An experimental and theoretical study of the aggregate structure of calix6arenes in Langmuir films at the water/air interface

LS de Lara and EC Wrobel and M Lazzarotto and SR de Lazaro and A Camilo and K Wohnrath, PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 18, 22906-22913 (2016).

DOI: 10.1039/c6cp04565k

In this paper, the aggregate formation of para-tert-butylcalix6 arene molecules (Calix6) in dimeric structures was investigated at the water/air interface using experimental and theoretical studies. A specific orientation for such Calix6 molecules was observed with an average area of 133 angstrom(2), which corresponds to a flat-on orientation with the OH groups parallel to the interface. By varying the pressure on the Calix6 monolayer, the molecules tend to organize at the water/air interface and subsequently, at higher pressures, aggregates were formed atop the monolayer as cluster structures. Morphological characterization by the Brewster Angle Microscopy technique showed the formation of larger domains at lower pressures. Based on such experimental evidence, molecular dynamics (MD) simulations were performed to investigate possible dimeric structures for aggregated Calix6 molecules, which are localized at the water/air interface, where one molecule remains in the water phase and the other remains in the air phase. By increasing surface pressure, experimental and theoretical results corroborate the intermolecular interactions among Calix6 molecules. These results are relevant because a dimeric structure has a molecular cavity, which is a candidate for host-guest chemistry, an ion receptor or a drug-delivery system.

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