2D QSAR Hydration Free Energy Calculations. Molecular descriptors were calculated with RDKit as described previously . Descriptors were also normalized by molecular weight; parameters with zero variance were removed from consideration, leaving 284 descriptors in total, which were scaled from 0 to 1. We then trained a Gaussian kernel support vector regressor (SVR ) with scikit-learn . The 642 ligands were split into a training and test set in a 70:30 ratio; the scaled descriptors (the independent variables) and hydration free energies (the dependent variables) for the training compounds were used to build an SVR model to predict hydration free energies; the model was then tested against the HFEs from the test set.