Ferric iron complexes of dopamine and 5,6-dihydroxyindole with nta, edda, and edta as ancillary ligands

Coordination of the neurotransmitter dopamine (DA) and the metal-binding component of neuromelanin 5,6-dihydroxyindole (DHI) with ferric iron has been studied in aqueous solution in the presence of ancillary ligands containing amine nitrogen and carboxylate oxygen donor sites. With nitrilotriacetic acid (nta) and ethylenediamine diacetic acid (edda) coligands, coordination of the catecholate ligands DA and DHI is observed to be complete at physiological pH. The resulting complexes of DA have the characteristic two-component electronic spectrum observed characteristically for L₄Fe(Cat) complexes. The spectrum obtained with DHI consists of a single broad absorption in the visible region. Both DA and DHI are able to coordinate with Fe³⁺ in the presence of edta, displacing carboxylate oxygen donors at pH values just above physiological pH. These results demonstrate the strong affinity of DA and DHI for Fe³⁺, pointing to in vivo complex formation in neuronal mixtures at physiological pH.     

Alpha-tocopherol induces calnexin in renal tubular cells: another protective mechanism against free radical-induced cellular damage

Pre-administration of alpha-tocopherol is protective against oxidative renal tubular damage and subsequent carcinogenesis by ferric nitrilotriacetate (Fe-NTA) in rats. We searched for mechanisms other than the scavenging effect of alpha-tocopherol with microarray analyses, which implicated calnexin, a chaperone for glycoproteins. Renal mRNA levels of calnexin significantly increased 3h after an injection of Fe-NTA in rats fed a standard diet whereas those fed an alpha-tocopherol-supplemented diet showed an increase prior to injection, but after injection showed a decrease in renal calnexin mRNA levels, with unaltered protein levels. In experiments using LLC-PK1 cells, addition of alpha-tocopherol was protective against oxidative stress by H2O2, concomitant with calnexin induction. Knockdown of calnexin by siRNA significantly reduced this protection. Furthermore, COS-7 cells transfected with the calnexin gene were more resistant to H2O2. Together with the fact that alpha-tocopherol induced N-acetylglucosaminyltransferase 3, our data suggest that alpha-tocopherol modifies glycoprotein metabolism partially by conferring mild ER stress. This adds another molecular mechanism of alpha-tocopherol toward cancer prevention.     

Utility of pentose colorimetric assay for the purification of potato lectin, an arabinose-rich glycoprotein

Potato lectin (Solanum tuberosum agglutinin, STA) is an unusual glycoprotein containing approximately 50% carbohydrates by weight. Of the total carbohydrates, 92% is contributed by L-arabinose, which are O-linked to hydroxyproline residues. The ferric chloride-orcinol assay (Bial’s test), which is specific for pentoses has so far been used only for the determination of free pentoses in biological samples. However, this colorimetric assay has not been used for the detection of pentoses in bound form as it occurs in Solanaceae lectins (potato, tomato, and Datura lectins). Utilizing the pentose colorimetric assay for monitoring the presence of potato lectin, a simpler and shorter procedure for the purification of this lectin from potato tubers has been developed. The yield of potato lectin (1.73 mg per 100 g potato tuber) is twice compared to the yields reported in earlier procedures. Although potato lectin is well known for its specificity to free trimers and tetramers of N-acetyl-D-glucosamine (GlcNAc), it possesses a similar specificity to the core (GlcNAc)₂ of N-linked glycoproteins. The utilization of the pentose assay in the purification of arabinose-rich lectins/agglutinins obviates the necessity for the use of agglutination assay in the various purification steps. The pentose assay appears to be a simple and convenient colorimetric assay for detecting any pentose-rich glycoprotein in plant extracts. The utility of the pentose assay appears to have a significant potential in the detection of hydroxyproline-rich glycoproteins (HRGPs), which are generally O-arabinosylated.     

Synthesis of 4-aryl-3,4-dihydropyrimidin-2(1H)-thione derivatives as potential calcium channel blockers

Biginelli reaction which involves condensation of methyl 3-oxopentanoate, aromatic aldehydes and thiourea with a catalytic amount of HCl at reflux temperature has been used for the synthesis of 4-aryl-6-ethyl-5-(methoxycarbonyl)-3,4-dihydropyrimidin-2(1H)-thiones (1–16). In addition, Lewis acids such as FeCl₃·6H₂O and/or H₃BO₃ were also used as catalysts for one-pot synthesis of the products. Compared to the classical Biginelli reaction conditions, the usage of Lewis acids has the advantage of good yields and short reaction times. The calcium channel blocker activities of 1–16 were screened by the tests performed on isolated rat ileum and thoracic aorta. Although product 11, 2-nitrophenyl-derivative, has potent antispasmodic activity on BaCl₂-stimulated rat ileum, it does not have vasodilator activity on KCl-stimulated rat thoracic aorta. Product 15, 2-ethoxyphenyl-derivative, exhibited significant antispasmodic and vasodilator activities in both screening paradigms.     

A wide family of pyridoxal thiosemicarbazone ferric complexes: Syntheses, structures and magnetic properties

This study reports the syntheses and the characterization of 12 ferric complexes of pyridoxal thiosemicarbazone. The richness of the coordination chemistry of this ligand is highlighted by the modulation of its charge from neutral H₂L to anionic L²⁻, thus leading to a wide family of ferric compounds with charge varying from +3 to −1. The structures of complexes [Fe(HL)₂]ClO₄ · 2H₂O and [Fe(HL)L] · 4.5H₂O were solved and discussed with a particular attention brought to the intermolecular interactions occurring between the complexes. The investigation of magnetic properties of these compounds revealed that two of them are in the HS state at any temperature, whereas the others are in the LS state. These results are discussed in relation to the modulation of the electronic properties of the ligand.     

The Nox/Ferric reductase/Ferric reductase-like families of Eumycetes

Reactive Oxygen Species (ROS) are involved in plant biomass degradation by fungi and development of fungal structures. While the ROS-generating NADPH oxidases from filamentous fungi are under strong scrutiny, much less is known about the related integral Membrane (or Ferric) Reductases (IMRs). Here, we present a survey of these enzymes in 29 fungal genomes covering the entire available range of fungal diversity. IMRs are present in all fungal genomes. They can be classified into at least 24 families, underscoring the high diversity of these enzymes. Some are differentially regulated during colony or fruiting body development, as well as by the nature of the carbon source of the growth medium. Importantly, functional characterization of IMRs has been made on proteins belonging to only two families, while nothing or very little is known about the proteins of the other 22 families.     

Anaerobic biodegradation of ethylthionocarbamate by the mixed bacteria under various electron acceptor conditions

Biodegradation behavior and kinetics of ethylthionocarbamate under nitrate, sulfate and ferric reducing conditions by mixed cultures enriched from the anaerobic digester sludge was investigated. The results showed that ethylthionocarbamate could be degraded independently by the mixed cultures coupled to nitrate, sulfate, and ferric reduction, and meanwhile, nitrite, sulfide, and ferrous were accumulated as a result of nitrate, sulfate and ferric reduction, respectively. Ferric was a more favorable terminal electron acceptor compared to nitrate and sulfate. The order of the electron acceptors with decreasing biodegradation rates of the ethylthionocarbamate was: ferric>nitrate>sulfate, and the corresponding maximum biodegradation rate was 7.240, 6.267, and 4.602 mg/(L·d), respectively. The anaerobic biodegradation of ethylthionocarbamate under various electron acceptor conditions can be accurately described by first order exponential decay kinetics.     

Selection of Leptospirillum ferrooxidans SRPCBL and development for enhanced ferric regeneration in stirred tank and airlift column reactor

Presence of Leptospirillum ferrooxidans plays significant role in ferric sulphate generation during bioleaching process. Thus, an attempt was made to select L. ferrooxidans from the polymetallic concentrate leachate and further developed it for enhanced ferric iron regeneration from the leachate in shake flask, stirred tank and column reactor. When ferric to ferrous iron ratio in the shake flask reached to 20:1, L. ferrooxidans out competed Acidithiobacillus ferrooxidans and accounted for more than 99% of the total population. The isolate was confirmed by 16S rRNA genes sequence analysis and named as L. ferrooxidans SRPCBL. When the culture was exposure to UV dose and the oxidation-reduction potential of the inoculation medium was adjusted to 40 0mV by ferrous:ferric iron ratio, the IOR reached to as high as 1.2 g/L/h in shake flask, even with initial ferrous iron concentration of 200 g/L. The chalcopyrite concentrate leachate containing 12.8, 15.7, and 42.0 g/L ferrous iron, ferric iron and copper, respectively was studied for ferric iron regeneration with the developed polymetallic resistant L. ferrooxidans SRPCBL in stirred tank and a developed biofilm airlift column, the highest IOR achieved were 2.20 g/L/h and 3.1 g/L/h, respectively, with ferrous oxidation efficiency of 98%. The ferric regeneration ability of the developed isolate from the leachate proves useful for a two-stage metal extraction process.