Journal Articles

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    On the origin of optical rotation changes during the κ-carrageenan disorder-to-order transition
    (Elsevier Ltd., 2024-06-01) Westberry BP; Rio M; Waterland MR; Williams MAK
    It 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.
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    Effect on the mechanical properties of type I collagen of intra-molecular lysine-arginine derived advanced glycation end-product cross-linking
    (Elsevier, 28/11/2017) Collier TA; Nash A; Birch HL; de Leeuw NH
    Non-enzymatic advanced glycation end product (AGE) cross-linking of collagen molecules has been hypothesised to result in significant changes to the mechanical properties of the connective tissues within the body, potentially resulting in a number of age related diseases. We have investigated the effect of two of these cross-links, glucosepane and DOGDIC, on the tensile and lateral moduli of the collagen molecule through the use of a steered molecular dynamics approach, using previously identified preferential formation sites for intra-molecular cross-links. Our results show that the presence of intra-molecular AGE cross-links increases the tensile and lateral Young’s moduli in the low strain domain by between 3.0 - 8.5 % and 2.9 - 60.3 % respectively, with little effect exhibited at higher strains.