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PubMed2004

Chemical nature, ligand denticity and quantification of fungal siderophores.

Thirtyfive siderophore producing fungi were categorized for their hydroxamate, catecholate or carboxylate nature by chemical and bioassays. Out of 35 fungi, 30 were hydroxamates and 5 showed carboxylate nature. However, none of the fungi produced catecholate type of siderophores. Eighteen out of 29 fungi were trihydroxamate and the rest 11 fungi were dihydroxamates. Twenty-three fungi were hexadentate and 6 were tetradentate in nature. Quantification of siderophores using standard compounds deferrioxamine mesylate and rhizoferrin revealed that Phanerochaete chrysosporium produced maximum among the hydroxamate producing fungi and Mycotypha africana resulted maximum among the carboxylate producing fungi.

Biological Assay↗
PubMed1998

Reactivity of 6-phosphogluconolactone with hydroxylamine: the possible involvement of glucose-6-phosphate dehydrogenase in endogenous glycation reactions.

The reactivity of 6-phosphogluconolactone and of delta-gluconolactone with hydroxylamine (a model compound in electrophilicity determination studies) was examined and compared with the reactivity of several other electrophiles, such as acid anhydrides and esters, some of which exhibit adverse biological effects (e.g. carcinogenicity). At pH 7.6 and 30 degrees C, and with an excess of hydroxylamine concentration, most of the compounds tested disappear from the medium in a monoexponential reaction. On the other hand, the reaction of 6-phosphogluconolactone with hydroxylamine is biexponential. This finding indicates the existence of 6-phosphogluconolactone in two interconvertible, isomeric forms. The reactivity, towards hydroxylamine, of 6-phosphogluconolactone and, to a lesser extent of delta-gluconolactone, is on the upper scale of reactivity of the electrophiles tested. It is concluded that 6-phosphogluconolactone (and in particular, one of its isomeric forms) is a highly electrophilic compound, and may possibly react with sundry intracellular nucleophiles, thereby exerting untoward metabolic effects. In this connection, it is of interest that a positive correlation has been found to exist between glucose-6-phosphate dehydrogenase activity and cell proliferation.

Ammonium Hydroxide↗
PubMed2005

Adsorption of atrazine, hydroxyatrazine, deethylatrazine, and deisopropylatrazine onto Fe(III) polyhydroxy cations intercalated vermiculite and montmorillonite.

This paper describes the modification of the clay minerals vermiculite (VT) and montmorillonite (MT) by intercalating Fe(III) polymers of different [OH(-)]:[Fe(III)] ratios with the aim of removing atrazine (AT) and its metabolites deethylatrazine (DEA), deisopropylatrazine (DIA), and hydroxyatrazine (ATOH) from aqueous solution. An enhancement of adsorption capacity was observed for both intercalated clay minerals in comparison to the potassium-saturated materials (KVT or KMT). The results showed that different [OH(-)]:[Fe(III)] molar ratios had a small influence on the adsorption capacity, as well as in the basal spacing, BET surface area, and porosity. For the lowest initial concentrations of AT, DIA, and ATOH (0.050 mg L(-)(1)) studied, the modified VT adsorbed almost 80% of AT and DIA, while ATOH was removed at concentration levels below the detection limit of the technique, implying in at least 99.5% of sorption. Weak interaction between intercalated VT and DEA was observed, although a significant adsorption enhancement occurred in comparison to KVT. Within a 24 h interval, desorption of AT and DIA in aqueous medium reached levels close to 20% of the amount initially adsorbed, while for ATOH only 3% of the adsorbed compound was desorbed. The adsorption capacity of the Fe(III)-intercalated VT decreased after the first adsorption/desorption cycle, implying that the material is not suitable for reutilization. The intercalated MT was a powerful sorbent for AT, DEA, DIA, and ATOH, removing all of these chemicals from solution almost quantitatively (sorption greater than 99.5%), even at initial concentrations as high as 1.0 mg L(-)(1). Additionally, desorption of AT, ATOH, and DIA in water was not measurable up to the tube corresponding to the initial concentration of 1.0 mg L(-)(1), suggesting strong irreversible binding of these compounds to the intercalated MT materials. Desorption of DEA from the intercalated MT was between 5 and 30%. Unlike what was observed for VT, the intercalated MT materials were recyclable, keeping an excellent performance when reutilized.

Adsorption↗
PubMed2004

The protonation status of compound II in myoglobin, studied by a combination of experimental data and quantum chemical calculations: quantum refinement.

Treatment of met-myoglobin (FeIII) with H2O2 gives rise to ferryl myoglobin, which is closely related to compound II in peroxidases. Experimental studies have given conflicting results for this species. In particular, crystallographic and extended x-ray absorption fine-structure data have shown either a short (approximately 170 pm) or a longer (approximately 190 pm) Fe-O bond, indicating either a double or a single bond. We here present a combined experimental and theoretical investigation of this species. In particular, we use quantum refinement to re-refine a crystal structure with a long bond, using 12 possible states of the active site. The states differ in the formal oxidation state of the iron ion and in the protonation of the oxygen ligand (O2-, OH-, or H2O) and the distal histidine residue (with a proton on Ndelta1, Nepsilon2, or on both atoms). Quantum refinement is essentially standard crystallographic refinement, where the molecular-mechanics potential, normally used to supplement the experimental data, is replaced by a quantum chemical calculation. Thereby, we obtain an accurate description of the active site in all the different protonation and oxidation states, and we can determine which of the 12 structures fit the experimental data best by comparing the crystallographic R-factors, electron-density maps, strain energies, and deviation from the ideal structure. The results indicate that FeIII OH- and FeIV OH- fit the experimental data almost equally well. These two states are appreciably better than the standard model of compound II, FeIV O2-. Combined with the available spectroscopic data, this indicates that compound II in myoglobin is protonated and is best described as FeIV OH-. It accepts a hydrogen bond from the distal His, which may be protonated at low pH.

Binding Sites↗
PubMed2005

Comparison of protease-resistant prion protein inhibitors in cell cultures infected with two strains of mouse and sheep scrapie.

The transmissible spongiform encephalopathies (TSEs) are fatal neurodegenerative diseases. A primary therapeutic target for TSE intervention has been a protease-resistant form of prion protein known as PrP(Sc) or PrP-res. In vitro testing of mouse scrapie-infected cell cultures has identified many PrP-res inhibitors that also have activity in vivo. Here we identify 32 new inhibitors of two strains of mouse scrapie PrP-res. Furthermore, to investigate the species-specificity of these and other PrP-res inhibitors, we have developed a high-throughput cell culture assay based on Rov9 cells chronically-infected with sheep scrapie. Of 32 inhibitors of murine PrP-res that were also tested in the Rov9 cells, only six showed inhibitory activity against sheep PrP-res. The three most potent inhibitors of both murine and ovine PrP-res formation (with 50% inhibition at < or =5 microM) were tannic acid, pentosan polysulfate and Fe(III) deuteroporphyrin 2,4-bisethyleneglycol. The latter two have anti-mouse scrapie activity in vivo. These results identify new inhibitors of murine and ovine PrP-res formation and reinforce the idea that compounds effective against PrP-res from one species or strain cannot be assumed to be active against others.

Animals↗
PubMed1999

Electrochemical and esr spin trap studies of a new iron tetra-catecholamide complex.

A new siderophore, N5,N6-thiodipropanoyl-bis[N1,N10-bis(2,3-dihydroxy benzoyl-spermidine)]-Fe (III) complex or H2LFe has been synthesised. The reaction of the reduced form of this complex with dioxygen has been investigated through electrochemical study and revealed the formation of a new species assumed to be H2O2. This species has been confirmed by esr spectroscopy using the diamagnetic compound 5-deutero-2,2,5-trimethylpyrrolidine-1-hydroxyl as spin trap. The resulting persistent radical is 5-deutero-2,2,5-trimethylpyrrolidine-1-yloxy (aN = 16.58 G, aD = 3.49 G).

Catecholamines↗
PubMed2003

Rates of hydroxyl radical generation and organic compound oxidation in mineral-catalyzed Fenton-like systems.

The iron oxide-catalyzed production of hydroxyl radical (*OH) from hydrogen peroxide (H2O2) has been used to oxidize organic contaminants in soils and groundwater. The goals of this study are to determine which factors control the generation rate of *OH (VOH) and to show that if VOH and the rate constants of the reactions of *OH with the system's constituents are known, the oxidation rate of a dissolved organic compound can be predicted. Using 14C-labeled formic acid as a probe, we measured VOH in pH 4 slurries of H2O2 and either synthesized ferrihydrite, goethite, or hematite or a natural iron oxide-coated quartzitic aquifer sand. In all of our experiments, VOH was proportional to the product of the concentrations of surface area of the iron oxide and H2O2, although different solids produced *OH at different rates. We used these results to develop a model of the decomposition rate of formic acid as a function of the initial formic acid and hydrogen peroxide concentrations and of the type and quantity of iron oxide. Our model successfully predicted the VOH and organic compound oxidation rates observed in our aquifer sand experiment and in a number of other studies but overpredicted VOH and oxidation rates in other cases, possibly indicating that unknown reactants are either interfering with *OH production or consuming *OH in these systems.

Ferric Compounds↗
PubMed2004

Reduction of arsenic content in a complex galena concentrate by Acidithiobacillus ferrooxidans.

BACKGROUND: Bioleaching is a process that has been used in the past in mineral pretreatment of refractory sulfides, mainly in the gold, copper and uranium benefit. This technology has been proved to be cheaper, more efficient and environmentally friendly than roasting and high pressure moisture heating processes. So far the most studied microorganism in bioleaching is Acidithiobacillus ferrooxidans. There are a few studies about the benefit of metals of low value through bioleaching. From all of these, there are almost no studies dealing with complex minerals containing arsenopyrite (FeAsS). Reduction and/or elimination of arsenic in these ores increase their value and allows the exploitation of a vast variety of minerals that today are being underexploited. RESULTS: Arsenopyrite was totally oxidized. The sum of arsenic remaining in solution and removed by sampling represents from 22 to 33% in weight (yield) of the original content in the mineral. The rest of the biooxidized arsenic form amorphous compounds that precipitate. Galena (PbS) was totally oxidized too, anglesite (PbSO4) formed is virtually insoluble and remains in the solids. The influence of seven factors in a batch process was studied. The maximum rate of arsenic dissolution in the concentrate was found using the following levels of factors: small surface area of particle exposure, low pulp density, injecting air and adding 9 K medium to the system. It was also found that ferric chloride and carbon dioxide decreased the arsenic dissolution rate. Bioleaching kinetic data of arsenic solubilization were used to estimate the dilution rate for a continuous culture. Calculated dilution rates were relatively small (0.088-0.103 day(-1)). CONCLUSION: Proper conditions of solubilization of arsenic during bioleaching are key features to improve the percentage (22 to 33% in weight) of arsenic removal. Further studies are needed to determine other factors that influence specifically the solubilization of arsenic in the bioleaching system such as: pH, dissolved oxygen concentration, redox potentials, nature of concentrate and temperature among others. At. ferrooxidans was able to completely oxidize the minerals present during the arsenic bioleaching. Other elements present originally in the concentrate such as Zn, Sb, and Cu were also solubilized. The process of bioleaching is expected to be influenced by mechanisms that still need to be established due to the diversity of the minerals involved and by the presence of traces of metals in the concentrate. The increase in pulp density generates a decrease in the dissolved arsenic concentration. This decrease is greater in runs where air was not injected to the system. The maximum rate of arsenic dissolution in the concentrate was found using; small surface area of particle exposure, low pulp density, injecting air and adding 9 K medium to the system. The effect of addition of ferric chloride during the arsenic bioleaching resulted in a decrease of the solubilized arsenic in the system. The presence of CO2 is associated to the decrease in arsenic dissolution.

Acidithiobacillus↗
PubMed2006

[A IL-6R antagonist 2520A produced by a fungal species].

AIM: To isolate IL-6R antagonists from the cultured broth of the strain Torulomyces ovatus. METHODS: Various column chromatographyes were used to separate and purify the compounds with IL-6R antagonist activity. The spectral data and physic-chemical properties were measured for structure identification. RESULTS: One compound namely 2520 was isolated from the cultured broth of Torulomyces ovatus. CONCLUSION: 2520A is a known compound (ferrichrome). It is first reported about its antagonistic activity of IL-6R and identification of iron atom in its structure.

Anti-Bacterial Agents↗
PubMed2001

Application of the Marcus cross relation to hydrogen atom transfer reactions.

The transfer of a hydrogen atom-a proton and an electron-is a fundamental process in chemistry and biology. A variety of hydrogen atom transfer reactions, involving iron complexes, phenols, hydroxylamines, tBuOOH, toluene, and related radicals, are shown to follow the Marcus cross relation. Thus, the Marcus theory formalism based on ground-state energetics and self-exchange rates, originally developed for electron transfer processes, is also valuable for hydrogen atom transfer. Compounds that undergo slow proton transfer (C-H bonds) or slow electron transfer (cobalt complexes) also undergo slow hydrogen atom transfer. Limitations of this approach are also discussed.

Chemical Phenomena↗
PubMed2001

Skin protection for photosensitized patients.

BACKGROUND AND OBJECTIVE: The goal of this study was to evaluate various creams for their capability to protect photosensitized skin from visible light. STUDY DESIGN/MATERIALS AND METHODS: Two cover creams and creams containing various combinations of Vaseline with TiO(2), ZnO, and Fe(2)O(3) were used to measure the reduced light transmission and the light absorption spectrum. In vitro and in vivo tests were performed to assess the protection from light by above mentioned compounds. RESULTS: The cover creams and the 50% TiO(2) cream showed similar efficacy in reducing light transmission, while the sunscreen was less efficient by a factor of 5. Cell protection by 25% TiO(2)+25% ZnO, TiO(2), or the cover creams was more efficient than protection by the sunscreen or other compounds. In vivo, the dark cover cream protected the skin by a factor of 3.4 better than the sunscreen. CONCLUSION: The dark cover cream has acceptable properties to protect photosensitized skin.

Absorption↗
PubMed1999

Reduction of ultraviolet light-induced oxidative stress by amino acid-based iron chelators.

The generation of free radicals by ultraviolet (UV) light accelerates skin aging, which is known as photoaging. Cutaneous iron catalyzes the generation of free radicals. We designed novel antioxidants that suppressed the iron-catalyzed free radical generation and the ensuing UV-induced damage by mimicking the binding site of iron sequestering proteins. These antioxidants, N-(2-hydroxybenzyl)amino acids, were prepared by condensation of amino acids such as glycine and L-serine with salicylaldehyde and followed by catalytic reduction. The compounds formed a 2:1 complex to iron ion. These amino acid derivatives inhibited the iron-induced hydroxyl radical generation (the Fenton reaction). The compounds also suppressed UV-induced lipid peroxidation in murine dermal fibroblast homogenates. In addition, N-(2-hydroxybenzyl)-L-serine showed protective activity against UV-induced cytotoxicity in murine dermal fibroblasts. Desferrioxamine, a strong iron sequestering compound, was effective in inhibiting the Fenton reaction and the lipid peroxidation, but it was ineffective in protecting against UV-induced cytotoxicity. The results suggest that UV-induced oxidative stress can be reduced by these amino acid derivatives.

Animals↗
PubMed2003

Monomeric MnIII/II and FeIII/II complexes with terminal hydroxo and oxo ligands: probing reactivity via O-H bond dissociation energies.

Non-heme manganese and iron complexes with terminal hydroxo or oxo ligands are proposed to mediate the transfer of hydrogen atoms in metalloproteins. To investigate this process in synthetic systems, the monomeric complexes [M(III/II)H(3)1(OH)](-/2-) and [M(III)H(3)1(O)](2-) have been prepared, where M(III/II) = Mn and Fe and [H(3)1](3-) is the tripodal ligand, tris[(N'-tert-butylureaylato)-N-ethyl)]aminato. These complexes have similar primary and secondary coordination spheres, which are enforced by [H(3)1](3-). The homolytic bond dissociation energies (BDEs(O-H)) for the M(III/II)-OH complexes were determined, using experimentally obtained values for the pK(a)(M-OH) and E(1/2) measured in DMSO. This thermodynamic analysis gave BDEs(O-H) of 77(4) kcal/mol for [Mn(II)H(3)1(O-H)](2-) and 66(4) kcal/mol for [Fe(II)H(3)1(O-H)](2-). For the M(III)-OH complexes, [Mn(III)H(3)1(OH)]- and [Fe(III)H(3)1(OH)]-, BDEs(O-H) of 110(4) and 115(4) kcal/mol were obtained. These BDEs(O-H) were verified with reactivity studies with substrates having known X-H bond energies (X = C, N, O). For instance, [Fe(II)H(3)1(OH)](2-) reacts with a TEMPO radical to afford [Fe(III)H(3)1(O)](2-) and TEMPO-H in isolated yields of 60 and 75%, respectively. Consistent with the BDE(O-H) values for [Mn(II)H(3)1(OH)](2-), TEMPO does not react with this complex, yet TEMPO-H (BDE(O-H) = 70 kcal/mol) reacts with [Mn(III)H(3)1(O)](2-), forming TEMPO and [Mn(II)H(3)1(OH)](2-). [Mn(III)H(3)1(O)](2-) and [Fe(III)H(3)1(O)](2-) react with other organic substrates containing C-H bonds less than 80 kcal/mol, including 9,10-dihydroanthracene and 1,4-cyclohexadiene to produce [M(II)H(3)1(OH)](2-) and the appropriate dehydrogenated product in yields of greater than 80%. Treating [Mn(III)H(3)1(O)](2-) and [Fe(III)H(3)1(O)](2-) with phenolic compounds does not yield the product expected from hydrogen atom transfer but rather the protonated complexes, [Mn(III)H(3)1(OH)]- and [Fe(III)H(3)1(OH)]-, which is ascribed to the highly basic nature of the terminal oxo group.

Electrochemistry↗
PubMed2000

Characterization of a membrane-bound NADH-dependent Fe(3+) reductase from the dissimilatory Fe(3+)-reducing bacterium Geobacter sulfurreducens.

Geobacter sulfurreducens produces a single, membrane-associated Fe(3+) reductase activity when grown on fumarate or Fe(3+). The activity was initially isolated by solubilization of membranes with the non-ionic detergent dodecyl-beta-D-maltoside, and partially purified by a combination of ion exchange chromatography and preparative non-denaturing gel electrophoresis. Molecular mass of the reductase, as determined by gel filtration chromatography, was approximately 300 kDa. Cofactor analysis of the purified reductase demonstrates that it contains a hemoprotein and flavin adenine dinucleotide. Kinetic and inhibitor studies show that the reductase is specific for NADH as electron donor, and confirm that the reductase enzymatically reduces Fe(3+). The cytochrome associated with the complex undergoes a reoxidation upon addition of Fe(3+) compounds, indicating an ability to pass reducing equivalents to Fe(3+). This is the first description of a purified NADH-dependent Fe(3+) reductase from a microorganism capable of coupling Fe(3+) reduction to growth.

Cell Membrane↗
PubMed1975

On the origin of molecular "handedness" in living systems.

Elementary particle effects (beta-decay) provide at best only a weakly handed radiation in the biologically effective energy ranges. Global magnetic effects coupled to sunlight are randomized by paleomagnetic reversals. Hence a persistent terrestrial handed bias at possible local biopoetic sites offers a more promising explanation for the origin of the "handedness" of the molecules found among living systems on earth. Magnetite in lava flows maintains a handed bias for surface catalysis through many magnetic reversals. Magnetite contaminated with sulfur has already been proposed by Granick as a biopoetic site because it provides a weak source of chemical energy derived by photochemical conversion. Indirect evidence for this hypothesis has been provided by the molecular structure of ferredoxin - a single strand of the 14 primordial amino acids wrapped around an FeS core. Lava flows have been suggested as biopoetic sites by Fox, since their temperature and chemical composition might allow for the rapid synthesis of prebiotic compounds at the surface of the primitive earth. The additional fact that magnetite in lave flows also provides a persistent handed site for surface catalysis offers a further argument for the experimental investigation of this specific biopoetic environment.

Biological Evolution↗
PubMed2006

The dicationic derivatives of DBTAA: Interactions with DNA/RNA and antiproliferative effects on human cell lines.

Three dibenzotetraaza[14]annulenes non-covalently interacted with double-stranded DNA and RNA by mixed minor groove and/or intercalative binding mode. Observed interactions were strongly dependent on the steric exposure of positive charges and the length of the linkers of studied compounds as well as on the secondary structure and basepair composition of DNA/RNA. Compound 2 showed pronounced selectivity toward dA-dT-rich sequences and binding mode switch from dominant minor groove binding to ds-DNA to dominant intercalation into ds-RNA. Antiproliferative effect of studied compounds on human tumor and normal cell lines was in good agreement with the strength of observed interactions with DNA/RNA.

Antineoplastic Agents↗