Standard pH values for potassium hydrogenphthalate reference buffer solutions in acetonitrile—water mixtures up to 70 wt% at various temperatures

Reference value standards, pHs, for 0.05 mol kg⁻¹ potassium hydrogenphthalate (KHPh) reference buffer solutions in 30, 50 and 70 wt% acetonitrile—water mixed solvents at temperatures from 288.15 to 308.15 K have been determined from emf measurements of the reversible cell Pt|Ag|AgCl|KHPh + KCl|Quinhydrone|Pt, in which the H⁺-reversible quinhydrone electrode replaces the ill-behaving hydrogen electrode. Values of the first ionization constant of the o-phthalic acid (H₂Ph; benzene-1,2 dicarboxylic acid) in these mixed solvents have also been determined from analogous measurements. The consistency of the present results with the previously determined pHs values in 5, 15 and 30 wt% acetonitrile—water mixtures is analysed by multilinear regression of pHs as a function of both solution composition and temperature. These smoothed standard pHs values are used to optimize the parameters of an equation predicting pHs values in different aqueous organic solvents.     

Wetting of fat crystals by triglyceride oil and water. 2. adhesion to the oil/water interface

Fat crystals influence the stability of food emulsions, such as margarine, butter, or cream, if adsorbed to the oil/water interface. During the adsorption process, a new fat crystal/water interface is created, while the oil/water interface is lost. The driving force for adsorption is therefore the difference between the interactions between fat crystal/water and oil/water. In this work, we have estimated this interaction difference and compared it to the displacement energy for fat crystals from the oil/water interface to the oil. Our calculations have shown that fat crystal adsorption to the oil/water interface (expressed by contact angle ϑ) is determined by polar energy, excess of fat crystal/water over oil/water (I _sw -I _ow ). The interfacial tension constitutes the resistance force for crystal adsorption to the interface. Polar interaction energy for fat crystal/water is stronger than the polar interaction energy for oil/water in all cases examined (I _sw -I _ow >0). The difference corresponds to about 10⁴–10⁶ hydrogen bonds for a hypothetical fat crystal with a diameter of 1 μm. The displacement energy for fat crystals to oil is lower than the polar energy excess in most cases examined. Thus, an additional interaction between fat crystals and oil makes it easy to displace the crystals to the oil. There is also a relationship between the adhesion tension (-γ _ow • cos ϑ) for the crystals at the oil/water interface and the interfacial tension γ _ow . A straight line of slope -1 is achieved for systems with low interfacial tensions (γ _ow ) and low polar energy excess (I _sw -I _ow ).     

Effect of solvent on the free radical polymerization of N,N‐dimethylacrylamide

The free radical photopolymerization of N,N‐dimethylacrylamide was investigated at 25 °C and at low conversion in several solvents ranging from weak polar solvents to water. The polymerization is strongly accelerated in the aqueous medium, with the polymerization rate increasing one order of magnitude when the solvent is changed from an organic one to aqueous medium. These results were analysed in terms of macroradical conformation, effect of medium viscosity, aggregate formation, hydrogen bond formation and effect of temperature. The results suggest that the main factor that controls the polymerization rate is a kinetic effect due to the hydrogen bonding between the amide carbonyl group and water molecules. Also, we found that polymer properties, such as the thermodynamic quality of the solvent for the polymer backbone and molecular weight control using transfer agents, are influenced by the intermolecular hydrogen bonding. Copyright © 2010 Society of Chemical Industry     

Surface passivation of CdSe-TOPO quantum dots by poly(acrylic acid): solvent sensitivity and photo-induced emission in water

The principal available methods for the preparation of high quality CdSe quantum dots (QDs) are based on organic ligands such as tri-n-octylphosphine oxide (TOPO) which lead to non-water soluble nanocrystal QDs. As most biological interactions take place in aqueous media, much effort has been made on preparation of water soluble QDs. In this report, the water soluble CdSe QDs were prepared via a ligand exchange process between organic soluble CdSe-TOPO quantum dots and poly(acrylic acid). The poly(acrylic acid) (PAA) can attach onto the surface of CdSe-TOPO quantum dots in a ligand exchange process to make water-soluble CdSe-PAA complexes. In spite of CdSe-TOPO QDs, the resultant CdSe-PAA QDs are soluble in polar solvents such as methanol or water. Optical properties of CdSe-PAA QDs in several solvents showed that the emission intensity of QDs was mainly decreased in protic solvents such as methanol or water. The TEM images of dots in different solvents were examined and some aggregation of dots was found in protic solvents. In comparison with PAA, the addition of PDMAEMA to the solution of CdSe-TOPO QDs in THF increased the emission intensity of QDs. Furthermore, we found that the entitled ligand exchange process was fast and conjugation process completed at short time intervals. The UV-irradiation of the CdSe-PAA conjugate in water showed that the emission was amplified by increasing the irradiation time.     

Swelling properties of amino acid containing cross-linked polymeric organogels and their respective polyelectrolytic hydrogels with pH and salt responsive property

Amino acid based superabsorbent polymer (SAP) organogel library has been synthesized from Boc-glycine/alanine/valine/leucine/isoleucine/phenylalanine methacryloyl-oxyethyl ester (Boc-Gly/Ala/Val/Leu/Ilu/Phe-HEMA), which can switch over to corresponding hydrogels by simple one step Boc deprotection method. Swelling behaviour of organogels is investigated in various organic solvents (dielectric constant (ε) between 2.25 and 46.7), shows superabsorbent property in nonpolar organic solvents (2.25 ≤ ε ≤ 10.26) and moderate degree of swelling in polar aprotic solvents like acetone, N,N-dimethylformamide (DMF), acetonitrile, dimethyl sulfoxide (DMSO), etc. Swelling property of organogels is greatly influenced by the –R group of pendant amino acids and increases as bulkiness and hydrophobicity of –R increased. Organogels release absorbed volatile organic compounds (VOCs) very rapidly at room temperature and bulkiness of –R group accelerate the deswelling kinetic. Deprotection of Boc groups in the organogel network converts them to superabsorbent cationic polyelectrolyte hydrogels with high degree of swelling (∼518 for hydrogel from leucine) due to the presence of –NH₃⁺ ion functionality, and the swelling ratio of hydrogels is drastically affected by the –R group of amino acids moiety, pH of aqueous medium and ionic strength of the solutions.     

Effect of lecithin on organogel formation of 12-hydroxystearic acid

Optically active 12-d-hydroxystearic acid (12-HSA) gives a thermally reversible organogel in several organic solvents. When a small amount of lecithin coexists with 12-HSA in organic solvents, the mechanical strength of the organogel is remarkably reduced. Interaction of lecithin with 12-HSA was studied by using infrared (IR) spectrometry, nuclear magnetic resonance (NMR) spectrometry, and scanning electron microscopy (SEM). Incorporating lecithin into 12-HSA reduced the absorbance in IR spectra, derived from hydrogen bonding between the hydroxyl groups and the carboxyl groups of 12-HSA molecules. Based on NMR measurements, the polar head groups of lecithin associate with the carboxyl groups of 12-HSA in a 1:1 molar ratio. SEM showed that the shape of the fibrous aggregates varied from a helically extended form to a spherical form. These results suggest that intermolecular 1:1 complexes were formed between lecithin and 12-HSA, which caused a structural change in the fibrous network in the 12-HSA organogel and consequently induced gel deformation.     

Upper critical solution temperature—type cononsolvency of poly(N,N-dimethylacrylamide) in water—organic solvent mixtures

The behaviour of linear poly(N,N-dimethylacrylamide) (PDMAM) chains was studied by turbidimetry and viscometry in mixtures of water with the polar organic solvents methanol, dioxane and acetone. The swelling-deswelling behaviour of PDMAM gels in the same solvent mixtures was also investigated. Contrary to the behaviour in water-methanol mixtures, in water-dioxane and water-acetone mixtures a significant shrinkage of polymer chains and deswelling of polymer gels, followed by phase separation, was observed for high organic solvent fractions. Cononsolvency phenomena were found to be temperature-dependent, as demixing occurred upon decreasing temperature. This upper critical solution temperature (UCST) phase separation behaviour in mixed solvents was studied by turbidimetry and compared to the well-known lower critical solution temperature (LCST) behaviour of poly(N-isopropylacrylamide) (PNIPAM) in similar solvents mixtures.     

Application of poly(butadiene-co-acrylic acid)–sucrose as gel in the separation of different substances

The synthesis of a new hydrophobic gel by reacting cooligomer of butadiene and acrylic acid (M_w 4500) with sucrose crosslinking in best conditions is described. Application of this new gel swelled in different organic solvents is studied. Separation of organic substances in benzene was achieved with higher retention of more polar substances. By this way, cholesterol was separated from lecithin, acrylic acid from polybutadiene with terminal carboxylic groups, and metals such as copper from organic solvents.     

Comparison of Partition Chromatographic Parameters of Lipophilic Organic Electrolytes for Solvents of Various Donor-Acceptor Properties. IV. Quinoline Bases in Systems of the Type Organic Solvent/Formamide + Formic Acid

Abstract

The solvent power of a number of weakly polar solvents is compared for systems of the type organic solvent/formamide solutions of formic acid, using a method elaborated by Rohrschneider for gas-liquid partition chromatography. The characteristics of the weakly polar solvents, determined mainly by their electron acceptor properties, were found to be similar to those obtained in the preceding work for systems containing McIlvaine's buffer solution (Na₂HPO₄ + citric acid) as the polar phase. The solvation of the solutes (quinoline bases) by the polar phase was found to be related to their pK_A values, both in the case of aqueous and formamide systems. Steric hindrance of solvation and molecular size effects were observed, the latter being much more strongly pronounced for aqueous systems.     

Copolymerization of 1-vinylpyrrolidone with N-substituted methacrylamides: monomer reactivity ratios and copolymer sequence distribution

In order to enhance their resistance to polar solvents and their film forming ability compared to these of neat polyvinylpyrrolidone (PVP), water soluble copolymers which combined rather large PVP sequences with ammonium groups were obtained. Free radical copolymerization of 1-Vinyl-2-Pyrrolidone (NVP) with 3-(dimethylamino)propyl-methacrylamide (DMA) and 3-(methacrylamido)propyltrimethyl-ammonium, methylsulfate (TMA) was investigated in water at 68 °C using a water soluble initiator (4,4′-azobis(4-cyanovaleric acid ACVA)). The copolymer samples obtained at low conversion levels (<10%) could not be recovered quantitatively for these particular copolymers. Therefore, a numerical integration modeling, accounting for change in copolymer composition with conversion, was preferred to determine the optimal reactivity ratios from experimental data obtained at moderate conversions. The reactivity ratios (system TMA-NVP: r_TMA 4.47, r_NVP 0.038, system DMA-NVP: r_DMA 5.67, r_NVP 0.37) proved a strong preferential incorporation of the methacrylamide monomers. The reactivity ratios were then used to estimate the copolymer sequence distributions. It is shown that rather large NVP sequences can be obtained with low TMA or DMA initial contents at moderate conversion. Moreover, these copolymers easily formed films which withstood polar solvents and could be readily cross-linked by thermal curing, opening interesting prospects for membrane separation systems.     

Selective Ethanolysis of Fish Oil Catalyzed by Immobilized Lipases

Selective ethanolysis of fish oil was catalyzed by immobilized lipases and their derivatives in organic media. Lipases from Candida antarctica B (CALB), Thermomyces lanuginosa (TLL) and Rhizomucor miehei (RML) were studied. The three lipases were immobilized by anion exchange and hydrophobic adsorption. The discrimination between the ethyl ester of eicosapentaenoic acid (EE-EPA) and the ethyl ester of docosahexaenoic acid (EE-DHA) depends on the lipase, the immobilization support, the physico-chemical modifications of the immobilized lipase derivatives and on the solvents used. TLL and RML were much more selective than CALB. EE-EPA is released 20-fold faster than EE-DHA when ethanolysis was catalyzed, in cyclohexane, by TLL hydrophobically adsorbed on Sepabeads C18. The selectivity and stability of the different derivatives in these polar organic solvents were further improved after physico-chemical modification. The best results for activity-selectivity-stability were obtained in cyclohexane for TLL adsorbed on Sepabeads C18 and further modified via solid-phase physical modification with a polyethylenimine polymer. In this case, the initial selectivity was higher than 20, and a 80 % of EPA was released as ethyl ester after 3 h at 25 °C. At this conversion, mixtures of ethyl esters highly enriched in the ethyl ester of EPA with less than 5 % of the EE-DHA were obtained. TLL derivatives remained fully active after incubation for 24 h in anhydrous solvents.     

Chemical modification of polysaccharides by the use of intramolecular associations in polar organic solvents

Precipitation from alcohol used against fractionation of polysaccharides was applied as an energy-efficient chemical modification with only a co-precipitation of polysaccharide and the modifying agent in polar organic solvents, and drying. Addition of ethanol caused a conformational change of polysaccharides with increasing intramolecular hydrogen bonding and a dense structure in close proximity to atoms, especially, in the presence of modifying agents. Extent of modification depended on the structure of polysaccharides and pH in polar organic solvents. The co-precipitates in polar organic solvents seem to act as a precursor while still maintaining the integrity of the modified polysaccharides. Eventually, a small amount of polar organic solvents (1.5 times volume to the weight of the mixtures) to disperse the reaction mixtures was enough to complete modification.     

Enzymatic esterification of lactic acid,utilizing the basicity of particular polar organic solvents to suppress the acidity of lactic acid

BACKGROUND: Lipase‐catalyzed esterification of lactic acid with ethanol was investigated; however, some difficulties exist with such a system. Because of its high polarity, lactic acid is immiscible with non‐polar organic solvents, which have generally been used for non‐aqueous enzyme reactions. In addition, the strong acidity of lactic acid causes acid inactivation of enzymes and acid‐catalyzed, non‐enzymatic esterification. RESULT: In the present study, particular polar organic solvents, such as 1,4‐dioxane, were found to suppress the enzyme inactivation and non‐enzymatic esterification caused by the acidity. The magnitude of this effect varied with solvents and strongly correlated with the Kamlet‐Taft parameter β, which indicates the basicity of the solvents in non‐aqueous systems. An immobilized lipase from Candida antarctica was found to be the most active and stable enzyme for the reaction. Based on the findings, lipase‐catalyzed esterification of lactic acid (1.0 mol L^?1) could be continued for up to 4 weeks without any loss of enzyme activity. CONCLUSION: In addition to miscibility with lactic acid, the effect of these polar solvents, which is to suppress the acidity of lactic acid and is presumably due to the basicity, appears to play a very important role in the efficient enzymatic reaction of lactic acid. Copyright © 2008 Society of Chemical Industry     

Crystal growth and ferroelectric property of Na0.5K0.5NbO3 and Mn-doped Na0.5K0.5NbO3 crystals grown by floating zone method

Na_0.5K_0.5NbO₃ (NKN) and Mn-doped NKN crystals, which are one of the promising candidates of lead-free piezoelectric materials, were grown by using a floating zone (FZ) method. The resulting crystal growth was compared with crystal growth that resulted from using a flux method in a previous study. In the crystal grown by FZ method under where the growth rate was controlled to 3 mm/h, thin layers formed parallel and perpendicular directions to the growth direction. In the crystal grown by FZ method, the crystal structure could not be classified as having the orthorhombic lattice of Amm2, which was observed in the crystal grown using a flux method. It was found that doped Mn was substituted in the perovskite-type lattice of NKN. Pure NKN crystals showed 90° domains that had a zig-zag shape, whereas Mn-doped NKN crystals were aligned to the domain layers in straight lines. It was confirmed that Mn-doped NKN crystal showed a square P–E hysteresis loop.     

Solubility of ethylene in several polar and non-polar solvents

Solubilities of ethylene at atmospheric pressure and temperatures ranging from ?9°C to 70°C are reported in solvents ranging from the non-polar ones, heptane, dodecane, carbon tetrachloride, carbon disulfide and chlorobenzene to the highly polar ones, isopropanol, butanol and ethylene glycol. A useful relation was observed between ethylene solubilities in non-polar solvents and those of methane, ethane and propane, along with the corresponding energy of vaporization at the normal boiling for those gases. In the highly polar solvents on the other hand, hydrogen bonding (H-bonding) factors were found more useful in relating solubilities in one hydrogen bonding solvent to those in other hydrogen bonding solvents.     

叔胺分解氟化铵制氨气和氟化氢探索研究

探索了叔胺分解氟化铵制氨气和氟化氢的方法。以叔胺作为萃取剂,在极性溶剂、水的存在下分解氟化铵释放出氨气;然后,加入高沸点的非极性溶剂蒸发出水和极性溶剂;最后,在更高的温度下,实现叔胺氟化盐的分解,释放出氟化氢;最终,达到将氟化铵分解,并分步释放出氨气和氟化氢。     

Thermodynamic studies of zinc chloride in mixed aqueous solvents from electromotive force measurements—II. Dioxan,acetone and acetic acid mixtures with water

From the emf measurements of the cell Pt/Zn(Hg)/ZnCl₂, H₂O, organic co-solvent/AgCl/Ag the standard emf of the cell have been determined for dioxan (10,20 and 30 wt%), acetone (10, 20 and 30 wt%) and acetic acid (10, 20, 30, 50, 70 and 90 wt%) mixtures with water at 298 K. These data were used in calculations of: (a) the mean activity coefficients of zinc chloride (b) the primary medium effect (c) the standard Gibbs energies of transfer of zinc chloride from water to mixed solvents. The standard Gibbs energies for the transfer process have been interpreted in regard to the acid-base (in Lewis meaning) properties of the water molecules in mixed solvents.     

Evaluation of solubility parameters for nonvolatile branched hydrocarbons by inverse gas chromatography

Flory‐Huggins interaction parameters determined by inverse gas chromatographic (IGC) technique have been used for the estimation of solubility parameters of nonvolatile branched hydrocarbon solvents. A family of isosteric branched hydrocarbons consists of one apolar stationary phase, 19,24‐dioctadecyldotetracontane (C78), and four polar stationary solvents formed by replacing one of the ? CH₃ groups of C78 by ? OH (POH), ? CN (PCN), ? SH (PSH), ? CF₃ (MTF), and two other polar solvents formed by replacing four ? CH₃ groups of C78 with four ? CF₃ (TTF) and ? OCH₃ (TMO) are investigated. The three‐dimensional Hansen solubility parameters of the solvents have been estimated following the approaches of Voelkel and the method of Huang at five different temperatures. In the three components estimated by Voelkel method, the dispersion component is decreasing rapidly, whereas the polar, and hydrogen bonding components of the solubility parameters are increasing with temperature. In the components of solubility parameter estimated by Huang method, the dispersion and hydrogen bonding components are slowly decreasing with temperature, however, the polar components are almost constant with temperature. The components of solubility parameters for different solvents have been discussed in terms of solvent polarity. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

High removal of chlorinated solvents by reusable polydimethylsiloxane based absorbents

The objective of this work is to prepare absorbent materials based on polydimethylsiloxane (PDMS) for the absorption of organic solvents by a relative simple method, with large absorption capacities and reusability. Different particles (ZnO, MgSO₄, ZnCl₂, and NaHCO₃) were first incorporated in PDMS and then removed by immersion in HCl (c) or water. The absorbent materials were characterized by TGA, mercury porosimetry, stress–strain curves, SEM, EDS, XPS, FTIR, and water contact angle. The materials can absorb polar organic chlorinated solvents (carbon tetrachloride, dichloroethene, dichloromethane, and chloroform) more than four times its own weight. Other solvents were also tested showing 2–3 times its own weight. Additionally, these materials show demulsification properties and absorption of oleophilic compounds. The reusability of the material makes them good candidates for remediation of polluted water.