Molecular rosette

Consistent with the principles outlined in Chapter 1, strong hydrogen-bonded association may be achieved by multiple complementary interactions, as in the barbiturate-appended porphyrin system shown in 11.21 (cf. molecular rosettes, Section 10.6.4). This receptor binds a complementary dansyl (dimethylaminonapthalene-sulfonyl) group with an association constant in excess of 106 M-1. In this case, electron transfer is from the photoabsorbing dansyl group to the porphyrin acceptor quenching is almost total, suggesting very fast electron transfer relative to the rate of fluorescence.12... 

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]. 

Vieekamp RH, van Duynhoven JPM, Hubert M, Verboom W, Reinhoudt DN. Molecular boxes based on calix[4]arene double rosettes. Angew Chem Int Ed Engl 1996 35 1215-1218. 

The lastest development is the completely reversible formation of the nanostructures comprising 8 different rosette layers (27 different components) that are held together by 144 cooperative hydrogen bonds. Regarding their size (—5.5 x 3.1 x 2.7 nm) and their molecular weight ( 20 kDa), these nanostructures are comparable to small proteins (Figure 4.4).14... 

Finally, we mention a remarkable example of lateral resolution reported for supramolecular nanostructures on hopg [96]. Held together by 72 hydrogen bonds, the molecular nanostructure is formed from three melamine-substituted calix[4]arene units and twelve 5,5-diethylbarbiturate molecules (Fig. 31a). The nanostructure, basically a stack of four rosettes, has chiral symmetry. With its components all being achiral, both enantiomers are formed upon self-assembly in solution. Deposition of the tetrarosettes on hopg leaves this nanostructure intact and allows surface self-assembly. AFM studies revealed close-packed 2D lattices formed by the tetrarosettes on hopg... 

It was demonstrated that hydrogen bonded hexamers ( rosettes ) can be formed not only in the crystalline state but also in apolar solvents and that various well-defined self-assembled species can be obtained from building blocks in which melamine and barbiturate/cyanurate fragments are covalently attached in an appropriate way to a molecular skeleton.279... 

Figure 2 The structure of the hydrogen-bonded CA M lattice. Three classes of aggregates that we have observed in solution and the solid state are highlighted the rosette, crinkled tape, and linear tape motifs. The molecular strucmres of melamine and cyanuric acid and their abbreviated representation as dark and light disks are shown...

Fig. 1 Molecular neuroanatomy of the zebrafish olfactory epithelium, a The zebrafish olfactory rosette, b A section of the olfactory rosette hybridized with an olfactory marker protein (OMP) complementary RNA probe. Dark signals represent ciliated olfactory sensory neurons (OSNs) in the olfactory epithelium (OE). c Three types of olfactory sensory neurons in fish, d Distinct locations and molecular signatures of ciliated and microvillous OSNs. The ciliated OSNs locate in a...

Fig. 85. A. Drawing displaying the distribution of mossy rosettes (dots) immunoreactive to monoclonal choline-acetyltransferase (ChAT) antibody. The section (40 fim thick) was cut sagittally through the middle vermis of rat cerebellum. A considerable number of immunoreactive mossy terminals are observed in lobules I through IXab, although they are much fewer than in lobules IXc and X. Calibration bar = 1 mm. B. Drawing of part of lobule IXab shows the overall distribution of immunoreactive fibers. Arrows indicate mossy fibers with glomerular rosettes. Small and large arrowheads point to some varicose fibers distributing in or near the Purkinje cell layer (PCL) and in the molecular layer (ML), respectively. The ML fibers are most frequently observed in this lobule and tend to be restricted to the inner half of the layer. Calibration bar = 200 jum. Ojima et al. (1989).

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