Self-assembly solvophobicity

It is general considered that the driving force for the self-assembly of amphiphilic molecules is a solvophobic effect, more specific in an aqueous environment, this is referred to as the hydrophobic effect. The type of aggregate morphology formed can be predicted... 

Block copolymers in selective solvents exhibit a remarkable capacity to self-assemble into a great variety of micellar structures. The final morphology depends on the molecular architecture, tlie block composition, and the affinity of the solvent for the different blocks. The solvophobic blocks constitute the core of the micelles, while the soluble blocks form a soft and deformable corona (Fig. Id). Because of this architecture, micelles are partially Impenetrable, just like colloids, but at the same time inherently soft and deformable like polymers. Most of their properties result from this subtle interplay between colloid-like and polymer-like features. In applications, micelles are used to solubilize in solvents otherwise insoluble compounds, to compatibilize polymer blends, to stabilize colloidal particles, and to control tire rheology of complex fluids in various formulations. A rich literature describes the phase behavior, the structure, the dynamics, and the applications of block-copolymer micelles both in aqueous and organic solvents [65-67],... 

A self-assembled coordination cage and micelles were found to accelerate Diels-Alder reactions in an aqueous media. The catalysis of Diels-Alder reactions via noncovalent binding by synthetic, protein, and nucleic acid hosts has been surveyed and compared to explore the origin of the noncovalent catalysis. These catalysts consist of binding cavities that form complexes containing both the diene with the dienophile and the reaction occurring in the cavity. The binding requires no formation of covalent bonds and is driven principally by the hydrophobic (or solvophobic) effect. ... 

The LMWGs have in common the property that they self-assemble into fibrous aggregates a process that can be driven by different noncovalent interactions like coulomb interactions, hydrogen bonding, n-n interactions, van der Waals forces, and solvophobic effects. For most of the early examples of LMWGs, the gelation prop-... 

Instructed, reproducible self-assembly of this type can be seen in numerous disciplines. In polymer chemistry, certain oligo(phenylene ethylenes) undergo solvophobic folding into helical conformations in polar solvents. " In peptide science, synthetic polypeptides containing unnatural P-amino acids spontaneously adopt helical dispositions in solution, despite being unable to form the hydrogen bonds that drive self-assembly in normal biopolymers. 

Alternatively, the level of stmctural complexity may be affected in a totally different manner employing co-assembly of chemically unlike molecules instead of self-assembly of chemically identical molecules [12-20]. We refer to the resultant micelles as mixed micelles or co-micelles to indicate that this type of micelle consists of more than one type of molecule, whereas classical micelles consist of identical molecules (polydispersity effects not taken into account). Consider two chemically distinguishable amphiphilic molecules A-B and C-D. Self-assembly into A/C or B/D micelles consisting of a core-shell structure, with a core solely consisting of A or C units and a shell solely consisting of B or D units, will only occur if the A or C units are solvophobic and the B or D units are solvophilic. However, if all units (A and B, or C and D) are solvophobic, phase separation will occur on a macroscopic level and result in a macroscopically inhomogeneous two-phase system. Conversely, if all units (A and B, or C and D) are solvophilic, phase separation... 

Amphiphilic molecules such as surfactants and block copolymers containing hydrophobic (water-insoluble) and hydrophilic (water-soluble) parts, serve as simple synthetic model systems for understanding self-assembly. Micellization is a common self-assembly process whereby amphiphilic molecules spontaneously aggregate into various nanostructures that are usually of spherical, ellipsoidal, cylindrical, or vesicular shapes [1, 2]. These processes usually occur in selective solvents, i.e., solvents that are good for one part but poor for the other. Here, self-assembly is primarily driven by the incompatibility of the insoluble (hydrophobic or more generally solvophobic ) part with water or other solvents, and is mainly counteracted by repulsions or unfavorable configurations experienced in the swollen corona of the resulting micelles. 

The ordered structures assembled from polypeptide homopolymers and copolymers in both bulk and solution have attracted a great deal of attention over the past few decades and could continue to be an active theme in the future [30-38]. In solution, both the a-helix and p-sheet conformations of polypeptides facilitate the formation of ordered structures in liquid crystals (LCs), gels, and micelles during the assembly process. Usually, LC structures are assembled from polypeptide homopolymers in concentrated solutions [39-41]. In solutions with moderate concentrations, gels are usually formed by both polypeptide homopolymers and copolymers [42-44]. In dilute solutions, polypeptide copolymers are able to self-assemble into diverse micelle structures with a solvophilic shell, while the solvophobic polypeptide chains are packed in an ordered manner in the micelle core [45 7]. 

Self-assembling systems selectively produce the most thermodynamically stable products and therefore both the enthalpic and entropic contributions towards the final species must be considered. The formation of a self-assembled product, by definition, necessitates the formation of new, favourable interactions, i.e. the process is enthalpically favourable. However, the formation of aggregate species occurs at an entropic cost as many degrees of freedom in the system are lost. The entropic penalty is offset somewhat by the release of solvent molecules that were previously interacting with the binding areas of the assembly components, in a solvophobic effect (see Chapter 1, Section 1.3.5). 

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