Dimeric capsules formed by tetra-CMPO derivatives of (thia)calix[4]arenes.

Thiacalix[4]arene 2, calix[4]arene 3a and its tetraether fixed in the cone conformation 3b form homo- and heterodimeric capsules in apolar solvents, which are held together by a seam of NH...

Fine-tuning the dimerization of tetraureacalix[4]arenes.

Calix[4]arenes substituted by four urea residues at their wide rim form hydrogen-bonded homo- and heterodimeric capsules in apolar solvents. If urea groups are covalently connected to loops or substituted by bulky residues, the dimerization may be restricted to those pairs in which the loops do not overlap and for which the residues are small enough to pass the loops. In the present study, we describe the dimerization properties of tetraureas with one, two (adjacent or opposite), three, or four loops and those bearing (additionally) up to four residues of different size: a = tolyl, b = 3,5-di-tert-butylphenyl, c = 4-propyloxy-3,5-di-(tert-butylphenyl)phenyl, and d = 4-[tris-(4-tert-butylphenyl)methyl]phenyl.

Macrocyclic oligoureas with xanthene and diphenyl ether units.

Two cyclic oligoureas with 64- and 80-membered rings in which two sets of three or four rigid xanthene (X) units are connected via flexible diphenyl ether (D) units were synthesized by a stepwise fragment condensation. The compounds were characterized by (1)H NMR and ESI mass spectrometry. The structure of the cyclic octamer (XXXDXXXD) was additionally confirmed by single crystal X-ray analysis.

Solid-state NMR and computational studies of tetratolyl urea calix[4]arene inclusion compounds.

Solid-state guest dynamics of tetratolyl tetraurea calix[4]arene tetrapentylether dimeric capsules filled with different types of aromatic guests such as benzene-d6, fluorobenzene-d5 and 1,4-difluorobenzene were studied. Upon inclusion, all guest moieties revealed complexation-induced shifts varying from 2.8 ppm to 5.

Mass spectrometric study of oligourea macrocycles and their anion binding behavior.

Two series, one of tris-urea macrocycles and another of hexakis-urea macrocycles, are examined by (tandem) Fourier-transform ion cyclotron resonance (FTICR) mass spectrometry with respect to their fragmentation patterns and anion binding properties. All macrocycles are based on two different building blocks, one of which is a very rigid xanthene unit and the other one is a more flexible diphenyl ether. The composition and the sequence of these units thus determine their flexibility.

A self-sorting scheme based on tetra-urea calix[4]arenes.

Size and shape do matter: When dimerized in nonpolar solvents, an equimolar mixture of eleven tetra-urea calix[4]arenes with different wide-rim substituents self-sorts into only six out of 35 different homo- and heterodimers (see picture). Since the calixarene scaffold and the four urea units are the same in all cases, the self-sorting process is driven only by the cooperative action of steric requirements and stoichiometry.

Mechanically interlocked calix[4]arene dimers display reversible bond breakage under force.

The physics of nanoscopic systems is strongly governed by thermal fluctuations that produce significant deviations from the behaviour of large ensembles. Stretching experiments of single molecules offer a unique way to study fundamental theories of statistical mechanics, as recently shown for the unzipping of RNA hairpins. Here, we report a molecular design based on oligo calix[4]arene catenanes-calixarene dimers held together by 16 hydrogen bridges-in which loops within the molecules limit how far the calixarene nanocapsules can be separated.

Tetra-urea calix[4]arenes 1,3-bridged at the narrow rim.

The synthesis of special tetra-urea calix[4]arene derivatives is described. Two propyl ether groups in 1,3-position and a 5-iodo-isophthalamide bridge connecting two aminopropylether residues in 2,4-position at the narrow rim keep the molecule fixed in the cone conformation. The aryl urea residues are substituted by decyloxy groups in p-position to increase the solubility in apolar solvents, while the iodo substituent allows further functionalization.

Macrocyclic hexaureas: synthesis, conformation, and anion binding.

Five macrocylic compounds XXXXXX, XXDXXD, XDXDXD, XDDXDD, and DDDDDD with 48-membered rings, in which six xanthene and/or diphenyl ether fragments are linked through six urea (-NH-C(O)-NH-) groups, have been synthesized. In the cyclization step, a linear diamine was allowed to react with the appropriate diisocyanate by using a [5+1] (i.e.

2,2'-Dimethyl-2,2'-(m-phenyl-ene-dimethyl-ene)propane-dinitrile.

The title compound, C(16)H(14)N(4), features an aromatic ring with two 2,2'-dicyano-propyl residues in positions 1 and 3, which are located above and below the ring plane. The two residues differ in their conformation with respect to the aromatic ring: whereas one of the C(meth-yl)-C-C(methyl-ene)-C(aromatic) torsion angles is gauche [68.93 (12)°], the other one is fully staggered [177.

Cyclic tetraureas with variable flexibility--synthesis, crystal structures and properties.

Macrocyclic molecules containing several amide or urea functions may serve as anion receptors. We describe the synthesis of 32-membered macrocycles, in which four rigid xanthene units (X) and/or diphenyl ether units (D) as flexible analogues are linked via urea groups. All six possible combinations of these units (XXXX, XXXD, XXDD, XDXD, XDDD and DDDD) were synthesized and two examples were characterised by single-crystal X-ray analyses (DDDD and two structures for XXXD).

Molecules with new topologies derived from hydrogen-bonded dimers of tetraurea calix[4]arenes.

Tetraurea calix[4]arenes 2 have been synthesized in which two adjacent aryl urea residues are connected to a loop by an aliphatic chain -O-(CH(2))(n)-O-. The remaining urea residues have a bulky 3,5-di-tert-butylphenyl residue and an omega-alkenyloxyphenyl residue. Since this bulky residue cannot pass through the loop, only one homodimer (22) is formed in apolar solvents, for steric reasons, in which the two alkenyl residues penetrate the two macrocyclic loops.

Self-assembled dendrimers with uniform structure.

Calix[4]arenes substituted at their wide rim by four aryl urea residues (1) form hydrogen-bonded dimers in apolar solvents. Replacement of one urea residue by an acetamido moiety leads to calix[4]arene derivatives (5) which form hydrogen-bonded tetramers under the same conditions. Both self-assembly processes occur independently.

Lanthanide complexation with CMPO and CMPO-calix[4]arenes in solution: spectrophotometric and electrospray mass spectrometric approaches.

The binding of lanthanide(III) cations with organophosphorous ligands like CMPO and related calix[4]arene-based derivatives have been investigated using two experimental methods. The stability constants of the lanthanum, europium and ytterbium complexes were first determined in methanol by UV absorption spectrophotometry in the presence of nitrate or chloride anions. The results showed that the stoichiometry and the stability of the complexes formed depend on the position of the CMPO moieties either on the wide or the narrow rim of the calixarene scaffold, the nature of the medium, the conformational mobility of the ligands.

Cyclic triureas--synthesis, crystal structures and properties.

The synthesis of 24-membered macrocycles is described, in which rigid xanthene units (X) and/or diphenyl ether units (D) as flexible analogues are linked via urea groups. All four possible combinations (XXX, XXD, XDD, DDD) have been obtained with yields of 40-72% for the cyclisation step. In two cases, the respective cyclic hexamers (XXDXXD, XXXXXX) were also isolated.

Guest exchange in dimeric capsules formed by tetra-urea calix[4]arenes.

Ten tetra-urea calix[4]arene derivatives with different ether residues (methyl, pentyl, benzyl, all combinations of methyl and pentyl, 1,3-dibenzyl-2,4-dipentyl), including also the tetrahydroxy compound and the 1,3-dipentyl ether, were synthesised. Their urea groups were substituted with a lipophilic residue to ensure sufficient solubility in cyclohexane. Thus, kinetics for the exchange of the included guest (benzene) against the solvent (cyclohexane) could be followed by 1H NMR spectroscopy.

Stepwise synthesis and selective dimerisation of bis- and trisloop tetra-urea calix[4]arenes.

Tetra-urea calix[4]arenes substituted with four mono- or bisalkenyl residues have been converted into bis- or tetraloop compounds by intramolecular olefin metathesis, with use of a tetratosylurea calix[4]arene as template. The same strategy has now been used to synthesise trisloop compounds and bisloop compounds with adjacent loops, completing the series of the loop-containing tetra-urea derivatives. A tetra-urea calix[4]arene of the AABB type, where A stands for a bisalkenyl- and B for a monoalkenyl-substituted urea unit, was used as precursor for the three loops.

Self-sorting dimerization of tetraurea calix[4]arenes.

Calix[4]arenes substituted by four urea functions are self-complementary molecules that spontaneously combine in apolar solvents in the presence of an ammonium salt to form dimeric capsules held together by a belt of hydrogen bonds. In the presence of tetraethylammonium salts, the Et4N+ cation is included as a guest. The sorting between dimeric capsules formed in a mixture of calix[4]arenes directly depends on the steric crowding of the substituents grafted on the urea groups whether aromatic derivatives or aliphatic chains linking urea functions in mono-, di-, or tetraloop structures.

Reasons for the exclusive formation of heterodimeric capsules between tetra-tolyl and tetra-tosylurea calix[4]arenes.

The selective heterodimerization of tetra-tolyl () and tetra-tosylurea () calixarenes, serendipitously found by Rebek et al. (R. K.

Calix[4]arene-based bis[2]catenanes: synthesis and chiral resolution.

The exclusive formation of hydrogen-bonded dimers between tetraaryl and tetratosylurea calix[4]arenes has been used to prepare a series of ten "bisloop" tetraurea calix[4]arenes 3, in which adjacent phenylurea groups are covalently linked through alpha,omega-dioxyalkane chains. This dimerization with tetratosylurea 2 as template preorganizes the alkenyl residues of tetra(m-alkenyloxyphenyl) ureas 1 and enables their selective connection in high yield (up to 95 %) by olefin metathesis followed by hydrogenation. The "bisloop" calixarenes 3 also exclusively form heterodimers with 1.

Hydrogen-bonded dimers of tetra-urea calix[4]arenes stable in THF.

[structure: see text]. Whereas tetra-urea derivatives of tetra-alkoxy calix[4]arenes 1 exist as single molecules in THF, dimeric hydrogen-bonded capsules are exclusively found for the corresponding calix[4]arene derivatives 3 and 2 with two or four free hydroxyl groups. Comparison with the rigidified tetra-urea 5 suggests that this increased stability of the dimers is due to the stabilization of their four-fold symmetry by intramolecular hydrogen bonds between the phenolic hydroxyl groups.

First protection of a wide-rim tetraamino calix[4]arene in opposite positions.

The importance of tetraamino calix[4]arenes as starting materials is distinctly increased by the first versatile protective group for opposite amino functions. Reaction with trityl chloride leads to the 1,3-dialkylated derivative easily isolated in 34% yield; after a first acylation of the remaining amino groups, the trityl residues can be removed by TFA to introduce a second acyl group. [reaction: see text]

Guest exchange in dimeric capsules of a tetraurea calix[4]arene in the solid state.

A solid powder of hydrogen bonded dimers of a tetraurea calix[4]arene is able to exchange the encapsulated guest in contact with the vapor of a second guest. The molecules of a guest-free powder obtained from a polar solvent cannot rearrange in the solid phase to form new guest-filled capsules under these conditions.

Tetraurea calix[4]arenes with sulfur functions: synthesis, dimerization to capsules, and self-assembly on gold.

Various calix[4]arene derivatives, fixed in the cone conformation by decylether groups and functionalized at their wide rim by urea residues, were synthesized. In two compounds (,) sulfur functions were attached to the urea groups via different spacers in order to allow binding to metal surfaces. While they exist as single molecules in polar solvents, tetraurea calix[4]arenes of this type () combine to form dimeric capsules in aprotic, apolar solvents.