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Supramolecular chemistry is an interdisciplinary scientific field, including chemical, physical and biological properties of more complex chemical species than the molecules themselves. Calixarenes/calixresorcinarenes are macrocyclic compounds, consisting of 'n' phenolic/resorcinolic units linked together by methylene bridges; these macrocycles are often used for molecular recognition. Thus, different modifications can be made to both the lower and upper rim, allowing the construction of well-defined multivalent buildings. In this work, three calix[4]resorcinarene macrocycles were synthesized, namely C-dec-9-en-1-ylcalix[4]resorcinarene (CAL 11U), C-trans-2, cis-6-octa-1,5-dien-1-ylcalix[4]resorcinarene (CAL 9U) and C-nonylcalix[4]resorcinarene (CAL 10) by a simple condensation reaction. The compounds CAL 11U and CAL 10 have been already synthesized by researchers, while the CAL 9U has been synthesized for the first time. Their structures were confirmed using ATR-FTIR, 1 H NMR and 13 C NMR. Thermal analysis combined with mass spectrometric evolved analysis of the vapors was used to study the thermal behavior of the different synthesized molecules, and they were the subject of characterization by X-ray powder diffraction in order to analyze their degree of crystallinity.

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Stable ultra‐thin Langmuir monolayers of calix[4]resorcinarene derivatives, namely: C‐dec‐9‐enylcalix[4]resorcinarene‐O‐(R+)‐α‐methylbenzylamine (Ionophore I), and C‐dec‐9‐enylcalix[4]resorcinarene‐O‐(S‐)‐α‐methylbenzylamine (Ionophore II), were prepared at the air‐water interface. Their interactions with a series of heavy metals (HM) ions (Cu2+, Pb2+, Hg2+ and Cd2+) present in the aqueous subphase were investigated by measuring surface pressure‐area isotherms, at different concentrations. The surface pressure‐area (Π‐A) isotherms were stable and demonstrated the HM amounts influence on the limiting area (Alim) values, therefore confirming the examined macrocycles capability to host the metallic toxicants. Additionally, a HM concentration dependence was realized and interpreted by a selective tendency of both ionophores towards Cu2+ and Cd2+ ions over Pb2+ and Hg2+, especially at high concentrations. The HM ions interactions with the applied calix[4]resorcinarene Langmuir ultra‐thin monolayers were interpreted based on the Gibbs‐Shishkovsky adsorption equation. Moreover, quartz crystal microbalance with impedance measurement (QCM‐I), was applied for the detection of HM ions in solutions. The QCM‐I results showed the effectiveness of the coated QCM‐I crystals in detecting the ions at different concentrations. The detection limit values were in the order of 0.16, 0.3, 0.65, 1.1 ppm (Ionophore I), as well 0.11, 0.45, 0.2, 0.89 (Ionophore II) for the Cu2+, Pb2+, Hg2+ and Cd2+ cations, respectively. Additionally, a selective tendency of both ionophores towards copper ions was shown.

A flow type quartz crystal microbalance with impedance analysis capability (QCM‐I) chemical sensor was tested for heavy metal (HM) ions detection in aqueous solutions. The sensor development is based upon the complexing ability of the functionalized AT‐cut quartz resonator gold surface, by calixresorcinarenes, towards the HM ions. These calixresorcinarenes coated QCM sensors were tested for selectively adsorbing HM ions, such as copper, lead, mercury, and cadmium, from solution over a wide range of concentration (5‐1000 ppm) through complexation with functional groups in the coating layers. QCM‐Calix based chemosensors, C‐dec‐9‐en‐1‐ylcalix[4]resorcinarene (ionophore I), C‐undecylcalix[4]resorcinarene (ionophore II), C‐dec‐9‐enylcalix[4]resorcinarene‐O‐(S‐)‐α‐methylbenzylamine (ionophore III) and C‐dec‐9‐enylcalix[4]resorcinarene‐O‐(R+)‐α‐methylbenzylamine (ionophore IV), were synthesized and immobilized to detect HM ions of Pb2+, Cd2+, Hg2+, and Cu2+ in aqueous solutions. Using the impedance analysis, which facilitates a complete description of the acoustic loading of the crystal surface, the full width at half maximum of the QCM resonance peak (FWHM) values are obtained from the impedance spectra. FWHM variations revealed the effectiveness of the proposed ionophores in detecting HM at different levels. Sensitivities and wide linear relationships between HM concentration and FWHM were interpreted. Detection limits of (0.32, 0.57, 0.37, 0.89 ppm) and (1.63, 0.18, 0.76, 0.2 ppm) were determined for ionophore I and II, for Cd2+, Cu2+, Hg2+ and Pb2+ ions, respectively. Ionophore (I) showed binding preferences towards Cd2+ ions where ionophore (II) produced similar selectivity toward Cu2+ and Pb2+ ions. Ionophores III and IV were used for the assessment of ▵FWHM values to comprehend the detection affinities of the ionophores toward HM ions.

The calix [4]resorcinarene macrocycles are excellent oligomers for the design of amphiphilic derivatives; they can form self-assemblies and stable sensing networks. Owing to their favorable properties, they are the focus of many exploitations and studies ranging from biological controls to heavy metal ion sensing. In this perspective, two calix[4]resorcinarene derivatives, namely: C-dec-9-en-1-ylcalix[4]resorcinarene (ionophore I) and C-undecylcalix[4]resorcinarene (ionophore II) were used to form stable ultra-thin Langmuir monolayer films at the air/water interface; their interactions with different harmful metal cations (Cd 2+ , Pb 2+ , Hg 2+ , and Cu 2+ ) were studied and highlighted via the pressurearea (Π-A) isotherms. The obtained results in the current investigation showed a dependence of both macrocycle interactions on the metal cation concentration in the subphase, confirming their complexation. In addition, the ionophore (I) exhibited high selectivity towards Pb 2+ and Cu 2+ cations, whereas the ionophore (II) showed tendency to bind with Cu 2+ cations over others, approving the potential applicability of these macrocycles as ion selective chemical sensors.

Calixresorcinarenes and calixarenes have seen extensive usage as receptors for cations, anions and even neutral molecules. Incorporation of binding capabilities and chemical groups that respond to analytes complexation has given these macrocycles additional advantages in applications as efficient selective chemical sensors. Three major types of macrocyclic calixresorcinarenes namely C-dec-9-en-1-ylcalix[4]resorcinarene (CAL 11U), C-trans-2, cis-6-octa-1,5-dien-1-ylcalix[4]resorcinarene (CAL 9U) and C-nonylcalix[4]resorcinarene (CAL 10) were synthesized. They differ in the alkyl/alkenyl side chains. They were characterized by different techniques (melting point measurements, Fourier Transform Infra-Red spectroscopy FT-IR, Thermal Gravimetric analysis and Differential Scanning Calorimetry coupled with Mass Spectrometry TG-DSC-MS, Nuclear Magnetic Resonance spectroscopy NMR, and Powder X-Ray Diffraction measurements PXRD). Calixresorcinarene derivatives, immobilized onto Au surfaces of quartz crystal resonators, have been successfully applied to detect the presence of lead in aqueous solution.