Synthesis and Structural Properties of 5,17-Bis(N-methyl-N-arylaminocarbonyl)calix[4]arenes. Directing the Substituents toward the Cavity by Use of the Cis-Generating Property of the N-Methylaminocarbonyl Linker

Synthesis and crystal structures of 5,17-di-bromo-26,28-dihy-droxy-25,27-dipropynyloxycalix[4]arene, 5,17-di-bromo-26,28-dipropoxy-25,27-dipropynyloxycalix[4]arene and 25,27-bis-(2-azido-eth-oxy)-5,17-di-bromo-26,28-di-hydroxy-calix[4]arene

The calixarenes, 5,17-di-bromo-26,28-dihy-droxy-25,27-dipropynyloxycalix[4]arene (C34H26Br2O4, 1), 5,17-di-bromo-26,28-dipropoxy-25,27-dipropynyloxycalix[4]arene (C40H38Br2O4, 2) and 25,27-bis-(2-azido-eth-oxy)-5,17-di-bromo-26,28-di-hydroxy-calix[4]arene (C32H28Br2N6O4, 3) possess a pinched cone mol-ecular shape for 1 and 3, and a 1,3-alternate shape for compound 2. In calixarenes 1 and 3, the cone conformations are additionally stabilized by intra-molecular O-H⋯O hydrogen bonds, while in calixarene 2 intra-molecular Br⋯Br inter-actions consolidate the 1,3-alternate mol-ecular conformation. The dense crystal packing of the cone dialkyne 1 is a consequence of π-π, C-H⋯π and C-H⋯O inter-actions. In the crystal of the diazide 3, there are large channels extending parallel to the c axis, which are filled by highly disordered CH2Cl2 solvent mol-ecules. Their contribution to the intensity data was removed by the SQUEEZE procedure that showed an accessible void volume of 585 Å3 where there is room for 4.5 CH2Cl2 solvent mol-ecules per unit cell. Rigid mol-ecules of the 1,3-alternate calixarene 2 form a columnar head-to-tail packing parallel to [010] via van der Waals inter-actions, and the resulting columns are held together by weak C-H⋯π contacts.

Time Programmable Locking/Unlocking of the Calix[4]arene Scaffold by Means of Chemical Fuels

In this work, we report that 2-cyano-2-phenylpropanoic acid and its p-Cl, p-CH₃ and p-OCH₃ derivatives can be used as chemical fuels to control the geometry of the calix[4]arene scaffold in its cone conformation. It is shown that, under the action of the fuel, the cone calix[4]arene platform assumes a "locked" shape with two opposite aromatic rings strongly convergent and the other two strongly divergent ("pinched cone" conformation). Only when the fuel is exhausted, the cone calix[4]arene scaffold returns to its resting, "unlocked" shape. Remarkably, the duration of the "locked" state can be controlled at will by varying the fuel structure or amount. A kinetic study of the process shows that the consume of the fuel is catalyzed by the "unlocked" calixarene that behaves as an autocatalyst for its own production. A mechanism is proposed for the reaction of fuel consumption.

A calixarene-based fluorescent ratiometric temperature probe

We report the first macrocycle-based ratiometric molecular thermometer exploiting the conformational thermosensitivity of a calixarene functionalized with two different fluorophores. Thanks to the dependence on temperature of the efficiency of excitation energy transfer between the organic fluorophores, the thermometer works over a 60 °C-wide temperature range with a sensitivity of 4% °C^-1.

Ring-opening polymerization of coordination complexes: silver(i) complexes with bis(amidopyridine) ligands derived from thiophene

The thiophene-based bis(N-methylamido-pyridine) ligand SC4H2-2,5-{C(=O)N(Me)-4-C5H4N}2 reacts with silver(I) salts AgX to give 1 : 1 complexes, which are characterized in the solid state as the macrocyclic complexes [Ag(2){SC4H2-2,5-(CONMe-4-C5H4N)2}2][X]2, which have the cis conformation of the C(=O)N(Me) group, when X = CF3CO2, NO3, or CF3SO3 but as the polymeric complex [Ag(n){SC4H2-2,5-(CONMe-4-C5H4N)2}n][X]n, with the unusual trans conformation of the C(=O)N(Me) group, when X = PF6. The bis(amido-pyridine) ligand SC4H2-2,5-{C(=O)NHCH2-3-C5H4N}2 reacts with silver(I) trifluoroacetate to give the polymeric complex [Ag(n){SC4H2-2,5-(CONHCH2-3-C5H4N)2}n][X]n, X = CF3CO2. The macrocyclic complexes contain transannular argentophilic secondary bonds. The polymers self assemble into sheet structures through interchain C=O...Ag and S...Ag bonds in [Ag(n){SC4H2-2,5-(CONMe-4-C5H4N)2}n][PF6]n and through Ag...Ag, C=O...Ag and Ag...O(trifluoroacetate)...HN secondary bonds in [Ag(n){SC4H2-2,5-(CONHCH2-3-C5H4N)2}n][CF3CO2]n.

Disilver(I) macrocycles: variation of cavity size with anion binding

Reaction of the N-methylated bis(amidopyridine) ligand, LL = C6H4(1,3-CONMe-4-C5H4N)2, with the silver salts AgNO3, AgO2CCF3, AgO3SCF3, AgBF4, and AgPF6 gave the corresponding cationic disilver(I) macrocycles [Ag2(micro-LL)2]X2, 2a-e. The transannular silver...silver distance in the macrocycles varies greatly from 2.99 to 7.03 A, and these differences arise through a combination of different modes ofanion binding and from the presence or absence of silver...silver secondary bonding. In all complexes, the ligand adopts a conformation in which the methyl group and oxygen atom of the MeNCO units are mutually cis, but the overall macrocycle can exist in either boat (X = PF6 only) or chair conformation. Short transannular silver...silver distances are found in complexes 2b,c, in which the anions CF3CO2- and CF3SO3- bind above and below the macrocycle, but longer silver...silver distances are found for 2a,d,e, in which the anions are present, at least in part, inside the disilver macrocycle. Easy anion exchange occurs in solution, and studies using ESI-MS indicate that the anion binding to form [Ag2X(micro-LL)2]+ follows the sequence X = CF3CO2- > NO3- > CF3SO3-.

A prototype calix[4]arene-based receptor for carbohydrate recognition containing peptide and phosphate binding groups

A novel class of macrobicyclic receptors for carbohydrate recognition based on upper rim, peptide-bridged calix[4]arenes has been designed and synthesized. Receptor 12, in which a charged phosphate group cooperates with peptide hydrogen-bonding donor and acceptor groups in the binding process, is the most efficient and selective in the complexation of simple carbohydrate derivatives. The selectivity observed is toward beta-glucoside 13a, which is better bound (DeltaG degrees = 19.6 kJ mol(-)(1)) compared to the corresponding alpha anomer 13b (DeltaG degrees = 17.0 kJ mol(-)(1)) and to the beta-galactoside 13c (DeltaG degrees = 17.7 kJ mol(-)(1)) in CDCl(3). A substantial drop in the stability constant is observed by esterification of the phosphate group in the host 12 or by alkylation of the OH groups in the 2 and 3 positions in the beta-glucoside and beta-galactoside derivatives. On the basis of a careful analysis of the (1)H NMR data available, a binding mode of the beta-octylglucoside 13a to receptor 12 is proposed.

Synthesis and structural characterization of new stiff rod oligomeric domains by X-ray crystallography and NMR

The monomers N,N'-dibenzylbenzene-1,4-diamine (1), N,N'-dibenzylnaphthalene-1,5-diamine (2), and N,N'-dibenzylanthracene-1,9-diamine (3) were reacted with phosgene in the presence of a base to produce the corresponding N,N'-dibenzyl-1,4-bis(chlorocarbonylamino)benzene (4), N,N'-dibenzyl-1,5-bis(chlorocarbonylamino)naphthalene (5), and N,N'-dibenzyl-9,10-bis(chlorocarbonylamino)anthracene (6). These monomers were used to create zigzag type stacks, in a stepwise fashion, of trimers and 9-mers of either 1,4-diureidobenzenes ((Phe)K(3) and (Phe)K(9)) or 1,5-diureidonaphthalenes ((Nap)K(3) and (Nap)K(9)). A byproduct in the formation of (Phe)K(9) was a cyclic hexamer (Phe)K(6). NMR gave evidence of the structure in solution while X-ray crystallographic information was obtained for 5, 6, (Nap)K(3), and the cyclic (Phe)K(6).

Glycoside-clustering round calixarenes toward the development of multivalent ligands. Synthesis and conformational analysis of Calix[4]arene O- and C-glycoconjugates

Bis- and tetra-O- and C-glycosyl calixarenes (calixsugars) have been prepared by tethering carbohydrate moieties to a tetrapropoxycalix[4]arene scaffold through alkyl chains. Two methodologies have been employed. One consisted of the stereoselective multiple glycosylation of upper rim calix[4]arene polyols leading to calix-O-glycosides; the other involved a multiple Wittig olefination of upper rim calix[4]arene-derived polyaldehydes by the use of sugar phosphoranes and reduction of the alkene double bonds affording calix-C-glycosides. The NMR spectra and NOE experiments of bis-glycosylated products indicate that compounds bearing sugar-protected residues exist preferentially in solution in a flattened cone arrangement (far conformation) whereas deprotected derivatives adopt a close conformation. Calculations by molecular mechanics of the latter compounds point to a close conformation as well in gas phase.

Effect of competing alkali metal cations on neutral Host's anion binding ability

Anion binding by neutral hosts in organic solvents can be inhibited by the presence of alkali metal cations. The binding inhibition is due to salt ion-pairing which increases in the order Cs(+) < K(+) < Na(+). The binding inhibition can be reversed by using heteroditopic hosts that simultaneously bind both the metal cation and the anion. The largest cation-induced enhancements are observed with the less basic anions.