneous transfer of octanol from water to the sugar solutions is entropic in nature and is attributed primarily to hydrophobic bond formation between the solute molecule and the hydrophobic surfaces of the sugar molecules.     

Use of cyclodextrins in enzymology to enhance the solubility of hydrophobic compounds in water

In enzyme catalysis, hydrophobic compounds are usually made soluble in water by the addition of low amounts of a water-miscible organic solvent. In the present study, taking advantage of the solu-bilizing properties of inclusion compounds (cyclodextrins), a new methodology is proposed. The hydrolysis of p-nitrophenyl esters catalyzed by several hydrolases (lipase from C.cylindracea, porcine pancreatic lipase,R. arrhizus lipase and cholesterol esterase) in the presence of cyclodextrins (CD), has been investigated. This procedure presents many advantages:

1. The enzyme parameters are not affected substantially (the catalytic constant may even increase);
2. The reproducibility is higher than with previous methods;
3. CDs enhance the solubility of substrates; and
4. CDs do not destabilize enzyme structure. In some cases a thermal stabilization is observed.

     

Rationalizing cellulose (in)solubility: reviewing basic physicochemical aspects and role of hydrophobic interactions

Despite being the world’s most abundant natural polymer and one of the most studied, cellulose is still challenging researchers. Cellulose is known to be insoluble in water and in many organic solvents, but can be dissolved in a number of solvents of intermediate properties, like N-methylmorpholine N-oxide and ionic liquids which, apparently, are not related. It can also be dissolved in water at extreme pHs, in particular if a cosolute of intermediate polarity is added. The insolubility in water is often referred to strong intermolecular hydrogen bonding between cellulose molecules. Revisiting some fundamental polymer physicochemical aspects (i.e. intermolecular interactions) a different picture is now revealed: cellulose is significantly amphiphilic and hydrophobic interactions are important to understand its solubility pattern. In this paper we try to provide a basis for developing novel solvents for cellulose based on a critical analysis of the intermolecular interactions involved and mechanisms of dissolution.     

Simultaneous correlation of hydrophobic interactions in HIC and protein solubility in aqueous salt solutions and mixed solvents

The chromatographic retention in hydrophobic and reversed phase chromatography and the solubility of proteins display some common features. The chromatographic retention, as well as the solubility, is modulated by the thermodynamic properties of the solute in the fluid phase. The retention measurements at linear conditions provide information of the solution properties of the protein at infinite dilution, and the solubility measurements produce the supplementary information about the solution properties at the saturation limit. This provides a useful approach to simultaneous correlation of the chromatographic retention and the solubility.The experimental data, used for the correlation, comprise retention measurements of lysozyme on different HIC adsorbents using an aqueous ammonium sulphate eluant, an aqueous ammonium sulphate eluant with an admixture of ethanol, as well as published solubility data.The chromatographic retention data and the corresponding solubility data have been correlated using a chemical potential model derived from Kirkwood's theory of solutions of charged macro-ions and zwitterions in electrolyte solutions. The model correlated the chromatographic retention factor and the solubility data within the precision of the measurements. The model was applied in a pH range from 4 to 11. It was demonstrated experimentally, as well as theoretically, that an admixture of ethanol to the aqueous eluant changes the thermodynamic retention factor on various adsorbents identically when compared to the thermodynamic retention factor in an ethanol free eluant.     

Flat orientation of hydrophobic cores induced by two-dimensional confinement of flexible bolaamphiphiles at the air-water interface

We designed and synthesized a new bolaamphiphile consisting of a biphenyl core, flexible trisiloxane spacers, and terminal ammonium groups. The compression of the trisiloxane-containing bolaamphiphile at the air-water interface led to the formation of monolayer films with the hydrophobic rigid core lying flat on the film surface. Such monolayer structures were formed through the compression-induced conformational change of the flexible bolaamphiphile from an extended state to a folded one as confirmed by surface pressure-area isotherm measurements, water contact angle measurements, atomic force microscopy, and UV-vis spectroscopy.     

Multistate empirical valence bond study of temperature and confinement effects on proton transfer in water inside hydrophobic nanochannels

Microscopic characteristics of an aqueous excess proton in a wide range of thermodynamic states, from low density amorphous ices (down to 100 K) to high temperature liquids under the critical point (up to 600 K), placed inside hydrophobic graphene slabs at the nanometric scale (with interplate distances between 3.1 and 0.7 nm wide) have been analyzed by means of molecular dynamics simulations. Water‐proton and carbon‐proton forces were modeled with a multistate empirical valence bond method. Densities between 0.07 and 0.02 Å^?3 have been considered. As a general trend, we observed a competition between effects of confinement and temperature on structure and dynamical properties of the lone proton. Confinement has strong influence on the local structure of the proton, whereas the main effect of temperature on proton properties is observed on its dynamics, with significant variation of proton transfer rates, proton diffusion coefficients, and characteristic frequencies of vibrational motions. Proton transfer is an activated process with energy barriers between 1 and 10 kJ/mol for both proton transfer and diffusion, depending of the temperature range considered and also on the interplate distance. Arrhenius‐like behavior of the transfer rates and of proton diffusion are clearly observed for states above 100 K. Spectral densities of proton species indicated that in all states Zundel‐like and Eigen‐like complexes survive at some extent. © 2016 Wiley Periodicals, Inc.     

Immunoassay of C-reactive protein by hot electron induced electrochemiluminescence using integrated electrodes with hydrophobic sample confinement

C-reactive protein (CRP) was determined in the concentration range 0.01–10 mg L⁻¹ using hot electron induced electrochemiluminescence (HECL) with devices combining both working and counter electrodes and sample confinement on a single chip. The sample area on the electrodes was defined by a hydrophobic ring, which enabled dispensing the reagents and the analyte directly on the electrode. Immunoassay of CRP by HECL using integrated electrodes is a good candidate for a high-sensitivity point-of-care CRP-test, because the concentration range is suitable, miniaturisation of the measurement system has been demonstrated and the assay method with integrated electrodes is easy to use. High-sensitivity CRP tests can be used to monitor the current state of cardiovascular disease and also to predict future cardiovascular problems in apparently healthy people.     

Alternating hydrophilic and hydrophobic pockets in the channel structures of organostannoxane prismanes: preferential confinement of guest molecules

A hydroxyl-rich hexameric organooxotin prismane has been prepared by reaction of n-BuSn(O)OH with 9-hydroxy-9-fluorenecarboxylic acid. The supramolecular structure of this cage shows channels with hydrophobic and hydrophilic segments, which selectively entrap guest molecules.     

Water solubility and octanol/water-partitioning of hydrophobic chlorinated organic substances determined by using SPME/GC

The critical step in the determination of water solubilitiy (S _w) and octanol-water partition coefficient (K _ow) of hydrophobic organic chemicals by using the generator-column technique and the slow-stirring procedure, respectively, is the exact quantification of the low water-phase concentrations of the substances under investigation. We have tested the applicability of solid-phase microextraction (SPME) and gas chromatography with seven chlorinated organic compounds. The substances cover a S _w range from 500 mg/L to 7 ng/L and a log K _ow range from 3 to 8. The results show that SPME can be a valuable alternative to common preconcentration techniques in the quantification of hydrophobic organics in pure and octanol-saturated water. The apparent SPME distribution constants K _SPME (obtained with the 100 μm-PDMS fiber for analyte’s partitioning between fiber coating and aqueous sample) do not correlate directly with octanol/water partition coefficients and thus cannot be recommended as a surrogate parameter for K _ow.     

Water solubility and octanol/water-partitioning of hydrophobic chlorinated organic substances determined by using SPME/GC

The critical step in the determination of water solubilitiy (S _w) and octanol-water partition coefficient (K _ow) of hydrophobic organic chemicals by using the generator-column technique and the slow-stirring procedure, respectively, is the exact quantification of the low water-phase concentrations of the substances under investigation. We have tested the applicability of solid-phase microextraction (SPME) and gas chromatography with seven chlorinated organic compounds. The substances cover a S _w range from 500 mg/L to 7 ng/L and a log K _ow range from 3 to 8. The results show that SPME can be a valuable alternative to common preconcentration techniques in the quantification of hydrophobic organics in pure and octanol-saturated water. The apparent SPME distribution constants K _SPME (obtained with the 100 μm-PDMS fiber for analyte’s partitioning between fiber coating and aqueous sample) do not correlate directly with octanol/water partition coefficients and thus cannot be recommended as a surrogate parameter for K _ow. Received: 15 January 1997 / Revised: 2 May 1997 / Accepted: 8 May 1997     

Gas solubility of carbon dioxide in poly(lactic acid) at high pressures

The sorption of carbon dioxide in poly(lactic acid) (PLA) was studied by quartz crystal microbalance at high pressures. To address the effect of the D isomer present in the polymer on the gas sorption, measurements were performed in PLA with two different L:D contents, 80:20 and 98:2. New data for the solubility of carbon dioxide in PLA 80:20 and PLA 98:2 over a temperature range from 303.2 to 323.2 K and up to 5 MPa are presented. The results obtained were correlated with the dual‐mode sorption model and the Flory‐Huggins equation. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1010–1019, 2006     

Chemistry in nanochannel confinement

This review addresses the questions of whether it makes sense to use lithographically defined nanochannels for chemistry in liquids, and what it is possible to learn from experiments on that topic. The behavior of liquids in different classes of pores (categorized according to their size) is reviewed, with a focus on chemical reactions and protein dynamics. A number of interesting phenomena are discussed for nanochannels with feature sizes that are manufacturable with modern photolithography-based fabrication technology. The use of spectroscopic methods to investigate chemistry in nanochannels, where both spectroscopic method and nanochannels are integrated into a single device, will be evaluated.     

Studying phase separation in confinement

Cells organize their interior through membrane-bound organelles and through membraneless condensates that are formed by liquid–liquid phase separation (LLPS). The complex process of coacervation that is involved in LLPS is challenging to study in living cells. Hence, studying coacervation in cell-mimicking synthetic containers can yield valuable insights. Here, we review recent progress with respect to studying LLPS (particularly coacervation) in artificial compartments, from water-in-oil droplets to membranous liposomes. We describe different strategies to form and control coacervates in microconfinements and to study their physicochemical and biological characteristics. We also describe how coacervation can itself be used in container formation. This review highlights the importance of in vitro coacervate studies for understanding cellular biology and for designing synthetic cells.     

Quantum confinement in hydrogen bond

In this work, the quantum confinement effect is proposed as the cause of the displacement of the vibrational spectrum of molecular groups that involve hydrogen bonds. In this approach, the hydrogen bond imposes a space barrier to hydrogen and constrains its oscillatory motion. We studied the vibrational transitions through the Morse potential, for the NH and OH molecular groups inside macromolecules in situation of confinement (when hydrogen bonding is formed) and nonconfinement (when there is no hydrogen bonding). The energies were obtained through the variational method with the trial wave functions obtained from supersymmetric quantum mechanics formalism. The results indicate that it is possible to distinguish the emission peaks related to the existence of the hydrogen bonds. These analytical results were satisfactorily compared with experimental results obtained from infrared spectroscopy. © 2015 Wiley Periodicals, Inc.     

Gas solubility calculations. II. Application of a new group-contribution equation of state

A new equation of state has been developed for polar as well as nonpolar components. It is based on the generalized van der Waals partition function and uses local-composition mixing rules. The group-contribution version of this equation of state (the GC-EOS) is described and tables containing parameters for 14 solvent groups and 9 gases (H₂, N₂, CO, O₂, CH₄, C₂H₄, CO₂, C₂H₆ and H₂S) are presented.The GC-EOS predicts vapor-liquid equilibria well for all kinds of systems involving the groups considered. The method requires only information concerning readily accessible pure-component properties. Calculations for multicomponent systems show that the method suggested provides very good predictions of multicomponent high-pressure vapor-liquid equilibria and fairly good predictions of Henry's constants in mixed solvents.     

Gas permeability,diffusivity, and solubility of poly(4-vinylpyridine) film

Although poly(4-vinylpyridine) is believed to have good gas permselectivity, the intrinsic gas permeation property is rarely reported in the literature. The objective of this work is to study the the intrinsic gas permeation property of poly(4-vinylpyridine) using a free-standing film. Because of its brittleness and strong adhesion with most solid surfaces, a free-standing poly(4-vinylpyridine) film was therefore prepared from casting on a liquid mercury surface. The permeation behavior of He, H₂, O₂, N₂, CH₄, and CO₂ through the film was tested over a pressure range of 252 to 800 cm Hg at 35°C. The permeability and solubility decrease slightly with an increase in pressure, whereas the diffusivity increases as pressure increases. The pressure-dependent phenomenon can be explained using the partial immobilization model and the dual sorption model. An effective gas molecule diameter, which is defined as the square root of the product of gas collision and kinetic diameters, was used to correlate the diffusivity and gas molecule size, and an empirical equation was derived. Solubility is also a strong function of gas physical properties such as critical temperature and Lennard–Jones force constant, which are the measures of gas condensability and molecule interaction, respectively. In general, higher solubility in a polymer is obtained for gases with greater condensability and stronger interaction. Typical gas permeabilities of poly(4-vinylpyridine) measured at 619 cm Hg and 35°C are: 12.36 (He), 12.64 (H₂), 3.31 (CO₂), 0.84 (O₂), 0.14 (CH₄), and 0.13 (N₂) barrers. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2851–2861, 1999     

Polyelectrolyte stars in planar confinement

We employ monomer-resolved molecular dynamics simulations and theoretical considerations to analyze the conformations of multiarm polyelectrolyte stars close to planar, uncharged walls. We identify three mechanisms that contribute to the emergence of a repulsive star-wall force, namely, the confinement of the counterions that are trapped in the star interior, the increase in electrostatic energy due to confinement as well as a novel mechanism arising from the compression of the stiff polyelectrolyte rods approaching the wall. The latter is not present in the case of interaction between two polyelectrolyte stars and is a direct consequence of the impenetrable character of the planar wall.