Supramolecular bond formation

The general chemistry used in this approach involves the combination of a limited amount of an amine-terminated dendrimer core reagent with an excess of carboxylic acid terminated dendrimer shell reagent [31]. These two charge differentiated species are allowed to self-assemble into the electrostatically driven supramolecular core-shell tecto(dendrimer) architecture. After equilibration, covalent bond formation at these charge neutralized dendrimer contact sites is induced with carbodiimide reagents (Scheme 1). 

Besides reactions with alkali salts, there are several groups investigating metal-ligand bond formation by mechanochemical methods. For example Orita et al. have shown that the supramolecular self-assembly of a number of complexes can take place under solvent-free conditions, leading to higher-order fabrications of two- or three-dimensional topology and even double... 

Fig. 3 Mechanisms for enzymatic supramolecular polymerisation (a) Formation of supramolecular assembly via bond cleavage, (b) Formation of supramolecular assemblies via bond formation. Examples are shown of biocatalytic supramolecular polymerisation of aromatic peptide amphiphiles via (i) phosphate ester hydrolysis, (ri) alkyl ester hydrolysis, and (iii) amide condensation or reversed hydrolysis using protease...

As far as the chemist is concerned, nanosized materials are huge macromolecules (with molecular weights of the order of 106 to 1010) constructed from millions of atoms. Atom-by-atom synthesis of nanostructures, via covalent bond formation, is a formidable task which has not as yet been achieved by synthetic chemists. Covalent polymerization is the best that chemists have done thus far [3]. Chemists have made spectacular progress, however, in forming self-organized and supramolecular materials in the size domain of nanostructures by the non-covalent bond assembly of molecules [7]. 

In contrast to the methods already presented, the supramolecular synthesis [40b] of dendrimers [40b] does not involve covalent bond formation, but instead exploits non-covalent interactions. 

F. Zordan et al., Supramolecular chemistry of halogens Complementary features of inorganic (M-X) and organic (C-X ) halogens applied to M-X—X -C halogen bond formation. J. Am. Chem. Soc. 127, 5979-5989 (2005)... 

Having introduced the major principles of complexation, association, and organization, it is important to review the physicochemical forces that lead to supramolecular ensemble formation. As mentioned above, supramolecular interactions are by definition noncovalent. In the order of the polarity of the partners involved, they comprise ionic or electrostatic interactions,17 18 ion-dipole interactions,19 dipole-dipole interactions, (ionic) hydrogen bonding, cation-tt and anion-tt interactions,... 

Turro NJ. From molecular chemistry to supramolecular chemistry to superdupermolecu-lar chemistry. Controlling covalent bond formation through non-covalent and magnetic interactions. Chem Commun 2002 2279-92. 

This dynamic process is commonly known as constitutional dynamic chemistry (CDC). While the concept of dynamic covalent chemistry defines systems in which the molecular (or supramolecular) reorganization proceeds via reversible covalent bond formation/breakage, dynamic systems based on noncovalent linkage exchanges define the concept of dynamic noncovalent chemistry. Dynamic combinatorial chemistry (DCC) can be defined as a direct application of CDC where libraries of complementary functional groups and/or complementary interactional groups interexchange via chemical (i.e., covalent) reactions or physical (i.e., noncovalent) interactions. 

Many types of amphiphile can form these supramolecular structures (see Fig. 4.52). Most of these have the abiUty to form hydrogen bonds - hydrogen bond formation significantly increases the stabihty of a supramolecular assembly. The presence of a chiral center sometimes leads to the formation of ribbon-Uke structure and twisted fibers. 

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