(463e) Integrated Process and Molecular Design Using Molecular Property Operators Based On Signature Descriptors
The reverse problem formulation is a technique used to design a process according to the specifications of the final product. Using the integrated process and product design techniques, the optimum solutions for process and product design problems have been obtained with out committing to any specific components in the solution step. The property targets to be satisfied by the product have been estimated in the process design stage based on the specifications of the final product. The property clustering techniques have been employed to represent the property target region in the form of algebraic equations. However, apart from the targets set by the process design, the molecule has to satisfy a number of other environmental and safety constraints in order to be used in an actual process. In this work, we are introducing an algorithm that uses the concept of molecular signature descriptors for molecular design. The signature is a systematic coding system of atom types and the signature of a molecule can be obtained as a linear combination of its atomic signatures (Visco et al 2002). It has been proved that any of the topological indices of molecules can be represented in terms of molecular signatures and it is possible to correlate the topological indices to the actual properties and biological activities. Here, the new algorithm utilizes molecular property operators based on signatures for solving the reverse problem of obtaining the molecular structures that satisfy the property targets estimated in the process design step. A new set of equations will be employed to ensure that the molecule meets the safety and environmental constraints as well. The principles in graph theory are incorporated to avoid the generation of infeasible structures. Since the molecular operators are formed based on molecular signatures, the property models based on different topological indices can be represented on the same property platform. Since different properties are described using different topological indices, the height of molecular signature required to describe those topological indices will be different. However, techniques have been developed to describe all topological indices with a single signature height. The final solution will be obtained as a set of the biggest signature height used to describe the topological indices. Therefore, the accuracy of prediction will not be compromised because off this transformation. The property models required to describe the target properties may be based on QSPR/QSAR (quantitative structure-property/activity relationship) models or in the form of group contribution methods. In the developed algorithm, the group contribution models can also be represented using the signatures which allow for the simultaneous consideration of all property targets irrespective of whether the targets are based on process design or other constraints. The accuracy of this method depends only on two factors- how well the actual property-topological index relationships are estimated and the height of atomic signatures used to describe the topological indices. Since, many topological indices can be used to describe each property, this algorithm generally provide reliable results. The algorithm has been extended for the design of acyclic molecules and molecules with multiple bonds. This contribution will illustrate the developed methods and highlight their use through a case study.