Spectral libraries cover the DreaMS Atlas nearly uniformly. The median length of the shortest path from a randomly selected node (n = 100,000 random nodes) to the nearest spectral library node is six edges. If spectral libraries are replaced with a random set of nodes of the same size, the median shortest path raises to seven edges (top). However, the difference in median minimum DreaMS similarities along these paths is significant (0.65 versus 0.74; MannWhitney U -test P < 0.05), suggesting that many DreaMS Atlas nodes represent structurally novel molecules relative to spectral library compounds (bottom). Each box plot displays the median (center line), quartiles (box bounds), whiskers extending to 1.5 times the interquartile range and outliers.
