engleski

Investigation of solution state structure of thiosemicarbazone derivatives by NMR and DFT methods

Salicylaldehyde thiosemicarbazones and their metal complexes belong to an important class of biologically active compounds (anticancer, antivirial, antibacterial, antiinflammatory and antifungal activity). They can exist in several tautomeric forms e.g. hydroxy-thione, hydroxy- thiol, keto-thione and keto-thiol with both intra- and inter-molecular hydrogen bonds. X-ray structural analysis has confirmed the existence of intra-molecular hydrogen bonds in different salicylaldehyde thiosemicarbazone derivatives. Bioactivity is closely related to molecular structure which is governed by the presence of hydrogen bonds. Therefore, the aim of our study was to investigate the influence of solvent and substituents on molecular conformation and structure of hydrogen bonds in salicylaldehyde thiosemicarbazones by combining NMR and DFT methods. Solvents of different polarities, i. e. of different proton donor and acceptor abilities were used (chloroform, acetone, methanol, dimethyl sulfoxide). Also, the effect of substituting OH with OMe group in salycilaldehyde residue, on the overall thiosemicarbazone structure and tautomerism was explored. Two-dimensional NOESY spectra indicated conformational changes in solution with respect to the structure observed in solid state owing to a relatively low barrier of the rotation arround N-N single bond thus enabling a molecule to posses a higher conformational flexibility in solution. The results presented here can help in a better understanding of the role hydrogen bonds can play in bioactivity of related thiosemicarbazone derivatives and their metal complexes.

solution ; structure ; thiosemicarbazones ; NMR ; DFT

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