Low Water Affinity Research Articles

Selective Etching of Nitrogen‐Doped Carbon by Steam for Enhanced Electrochemical CO2 Reduction

AbstractNitrogen‐doped carbon structures have recently been demonstrated as a promising candidate for electrocatalytic CO2 reduction, while in the meantime the pyridinic and graphitic nitrogen atoms also present high activities for electroreduction of water. Here, an etching strategy that uses hot water steam to preferentially bind to pyridinic and graphitic nitrogen atoms and subsequently etch them in carbon frameworks is reported. As a result, pyrrolic nitrogen atoms with low water affinity are retained after the steam etching, with a much increased level of among all nitrogen species from 22.1 to 55.9%. The steam‐etched nitrogen‐doped carbon catalyst enables excellent electrocatalytic CO2 reduction performance but low hydrogen evolution reaction activity, suggesting a new approach for tuning electrocatalyst activity.

Hot-spot identification on a broad class of proteins and RNA suggest unifying principles of molecular recognition.

Chemically diverse fragments tend to collectively bind at localized sites on proteins, which is a cornerstone of fragment-based techniques. A central question is how general are these strategies for predicting a wide variety of molecular interactions such as small molecule-protein, protein-protein and protein-nucleic acid for both experimental and computational methods. To address this issue, we recently proposed three governing principles, (1) accurate prediction of fragment-macromolecule binding free energy, (2) accurate prediction of water-macromolecule binding free energy, and (3) locating sites on a macromolecule that have high affinity for a diversity of fragments and low affinity for water. To test the generality of these concepts we used the computational technique of Simulated Annealing of Chemical Potential to design one small fragment to break the RecA-RecA protein-protein interaction and three fragments that inhibit peptide-deformylase via water-mediated multi-body interactions. Experiments confirm the predictions that 6-hydroxydopamine potently inhibits RecA and that PDF inhibition quantitatively tracks the water-mediated binding predictions. Additionally, the principles correctly predict the essential bound waters in HIV Protease, the surprisingly extensive binding site of elastase, the pinpoint location of electron transfer in dihydrofolate reductase, the HIV TAT-TAR protein-RNA interactions, and the MDM2-MDM4 differential binding to p53. The experimental confirmations of highly non-obvious predictions combined with the precise characterization of a broad range of known phenomena lend strong support to the generality of fragment-based methods for characterizing molecular recognition.

Consideration of enthalpic and entropic energy contributions to the relative rates of chalcopyrite dissolution in the presence of aqueous cationic impurities

To understand the effect of aqueous impurities on chalcopyrite dissolution during acid metalliferous drainage and hydrometallurgical processes, batch dissolution experiments were carried out at 650 and 750mV (SHE), pH1 and 35–75°C in the presence or absence of aqueous cationic additives. Activation energies (Ea) for chalcopyrite dissolution in the presence of additives at 750mV, derived using a modified ‘time to a given fraction’ method, demonstrate that Ea varies with reaction extent. The overall trend of evolution from interface- to transport-controlled mechanism was independent of additive type or addition. This suggests that it is not primarily variation in the enthalpy of dissolution that controls the significant changes in relative dissolution rates on addition of additives.Rather, the relative dissolution rates on addition of aqueous cations are found to relate to the M–O framework volume (M and O being the cationic additive and oxygen within H2O in the first sphere of hydration, respectively). There is good inverse linear correlation between this volume and the relative dissolution rate per unit ionic strength which varies as K+>Al3+>no additive>Mg2+>Na+>Ca2+. It is proposed that this effect is related to the relative strength of hydration of the additives with the commensurate entropic effect on solute hydration being advantageous for chalcopyrite dissolution on K+ and Al3+ addition and detrimental for the other additives. H4SiO4, the dominant aqueous species upon Si addition under the conditions examined, has low affinity for water, resulting in a detrimental entropic contribution to solute hydration and dissolution. The effect of Fe addition on relative dissolution rate is convoluted by the role of Fe3+ as the primary oxidant for chalcopyrite dissolution. On addition of aqueous Fe to dissolution at 750mV, the effect is detrimental due to the detrimental effect on the entropy of hydration of the solute and the relative abundance of Fe3+. At 650mV the effect of the greater presence of Fe3+ due to Fe addition dominates and the dissolution rate is enhanced.

Adsorption of equimolar aqueous sodium dodecyl sulphate/dodecyl trimethylammonium bromide mixtures at solution/air and solution/oil interfaces

Two oppositely charged surfactants in an aqueous solution interact with each other via electrostatic interactions and produce surfactant complexes—catanionics. However, their quantitative influence on the interfacial tension at the solution/air and solution/oil interfaces is still unknown. We have measured the interfacial tension of sodium dodecyl sul- phate (SDS) and dodecyltrimethylammonium bromide (DoTAB) aqueous mixtures using the du Nouy ring tensiom- eter and drop profile analysis tensiometry (PAT-1). For the oil phase, we used hexane. The obtained kinetic and equilibrium experimental results were fitted with the common theoretical Frumkin adsorption model. We found that SDS+DoTAB complexes show much higher surface activity than the single surfactants. At solution/air and solution/oil interfaces, SDS and DoTAB produce ion pairs with low water affinity and relatively low oil solubility. SDS+DoTAB partition coeffi- cient between hexane and water phases is 0.32. Such surfac- tant complexes with advanced surface characteristics may be beneficial in different industrial branches nowadays.

Sorption Isotherms of Water in Nanopores: Relationship Between Hydropohobicity, Adsorption Pressure, and Hysteresis

The motivation of this study is to elucidate how the condensation and desorption pressures in water sorption isotherms depend on the contact angle. This question is investigated for cylindrical pores of 2.8 nm diameter by means of molecular dynamics simulations in the grand canonical ensemble, in combination with the mW coarse-grained model for water. The contact angle is characterized for different sets of water–surface interactions. First, we show that desorption in open-ended pores with moderate or low water affinity, with contact angles greater or equal than 24°, is a nonactivated process in which pressure is accurately described by the Kelvin equation. Then, we explore the influence of hydrophobicity on the capillary condensation and on the width of the hysteresis loop. We find that a small increase in the contact angle may have a significant impact on the surface density and consequently on the nucleation free energy barrier. This produces a separation of the adsorption and desorption branches, exacerbating the emerging hysteresis. These results suggest that the contact angle is not as relevant as the adsorption energy in determining condensation pressure and hysteresis. Finally, we consider nonequilibrium desorption in pores with no open ends and describe how homogeneous and heterogeneous cavitation mechanisms depend on hydrophilicity.

Gas-Phase and Microsolvated Glycine Interacting with Boron Nitride Nanotubes. A B3LYP-D2* Periodic Study

The adsorption of glycine (Gly) both in gas-phase conditions and in a microsolvated state on a series of zig-zag (n,0) single-walled boron nitride nanotubes (BNNTs, n = 4, 6, 9 and 15) has been studied by means of B3LYP-D2* periodic calculations. Gas-phase Gly is found to be chemisorbed on the (4,0), (6,0) and (9,0) BNNTs by means of a dative interaction between the NH2 group of Gly and a B atom of the BNNTs, whose computed adsorption energies are gradually decreased by increasing the tube radius. On the (15,0) BNNT, Gly is found to be physisorbed with an adsorption driving force mainly dictated by p-stacking dispersion interactions. Gly adsorption in a microsolvated environment has been studied in the presence of seven water molecules by progressively microsolvating the dry Gly/BNNT interface. The most stable structures on the (6,0), (9,0) and (15,0) BNNTs present the Gly/BNNT interface fully bridged by the water solvent molecules; i.e., no direct contact between Gly and the BNNTs takes place, whereas on the (4,0) BNNT the most stable structure presents a unique direct interaction between the COO− Gly group and a B atom of the nanotube. Further energetic analyses indicate that the (6,0), (9,0) and (15,0) BNNTs exhibit a low water affinity, which favors the Gly/water interactions upon BNNT coadsorption. In contrast, the (4,0) BNNT has been found to show a large water affinity, bringing the replacement of adsorbed water by a microsolvated glycine molecule as an unfavorable process.

Preparation and evaluation of chitosan–hydrophobic silica composite microspheres: Role of hydrophobic silica in modifying their properties

Biodegradable microspheres used as controlled release systems are important in pharmaceutics. Chitosan biopolymer represents an attractive alternative to other biomaterials because of its significant physicochemical and biological behaviors. Chitosan microspheres are expected to become promising carrier systems for drug and vaccine delivery, especially via oral, mucosal and transdermal routes. Controlling the swelling rate and swelling capacity of the hydrogel and improving the fragile nature of microspheres under acidic conditions are the key challenges that need to be overcome to allow the use of chitosan microspheres for controlled or sustained release specially via these non-invasive administration routes.There have been many studies on the modification of chitosan microsphere structures with cross-linkers, blends with various kinds of polymers and new organic–inorganic hybrid systems in order to obtain some improved properties. In this work, microspheres composed of chitosan and nanosized hydrophobic silica commercialized under the name Aerosil R972 were generated by a method consisting of two steps: first, preparation of a macroscopically homogeneous chitosan–hydrophobic silica dispersion by an optimized procedure, and then drying. Spray drying was the technique used here. FTIR spectroscopy, X-ray powder diffraction, differential scanning calorimetry, thermal gravimetric analysis, Scanning Electron Microscopy (SEM) and high resolution Transmission Electron Microscopy (TEM) were used to characterize the microspheres, besides acid stability, moisture sorption capacity, release properties and biological assays.The chitosan–hydrophobic silica composite microspheres showed improved thermal degradation, lower water affinity, better acid stability and ability to retard rifampicin (drug model) release under simulated gastric conditions. In vitro biocompatibility studies indicated low cytotoxicity and low capacity to activate cell production of the pro-inflammatory mediator nitric oxide, encouraging further studies on the use of the new chitosan–hydrophobic silica composite microspheres as drug carrier systems via oral or nasal routes.

Optical fibre Bragg grating recorded in TOPAS cyclic olefin copolymer

A report is presented on the inscription of a fibre Bragg grating into a microstructured polymer optical fibre fabricated from TOPAS cyclic olefin copolymer. This material offers two important advantages over poly (methyl methacrylate), which up to now has formed the basis for polymer fibre Bragg gratings: TOPAS has a much lower water affinity and has useful properties for biosensing. The grating had a Bragg wavelength of 1569 nm and a temperature sensitivity of -36.5±0.3 pm/°C.

Controlling solvent diffusivity via architecture of nanopore structures in porous low-k films

Three kinds of porous silsesquioxane-based thin films with different pore structures and porosities were prepared in order to investigate the relationship between the behaviors of wet chemical diffusion and pore structure. The first model of the films contains only partially interconnected small mesopores (∼2 nm), the second includes fully interconnected large mesopores (10–20 nm) and the last porous film model embeds isolated macropores (60–90 nm). Dependence of the diffusion coefficient of solvent (toluene and methanol) on the pore size and pore structure of the porous films is discussed. The diffusion coefficient of the porous films was found to be dependent not only on porosity but also significantly on the pore structure such as pore size and pore interconnectivity. As porosity and pore interconnectivity increased, the diffusion coefficient of solvent increased as expected. In the case of isolated macroporous film (model III), the diffusion coefficients were almost constant with varying porosity. Moreover, the porous films with isolated macropores showed extremely low solvent diffusivity (<10 −8 cm 2/s) and water affinity ( D Tol/ D MeOH ∼ 0.05).

KLa measurement in two‐phase partitioning bioreactors: new insights on potential errors at low power input

AbstractBACKGROUND: Two‐phase partitioning bioreactors (TPPBs) are based on the addition of a non‐aqueous phase (NAP) to a biological process in order to overcome a limited delivery of gaseous substrates to the microorganisms in the case of compounds with low affinity for water. However, the high power input (Pg/V) required to disperse the NAP is often the major limitation for TPPB applications at full scale. Therefore, the accurate determination of the overall mass transfer coefficient (KLa) at low Pg/V values is a critical issue as these operational conditions are more attractive from a scale‐up point of view.RESULTS: NAP addition altered the typical shape of the dissolved oxygen curves used for KLa determination at the lowest Pg/V values tested (70–80 W m−3). Below a threshold Pg/V value of 600 W m−3, the presence of the NAP increased the error in KLa measurements up to 115% relative to controls deprived of NAP.CONCLUSIONS: The error in KLa measurements at low Pg/V values might be related to failures in the fundamental assumption regarding liquid phase homogeneity in the mass transfer model used. Copyright © 2010 Society of Chemical Industry

Transfer of Highly Hydrophilic Ions from Water to Nitrobenzene, Studied by Three-Phase and Thin-Film Modified Electrodes

The study by voltammetry of hydrophilic ion transfers across the interface between an aqueous solution and an immiscible organic solvent is limited by the presence of supporting electrolytes in both phases. Such a study is impossible for ions having a higher affinity for water than ions of the electrolytes. Indirectly, methods based on modified solid electrodes can be used; these are obtained by the deposition of an organic phase containing a molecule having redox properties, the modified electrode being in contact with an aqueous solution of the appropriate electrolyte. The three-phase electrode is very convenient for that purpose. However, this experimental tool also has its own limitation, due mainly to the redox species produced in the organic phase. The oxidized, or reduced, form of the redox molecule must have a very low affinity for water, as otherwise its transfer masks that of the ion under study. Ferrocene is almost useless because of the affinity of the ferrocenium cation for water, decamethylferrocene being a better choice. The present work illustrates how the use of lutetium bisphthalocyanines widely expands the possibilities, as these molecular sandwich complexes can be reduced as well as oxidized, the products of the reactions having a very low affinity for water. This made the determination of the Gibbs energy possible for the transfers of highly hydrophilic ions from water to nitrobenzene: Cl(-) (40 kJ mol(-1)), F(-) (57 kJ mol(-1)), H2PO4(-) (64 kJ mol(-1)). Nothing being really known about the transfer of F(-) or H2PO4(-) from water to organic solvents, these are the first values ever published. H(+), OH(-), and HSO4(-) have also been studied, showing that these species, which have a poor affinity for nitrobenzene, are prone to association reactions with the reduced or oxidized forms of the lutetium bisphthalocyanine.

Effect of heat treatment on the wettability of white ash and soft maple by water

Heat treatment of wood has attracted a lot of attention both in Europe and recently in North America as an environmentally-friendly wood-protection method. The untreated wood is hydrophilic (high affinity for water). During the heat treatment, wood becomes more and more hydrophobic (low affinity for water) with increasing heat treatment temperature. As a result, it becomes more resistant to biological attacks. Furthermore, it becomes dimensionally more stable compared to untreated wood. Its hardness increases. As the wood becomes more hydrophobic, its wettability by water decreases. The effect of heat treatment is different for each species. Studying the wetting characteristics of heat treated wood gives a good indication of the heat treatment effects on certain wood properties which are related to its degree of hydrophobic character. The aim of this work was to study the characteristics of dynamic wetting process for two different heat-treated North American wood species white ash (Fraxinus americana) and soft maple (Acer rubrum). Contact angle measurements before and after heat treatment showed a significant increase in wood hydrophobicity. Advancing contact angles of a water drop were in all cases higher for heat-treated wood than for untreated wood.

Water properties in fern spores: sorption characteristics relating to water affinity, glassy states, and storage stability

Ex situ conservation of ferns may be accomplished by maintaining the viability of stored spores for many years. Storage conditions that maximize spore longevity can be inferred from an understanding of the behaviour of water within fern spores. Water sorption properties were measured in spores of five homosporeous species of ferns and compared with properties of pollen, seeds, and fern leaf tissue. Isotherms were constructed at 5, 25, and 45 degrees C and analysed using different physicochemical models in order to quantify chemical affinity and heat (enthalpy) of sorption of water in fern spores. Fern spores hydrate slowly but dry rapidly at ambient relative humidity. Low Brunauer-Emmet-Teller monolayer values, few water-binding sites according to the D'Arcy-Watt model, and limited solute-solvent compatibility according to the Flory-Huggins model suggest that fern spores have low affinity for water. Despite the low water affinity, fern spores demonstrate relatively high values of sorption enthalpy (DeltaH(sorp)). Parameters associated with binding sites and DeltaH(sorp) decrease with increasing temperature, suggesting temperature- and hydration-dependent changes in volume of spore macromolecules. Collectively, these data may relate to the degree to which cellular structures within fern spores are stabilized during drying and cooling. Water sorption properties within fern spores suggest that storage at subfreezing temperatures will give longevities comparable with those achieved with seeds. However, the window of optimum water contents for fern spores is very narrow and much lower than that measured in seeds, making precise manipulation of water content imperative for achieving maximum longevity.

Nitrogen and Water Adsorption in Aluminum Methylphosphonate α: A Molecular Simulation Study

We present here Monte Carlo simulation and experimental results on the adsorption of nitrogen and water in aluminum methylphosphonate polymorph alpha (AlMePO-alpha). We have assumed a detailed atomic model for the material, using experimental information to construct the simulation cell. Nitrogen was modeled with two different approaches: as a simple Lennard-Jones (LJ) sphere with no charges, and as a diatomic molecule with charges explicitly included. Water was represented by the TIP4P model. Experimental adsorption isotherms were used to tune the proposed molecular model for the adsorbent. Simulated adsorption capacities were in agreement with the experimental results obtained for the studied systems. The influence of the surface model on the adsorption behavior was taken into account by considering different values of the surface methyl group size parameter. Our results corroborate the strong sensitivity of the simulation results to this parameter, as previously observed by Schumacher and co-workers. It is also observed that charged models are essential to accurately describe the low-pressure region of the adsorption isotherm, where the solid-fluid interaction rules the system behavior. However, a simple uncharged molecular model for nitrogen is able to describe the three loci arrangement at maximum loading. Experimental and simulation results presented here also confirm the low water affinity of AlMePO-alpha. These results enforce the application of this methodology to achieve quantitative predictions on similar systems, with the appropriate transferability of the molecular parameters.

High-Temperature Sorbents for CO2 Made of Alkali Metals Doped on CaO Supports

A number of basic sorbents based on CaO were synthesized, characterized, and tested for the sorption of CO2 and selected gas mixtures simulating flue gas. Our studies resulted in highly promising sorbents based on Cs/CaO, which demonstrated zero affinity for N2 and O2 and very low affinity for water. Moreover, we observed high CO2 sorption capacities and rapid sorption/desorption characteristics in a wide temperature range reaching temperatures as high as 700 °C. The “key” feature of this family of sorbents is their basic nature, which allows for the selective chemisorption of CO2. These unique characteristics of this family of sorbents offer high promise for the development of advanced industrial sorbents for the effective CO2 removal. The performance of the alkali metals as dopants on CaO follows the order Li < Na < K < Rb < Cs, which reveals a strong relationship between the sorption characteristics and the increase of the electropositivity or equivalently atomic radii of the alkali metals. From XPS in...

Sol–gel preparation of non-hygroscopic siliceous thin films enriched with alkaline-earth ions

Thin film layers of silica with calcium or magnesium ions were prepared by the sol–gel method in order to obtain protective coatings with low water affinity for historical glasses. The films were synthesised by pre-polymerised solutions of tetraethoxysilane [Si(OC 2H 5) 4] (TEOS) and deposited by dipping soda-lime glasses. Then they were immersed in saturated solutions of Ca(OH) 2 or Mg(OH) 2 for time intervals of 1, 24 and 36 h to adsorb calcium or magnesium ions. No heat treatment was done, to apply this method to cover real historical glasses, which could be irreversibly damaged by high temperature. The X-ray photoelectron spectroscopy and secondary ions mass spectrometry analyses show that the films present an almost homogeneous in depth distribution of calcium or magnesium. Magnesium adsorbed films also present a decrease of free non-bridging oxygen (SiOH groups). By atomic force microscopy it was observed that the average roughness is low (around 10 Å). Contact angle measurements reveal a degree increase starting from soda-lime uncoated glasses, through silica coated glasses up to calcium or magnesium adsorbed silica coated glasses. The data obtained revealed a real decrease of water affinity, strictly important to improve the protective performances of the films.

Hydrophobic interfacing layers for improvement of corrosion protection by polymeric coatings

Water sorption of coating materials is the main cause of coating deterioration, adhesion loss and substrate corrosion. By introducing alkanethiol self-assembled monolayers (SAMs), a hydrophobic interfacing layer between coating and substrate metal can be constructed. The effect of the hydrophobic SAMs interfacing layer on the corrosion protection of epoxy coatings was evaluated using electrochemical techniques including Tafel polarization, electrochemical impedance spectroscopy and impedance–time transition measurement. It was found that the SAMs interfacing layer improved the corrosion protection of the coating significantly. The improvement was attributed to the strong interaction between SAMs and the metal substrate, the compact structure and low water affinity of the SAMs interfacing layer, which prevent water absorbed by the coating from reaching the coating–metal interface and spreading along the interface.

Applications of Diethoxymethane as a Versatile Process Solvent and Unique Reagent in Organic Synthesis

Diethoxymethane (DEM) has recently become available in commercial quantities. It has unique properties and is useful in a variety of applications in organic synthesis. It is low boiling (88 °C), azeotropes with water, and has a very low affinity for water. It is stable under basic conditions and as manufactured does not require drying for use as a solvent, even for organometallic reactions. DEM is useful as a process solvent especially for sodium hydride reactions, organolithium chemistry, copper-catalyzed conjugate additions, and phase-transfer reactions. As such, DEM is a potential replacement for tetrahydrofuran (THF), dichloromethane (CH2Cl2), glyme (1,2-dimethoxyethane), and methylal (1,1-dimethoxymethane). DEM is also useful as an ethoxymethylating agent, a formaldehyde equivalent, and a carbonylation substrate. Due to these unique properties and applications, DEM has exciting potential for widespread use both as a reagent and especially as a preferred solvent.

A novel ceramic-supported polymer membrane for pervaporation of dilute volatile organic compounds

A novel asymmetric ceramic-supported polymer (CSP) pervaporation membrane was developed using free-radical graft polymerization of polyvinyl acetate (PVAc) onto a porous tubular silica substrate. The resulting membrane was characterized by pervaporation removal of trichloroethylene (TCE) and chloroform from dilute aqueous solutions. PVAc was chosen since it has a high affinity for TCE and chloroform and a low affinity for water, thus making the membrane permselective toward these solutes. This study has shown, for the first time, that pervaporation is possible even with a large substrate starting pore size (∼500 Å) and where the active separation phase is a macromolecular layer of terminally anchored chains. Performance of the CSP membrane was assessed at various hydrodynamic conditions and feed concentrations. Resistance of the PVAc/CSP membrane was found to be negligible compared with the concentration boundary layer resistance. The enrichment factor, defined as the ratio of total solute concentration in the permeate to that in the feed, increased with polymer graft yield. For a given graft yield, the enrichment factor approached an asymptotic plateau value, as the tube-side Reynolds number was increased due to increased water flux in response to the rise in transmembrane pressure. Preliminary analysis suggests that the CSP pervaporation membrane performance could be substantially increased by optimizing reaction conditions to produce a higher polymer graft density.

Water relations in freeze-dried powdered shortenings from babassu fat

Shortening powders are simple, versatile and convenient ways to enhance functional properties of foods. The objective of this study was to evaluate the water relations of shortening powders, produced by freeze-drying emulsions. Shortening powders were obtained by drying oil-in-water emulsions of skim milk solids and babassu fat, with no added emulsifier, by lyophilization. The hygroscopic behaviour of the shortening powders was characterized by water sorption isotherms and sorption kinetics. Low affinity for water as well as the recrystallization phenomena of lactose was observed. Structural alterations were not observed in the shortening powders submitted to the thermal treatment. This shows good thermal stability of the product. It was concluded that the shortening powders showed high fat content, low affinity for water and good thermal stability.