Macrocycle double helical

FIG. 14 Construction of periodic framework and geometric objects from DNA. (a) Construction of two-dimensional DNA lattices from tetravalent four-arm DNA junctions (14) [8]. (b) Synthesis of a macrocyclic molecule from bivalent three-arm DNA junctions (13a) containing two cohesive ends [83]. For simplification, linear double-helical stretches are represented by parallel lines. 

We are now left with another question - what is this new structure that we have drawn with the three crossing points However we twist and turn the molecule (hint try this with pipe-cleaners) the crossing points remain. If we start at any point on the structure and trace around we eventually end up at the same point. In other words, there is only a single cyclic molecule, but the twisting means that it is not the same as the [2+2] macrocyclic product. This view serves to emphasise the relationship with the double-helical structures that... 

An indole-terminated tris(macrocycle) designed to be a channel-former and which is an effective carrier in bulk membranes but fails to function in a lipid bilayer owing to hydrogen-bond formation has been described <1996CC2147>. Tryptophan- and tryptamine-derived tetraazacyclooctadecane macrocycles have been synthesized <1996J(P1)2427>. Transannular hydrogen bonding stabilizes a left-handed double-helical conformation of the... 

Figure 6.27 Structure of the double-helical, macrocyclic complex, [PbLp (L = 61) ...

Rajca and coworkers have elaborated on the core structure of the cycUc ortho-tetraphenylene via the synthesis of a helical l,l -binaphthyl dimer as outlined in Scheme 6.19 [51]. This work represents the first example of a non-racemic macrocycle provided in this discussion. (R)-2,2 -Dibromo-l,l -binaphthyl 123 was fully lithiated and subsequently oxidatively coupled using CuBr2 to form the double helical 124 in >95% ee. The authors noted that similar reactions performed with racemic 123 led to complex mixtures of products and low isolated yields of the desired cyclic species 124. 

If one cuts the macrocycle of porphyrins by oxidation, helical structures become dominant. The most spectacular case has been found with zinc octaethylformyl-biliverdinate. At neutral pH, the central zinc ion is hydrated and a helix is formed with a disturbed square planar ligand field and one axial water molecule. Upon acidification, however, the water molecule is removed and the zinc ion enforces a tetrahedral ligand field by binding to two different formyl-biliverdinate molecules, rearranging to form a double-helix. Upon neutralization, hydration takes place again and the planar, monomeric monohydrate is reformed in quantitative yield. Both the helical monomer and dimer structures have been solved by single crystal analysis (Fig. 6.2.16). 

Fig. 52 a) Sketch of empty helical stacks formed by shape-persistent macrocycles, b) A pitch angle of Ri60° between adjacent macrocycles was determined from 2D double quantum NMR correlation spectra in agreement with NICS maps, c) Side-chain packing [201]... 

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