Fig. 2.

Functional-group statistics and aqueous solubilities of biological compounds in the four-carbon linear-chain redox chemical space. (A) The subset of molecules in four-carbon linear-chain redox chemical space that matches biological metabolites in the KEGG database. Compounds that match KEGG metabolites but with alcohol groups substituted by either amines or phosphates are marked with black and red squares, respectively. (B) Enrichment and depletion of functional groups in the set of biological compounds. The vertical position of each colored circle corresponds to the number of times each functional group appears in the set of biological compounds. The light gray rectangles show the corresponding expected null distributions for random sets of molecules sampled from redox chemical space. See SI Appendix, Fig. S1 for statistical analysis of functional-group pairs and triplets. (C) Comparison of predicted aqueous solubility log(S) at pH 7 for biological and nonbiological compounds in the four-carbon linear-chain redox chemical space. Biological compounds have significantly higher solubilities than the nonbiological set (P < 0.005).