Molecular engineered layer structures

Bakke et al. (1982) have shown how montmorillonite catalyses chlorination and nitration of toluene nitration leads to 56 % para and 41 % ortho derivative compared to approximately 40 % para and 60 % ortho derivatives in the absence of the catalyst. Montmorillonite clays have an acidity comparable to nitric acid / sulphuric acid mixtures and the use of iron-exchanged material (Clayfen) gives a remarkable improvement in the para, ortho ratio in the nitration of phenols. The nitration of estrones, which is relevant in making various estrogenic drugs, can be improved in a remarkable way by using molecular engineered layer structures (MELS), while a reduction in the cost by a factor of six has been indicated. With a Clayfen type catalyst, it seems possible to manipulate the para, ortho ratio drastically for a variety of substrates and this should be useful in the manufacture of fine chemicals. In principle, such catalysts may approach biomimetic chemistry our ability to predict selectivity is very limited. 

Organic phosphonates represent another class of anchoring agents, which react with zirconium hydroxide to form pillared structures. These are also referred to as molecularly engineered layered structures (MELS). Layered compounds of organic phosphonates of zirconium with the formula of Zr(RP03)2 have been rec-... 

For example, the synthesis and preparation of new materials has expanded to over 200 combinations of chemical compositions and crystal structures, not to mention the possible variety of molecularly engineered layered structures such as the MGLS from Catalytica (1 ) and many other pillared clays. 

Tetravalent metal phosphonates, or MELS (for Molecularly Engineered Layered Structures), provide a novel class of materials that combine many of the properties of incn-ganic metal oxides with the organic functionality more commonly found in functionalized polymeric resins. Early development work on these materials was carried out by Alberti and co-woikers [ref. 1] and Dines et al. [ref. 2]. Synthesis and characterization of related zirconium phosphates that also contain phosphonate groups as pillars have been described by Clearfield [ref 3]. There is a substantial patent estate for tetravalent metal phosphonates, and exclusive rights to this estate are owned by Catalytica [ref 4]. 

The topochemical polymerization of 1,3-diene monomers based on polymer crystal engineering can be used not only for tacticity but also for the other chain structures such as molecular weight [ 102], ladder [84] or sheet [ 103] structures, and also polymer layer structures using intercalation reactions [ 104-107]. Some mechanical and structural properties have already been revealed with well-defined and highly or partly crystalline polymers [ 108-111 ]. A totally solvent-free system for the synthesis of layered polymer crystals was also reported [112]. 

Recently reported meso- and macroscale self-assembly approaches conducted, respectively, in the presence of surfactant mesophases [134-136] and colloidal sphere arrays [137] are highly promising for the molecular engineering of novel catalytic mixed metal oxides. These novel methods offer the possibility to control surface and bulk chemistry (e.g. the V oxidation state and P/V ratios), wall nature (i.e. amorphous or nanocrystalline), morphology, pore structures and surface areas of mixed metal oxides. Furthermore, these novel catalysts represent well-defined model systems that are expected to lead to new insights into the nature of the active and selective surface sites and the mechanism of n-butane oxidation. In this section, we describe several promising synthesis approaches to VPO catalysts, such as the self-assembly of mesostructured VPO phases, the synthesis of macroporous VPO phases, intercalation and pillaring of layered VPO phases and other methods. 

The Langmuir-Blodgett (LB) films are solid organized media, where the studies of the chemical reactivity lead to a better comprehension of molecular interactions in the solid state, and to a development of a true molecular engineering. The LB technique allows the building of different structures at the molecular level, such as mixed layers and alternating layers. These molecular assemblies appear as sets of molecules, which can interlock, to give rise to specific physico-chenucal properties. 

A fifth option for detector materials is really a combination of materials and molecular size crystalline structure. By laying down many thousands of alternating layers, each only a few atoms thick, we can create a new or artificial or lattice-engineered material with a unique band structure. Such layers in delineated volumes can create energy boxes that can confine our carriers. Analysis of that situation ( The particle in a box ) is a standard problem or example in every elementary quantum... 

The importance of surface characterization in molecular architecture chemistry and engineering is obvious. Solid surfaces are becoming essential building blocks for constructing molecular architectures, as demonstrated in self-assembled monolayer formation [6] and alternate layer-by-layer adsorption [7]. Surface-induced structuring of liqnids is also well-known [8,9], which has implications for micro- and nano-technologies (i.e., liqnid crystal displays and micromachines). The virtue of the force measurement has been demonstrated, for example, in our report on novel molecular architectures (alcohol clusters) at solid-liquid interfaces [10]. 

This would create a tremendous boost to the work of the product innovators, as well as to the work of researchers who seek to develop theory and correlations between molecular structure and properties. The searchers in product innovations also need better search engines, in the form of databases that are designed and compiled to be reverse searchable, so that one can state a set of desired properties and find a set of materials that have them. This would address the modern Thomas Midgley problem, of finding the set of all compounds that boil between -30 and 0 °C, that are nonflammable and nontoxic, that do not harm the stratospheric ozone layer, and that do not cause global warming. 

---