Cerimetry in nonaqueous media

Summary The reaction between ascorbic acid and ammonium hexa nitrato cerate was studied potentiometrically in the mixed solvent glacial acetic acid acetonitrile medium. It was found that one mole of ascorbic acid consumes four equivalents of cerate in non-aqueous medium. This reaction can be made use of to estimate potentiometrically ascorbic acid with ammonium nitrato cerate in non-aqueous media, using either glass or antimony as reference electrode and platinum as indicator electrode.

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Zusammenfassung Die Reaktion zwischen Ascorbinsäure und Ammoniumhexanitratocerat wird in einem Medium von Eisessig + Acetonitril untersucht. Im nichtwäßrigen Medium verbraucht 1 Mol Ascorbinsäure 4 Äquivalente Cerat. Die Reaktion kann zur potentiometrischen Bestimmung von Ascorbinsäure benutzt werden; dabei wird als Indicatorelektrode Platin und als Vergleichselektrode die Glas- oder Antimonelektrode verwendet.

     

Electroinitiated polymerization of acrylamide in nonaqueous media

Anodic electroinitiated polymerization of acrylamide has been studied in DMF and DMSO in the presence of Co(NO₃)₂ or Co(ClO₄)₂ in the temperature range 25–40°C. The kinetics and mechanism of the process has been investigated as a function of variables and a suitable mechanism proposed. From the experimental observations, the rate of polymerization is seen to be proportional to [AM]^1.5, [I]^0.5, and [Co²⁺]¹. Current densities exceeding 15 mA/cm² have no effect on the rates. The average degrees of polymerisation (P?_n) increase with increasing [AM] and decreasing [Co²⁺] and applied current, I. It has been shown that a monomer-metal ion complex is oxidized at the anode, generating radical species. The polymerization and termination are confined to the anode compartment. The process is very efficient compared to the NO mediated reaction.     

The hydration of anions in nonaqueous media

A very simple isopiestic method based on that of S. Christian is used for measuring the salting-in of water into nonpolar, low-volatility solvents by tetraalkylammonium salts. The quantity of excess water which is dissolved in such solvents is directly proportional to the salt concentration and is sharply dependent on the nature of the anion but is nearly insensitive to that of the R₄N⁺ cation. The hydration ratioH, which we define as the moles of excess solubilized water per mole of R₄N⁺ X^–, is directly relatable to the enthalpy of hydration of the anion X^– in several solvents and in the gas phase. The quantityH is also correlated with many free-energy terms including those for the Hofmeister lyotropic series, for the ability of the anions to salt nonelectrolytes out of water, for the free-energy terms for separation of these ions by reverse osmosis membranes, and for their nucleophilicities. A surprising (but not unprecedented) feature of the hydration ratio is that it, rather than its logarithm, behaves as a free-energy term. It is proposed that all these properties have in common the free energy of hydration of the anions, and this notion is supported by a close correspondence between the anionic hydration ratio and their hydrogen-bonding energies with proton donors in aprotic solvents. The results support scattered observations by other workers that isolated water molecules do not have an unusual inherent affinity for anions. Accordingly, large anionic hydration energies in bulk aqueous media reflect extensive cooperative interactions in the solvent. Implications for nucleophilic activity in phase transfer catalysis and enzyme activity are mentioned.     

Solvation of crown ethers in nonaqueous media

The data on the solvation of macrocyclic polyethers in individual and binary non-aqueous solvents are summarized and analyzed.     

Patents and literature biocatalysis in nonaqueous media

Biocatalysis in nonaqueous media is being used in increasing regularity both in academic and industrial research. A variety of biocatalysts have been used in organic media including enzymes, multi-enzyme systems, and whole cells. In addition, the nonaqueous media has encompassed both monophasic and biphasic solvent systems, enzymes and whole cells in reversed micelles, enzymes and cells in nearly anhydrous (no added water) solvents, and enzymes catalytically active in supercritical fluids and the gas phase. Recent US and overseas patents and scientific literature on biocatalysis in nonaqueous media are surveyed. Patent abstracts are summarized individually, and literature references are divided into major subheadings.     

Measuring the electrophoretic mobility of concentrated suspensions in nonaqueous media

We present a new method of measuring the electrophoretic mobility of a particle in a concentrated suspension. The method is used to measure the electrophoretic mobility of PMMA particles (diameter 10 microm) suspended in a mixture of liquid hydrocarbons. The particle volume fraction of the suspension is varied from 0 up to 0.30 and the resulting variation of the electrophoretic mobility is discussed. The suspending liquid is such that its refractive index is very close to that of the particles. Thus the suspension is almost transparent and it is possible to follow through a microscope the motion of one particle. The suspension is subjected to a low-frequency electric field (0.5 Hz). The cell containing the suspension is mounted on a piezoelectric crystal. The displacement that compensates for the particle motion (when the particle image is steady) is determined.     

Polarographic reduction of D-glucurono-γ-lactone in nonaqueous media

Summary The nonaqueous polarographic reduction of D-glucurono--lactone in dimethylformamide using tetrabutylammonium iodide as the supporting electrolyte (apparent E_1/2=– 1.94 V versus mercury pool) is analytically applicable over the concentration range of 50–300g/ml.

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Zusammenfassung Die polarographische Reduktion von D-Glucuronsäure--lacton in Dimethylformamid mit Tetrabutylammoniumjodid als Trägerelektrolyt (E_1/2=–1,94 V gegen Quecksilber) ist im Konzentrationsbereich 50 bis 300g/ml analytisch anwendbar.

     

Specific anion effects on enzymatic activity in nonaqueous media

The present work shows that salt anions affect the activity of Pseudomonas cepacia lipase both in aqueous and in nonaqueous media (NAM) according to a Hofmeister series. The biocatalytic assay in water was the hydrolysis of p-nitrophenyl acetate, whereas the esterification between 1-hexyl-beta-D-galactopyranoside and palmitic acid was followed in an organic solvent. The solid lipase preparations to be used in NAM were obtained through lyophilization in the presence of concentrated solutions of Hofmeister salts (Na2SO4, NaH2PO4/Na2HPO4, NaCl, NaBr, NaI, NaSCN). Salts affect enzyme activity in organic media through two mechanisms: (1) enzyme protection during lyophilization; (2) enzyme activation during the reaction. At least in our case, the latter seems to be more important than the former. The decrease of the activation energy caused by the stabilization of the transition state due to "kosmotropic" anions might be the driving force of enzyme activation. According to the most recent findings, dispersion forces may be responsible of specific anion enzyme activation/deactivation in NAM.     

Note on nonaqueous electrokinetic transport in charged porous media

A model for electrokinetic transport in charged capillaries is compared with experiments using nonaqueous lithium chloride solutions. The electrokinetic parameters considered are the pore fluid conductivity and the concentration potential. Methanol/water mixtures were the solvent, and track-etched mica membranes with a well-characterized pore structure were the porous medium. The electrolyte concentrations used were such that the Debye lengths of solutions in pores ranged from much smaller to much larger than the radius of pores. The space-charge model is found to be capable of qualitatively describing the trend of the electrokinetic data, but as expected, at higher concentrations the model fails, probably because the assumption that ion—ion interactions are negligible no longer holds. The experimental results show that the pore fluid conductivity depends strongly on the dielectric constant of the solvent, that the absolute value of the pore wall charge tends to decrease with the lowering of the solvent dielectric constant, and that the wall charge tends to increase with the concentration of the chloride ion.     

Interactions of a sulfonated ionomer with surfactant in nonaqueous media

The viscometric behavior of dilute solutions of the sodium salt of sulfonated polystyrene (0–6 mol % sulfonation level), with and without surfactant, is investigated to determine the extent of interaction as the structure of the solvent surfactant, and polymer concentration is varied. Reduced viscosity measurements confirm that formation of a polymer–surfactant complex in a relatively polar solvent is controlled to a large extent by charge–charge and hydrophobic forces. The magnitude of these specific interactions is dependent upon the relative polarity of the solvent medium. In a polar solvent, such as dimethylsulfoxide, the hydrophobic forces are strong enough to prevent expansion of the polymer chain at all surfactant concentrations studied. However, in a less polar medium (as in dimethylformamide) the hydrophobic forces are weaker and cannot prevent some chain expansion. It is interesting to note that in this solvent the polystyrene–cationic surfactant complex exhibits a polyelectrolyte effect. Finally, in a lower-polarity medium (cyclohexanone) where the hydrophobic forces are weak, solution behavior is dominated by the interaction of the surfactant with the intramolecular sulfonate ion-pair aggregates.