Molecular dynamics simulations and X-ray scattering show the ir-carrageenan disorder-to-order transition to be the formation of double-helices

Recent molecular dynamics simulations, verified experimentally by solution-state x-ray scattering experiments, have found that ir-carrageenan chains contain helical secondary structure, akin to that found in the solid-state, even in aqueous solution. Furthermore, upon the addition of ions to single chains the simulations found no evidence that any conformational transitions take place. These findings challenge the long-held assumption that the so-called disorder-to-order transition in carrageenan systems involves a uni-molecular 'coil-to-helix transition'. Herein, the results of further molecular dynamics simulations undertaken using pairs of ir-carrageenan chains in 0.1 M NaI solutions are reported, and are validated experimentally using state-of-the-art solution-state WAXS experiments. From initially separated chains double-helices are shown to form, leading the authors to propose 'two single helices-to-stabilized double-helix' as a description of the molecular events taking place during the disorder-to-order transition.

Automated summary

Recently, molecular dynamics simulations and solution-state x-ray scattering experiments have shown that ir-carrageenan chains have a helical structure even in aqueous solution. The addition of ions to single chains does not result in conformational transitions. Further simulations using pairs of ir-carrageenan chains in 0.1 M NaI solutions confirm the formation of double helices during the disorder-to-order transition.