Substituent distribution in carboxymethl glucans: development of a quantitative method for the determination of the substituent distribution along and over the polymer chains

• Applicant: Professorin Dr. Petra Mischnick
• Subject Area: Analytical Chemistry ; Polymer Materials
• Term: from 2013 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 236656131

Polysaccharide derivatives are complex mixtures which beside molecular weight vary with respect to the degree and distribution of substituents. The latter has to be considered on various, related hierarchical structure levels (in the glucosyl unit, along the polysaccharide chain, and over the polysaccharide chains). While for nonionic cellulose ethers powerful methods for the various levels of substitution patterns have been developed and improved, no such methods exist for the anionic carboxymethyl ethers.Carboxymethyl cellulose (CMC) is the most abundant cellulose derivative. The relationship between the properties (e.g. water solubility) of this polyelectrolyte and the substituent distribution are not fully understood, since the latter cannot be described in detail, but is restricted to average values. Carboxymethylation is also applied to other polysaccharides like starch, dextran and hemicelluloses and raises the same questions.Therefore, it is the aim of the project, based on long-year experience in the field of the analysis of substituent patterns of polysaccharide derivatives, to develop a powerful method for the determination of the CM-distribution in carboxymethyl glucans (CMG). To obtain correct patterns of CM groups, representative mixtures of oligomeric sequences must be prepared from the polymer molecules, and for each DP, the substituent profiles must be determined quantitatively.Taking all data into account, the comparison of the oligomer profiles with the random model, and the change of the profiles with DP, shall allow to draw conclusions on heterogeneities (DS gradient, bimodal distributions). Based on the preliminary work, an LC-MS method shall be worked out. Essential is an appropriate sample preparation and control of all steps with respect to discriminating effects. Concretely, the following milestones shall be investigated and worked out: disintegration of the material, kinetic studies of partial depolymerization and control of randomness, derivatisation- and labeling strategies, development of separation and mass spectrometric methods (LC-ESI-MS, MALDI-ToF-MS), quantitative evaluation and model calculations; methods worked out shall be applied to various CMG with the same DS but different properties.Furthermore, a multiple-step depolymerization-labeling strategy shall allow to differentiate heterogeneities of second and first order.

• DFG Programme: Research Grants