NMR investigation on oligo‐ and poly(galacturonic acid)s; gel formation in the presence of Ca2+ counterions

Wiley - Tập 181 Số 5 - Trang 1059-1070 - 1980
Marguerite Rinaudo1, G. Ravanat1, M. Vincendon2
1Centre de Recherches sur les Macromolécules Végétales. Laboratoire propre du C.N.R.S. associé à l'Université Scientifique et Médicale de Grenoble, 53 X. 38041 Grenoble Cedex, France
2Laboratoire de Chimie Organique Physique, Département de Recherche Fondamentale, Centre d'Etudes Nucléaires, 85 X, 38041 Grenoble Cedex, France

Tóm tắt

AbstractIn this paper, the assignment of the 1H and 13C NMR spectra of poly(galacturonic acid)s is proposed; the 4C1 chair conformation of the monomeric unit in poly(galacturonic acid) is confirmed and the composition of the anomeric mixture at the reducing end (α−D)/(β−D) = 35 : 65 mol/mol independent of the degree of polymerization DP (2 ⩽ DP ⩽ 5) is given. It is demonstrated on oligomers that both 13C and 1H chemical shifts and coupling constants are nearly unaffected by exchanging Na counterions with Ca; the osmotic coefficient of Ca depends on the DP just as predicted by an electrostatic mechanism. The intrinsic viscosity of the polymer increases and the intensity of 13C NMR signals decreases suddenly for 0,3 equivalents Ca2+ per carboxylic site. These results confirm a multichain association followed by a rigid gel formation; the crosslink is proposed to correspond to a cooperative “egg‐box” mechanism on chain segments randomly distributed in the gel.

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Wiley

Tập 181 Số 5

1059-1070

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