Three Schiff bases of Mannich bases of resacetophenone have been synthesized by using three variable electronegative atoms (X=O/S/NH) of urea/thiourea/guanidine and tested for antimicrobial activity and antioxidant screening by DPPH. It has been found that Compound-3a (X=O) showed maximum zone of inhibition in E.coli & S.aureus and minimum zone of inhibition in B.subtilis, Compound-3b (X=S) showed maximum zone of inhibition in E.coli in comparison with standard drug streptomycin. There is no activity found in case of Compound-3c (X=NH). Antimicrobial activity profile of three compounds is as follows: Gm positive bacteria: Compound-3a (S.aureus > B.subtilis) Gm negative bacteria: Compound-3b (E.coli) > Compound-3a (E.coli) LogP values of three compounds were found to be X=O: 4.03, X=S: 4.63 and X=NH: 3.79. So, the partition coefficient is in this order: X=S: 4.63 > X=O: 4.03 > X=NH: 3.79. Partition coefficient of X=S is 4.63 which is greater than X=O (4.03) and X=NH (3.79) electronegativity of S is 2.58 which is in between O=3.44 and NH=3.04. Electronegative atoms O and S both have two lone pair of electrons but electronegativity for O: 3.44 > N: 3.04 > S: 2.58 and the % inhibition of oxidation by DPPH has been observed as NH (45.56) > O (37.76) > S > (36.5). The electronegativity of N is 3.04 so the NH compound (guanidine) showed maximum inhibition 45.46%, electronegativity of O is 3.44 so the O compound (urea) showed 37.76% inhibition and the electronegativity of S is 2.58 so the S compound (thiourea) showed 36.5% inhibition. The log P values of NH compound (guanidine) is 3.79 which is minimum but showed maximum inhibition 45.46%, log P value of O compound (urea) is 4.03 which showed in 37.76 % inhibition and log P value of S compound (thiourea) is 4.63 which showed 36.5% inhibition. Oxygen and Sulfur both have two lone pairs of electrons so the % inhibition values are under very narrow range O (37.76), S (36.5) but this slight variation is due to the difference in electronegativity: O: 3.44 and S: 2.58.
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