Zwitterionic compounds were found by evaluating the difference between acidic and basic pKa in conjunction with ChemAxon's calculator of protonated species distribution in function of pH. Zwitterionic and amphoteric species were also classified as acidic or basic based on the behavior of their lipophilicity profiles, which were evaluated using the ChemAxon partitioning calculator. Figure shows the distribution of the molecules along several descriptors of their chemical space. Most compounds can be considered small molecules because they tend to have small molecular weights (< 400 gmol -1 ) and topological polar surface areas (< 100 Å 2 ). Our database consists mostly of lipophilic species since the clogP values are mostly positive, which coincides with the low polarity of our molecules, demonstrated by the tendency of low counts of hydrogen bond donors (< 3) and acceptors (< 7).