Cooperative isolation effect

The assumption of a strict, vapor-phase derived pair potential appears acceptable only in those cases where a weak intermolecular interaction does not cause appreciable structural relaxations in the monomers. In the case of hydrogen-bonded systems, the use of the frozen monomer assumption precludes, however, almost always the investigation of all the observable structural and spectroscopic features of the A—H moiety. Therefore, the reference system for the discussion of cooperative, nonadditive effects is exclusively the structurally fully optimized hydrogen-bonded dimer with a single isolated hydrogen bond and with all the properties derivable from the global 3N-6 dimensional potential energy surface of the dimer. 

The comparison between isolated features and the same feature embedded in a more or less complex H-bond network enables one to document the existence of cooperative electronic effects, presumably caused by an electronic polarisation of the amide groups favoured by the H-bond network, especially when a circular chain is formed [82,107,121,134,139]. As expected for a vibrational motion coupled to... 

Another point that requires furtlier research is the cooper-ativity effect. In a long. sequence of donor-acceptor-donor-acceptor.. . interactions, as found in most crystalline carbohydrates. cooperativity is thought to confer a higher strength (and shorter H O distances) on the individual bonds than would apply to isolated hydrogen bonds. Current modeling... 

In this chapter, we summarize the recent advances in the development of nanaoreactors based on porous solid materials for chemical reactions, including the general methods for the fabrication of typical porous materials, (mesoporous silicas (MSs), carbon nanotubes (CNTs), and the MOFs), the assembly of the molecular catalysts in the cavities and pores of the porous materials, the chemical reactions in the porous-material-based nanoreactors, and some important issues concerning the porous-material-based nanoreactor, such as the pore confinement effect, the isolation effect, and the cooperative activation effect We close this chapter with an outlook of the future development of the nanoreactors. 

Through covalent and noncovalent bonding methods, different kinds of molecular catalysts could be incorporated into MSs and MOFs. These porous materials with the incorporated molecular catalyst could catalyze various kinds of chemical reactions. A review of all the related works is impossible and not necessary in this chapter. We only review some representative examples for demonstrating the unique properties of the nanoreactor for catalytic reactions, including the pore confinement effect, the enhanced cooperative activation effect, and the isolation effect, as well as the microenvironment and the porous structure engineering of the nanoreactor and the catalytic nanoreactor engineering. 

In addition to the enhanced cooperative activation effect of the nanoreactor, the isolation effect could also be expected in the confined nanospace if the diameter of nanopore is similar to the size of the molecular catalysts, because the limited nanospace could restrict the free movement of the molecular catalysts. Two issues relevant to the isolation effect of the nanoreactor, namely selectivity control in organic reactions and inhibition dimerization of the molecular catalysts, will be discussed. 

It is concluded that the cooperative effect observed is of long-range nature and therefore of elastic rather than of electronic origin. Recently, the additional suggestion has been made [138] that, due to intermolecular interactions in the crystal environment of [Fe(ptz)g](BF4)2, domains of iron(II) complexes interconvert together. The observed kinetics would then correspond to a first- or higher-order phase transition rather than to the kinetics which are characteristic for the conversion of isolated molecules. 

This is a prime example of how plant constituents can act cooperatively, and isolation of a single constituent may reduce its effectiveness. 

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