Supramolecular ribbon

Fig. 37. Self-assembly of either a supramolecular ribbon (top) or a supramolecular macrocycle (bottom) from barbituric acid and 2,4,6-triaminopyrimidine units [9.122].

An interesting supramolecular methodology was recently applied by the Resnati group for the synthesis of hybrid -type macrocycles. Photochemical reaction of the preformed complex leads to the formation of supramolecular ribbon 140. 

In supramolecular chemistry [31] iterative synthesis is frequently used for the construction of ribbon and belt shaped molecules [32]. The repeated Diels-Alder reaction is suitable for the preparation of beltenes, collarenes and cycla-cenes containing partially or fully unsaturated annelated six-membered rings. They are potential molecular receptors for appropriate substrates. Stoddart et al. synthesized the cyclacene 18 by Diels-Alder cyclization of the bisdiene 15 and the bisdienophil 16 [33] (Fig. 10). 

Eiichi Kimura is retired from the Department of Medicinal Chemistry at Hiroshima University in Japan. His recent research interests have included the supramolecular chemistry of macrocyclic polyamines and their use in molecular recognition and as zinc-enzyme models. These interests have led to the development of fluorophore sensors for Zn(II) [8] use of macrocycles to effect selective recognition of anions [9], nucleobases in polynucleotides [10], thymidine mono- and diphosphate nucleotides (11), carbonic anhydrase and carboxypeptidase [12], and development of Zn(II)-macrocycle anti-HIV agents [13], In May 2004, he received a Purple Ribbon Award from the Emperor of Japan. 

A, while that between the pairs is 3.383(6) A. The 7r-stacked arrays of cations are linked by centrosymmetric pairs of Se(2)—N(l ) contacts, thereby generating ribbons running along the y-direction. These four-center Se—N supramolecular synthons, which are common in diselenadiazolylium salts and diselenadiazolyl radicals, are likely to dominate the solid-state structures of reduced diselenazolyl materials. 

Fig. 9 Cation-template resolution of a dynamic supramolecular guanine system in which G-quartet is reversibly exchanging with linear ribbons followed by a secondary irreversible sol-gel selection of G-quadruplex hybrid materials...

Hierarchical Higher Organization - From Bilayers to Fibers and Rods Amphiphile assembly sometimes results in higher order supramolecular assemblies. Fibrous structures and helical ribbons with molecular dimensions are formed spontaneously. 

Many types of amphiphile can form these supramolecular structures (see Fig. 4.52). Most of these have the abiUty to form hydrogen bonds - hydrogen bond formation significantly increases the stabihty of a supramolecular assembly. The presence of a chiral center sometimes leads to the formation of ribbon-Uke structure and twisted fibers. 

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