Teruo Horiuchi

Insoluble monolayer of [14C] chloramphenicol palmitate at the air-water interface

Abstract The nature of the insoluble monolayer of chloramphenicol palmitate (CPP) at the air-water interface has been studied by simultaneous measurements of surface pressure, π, potential, ΔV, and radioactivity, R, of 14C-labeled CPP as functions of apparent molecular area, A, and time, t, elapsed from the delivery of CPP solution at the interface. The observed time dependences of π, ΔV, and R in relation to A have been accounted for only by reorientation of CPP molecules in the monolayer, with elimination of the possibilities of their evaporation, dissolution, and hydrolysis. The reorientation process from A = 93 A 2 /molecule at t = 0 to A = 152 A2/molecule at t = ∞ is explicable solely by the conformational change of cis- → trans-form of the CPP molecules. It has been shown that the change corresponds to the polymorphic transition of CPP-α → CPP-β in three-dimensional crystals, as has been revealed in the hydrolyzability of CPP molecules upon injection of a lipase solution beneath the monolayer.