Molecular strings

The synthesis of [3]- (figuratively shown as 7) and a [5]rotaxane (8) with one central and two terminal porphyrins in the open configuration has been reported <96AG(E)906> also a rotaxane with two Ru(terpy>2 stoppers has appeared <96CC1915>. A pseudorotaxane comprised of a macroring of 2,9-diphenyl-1,10-phenanthroline unit and a molecular string... 

We realized that improvement in the yields of trefoil knots would be determined by (i) the proportion of double helix precursor formed compared with face-to-face open chain complex (Figure 18) (ii) the spatial arrangement of the four reacting ends of the helical dinuclear complex. This latter factor will reflect the extent of winding of the two molecular strings interlaced around the copper atoms. The various complexes synthesized and studied are depicted in Figure 21 [96]. 

Yoshikawa, K. (1997) Complexity in a molecular string Hierarchical structure as is exemplified in a DNA chain. In Complexity and Diversity. Springer-Verlag, Tokyo, pp. 81-90. 

Lateral Translation of a Ring on the Molecular String on which it is Threaded Electrochemically-driven Motion... 

Fig. 9 (a) and (b) Copper(i)-induced threading of one or two rings onto a molecular string. Compound 4 is a 30-membered ring, containing a bidentate ligand. 

The repeating unit is a distinct sequence of choices from (1) and (2) in the molecule this sequence corresponds to a row of successive atoms, the relative positions of which are fixed if bond and dihedral angles are kept constant. Such a repeating sequence of atoms is called a motif (or module). In general, a motif will coincide with its successor in the molecular string after a translation combined with a rotation in space. This implies that in general these molecular conformations are... 

Stoddart and co-workers have developed molecular switch tunnel junctions [172] based on a [2]rotaxane, sandwiched between silicon and metallic electrodes. The rotaxane bears a cyclophane that shuttles along the molecular string toward the electrode and back again driven by an electrochemical translation. They used electrochemical measurements at various temperatures [173] to quantify the switching process of molecules not only in solution, but also in self-assembled monolayers and in a polymer electrolyte gel. Independent of the environment (solution, self-assembled monolayer or solid-state polymer gel), but also of the molecular structure - rotaxane or catenane - a single and generic switching mechanism is observed for all bistable molecules [173]. 

Figure 68. The compounds used as the molecular string (123) and rings (124) and the prototypical homoporphyrin threaded system (125) derived from 123.

Transition Metal Directed Threading of Molecular Strings into Coordinating Rings... 

Figure 11. Principle of the strategy leading to a dimetallic tr oil knot. First step interlacing of two molecular strings around two transition-metal coordinating centres, with formation of a helicoidal precursor. Second step connection, with the appropriate linkers, between the four ends of the double helix to afford the knot.

Willner et al. developed a redox-active rotaxane (Figure 50) as a monolayer assembly on an Au electrode. The rotaxane comprises a CBPQT + cyclophane threaded onto a molecular string, which includes a rr-donor diiminobenzene unit stoppered by an adamantane unit. The cyclophane localizes on the diiminobenzene unit initially, and shuttling can be induced by the reduction or oxidation of the cyclophane, which can be characterized... 

Molecular motion based on the electrochemical-induced ligand substitution reaction has been reported in a copper(I) rotaxane (Figure 37). This rotaxane is composed of a 2,9-diphenyl-l,10-phenanthroline-containing cyclic poly ether ring, a tetraphenylmethane-stoppered molecular string that contains another 2,9-disubstitnted phenanthroline chelate... 

At this step the difference between the axes of 2 type that define the hyper-symmetry and the axes of the 2 type can be made, impl5ting an operation that acts on an entire reticular (molecular) string. 

Another particularity of knotted molecules is that the double-helical multimetallic complex that has been used as a templating core will be more or less frozen. In other words, the stability of the double helix will be insured by tying the molecular string used to make the knot in such a way as to make ligand exchange, helicity inversion, etc... 

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