Calorimetric and chiroptical evidence of aggregate-driven helix formation in carrageenan systems

摘要: Abstract Thermally induced, order-disorder transitions of iota- and kappa-carrageenan have been monitored by optical rotation differential-scanning calorimetry in various ionic environments. Conformational ordering is observed only the presence cations that shown previously to promote helix-helix aggregation, shows marked hysteresis between heating cooling. Iota-carrageenan, contrast, an transition non-aggregating, tetramethylammonium salt form, at substantially lower temperature than for kappa-carrageenan, without hysteresis. In potassium ions, which are known iota-carrageenan two distinct thermal-transitions, one same as under non-aggregating conditions, with significant close transition. We interpret these helix-to-coil aggregated helix-to-coil, respectively. This interpretation supported measurements enthalpy changes transitions; ΔH values show a systematic increase increasing aggregation conclude double helix can exist stable entity isolation, but may be further stabilised whereas when aggregated.