Acid/Base Controlled Size Modulation of Capsular Phosphates, Hydroxide Encapsulation, Quantitative and Clean Extraction of Sulfate with Carbonate Capsules of a Tripodal Urea Receptor

A simple tris-(2-aminoethyl) amine based pentafluorophenyl substituted tripodal urea receptor L has been extensively studied as a versatile receptor for various anions. Combined H-1-NMR, Isothermal Titration Calorimetry (ITC) and single crystal X-ray diffraction studies reveal that mononegative anions like F-, OH- and H2PO4- are encapsulated into the pseudocapsular dimeric assemblies of L with 1 : 1 stoichiometry whereas dinegative anions like CO32-, SO42- and HPO42- form tight capsular dimeric assemblies of L with 1 : 2 stoichiometries. Single crystal X-ray diffraction study clearly depicts that the size of the dimer of H2PO4- encapsulated pseudocapsule is 13.8 angstrom whereas the size of the tight HPO42- encapsulated capsular assembly is only 9.9 angstrom. The charge dependent anion encapsulated capsular size modulation of phosphates has been demonstrated by simple acid/base treatment via solution state P-31-NMR and single crystal X-ray diffraction studies. L is also capable of encapsulating hydroxide in its C-3v-symmetric cavity that is achieved upon treating a DMSO solution of L with tetrabutylammonium (TBA) cyanide and characterized by single crystal X-ray diffraction study. To the best of our knowledge this is the first report on the encapsulation of hydroxide in a neutral synthetic receptor. The excellent property of L to quantitatively capture aerial CO2 in the form of CO32- capsules [L-2(CO3)][N(n-Bu)(4)](2) in basic DMSO solution has been utilized to study the liquid-liquid extraction of SO42- from water via anion exchange. Almost quantitative and clean extraction of SO42- from water (99% from extracted pure mass and > 95% shown gravimetrically) has been unambiguously demonstrated by NMR, FT-IR, EDX, XRD and PXRD studies. Selective SO42- extraction is also demonstrated even in the presence of H2PO4- and NO3-. On the other hand the mixtures of L and TBACl (to solubilize L in CHCl3) results impure sulfate extraction even when 1 : 1 L/TBACl is used. Similar impure SO42- extraction is also observed when organic layers containing [L(Cl)][N(n-Bu)(4)] are used as the extractant, obtained upon precipitating SO42- from the extracted mass, [L-2(SO4)][N(n-Bu)(4)](2) in the carbonate capsules method using aqueous BaCl2 solution.Department of Science and TechnologyCSIR, IndiaChemistr

Cu(I)/Cu(II) templated functional pseudorotaxanes and rotaxanes

Threaded complexes like pseudorotaxanes, rotaxanes based on Cu(I)/Cu(II) ions have shown to be promising for the construction of mechanically interlocked molecular-level architectures. In this short review, we focus on the synthetic strategies developed to construct pseudorotaxanes and rotaxanes using Cu(I)/Cu(II) ions as template. Further, brief discussions on chemical and mechanical properties associated with some of the selected to Cu(I)/Cu(II) based pseudorotaxanes and rotaxanes are presented

Synthesis, characterization and complexation properties of aheteroditopic cryptand L towards Cu<SUP>II</SUP> and Zn<SUP>II</SUP>: crystal structures of L&#183;3H<SUB>2</SUB>O and[ZnL][ClO<SUB>4</SUB>]<SUB>2</SUB>&#183;2H<SUB>2</SUB>O

A new heteroditopic cryptand (L) has been synthesized in high yields, at 5 &#176;C and in absence of any templating metal ion, by tripod-tripod Schiff-base condensation of tris(3-aminopropyl)amine and 2,2',2''-nitrilotris- (ethyleneoxy)tris(benzaldehyde) followed by reduction in situ with NaBH4. The molecule has an endo-endo conformation with a distance of 5.291 &#197; between the two bridgehead nitrogens. The cryptand forms mononuclear cryptates of the general formula [ML][ClO4]2 with copper(II) and zinc(II) perchlorates. The crystal structure of [ZnL][ClO4]2&#183;2H2O was determined. The ZnII occupies the N4 end of the cavity in an almost ideal tetrahedral geometry. The blue copper(II) cryptate exhibits ligand-field bands at 875 and 745 nm and a ligand-to-metal charge transfer at 275 nm in acetonitrile solution at 298 K indicative of pseudo-tetrahedral CuN4 co-ordination. However, its EPR spectral characteristics in the solid state or in solution are typical of a magnetically concentrated complex

A Comparative Study on Factors Shaping Buying Behaviour on B2B and B2C E-Commerce Platforms in India

The retail landscape in India has undergone a stark metamorphosis over the years. Traditional “Brick and Mortar” style retailing is facing staunch competition from the rapid emergence of e-commerce platforms. Having aligned themselves to ever evolving consumer sensibilities, these robust platforms are revolutionizing the Indian retail industry like never before. Our research revealed that while the ease/method of payment and a value driven return policy take precedence in B2C markets, various bulk purchase options are given due importance in B2B e-commerce markets. Moreover, on-time delivery is a common critical factor/parameter common to both markets. In a nutshell, e-commerce appears to be the future with regards to both B2B and B2C markets. However, the onus is on the e-commerce platforms to offer a holistic retail experience whilst carving a niche for themselves in an increasingly cluttered market. Keywords: Brick and Mortar, Competition, Consumer Sensibilities, e-commerce, India, Retai

Structural studies on encapsulation of tetrahedral and octahedral anions by a protonated octaaminocryptand cage

Structural aspects of the binding of inorganic anions such as perchlorate, hydrogen sulfate, and hexafluorosilicate with the proton cage of octaaminocryptand L1, N(CH2CH2NHCH2-p-xylyl-CH2NHCH2CH2)3N), are examined thoroughly. Crystallographic results for a hexaprotonated perchlorate complex of L1, [(H6L1)6+(ClO4-)]5(ClO4-)·11H2O·CH3CN (1), an octaprotonated hydrogen sulfate complex of L1, [(H8L1)8+(HSO4-)]7(HSO4-)·3H2O·CH3OH (2) and an octaprotonated fluorosilicate complex of L1,[(H8L1)8+(HSiF6-)]3(SiF62-)·(HSiF6-)·15H2O (3), show encapsulation of one perchlorate, hydrogen sulfate and hexafluorosilicate, respectively inside the cage of L1 in their protonated states. Further, detailed structural analysis on complex 1 reveals that the hexaprotonated L1 encapsulates a perchlorate via two N–H···O and five O–H···O hydrogen bonds from protonated secondary nitrogen atoms of L1 and lattice water molecules, respectively. Encapsulated hydrogen sulfate in complex 2 is “glued” inside the octaprotonated cage of L1 via four N–H···O and six C–H···O hydrogen bonds whereas encapsulated HSiF6− in complex 3 has short contacts via six N–H···F and three C–H···F hydrogen bonds with [H8L1]8+. In the cases of complexes 2 and 3, the cryptand L1 in octaprotonated state shows monotopic encapsulation of the guest and the final conformation of these receptors is spherical in nature compared to the elongated shape of hexaprotonated state of L1 in complex 1

Mechanistic Insight into Fast and Highly Efficient Organocatalytic Activity of a Tripodal Dimeric Hexaurea Capsular Assembly in Michael Addition Reactions

A tris­(2-aminoethyl)-amine-based dimeric capsular assembly of pentafluorophenyl urea (C1) has been employed as a catalyst in a wide range of Michael addition reactions. This capsular catalyst assembly dramatically accelerates the Michael addition reaction of β-nitrostyrenes (2a–2d) with various Michael donors such as ketoesters (3a, 3e), 1,3-diketones (3b), diesters (3C), and cyanoesters (3d) at room temperature to yield the corresponding nitroalkanes in significantly high yields within a very short reaction time. Significant improvement in solubility and use of conventional organic solvents in reaction along with a drastic decrease in reaction time (high value of the rate constant of the reaction) has been achieved through C1 as compared to the previously reported homologous tripodal monomeric urea catalyst (L1). The addition of enolate to β-nitrostyrenes to generate an anionic intermediate seemed to be highly stabilized by the six urea units of capsular assembly. Control experiments and in situ kinetic studies are performed for this addition reaction and based on the results, a plausible mechanism has been proposed for the formation of Michael adduct inside the capsular cavity

Recognition of nitrates in a discrete dimeric capsular assembly of a triamide half-capsule

1343-1349A newly synthesized tripodal amide receptor for the recognition of planar anions such as nitrate and acetate is described. The tripodal host, L1, features a 1,3,5-substituted 2,4,6-trimethylbenzene scaffold bearing three convergent amide hydrogen bonding functionality and electron-withdrawing p-cyanobenzoyl terminals. The single-crystal X-ray crystallographic analysis on crystals obtained upon complexation of L1 with tetrabutylammonium nitrate in acetone shows the encapsulation of two NO3¯ ions inside the staggered dimeric capsular assembly of L1. On the other hand, complexation with tetrabutylammonium acetate in the same solvent system shows non-capsular recognition of acetate and a water molecule inside the receptor bowl. The p-cyano substitution in the aryl terminals assists the formation of dimeric capsular assembly of L1 by enhancing the hydrogen bonding tendency of the aryl C-H protons. Though L1 demonstrates capsule formation upon complexation with NO3¯, the geometrically similar AcO¯ shows non-capsular recognition in the solid state, which may be due the structural difference between the two anions

Various coordination modes of sulfate by cyanuric acid platform-based first- and second-generation urea receptors

Cyanuric acid platform-based first-generation p-nitrophenyl- (L1), p-cyanophenyl- (L2) and pentafluorophenyl- (L3) substituted tris-ureas and second-generation p-nitrophenyl-functionalized hexakis-urea receptor (L4) have been synthesized. Detailed solid-state structural studies on the binding of sulfate to L1, L2 and L4 have been examined thoroughly by single-crystal X-ray diffraction and compared with the binding modes of SO<SUB>4</SUB><SUP>2–</SUP> to the pentafluorophenyl analogue of the tris-urea receptor L3 to evaluate the various modes of SO<SUB>4</SUB><SUP>2–</SUP> binding in this new generation of cyanuric acid platform-based anion receptors. The crystallographic results show a 1:1 binding pattern between L1 and SO<SUB>4</SUB><SUP>2–</SUP> through six N–H···O interactions with the three urea moieties of the receptor and one C–H···O interaction with one of the tetrabutylammonium counter cations in complex 1. Thus, this complex shows an uncommon example of a seven-coordinate SO<SUB>4</SUB><SUP>2–</SUP>, which is structurally similar to that of the sulfate-binding protein (SBP). Interestingly, L2 shows a 2:1 host/guest binding pattern with SO<SUB>4</SUB><SUP>2–</SUP> that generates a dimeric capsular assembly with dimensions of approximately 10.398 Å in complex 2. In this case, each of the oxygen atoms of SO<SUB>4</SUB><SUP>2–</SUP> forms a trifurcated hydrogen bond with the urea NH groups and thus a total of 12 N–H···O hydrogen-bonding interactions can be observed for SO<SUB>4</SUB><SUP>2–</SUP>. In contrast, L3 shows 11 hydrogen-bonding interactions with the encapsulated SO<SUB>4</SUB><SUP>2–</SUP> in complex 3 assisted by two nBu<SUB>4</SUB>N<SUP>+</SUP> counter cations through six N–H···O and five C–H···O interactions. In the case of the SO<SUB>4</SUB><SUP>2–</SUP> complex of L4, complex 4 shows 1:1 encapsulation of SO<SUB>4</SUB><SUP>2–</SUP> in its inner cavity with 10 N–H···O interactions. A binding study of SO<SUB>4</SUB><SUP>2–</SUP> in solution was performed with L4 in dmso by isothermal titration calorimetry (ITC). This study also showed a 1:1 binding pattern of SO<SUB>4</SUB><SUP>2–</SUP> with an association constant of approximately 5.11 (log K). Furthermore, the binding of SO<SUB>4</SUB><SUP>2–</SUP> in the gas phase was examined by ESI mass spectrometry

Artificial receptors for nitrate: a comprehensive overview

This feature article highlights recent developments in the field of synthetic receptors designed to recognize nitrate with a particular emphasis on: (i) synthetic receptors for nitrate in competitive media, (ii) assembly processes driven by nitrate recognition and (iii) synthetic transporters and extractants for nitrate

Zinc(II) and PPi selective fluorescence OFF–ON–OFF functionality of a chemosensor in physiological conditions

A fluorescent chemosensor based on a quinoline derivative, L<SUP>2</SUP> (OFF state), selectively senses Zn<SUP>2+</SUP> 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