Higher-order Catenanes

In contrast, when a larger tetracationic cyclophane ring was employed in another set of experiments, the formation of new [3]-catenanes was found to be more facile. ° The expanded ring was obtained by replacing the phenylene linker units in the normal tetracationic cyclophane with biphenylene units. This larger ring was found to form readily around two threaded crowns when the latter are present in the acetonitrile reaction mixture in several-fold excess. Both bis-p-phenylene-34-crown-lO and l,5-dinaphtho-38-crown-10 were successfully employed in separate reactions to produce the corresponding [3]-catenanes in 20 and 31% yields, respectively. 

There has now been a range of studies aimed at extending the self-assembly process to the synthesis of other [ ]-catenanes.  

It is noted that the synthesis of [3]-catenanes in low yield via multistep, direct procedures had also been achieved quite early G. Schill and C. Zurcher, Angew Chem., Int. Ed. Engl., 1969, 8, 988 G. Schill, K. Murjahn and W. Vetter, Justus Liebigs Ann. Chem., 1970, 740, 18 G. Schill, K. Rider, H. Fritz and W. NeXter, Angew. Chem., Int. Ed. Eng., 1981, 20, 187 G. Schill, W. Beckmann and H. Fritz, Chem. Ber., 1982, 115, 2683. 

The X-ray structure of the deep violet [7]-catenane confirmed its structure and indicated that all recognition sites are beautifully involved in rriutually compatible Ji-stacking interactions. 

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The winding of DNA in higher-order forms such as knots and catenanes was also shown in electron micrographs of DNA molecules coated with Escherichia coli RecA protdn. It was found that DNA topoisomerase I of E. coli generates an equal mixture of (+) and (-) duplex DNA knots, and that one product was a catenane. It was later shown that RecQ helicase and topoisomerase III (Topo III) of E. coli together mediate a potent DNA strand passage activity that can catenate covalendy dosed DNA." The structure of the catenated DNA spedes formed by... 

It should be noted that in addition to interlocked structures consisting of two components, higher-order [n]-catenanes and [n]-rotaxanes and even polymeric interlocked structures may be constructed. However, this chapter will focus on the synergistic concepts behind the preparation and behavior of [2]-catenanes and [2]-rotaxanes that may be applied to larger systems. 

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