Abstract
Phenolic Schiff bases are known as powerful antioxidants. To select the electronic, 2D and 3D descriptors responsible for the free radical scavenging ability of a series of 30 phenolic Schiff bases, a set of molecular descriptors were calculated by using B3P86 (Becke’s three parameter hybrid functional with Perdew 86 correlation functional) combined with 6-31 + G(d,p) basis set (i.e., at the B3P86/6-31 + G(d,p) level of theory). The chemometric methods, simple and multiple linear regressions (SLR and MLR), principal component analysis (PCA) and hierarchical cluster analysis (HCA) were employed to reduce the dimensionality and to investigate the relationship between the calculated descriptors and the antioxidant activity. The results showed that the antioxidant activity mainly depends on the first and second bond dissociation enthalpies of phenolic hydroxyl groups, the dipole moment and the hydrophobicity descriptors. The antioxidant activity is inversely proportional to the main descriptors. The selected descriptors discriminate the Schiff bases into active and inactive antioxidants.
Highlights
Phenolic Schiff bases have been widely studied due to their various applications in different fields, such as inorganic chemistry, analytical chemistry and biochemistry [1,2]
Proton-coupled electron transfer (PC-ET), electron transfer-proton transfer (ET-PT), sequential proton-loss-electron-transfer (SPLET) and adduct formation are the most common mechanisms involved in free radical scavenging
The results indicated that some structural features are the most significant in enhancing the antioxidant activity, such as: (i) the presence of a catechol moiety; (ii) the catechol group conjugated to a double bond; and (iii) the number of free hydroxyl groups, as in flavonoids and phenolic acids [17], oligomers of guaiacol [13] and Schiff bases [19]
Summary
Phenolic Schiff bases have been widely studied due to their various applications in different fields, such as inorganic chemistry, analytical chemistry and biochemistry [1,2]. They are reported as effective corrosion inhibitors on mild steel [3]. Proton-coupled electron transfer (PC-ET), electron transfer-proton transfer (ET-PT), sequential proton-loss-electron-transfer (SPLET) and adduct formation are the most common mechanisms involved in free radical scavenging. B3P86/6-31+G(d,p) level of theory to explore and calculate more representative descriptors able to express the electronic, 2D and 3D properties that can be related to the free radical scavenging ability of a series of 30 Schiff bases (Table 1). The pattern recognition methods, such as simple and multiple linear regressions (SLR and MLR), principal component analysis (PCA) and hierarchical cluster analysis (HCA), have been employed with the aim of selecting the variables responsible for the free radical scavenging activity and to describe properly the relationship between the calculated descriptors and the antioxidant activity of these Schiff bases
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