Hydrogen-bonded dimers of tetraurea calix[4]arenes: unambiguous proof by single crystal X-ray analysis

Mogck, O.; Paulus, E. F.; Böhmer, Volker; Thondorf, Iris; Vogt, Walter

doi:10.1039/cc9960002533

Cited by 127 publications

(106 citation statements)

References 11 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The encapsulated benzene gives rise to the sharp singlet at 4.2 ppm, the integration of which indicates that only one benzene molecule is accommodated by the interior of the capsule (spectrum not shown). This behavior is as expected from earlier studies in solution, but encapsulation of benzene has even been observed in the solid state (16).…”

Section: Resultssupporting

confidence: 76%

Polycaps: Reversibly formed polymeric capsules

Castellano

Rudkevich²,

Rebek³

1997

Proc. Natl. Acad. Sci. U.S.A.

205

142

View full text Add to dashboard Cite

Described are assemblies consisting of polymeric capsules, ''polycaps,'' formed from two calix[4]arene tetraureas covalently connected at their lower rims. In these structures self-assembly leads to reversibly formed capsule sites along a chain, reminiscent of beads on a string. Their dynamic behavior is characterized by 1 H NMR spectroscopy through encapsulation of guest species, reversible polymerization, and the formation of sharply defined hybrid capsules.Molecule-within-molecule complexes represent an unusual arrangement of matter (1) with promising applications in mechanistic and physical organic chemistry (2, 3). More complicated synthetic systems that begin to resemble complexes found in biology are molecules that assemble through weak intermolecular forces. Specifically, cup-shaped molecules with hydrogen bonding sites on their larger rims have interesting capacities for molecular assembly. When the hydrogen bonding sites are self-complementary, the molecules dimerize to form capsules. These assemblies reversibly encapsulate smaller guest species of suitable size and shape, but show dynamic qualities (4): the capsules form and dissipate at rates that vary from microseconds to hours-long enough for chemical reactions to occur within them (5). Several such systems derived from resorcinarenes and calixarenes have been extensively characterized (6-8).In the calix[4]arenes ( Fig. 1) the cup-like shape provides half of each capsule, while the ureas on its larger (upper) rim provide the hydrogen bonds that permit the molecules to assemble. The alkyl (R 1 ) groups on the phenolic oxygens of the lower rim maintain (on average) the cup-like conformation (9), and the R 2 groups on the distal urea nitrogen (N ␤ ) provide for reasonable solubility in organic media. Their ready synthetic accessibility has raised the possibility (8, 10) that covalent connection at their lower rims could lead to polymeric capsules, or polycaps, on assembly (Fig. 2). MATERIALS AND METHODSGeneral. All chemicals were used without further purification unless otherwise specified. p-Heptylphenyl isocyanate was prepared from the corresponding acid based on a literature procedure (11). 5,11,17,26,27,arene (1, R 1 ϭ n-propyl, R 2 ϭ n-octyl) was prepared from the known tetraamine (12) by treatment with octyl isocyanate in a manner similar to 6 and 7. The 5,11,17,26,arene 2 was prepared according to the literature (13). Proton ( 1 H) NMR spectra were recorded on Bruker (Billerica, MA) DRX-600 (600 MHz) or AM-300 (300 MHz) spectrometers. Carbon ( 13 C) spectra were recorded on a Bruker DRX-600 (151 MHz) spectrometer. IR spectra were recorded on a Perkin-Elmer Paragon 1000PC FT-IR spectrometer. The fast atom bombardment (FAB) positive ion mass spectra were obtained on a VG ZAB-VSE double-focusing high resolution mass spectrometer equipped with a cesium ion gun. Matrix-assisted laser desorption ionization mass spectrometry experiments were performed on a PerSeptive Biosystems (Cambridge, MA) Voyager-Elite mass spectrometer with delayed extra...

show abstract

Section: Resultssupporting

confidence: 76%

Polycaps: Reversibly formed polymeric capsules

Castellano

Rudkevich²,

Rebek³

1997

Proc. Natl. Acad. Sci. U.S.A.

205

142

View full text Add to dashboard Cite

show abstract

“…The volume calculated for the cavity is 190 3 , a value supported by a recent crystal structure. [23] An excellent guest for this cavity was cubane (V 103 3 , PC 0.54). The calixarene capsule also binds smaller guests such as 1,4-difluorobenzene (PC 0.44) and pyrazine (PC 0.38).…”

Section: Methodsmentioning

confidence: 99%

The 55 % Solution: A Formula for Molecular Recognition in the Liquid State

1998

View full text Add to dashboard Cite

Evidence is presented that molecular recognition through encapsulation processes is largely determined by the volumes of the guest and host. Binding of molecules of suitable dimensions in the internal cavity of a molecular receptor in solution can be expected when the packing coefficient, the ratio of the guest volume to the host volume, is in the range of 0.55 AE 0.09. Larger packing coefficients, up to 0.70, can be reached if the complex is stabilized by strong intermolecular forces such as hydrogen bonds. These considerations also apply to situations in which more than one molecule is encapsulated. Organic liquids are generally characterized by the same packing factors as encapsulation complexes, and it is proposed that the short-range structure of liquids and the complexes resulting from encapsulation are two aspects of the same phenomenon. Similar volume considerations are expected to apply to the binding of substrates in biological receptors.

show abstract

“…3,4 In our case, a mixture of equimolecular amounts of the dimers 1·1 and 2·2 in CDCl 3 did not show the formation of heterodimers. However, the 1 H NMR spectrum of an equimolecular mixture of 2·2 and 3·3 revealed the appearance of signals attributable to the heterodimer 2·3, besides those of homodimers 2·2 and 3·3 and monomers 2 and 3.…”

mentioning

confidence: 90%

“…1 Urea or thiourea functionalities are excellent candidates to construct molecules that self-assemble by hydrogen-bonding not only in the solid state but are able to persist in solution. 2 Rebek 3 and Böhmer 4 have independently established that calix [4]arenes containing four urea functions at the upper rim form dimers by interdigitation of the all eight ureas in a head-to-tail directional array of 16 hydrogen bonds. Mendoza and coworkers have described dimeric capsules derived from tris(ureido)calix [6]arenes.…”

mentioning

confidence: 99%

Dimerization of tris(o-ureidobenzyl)amines: a novel class of aggregates

et al. 2001

View full text Add to dashboard Cite

Dimeric aggregates are formed by the assembly of two tripodal moieties which are held together, both in solution and in the solid state, by a belt of 6 hydrogen-bonded urea functions.When two or more identical subunits are geometrically and functionally complementary, they may self-assemble to form a super molecule. 1 Urea or thiourea functionalities are excellent candidates to construct molecules that self-assemble by hydrogen-bonding not only in the solid state but are able to persist in solution. 2 Rebek 3 and Böhmer 4 have independently established that calix [4]arenes containing four urea functions at the upper rim form dimers by interdigitation of the all eight ureas in a head-to-tail directional array of 16 hydrogen bonds. Mendoza and coworkers have described dimeric capsules derived from tris(ureido)calix[6]arenes. 5 Herein we report a novel type of self-assembled dimeric aggregate derived from tris(o-ureidobenzyl)amines which resemble the structure of ureidocalixarenes.The tris(ureas) 1-3 6 shown in Scheme 1, easily available 7 from previously reported tris(o-azidobenzyl)amines, 8 showed dramatic differences in their 1 H NMR spectra when recorded in CDCl 3 or DMSO-d 6 . While the spectra of 1-3 in DMSO-d 6 displayed the expected patterns consistent with averaged C 3v symmetries (Fig. 1a), by changing the solvent to CDCl 3 a new set of signals corresponding to a dimer (see below) emerged in each case. The ratio in which both species, monomer and dimer, were present in CDCl 3 depended on the substituent R 2 to a great extent. Thus, while for the tris(urea) 1 (R 2 = p-tolyl) only the signals attributed to the dimer were apparent, for the tris(ureas) 2 and 3 (R 2 = Bn) their spectra were interpreted as corresponding to equilibrium mixtures of both compounds (Fig. 1b).The dimeric species featured two well separated doublets assigned to the diastereotopic methylenic protons of the (ArCH 2 ) 3 N fragment (J gem = 14.5-15.7 Hz), instead of the singlet observed for the same nuclei in DMSO-d 6 . In the dimers emerging from 2 and 3 the ABX systems formed by the three protons of the -CH 2 NH-fragments were clearly evident. The signals assigned to the NH protons of the dimers (near 6.0 and 7.6 ppm, in 2·2 and 3·3) appeared significantly sharp and shifted to lower field when compared to those attributed to the monomers (near 5.2 and 6.3 ppm). The involvement of the urea carbonyl groups as hydrogen bonding acceptors is supported by the d value of their carbon atoms in the 13 C NMR spectra, which were shifted to downfield in CDCl 3 (Dd = 2.8-3.2 ppm). FT-IR of CHCl 3 solutions of 1 (13.7 mM) and 2 (16.4 mM) revealed typical hydrogen-bonded NH-stretching bands 9 at 3317-3327 cm 21 .All those data revealed that the dimers 1·1, 2·2 and 3·3 should possess a highly ordered, hydrogen-bonded structure. Further indication of the existence of 1·1 and 3·3 in solution came from ESI-MS experiments. This technique was used in virtue of its gentle ionization and has been reported to reflect, at least qualitatively, solution phenome...

show abstract

Hydrogen-bonded dimers of tetraurea calix[4]arenes: unambiguous proof by single crystal X-ray analysis

Cited by 127 publications

References 11 publications

Polycaps: Reversibly formed polymeric capsules

Polycaps: Reversibly formed polymeric capsules

The 55 % Solution: A Formula for Molecular Recognition in the Liquid State

Dimerization of tris(o-ureidobenzyl)amines: a novel class of aggregates

Contact Info

Product

Resources

About