Topological chemistry

Lignite) 854 (Peat) 1067 (Splint) 1084 (Sub-bituminous) 25)0. W. van Krevelen, "Coal Topology, Chemistry, Physics and Constitution Elsevier, Amsterdam (1961) 26)ASTM Stds 1961, Part 8, Method D388-38, ppl227-37 (Classification of coals) 27)H.H. Lowry,... 

Intermolecular interactions and metal coordination have been used very effectively for the synthesis of novel organic and inorganic entities that would be of difficult access otherwise, leading in particular to the development of a topological chemistry [16]. Inorganic templating and self-assembly provide coordination compounds whose geometries make possible the synthesis of a variety of complex structures, such as... 

Contents Introduction. - Chemistry and Topology Topological Aspects in Chemistry. Molecular Topology. - Chemistry and Graph Theory Chemical Graphs. Fundamentals of Graph Theory. 

Van Krevelen, D. W., "Coal Topology, Chemistry, Physico and Constitution", Elsevier, New York, 1961. 

Mixtures containing up to several thousand distinct chemical entities are often synthesized and tested in mix-and-split combinatorial chemistry. The descriptor representation of a mixture may be approximated as the descriptor average of its individual component molecules, e.g., using atom-pair and topological torsion descriptors. 

Because of constitutional complexity, the exact chemistries of nickel-base superalloys must be controlled carehiUy in order to avoid the precipitation of deleterious topologically close-packed (TCP) phases and extraneous carbides after long-term high temperature exposure. Heat-treatment schedules and thermomechanical treatments in the case of wrought alloys also are important to provide optimum strength and performance. 

Up to this point, we have emphasized the stereochemical properties of molecules as objects, without concern for processes which affect the molecular shape. The term dynamic stereochemistry applies to die topology of processes which effect a structural change. The cases that are most important in organic chemistry are chemical reactions, conformational changes, and noncovalent complex formation. In order to understand the stereochemical aspects of a dynamic process, it is essential not only that the stereochemical relationship between starting and product states be established, but also that the spatial features of proposed intermediates and transition states must account for the observed stereochemical transformations. 

The chemical nature of the packing has the largest influence on the retention of molecules and a big impact on the efficiency of the separation itself. The chemical and physical properties of the sorbent are determined by the choice of the comonomers for the copolymerization. The type of the copolymerization process employed by the synthetic chemist introduces the macroporous structure into the sorbent and determines the surface topology (accessibility, resolution) and the surface chemistry of the packing (4). 

Not all chemistry textbooks provide a clear description of what stereo- and structural formulas imply. Maybe the concepts of spatial and topological congruence of graphs could contribute to the clarification of the chemical terminology. 

In pentacoordinate chemistry, the Berry mechanism may be depicted by a graph which was first used in chemistry by Balaban. Equivalent illustrations of the topology of Berry steps have been provided... 

A Brief Review of the QSAR Technique. Most of the 2D QSAR methods employ graph theoretic indices to characterize molecular structures, which have been extensively studied by Radic, Kier, and Hall [see 23]. Although these structural indices represent different aspects of the molecular structures, their physicochemical meaning is unclear. The successful applications of these topological indices combined with MLR analysis have been summarized recently. Similarly, the ADAPT system employs topological indices as well as other structural parameters (e.g., steric and quantum mechanical parameters) coupled with MLR method for QSAR analysis [24]. It has been extensively applied to QSAR/QSPR studies in analytical chemistry, toxicity analysis, and other biological activity prediction. On the other hand, parameters derived from various experiments through chemometric methods have also been used in the study of peptide QSAR, where partial least-squares (PLS) analysis has been employed [25]. 

Dendrimers are complex but well-defined chemical compounds, with a treelike structure, a high degree of order, and the possibility of containing selected chemical units in predetermined sites of their structure [4]. Dendrimer chemistry is a rapidly expanding field for both basic and applicative reasons [5]. From a topological viewpoint, dendrimers contain three different regions core, branches, and surface. Luminescent units can be incorporated in different regions of a dendritic structure and can also be noncovalently hosted in the cavities of a dendrimer or associated at the dendrimer surface as schematically shown in Fig. 1 [6]. 

In the case of n-butene isomerization it was demonstrated (Figure 2) that the ideal micro-pore topology led to retardation of the C8 dimer intermediate and that the catalyst based on the ferrierite structure was close to optimal in this respect [1). For selective isodewaxing a one-dimensional pore structure which constrained the skeletal isomerization transition state and thereby minimized multiple branching such as the SAPO-11 structure was found to meet these criteria. Clearly, these are ideal systems in which to apply computational chemistry where the reactant and product molecules are relatively simple and the micro-porous structures are ordered and known in detail. 

Voelkel, A. Structural descriptors in organic chemistry - new topological parameter based on electrotopological state of graph vertices. Comput. Chem. 1994, 18, 1. ... 

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