Bistripodand Amide Host for Compartmental Recognition of Multiple Oxyanions

A new benzene-based hexasubstituted bistripodal receptor is synthesized and explored as a new generation receptor for multiple anion binding. The solid state crystal structure showed the encapsulation of four nitrate anions in a bistripodand fashion with “ababab” conformation of the receptor, and upon complexation with acetate anions, the receptor adopted less favorable “aaabbb” conformation with two encapsulated acetate ions

A Versatile Tripodal Amide Receptor for the Encapsulation of Anions or Hydrated Anions via Formation of Dimeric Capsules

A bowl-shaped tripodal receptor with an appropriately positioned amide functionality on the benzene platform and electron-withdrawing p-nitrophenyl terminals (L1) has been designed, synthesized, and studied for the anion binding properties. The single-crystal X-ray crystallographic analysis on crystals of L1 with tetrabutylammonium salts of nitrate (1), acetate (2), fluoride (3), and chloride (4) obtained in moist dioxane medium showed encapsulation of two NO3−, [(AcO)2(H2O)4]2−, [F2(H2O)6]2−, and [Cl2(H2O)4]2− respectively as the anionic guests inside the staggered dimeric capsular assembly of L1. The p-nitro substitution in the aryl terminals assisted the formation of dimeric capsular assembly of L1 exclusively upon binding/encapsulating above different guests. Though L1 demonstrates capsule formation upon anion or hydrated anion complexation for all of the anions studied here, its positional isomer with the o-nitro-substituted tripodal triamide receptor L2 selectively formed the dimeric capsular assembly upon encapsulation of [F2(H2O)6]2− and noncapsular aggregates in the cases of other anions such as Cl−, NO3−, and AcO−. Interestingly, structural investigations upon anion exchange of the complexes revealed that both isomers have selectivity toward the formation of a [F2(H2O)6]2− encapsulated dimeric capsule. In contrast, solution-state 1H NMR titration studies of L1 and L2 in DMSO-d6 with AcO− indicated 1:3 (host:guest) binding

Zinc(II) and PPi Selective Fluorescence OFF–ON–OFF Functionality of a Chemosensor in Physiological Conditions

A fluorescent chemosensor based on a quinoline derivative, L2 (OFF state), selectively senses Zn2+ by effective chelate-enhanced fluorescence (ON state), which further shows selectivity toward PPi over competing anions like Pi, AMP, and ATP via fluorescence quenching (OFF state) in a 100% aqueous HEPES buffer (pH 7.4). A plausible mode for the selective binding of PPi to 1 has been demonstrated by quantum mechanical density functional theory calculations and high-resolution mass spectrometry analysis

Bistripodand Amide Host for Compartmental Recognition of Multiple Oxyanions

A new benzene-based hexasubstituted bistripodal receptor is synthesized and explored as a new generation receptor for multiple anion binding. The solid state crystal structure showed the encapsulation of four nitrate anions in a bistripodand fashion with “ababab” conformation of the receptor, and upon complexation with acetate anions, the receptor adopted less favorable “aaabbb” conformation with two encapsulated acetate ions

Zinc(II) and PPi Selective Fluorescence OFF–ON–OFF Functionality of a Chemosensor in Physiological Conditions

A fluorescent chemosensor based on a quinoline derivative, L2 (OFF state), selectively senses Zn2+ by effective chelate-enhanced fluorescence (ON state), which further shows selectivity toward PPi over competing anions like Pi, AMP, and ATP via fluorescence quenching (OFF state) in a 100% aqueous HEPES buffer (pH 7.4). A plausible mode for the selective binding of PPi to 1 has been demonstrated by quantum mechanical density functional theory calculations and high-resolution mass spectrometry analysis

A Versatile Tripodal Amide Receptor for the Encapsulation of Anions or Hydrated Anions via Formation of Dimeric Capsules

A bowl-shaped tripodal receptor with an appropriately positioned amide functionality on the benzene platform and electron-withdrawing p-nitrophenyl terminals (L1) has been designed, synthesized, and studied for the anion binding properties. The single-crystal X-ray crystallographic analysis on crystals of L1 with tetrabutylammonium salts of nitrate (1), acetate (2), fluoride (3), and chloride (4) obtained in moist dioxane medium showed encapsulation of two NO3−, [(AcO)2(H2O)4]2−, [F2(H2O)6]2−, and [Cl2(H2O)4]2− respectively as the anionic guests inside the staggered dimeric capsular assembly of L1. The p-nitro substitution in the aryl terminals assisted the formation of dimeric capsular assembly of L1 exclusively upon binding/encapsulating above different guests. Though L1 demonstrates capsule formation upon anion or hydrated anion complexation for all of the anions studied here, its positional isomer with the o-nitro-substituted tripodal triamide receptor L2 selectively formed the dimeric capsular assembly upon encapsulation of [F2(H2O)6]2− and noncapsular aggregates in the cases of other anions such as Cl−, NO3−, and AcO−. Interestingly, structural investigations upon anion exchange of the complexes revealed that both isomers have selectivity toward the formation of a [F2(H2O)6]2− encapsulated dimeric capsule. In contrast, solution-state 1H NMR titration studies of L1 and L2 in DMSO-d6 with AcO− indicated 1:3 (host:guest) binding

Unusual Recognition and Separation of Hydrated Metal Sulfates [M₂(μ-SO₄)₂(H₂O)_<i>n</i>, M = Zn^II, Cd^II, Co^II, Mn^II] by a Ditopic Receptor

A ditopic receptor <b>L1</b>, having metal binding bis­(2-picolyl) donor and anion binding urea group, is synthesized and explored toward metal sulfate recognition via formation of dinuclear assembly, (<b>L1</b>)₂M₂(SO₄)₂. Mass spectrometric analysis, ¹H-DOSY NMR, and crystal structure analysis reveal the existence of a dinuclear assembly of MSO₄ with two units of <b>L1</b>. ¹H NMR study reveals significant downfield chemical shift of −NH protons of urea moiety of <b>L1</b> selectively with metal sulfates (e.g., ZnSO₄, CdSO₄) due to second-sphere interactions of sulfate with the urea moiety. Variable-temperature ¹H NMR studies suggest the presence of intramolecular hydrogen bonding interaction toward metal sulfate recognition in solution state, whereas intermolecular H-bonding interactions are observed in solid state. In contrast, anions in their tetrabutylammonium salts fail to interact with the urea −NH probably due to poor acidity of the tertiary butyl urea group of <b>L1</b>. Metal sulfate binding selectivity in solution is further supported by isothermal titration calorimetric studies of <b>L1</b> with different Zn salts in dimethyl sulfoxide (DMSO), where a binding affinity is observed for ZnSO₄ (<i>K</i>_a = 1.23 × 10⁶), which is 30- to 50-fold higher than other Zn salts having other counteranions in DMSO. Sulfate salts of Cd^II/Co^II also exhibit binding constants in the order of ∼1 × 10⁶ as in the case of ZnSO₄. Positive role of the urea unit in the selectivity is confirmed by studying a model ligand <b>L2</b>, which is devoid of anion recognition urea unit. Structural characterization of four MSO₄ [M = Zn^II, Cd^II, Co^II, Mn^II] complexes of <b>L1</b>, that is, complex <b>1</b>, [(<b>L1</b>)₂(Zn)₂(μ-SO₄)₂]; complex <b>2</b>, [(<b>L1</b>)₂(H₂O)₂(Cd)₂(μ-SO₄)₂]; complex <b>3</b>, [(<b>L1</b>)₂(H₂O)₂(Co)₂(μ-SO₄)₂]; and complex <b>4</b>, [(<b>L1</b>)₂(H₂O)₂(Mn)₂(μ-SO₄)₂], reveal the formation of sulfate-bridged eight-membered crownlike binuclear complexes, similar to one of the concentration-dependent dimeric forms of MSO₄ as observed in solid state. Finally, <b>L1</b> is found to be highly efficient in removing ZnSO₄ from both aqueous and semiaqueous medium as complex <b>1</b> in the presence of other competing Zn^II salts via precipitation through crystallization. Powder X-ray diffraction analysis has also confirmed bulk purity of complex <b>1</b> obtained from the above competitive crystallization experiment

A Perfect Linear Cu−NNN−Cu Unit Inside the Cryptand Cavity and Perchlorate Entrapment within the Channel Formed by the Cascade Complex

Dicopper complexes of bis-tren cryptand L1 having 1,4-xylyl spacers, becoming a potential receptor for perfect linear recognition of N3-, generate a Cu−NNN−Cu unit inside the cryptand cavity. Solid-state packing of this cascade complex shows the formation of a thorough channel which encapsulate perchlorate anion within the channel

A New Hexaaza Bicyclic Cyclophane with Dual Binding Sites

A new C3-symmetric drum-shaped homoditopic haxaamino bicyclic cyclophane and its hexachloride and hexaiodide complexes have been synthesized and characterized and dual recognition of guests has been demonstrated. Single-crystal X-ray analysis illustrates that bicyclic cyclophane has a cavity and side pockets for acetone molecules. The hexaprotonated state of this bicycle shows encapsulation of an iodide inside its cavity, and in hexachloride complex, chloride is recognized as Cl−···H2O in each of the three side pockets which are in extensive hydrogen bonding interactions with the water and chlorides. 1H NMR experiments have also been carried out on hexatosylated cyclophane with the halides to study solution state binding

A New Hexaaza Bicyclic Cyclophane with Dual Binding Sites

A new C3-symmetric drum-shaped homoditopic haxaamino bicyclic cyclophane and its hexachloride and hexaiodide complexes have been synthesized and characterized and dual recognition of guests has been demonstrated. Single-crystal X-ray analysis illustrates that bicyclic cyclophane has a cavity and side pockets for acetone molecules. The hexaprotonated state of this bicycle shows encapsulation of an iodide inside its cavity, and in hexachloride complex, chloride is recognized as Cl−···H2O in each of the three side pockets which are in extensive hydrogen bonding interactions with the water and chlorides. 1H NMR experiments have also been carried out on hexatosylated cyclophane with the halides to study solution state binding