Templated structures formation

Loeb has reported a series of pseudorotaxanes [84,85] and rotaxanes [86,87] where C-H- 0 hydrogen bonding interactions (together with N+- -O attractive forces) play an important contribution in templating the formation of the interlocked species. In particular, the formation of a pseudorotaxane was observed when equimolar amounts of [pyCH2CH2py]2+ and the crown ether 20 were mixed. The structural characterization of the resulting host-guest complex... 

In the first part of this chapter we will describe some general aspects of hydrothermal carbonization, using either carbohydrates or complex biomass to control structure formation in the presence of various catalysts and/or templates. In the second part, we then describe some of the most promising applications of these car-bon/hybrid materials in energy applications. 

The double-helical structure of DNA and the ability of the molecule to unravel in order to template the formation of copies of itself and transcribe RNA is clearly connected intimately with the supramolecular interactions that bind the two nucleotide strands together. It is the information encoded within the individual nucleobases that tells the molecule to form a double helix. This is an... 

There are many curious features of zeolite synthesis. Thus, different framework structures are formed by the same amine, and the same framework structure is also formed by the use of different amines [11]. Such observations have prompted investigations into the role of the amines in the formation of these structures. The role of the organic amine in the synthesis of zeolites can be classified into three types templating , structure-directing and space-filling. Here,... 

We have seen how elegantly transition metals can template the formation of knots, but what about Nature s favourite templating interaction, the hydrogen bond A remarkably efficient molecular trefoil knot synthesis based on this interaction was reported by Vogtle and co-workers, who made a knotane in 20% yield [39]. This amazing route (Fig. 11) was uncovered serendipitously during the synthesis of catenanes. The crystal structure of the compound was the definitive proof for the structure, because neither NMR nor mass spectrometry could tell it apart conclusively from the macrocycles that are also formed. 

As already described, the counterion can template the formation of different oxalate frameworks. For example, the synthesis of a heterobimetallic 3D framework K" [Cr " (ox)3] was achieved with [Cu(trans[14]dien)] " (trans[14] dien = 5,7,7,12,14,14-hexamethyl-l,4,8,11-tetraazacyclotetradeca-4-11-diene) (66). While each and Cr atom is octahedrally coordinated, each Cu " " ion coordinates an oxalate oxygen atom in a monodentate fashion producing 21 X 9 A helical channels (Fig. 4). This generates a ths net (7) structure, while the previous 3D oxalate networks consist of chiral srs nets. Magnetic studies showed an antiferromagnetic interchain interaction between the copper and chromium centers. 

It is interesting to note that although apparently unaware of the development of molecular imprinting, Pande et al. [28] proposed the use of thermodynamic control for the preparation of synthetic polymer systems with a memory for a template structure. Monte Carlo computer simulations were performed to validate their hypothesis. From these calculations they identified the formation of non-random polymer sequences arising from an evolution-like preferred selection of various monomer components by similar species. These studies have since been expanded upon using statistical mechanics to examine the consequences for protein folding [29]. 

Some important metal oxide materials that have used molecular and supramole-cular templates to direct structure formation are the zeolites and related semi-crystalline aluminosilicates. In this section we shall discuss the use of ammonium cations that direct formation of microporous zeolites and finish with some of the possibilities that exist with the use of surfactant systems and molecular aggregates to create mesoporous structure. Excellent books and reviews are suggested for additional reading into the detailed description of the art [58-60]. The intention of this section is to briefly introduce this area and describe the types of materials being produced using various imprinting techniques in metal oxide materials. 

Fig. 8.16. Supramolecular assembly of surfactants to create organised rod-like micelles can template the formation of metal oxides with well defined mesoporous structure, i.e. MCM-41 materials. Adapted from [66].

---