Self-assembly linear aggregates

Figure 6 Theoretical phase diagram of a system of monodisperse, self-assembling linear aggregates. Ref. 51. 

Maointosh F C, Safran S A and Pinous P A 1990 Self-assembly of linear aggregates the effeot of eleotrostatios on growth Europhys. Lett. 12 697-702... 

Probably the best example of the manifestation of self-assembly processes in dendritic systems via H-bonds is seen in the recent work of Zimmerman et al. [156]. Dendritic wedges possessing tetraacid moieties (67) self-assembling into a hexameric, disc-like framework (68) was confirmed by SEC and -NMR studies. The tetraacid unit (69) is known to form cyclic as well as linear aggregates in solution via carboxylic acid dimerization (Fig. 30). However, with incorporation of larger dendritic wedges on 69, the hexamer form is preferred. 

The addition of large linear blocks to dendrons with opposite polarity creates a desymmetrized structure predisposed to sequester insoluble components by aggregation rather than intramolecular hydrogen-bonding. Amphiphilic, linear-dendritic diblock (AB) and triblock (ABA) copolymers self-assemble into multimolecular micelles with CMC values that are well below those of low molecular weight surfactants. Typically, a hydrophilic linear block such as PEG is attached to the focal point... 

Fig. 11 Schematic representation of short DNA self-assembly stages, (a) Pairing of complementary strands yield double helices, (b) Blunt-ended or sticky-ended helices stack and form linear aggregates, while helices with unpaired dangling ends cannot aggregate, (c) Helices capable of linear aggregation display N and COL LC phases, (d) Complementary sequences segregate from mixtures of unpaired sequences through the nucleation of LC domains...

Electrostatic self-assembly was combined with supramolecular chemistry to obtain inclusion complexes of a polymeric nonlinear optical (NLO) active dye and modified [3-cyclodextrin with induced chromophore orientation [37], The polyanion is a N,N-diallyl-aniline and sodium-2-acrylamido-2-methylpropanesulfonate copolymer functionalized with pendant azo group. The modified /i-cyclodextrin oligo-cation was obtained by treatment of hcptakis(6-dco y-6-iodo-/i-cyclodcxtrin) with excess pyridine. A linear polyamine, chitosan, was also combined with the polyanion, for comparison. Films were deposited on glass slides by dipping them alternatively in aqueous solutions of the cation and the polyanion. UV-visible spectra indicate dye aggregation and suggest the formation of an inclusion complex of the dye with the cyclodextrin, thus isolating the chromophores. 

Air-Water Interface. Organized films of surfactants and phospholipids at the air-water interface are of interest in biophysics, general interfacial chemistry, and have relevance to the self-assembling aggregates, which are viewed as having potential applications in non-linear optics and as microelectronic devices (122). FT-IR spectroscopy has recently been applied to the problem of obtaining information about amphiphiles at the air-water interface. 

Figure 5.3. Turbidity-time curve illustrating collagen self-assembly.Turbidity-time curve illustrating lag phase, during which small linear and lateral aggregates form, and growth phase, during which unit fibers form that rapidly grow into fibers. The plateau is characteristic of termination of fibril growth.

Figure 5.6. Collagen self-assembly. The diagram models the initiation of collagen self-assembly via formation of linear aggregates containing about three molecules that then laterally associate. The lateral assembly step may require a supramolecu-lar twist, explaining why linear aggregation precedes lateral aggregation.

Figure 5.7. Diagram showing role of N- and C-propeptides in collagen self-assembly. The procollagen molecule is represented by a straight line with bent (N-propeptide) and circular (C-propeptide) regions. Initial linear and lateral aggregation is promoted by the presence of both the N- and C-propeptides. In the presence of both propeptides lateral assembly is limited and the fibrils are narrow. Removal of the N-propeptide results in lateral assembly of narrow fibrils removal of the C-propeptide results in additional lateral growth of fibrils. As indicated in the diagram, the presence of the N- and C-propeptides physically interferes with fibril formation.

Noncovalent self-assembly of complementary pairs of homoditopic building blocks (AA/BB-type), such as bis(crown ether) 125 and diammonium salt 126, has afforded well-defined supramolecular oligomeric/polymeric assemblies <2003JA3522>. In dilute solutions, entropy favored the formation of the cyclic dimer, whereas high equimolar concentration (>0.5 M) of the two components led almost exclusively to linear species aggregation, as revealed by H NMR analysis and viscosity measurements. Closely related linear poly[3]pseudorotaxane supramolecular arrays have also been prepared from cylindrical bis(crown ether) 127 and bisparaquat derivative 128 <2005CC1696>. 

Polycatenar compounds, with more than one terminal chain at each end of a rod-like molecule can also exhibit columnar phases, although they possess a linear molecular structure. Three linear molecules aggregate together to form a self-assembled disc. These discs then stack up to form a fluid columnar structure. Non-dispersive charge-carrier mobility in such polycatenar compounds has also been found. ... 

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