Interfacial binding of divalent cations to calixarene-based Langmuir monolayers

Coordination-Driven Monolayer-to-Bilayer Transition in Two-Dimensional Metal-Organic Networks

We report on monolayer-to-bilayer transitions in 2D metal-organic networks (MONs) from amphiphiles supported at the water-air interface. Functionalized calix[4]arenes are assembled through the coordination of selected transition metal ions to yield monomolecular 2D crystalline layers. In the presence of Ni(II) ions, interfacial self-assembly and coordination yields stable monolayers. Cu(II) promotes 2D coordination of a monolayer which is then diffusively reorganizing, nucleates, and grows a progressive amount of second layer islands. Atomic force microscopic data of these layers after transfer onto solid substrates reveal crystalline packing geometries with submolecular resolution as they are varying in function of the building blocks and the kinetics of the assembly. We assign this monolayer-to-bilayer transition to a diffusive reorganization of the initial monolayers owing to chemical vacancies of the predominant coordination motif formed by Cu²⁺ ions. Our results introduce a new dimension into the controlled monolayer-to-multilayer architecturing of 2D metal-organic networks.

Inorganic mixed phase templated by a fatty acid monolayer at the air-water interface: the Mn and Mg case

We studied by means of Grazing Incidence X-ray Diffraction (GIXD) coupled with X-ray fluorescence spectroscopy the structure of a behenic acid monolayer spread at the surface of Mg²⁺/Mn²⁺ mixed aqueous solutions. For the pure Mg²⁺ and Mn²⁺ aqueous solutions, the cations induce at the surface different 2D lattice superstructures of the organic monolayer. These superstructures correspond to an inorganic organized monolayer anchored to the hydrophilic group of the ordered behenic acid monolayer. Among the various diffraction peaks, we focused on those characteristics of the behenic acid oblique cell. As the Mg²⁺ mole fraction x increases in the Mg²⁺/Mn²⁺ mixed subphase, a continuous evolution of the oblique cell parameters is observed indicating the insertion of Mg²⁺ cations in the Mn²⁺ ordered monolayer. Then, a further increase leads to the appearance of a coexistence between two oblique surface phases. The cell parameters of both phases evolve continuously along the x range of the transition until a single Mg-rich ordered phase is detected. However, although the intensities of the peaks in the coexistence region are in agreement with a first-order phase transition, the cell parameters evolve simultaneously. Considering a thermodynamics analysis, this evidences that, apart from the concentration, another unidentified intensive parameter is varying. We suggest that it is the ionic strength, which appears to be strongly related to the concentrations.

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

A flexible and versatile method to fabricate two-dimensional metal-organic coordination networks (MOCNs) by bottom-up self-assembly is described. 2D crystalline layers were formed at the air-water interface, coordinated by ions from the liquid phase, and transferred onto a solid substrate with their crystallinity preserved. By using an inherently three-dimensional amphiphile, namely 25,26,27,28-tetrapropoxycalix[4]arene-5,11,17,23-tetracarboxylic acid, and a copper metal node, large and monocrystalline dendritic MOCN domains were formed. The method described allows for the fabrication of monolayers of tunable crystallinity on liquid and solid substrates. It can be applied to a large range of differently functionalized organic building blocks, also beyond macrocycles, which can be interconnected by diverse metal nodes.

Binding of calixarene-based Langmuir monolayers to mercury chloride is dependent on the amphiphile structure

Langmuir monolayers of the tetra and two regioselective diamino-substituted amphiphilic calix[4]arenes show different recognition properties towards HgCl₂ at the air–water interface, despite the macrocycles have highly similar structures.

Enhanced cation recognition by a macrocyclic ionophore at the air–solution interface probed by mass spectrometry

The cation binding selectivity of a benchmark calixarene is enhanced at the air–solution interface, as demonstrated by a novel mass spectrometry method.