Calix[4]Resorcinarene Macrocycles Interactions with Cd²⁺, Hg²⁺, Pb²⁺, and Cu²⁺ Cations: A QCM‐I and Langmuir Ultra‐thin Monolayers Study

Abstract

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.

Comparative Study of a Sensing Platform via Functionalized Calix[4]resorcinarene Ionophores on QCM Resonator as Sensing Materials for Detection of Heavy Metal Ions in Aqueous Environments

“…The results can be applied to show the stability of the apparatus during the detection measurement. The QC normalized ▵FWHM variation as a result of the injection of HM cations (Cd 2+ , Hg 2+ , Cu 2+ , and Pb 2+ ), at different concentrations on bare Au surface was shown [34]. The results confirm that the addition of the cations had no effect on the ▵FWHM of the resonator's gold surface therefore it indicates that neither chemical nor physical interaction between the cations and the gold surface occurred.…”

“…Detection capacities of the studied ionophores towards Cd 2+ , Cu 2+ , Pb 2+ , and Hg 2+ in aqueous solutions were obtained through the application of in‐situ QCM‐I, with the objective of identifying the most effective sensing platform in terms of detection characteristics: FWHM variations, sensitivity and selectivity, linear ranges, and detection limits and quantification. For the impedance analysis, the procedure to obtain data of typical normalized values of ▵FWHM in time is explained in details previously [34].…”

“…As shown in Table 1, a trend that the ΔFWHM shifts are a concentration‐dependent, i. e. varies by increasing HM ions concentrations, displaying the ability of the Calix‐QCM based platforms to monitor the HM ions detection. Values of ΔFWHM variations associated to ionophores III and IV are denoted for comparison purposes and are reported previously [34].…”

“…This approach is advantageous to understand the sensing performance of calix[4]‐coated QCM sensors towards different HM ions in aqueous solution. Ionophores I and II are part of the present work, and III and IV are from the previous investigation [34]. The variations in ▵FWHM are presented for each HM ion (Cd 2+ , Hg 2+ , Pb 2+ , and Cu 2+ ), at each concentration (5, 25, 250, 500, and 1000 ppm), and combining the response of the four calixresorcinarenes at the same time.…”

Highly selective sensor for the detection of Hg 2+ ions using homocysteine functionalised quartz crystal microbalance with cross‐linked pyridinedicarboxylic acid

“…The QCM‐based sensor for selective mercury detection using thymine‐Hg 2+ ‐thymine interaction proposed by Sheng et al [57] and Chen et al [58] with oligonucleotide‐functionalised gold NPs (AuNPs), but LOD is limited to the nanomolar range, and higher concentration (millimolar) for a dynamic range not tested. Eddaif et al [59] proposed a QCM sensor with Calix(4) resorcinarene macrocycles interactions to detect different HMIs, and QCM loaded with thiol‐functionalised SBA‐15 proposed by Loua et al [60] but having higher LOD and selectivity is absent for Hg 2+ ions.…”