Self-assembly of molecules

As materials chemistry has developed, it has come to pay more and more attention to that archetypal concern of materials scientists, microstructure. That concern came in early when the defects inherent in non-stoichiometric oxides were studied by the Australian. I.S. Anderson and others (an early treatment was in a book edited by Rabenau 1970), but has become more pronounced recently in the rapidly growing emphasis on self-assembly of molecules or colloidal particles. This has not yet featured much in books on materials chemistry, but an excellent recent popular account of the broad field has a great deal to say on self-assembly (Ball 1997). The phenomenon of graphoepitaxy outlined in Section 10.5.1.1 is a minor example of what is meant by self-assembly. 

It will be clear that L-B films are intrinsically linked to self-assembly of molecules, and this has been recognised in the title of a recent overview book (Ulman 1991), An Introduction to Ultra thin Organic Films from Langnmir-Blodgett to Self-Assembly An Overview. 

The self-assembly of molecules containing two AADD faces into supramole-cular polymers has been observed by employing molecules containing two ureidopyrimidone moieties such as 45 [27], and the same logic has been used to construct tapes in which fullerenes [205] and siloxanes [206] are present as part of the backbone. 

Many organoantimony(III) halides are Lewis amphoteric. They have acidic sites on the Sb atoms and they are also basic through the lone pairs of electrons on the halogen atoms. A frequently encountered consequence of this dual nature is the formation of coordination polymers in the solid state. The resulting structures formed through self-assembly of molecules were considered in a book and in a review article. The Lewis acidity of organoantimony halides is also reflected in the tendency to form stable adducts with neutral donors or with halide anions. The 1 1 adduct (2) is formed by reaction of methylantimony dichloride with 2,2 -bipyridine. " ... 

Self-assembly of molecules and nanoparticles to build well-defined structures, constitutes another approach to make model catalysts [33,34]. Here, nano-structured surfaces are made from nanoscale building blocks that are synthesized from atoms and molecules by chemical means. There has been a tremendous development in this field during the past decade, which includes a number of different strategies, including microemulsions [33], (micellar) block copolymers [35,36], and template CVD growth [37]. Relatively little work has, however, so far been directed toward heterogeneous catalysis in the sense described in this chapter, i.e., to make supported catalysts [38]. There are many reports on preparations but relatively much fewer on evaluations of catal3dic activity, trends, or reactivity versus particle size, etc. A main issue for model catalysts prepared by self-assembly is whether they maintain the well-defined character after, e.g., template removal and calcinations and other pretreatment steps, before they can be used as model catalysts. 

Rebek and co-workers have studied the self-assembly of molecules containing substituted ureas.65 Dimerization of two calixarenes (where Bn is benzyl and Ar is 4-fluo-rophenyl ) (7.8) by hydrogen bonding produces a host that encapsulates benzene, fluorobenzene, p-difluorobenzene, and pyrazine, but not toluene. 

For all of the causes described above, in addition to traditional and relatively simple methods of carbon surface modifications (e.g., oxidation in liquid or gaseous phases), more sophisticated approaches are proposed which employ newly developed techniques such as intercalation [46,47], chemical vapor deposition (CVD) [48,49], and self-assembly of molecules [50]. 

Self-assembly of molecules relies on the selforganization properties of the oligomers. In particular oligothiophenes with long alkyl chains as substituents... 

In addition to molecule-molecule and molecule-substrate interactions, also the solvent plays an important role. This is actually an aspect which to a large extent has been neglected. Insight in the role of solvents is still in its infancy. The choice of solvents is mainly motivated by practical considerations solubility of the molecules, low vapor pressure, chemical inertness, and low affinity for self-adsorption. However, it is our belief that the choice of solvent will become more and more important to direct the self-assembly of molecules at the liquid-solid interface. From time to time, it is reported that in a given solvent pattern x is formed and in another solvent pattern y, without going into the details of the effect of the solvent. Recently, a number of studies appeared with a clear focus on the effect of solvent on the self-assembly process. Basically, two different phenomena are observed. 

In the recent past, there have been a number of reports on self-assemblies of molecules as advanced materials or smart materials . Without question, the inspiration for this exciting work comes from the biological world, where, e.g., the lipid bilayer of cell membranes plays a pivotal role. In this cormection it should be stated that many other researchers have also described self-assembling systems such as the liposome. Liposomes are modeled after biomembranes, which have been extensively investigated since the late 1960s (see Table 1 for references). 

Supramolecular noncovalent interactions [13], such as metal coordination, hydrogen bonding, hydrophobic forces, van der Waals forces, pi-pi interactions, and electrostatic interactions, are very appealing for the self-assembly of molecules, and they could be used to create nanostractured materials. Metal coordination, for instance in metal organic frameworks (MOFs) [14] or coordination polymers [15], has been applied to construct nanoporous supramolecular networks. 

Mikhailov, O. V.. Self-Assembly of Molecules of Metal Macrocyclic Compounds in Nanoreactors on the Basis of Biopolymer-Immobilized Matrix Systems. Nanotechnol. Russ., (1-2), 1825 (2010). 

TEMPO is disproportionated into the OA and the AA by the acids [46]. The disproportionation of TEMPO also promoted the micellization of the PVTEMPO-i-PSt copolymer [51]. The series of micellizations using the TEMPO redox systems indicate that the electron transport becomes a trigger that causes self-assembly of molecules, in addition to external triggers such as temperature, pressure, pH, salt formation, and noncovalent bond cross-linking. 

Monolayers called Langmuir-Blodgett (LB) films also involve self-assembly of molecules on a surface. In fhis case, however, the molecules do not beoome covalently attached to the surface. These LB films are inherenfly less sfable fhan covalently bonded monolayers, but they have oharacteristics that are useful for certain applications in nanotechnology. For example, an LB film made from phospholipid (Seotion 23.6) and catenane molecules was used in making fhe array of molecular swifches we discussed in... 

The self-assembly of molecules such as thiols and dithiols on metal surfaces is well-established and has been used to attach cadmium chalcogenide nanocrystals, for example, to Au surfaces [42], and to measure their electrical properties [43,44]. Attachment of CdS nanoparticle mono-layer onto bifunctional 1,5-hexanedithiol or 1,10-decanedithiol SAM has been reported [36, 42, 45]. In addition, various authors have also demonstrated assembly of monolayers of alkanethiols and other molecules on GaAs surfaces [46-49]. The alkanethiols were presumed to bind selectively to arsenic atoms on GaAs (100) surface [48, 49]. 

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