Catenanes molecular topology

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. 

The plectonemic nature of the DNA double-helix makes it a tractable molecule for experiments in molecular topology. This is a very rich vein for the exploration of the topological properties of matter. In this chapter, we have tried to illuminate some of the techniques by which the single-stranded topology of DNA can be directed in synthetic molecules. Catenanes and knots, periodic braids, and Borro-mean rings are available from simple protocols, and it is to be hoped that the physical properties associated with complex topologies (Moffatt 1990) will become available through the medium of DNA constructions. 

Heim, C., Udelhofen, D., Vogtle, F. Amide-Based Catenanes, Rotaxanes and Pretzelanes in J.-P. Sauvage, C. Dietrich-Buchecker (eds.), Molecular Catenanes, Rotaxanes and Knots. A Journey Through the World of Molecular Topology, Wiley-VCH, 1999, pp. 177-222. 

Sauvage J-P, Dietrich-Buchecker C (eds) (1999) Molecular catenanes, rotaxanes and knots a journey through the world of molecular topology. Wiley-VCH, Weinheim... 

Catenanes, Rotaxanes and Knots A Journey through the World of Molecular Topology... 

A natural extension of the work described in Sect. 2.4 was to prepare a Cu(l)-complexed [2]catenane with macrocycles incorporating the Zn and Au porphyrins. [2]catenanes are topologically non-trivial molecules (non-planar molecular graph) in which two rings are interlocked but not linked [23,24]. Therefore, differentiating the rings with Zn- and Au-porphyrins enables us to study photoinduced electron transfer in mechanical bond systems and also to have information on the conformation of the system. 

Let us assume that a rotaxane is formed from an axle with two different stoppers and a wheel that bears a directionality defined by the sequence of atoms in the macrocycle. Both of these subunits are achiral, both are identical to their mirror images. Nevertheless, the corresponding rotaxane exists in two enantiomeric forms, although no chiral center is present in the molecule (Fig. 4). It is the molecular topology that makes these species chiral, and consequently, this phenomenon was coined "topological chirality.. It also exists for catenanes, knots, and other mechanically bound molecules. Shown in Fig. 4 is a detailed structure of such a rotaxane. The wheel contains one sulfonamide group that provides the directionality of... 

Molecular Catenanes, Rotaxanes and Knots A Journey Through the World of Molecular Topology Sauvage, J. P. Dietrich-Buchecker, C., Eds. Wiley Weinheim, 2008. 

The template-directed preparation of cycloi is(paraquat-4,4 -biphenylene (a molecular square ) has been achieved the use of a macrocyclic hydroquinone-based polyether template incorporating an ester moiety in one polyether chain afforded a 1 1 mixture of two topologically stereoisomeric [3]catenanes <96CEJ877>. 

Some racemates (Figure 3.23) are more efficiently resolved on the bonded-type CSP than the coated-type CSP by using chloroform as a component of the eluent. On the bonded-type CSP of 24n, topologically interesting catenanes and molecular knots are successfully resolved using a hexane-chloroform-2-propanol mixture.185 The first direct HPLC resolution of the smallest chiral... 

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... 

We can use this same approach to prove that other molecular knots and links are topologically chiral. For example, consider the molecular link illustrated in Figure 18. This catenane was synthesized by Nierengarten et al. [12]. For this molecule the set T(G) consists of many unlinks together with many copies of the (4,2)-torus link, illustrated as L in Figure 12. However we saw earlier that this unoriented link is topologically chiral. Therefore, the molecular (4,2)-torus link is topologically chiral as well. 

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