Cytoglobin has potent superoxide dismutase function

Cytoglobin (Cygb) was discovered as a novel type of globin that is expressed in mammals; however, its functions remain uncertain. While Cygb protects against oxidant stress, the basis for this is unclear, and the effect of Cygb on superoxide metabolism is unknown. From dose-dependent studies of the effect of Cygb on superoxide catabolism, we identify that Cygb has potent superoxide dismutase (SOD) function. Initial assays using cytochrome c showed that Cygb exhibits a high rate of superoxide dismutation on the order of 108 M−1 ⋅ s−1. Spin-trapping studies also demonstrated that the rate of Cygb-mediated superoxide dismutation (1.6 × 108 M−1 ⋅ s−1) was only ∼10-fold less than Cu,Zn-SOD. Stopped-flow experiments confirmed that Cygb rapidly dismutates superoxide with rates within an order of magnitude of Cu,Zn-SOD or Mn-SOD. The SOD function of Cygb was inhibited by cyanide and CO that coordinate to Fe3+-Cygb and Fe2+-Cygb, respectively, suggesting that dismutation involves iron redox cycling, and this was confirmed by spectrophotometric titrations. In control smooth-muscle cells and cells with siRNA-mediated Cygb knockdown subjected to extracellular superoxide stress from xanthine/xanthine oxidase or intracellular superoxide stress triggered by the uncoupler, menadione, Cygb had a prominent role in superoxide metabolism and protected against superoxide-mediated death. Similar experiments in vessels showed higher levels of superoxide in Cygb−/− mice than wild type. Thus, Cygb has potent SOD function and can rapidly dismutate superoxide in cells, conferring protection against oxidant injury. In view of its ubiquitous cellular expression at micromolar concentrations in smooth-muscle and other cells, Cygb can play an important role in cellular superoxide metabolism.

Spectroscopic Analysis of the Binding of Paraquat and Diquat Herbicides to Biosubstrates

The study of the interaction of persistent organic pollutants with biosubstrates helps to unravel the pathways for toxicity, however, few mechanistic data are present in the literature for these systems. We analyzed the binding of paraquat (PQ) and diquat (DQ) herbicides to natural calf thymus DNA and a DNA G-quadruplex by spectrophotometric titrations, ethidium bromide exchange tests, viscometry, and melting experiments. The interaction with bovine serum albumin (BSA) protein was studied spectrofluorimetrically at different temperatures. The retention of the targets on positive, negative, and neutral micellar aggregates and liposomes was analyzed by ultrafiltration experiments. Despite some favorable features, PQ and DQ only externally bind natural DNA and do not interact with DNA oligonucleotides. Both herbicides bind bovine serum albumin (BSA). PQ binds BSA mainly according to an electrostatics-driven process. However, ultrafiltration data also show that some hydrophobic contribution participates in the features of these systems. The practical problems related to unfavorable spectroscopic signals and inner filter effects are also discussed. Overall, both herbicides show a low affinity for nucleic acids and weak penetration into liposomes; in addition, the equilibrium constants values found for BSA system suggest optimal conditions for transport in the body.

Copper(II) Complexes with Tetradentate Piperazine-Based Ligands: DNA Cleavage and Cytotoxicity

Five-coordinate Cu(II) complexes, [Cu(Ln)X]ClO4/PF6, where Ln = piperazine ligands bearing two pyridyl arms and X = ClO4− for Ln = L1 (1-ClO4), L2 (2-ClO4), L3 (3-ClO4), and L6 (6-ClO4) as well as [Cu(Ln)Cl]PF6 for Ln = L1 (1-Cl), L4 (4-Cl), and L5 (5-Cl) have been synthesized and characterized by spectroscopic techniques. The molecular structures of the last two complexes were determined by X-ray crystallography. In aqueous acetonitrile solutions, molar conductivity measurements and UV-VIS spectrophotometric titrations of the complexes revealed the hydrolysis of the complexes to [Cu(Ln)(H2O)]2+ species. The biological activity of the Cu(II) complexes with respect to DNA cleavage and cytotoxicity was investigated. At micromolar concentration within 2 h and pH 7.4, DNA cleavage rate decreased in the order: 1-Cl ≈ 1-ClO4 > 3-ClO4 ≥ 2-ClO4 with cleavage enhancements of up to 23 million. Complexes 4-Cl, 5-Cl, and 6-ClO4 were inactive. In order to elucidate the cleavage mechanism, the cleavage of bis(4-nitrophenyl)phosphate (BNPP) and reactive oxygen species (ROS) quenching studies were conducted. The mechanistic pathway of DNA cleavage depends on the ligand’s skeleton: while an oxidative pathway was preferable for 1-Cl/1-ClO4, DNA cleavage by 2-ClO4 and 3-ClO4 predominantly proceeds via a hydrolytic mechanism. Complexes 1-ClO4, 3-ClO4, and 5-Cl were found to be cytotoxic against A2780 cells (IC50 30–40 µM). In fibroblasts, the IC50 value was much higher for 3-ClO4 with no toxic effect.

Mechanistic Insight of Sensing Hydrogen Phosphate in Aqueous Medium by Using Lanthanide(III)-Based Luminescent Probes

The development of synthetic lanthanide luminescent probes for selective sensing or binding anions in aqueous medium requires an understanding of how these anions interact with synthetic lanthanide probes. Synthetic lanthanide probes designed to differentiate anions in aqueous medium could underpin exciting new sensing tools for biomedical research and drug discovery. In this direction, we present three mononuclear lanthanide-based complexes, EuLCl3 (1), SmLCl3 (2), and TbLCl3 (3), incorporating a hexadentate aminomethylpiperidine-based nitrogen-rich heterocyclic ligand L for sensing anion and establishing mechanistic insight on their binding activities in aqueous medium. All these complexes are meticulously studied for their preferential selectivities towards different anions such as HPO42−, SO42−, CH3COO−, I−, Br−, Cl−, F−, NO3−, CO32−/HCO3−, and HSO4− at pH 7.4 in aqueous HEPES (2-[4-(2-hydroxyethyl)piperazin-1-yl]ethanesulfonic acid) buffer. Among the anions scanned, HPO42− showed an excellent luminescence change with all three complexes. Job’s plot and ESI-MS support the 1:2 association between the receptors and HPO42−. Systematic spectrophotometric titrations of 1–3 against HPO42− demonstrates that the emission intensities of 1 and 2 were enhanced slightly upon the addition of HPO42− in the range 0.01–1 equiv and 0.01–2 equiv., respectively. Among the three complexes, complex 3 showed a steady quenching of luminescence throughout the titration of hydrogen phosphate. The lower and higher detection limits of HPO42− by complexes 1 and 2 were determined as 0.1–4 mM and 0.4–3.2 mM, respectively, while complex 3 covered 0.2–100 μM. This concludes that all complexes demonstrated a high degree of sensitivity and selectivity towards HPO42−.

Rigid trisporphyrin with 1,3,5-triazine core: Synthesis, spectroscopy, and DABCO-induced self-assembly properties

A rigid Zn–trisporphyrin (1), the Zinc complex of 2,4,6-tris(5,10,15-triphenylporphyrinatozinc)-1,3,5-triazine (2) with three porphyrin moieties bridged by a rigid 1,3,5-triazine group, was synthesized and characterized by a series of spectroscopic methods including mass, 1H NMR, electronic absorption, and IR spectroscopy in addition to elemental analysis. The UV-vis spectrophotometric titration results revealed that along with the addition of the 1,4-diazabicyclo[2.2.2]octane (DABCO) form 0 to 3 equiv, 1 could form a 2:3 sandwich-type coordination cage in chloroform, which then transformed into a 1:3 open complex when the DABCO concentration was more than 3 equiv. Such DABCO-induced self- and disassembly processes were also confirmed by 1H NMR spectrophotometric titrations. In particular, it was demonstrated by comparative studies that the synergistic effect of the three porphyrin moieties linked together by the rigid 1,3,5-triazine group in 1 promoted the formation and stabilization of the 2:3 sandwich-type coordination cage. This result will be helpful towards the fabrication of various self-assembly structures based on metalloporphyrins with application potential in diverse areas such as molecular recognition and separation.

8-Hydroxyquinoline-2-Carboxylic Acid as Possible Molybdophore: A Multi-Technique Approach to Define Its Chemical Speciation, Coordination and Sequestering Ability in Aqueous Solution

8-hydroxyquinoline-2-carboxylic acid (8-HQA) has been found in high concentrations (0.5–5.0 mmol·dm−3) in the gut of Noctuid larvae (and in a few other lepidopterans), in which it is proposed to act as a siderophore. Since it is known that many natural siderophores are also involved in the uptake and metabolism of other essential elements than iron, this study reports some results on the investigation of 8-HQA interactions with molybdate (MoO42−, i.e., the main molybdenum form in aqueous environments), in order to understand the possible role of this ligand as molybdophore. A multi-technique approach has been adopted, in order to derive a comprehensive set of information necessary to assess the chemical speciation of the 8-HQA/MoO42− system, as well as the coordination behavior and the sequestering ability of 8-HQA towards molybdate. Chemical speciation studies have been performed in KCl(aq) at I = 0.2 mol·dm−3 and T = 298.15 K by ISE-H+ (glass electrode) potentiometric and UV/Vis spectrophotometric titrations. CV (Cyclic Voltammetry), DP-ASV (Differential Pulse-Anodic Stripping Voltammetry), ESI-MS experiments and quantum mechanical calculations have been also performed to derive information about the nature and possible structure of species formed. These results are also compared with those reported for the 8-HQA/Fe3+ system in terms of chemical speciation and sequestering ability of 8-HQA.

Potentiometric and UV-Vis spectrophotometric titrations for evaluation of the antioxidant capacity of chicoric acid

Potentiometric/spectrophotometric titrations have revealed the antioxidation behavior and mechanisms of chicoric acid (ChA, versus trolox) against ABTS˙+ radical cations.

Microwave-Assisted Synthesis, Proton Dissociation Processes, and Anticancer Evaluation of Novel D-Ring-Fused Steroidal 5-Amino-1-Arylpyrazoles

Taking into account the pharmacological relevance of heterocycle-fused natural steroids, the objective of the current study was to develop a multistep reaction sequence for the efficient synthesis of novel D-ring-condensed 5-amino-1-arylpyrazoles from dehydroepiandrosterone (DHEA). A condensation reaction of 16-formyl-DHEA with hydroxylamine afforded the corresponding oxime, which was demonstrated to be stable in one of its cyclic isoxazoline forms due to possible ring-chain tautomerism. The subsequent base-induced dehydration to a diastereomeric β-ketonitrile, followed by microwave-assisted heterocyclization with different arylhydrazines led to the desired pyrazoles. The generally good yields of the products depended slightly on the electronic character of the substituent present on the aromatic ring of the reagent. The proton dissociation processes of the DHEA-derived heterocycles were investigated in aqueous solution by UV-visible spectrophotometric titrations to reveal their actual chemical forms at physiological pH. The determined pKa values attributed to the pyrazole NH+ moiety were low (1.8–4.0) and varied by the different substituents of the benzene ring. The antiproliferative effects of the structurally similar compounds were screened in vitro on human cancer cells (namely on HeLa, U2Os, MCF-7, PC-3, and A549), along with a noncancerous cell line (MRC-5). The IC50 values of the most active derivative were determined on all cell lines.

Analysis of solvent-accessible voids and proton-coupled electron transfer of 2,6-bis(1H-imidazol-2-yl)pyridine and its hydrochloride

The crystal structures of the solid form of solvated 2,6-bis(1H-imidazol-2-yl)pyridine (H2dimpy) trihydrate, C11H9N5·3H2O·[+solvent], I, and its hydrate hydrochloride salt 2-[6-(1H-imidazol-2-yl)pyridin-2-yl]-1H-imidazol-3-ium chloride trihydrate, C11H10N5 +·Cl−·3H2O, II, are reported and analysed in detail, along with potentiometric and spectrophotometric titrations for evaluation of the acid–base equilibria and proton-coupled electron-transfer reactions. Compound I crystallizes in the high-symmetry trigonal space group P3221 with an atypical formation of solvent-accessible voids, as a consequence of the 32 screw axis in the crystallographic c-axis direction, which are probably occupied by uncharacterized disordered solvent molecules. Additionally, the trihydrated chloride salt crystallizes in the conventional monoclinic space group P21/c without the formation of solvent-accessible voids. The acid–base equilibria of H2dimpy were studied by potentiometric and spectrophotometric titrations, and the results suggest the formation of H3dimpy+ (pK a1 = 5.40) and H4dimpy2+ (pK a2 = 3.98), with the electrochemical behaviour of these species showing two consecutive irreversible proton-coupled electron-transfer reactions. Density functional theory (DFT) calculations corroborate the interpretation of the experimental results and support the assignment of the electrochemical behaviour.

Spectrophotometric Determination of the First Hydrolysis Constant of Praseodymium (III)

The behavior of the trivalent ion praseodymium in 2M of NaCl at 303 K and in CO2 free conditions, was studied. Spectrophotometric titrations of the soluble species were used, in order to obtain the value of the first hydrolysis constant of Pr(III). The data obtained were treated with both the program SQUAD and by a graphic method, respectively. The result obtained using SQUAD was log*ß1 = –8.94 ± 0.03, while it was log*ß1 = –8.77 ± 0.03, when calculated graphically. These results are similar to the value obtained previously with the potentiometric method.