The interaction of calixpyrrole with several chloride salts has been studied in the solid state by X-ray crystallography as well as in solution by isothermal titration calorimetry (ITC) and (1)H NMR spectroscopic titrations. The titration results in dimethylsulfoxide, acetonitrile, nitromethane, 1,2-dichloroethane, and dichloromethane, carried out using various chloride salts, specifically tetraethylammonium (TEA), tetrapropylammonium (TPA), tetrabutylammonium (TBA), tetraethylphosphonium (TEP), tetrabutylphosphonium (TBP), and tetraphenylphosphonium (TPhP), showed no dependence on method of measurement. The resulting affinity constants (K(a)), on the other hand, were found to be highly dependent on the choice of solvent with K(a)'s ranging from 10(2)-10(5) M(-1) being recorded in the test solvents used for this study. In dichloromethane, a strong dependence on the countercation was also seen, with the K(a)'s for the interaction with chloride ranging from 10(2)-10(4) M(-1). In the case of TPA, TBA, and TBP, the ITC data could not be fit to a 1:1 binding profile.

A series of easy-to-make fluorinated tripodal anion transporters containing urea and thiourea groups have been prepared and their anion transport properties studied. Vesicle anion transport assays using ion-selective electrodes show that this class of compound is capable of transporting chloride through a lipid bilayer via a variety of mechanisms, including chloride/H+ cotransport and chloride/nitrate, chloride/bicarbonate, and to a lesser extent an unusual chloride/sulfate antiport process. Calculations indicate that increasing the degree of fluorination of the tripodal transmembrane transporters increases the lipophilicity of the transporter and this is shown to be the major contributing factor in the superior transport activity of the fluorinated compounds, with a maximum transport rate achieved for clog P = 8. The most active transporter 5 contained a urea functionality appended with a 3,5-bis(trifluoromethyl)phenyl group and was able to mediate transmembrane chloride transport at receptor to lipid ratios as low as 1:250000. Proton NMR titration and single crystal X-ray diffraction revealed the ability of the tripodal receptors to bind different anions with varying affinities in a 1:1 or 2:1 stoichiometry in solution and in the solid state. We also provide evidence that the most potent anion transporters are able to induce apoptosis in human cancer cells by using a selection of in vitro viability and fluorescence assays.

Abstract:The cavity inside fullerenes provides a unique environment for the study of isolated atoms and molecules. We report encapsulation of hydrogen fluoride inside C 60 using molecular surgery to give the endohedral fullerene HF@C 60 . The key synthetic step is the closure of the open fullerene cage while minimizing escape of HF. The encapsulated HF molecule moves freely inside the cage and exhibits quantization of its translational and rotational degrees of freedom, as revealed by inelastic neutron scattering and infrared spectroscopy. The rotational and vibrational constants of the encapsulated HF molecules were found to be redshifted relative to free HF. The NMR spectra display a large 1 H-19 F Jcoupling typical of an isolated species. The dipole moment of HF@C 60 was estimated from the temperature-dependence of the dielectric constant at cryogenic temperatures and showed that the cage shields around 75% of the HF dipole.Molecular endofullerenes consist of fullerene cages encapsulating small molecules, which are free to rotate and translate inside the cage. 1 The dihydrogen and water endofullerenes H 2 @C 60 , H 2 O@C 60 , and their isotopologues, have been synthesized by the procedure known as 'molecular surgery', in which synthetic operations are used to open a hole in the fullerene allowing encapsulation of the guest, followed by a suturing technique to reform the pristine fullerene shell. [2][3][4] Recently the approach has been extended to C 70 and C 59 N. [5][6][7] The confined molecules display quantization of their coupled translational and rotational degrees of freedom, and exhibit phenomena such as nuclear spin isomerism and orthopara conversion. [8][9][10][11][12] Recently it was shown that nuclear spin conversion of the encapsulated water molecules in H 2 O@C 60 leads to a change in the dielectric constant of the material. 13 One system of great interest is HF@C 60 , in which each fullerene cage contains a single hydrogen fluoride (HF) molecule. This material offers the possibility to study the spectroscopic properties of nearisolated and freely rotating HF molecules under a wide range of conditions, free from the complications of dimerization and hydrogen bonding. Predictions of the properties of HF@C 60 have been made using classical, 14 semiempirical 15,16 and quantum chemistry techniques. [17][18][19][20] Furthermore it has been postulated that endofullerenes containing freely rotating electric dipoles could exhibit ferroelectricity, due to cooperative alignment of the interacting electric dipole moments. 21 2The first examples of open-cage endofullerenes encapsulating a hydrogen fluoride molecule have recently appeared, including HF@1. 22,23 Herein we report the successful suturing of HF@1 to give the closed-cage species HF@C 60 . We present NMR, infrared, and neutron scattering data on HF@C 60 which show that the translational and rotational motions of the HF molecule inside the cage are quantized. Interactions with the cage modify the rotational and vibrational constants of the encapsula...

The development of ion-pair receptors, with the goal of achieving a higher level of control over recognition than that obtainable from simple ion binding, has intrigued researchers in supramolecular chemistry over the past decade.[1] Many reports have appeared during this period that describe the synthesis and study of very sophisticated receptor designs incorporating a range of electron-pair donor and acceptor groups. Most, if not all, of this work has been performed in the context of creating so-called ion-pair or salt hosts that will bind cation-anion pairs in homogeneous solution or enhance their extraction or transport under interfacial conditions. Whether the ditopic architecture in such systems confers real advantages over simpler combinations of single-ion receptors remains an open question. However, the utility of ion-pair

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Easy-to-make tripodal tris-thiourea receptors based upon tris(2-aminoethyl)amine are capable of chloride/bicarbonate transport and as such represent a new class of bicarbonate transport agent.The key roles that anions play in a whole range of biological 10 processes has lead to much recent interest in the design of transporters and channels capable of carrying guests 1 such as chloride 2 or bicarbonate 3 across lipid bilayer membranes. Compounds based on tris(2-aminoethyl)amine (tren) have proven to be effective receptors for a variety of anionic 15 species. 4 Recently tren-based tris-ureas have been employed by Custelcean as agents to selectively crystallise strongly solvated tetrahedral oxo-anions such as sulfate. 5 In the anion transport arena, D.K. Smith and co-workers have shown that tren-based tris amides are capable of HCl co-transport through The results show that the thiourea derivatives are capable of both chloride/nitrate and more significanly of transporting the more hydrophilic bicarbonate anion via a chloride/bicarbonate antiport mechanism. 3 35Compounds 1-4 were synthesised by modifications of literature procedures (see ESI). 9 Proton NMR titration techniques were used to assess the stability of the receptor:anion complexes. Stability constants for the ligand-anion complexes were determined using the 40 EQNMR computer programme. 10 NMR titrations were conducted in DMSO-d 6 /0.5% water solutions with tetrabutylammonium anion salts (except for bicarbonate which was added as the tetraethylammonium salt). The results show that in all cases the receptors bind sulfate strongly with K a > bicarbonate. ¶ The X-ray crystal structure revealed that two equivalents of receptor 4 bind to a single carbonate anion in the solid state via twelve hydrogen bonds in the range 2.824(6)-3.070(7)Å with several other longer range NH … O interactions ( Figure 1a). We have previously observed that 60 anion receptors that form multiple hydrogen bond to oxoanions can perturb the pKa of the guest to the extent that the guest anion is deprotonated by free anion in solution. 11 This process may also occur here and account for the difficulty in fitting the bicarbonate NMR titration results to a simple 65 binding model. The structure itself shows the carbonate anion encapsulated between two receptors effectively shielded from the environent external to the complex. The sulfur atoms of the thiourea groups decorate the surface of the capsule-like complex (Figure 1b). 70In order to study the chloride transport properties of compounds 1-4 we prepared a series of unilamellar 1-palmitoyl-2-oleoylphophatidylcholine (POPC) vesicles loaded with sodium chloride (489 mM) and suspended them in an external NaNO 3 (489 mM) solution. A sample of receptor 1-4 75 or control compound trihexylamine (2% molar carrier to lipid) was added as a DMSO solution and the resultant Cl -efflux monitored using a chloride selective electrode. 12 After 300 s, the vesicles were lysed by addition of detergent and the final reading of the electrode was used to cali...

The encapsulation of a fluoride ion in an octaphenylsilsesquioxane cage is described by A. Bassindale, P. G. Taylor, and co-workers on the following pages. Viewed from above, the fluoride ion is shown to reside at the center of the cage, rather like the bird depicted; a tetrabutylammonium counterion is located between the phenyl groups of the cage.