Crystallographic registry

Once a paper of interest has been identified, all the crystallographic information in that paper can be examined because the crystal serial number of the paper can be used in the crystallographic search system to retrieve that information. Alternatively, the CAS Registry number of any particular compound can be used to retrieve any data of interest on that compound from other files of the CIS. 

Adsorption processes on crystallographically well-defined substrate surfaces lead to the formation of 2D Meads phases with well-ordered structures denoted as overlayers". Generally, three different types of overlayers, depending on the degree of registry between overlayer and substrate, can be distinguished commensurate, higher-order commensurate or incommensurate overlayers, as illustrated schematically in Fig. 3.14. TTie term superlattice stmcture" is frequently used for commensurate overlayers which can be characterized by either the Wood or the matrix notation [3.271-3.274]. 

In absence of Me-S lattice misfit, the structure of growing 3D Me layers usually continues that of the condensed and commensurate 2D Meads overlayer and or 2D Me-S surface alloy formed in the UPD range at high For low AEi. The structure of a 3D Me film is usually in complete registry with the structure of the modified substrate surface SQikl) [hkl] II Me(M0 [hkl], where (hkl) and [hkl] are the Miller indices and crystallographic directions, respectively. 

Fig. 4 Space-filling model of the supramolecular helical array of the tetrapeptide Boc-Aib-Val-Aib-p-Ala-OMe showing the staking of subunits maintaining proper registry, generating a helical structure as determined by x-ray crystallographic analysis. Nitrogen atoms are blue, oxygen atoms are red. and carbon atoms are gray. Hydrogen atoms are omitted for clarity. View this art in color at www.dekker.com.)...

Structural (topological) Databases The structural databases play a central role in chemistiy because they contain information on chemical stmctures. Examples of this type are CAS registry, National Cancer Institute (NCI) database, Crystallographic Stracture Database (ICSD), CSD, Protein Data Bank (PDB), etc. The structure databases are usually designed to store chemical stmctinal information representing the chemical bonds and atoms in such a way to use them for computational operations, such as structure search, data mining, etc. 

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