Westberry BPRio MWaterland MRWilliams MAK2024-12-022024-12-022024-06-01Westberry BP, Rio M, Waterland MR, Williams MAK. (2024). On the origin of optical rotation changes during the κ-carrageenan disorder-to-order transition.. Carbohydr Polym. 333. (pp. 121975-).0144-8617https://mro.massey.ac.nz/handle/10179/72152It is well established that solutions of both polymeric and oligomeric κ-carrageenan exhibit a clear change in optical rotation (OR), in concert with gel-formation for polymeric samples, as the solution is cooled in the presence of certain ions. The canonical interpretation - that this OR change reflects a 'coil-to-helix transition' in single chains - has seemed unambiguous; the solution- or 'disordered'-state structure has ubiquitously been assumed to be a 'random coil', and the helical nature of carrageenan in the solid-state was settled in the 1970s. However, recent work has found that κ-carrageenan contains substantial helical secondary structure elements in the disordered-state, raising doubts over the validity of this interpretation. To investigate the origins of the OR, density-functional theory calculations were conducted using atomic models of κ-carrageenan oligomers. Changes were found to occur in the predicted OR owing purely to dimerization of chains, and - together with the additional effects of slight changes in conformation that occur when separated helical chains form double-helices - the predicted OR changes are qualitatively consistent with experimental results. These findings contribute to a growing body of evidence that the carrageenan 'disorder-to-order' transition is a cooperative process, and have further implications for the interpretation of OR changes demonstrated by macromolecules in general.(c) 2024 The Author/sCC BY 4.0https://creativecommons.org/licenses/by/4.0/CarrageenanDensity-functional theoryMachine learningMolecular dynamicsOptical rotationJournal article10.1016/j.carbpol.2024.1219751879-1344journal-article121975-https://www.ncbi.nlm.nih.gov/pubmed/38494229121975S0144-8617(24)00201-7