INTERACTIONS BETWEEN LOCUST BEAN GUM AND CELLULOSE CHARACTERIZED BY C-13 NMR SPECTROSCOPY

Molecular interactions between locust bean gum (LEG) and cellulose cry stallite surfaces appear to involve most mannosyl residues of the mann an backbone, not just the small proportion contained in long segments which lack galactosyl residues. This conclusion is based on: (1) relat ive strengths of C-13 n.m.r. signals at 102.2 ppm in the cross-polariz ation (CP) spectrum and 101.3 ppm in the single-pulse excitation (SPE) spectrum, assigned to mannosyl C-l in bound and non-bound segments of LEG, respectively; (2) displacement of a C-13 n.m.r. signal assigned to mannosyl C-4 to 81 ppm, indicating a change of conformation in the mannan backbone relative to a gel phase; (3) similarities between prot on spin relaxation time constants for cellulose and LEG, indicating pr oton spin diffusion between polymers in close contact; (4) broadening of CP n.m.r. signals at 83.9 and 85.0 ppm, assigned to C-4 of cellulos e chains exposed on crystallite surfaces. The galactosyl C-1 signal ap pears at 99.9 ppm in the SPE n.m.r. spectrum of the LEG-cellulose comp lex but shows a poor response to CP n.m.r., indicating that galactosyl residues are not fixed in rigid conformations relative to the mannan backbones. (C) 1998 Elsevier Science Ltd. All rights reserved.