Molecule, design physical properties, estimation

Research findings from the areas of physical property estimation and chemical products selection are applicable to the design of molecules. A brief review of research in these areas is presented along with previous work in molecular design. 

An area that has used chemical stmctures for predictive purposes quite successfully is the estimation of thermophysical properties of compounds. There has been an extensive compilation of estimation methods (81), and prediction of physical properties has been automated using these techniques (82). More recendy, the use of group contribution techniques to design new molecules that have specified properties has been described (83). This approach to compound design is being used to develop replacement materials for chloroduorocarbons. 

This is also a two-step procedure similar to that of selecting a desired chemical from a list of candidate molecules. Unlike the selection from an existing set of compounds, the design of compounds implies the synthetic stipulation of molecules for which there are no experimental data of their physical properties. Therefore, using some of the available estimation techniques, different approaches have been proposed in the past and will be discussed in the following paragraphs. 

The generate-and-test search paradigm, used by the automatic design algorithm for the synthesis of molecules, is composed of two modules. The first module, the generator, enumerates candidate molecules. The second, the tester, evaluates each molecule, estimating its physical properties and checking for structural feasibility, and either accepts or rejects it. We... 

As the limitations of the additive group-contribution techniques become more apparent, new representational models will be required to solve the product design problem. These models must maintain some simplicity in the structure-property relationships, which can be inverted in an efficient and explicit manner to yield the structure(s) of the feasible molecule(s). Such models have yet to be invented, but it is important to keep in mind the needs of the product design, as new theories and techniques are being written for the estimation of physical properties. 

This work has focused on the use of optimization techniques within a molecular design application to derive novel catalyst structures. The use of connectivity indices to relate internal molecular structure to physical properties of interest provides an efficient way to both estimate property values and recover a complete description of the new molecule after an optimization problem is solved. The optimization problem has been formulated as an MINLP, and the fact that the problem has been formulated in a manner which is not computationally expensive to solve (using Tabu search) gives rise to the possibility that the synthesis route for such a molecule could be derived and evaluated along with the physical properties of that molecule. Further work will include such synthesis analysis, as well as the inclusion of a much larger set of physical properties and basic groups from which to build molecules, and will work toward the design of mixtures and the prediction of mixture properties via connectivity indices. 

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