Theoretical Study of Biopolymer Gelation

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Focusing on the correlation and sequential property of hydrogen bonds, this project studied thermoreversible gelation of polysaccharides and proteins, their helix formation, and structure of zipper-like crosslink junctions by statistical-mechanical method. It also carried out Molecular Dynamics- and Monte Carlo simulation by using coarse-grained bead-spring model chains to compliment theoretical study. The main results obtained are summarized as follow :1.Coil/Helix Transition and Gelation by Association of HelicesWe classified association of helices into two different categories : multiple association of single helices and association by multiple helices. When nucleation and growth of helices are fast compared by the following cross-linking association, for instance gelation of k-carrageenan solution, we derived the sol/gel transition curve on the temperature-concentration phase plane and compared with the experiments. We have established a new method to simultaneously estimate the mu … More ltiplicity and the length of cross-links (Augmented Eldridge-Ferry method). It was shown that, for double helical junctions, the structure of the gel networks changes from TypeI (random coils cross-linked by short helices) to TypeII (long rod-like helices connected by short random coils), and from TypeII to separated helical pairs. The theoretically calculated CD intensity as a function of the temperature agreed well with the reported experimental data.2.Gelation by Side-Chain HelicesThermoreversible gelation of water-soluble polymers carrying side-chain helix-forming polysaccharides was studied by theory and MC simulation. The splicing force of coiled-coil (supercoil) was calculated to estimate elasticity of the gels.3.Sequential Hydrogen BondsSequential hydration of water-soluble polymers (PNIPAM), gelation by sequential hydrogen bonds (zipper cross-links), loop formation, etc were studied by theory of associating polymer solutions and by MC simulations. The results were compared by the phase diagrams reported in the literature. Less