MADALINA MIHALACHE, OVIDIU OPREA, CORNELIA GURAN, IOANA LAVINIA ARDELEAN SYNTHESIS, CHARACTERIZATION AND BIOLOGICAL ACTIVITY OF THE MANGANESE COMPLEXES WITH ALFA-KETOGLUTARIC ACID AND 1-0(O-TOLYL) BIGUANIDE This paper presents the synthesis and characterization of three complexes of Mn (II,III), with the a-ketoglutaric acid (H2A) and 1- (o-tolyl) biguanide (TB) as ligands. The complexes corresponding formulas are: Cl2 . 0.5C2H5OH (C1), (NO3)2. C2H5OH (C2) and (CH3COO)2 . 3H2O (C3), where A is H2A without 2 protons. C1-C3 compounds were characterized by standard physico-chemical methods: chemical elemental analysis, IR spectroscopy, UV-Vis-NIR spectroscopy, molar conductivity and thermal analysis. For the obtained C1-C3 complexes, but also for the ligands (H2A and TB) was tested the antibacterial activity against Staphylococcus aureus ATCC 25923 and Pseudomonas aeruginosa ATCC 27853 and antitumor activity on HeLa tumour cells. It has been observed a moderate cytotoxic effect of the complexes C1-C3 on growth and metabolic activity of HeLa cells, while the ligands show a very weak effect on them. The obtained complexes inhibits the adhesion on the substrate of bacterial strains Staphylococcus aureus and Pseudomona aeruginosa, which recommends them for possible therapeutic applications.