Supramolecular triple helical

Y. Garcia, C.M. Grunert, S. Reiman, O. van Campenhoudt, Gutlich P (2006) The two-step spin conversion in a supramolecular triple helicate dinuclear iron(II) complex studied by Mossbauer spectroscopy. Eur. J. Inorg. Chem. 17, 3333-3339 (2006)... 

We have tried to explore the gel structure at several microscopic scales the left handed helix conformation, the supramolecular structure, showing the kind of helix association (triple helices, fibers, aggregates,. ..), the role of the solvent. 

Fig. 41. Schematic representation of the columnar triple-helical superstructure derived from the X-ray data for (LP2, LU2) each spot represents a PU or UP base pair spots of the same type belong to the same supramolecular strand the dimensions are compatible with an arrangement of the PTP and UTU components along the strands indicated (see also text) the aliphatic chains stick out of the cylinder, more or less perpendicularly to its axis a single helical strand and the full triple helix are respectively represented at the bottom and at the top of the column [9.152].

Hairy rigid rod polymers, in which flexible side chains are attached to a rigid core, present attractive properties [9.155]. A supramolecular version of such materials may be the triple helical supramolecular species described above (Figure 41), which presents the features of a hairy cylinder. Similarly, the components 176 and 177 bearing long R chains yield self-assembled, supramolecular hairy rigid rods. 

Similarly, when a mixture of the two tris-bipyridine ligands 129 and 148 is allowed to react simultaneously with copper(l) and nickel(il) ions, only the double helicate 132 and the triple helicate 149 are formed (Figure 49). Thus, parallel operation of two programmed molecular systems leads to the clean self-assembly of two well-defined helical complexes from a mixture of their four components in a process involving the assembly of altogether 11 particles of four different types into two supramolecular species. 

Recombinant [oil (VIII) ] 3 and [a2(VIII)]s molecules form highly ordered supramolecular assemblies. These assemblies may be formed by four triple-helical collagen VIII molecules that come together to form a tetrahedron via the hydrophobic patches on their G-termini. It has also been suggested that these tetrahedral structures may further associate to form hexagonal lattices, with the N-terminals of individual molecules interacting with either the N-terminals or with the triple-helical portion of molecules in other tetrahedrons (Stephan et al., 2004). 

We present here a few examples of enantiomeric supramolecular absolute structures. In fact, many supramolecular diastereomers with chiral ligands have been isolated stereoselectively. For example, enantiomers of the chiral self-assembled triple helicates trinuclear [Ni3(L)3](C104)6 (L = tris(bpy)) and dinuclear [Co2(L)3]4 + (L = 5-bismpmb) were partially resolved by SP Sephadex chromatography.63,64 The ligands and structures are given in Figure 5.17a and b. 

The remarkable cylindrical supramolecular structure 56 forms by spontaneous assembly from 11 particles five ligand molecules (three 5,5 -linked bis-bipyridines and two hexa-azatriphenylene ligands) and six copper(I) ions. The hexa-azatri-phenylene ligands remain flat and are orientated almost parallel to each other they are not eclipsed as shown in 56 but are rotated with respect to each other by 27°. Reflecting this, the overall structure has a triple-helical twist. After allowing for van der Waals radii, the internal cavity is about 4 A in diameter and 4 A high. 

Fig. 13A-C. Topological switching of supramolecular structures by oxidation and reduction on metal ions. A The translocation of an Fe2+/3+ ion within a triple helical structure. B The conformation change of a calixarene in response to the oxidation state of an Fe2+/3+ ion. C The translocation of a cyclophane upon the change in oxidation state of a Cu+/2+ ion...

Figure 10.82 (a) Electron microscope images of materials formed by PLP + ULU (right-handed helix), (b) PDP + UDU (left-handed) and (c) PMP -I- UMU (nonhelical), (d) Schematic representation of the model for the triple-helical organisation of three self-assembled homochiral polymer strands (PTP, UTU)n (T = L or d not m). PU hydrogen-bonded pairs on the same strand are represented by circles of the same shading. Alkyl chains stick ont of the side of the cylinder. (Reproduced with permission from J.-M. Lehn, Supramolecular Chemistry, VCH Weinheim, 1995.)... 

Finally, there is considerable interest in polymeric assemblies both in solution and in liquid crystalline phases [87]. In a seminal report, Meijer and co-workers [49] have synthesized dimers of module 75 (e.g. 101) and shown that its solutions have rheological properties similar to those shown by normal polymer solutions (Fig. 25). In this regard, the high dimerization constant of 75 allows a high degree of polymerization at accessible concentrations. Likewise, Lehn has shown that 1 1 mixtures of 102 103 and 33 104 form supramolecular, polymeric, liquid crystalline phases (Fig. 25). The structure of 102 103 is believed to contain a triple helical superstructure [88], whereas rigid assembly 33 104 forms a lyotropic mesophase [89]. 

Fig. J Supramolecular organizations of some nonfibrillar collagens. The steps leading to the formation of supramolecular structures from monomeric molecules. Nand C A-terminus and C-terminus of the molecules closed circles and thick black lines indicate noncollagenous and triple-helical domains, respectively GAG glycosaminoglycan 7S is the triple-helical region of the Type IV collagen molecules involved in the formation of tetramers NCI is the carboxyl-terminal noncollagenous domain of Type IV collagen molecules involved in the formation of dimers.

The cobalt(II) complex is labile, and self-assembles to triple-helical [Co2(5-bismbmp)3] [24] which is readily oxidized to the cobalt(III) complex [Co2(5-bismbmp)3] which is sufficiently inert for the two enantiomers to be separated by classical methods [25]. The transformation of labile species to kinetically stable ones offers the possibility of using these elements as building blocks for further supramolecular construction. On the basis of our results with sophisticated ligand systems such as L232, we suspect that complicated, multicomponent self-assembly reactions without some element of kinetic stability will be rather difficult to develop. 

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