The impact of ozone treatment on enamel physical properties

PURPOSE: To assess the effects of the highly reactive molecule of ozone on sound enamel physical properties and its effects on sealing ability. METHODS: The effect of ozone on sealant tag length, microleakage and unfilled area proportion were evaluated on intact and prepared sound molar fissures. Microhardness, contact angle and acid resistance tests were performed on ground sound smooth surfaces. The samples were treated with ozone for 40 seconds (HealOzone). Control samples were treated with air (modified HealOzone) or left untreated. RESULTS: No statistically significant difference was observed between the control and ozone treated samples in all tests. Prepared fissures exhibited no unfilled areas and a statistically significantly lower microleakage compared to intact fissures. Ozone was shown to dehydrate enamel and consequently enhance its microhardness, which was reversible.

Expansion of mortar bars in the presence of potassium acetate deicer

Carboxylate-based deicing and anti-icing chemicals became widely used in the mid 1990s, replacing more environmentally burdensome chemicals. Within a few years of their adoption, distress of portland cement concrete runways was reported by a few airports using the new chemicals. Distress manifested characteristics identical to that of alkali silica reactivity (ASR), but onset occurred early in the pavement’s operating life and with pavements thought to contain innocuous aggregate. The carboxylate-based deicing chemicals were suspected of exacerbating ASR-like expansion. Innocuous, moderately, and highly reactive aggregates were tested using modified ASTM C1260 and ASTM C1567 procedures with soak solutions containing deicer solutions and sodium hydroxide or potassium hydroxide. ASR-like expansion is exacerbated in the presence of potassium acetate. The expansion rate produced by a given aggregate is also a function of the alkali hydroxide used. Petrographic analyses were performed on thin sections prepared from mortar bars used in the experiments. Expansion occurred via two mechanisms; rupture of aggregate grains and expansion of paste.

Carbon dioxide sequestration in cement kiln dust through miner carbonation

The feasibility of carbon sequestration in cement kiln dust (CKD) was investigated in a series of batch and column experiments conducted under ambient temperature and pressure conditions. The significance of this work is the demonstration that alkaline wastes, such as CKD, are highly reactive with carbon dioxide (CO2). In the presence of water, CKD can sequester greater than 80% of its theoretical capacity for carbon without any amendments or modifications to the waste. Other mineral carbonation technologies for carbon sequestration rely on the use of mined mineral feedstocks as the source of oxides. The mining, pre-processing and reaction conditions needed to create favorable carbonation kinetics all require significant additions of energy to the system. Therefore, their actual net reduction in CO2 is uncertain. Many suitable alkaline wastes are produced at sites that also generate significant quantities of CO2. While independently, the reduction in CO2 emissions from mineral carbonation in CKD is small (~13% of process related emissions), when this technology is applied to similar wastes of other industries, the collective net reduction in emissions may be significant. The technical investigations presented in this dissertation progress from proof of feasibility through examination of the extent of sequestration in core samples taken from an aged CKD waste pile, to more fundamental batch and microscopy studies which analyze the rates and mechanisms controlling mineral carbonation reactions in a variety of fresh CKD types. Finally, the scale of the system was increased to assess the sequestration efficiency under more pilot or field-scale conditions and to clarify the importance of particle-scale processes under more dynamic (flowing gas) conditions. A comprehensive set of material characterization methods, including thermal analysis, Xray diffraction, and X-ray fluorescence, were used to confirm extents of carbonation and to better elucidate those compositional factors controlling the reactions. The results of these studies show that the rate of carbonation in CKD is controlled by the extent of carbonation. With increased degrees of conversion, particle-scale processes such as intraparticle diffusion and CaCO3 micropore precipitation patterns begin to limit the rate and possibly the extent of the reactions. Rates may also be influenced by the nature of the oxides participating in the reaction, slowing when the free or unbound oxides are consumed and reaction conditions shift towards the consumption of less reactive Ca species. While microscale processes and composition affects appear to be important at later times, the overall degrees of carbonation observed in the wastes were significant (> 80%), a majority of which occurs within the first 2 days of reaction. Under the operational conditions applied in this study, the degree of carbonation in CKD achieved in column-scale systems was comparable to those observed under ideal batch conditions. In addition, the similarity in sequestration performance among several different CKD waste types indicates that, aside from available oxide content, no compositional factors significantly hinder the ability of the waste to sequester CO2.

Obtención de un estándar secundario de cuantificación para la síntesis y purificación de allicina.

Desde tiempos ancestrales, el ajo (Allium sativum L.) ha sido utilizado para la prevención y el tratamiento de dolencias. Sus efectos benéficos para la salud han sido atribuidos a los tiosulfinatos, siendo la allicina el más abundante. La determinación rutinaria de la allicina es dificultosa dada su inestabilidad y la naturaleza reactiva de la misma. El objetivo del trabajo fue obtener un estándar secundario para la cuantificación de allicina mediante Cromatografía Líquida de Alta Resolución (HPLC). Fueron ensayadas diferentes metodologías de síntesis y purificación de allicina. En el Laboratorio de Residuos Tóxicos de la Fac. Cs. Agrarias (UNCuyo), bajo condiciones controladas, se preparó polvo de ajo para ser utilizado como estándar secundario de cuantificación. La cuantificación de muestras problema contra ambos estándares (allicina pura y polvo de ajo estandarizado, respectivamente) no presentó diferencias significativas. El empleo de polvo de ajo estandarizado ofrece una alternativa viable simple para la cuantificación de allicina.

Scaling up the production of biogenic magnetite nanoparticles

Although there are numerous examples of large-scale commercial microbial synthesis routes for organic bioproducts, few studies have addressed the obvious potential for microbial systems to produce inorganic functional biomaterials at scale. Here we address this by focusing on the production of nano-scale biomagnetite particles by the Fe(III)-reducing bacterium Geobacter sulfurreducens, which was scaled-up successfully from lab-scale to pilot plant-scale production, whilst maintaining the surface reactivity and magnetic properties which make this material well suited to commercial exploitation. At the largest scale tested, the bacterium was grown in a 50 L bioreactor, harvested and then inoculated into a buffer solution containing Fe(III)-oxyhydroxide and an electron donor and mediator, which promoted the formation of magnetite in under 24 hours. This procedure was capable of producing up to 120 g biomagnetite. The particle size distribution was maintained between 10 and 15 nm during scale-up of this second step from 10 ml to 10 L, with conserved magnetic properties and surface reactivity; the latter demonstrated by the reduction of Cr(VI). The process presented provides an environmentally benign route to magnetite production and serves as an alternative to harsher synthetic techniques, with the clear potential to be used to produce kg to tonne quantities.

Superoxide decay rates during METEOR cruise M83/1

Superoxide is an important transient reactive oxygen species (ROS) in the ocean formed as an intermediate in the redox transformation of oxygen (O2) into hydrogen peroxide (H2O2) and vice versa. This highly reactive and very short-lived radical anion can be produced both via photochemical and biological processes in the ocean. In this paper we examine the decomposition rate of O2- throughout the water column, using new data collected in the Eastern Tropical North Atlantic (ETNA) Ocean. For this approach we applied a semi factorial experimental design, to identify and quantify the pathways of the major identified sinks in the ocean. In this work we occupied 6 stations, 2 on the West African continental shelf and 4 open ocean stations, including the CVOO time series site adjacent to Cape Verde. Our results indicate that in the surface ocean, impacted by Saharan aerosols and sediment resuspension, the main decay pathways for superoxide is via reactions with Mn(||) and organic matter.

Pore-water chemistry of ODP sites 111-677 and 111-678

Sites 677 and 678 were drilled on ODP Leg 111 to test hypotheses about the nature and pattern of hydrothermal circulation on a mid-ocean ridge flank. Together with earlier results from DSDP Site 501/504 and several heatflow and piston coring surveys covering a 100-km**2 area surrounding the three drill sites, they confirm that hydrothermal circulation persists in this 5.9-m.y.-old crust, both in basement and through the overlying sediments (Langseth et al., 1988, doi:10.2973/odp.proc.ir.111.102.1988). Profiles of sediment pore-water composition with depth at the three drill sites show both vertical and horizontal gradients. The shapes of the profiles and their variation from one site to another result from a combination of vertical and horizontal diffusion, convection, and reaction in the sediments and basement. Chemical species that are highly reactive in the siliceous-calcareous biogenic sediments include bicarbonate (alkalinity), ammonium, sulfate, manganese, calcium, strontium, lithium, silica, and possibly potassium. Reactions include bacterial sulfate reduction, mobilization of Mn2+, precipitation of CaCO3, and recrystallization of calcareous and siliceous oozes to chalk, limestone, and chert. Species with profiles more affected by reaction in basaltic basement than in the sediments include Mg, Ca, Na, K, and oxygen isotopes. Reaction in basement at 60?C and at higher temperatures has produced a highly altered basement formation water that is uniform in composition over distances of several kilometers. As inferred from the composition of the basal sediment pore water at the three sites, this uniformity extends from up flow zone to downflow zone in basement and the sediments. It exists in spite of large variations in heat flow and depth to basement, apparently as a result of homogenization by hydrothermal circulation in basement. Profiles for chlorinity, Na, Mg, and other species in the sediment pore waters confirm that Site 678, drilled on a localized heatflow high identified by Langseth et al. (1988), is a site of long-lived upwelling of warm water from basement through the sediments at velocities of 1 to 2 mm/yr. The upflow through the anomalously thin sediments is apparently localized above an uplifted fault block in basement. This site and other similar sites in the survey area give rise to lateral diffusion and possibly flow through the sediments, which produces lateral gradients in sediment pore-water composition at sites such as 501/504. The complementary pore-water profiles at the low-heatflow Site 677 2 km to the south indicate that downflow is occurring through the sediments there, at comparable rates of 1 to 2 mm/yr.

Propeptide and glutamate-containing substrates bound to the vitamin K-dependent carboxylase convert its vitamin K epoxidase function from an inactive to an active state

The vitamin K-dependent γ-glutamyl carboxylase catalyzes the posttranslational conversion of glutamic acid to γ-carboxyglutamic acid in precursor proteins containing the γ-carboxylation recognition site (γ-CRS). During this reaction, glutamic acid is converted to γ-carboxyglutamic acid while vitamin KH2 is converted to vitamin K 2,3-epoxide. Recombinant bovine carboxylase was purified free of γ-CRS-containing propeptide and endogenous substrate in a single-step immunoaffinity procedure. We show that in the absence of γ-CRS-containing propeptide and/or glutamate-containing substrate, carboxylase has little or no epoxidase activity. Epoxidase activity is induced by Phe-Leu-Glu-Glu-Leu (FLEEL) (9.2 pmol per min per pmol of enzyme), propeptide, residues −18 to −1 of proFactor IX (3.4 pmol per min per pmol of enzyme), FLEEL and propeptide (100 pmol per min per pmol of enzyme), and proPT28 (HVFLAPQQARSLLQRVRRANTFLEEVRK, residues −18 to +10 of human acarboxy-proprothrombin), (5.3 pmol per min per pmol of enzyme). These results indicate that in the absence of propeptide or glutamate-containing substrate, oxygenation of vitamin K by the carboxylase does not occur. Upon addition of propeptide or glutamate-containing substrate, the enzyme is converted to an active epoxidase. This regulatory mechanism prevents the generation of a highly reactive vitamin K intermediate in the absence of a substrate for carboxylation.

Iron accumulation in Alzheimer disease is a source of redox-generated free radicals

Damage from free radicals has been demonstrated in susceptible neuronal populations in cases of Alzheimer disease. In this study, we investigated whether iron, a potent source of the highly reactive hydroxyl radical that is generated by the Fenton reaction with H2O2, might contribute to the source of radicals in Alzheimer disease. We found, using a modified histochemical technique that relies on the formation of mixed valence iron complexes, that redox-active iron is associated with the senile plaques and neurofibrillary tangles—the pathological hallmark lesions of this disease. This lesion-associated iron is able to participate in in situ oxidation and readily catalyzes an H2O2-dependent oxidation. Furthermore, removal of iron was completely effected using deferoxamine, after which iron could be rebound to the lesions. Characterization of the iron-binding site suggests that binding is dependent on available histidine residues and on protein conformation. Taken together, these findings indicate that iron accumulation could be an important contributor toward the oxidative damage of Alzheimer disease.

On the acidity and reactivity of HNO in aqueous solution and biological systems

The gas phase and aqueous thermochemistry and reactivity of nitroxyl (nitrosyl hydride, HNO) were elucidated with multiconfigurational self-consistent field and hybrid density functional theory calculations and continuum solvation methods. The pKa of HNO is predicted to be 7.2 ± 1.0, considerably different from the value of 4.7 reported from pulse radiolysis experiments. The ground-state triplet nature of NO− affects the rates of acid-base chemistry of the HNO/NO− couple. HNO is highly reactive toward dimerization and addition of soft nucleophiles but is predicted to undergo negligible hydration (Keq = 6.9 × 10−5). HNO is predicted to exist as a discrete species in solution and is a viable participant in the chemical biology of nitric oxide and derivatives.

Potency of Michael reaction acceptors as inducers of enzymes that protect against carcinogenesis depends on their reactivity with sulfhydryl groups

Induction of phase 2 enzymes and elevations of glutathione are major and sufficient strategies for protecting mammals and their cells against the toxic and carcinogenic effects of electrophiles and reactive forms of oxygen. Inducers belong to nine chemical classes and have few common properties except for their ability to modify sulfhydryl groups by oxidation, reduction, or alkylation. Much evidence suggests that the cellular “sensor” molecule that recognizes the inducers and signals the enhanced transcription of phase 2 genes does so by virtue of unique and highly reactive sulfhydryl functions that recognize and covalently react with the inducers. Benzylidene-alkanones and -cycloalkanones are Michael reaction acceptors whose inducer potency is profoundly increased by the presence of ortho- (but not other) hydroxyl substituent(s) on the aromatic ring(s). This enhancement correlates with more rapid reactivity of the ortho-hydroxylated derivatives with model sulfhydryl compounds. Proton NMR spectroscopy provides no evidence for increased electrophilicity of the β-vinyl carbons (the presumed site of nucleophilic attack) on the hydroxylated inducers. Surprisingly, these ortho-hydroxyl groups display a propensity for extensive intermolecular hydrogen bond formation, which may raise the reactivity and facilitate addition of mercaptans, thereby raising inducer potencies.

Synthesis and characterization of a photoactivatable analog of corticotropin-releasing factor for specific receptor labeling.

A novel photoactivatable analog of ovine corticotropin-releasing factor (ovine photoCRF) has been synthesized and characterized. A diazirine group, the 4-(1-azi-2,2,2-trifluoroethyl)benzoyl residue, was covalently bound to the amino terminus of ovine CRF (oCRF), which was N-terminally extended by a tyrosyl residue for radioactive labeling with 125I. Under mild conditions, photolysis yielded highly reactive carbenes, responsible for the formation of covalent bonds to the CRF receptor. Ovine photoCRF was shown to bind to the high-affinity site of the CRF receptor with a similar Kd value as oCRF. When radioactively iodinated ovine photoCRF (ovine 125I-photoCRF) was covalently linked to rat CRF receptor, type 1 (rCRFR1), permanently transfected into human embryonic kidney (HEK) 293 cells, a highly glycosylated 75-kDa protein was identified with SDS/PAGE. The specificity of ovine 125I-photoCRF was demonstrated by the finding that this analog could be displaced from the receptor by oCRF, but not other unrelated peptides such as vasoactive intestinal peptide. The observed size of the 75-kDa cross-link was in agreement with the molecular weight reported earlier for native CRFR1 from rat brain. Deglycosylation of the 75-kDa cross-link with peptide:N-glycosidase (PNGase) yielded a 46-kDa protein, in agreement with the molecular weight estimated from cDNA coding for rat CRFR1. The developed CRF analog, photoCRF, is expected to facilitate future biochemical and physiological analysis of CRF receptors and--by analogous strategies--of other peptide receptors.

Mitigating Risk For Anxiety Among Preschool-Age Children Living In Poverty: Evaluating The Impact Of Adult-Provided Social Support On Autonomic Stress Reactivity

Poverty increases children's exposure to stress, elevating their risk for developing patterns of heightened sympathetic and parasympathetic stress reactivity. Repeated patterns of high sympathetic activation and parasympathetic withdrawal place children at risk for anxiety disorders. This study evaluated whether providing social support to preschool-age children during mildly stressful situations helps reduce reactivity, and whether this effect partly depends on children's previously assessed baseline reactivity patterns. The Biological Sensitivity to Context (BSC) theory proposes that highly reactive children may be more sensitive than less reactive children to all environmental influences, including social support. In contrast, conventional physiological reactivity (CPR) theory contends that highly reactive children are more vulnerable to the impact of stress but are less receptive to the potential benefits present within their social environments. In this study, baseline autonomic reactivity patterns were measured. Children were then randomly assigned to a high-support or neutral control condition, and the effect of social support on autonomic response patterns was assessed. Results revealed an interaction between baseline reactivity profiles and experimental condition. Children with patterns of high-reactivity reaped more benefits from the social support in the experimental condition than did their less reactive peers. Highly reactive children experienced relatively less reactivity reduction in the neutral condition while experiencing relatively greater reactivity reduction in the support condition. Despite their demonstrated stability over time, reactivity patterns are also quite susceptible to change at this age; therefore understanding how social support ameliorates reactivity will further efforts to avert stable patterns of high-reactivity among children with high levels of stress, ultimately reducing risk for anxiety disorders.

Successful functionalization of superporous zeolite templated carbon using aminobenzene acids and electrochemical methods

A novel and selective electrochemical functionalization of a highly reactive superporous zeolite templated carbon (ZTC) with two different aminobenzene acids (2-aminobenzoic and 4-aminobenzoic acid) was achieved. The functionalization was done through potentiodynamic treatment in acid media under oxidative conditions, which were optimized to preserve the unique ZTC structure. Interestingly, it was possible to avoid the electrochemical oxidation of the highly reactive ZTC structure by controlling the potential limit of the potentiodynamic experiment in presence of aminobenzene acids. The electrochemical characterization demonstrated the formation of polymer chains along with covalently bonded functionalities to the ZTC surface. The functionalized ZTCs showed several redox processes, producing a capacitance increase in both basic and acid media. The rate performance showed that the capacitance increase is retained at scan rates as high as 100 mV s−1, indicating that there is a fast charge transfer between the polymer chains formed inside the ZTC porosity or the new surface functionalities and the ZTC itself. The success of the proposed approach was also confirmed by using other characterization techniques, which confirmed the presence of different nitrogen groups in the ZTC surface. This promising method could be used to achieve highly selective functionalization of highly porous carbon materials.

Molecular basis of intramolecular electron transfer in sulfite-oxidizing enzymes is revealed by high resolution structure of a heterodimeric complex of the catalytic molybdopterin subunit and a c-type cytochrome subunit

Sulfite-oxidizing molybdoenzymes convert the highly reactive and therefore toxic sulfite to sulfate and have been identified in insects, animals, plants, and bacteria. Although the well studied enzymes from higher animals serve to detoxify sulfite that arises from the catabolism of sulfur-containing amino acids, the bacterial enzymes have a central role in converting sulfite formed during dissimilatory oxidation of reduced sulfur compounds. Here we describe the structure of the Starkeya novella sulfite dehydrogenase, a heterodimeric complex of the catalytic molybdopterin subunit and a c-type cytochrome subunit, that reveals the molecular mechanism of intramolecular electron transfer in sulfite-oxidizing enzymes. The close approach of the two redox centers in the protein complex (Mo-Fe distance 16.6 angstrom) allows for rapid electron transfer via tunnelling or aided by the protein environment. The high resolution structure of the complex has allowed the identification of potential through-bond pathways for electron transfer including a direct link via Arg-55A and/or an aromatic-mediated pathway. A potential site of electron transfer to an external acceptor cytochrome c was also identified on the SorB subunit on the opposite side to the interaction with the catalytic SorA subunit.