Polyol Solution Research Articles

Solubilities and Transfer Free Energies of Hydrophobic Amino Acids in Polyol Solutions: Importance of the Hydrophobicity of Polyols

The purpose of this work was to investigate the difference in the hydrophobicities of various polyols and the nature of interactions between hydrophobic amino acid side chains and polyols. The interactions were explored by conducting solubility studies of three amino acid derivatives, N-acetyl tryptophanamide (NATA), N-acetyl leucinamide (NALA), and N-acetyl glycinamide (NAGA), in the solutions of sorbitol, sucrose, trehalose, glycerol, ethylene glycol, ribose, and deoxyribose. Hydrophobicity index of polyols was calculated using molecular modeling. An increase in the solubility of the hydrophobic side chains of tryptophan and leucine was observed with an increase in the hydrophobicity index of polyols. Transfer free energies of NATA from water to polyols solutions were negative, whereas those for NALA were positive for all polyols except glycol. This study shows that the hydrophobic nature of polyols plays an important role in polyol-side chain interactions. Solubility behavior observed for NATA and NALA in different polyols indicates that polyols can interact differently with the same side chain depending on the nature of the polyol and the side chain.

Influence of polyols and bulking agents on flavour release from low-viscosity solutions

The release of four volatile flavour compounds (cis-3-hexen-1-ol, benzaldehyde, ethyl butanoate and butylisovalerate) from pure water and various low-viscosity aqueous solutions (sucrose, maltitol, erythritol, polydextrose and oligofructose, each at 20% (w/w)) was investigated. Dynamic headspace concentrations of the flavour compounds at thermodynamic equilibrium were monitored by proton-transfer-reaction mass spectrometry (PTR-MS). The rheological properties of the solutions were characterised by their viscosity. Flavour release from pure water increased with increasing hydrophobicity and volatility of the flavour compounds. The highly volatile compounds were retained more extensively in the presence of sucrose, polyols and bulking agents, compared to in pure water, whereas an increase in the release of the less volatile cis-3-hexen-1-ol was observed. All aqueous solutions had similar viscosities, although bulking agent solutions tended to have higher viscosities than polyol solutions of the same concentration. A correlation between viscosity and flavour release in the low-viscosity solutions was not evident.

The Viscosity of Glycerol−Water Mixtures Including the Supercooled Region

The dynamic viscosity of water, glycerol, and its mixtures over a wide range of temperatures, including the supercooled region, was calculated resorting to several predictive approaches and compared to published data. The temperature dependence of the viscosity of the pure components can be described within the experimental error using different empirical equations. However, the best fit is obtained by the Avramov−Milchev equation, taking into account that this equation has only two adjustable parameters. The same model was also used to describe the viscosity of the mixtures over the entire range of temperatures and compositions where experimental data are available and to extrapolate the viscosities of the mixtures at temperatures close to the glass transition. We calculated the viscosities of glycerol−water mixtures, over the entire range of compositions, between (238.15 and 273.15) K. The agreement with experimental data in the stable liquid region is very good, which makes our predictions in the supercooled region fairly reliable. The analysis of the glycerol−water mixtures reveals that, in contrast to that previously found in other aqueous polyol solutions such as sucrose and trehalose, the temperature and composition dependence of the viscosity cannot be described with a scaled Arrhenius equation. At low temperatures, the excess viscosity of the glycerol−water mixtures can be very well described by a regular-like solution coefficient.

One-pot synthesis of hierarchical magnetite nanochain assemblies with complex building units and their application for water treatment

We report that unique hierarchical magnetite (Fe3O4) nanochain assemblies with complex flower-like nanostructures as secondary building blocks and smaller nanoparticles as primary building blocks can be prepared by a facile and surfactant-free one-pot approach using Fe(acac)3 as precursor in polyol solution. The resultant Fe3O4 nanochains possess superparamagnetic property, large saturation magnetization (82.1 emu/g), high Brunauer–Emmett–Teller (BET) specific surface area (43.5 m2 g−1), and also good water-dispersibility. Thanks to these wonderful intrinsic properties, the Fe3O4 nanochains exhibit excellent ability to remove an organic pollutant in waste water. For example, Congo red, a common azo-dye in textile industry, can be completely removed within 5 min at room temperature when the initial concentration of Congo red in solution was 100 mg/L. In addition, the Fe3O4 assembled tertiary chain-like structures can be recycled by a simple heat treatment, which keeps almost the same removal ability and a litter slower adsorption rate even used for the third time. Beyond as an adsorbent for water treatment, these Fe3O4 nanochain assemblies may be useful in other fields such as magnetic resonance imaging (MRI), and drug delivery based on their novel structures and intrinsic multi-functionalities.

Cu–In intermetallic compound inks for CuInS2 solar cells

In this paper, we report on the synthesis of Cu–In intermetallic compound nanoparticles which were used to fabricate CuInS2 thin films and solar cells. Cu–In nanoparticles with adjustable Cu/In ratio were prepared by the introduction of hot-injection technology in the polyol solution. The particle sizes were in the range of 10–100 nm, which wa quite suitable for the fabrication of Cu–In metal inks. Metal precursor films were then made from the metal inks, and then converted to compact CuInS2 films in a sulfur atmosphere. A CuInS2 solar cell with an efficiency of 1.48% from the film was achieved.

Ag/Al(OH) 3 mesoporous nanocomposite film as antibacterial agent

In this study, Ag/Al(OH) 3 mesoporous nanocomposite film was fabricated for antibacterial agent. As a matrix, a mesoporous Al(OH) 3 layer was prepared by alkali surface modification of an Al substrate. Subsequently, mesoporous Al(OH) 3 matrix was immersed in a polyol solution for 4 h at an elevated temperature to deposit silver nanoparticles (Ag NPs) by in situ dispersion. The Al(OH) 3 porous matrix had flaky crystals weaved and covered all substrate surface so that the specific surface area was considerably increased because of voids having several tens of nanometers between the flakes. After in situ dispersion of Ag NPs by polyol process, the Ag NPs were nucleated and grown at the surface of mesoporous Al(OH) 3 layer with tight binding. In antibacterial activity, Ag/Al(OH) 3 mesoporous nanocomposite film demonstrated an excellent bacterial growth inhibition property. It is believed that the Ag/Al(OH) 3 mesoporous nanocomposite film is suitable for the antibacterial agent in a wide variety of biomedical applications.

Molecular basis for polyol-induced protein stability revealed by molecular dynamics simulations

Molecular dynamics simulations of chymotrypsin inhibitor 2 in different polyols (glycerol, xylitol, sorbitol, trehalose, and sucrose) at 363 K were performed to probe the molecular basis of the stabilizing effect, and the data in water, ethanol, and glycol were compared. It is found that protein protection by polyols is positively correlated with both the molecular volume and the fractional polar surface area, and the former contributes more significantly to the protein's stability. Polyol molecules have only a few direct hydrogen bonds with the protein, and the number of hydrogen bonds between a polyol and the protein is similar for different polyols. Thus, it is concluded that the direct interactions contribute little to the stabilizing effect. It is clarified that the preferential exclusion of the polyols is the origin of their protective effects, and it increases with increasing polyol size. Namely, there is preferential hydration on the protein surface (2 A), and polyol molecules cluster around the protein at a distance of about 4 A. The preferential exclusion of polyols leads to indirect interactions that prevent the protein from thermal unfolding. The water structure becomes more ordered with increasing the polyol size. So, the entropy of water in the first hydration shell decreases, and a larger extent of decrease is observed with increasing polyol size, leading to larger transfer free energy. The findings suggest that polyols protect the protein from thermal unfolding via indirect interactions. The work has thus elucidated the molecular mechanism of structural stability of the protein in polyol solutions.

Liquid nucleating additives for improving thermal insulating properties and mechanical strength of polyisocyanurate foams

The effects of liquid-type nucleating silane additives on the cell structure, mechanical strength, and thermal insulating properties of the polyisocyanurate (PIR) foams have been studied. The PIR foams synthesized with hexamethyldisilazane (HMDS) as a silane additive showed the smaller average cell size and lower thermal conductivity than those of the PIR foams prepared with the hexamethyldisiloxane, dimethoxydimethylsilane, and hexadecyltrimethoxysilane. When HMDS was added, average cell size of the PIR foam was becoming smaller due to lower surface tension of the polyol solution, thereby the nucleation rate and number of bubbles produced were increased and then the cell size becomes smaller. The additives likely act as nucleating agents during the formation of PIR foams. The smaller cell size appears to be one of the major reasons for the improvement of thermal insulation properties and mechanical properties of the PIR foams. From the results of cell size, thermal conductivity, and mechanical strength of the PIR foams, it is suggested that the HMDS may be the efficient liquid-type additive for the reduction of cell size and improvement of the thermal insulation property of the PIR foams.

Highly site‐selective stability increases by glycosylation of dihydrofolate reductase

Post-translational glycosylation is one of the most abundant forms of covalent protein modification in eukaryotic cells. It plays an important role in determining the properties of proteins, and stabilizes many proteins against thermal denaturation. Protein glycosylation may establish a surface microenvironment that resembles that of unglycosylated proteins in concentrated solutions of sugars and other polyols. We have used site-directed mutagenesis to introduce a series of unique cysteine residues into a cysteine-free double mutant (DM, C85A/C152S) of dihydrofolate reductase from Escherichia coli (EcDHFR). The resulting triple mutants, DM-N18C, DM-R52C, DM-D87C and DM-D132C EcDHFR, were alkylated with glucose, N-acetylglucosamine, lactose and maltotriose iodoacetamides. We found little effect on catalysis or stability in three cases. However, when DM-D87C EcDHFR is glycosylated, stability is increased by between 1.5 and 2.6 kcal.mol(-1) in a sugar-dependent manner. D87 is found in a hinge region of EcDHFR that loses structure early in the thermal denaturation process, whereas the other glycosylation sites are found in regions involved in the later stages of temperature-induced unfolding. Glycosylation at this site may improve the stability of EcDHFR by protecting a region of the enzyme that is particularly prone to denaturation.

Synthesis and characterization of calcite and aragonite in polyol liquids: Control over structure and morphology

An innovative precipitation process, achieved through the thermal decomposition of urea in polyols containing hydrated calcium salts, was used to prepare calcite and aragonite at elevated temperatures (120-180 degrees C). The effect of various experimental conditions, such as the media of different polyols (ethylene glycol, EG; diethylene glycol, DEG; and tetraethylene glycol, TEG), the temperature, the reaction time, and the addition of magnesium salts, on the structure, size, and morphology of the obtained solids is described. It was found that the formation of calcium carbonate polymorphs, i.e., calcite or aragonite, their morphology and their size was predominantly influenced by the type of polyols used, and by the diverse growing mechanisms occurring in the different polyol systems. Structurally and morphologically different calcite precipitates were formed in the DEG and TEG solvents via classical crystallization processes, while colloidal and nanostructured aragonite particles were assembled in the EG through a recently reaffirmed mechanism based on the role of nanoscale aggregation processes in the formation of carbonate solids. This study highlights the importance of the presence and concentration of magnesium ions in the inhibition of the crystal growth of nanosized aragonite, and in the stabilization of amorphous calcium carbonate (ACC) precipitates in polyol solutions.

Synthesis, characterization, and promoter effect of Cu-Zn/γ-Al 2O 3 catalysts on NO reduction with CO

The role of the Zn promoter and the preparation route in the catalytic properties of Cu-Zn/γ-Al 2O 3 catalysts towards NO reduction with CO were investigated in this study. The catalysts were prepared by chemical reduction of the corresponding metal species (Cu(NO 3) 2·2.5H 2O and Zn(NO 3) 2·6H 2O) by a liquid polyol solution. The nano-bimetallic catalysts were obtained through this method, in which heterogeneous nucleation by seeding the reactive medium with foreign nuclei, Cu, was synthesized by the addition of an easier reductive metallic precursor to replace the homogeneous nucleation. Several samples were prepared with a variation in the reduction temperature, reduction time, Cu/Zn atomic ratio, and Cu and/or Zn loading weight in the catalysts. The morphology and surface chemical structure of the samples were assessed by transmission electron microscopy (TEM), BET surface area measurements, and X-ray photoelectron spectroscopy (XPS). Based on TEM evidence, the Cu-Zn/γ-Al 2O 3 catalysts were found to be composed of a spherical Cu-Zn nanoparticle, and the particle size decreased with the addition of Zn. XPS was used to study the different chemical states of the Zn-promoted Cu/γ-Al 2O 3, which indicated that the concentration of the reduced Cu species was related to the addition of Zn, thus increasing the NO conversion. The results obtained suggest that the use of Zn as a promoter and the polyol method as a preparation route played important roles in the properties of the catalysts, the Cu particle size, the reduction/oxidation efficiency of Cu/Zn, and the catalytic properties of NO reduction with CO.

Furan formation from vitamin C in a starch-based model system: Influence of the reaction conditions

The generation of furan from vitamin C during thermal treatment of a starch-based model system, which simulated baby food, was studied. Results indicated that the amount of sample heated in the vial influenced the furan generation from ascorbic acid. Increasing the amount of heated sample from 5% to approximately 98% of the total vial volume, drastically reduced furan formation from 70 ppb to 16 ppb. Changes in ascorbic acid concentrations from 0.1 to 4.5 mg/g did not influence furan concentration nor did different ascorbic/dehydroascorbic acid molar ratios. Interestingly, waxy corn starch itself considerably enhanced furan generation from ascorbic acid. Under the same conditions, 13.2 ppb of furan was generated in starch-based samples, while in ascorbic acid buffered solutions only 0.4 ppb of furan was formed. Application of other matrices, in particular agar and hydrolysed starch, resulted in similar furan concentrations as for native starch, while in polyol solutions furan concentrations were comparable to those obtained for the buffered ascorbic acid solutions.

In situ controllable synthesis of magnetite nanocrystals/CoSe2 hybrid nanobelts and their enhanced catalytic performance

Fe3O4 nanoparticles (NPs) with sizes of ca 5.3, 6.6, and 9.8 nm can be successfully loaded on the surface of CoSe2-DETA hybrid nanobelts via a facile thermal reduction process in polyol solution. The resulting multifunctional nanocomposites are superparamagnetic at room temperature. Most interestingly, the electrocatalytic activity for the O2 reduction reaction (ORR) of the constructed Fe3O4-decorated CoSe2 nanobelts yield a decent enhancement compared with original CoSe2-DETA catalysts, i.e., the onset potential and current density show 1.01 mA cm−2 and 0.05 V increase at 0.3 V, 1600 rpm, respectively. Additionally, the number of electrons transferred (n) increases from 2.1 to 3.6 after integrating with Fe3O4 nanoparticles. The work described here has provided a promising route to the design and development of new Pt-free catalysts with high-performance by introducing other cheap NPs.

Uniform YF3:Yb,Er up-conversion nanophosphors of various morphologies synthesized in polyol media through an ionic liquid

We describe a facile procedure for the synthesis at low temperature (120 °C) of water-dispersible uniform YF3:Yb,Er up-conversion nanophosphors of various morphologies (rhombic and spheroidal) by homogeneous precipitation in polyol solutions containing different lanthanide salts and an ionic liquid (1-butyl, 2-methylimidazolium tetrafluoroborate) as fluoride source. It is shown that the shape of the obtained nanoparticles is mainly determined by the nature of both, the polyol and the lanthanide precursors, which also affects to their colloidal stability in water suspensions. These morphological differences are explained on the basis of a different mechanism of particle formation. The efficiency of the up-conversion processes in the synthesized rhombic and spheroidal nanoparticles is also comparatively analyzed and the observed differences are justified on the basis of the different impurities incorporated to the nanophosphors during their synthesis process.

Composite silicone rubber of high piezoresistance repeatability filled with nanoparticles

The ruthenium oxide nanoparticles with size less than 20 nm were fabricated by annealing the metallic ruthenium nanoparticles in air, which were synthesized by using the thermal reduction in the polyol solution. The rutile structure of the ruthenium oxide was proved by using transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The oxide has good electron conductivity. The surface of the ruthenium oxide was modified by a vinyl silane coupling agent. The assembling of the silane to the oxide surface was proved by Infrared (IR) absorption spectroscopy. By mixing the nanoparticles with poly(methylvinylsiloxane) (PMVS) silicone rubber, a composite filled with dispersive conducting phase was fabricated. The temperature dependent conductivity shows that the electron transportation through composite is mainly dominated by tunneling. The measurement of piezoresistance shows that the composite at low strain has high piezoresistance repeatability. The 3D reconstruction images of the composite filled with carbon black or ruthenium oxide show that the aggregation of the nanoparticles differs much for two composites. The narrow distribution range of the particle size was thought to be the main factor for the high piezoresistance recurrence.

Decoration of carbon nanotubes with nearly monodisperse M IIFe 2O 4 (MFe 2O 4, M = Fe, Co, Ni) nanoparticles

Magnetic monodisperse ferrite MFe 2O 4 (M = Fe, Co, Ni) nanoparticles have been successfully deposited on carbon nanotubes (CNTs) by in situ high-temperature hydrolysis and inorganic polymerization of metal salts and CNTs in polyol solution. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectrometry (EDS) and vibrating sample magnetometer (VSM) investigations were used to characterize the final products. The influencing factors for formation of CoFe 2O 4 nanoparticles along CNTs have also been discussed briefly. The main advantage of this synthetic strategy is that it is beneficial for the fabrication of magnetic CNTs with a compact layer of nanoparticles and could be extended to prepare series of ferrite/CNTs nanocomposites via the substitution of metal cations.

Formation of unsaturated products during radiolysis of polyol solutions

By means of high-performance liquid chromatography, spectrophotometry, and chemical analysis, it was found that UV absorption of γ-irradiated aqueous solutions of polyols, such as glycerol, inositol, and xylitol, is due to the presence of malonic dialdehyde (MDA) and other β-dicarbonyl radiolytic products in the form of ketols. The contribution of MDA to these spectra is determined by the structure of the initial polyol, the pH of the solvent, and the absorbed dose of irradiation. Mechanisms for the formation of the radiolysis products in question are proposed.

Catalytic conversion of biomass-derived carbohydrates to fuels and chemicals by formation and upgrading of mono-functional hydrocarbon intermediates

Aqueous solutions of sugars and polyols can be converted in a single catalytic process to produce a spontaneously separating organic phase consisting of hydrophobic mono-functional hydrocarbons. The process is shown to be stable for over 2 months time on stream at typical reaction conditions (e.g., 503 K and 18 bar total pressure). The composition and yield of this organic phase can be controlled by adjusting process variables, such as temperature, pressure and space velocity. This organic phase contains primarily mono-functional species such as ketones, alcohols, heterocycles, and organic acids. These oxygenated hydrocarbons can serve as an intermediate platform for the conversion of renewable biomass resources into chemicals and fuels. The organic phase can be separated into individual chemicals or can be upgraded to yield specific classes of chemicals. For example, heterocycles can be separated and used as solvents, additives or blending agents for transportation fuels, while aldol-condensation of the ketones and alcohols can produce long chains species for use as alkane fuels. Alternatively, this platform can be tuned to produce alcohols by reducing the ketone and acid groups. Dehydration of these alcohols produces olefins that have use in either the polymer industry, or as feeds for liquid fuels.

Polyol synthesis of palladium hydride: bulk powders vs. nanocrystals

Palladium is converted into palladium hydride, beta-PdH(x), in polyol solution using NaBH(4) as a hydrogen source; nanocrystalline Pd reacts to form PdH(x) faster and at lower temperatures than bulk Pd, and can be made to release hydrogen to regenerate Pd.

A comparative study of the volumetric properties of dilute aqueous solutions of 1-propanol, 1,2-propanediol, 1,3-propanediol, and 1,2,3-propanetriol at various temperatures

Excess molar volumes V m E and partial molar volumes V ¯ 2 were determined for dilute aqueous solutions of 1-propanol, 1,2-propanediol, 1,3-propanediol, and 1,2,3-propanetriol, at temperatures of (283.15, 288.15, 293.15, 298.15, 303.15, and 308.15) K from density measurements. The infinite dilution partial molar volumes V ¯ 2 ∞ of alcohols in aqueous solution were obtained by extrapolation at each temperature. The volumetric behavior of aqueous alcohol and polyol solutions is discussed in terms of the relationship between polar and non-polar groups and its effect on water structure.