Thermodynamic study of functionalized calix[n]arene and resorcinol[n]arene monolayers spreaded at an aqueous pendant drop

Abstract

The behavior of insoluble calix[n]arene and resorcinol[n]arene derivatives monolayers were studied through the use of a constant
surface Langmuir balance based on Axisymmetric Drop Shape Analysis (ADSA). In each case, a stable monolayer was obtained and
different transitions (induced for lateral compression) could be identified. Thermodynamic parameters were computed through
two dimensional Clausius–Clayperon equations and used to valuate the monolayer stability. A noticeable reduction of thermodynamic
parameters occurred at highly tested temperatures (328 and 338K) for those compounds that had hydrocarbon tails or benzene
rings attached to one side of macrocyclic rim. Such fact was related to a monolayer rearrangement where the macrocyclic ring
changed from a parallel to a perpendicular orientation. In this orientation the hydrophobic interactions between hydrocarbon
chains and benzene rings were maximized. At highly temperature, where vigorous molecular motion existed, those interactions
were superior to the stabilization effect through hydrogen bond.

KeywordsLangmuir monolayers-Calix[n]arenes-Resorcinol[n]arenes-ADSA-Conformational changes-Thermodynamic