3D- QSAR STUDIES, BIOLOGICAL EVALUATION STUDIES ON SOME SUBSTITUTED 3-CHLORO-1-(5-(5-CHLORO-2-PHENYL-BENZIMIDAZOLE-1- YLMETHYL)-(1, 3, 4) THIADIAZOLE-2-YL)-AZETIDIN-2-ONE AS POTENTIAL ANTIMICROBIAL ACTIVITY