Ein selbstassoziierender difunktioneller Rezeptor

Durch Komplexierung eines Na+ ‐Ions „einschalten”︁ läßt sich die Fähigkeit des Kationenrezeptors 1, eines Calixarens, Wasserstoffbrückenbindungen zwischen der Diamidopyridingruppe und einer komplementären Gruppe wie Thymin zu bilden. Ist diese ihrerseits an einen Anionenrezeptor (z.B. ein metalliertes Porphyrin) gebunden, erhält man einen nichtkovalent zusammengesetzten, difunktionellen Rezeptor, in dem Kation und Anion eines anorganischen Salzes wie NaSCN gleichzeitig komplexiert vorliegen

Supramolecular Catalysis in the Synthesis of Substituted 1H-Tetrazoles from Isonitriles by a Self-Assembled Hexameric Capsule

The synthesis of substituted 1H-tetrazoles from aliphatic or aromatic isonitriles and trimethylsilyl azide can be efficiently promoted by the hexameric capsule of resorcin[ 4]arene as a supramolecular self-assembled catalyst. The reaction is sensitive to the size and nature of the substrate and is driven by encapsulation of the reagents within the cavity of the supramolecular catalyst.The synthesis of substituted 1H-tetrazoles from aliphatic or aromatic isonitriles and trimethylsilyl azide can be efficiently promoted by the hexameric capsule of resorcin[4]arene as a supramolecular self-assembled catalyst. The reaction is sensitive to the size and nature of the substrate and is driven by encapsulation of the reagents within the cavity of the supramolecular catalyst

Supramolecular Encapsulation of Neutral Diazoacetate Esters and Catalyzed 1,3-Dipolar Cycloaddition Reaction by a Self-Assembled Hexameric Capsule

Diazoacetate esters proved to be suitable neutral guests for the self-assembled resorcin[4]arene hexameric capsule. The hydrogen- bonded supramolecular host catalyzed the 1,3-dipolar cycloaddition reaction between diazoacetate esters and electron- poor alkenes such as acrolein, acrylonitrile, crotonaldehyde, trans-2-hexenal, methyl, and butyl acrylate, which led to the corresponding 4,5-dihydro-1H-pyrazole derivatives. The cycloaddition reaction occurred within the cavity of the capsule. In fact, substantial inhibition of the catalytic activity was observed by employing tetraethylammonium tetrafluoroborate characterized by greater affinity for the hexameric capsule as a competitive guest; its presence inhibited access of the substrates. The 1,3-dipolar cycloaddition reaction between diazoacetate esters and acrylate esters of different lengths showed a significant degree of substrate selectivity owing to the encapsulation of the reagents before the cycloaddition reaction.Diazoacetate esters proved to be suitable neutral guests for the self-assembled resorcin[4]arene hexameric capsule. The hydrogen-bonded supramolecular host catalyzed the 1,3-dipolar cycloaddition reaction between diazoacetate esters and electron-poor alkenes such as acrolein, acrylonitrile, predominantly trans-crotonaldehyde, trans-2-hexenal, methyl, and butyl acrylate, which led to the corresponding 4,5-dihydro-1H-pyrazole derivatives. The cycloaddition reaction occurred within the cavity of the capsule. In fact, substantial inhibition of the catalytic activity was observed by employing tetraethylammonium tetrafluoroborate characterized by greater affinity for the hexameric capsule as a competitive guest; its presence inhibited access of the substrates. The 1,3-dipolar cycloaddition reaction between diazoacetate esters and acrylate esters of different lengths showed a significant degree of substrate selectivity owing to the encapsulation of the reagents before the cycloaddition reaction

Substrate selectivity in the alkyne hydration mediated by NHC–Au(i) controlled by encapsulation of the catalyst within a hydrogen bonded hexameric host

Significant alterations in the substrate selectivity in the alkyne hydration reaction catalyzed by NHC-Au(i) 1 are observed as a consequence of encapsulation of the homogeneous catalyst within a hexameric resorcin[4]arene based hydrogen bonded self-assembled host

Aqueous Self-Sorting in Extended Supramolecular Aggregates

Self-organization and self-sorting processes are responsible for the regulation and control of the vast majority of biological processes that eventually sustain life on our planet. Attempts to unveil the complexity of these systems have been devoted to the investigation of the binding processes between artificial molecules, complexes or aggregates within multicomponent mixtures, which has facilitated the emergence of the field of self-sorting in the last decade. Since, artificial systems involving discrete supramolecular structures, extended supramolecular aggregates or gel-phase materials in organic solvents or—to a lesser extent—in water have been investigated. In this review, we have collected diverse strategies employed in recent years to construct extended supramolecular aggregates in water upon self-sorting of small synthetic molecules. We have made particular emphasis on co-assembly processes in binary mixtures leading to supramolecular structures of remarkable complexity and the influence of different external variables such as solvent and concentration to direct recognition or discrimination processes between these species. The comprehension of such recognition phenomena will be crucial for the organization and evolution of complex matter

Host-Catalyzed Cyclodehydration–Rearrangement Cascade Reaction of Unsaturated Tertiary Alcohols

The Brønsted acidic resorcin[4]arene hexamer can be applied as an effective catalyst in the dehydrative cyclization and subsequent rearrangement of unsaturated tertiary alcohols. This is the first report on catalyzing such a reaction with a Brønsted acid. Scope and limitations of this cyclopentene-forming reaction sequence are presented. Furthermore, substrate-selective conversion as well as competitive inhibition are described and provide evidence that the reactions proceed within the cavity of the self-assembled structure. Additionally, a cyclobutanone-forming intramolecular hydride transfer of an encapsulated cyclopropyl acetate is reported

Binding of hydrophobic guests in a coordination cage cavity is driven by liberation of 'high-energy' water

The cavity of an M8L12 cubic coordination cage can accommodate a cluster of ten water molecules in which the average number of hydrogen bonds per water molecule is 0.5 H-bonds less than it would be in the bulk solution. The presence of these 'hydrogen-bond frustrated' or 'high-energy' water molecules in the cavity results in the hydrophobic effect associated with guest binding being predominantly enthalpy-based, as these water molecules can improve their hydrogen-bonding environment on release. This contrasts with the classical form of the hydrophobic effect in which the favourable entropy change associated with release of ordered molecules from hydrophobic surfaces dominates. For several guests Van't Hoff plots showed that the free energy of binding in water is primarily enthalpy-driven. For five homologous pairs of guests related by the presence or absence of a CH2 group, the incremental changes to ∆H and T∆S for guest binding ¬- i.e. ∆∆H and T∆∆S, the difference in contributions arising from the CH2 group - are consistently 5±1 kJ mol-1 for ∆∆H and 0±1 kJ mol-1 for T∆∆S. This systematic dominance of ∆H in the binding of hydrophobic guests is consistent with the view that guest binding is dominated by release of 'high energy' water molecules into a more favourable solvation environment, as has been demonstrated recently for some members of the cucurbituril family