Molecular reaction vessels

The robust, well-shielded cavity found in hemicarcerands offers tremendous scope for the use of these hosts as micro-reaction vessels in order to protect reactive species from bimolecular decomposition by isolating them from the outside medium. Furthermore, the unique intracavity environment with its fluid-like properties in which guest species are, formally, in a very condensed state at very high pressures, may well result in unique inclusion reactivity. Indeed, the inner volume of carcerands and hemicarcerands has been described as a new phase of matter distinct from solid, liquid and gas. A number of elegant demonstrations have been made of the potential of inclusion reactions, and there is clearly a great deal of scope for their use as molecular reaction vessels. 

Self-assembled capsules are of significant interest as molecular reaction vessels and in the control of confined inner space . 

Moreover, solvent reorganization energies, which are required for fhe reaction to occur in a bulk solvent, are not needed in the presence of fhe cucurbit[6]uril. This mechanism probably also contributes to the large rate enhancement. The inclusion of fhe reacting groups into the "molecular reaction vessel" eliminates any retardation of the reaction by the solvent environment. 

Apart from the use of molecular reaction vessels, there is much promise for the use of solids prepared by Yaghi and others which are highly porous and serve as excellent host stmctures. The MOFs of composition Zn40(BDC)3 with a cubic three-dimensional extended porous stmcture absorbs hydrogen gas up to 4.5 wt %, that is, 17 hydrogen molecules/formula unit at 78 K and 1.0 wt % at room temperature and pressure of 20 bar, respectively. ... 

The reactive behavior of a carbene within a molecular reaction vessel is expected to be very different from that of a carbene in any other reaction medium. Host vessels may have any variety of different channel or cavity sizes that can restrict the mobility of carbene guests and any other reaction partner that might also be included.54 One should even be able to generate, within the host domain, a carbene that has no intramolecular reaction pathways available. Situated like a model ship... 

With so much uncertainty regarding true carbene intermediacy within molecular reaction vessels, a reaction demonstrating a unique process only attributable to carbenes needed to be performed. 

Upon photolysis of azicyclooctane (40), cw-cyclooctene (44) is readily formed, but so too are products derived from intramolecular C-H insertions of carbene 41. Of special interest is bicyclo[3.3.0]octane (42). Created from a 1,5-CH insertion within carbene 41 (Scheme 8),124 r/.v-fused 42 needs space to form. Since the free volume (A V) of a CyD depends on the number of monomer units of which it is comprised, it is not surprising that these factors conspire to limit bicyclo[3.3.0]octane (42) formation when azicyclooctane (40) is photolyzed within ot-CyD (Table 4).42,125 The occurrence of transannular C-H insertion becomes less probable as the cavity within the molecular reaction vessel gets smaller. 

Perhaps ironically, as science grows larger in scope and broader in focus, some of the most promising tools to synthesize the hows, whats, and wheres of human biology are exceedingly tiny. Micromachines, tiny biosensors, and miniature molecular reaction vessels will undoubtedly be standard items in a chemist s toolbox in 10 or 20 years. 

Meng ZH, Sode K (2005) The molecular reaction vessels for a transesterification process created by molecular imprinting technique. I Mol Recogn 18(3) 262—266... 

Isolating the reaction center from some unwanted neighbothood (Fig. 13.23a2), which in the extreme ease leads to molecular reaction vessels, even such large ones as a biological cell. 

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