Self-assembly with

The characteristic coiled-coil motifs found in proteins share an (abcdefg) heptad repeat of polar and nonpolar amino acid residues (Fig. 1). In this motif, positions a, d, e, and g are responsible for directing the dimer interface, whereas positions b, c, and f are exposed on the surfaces of coiled-coil assemblies. Positions a and d are usually occupied by hydrophobic residues responsible for interhelical hydrophobic interactions. Tailoring positions a, d, e, and g facilitates responsiveness to environmental conditions. Two or more a-helix peptides can self-assemble with one another and exclude hydrophobic regions from the aqueous environment [74]. Seven-helix coiled-coil geometries have also been demonstrated [75]. 

When one, or both, the interactive modules are tridentate, bidimensional (2D) architectures can be formed. A frequently recurring pattern is the (6,3) network (honeycomb structure), which is sometimes formed when onium halides self-assemble with dihalocarbons. Halide anions work as tridentate XB acceptors and occupy the nodes while the dihalocarbons work as bidentate XB donors and form the sides that space the nodes. Such architectures are present in the co-crystals l,4-DITFB/Ph4P+Br , l,4-DITFB/Me4N+r [155], and a,oo-diiodoperfluoroalkanes/K.2.2.2.cKI [128,189]. The less planar the trigonal arrangement around the nodes, the more corrugated the honeycomb structure (Fig. 9). 

Additional combinatorial variation sites allow the heterocyclic self-assembly units. Thus, it has been shown that heterocycles 11 and 14-17 can serve as A-analogous donor-acceptor ligands self-assembling with the T-analogous acceptor-donor ligands isoquinolone 12 and 7-azaindole 18 (Scheme 30) [92]. All combinations form the heterobidentate ligands exclusively upon simple mixing in the presence of a transition metal salt (proven by X-ray, NMR). 

Polymeric Self-Assemblies with a Core-Shell Structure... 

Formation of a complex between DNA and polycationic compounds appears to be the initial and quite possibly a critical parameter for nonviral gene delivery. Several synthetic vector systems, which are generally cationic in nature, including poly(lysines), cationic liposomes or various types of block copolymers and recently dendrimers, have been shown to self-assemble with plasmid DNA [13-15] [16]. Specific physicochemical properties manifested by these DNA complexes depend on the type of cationic agent used however, interesting patterns for such interactions are beginning to evolve [17, 18]. Under certain conditions, the interaction of DNA with polyvalent cations results in... 

Figure 2.25 Dependence of the catalytic current for the oxidation of p-D-glucose mediated by the redox polyelectrolyte film for different number of COx layers self-assembled with (PAH-Os) (COx) (n=m = 2, 4, 6). Taken from [182].

Srivastava S, Frankamp BL, Rotello VM. Controlled plasmon resonance of gold nanoparticles self-assembled with PAMAM dendrimers. Chem Mater 2005 17 487-490. 

The formation of dynamic artificial supramolecular nanoscale assemblies within living cells will be of interest to find out its influence on cell behaviour since it will integrate molecular self-assembly with biochemical reactions, giving rise to better understanding of biological processes and possible new approaches to tackle diseased states. 

Much work by Lehn et al. has been dedicated to the self-assembly of helical coordination complexes. Recently, ligand 59 has been shown to self-assemble with five iron(II) ions to form an intricate circular double helicate of 10" charge which surrounds and encapsulates a chloride ion. This chloride ion seemingly cannot be exchanged for larger ions as the inner core of the helicate = 1.75 A) is nearly... 

R,R)- and (S -cyclohexanediamines 102 self-assemble with cyclohexane-1,2-diol 103 forming helical fibers of 40-70 nm length whilst the racemate produces platelets [53]. 

Several major barriers need to be overcome for the development of nonviral gene delivery systems into true therapeutic products for use in humans. These barriers fall into three classes manufacturing, formulation, and stability (extracellular barriers and intracellular barriers) (85). Cationic lipids and cationic polymers self-assemble with DNA to form small particles that are suitable for cellular uptake. At the therapeutic doses positively charged particles readily aggregate as their concentration increases, and are quickly precipitated above their critical flocculation concentration. 

Finally, when the methylated ligands bpz prz and bpz qnox are self-assembled with Cu or Ag ions, metallopolymers with an M hgand ratio of 1 1 are formed. In one case [Eq. (12), (122)], the structure was determined by X-ray diffraction (see below) and consists of a sequential arrangement of metal and organic components. 

In both experiments, the desired helicates are generated from a mixture of starting compounds by self-assembly with self-recognition it involves the spontaneous selection and preferential binding of like metal ions by like ligand strands in a mixture to selectively assemble into the corresponding helicates. 

Recently fluorinated chains were also attached to amine based dendrimers, like PPI and poly(amido amine) (PAMAM), by means of ionic self assembly with semiperfluorinated alkanoic acids (Fig. 71, 216, 217). All dendrimer complexes 216 with perfluorinated alkanoic acids show SmA phases except the fifth generation dendrimer which shows a Colrec phase [378]. Also semiperfluorinated 4-alkoxybenzoic acids 217 [379] and mixed systems combining fluorinated and nonfluorinated alkanoic or benzoic acids (216, 217) have been reported [379-381]. In most cases layer structures (SmA) and for higher generation dendrimers also modulated SmA phases (Colrec phases) were observed. The layer thickness of the SmA phases of the mixed complexes 216 depends on the ratio of fluorinated and non-fluorinated acids, where smaller d values were observed for dendrimers with low Rp-content for Rp-rich dendrimers the more rigid Rp-chains provide... 

Howard, K.A., Dash, P.R., Read, M.L., Ward, K., Tomkins, L.M., Nazarova, O., Ulbrich, K. and Seymour, L.W. (2000) Influence of hydrophilicity of cationic polymers on the biophysical properties of polyelectrolyte complexes formed by self-assembly with DNA. Biochim. Biophys. Acta., 1475, 245-255. 

Lynn DM, Langer R (2000) Degradable poly(-amino esters) synthesis, characterization, and self-assembly with plasmid DNA. J Am Chem Soc 122 10761-10768... 

This process involves the covalent locking in of structures formed by reversible self-assembly. The irreversible, post-assembly step switches off the equilibrium process involved in the self-assembly. As we will see in the following sections, self assembly with covalent postmodification is involved in a range of biochemistry (e.g. insulin synthesis) and elegant abiotic supramolecular synthesis as in the formation of catenanes and knots. 

Classy. Self-Assembly with Intermittent Processing... 

---