No abstract

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.

o-(Pyrrolidinylmethyl)phenylboronic acid (4) and its complexes with bifunctional substrates such as catechol, alpha-hydroxyisobutyric acid, and hydrobenzoin have been studied in detail by X-ray crystallography, (11)B NMR, and computational analysis. The N-B interactions in analogous boronic acids and esters have been extensively cited in molecular recognition and chemosensing literature. The focal point of this study was to determine the factors that are pertinent to the formation of an intramolecular N-B dative bond. Our structural study predicts that the formation of an N-B dative bond, and/or solvent insertion to afford a tetrahedral boronate anion, depends on the solvent and the complexing substrate present. Specifically, from (11)B NMR studies, complexation of 4 with electron-withdrawing and/or vicinally bifunctionalized substrates promotes both the formation of N-B dative bonds and the solvation of sp(2) boron to a tetrahedral sp(3) boronate. In the solid state, the presence of an N-B dative bond in the complex of 4 and catechol (7) depends on the solvent from which it crystallizes. From chloroform, an N-B bond was observed, whereas from methanol, a methoxylated boronate was formed, where the methoxy group is hydrogen-bonded with the neighboring tertiary ammonium ion. The structural optimization of compounds 4 and 7 using density functional theory in a simulated water continuum also predicts that complexation of 4 and catechol promotes either the formation of an N-B bond or solvolysis if 1 equiv of water is present. The conclusion from this study will help in the design of future chemosensing technologies based on o-(N,N-dialkylaminomethyl)arylboronate scaffolds that are targeting physiologically important substances such as saccharides, alpha-hydroxycarboxylates, and catecholamines.

Anion transporters based on small molecules have received attention as therapeutic agents because of their potential to disrupt cellular ion homeostasis. However, a direct correlation between a change in cellular chloride anion concentration and cytotoxicity has not been established for synthetic ion carriers. Here we show that two pyridine diamide-strapped calix[4]pyrroles induce coupled chloride anion and sodium cation transport in both liposomal models and cells, and promote cell death by increasing intracellular chloride and sodium ion concentrations. Removing either ion from the extracellular media or blocking natural sodium channels with amiloride prevents this effect. Cell experiments show that the ion transporters induce the sodium chloride influx, which leads to an increased concentration of reactive oxygen species, release of cytochrome c from the mitochondria and apoptosis via caspase activation. However, they do not activate the caspase-independent apoptotic pathway associated with the apoptosis-inducing factor. Ion transporters, therefore, represent an attractive approach for regulating cellular processes that are normally controlled tightly by homeostasis.

COMMUNICATIONS ration of metal flakes. Raman and NMR spectra of solutions between -40 and 20°C indicate an equilibrium of two distinct species, probably [GaCp*]+n[GaCp*], as both series of spectra can be interpreted for the presence of hexameric and monomeric species. The Raman spectra show low-lying u, modes for (GaCp*), at 158 cm-' (Ga,) and 130 cm-' (Cp,'). A ring-tilt mode mixes with the out-of-plane mode of five CH, ligands of the Cp* ring at 331 cm-1;GaCp*monomermodesappearat318cm-' and 180cm-'(shoulder). The two normal modes for the Ga-Cp* stretch and out-of-plane vibrations are strongly mixed. The 'HNMR spectrum at -50°C shows a single, broad signal at 6 = 1.738, which sharpens and shifts to high field upon raising the temperature to 1 O T (6 =1.672); it can be attributed to a hexamer. An additional signal for a monomer species IS observed first as a shoulder (6 =1.803, -3O'C) and then as a sharp signal (6 =1.741, 10°C). From both spectroscopic studies the formation of a tetrameric cluster instead of a hexameric one cannot be ruled out [12] X-ray structure analysis: Stoe Stadi IV diffractometer, Mo,, radiation, T = 2 0 0 K , a=b=1993.3(3), c=1317.0(3)pm, r = B = 9 0 0 0 . ;'=120.00", V = 4531.9(13)x 10, pm3, space group R3 (no. 148), 2=18, pcZlrd = 1.352 g~m -~, F(OO0) = 1908, o> scan, p(MoKI) = 2.671 mm-', 28,., = 36.96", of 2240 measured reflections 751 were symmetry-independent (R,", = 0.1050); 621 reflections with JFI >4o(lFJ) were considered observed. Calculations with SHELXS, 105 parameters refined, H atoms positioned by a riding model. R1 = 0.0869, nR2 = 0.0872 (all data), final AFsynthesis maximum and minimum: +0.389 and -0.326 x lo-, epm-3. Further details of the crystal structure investigation may be obtained from the Fachinformationszentrum Karlsruhe, D-76344 Eggenstein-Leopoldshafen (Germany) on quoting the depository number CSD-406-387.[13] C . Janiak, R. Hoffmann, J Am. Chem. Soc. 1990, 1f2, 5924-5946. [14] Chemistry of Aluminium, Galhum. Indium and Thallium (Ed.: A. J. Downs), Blackie, Glasgow, 1993. 1151 Likewise, the dimensions of the monomer [InCp*] do not change significantly upon aggregation [6] By contrast, aggregation is accompanied by a slight shortening of the metal-ring distance for [AlCp'] (to give [AI,Cp*,] [4,8]), pronounced elongation of this distance is observed for [TICp*] (to give polymeric [TlCp*] 17. lo]).

Layered phosphonate salts of divalent metal ions (Mg, Mn, Zn, Ca, Cd) are precipitated by combining aqueous solutions of a phosphonic acid and a soluble metal salt. In this way compounds in the series M(03C^72n+i)'H20 (

ChemInform Abstract Sapphyrin acts as an efficient sensitizer for the in vitro photoeradication of both herpes simplex virus and HIV-1. The sapphyrin derivative (IIIa) shows the typical spectroscopic features of decaalkyl sapphyrins. An X-ray analysis of the mixed hexafluorophosphate fluoride salt of (IIIa) (space group P21/c with Z=4) shows that the 22π electron system is suitable for the binding of anions.

A new. general synthesis of the first /?-substituted tetra-and hexaalkyl terpyrroles is described. Also described are two new classes of expanded porphyrins derived from the hexaalkyl terpyrrole. The key step in the terpyrrole formation is the copper(i1)-mediated oxidative coupling of the LDA-derived enolates of a-keto pyrroles. The first new expanded porphyrin reported here, the so-called "orangarin", contains five new class of expanded porphyrins, the pyrrolic subunits and two bridging carbon "arnethyrins", are 24n-electron nonaroatoms, and is formally a 20n-electron matic macrocycles containing six pyrrole nonaromatic macrocycle.