Remarkable hexafunctional anion receptor with operational urea-based inner cleft and thiourea-based outer cleft: Novel design with high-efficiency for sulfate binding

Abstract

The recognition of anions by designed receptors has attracted much attention in recent days. In particular, the selective binding of sulfate with artificial receptors is important because of its relevance to many biological and environmental applications. However, the development of organized molecular receptors with high-efficiency for sulfate binding still remains a significant challenge. We report a novel para-phenylene-bridged hexafunctional tripodal receptor that contains a urea-based inner cleft and a thiourea-based outer cleft, providing perfect sites for step-wise binding of two anions within a single cavity. The new receptor was synthesized in a three-step process, and was investigated for its anion binding properties by 1H NMR titrations, 2D NOESY experiments and computational studies. As indicated by solution binding studies, the receptor selectively binds sulfate over other oxoanions, forming a 1:2 stoichiometric complex that is stabilized via strong H-bonding interactions. High-level DFT calculations reveal that the receptor, owing to the enhanced H-bonding ability of thiourea groups, initially encapsulates one sulfate in its thiourea-based outer cleft, followed by a second encapsulation in its urea-based inner cleft. Such a functionalized receptor with the unique combination of urea-based cleft and thiourea-based cleft in a single receptor has not been reported previously.

Structural factors affecting 13C NMR chemical shifts of cellulose: a computational study

“…To assess the effect of different glycosidic bond angles (Rassolov et al 2001;Zhao and Truhlar 2008) in Gaussian 09 (Frisch et al 2010), a reliable method that has been applied constantly to obtain reasonable molecular structures for organic molecules (Fradon et al 2017;Khansari et al 2017;Zhao and Truhlar 2008;Zhou et al 2017). Forty-nine cellulose tetramer chain conformations with different U/W angles were generated for each C6 conformers (gg: C4-C5-C6-O6 = 57.2°; gt: C4-C5-C6-O6 = 178.1°; tg: C4-C5-C6-O6 = 285.7°).…”

Highly selective and sensitive macrocycle-based dinuclear foldamer for fluorometric and colorimetric sensing of citrate in water

“…In particular, there is a growing interest in designing artificial receptors that can selectively recognize anions and act as sensors 2 , 3 . A wide variety of host receptors have been reported that can effectively bind anions in solution and in the solid states, exhibiting selectivity toward certain anions 4 – 7 . In this regard, carboxylates are of great interest due to their important roles in chemistry and biology 8 – 10 .…”

Anion Complexation Studies of 3-Nitrophenyl-Substituted Tripodal Thiourea Receptor: A Naked-Eye Detection of Sulfate via Fluoride Displacement Assay

“… 17 − 23 In particular, the electron-withdrawing nature of sulfur on thiourea functionalities increases the acidity of NH for H-bonding interactions with an anionic guest. 23 For example, a chlorosubstituted tris(thiourea) receptor reported by Das et al was shown to encapsulate a thiosulfate anion with a dimeric capsular assembly. 20 A tris(4-nitrophenyl)thiourea receptor was reported to exhibit selective complexation of fluoride and phosphate.…”