Design, synthesis and crystal structure of six macrocyclic complexes as efficient and effective nitric oxide scavengers

Four new complexes of Robson-type macrocycles, [CuH(L1)]2(ClO4)2(H2O)2 (1), [CuH(L2)] ClO4 (2), [Cu H(L3)]2(ClO4)2 (3), [Cu H(L4)]2(ClO4)2(CH3CH2OH)2(CH3CN)2(4) and two reported Robson-type macrocycles polymers {[CuL5](H2O)2}n(5), {[MnL5](H2O)2}n (6) were obtained. The ligands (H2L1, H2L2, H2L3) are the products from the condensation between bata and N,N′-bis(3-formyl-5-X-salicylimine)-1,2-ethylenediimine (X = CH3, Cl, F), respectively. Ligands H2L4 and H2L5 are the products of N,N′-bis(3-formyl-5-methylsalicylimine)-1,2-propylenediimineand condensation with bafa and bapa, respectively. All the metal ions have unsaturated coordinated sites, which are available for NO binding. The binding of the complexes with NO molecules have been confirmed by UV–Vis spectrophotometry. The binding constants were calculated to be 1.28 × 103 M−1, 8.9 × 102 M−1, 7.7 × 103 M−1, 1.2 × 103 M−1, 1.2 × 103 M−1, 1.3 × 103 M−1 for 1, 2, 3, 4, 5 and 6, respectively. The control experiments revealed there was non-reversible binding of NO, which can be ascribed to specially coordination environment of the central ions. Moreover, the interactions of the complexes with calf thymus DNA (CT-DNA) have been measured by agarose gel electrophoresis, and unobvious DNA cleavage ability of complexes 1, 3 and 4 indicating no damage to DNA. The results reveal that complexes 1, 3 and 4 can be served as potential NO scavengers.