(203ah) Utilization of Molecular Signature Descriptors for the Generation of Candidate Reactant Structures
Maximization of process efficiency through the selection of optimal chemicals has been one of the highlights of recent process design methods that include product design considerations in their algorithms. These integrated process and product design techniques are exhaustive as they do not commit to a specific chemical component until the final step. These techniques, however, are limited to non-reactive systems. A property based algorithm focusing on the product/molecular design aspects in reactive systems in which all reactants are unknown is introduced in this work. The product of the reaction is constrained by property bounds arising from the process to ensure the optimality of the process. An optimization problem is formulated to select the chemical structures that satisfy the property bounds and have the best dominant property. Molecular design is performed by utilizing the recently developed molecular signature descriptors. The molecular signature of a molecule is the systematic coding of constituent atoms that represents the extended valencies of the atoms to a pre-defined height. The signature of a molecule can be expressed as a linear combination of its atomic signatures . Molecular signatures can assist in tracking the changes in the structure of a molecule due to reactions in the system . This is achieved by generating atomic signatures for the target products through the knowledge of their general structural formula. Different qualitative structure activity/property relationships (QSARs/QSPRs) have been applied in the developed algorithm to estimate properties from the molecular structure. QSARs/QSPRs can be expressed in terms of different topological indices while the topological indices of molecules can be represented in terms of molecular signature descriptors . Thus the target properties have been related to the signatures. In the developed method, the problem is formulated in terms of the number of occurrences of each signature, i.e. the number of times each signature appears in the molecular structure. This allows for the dominant property and the associated property constraints to be expressed in terms of the number of occurrences of the signatures in the product molecule. After identifying the occurrence values, the molecular structure of the reaction product is generated using the algorithm developed by N.G. Chemmangattuvalappil . Next, from the chemical equation, the structure of the reactants is determined by considering the appropriate addition and/or removal of groups. Thus, candidate reactant structures can be generated irrespective of the type and number of reactions as the introduced algorithm focuses on the design of products first and then uses the chemical equations to identify the reactant structures. Safety and environmental constraints can also be considered in the set of property constraints. Graph theory principles have been utilized to track the signatures and to avoid the generation of infeasible molecular structures. This contribution will illustrate the developed methods and highlight their use through a case study.
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