Assessing the Validity of QSARs for Ready Biodegradability of Chemicals: An Applicability Domain Perspective
Faizan Sahigara, Davide Ballabio, Roberto Todeschini and Viviana Consonni
Affiliation: Milano Chemometrics and QSAR Research Group, Department of Earth and Environmental Sciences, University of Milano-Bicocca, P.za della Scienza 1 - 20126 Milano, Italy.
Several classical and two recently proposed Applicability Domain (AD) approaches were implemented on a set
of three classification models retrieved from a published study to assess the ready biodegradability of chemicals. Each
model was associated with an optimal AD approach based on its ability to a) retain maximum test molecules within the
model’s AD, b) be appropriate for the strategy used towards model development and c) show reasonably converging
results with those derived with other AD approaches used. A decision criterion was also set to evaluate the AD of two
consensus models that were developed in the original study. An overview of test molecules excluded from the AD of all
the five biodegradability models was provided including an attempt to identify the major structural features and molecular
descriptors possibly relevant in deciding upon their ready biodegradability. Apart from the test set, an overview of the
results derived on the external validation set molecules was provided.
Keywords: Applicability domain, biodegradability, local-centred mahalanobis distance, model validation, QSAR.
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