Johannes P. Roubroeks

Molecular weight, structure, and shape of oat (1-->3),(1-->4)-beta-D-glucan fractions obtained by enzymatic degradation with lichenase.

Oat beta-glucan was partially degraded by lichenase for different periods of time. Weight-average molecular weights were obtained from SEC-RI-RALLS-Visc and ranged from 5300 to 257,200. Weight-average intrinsic viscosities ranged from 7 to 160 mL/g. The determined viscosity equation, [eta] = 5.47 x 10(-3) M 0.82, indicated an extended coil conformation. When the coil was modeled as a wormlike chain a persistent length of 2.30 nm was obtained. 1H and 13C NMR spectroscopy were used to identify the structural units in the partially degraded beta-glucan. The identification of the disaccharide laminaribiose in the hydrolysates may suggest the presence of a new structural feature in cereal beta-glucan.

Effect of Ozonation on Assembly of Xylans

Summary In this study the molecular structure of birch xylan was altered by ozonation. Longer ozonation times increased the cleavage of aromatic rings in the lignin residues attached to the xylan molecules, resulting in the formation of muconic acid derivatives and other carboxylic acid structures. Size exclusion chromatography showed a decreasing molar mass of xylan after ozonation. The ozonation improved xylan solubility as evidenced by the reduced amounts of aggregates in aqueous solution. Atomic force microscopy showed increases in the sizes of the aggregates. Furthermore, the ozonation resulted in a decreased ability of xylan to assemble into particle-like structures on cellulose surfaces. We therefore believe that there is a relationship between xylan aggregation in aqueous solution and the formation of xylan surface structures on cellulose.

Thermal degradation and stability of sodium hyaluronate in solid state

The kinetics and mechanism of depolymerisation of solid sodium hyaluronate at elevated temperatures and various pH have been investigated. Depolymerisation was found to be governed by random chain scission. The activation energy at neutral pH was found to be 127 kJ/mol. The solid polymer was most stable at neutral pH. Results suggest the depolymerisation mechanism in solid- and solution state to be the same. Correlation of log intrinsic viscosity to log weight-average molecular weight was investigated to ensure high quality data for polymer size. Based on more than sixty hyaluronate samples spanning from 0.4 to 2.3 MDa, it was concluded that a second order polynomial regression gives a better fit than the linear regression offered by classical Mark-Houwink-Kuhn-Sakurada description. This finding was supported by literature data and could be expanded to other simple, well behaving linear polymers, such as polystyrene and polyethylene.

Nano-and microstructures in stretched and non-stretched blend gels of cellulose and hemicelluloses

Abstract Molecular interactions between cellulose and hemicelluloses, such as xyloglucan and xylan, play an important role in the formation of ordered layers in the cell wall of higher plants. This study attempts to characterize an ordered state of a matrix consisting of cellulose and hemicellulose induced by stretching never-dried binary blended films. In non-stretched films, the xylan component easily adapted into the semicrystalline state, while the xyloglucan component remained amorphous. Once both blended films were stretched, each component tended to be close enough to the adherent macromolecule, and the interaction resulted in typical morphological orders at the nano- and microscale levels. These studies could be useful in constructing new bio-derived materials, as well as understanding the molecular interactions between the polymers.