Spectroscopic study of phenyl- and 4-pyridylmalondialdehydes

4-Pyridylmalondialdehyde (1) and phenylmalondialdehyde (2) and their potass ium salts were investigated by H-1 and C-13 NMR, Raman and UV spectroscopy. Three forms of 1 and two forms of 2 were found in water or DMSO solution d epending on the pH by means of UV, H-1 and C-13 NMR spectroscopy. For 2 the chemical exchange between two cis-enol tautomers was observed, while the s tructure of 1 in the solution is zwitterionic. From the UV measurements and potentiometric titrations pK(1) = 1.9 +/- 0.1, pK(2) = 7.2 +/- 0, 1 for 1 acid pK = 4.0 +/- 0.2 for 2 were evaluated. For I the Raman spectra of soli d state and DMSO solution are very similar, while for 2 they differ signifi cantly. Butylamine was used as a model compound for the study of the potential inte raction of malondialdehyde with compounds containing amino groups. The effe ct of addition of butylamine on the spectra of both malondialdehyde derivat ives were indistinguishable from that corresponding to protonation-deproton ation processes. (C) 2001 Elsevier Science B.V. All rights reserved.