Supramolecular cyclic structures

Another case of a supramolecular cyclic structure is illustrated in the formation of the four-component porphyrin cage 13 (Fig. 9) [42]. In the absence of triaminopyrimidine, the uracil moieties appended to the porphyrin exist as a mixture of syn- and antz-atropisomers. Upon introduction of triaminopyrimidine, the presence of the anti isomer decreases to less than 20%, suggesting formation of 13. The presence of 13 is further supported by electrospray mass spectroscopy and vapor pressure osmometry analyses. Similarly, rigid scaffolds bearing complementary DNA bases form closed ensembles, rather than linear polymers, as evidenced by the solution-state dimerization of 14 (Fig. 10) [43]. 

When triethanolamine H3L13 (35) was reacted with sodium hydride and iron(III) chloride, the hexanuclear centrosymmetric ferric wheel [Nac Fe6(L13)6 )Cl (36) was isolated. Amidst a set of possibilities in the template-mediated self-assembly of a supramolecular system, the one combination of building blocks is realized that leads to the best receptor for the substrate [112]. Therefore, the six-membered cyclic structure 36 is exclusively selected from all the possible iron triethoxyamine oligomers, when sodium ions are present. The iron(III) complex 36 is present as an Sg-symmetric wheel, with an encapsulated sodium ion in the center and a chloride counterion. Consequently, the trianion (L13)3- acts as a tripodal, tetradentate, tetratopic ligand, which each links three iron(III) ions and one sodium ion. In the presence of cations with different ionic radii, different structures are expected. Therefore, when triethanolamine H3L13 (35) was reacted with cesium carbonate and iron(III) chloride, the octanuclear centrosymmetric ferric wheel [Csc Fe8(L13)8 ]Cl (37) was isolated (Scheme 13) [113]. 

According to Lehn et al. [34], in the case of the template mediated selfconstruction of a supramolecular system, amidst a set of possibilities, a combination of building blocks is realized, which leads to the best receptor for the substrate. Therefore, it is possible that the six-membered cyclic structure Na c Fe(i[N(CH2CH20)3]5 Cl 19 is exclusively selected from all the imaginable iron triethanolamine oligomers, when sodium ions are present. Thus, in the presence of cations with ionic radii that differ from that of sodium, variant structures are expected. 

Two types of supramolecular synthons are possible in SAM salts—extended ID polymer chain involving alternating cation and anion sustained by N-H O hydrogen bonding and a discrete or OD HBN wherein the ion pairs form a discrete cyclic structure sustained by N-H- -0 interactions [68]. Thus, it was considered worthwhile to study SAM salts for stracture-property correlation-driven design and development of LMWGs. 

Benzoic acid dimerization was also applied for the building of closed complex structures in crystalline states. For example, 5-substituted isophthalic acid derivatives form well-defined structures of cyclic hexameric aggregate 21 (Figure 18) [88]. Supramolecular cyclic hydrogen-bonded complex 22 is formed from cyanuric acid and melamine (Figure 19) [89]. A cyclic structure is formed by 1 1 complexation. 

In addition to supramolecular polymers constructed from 9, bifunctional monomer 10 (Scheme 10.3), incorporating a less-flexible trimethylhexyl linker, exists in an equilibrium between cyclic and linear aggregates in solution as evidenced by viscosity studies and diffusion-ordered NMR spectroscopy (DOSY). These results are in line with the proposal of equilibrium between linear polymeric and oligomeric cyclic structures (i.e., ring-chain equilibrium). Because of its restricted conformational freedom, 10 is more prone to the formation of rings than 9. 

Here, we describe the design and preparation of antibody supramolecular complexes and their application to a highly sensitive detection method. The complex formation between antibodies (IgG) and multivalent antigens is investigated. When an antibody solution is mixed with divalent antigen, a linear or cyclic supramolecule forms [26-29]. With trivalent antigens, the antibody forms network structures. These supramolecular formations are utilized for the ampH-fication of detection signals on the biosensor techniques. 

Burini, A., Mohamed, A. and Fackler, J.P. (2003) Cyclic trrnudear Gold(I) compounds synthesis, structures and supramolecular add-base m-stacks. Comments on Inorganic Chemistry,... 

Hawthorne and co-workers have also produced a series of macrocyclic Lewis acid hosts called mercuracarborands (156, 157, and 158) (Fig. 84) with structures incorporating electron-withdrawing icosahedral carboranes and electrophilic mercury centers. They were synthesized by a kinetic halide ion template effect that afforded tetrameric cycles or cyclic trimers in the presence or absence of halide ion templates, respectively.163 These complexes, which can bind a variety of electron-rich guests, are ideal for catalytic and ion-sensing applications, as well as for the assembly of supramolecular architectures. 

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