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  • 1
    Electronic Resource
    Electronic Resource
    Synthesis, characterization, and solution properties of 5-ethyl-substituted poly(L-prolines). Synthesis of cis- and trans-5-ethyl-L-proline and optically active poly(cis-5-ethyl-D-proline) (1983)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 21 (1983), S. 1643-1656 
    Details
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: This article reports a continuation of our work on the substituent effects on the preferred helical conformations and the mutarotation of substituted poly(L-prolines). The size of the substituent has been increased from a methyl group to an ethyl group in the 5 position. The purpose is twofold: (i) according to our theoretical conformational energy calculations, an ethyl group in the 5 position can exert a greater steric effect than can a methyl group; and (ii) the rotation-isomerization of the ethyl group introduces a new intriguing fact to the problem. The cis isomer of 5-ethylproline was synthesized by catalytic hydrogenation of Δ′-2-ethylpyrroline-5-carboxylic acid, whereas for trans-5-ethylproline, a chemical separation method involving p-toluenesulfonyl chloride was used. The resolution of cis-5-ethylproline and the assignment of absolute configurations have been carried out by fractional crystallization and circular dichroism spectroscopic techniques, respectively. Poly(cis-5-ethyl-D-proline) was obtained from its corresponding N-carboxyanhydrides via a ring opening polymerization.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1983.170210607
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  • 2
    Electronic Resource
    Electronic Resource
    Conformational studies of poly(cis-5-ethyl-D-proline) (1983)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 21 (1983), S. 1751-1761 
    Details
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Two possible conformations for poly(cis-5-ethyl-D-proline) have been identified and characterized by using combinations of 1H- and 13C-NMR, CD, and ORD spectroscopic techniques. Both forms have helical conformations similar to those of poly(L-proline) characterized by different amide bonds (cis and trans). However, the carbonyl group of the amide in poly(cis-5-ethyl-D-proline) form II (trans) seems to be closer to perpendicular orientation with respect to the helical axis than in poly(L-proline) form II. The pyrrolidine ring conformation of form I (cis) is probably β+γ--puckered, whereas for form II it is probably β+-puckered in nature. The side-chain ethyl groups prefer to adopt anti conformations to the C5—H bond, or prefer to have χ = 180°, regardless which of the two forms poly(cis-5-ethyl-D-proline) may like to assume. The experimental results agree well with our previous theoretical conformational energy calculations.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1983.170210617
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Mutarotation of optically active poly(cis-5-ethyl-D-proline) (1983)
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Chemistry Edition 21 (1983), S. 1741-1749 
    Details
    ISSN: 0360-6376
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The mutarotation between form I and form II of poly(cis-5-ethyl-D-proline) has been experimentally realized. A number of hydrogen-bond-forming solvents have been found effective in initiating the mutarotational process. The rate of mutarotation seems to be proportional to the acidity of the active solvent. The enthalpy of activation energy for the mutarotation is estimated from the first-order kinetics at the lower conversion by means of the Arrhenius equation to be approximately 16.7 kcal/mol. The solvent-polymer interactions are proven to be one of the important driving forces for the mutarotation. The specific site at which hydrogen bonding takes place has been determined to be the carbonyl group of the amide by infrared spectroscopic techniques. The molecular reason for the greater susceptibility of poly(cis-5-ethyl-L-proline) II to the solvent effect than poly(cis-5-ethyl-L-proline) I can be satisfactorily explained by the relatively more extended structure of form I than form II. The mechanism for the mutarotation undoubtedly involves a cis-trans isomerization of the amide bond. The conformation of the transient states during the mutarotational process is still evidently helical in nature, probably consisting of long poly(cis-5-ethylproline) I and II segments.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pol.1983.170210616
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    Paper (German National Licenses)
    Fulltext
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