Polysaccharides Collaboration with Prof. Walther Burchard at the University of Freiburg, Germany

Cellulose is a biological chain molecule abundantly found in plants. The fibrous material is semi-crystalline and insoluble in water and common organic solvents. Water solubility is obtained when the chains are partially derivatized, i.e. not all hydroxyl groups of the chain are substituted. In contrast to most synthetic chain molecules these cellulose derivatives do not dissolve molecularly, but the dissolution process stops at a colloidal level [1]. The reason for this unusual behavior is supposed in an uneven derivatization along the chain. The amorphous regions of the fiber become preferably derivatized while the crystalline regions remain largely not affected by the chemical reagents. Structure and properties of these colloidal particles were extensively studied by static and dynamic light scattering and small angle neutron scattering [2]. A fringed micellar structure was deduced, in which f chains are side-by-side aligned thus forming a quasi-crystalline short stem with coronas of dangling chains at the two ends of the stem. Our actual interest is focused on the relaxation dynamics of the dangling ends as a function of the cellulose concentration by means of neutron spin-echo spectroscopy. [1] L. Schulz et al.; Cellulose Derivatives; Modification, Characterization and Nanostructures (Eds. T.J. Heinze, W.G. Glasser) ACS Symposium Series 688 (1998) 218. [2] W. Burchard and H. J. Vogel, Comput. Theor. Polym. Sci. 10 (2000) 133.

Collaboration with Prof. Walther Burchard at the University of Freiburg, Germany

Glycogen is considered the principal storage form of glucose and is found mainly in liver and muscle, with kidney and intestines adding minor storage sites. High branching density is an efficient way to keep the energy stored in a rather compact, space-saving structure. On the other hand, the enzymes should have fast access to the internal parts to guarantee a quick degradation when glycose is needed as energy source. Glycogen is a randomly branched (hyperbranched) macromolecule build of a(1,4) glycoside bonds with about 8% a(1,4) glycoside units added providing branching sites of type . Bonds are only possible between sites A and B1 or A and B2. The protein glycogenin, that acts as a primer builds the core of the molecule. We are studying the architecture of individual macromolecules at low glycogen content in water by means of small angle neutron scattering. In addition the packing (inter-particle interaction) well above the overlap concentration is of special interest. [1] E. Meléndez-Hevia et al., in Technological and Medical Implications of Metabolic Control Analysis, Kluwer Academic Publishers, Dordrecht (2000).