Molecular modeling of xanthan:galactomannan interactions

X-ray diffraction patterns from stretched fibers of xanthan, guaran and the complex between the two are indicative of good orientation and reasonable crystallinity. The ordered structures of xanthan and guaran appear to be a 5-fold helix of pitch 47.4 Angstrom and a 2-fold helix of pitch 10.3 Angstrom, respectively. The diffraction pattern of the complex is a hybrid of those of the individual components. Both xanthan and guaran in the complex may adopt cellulose-like helices having a slightly longer pitch of 10.5 Angstrom and form a non-coaxial duplex. Alternately, the complex may adopt a xanthan-like, coaxial, 5-fold, double helix in which one strand is xanthan and the other is guaran. The association of a pair of these hybrid helices can take place by direct cross linking of the carboxylate groups in the side chains of xanthan by divalent ions. The morphologies of these arrangements have now been visualized by computer modeling. (C) 1997 Elsevier Science Ltd.