Thiacalixarenes with Sulfur Functionalities at Lower Rim: Heavy Metal Ion Binding in Solution and 2D-Confined Space

Abstract

Sulfur-containing groups preorganized on macrocyclic scaffolds are well suited for liquid-phase complexation of soft metal ions; however, their binding potential was not extensively studied at the air–water interface, and the effect of thioether topology on metal ion binding mechanisms under various conditions was not considered. Herein, we report the interface receptor characteristics of topologically varied thiacalixarene thioethers (linear bis-(methylthio)ethoxy derivative L2, O2S2-thiacrown-ether L3, and O2S2-bridged thiacalixtube L4). The study was conducted in bulk liquid phase and Langmuir monolayers. For all compounds, the highest liquid-phase extraction selectivity was revealed for Ag+ and Hg2+ ions vs. other soft metal ions. In thioether L2 and thiacalixtube L4, metal ion binding was evidenced by a blue shift of the band at 303 nm (for Ag+ species) and the appearance of ligand-to-metal charge transfer bands at 330–340 nm (for Hg2+ species). Theoretical calculations for thioether L2 and its Ag and Hg complexes are consistent with experimental data of UV/Vis, nuclear magnetic resonance (NMR) spectroscopy, and single-crystal X-ray diffractometry of Ag–thioether L2 complexes and Hg–thiacalixtube L4 complex for the case of coordination around the metal center involving two alkyl sulfide groups (Hg2+) or sulfur atoms on the lower rim and bridging unit (Ag+). In thiacrown L3, Ag and Hg binding by alkyl sulfide groups was suggested from changes in NMR spectra upon the addition of corresponding salts. In spite of the low ability of the thioethers to form stable Langmuir monolayers on deionized water, one might argue that the monolayers significantly expand in the presence of Hg salts in the water subphase. Hg2+ ion uptake by the Langmuir–Blodgett (LB) films of ligand L3 was proved by X-ray photoelectron spectroscopy (XPS). Together, these results demonstrate the potential of sulfide groups on the calixarene platform as receptor unit towards Hg2+ ions, which could be useful in the development of Hg2+-selective water purification systems or thin-film sensor devices.

Solvent Effects and Metal Ion Recognition in Several Azulenyl-Vinyl-Oxazolones

“…The evolution of the UV-Vis spectra of O2 and O5 derivatives with the four metal ions at different concentrations is depicted in Figures 6, 7, S6 and S7. The addition of each cation caused the progressive decrease in intensity of the absorption bands of azulene derivatives (Figures 6, 7, S6 and S7), with the exception of the absorption band in the 250-270 nm range where, during titration, an increase in absorbance was noticed due to the absorption of metal salts [41] (Figure 7b inset). A good linear relationship (R 2 = 0.99) was obtained for the plot of absorbance of the longer wavelength band versus the metal ion concentration for O2 during titration with Cd 2+ ions over the range of 2.71 × 10 −5 to 5.35 × 10 −4 M Cd 2+ content (Figure 8).…”

Synthetic approaches to metal-coordination-directed macrocyclic complexes

“…The first type of macrocycles is ubiquitous in nature, such as cytochrome C, chlorophyll, vitamin B 12 ( Lindoy et al, 2013 ; Joshi et al, 2015 ). A variety of their synthetic analogues has also been synthesized with considerable success, using macrocycles with inward metal ion coordination sites ( Edwards et al, 2006 ; Kubota et al, 2016 ; Feng et al, 2017 ; Yogendra et al, 2017 ; Haaf et al, 2021 ; Wang et al, 2021 ; Bodman et al, 2022 ; Muravev et al, 2022 ; Nystrom et al, 2022 ; Wang et al, 2022 ). By contrast, the synthesis of the second type of macrocycles remains a challenging task.…”