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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of solution chemistry 19 (1990), S. 193-205 
    ISSN: 1572-8927
    Keywords: Dimethylacetamide-water mixtures ; rotational molecular motion ; solvent-solvent interaction ; 14N,2H,23Na+,133Cs+ NMR ; Na+ and Cs+ solvation ; preferential solvation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Nuclear magnetic relaxation by intra- and intermolecular quadrupoleelectric field gradient interaction has been used for the study of the systems DMA-water-NaI and DMA-water-CsI at 25°C.14N relaxation of DMA and2H relaxation of D2O measured over the complete mixture range reveal the behavior of the rotational molecular motion of the two solvent components. For both solvent components a marked maximum of the reorientational correlation time has been found, reflecting hydrophobic effects and strong DMA-water interaction. The quadrupolar relaxation rates of23Na+ and133Cs+ in pure DMA were evaluated giving an indication that the electric solvent dipoles in the solvation shell are not located on positions of cubic symmetry. A quantitative study of preferential solvation of the cations in the mixed solvent has been performed by using the H2O-D2O isotope effect on23Na+ and133Cs+ relaxation. For both cations an obviously typical change in the selectivity occurs. In the range l〉x H2 O〉0.7 we find weak preferential hydration, but in the range 0.7〉xH 2 O〉0 strong preferential solvation by DMA is reflected.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of solution chemistry 7 (1978), S. 689-704 
    ISSN: 1572-8927
    Keywords: 2D and14N nmr ; rotational correlation times ; aqueous mixtures ; H bonding and hydrophobic effects ; formamide ; N-methylformamide ; N,N-dimethylformamide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Nuclear magnetic relaxation rates of2D and14N in binary aqueous mixtures of formamide,N-methylformamide (NMF), andN,N-dimethylformamide (DMF) are reported as a function of the mixture composition. From these intramolecular quadrupolar relaxation data separate rotational correlation times for the two components of the mixture can be determined. The relative variation of the single correlation time as a function of the composition is interpreted in terms of structural changes caused by hydrogen bonding and hydrophobic effects. The results also clearly reflect the expected characteristic variation of these effects on the rotational molecular motions in going from formamide to NMF and DMF. The maximum correlation time retardation of DMF in the aqueous mixture is compared with those of other hydrophobic solvents. A correlation between this maximum retardation and the excess enthalpy of mixing of hydrophobic solvents in aqueous solution can be established graphically.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of solution chemistry 7 (1978), S. 705-720 
    ISSN: 1572-8927
    Keywords: 23Na+ and81Br− NMR relaxation ; ion-solvent interactions ; preferential solvation ; H2O + amide mixtures ; hydrophobic effects ; formamide ; N-methylformamide ; N,N-dimethylformamide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Ion-solvent interactions of Na+ and Br− in binary aqueous mixtures of formamide,N-methylformamide (NMF), andN,N-dimethylformamide (DMF) are studied by use of23Na and81Br magnetic relaxation times, extrapolated to zero salt concentration. The relaxation times, which are controlled by quadrupolar interaction, have been measured over the complete mixture range and are compared with a simplified theoretical formula. It turned out that the23Na+ relaxation in H2O-formamide and H2O-NMF mixtures is in excellent agreement with theoretical predictions, implying nonpreferential solvation of Na+ in these systems. Small deviations of experimental from theoretical results in H2O+DMF possibly indicate weak selective hydration of the cation. In the case of the anionic nuclei81Br−, deviations from the theoretical curve occur which are to be expected, especially for systems where hydrophobic effects play a role. On the other hand, it is demonstrated that these deviations can easily be explained within the electrostatic theory by differences in structural details of the anionic solvation sphere in the mixtures compared to the pure solvents.
    Type of Medium: Electronic Resource
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