title: Direct visualization of changes in deacylated Na(+) gellan polymer morphology during the sol-gel transition.
abstract: Changes in gellan polymer morphology during the sol-gel transition were directly visualized by transmission electron microscopy and a model incorporating these changes and existing physical data is proposed. Our observations suggest that the most thermodynamically stable conformations of gellan polymers in solution, in the absence of added cations, are the double helix and double-helical duplexes. We have demonstrated two forms of lateral aggregation of gellan helices in the presence of Ca(2+) and K(+) ions. One type forms junction zones that lead to network formation and gelation, while the second type leads to the formation of isolated fibers of aggregated helices and inhibition of gelation. The proposed model of gellan gelation is based on these observations where thermoreversibility, gel strength, and endothermic transitions of gellan gels can be explained.
authors.affiliation: Institute for Applied Biology, Department of Biology, University of York, P. O. Box 373, York YO10 5YW, UK.
authors.forename: N
authors.initials: N
authors.lastname: Atkin
authors.forename: R M
authors.initials: RM
authors.lastname: Abeysekera
authors.forename: E C
authors.initials: EC
authors.lastname: Kronestedt-Robards
authors.forename: A W
authors.initials: AW
authors.lastname: Robards
mesh_terms: D000107:Acetylation; D002118:Calcium; D005782:Gels; D008854:Microscopy, Electron; D011135:Polysaccharides, Bacterial / Q000737:chemistry* / Q000648:ultrastructure; D011188:Potassium; D000644:Quaternary Ammonium Compounds; D012964:Sodium; D013816:Thermodynamics
chemical_list: D005782:Gels; D011135:Polysaccharides, Bacterial; D000644:Quaternary Ammonium Compounds; C048288:gellan gum; D012964:Sodium; C027917:tetramethylammonium; D011188:Potassium; D002118:Calcium