Cation effect on thermal transition of iota-carrageenan: a photon transmission study.

Coil-to-double helix (c-h) and double helix-to-dimer (h-d) phase transitions of iota-carrageenan in various cation (CaCl2) solutions upon heating and cooling were studied using the photon transmission technique. Photon transmission intensity, Itr, was monitored against temperature to determine the (c-h) and (h-d) transition temperatures (Tch and Thd) and activation energies (DeltaEch and DeltaEhd). An extra dimer-to-dimer (d-d) transition was observed during cooling at low temperature region. However, upon heating dimers directly decompose into double helices by making dimer-to-double helix (d-h) transition. Further heating results in double helix-to-coil (h-c) transition at high temperature region. Tdh and Thc temperatures and Delta Edh and DeltaEhc activation energies were determined. It was observed that Thc and Tch temperatures and DeltaEch and DeltaEhc activation energies were found to be strongly correlated to the CaCl2 content in the system.