Quantum calculation based on the density functional theory (DFT) level at 6-311++G (d,p) basis set was employed to study the relation between the structure and radical scavenging activity of a series of hydroxybenzohydroxamic acid derivatives, namely: [HU]; hyroxyurea, [4-HBA]; 4-hydroxybenzohydroxamic acid, [DX]; 3,4-dihydroxybenzohydroxamic acid, [3,5-DHBA]; 3,5-Dihydroxybenzohydroxamic acid, [2-HBA]; 2-hydroxybenzohydroxamic acid, [2,3-DHBA]; 2,3-Dihydroxybenzohydroxamic acid and [TX]; 3,4,5-trihydroxybenzamidoxime in the gas phase, water and benzene environments. The hydrogen bond property of the studied structures and their radicals as well as radical cations was investigated using the quantum theory of atoms in molecules (QTAIM) analysis. Bond dissociation energy (BDE) and adiabatic ionization potential (AIP) were also determined to know if the radical scavenging activity of these compounds proceeds via an H-atom or an electron-transfer mechanism. Calculations showed that the presence of the adjacent hydroxyl groups on benzene ring increases the radical stability through intramolecular hydrogen bonds and favors the hydrogen atom abstraction by free radical. The calculated BDE values for hydroxyl groups on benzene ring of studied compounds clearly reveal the important role of the hydrogen bonding and resonance in stability of radical obtained from the hydrogen atom abstraction by free radical. Results of calculation revealed that the radical scavenging capacity of TX is more than other molecules in the studied environment. The results obtained demonstrate that the H-atom transfer mechanism for scavenging of free radical by studied compounds, with the exception of HU, is more preferable than the single-electron transfer in considered environments. However, in the case of HU radical scavenging activity occurs just through electron transfer mechanism. This result is also supported by experimental data.

DFT study on the radical scavenging properties of anticancer hydroxyurea and hydroxybenzohydroxamic acid derivatives

244th National Meeting (2012)

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