Structure and chain conformation characteristics of high acyl gellan gum polysaccharide in DMSO with sodium nitrate

Abstract

High acyl gellan gums have been widely considered using as gelling biopolymers in colloidal products although their structure and chain conformation characteristics have been poorly understood. Five fractions of high acyl gellan gum (HG) with a molecular weight (Mw) ranging from 4.2 × 105 to 10.1 × 105, obtained by ultrasonic depolymerization from a native gellan, have been used to determine their molecular parameters and conformation characteristics in the good solvent of 50 mM NaNO3 dimethyl sulphoxide solution by using capillary viscometry and laser light scattering. The influence of ultrasound on the chemical structure and Mw of HG is investigated by GPC, FT-IR and NMR. The chain architectures of HG fractions are confirmed to be very similar to that of the native one without either deacylation or deglycerylation. Mark−Houwink equation and the relationship between radius of gyration (Rg) and Mw are established to be [η] = 1.16 × 10−3Mw0.67 (dl/g) and Rg = 2.06 × 10−2Mw0.61 (nm) for HG with a ratio of geometric to hydrodynamic radius (Rh) of 1.67 that is independent of the Mw of HG. In term of Zimm model, a relationship among these molecular parameters is founded as [η]≈4NARg2Rh/Mw. On the basis of unperturbed chain models, the conformation parameters of HG are also calculated and compared. The results indicate that HG macromolecules with an estimate of about 9 nm for persistence length Lp take the conformation of relatively extended semi-flexible chains in solution.