Amphiphilic micellar assemblies

Similar to micellar assemblies in water, reverse micelles have also been utilized to bring about nonspecific binding interactions in organic solvents. Akiyoshi et al. (2002) have synthesized an amphiphilic block copolymer containing PEO and an amylase chain as receptor for methyl orange (MO Chart 2.2). Amylases are insoluble and methoxy-PEO (MPEO) is soluble in chloroform. Hence, an MPEO-amylase block copolymer forms reverse micelles in chloroform. Akiyoshi et al. established the capability of the buried receptors to extract the complementary analyte by studying the ultraviolet visible (UV-vis) spectra. A solution of polymer was shaken... 

Basu et al. (2004) reported a series of amphiphilic homopolymers in which the hydrophUic moiety is a carboxylic acid moiety and the hydrophobic moiety can be based on either an alkyl chain or an aromatic ring (Chart 2.7). These polymers self-assemble into either micelles or reverse micelles, depending on the solvent environment. Figure 2.7 represents the formation of a micellar assembly in a polar... 

Figure 2.7 Formation of micellar and inverted micellar assemblies from amphiphilic homopolymer.

FIGURE 7.44. Transmission electron micrographs of the micellar assemblies formed by the aggregation of a lipase-polystyrene giant amphiphile in water. Expansion reveals a single micellar fiber with a diameter of 20-30 nm. Schematic representation of the micellar rod which possesses a polystyrene core. 

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... 

The SF-SCF approach has been used to consider many aspects of amphiphile self-assembly [77, 82, 88, 93-96]. Here, we focus on results that are relevant for the self-assembly of non-ionic copolymers in spherical micelles. The self-assembly of non-ionic copolymers is characterized by relatively few parameters, and we will use this system to show the micellar properties as a function of the most relevant molecular parameters. 

Figure 19.27. Amphiphile self-assembly structures can be divided into discrete micellar-type and connected forms. There may be connectivity in one, two or three dimensions...

Ben-Shaul, A. and Gelbart, W.M., Statistical thermodynamics of amphiphile self-assembly Structure and phase transition in micellar solution, in Micelles, Microemulsions, and Monolayers, W.M. Gelbart, A. Ben-Shaul, and D. Roux (eds.). Springer, New York, 1994, p. 1. 

From these examples, it is clear that self-assembly of facial amphiphiles results in the formation of a variety of common and less common aggregate morphologies. Most notable is the low aggregation number of micellar assemblies and the high degree of order in interfacial assemblies. These properties are related to the large and comparable size of the hydrophobic and hydrophilic surface areas of facial amphiphiles compared to those of classic head/tail amphiphiles. 

An alternative strategy, which utilizes micelle-forming amphiphilic block copolymers in the stabilization of metal nanoparticles, has been extensively studied and can be described as nanoreactors as the metal colloids are synthesized within their interior. This has enabled the formation of nanosized (l-2nm) metal colliods or clusters within polystyrene-Z -polyvinylpyridine (PS- -PVP) micellar assemblies, with diameters around 30 mn, and these... 

Here, the distinct domains of the resulting hybrid polymer are responsible for the self-assembly of the material. It should be noted that there are several other approaches to nanomaterials via ROMP, including the synthesis of dispersed latex nanoparticles, [29-34] hybrid nanoparticles via scaffolded initiation [35-39], and nanoparticles encapsulated in polymer matrices [40,41]. Amphiphilic micellar nanoparticles are by far the most prevalent systems in the literature relevant to a discussion of ROMP in nanoparticle synthesis, particularly those fully characterized in terms of particle formation and morphological characterization of the resulting polymer aggregates. Amphiphilic copolymers synthesized by ROMP that are not studied in this manner [42-45] or those nanoscale architectures involving only covalent interactions [46, 47] are not discussed here. 

Due to it s highly efficient and orthogonal nature, copper-catalyzed click chemistry is an attractive route to post-polymerization functionalization of ROMP copolymer backbones yielding amphiphilic micellar nanoparticles [103, 104]. However, it should be noted that post polymerization modification is necessary to yield azide or acetylene modified polymers, as azide and acetylene functionalities are not compatible with current ROMP catalysts. Ohe and coworkers [104] have synthesized amphiphihc triblock copolymers capable of assembly into discrete micellar nanoparticles by clicking an acetylene-modified hexaethylene... 

The hydrophobic effect , firstly recognized by Tanford, is responsible of selfassociation phenomena. Amphiphilic molecules can form micellar systems provided that their packing parameter, vjal, is not too close to unity. Significant changes of NMR parameters are observed as a result of amphiphiles self-assembly. Indeed molecules experience strong intermolecular interactions due to the interplay of both electrostatic and van der Waals forces. Micellar aggregates usually form isotropic liquid systems, thus NMR experiments can be easily performed and modeled. Hence chemical shifts, relaxation, and self-diffusion NMR measurements can provide reliable information, at a molecular level, on critical micelle concentration (c.m.c.), molecular conformations and interactions, counterion binding, hydration also in mixtures of different amphiphiles. 

Conventional amphiphiles often assemble into micellar and vesicular structures by supramolecular interactions such as hydrophilic and hydro-phobic interactions in H2O. In some cases, amphiphiles themselves are also prepared from various precursors through supramolecular interactions, e.g., host-guest interaction, and the supramolecular amphiphiles obtained then form more complicated architectures. As a matter of fact, the supramolecular dimer mentioned above is also a kind of supramolecular amphiphile. 

Most work on amphiphilic conjugates to date is based either on simple a-helix-fotming polypeptides or on complex pro-teins/enzymes. Work on biomolecular building blocks that fall between the two aforementioned groups, such as the coiled-coil protein tertiary stmctural motif, has been lim-ited. " Recendy, a heterodimer coiled-coil was used to noncovalendy link PEG and PS blocks and the resultant amphiphilic PEG-peptide-PS triblock copolymer assembled into thermoresponsive micellar assemblies in aqueous solution that transformed from rodlike micelles to spherical micelles upon heating, as depiaed in Figure 10(b). ... 

FIG. 1 Self-assembled structures in amphiphilic systems micellar structures (a) and (b) exist in aqueous solution as well as in ternary oil/water/amphiphile mixtures. In the latter case, they are swollen by the oil on the hydrophobic (tail) side. Monolayers (c) separate water from oil domains in ternary systems. Lipids in water tend to form bilayers (d) rather than micelles, since their hydrophobic block (two chains) is so compact and bulky, compared to the head group, that they cannot easily pack into a sphere [4]. At small concentrations, bilayers often close up to form vesicles (e). Some surfactants also form cyhndrical (wormlike) micelles (not shown). 

Kim W, Thevenot J, Ibarboure E et al (2010) 5elf-assembly of thermally responsive amphiphilic diblock copolypeptides into spherical micellar nanoparticles. Angew Chem Int Ed 49 4257 260... 

Mortensen K (2000) Small angle scattering studies of block copolymer micelles, micellar mesophases and networks. In Alexandridis P, Lindman B (eds) Amphiphilic block copolymers self assembly and applications. Elsevier, Amsterdam... 

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