Switching Ion Binding Selectivity of Thiacalix[4]arene Monocrowns at Liquid–Liquid and 2D-Confined Interfaces

Abstract

Understanding the interaction of ions with organic receptors in confined space is of fundamental importance and could advance nanoelectronics and sensor design. In this work, metal ion complexation of conformationally varied thiacalix[4]monocrowns bearing lower-rim hydroxy (type I), dodecyloxy (type II), or methoxy (type III) fragments was evaluated. At the liquid–liquid interface, alkylated thiacalixcrowns-5(6) selectively extract alkali metal ions according to the induced-fit concept, whereas crown-4 receptors were ineffective due to distortion of the crown-ether cavity, as predicted by quantum-chemical calculations. In type-I ligands, alkali-metal ion extraction by the solvent-accessible crown-ether cavity was prevented, which resulted in competitive Ag+ extraction by sulfide bridges. Surprisingly, amphiphilic type-I/II conjugates moderately extracted other metal ions, which was attributed to calixarene aggregation in salt aqueous phase and supported by dynamic light scattering measurements. Cation–monolayer interactions at the air–water interface were monitored by surface pressure/potential measurements and UV/visible reflection–absorption spectroscopy. Topology-varied selectivity was evidenced, towards Sr2+ (crown-4), K+ (crown-5), and Ag+ (crown-6) in type-I receptors and Na+ (crown-4), Ca2+ (crown-5), and Cs+ (crown-6) in type-II receptors. Nuclear magnetic resonance and electronic absorption spectroscopy revealed exocyclic coordination in type-I ligands and cation–π interactions in type-II ligands.

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

“…Thus, preorganization of sulfur functionalities from the linear chain in compound L 2 to the crown-ether macrocycle L 3 and tube in compound L 4 seems not to promote the receptor ability of the ligand at the air-water interface. This finding is opposite to the trend recently determined by us for oxyethylene derivatives on the lower rim of thiacalixarene derivatives [30]. In that work, the oxacrown-5 macrocycle on the 1,3-alternate thiacalixarene scaffold demonstrated Ca 2+ selectivity in Langmuir monolayers expressed by the degree of monolayer expansion, whereas monolayer characteristics of linear oligooxyethylene counterpart did not change with the addition of Ca 2+ ions to the water subphase.…”

“…In that work, the oxacrown-5 macrocycle on the 1,3-alternate thiacalixarene scaffold demonstrated Ca 2+ selectivity in Langmuir monolayers expressed by the degree of monolayer expansion, whereas monolayer characteristics of linear oligooxyethylene counterpart did not change with the addition of Ca 2+ ions to the water subphase. This difference can be rationalized by different coordination modes of metal cations by the literature oxacrown ligands and thioether receptors studied in this work: exocyclic coordination of sulfur atoms, at which linear thioethers are equally well suited as cyclic counterparts (this study), and endocyclic coordination involving oxygen atoms, at which cyclic compounds provide gain in entropy as compared to podands due to pre-organization (oxyethylene derivatives in [30]).…”

“…On the one hand, metal ions render thioether hydrophilic upon complexation, and true Langmuir monolayers can be formed. On the other hand, sulfur atoms of the thiacalix [4]arene macrocycle rim were ineffective in Ag + binding at the air-water interface [30], which suggests a high barrier to transfer these moieties from air to water.…”

The Physical Chemistry and Chemical Physics (PCCP) Section of the International Journal of Molecular Sciences in Its Publications: The First 300 Thematic Articles in the First 3 Years

“…Other objects from the list mentioned in the title of this thematic area were studied, only sporadically. The structure and dynamics of the molecules of inorganic compounds were considered in publications [ 107 , 111 , 170 , 175 ], inorganic ions in [ 145 , 167 , 184 ], and inorganic polymers only in article [ 110 ]. In [ 107 ], this object was methane hydrate; in [ 111 ], a Cu(II) complex with polyvinyl alcohol; in [ 170 ], a heteronuclear complex of Cu(II) and Cd(II) with a “cubane” core; and in [ 175 ], Co(III) with ammonia or 1,10-phenanthroline.…”

“…In [ 107 ], this object was methane hydrate; in [ 111 ], a Cu(II) complex with polyvinyl alcohol; in [ 170 ], a heteronuclear complex of Cu(II) and Cd(II) with a “cubane” core; and in [ 175 ], Co(III) with ammonia or 1,10-phenanthroline. The articles [ 118 , 184 ] should be noted among the works devoted to inorganic ions. In the first of them, as it was already mentioned earlier, the structure of the N , N –di(4–bromo) nitrenium ion was considered, and, in the second, the processes of chemisorption of s-element ions of group I in the periodic table with thiacalix[4]arene mono crown.…”