Beyond Size Complementary Factors in Anion-Tetralactam Macrocycle Complexes: From Intrinsic Gas-Phase to Solvent-Predicted Stabilities.
ABSTRACT: The gas-phase affinities of different types of anions X- (halogen anions, oxoanions, and hydrogenated anions) toward a model tetralactam-based macrocycle receptor (1), defined in terms of stability of an anion-receptor complex (1 + X-) against its disintegration, were evaluated by dissociation studies using a mass spectrometry-based methodology and supported by theoretical calculations (density functional theory-PBE0). The gas-phase complex with Cl- was found to be tailor-made for the macrocycle 1, while 1 + SA- (SA- = salicylate anion) and 1 + HSO4- were the weakest ones. Other complexes displayed a relatively low-stability dispersion (<1.2 kcal·mol-1). The 1/?r approach of the electrostatic contribution scaling method was used to predict the stability trends in a dimethyl sulfoxide solvent from the gas-phase binding energy partition using the symmetry-adapted perturbation theory. High deformation energy and differences in solvation energies were suggested to be the main sources of inconsistency in the predicted and experimental stabilities of 1 + F- and 1 + H2PO4- complexes.
Project description:A novel eight-membered macrocycle of the hemicucurbit[n]uril family, chiral (all-R)-cyclohexanohemicucurbituril (cycHC) ‡The name cyclohexylhemicucurbituril, previously used for these macrocycles, is changed in accordance with the IUPAC nomenclature for fused cycles, as the cyclohexane substituents are fused with the parent hemicucurbituril. binds anions in a purely protic solvent with remarkable selectivity. The cycHC portals open and close to fully encapsulate anions in a 1?:?1 ratio, resembling a molecular Pac-Man™. Comprehensive gas, solution and solid phase studies prove that the binding is governed by the size, shape and charge distribution of the bound anion. Gas phase studies show an order of SbF6- ? PF6- > ReO4- > ClO4- > SCN- > BF4- > HSO4- > CF3SO3- for anion complexation strength. An extensive crystallographic study reveals the preferred orientations of the anions within the octahedral cavity of cycHC and highlights the importance of the size- and shape-matching between the anion and the receptor cavity. The solution studies show the strongest binding of the ideally fitting SbF6- anion, with an association constant of 2.5 × 105 M-1 in pure methanol. The symmetric, receptor cavity-matching charge distribution of the anions results in drastically stronger binding than in the case of anions with asymmetric charge distribution. Isothermal titration calorimetry (ITC) reveals the complexation to be exothermic and enthalpy-driven. The DFT calculations and VT-NMR studies confirmed that the complexation proceeds through a pre-complex formation while the exchange of methanol solvent with the anion is the rate-limiting step. The octameric cycHC offers a unique example of template-controlled design of an electroneutral host for binding large anions in a competitive polar solvent.
Project description:Tris(3-aminopropyl)amine-based tripodal urea and thiourea receptors, tris([(4-cyanophenyl)amino]propyl)urea (L1) and tris([(4-cyanophenyl)amino]propyl)thiourea (L2), have been synthesized and their anion binding properties have been investigated for halides and oxoanions. As investigated by 1H NMR titrations, each receptor binds an anion with a 1:1 stoichiometry via hydrogen-bonding interactions (NH?anion), showing the binding trend in the order of F- > H2PO4- > HCO3- > HSO4- > CH3COO- > SO42- > Cl- > Br- > I in DMSO-d6 . The interactions of the receptors were further studied by 2D NOESY, showing the loss of NOESY contacts of two NH resonances for the complexes of F-, H2PO4-, HCO3-, HSO4- or CH3COO- due to the strong NH?anion interactions. The observed higher binding affinity for HSO4- than SO42- is attributed to the proton transfer from HSO4- to the central nitrogen of L1 or L2 which was also supported by the DFT calculations, leading to the secondary acid-base interactions. The thiourea receptor L2 has a general trend to show a higher affinity for an anion as compared to the urea receptor L1 for the corresponding anion in DMSO-d6 . In addition, the compound L2 has been exploited for its extraction properties for fluoride in water using a liquid-liquid extraction technique, and the results indicate that the receptor effectively extracts fluoride from water showing ca. 99% efficiency (based on L2).
Project description:A macrocyclic-based fluorescence chemosensor has been designed and synthesized from the reaction of dansyl chloride and a hexaaminomacrocycle containing four secondary and two tertiary amines. The new chemosensor has been examined for its binding ability toward phosphate, sulfate, nitrate, iodide, bromide, chloride, and fluoride by fluorescence spectroscopy in DMSO. The results indicate that the compound binds each of the anions with a 1:1 stoichiometry, showing high affinity for the oxoanions, chloride and iodide with the binding constants up to four orders of magnitude. Ab initio calculations based on density functional theory (DFT) suggest that the ligand is deformed in order to encapsulate an anion, and each anion, except fluoride, is bonded to the macrocycle through two NH…X(-) and four CH…X(-) interactions.
Project description:Two new tetralactam macrocycles with 2,3-dibutoxynaphthalene groups as sidewalls have been synthesized and characterized. The macrocycle containing isophthalamide bridges can bind square-planar chloride coordination complexes of gold(III), platinum(II), and palladium(II) in CDCl3, while the macrocycle with 2,6-pyridine dicarboxamide bridging units cannot. This may be due to the shrunken cavity caused by intramolecular hydrogen bonds in the latter tetralactam macrocycle. The binding of the isophthalamide-based macrocycle is mainly driven by hydrogen bonds and electrostatic interactions. This naphthalene-based macrocycle has similar binding affinities to all the three abovementioned precious metal chloride complexes. This is in contrast to the fact that the tetralactam macrocycle with anthracene as the sidewalls only show good binding affinities to AuCl4 -. The superior binding to all three complexes may be due to the conformational diversity of the naphthalene-based macrocycle, which make it conformationally adaptive to maximize the binding affinities. In addition, the macrocycle shows fluorescent quenching when adding the chloride metal complexes in its solution and may be used as a fluorescent sensor for the detection of these coordination complexes.
Project description:In the title salt, [(CH3)2NH2][Cu(HSO4)(SO4)(H2O)4], one type of cation and anion is present in the asymmetric unit. The Cu(II) atom in the complex anion, [Cu(HSO4)(SO4)(H2O)4](-), has a tetra-gonal bipyramidal [4 + 2] coordination caused by a Jahn-Teller distortion, with the aqua ligands in equatorial and two O atoms of tetra-hedral HSO4 and SO4 units in apical positions. Both types of ions form sheets parallel to (010). The inter-connection within and between the sheets is reinforced by O-H?O and N-H?O hydrogen bonds, respectively, involving the water mol-ecules, the two types of sulfate anions and the ammonium groups.
Project description:New tetrakis- and hexakis(1H-pyrrole-2-carbaldehyde) anion receptors are described. The anion binding properties of these receptors were studied in organic media and in the solid state. The receptors displayed good affinity for the dihydrogenphosphate and pyrophosphate anions (as the tetrabutylammonium salts) in chloroform even in the presence of a polar protic solvent, methanol. Solution phase spectroscopic analyses proved consistent with the binding mode seen in single crystal structural studies of the dihydrogenphosphate and pyrophosphate complexes and provided support for the contention that these receptors undergo conformational reorganization in order to accommodate the bound oxoanions both in chloroform solution and in the solid state.
Project description:Pseudorotaxane complexes of squaraine dyes and tetralactam macrocycles are converted into permanently interlocked rotaxane structures using copper-catalyzed and copper-free cycloaddition reactions with bulky stopper groups. The photophysical properties of the encapsulated squaraine depend on the structure of the macrocycle. In one case, squaraine rotaxanes are produced in near-quantitative yields and with intense near-IR fluorescence. In another case, squaraine fluorescence is greatly diminished upon macrocyclic encapsulation but the signal can be restored by dye displacement with anions.
Project description:Borosulfates are an ever-expanding class of compounds and the extent of their properties is still elusive. Herein, the first two copper borosulfates Cu[B2 (SO4 )4 ] and Cu[B(SO4 )2 (HSO4 )] are presented, which are structurally related but show different dimensionalities in their substructure: While Cu[B2 (SO4 )4 ] reveals an anionic chain, ?1 [B(SO4 )4/2 ]- , with both a twisted and a unique chair conformation of the B(SO4 )2 B subunits, Cu[B(SO4 )2 (HSO4 )] reveals isolated [B2 (SO4 )4 (HSO4 )2 ]4- anions showing exclusively a twisted conformation. The complex anion can figuratively be obtained as a cut-out from the anionic chain by protons. Comparative DFT calculations based on magnetochemical measurements complement the experimental studies. Calculation of the pKa ?values of the two conformers of the [B2 (SO4 )4 (HSO4 )2 ]4- anion revealed them to be more similar to silicic than to sulfuric acid, highlighting the close relationship to silicates.
Project description:A combination of anion photoelectron spectroscopy and density functional theory calculations has elucidated the geometric and electronic structure of gas-phase endohedral Pt/Pb cage cluster anions. The anions, Pt@Pb???¹ and Pt@Pb??¹? were prepared from "preassembled" clusters generated from crystalline samples of [K(2,2,2-crypt)]?[Pt@Pb??] that were brought into the gas phase using a unique infrared desorption/photoemission anion source. The use of crystalline [K(2,2,2-crypt)]?[Pt@Pb??] also provided access to K[Pt@Pb(n)](-) anions in the gas phase (i.e., the K? salts of the Pt@Pb(n)²? anions). Anion photoelectron spectra of Pt@Pb???¹, Pt@Pb??¹?, and K[Pt@Pb??]¹? are presented. Extensive density functional theory calculations on Pt@Pb??³?/²?/¹?/? and Pt@Pb??²?/¹? provided candidate structures and anion photoelectron spectra for Pt@Pb???¹ and Pt@Pb??¹?. Together, the calculated and measured photoelectron spectra show that Pt@Pb???¹ and Pt@Pb??²?/¹? endohedral complexes maintain their respective D(4d) and slightly distorted I(h) symmetries in the gas phase even for the charge states with open shell character. Aside from the fullerenes, the Pt@Pb??²? endohedral complex is the only bare cluster that has been structurally characterized in the solid state, solution, and the gas phase.
Project description:The photophysical properties of a deep-red fluorescent squaraine dye can be improved by encapsulating it within a tetralactam macrocycle. Three new tetralactams are described with different substituents (methyl, methoxy, methylenedioxy) on the macrocycle aromatic sidewalls. The capability of each tetralactam to encapsulate a squaraine dye in chloroform solution was determined experimentally using absorption, fluorescence, and NMR spectroscopy. Two of the tetralactams were found to thread a squaraine dye with association constants on the order of 106 M-1, while a third macrocycle exhibited no squaraine affinity. An X-ray crystal structure of the third tetralactam showed that the substituents sterically blocked squaraine association. Of the two tetralactams that encapsulate a squaraine, one induces an increase in squaraine fluorescence quantum yield, while the other quenches the squaraine fluorescence. The results suggest that these new squaraine binding systems will be useful for biological imaging and diagnostics applications.