Geometric environment

As mentioned previously, the chemistry and biochemistry of compartmentation in cubic phases is not as actively studied as that of hposomes and micelles however, these cubic phases have potential that should be explored further, mostly due to the large capacity to incorporate biomaterials, and the peculiarity of the restricted geometrical environment. For example the polycondensation of amino acids or other monomers inside the lipid, chiral channels might be explored, or other reactions where it would be advantageous to have relatively high concentrations of reagents in a restricted tubular environment. 

Boudart (223) suggested that all reactions might not be equally sensitive to the geometric arrangements in various metal surfaces or to the differences in the electronic structure of sites in different geometric environments (coordination). Boudart divided the reactions into two groups (I) structure insensitive and (II) structure sensitive. The operational criterion of structure sensitivity is the specific activity (the rate per unit surface area) or, the turnover numbers (TONs) (the rate per site) TONs should differ by more than a factor of 5-10 when the dispersion D is varied sufficiently. Bond (224) formulated similar ideas and also suggested several reasons why the variations of TONs with D can monotonically decrease (antipathic), mono-tonically increase (sympathetic), or show a maximum. 

Metals are modified by a second element due to the change of either electronic or geometric environment. Formation of stable bimetallic particles or alloys is prerequisite for improved catalytic properties. It seems even more important when metal particles are entrapped inside zeolite cages, like faujasite-type zeolite which is remarkably different from oxide supports. 

Up to now we have considered unreconstructed, defect-free low-index surfaces, where all surface atoms have the same geometric environment. In the real world, large defect-free terraces of low-index surfaces are the exception rather than the rule, and in nanometer-sized metal particles (clusters) such as those found in industrial catalysts a significant fraction of all surface atoms sit at steps, edges or corners and therefore have lower coordination than those in the terraces. There are many indications that such sites are more reactive than terraces [59],... 

Formation of Cu (phen)2 is described by equilibriums summarized in Eqs. (1), (2) in Fig. 2 (9,10). Phen binds also Cu ions with equilibrium constants log Ki and log K2 of 8.8 and 6.6, respectively (10). Analysis by X-ray diffraction of monocrystals showed that the geometrical environment of the metal ion in Cu (phen)2 is tetrahedral (11 but the Cu (phen)2 complex adopts different coordination geometries as trigonal bipyramid or octahedron with one or two additional ligand(s) as H2O or chloride (12). The complex was often... 

In parent fullerenes not every individual bond but, rather, sets of bonds are labeled. Sets of bonds are bonds with identical geometrical environment. Each bond of a given set can be transferred into any other bond of this set using suitable symmetry operations. In fullerene adducts, in addition, reference sites as well as further priority orders need to be defined. For details of the bond labeling algorithm see [189]. 

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