Coordinate-based chemical spaces, molecular

The measurement of molecular diversity requires the definition of a chemical space. This A-dimensional chemical space is represented by a group of selected molecular descriptors. Each compound in a collection can be assigned coordinates based on the measurement of its descriptor values. Increasing distance, within the dimensions of the assigned coordinate space, should correlate with increasing diversity (or decreasing similarity) between compounds. 

Rg. 6-10 Mapping chemical space [76]. Principle component models of chemical space are shown for 480 small molecules analyzed using 24 computed molecular descriptors and 60 measured phenotypic descriptors derived from a cell-based assay of cell proliferation. By considering the elements of S as coordinates, small molecules can be modeled as vectors,... 

Fortunately, the need to amass coordinates of atoms in reported crystal structures has already been appreciated, and efficient computer-based databases are now available. As a result, it is not necessary to type large sets of numbers into a computer, because they can be derived in computer-ready form from a database. In addition to the ready access to atomic coordinate tables, there are many excellent computer-graphics, geometrical, and statistical programs available for comparisons of structures. In practice, however, it is additionally advantageous to build molecular models either of the ball-and-stick variety or the space-filling variety, if chemical or biochemical insight is required from a comparison of molecular structures observed by crystal structure analyses. 

Molecular photochemistry of porphyrins and metalloporphyiins has exhibited novel aspects even at the current state whereby comprehensive efforts have been accumulated to understand their chemistry in the excited states. As described in the Introduction, the chemistry of porphyrins is inherently an aspect of supramo-lecular chemistry, since the central metal ion, porphyrin macrocycles, and axial ligands are all associated with coordination interaction. Porphyrin chemistry has multiple aspects of chemistry on 1.) the large n-electron system, 2.) the substituents, 3.) the central metal ion, 4.) the axial ligands, and S.) the special space for chemical reactions provided by the porphyrin plane and the metal-axi ligand microenvironment. The molecular photochemistiy based on their characteristic electronic structures, photophysical properties, and redox properties, which are summarized in Tables 1-3, has been surveyed in this chapter. Comprehensive understanding of porphyrin photochemistry would provide impetus or creation of unit devices in prospective supramolecular systems. Though we are obliged to say that we have not yet had a satisfactory supramolecular system, recent... 

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