Chain dimensions and scattering function of (1 → 3)- β- d-glucan simulated by the Monte Carlo method

Abstract

A Monte Carlo method was used to evaluate the chain dimensions and scattering function of (1 → 3)- β- 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. β-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)- β- 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 ≤ 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 A ̊ . The scattering function was calculated from the ensemble of generated (1 → 3)- β- d-glucan chains as a function of x ( x ≤ 40) in the q range up to 1.0 A ̊ −1 ( q is the scattering vector). The scattering function in the range 0.1 ≤ q ≤ 0.8 A ̊ −1 , where the scattering function is sensitive to the local chain conformation, reveals an appreciable oscillation. The calculated scattering function and 〈 S 2〉 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.