Acid-base equilibria of some pyridinol derivatives in binary water/organic solvent systems

Summary pK _a values of 2-hydroxy 3-pyridinol (HHP), 2-mercapto 3-pyridinol (MHP), and 2-carboxy-3-pyridinol (CHP) were determined by potentiometric titration in water/organic solvent mixtures containing 20 mole% of organic solvent at 25±0.1 °C and 0.1M ionic strength (KNO₃) applying an empiricalpH correction for mixed aqueous solvents. The influence of the organic solvents on the dissociation constants and tautomeric equilibria of the pyridinol derivatives is discussed. The effect of the molecular structure of the compounds onpK _a is also explained. Titrations of a mixture of two weak diprotic acids (HHP andCHP) in a water/dimethylsulphoxide medium containing 20 mole% organic solvent at constant ionic strength were evaluated using theGran method.

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Säure-Basen-Gleichgewichte einiger Pyridinolderivate in binären Systemen aus Wasser und organischen Lösungsmitteln

Zusammenfassung DiepK _a-Werte von 2-Hydroxy-3-pyridinol (HHP), 2-Mercapto-3-pyriodinol (MHP) und 2-Carboxy-3-pyridinol (CHP) wurden durch potentiometrische Titration in wäßrigen Systemen mit 20 mol% organischem Lösungsmittelanteil bei 25±0.1 °C und einer lonenstärke von 0.1M KNO₃ unter Anwendung einer empirischenpH-Korrektur für Lösungsmittelgemische bestimmt. Der Einfluß der organischen Lösungsmittel auf die Dissoziationskonstanten und die tautomeren Gleichgewichte der untersuchten Verbindungen und der Einfluß der molekularen Strukturen auf diepK _a-Werte werden diskutiert. Die Titration eines Gemisches von zwei schwachen zweibasigen Säuren (HHP undCHP) in Wasser/Dimethylsulfoxid bei konstanter Ionenstärke wurde mit Hilfe derGranschen Methode ausgewertet.

     

Distribution of 5,7-dichloro-2-methyl-8-hydroxyquinoline in some organic solvent-aqueous buffer systems

Microchimica Acta - The distribution of 5,7-dichloro-2-rnethyl-8-hydroxyquinoline, at 25.0±0.1° C and 0.1 ionic strength, has been studied for the systemsn-hexane-water, benzene-water,...     

Aromatic hydroxylation catalyzed by toluene 4-monooxygenase in organic solvent/aqueous buffer mixtures

Toluene 4-monooxygenase is a four-protein component diiron enzyme complex. The enzyme catalyzes the hydroxylation of toluene to give p-cresol with ∼96% regioselectivity. The performance of the enzyme in two-phase reaction systems consisting of toluene, hexane, or perfluorohexane and an aqueous buffer was tested. In each of the cosolvent systems, containing up to 93% (v/v) of solvent, the enzyme was active and exhibited regioselectivity indistinguishable from the aqueous reaction. Using the perfluorohexane/buffer system, a number of polycyclic aromatic hydrocarbons were oxidized that were not readily oxidized in aqueous buffer. An instability of the hydroxylase component and a substantial uncoupling of NADH utilization and product formation were observed in reactions that were continued for longer than ∼3 min. More stable enzyme complexes will be needed for broad applicability of this hydroxylating system in nonaqueous media.     

Investigation of photobleaching of hypocrellin B in non-polar organic solvent and in liposome suspension

Hypocrellin B (HB) is a natural pigment with a promising application in the photodynamic therapy (PDT) for anticancer treatment. The photobleaching of HB in non-polar organic solvents and in liposomes in aqueous solution were investigated by the measurements of absorption spectra, quenching experiments and determination of photoproducts. Control experiments indicated that the sensitizer, oxygen and light were all essential for the photobleaching of HB, which suggested that it was mainly self-sensitized photooxidation. The illumination of HB with visible light in aerobic non-polar solvent generated singlet oxygen efficiently [Phi(1O(2))=0.76] which then attacked the sensitizer HB with formation of an endoperoxide product. The endoperoxide of HB was unstable at room temperature and underwent predominantly loss of singlet oxygen with regeneration of parent HB. The singlet oxygen released from the endoperoxide of HB was detected with chemical trapping experiments. When HB was embedded in EPC liposomes, no endoperoxide product and no singlet oxygen release from the photobleaching process of HB were detected. The quenching experiments indicated that the singlet oxygen mechanism (type II) played an important role in the non-polar solvent and the free radical mechanism (type I) was predominant in liposomal aqueous solution for the photobleaching of HB.     

On the influence of some strong electrolytes on the partitioning of acetic acid to aqueous/organic two-phase systems in the presence of tri-n-octylamine: Part I: Methyl isobutyl ketone as organic solvent

The recovery of carboxylic acids from aqueous phases is often achieved by reactive extraction with water-insoluble amines which are dissolved in an organic solvent. The basic design of such downstream processes requires a thermodynamic framework for the encountered liquid–liquid equilibrium. The thermodynamic framework should be able to describe the rather uncommon and surprising effects that comparatively small amounts of strong electrolytes might have. Such strong electrolytes can either reduce or increase the affinity of a carboxylic acid for the organic phase in particular at low aqueous phase concentrations of the carboxylic acids. That behavior was explained in previous investigations with citric acid as a model compound for a carboxylic acid and modeled by combining the dissociation/protonation equilibrium in the aqueous phase with the formation of organic phase complexes of (amine + acid(s) + water). In the present investigation this work is extended to acetic acid as another example for a carboxylic acid. New experimental results are reported for the influence of sodium chloride, sodium nitrate, sodium sulfate, sodium citrate and hydrochloric acid on the partitioning of acetic acid to coexisting aqueous/organic liquid phases of the system (water + methyl isobutyl ketone (organic solvent) + tri-n-octylamine (chemical extractant)) at 25 °C. The phase behavior is described by an extension of the previously published thermodynamic framework that is able to describe/predict the influence of a strong electrolyte on the partitioning of acetic acid.     

有机溶剂/缓冲液两相体系中全细胞催化拆分环氧氯丙烷

研究了有机溶剂/缓冲液两相体系中重组大肠杆菌E.coli BL21 (DE3)全细胞水解动力学拆分外消旋环氧氯丙烷制备(R)-环氧氯丙烷的过程.结果表明,最适反应条件为:最适有机溶剂异辛烷与缓冲液的体积比7:3,最适缓冲液pH 8.0,底物浓度574mmol/L,全细胞加入量0.07g湿菌体/ml溶液,温度30℃.在此条件下于1L反应器中反应45min,(R)-环氧氯丙烷的摩尔产率、光学纯度和时空产率分别达到37.5%,99.3%ee和0.286mol/(L·h).与单一水相体系相比,异辛烷/缓冲液两相体系中底物浓度和(R)-环氧氯丙烷时空产率分别提高了55.2%和98.6%.     

New fluorous/organic biphasic systems achieved by solvent tuning

Miscibility tests between 60 pairs of fluorous and organic solvents have been performed, and a number of biphasic systems based on hydrofluoroether solvents have been identified. Mutual solubilities of a series of fluorous and organic solvents have been measured to ascertain the compositions of the biphasic systems. A qualitative solvent tuning strategy based on solvent polarity and fluorophilicity/phobicity is introduced. Solvent tuning is then used to modulate the partition coefficients (P) of triarylphosphines with 0-3 fluorous tags. The results lay a foundation for future applications of these and related biphasic systems in catalysis and extraction.     

Acid-base equilibria in binary water/organic solvent systems Dissociation of citric acid in water/dioxan and water/methanol solvent systems at 25 degrees

The thermodynamic constants of citric acid were determined at 25 degrees in water/dioxan and water/methanol mixtures with 10, 20, 30, 40 and 50% v/v organic co-solvent content. Simple relations allowing the calculation of palpha*(H) of citrate buffer solutions are proposed (alpha*(H) being the hydrogen-ion activity referred to the standard state in the corresponding medium). The palpha*(H) values of some citrate buffer solutions, suitable for standardization, are reported. The pK values obtained are discussed in relation to the nature and composition of the solvent, as well as the structure of the acid molecule.     

Polarography of some anions in aqueous organic solvent mixtures

The present investigation deals with the polarographic behaviour of iodate ions in various aqueous mixtures of methanol, ethanol, n-propanol, iso-propanol, 1,2-propanediol, 1,3-propanediol, and glycerol at 30°C. 0.1M-NaOH was used as a base electrolyte. The half-wave potential ranges from 1.24 to 1.46 and the diffusion current decreases with increasing percentage of the solvent. The plots ofi _d vs. andi _d vs.c were linear and pass through origin for all the solvent mixtures, showing that the limiting current is diffusion controlled. The plots of logi/(i_d–i) vs.E _d.e. were linear for all the aqueous organic solvent mixtures, but the value of slope suggested that the reductions are irreversible. The electrode kinetics was studied byKoutecky's method for irreversible electrode process.     

Colloidal suspensions of N-modified graphene nano-platelets in water and organic solvent/water mixed systems

The production of colloidal suspensions of graphene-based nano-platelets in large scale is highly important for their use in practical applications. In this work, we developed a new route for generation of colloidal suspensions of N-modified graphene-based nano-platelets (A-rG-O) with high concentration in water or organic solvent/water mixed systems by the reaction between graphene oxide and ammonium hydroxide. Graphene oxide was reduced by the ammonium hydroxide and N atoms (up to 6 at%) were introduced into A-rG-O materials using solution process without further thermal treatment. Such A-rG-O nano-platelets were well dispersed as individual layers in both systems. Macroscopic free-standing A-rG-O paper materials with good electrical conductivity were produced by filtration of such colloidal suspensions.     

Polyol-induced partitioning of essential oils in water/acetonitrile solvent mixtures

Polyol-induced extraction (PIE) is applied to the extraction of essential oils, using glycerol as a mass separating agent. In 1:1 acetonitrile (ACN)/water solvent mixtures, two immiscible phases can be generated. PIE as an alternative extraction technique was assessed by the extraction of the main flavor and fragrance compounds that comprise six essential oils. In the extraction of eugenol (4-allyl-2-methoxyphenol) from clove buds, the partition coefficients were determined and the % recovery and thermodynamic data in the temperature range of ?20 to 20°C were calculated. The main components present in each essential oil extract were identified through gas chromatography/mass spectrometry (GC/MS) and the compositional profile was compared to traditional extraction techniques. The optimized extraction conditions (?10°C, 1:1 ACN/water (v/v), 20% glycerol) for eugenol at ?10°C give a partition coefficient (K_PC) of 87 and an extraction efficiency of 97% in the acetonitrile-rich phase. The eugenol migration to the organic phase is a spontaneous process (ΔG°?=??9.3?kJ/mol) and an endothermic process (ΔH°?=?9.2?kJ/mol) with entropy being the driving force behind the reaction (ΔS°?=?70?J/K, TΔS°?=?18.4?kJ). The technique was applied to five other essential oils (cinnamon bark, caraway seed, spearmint leaf, peppermint leaf, and anise seed oils) with similar results.     

Development apparatus for thin-layer gel chromatography in organic solvent systems

An apparatus is devised for development of thin-layer gel chromatograms, which is easy to handle and gives reproducible results even with volatile organic solvent systems. The print technique with a silicone-treated paper can facilitate detection of the samples chromatographed.     

Two-phase buffer systems in which acid dimerization occurs in the organic phase

Two-phase buffer systems in which acid dimerization occurs in the organic phase are described. The equations for the dependence of buffer capacity on pH and for evaluation of dilution effects in two-phase buffers of this type are derived and experimentally verified. The rule of additivity of buffer capacities is not valid for the two-component, two-phase buffers investigated because mixed dimers are formed in the organic phase.     

Enzymatic hydrolysis of starch in water-immiscible organic solvent,two-phase systems

Enzyme-catalyzed hydrolyzations of starch by α-amylase have been studied in various two-phase systems, consisting of water and a water-immiscible organic solvent. The hydrolytic conversion of soluble starch to malto-oligosaccharides by α-amylase was greatly accelerated in 10% (v/v) water content of water-dodecane two-phase systems. However, a rapid inactivation of the enzyme has been observed in these systems. Addition of surfactant to these systems, such as polyoxyethylene (20) sorbitan monopalmitate (Tween 60) or bis(2-ethylhexyl) sodium sulfosuccinate (AOT), was effective for the enzyme stability. Effects of enzyme immobilization on the stability of α-amylase, using Ca-alginate and chitosan beads, also have been studied. The stability of immobilized enzyme was clearly enhanced in a 5–10% (v/v) water content two-phase system, whereas the free enzyme was inactivated within 41 h, remaining at a relative activity of 47–76% after 41 h of treatment. Furthermore, scanning electron micrographs (SEM) were taken to observe the effect of the two-phase system on the hydrolysis of starch. Potato starch granules have been extremely swelled and burst out in the stirred 10% (v/v) water content system, which did not contain enzymes.     

Photoacoustic study of CO2-laser coincidences with absorption of some organic solvent vapours

Detection of specific molecules in the atmosphere is motivated by the need for monitoring the emission of industrial pollutants. CO₂-laser photoacoustic (PA) spectroscopy was used here to obtain coincidence spectra of the vapours of three organic solvents: trichloroethylene (TCE), benzene, and dioxan. Spectra of coincidences were obtained as a function of total pressure, adding dry air to the vapour of the solvents up to 1000 mbar.A narrow cavity photoacoustic cell with window acoustic buffers was built for improved sensitivity, and is reported here.The vapour molecules studied do have some significant absorption in the CO₂-laser region, or close to it, but that fact does not necessarily lead to usable coincidences with the narrow laser lines. The results reveal several prominent coincidences that can be used for practical purposes, especially in the case of trichloroethylene.     

On the influence of some inorganic salts on the partitioning of citric acid between water and organic solutions of tri-n-octylamine: Part I: Methyl isobutyl ketone as organic solvent

Reactive extraction is a commonly applied process to recover carboxylic acids from aqueous solutions. Such processes are nowadays designed using process simulation software. However, the essential prerequisite for such a simulation is the availability of a reliable thermodynamic model for the encountered phase equilibrium. Industrial experience revealed that even very small amounts of a strong electrolyte (e.g., sodium chloride) can considerably reduce the amount of carboxylic acid extracted from the aqueous into the organic phase. This contribution presents new experimental results for the influence of sodium nitrate, sodium chloride, sodium sulfate, sodium citrate and hydrochloric acid on the partitioning of citric acid to the coexisting aqueous/organic liquid phases of the system water + methyl isobutyl ketone (organic solvent) + tri-n-octylamine (chemical extractant) at 25 °C. A detailed discussion of the experimental results reveals that the dramatic decrease of the partition coefficient of carboxylic acid is caused by the chemical loading of the extractant by the inorganic acid, i.e. both acids (the weak carboxylic acid as well as the strong inorganic acid) compete for the sodium ions (in the aqueous phase) and for the amine (in the organic phase). In phase equilibrium the amine is predominantly loaded with the inorganic acid while the sodium salt of the carboxylic acid remains in the aqueous phase. That behavior is described by a thermodynamic framework that is able to predict the complex liquid–liquid equilibrium from information determined exclusively from investigations on subsystems.     

Effects of organic solvents on the partitioning of enzymes in aqueous two-phase systems

Organic solvents (ethylene glycol, glycerol, dimethyl sulphoxide, dimethylformamide, dioxane, methanol and propanol-2, as well as sucrose and urea) have been included in aqueous two-phase (liquid-liquid) systems comprised of water, dextran and poly(ethylene glycol). The concentration of the organic solvent was in most cases 20% (w/w). The influence of these solvents on the phase-forming properties, the volume ratio, the freezing point and the partitioning of a polymer-bound ligand, Procion Red HE-3B poly(ethylene glycol), has been studied. The partition coefficients for alkaline phosphatase decrease with ethylene glycol, glycerol, sucrose and urea (factors of 0.25-0.5), but increase with the other substances (factors of 1.2-1.6). The temperature effects on the partitioning of alkaline phosphatase from calf intestine as well as of phosphofructokinase from yeast in systems containing ethylene glycol have been studied and compared with partitioning in standard systems, not containing solvents. The possible uses of the above systems for partitioning studies of enzymes are discussed.