Utilization of iron sulfides for wastewater treatment: a critical review

Acid mine drainage due to weathering of iron sulfide minerals is one of the biggest global environmental issues. However, due to the unique physicochemical properties of natural and synthesized iron sulfides (i.e. pyrite, pyrrhotite, and mackinawite), they can be effectively used for wastewater treatment. These properties, such as ≡SH functional groups as Lewis bases, reducibility of surface Fe and S species, dissolved Fe²⁺ as a catalyst, and dissolved S^2? as an electron donor, are extensively reviewed in this article. The target water pollutants include toxic metals (i.e. lead, mercury, cadmium, and hexavalent chromium) and metalloid (i.e. arsenic), radionuclides (i.e. uranium and selenium), organic contaminants (i.e. chlorinated organic pollutants, benzene and polycyclic aromatic hydrocarbons), and nutrients (i.e. nitrogen and phosphorus). The dominant interaction mechanisms between iron sulfides and these contaminants, and the removal efficiencies are elucidated. This article focuses on the role of iron sulfides as functional materials for wastewater treatment. A recent development of nanostructured pyrrhotite with a high specific surface area for wastewater treatment is also highlighted.     

The 1.13-Å structure of iron-free cytochrome c peroxidase

The iron-free cytochrome c peroxidase (CCP) crystal structure has been determined to 1.13 Å and compared with the 1.2-Å ferric-CCP structure. Quite unexpectedly, removal of the iron has no effect on porphyrin geometry and distortion, indicating that protein–porphyrin interactions and not iron coordination or formation of the axial His–Fe bond determines porphyrin conformation. However, there are changes in solvent structure in the distal pocket, which lead to changes in the distal His52 acid–base catalyst. The observed ability of His52 to move in response to small changes in solvent structure is very likely important for its role as a catalyst in assisting in the heterolytic fission of the peroxide O–O bond.     

Computational detection of significant variation in binding affinity across two sets of sequences with application to the analysis of replication origins in yeast

Background  

In analyzing the stability of DNA replication origins in Saccharomyces cerevisiae we faced the question whether one set of sequences is significantly enriched in the number and/or the quality of the matches of a particular position weight matrix relative to another set.     

Possible degradation/biotransformation of lutein in vitro and in vivo: isolation and structural elucidation of lutein metabolites by HPLC and LC-MS (atmospheric pressure chemical ionization)

Metabolites of lutein are highly concentrated in the human macula and are known to provide protection against age-related macular degeneration. The aim of this investigation was to characterize the in vitro oxidation products of lutein obtained through photo-oxidation and to compare them with biologically transformed dietary lutein in intestine, plasma, liver, and eyes of rats. In vivo studies involved feeding rats a diet devoid of lutein for 2 weeks to induce deficiency. Rats were divided into two equal groups (n=6/group) and received either micellar lutein by gavage for 10 days or diet supplemented with fenugreek leaves as a lutein source for 4 weeks. Lutein metabolites/oxidation products obtained from in vivo and in vitro studies were characterized by HPLC and LC-MS (APCI) techniques to elucidate their structure. The characteristic fragmented ions resulting from photo-oxidation of lutein were identified as 523 (M(+)+H(+)-3CH(3)), 476 (M(+)+H(+)-6CH(3)), and 551 (M(+)+H(+)-H(2)O). In the eyes, the fragmented molecules resulting from lutein were 13-Z lutein, 13'-Z lutein, 13-Z zeaxanthin, all-E zeaxanthin, 9-Z lutein, 9'-Z lutein, and 3'-oxolutein. Epoxycarotenoids were identified in liver and plasma, whereas anhydrolutein was identified in intestine. This study emphasizes the essentiality of dietary lutein to maintain its status in the retina.     

Comparative effects of β-carotene and fucoxanthin on retinol deficiency induced oxidative stress in rats

This study aimed at comparing antioxidant potential of fucoxanthin (FUCO) with β-carotene in relieving lipid peroxidation (Lpx) caused by retinol deficiency (RD) in rats. RD rats (n = 45) were fed a dose of either β-carotene (0.81 μmol) or FUCO (0.83 μmol). Plasma and liver lipid peroxide levels and activity of antioxidant enzymes catalase (CAT) and glutathione transferase (GST) were measured for 8 h. Results revealed that RD increased (P < 0.05) Lpx in plasma and liver by 34.3% and 19.4%, while the CAT activity in plasma (89%) and liver microsomes (91%) and GST in liver homogenate (31%) and liver microsomes (30%) were decreased (P < 0.05) compared to control (rats fed basal diet). FUCO suppressed (P < 0.05) the Lpx level by 7–85% (plasma) and 24–72% (liver) as compared to β-carotene (51–76%, 33–65%) over a period of 8 h. The activity of CAT in plasma and liver microsomes was higher (P < 0.05) in FUCO (90–95%, 85–93%) and β-carotene (87–96%, 79–91%) groups as compared to RD group. Similarly, the activity of GST in liver and its microsomes was also elevated (P < 0.05) in FUCO (44–51%, 22–51%) and β-carotene (19–54%, 30–43%) groups as compared to RD group. Results demonstrate that FUCO has greater potential than β-carotene in modulating Lpx, CAT, GST in plasma and liver of RD rats.     

Screening and Identification of New Isolate: Thermostable <Emphasis Type="Italic">Escherichia coli</Emphasis> with Novel Thermoalkalotolerant Cellulases

A cellulase-producing bacterium strain was isolated from soil that produced novel thermoalkalotolerant cellulases after growth on CMC-Na agar screening plate at 37°C. It was identified as Escherichia coli using the method of 16S rRNA and intergenic spacer gene analysis combined with morphological, physiological, and biochemical tests. Three major components of the cellulases [carboxymethyl cellulase (CMCase), filter paper cellulase, and β-glucosidase] were produced with maximal activities (0.23, 0.08, and 0.15 U/ml) and maximum specific activities 4.13, 0.56, and 0.50 U/mg protein after 72, 96, and 120 h growth, respectively. Maximum CMCase activity was measured at 50°C and pH 6.0, respectively, and it also retained more than 60% of its maximal activity for at least 20 min at 50–70°C and 10 min at 80°C, respectively, and retained approximately 50% of its maximal activity after incubating at 90°C for 10 min. The enzyme could be applied in bioconversion of lignocellulosic agricultural wastes.     

Studies on tamoxifen encapsulated in lipid vesicles: effect on the growth of human breast cancer MCF-7 cells

Tamoxifen is a nonsteroidal estrogen-receptor modulator widely used in the treatment of breast cancer. Apoptosis has been reported to be a major mechanism for its antitumor effect. In the current studies, an endeavor was made to investigate the efficacy of vesicularly encapsulated tamoxifen on human breast cancer MCF-7 cells. Phospholipid-based vesicular systems viz. conventional liposomes and elastic-membrane liposomes were employed to encapsulate the drug. The MTT colorimetric assay was used to determine the efficacy of the tested formulations. The results demonstrated composition-dependent strong inhibition in the viability of MCF-7 cells with encapsulated tamoxifen vis-à-vis free drug. The encouraging findings from the current work construe immense potential of the lipid-based vesicular systems in the treatment of breast cancer.     

Studies on the dephosphorylation of phytic acid in livestock feed using phytase from Aspergillus niger van Teighem

Phytase from Aspergillus niger van Teighem efficiently hydrolyses phytate phosphorus present in various commercial live stock feeds and was not inactivated by various formulations and antibiotics present. The enzyme retained 90-95% phytase activity at 55 degrees C, pH 2.5 after 72 h of incubation with all the commercial feeds tested, thus indicating its suitability in feed application. The phytase hydrolysis increased with the increase in temperature and a significant release of 41 nmols P(i)/ml in phytase-treated feed over control sample was observed at 55 degrees C after 48 h. Besides this, the enzyme was maximally effective when used under acidic condition, releasing 21 and 42 nmols P(i)/ml at pH 1.5 and 2.5, respectively. As the pH shifted towards 5.5, significant decline in phosphorus release was observed. However, the enzyme was able to retain almost complete phytase activity in the presence of feed constituent even after 48 h over various pH tested. Thus it can be a potential candidate in animal nutrition where the ability of present phytase to retain activity over period of time in the presence of feed constituent is desired.