Showing papers on "Solvent published in 1977"

Solvent-dependent fluorescence of pyrene-3-carboxaldehyde and its applications in the estimation of polarity at micelle-water interfaces

Abstract: The monomer fluorescence of pyrene-3-carboxaldehyde shows a strong dependence on solvent polarity. The fluorescence in nonpolar solvents such as n-hexane is very weak (quantum yield less than 0.001), but becomes quite intense in polar solvents (phi/sub F/ in methanol = 0.15). The fluorescence maximum shows a significant red shift with increased solvent polarity, which is linear with solvent dielectric constant at values greater than ten. This strong dependence of fluorescence on solvent polarity is used to obtain estimates of the polarity at the micelle--water interfaces for various ionic and nonionic detergent micelles. The measured values are in excellent agreement with zeta potential estimates for the micellar Stern layer, derived from double layer theory, and similar estimates using other fluorescence probes. The observed variations in the surface polarity at the micelle--water interfaces in the presence of external additives are also consistent with predictions from other data. The formation of Schiff's base by reaction of pyrenecarboxaldehyde with amines has also been investigated. Data on absorption and emission spectra of Schiff's bases are presented.

Process and amine-solvent absorbent for removing acidic gases from gaseous mixtures

Abstract: Acidic gases are substantially removed from a normally gaseous mixture by a process comprising contacting the normally gaseous mixture with an amine-solvent liquid absorbent comprising (i) an amine comprised of at least about 50 mol % of a sterically hindered amine, and (ii) a solvent for said amine mixture which is also a physical absorbent for said acidic gases. The liquid absorbent may also include up to about 35 weight percent water.

The triple helix ⇌ coil conversion of collagen‐like polytripeptides in aqueous and nonaqueous solvents. Comparison of the thermodynamic parameters and the binding of water to (L‐Pro‐L‐Pro‐Gly)n and (L‐Pro‐L‐Hyp‐Gly)n

Abstract: The collagen-like peptides (L-Pro-L-Pro-Gly)n and (L-Pro-L-Hyp-Gly)n with n = 5 and 10, were examined in terms of their triple helix ⇌ coil transitions in aqueous and nonaqueous solvents. The peptides were soluble in 1,2-propanediol containing 3% acetic acid and they were found to form triple-helical structures in this solvent system. The water content of the solvent system and the amount of water bound to the peptides were assayed by equilibrating the solvent with molecular sieves and carrying out Karl Fischer titrations on the solvent phase. After the solvent was dehydrated, much less than one molecule of water per tripeptide unit was bound to the peptides. Since the peptides remained in a triple-helical conformation, the results indicated that water was not an essential component of the triple-helical structure. Comparison of peptides with the same chain length demonstrated that the presence of hydroxyproline increased the thermal stability of the triple helix even under anhydrous conditions. The results, therefore, did not support recent hypotheses that hydroxyproline stabilizes the triple helix of collagen and collagen-like peptides by a specific interaction with water molecules. Analysis of the thermal transition curves in several solvent systems showed that although the peptides containing hydroxyproline had tm values which were 18.6° to 32.7°C higher, the effect of hydroxyproline on ΔG was only 0.1 to 0.3 kcal per tripeptide unit at 25°C. The results suggested, therefore, that the influence of hydroxyproline on helical stability may be explained by intrinsic effects such as dipole–dipole interactions or by changes in the solvation of the peptides by alcohol, acetic acid, and water. A direct calorimetric measurement of the transition enthalpy for (L-Pro-L-Pro-Gly)n in 3% or 10% acetic acid gave a value of −1.84 kcal per tripeptide unit for the coil-to-helix transition. From the value for enthalpy and from data on the effects of different chain lengths on the thermal transition, it was calculated that the apparent free energy for nucleation was +5 kcal/mol at 25°C (apparent nucleation parameter = 2 × 10−4M−2). The value was dependent on solvent and on chemical modification of end groups.

Processes of making a porous membrane material from polyvinylidene fluoride, and products

Abstract: Covers processes for making microporous membranes and molecular filtration membranes from vinylidene fluoride polymers, and the products so produced. A continuous version of the process consists of applying a layer of a solution of a polyvinylidene fluoride polymer to a rigidly supported surface of a backing belt to form a film, then passing the belt through a formation bath, in which the membrane is formed. To form the polymer solution, the polymer is dissolved in a liquid vehicle that will dissolve up to about 25% by weight of the polymer at a temperature of at least 50° C. but that dissolves substantially less of the polymer at about 20° C. (room temperature). The polymer solution is formed at 50° C. or higher, and the formation bath is maintained at about room temperature. The formation bath is a mixture of the liquid vehicle solvent with a second liquid that is miscible with the solvent but that is not itself a solvent for the polymer. The film is maintained immersed in the formation bath until it has been converted to a porous membrane whose pore structure is essentially fully formed, by leaching of the solvent from the film and its replacement with the non-solvent liquid. Thereafter the residual solvent is extracted from the porous membrane, and after separation of the membrane from the backing belt, the membrane is dried. The preferred solvent - non-solvent system for the formation bath is acetone-water. A preferred formation bath composition is from about 70% to about 80% acetone by volume.

Methyl chloroform in the troposphere as an indicator of OH radical abundance

Abstract: METHYL chloroform (111 trichloro ethane) was introduced into general use in 1955–60 in response to the need for a general solvent which was less toxic than those then in use. Its ubiquitous presence in the northern and southern hemispheres, first reported in 1974 (ref. 1), has since been confirmed2,3. The only significant sources of methyl chloroform are industrial releases from its use as a cleaning agent and solvent. A principal sink for its removal from the atmosphere seems to be the reaction with OH radicals. The rate of its release to the atmosphere is known with some accuracy, and consequently the measurements of its growth in the atmosphere could provide valuable information on the strength of the OH reaction sink, not only for methyl chloroform but also for other important atmospheric gases which undergo similar reactions. This communication reports measurements of the abundance of methyl chloroform made during 5 yr in the northern and southern tropospheres.

Solvent and temperature effects on diffusion in polymer–solvent systems

Abstract: The temperature dependence of the mutual diffusion coefficient at zero solvent concentration for a number of polystyrene–solvent systems is satisfactorily represented by an equation derived from a new version of the free-volume theory of molecular transport. The free-volume parameter which governs the temperature dependence of the diffusion rate is linearly related to the size of the solvent as estimated by its molar volume at OK. Data taken on various polystyrene–solvent systems are used to deduce information on the mechanism of solvent transfer in polymeric systems.

Cesium-133 nuclear magnetic resonance study of complexation by cryptand C222 in various solvents: evidence for exclusive and inclusive complexes

Abstract: The chemical shift of the /sup 133/Cs resonance was studied as a function of the mole ratio of cryptand C222 to Cs/sup +/ at various temperatures in six solvents, pyridine, acetone, propylene carbonate, N,N-dimethylformamide, acetonitrile, and dimethyl sulfoxide. The variation of the chemical shift with the mole ratio was used to determine the apparent complexation constants at temperatures high enough to yield a single, exchange-narrowed line. At lower temperatures, complete line-shape analysis was used to determine apparent exchange rates. The limiting chemical shift at high C222/Cs/sup +/ mole ratios was found to be strongly dependent upon both solvent and temperature but converged to a solvent-independent value of -245 +- 5 ppM (downfield) at low temperatures. The behavior of the chemical shift and the variation of the line shape and apparent activation energy with temperature suggest the presence of two types of 1 : 1 complexes in solution, an exclusive complex in which the ion may interact with the solvent, and an inclusive complex which has a solvent-independent chemical shift. The temperature dependence of both the thermodynamic and the rate parameters is consistent with this model.

Complexation of the cesium cation by macrocyclic polyethers in various solvents. A cesium-133 nuclear magnetic resonance study of the thermodynamics and kinetics of exchange

Abstract: The formation constants for the complexation of Cs/sup +/ in six solvents by three crown ethers, 18-crown-6, dibenzo-18-crown-6, and dicyclohexyl-18-crown-6, were studied at 25/sup 0/C by cesium-133 NMR techniques. The solvents used, in the approximate order of decreasing first complexation constant for all crown ethers, were pyridine, acetone, propylene carbonate, acetonitrile, N,N-dimethylformamide, and dimethyl sulfoxide. In all solvents, 18-crown-6 formed both 1:1 and 2:1 (ligand to metal) complexes with enough difference between the complexation constants that the second constant could be determined. The formation of 2:1 complexes by the other two crown ethers was also indicated in most solvents but the second complexation constant could only be measured for the dibenzo-18-crown-6 complex in pyridine. In many cases the first complexation constant was too large to measure by the NMR technique so that only lower bounds could be established. The rate of loss of the Cs/sup +/ ion from dicyclohexyl-18-crown-6 and from monobenzo-2,2,2-cryptand in propylene carbonate was measured as a function of temperature. The activation energy for the latter case (15 kcal mol/sup -1/) is substantially larger than for the crown ether complex (8.5 kcal mol/sup -1/). Although the chemical shifts of both Cs/sup +/ and its 1:1 complex with 18-crown-6more » are strongly solvent dependent, the chemical shift of the 2:1 complex is independent of solvent, indicating that in the ''sandwich'' complex the cesium ion is effectively shielded from the solvent.« less

Cyclic carbonic acid esters as solvents for poly-(β-hydroxybutyric acid

Abstract: The use of cyclic carbonic acid esters of the formula: ##STR1## wherein R 1 , R 2 , R 3 and R 4 , which may be the same or different, are hydrogen or alkyl with 1 to 6 C-atoms, as a solvent for racemic or optically active poly-(β-hydroxybutyric acid). The preferred embodiment uses hot (120° to 150° C) ethylene carbonate or 1,2-propylene carbonate to extract poly-(β-hydroxybutyric acid) from moist or dry fermentation masses. These solvents have the advantage that the extracted poly-(β-hydroxybutyric acid) is precipitated in good yield from them on cooling. In addition they may be recycled without the need for a solvent regeneration step. These cyclic carbonic acid esters may also be used as the solvent in the processing of poly-(β-hydroxybutyric acid) by e.g. wet spinning.

1H nuclear magnetic resonance studies of N-acetyl-L-proline N-methylamide. Molecular conformations, hydrogen bondings, and thermodynamic quantitites in various solvents.

Abstract: Concentration and temperature dependences of the 1H nmr spectra of N-acetyl-L-proline N-methylamide were observed in various solvents [CCl4, CDCl3, (CD3)2CO, (CD3)2SO, H2O, and D2O]. The fraction of the cis isomer (with respect to the bond between the acetyl carbonyl carbon and prolyl nitrogen atoms) depends greatly on the solvent used; the fraction of the cis isomer is higher in polar solvents than in nonpolar solvents. It depends also on concentration and temperature in nonpolar solvents but not in polar solvents. In nonpolar solvents the trans isomer mostly exists in the γ-turn structure with an intramolecular hydrogen bond and the cis isomer tends to form molecular aggregates by intermolecular hydrogen bonds. In polar solvents both the cis and trans isomers exist in monomeric forms which interact with solvent molecules. The pH dependences of the N-methyl proton resonances indicate that the γ-turn structure of the trans isomer is present also in aqueous solution, though its population is difficult to determine. Apparent enthalpy and entropy changes for the conversion of the trans isomer to cis isomer are evaluated for various solvents. The results are discussed in terms of the intra- and intermolecular hydrogen bondings.

Production of fats and oils from vegetable and animal products

Abstract: Fats or oils are extracted from animal or vegetable products by a process of contacting the product with a solvent in the liquid phase and at a temperature below the critical temperature of the solvent to extract fat or oil from the product, separating the solvent containing extracted fat or oil from the residue of the product, and precipitating the extracted fat or oil from the solvent by heating the solvent to above the critical temperature of the solvent without taking up heat of vaporization. The resultant precipitated fat or oil contains no more than 3 ppm of solvent which makes the fat or oil suitable for use in foodstuffs without further processing to remove solvent. The temperatures of the solvent may be 0°-100° C. during extraction and 50°-200° C. during precipitation, and the pressure may be the same during extraction and precipitation.

NMR-spectroscopic studies on solvent electrophilic properties, Part II: Binary aqueous-non aqueous solvent systems

Abstract: Acceptor numbers have been determined for binary mixtures of water with acetonitrile (AN), dioxane, acetone (AC), pyridine (PY), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), hexamethylphosphoramide (HMPA), methanol, ethanol andi-propyl alcohol. The electrophilic properties of binary aqueous-non aqueous solvent mixtures are determined both by selective solvation and specific solvent-solvent interactions. The variation of the acceptor number as a function of solvent composition is interpreted in terms of the previously determined nucleophilic and electrophilic properties of the pure components and their specific solvent structure.

Use of solvent cavity area and number of packed solvent molecules around a solute in regard to hydrocarbon solubilities and hydrophobic interactions

Abstract: Two currently used methods of calculating the area of contact between a solute molecule and the solvent are examined and some important differences are pointed out. Some pitfalls and uncertainties in the application of the concept of molecular surface area to the quantitative estimation of unitary free energies of solution are discussed.

Solvent Effect on Radical Polymerization of Phenyl Methacrylate

Abstract: The radical polymerization of methyl methacrylate (MMA) in various aromatic solvents was studied under the same conditions as that of phenyl methacrylate (PMA) reported previously. The propagation-rate constants (kp) and termination-rate constants (kt) were determined by intermittent illumination methods. The variation in the kp values for MMA with aromatic solvents had the same trend as that for PMA, although the solvent effect on the former values was somewhat smaller than that on the latter. Variation in kp values with solvents can be explained by the formation of an electron donor–acceptor complex and is correlated with the delocalization stabilization of the complex formation. The dependence of kp value on the monomer concentration supports the view that a propagating radical complexed with a solvent is in the dormant state. A study of temperature dependence on kp and kt values was also carried out in benzene and activation energy of these values determined to be 5.0±0.8 and 0.38±0.10 kcal mol−1, respectively.

Removing phenols from waste water

Abstract: A process for removing phenols from waste water resulting from the gasification or carbonization of coal and containing CO2, H2 S and NH3, comprising mixing the waste water with a low-boiling organic solvent, separating the mixture into a solvent layer and an aqueous layer, stripping off from the aqueous layer under superatmospheric pressure the vapors of CO2, H2 S and organic solvent contained therein, then stripping off from the aqueous layer the NH3 contained therein leaving a refined aqueous product layer suitable for discharge, scrubbing the stripped vapors under superatmospheric pressure with a portion of the cold refined product to remove organic solvent contained therein, condensing part of the solvent and separating it under superatmospheric pressure, and scrubbing the remaining acid gases still containing ammonia and solvent with recirculated cooled raw phenol to remove the ammonia and solvent.

Photoreduction of 1,10-phenanthroline

Abstract: The effects of solvent polarity on the photophysical properties of 1,10-phenanthroline indicate the close proximity of (n, π*) and (π, π*) excited singlet states, whilst the lowest triplet state is (π, π*) in all solvents. In hydrocarbon solvent, the first excited singlet state is of (n, π*) character but in water a (π, π*) is situated ∼ 700 cm–1 below this state. Even in water, the (n, π*) state is capable of abstracting a hydrogen atom from the solvent forming an intermediate semidiaza radical. The radical can be detected by flash photolysis and e.s.r. techniques and, in organic solvents, it decays with second order kinetics due to a disproportionation reaction. The major product of reaction is dihydrophenanthroline which, in hydrocarbon solvents, is formed with a quantum efficiency of ∼ 25 %. In aqueous solvent, the yield and rate of decay of the semidiaza radical are pH dependent, and the pK for protonation of the radical is 7.3. Thus, irradiation in water at pH 5 results in formation of the stable diprotonated radical cation.

Adhesive compositions consisting essentially of a vinyl alcohol polymer, a crystalline solvent and a viscosity reducing diluent

Abstract: Adhesives consisting essentially of polyvinyl alcohol or ethylene/vinyl alcohol copolymer, a crystalline solvent for the polymer component (such as urea, thiourea, acetamide, ammonium formate, etc.) and a viscosity reducing diluent (such as water, glycols, etc.) are disclosed. The adhesives are particularly suitable for cellulosic substrates and provide excellent ambient temperature water resistance while being fully repulpable in hot water.

Influence of the solvent on the rates of SN1-type solvolysis reactions of metal complexes in water + co-solvent mixtures

Abstract: The relationships developed for the variation of rate with dielectric constants have been extended to include effects derived from changes in solvent structure in order to interpret the linear plots for log (rate constant) against reciprocal of dielectric constant which show slope invariant with the identity of the co-solvent for some metal complexes in water + co-solvent mixtures. In order to apply free energy cycles to such reactions, the free energies of transfer of halide ions from water into water + co-solvent have been determined for water + ethanol and water + dioxan mixtures. The application of these cycles to SN1-type solvolysis shows that, not only do changes in solvation of the transition state have a dominant effect on the rate for a wide range of metal complexes with a range of co-solvents, but that the same conclusion can be drawn for some organic halides.

Ink jet printing composition comprising a solvent, a dye stuff, a volatile base, a multi-valent metal and a polymer containing carboxyl groups

Abstract: Jet printing is described employing an ink of low viscosity and resistivity having improved resistance to abrasion and solvents after drying. The ink comprises an acrylic polymer, dyestuff, volatile basic compounds, and a complexed multivalent metal ion cross-linking agent dissolved in a solvent vehicle which is predominantly water, a lower alcohol, or mixtures thereof.

Aprotic solvent electrolytes and batteries using same

Abstract: The invention comprises using selected alkylated analogs of tetrahydrofuran and tetrahydropyran as solvents for electrolytes in batteries having alkali metal negative electrodes.