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At least 163 records · Page 9Linked to original sources

PubMed2006

Photo-assisted Fenton type processes for the degradation of phenol: a kinetic study.

In this study the application of advanced oxidation processes (AOPs), dark Fenton and photo-assisted Fenton type processes; Fe(2+)/H(2)O(2), Fe(3+)/H(2)O(2), Fe(0)/H(2)O(2), UV/Fe(2+)/H(2)O(2), UV/Fe(3+)/H(2)O(2) and UV/Fe(0)/H(2)O(2), for degradation of phenol as a model organic pollutant in the wastewater was investigated. A detail kinetic modeling which describes the degradation of phenol was performed. Mathematical models which predict phenol decomposition and formation of primary oxidation by-products: catechol, hydroquinone and benzoquinone, by applied processes were developed. The study also consist the modeling of mineralization kinetic of the phenol solution by applied AOPs. This part, besides well known reactions of Fenton and photo-Fenton chemistry, involves additional reactions which describe removal of iron from catalytic cycle through formation of ferric complexes and its regeneration induced by UV radiation. Phenol decomposition kinetic was monitored by HPLC analysis and total organic carbon content measurements (TOC). Complete phenol removal was obtained by all applied processes. Residual TOC by applied Fenton type processes ranged between 60.2 and 44.7%, while the efficiency of those processes was significantly enhanced in the presence of UV light, where residual TOC ranged between 15.2 and 2.4%.

Algorithms↗

PubMed2006

Characterization and photo-Fenton treatment of used tires leachate.

In this study the leachates derived from used tires were firstly characterized by means of the evaluation of their organic matter content. The leachate from tire powder presented a COD value of 508 mg O(2) l(-1) and a TOC of 214 mg Cl (-1). The main identified organic substances were constituents of the rubber structure: benzothiazole derivatives, phthalates, phenolic derivatives, hydrocarbons and fatty acids. The application of photo-Fenton treatment was investigated in order to obtain the maximum organic matter removal. When a solar chamber as light source was used (light intensity=500 Wm(-2)), the best operational conditions were the following: [H(2)O(2)]=3703 mg l(-1), [Fe(2+)]=92.1 mg l(-1), initial pH 2.7-3.0, reaction time=100 min. After the photo-Fenton treatment at optimum conditions, the reached COD and TOC reduction was 64% and 48%, respectively. The main initial organic substances were eliminated after the reaction and no significant by-products were identified. A complementary treatment consisted of coagulation-flocculation carried out with FeCl(3) x 6H(2)O at pH 12 produced a maximum organic matter removal of 43% as COD and 39% as TOC. A combination of photo-Fenton followed by coagulation-flocculation enhanced the organic matter removal: a reduction of 77% of COD and 64% of TOC was attained.

Chemical Phenomena↗

PubMed2006

Calorimetric studies on the thermal hazard of methyl ethyl ketone peroxide with incompatible substances.

In Taiwan, Japan, and China, methyl ethyl ketone peroxide (MEKPO) has caused many severe thermal explosions owing to its thermal instability and reactivity originating from the complexity of its structure. This study focused on the incompatible features of MEKPO as detected by calorimetry. The thermal decomposition and runaway behaviors of MEKPO with about 10wt.% incompatibilities, such as H(2)SO(4), HCl, NaOH, KOH, FeCl(3), and FeSO(4), were analyzed by dynamic calorimeter, differential scanning calorimetry (DSC) and adiabatic calorimeter, vent sizing package 2 (VSP2). Thermokinetic data, such as onset temperature, heat of decomposition, adiabatic temperature rise, and self-heat rate, were obtained and assessed. Experimental data were used for determining the incompatibility rating on hazards. From the thermal curves of MEKPO with assumed incompatible substances detected by DSC, all the onset temperatures in the other tests occurring earlier advanced, especially with alkaline or ferric materials. In some tests, significant incompatible reactions were found. Adiabatic runaway behaviors for simulating the worst case scenario were performed by using VSP2. These calorimetric data led to the same results that the alkaline or ferric solution was the most incompatible with MEKPO.

Butanones↗

PubMed2005

Electron transfer kinetics and mechanistic study of the thionicotinamide coordinated to the pentacyanoferrate(III)/(II) complexes: a model system for the in vitro activation of thioamides anti-tuberculosis drugs.

The mechanism of activation thioamide-pyridine anti-tuberculosis prodrugs is poorly described in the literature. It has recently been shown that ethionamide, an important component of second-line therapy for the treatment of multi-drug-resistant tuberculosis, is activated through an enzymatic electron transfer (ET) reaction. In an attempt to shed light on the activation of thioamide drugs, we have mimicked a redox process involving the thionicotinamide (thio) ligand, investigating its reactivity through coordination to the redox reversible [Fe(III/II)(CN)(5)(H(2)O)](2-/3-) metal center. The reaction of the Fe(III) complex with thionicotinamide leads to the ligand conversion to the 3-cyanopyridine species coordinated to a Fe(II) metal center. The rate constant, k(et)=10 s(-1), was determined for this intra-molecular ET reaction. A kinetic study for the cross-reaction of thionicotinamide and [Fe(CN)(6)](3-) was also carried out. The oxidation of thionicotinamide by [Fe(CN)(6)](3-) leads to formation of mainly 3-cyanopyridine and [Fe(CN)(6)](4-) with a k(et)=(5.38+/-0.03) M(-1)s(-1) at 25 degrees C, pH 12.0. The rate of this reaction is strongly dependent on pH due to an acid-base equilibrium related to the deprotonation of the R-SH functional group of the imidothiol form of thionicotinamide. The kinetic results reinforced the assignment of an intra-molecular mechanism for the ET reaction of [Fe(III)(CN)(5)(H(2)O)](2-) and the thioamide ligand. These results can be valuable for the design of new thiocarbonyl-containing drugs against resistant strains of Mycobacterium tuberculosis by a self-activating mechanism.

Antitubercular Agents↗

PubMed2005

Assessments of the chemistry and vasodilatory activity of nitrite with hemoglobin under physiologically relevant conditions.

Hypoxic vasodilation involves detection of the oxygen content of blood by a sensor, which rapidly transduces this signal into vasodilatory bioactivity. Current perspectives on the molecular mechanism of this function hold that hemoglobin (Hb) operates as both oxygen sensor and a condition-responsive NO reactor that regulates the dispensing of bioactivity through release of the NO group from the beta-cys93 S-nitroso derivative of Hb, SNO-Hb. A common path to the formation of SNO-Hb involves oxidative transfer of the NO-group from heme to thiol. We have previously reported that the reaction of nitrite with deoxy-Hb, which furnishes heme-Fe(II)NO, represents one attractive route for the formation of SNO-Hb. Recent literature, however, posits that the nitrite-reductase reaction of Hb might produce physiological vasodilatory effects through NO that evades trapping on heme-Fe(II) and may be stored before release as Fe(III)NO. In this article, we briefly review current perspectives in NO biology on the nitrite-reductase reaction of Hb. We report in vitro spectroscopic (UV/Vis, EPR) studies that are difficult to reconcile with suggestions that this reaction either generates a heme-Fe(III)NO reservoir or significantly liberates NO. We further show in bioassay experiments that combinations of nitrite and deoxy-Hb--under conditions that suppress SNO-Hb formation--exhibit no direct vasodilatory activity. These results help underscore the differences between physiological, RBC-regulated, hypoxic vasodilation versus pharmacological effects of exogenous nitrite.

Biosensing Techniques↗

PubMed2006

Iron(III) complexes of certain meridionally coordinating tridentate ligands as models for non-heme iron enzymes: the role of carboxylate coordination.

The iron(III) complexes [Fe(pda)Cl(H(2)O)(2)] (1), [Fe(tpy)Cl(3)] (2), and [Fe(bbp)Cl(3)] (3), where H(2)pda is pyridine-2,6-dicarboxylic acid, tpy is 2,2':6,2''-terpyridine and bbp is 2,6-bis(benzimidazolyl)pyridine, have been isolated and studied as functional models for the intradiol-cleaving catechol dioxygenase enzymes. Mixed ligand complexes of H(2)pda with the bidentate ligands 2,2'-bipyridine (bpy) and 1,10-phenanthroline (phen) have been also prepared and studied. All the complexes have been characterized using absorption spectral and electrochemical methods. The spectral changes in the catecholate adducts of the complexes generated in situ have been investigated. Upon interacting the complexes with catecholate anions a low energy catecholate to iron(III) charge transfer band appears, which is similar to that observed for enzyme-substrate complexes. All the complexes catalyze the oxidative intradiol cleavage of 3,5-di-tert-butylcatechol (H(2)dbc) in the presence of dioxygen. Interestingly, on replacing the pyridyl groups in 2 and the bulky benzimidazole groups in 3 by the carboxylate groups, the yields of the intradiol cleavage products of dioxygenation increases, 1 (50%)>2 (20%)>3 (10%). The higher intradiol yield for 1 has been ascribed to the meridional coordination of two carboxylate groups of pda(2-). In contrast to the trend in the intradiol cleavage yields, a tremendous decrease in the rate (200 times) is observed on replacing the two pyridyl moieties in 2 by two carboxylates as in 1 and a significant decrease in rate is observed on replacing the pyridyl moieties in 2 by strongly sigma-donating benzimidazole moieties as in 3. This is in conformity with the decrease in Lewis acidities of the iron(III) centers.

Carboxylic Acids↗

PubMed2005

Preparation and characterization of a copper based Indian traditional drug: tamra bhasma.

The copper based Indian traditional drug 'tamra bhasma' is administered for various ailments since long. Its synthesis involves treating metallic copper with plant juices and then repeated calcination in presence of air so that the metallic state is transformed into the corresponding oxide form traditionally known as 'bhasma'. In this work, we present a systematic characterization of this traditional drug using various techniques like X-ray diffraction (XRD), scanning electron microscopy (SEM)-energy dispersive X-ray analysis (EDX), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR), thermogravimetry (TG) and surface area measurement. The results obtained were found to match very well with those of a standard copper oxide confirming the composition of the drug sample. In addition, some specific findings were also made which could help in interpreting the therapeutic properties of the traditional drug 'tamra bhasma'.

Ascorbic Acid↗

PubMed2005

The chemical reactions in the human stomach and the relationship to metabolic disorders.

Acid hydrolysis of components from the diet in the stomach require the presence of an acid and a hydrolysing agent. The acid involved is hydrochloric acid. The present mechanism of hydrochloric acid production in the stomach is demonstrated to be incompatible with measured intracellular or intercellular concentrations of the relevant ions. An alternative set of chemical reactions whereby hydrochloric acid is formed in the stomach is presented. The hydrolysing agent is identified and a mechanism of transfer of chemical compounds into the metabolism is described. The hypothesis demonstrates that some of chemical compounds produced in the stomach can induce conditions such as asthma and that the conditions of osteoporosis and hemochromatosis can be linked to the function of the stomach. Possible treatments for these and other conditions such as stomach acidity and anaemia are proposed.

Adult↗

PubMed2004

MR imaging of the her2/neu and 9.2.27 tumor antigens using immunospecific contrast agents.

Molecular imaging of tumor antigens using immunospecific magnetic resonance (MR) contrast agents is a rapidly evolving field, which can potentially aid in early disease detection, monitoring of treatment efficacy, and drug development. In this study, we designed, synthetized, and tested in vitro two novel monocrystalline iron oxide nanoparticles (MION) conjugated to antibodies against the her2/neu tyrosine kinase receptor and the 9.2.27 proteoglycane sulfate. MION was synthetized by coprecipitation of iron II and iron III salts in 12-kD dextran solution; antibody coupling was performed by reductive amination. The relaxivity of the conjugates was 24.1-29.1 mM(-1) s(-1), with 1.8 to 2.1 antibody molecules per nanoparticle. A panel of cultured melanoma and mammary cell lines was used for testing. The cells were incubated with the particles at 16-32 microg Fe/ml in culture medium for 3 h at 37 degrees C, and investigated with immune fluorescence, transmission electron microscopy (TEM), MRI of cell suspensions in gelatine, and spectrophotometric iron determination. All receptor-positive cell lines, but not the controls, showed receptor-specific immune fluorescence, and strong changes in T(2) signal intensity at 1.5 T. The changes in 1/T(2) were between 1.5 and 4.6 s(-1) and correlated with the amount of cell-bound iron (R = 0.92). The relaxivity of cell-bound MION increased to 55.9 +/- 10.4 mM(-1) s(-1). TEM showed anti-9.2.27 conjugates binding to the plasma membrane, while the anti-her2/neu conjugates underwent receptor-mediated endocytosis. In conclusion, we obtained receptor-specific T(2) MR contrast with novel covalently bound, multivalent MION conjugates with anti-9.2.27 and anti-her2/neu to image tumor surface antigens. This concept can potentially be expanded to a large number of targets and to in vivo applications.

Antibodies, Monoclonal↗

PubMed2005

Recombinant PAS-heme domains of oxygen sensing proteins: high level production and physical characterization.

Details of a high-level recombinant production method for the heme-PAS domains of heme oxygen sensing proteins from Sinorhizobium meliloti (Sm) (formerly Rhizobium meliloti, Rm), Bradyrhizobium japonicum (Bj), and Escherichia coli (Ec) are described. Using a newly proposed, concise, and unambiguous naming system (also described here) these proteins are: SmFixLH(128-264), BjFixLH(140-270), and EcDosH(1-147). In addition, high-level production of BjFixL(140-505), the soluble full-length protein containing both heme (oxygen sensing) and kinase (catalytic) domains is described. Using an IPTG-inducible pET/BL21 expression system and a rapid, two-column purification has resulted in increased yields of 3- to 17-fold over literature values. The recombinant proteins are highly pure as judged by SDS-PAGE, MALDI-TOF mass spectrometry, and a UV-visible purity index. To our knowledge, this work includes the first mass spectrometry analysis of any PAS-heme protein and provides high-resolution confirmation of each protein's identity. These production and characterization improvements make possible future spectroscopic and dynamics studies designed to elucidate the intramolecular/interdomain signal that follows heme-domain oxygen dissociation.

Bacterial Proteins↗

PubMed2005

Raman spectroscopy of halotrichite from Jaroso, Spain.

Raman spectroscopy complimented with infrared ATR spectroscopy has been used to characterise a halotrichite FeSO(4) x Al(2)(SO(4))(3) x 22 H(2)O from The Jaroso Ravine, Aquilas, Spain. Halotrichites form a continuous solid solution series with pickingerite and chemical analysis shows that the jarosite contains 6% Mg(2+). Halotrichite is characterised by four infrared bands at 3569.5, 3485.7, 3371.4 and 3239.0 cm(-1). Using Libowitsky type relationships, hydrogen bond distances of 3.08, 2.876, 2.780 and 2.718 Angstrom were determined. Two intense Raman bands are observed at 987.7 and 984.4 cm(-1) and are assigned to the nu(1) symmetric stretching vibrations of the sulphate bonded to the Fe(2+) and the water units in the structure. Three sulphate bands are observed at 77K at 1000.0, 991.3 and 985.0 cm(-1) suggesting further differentiation of the sulphate units. Raman spectrum of the nu(2) and nu(4) region of halotrichite at 298 K shows two bands at 445.1 and 466.9 cm(-1), and 624.2 and 605.5 cm(-1), respectively, confirming the reduction of symmetry of the sulphate in halotrichite.

Alum Compounds↗

PubMed2006

FTIR features of lithium-iron phosphates as electrode materials for rechargeable lithium batteries.

The essential structural features of lithium-metal phosphates (LMP) have been studied using FTIR spectroscopy which is a sensitive tool to probe the local environment in the solid materials. Various LMP materials where M is iron have been investigated including phospho-olivine LiFePO(4), diphosphate LiFeP(2)O(7), Nasicon-type phosphate Li(3)Fe(2)(PO(4))(3) and dihydrate FePO(4).2H(2)O. Vitreous and amorphous materials are also considered. Analysis of internal and external modes of vibration allows to distinguish between the different phases and the type of cationic environment in the framework. Results corroborate the contribution of the main factors which are responsible for the complexity of the spectra, i.e. departure from ideal symmetry, interactions between polyhedra, bridging atoms and lattice distortion.

Diphosphates↗

PubMed2006

Sulphate efflorescent minerals from El Jaroso Ravine, Sierra Almagrera--An SEM and Raman spectroscopic study.

Two sulphate efflorescent evaporite mineral samples from Jaroso, Spain have been studied by scanning electron microscopy and Raman spectroscopy. SEM by comparison with known minerals shows the evaporite mineral is a mixture of halotrichite and jarosite, whilst the oxidised mineral is predominantly jarosite. SEM characterises the halotrichite as long narrow crystals and the jarosite as distorted rhombohedral crystals. Raman spectra of the sulphates of K, Mg, Fe(II), Fe(III) are compared with the spectra of halotrichite, jarosite and the two sulphate efflorescent samples. The efflorescent sample was proven by Raman spectroscopy to be a mixture of halotrichite and jarosite and the oxidised efflorescent sample to be jarosite and a complex mixture of sulphates.

Alum Compounds↗

PubMed1999

Action of agents on glucosyltransferases from Streptococcus mutans in solution and adsorbed to experimental pellicle.

Glucosyltransferase (Gtf) activity mediates sucrose-dependent adherence of mutans streptococci to the tooth surface, is essential for the cariogenicity of these micro-organisms, and contributes significantly to the exopolysaccharide component of the dental-plaque matrix. Clearly, agents that inhibit Gtfs could have therapeutic benefit. Here the effects of agents that inhibit Gtfs in solution and adsorbed to a surface were explored. Various classes of chemical reagents were tested for their ability to inhibit the enzymes responsible for insoluble-glucan synthesis (GtfB), insoluble/soluble glucan synthesis (GtfC), and soluble-glucan (GtfD) from Streptococcus mutans. Standard inhibition assays were done with Gtf enzyme in solution or with Gtf adsorbed to parotid saliva-coated hydroxylapatite (surface phase). Reagents tested included the metallic cations Li+, Zn2+, Cu2+, Fe2+ and Fe3+; the oxidizing compounds hypochlorite, Rose Bengal, perborate, and sodium-meta-periodate; and a panel of sugars and sugar analogues including sorbitol, xylitol, 1',4',6' trideoxy-trichloro-galactosucrose (TGS), and 1-deoxynojirimycin (dNJ). In solution, Gtf activity was inhibited significantly, at the highest concentrations tested: by the metal ions Zn2+, Cu2+, Fe2+ and Fe3+ (approx. 40-80% inhibition); by Rose Bengal and hypochlorite (approx. 80-90% inhibition); and by TGS and dNJ (approx. 50-80%). However, surface-adsorbed Gtfs displayed increased resistance to inhibition by the same metal cations and oxidizing compounds that inhibited them in solution. In contrast, both TGS and dNJ possessed similar inhibition profiles for both surface-bound Gtf and enzyme in solution. These data indicate that the nature of the inhibitor is important, and also whether the Gtf enzyme is in solution or adsorbed to saliva-coated hydroxylapatite.

1-Deoxynojirimycin↗

PubMed2001

Iron-induced oxidative damage of corn root plasma membrane H(+)-ATPase.

The effect of iron on the activity of the plasma membrane H(+)-ATPase (PMA) from corn root microsomal fraction (CRMF) was investigated. In the presence of either Fe(2+) or Fe(3+) (100-200 microM of FeSO(4) or FeCl(3), respectively), 80-90% inhibition of ATP hydrolysis by PMA was observed. Half-maximal inhibition was attained at 25 microM and 50 microM for Fe(2+) and Fe(3+), respectively. Inhibition of the ATPase activity was prevented in the presence of metal ion chelators such as EDTA, deferoxamine or o-phenanthroline in the incubation medium. However, preincubation of CRMF in the presence of 100 microM Fe(2+), but not with 100 microM Fe(3+), rendered the ATPase activity (measured in the presence of excess EDTA) irreversibly inhibited. Inhibition was also observed using a preparation further enriched in plasma membranes by gradient centrifugation. Addition of 0.5 mM ATP to the preincubation medium, either in the presence or in the absence of 5 mM MgCl(2), reduced the extent of irreversible inhibition of the H(+)-ATPase. Addition of 40 microM butylated hydroxytoluene and/or 5 mM dithiothreitol, or deoxygenation of the incubation medium by bubbling a stream of argon in the solution, also caused significant protection of the ATPase activity against irreversible inhibition by iron. Western blots of CRMF probed with a polyclonal antiserum against the yeast plasma membrane H(+)-ATPase showed a 100 kDa cross-reactive band, which disappeared in samples previously exposed to 500 microM Fe(2+). Interestingly, preservation of the 100 kDa band was observed when CRMF were exposed to Fe(2+) in the presence of either 5 mM dithiothreitol or 40 microM butylated hydroxytoluene. These results indicate that iron causes irreversible inhibition of the corn root plasma membrane H(+)-ATPase by oxidation of sulfhydryl groups of the enzyme following lipid peroxidation.

Butylated Hydroxytoluene↗

PubMed1998

Strong dependence of the lipid peroxidation product spectrum whether Fe2+/O2 or Fe3+/O2 is used as oxidant.

Catalytic amounts of Fe2+ or Fe3+ ions are widely applied to induce simulated biological lipid peroxidation reactions. Independently, whether Fe2+ or Fe3+ were used, similar products were obtained. We show in this paper that the product spectrum is indeed very different, whether one ion species, either Fe2+ or Fe3+, is present in excess; thus, decomposition of (13S,9Z,11E) 13-hydroxyperoxy-9, 11-octadecadienoic acid (13S-HPODE) generates in the presence of equimolar amounts of Fe2+ ions mainly the corresponding alcohol (13S, 9Z,11E) 13-hydroxy-9,11-octadecadienoic acid besides 12,13-epoxy-11-hydroxy-9-octadecenoic acid (12,13-epHOD) and 13-oxo-9,11-octa-decadienoic acid (13-KODE), while decomposition of 13S-HPODE with equimolar amounts of Fe3+ produces mainly 12,13-epHOD, hydrolysis products thereof and other oxidized products, e.g., hydroxyoxo acids. In addition, unusually large amounts of aldehydes are formed, e.g., the amount of 4-hydroxy-nonenal was found to exceed that obtained by Fe2+ induced air oxidation for a factor of about 100. Since these further oxidation products are suspected to cause cell damage, liberated Fe3+ ions seem to be responsible for generation of toxic products in inflammatory diseases, e.g., atherosclerosis.

Chromatography, Thin Layer↗

PubMed1991

A mixed valence form of the iron cluster in the B2 protein of ribonucleotide reductase from Escherichia coli.

A mixed valent form of the iron cluster (Fe(II)Fe(III) in the B2 protein of ribonucleotide reductase has been isolated and characterized. The irons in this state of the protein are ferromagnetically coupled as indicated by the observation of a novel S = 9/2 EPR spectrum. This is the first ferromagnetically coupled Fe(II)Fe(III) cluster reported for a protein and the first observation of the mixed valence form of ribonucleotide reductase.

Electron Spin Resonance Spectroscopy↗

PubMed2000

Increased ferric iron content and iron-induced oxidative stress in the brains of scrapie-infected mice.

Scrapie is a transmissible neurodegenerative disease of sheep and goats. The neuropathological changes include vacuolation, astrocytosis, the development of amyloid plaques in some instances, and neuronal loss. The mechanisms involved in neuronal cell death in scrapie are not known. Recently, we reported the presence of oxidative stress in the brains of scrapie-infected animals and suggested that this is the main mechanism that induces neuronal cell loss. It is known that oxidative stress induced by free radicals is associated with iron accumulation; this association led to an examination of the levels of iron (total iron, Fe(2+) and Fe(3+)) in the brains of control and scrapie-infected mice by biochemical methods. In the scrapie-infected group, both the level of total iron and the Fe(3+) level were significantly increased in cerebral cortex, striatum, and brainstem as compared to the values in the control group. A shift in the ratio of Fe(2+)/Fe(3+) was observed in the same regions of infected mice. Additionally, in this scrapie model, we confirmed the presence of oxidative stress, as evidenced by the increase of free malondialdehyde. These results suggest that iron metabolism is changed and that iron-induced oxidative stress partly contributes to neurodegeneration in scrapie infection.

Animals↗