Search results for "calixarenes"

Piperazine bridged resorcinarene cages.

2010

The one-pot Mannich condensation of resorcinarenes with piperazine and an excess of formaldehyde under high dilution conditions results in a helical cage, namely, a covalently linked dimer of two resorcinarenes connected via four piperazine bridges in yields ranging from 20 to 40%. The compounds were analyzed by NMR spectroscopy, ESI mass spectrometry, and single crystal X-ray diffraction. The helical cages can encapsulate small guest molecules by adapting the cavity volume by changing the helical pitch according to the guest size.

Selective recognition of neutral guests in an aqueous medium by a biomimetic calix[6]cryptamide receptor

2015

The design of artificial receptors that can efficiently work in water is a challenging research area. A possible biomimetic approach for the elaboration of such receptors consists of associating a hydrophobic cavity with a polar polyfunctional binding site. On this basis, a hydrophilic calix[6]cryptamide decorated with oligo(ethylene glycol) units (i.e. 8) was synthesized through an efficient [1 + 1] macrocyclization reaction as the key-step. The complexation of neutral molecules was evaluated by NMR spectroscopy through competition experiments either in apolar or aqueous media. In both media, host 8 can bind neutral species that display H-bonding acceptor and donor groups such as amides or…

Polymorphism control of an active pharmaceutical ingredient beneath calixarene-based Langmuir monolayers.

2014

This communication demonstrates the possibility to nucleate and grow different crystalline polymorphic forms of gabapentin (GBP) using, as nucleation templates, Langmuir monolayers of an amphiphilic calixarene at different packing densities.

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

2009

The physics of nanoscopic systems is strongly governed by thermal fluctuations that produce significant deviations from the behaviour of large ensembles1,2. Stretching experiments of single molecules offer a unique way to study fundamental theories of statistical mechanics, as recently shown for the unzipping of RNA hairpins3. 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. This mechanically locked structure tunes the energy landscape of dimers, thus permitting the reversible rupture and rejoining of the individual n…

Calix[4]arene-Based Bis[2]catenanes: Synthesis and Chiral Resolution

2007

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. Thus, in a separated metathesis/hydrogenation sequence, a series of 14 cyclic bis[2]catenanes 4, in which two ca…

Orientational preferences of aromatic guests in dimeric capsules of tetraurea calix[4]arenes—MD and NMR studies

2006

Molecular dynamics (MD) simulations have been performed for complexes of a dimeric capsule of a tetraurea calixarene with a series of twelve aromatic guests. A distinct orientational preference and a restriction of the internal mobility was found which depend on the size and electronic properties of the guests. The results are in agreement with the CIS values obtained from (1)H NMR spectroscopic measurements and with complexation selectivities obtained by competition experiments.

Self-assembly of programmed building blocks into structurally uniform dendrimers.

2005

Selective and independent dimerization of tri- and tetraurea derivatives was used to build up dendritic assemblies which are uniform in size and structure. Dendrimers with the total molecular masses of about 25 000 g/mol were obtained. The existence of uniform assemblies was proved by 1H and 1H DOSY NMR experiments and also by dynamic light scattering.

Synthesis and structure of mono-bridged resorcinarene host: a ditopic receptor for ammonium guests.

2009

The synthesis and structural properties of tetramethoxy resorcinarene mono-crown-5 (1) are described. The binding characteristics of 1 toward acetylcholine and tetramethylammonium salts were investigated by 1H NMR titration. It was observed that the cavity of 1 provides a better fit to acetylcholine compared to the smaller tetramethylammonium cation, as acetylcholine is able to interact with both the crown ether moiety and the free hydroxyl groups of receptor 1 simultaneously.

Fourfold [2]rotaxanes of calix[4]arenes by ring closure.

2006

Ion-Pair Recognition of Tetramethylammonium Salts by Halogenated Resorcinarenes

2011

The non-covalent interactions of different upper-rim-substituted C(2)-resorcinarenes with tetramethylammonium salts were analyzed in the gas phase in an Electrospray Ionization Fourier-transform ion-cyclotron-resonance (ESI-FTICR) mass spectrometer and by (1)H NMR titrations. The order of binding strengths of the hosts towards the tetramethylammonium cation in the gas phase reflects the electronic nature of the substituents on the upper rim of the resorcinarene. In solution, however, a different trend with particularly high binding constants for halogenated resorcinarenes has been observed. This trend can be explained by a synergetic effect originating from the interaction of the halogenate…