Computer modeling ofα‐ toβ′‐ form phase transitions using theoretical triglyceride structures

Abstract

AbstractIntermolecular energy calculations were performed on theoretical triarachidinα‐form structures as selected bond rotations converted them intoβ′‐forms with a chain‐tilt change in the glycerol region. Interactions across the methyl gaps amounted to only 2‐3% of the total energy in initialα‐ and finalβ′‐forms, but computer generated energy profiles duringα‐ toβ′‐phase transitions revealed highly repulsive regions due to the close approach of methyl groups. This methyl gap interaction, plus additional repulsive interactions in the lateral packing of molecules during rigid chain rotations, necessitated modification of certain chain movements during phase transition to reduce excessive repulsive energy. These results suggest that phase transitions proceed in a particular sequence of events that either distribute energy to promote further phase excitation or that lead to collapse into the stable polymorphic form. Phase transition energy curves also reveal that secondaryα‐ andβ′‐forms are possible and are dependent on the startingα‐forms, the direction of chain rotation and the subcell arrangement.