Self-assembly phenomena

The all-important finding that carboxylate-appended sapphyrins can self-assem-ble was confirmed in the case of the sapphyrin monocarboxylate 6. ° For both compounds the self-assembly phenomena were shown to take place not only in the solid state, but also in solution and in the gas phase (see Section 3.3). This meant that the carboxylate-binding properties of the sapphyrins could be used as the key molecular recognition basis for engendering the spontaneous self-assembly of appropriately designed supramolecular ensembles. 

Self-assembly phenomena on solid substrates are usually studied in ultra-high vacuum (UHV) or at the liquid-solid interface. Surface analytical methods involving electrons require vacuum. But UHV has also the advantage that reactive metal and metal oxide surfaces can be used as substrate since the very low background pressure also guarantees long investigation times on a non-altered sample. 

This approach mimics familiar biological self-assembly phenomena such as protein folding [ 192], protein aggregation [ 192] and nucleotide pairing [ 188]. It incorporates features described in each of the above strategies (i.e., I—III), to give specialized nanoscopic structures, that can be precisely designed, usually with excellent control over CMDPs. Recent examples include so called structure directed synthesis by Stoddart [3a] (see Chapter 1 of this book) to produce toroidal bis-bipyridinium cyclophanes that are reminiscent of a molecular abacus , melamine-cyanuric acid lattices by Whitesides [193] and unique helical structures based on coordination of bipyridyl units to copper (II) ions by Lehn [194],... 

There are excellent reviews that address the structures of finite molecular assemblies.3 The literature principally involves molecular assemblies designed, constructed, and characterized in the liquid phase. This is unsurprising since interests in finite molecular assemblies largely originate from studies of molecular recognition and self-assembly phenomena in solution. 

The wide spectrum of self-assembly phenomena can be categorized in various ways. In this entry, we discuss the similarities and the differences between two- and three-dimensional systems. The last section of this entry describes recent and possible future applications of self-assembly processes, mainly related to advanced materials, environmental issues, biotechnology, and nanotechnology. Emulsions, microemulsions, and foams are examples of important and common applications in which self-assembly plays a key role. These have a wide variety of industry applications from cosmetics, foods, detergents, oil recovery, drug formulation/delivery, petroleum refining, and mining. As these are the subjects of other topics in this encyclopedia, they are not covered here. 

To date, helicates represent the best-developed and most investigated supramolecular architectures [12,13,74]. Exploiting the experiences gained over the years, self-assembly phenomena through metal coordination have shown remarkable potential in the construction of molecular frameworks. Of these architectures, the following chapters deal with metallacryptands (helicates) and 2 -metallacryptates. 

M. Brun, R. Demadrille, P. Rannou, A. Pron, J.P. Travers, and B. Grevin, Multiscale scanning tunneling microscopy study of self-assembly phenomena in two-dimensional polycrystals of pi-conjugated polymers the case of regioregular poly (dioctylbithiophene-alt-fluore-none). Adv. Mater., 16, 2087 (2004). 

Boehmer. V. Shivanyuk, A. Calixarenes in self-assembly phenomena. Calixarenes in Action 2000, 203-240. 

It is usually difficult to add functionalities (i.e., to insert other amphiphilic molecules into a bilayer membrane) to self-assemble a bilayer nanoparticle after its self-assembly in solvents because the assembled bilayer membrane is a thermodynamically stable. If one can controlled the self-assemble phenomena, more complexed nanostrucutres can be achieved, and it will open a new stage of drug/gene delivery system. Bui et al. prepared a bilayer membrane nanoparticle via two-step self-assemblies using a solubility of amphiphilic block copolymer (Fig. 2.1.8) [108], The nanoparticles were composed of a positively charged complex core (siRNA and polyethyleneimine [PEI]) and a capsid-like (bilayer) shell. The preparation processes were divided into two steps (1) an electrostatic... 

In addition to the adsorption process, in which the molecules reach the interface depending on their structure and relationship with the solvents, amphiphilic molecules show the tendency to organize and coordinate themselves into ordered sttuctures in water or solvent including the formation of aggregates such as micelles, liquid crystals (LCs), or bilayers. Such self-assembly phenomena can be described when the hydrophobic tails of surfactant molecules form a cluster to produce small aggregates, such as micelles, or large layered structures such as bilayers that are similar to a cell wall. ... 

Abstract Self-assembly phenomena in block copolymer systems are attracting considerable interest from the scientific community and industry alike. Particularly interesting is the behavior of amphiphilic copolymers, which can self-organize into nanoscale-sized objects such as micelles, vesicles, or tubes in solution, and which form well-defined assemblies at interfaces such as air-liquid, air-solid, or liquid-solid. Depending on the polymer chemistry and architecture, various types of organization at interfaces can be expected, and further exploited for applications in nanotechnology, electronics, and biomedical sciences. 

ExpUfres simpfe adsorption processes and complicated self-assembly phenomena. 

Basic Engineering Principles for Micro- and Nano-Fabrication Based on Molecular Self-Assembly Phenomena... 

Understanding of ordered self-assembling phenomena in binary PIL-water systems has been largely lagging behind. The formation of clusters and continuous structures of PIL molecules in aqueous systems and their influence on molecular self-assembly are of pivotal importance not only for fundamental science but also for their wide range of technological applications. 

Self-assembly phenomena based upon secondary forces have been widely observed in biological systems such as DNA, viruses, bacterial cell surface layers etc [70-73]. Nature-made supramolecular objects are very sophisticated in size and shape, and show tremendous specific and efficient functions. For example, we know many enzymes are responsible for specific catalytic processes. In this context, creation of supramolecular architectures with biomimetic or bioconjugate features would be desirable and worth investigating. In particular, a few examples related to the title of this review article have been reported. 

Since the self-assembly phenomena requires well-defined block copolymers with narrow molecular weight distribution, only living/controlled polymerization techniques have been exploited for the preparation of polymeric nanoparticles via PISA. In particular, in aqueous media, the controlled radical polymerizations have been the methods of choice, taking the advantage of the compatibility of the reactions with water and the ability to create a wide variety of amphiphilic polymers. Atom transfer radical polymerization (ATRP), nitroxide-mediated polymerization (NMP), and reversible addition-fragmentation chain transfer (RAFT) polymerization have been the most studied techniques. The three methods possess certain advantages however, RAFT remains particularly the most attractive due to the wide variety of polymers that can be produced in a controlled manner at low polymerization temperatures. 

Charleux and coworkers have made considerable progress toward the understanding of self-assembly phenomena of nanoparticles obtained via aqueous emulsion polymerization. Thus, poly(ethylene oxide) and poly(N,... 

POSS not only leads to self-assembling phenomena but also it has a strong effect on the chain mobility in polymers. POSS has a very low mobility in the polymer structures and therefore can be viewed as anchoring points linked to the macromolecules [70]. This effect is based not only on the rigid POSS core structure but also on the chemical structure of the organic ligands. Therefore different substitution patterns at the POSS cage can lead to variations in the macroscopic properties of the polymers. 

---