Search

A straightforward, rapid, green, and efficient synthetic procedure has been introduced for easy access to the synthetically highly substituted arylideneisoxazol-5-(4H)-one products. A wide scope of the heterocyclic products was obtained via the three-component cyclocondensation of various aryl aldehydes, NH2OH·HCl, and β-dicarbonyls by zinc oxide nanoparticles (ZnO NPs) as the catalyst. Optimizing the reaction conditions indicated that a relatively small amount of catalyst was required and arylideneisoxazol-5-(4H)-ones were obtained in very short reaction times. Purification of synthesized heterocyclic molecules was carried out with the help of simple filtration and crystallization from ethanol. In this method, exhausting and expensive chromatography methods were not used to purify the products, and the use of organic solvents was also avoided. In addition, this method is important from the point of view of green chemistry. The simplicity of the method, cost-effective catalyst, less time-consuming, mild reaction conditions, conducting experiments at room temperature, as well as recyclability and reusability of ZnO nano-catalyst are among other advantages of this powerful process. [ABSTRACT FROM AUTHOR]

Seeking a more environmentally balanced method of peptide synthesis, we are focusing on developing organic solvent-free synthetic methods using water, an environmentally friendly solvent. In current peptide synthesis, the most common building blocks are Boc- and Fmoc-protected amino acids, which are highly soluble in organic solvents. We previously reported a technique for solid-phase peptide synthesis in water that utilizes Fmoc-amino acids converted to water-dispersible nanoparticles. The Boc strategy is well-known to be suitable for the industrial chemistry and green chemistry, because only gases are generated without any other by-products in the deprotection step of Boc group. Here we summarize in-water both liquid and solid-phase method using Boc-amino acids based on MW-assisted coupling reaction of nanosized reactants, nanoparticles and nanomicelles. [ABSTRACT FROM AUTHOR]

The first example of the sulfinylation of indoles with arylsulfinamides in water in the presence of trifluoroacetic acid as a promoter is described. The reaction occurs smoothly at room temperature under environmentally benign conditions without any catalyst, additive, ligand, or organic solvent. The developed sulfoxide synthetic protocol is attractive due to the use of water as the solvent and provides a novel and efficient route to a wide range of functionalized diaryl sulfoxides. [ABSTRACT FROM AUTHOR]

Nitroaromatic compounds were massively used in the formulation of explosives during both world wars. Even several decades after the end of these wars, their residues are suspected to be widely present in the environment. Their occurrence and effect on ecosystems and human health are still not fully determined. This paper describes the development of a method for the determination of 28 nitroaromatic compounds in water, including isomers of nitrotoluene (NT), dinitrotoluene (DNT), trinitrotoluene (TNT), nitrobenzene (NB), dinitrobenzene (DNB), chloronitrobenzene (ClNB), chlorodinitrobenzene (DNCB), nitronaphthalene (NN), dinitronaphthalene (DNN), nitroaniline (NA), dinitroanisole (DNAN), diphenylamine (DPA), and nitrodiphenylamine (nitro-DPA). In order to separate and individually quantify all the analytes with the best possible sensitivity, stir bar sorptive extraction (SBSE) was chosen as the extraction and pre-concentration step prior to gas chromatography (GC) separation and tandem mass spectrometry detection (MS/MS). Our SBSE optimization efforts focused on parameters such as the type of stir bar, ionic strength, addition of organic solvent, and extraction and desorption times. After these optimizations, the analytical method enabled us to reach limits of quantification (LOQs) between 1 and 50 ng/L in tap water, groundwater, and surface water. The method was applied to the determination of targeted nitroaromatic explosive residues in spring and groundwater samples collected in an area where mine warfare had raged during World War I. Up to 16 different nitroaromatic compounds were detected in the same sample. The highest concentrations were recorded for 2,4-DNT and 1,3-DNB (1700 and 2690 ng/L respectively). [ABSTRACT FROM AUTHOR]

A smartphone-based ratiometric fluorescence device was designed to monitor the reaction kinetic process under vigorous mixing conditions, demonstrated by the hydrolysis of Cs4PbBr6 nanocrystals (NCs). In the presence of trace water, part of Cs4PbBr6 NCs (non-fluorescent) was converted to CsPbBr3 NCs (strong fluorescent). Using anthracene as the reference fluorophore, the brightness ratio of the green (from CsPbBr3 NCs) to blue (from anthracene) components in the fluorescence image which was recorded in situ by the smartphone camera was measured as the signal for kinetic analysis. It was shown that the water-triggered conversion reaction from Cs4PbBr6 NCs to CsPbBr3 NCs follows the pseudo-second-order kinetic model in the early rapid hydrolysis stage (up to 4 min). With increasing water content, the hydrolysis of Cs4PbBr6 NCs is promoted to yield more CsPbBr3 NCs, which was used to determine trace water in n-hexane, dichloromethane, and toluene with detection limits of 0.031, 0.043, and 0.057 μL mL−1, respectively. The device offers the advantages of portability and low cost for rapid field determination of trace water in hydrophobic organic solvents. [ABSTRACT FROM AUTHOR]

Oxidation of aldehydes to carboxylic acids is a major reaction. Conventionally, this reaction is carried out with oxidants and metal catalysts, thus producing unwanted metal waste. Recently, aqueous media have been used as an alternative for toxic organic solvents. Here, we tested the clathrate-structured, neutral hydrogen peroxide adduct 4NaSO·2HO·NaCl for the oxidation of aldehydes to acids in aqueous solution. We found that various aromatic, heteroaromatic and aliphatic aldehydes were selectively oxidized to corresponding acids in 70-98% yields. This simple acid-base treatment allows to separate easily the acid product in high purity without any organic solvent. Moreover, the adduct is produced using 25% HO, with inexpensive sodium sulphate, NaSO, and sodium chloride, NaCl. The adduct is a non-toxic white crystalline solid, readily soluble in water, and easy to handle. [ABSTRACT FROM AUTHOR]

2-Hydroxy-5-sulfobenzoic acid (2-HSBA) efficiently catalyzed the one-pot three-component synthesis of a wide variety of 1-amidoalkyl-2-naphthols and 3,4-disubstituted isoxazol-5(4 H)-ones. The three-component process of substituted benzaldehydes, 2-naphthol, and amides (benzamide and acetamide) or urea occur using 10 mol% of 2-HSBA as an organocatalyst under solvent-free reaction conditions (SFRCs) at 100 °C. It was also found that the best results for the preparation of 3,4-disubstituted isoxazol-5(4 H)-ones were achieved using 15 mol% of 2-HSBA under aqueous conditions at room temperature. The reactions are easy to do and were completed within 3-25 min (for amidoalkyl naphthols), and 70-120 min (for 3,4-disubstituted isoxazol-5(4 H)-ones), while the expected products were obtained in 82-97 % yields. The catalyst can be recovered and reused several times in the template reactions. This procedure offers the advantages of convenience, simple operational procedure, cost-effectiveness, no use of hazardous organic solvents, and the commercial availability of the catalyst. [ABSTRACT FROM AUTHOR]

As media for an enzymatic reaction, ionic liquids (ILs) have many advantages over conventional molecular organic solvents, but some drawbacks still remain unsolved. In this review, we focus our attention on the various strategies that have been tried in recent years for improving the enzymatic performance in ILs. For clarity, this review is divided into several parts based on the hydrophilicity/hydrophobicity of ILs. For hydrophobic ILs, we put the emphasis on the construction of new macroscopically homogenous but microscopically heterogenous water-in-IL microemulsion systems and the catalytic performance of solubilized enzymes in them. For hydrophilic ILs, we highlight the enzyme performance related Hofmeister anions or cations series and the surface active effect of ILs. [ABSTRACT FROM AUTHOR]

The feasibility of sapphire fiber-optic sensors based on evanescent wave absorption spectroscopy in the infrared range for quantitative determination of water content in polar organic solvents has been investigated. Evanescent wave absorption spectra of sapphire fiber-optic sensors in glycerol, ethanol, and glycol with different water concentrations obtained and analyzed, respectively. Evanescent absorbance of the sensors in those organic solvents has been utilized to implement for in situ monitoring water concentration in organic solvents. The evanescent absorbance of sensors in glycerol and glycol has been found to vary linearly with water content in the range 0-30 % and in ethanol in the range 0-10 %, respectively. The fiber-optic sensors based on evanescent absorbance for monitoring water concentrations in those organic solvents are acceptably accurate, cost-effective, and reliable. Some methods to improve the accuracy of predicated water content in those organic solvents are also suggested. Overall, the results demonstrate that the sapphire fiber-optic sensor based on evanescent absorption spectroscopy is a promising candidate for prediction of water content in polar organic solvents in on-line and remote situation. [ABSTRACT FROM AUTHOR]

We have developed a simple and effective method for the activation of palladium phosphine complexes in the Suzuki reaction (TON up to 9800, TOF up to 58800 h) by selecting an aqueous reaction medium instead of organic solvents. This method was elaborated for a high yield synthesis of heteroaromatic biaryls with furyl and thienyl groups. [ABSTRACT FROM AUTHOR]

Specific features of formyl- and acetylferrocene oxidation with peroxides ROOR (R = H, tert-CH) in different solvents are studied. It is shown that despite of the presence in complexes of strong electronacceptor substituents they can be oxidized with hydrogen peroxide in the absence of strong Brønsted acids. Dilution of water with organic solvent leads to deceleration and complete standstill of the reaction. In the absence of acids the second order of the process with respect to peroxide and first one with respect to the metal complex was evaluated. In the presence of perchloric or trifluoroacetic acid the order with respect to peroxide decreases to the first one. The dependence of the reaction rate on the concentration of acid has an extremum point. The activity of other peroxides in the reaction with the above-mentioned compounds is significantly lower than the activity of hydrogen peroxide. Probable alternative mechanisms of oxidation of the abovementioned ferrocenes with hydrogen peroxide in the presence and in the absence of acids differing in the way of coordination of reagents with one another and considering direct participation of substituent in the oxidation is suggested. [ABSTRACT FROM AUTHOR]

Heterogeneous cyanation reaction of aryl halides with K 4[Fe(CN) 6] was studied over a polymer supported macrocyclic palladium complex. The reaction proceeded smoothly by adding TX100 (2 wt%) in water without organic solvents. The catalyst exhibited effective catalytic activities to afford the corresponding products in good to excellent yields. Furthermore, the catalyst could be easily recovered and reused for several times without a significant loss of its activity. Graphical Abstract: Heterogeneous cyanation reaction of aryl halides with K 4[Fe(CN) 6] was studied over a polymer supported macrocyclic palladium complex. The reaction proceeded smoothly by adding TX100 (2 wt%) in water without organic solvents. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Glucopyranose is the most stable form of glucose in solution. Identification of molecular structure of glucopyranose is very important because of its biological and synthetic significance; it is not an easy task because of the large number of possible configurations. Relative energies of exocyclic hydroxymethyl rotamers and α-β anomers of D-glucopyranose have been determined at the reference MP2/6-31G(d,p) level geometry by ab initio calculations at the infinite basis set limit of MP2 approach and with inclusion of CCSD(T) correction term evaluated with the aug-cc-pVDZ basis set in vacuum, water, dimethylsulfoxide, tetrahydrofurane and ethanol. The infinite basis set limit of MP2 level was determined by two point extrapolation using aug-cc-pVTZ and aug-cc-pVQZ basis sets. Solvent effects, relative energies and binding energies have been considered applying explicit calculations and implicit solvent models. [ABSTRACT FROM AUTHOR]

We have prepared an ~1.4 μm thin hybrid film from polyurethane (PU) hydrogel and tetraethylorthosilicate (TEOS) by a sol-gel method, and have incorporated the red-luminescent ruthenium-tris-bipyridyl complex. At an optimized ratio of PU/TEOS (1.5:1; w/w) and annealing temperature (60 °C), the membrane sensor exhibits good capability to extract water from organic solvents but also can well retain the ruthenium dye. If contacted with water-containing organic solvents such as acetone or THF, both the luminescence intensity and wavelength change significantly. The response of luminescence intensity to the water fraction in organics is sigmoidal, which can be well fitted with a modified Stern-Volmer equation. The sensor works in the ranges of 0-6 % and 0-12 % (v/v) of water in acetone and THF, respectively, with detection limits of 0.13 % and 0.486 % (v/v). [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Formamide and its derivatives have a large number of practical applications; also they are structural fragments of many biomolecules. Hydrogen bonds strongly affect their physicochemical properties. In the present work a calorimetric study of formamide and its methyl derivatives was carried out. Enthalpies of solution at infinite dilution of formamide, N-methylformamide, and N, N-dimethylformamide in organic solvents at 298.15 K were measured. The relationships between the obtained enthalpies of solvation and the structure of the studied compounds were observed. Hydrogen-bond enthalpies of amides with chlorinated alkanes, ethers, ketones, esters, nitriles, amines, alcohols, and water were determined. The strength of hydrogen bonds of formamide, N-methylformamide, and N, N-dimethylformamide with proton donor solvents is practically equal. Enthalpies of hydrogen bonds of formamide with the proton acceptor solvents are two times larger in magnitude than the enthalpies of N-methylformamide. The process of hydrogen bonding of amides in aliphatic alcohols and water is complicated. The obtained enthalpies of hydrogen bonding in aliphatic alcohols vary considerably from the amide structure due to the competition between solute-solvent and solvent-solvent hydrogen bonds. Fourier transform infrared spectroscopic measurements were carried out to explain the calorimetric data. Hydration enthalpies of methyl derivatives of formamides contain a contribution of the hydrophobic effect. New thermochemical data on the hydrogen bonding of formamides may be useful for predicting the properties of biomacromolecules. [ABSTRACT FROM AUTHOR]

Hierarchical fascine-like bundles of copper(II) 1,8,15,22-tetranitrophthalocyanine were prepared by an water-phase method, and showed desirable superhydrophobic characteristics without additional surface modification. Prominent advantages of this approach include: the use of water as reaction solvent obviously avoid environmental problems associated with organic solvents and the directly obtained hierarchical structures could be used as superhydrophobic materials. Based on the investigation of various experiment conditions, including additives, copper powders and reaction time, a growth and assembly mechanism has been proposed, that it follows a self-assembly and oriented attachment process. [ABSTRACT FROM AUTHOR]

A simple, efficient and eco-friendly procedure has been developed using tetrabutylammonium chloride as catalyst for the synthesis of 2-amino-4H-chromene derivatives in water and solvent-free neat conditions. The present methodology offers several advantages such as excellent yields, short reaction time and environmentally benign milder reaction conditions. [ABSTRACT FROM AUTHOR]

Candle soot deposited on copper plate was collected, and dispersed in various organic solvents, and in water. These non-functionalized samples were probed with an array of experimental techniques. Results of energy-dispersive X-ray analysis confirmed the absence of metallic elements and X-ray diffraction (XRD) study confirmed the presence of amorphous as well as graphitized carbon in these nanostructures with minimum grain size ≈2 nm. TEM data revealed the presence of 30 nm diameter spherical carbon nanoparticles and dynamic light scattering determined the average hydrodynamic diameter ≈120 nm in water, implying the packing of these nanoparticles into clusters. Raman spectroscopy showed characteristic peaks located at 1324 and 1591 cm corresponding to the D (diamond) and G (graphite) phase of carbon with the characteristic ratio I /I ≈ 1.77, yielding 2.4 nm grain size consistent with XRD data. The electrophoresis measurements yielded mean zeta potential values ≈−22 mV in water. The UV-Vis absorption and photoluminiscence (PL) spectra were found to be independent of the solvent nature and polarity, with absorption bands located around 430, 405, 385, and 335 nm, and PL emission peaks lying in the region 390 to 465 nm. Average emission lifetime measured by time resolved fluorescence spectroscopy was observed to decrease with increase in solvent polarity for a particular excitation, and with increasing excitation wavelength in all solvents. It is shown that these nanoparticles have the potential to be used as green fluorescence probes. [ABSTRACT FROM AUTHOR]

The enthalpies of solution of ethylacetate (EtOAc) in water, octane and 1-octanol (OctOH) were measured at 298, 308 and 318 K using a precise isoperibol calorimeter. The standard enthalpies and heat capacities of these non-electrolyte solution were computed and compared with the previously obtained Δ H and $\Delta C_{p}^{\circ}$ values in N,N-dimethylformamide (DMF). Partial molal heat capacities of EtOAc in water and in organic solvents were calculated and compared with the available literature values. [ABSTRACT FROM AUTHOR]

The results of calorimetric investigations of electrolyte solutions in the mixtures of water, methanol, N, N-dimethylformamide, and acetonitrile with numerous organic cosolvents are discussed with regard to the intermolecular interactions that occur in the solution. Particular attention is given to answer the questions how and to what extent the properties of the systems examined are modified by the cosolvent added and how much the properties of the cosolvent are revealed in the mixtures with the solvents mentioned above. To this goal, the analysis of the electrolyte dissolution enthalpies, single ionic transfer enthalpies, and enthalpic pair interaction coefficients as well as the preferential solvation (PS) model are applied. The analysis performed shows that in the case of the dissolution enthalpies of simple inorganic electrolytes in water-organic solvent mixtures, the shape of the dependence of the standard dissolution enthalpy on the mixed solvent composition reflects to a large extent the hydrophobic properties of the organic cosolvent. In the mixtures of methanol with organic cosolvents, the ions are preferentially solvated either by methanol molecules or by molecules of the cosolvent, depending on the properties of the mixed solvent components. The behavior of inorganic salts in the mixtures containing N, N-dimethylformamide is mostly influenced by the DMF which is a relatively strongly ion solvating solvent, whereas in acetonitrile mixtures, the thermochemical behavior of electrolyte solutions is influenced to a large extent by the properties of the cosolvent particularly due to the PS of cation by the cosolvent molecules. [ABSTRACT FROM AUTHOR]

We describe an efficient method for producing both enantiomers of chiral alcohols by asymmetric hydrogen-transfer bioreduction of ketones in a 2-propanol (IPA)-water medium with E. coli biocatalysts expressing phenylacetaldehyde reductase (PAR: wild-type and mutant enzymes) from Rhodococcus sp. ST-10 and alcohol dehydrogenase from Leifsonia sp. S749 (LSADH). We also describe the detailed properties of mutant PARs, Sar268, and HAR1, which were engineered to have high activity and productivity in media composed of polar organic solvent and water, and the construction of three-dimensional structure of PAR by homology modeling. The K and V values for some substrates and the substrate specificity of mutant PARs were quite different from those of wild-type PAR. The results well explained the increased productivity of engineered PARs in IPA-water medium. [ABSTRACT FROM AUTHOR]

Process in which composites are formed in sol-gel systems based on 3-aminopropyltriethoxysilane and vinyl derivatives of nitrogen-containing heterocyclic compounds was studied. These products are highly dispersed and thermally stable interpenetrating polymers insoluble in water and organic solvents. Their composition and structure were examined. [ABSTRACT FROM AUTHOR]

The partition coefficients, P, for different probe molecules as well as for compounds of biological interest between the room-temperature ionic liquids (RTILs) 1-butyl-3-methylimidazolium hexafluorophosphate, [BMIM][PF], 1-hexyl-3-methylimidazolium hexafluorophosphate, [HMIM][PF], 1-octyl-3-methylimidazolium tetrafluoroborate, [OMIM][BF] and water were accurately measured. [BMIM][PF] and [OMIM][BF] were synthesized by adapting a procedure from the literature to a simpler, single-vessel and faster methodology, with a much lesser consumption of organic solvent. We employed the solvation-parameter model to elucidate the general chemical interactions involved in RTIL/water partitioning. With this purpose, we have selected different solute descriptor parameters that measure polarity, polarizability, hydrogen-bond-donor and hydrogen-bond-acceptor interactions, and cavity formation for a set of specifically selected probe molecules (the training set). The obtained multiparametric equations were used to predict the partition coefficients for compounds not present in the training set (the test set), most being of biological interest. Partial solubility of the ionic liquid in water (and water into the ionic liquid) was taken into account to explain the obtained results. This fact has not been deeply considered up to date. Solute descriptors were obtained from the literature, when available, or else calculated through commercial software. An excellent agreement between calculated and experimental log P values was obtained, which demonstrated that the resulting multiparametric equations are robust and allow predicting partitioning for any organic molecule in the biphasic systems studied. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Phase and extraction equilibria were studied in water-surfactant (Synthamide-5, Oxyphos B, Catamine AB)-salting-out agent (inorganic salts and acids) systems. [ABSTRACT FROM AUTHOR]

Abstract  Poly(terephthalamide) microcapsules can be reproducibly and easily prepared by interfacial polycondensation around emulsion droplets in water. Oil drops of cyclohexane/chloroform mixture stabilized with poly(vinyl alcohol) containing terephthaloylchloride serve as soft template. The interfacial polycondensation starts immediately after addition of an amine mixture (hexamethylenediamine/diethylenetriamine). Light and scanning electron microscopy prove the formation of capsules with size distribution in the range from a few up to 100 µm depending on particular composition of the reaction mixture. The morphology of the capsule wall is characterized by precipitated particles. If instead of pure organic solvents a reactive oil phase is used as template, the capsules can serve in subsequent reactions as templates for the synthesis of composite particles. In this way, styrene can be radically polymerized inside the capsule leading to composite capsules. The capsule morphology is determined by the partition of all components between all phases. [ABSTRACT FROM AUTHOR]

Abstract  The enthalpies of solution of benzo-15-crown-5 ether in methanol–water mixtures and methanol–water–sodium iodide systems have been measured at 298.15 K. The values of standard enthalpies of solution of benzo-15-crown-5 ether are positive in the mixtures of water and methanol within the whole range of mixture composition. The equilibrium constants of complex formation of benzo-15-crown-5 ether with the sodium cation have been determined by conductivity measurements at 298.15 K. The thermodynamic functions of the formation of these complexes have been calculated. The Gibbs energy of complex formation depends on the base–acid properties of methanol–water mixture. [ABSTRACT FROM AUTHOR]

Luminescent nanospheres with strong red fluorescence were prepared from a europium(III) mixed complex with 2-thenoyltrifluoroacetone and 1,10-phenanthroline, and characterized by scanning electron microscopy and Fourier-transform infrared spectroscopy. The fluorescence of the nanospheres is quenched by traces of water, resulting in a method for determination of water in organic solvents. If excitated at 386 nm, the fluorescence intensity at 618 nm decreases linearly with the water content (vol % in ethanol) in the range 0.05 to 6.0%. The detection limit (S/N = 3) is as low as 0.002%. [ABSTRACT FROM AUTHOR]

The possibility of the quantitative determination of water in organic solvents containing strong acids by IR spectrophotometry at 3500–3700 cm−1 was studied. The molar absorption coefficients at the maximum of the most intense absorption bands of water in acetonitrile, chloroform, and 1,2-dichloroethane were 115, 43, and 88 M−1 cm−1, respectively. The study of the effect of acid additions to acetonitrile showed that hydrochloric and nitric acids had little on the shape and intensity of the IR spectra of water. The presence of perchloric acid reduces the intensity (for 0.027 M HClO4, by 40% at 3618 cm−1), which was due to the state of acids in the solvents. Conductometric measurements showed that, under these conditions, HCl and HNO3 were unionized, while HClO4 dissociated almost completely. [ABSTRACT FROM AUTHOR]

The activity of lignin peroxidase (LiP) and the partition of its optimum substrate veratryl alcohol (VA) in sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/isooctane/toluene/water reverse micelles were studied in this paper to understand the microheterogeneous effect of the medium on the catalytic properties of LiP hosted in the reverse micelle. Results showed that LiP from Phanerochaete chrysosporium could express its activity in the reverse micelles, but its activity depended, to a great extent, on the composition of the reverse micelles. Optimum activity occurred at a molar ratio of water to AOT (ω0) of 11, a pH value of 3.6, and a volume ratio of isooctane to toluene of 7–9. Under optimum conditions, the half-life of LiP was circa 12 h. The dependence of LiP activity on the volume fraction of water in the medium (θ), at a constant ω0 value of 11, indicated that VA was mainly solubilized in the pseudophase of the reverse micelle. Based on the pseudobiphasic model and the corresponding kinetic method, a linear line can be obtained in a plot of apparent Michaelis constant of VA vs θ, and the partition coefficient of VA between the pseudophase and the organic solvent phase was determined to be 35.8, which was higher than that (22.3) between bulk water and the corresponding mixed organic solvent. H2O2 inhibited LiP at concentrations higher than 80 μM; this concentration value seems to be different from that in aqueous solution (about 3 mM). The differences mentioned above should be ascribed to the microheterogeneity and the interface of the AOT reverse micelle. [ABSTRACT FROM AUTHOR]

This paper describes a potentiometric titration method for the determination of stoichiometric autoprotolysis constants (pKs) in binary mixtures of water with methanol, ethanol, 1-propanol, 2-propanol, dioxane, and acetonitrile. A combined pH electrode modified by replacing its aqueous KCl solution with 0.01 M NaCl + 0.09 M NaClO4 saturated with AgCl was used for the first time in aqueous organic solvent mixtures. The potentiometric cell was calibrated before each experiment so that the hydrogen ion concentration rather than the activity was measured. The calibration constants E° and k were determined by titrating a solution of perchloric acid with sodium hydroxide solution for each medium studied at 25 °C and under nitrogen atmosphere. During each titration the concentration of NaClO4 was maintained at 0.1 M and the pKs values were calculated by using this titration data. It is shown that the combined electrode system could be successfully used to determine autoprotolysis constants in water-organic solvent mixtures. Furthermore, the variation of the pKs values with solvent composition is discussed. [ABSTRACT FROM AUTHOR]

The activity and stability of native subtilisin 72, its complex with poly(acrylic acid), and subtilisin covalently attached to poly(vinyl alcohol) cryogel were studied in aqueous and organic media by hydrolysis of specific chromogenic peptide substrates. Kinetic parameters of the hydrolysis of Glp-Ala-Ala-Leu-pNA by native subtilisin and its complex with poly(acrylic acid) were determined. Based on the comparative study of stability of native and modified subtilisins in media of various compositions, it was established that covalent immobilization of subtilisin on poly(vinyl alcohol) cryogel is the most effective approach to improve enzyme stability in water as well as in mixtures with low water content. [ABSTRACT FROM AUTHOR]

The article presents information on a study conducted on the synthesis of boratrane in water medium. In this method, boric acid was reacted with mono- and diethanolamines in aqueous media along with gentle heating. Crystalline boratrane was obtained through filtration and drying under reduced pressure. It is stated that organic solvents are inflammable, and use of aqueous solvent systems such as water offer several advantages for chemical reactions.

A test procedure is developed for determining water in acetone, dioxane, isobutanol, ethanol, petroleum ether, and ethyl acetate in the ranges 0.5–12; 0.5–10; 0.5–8; 0.5–6, and 0.5–4 vol %, respectively. Determination is based on the measurement of the acidity of a solution obtained upon adding citric acid or sodium hydrogen sulfate to organic solvents using an indicator test strip containing Congo red. The relative standard deviation of the results of analysis is 0.05–0.1; the duration of analysis is about 30 min. [ABSTRACT FROM AUTHOR]

The article presents questions and answers related to green chemistry including the causes of chemical manufacturing unsustainability, the replacement of organic solvents with water, and the role of chemical engineering in green chemical processes.