Metal-controlled assembly and selectivity of a urea-based anion receptor

1-(3-[1,10]phenanthrolin-2-yl-phenyl)-3-(4-trifluoromethyl-phenyl)-urea (1) forms a solution-stable 1:2 complex with copper(I), [CuI(1)2]+, which behaves as an anion receptor in aprotic media. The [CuI(1)2]+ receptor may adopt a geometrical arrangement in which the two facing urea subunits give tetrafurcate H-bond interaction with a spherical anion (halides and H2PO4-). In the presence of the Y-shaped acetate, the [CuI(1)2]+ receptor rearranges to interact with two CH3COO- ions, according to two stepwise equilibria. Thus, in the presence of substoichiometric amounts of the anions, [CuI(1)2]+ discriminates H2PO4- over CH3COO-, inverting the basicity trend.     

A conformationally flexible, urea-based tripodal anion receptor: solid-state, solution, and theoretical studies

Tripodal tris(urea) cationic receptors 1 and 2 containing p-tolyl or octyl substituents, respectively, have been synthesized, and their association behavior with anionic guests has been studied via a variety of methods. The receptors are based around a hexasubstituted aryl core and contain both urea and pyridinium functionalities. For 1:1 complexes, anions reside within the central cavity of the host species, held by hydrogen bonds from both NH and CH donors. The following host-anion complexes have been characterized by X-ray crystallography: 1-(Br)3, 1-(PF6)3.2(CH3)2CO, and 1-(NO3)1.5(PF6)1.5. Each structure contains the receptor in a significantly different geometry, highlighting the anion-dependent conformational flexibility of 1. Solution 1H NMR spectroscopic titrations have shown the two host species to display significant affinity for both halides and hydrogen sulfate and strongly suggest the persistence of CH...X- interactions despite the presence of "stronger" NH donor groups. Variable-temperature 1H NMR studies on the more soluble octyl derivative 2 show that there is a distinct change in conformation associated with the formation of a 1:1 host/guest complex. Computations using density functional theory (with the B3LYP functional) have been employed to aid in understanding the geometry of the 1:1 host/chloride complexes of 1 and 2. These experiments suggest that the lowest energy conformation for 1-Cl is one in which the ureidopyridinium arms are orientated upward forming a cavity that is sealed by CH...pi interactions, effectively forming a unimolecular capsule, whereas for 2 a less symmetrical "2-up, 1-down" geometry is favored.     

A novel anion receptor employing the pyrrole and amide moieties in the cooperative binding of anions

A novel anion receptor 1 based on pyrrole and amide moieties was designed, synthesized and characterized by X-ray crystallography, ¹H NMR, ESI-MS and so on. Its anions (such as AcO^?, F^?, Cl^? and H₂PO₄ ^?) binding properties was studied in detail by the ¹H NMR titrations in DMSO-d ₆ .     

Kinetics and exchange behaviour of certain sulphur anions on strongly basic anion exchangers in aqueous KCl medium

The kinetics of the exchange of sulphate and chloride ions on the strongly basic anion exchanger Dowex 1X8, of different particle diameters is investigated. The diffusion coefficient values are calculated by two diferent methods, discussed in the light of the processes governing the exchange reactions encountered, and found to be mainly controlled by particle diffusion. The distribution behaviour of sulphate, sulphite, thiosulphate and sulphide between aqueous KCl solutions of different concentrations and a number of selected anion exchange resins is studied. The data are explained on the premises of the different interactions involved in both aqueous and resineous phases. The effect of the alkali metal chloride molarities in the aqueous phase (LiCl, NaCl and KCl) on the exchange behaviour of the different S-anions is also investigated. The results are interpreted in the light of the water—water interaction and the competition for hydration between the alkali metal cations and the exchanged S-anions.     

Pyridinium CH...anion and pi-stacking interactions in modular tripodal anion binding hosts: ATP binding and solid-state chiral induction

The preparation of two new tripodal "pinwheel" type anion hosts based on a triethylbenzene core and bipyridinium or ethylnicotinium arms is reported. The new materials bind anions via CH...anion interactions. Complexes with Br(-) and PF(6)(-) have been characterised by X-ray crystallography as both solvates in a pure form. In the bipyridinium host CH...F interactions to PF(6)(-) induce a chiral C(3) symmetric conformation that is disrupted in the hydrate. The compound is also selective for ATP(2-) in aqueous acetonitrile.     

What anions do inside a receptor's cavity: a trifurcate anion receptor providing both electrostatic and hydrogen-bonding interactions

The trifurcate receptor 1(3+) forms stable 1:1 complexes with halide and oxo anions in MeCN solution, as shown by spectrophotometric and 1H NMR experiments, and selectively recognizes chloride (lg K(ass) > 7) in the presence of fluoride and bromide. The high stability reflects the receptor's ability to donate up to six hydrogen bonds (from three pyrrole N-H and three C-H fragments, polarized by the proximate positive charge) to the included anion. Addition of an excess of more basic anions (F- and CH3COO-) induces stepwise deprotonation of the N-H groups, an event signalled by the appearance of a bright yellow color. Crystal and molecular structures are reported for the complex with NO3(-) and a capsule consisting of two interconnected trifurcate subunits, one of which includes an H-bound Br- ion, while the other is doubly deprotonated and includes an H-bound water molecule. Finally, evidence is given for the formation in solution of an authentic complex of OH-, in which H-bound hydroxide is included within the cavity of 1(3+).     

Valence anions of N-acetylproline in the gas phase: computational and anion photoelectron spectroscopic studies

We report the photoelectron spectrum of anionic N-acetylproline, (N-AcPro)(-), measured with 3.49 eV photons. This spectrum, which consists of a band centered at an electron binding energy of 1.4 eV and a higher energy spectral tail, confirms that N-acetylproline forms a valence anion in the gas phase. The neutrals and anions of N-AcPro were also studied computationally at the B3LYP∕6-31++G(d,p) level. Based on the calculations, we conclude that the photoelectron spectrum is due to anions which originated from proton transfer induced by electron attachment to the π* orbital localized at the acetyl group of N-AcPro. We also characterized the energetics of reaction paths leading to pyrrolidine ring opening in the anionic N-AcPro. These data suggest that electron induced decomposition of peptides/proteins comprising proline strongly depends on the presence of proton donors in the close vicinity to the proline residue.     

Pyridinium N-heteroarylaminides: synthesis of N-heteroarylpolyamines

The synthesis of a set of new N-heteroarylpolyamines is reported. A multiple and regioselective alkylation on the exo nitrogen of pyridinium N-(heteroaryl)aminides with several polybromo compounds, followed by a clean N-N bond reduction of the corresponding pyridinium salts, provides an easy and general method to obtain the title compounds.     

Coexistence of two different anion states in polyacene nanocluster anions

Two types of anion states are shown to coexist in nanometer-scale polyacene cluster anions. Naphthalene and anthracene nanoclusters having a single excess electron were produced in the gas-phase. Photoelectron spectra of size-selected cluster anions containing 2 to 100 molecules revealed that rigid "crystal-like" cluster anions emerge, greater than approximately 2 nanometers in size, and coexist with the "disordered" cluster anion in which the surrounding neutral molecules are reorganizing around the charge core. These two anion states appear to be correlated to negative polaronic states formed in the corresponding crystals.     

Sorption equilibrium of aromatic anions in an anion exchange membrane

Ion exchange and water content measurements were performed with an anion exchange membrane, ADS XL 10 (Solvay), equilibrated in aqueous solutions containing mineral electrolyte as NaCl, and/or organic electrolyte as sodium benzene carboxylate (ΦCO₂Na) and sodium 4-hydroxy-1-naphthalenesulfonate (ΦΦOHSO₃Na). By using radiotracers, it was possible to determine the amount of the total mineral and organic ionic species present inside the membrane. The fixation of big organic ions balancing the exchanging sites of the membrane can modify the membrane structure, creating micropores able to sorb more electrolytes. It was established that the sorption of hydrophobic organic ions corresponds to a ‘micelle mechanism’, The penetration of hydrophobic ions into the membrane induces a change in the molar volume of the wet membrane in relation to the variation of the water content.     

Pyridinium ion reactivities: substituent effect on the reverse menschutkin reaction of 1-methylpyridinium cations with iodide anion

Substituent effect on the reverse Menschutkin reaction of 1-methylpyridinium cations with iodide anion can be described in terms of the LArSR equation with ?=3.60 which provides evidence against very late transition state of the nitrogen-to-iodine transmethylation.     

Tris(indolyl)methene molecule as an anion receptor and colorimetric chemosensor: tunable selectivity and sensitivity for anions

Simple tris(indolyl)methene receptors 1-3 containing conjugated bisindole skeletons have been designed and synthesized. The anion binding and sensing properties have been studied using UV-vis spectroscopy and (1)H NMR titration technique. Compared with 3,3'-bis-indolyl phenylmethene (4), tris(indolyl)methene receptors could highly selectively detect F(-) based on two stages of proton transfer, along with stepwise drastic color changes. The introduction of the electron withdrawing or donating groups into indole unit, which tunes the acidities of the hydrogen bond sites, partially enhanced or inhibited the occurrence of the deprotonation of receptor and has a positive effect on the selectivity and sensitivity of such "proton-transfer" chemosensors for anions.     

A novel ditopic receptor and reversal of anion binding selectivity in the presence and absence of bound cation

A calix[4]arene-derived ditopic receptor 1 has been synthesized. In the absence of Na+, the receptor binds acetate in preference to diphenyl phosphate (as the tetrabutylammonium salts), but in the presence of Na+, the selectivity is reversed and the receptor, instead, binds diphenyl phosphate, and not acetate, which preferentially forms a salt ion-pair in free solution. [structure: see text]     

How elementary mercury reacts in the presence of halogen radicals and/or halogen anions: a DFT investigation

Reactions of elementary mercury in the gas phase (GEM) have been investigated at the DFT level in the presence of halogen radicals and/or halogen anions. In the presence of radicals, the formation of HgX(3)* and HgX(4)* is predicted to be favourable. Moreover, in the presence of anions, the free-radical liberation is enhanced from these two species allowing the presence of halogen free radicals even without the presence of light radiation. This enhancement is associated with the formation of HgX(3)(-), which is predicted to be the most stable species. In solution, redox chemistry can occur and transform GEM in the presence of X(2). The redox potentials of the couples HgX(2)/Hg for X=Cl, Br and I were calculated to be 0.52, 0.48 and 0.04 V, respectively. This study gives new opportunities to elucidate the environmental chemistry of Hg in the polar regions. In these areas GEM has a unique and fast reactivity due to a combination of factors such as the polar sunrise, the presence of halogenated radicals, snow and ice surfaces and cold temperatures. This reactivity, known as atmospheric mercury depletion events (AMDEs), leads to the deposition of significant amounts of Hg(2+) in these regions. The reaction pathways of AMDEs are as yet unknown and the DFT approach may contribute to their elucidation and to the proposal of new mechanisms. Additionally, this study introduces hypotheses concerning the reactivity of GEM inside snowpacks.     

The hydration of MG-1 weakly basic anion exchanger in the basic and citrate forms

The hydration of MG-1 weakly basic anion exchanger in the basic and citrate forms was studied by IR spectroscopy and optical microscopy. It was found that the OH^? from of the ion exchanger contained the largest amount of water with different degrees of binding.     

Simplified column-switching technology for the determination of traces of anions in the presence of high concentrations of other anions

A binary eluent model was proposed to study the retention behavior of trace anions in the presence of high concentrations of co-eluent anions. According to this model, the effect of the matrix on the retention of trace anions can be suppressed by using a high-concentration eluent. Based on the model, a simplified 'heart-cut' column-switching technology was proposed, in which the column-switching time window can be determined directly by standard solution of the analyte. By using this technology, a detection limit of 50 microg/l was obtained for nitrate in the presence of 5,000 mg/l chloride and 250 mg/l sulfate. The effect of the matrix on the concentration efficiency of weak acid anions was studied according to the result of phosphate. The possibility of the determination of weak acid anion by the 'heart-cut' technology was also discussed. The technology has been applied for the determination of nitrate in high salinity sea water, the spike recovery is in the range of 89.2-101.3%.     

Formation of strongly basic functional groups in weakly basic anion exchanger at oxidation of hydrogen sulfide on Fe(II)-ethylenediaminetetraacetate/anion exchanger catalytic system

Changes in the nature and concentration of functional groups in the anion exchanger at oxidation of hydrogen sulfide in Fe(II)-ethylenediaminetetraacetate/anion exchanger catalytic system were studied.