Supramolecular helical complex

A particular point of interest included in these helical complexes concerns the chirality. The lielicates obtained from the achiral strands are a racemic mixture of left- and right-handed double helices. This special mode or recognition where homochiral supramolecular entities, as a consequence of homochiral. self-recognition, result from racemic components is known as optical self-resolution. It appears in certain cases from racemic solutions or melts (spontaneous resolution) and is often cited as one of the possible sources of optical resolution in the biological world. 

Similarly, when a mixture of the two tris-bipyridine ligands 129 and 148 is allowed to react simultaneously with copper(l) and nickel(il) ions, only the double helicate 132 and the triple helicate 149 are formed (Figure 49). Thus, parallel operation of two programmed molecular systems leads to the clean self-assembly of two well-defined helical complexes from a mixture of their four components in a process involving the assembly of altogether 11 particles of four different types into two supramolecular species. 

Supramolecular Metal Complexes Chiral Self-Assembled Supramolecular Helicates Since the first introduction of the term helicate by Lehn et al. in 1987,58 there have been a number of investigations of self-assembled supramolecules with... 

V. Percec, M. Glodde, T. K. Bera, Y. Miura, I. Shiyanovskaya, K. D. Singer, V. S. K. Balagurusamy, P. A. Heiney, I. Schnell, A. Rapp, H.-W. Spiess, S. D. Hudson, H. Duan, Self-organization of Supramolecular Helical Dendrimers into Complex Electronic Materials, Nature 2002, 419, 384-387. 

Percec V, Glodde M, Bera TK, Miura Y, Shiyanovskaya I, Singer KD, Balagumsamy VSK, Heiney PA, Schnell I, Rapp A, Spiess HW, Hudson SD, Duan H. Self-organization of supramolecular helical dendrimers into complex electronic materials. Natiue 2002 417 384-7. 

Helical complexes have been of great concern as examples of self-assembled supramolecular structures in an artificial system and as a model for the DNA and RNA structures in Nature. Among them, one astonishing example is the chirality control of... 

Sanders and coworkers have recently found supramolecular helical arrays of C o molecules in the tubular cavity of helical organic nanotubes composed of a-amino acid functionalized naphthalenediimides (10), which self-assembled to form hydrogen-bonded helical nanotubes in a nonpolar solution and in the solid state (Figure 6.11) [59]. The CD spectrum of the L-10-C,so complex exhibited weak but apparent Cotton effects at 595 and 663 nm due to electronic transitions of C o as... 

From the atomic to the macroscopic level chirality is a characteristic feature of biological systems and plays an important role in the interplay of structure and function. Originating from small chiral precursors complex macromolecules such as proteins or DNA have developed during evolution. On a supramolecular level chirality is expressed in molecular organization, e.g. in the secondary and tertiary structure of proteins, in membranes, cells or tissues. On a macroscopic level, it appears in the chirality of our hands or in the asymmetric arrangement of our organs, or in the helicity of snail shells. Nature usually displays a preference for one sense of chirality over the other. This leads to specific interactions called chiral recognition. 

Reference [33] describes recent progress on cyanine probes that bind noncova-lently to DNA, with a special emphasis on the relationship between the dye structure and the DNA binding mode. Some of the featured dyes form well-defined helical aggregates using DNA as a template. This reference also includes spectroscopic data for characterizing these supramolecular assemblies as well as the monomeric complexes. 

A second example of homochiral columns formed by discotics are the complexes of tetrazoles (59 and 60) with l,3,5-tris(4,5-dihydroimidazol-2-yl)benzene (61).74 Four molecules self-assemble to give a supramolecular disc and these discs subsequently form columns in nonpolar solvents. Chiral discs were obtained from the self-assembly of the chiral tetrazole (60) with 61. The chirality of the side chains was found to induce a bias in the helic-ity of the supramolecular assembly. Sergeants-and-soldiers measurements75 were performed for which chiral (60) and achiral (59) molecules were mixed. The experiments showed no amplification of chirality, thus revealing that in these systems chirality transfer from the side chains into the column is... 

The design and synthesis of supramolecular architectures with parallel control over shape and dimensions is a challenging task in current organic chemistry [13, 14], The information stored at a molecular level plays a key role in the process of self-assembly. Recent examples of nanoscopic supramolecular complexes from outside the dendrimer held include hydrogen-bonded rosettes [15,16], polymers [17], sandwiches [18, 19] and other complexes [20-22], helicates [23], grids [24], mushrooms [25], capsules [26] and spheres [27]. 

The Ag cations are coordinated to two sulfur atoms of different cavitands with Ag-S distances in the range 2.47-2.50 A. In the solid, efficient r-stack-ing of the P-phenyl groups with the picrate anions stabilizes the supramolecular complex (Fig. 10). The two cavitands are aligned along their common C4 axis and offset by about 45°, leading to a helical structure. The inner space is reduced by the occupancy of the sulfur atoms, and there is probably not enough room to accommodate small guests inside the cavity. 

A helical homobimetallic mercury(II) complex with a bridging bis(NHC) ligand serves as a starting point for a supramolecular assembly. Also tetrameric cyclic palladium(II) complexes have been obtained with bridging NHC-pyridine ligands. 

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