Many chemicals of interest in the domain of environmental chemistry fall in the class of substances referred to as Unknown, Variable composition, Complex reaction product or Biological origin (UVCB) substances. These chemicals generally cannot be represented with a single structure and, therefore, pose a significant challenge when trying to accurately characterize and share research results via chemical databases that rely primarily on distinct chemical structures to index and merge substance information. For this reason, it is not uncommon for public chemical databases to include questionably mapped structures associated with names or registry numbers that indicate a UVCB. To provide a more accurate documentation of the substance and clarify these data linkages, EPA’s DSSTox project has started employing Markush representations to represent UVCBs. Whereas the use of a Markush representation is more accurate than a single “representative” structure, it yields a new set of problems, including difficulty with determining uniqueness, storage format limitations, and inconsistencies in different software’s handling of the representations. It has, however, enabled the automated linking of a UVCB with the associated, well-defined chemical components which can be auto-enumerated within the software package employed. It also provides an interpretable depiction of the substance, and clarifies the linkage of research results to the appropriate chemistry. Additionally, it greatly increases the efficiency of collecting information associated with all components of a UVCB from within EPA databases, providing the ability to quickly identify and gather the compendium of data associated with either the UVCB or any of its structural components.

Integration of Markush structures into EPA’s DSSTox database to represent and enumerate UVCB substances

255th National Meeting (2018)

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