Sedimentation equilibrium analysis of glycopolymers

Abstract

The glycopolymers — a general term used to represent polysaccharides and glycoconjugates collectively — present the analytical ultracentrifuge — and in particular sedimentation equilibrium analysis — with one of its greatest challenges. In this paper the difficult nature of these substances will be described as well as why the inherent fractionation nature of the sedimentation equilibrium method gives it an edge over other techniques. The problems of limited choice of optical system which can be applied (through lack of naturally occurring chromophores), the importance of both the Rayleigh and Schlieren optical systems for these substances, the inapplicability of the meniscus depletion method, how we can get meniscii concentrations out, automatic data capture and analysis, extraction of “whole distribution” and point average molar masses, coping with the severe non-ideality one often finds with solutions of these substances and how we can distinguish between “polydispersity” (i.e., the presence of species of different molar mass or density not in chemical equilibrium) and self-association are all discussed. Finally, and after taking on-board the non-ideality problem, four methods of extracting distributions of molar mass are considered, focussing on one method which combines sedimentation equilibrium with gel permeation chromatography. In concluding, this theme of the importance of combining data with that from other techniques is continued by discussing the important relation sedimentation equilibrium has with classical (i.e., so-called “static”) light scattering procedures.