Figure 1: Non-unique labeling of atoms in databases.

From: Unique identifiers for small molecules enable rigorous labeling of their atoms

Figure 1: Non-unique labeling of atoms in databases.
Figure 1

(a) 2D representation of the structure file of L-leucine (Data Citation 5: Biological Magnetic Resonance Data Bank bmse000042) downloaded from BMRB21. (b) 2D representation of the structure file of L-leucine (Data Citation 6: The Human Metabolome Database HMDB00687) downloaded from HMDB22,23,24. As shown in the diagram the two structural representations utilize different atom numberings. As a result, the relationship between atoms and their labels (numbers) is database-specific.