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SYNTHESIS, CHARACTERIZATION, ANTIFUNGAL ACTIVITY AND STRUCTURE– ACTIVITY RELATIONSHIPS: STUDY OF SOME MONO- AND DI-SCHIFF BASES


Schiff bases (SB) are an important type of organic compounds and have a wide range of biological activities due to commercial and pharmaceutical trading uses. The different activities of these compounds induced the researchers to synthesized and studied new types of these compounds. Two series of Schiff base derivatives were synthesized by the condensation reactions of substituted aldehydes salicylaldehyde, 4-(N,Ndimethylamino) benzaldehyde or 2,4-dimethoxybenzaldehyde with 2-amino-5-iodobenzoic acid (1:1) or with 3,5- diamenobenzoic acid (1:2) in ethanol absolute as a solvent. Different analytical techniques characterized the structure of the synthesized Schiff bases; for instance, Fourier transform infrared FT-IR and proton nuclear magnetic resonance 1H-NMR. The purity of the synthesized compounds was tested by elemental microanalysis CHN and thin layer chromatography TLC. The structural properties of the studied molecules were investigated theoretically by performing density functional theory (DFT) using the HyperChem software. The lipophilicity of the tested compounds showed that the compounds 2c, 2b, 2a, and 1c have logP values less than (5), 2.90, 3.78, 3.82 and 4.57, respectively, whereas, 1b and 1a have logP values higher than (5), 5.01 and 5.03, respectively. The Mulliken charge distribution showed that the carbonyl oxygen atom of the carboxylic group is more negative (~ - 0.4) as compared to other oxygen atoms (~ -0.3) in all selected compounds. Frontier molecular orbitals energy diagram and their bandgap provided indications about chemical reactivity and kinetic stability of the molecules. The synthesized compounds were tested for antifungal effects against Aspergillus niger and Candida albicans, which indicated that the compounds had good antifungal activity.
