We report the studies on Langmuir monolayer of gamma oryzanol (gamma-Or) in trans and cis states and kinetics of photo-isomerization and thermal isomerization of gamma-Or at air-water interface. The surface manometry studies show that the monolayer of trans - gamma-Or on compression exhibits gas and liquid expanded phases with a small region of gas-liquid expanded coexistence region. The monolayer collapses at a surface pressure of 34 mNm- 1. In contrast to this, the cis - gamma-Or monolayer on compression exhibits an extended gas-liquid expanded coexistence region between gas and liquid expanded phases before collapsing at a surface pressure of 38 mNm- 1. The studies on isomerization of gamma-Or in the Langmuir monolayer show that the photo-isomerization process follows first order kinetics and thermal isomerization follows second order kinetics. The rate constants of photo-isomerization and thermal isomerization of gamma-Or at air-water interface obtained at different temperatures show Arrhenius temperature dependence. The activation energy for the photo-isomerization was found to be 85.34 kJ/mol and for thermal isomerization it was found to be 51.33 kJ/mol.
