Supramolecular assemblies from dimers

Type IV collagen subtype [ctl(IV)]2Q 2(IV) from bovine lens capsule forms a fine meshwork structure containing many branches with about 20 nm between the branching points. There are three types of supramolecular assembly of type IV collagen molecules dimer formation (with six polypeptide chains) at the C-terminal NCI domain, the association of four molecules (12 chains) in a 30 nm tetramer formation at the N-terminal 7S domain, and lateral interaction at the collagenous domain (Figure 5(a)). ° ... 

One point to address concerns the use of the words s pramolecular and supermolecule. The concept of supramolecular chemistry has become a unifying attractor, in which areas that have developed independently have spontaneously found their place. The word supramolecular has been used in particular for large multiprotein architectures and organized molecular assemblies [1.16]. On the other hand, in theoretical chemistry, the computational procedure that treats molecular associations such as the water dimer as a single entity is termed the supermolecule approach [1.34,1.35]. Taking into account the existence and the independent uses of these two words, one may then propose that supramolecular chemistry be the broader term, concerning the chemistry of all types of supramolecular entities from the well-defined supermolecules to extended, more or less organized, polymolecular associations. The term super molecular chemistry would be restricted to the specific chemistry of the supermolecules themselves. 

While self-assembled and aggregated chirogenic systems are mainly based on monomeric porphyrinoids, a further increase of the pigment multiplicity, despite raising the overall complexity of supramolecular structures, may lead to novel functional properties and new applications. Therefore, in the last section we shall show a few examples of self-assembled and aggregated systems constructed from dimeric and oligomeric porphyrins. 

Self-assembly is used to organize molecules into amazing and complex structures. Small molecular weight molecules can be assembled into structures of varying degrees from dimers and trimers all the way up to and including supramolecular polymers. Simple amphiphiles form micelles and vesicles. Dendrimers, DNA-based materials, peptides, and peptides amphiphiles have been assembled into nanostructured fibrals reminiscent of the extracellular matrix. Obviously, we cannot cover here even a fraction of the creative and functional assembled systems reported. In this section, we highlight selected symmetrical self-assembled systems to illustrate how different... 

Binding of hard anions occurs strongly at the hard Lewis acidic uranyl center, whereas cation- tt interactions are established between the aromatic side arms and the cation counterpart of the ion pair. Thus, complexation of alkali metal salts (MX) such as CsCl and RbCl with 15 resulted in the formation of isomorphous supramolecular assemblies in the solid state. In the dimeric [15-CsCl], each cation is coordinated to six oxygens, three from each receptor, thus creating a pseudo-crown-ether-Uke environment for the cation. Additionally, each metal ion in the dimeric unit is coordinated to both halide ions and, most importantly, to two aromatic side arms, one from each of the receptors giving decacoordination for the cation. The closest metal ion-aromatic carbon distances of 3.44(1) A for CsCl, 3.34-3.38(1) A for RbCl, and 3.58(1) A for CsF are observed in the respective alkali halide complexes [15 MX] indicating the conformational flexibility of the side arms and adaptability of the receptors 15 and 16 to form multiple cation- rt interactions with the hosted cations. 

Wang and co-workers used the mono-bromide 3.58 as a key compound to construct a pillar[5]arene-based supramolecular assembly. The monobromide 3.58 was substituted with an amino group by Gabriel synthesis. A mono-ureidopyrimidinone-functionalized pillar[5]arene (3.65) was synthesized from the mono-amine 3.64. 3.65 formed a supramolecular dimer by a quadruple hydrogen bond between ureidopyrimidinone moieties, and addition of a bisparaquat derivative afforded supramolecular polymers at high concentration. 

In their communication, however, the authors only reported overall yields of photoproducts, and no kinetic or binding data are available to characterize the intervention of the supramolecular assembly during the photocycloaddition step. In this regard, the choice of ethyl cinnamate as a model compound is also unfortunate, as it cannot be ruled out that the enhancement in yield results from an increase in the single state hfetime of the cinnamate chromophore due to hindered ,Z-isomerization. Although the observed products are the P- and 5-truxinate dimers, which are usually the major products from solution photodimerization, the presence of methylene tethers of different lengths could, in principle, be used to provide evidence for the proposed hydrogen-bonded assembly. 

Size and shape Certain steric effects can be achieved using characteristically wedge-shaped dendrons. Thus, self-assembling dendrons have been connected to supramolecular aggregates with defined dimeric or hexameric structures. Such aggregates can form columnar superstructures which reveal liquid-crystalline properties. Spherical superstructures arise from the self-assembly process when conical dendrons are used14 14,161 Similar... 

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