ORDER[--]DISORDER TRANSITIONS IN BIOMOLECULES

The phospholipids exhibit a variety of phase transitions such as gel < ----> liquid crystalline and pretransition which involves the rotation of the whole hydrocarbon-type chain. These transitions are accompanie d by specific heat anomaly. In some situations the order of these tran sitions is believed to be fractional in nature, and in some other case s the transition has a fine structure which results from the presence of transitions due to multiple components in the system. Zimm and Brag g theory has been suitably modified to interpret the specific heat mea surements in the phosphatidylcholines containing sulphur atoms in thio ester and thioether linkages. The thermodynamic parameters associated with the transition are those reported by Hadju and Sturtevant. The sh arpness of transition (Delta Gx T-c) and the variation of nucleation p arameter a are consistent with the structural differences in the phosp holipids studied. The asymmetry at the tail ends of the specific heat is a result of the presence of multiple components and asymmetry assoc iated with the head group interaction.