The C1q binding activity of IgG is modified in vitro by reactive oxygen species: implications for rheumatoid arthritis

IgG can be denatured in vitro by reactive oxygen species (ROS). Native IgG activates the complement cascade through C1q. Using a modified ELISA, C1q binding activity of rheumatoid IgG has been compared to IgG denatured by neutrophil-derived ROS. The C1q binding activity of rheumatoid synovial fluid IgG is greater than the corresponding serum IgG (P < 0.01). Denaturation of IgG by activated polymorphs or the Fenton reaction decreased its C1q binding activity (P < 0.01). In vitro exposure of IgG to OH. and ROO. increased its interaction with C1q (P < 0.01). Hypochlorous acid had no effect. ROS-induced alteration to IgG-C1q binding activity may promote the inflammatory response in rheumatoid arthritis.

Protocol optimization for the mild detemplation of mesoporous silica nanoparticles resulting in enhanced texture and colloidal stability

Porosity development of mesostructured colloidal silica nanoparticles is related to the removal of the organic templates and co-templates which is often carried out by calcination at high temperatures, 500-600 °C. In this study a mild detemplation method based on the oxidative Fenton chemistry has been investigated. The Fenton reaction involves the generation of OH radicals following a redox Fe3+/Fe2+ cycle that is used as catalyst and H2O2 as oxidant source. Improved material properties are anticipated since the Fenton chemistry comprises milder conditions than calcination. However, the general application of this methodology is not straightforward due to limitations in the hydrothermal stability of the particular system under study. The objective of this work is three-fold: 1) reducing the residual Fe in the resulting solid as this can be detrimental for the application of the material, 2) shortening the reaction time by optimizing the reaction temperature to minimize possible particle agglomeration, and finally 3) investigating the structural and textural properties of the resulting material in comparison to the calcined counterparts. It appears that the Fenton detemplation can be optimized by shortening the reaction time significantly at low Fe concentration. The milder conditions of detemplation give rise to enhanced properties in terms of surface area, pore volume, structural preservation, low Fe residue and high degree of surface hydroxylation; the colloidal particles are stable during storage. A relative particle size increase, expressed as 0.11%·h-1, has been determined.

Detemplation of soft mesoporous silica nanoparticles with structural preservation

A mild protocol that allows the template removal of soft un-aged silica nanoparticles was investigated. After oxidizing the organic template by Fenton chemistry, a good structural preservation is only achieved when the material is equilibrated and dried in a low-surface tension solvent. This avoids excessive capillary stress induced by the high surface tension of water, a major component in the Fenton reaction medium. The Fenton reaction should be carried out under mild conditions as well; otherwise the sample deteriorates by extensive hydrolysis, and capillary stress, and the structural ordering diminishes severely. We propose employing 10 ppm Fe concentration at 70 °C for 24 h for the cetyltrimethylammonium bromide template. The proposed protocol involves 2 steps resulting in an overall significantly higher pore volume attributed to the wider pores and limited particle agglomeration, while the calcined counterpart evidences aggregation and loss of the hexagonal ordering. n-BuOH exchange is unnecessary when the mesophase is stabilized by ageing, as the structure resists the water capillary stress. © The Royal Society of Chemistry 2013.

Identificação dos produtos de oxidação de glicosfingolípidos por espectrometria de massa

O stress oxidativo está associado ao envelhecimento e a inúmeras patologias, nomeadamente a doenças neurodegenerativas e cardiovasculares, e a diversos outros fatores. O stress oxidativo leva à oxidação de importantes biomoléculas como os lípidos e, ao contrário da maior parte dos produtos de oxidação de fosfolípidos e ácidos gordos insaturados (PUFAS), os produtos de oxidação de glicosfingolípidos (GSLs) têm sido escassamente estudados. Os glicosfingolípidos são moléculas muito diversificadas estruturalmente e com importantes funções, essencialmente no sistema nervoso central (SNC) onde estão localizados maioritariamente. Deste modo, alterações na estrutura dos GSLs conduzirão a consequente comprometimento das suas funções e ao possível desenvolvimento de patologias. Assim para identificar as modificações oxidativas que ocorrem em glicosfingolípidos e pressupor consequentes efeitos biológicos nas células sob stress oxidativo, prepararamse sistemas modelo biomiméticos com diferentes GSLs os quais foram expostos a radicais hidroxilo gerados sob condições da reação de Fenton (H2O2 e Fe2+) e as reações foram monitorizadas por diferentes metodologia utilizando a espectrometria de massa. Os resultados obtidos com este estudo permitiram-nos identificar vários produtos de oxidação produzidos durante a oxidação desta classe de lípidos. Os produtos de oxidação observados em comum, em todos os GSLs estudados (C16:0GalCer, C24:1GalCer, C24:1LacCer e GM1) foram as suas correspondentes ceramidas. Estas atuam como agentes pro-apoptóticos e podem in vivo promover a neurodegeneração nas células sob stress oxidativo. Também foi possível observar produtos com inserção de oxigénio junto às duplas ligações ou na cadeia de esfingosina (no caso do GM1) ou na cadeia de ácido gordo monoinsaturada (no caso da C24:1GalCer, C24:1LacCer), corroborando o facto de que ácidos gordos saturados não são susceptíveis à oxidação por radicais. Interessantemente em ambos os GSLs de cadeias glicosiladas compostas com mais de um açúcar (C24:1LacCer e GM1) observou-se a despolimerização oxidativa da porção glicosilada por quebra das correspondentes ligações glicosídicas. Esta degradação leva à formação de GlcCer no caso de oxidação de LacCer ou na formação de outros gangliósidos (GM2, GM3, asialoGM1 e asialoGM2) e glicolípidos (LacCer e GlcCer), no caso de oxidação de GM1. A formação por via radicalar não enzimática destes GSLs leva a distúrbios no perfil lipídico. Previamente, em certas doenças, foram observadas variações na concentração do perfil de gangliósidos e de ceramidas. Estes dados permitem sugerir que em células em condições de stress oxidativo, a acumulação de gangliósidos mais simples e ceramidas poderá ter uma contribuição de produtos da degradação oxidativa dos gangliósidos e GSLs mais complexos. Este trabalho contribui assim para uma melhor compreensão das modificações estruturais que ocorrem em alguns glicosfingolípidos em condições de stress oxidativo. Os produtos de oxidação aqui identificados suportam a sua possível futura deteção em sistemas biológicos.

Photocatalytic production of chemicals and hydrogen from biomass

In this work, with the aim to tackle several approaches towards sustainable chemistry, two reactions were studied: aerobic photo-oxidation of biomass derived 5-hydroxymethyl-2-furfural (HMF), and anaerobic photo-reforming of glycerol known as a by-product in biodiesel industry, towards production of chemicals and hydrogen. Solar-assisted reactions were performed by means of heterogeneous photocatalysis, in mild conditions such as atmospheric pressure, room temperature and water as a benign solvent. Titanium dioxide (lab-synthesized and commercial) was used as a photo-active catalyst, which surface was modified by introducing different metal (e.g. Au, Au-Cu, Pt) and metal oxide (e.g. NiO) nanoparticles. The prepared materials were characterized by XRD, DRS, BET, TEM, SEM, RAMAN and other techniques. The influence of the support, the size and type of the deposited metal and metal oxide nanoparticles on the photo-catalytic transformation of HMF and glycerol was evaluated. In the case of HMF, the influence of the base addition and the oxygen content on the reaction selectivity was also studied. The effect of the crystalline phase composition and morphology of TiO2 in the glycerol photo-reforming reaction was assessed as well. The surface of the synthesized TiO2 nano-powders was investigated by means of Surface Organometallic Chemistry (SOMC) approach. In particular, the surface was characterized by chemical titration and DRIFT techniques. Furthermore, the SOMC concept allowed preparing of well-dispersed Pt nanoparticles on the TiO2 surface. The photo-catalytic activity of this sample in the glycerol photo-reforming process was tested and compared to that of other Pt-containing catalysts prepared by conventional technics. In view of avoiding the agglomeration and sedimentation of suspended titania powders in water media, thick films of synthesized and commercial TiO2 were deposited on a conductive substrate using screen-printing technique. The prepared electrodes were characterized by profilometry, SEM, XRD, optical, electrochemical and photo-electrochemical methods.

Kinetics of photo-induced electron transfer from high-potential iron-sulfur protein to the photosynthetic reaction center of the purple phototroph Rhodoferax fermentans.

The kinetics of photo-induced electrontransfer from high-potential iron-sulfur protein (HiPIP) to the photosynthetic reaction center (RC) of the purple phototroph Rhodoferarfermentans were studied. The rapid photooxidation of heme c-556 belonging to RC is followed, in the presence of HiPIP, by a slower reduction having a second-order rate constant of 4.8 x 10(7) M(-1) x s(-1). The limiting value of kobs at high HiPIP concentration is 95 s(-1). The amplitude of this slow process decreases with increasing HiPIP concentration. The amplitude of a faster phase, observed at 556 and 425 nm and involving heme c-556 reduction, increases proportionately. The rate constant of this fast phase, determined at 425 and 556 nm, is approximately 3 x 10(5) s(-1). This value is not dependent on HiPIP concentration, indicating that it is related to a first-order process. These observations are interpreted as evidence for the formation of a HiPIP-RC complex prior to the excitation flash, having a dissociation constant of -2.5 microM. The fast phase is absent at high ionic strength, indicating that the complex involves mainly electrostatic interactions. The ionic strength dependence of kobs for the slow phase yields a second-order rate constant at infinite ionic strength of 5.4 x 10(6) M(-1) x s(-1) and an electrostatic interaction energy of -2.1 kcal/mol (1 cal = 4.184 J). We conclude that Rhodoferar fermentans HiPIP is a very effective electron donor to the photosynthetic RC.

A novel laponite clay-based Fe nanocomposite and its photo-catalytic activity in photo-assisted degradation of Orange II

A novel laponite RD clay-based Fe nanocomposite (Fe-Lap-RD) has been successfully synthesized through a reaction between a solution of iron salt and an aqueous dispersion of laponite RD clay. The X-ray diffraction (XRD) results reveal that the Fe-Lap-RD mainly consists of Fe2O3 (maghemite) and Fe2Si4O10(OH)2 (iron silicate hydroxide), which have tetragonal and monoclinic structures, respectively, and has a high specific surface area as well as a high pore volume. The photo-catalytic activity of the Fe-Lap-RD was examined in the photo-assisted degradation of an organic azo dye Orange II. It was found that the mineralization of Orange 11 undergoes a slower kinetics than discoloration, and 70% total organic carbon (TOC) of 0.2 mM Orange 11 can be removed in 90 min, implying that the Fe-Lap-RD exhibited a high photo-catalytic activity in the presence of H2O2 and UV light (254 nm) in the photo-assisted degradation of Orange II. In addition, our experiments also illustrate that the Fe-Lap-RD has a long-term stability but is of low cost. This study illustrates the possibility of photo-assisted degradation of organic compounds without the requirements to remove the Fe ions after reaction. Two possible catalytic reaction mechanisms are also proposed. (C) 2003 Elsevier Science Ltd. All rights reserved.

Avaliação da degradação do diclofenaco sódico utilizando H2O2/fenton em reator eletroquímico

This paper describes a degradation study of the anti-inflammatory sodium diclofenac in aqueous medium using an electro-chemical flow reactor with a gas diffusion electrode as cathode. Two degradation processes were compared: by H2O2 electro-generated and H2O2 electro-generated/Fe(II). Concentration of sodium diclofenac was determined during the experiments by HPLC. The changes in chemical oxigen demand (COD) were also evaluated. Under the specific reaction conditions, 350 mg L-1 of H2O2 was electro-generated and 99.2% of sodium diclofenac was degradated, with 27.4% COD reduction. At the same conditions, but using Fe(II), drug degradation was 99.4% and the COD reduction was 63.2%.

Avaliação da potencialidade de processos pseudo-fenton para remediação de solos contaminados por diesel

The use of the Fenton's reagent process has been investigated for the remediation of a Brazilian soil contaminated by diesel. Laboratory experiments were conducted in batch experiments. Slurries, consisting of 10 g of diesel-contaminated soil and 30 mL of Fenton's Reagent (0.41 mol L-1 H(2)0(2) and 0.18 mol L-1 FeSO4). The experiments were monitored during 24, 48 and 72 h. The efficiency of the Fenton treatment was dependent on the time of contact between soil and Fenton's reagents and matrix characteristics, probably iron content. Data suggested that no iron addition is needed for the application of Fenton-like treatment for the remediation of diesel-contaminated iron rich soils after 72 h reaction.

Degradação de corantes reativos por processo foto-fenton envolvendo o uso de peneira molecular 4A modificada com Fe3+

In this work the preparation and characterization of a supported catalyst intended for degradation of reactive dyes by Fenton-like processes is described. The photocatalyst was prepared by immobilization of Fe3+ into the molecular sieve (4A type) surface and characterized by x-ray diffractometry and infrared, Mössbauer and EPR spectroscopy. The solid containing 0.94% (w/w) of ferric ions was used in degradation studies of aqueous reactive-dyes samples with really promissory results. Generally, Vis-assisted photochemical processes leads to almost total decolorization of all tested dyes at reaction times lower than 30 min. It was also observed that the iron-molecular sieve matrix can be reused.

Colour Removal From Dye-House Efiluents Using Zero-Valent iron and Fenton Oxidation

This thesis Entitled Colour removal from dye house effluents using zero valent iron and fenton oxidation.Findings reported on kinetic profile during oxidation of dyes with Fenton’s reagent are in good agreement with observations of earlier workers on other organic substrates. This work goes a step further. Critical concentration of the dye at which the reaction mechanism undergoes transition has been identified.The oxidation of Reactive Yellow showed that the initial rates for decolorization increased linearly with an increase in hydrogen peroxide concentration over the range studied. Fenton oxidation of all dyes except Methylene Blue showed that the initial rates increased linearly with an in the ferrous sulphate concentration. This increase was observed only up to an optimum concentration beyond which further increase resulted in a decrease in the initial rates. Variation of initial rates with Ferrous sulphate concentration resulted in a linear plot passing through the origin indicating that the reaction is first order with respect to ferrous sulphate.

Multivariate analysis of phenol mineralisation by combined hydrodynamic cavitation and heterogeneous advanced Fenton processing

Phenolic compounds in wastewaters are difficult to treat using the conventional biological techniques such as activated sludge processes because of their bio-toxic and recalcitrant properties and the high volumes released from various chemical, pharmaceutical and other industries. In the current work, a modified heterogeneous advanced Fenton process (AFP) is presented as a novel methodology for the treatment of phenolic wastewater. The modified AFP, which is a combination of hydrodynamic cavitation generated using a liquid whistle reactor and the AFP is a promising technology for wastewaters containing high organic content. The presence of hydrodynamic cavitation in the treatment scheme intensifies the Fenton process by generation of additional free radicals. Also, the turbulence produced during the hydrodynamic cavitation process increases the mass transfer rates as well as providing better contact between the pseudo-catalyst surfaces and the reactants. A multivariate design of experiments has been used to ascertain the influence of hydrogen peroxide dosage and iron catalyst loadings on the oxidation performance of the modified AFP. High er TOC removal rates were achieved with increased concentrations of hydrogen peroxide. In contrast, the effect of catalyst loadings was less important on the TOC removal rate under conditions used in this work although there is an optimum value of this parameter. The concentration of iron species in the reaction solution was measured at 105 min and its relationship with the catalyst loadings and hydrogen peroxide level is presented.

Monitoring one-electron photo-oxidation of guanine in DNA crystals using ultrafast infrared spectroscopy

To understand the molecular origins of diseases caused by ultraviolet and visible light, and also to develop photodynamic therapy, it is important to resolve the mechanism of photoinduced DNA damage. Damage to DNA bound to a photosensitizer molecule frequently proceeds by one-electron photo-oxidation of guanine, but the precise dynamics of this process are sensitive to the location and the orientation of the photosensitizer, which are very difficult to define in solution. To overcome this, ultrafast time-resolved infrared (TRIR) spectroscopy was performed on photoexcited ruthenium polypyridyl–DNA crystals, the atomic structure of which was determined by X-ray crystallography. By combining the X-ray and TRIR data we are able to define both the geometry of the reaction site and the rates of individual steps in a reversible photoinduced electron-transfer process. This allows us to propose an individual guanine as the reaction site and, intriguingly, reveals that the dynamics in the crystal state are quite similar to those observed in the solvent medium.

Nanoparticle Platform to Modulate Reaction Mechanism of Phenothiazine Photosensitizers

Herein, we report on the synthesis of photosensitizing nanoparticles in which the generation of different oxidizing species, i.e., singlet oxygen ((1)O(2)) or radicals, was modulated. Sol gel and surface chemistry were used to obtain nanoparticles with specific ratios of dimer to monomer species of phenothiazine photosensitizers (PSs). Due to competition between the reactions involving electron transfer within dimer species and energy transfer from monomer triplets to oxygen, the efficiency of (1)O(2) generation could be controlled. Nanoparticles with an excess of dimer have an (1)O(2) generation efficiency (S(Delta)) of 0.01 while those without dimer have a S, value of 0.4. Furthermore, we demonstrate that the PS properties of the nanoparticles are not subjected to interference from the external medium as is commonly the case for free PSs, i.e., PS ground and triplet states are not reduced by NADH and ascorbate, respectively, and singlet excited states are less suppressed by bromide. The modulated (1)O(2) generation and the PS protection from external interferences make this nanoparticle platform a promising tool to aid in performing mechanistic studies in biological systems. Also, it offers potential application in technological areas in which photo-induced processes take place.

Study of photo-assisted electrochemical degradation of carbaryl at dimensionally stable anodes (DSA (R))

This paper presents the results concerning the degradation of the pesticide carbaryl comparing two methods: electrochemical (EC) and photo-assisted electrochemical (PAEC). The experimental variables of applied current density, electrolyte flow-rate and initial carbaryl concentration were investigated. The results demonstrate that the electrochemical degradation of carbaryl was greatly enhanced when simultaneous UV light was applied. The greatest difference between the PAEC and EC method was apparent when lower current densities were applied. The extent of COD removal was much enhanced for the combined method, independent of the applied current density. It should be noted that the complete removal of carbaryl was achieved with out the need to add NaCl to the reaction mixture, avoiding the risk of chlorinated organic species formation. (C) 2009 Elsevier B.V. All rights reserved.