Chain dimensions and scattering function of (1->3)-beta-D-glucan simulated by the Monte Carlo method

A Monte Carlo method was used to evaluate the chain dimensions and scattering function of(1 --> 3)-beta-D-glucan in solution. Monte Carlo samples of the glucan chain were generated on the basis of a conformational energy map of the dimeric subunit, i.e. beta-laminarabiose. The effect of the excluded volume was introduced into the model by placing hard spheres with a radius R-ex at the center of mass of each glucose unit in the chain sequence. The results for the chain length dependence of the quantity [S-2]/x ([S-2] is the mean square radius of gyration and x is the degree of polymerization) and the radial distribution of the end-to-end distance have confirmed that the unperturbed(1 --> 3)-beta-D-glucan chain shows non-Gaussian-type behavior in the region of x < 200, above which the chain behaves in a Gaussian manner in its overall conformational character. However, local helical character was observed throughout the x range. In contrast with the unperturbed chain, the perturbed chain is characterized by non-Gaussian behavior over the chain length examined (x less than or equal to 2000). The experimental [S-2]/x vs. x data of the curdlan fractions in water-diluted cadoxen, evaluated by light scattering, were found to be simulated by perturbed chains with an excluded volume R-ex = 1.0 Angstrom. The scattering function was calculated from the ensemble of generated (1 --> 3)-beta-D-glucan chains as a function of x (x less than or equal to 40) in the q range up to 1.0 Angstrom(-1) (q is the scattering vector). The scattering function in the range 0.1 less than or equal to q less than or equal to 0.8 Angstrom(-1), where the scattering function is sensitive to the local chain conformation, reveals an appreciable oscillation. The calculated scattering function and (SZ) for the Monte Carlo chains with x = 2-7 were in reasonable agreement with preliminary experimental results obtained by small-angle X-ray scattering for the corresponding laminara-oligosaccharides in water. (C) 1997 Elsevier Science B.V.