Structure-based chemical data systems

Computer-based chemical information systems are now widely used for the storage and retrieval of chemical structure information. Efficient searching algorithms are available which allow structure-based searches to be carried out on databases containing many thousands, or even millions, of chemical compounds. In addition, the ease with which machine-readable structural data can be manipulated has led to a wide range of related activities, such as computer-aided s)uithesis design and studies of quantitative structure-activity relationships (QSAR). ... 

Despite the broad definition of chemometrics, the most important part of it is the application of multivariate data analysis to chemistry-relevant data. Chemistry deals with compounds, their properties, and their transformations into other compounds. Major tasks of chemists are the analysis of complex mixtures, the synthesis of compounds with desired properties, and the construction and operation of chemical technological plants. However, chemical/physical systems of practical interest are often very complicated and cannot be described sufficiently by theory. Actually, a typical chemometrics approach is not based on first principles—that means scientific laws and mles of nature—but is data driven. Multivariate statistical data analysis is a powerful tool for analyzing and structuring data sets that have been obtained from such systems, and for making empirical mathematical models that are for instance capable to predict the values of important properties not directly measurable (Figure 1.1). 

Source characterization results are not located in a centralized facility which is constantly updated. The Environmental Protection Agency has established the Environmental Assessment Data System (EADS) (31) which contains chemical compositions of particulate matter emissions tests. This existing computerized structure can provide the centralized location for receptor model source characterization information. Procedures such as those described for ambient data in the previous section need to be developed in order to allow receptor model users access to this data base over telephone lines. The data required of receptor model source tests should be incorporated into the EADS, and source characterization results should report this information in an EADS compatible format. 

There are two competing and equivalent nomenclature systems encountered in the chemical literature. The description of data in terms of ways is derived from the statistical literature. Here a way is constituted by each independent, nontrivial factor that is manipulated with the data collection system. To continue with the example of excitation-emission matrix fluorescence spectra, the three-way data is constructed by manipulating the excitation-way, emission-way, and the sample-way for multiple samples. Implicit in this definition is a fully blocked experimental design where the collected data forms a cube with no missing values. Equivalently, hyphenated data is often referred to in terms of orders as derived from the mathematical literature. In tensor notation, a scalar is a zeroth-order tensor, a vector is first order, a matrix is second order, a cube is third order, etc. Hence, the collection of excitation-emission data discussed previously would form a third-order tensor. However, it should be mentioned that the way-based and order-based nomenclature are not directly interchangeable. By convention, order notation is based on the structure of the data collected from each sample. Analysis of collected excitation-emission fluorescence, forming a second-order tensor of data per sample, is referred to as second-order analysis, as compared with the three-way analysis just described. In this chapter, the way-based notation will be arbitrarily adopted to be consistent with previous work. 

For this purpose, one needs to include into the knowledge base of the system, the different parameters and concepts that lead to those interpretations. One has to consider data on acidity, i.e., the number, density, force, and location of acid sites, and three-dimensional structural factors of the zeolite, i.e., the type of framework, and the characterization of pores, channels, and cavities by their form, internal volxune, opening,. .. One of our contributions is also devoted to the mechanisms of reaction. A module vdll allow to generate possible mechanisms for a given reaction catalyzed by one particular zeolite. This may be achieved by characterization of the guest molecules (reactants and products), as well as the transition states, and the reaction intermediates according to their shape, size, and volume, but also their chemical functions. 

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