Synthesis, Langmuir and Langmuir–Blodgett films of a calix[7]arene ethyl ester

Abstract

Calixarenes are promising compounds to be used as ionophores and for molecular recognition. Their ability to form Langmuir and Langmuir-Blodgett (LB) films is of great interest in order to obtain small sensor devices which incorporate an active nanometric film. The p-tert-butylcalix [7]arene ethyl ester compound has been synthesised and its ability to form Langmuir and LB films has been shown. This macrocycle forms monolayers but it tends to form multilayers at higher compressions, as corroborated by AFM. BAM images show a uniform layer till the multilayer process occurs and a good correspondence with the features of the surface pressure-area 2 isotherm. AFM images reveal that, in water subphase, films are quite homogeneous but the presence of small islands has also been observed. The presence of ions in the subphase, as sodium, potassium, rubidium, cesium, calcium, barium, cadmium and tin chloride salt solutions, leads to some changes in the surface pressure-area isotherms, but the more important changes are observed by AFM. More uniform films are observed for rubidium, cesium, cadmium and tin ions. A very different nanometric structure has been observed for tin ions. Some characteristics of the films, molecular area and height, are correlated with molecular modelling calculations.

Interaction of para-tert-butylcalix[6]arene molecules in Langmuir films with cadmium ions and their effects on molecular conformation and surface potential

“…31,39,40 The difference in the experimentally observed value (135 Å 2 ) may be ascribed to two factors: (i) the theoretical calculations were performed using zero Kelvin temperature, under vacuum, with no water molecules that could H-bond to Calix6 and (ii) repulsion between Calix6 molecules, which is not taken into account in the theoretical modeling. A similar reasoning was adopted by Torrent-Burgués et al 10 for the derivative p-tertbutylcalix [7]arene ethyl ester. A comparison with the literature is not straightforward because the packing of Calix6 molecules appears to depend on the experimental conditions.…”

“…It should also be stressed that Calix6 dimers in the multilayers should not contribute to the SFG spectra, since they would have inversion symmetry and therefore a vanishing second-order nonlinear polarizability. The concentration of Cd 2+ ions was chosen based on studies to detect Cd 2+ ions in Langmuir films, since Torrent-Burgués et al 10 observed the isotherms of p-tert-butylcalix[n]arene-ethyl ester (n = 4 and 7) to be affected by Cd 2+ ions at concentrations close to 1 Â 10 À2 mol L À1 .…”

“…[1][2][3][4][5] With such properties, calixarenes have been used in detecting metallic ions, such as alkaline [6][7][8] and alkaline earth [8][9][10] metals, cadmium, [10][11][12] copper, 7,13,14 and for incorporating neutral molecules, [15][16][17][18][19][20] including dopamine, 15 volatile organic compounds 16 and aminoacids. 17 They have also been studied in biological membranes, [18][19][20] and in the formation of molecularly organized films using self-assembled monolayers [21][22][23] and LangmuirBlodgett (LB) [6][7][8][9][10][11][12][13][15][16][17][18][19][20] techniques. These organized films have been applied in metal ion sensors, biosensors, immunosensors and for encapsulating nanoparticles.…”

“…10 Ye et al 13 observed trimers of p-tert-butylthiacalix [4]arene and Cu 2+ ions in Langmuir and LB films, where the area per molecule at the air/water interface increased due to electrostatic repulsion among Cu 2+ ions bound to the complex. Hg 2+ ions coordinated with p-tert-butylthiacalix [4]arene through the bridgingsulfur atom and its phenolic oxygen atoms, and were not located inside the calixarene cavities.…”

“…25 Dong et al 11 produced a sensor to measure trace levels of Tl + and Cd 2+ made with an LB film of p-tertbutylthiacalix [4]arene, where the use of differential pulse stripping voltammetry led to a detection limit for Cd 2+ of 2 Â 10 À8 mol L À1 . Recognition of metal ions through calixarenes has been studied theoretically 26,27 and experimentally, [6][7][8][9][10][11][12][13][14]24,25 in many cases motivated by the concern with the environment as heavy metals accumulate in biological systems. 24,[28][29][30] In this study, we investigate Langmuir films of the calixarene derivative p-tert-butylcalix [6]arene (referred to as Calix6), which has been the subject of previous studies.…”