Spectroscopic, thermodynamic, kinetic studies and oxidase/antioxidant biomimetic catalytic activities of tris(3,5-dimethylpyrazolyl)borate Cu(II) complexes

A series of copper(II) complexes, viz. [TpMeMeCu(Cl)(H2O)] (1), [TpMeMeCu(OAc)(H2O)] (2), [TpMeMeCu(NO3)] (3) and [TpMeMeCu(ClO4)] (4) containing tris(3,5-dimethylpyrazolyl)borate (KTpMeMe), have been synthesized and fully characterized. The substitution reaction of 1 with thiourea was studied under pseudo-first-order conditions as a function of concentration, temperature and pressure in methanol and acetonitrile as solvents. Two reaction steps that both depended on the nucleophile concentration were observed for both solvents. Substitution of coordinated methanol is about 40 times faster than the substitution of chloride. In acetonitrile, the rate constant for the displacement of coordinated acetonitrile was more than 20 times faster than the substitution of chloride. The reported activation parameters indicate that both reaction steps follow a dissociative mechanism in both solvents. On going from methanol to acetonitrile, the rate constant for the displacement of the solvent becomes more than 200 times faster due to the more labile acetonitrile, but the substitution mechanism remained to have a dissociative character. The antioxidant activities of 1–4 were evaluated for superoxide dismutase (SOD), glutathione-s-transferase (GST0 and glutathione reduced (GSH-Rd) activity. 1 and 2 were found to show (p < 0.05) the highest antioxidant activity in comparison to 3 and 4, which can be ascribed to the geometric configuration as well as the nature of the co-ligand. 1 showed catechol oxidase activity with turnover numbers of 20 min−1 and a coordination affinity for 3,5-DTBC of K1, = 31 mM−1. K1 is rather large and seems to be typical for faster biomimetic models, and also for the enzyme itself (25 mM−1). The reaction rate depended linearly on the complex concentration, indicating a first-order dependence on the catalyst concentration

BSA Interaction, Molecular Docking, and Antibacterial Activity of Zinc(II) Complexes Containing the Sterically Demanding Biomimetic N3S2 Ligand: The Effect of Structure Flexibility

Two zinc(II) complexes, DBZ and DBZH4, that have (ZnN3S2) cores and differ in the bridging mode of the ligating backbone, effectively bind to BSA. The binding affinity varies as DBZ > DBZH4 and depends on the ligand structure. At low concentrations, both complexes exhibit dynamic quenching, whereas at higher concentrations they exhibit mixed (static and dynamic) quenching. The energy transfer mechanism from the BSA singlet excited state to DBZ and DBZH4, is highly likely according to steady-state fluorescence and time-correlated singlet photon counting. Molecular docking was used to support the mode of interaction of the complexes with BSA and showed that DBZ had more energy for binding. Furthermore, antibacterial testing revealed that both complexes were active but to a lesser extent than chloramphenicol. In comparison to DBZH4, DBZ has higher antibacterial activity, which is consistent with the binding constants, molecular docking, and particle size of adducts. These findings may have an impact on biomedicine

Spectroscopic, thermodynamic, kinetic studies and oxidase/antioxidant biomimetic catalytic activities of tris(3,5-dimethylpyrazolyl)borate Cu(II) complexes

A series of copper(II) complexes, viz. [TpMeMeCu(Cl)(H2O)] (1), [TpMeMeCu(OAc)(H2O)] (2), [TpMeMeCu(NO3)] (3) and [TpMeMeCu(ClO4)] (4) containing tris(3,5-dimethylpyrazolyl)borate (KTpMeMe), have been synthesized and fully characterized. The substitution reaction of 1 with thiourea was studied under pseudo-first-order conditions as a function of concentration, temperature and pressure in methanol and acetonitrile as solvents. Two reaction steps that both depended on the nucleophile concentration were observed for both solvents. Substitution of coordinated methanol is about 40 times faster than the substitution of chloride. In acetonitrile, the rate constant for the displacement of coordinated acetonitrile was more than 20 times faster than the substitution of chloride. The reported activation parameters indicate that both reaction steps follow a dissociative mechanism in both solvents. On going from methanol to acetonitrile, the rate constant for the displacement of the solvent becomes more than 200 times faster due to the more labile acetonitrile, but the substitution mechanism remained to have a dissociative character. The antioxidant activities of 1–4 were evaluated for superoxide dismutase (SOD), glutathione-s-transferase (GST0 and glutathione reduced (GSH-Rd) activity. 1 and 2 were found to show (p < 0.05) the highest antioxidant activity in comparison to 3 and 4, which can be ascribed to the geometric configuration as well as the nature of the co-ligand. 1 showed catechol oxidase activity with turnover numbers of 20 min−1 and a coordination affinity for 3,5-DTBC of K1, = 31 mM−1. K1 is rather large and seems to be typical for faster biomimetic models, and also for the enzyme itself (25 mM−1). The reaction rate depended linearly on the complex concentration, indicating a first-order dependence on the catalyst concentration

Synthesis, Biophysical Interaction of DNA/BSA, Equilibrium and Stopped-Flow Kinetic Studies, and Biological Evaluation of bis(2-Picolyl)amine-Based Nickel(II) Complex

Reaction of bis(2-picolyl)amine (BPA) with Ni(II) salt yielded [(BPA)NiCl2(H2O)] (NiBPA). The Ni(II) in NiBPA bound to a BPA ligand, two chloride, and one aqua ligands. Because most medications inhibit biological processes by binding to a specific protein, the stopped-flow technique was used to investigate DNA/protein binding in-vitro, and a mechanism was proposed. NiBPA binds to DNA/protein more strongly than BPA via a static quenching mechanism. Using the stopped-flow technique, a mechanism was proposed. BSA interacts with BPA via a fast reversible step followed by a slow irreversible step, whereas NiBPA interacts via two reversible steps. DNA, on the other hand, binds to BPA and NiBPA via the same mechanism through two reversible steps. Although BSA interacts with NiBPA much faster, NiBPA has a much higher affinity for DNA (2077 M) than BSA (30.3 M). Compared to NiBPA, BPA was found to form a more stable BSA complex. When BPA and NiBPA bind to DNA, the Ni(II) center was found to influence the rate but not the mechanism, whereas, for BSA, the Ni(II) center was found to change both the mechanism and the rate. Additionally, NiBPA exhibited significant cytotoxicity and antibacterial activity, which is consistent with the binding constants but not the kinetic stability. This shows that in our situation, biological activity is significantly more influenced by binding constants than by kinetic stability. Due to its selectivity and cytotoxic activity, complex NiBPA is anticipated to be used in medicine

Synthesis and characterization of N₃S₂ donors macrocyclic copper(II) complexes. Catechol oxidase and phenoxazinone synthase biomimetic catalytic activity

<p>A new series of copper(II) complexes have been synthesized with macrocyclic ligands L¹ and L² having N₃S₂-donating atoms in the 12-membered macrocyclic ring. The structure characterization of these newly synthesized copper(II) complexes was achieved by various physicochemical techniques. It has been shown that the stereochemistry of complexes is dependent on the type of counter anions incorporated in the complex molecule. Mimicking copper oxidase enzymes, namely catechol oxidase and phenoxazinone synthase, was investigated and the results obtained demonstrated that there is a correlation between the structural properties of these copper(II) complexes and the oxidase biomimetic catalytic activities. Kinetic measurements revealed second-order dependence on the catalyst concentration for 3,5-DTBCH₂ and first order in the case of OAPH. On the other hand, for the substrate concentration dependence, a saturation-type behavior was detected for both 3,5-DTBCH₂ and OAPH. Addition of Lewis base, triethylamine, in both systems exhibits dramatic effect on the rate of these catalytic aerobic oxidation reactions. The probable mechanistic implications of both catalytic systems are discussed.</p