Showing papers on "Solvent effects published in 1974"
TL;DR: The shape of the hydrophobic barrier of lipid bilayers, fatty acids andl-α-lecithins with doxyl is plotted as a polarity index operationally defined in terms of the ΔA of the lipid spin labels.
Abstract: Previous work has shown that there is a small solvent effect on the electron spin resonance spectra of nitroxide spin labels. The aim of this paper is to develop a semiquantitative treatment of the solvent effects and to use this treatment to estimate the shape of the hydrophobic barrier (i.e., polarity profile) of lipid bilayers. In this semiquantitative treatment of solvent effects, the total effect on the isotropic14N coupling constant, ΔA, is expressed as a sum of terms associated with van der Waals interactions, hydrogen bonding, the charged double layer of phospholipid polar groups and the membrane potential. The magnitude of ΔA as a function of the electric field is estimated with Huckel molecular orbital theory and, independently, using the Onsager model. With these relations, estimates of the relative importance of the various solvent effect terms are obtained from accurate ESR measurements on dilute solutions of di-t-butyl nitroxide in thirty-three solvents and calculations of the electric field produced by the charged double layer and the membrane potential. To estimate the shape of the hydrophobic barrier of lipid bilayers, fatty acids andl-α-lecithins with doxyl (i.e., 4′, 4′-dimethyloxazolidine-N-oxyl) labels bonded to various positions along the lipid chains were diffused into phospholipid vesicles and membranes (from the calf liver microsomal fraction). The shape of the hydrophobic barrier is plotted as a polarity index operationally defined in terms of the ΔA of the lipid spin labels. The effect of the charged double layers is less important than water penetration except when the spin label is within a few Angstroms of the charged groups. Any effects of a membrane potential on ΔA are insignificant. A comparison of ESR spectra indicates that significant water penetration into the bilayer occurs in both the pure lipid bilayers and in the membrane preparations.
402 citations
TL;DR: The effects of substitution, lanthanide-shift reagents, solvent changes, and tautomerism were investigated in this article, where it was concluded that chemical shifts are of limited value to ascertain the positions of tautomers.
Abstract: The effects of substitution, lanthanide-shift reagents, solvent changes, and tautomerism were investigated on
the ^(13)C chemical shifts of pyrrole, pyrazole, imidazole, s- and v-triazole, and tetrazole. It was concluded that
^(13)C chemical shifts are of limited value to ascertain the positions of tautomeric equilibrium for rapidly interconverting azole tautomers.
174 citations
TL;DR: In this article, the effects of a solvent on a molecular system are incorporated into the Hartree-Fock SCF molecular orbital formalism prior to the solution of the quantum mechanical problem.
Abstract: A theoretical model is presented by which the effects of a solvent on a molecular system are incorporated into the Hartree-Fock SCF molecular orbital formalism prior to the solution of the quantum mechanical problem. The proposed model assumes that the polar nature of the solvent can be characterized by a single parameter. The effects of aprotic solvents on certain molecular parameters of N,N-dimethylformamide and N-nitrosodimethylamine have been studied, using a semiempirical Mulliken type MO method incorporating the proposed solvent interaction model. These molecular parameters include the hindered rotation barrier, net charges at the atomic center, and the initial n→π* transition.
107 citations
97 citations
TL;DR: In this paper, the inductive and mesomeric substituent effects on the polarisation and charge density of the CNC bonds were discussed in terms of the inductively and mesomally substituents.
Abstract: 13C chemical shifts and 1J(14N13C) coupling constants as well as stretching frequencies of the isocyano group are reported for some representative aliphatic, unsaturated and aromatic isocyanides and for two copper(I) isocyanide complexes. The results are discussed in terms of the inductive and mesomeric substituent effects on the polarisation and charge density of the CNC bonds. The marked solvent effect on the chemical shifts of the isocyano carbon hampers comparison of our data with previously reported data. The hydrogen bonding shift of this carbon in water or methanol is much smaller than previous data suggest.
95 citations
76 citations
TL;DR: In this article, a theory of solvent-solute interactions is presented, in which a classical model due to Kirkwood is used to derive an expression for the potential affecting a molecule due to a solvent.
67 citations
TL;DR: In this paper, the authors defined two broad categories of shift phenomena: (1) chemical effects of the solvent on one or both electronic states of the chromaphore, and (2) physical intractability.
Abstract: Electronic absorption and emission spectra of a molecule dissolved in a solvent medium in general are shifted in energy relative to the spectra of the isolated molecule. In some cases, these solvent shifts amount to more than 30% of the energy of the isolated-molecule transition, although shifts of the order of 102 to 103 cm-1 are more common. These effects have been the subjects of many investigations directed toward defining the molecular bases of the shifts [1–14]. Two broad categories of shift phenomena have been defined: (1) Many, especially the larger, shifts are attributed to specific chemical effects of the solvent on one or both electronic states of the chromaphore. Some important specific effects are: hydrogen-bond formation; proton or charge transfer between solvent and solute; and solvent-dependent aggregation, ionization, and isomerization equilibria. Such specific effects are outside the scope of this discussion. (2) The second broad category of shifts are attributed to physical int...
67 citations
01 Feb 1974
TL;DR: In this paper, a broad theoretical and experimental investigation of retention in thermal field-flow fractionation is reported, and new equations are developed to account for the distortion of the flow profile caused by a variable viscosity.
Abstract: A broad theoretical and experimental investigation of retention in thermal field-flow fractionation is reported here. Equations connecting retention parameters with underlying thermal diffusion constants are reviewed, and new equations are developed to account for the distortion of the flow profile caused by a variable viscosity. Parameters investigated experimentally include channel width, solute molecular weight, channel temperature drop, cold-wall temperature, sample size, and solvent effects. All but the last two of these experimental studies showed good conformity with theoretical predictions. No theory exists for the prediction of sample-size or solvent effects. With regard to the latter, experimental results show that a variety of organic solvents are very effective, at roughly equal levels, in providing retention, while aqueous solvents are generally ineffective.
62 citations
61 citations
TL;DR: In this paper, the stability and stability constants of metal complexes with ethylenediamine and glycine were determined at 25 °C and in 0.1 M ionic strength.
Abstract: Acidity constants and stability constants of certain metal complexes (nickel(II), zinc(II), and manganese(II)) with ethylenediamine and glycine were determined at 25 °C and in 0.1 M ionic strength ...
TL;DR: In this article, a range of ortho-disubstituted C-aryl aldimines has been synthesized and a significant proportion of the Z-isomer at equilibrium in solution.
Abstract: A range of ortho-disubstituted C-aryl aldimines has been synthesized. N.m.r. spectroscopic analysis revealed a significant proportion of the Z-isomer at equilibrium in solution. The E–Z-isomer distribution is critically examined in terms of electronic, steric, and solvent effects. The effect of trace amounts of carboxylic acid on imine stereomutation is discussed.
TL;DR: In this article, the influence of various solvents (water, methanol, diethyl ether, n -hexane, cyclohexane) and of the excitation energy (λ exc ) on the fluorescence quantum yield (Q F ) of phenol has been investigated in O 2 - free solutions.
TL;DR: In this paper, the variations in the vibrational structures of the fluorescence spectra of coronene and triphenylene in a variety of solvents have been studied in connection with the solvent polarities.
TL;DR: In this article, the authors demonstrate that it is possible to approach the subject of solvent effects from more than one direction and demonstrate that an increased effort in this area may well add to our knowledge of the influence of the solvent effects on the performance of a given application.
Abstract: The authors demonstrate that it is possible to approach the subject of solvent effects from more than one direction. An increased effort in this area may well add to our knowledge of the influence ...
TL;DR: In this paper, the solubilities of several solvents were measured in four molten polymers by using an isobaric vapor-pressure apparatus, and a theory was analyzed with a theory which took into account adsorption of solvent by polymer in addition to differences in free volumes and intermolecular forces.
Abstract: Solubilities of several solvents were measured in four molten polymers by using an isobaric vapor-pressure apparatus. Solvent concentration ranged from 0.5 to 15 wt-%. The systems polyisoprene–benzene and polyisobutylene–benzene were studied at 80.0°C; polyisobutylene–cyclohexane was studied at 100.0°C; ethylene–vinyl acetate copolymer (EVA)–cyclohexane, EVA–isooctane, and poly(vinyl acetate)–isooctane were studied at 110.0°C. Of six polymer–solvent systems studied, all except poly(vinyl acetate)–isooctane appear to exhibit hysteresis in a single sorption–desorption cycle starting with dry polymer. The desorption curves of solvent activity plotted versus solvent weight fraction show an inflection point, suggesting localized adsorption of solvent molecules. Experimental data were analyzed with a theory which takes into account adsorption of solvent by polymer in addition to differences in free volumes and intermolecular forces. The theory gives a semiquantitative representation of the experimental data.
TL;DR: In this paper, the effects of several water-soluble organic solvents on the micellar destruction of the nonionic surfactant, homogeneous hepta-ethylene glycol dodecyl ether, is discussed from the viewpoint of the charge transfer (CT) interaction of TCNQ with micelles in connection with the solubility parameter (SP) of added solvalents.
TL;DR: In this paper, the polymerization of methyl methacrylate by alkali metal alkoxides was carried out in aprotic dipolar solvents such as hexamethylphosphoramide, dimethylsulfoxide, and dimethylacetamide.
Abstract: The polymerization of methyl methacrylate by alkali metal alkoxides was carried out in aprotic dipolar solvents such as hexamethylphosphoramide, dimethylsulfoxide, and dimethylacetamide. The polymerization was drastically promoted by these solvents, even by the presence of small quantities of them. Tetramethylethylenediamine and ethereal solvents also promoted the reaction, although these solvents were less effective than the aprotic dipolar type. Such an effect of the solvent was explained in terms of the donor property and the dielectric constant of the solvent. Alkali metal salts of 2-substituted ethanols such as 2-methoxyethanol and 2-dimethyl-aminoethanol were effective as the initiator. The structure of the polymer was discussed with regard to the property of the propagating active end.
TL;DR: The pK values for the two acidic dissociation steps of the ampholyte N-tris-(hydroxymethyl)methyl glycine (“tricine”) in 50 mass % methanol-water solvent have been determined by emf measurements of cells of the type Pt|H2(g, 1 atm), tricine buffer, Br−, AgBr|Ag over the range 5 to 50°C (pK¯¯¯¯1) and 5 to 60°C(pK fixme2) as mentioned in this paper.
Abstract: The pK values for the two acidic dissociation steps of the ampholyte N-tris-(hydroxymethyl)methylglycine (“tricine”) in 50 mass % methanol-water solvent have been determined by emf measurements of cells of the type Pt|H2(g, 1 atm), tricine buffer, Br−, AgBr|Ag over the range 5 to 50°C (pK
1)and 5 to 60°C (pK
2).The standard thermodynamic quantities ΔHo, ΔSo, and ΔC
p
o
for the two dissociation processes have been derived and are compared with the corresponding values for tricine and the parent glycine in water and with those for other acids in 50 mass % methanol-water solvent. Both tricine and protonated tricine become weaker acids when methanol is added to the aqueous solvent. It appears that a strong stabilization of the zwitterion in water is responsible for this behavior. This conclusion is supported by comparing the changes in entropy and heat capacity for the dissociation of tricine with the values of these quantities for the dissociation of “model” acids of simple structure, such as ammonium ion and acetic acid.
TL;DR: In this paper, the effects of polymer homology and solvent character have been successfully analyzed under these conditions and relationships are proposed for the observed effects, and the reduction in turbulent friction (drag reduction) has been catalogued through evaluation of the polymer intrinsic concentration.
Abstract: Turbulent friction reduction by high molecular weight poly(ethylene oxide) polymers has been examined in a series of salt solutions ranging from pure water to nearly theta solvent conditions. The effects of polymer homology and solvent character have been successfully analyzed under these conditions and relationships are proposed for the observed effects. The reduction in turbulent friction (drag reduction) has been catalogued through evaluation of the polymer intrinsic concentration—an index of drag reduction effectiveness. Plots of the reciprocal of the polymer intrinsic concentration versus salt molarity are approximately linear and are similar to the plots of intrinsic viscosity versus molarity reported by other workers. An attempt is made to graphically and numerically combine these results. The suggestion is advanced that those solvent properties which bring about decided conformational changes in these polymer molecules (as indexed by intrinsic viscosity effects) also affect, in an apparently analogous fashion, the turbulent friction reduction efficiencies of these molecules. The decreases in turbulent friction reduction resulting from the increasingly collapsed state of the polymer coil suggest the possibility of correlating friction reduction with changes in the polymer expansion factor α. On the basis of the limited data available, the suggestion is also made that drag reduction studies might best be made under theta solvent conditions where different polymer families might be more meaningfully compared in the absence of solvent effects.
TL;DR: In this paper, chemical shifts are reported for the compounds (CH3)4−nPb Xn, where n = 1 · 4, X = 4-FC6H4, n = 2, 2, 4, x = CH3 CC, n= 1, 4.
TL;DR: In this article, the chemical shifts of the aldehydic proton in furfural, thiophenealdehyde and benzaldehyde have been measured in fourteen solvents, and the correlation of chemical shifts was shown to correlate with benzaldehyde, (r = 0·992; 0·993).
Abstract: The chemical shifts of the aldehydic proton in furfural, thiophenealdehyde and benzaldehyde have been measured in fourteen solvents. The correlation of the chemical shifts of thiophenealdehyde and benzaldehyde is excellent (r = 0·996) while it is lower for furfural–benzaldehyde (r = 0·956). The long range coupling constant Jα5 of furiurai has been measured in twelve solvents and the rotameric mole fractions determined. The chemical shifts of individual rotamers are calculated and shown to correlate with benzaldehyde, (r = 0·992; 0·993). Only one rotamer is predominant for thiophenaldehyde in all solvents. The intrinsic solvent effects of the three aldehydes are similar.
TL;DR: In this article, the dissolution mechanism of Nylon 6 was investigated in connection with the chain conformations of the polymer in some complex solvents, such as the metal halide-alcohol systems.
Abstract: The dissolution mechanism of Nylon 6 was investigated in connection with the chain conformations of the polymer in some complex solvents, such as the metal halide—alcohol systems Infrared studies on both the polymer solutions and the metal halide—alcohol mixtures revealed that Nylon 6 forms a complex with the metal halide—alcohol complex solvent The characteristic ratio (‹R02›/nl2=941) of Nylon 6 was determined in a 15-g CaCl2/100-ml CH3OH mixture at 35°C, a theta solution, and is considerably larger than Flory’s value, 608, in which the specific solvent effects were not taken into account It is pointed out how the solvent interactions affect the short-range interferences in the chain conformations in the complex solvent used in this work