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Herein, we report the synthesis and characterization, through elemental analysis, electronic spectroscopy, electrochemistry, potentiometric titration, electron paramagnetic resonance, and magnetochemistry, of two dinuclear copper(II) complexes, using the unsymmetrical ligands N',N',N-tris(2-pyridylmethyl)-N-(2-hydroxy-3,5-di-tert-butylbenzyl)-1,3-propanediamin-2-ol (L1) and N',N'-bis(2-pyridylmethyl)-N,N-(2-hydroxybenzyl)(2-hydroxy-3,5-di-tert-butylbenzyl)-1,3-propanediamin-2-ol (L2). The structures of the complexes [Cu(2)(L1)(μ-OAc)](ClO(4))(2)·(CH(3))(2)CHOH (1) and [Cu(2)(L2)(μ-OAc)](ClO(4))·H(2)O·(CH(3))(2)CHOH (2) were determined by X-ray crystallography. The complex [Cu(2)(L3)(μ-OAc)](2+) [3; L3 = N-(2-hydroxybenzyl)-N',N',N-tris(2-pyridylmethyl)-1,3-propanediamin-2-ol] was included in this study for comparison purposes only (Neves et al. Inorg. Chim. Acta2005, 358, 1807-1822). Magnetic data show that the Cu(II) centers in 1 and 2 are antiferromagnetically coupled and that the difference in the exchange coupling J found for these complexes (J = -4.3 cm(-1) for 1 and J = -40.0 cm(-1) for 2) is a function of the Cu-O-Cu bridging angle. In addition, 1 and 2 were tested as catalysts in the oxidation of the model substrate 3,5-di-tert-butylcatechol and can be considered as functional models for catechol oxidase. Because these complexes possess labile sites in their structures and in solution they have a potential nucleophile constituted by a terminal Cu(II)-bound hydroxo group, their activity toward hydrolysis of the model substrate 2,4-bis(dinitrophenyl)phosphate and DNA was also investigated. Double electrophilic activation of the phosphodiester by monodentate coordination to the Cu(II) center that contains the phenol group with tert-butyl substituents and hydrogen bonding of the protonated phenol with the phosphate O atom are proposed to increase the hydrolase activity (K(ass.) and k(cat.)) of 1 and 2 in comparison with that found for complex 3. In fact, complexes 1 and 2 show both oxidoreductase and hydrolase/nuclease activities and can thus be regarded as man-made models for studying catalytic promiscuity.

Catalytic promiscuity has emerged as an important property of many enzymes since the relationship of this property to enzymatic evolution became clear. Simultaneously, the development of suitable biomimetic catalytic systems capable of mimicking the promiscuous catalytic properties of such enzymes represents a new challenge for bioinorganic chemists. In this paper we report on the X-ray structure, the solution studies and the promiscuous catalytic activity of the mixed-valence complex [(bpbpmp)FeIII(µ-OAc)2FeII](ClO4), (1), containing the unsymmetrical dinucleating ligand 2-{[(2-hydroxybenzyl)(2-pyridylmethyl)aminomethyl]-4-methyl-6-[bis(2-pyridylmethyl)aminomethyl]}phenol (H2bpbpmp). Potentiometric and spectrophotometric titrations and kinetics studies showed that this coordination compound generates active species that promote hydrolytic cleavage of double strand DNA (dsDNA), with a rate enhancement of 1.9×10(8) over the non-catalyzed reaction, as well as promote oxidation of 3,5-di-tert-butylcatechol (3,5-dtbc), with k cat = 1.16 × 10-2 s-1 and K M = 7.1×10-4 mol L-1. Thus, complex 1 shows both hydrolase and oxidoreductase activities and can be regarded as a man-made model for studying catalytic promiscuity. Os estudos sobre enzimas têm mostrado que existe uma relação clara entre a evolução enzimática e a propriedade de promiscuidade catalítica que elas podem apresentar. Com isto, o desenvolvimento de sistemas biomiméticos capazes de atuar de modo promíscuo, de forma similar a algumas enzimas, mostrou-se um novo desafio para os químicos bioinorgânicos. Neste trabalho, reportamos a estrutura de raios X e os estudos em solução e de promiscuidade catalítica do complexo [(bpbpmp)FeIII(µ-OAc)2FeII](ClO4), (1), contendo o ligante binucleante não-simétrico 2-{[(2-hidroxibenzil)(2-piridilmetil)aminometil]-4-metil-6-[bis(2-piridilmetil)aminometil]}fenol (H2bpbpmp). Estudos de titulações potenciométrica e espectrofotométrica e cinéticos mostraram que esse composto de coordenação gera espécies ativas capazes de clivar o dsDNA (DNA de fita dupla) hidroliticamente, com um aumento de 1,9×10(8) na taxa de reação em comparação com a reação não catalisada, e capazes de oxidar o 3,5-di-terc-butilcatecol (3,5-dtbc), com k cat = 1,16 × 10-2 s-1 e K M = 7,1×10-4 mol L-1. Assim, o complexo 1 apresenta atividades de hidrolase e oxidoredutase, sendo um interessante modelo sintético para estudos de promiscuidade catalítica.

Hydrolysis of DNA is of increasing importance in biotechnology and medicine. In this Letter, we present the DNA-cleavage potential of metal-free hydroxylamines and oximes as new members of nucleic acid cleavage agents.

The synthesis, structure, and hydrolase-like catalytic activity of a new mononuclear gadolinium complex [Gd(L)(NO3)(H2O)3](NO3)2 (1) are reported. A clean two-stage kinetic reaction for hydrolysis of the diester 2,4-bis(dinitrophenyl)phosphate by 1 was followed, and the rate constants were determined. A high DNA cleavage activity was also demonstrated. The active species in the hydrolytic process is proposed based on the X-ray structure, electrospray ionization mass spectrometry analysis, and kinetic and potentiometric equilibrium studies of 1.

This paper reports on the synthesis and characterization of two new ternary copper(II) complexes: [Cu(doxycycline)(1,10-phenanthroline)(H(2)O)(ClO(4))](ClO(4)) (1) and [Cu(tetracycline)(1,10-phenanthroline)(H(2)O)(ClO(4))](ClO(4)) (2). These compounds exhibit a distorted tetragonal geometry around copper, which is coordinated to two bidentate ligands, 1,10-phenanthroline and tetracycline or doxycyline, a water molecule, and a perchlorate ion weakly bonded in the axial positions. In both compounds, copper(II) binds to tetracyclines via the oxygen of the hydroxyl group and oxygen of the amide group at ring A and to 1,10-phenanthroline via its two heterocyclic nitrogens. We have evaluated the binding of the new complexes to DNA, their capacity to cleave it, their cytotoxic activity, and uptake in tumoral cells. The complexes bind to DNA preferentially by the major groove, and then cleave its strands by an oxidative mechanism involving the generation of ROS. The cleavage of DNA was inhibited by radical inhibitors and/or trappers such as superoxide dismutase, DMSO, and the copper(I) chelator bathocuproine. The enzyme T4 DNA ligase was not able to relegate the products of DNA cleavage, which indicates that the cleavage does not occur via a hydrolytic mechanism. Both complexes present an expressive plasmid DNA cleavage activity generating single- and double-strand breaks, under mild reaction conditions, and even in the absence of any additional oxidant or reducing agent. In the same experimental conditions, [Cu(phen)(2)](2+) is approximately 100-fold less active than our complexes. These complexes are among the most potent DNA cleavage agents reported so far. Both complexes inhibit the growth of K562 cells with the IC(50) values of 1.93 and 2.59 μmol L(-1) for compounds 1 and 2, respectively. The complexes are more active than the free ligands, and their cytotoxic activity correlates with intracellular copper concentration and the number of Cu-DNA adducts formed inside cells.

The synthesis and structures of two new isostructural mononuclear [Ln(L)(NO(3))(H(2)O)(3)](NO(3))(2) complexes, with Ln = Tb (complex 1) and Eu (complex 2), which display high activity in the hydrolysis of the substrate 2,4-bis(dinitrophenyl)phosphate, are reported. These complexes displayed catalytic behavior similar to the mononuclear gadolinium complex [Gd(L)(NO(3))(H(2)O)(3)](NO(3))(2) previously reported by us (Inorg. Chem. 2008, 47, 2919-2921); one hydrolysis reaction in two stages where the diesterase and monoesterase activities could be monitored separately, with the first stage dependent on and the second independent of the complex concentration. Through potentiometric studies, electrospray ionization mass spectrometry (ESI-MS) analysis, and determination of the kinetic behaviors of 1 and 2 in acetonitrile/water solution, the species present in solution could be identified and suggested a dinuclear species, with one hydroxo group, as the most prominent catalyst under mild conditions. The complexes show high activity (k(1) = 7 and 18 s(-1) for 1 and 2, respectively) and catalytic efficiency. Complexes 1 and 2 were found to be active toward the cleavage of plasmid DNA, and complete kinetic studies were carried out. Studies with a radical scavenger (dimethylsulfoxide) confirmed the hydrolytic action of 1 and 2 in the cleavage of DNA. Studies on the incubation of distamycin with plasmid DNA suggested that 1 and 2 are regio-specific, interacting with the minor groove of DNA. These complexes displayed luminescent properties. Complex 1 showed higher emission intensity than 2 due to a more efficient energy transfer between triplet and emission levels of terbium (T --(5)D(4)), along with nonradiative deactivation mechanisms of the excited states of europium via multiphonon decays and the ligand-to-metal charge transfer state. Lifetime measurements of the (5)D(4) and (5)D(0) excited levels for 1 and 2, respectively, indicated the numbers of coordinated water molecules for the complexes.

A new iron(ii) complex was synthesized and its photonuclease activity against plasmid DNA was evaluated. After kinetic experiments a k(cat) of 18.86 +/- 2.9 h(-1) was obtained, one of the highest nuclease activities of synthetic metallonucleases, selectively activated by 365 nm UV light.

The new trinuclear gadolinium complex [Gd(3)L(2)(NO(3))(2)(H(2)O)(4)]NO(3).8H(2)O (1) with the unsymmetrical ligand 2-[N-bis-(2-pyridylmethyl)aminomethyl]-4-methyl-6-[N-bis(2-hydroxy-2-oxoethyl)aminomethyl] phenol (H(3)L) was synthesized and characterized. The new ligand H(3)L was obtained in good yield. Complex 1 crystallizes in an orthorhombic cell, space group Pcab. Kinetic studies show that complex 1 is highly active in the hydrolysis of the substrate 2,4-bis(dinitrophenyl)phosphate (K(m) = 4.09 mM, V(max) = 2.68 x 10(-2) mM s(-1), and k(cat) = V(max)/[1] = 0.67 s(-1)). Through a potentiometric study and determination of the kinetic behavior of 1 in acetonitrile/water solution, the species present in solution could be identified, and a trinuclear monohydroxo species appears to be the most prominent catalyst under mild conditions. Complex 1 displays high efficiency in DNA hydrolytic cleavage, and complete kinetic studies were carried out (K(m) = 4.57 x 10(-4) M, k'(cat) = 3.42 h(-1), and k'(cat)/K(m) = 7.48 x 10(3) M(-1) h(-1)). Studies with a radical scavenger (dimethyl sulfoxide, DMSO) showed that it did not inhibit the activity, indicating the hydrolytic action of 1 in the cleavage of DNA, and studies on the incubation of distamycin with plasmid DNA suggest that 1 is regio-specific, interacting with the minor groove of DNA.

Presented herein is the synthesis and characterization of a new Fe(III)Zn(II) complex containing a Fe(III)-bound phenolate with a carbonyl functional group, which was anchored to 3-aminopropyl-functionalized silica as the solid support. The catalytic efficiency of the immobilized catalyst in the hydrolysis of 2,4-bis(dinitrophenyl)phosphate is comparable to the homogeneous reaction, and the supported catalyst can be reused for subsequent diester hydrolysis reactions.

In this study, four new mononuclear copper(ii) complexes, [Cu(L(1))(dpq)]ClO(4) (), [Cu(L(1))(phen)]ClO(4) (), [Cu(L(2))(dpq)]ClO(4) (), [Cu(L(1))(OAc)] (), and the known complex [Cu(dpq)(2)(H(2)O)]ClO(4) (), were synthesized and characterized by various methods (dpq = dipyrido[3,2-d:2',3'-h]quinoxaline, L(1) = (3,5-di-tert-butyl-2-hydroxybenzyl)(2-pyridylmethyl)imine, L(2) = (2-hydroxybenzyl)(2-pyridylmethyl)imine). The structure of [Cu(L(1))(dpq)]ClO(4) () was determined by X-ray crystallography and reveals that the Cu(II) center is coordinated by dpq and by the N(2)O donor ligand L(1) in a distorted square pyramidal arrangement. The interaction of with calf thymus DNA was measured and the binding constant K(b) was obtained for the complexes, with values strongly dependent on the intercalating and/or binding properties of the ligands present in the structure of each complex. Also, the nuclease and photonuclease activity in terms of plasmid DNA cleavage with addition of reactants was monitored, in order to verify the mechanism through which the complexes cleave DNA. The complexes displayed good activity under both UV (365 nm) and red light (635 nm) irradiation, with the Type II mechanism prevailing in the case of the former and Type I mechanism for the latter. Finally, two new correlations between the experimental and theoretical parameters are discussed and some hypotheses regarding the active species generation are proposed.

The antitumoral properties of PtII compounds and the favorable characteristics of tetracyclines led us to study PtII compounds of tetracycline (tc) and doxycycline (dox) as candidates for anticancer agents. [PtCl2(dox)], 1, is more potent than [PtCl2(tc)], 2, in inhibiting the growth of chronic myelogenous leukemia cells. Compounds 1 and 2 form a ternary complex with DNA withK values of 3.85×10(4) and 5.43×10(4), respectively. The compounds displace ethidium bromide from DNA sites, which points to an intercalative mechanism. Both complexes decrease DNA eletrophoretic mobility and melting temperature. After incubation of cells with 1 and 2, the DNA was extracted and the adducts formed were quantified. At the concentration that the compounds are cytotoxic to cancer cells, they do not affect macrophages viability. The rate of uptake of the doxycycline complex in cells is three times higher than that of the tetracycline complex and this seems to be determinant for its higher activity. As propriedades antitumorais de complexos de PtII e as características favoráveis das tetraciclinas levaram-nos a estudar compostos de PtII da tetraciclina (tc) e doxiciclina (dox) como candidatos a agentes antitumorais. [PtCl2(dox)], 1, é mais potente que[PtCl2(tc)], 2,em inibir o crescimento de células de leucemia mielóide crônica.Os compostos 1 e 2 formam um complexo ternário com o ADN com valores de K iguais a 3,85×10(4) e 5,43×10(4), respectivamente. Os complexos deslocam o brometo de etídeo dos sítios no ADN, o que indica um mecanismo intercalativo. Ambos os complexos diminuem a mobilidade eletroforética e a temperatura de fusão do ADN. Após a incubação das células com 1 e 2, o ADN foi extraído e os adutos formados foram quantificados. Na concentração em que os compostos são citotóxicos contra células cancerosas, eles não afetam a viabilidade de macrófagos. A velocidade de entrada do complexo da doxiciclina nas células é três vezes maior do que a do complexo da tetraciclina e isto parece ser determinante para a sua maior atividade.