Geometrical criteria

Table 7 Aromaticity based on geometric criteria (TDA=thiadiazole)...

Not all quantum chemical calculations on zeolite clusters involve necessarily millions of integrations, and in the case of iso-electronic chemical systems fulfilling certain geometrical criteria, almost trivial back-of-an-envelope type calculations can yield rigorous upper and lower energy bounds. Fortunately, some zeolite structural units fulfill these geometric criteria. 

The above-mentioned topological criteria are very useful since the geometrical criteria are often not sufficient to establish whether or not hydrogen bonding exists. As we will see below, these theoretical criteria are universal and quite suitable for nonconventional hydrogen bonds as well as for dihydrogen bonding. 

Peters KP, Fauck J, Frommel C (1996) The automatic search for ligand binding sites in proteins of known three-dimensional structure using only geometric criteria. J Mol Biol 256 201-213... 

Fig. 3. (a) The general case of a hydrogen bond (b) some simple examples of molecular association by way of hydrogen bonding (c) some geometrical criteria for hydrogen bonding. 

The point arose as to the actual site of action of moniliformin in plants. Earlier, it had been stated that the geometrical criteria of hydrogen bond formation suggested that MH could be regarded as either a purine or pyrimidine analogue and, therefore, could substitute as one of the base pairs in nucleic acid.11 And the fact that it had shown plant growth regulatory activity had led an industrial company to become interested in the product as a potential herbicide. 

On the other hand, all the sulfur-containing heterocycles are located in the close vicinity of the model aromatic structure, the cyclopentadienyl anion 131. Thus, one can assign higher aromaticity to the sulfur-containing heterocycles relative to the oxygen-containing ones, not only on the basis of geometric criteria but also from the 2-D dimensional perspective. 

This sensing model also implies that the geometric properties, instead of solely the physical properties of the auxiliary phase at the working electrode, are critical to kinetic performance. Accordingly, the four most important geometric criteria for an auxiliary phase are as follows ... 

In what is the essence of materials engineering, structure and preparation will undoubtedly be of vital important to final properties. In order to deposit better auxiliary phases with close control to meet all six geometric criteria, PEVD has recently been applied to deposit auxiliary phases at the working electrodes of gaseous oxide sensors. ... 

Geometric Criteria PEVD Melting -Quenching In-Situ Disc... 

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