Vesicular assemblies

Holowka EP, Sun VZ, Kamei DT, Deming TJ (2007) Polyarginine segments in block copolypeptides drive both vesicular assembly and intracellular delivery. Nat Mater 6 52... 

Figure 2.2 Representation of formation of (a) micellar and (b) inverse micellar vesicular assemblies from diblock and triblock copolymers, respectively.

In the MLM and BLM vesicles, the cmc is small (< 10 M). In MLMs, the solubility of the individual monomers may be relatively large, if they contain charged head groups. Once the bolaamphiphiles are entrapped in a vesicular assembly they cannot escape, as the polar head group would have to pass through an apolar membrane, which is an unlikely process. At pH = 9, for example, the diacetic acid la dissolves reasonably well as the dianion in water. 

Spherical vesicles (see Sec. 2.5.4) are made by the same kind of amphiphiles that form micelles. Highly soluble amphiphiles (e.g., sodium salts of fatty acids or soaps) form micelles badly soluble amphiphiles (e.g., free fatty acids) give vesicles or crystallize. Amphiphilic monomers with two or three long alkyl chains are often totally water insoluble as monomers but dissolve well as vesicular assemblies. Vesicles usually collapse upon drying (Fig. 1.5.8a), but one isolable monolayer vesicle made of rigid carotenoid bolaamphiphiles has also been reported (Fig. 5.5). Hydrogen bond chains convert spherical vesicles to tubules. Such tubules can again be isolated in the dry form and can be stored. They are particularly stable if monolayer membranes are used (Fig. 1.5.8b). 

Figure 6.6.4 Acid titration of the aminoporphyrin changes the lateral vesicular assembly with a 450 nm Soret band into a micellar stack with a 380 nm Soret band. (Fuhrhop, Bindig, et al, 1993,1994.)...

Surfactants Two other classes of host molecule, with, however, flexible cavities, are amphiphilic micellar and vesicular assemblies. In a simple view, these molecules bear a hydrophilic headgroup (e.g., ionic, zwitter ionic, or non-ionic) and a hydrophobic tail (carbon hydrogen chain). Depending on the solvent environment they organize in 3-dimensional surface-active assemblies. For example, in aqueous solutions their alignment... 

Fujikawa D, Uota M, Sakai G, Kijima T (2007) Shape-controlled synthesis of nanocarbons from resorcinol-formaldehyde nanopolymers using surfactant-templated vesicular assemblies. Carbon 45 1289-1295... 

Dendrimers have an architecture which is intrinsically accessible, because their branched structure allows the passage of substfates and products. In the case of PICsomes, the use of polyelectrolytes, which self-assemble into intrinsically porous systems, favors accessibility to the inner cavity where the active compounds are located [25]. Their membranes are permeable to small molecules, such as Tokyo-Green- 3-galactoside, while encapsulated active biomacromolecules, such as trypsin, cannot escape from the vesicular assemblies [25]. In the case of LbL capsules, permeabiUzation of the shell is tuned by its polymer composition, thickness, solvent, pH, or ionic strength [88,89]. 

Micellar and Vesicular Assemblies (Zero Dimensional Morphology)... 

Thus, the formation of a cylinder-like supramolecular dimer is the key step in the construction of some micellar and vesicular assemblies. Several methods can be employed to make building blocks having cylinder-shaped structures. For example, cylinder-like supramolecular dimers can be initially formed from mono-functionalized pillararenes through supramolecular interactions such as ti-ti stacking. Functional groups can be used to modify pillararenes, and the pillararene derivatives obtained may form daisy-chain type dimers through the complexation. However, such dimers prefer to form further supramolecular polymers rather than spherical assemblies at certain concentrations. Therefore, it should be noted that the functional groups... 

Figure 9.1 (Top) Structural representations of DMpillar[5]arene and guest G9.1, as well as the proposed mechanism for the formation of vesicular assemblies. (Bottom) Microscopic morphology of the vesicular assemblies formed from the complex between DMpillar[5]arene and G9.1 in Me2CO (1 mM). Negative-stained transmission electron microscopy (TEM) images with scale bars of (a) 1 pm and (b) 0.2 pm. Gold sputtering scaiming electron microscopy (SEM) images with scale bars of (c) 10 pm and (d) 100 nm.

Figure 9.9 (Left) Structural representations of pillararene trimer H9.14, guest G9.1, and the proposed mechanism for the formation of vesicular assemblies under low concentration. (Right) Morphologies of the complex between pillararene trimer H9.14 and guest G9.1 at low concentration, (a) Negative-stained TEM image (scale bar 0.5 pm), and (b) gold sputtering SEM image (scale bar 10 pm) at a sample concentration of 1 mM.

To date, many types of block copolypeptide amphiphiles that form stable vesicular assemblies have been developed. The first of these utilized diethylene glycol-modified lysine residues (i.e., K ) that impart both non-ionic water solubility as well as ordered a-helical conformations to the hydrophilic polypeptide domains... 

Scheme 6.9 Top Structure and vesicular assembly of NDI-1. Bottom CT-interaction-mediated morphological transition (2D-to-lD vesicle-to-fiber) and gelation by pyrene intercalation. Reproduced with permission om Ref. [66], copyright 2012 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim...

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