Interfacial Binding of Divalent Cations to Calixarene-Based Langmuir Monolayers

Abstract

The interactions of Langmuir monolayers produced through the self-assembly of an amphiphilic p-carboxycalix[4]arene (1) with a series of divalent, fourth-period transition metals, at the air-water interface, were investigated. Changes in the interfacial behavior of 1 in response to the presence of CuCl2, CoCl2, MnCl2, and NiCl2 were studied by means of Langmuir compression isotherms and Brewster angle microscopy (BAM). The measurements revealed that the self-assembly properties of 1 are significantly affected by Cu(2+) ions. The interactions of 1-based monolayers with Co(2+) and Cu(2+) ions were further investigated by means of synchrotron radiation-based X-ray reflectivity (XRR), X-ray near-total-reflection fluorescence (XNTRF), and grazing incidence X-ray diffraction (GIXD). XNTRF and XRR analyses revealed that the monolayer of 1 binds more strongly to Cu(2+) than Co(2+) ions. In the presence of relatively high concentrations of Cu(2+) ions in the subphase (1.4 × 10(-3) M), XNTRF exhibited anomalous depth profile behavior and GIXD measurements showed considerably strong diffuse scattering. Both measurements suggest the formation of Cu(2+) clusters contiguous to the monolayer of 1.

Switching the Ion Selectivity from Fe3+ to Al3+ by a Triazole‐Appended Calix[4]arene‐Based Amphiphile†

“…Since the conjugates of calix[4]arenes possesses both hydrophobic and hydrophilic regions, these are well suited to make Langmuir films and hence can be used for the study of ion and molecular sensing on any substrate by using its functional moieties. The studies on Langmuir films of calixarenes are primarily focused on molecular, ion as well as gas sensing because of its supramolecular nature. The corresponding selectivity studies of the conjugates of calixarenes at air‐water interface is limited and hence deserves greater attention.…”

“…With increase of surface pressure, the isolated particle like morphology of L changed to an aggregated type in presence of Al 3+ (Figure e‐g) and this is reflected as an increase in the particle density in AFM (Figure h). Similar results were reported in case of HgCl 2 , NiCl 2 , MnCl 2 and CoCl 2 with two different calix[4]arene derivatives ,. However, the micrographs observed for L in the presence of Zn 2+ showed only marginal changes (Figure i–k, 6l).…”

Two‐Dimensional Calix[4]arene‐based Metal–Organic Coordination Networks of Tunable Crystallinity

“…The formation of crystalline domains at the air–water interface, even prior to compression, can be attributed to the directional π–π stacking of the aromatic rings, which is possible with a minor contribution of the short aliphatic chains of 1 . Longer‐chain analogues do not show this behavior . In the presence of CuCl 2 , however, large domains with a dendritic shape, in coexistence with an amorphous matrix, were observed.…”

“…The shift of the takeoff value is attributed to the interaction of carboxylate groups with Cu 2+ causing an expansion of the footprint of 1 in the formed monolayer. The rigidity of the Langmuir monolayer of 1 was examined by calculating the isotherm slope, that is, δ π /δ A . At the takeoff, the surface‐pressure isotherm exhibits a higher modulus in the presence of Cu 2+ , recognized by the higher slope (0.4) compared to the isotherm on pure water (0.2; see Figure S1 in the Supporting Information; SI).…”

“…Thes urface-pressure-area-compression isotherm shows that 1 can form stable Langmuir monolayers at the air-water interface with ac ollapse pressure of 34 mNm À1 .T his fairly high value,d espite the short aliphatic chains of the amphiphile,can be ascribed to p-p stacking stabilization among the aromatic rings of neighboring amphiphiles.T he limiting area (A lim )o f1 05 2 molecule À1 is in agreement with the orientation of 1 with the pseudo C 4 axis orthogonal to the air-water interface. [11] At the surface of asolution with aconcentration as low as 10 mm CuCl 2 ,the isotherm shows alarger molecular area at takeoff (112 2 molecule À1 )a nd as lightly increased collapse pressure of 36 mNm À1 .The shift of the takeoff value is attributed to the interaction of carboxylate groups with Cu 2+ causing an expansion of the footprint of 1 in the formed monolayer.T he rigidity of the Langmuir monolayer of 1 was examined by calculating the isotherm slope,that is, dp/dA. [11c] At the takeoff,the surface-pressure isotherm exhibits ahigher modulus in the presence of Cu 2+ ,r ecognized by the higher slope (0.4) compared to the isotherm on pure water (0.2;see Figure S1 in the Supporting Information;S I).…”