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United States Department of Agriculture

Agricultural Research Service

Title: A Comparison Between Dentritically Branched Macromolecules and Linear Polysaccharides: Size Exclusion Chromatography and Molecular Dynamics Study

Authors
item Striegel, Andre
item Willett, Julious

Submitted to: International Gel Permeation Chromatography Symposium
Publication Type: Proceedings
Publication Acceptance Date: December 9, 1998
Publication Date: N/A

Interpretive Summary: Starch, one of the most abundant biopolymers on earth, is composed mainly of two carbohydrates, amylose and amylopectin. The structure of starch, while studied for many years, is still not well understood. Any advances in the understanding of said structure will result in immediate, tangible benefits to the end-user, i.e., the consumer, by means of superior quality in starch-derived products, be these food-based or more utilitarian in purpose and design. To this end, we have compared degradation products of starch, known as dextrins, to model synthetic and natural polymers with well-known, well-characterized structures. The structures of the dextrins were found to be more varied than the structures of either of the model compounds. The properties of the dextrins resembled the properties of the natural models more than the properties of the synthetic models. We expect the results of these studies to be of direct benefit to those studying the structure of starch and, indirectly, to those who use the various products derived from this plant polymer.

Technical Abstract: Starch, one of the most abundant biopolymers on earth, is composed mainly of the polysaccharides, amylose and amylopectin. The latter is an extremely highly branched macromolecule, with molecular weights in the 10**7 to 10**9 Da range. Even though the object of much study over the years, the structure of amylopectin remains poorly understood. Dendritic macromolecules, or dendrimers, are theoretically the most highly branched structures achieveable. They may also serve as models for hyperbranched synthetic and natural polymers. In the initial study, we compare the solution behavior of Starburst poly(amido amine) dendrimers, as determined utilizing size exclusion chromatography (SEC), to that of low-molecular weight linear dextrans and the starch degradation products known as maltodextrins, of equivalent molar mass. Utilizing SEC we have determined molecular weight averages, polydispersities, and intrinsic viscosities of these molecules. The more compact solution structure of the dendrimers resulted in lower intrinsic viscosities as compared to both dextrans and maltodextrins of equivalent molecular weights. For the dextrins, solution behavior indicates that debranching during the manufacturing process appears to have been more thorough than in that of beta-limiting dextrins studied by other groups. To study the size of the dendrimers in solution, hydrodynamic radii calculated from SEC-determined intrinsic viscosities and molecular weights were compared and contrasted to radii of gyration determined by molecular dynamics applying the CVFF force field. Results show that the tri-functional Starburst dendrimers behave as theta-stars with functionalities between 1 and 4.

Last Modified: 8/29/2014
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