Selective total encapsulation of the sulfate anion by neutral nano-jars

Nano-sized toroidal copper(II)-hydroxide/pyrazolate assemblies, lined by H-bond donors on the inside and hydrophobic on the outside, selectively extract sulfate from mixtures with nitrate or perchlorate. Tetrabutylammonium "lids" seal the "nano-jars" and render the encapsulated sulfate anion completely buried and inaccessible, so that it is not precipitated by Ba(2+) ions.     

Anion-aromatic bonding: a case for anion recognition by pi-acidic rings

The basis for unprecedented noncovalent bonding between anions and the aryl centroid of electron-deficient aromatic rings has been demonstrated by an ab initio study of the interaction between 1,3,5-triazine and the fluoride, chloride, and azide ion at the MP2 level of theory. Minima are also located corresponding to C[bond]H...X(-) hydrogen bonding, reactive complexes for nucleophilic attack on the triazine ring, and pi-stacking interactions (with azide). Trifluoro-1,3,5-triazine also participates in aryl centroid complexation and forms nucleophilic reactive complexes with anions. This novel mode of bonding suggests the development of new cyclophane-type receptors for the recognition of anions.     

Conformational effects induced by guest encapsulation in an enantiopure water-soluble cryptophane

A new water-soluble cryptophane 1 derivative (penta-hydroxyl cryptophane-A) has been synthesized from cryptophanol-A and the chiroptical properties of its two enantiomers MM-1 and PP-1 have been studied by polarimetry, electronic circular dichroism (ECD), and vibrational circular dichroism (VCD). Cryptophane 1 shows specific circular dichroism responses upon complexation that depend on the size of the guest and on the nature of the counterion (Li(+), Na(+), K(+), Cs(+)) present in the solution. In LiOH and NaOH solutions, chiroptical changes induced by the encapsulation of guests and by the presence of cations in the vicinity of hosts can be interpreted from molecular dynamics (MD) and ab initio calculations by subtle conformational changes of the bridges. In KOH solution, the exchange dynamics is dependent on the size of the guest molecules, whereas in CsOH solution no encapsulation effect is observed whatever the size of the guest molecule. This last behavior comes from the fact that host 1 exhibits a very high affinity for cesium cations.     

Selective guest encapsulation by a cobalt-assembled cage molecule

Metal-assembled resorcinarene-based cages enclose space and entrap organic molecules from water. Addition of cobalt(II) ions to a neutral, aqueous solution of a resorcinarene that has iminodiacetic acids attached to its upper rim results in the formation of cages. These cages not only entrap organic molecules, but they do so in a selective manner. Guests with optimum size, shape, and polarity are preferentially entrapped. For example, selection of p-xylene is twenty thousand times more favorable than that of m-xylene. The enthalpy of resorcinarene deprotonation and cage formation was calculated by performing calorimetry studies and ranged from -305 to -348 kJ mol(-1). The change in enthalpy of guest encapsulation varied by as much as 43 kJ mol(-1). The differences in change in free energy of guest encapsulation varied by -16 kJ mol(-1). The changes in enthalpy and free energy of guest encapsulation were used to calculate the changes in entropy, which ranged from -97 to +37 J mol(-1) K(-1). An enthalpy-entropy compensation of guest encapsulation was observed.     

Acceleration of amide bond rotation by encapsulation in the hydrophobic interior of a water-soluble supramolecular assembly

The hydrophobic interior cavity of a self-assembled supramolecular assembly exploits the hydrophobic effect for the encapsulation of tertiary amides. Variable-temperature (1)H NMR experiments reveal that the free energy barrier for rotation around the C-N amide bond is lowered by up to 3.6 kcal/mol upon encapsulation. The hydrophobic cavity of the assembly is able to stabilize the less polar transition state of the amide rotation process. Carbon-13 labeling studies showed that the (13)C NMR chemical shift of the carbonyl resonance increases with temperature for the encapsulated amides, which suggests that the assembly is able to favor a twisted form of the amide.     

Selective aldehyde reductions in neutral water catalysed by encapsulation in a supramolecular cage

The enhancement of reactivity inside supramolecular coordination cages has many analogies to the mode of action of enzymes, and continues to inspire the design of new catalysts for a range of reactions. However, despite being a near-ubiquitous class of reactions in organic chemistry, enhancement of the reduction of carbonyls to their corresponding alcohols remains very much underexplored in supramolecular coordination cages. Herein, we show that encapsulation of small aromatic aldehydes inside a supramolecular coordination cage allows the reduction of these aldehydes with the mild reducing agent sodium cyanoborohydride to proceed with high selectivity (ketones and esters are not reduced) and in good yields. In the absence of the cage, low pH conditions are essential for any appreciable conversion of the aldehydes to the alcohols. In contrast, the specific microenvironment inside the cage allows this reaction to proceed in bulk solution that is pH-neutral, or even basic. We propose that the cage acts to stabilise the protonated oxocarbenium ion reaction intermediates (enhancing aldehyde reactivity) whilst simultaneously favouring the encapsulation and reduction of smaller aldehydes (which fit more easily inside the cage). Such dual action (enhancement of reactivity and size-selectivity) is reminiscent of the mode of operation of natural enzymes and highlights the tremendous promise of cage architectures as selective catalysts.

Herein, we use a supramolecular coordination cage as a catalyst for the reduction of aldehydes to the corresponding alcohols using a weak hydride donor in neutral water, with a mode of action reminiscent of natural enzymes.     

Spherical versus linear anion encapsulation in the cavity of a protonated azacryptand

Grams scale synthesis of an octaaminocryptand L(2) with high yield is obtained in one-pot by low-temperature [2 + 3] condensation of tris(2-aminoethyl)amine with isophthalaldehyde, followed by sodium borohydride reduction. Structural aspects of octaaminocryptand L(2) x MeOH, binding of iodide (spherical) and bichloride (linear) in L(2), (1,4,11,14,17,24,29,36-octa-azapentacyclo-[12.12.12..2(6,9).2(19,22).2(31,34)]-tetratetraconta 6(43),7,9(44),19(41),20,22(42),31(39),32,34(40)-nonane, N(CH2CH2NHCH2-m-xylyl-CH2NHCH2CH2)3N), in the hexaprotonated and tetraprotonated states, respectively, are examined. Crystallographic results show binding of single iodide [H6L(2)I](I)5 x 4 H2O, (2), in a hexaprotonated cryptand L(2). Monotopic recognition of iodide is observed via (N-H)(+)...iodide interactions. The tetraprotonation of L(2) by hydrochloric acid showed the formation and encapsulation of a bichloride inside the cavity, which is examined from the single-crystal X-ray study. Encapsulation and binding of a proton-bridged linear bichloride inside the cavity of tetraprotonated L(2), [H4L(2)(ClHCl)](Cl)3 x nH2O (3), via (N-H)(+)...chloride interactions is observed in the structural investigation. This study shows that degree of protonation and its distribution in the receptor architecture play an important role in guest encapsulation. Further, it represents the first example of an encapsulated bichloride inside the cavity of an organic host.     

Concurrent anion...pi interactions between a perchlorate ion and two pi-acidic aromatic rings, namely pentafluorophenol and 1,3,5-triazine

The rational design of a ligand containing two electron-poor pi-rings, i.e. a triazine and a pentafluorophenoxy groups, has allowed the preparation of a copper complex where both the anticipated anion...pi interactions are present.     

Selective anion binding by a cofacial binuclear zinc complex of a Schiff-base pyrrole macrocycle

The synthesis of the new cofacial binuclear zinc complex [Zn(2)(L)] of a Schiff-base pyrrole macrocycle is reported. It was discovered that the binuclear microenvironment between the two metals of [Zn(2)(L)] is suited for the encapsulation of anions, leading to the formation of [K(THF)(6)][Zn(2)(μ-Cl)(L)]·2THF and [Bu(n)(4)N][Zn(2)(μ-OH)(L)] which were characterized by X-ray crystallography. Unusually obtuse Zn-X-Zn angles (X = Cl: 150.54(9)° and OH: 157.4(3)°) illustrate the weak character of these interactions and the importance of the cleft preorganization to stabilize the host. In the absence of added anion, aggregation of [Zn(2)(L)] was inferred and investigated by successive dilutions and by the addition of coordinating solvents to [Zn(2)(L)] solutions using NMR spectroscopy as well as isothermal microcalorimetry (ITC). On anion addition, evidence for deaggregation of [Zn(2)(L)], combined with the formation of the 1:1 host-guest complex, was observed by NMR spectroscopy and ITC titrations. Furthermore, [Zn(2)(L)] binds to Cl(-) selectively in THF as deduced from the ITC analyses, while other halides induce only deaggregation. These conclusions were reinforced by density functional theory (DFT) calculations, which indicated that the binding energies of OH(-) and Cl(-) were significantly greater than for the other halides.     

Selective removal of nitrate by using a novel macroporous acrylic anion exchange resin

An anion exchange resin NDP-5 has been prepared successfully and applied on the selective removal of nitrate from SO₄^2-/ NO₃^- binary co-existence system.The composition and morphology of NDP-5 were confirmed by FT-IR and SEM.The NDP-5 resin exhibits the completely different behavior on the adsorption capacity,adsorption kinetic and the effect of the completing anion in the absence or presence of sulfate,compared to D213.And,the resultants of kinetic are well fitted by the pseudo-first-order and pseudo-second-order models.These results are very important to develop novel resins with great features.     

Extended calix[4]arene analogues by two P-CuI-P bridges and anion encapsulation

Two novel extended calix[4]arene analogues by two P-Cu(I)-P bridges have been synthesized. The molecular structures and anion encapsulation ability for ClO4- and BF4- have been studied by X-ray analysis.     

Selective syntheses of metalated pyridines from two different unsymmetrical acetylenes, a nitrile, and a titanium(II) alkoxide

Cyclotrimerization of two different, unsymmetrical acetylenes and p-toluenesulfonylnitrile with a divalent titanium alkoxide reagent, Ti(O-i-Pr)4/2 i-PrMgCl, yielded single pyridyltitanium compounds in a highly selective manner. These metalated pyridines were confirmed by deuteriolysis to give the corresponding deuterated pyridines and underwent iodinolysis and copper-catalyzed alkylation to demonstrate their synthetic utility. Alternatively, a different type of cyclotrimerization of an alkynamide, terminal acetylenes, and alpha-alkoxynitriles mediated by the same titanium(II) alkoxide again proceeded in a highly selective manner to give single pyridines having a titanated side chain.     

Selective anion recognition by retarding the cooperative polarization effect of amide linkages

A novel benzthiazole-based fluorescent receptor was synthesized, and its anion recognition properties were compared with those of similarly designed benzimidazole-based receptors. The selectivity of this receptor for the recognition of dihydrogen phosphate is enhanced by employing hydrogen bonding, in which cooperative polarization effect to the carbonyl group of amide linkages is lacking.     

Selective anion sensing by a ruthenium(II)-bipyridyl-functionalized tripodal tris(urea) receptor

A tripodal tris(urea) ligand with 2,2'-bipyridyl (bpy) substituents (L) has been designed and synthesized, which coordinates with three equivalents of Ru(bpy)(2)Cl(2)·2H(2)O, followed by treatment with NH(4)PF(6), to afford the anion receptor [(bpy)(6)Ru(3)L](PF(6))(6) (1). The anion-binding behavior of the ligand L and the Ru(II)-bpy functionalized receptor 1 toward different anions was investigated by (1)H NMR (for L and 1), fluorescence, and UV-vis spectroscopy (for 1). Both compounds showed selective recognition of SO(4)(2-) or H(2)PO(4)(-) ions in the 1:1 binding mode in the NMR studies. The Ru(II) complex 1 displayed the metal-to-ligand charge transfer emission at 600 nm, which was quenched on addition of the sulfate and dihydrogen phosphate ions. Quantitative fluorescence titration experiments were carried out and the stability constants (log K) of the complex 1 with SO(4)(2-) and H(2)PO(4)(-) ions were obtained to be 4.73 and 4.69 M(-1) (1:1 binding mode), respectively.     

Understanding the extraordinary deshielding of 129Xe in a permetallated cryptophane by relativistic DFT

Shift change: Relativistic ZORA DFT calculations highlight the various factors (solvent effect, spin-orbit coupling, number and type of metal centres) responsible of the extraordinarily large deshielding of xenon encapsulated in a metallated cryptophane (see figure).     

Dihydrogen addition in a dinuclear rare-earth metal hydride complex supported by a metalated TREN ligand

The dinuclear lutetium dihydride dication supported by metalated tripodal ligands undergoes facile hydrogenolysis with H(2) to form a trihydride dication. Molecular orbital analysis shows that the LUMO is a bonding Lu···Lu orbital that is poised to activate dihydrogen.     

From encapsulation to polypseudorotaxane: unusual anion networks driven by predesigned metal bis(terpyridine) complex cations

Solvothermal reactions of CuSCN, metal (Mn2+, Fe2+, Co2+, Ni2+, Cu2+) sulfate, and terpyridine (2,2':6',2' '-terpyridine or 4'-p-tolyl-2,2':6',2' '-terpyridine) in the presence of triphenylphosphine yielded a series of hybrid coordination compounds, in which in situ formed metal bis(terpyridine) complex cations are encapsulated by a 3D anionic network or entangled by 2D heartlike networks, forming encapsulation or polypseudorotaxane supramolecules. The complex cations play a role as template to direct the fabrication of the structures.     

Selective attachment and release of a chemotherapeutic agent from the interior of a protein cage architecture

The antitumor agent doxorubicin was covalently bound and selectively released in a pH dependent manner from the interior surface of a genetically modified small heat shock protein (Hsp) cage.