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

A monomeric StayGold fluorescent protein

StayGold is an exceptionally bright and stable fluorescent protein that is highly resistant to photobleaching. Despite favorable fluorescence properties, use of StayGold as a fluorescent tag is limited because it forms a natural dimer. Here we report the 1.6 Å structure of StayGold and generate a derivative, mStayGold, that retains the brightness and photostability of the original protein while being fully monomeric

Design and Syntheses of Metal Ion Templated Self-Assemblies and Anion Recognition through Second Sphere Coordination

Self-assembly is used to describe the process in which a disordered system of pre-existing components forms an organized structure or pattern as a consequence of non-covalent interactions among the components themselves, without external direction. Self-assembly suggests the distinction between ‘‘self’’ and ‘‘non-self,’’ with recognition and selection between the two during assembly. According to Lehn, supramolecular chemistry can be described as an information science in which molecular components that contain the necessary information, self-assemble into large specific structures.Consequently, self-assembly has been recognized as a powerful tool for the construction of supramolecular scaffolds, as established by several excellent contributions.To achieve self-assembled systematized architecture, the necessary instructions must be incorporated into the structures of the building blocks by chemical synthesis. Thus, molecules can be made to self-assemble spontaneously into multi-component complex structures when they are instructed to do so. The instructions exist in the form of the molecule’s shape, its chemical properties, and how well it fit into the space where the assembly takes place etc. Each step in the assembly process is reversible and dynamic, that means the complex product is constantly forming, dissipating and proceeds via an error correcting method. Over the last two decades, the field of metallo-supramolecular selfassembly has emerged as a promising area of research for the development of specific, three-dimensional structures of increasing complexity and functionality.The beginning of this area of research has been benefited from design principles that consist of the ligand geometry and metal coordination geometry, thus opening up routes towards rationally designed classical supramolecular architectures. The success of this melal assisted self-assembled supramolecular architectures lies in its wide range of applications. Metal ion mediated self-assembled helical compounds are one of the most important and remains a crucial area for research over the last two decades.The research was carried out under the supervision of Prof. Pradyut Ghosh, Inorganic Chemistry division under the SCS [School of Chemical Sciences]The research was conducted under CSIR fellowship and projec

Selective recognition and extraction of KBr via cooperative interactions with a urea functionalized crown ether dual-host

Selective solid–liquid extraction of KBr is demonstrated for the first time with a crown ether based pentafluorophenyl urea functionalized dual-host receptor. <SUP>1</SUP>H-NMR and ITC studies have been carried out to illustrate the effect of cooperativity towards the recognition of alkali metal salts

Selective recognition of sulphate in a Cu(II) assisted 1D polymer of a simple pentafluorophenyl substituted pyridyl-urea via second sphere coordination

A pentafluorophenyl (–C6F5) substituted 3-pyridyl urea, L1, is explored extensively to demonstrate SO42− binding exclusively via second sphere coordination in the cavity of a 1D polymeric self-assembly of L1, selectively assisted by Cu2+. A single crystal X-ray diffraction study depicts SO42− encapsulation in the C2 symmetric cleft via nine hydrogen bonding interactions contributed by eight urea protons of four L1 moieties in [CuL14(DMF)2]SO4 (1). To revalidate the importance of Cu2+ selective anion coordination via exclusive second sphere coordination, a complex of L1 and Cu(NO3)2, i.e. [CuL14(H2O)2](NO3)2 (2), is also isolated and characterized by a single crystal X-ray diffraction study. When SO42− salts of different metal ions such as Co2+/Ni2+ are employed, the first sphere coordination of SO42− is observed in cases of complexes [CoL13(DMF)2SO4] (3) and [NiL13(DMF)2SO4] (4) respectively. These results clearly suggest the importance of Cu2+ towards anion recognition via purely second sphere coordination in the case of complexes 1 and 2. To understand the importance of (–C6F5) substitution in the design of L1 towards such recognition of SO42− in 1, the phenyl (–C6H5) analogue of L1, i.e.L2, is allowed to complex with the SO42− salt of Cu2+. Interestingly, L2 shows first sphere SO42− coordination in the complex [CuL22(DMF)(H2O)2SO4] (5). Solution state UV-Vis experiments of L1 with various copper salts such as Cu(ClO4)2, CuSO4, Cu(NO3)2, CuCl2 and CuBr2 in DMF show the formation of a binary complex corresponding to 1. Further, Cu2+ selective second sphere coordination of SO42− in solution is also demonstrated by UV-Vis studies of complexes isolated from the mixtures of various Cu2+ salts and/or SO42− salts of different metal ions

Encapsulation of [(SO<SUB>4</SUB>)<SUB>4</SUB>(H<SUB>2</SUB>O)<SUB>12</SUB>]<SUP>8−</SUP> clusters in a metal organic framework of pyridyl functionalized cyanuric acid based tris-urea

Encapsulation of hydrated sulfate in a bowl-shaped metal organic coordination polymer formed by Zn2+ assisted self-assembly of a 3-pyridyl terminated cyanuric acid platform based urea receptor is reported in aqueous medium. Trapping of an unusual [(SO4)4(H2O)12]8− cluster in a [Zn(H2O)6]2+ capped self-assembled structure is characterized by single crystal X-ray crystallography. Furthermore, selective binding of SO42− is established from the 1H-NMR titration study

Effect of coordinating (–CN) vs. non-coordinating (–F) substituents in 3-pyridyl urea receptors toward second sphere sulfate recognition: selective crystallisation of CuSO<SUB>4</SUB> from mixtures of competing anions/cations

4-Fluorophenyl and 4-cyanophenyl substituted 3-pyridyl urea, L1111 and L2222 respectively, were synthesized and explored extensively to demonstrate SO42− binding via second sphere coordination in their respective self-assembled structures assisted by Cu2+, Cd2+ and Co2+. A single crystal X-ray diffraction study depicts second sphere SO42− recognition in the C4v symmetric cleft formed by the assembly of four molecules of the Cu2+ complex of L1111, [CuL11114(H2O)2]SO4, (1), via eight N–H⋯O interactions from four urea moieties. Similarly, second sphere SO42− recognition via twelve hydrogen bonding interactions (N–H⋯O and C–H⋯O) is also demonstrated in the assembly of the Cd2+ complex of L1111 i.e. [CdL11114(H2O)2]SO4, (2). Detailed structural analysis of 1 and 2 shows the formation of the coordination complexes of Cu2+ and Cd2+ with four units of pyridyl urea, which further assemble to generate a suitable coordination environment for the recognition of SO42− via second sphere coordination. On the other hand, L2222 with a coordinating substituent shows second sphere SO42− coordination with eleven hydrogen bonding interactions (N–H⋯O and C–H⋯O) via the formation of a Cu2+ assisted 1D coordination polymer [{CuL22224}SO4]α, (3). The coordinating property of the –CN of L2222 is reflected in 3, as it directly coordinates to the Cu2+ that assists the formation of the 1D coordination polymer. Second sphere coordination of SO42− in the assembly of L2222 is also established with Co2+ in its complex, [CoL22222(H4O)2]SO4, (4). However, in this case the metal ion prefers to form a coordination complex, as observed in 1 and 2, instead of the 1D-polymeric network in 3. The solution state UV-Vis studies of L1111 with various copper salts, such as Cu(ClO4)2, CuSO4, Cu(NO3)2, CuCl2 and their mixtures show the selective formation of 1. Cu2+ selective second sphere coordination of SO42− in solution is also demonstrated by UV-Vis studies of the complex isolated from the mixtures of various Cu2+ salts or SO42− salts of different metal ions. Furthermore, the selective formation of complex 1 is also demonstrated when complexation of CuSO4 is carried out with mixtures of L1111 and L2222 in MeOH–H2O

[2]Rotaxane with multiple functional groups

High-yield syntheses of Cu(II)- and Ni(II)-templated [2]pseudorotaxane precursors (CuPRT and NiPRT, respectively) were achieved by threading bis(azide)bis(amide)-2,2′-bipyridine axle into a bis(amide)tris(amine) macrocycle. Single-crystal X-ray structural analysis of CuPRT revealed complete threading of the axle fragment into the wheel cavity, where strong aromatic π–π stacking interactions between two parallel arene moieties of the wheel and the pyridyl unit of axle are operative in addition to metal ion templation. Attachment of a newly developed bulky stopper molecule with a terminal alkyne to CuPRT via a Cu(I)-catalyzed azide–alkyne cycloaddition reaction failed as a result of dethreading of the azide-terminated axle under the reaction conditions. However, the synthesis of a metal-free [2]rotaxane containing triazole with other functionalities in the axle was achieved in ∼45% yield upon coupling between azide-terminated NiPRT and the alkyne-terminated stopper. The [2]rotaxane was characterized by mass spectrometry, 1D and 2D NMR (COSY, DOSY, and ROESY) experiments. Comparative solution-state NMR studies of the [2]rotaxane in its unprotonated and protonated states were carried out to locate the position of the wheel on the axle of the metal-free [2]rotaxane. Furthermore, a variable-temperature 1H NMR study in DMSO-d6 of [2]rotaxane supported the kinetic inertness of the interlocked structure, where the newly developed stopper prevents dethreading of the 30-membered wheel from the axle

Experimental results on low cost microcontroller based DC drive implementation

This paper presents the experimental results for an attractive control scheme implementation using an 8 bit microcontroller. The power converter involved is a 3 phase full controlled bridge rectifier. A single quadrant DC drive has been realized and results have been presented for both open and closed loop implementations

Tris-ureas as versatile and highly efficient organocatalysts for Michael addition reactions of nitro-olefins: mechanistic insight from in-situ diagnostics

Tris(2-aminoethyl)-amine, TREN based tris-ureas (1a–1d) and tris-thiourea (1e) have been explored towards a wide range of catalytic Michael addition reactions. These tris-ureas, 1a–1d efficiently catalyze the addition reaction of β-nitro styrenes (2a–2d) with various nucleophiles such as β-ketoesters (3a–3c), 1,3-dicarbonyl compound (3d), a cyanoester (3e) and a nitroester (3f) under ambient conditions to produce corresponding nitro alkanes in high yields. Pentafluorophenyl attached tris-urea, 1d is found to be the most effective catalyst in the series that yields 78–98% products conversion. In case of the reaction between β-nitro styrenes and malononitrile (3g) in presence of 1d, 2-amino-5-nitro-4,6-diphenylcyclohex-1-ene-1,3,3-tricarbonitriles are also isolated as a minor product along with the corresponding Michael adduct. The added advantage of bridge-head nitrogen center in tris-urea organocatalysts, 1a–1d has been established by studying analogous benzene platform based tris-ureas (1f, 1g, 1h) in similar experimental conditions. Furthermore, a plausible reaction mechanism has also been established based on in-situ 1H NMR kinetic studies