Self-assembled Molecular Capsule Research Articles

A Calix[6]arene Dimer Linked Through Amino Acid Hydrogen Bond Interactions

A calix[6]arene containing three leucine residues at the lower rim dimerizes in apolar solvents with the formation of up to eighteen hydrogen bonds, giving rise to a self-assembled molecular capsule. The dimerization in chloroform was conformed by NMR spectroscopy and gel permeation chromatography, as well as by molecular mechanics and dynamics calculations. The highly flexible structure is unable to encapsulate guests of complementary size, probably because six methoxy groups and one of the leucyl residues permanently occupy the cavity.

A Self-Assembled Homooxacalix[3]arene-based Dimeric Capsule Constructed by a PdII−Pyridine Interaction Which Shows a Novel Chiral Twisting Motion in Response to Guest Inclusion

A capsule-like molecule was constructed by dimerization of pyridine-containing homooxacalix[3]aryl esters utilizing a Pd(II)-pyridine interaction when Li(+) ions were bound to the ionophoric lower rims. (1)H NMR spectral studies showed that the self-assembled molecular capsule 3b.(Li(+))(2) has a highly symmetrical D(3)(h)-structure. It was also found that this self-assembled molecular system can form capsular structures in the presence of Na(+) or ammonium (RNH(3)(+)) ions. Very interestingly, these molecular capsules are twisted into triply bridged helical structures, and chiral RNH(3)(+) guests included in the cavity induce a change in the (P) versus (M) ratio, resulting in high chiral induction ( approximately 70%). These results indicate that the self-assembled molecular capsule 3b has a novel chiral factor in which the (P) versus (M) equilibrium is readily controllable by the inclusion of chiral guest molecules.

A self-assembled porphyrin-based dimeric capsule constructed by a Pd(II)-pyridine interaction which shows efficient guest inclusion

Novel self-assembled molecular capsules were constructed from two moles of pyridine-containing porphyrin derivatives and four moles of Pd(II) complexes utilizing a pyridine-Pd(II) interaction. The (1)H NMR spectral studies established that these self-assembled molecular capsules 5 and 6 have a highly symmetrical D(4)(h)() structure as well as a large inside cavity. It was shown that molecular capsule 6 can include a large bipyridine guest by a two-point simultaneous pyridine-Zn(II) interaction.

Confinement of dimeric sulfuric acid in a self-assembled molecular capsule: [(H2SO4)2⊂(calix[5]arenesulfonic acid)2

Self-assembled molecular capsules are formed on crystallisation of calix[5]arenesulfonic acid resulting from treating calix[5]arene with sulfuric acid; the calix[5]arenesulfonic acid molecules dimerise via hydrogen bonding through the sulfonic acid groups, shrouding two hydrogen-bonded sulfuric acid molecules as the supermolecule [(H2SO4)2}⊂{(calix[5]arenesulfonic acid)2].

Acceleration of a Diels–Alder reaction by a self-assembled molecular capsule

The interior of cage-like molecules can be considered to provide a new phase of matter, in which it becomes possible to stabilize reactive intermediates and to observe new forms of stereoisomerism. Cage-like molecular complexes that self-assemble through weak intermolecular forces are dynamic species, encapsulating guest molecules reversibly. They can persist over timescales ranging from microseconds to hours, long enough for chemical processes to take place within them. Here we report the acceleration of a Diels-Alder reaction by encapsulation of the reactants in a self-assembling molecular capsule. Although product inhibition (lack of dissociation) prevents the system from showing true catalytic behaviour, there is clear evidence for a rate increase of over two orders of magnitude owing to the effective enhancement of concentration inside the capsule.

Encapsulation of small organic molecules by a self-assembled molecular capsule through charged hydrogen bonding interaction

Self-assembled heterodimeric molecular capsule based on the charged hydroge bonding interaction between two different CTV monomers ( 1 and 2) was developed. The formation of the molecular capsule was confirmed by inclusion phenomena of complementary neutral guests in DMSO- d 6. The encapsulated TMS was released by prolonged heating or pH adjustment. Molecular modeling and intermolecular NOEs suggested the three-dimensional structure of the termolecular inclusion complex.

Self-assembled molecular capsule based on the hydrogen-bonding interaction between two different calix[4]arenes

Intermolecularly hydrogen-bonded molecular container constructed from two calix[4]arene derivatives having carboxylic acids ( 1) or pyridyl groups ( 2) on their upper rim was designed for the first time. The formation of a simple but very interesting self-assembled molecular capsule was confirmed by physical measurements: i.e., solubility, molecular weight, and fluorescence spectroscopy.