X-Ray Diffraction Study of Glucomannans and Their Acetates

Abstract

Crystalline polymorphs of four glucomannans with a different mannose/glucose ratio from 1.5 to 4.0 and their acetyl derivatives was studied by X-ray diffraction measurements. The glucomannans showed an amorphous or similar crystal structure (Mannan I or Mannan II polymorph) of /?-l,4-D-mannan depending on their mannose content, indicating the occurrence of isomorphous replacement of mannose by glucose during glucomannan crystallization. Whenthese glucomannans were annealed, however, Konjac glucomannan (mannose/glucose ratio = 1.6) showed a different powder pattern from both MannansI and II. The fiber pattern of the annealed Konjac glucomannan indicated that it took an extended twofold helical structure. Amongthe acetylated glucomannans, Higanbana glucomannan with a high mannosecontent (mannose/glucose = 4.0) showed a similar diffraction pattern

Synthesis and Characterization of Konjac Glucomannan-Graft-Polyacrylamide via γ-Irradiation

“…For the grafted copolymer, the peak at 2θ = 20 ο decreased significantly, indicating that the conjugation of KGM with PAM reduced the crystallinity of KGM. KGM was reported to have a hydrated crystal of low crystallinity [ 30 ] and PAM to be an amorphous material, which did not show any significant crystallinity peak [ 31 ]. The decrease of crystallinity might due to the intra- and intermolecular- hydrogen bonding interactions between KGM and PAM, which destroyed the original molecular orientation of KGM.…”

Review on Modification of Glucomannan as an Excipient in Solid Dosage Forms

“…GM, which is abundantly available, shows potential as an excipient for solid dosing. GM has an orthorhombic unit cell pattern-its physical structure contains possible sliding planes, which may be responsible for increased crystal plasticity [10,110,111]. This is why it exhibits good compressibility, and it is not capped at higher compression pressures during decompression due to decreased relaxation stress.…”

Effects of Molar Mass on Water Binding Properties of γ-irradiated Konjac Glucomannan

“…KM is a branched neutral polysaccharide which shows amorphous X-ray patterns [5]. The low aqueous solubility of KM has been attributed to strong structural hydrogen bonding [6] and high molar mass of 1.17 10 6 Da having α value of 0.78 in Mark-Houwink-Sakurada equation [3].…”