Solute-solvent interactions in acid-base dissociation: nine protonated nitrogen bases in water-DMSO solvents

A titration method utilizing glass electrodes and silver-silver chloride electrodes in a cell without liquid junction has been used to determine the acidic dissociation constants at 15, 25, and 35°C of nine protonated nitrogen bases in mixtures of water and dimethyl sulfoxide (DMSO). The mole fraction of DMSO in the mixed solvents was 0.2, 0.4, 0.6, and 0.8. The cell was calibrated with HCl (molality=0.01 mole-kg^?1) in the mixed solvents, and the ionic strength and chloride molality remained substantially unchanged during the titration with added base. This method minimizes the errors resulting from the formation of AgCl ₂ ^? in the media rich in DMSO. The pK _a of all the protonated bases passes through a minimum at a solvent composition close to that at which H₂O-DMSO mixtures display a maximum solvent structure. The results are discussed in terms of the preferential solvation of ions by the two types of solvent molecules. They are consistent with the hypothesis that increased solvent structure is accompanied by increased desolvation of the cation acids.     

Liquidus and glass transition temperatures of the ammonium nitrate-dimethylsulfoxide-water system

The liquidus temperature was measured in the ammonium nitrate-dimethylsulfoxide-water system over in the concentration range 0–60 mole% ammonium nitrate. The probable formation of the NH₄NO₃·nDMSO solvate with n=1.3–1.5 and the mixed solvate NH₄NO₃·DMSO·H₂O at 30 mole% ammonium nitrate and a DMSO:H₂O ratio of 4∶1 are indicated. The glass transition temperatures T _g were measured over a salt concentration range of 0–50 mol% ammonium nitrate and at various compositions of the mixed solvent (y _DMSO =0.1–0.9 mole fraction). At a constant mixed solvent composition, the dependence of the glass transition temperature on the salt concentration can be approximated by a linear relationship, as can its dependence on the DMSO content in the solution at constant salt concentration. The glass-forming composition regions were found and the limits of this region are discussed.     

Thermochemical properties of 2,4-dinitroanisole in N-methyl pyrrolidone and dimethyl sulfoxide

The thermochemical properties of 2,4-dinitroanisole (DNAN) in N-methy pyrrolidone (NMP) and dimethyl sulfoxide(DMSO) were studied using a RD496-2000 Calvet microcalorimeter at four different temperatures. The heat effects were measured for DNAN dissolved in NMP and DMSO and the relationships between the heat effects and the amounts of the substance were determined. The molar enthalpies and the differential molar enthalpies of dissolution processes were also obtained from the experimental data. The corresponding kinetic equations describing the two dissolution processes at different temperatures were discussed.     

The role of cations in homogeneous succinoylation of mulberry wood cellulose in salt-containing solvents under mild conditions

The role of two cations [tetraethylammonium⁺ (TEA⁺) and tetrabutylammonium⁺ (TBA⁺)] in the homogeneous succinoylation of mulberry wood (MW) cellulose in dimethyl sulfoxide (DMSO)/tetraethylammonium chloride (TEACl) and DMSO/tetrabutylammonium fluoride (TBAF) was investigated using the intrinsic viscosity and two-dimensional nuclear Overhauser effect NMR spectroscopy (2D NOESY). The intrinsic viscosity of MW cellulose solution strongly depends on the salt dosage for both TEACl and TBAF, indicating that the increase in the hydrodynamic size of cellulose chains was caused by the interactions between salts and cellulose, which promotes the solvation process of cellulose in solution. Two-dimensional NOESY spectra reveal that cations bind to cellobiose in DMSO by the interactions between α-methylene groups of TEA⁺ (or TBA⁺) and C1/C1′ groups of cellobiose, and the intensities of the respective crosspeaks increase with increasing TEACl dosage from 5 to 10 mg/ml, but no change was present with TBAF at the same concentration range. Taking cellobiose as a model compound for cellulose, it can be expected that TEA⁺ (or TBA⁺) and cellulose form polyelectrolyte-like complexes. The degree of substitution (DS) of homogeneous succinoylation of MW cellulose benefits from the interactions between TEA⁺ (or TBA⁺) and cellulose evidenced by FT-IR spectra and CP/MAS ¹³C NMR spectra. The DS of the succinylated cellulose declines at TBAF concentrations higher than 11 wt% probably because of the steric hindrance effects of TBA⁺.     

Facile formation of stimuli-responsive,fluorescent and magnetic nanoparticles based on cellulose stearoyl ester via nanoprecipitation

In comparison to stimuli-responsive, multi-functional nanoparticles (NPs) from synthetic polymers, such NPs based on sustainable, naturally occurring polysaccharides are still scarce. In the present study, stable stimuli-responsive, fluorescent and magnetic NPs were fabricated using cellulose stearoyl esters (CSEs) consisting of cellulose and stearoyl groups. The multifunctional NPs with the average diameters between 80 and 250 nm were obtained after facile nanoprecipitation using CSE solutions containing Fe₃O₄-NPs. Using the aqueous solution of fluorescent rhodamine B as precipitant, NPs with rhodamine B on NP surface were obtained. Rhodamine B could be released depending on the temperature. In comparison, stearoylaminoethyl rhodamine B can be encapsulated in CSE-NPs, which renders obtained NPs reversible fluorescence in response to UV illumination and heat treatment.     

A new synthesis of bicyclic N,O- and N,S-enaminals by the anionic cyclization of alk-4-ynals with amino alcohols and amino thiols

A reaction of alk-4-ynals with aliphatic amino alcohols or 2-aminoethanethiol in the system DMSO—KOH gives bicyclic N,O- and N,S-enaminals: 6-methylidenehexahydro-2H-pyrrolo[2,1-b][1,3]oxazines, 5-methylidenehexahydropyrrolo[2,1-b]oxazoles, or 5-methyl-idenehexahydropyrrolo[2,1-b]thiazoles. The reaction proceeds through the formation of equilibrium mixtures of the corresponding imines and monocyclic aminals with subsequent 5-exodig-cyclization catalyzed by the superbasic system DMSO-KOH.     

Dehydrogenation of 4-aryl(hetaryl) spinacine derivatives with dimethyl sulfoxide

Aromatization of 4-aryl(hetaryl)tetrahydroimidazo[4,5-c]pyridine-6-carboxylic acids and their lithium salts by the action of dimethyl sulfoxide has been revealed for the first time. Heating of these compounds in DMSO for 5–7 h at 90–95°C leads to the formation of 4-aryl(hetaryl)imidazo[4,5-c]pyridine derivatives as a result of dehydrogenation and decarboxylation. Heating of the corresponding lithium salts generated in situ (DMSO, 90–95°C, 3–5 h) affords difficultly accessible 4-aryl(hetaryl)imidazo[4,5-c]pyridine-6-carboxylic acids.     

Impact of PS/SiO2 morphologies on the SERS activity of PS/SiO2/Ag nanocomposite particles

To understand the relationship between the morphology of carboxyl-functionalized polystyrene/silica (PS/SiO₂) nanocomposite microspheres and the surface-enhanced Raman scattering (SERS) performance of PS/SiO₂/Ag nanocomposite particles, core-shell and raspberry-like PS/SiO₂ composite microspheres were used as templates to prepare PS/SiO₂/Ag nanocomposite particles. The core-shell and raspberry-like structured PS/SiO₂ templates were prepared via in situ sol-gel reaction by hydrolysis tetraethyl orthosilicate (TEOS) in alkali solution. Silver nanoparticles (10–50 nm) were loaded on the PS/SiO₂ templates’ surface by chemical reduction. The morphology and structure of the PS/SiO₂/Ag particles were characterized by TEM, SEM, X-ray diffraction (XRD), and ultraviolet-visible (UV-vis) spectroscopy. Rhodamine 6G (R6G) was selected as a model chemical to study the enhancement performance of substrate constructed by PS/SiO₂/Ag nanocomposite. Results indicated that the PS/SiO₂/Ag nanocomposite prepared based on the core-shell templates showed higher SERS activity. The beneficial effect was associated with a lower specific area of core-shell structure and the larger average diameter of nanosilvers than that of the raspberry-like templates.     

Quantitative estimation of the conditions of titrating hydroxyanthraquinones in nonaqueous solvents

In order to determine the optimum conditions of potentiometric titration, an investigation has been made of the relative acidities of 13-hydroxyanthraquinones in water, methanol, acetone (ac), dimethylformamide (DMFA), and dimethyl sulfoxide (DMSO) on the basis of a calculation of the indices of the relative acidity constants (pK_a) by Henderson's method. The existence of a relationship between pK_a in water and pK_a in acetone, dimethylformamide, and dimethyl sulfoxide has been established which is characterized by the linear equations $$pK_a^{DMSO} = 1.54pK_a^{H_2 O} + 11.88$$ , $$pK_a^{DMFA} = 1.38pK_a^{H_2 O} + 8.50$$ , $$pK_a^{ac} = 1.11pK_a^{H_2 O} + 10.26$$ . The sequence of neutralization of the hydroxyls in the titration of polyhydroxy-anthraquinones has been determined from the pK_a values in DMSO and the results of a calculation of electronic structures by the Pariser-Parr-Pople method. A quantitative evaluation of the conditions of titration in the five solvents on the basis of indices of the titration constants (pK_t) has shown that the optimum conditions for the quantitative determination by potentiometric titration are achieved in dimethyl sulfoxide.     

Heat of reaction and curing of epoxy resin

The heat of reaction and kinetics of curing of diglycidyl ether of bisphenol-A (DGEBA) type of epoxy resin with catalytic amounts of ethylmethylimidazole (EMI) have been studied by differential power-compensated calorimetry as a part of the program for the study of process monitoring for composite materials. The results were compared with those from 1∶1 and 1∶2 molar mixtures of DGEBA and EMI. A method of determination of heat of reaction from dynamic thermoanalytical instruments was given according to basic thermodynamic principles. The complicated mechanism, possibly involving initial ionic formation, has also been observed in other measurements, such as by time-domain dielectric spectroscopy. The behavior of commercially available DGEBA resin versus purified monomeric DGEBA were compared. The melting point of purified monomeric DGEBA crystals is 41.4 °C with a heat of fusion of 81 J/g. The melt of DGEBA is difficult to crystallize upon cooling. The glass transition of purified DGEBA monomer occurs around ?22 °C with aΔC _p of 0.60 J/K/g.     

Microwave synthesis of secondary phosphines and phosphine oxides from red phosphorus and allyl(methoxy)benzenes in KOH-DMSO

Bis[1-(methoxyphenyl)propan-2-yl]phosphines and bis[1-(methoxyphenyl)propan-2-yl]phosphine oxides were synthesized by phosphorylation of allyl(methoxy)benzenes in the system red phosphorus-KOH · 0.5 H₂O-DMSO under microwave irradiation.     

Structural and thermal properties of HDPE/n-AlN polymer nanocomposites

High-density polyethylene (HDPE) containing various volume fractions (0–20 vol%) of aluminum nitride nanoparticles (n-AlN) is prepared by melt mixing. Structural and morphological characterizations of the prepared composites are carried out by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), and atomic force microscopy (AFM). Thermal stability and degradation kinetics of HDPE/AlN (nano) composites are investigated by Thermogravimetric analysis (TG). HR-TEM micrographs confirm fairly uniform dispersion of AlN nanoparticles, as well as the existence of long interconnected chain-like aggregates. AFM images also confirm homogeneous dispersion of n-AlN in the polymer matrix. Roughness analysis from the AFM data indicates the presence of substantial undulation from the mean surface level. Thermogravimetric data indicate small improvement in the thermal stability of the composites. Kinetic parameters, viz., the activation energy (E _a), frequency factor (A), and reaction order (n) are estimated using the isoconversional methods of Kissinger, Flynn–Wall–Ozawa (FWO), KAS, and Friedman. Activation energies (E _a) calculated by the above four models display nearly similar features and are enhanced by the presence of AlN nanoparticles. Kinetics of degradation of HDPE-AlN (nano) composites follows a first-order reaction.     

Thermal decomposition of polymethylmethacrylate synthesized with anionic catalysts

TG and DTA data are used to show that the thermal decomposition of polymethylmethacrylate (PMMA) synthesized with anionic catalysts depends on the nature of the catalyst. It is found that the thermal stability of PMMA obtained by using anionic amide catalysts is higher than that of radical PMMA and of PMMA obtained with other anionic catalysts, and depends on the temperature of polymerization and on the molecular weight of the polymer.     

A direct hydrogen-1 and phosphorus-31 nuclear magnetic resonance cation solvation study of Al(ClO4)3, Ga(ClO4)3, In(ClO4)3, UO2(ClO4)2, and UO2(NO3)2 in water-acetone-dimethylsulfoxide and water-acetone-hexamethylphosphoramide mixtures

A competitive solvation study of Al(ClO₄)₃, Ga(ClO₄)₃, In(ClO₄)₃, UO₂(ClO₄)₂, and UO₂(NO₃)₂ in water-acetone-dimethylsulfoxide (DMSO) and water-acetone-hexamethylphosphoramide (HMPT) mixtures has been carried out by direct H¹ and P³¹ nuclear magnetic resonance (NMR) techniques. At low temperature, proton and ligand exchange are slow enough in these systems to permit the observation of signals for bulk and coordinated molecules of water and the organic bases (DMSO and HMPT). Both DMSO and HMPT compete effectively with water for coordination sites in the Al³⁺, Ga³⁺, and In³⁺ systems, with steric effects dominating the HMPT results. Both Al³⁺ and In³⁺ are able to bind a maximum of two to three HMPT molecules, for example. In contrast, UO²⁺ is solvated selectively by the organic molecules to the allowed maximum of 4 molecules per cation. H¹ and P³¹ NMR spectral results support the formation of only the mono-, tri-, and tetra-HMPT solvation complexes.     

Isolation and purification of biopolymers by affinity chromatography. VI. Preparation and properties of an affinity adsorbent with a polysaccharide spacer for the purification of proteolytic enzymes

A new affinity sorbent has been synthesized — soybean trypsin inhibitor (STI)-amylopectin-hydrazidosuccinyl-Sepharose — and its properties have been studied in comparison with those of an analogous adsorbent without the spacer STI-Sepharose. The STI-amylopectin-hydrazidosuccinyl-Sepharose adsorbent has been used for the purification of trypsin from porcine pancreas and of callicrein from human blood plasma.     

SDS 800 — The new data system for quantitative depth profiling of inhomogeneous samples by SIMS

More than 13 years of SIMS application field experience of numerous users of the ATOMIKA Ionmicroprobes have been the basis for the new SIMS Data System SDS 800. The hardware and software concept of the SDS 800, therefore, pays special attention to the following requirements:

1. Convenient set-up, modification and re-use of the measuring parameter sets for easy, time-saving operation.
2. Individual parameter selection from the very broad range of SIMS measuring parameters for optimum SIMS data quality.
3. Multitasking operation for simultaneous handling of SIMS measurement, data processing, data output and of auxiliary techniques.
4. Simultaneous depth profile/ion image acquisition and processing to enhance data quality and to validate data interpretation.
5. User-friendly data processing and output.

     

Polyoxotungstate nanoclusters supported on silica as an efficient solid-phase microextraction fiber of polycyclic aromatic hydrocarbons

A highly porous silica-supported tungstophosphoric acid (PW) nanocluster was prepared for use in solid-phase microextraction (SPME) of polycyclic aromatic hydrocarbons (PAHs). The PWs represent a class of discrete transition metal-oxide nanoclusters and their structures resemble discrete fragments of metal-oxide structures of definite size and shape. Transition metal-oxide nanoclusters display large structural diversity, and their monodisperse sizes can be tuned from several Ångstroms up to 10 nm. The highly porous silica-supported tungstophosphoric acid nanocluster material is found to be capable of efficiently extracting PAHs from aqueous sample solutions. The nanomaterial was immobilized on a stainless steel wire for fabrication of the SPME fiber. Following thermal desorption, the PAHs were quantified by GC-MS. Analytical merits include limits of detection that range from 0.02 to 0.1 pg mL^?1 and a dynamic range as wide as from 0.001 to 100 ng mL^?1. Under optimum conditions, the repeatability for one fiber (n?=?3), expressed as the relative standard deviation, is between 4.3 % and 8.6 %. The method is simple, rapid, and inexpensive. The thermal stability of the fiber and the high relative recovery make this method superior to conventional methods of extraction.

The highly porous silica-supported tungstophosphoric acid nanocluster material is found to be capable of efficiently extracting PAHs from aqueous sample solutions. The prepared nanomaterial was immobilized onto a stainless steel wire for fabrication of the SPME fiber. Following thermal desorption, the PAHs were quantified by GC-MS.     

On synthesis of Fe2SiO4/SiO2 and Fe2O3/SiO2 composites through sol–gel and solid-state reactions

Major processing factors in forming Fe₂SiO₄/SiO₂ and Fe₂O₃/SiO₂ powders via sol–gel synthesis followed by solid-state reactions are investigated. The results clearly indicate that the chemical compositions of the precursors, the ratio of the precursors, the nature of the catalyst used, and the gas atmosphere during solid-state reactions can all affect the outcome of the reaction product(s). The formation of Fe₂SiO₄/SiO₂ is enhanced by using the precursor iron(III) acetylacetonate as the Fe source with the precursor ratio of iron(III) acetylacetonate to tetraethyl orthosilicate being 1:1 and the addition of formic acid. Otherwise, crystalline Fe and Fe₃C are formed in place of Fe₂SiO₄. By altering the gas atmosphere during solid-state reactions from argon to oxygen, the reaction products change from Fe₂SiO₄/SiO₂ to Fe₂O₃/SiO₂. All of the observed phenomena can be rationalized via the degree of mixing of the Fe–O and Si–O domains at the molecular level in the gel network during sol–gel reactions and the presence of a reducing or oxidizing atmosphere during the solid-state reaction.     

The role of octanol in the extraction of hydrochloric acid by trilaurylamine dissolved in benzene

The extraction of hydrochloric acid by trilaurylamine (TLA) dissolved in benzene was studied in the presence and in absence of n-octanol. The extraction of HCl was found to be enhanced by the addition of octanoi to the organic phase. In order to explain this effect by means of the law of mass action, the systems TLA-HCL-benzene and n-octanol-HCl-benzene as well as TLA-octanol-benzene were also studied. It was found that TLA reacts with octanol to form a complex, TLAROH, while the octanol itself associates in benzene to form dimers and tetramers, although it does not extract HCl alone from the dilute solutions used in the present study. The enhancement of the extraction of HCl by TLA upon the addition of n-octanol could be described by the formation of the species TLA·ROH·HCl and its stability constant was determined.