Adolfo Horn

Hydrolytic DNA cleavage promoted by a dinuclear iron(III) complex

Abstract The dinuclear iron complex [Fe 2 III (BPClNOL) 2 (H 2 O) 2 ](ClO 4 ) 2 ( 1 ) [N–(2-hydroxybenzyl)–N–(pyridylmethyl)[(3-chloro)(2-hydroxy)]propylamine] was investigated focusing on its hydrolytic activity towards phosphate esters and DNA. The activity was evaluated within the pH range 6.1–8.0 when the hydroxo molecules are coordinated to the Fe III centers of ( 1 ). The complex did not show hydrolytic activity on the 4-nitrophenyl phosphate and bis(2,4-dinitrophenyl)phosphate. However, the complex successfully promoted the hydrolytic cleavage of plasmid DNA, producing single and double DNA strand breaks.

A facile catalytic synthesis of trimethylene carbonate from trimethylene oxide and carbon dioxide

The coupling of oxetane (trimethylene oxide) and carbon dioxide catalyzed by VO(acac)2 in the presence of an onium salt was studied. The process was found to be highly selective and quantitative for the production of the six-membered cyclic carbonate, trimethylene carbonate, under very mild reaction conditions of 60 °C and 1.7 MPa. Other derivatives of trimethylene oxide were shown to similarly selectively afford the corresponding cyclic carbonates upon reaction with CO2.

Iron, copper, and manganese complexes with in vitro superoxide dismutase and/or catalase activities that keep Saccharomyces cerevisiae cells alive under severe oxidative stress

Due to their aerobic lifestyle, eukaryotic organisms have evolved different strategies to overcome oxidative stress. The recruitment of some specific metalloenzymes such as superoxide dismutases (SODs) and catalases (CATs) is of great importance for eliminating harmful reactive oxygen species (hydrogen peroxide and superoxide anion). Using the ligand HPClNOL {1-[bis(pyridin-2-ylmethyl)amino]-3-chloropropan-2-ol}, we have synthesized three coordination compounds containing iron(III), copper(II), and manganese(II) ions, which are also present in the active site of the above-noted metalloenzymes. These compounds were evaluated as SOD and CAT mimetics. The manganese and iron compounds showed both SOD and CAT activities, while copper showed only SOD activity. The copper and manganese in vitro SOD activities are very similar (IC50~0.4 μmol dm(-3)) and about 70-fold higher than those of iron. The manganese compound showed CAT activity higher than that of the iron species. Analyzing their capacity to protect Saccharomyces cerevisiae cells against oxidative stress (H2O2 and the O2(•-) radical), we observed that all compounds act as antioxidants, increasing the resistance of yeast cells mainly due to a reduction of lipid oxidation. Especially for the iron compound, the data indicate complete protection when wild-type cells were exposed to H2O2 or O2(•-) species. Interestingly, these compounds also compensate for both superoxide dismutase and catalase deficiencies; their antioxidant activity is metal ion dependent, in the order iron(III)>copper(II)>manganese(II). The protection mechanism employed by the complexes proved to be independent of the activation of transcription factors (such as Yap1, Hsf1, Msn2/Msn4) and protein synthesis. There is no direct relation between the in vitro and the in vivo antioxidant activities.

Synthesis, structure and properties of the first dinuclear copper(II) complex as a structural model for the phenolic intermediate in tyrosinase–cresolase activity

Abstract The synthesis, X-ray crystal structure and spectroscopic and electrochemical properties of the new dinuclear copper(II) complex [Cu2(Hbtppnol)CH3COO](ClO4)2 (1), employing the novel unsymmetric dinucleating ligand N-(2-hydroxybenzyl)-N,N′,N′-tris(2-pyridylmethyl)-1,3-diaminopropan-2-ol (H2btppnol), are presented. This complex could be a relevant model for the axial interaction of a phenolic substrate to tyrosinase during cresolase activity.

Catalase vs Peroxidase Activity of a Manganese(II) Compound: Identification of a Mn(III)―(μ-O)2―Mn(IV) Reaction Intermediate by Electrospray Ionization Mass Spectrometry and Electron Paramagnetic Resonance Spectroscopy

Herein, we report reactivity studies of the mononuclear water-soluble complex [Mn(II)(HPClNOL)(eta(1)-NO(3))(eta(2)-NO(3))] 1, where HPClNOL = 1-(bis-pyridin-2-ylmethyl-amino)-3-chloropropan-2-ol, toward peroxides (H(2)O(2) and tert-butylhydroperoxide). Both the catalase (in aqueous solution) and peroxidase (in CH(3)CN) activities of 1 were evaluated using a range of techniques including electronic absorption spectroscopy, volumetry (kinetic studies), pH monitoring during H(2)O(2) disproportionation, electron paramagnetic resonance (EPR), electrospray ionization mass spectrometry in the positive ion mode [ESI(+)-MS], and gas chromatography (GC). Electrochemical studies showed that 1 can be oxidized to Mn(III) and Mn(IV). The catalase-like activity of 1 was evaluated with and without pH control. The results show that the pH decreases when the reaction is performed in unbuffered media. Furthermore, the activity of 1 is greater in buffered than in unbuffered media, demonstrating that pH influences the activity of 1 toward H(2)O(2). For the reaction of 1 with H(2)O(2), EPR and ESI(+)-MS have led to the identification of the intermediate [Mn(III)Mn(IV)(mu-O)(2)(PClNOL)(2)](+). The peroxidase activity of 1 was also evaluated by monitoring cyclohexane oxidation, using H(2)O(2) or tert-butylhydroperoxide as the terminal oxidants. Low yields (<7%) were obtained for H(2)O(2), probably because it competes with 1 for the catalase-like activity. In contrast, using tert-butylhydroperoxide, up to 29% of cyclohexane conversion was obtained. A mechanistic model for the catalase activity of 1 that incorporates the observed lag phase in O(2) production, the pH variation, and the formation of a Mn(III)-(mu-O)(2)-Mn(IV) intermediate is proposed.

Spectroscopic and catalytic characterization of a functional FeIIIFeII biomimetic for the active site of uteroferrin and protein cleavage

A mixed-valence complex, [Fe(III)Fe(II)L1(μ-OAc)(2)]BF(4)·H(2)O, where the ligand H(2)L1 = 2-{[[3-[((bis(pyridin-2-ylmethyl)amino)methyl)-2-hydroxy-5-methylbenzyl](pyridin-2-ylmethyl)amino]methyl]phenol}, has been studied with a range of techniques, and, where possible, its properties have been compared to those of the corresponding enzyme system purple acid phosphatase. The Fe(III)Fe(II) and Fe(III)(2) oxidized species were studied spectroelectrochemically. The temperature-dependent population of the S = 3/2 spin states of the heterovalent system, observed using magnetic circular dichroism, confirmed that the dinuclear center is weakly antiferromagnetically coupled (H = -2JS(1)·S(2), where J = -5.6 cm(-1)) in a frozen solution. The ligand-to-metal charge-transfer transitions are correlated with density functional theory calculations. The Fe(III)Fe(II) complex is electron paramagnetic resonance (EPR)-silent, except at very low temperatures (<2 K), because of the broadening caused by the exchange coupling and zero-field-splitting parameters being of comparable magnitude and rapid spin-lattice relaxation. However, a phosphate-bound Fe(III)(2) complex showed an EPR spectrum due to population of the S(tot) = 3 state (J= -3.5 cm(-1)). The phosphatase activity of the Fe(III)Fe(II) complex in hydrolysis of bis(2,4-dinitrophenyl)phosphate (k(cat.) = 1.88 × 10(-3) s(-1); K(m) = 4.63 × 10(-3) mol L(-1)) is similar to that of other bimetallic heterovalent complexes with the same ligand. Analysis of the kinetic data supports a mechanism where the initiating nucleophile in the phosphatase reaction is a hydroxide, terminally bound to Fe(III). It is interesting to note that aqueous solutions of [Fe(III)Fe(II)L1(μ-OAc)(2)](+) are also capable of protein cleavage, at mild temperature and pH conditions, thus further expanding the scope of this complexs catalytic promiscuity.

Synthesis, characterization and antibacterial activity of FeIII, CoII, CuII and ZnII complexes probed by transmission electron microscopy

We synthesized iron(III), cobalt(II), copper(II) and zinc(II) complexes [Fe(III)(HBPClNOL)Cl(2)]·H(2)O (1), [Co(II)(H(2)BPClNOL)Cl(2)] (2), [Cu(II)(H(2)BPClNOL)Cl]Cl·H(2)O (3), and [Zn(II)(HBPClNOL)Cl] (4), where H(2)BPClNOL is the ligand (N-(2-hydroxybenzyl)-N-(2-pyridylmethyl)[(3-chloro)(2-hydroxy)]propylamine). The complexes obtained were characterized by elemental analysis, IR and UV-visible spectroscopies, electrospray ionization mass spectrometry (ESI-MS), tandem mass spectrometry (MS/MS), and cyclic voltammetry. X-ray diffraction studies were performed for complexes (3) and (4) revealing the presence of mononuclear and dinuclear structures in solid state for (3). However, the zinc complex is mononuclear in solid state. Biological studies of complexes (1)-(4) were carried out in vitro for antimicrobial activity against nine Gram-positive bacteria (Staphylococcus aureus strains RN 6390B, COL, ATCC 25923, Smith Diffuse, Wood 46, enterotoxigenic S. aureus FRI-100 (SEA+), FRI S-6 (SEB+) and SEC FRI-361) and animal strain S. aureus LSA 88 (SEC/SED/TSST-1+). The following sequence of inhibition promoted by the complexes was observed: (4)>(2)>(3)>(1), showing the effect of the metal on the biological activity. To directly observe the morphological changes of the internal structure of bacterial cells after the treatment, transmission electron microscopy (TEM) was employed. For the most active complex [Zn(II)(HBPClNOL)Cl] (4), granulation deposits around the genetic material and internal material leaking were clearly detected.

An iron-based cytosolic catalase and superoxide dismutase mimic complex.

The development of metallodrugs with antioxidant activities is of importance as a way to protect organisms exposed to stressful conditions. Although iron chemistry in the presence of H(2)O(2) is usually associated with pro-oxidant activity, mainly via the Fenton reaction, we found that the mononuclear compound [Fe(HPClNOL)Cl(2)]NO(3) (1; C(15)H(18)Cl(3)FeN(4)O(4), a = 8.7751(3) A, b = 9.0778(4) A, c = 24.3869(10) A, beta = 93.370(2) degrees , monoclinic, P2(1)/c, Z = 4), containing the tripodal ligand 1-[bis(pyridin-2-ylmethyl)amino]-3-chloropropan-2-ol, decomposes hydrogen peroxide and superoxide anion in vitro as well as shows in vivo protection because it prevents the harmful effects promoted by H(2)O(2) on Saccharomyces cerevisiae cells, decreasing the level of lipid peroxidation. This protective effect was observed for wild-type cells, as well as for mutant cells, which do not present the antioxidant metalloenzymes catalase (Ctt1) or copper/zinc superoxide dismutase (Sod1).

A new dinucleating N,O donor ligand (H2BPClNOL) and the structural and magnetic properties of two diiron complexes with the di-m-alkoxo motif

Dois complexos binucleares de FeIII, obtidos a partir de um novo ligante polidentado (H2BPClNOL =N-(2-hidroxibenzil)-N-(2-piridilmetil)[(3-cloro)(2-hidroxi)] propilamina e contendo a unidade estrutural FeIII(m-alcoxo)2FeIII, foram caracterizados estruturalmente atraves de estudos cristalograficos e magneto-quimicos. Os complexos [Fe2(BPClNOL)2(OAc)]ClO4 (1) [Fe2(BPClNOL)2(H2O)2](ClO4)2. 4H2O (2) diferem entre si pela presenca de um grupo acetato em ponte entre os sitios de FeIII no complexo (1). O complexo contendo a ponte acetato apresenta constante de acoplamento antiferromagnetico aproximadamente 20 % menor quando comparado ao complexo sem ponte acetato.

Highly efficient synthetic iron-dependent nucleases activate both intrinsic and extrinsic apoptotic death pathways in leukemia cancer cells

The nuclease activity and the cytotoxicity toward human leukemia cancer cells of iron complexes, [Fe(HPClNOL)Cl2]NO3 (1), [Cl(HPClNOL)Fe(μ-O)Fe(HPClNOL)Cl]Cl2·2H2O (2), and [(SO4)(HPClNOL)Fe(μ-O)Fe(HPClNOL)(SO4)]·6H2O (3) (HPClNOL=1-(bis-pyridin-2-ylmethyl-amino)-3-chloropropan-2-ol), were investigated. Each complex was able to promote plasmid DNA cleavage and change the supercoiled form of the plasmid to circular and linear ones. Kinetic data revealed that (1), (2) and (3) increase the rate of DNA hydrolysis about 278, 192 and 339 million-fold, respectively. The activity of the complexes was inhibited by distamycin, indicating that they interact with the minor groove of the DNA. The cytotoxic activity of the complexes toward U937, HL-60, Jukart and THP-1 leukemia cancer cells was studied employing 3-(4,5-dimethythiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT), fluorescence and electronic transmission microscopies, flow cytometry and a cytochrome C release assay. Compound (2) has the highest activity toward cancer cells and is the least toxic for normal ones (i.e. peripheral blood mononuclear cells (PBMCs)). In contrast, compound (1) is the least active toward cancer cells but displays the highest toxicity toward normal cells. Transmission electronic microscopy indicates that cell death shows features typical of apoptotic cells, which was confirmed using the annexin V-FITC/PI (fluorescein isothiocyanate/propidium iodide) assay. Furthermore, our data demonstrate that at an early stage during the treatment with complex (2) mitochondria lose their transmembrane potential, resulting in cytochrome C release. A quantification of caspases 3, 9 (intrinsic apoptosis pathway) and caspase 8 (extrinsic apoptosis pathway) indicated that both the intrinsic (via mitochondria) and extrinsic (via death receptors) pathways are involved in the apoptotic stimuli.