Temperature- and sodium-hydroxide-dependent regulation of single-helix curdlan conformations.

Curdlan exhibits diverse biological activities. However, elucidating the structure-activity relationship of curdlan remains challenging owing to its conformational complexity and variability in well-defined systems. This study systematically examines the impact of temperature, sodium hydroxide (NaOH) concentration, and curdlan concentration on the single-helix conformation of curdlan. 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, small-angle X-ray scattering, gel permeation chromatography, and dynamic light scattering analyses confirm that the single-helix conformation of curdlan is successfully formed in dilute (0.15 M-0.24 M) NaOH solutions within the temperature range of 35 °C-50 °C, whereas partial conversion to aggregated or mixed helical structures occurs at lower temperatures (5 °C-25 °C). 23Na NMR parameter variations reveal direct Na+ interactions with the random-coil or single-helix conformations of curdlan. NMR and ultraviolet-visible absorption spectroscopy experiments confirm that the single-helix structure of curdlan facilitates stable encapsulation of Congo red via supramolecular assembly at 35 °C-50 °C. This study provides new insights into the conformation-activity relationships of β-(1,3)-glucans.