Recognition-guided sulfate extraction and transport using tripodal hexaurea receptors

Abstract

Separation of sulfate anion (SO42–) from water is of great challenge as of its high hydration energy. By using synthetic receptors that are designed with size-complementary cavity for sulfate binding,...

Assemblies of salts of urea and thiourea derivatives and release of hosts from composites with calcium oxide

“…The calcium-based compounds are bio-friendly and calcium oxide transforms into calcium hydroxide in water. 83 Furthermore, chemical reactivity and pH, help in controlled release; 51,52 in the present case it is the modulation of the hydrolytic reactivity of the calcium oxide support with water that has helped the environmentally benign calcium hydroxide to release the substrate in the neutral form (as reflected in the fluorescence on process). The release of the naphurea salts is interesting as the calcium oxide can help in easy diffusion of urea to an aqueous medium in a controlled manner in about 20 hours’ time.…”

“…49,50 The supramolecular self-assemblies of urea and thiourea derivatives of their own and metal complexes have generated interest in developing new properties. [51][52][53][54] On the other hand, the controlled release of molecules from composite materials through chemical reactivity 55 or due to the effect of pH 56 or stimuli 57 has great values. In general, urea is highly soluble in water; hence, for practical use the controlled release and transforming them to an optimum soluble forms are challenges.…”

One-Pot Cyclization to Large Peptidomimetic Macrocycles by In Situ-Generated β-Turn-Enforced Folding

“…Given the widespread existence of SO 4 2– in various industrial wastewaters and its interference with vitrification of radioactive waste, methods for efficient removal of SO 4 2– from water have received significant interest. − Yet, simple and efficient separation of SO 4 2– is still challenging due to the higher hydration energy of SO 4 2– (−1080 kJ/mol) than other anions . Liquid–liquid extraction is one of the most promising approaches for SO 4 2– separation in recent years, and the key is to find an efficient receptor. − Given the high affinity of macrocycles 1 for SO 4 2– anions, we examined the ability of 1L to separate SO 4 2– anions from water. As shown in Figure S53a, an organic layer of 1L (1 mM) in 95:5 (v/v) CHCl 3 /DMSO with 4 equiv of A464Cl salts (a commercially available salt as the auxiliary reagent for extraction) and an aqueous solution of Na 2 SO 4 (2 mM) were prepared and mixed.…”

Anion-exchange facilitated selective extraction of sulfate and phosphate by overcoming the Hofmeister bias

“…Both urea and thiourea are strong hydrogen bond donor groups and the receptor–anion interactions can simply be observed in 1 H-NMR spectroscopy, where a downfield chemical shift of the urea/thiourea –NH signals suggest hydrogen bonding between a receptor and an anion in the solution-state. 14–17 In general, a large downfield shift of the –NH signals correspond to strong receptor–anion binding where the receptor–anion complementarity plays an important role in determining the anion selectivity i.e. , the acidity of the urea/thiourea groups of a receptor should complement the basicity of the anion for selective anion recognition.…”

“…Motivated by the current research interest on the selective separation of oxoanions from highly competitive aqueous media, 14–16 herein we report the LLE of sulfate by tris-urea receptors ( L 1 , L 2 and L 3 ) from alkaline aqueous media in the presence of several competing anions (SeO 4 2− , HPO 4 2− , HAsO 4 2− , CO 3 2− , CH 3 CO 2 − , NO 3 − , Cl − and F − ). Unlike the previous reports on sulfate extraction by HBD receptors using quaternaryammonium salts of chloride or nitrate, here we have used a sulfate selective tris-urea receptor mixed with tetrabutylammonium hydroxide, ( n -Bu 4 N) + OH − for anion-exchange between the immiscible aqueous–organic phases.…”