Background¶

Sort and Slice (SNS) was developed by a former OPIGlet, Markus, as a method for improving Extended Connectivity Fingerprints (ECFPs) by overcoming bit collisions. ECFPs are a form of topological fingerprint which denote the absence and presence of circular substructures in a molecule. The steps for deriving an ECFP from a molecule are as follows:

1. Identifier assignment:

   Each atom in the molecule is assigned an initial numerical identifier; this is typically generated by hashing a tuple of atomic properties called Daylight atomic invariants into a 32-bit integer. These properties are:

   1. Number of non-hydrogen neighbours.
   2. Valence – number of neighbouring hydrogens.
   3. Atomic number.
   4. Atomic mass.
   5. Atomic charge.
   6. Number of hydrogen neighbours.
   7. Ring membership.*

   *Ring membership is an additional property that is often used but is not one of the original Daylight atomic invariants.

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