The syntheses and characterizations of vanadium complexes with 1,2-dihydroxyanthraquinone and the structure–effect relationship in their in vitro anticancer activities

[VVO2(O2C14H6O2)(C5N2H12)](C5N2H13)(CH3OH) (1) and {Na[VVO(O2C14H6O2)2][(CH3)2NCHO]}n (2) have been synthesized by the reaction of V2O5 and NaVO3 with aromatic 1,2-diol (1,2-dihydroxyanthraquinone), and their molecular and crystal structures have been determined by X-ray diffraction. MTT assay tests of the VVO2LALB and VVOL2 complexes against cancer cells have revealed that, when L is catechol, VOL2 showed broad-spectrum, high anticancer activities which were proportional to their concentration; however when L is naphthol or alizarin, VOL2 displayed little effect towards the cancer cells; moreover, complex 1 in the coordination model of VVO2LALB showed specifically higher inhibition (88.65%) against HCT-8 than the clinical anticancer drug Fu-5 (69.97%). The results revealed that both the V(V) and the ligands cannot influence the inhibition against cancer cells individually. The mechanism of the broad-spectrum anticancer activities of VOL2 when L is catechol ligand might originate from the redox activities of VV/VIV which regulate the concentration of ROS (reactive oxygen species). N-Methylpiperazine formed as a by-product in complex 1 was confirmed by 1H NMR and its formation mechanism catalyzed by V2O5 has been deduced.