Biopolym. Cell. 2003; 19(2):202-204.
Short Communications
Prototropic tautomerism, proton acceptor and proton donor properties of isatin: quantum chemical calculation data
1Potyahaylo A. L., 1Bolsunova O. I., 1Zayika L. A., 1Potopalsky A. I.
  1. Institute of Molecular Biology and Genetics, NAS of Ukraine
    150, Akademika Zabolotnoho Str., Kyiv, Ukraine, 03680


By semi-empirical quantum chemical method AMI it was first established that the diketoform is the main prototropic tautomer of isatin, the relative energy of enolic tautomers exceeding 16 kcal/mol. It is expected that exactly the diketoform of isatin must be observed in polar environment, since it has a significant dipole moment (5,1 D), which is distinctly higher than analogous values for most energy- favorable enolic tautomers (2,4 and 2,7 D). For the first time the acid-base properties of this amphoteric compound have been calculated in main tautomeric state. Imino group was shown to be the most acidic, while 'the oxygen atom of adjacent carbonyl gruop – the most basic, the associated proton acguiring trans- orientation against the adjacent imino group. As compared with nucleotide bases, isatin possesses much weaker properties both as proton acceptor and proton donor.


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