Multiple catenanes

The olefin metathesis between alkenyl groups has been frequently used in recent years to stabilize molecules (e.g., dendrimers [46]) or molecular assemblies [47] by additional covalent connectivities [48] and to synthesize macrocydes or more demanding structures like multiple catenanes [24]. Therefore, this reaction was chosen for the connection of alkenyl residues attached to a calix[4]arene via the urea residues. To avoid complications by ds/trans isomerism around the newly formed double bond, the crude reaction mixture was always hydrogenated before working up (Scheme 5.10). 

H NM R spectra in apolar solvents are less informative. Broad unresolved signals indicate the presence of undefined species. Obviously, the multicydic structure does not allow the formation of regular dimers, which would lead to an unfavorable overlap of the loops, but the interaction via the urea functions creates irregular aggregates. This inability to form hydrogen-bonded homodimers can be exploited in further reactions, e.g., for the construction of multiple catenanes (see Section 5.5). 

Scheme 5.16 Possible synthetic pathways to calix[4]arene-based multiple catenanes involving trisloop derivatives. 

Multiple catenanes derived from calix[4]arenes, L. Wang, M. O. Vysotsky, A. Bogdan, M. Bolte and V. Bohmer, Science, 2004, 304, 1312. 

NMR studies showed that in polar solvents (DMSO, DMF) catenane 45 adopts a supramolecular conformation (II) that allows the amide protons to interact via multiple hydrogen bonds with solvent molecules and at the same time buries the lipophilic chains in the center of the molecule (Figure 18). In contrast, NMR spectra in nonpolar solvents indicate that the aliphatic chains are situated on the outer sphere of the catenane, whereas the isophthaloyl units are arranged in a way that ensures optimal intramolecular hydrogen-bonding (I). 

Whereas neither I.U.P.A.C. nor nodal nomenclature bother to extend their system to what is, at present, a very small group of topologically restrained compounds, the proposed system allows for a simple extension to the set of catenanes and rotaxanes. Also, one may readily adapt this system to canonically naming endothelial compounds, such as endothelial fullerenes, etc. Moreover, extension to "chemical" knots having multiple interconnections and windings, without having to resort to the tedium employed by Schill to extend I.U.P.A.C. nomenclature to these compounds, is straightforward. 

Figure 8 Ring-and-strings self-assembly filamentous ligand (17) combines with cyclic ligand (18) to form pseudorotaxane [Cu(17)(18)]+ upon treatment with Cu1. Multiple-interaction self-assembly (uni-/metal-mediated) combining (17), (18), Cu1 and Ru11 generates the catenane (19).

There are also a number of other fairly obvious stereoisomeric possibilities (i.e., ones transparent to graph theory) that have as yet received no attention, e.g., multiple toroidal rings (or Klein bottles) with a catenane type of interlocking knots tied in the torus tube concentric multilayered toroidal tubes. 

Topologically novel multiple rotaxanes and catenanes based on tetraurea calix[4]arenas 06CC2941. 

The foniiation of 4, therefore, involved several different noncovalent interactions. The cyclization step was brought about by the formation of Pd—N coordinate bonds that is, by a metal-mediated process. The interlocking step involved n- and hydrophobie/hydrophilic-mediated processes, along with an entropic effect. Catenane 4 can. therefore, be considered an example of a multi-mediated,"" multiple-interaction self-assembly. Fujita referred to such processes as ""double-molecular recognition"" procedures, in which the two interlocking molecules bind each other in their cavities. 

Fig. 1 Multiple molecular recognition Free metallocycle 1 is formed in dilute solution because of the enthalpy of formation of the Pd—N coordination bonds. When the solution is concentrated from 2-50 mM, the lability of these bonds allows the in situ formation of the interlocked catenane 2. This is driven by hydrophobic interactions to minimize the contact of the metallocycle cavities with the water solvent, the formation of 7t-stacking interactions between two such rings, and an entropic effect due to a decline in the number of species present in solution after interlocking.

RecQ helicase and Topo III was then direaly assessed by AFM. Images show complex catenated DNA species involving crossovers between multiple double-stranded DNA molecules that are consistent with full catenanes. ... 

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