Mechanical catenanes

R. Jager, F. Vogtle, A New Synthetic Strategy towards Molecules with Mechanical Bonds Nonionic Template Synthesis of Amide-Linked Catenanes and Rotaxanes , Angew. Chem Int. Ed. Engl. 1997,36,930-944. 

In this kind of pseudorotaxanes, rotaxanes, and catenanes, the stability of a specific (supra)molecu-lar structure is a result, at least in part, of the CT interaction. In order to cause mechanical move ments, such a CT interaction has to be destroyed. 

Catalytic titration, 27 114-118 gas-liquid chromatography, 27 115, 116 pulse reactors, 27 115, 116 Catalyzed reactions, mechanisms, 38 234-236 Catenanes, 24 135 Cathodes... 

Besides their topology, rotaxanes and catenanes are also appealing systems for the construction of molecular machines because (i) the mechanical bond allows a large variety of mutual arrangements of the molecular components, while conferring stability to the system, (ii) the interlocked architecture limits the amplitude of the intercomponent motion in the three directions, (iii) the stability of a specific... 

So, when either replication fork encounters a functional Tus-Ter complex, it halts the other fork halts when it meets the first (arrested) fork. The final few hundred base pairs of DNA between these large protein complexes are then replicated (by an as yet unknown mechanism), completing two topologically interlinked (catenated) circular chromosomes (Fig. 25-17b). DNA circles linked in this way are known as catenanes. Separation of the catenated circles in E. coli requires topoi-somerase IV (a type II topoisomerase). The separated chromosomes then segregate into daughter cells at cell... 

For catenane formation from two separate rings, the most reasonable explanation involves dissociation of a ring, threading another ring on the thread, and reconnection of the ends of the thread (Scheme 2 a). However, careful mechanistic consideration of the rapid interconversion suggested a Mobius strip mechanism which involves molecular topology reminiscent of the well-known Mobius strip. 

Supposing this mechanism and considering the restricted circumrotation, the positioning of substituents on the reactants should result in stable isomeric [2]catenanes. Indeed the well-aimed variation of the substitution pattern resulted in three different [2]catenanes - 14-16 (Figures 6 and 7) [20, 21], When isophthaloyl dichloride (3) was reacted with the methoxy-substituted diamine 13 (pathway... 

Figure 7. Mechanism of catenane formation (amide type) the guest is orthogonally embedded in an intermediate macrocycle, the concave template. Depending on the substitution pattern of the reactants (pathways A and B) isomeric catenanes are obtained. For the sake of clarity the diacid dichloride is drawn here to be the nesting guest even though there is clear indication that the effective interactions take place between the corresponding monoamide and the macrocycle.

Numerous examples of catenanes 1, rotaxanes 2, and trefoil knots 3 (Scheme 1) have been previously reported in the literature and are still attracting considerable attention (see Chapters 4 and 6-8) [1-5]. These aesthetically appealing molecules have in common that the topological bonds occurring in catenanes 1 and trefoil knots 2 and the mechanical bonds connecting the component parts of rotaxanes 3 are defined at a molecular scale without ambiguity [1, 2, 4]. 

---