Anion Binding Studies of Urea and Thiourea Functionalized Molecular Clefts

Abstract

Two rationally designed 4-nitrophenyl-based molecular clefts functionalized with thiourea (L1) and urea (L2) have been synthesized and studied for a variety of anions by UV-Vis and colorimetric techniques in DMSO. Results from the binding studies suggest that both L1 and L2 bind halides showing the order: fluoride > chloride > bromide > iodide; and oxoanions showing the order: dihydrogen phosphate > hydrogen sulfate > nitrate > perchlorate. Each receptor has been shown to form a 1:1 complex with an anion via hydrogen bonding interactions, displaying distinct color change for fluoride and dihydrogen phosphate in solution. As compared to the urea-based receptor L2, the thiourea-based receptor L1 exhibits stronger affinity for anions due the presence of more acidic thiourea functional groups.

Spectroscopic and Colorimetric Studies for Anions with a New Urea-Based Molecular Cleft

“…The calculated binding constants as obtained from the NMR titrations studies are listed in Table 2, showing the binding constants (in log β) of 4.48, 4.63, 4.54 and 4.96 for chloride, dihydrogen phosphate, bicarbonate and acetate, respectively, which are approximately close to those obtained from the UV-titrations. A similar anion binding order was observed by previously reported 4-nitrophenyl-based molecular clefts with an m-xylene linker [8]; however, the receptor L exhibits overall strong affinities for anions because of its ability to bind two anions simultaneously as opposed to one anion that was shown by the reported receptors. A slight variation of the results obtained from the two different techniques could be due to the different conditions used for UV-Vis and 1 HNMR titrations [46].…”

“…However, when the concentration of anions becomes higher than the normal permissible range, they may adversely affect both biological systems as well as the environment. For example, an elevated amount of fluoride in drinking water causes dental and skeletal fluorosis [7] and is responsible for a bone cancer known as osteosarcoma [8]. The presence of an excess phosphate in the environment leads to eutrophication [9,10] of natural water bodies deteriorating normal aquatic life.…”

“…An ideal cleft-based chemosensor should possess active binding sites linked with a suitable spacer to create a naked cavity functionalized with signaling units (Scheme 1), thus ensuring to stabilize an encapsulated complex by essential binding forces. Previously, we reported m-xylyl-based molecular clefts possessing confined cavities that showed excellent anion binding capabilities in solution [8]. In an attempt to explore selective colorimetric probes [22,[42][43][44], we synthesized a simple para-xylyl-based dipodal molecular urea L containing a flexible cavity that is appended with two aryl nitro-groups as signaling units (Scheme 2).…”

Chloride ion-selective dye liquid nanoemulsion: improved sensor performance due to intermolecular interactions between dye and ionophore

“…This indicates that the phenolic oxygen of the dye strongly interacts with the thiourea groups of the ionophore by hydrogen bonding interactions. 30–34 The chemical shift of peak A (the proton adjacent to the phosphorus atom of the lipophilic cation) was also large, indicating that the direct interaction of the cation–anion pair, (P 66614 and 12-HC), was suppressed by the ionophore, as described above. A possible interaction is shown in Fig.…”

Urea- and Thiourea-Based Receptors for Anion Binding

“…Two dipodal receptors 2 (urea) and 3 (thiourea) appended on rigid m -xylyl-based frameworks were synthesized and investigated for anions by UV–vis and colorimetric techniques in DMSO . The presence of nitrophenyl units as chromophores in 2 and 3 makes the hosts effective as viable colorimetric probes for anions, displaying a sharp color change for fluoride and dihydrogen phosphate (from light yellow to red) due to complex formation.…”