Streulicht‐ und Viskositätsmessungen an wäßrigen Amyloselösungen. II.

Abstract

ZUSAMMENFASSUNG:An einer Reihe von synthetischen Amylosen in Wasser wurden Streulicht-und Viskositatsmessungen durchgefiihrt. Die Abhhgigkeiten des Triigheitsradius und der Viskositiitszahl [q] vom Polymerisationsgrad zeichnen sich durch keine Besonderheiten aus und entsprechen denen eines verknauelten linearen Fadenmolekiils. Dagegen ergibt sich fiir den 2. Virialkoeffkienten A, eine ungewohnliche Molekulargewichtsabhiingigkeit. Nach vergleichenden Messungen einer Amylose in verschiedenen Losungsmitteln erhiilt man fur alle Losungsmittel, die stabile Losungeo bilden, einen eindeutigen Zusammenhang zwischen Trlgheitsradius und 2. Virialkoeffizienten; der Wert von A, in Wasser jedoch ordnet sich nicht in diesen Zusammenhang ein. Die Abweichungen werden mit dem Potential von Wasserstoffbriicken erkliirt. SUMMARY:A series of amyloses was investigated in aqueous solution by means of light scattering and viscosity measuremendThe relations between the degree of polymerization and the radii of inertia, and the intrinsic viscosity [q] do not show strangeness and correspond to those of a coiled linear chain molecule. The second virial coefficient A, however shows an uncommon variation with the molecular weight. Comparative measurements of an amylose in different solvents gave clear relationships between the radius of inertia and the 2nd virial coefficient in all solutions which form stable solutions, whereas the A, value irf water does not agree with these relationships. The deviations are explained by the potential of hydrogen bonds.A. Einleitung

Conformation of Amylose and Excluded-Volume Effects on Its Chain Dimensions

“…However, the chain conformation in this organic solvent has long been controversial as to whether it is a random coil or a semiflexible helix. 6 Conformational energy calculations 2 • 7 -9 predict that amylose should be flexible but locally helical.Very recently, Nakanishi et al 10 demonstrated from light scattering, sedimentation equilibrium, and viscosity measurements on narrow-distribution samples of synthetic amylose at 25°C that the chain conformation in DMSO is a random coil expanded by excluded-volume effect if Mis higher than 10 5 • They, analyzing intrinsic viscosity ([17]) data for M between 342 (the dimer) and 10 4 in terms of the unperturbed helical wormlike (HW) chain, 11 • 12 derived the following conclusions from the estimated HW model parameters: (1) The value of C 00 in DMSO (at 25°C) is about 5, so that without excluded-volume effect, the global conformations in DMSO and aqueous solvents are similar, and (2) though flexible, the amylose chain in DMSO has some helical nature locally. This molecular picture, i.e., an irregular helical conformation with high flexibility, appears to resemble that predicted from conformational calculations.…”

“…M between 342 (the dimer) and 10 4 in terms of the unperturbed helical wormlike (HW) chain, 11 • 12 derived the following conclusions from the estimated HW model parameters: (1) The value of C 00 in DMSO (at 25°C) is about 5, so that without excluded-volume effect, the global conformations in DMSO and aqueous solvents are similar, and (2) though flexible, the amylose chain in DMSO has some helical nature locally. This molecular picture, i.e., an irregular helical conformation with high flexibility, appears to resemble that predicted from conformational calculations.…”

Addition Polymers of Monofunctional Isocyanates

“…They show analogously high diffusion and low sedimentation exponents in the respective equations [30,41], Table 2 gives the Mark-Houwink constants collected from the published literature.…”

“…High Mark-Houwink and low sedimentation exponents led Burchard [30] to the conclusion that polybutyl isocyanate (PBIC) molecules behave as stiff highly expanded chains. An early light-scattering study [31] confirmed directly that polyhexyl isocyanate (PHIC) molecules exhibit extraordinarily high radii of gyration.…”

Viscosity and the prolate ellipsoid model applied to low molecular weight cellulose triacetate fractions

“…The depend.ence of intrinsic viscosity on molecular weight to the oligomer level has been investigated for a number of synthetic polymers [5] and for amylose [ 6 ] . Cellulose of low molecular weight obtained by acid hydrolysis was investigated by Vink [7] who showed that the exponent in the modified Staudinger relation, [q] = K Ma approaches zero at the oligomer level but increases to exceed unity at intermediate levels below a degree of polymerization of 100.…”