Nanovessels

In addition to their beauty, many of the described nanovessels also show interesting endo/exo chemistry ( inside and outside ). In the interior, species can be bound, and highly reactive intermediates can be stabilized, or chemical reactions supported or catalyzed. In the latter case, unusual reactivity or selectivity might be observed. Thus, container molecules act as homogeneous equivalents of heterogeneous porous materials like zeolites or MOFs. 

Due to the immense interest in this type of chemistry, the field has rapidly expanded and diversified over the last two decades. In this volume, some of the most prominent scientists in the field contribute extensive reviews, which show the versatility of approaches towards nanocontainers, and give some examples of processes occurring in their interior. The science of nanovessels is still in its infancy and therefore this field is expected to emerge further and develop a high impact in future chemistry. With the size and the special properties of the described derivatives, it bridges the gap between traditional chemistry and nanotechnology. 

The zeolite cavities can be considered as peculiar reaction nanovessels where the chemical processes carried out inside them and their products are affected by the confines in which they are being performed. This main principle was proven in mid-70 s when the first synthesis of neutral phthalocyanine complexes encapsulated in Y zeolites via intracrystalline assembling was performed at Moscow State University [1,2]. Once formed within the bottle-shaped supercages of Y zeolite, the resulting electroneutral complexes cannon leave them because of spacial restrictions. Later, this new type of inclusion compounds was termed as "ship-in-a-bottle" systems [3]. 

An analogous approach is the stabilization of phosphonium ions by addition of phos-phanes (PMcs, PEts, PPhMca, and PPhaMe) to methyl ketones (acetone, methyl ethyl ketone, 1,1,1-trifluoroacetone, and fluoroacetone) in an aqueous solution of Ga4L (Scheme 10.4). These cations decompose in water but they are persistent for weeks in the nanovessel. However, this stability is pH-dependant. The pH should be low because the guest should be protonated and is regularly exposed to the bulk of water as a consequence of the dynamic behavior of the assembly, but the pH should not be too low because in that case the host would disassemble. Therefore, the optimal value is 5.2. The exact mechanism is still unknown it has been ascertained that the protonated phosphane can be encapsulated but it is not possible to determine where the addition to the ketone occurs, inside or outside the cavity. Due to the chirality of the Ga4L tetrahedron, a kinetic diastereoselectivity is also obtained with chiral ions leading to diastereomeric excesses of 30-50%. 

In a restrieted spaee, some other chemical reactions will take place (new chemistry - chemistry in nanovessels ). 

Some unstable moleeules may become stable when enelosed in a nanovessel. 

Chemieal reactions in nanovessels, which may run in another way than without them, suggest that the atomic structure of materials may change under inereasing pressure. Suppose that we are dealing with a molecular crystal and we are studying what happens after applying isotropie pressure. 

Fig. 25 a Image of C50 heptamers trapped in nanovessels formed by the 2-melamine network. The scale bar is 5 nm. b Model. (Reproduced with permission from Ref. [126])... 

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