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Climate change has evidenced the need to reduce carbon dioxide emissions into the atmosphere, and so for transport applications, lighter weight alloys have been studied, such as magnesium alloys. However, they are susceptible to corrosion; therefore, surface treatments have been extensively studied. In this work, the influence of argon plasma pretreatment on the surface properties of an AZ31 magnesium alloy focus on the enhancement of the reactivity of the surface, which was examined by surface analysis techniques, electrochemical techniques, and gravimetric measurements. The samples were polished and exposed to argon plasma for two minutes in order to activate the surface. Contact angle measurements revealed higher surface energy after applying the pretreatment, and atomic force microscopy showed a roughness increase, while X-Ray photoelectron spectroscopy showed a chemical change on the surface, where after pretreatment the oxygen species increased. Electrochemical measurements showed that surface pretreatment does not affect the corrosion mechanism of the alloy, while electrochemical impedance spectroscopy reveals an increase in the original thickness of the surface film. This increase is likely associated with the high reactivity that the plasma pretreatment confers to the surface of the AZ31 alloy, affecting the extent of oxide formation and, consequently, the increase in its protection capacity. The weight loss measurements support the effect of the plasma pretreatment on the oxide thickness since the corrosion rate of the pretreated AZ31 specimens was lower than that of those that did not receive the surface pretreatment.

The protective properties of polymethacrylate coatings with different side chain lengths for 2024 aluminum alloys were studied, focusing on the chain length increase but also on the Ar-plasma pretreatment applied to the metal surface. The coatings were obtained by photopolymerization, obtaining reproducible molecular weight polymers during each process that were determined by high-performance liquid chromatography. AA2024 alloy were immersed into the polymethacrylate solution using methyl, butyl, and hexyl as monomers. Their roughness was then evaluated using atomic force microscopy. Surface hydrophobicity and contact angle hysteresis were analyzed in water and diiodomethane. Protective properties were evaluated by electrochemical impedance spectroscopy after 56 days of immersion in a 0.1 M Na2SO4. The alloy cross-sections were examined by field emission scanning electron microscopy and glow discharge optical emission spectroscopy, allowing the estimation of film thickness. Surface analysis revealed that the defect population densities in the coatings increased the monomer alkyl chain length. The immersion thickness increase was consistent with contact angle measurements taken over time, and independent from the chain length. Contradicting expectations, the results showed the protective efficacy was not related to the chain length, since after exposure, the PBMA film revealed the best anti-corrosive coating performance on the AA2024. This was possibly influenced by its polymeric film conformation, hydrophilicity, ordering and lower density of defects on the metal surface.

The increase in longevity worldwide has intensified the use of different types of prostheses for the human body, such as those used in dental work as well as in hip and knee replacements. Currently, Ti-6Al-4V is widely used as a joint implant due to its good mechanical properties and durability. However, studies have revealed that this alloy can release metal ions or particles harmful to human health. The mechanisms are not well understood yet and may involve wear and/or corrosion. Therefore, in this work, commercial pure titanium and a Ti-6Al-4V alloy were investigated before and after being exposed to a simulated biological fluid through tribological tests, surface analysis, and ionic dissolution characterization by ICP-AES. Before exposure, X-ray diffraction and optical microscopy revealed equiaxed α-Ti in both materials and β-Ti in Ti-6Al-4V. Scratch tests exhibited a lower coefficient of friction for Ti-6Al-4V alloy than commercially pure titanium. After exposure, X-ray photoelectron spectroscopy and surface-enhanced Raman spectroscopy results showed an oxide film formed by TiO2, both in commercially pure titanium and in Ti-6Al-4V, and by TiO and Al2O3 associated with the presence of the alloys. Furthermore, inductively coupled plasma atomic emission spectroscopy revealed that aluminum was the main ion released for Ti-6Al-4V, giving negligible values for the other metal ions.

Here we demonstrate that the metal ion excess after precipitating a sparingly soluble metal salt can be conveniently determined by a secondary precipitation of a metal salt on an electrode surface, followed by measuring the solid-state electrochemical response of that salt. As an example, the analysis of the arsenic content of solutions is presented.

Violacein is an intensely purple pigment synthesized by various genera of bacteria that has been discovered to have a wide range of interesting biological activities which range from anticarcinogenic to antibacterial. One of the hindrances for its real-life application is that the first microorganisms found to produce the compound may act as opportunistic pathogens. Here, we report the isolation and characterization of violacein from a non-pathogenic Antarctic Iodobacter strain. Its anti-microbial properties were also tested. The method proposed here for the purification of violacein shows high yields, indicating that this Antarctic microorganism could be a valuable source for this important pigment. This is the first characterization of violacein from an Antarctic Iodobacter strain and here we also present a viable method to obtain this pigment for potential biotechnological applications.

New experimental techniques and protocols are needed to study microbiologically influenced corrosion (MIC). In this work, we studied the capacity of microorganisms to modify their environment in vitro. The methodology involved cyclic voltammetry measurements using carbon electrodes modified with cobalt phthalocyanine, which is a known catalyst for the two-electron reduction of O2 to give peroxide. Mueller-Hinton (21 g/L) was used as an electrolyte in a sterilized aqueous medium. The open circuit potential (OCP) and oxygen concentration behaved similarly over time, with generally similar growth curves. However, there were peculiarities that indicated the presence of peroxide and catalase. Catalase activity was demonstrated by comparing the voltammetric responses of the culture medium in the absence and presence of bacterial strains of Escherichia coli (Gram +) and Staphylococcus aureus (Gram-), both facultative and catalase positive. With this system, which is capable of discriminating O2 and hydrogen peroxide, catalase activity is highly evident, and at its maximum at the end of the exponential stage of the growth curve.

Silver nanoparticles (AgNPs) have been widely recognized as antibacterial agents. However, its stability and activity over time have been poorly studied. In this work, the properties and characteristics of differently stabilized AgNPs were evaluated during a span of time. The surface capping agents were diclofenac (d), and ketorolac (k), which currently are used as anti-inflammatory in human medicine. On evaluating the size variation over time, it was observed that the AgNPs-k are the most stable, unlike the non-capped nanoparticles agglomerate and precipitate. UV–Vis spectroscopy analysis showed that the absorbance during time decreases for the three types of nanoparticles, but the decrease is less marked for the two types of anti-inflammatory-capped AgNPs. The rapid loss of the optical prop- erties of bare AgNPs, is mainly due to oxidation, agglomeration, and precipitation of this nanoparticles. The potential cytotoxicity of the AgNPs, evaluated through the formation of the superoxide anion using XXT, showed that both, AgNPs-k and AgNPs-d, generate the radical anion when the samples are irradiated with UV light at 365 nm. This effect appears associated with the capping agents, since the bare nanoparticles did not promote the formation of the superoxide anion. The antibacterial activity of the AgNPs throughout time, against two microorganisms (Escherichia coli and Staphylococcus aureus), was also evaluated. The results showed that capping agents played a decisive role in the antibacterial ability of AgNPs and also in enhancing the antibacterial activity over time.

To better understand the effect of surface treatments on the efficiency of protective coatings of aluminum alloys, this study assessed different surface treatments for the aluminum alloy AA2024, including mechanical polishing, chemical etching and Ar-plasma pretreatment followed by deposition of poly(methyl methacrylate). Surface morphology, surface chemical analysis and wettability of the treated samples were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy and contact angle, respectively. Open circuit potential and electrochemical impedance spectroscopy were carried out in a 0.1 M solution of Na2SO4 as a function of exposure time. SEM images revealed that a homogeneous and well incorporated poly-(methyl methacrylate) coating was obtained by using Ar-plasma as a pretreatment. XPS spectra showed that the Al O/Al OH intensity ratio of the Ar-plasma pretreated samples does not show clear dependence on angle measurement, which indicates that Al(OH) and Al2O3 are not homogenously distributed on the sample surfaces. Al2O3 does not completely cover the aluminum surface, leaving some areas exposed. The measurements of the hysteresis angle showed that the Ar-plasma pretreatment favors chemical heterogeneity, which in turn increases the hydrophilicity of the coated samples, resulting in lower wettability and a greater hysteresis angle. The electrochemical results showed that the Ar-plasma pretreatment significantly improves the protective capacity of poly(methyl methacrylate).

Previous studies have reported lower fecal bacterial diversity in urban populations compared with those living in rural settings. However, most of these studies compare geographically distant populations from different countries and even continents. The extent of differences in the gut microbiome in adjacent rural versus urban populations, and the role of such differences, if any, during enteric infections remain poorly understood. To provide new insights into these issues, we sampled the gut microbiome of young children with and without acute diarrheal disease (ADD) living in rural and urban areas in northern Ecuador. Shotgun metagenomic analyses of non-ADD samples revealed small but significant differences in the abundance of microbial taxa, including a greater abundance of Prevotella and a lower abundance of Bacteroides and Alistipes in rural populations. Greater and more significant shifts in taxon abundance, metabolic pathway abundance, and diversity were observed between ADD and non-ADD status when comparing urban to rural sites (Welch’s t-test, P < 0.05). Collectively our data show substantial functional, diversity, and taxonomic shifts in the gut microbiome of urban populations with ADD, supporting the idea that the microbiome of rural populations may be more resilient to ADD episodes.

In this work, electrochemical techniques were employed to evaluate the contribution to the corrosion and corrosion inhibition of 2024-T3 aluminum alloy by two Gram-positive bacteria. In addition, polarized impedance was used to determine the microbial effect on the cathodic and anodic reactions. These microorganisms were collected from a tropical environment due to the favorable bacterial growth of this kind of climate. The alloy was exposed to the sterile medium and inoculated for up to 12 days evaluating the microbiological and electrochemical behavior. The results by linear scanning voltammetry showed that the B. safensis and B. pumilus caused a dual effect of increase and decrease currents, and through electrochemical impedance spectroscopy, showed in some cases, inductive loop, which could be associated with local corrosion and another case, an increasing impedance could be related to protection. In addition, a morphological characterization was performed by scanning electron microscopy before and after exposure, showing an increase in copper precipitation in the vicinity of the intermetallic phases by bacteria, attributed to local corrosion, but, in general, a significant effect of damages was not observed.

The Mn +/M(n − 1)+ redox potential of MN4 macrocyclic molecular catalysts is a very good reactivity descriptor for several electrochemical reactions. One important feature about this reactivity descriptor is that it can be determined experimentally under the same conditions of the kinetic measurements in contrast to other descriptors like intermediate binding energies that are estimated from DFT calculations. However a linear correlation between both descriptors seems to exist. Plots of activity as (logj)E at constant E versus the Mn +/M(n − 1)+ redox potential gives volcano correlations. Another important aspect about this parameter is that it is possible to tune the Mn +/M(n − 1)+ redox potential of the MN4 catalyst by manipulating the structure of the macrocyclic complex and tailoring the electron-withdrawing power of the ligands to obtain the maximum activity. In this work we have probed the redox potential as a reactivity descriptor for the oxidation of cysteamine studying a series of substituted Fe phthalocyanines and Fe porphyrins adsorbed on glassy carbon and pyrolytic graphite in alkaline media. As expected the catalytic activity of these FeN4 species varies strongly with the Fe (II)/(I) redox potential of the different Fe phthalocyanines and a plot of activity as (logj)E versus E°Fe(II/I) gives a volcano-shaped correlation so a formal potential value exists for which the highest activity can be achieved demonstrating that the formal potential of the complexes seems to be an universal reactivity descriptor for electrochemical reactions.

This work studied the microbiologically influenced corrosion susceptibility of the AA2024-T3 alloy exposed to sterile and inoculated media with three coccoidal bacteria, which were isolated from the corrosion product of a fuel outlet, belonging to a Twin Otter aircraft exposed to Antarctic environmental conditions. The consortium was mainly constituted by three bacteria, which have a close affiliation to Kocuria rhizophila, Staphylococcus epidermidis and Staphylococcus aureus. Electrochemical methods and surface analysis were carried out to investigate the corrosion susceptibility of the alloy under study in the presence of these bacteria. Electrochemical analysis suggested that the protective character of the oxide of the alloy film was modified during the immersion time in all media. Moreover, the surface analysis showed also that these bacteria influenced homogeneity of this oxide. In particular, the K. rhizophila increased slightly the current and decreased the resistance of AA2024-T3 against corrosion, instead the S. epidermidis showed a slight protective effect, while non-significant effect was observed with the presence of the consortium in the medium.

Escherichia coli is a leading contributor to infectious diarrhea and child mortality worldwide, but it remains unknown how alterations in the gut microbiome vary for distinct E. coli pathotype infections and whether these signatures can be used for diagnostic purposes. Further, the majority of enteric diarrheal infections are not diagnosed with respect to their etiological agent(s) due to technical challenges. To address these issues, we devised a novel approach that combined traditional, isolate-based and molecular-biology techniques with metagenomics analysis of stool samples and epidemiological data. Application of this pipeline to children enrolled in a case-control study of diarrhea in Ecuador showed that, in about half of the cases where an E. coli pathotype was detected by culture and PCR, E. coli was likely not the causative agent based on the metagenome-derived low relative abundance, the level of clonality, and/or the virulence gene content. Our results also showed that diffuse adherent E. coli (DAEC), a pathotype that is generally underrepresented in previous studies of diarrhea and thus, thought not to be highly virulent, caused several small-scale diarrheal outbreaks across a rural to urban gradient in Ecuador. DAEC infections were uniquely accompanied by coelution of large amounts of human DNA and conferred significant shifts in the gut microbiome composition relative to controls or infections caused by other E. coli pathotypes. Our study shows that diarrheal infections can be efficiently diagnosed for their etiological agent and categorized based on their effects on the gut microbiome using metagenomic tools, which opens new possibilities for diagnostics and treatment. IMPORTANCEE. coli infectious diarrhea is an important contributor to child mortality worldwide. However, diagnosing and thus treating E. coli infections remain challenging due to technical and other reasons associated with the limitations of the traditional culture-based techniques and the requirement to apply Koch’s postulates. In this study, we integrated traditional microbiology techniques with metagenomics and epidemiological data in order to identify cases of diarrhea where E. coli was most likely the causative disease agent and evaluate specific signatures in the disease-state gut microbiome that distinguish between diffuse adherent, enterotoxigenic, and enteropathogenic E. coli pathotypes. Therefore, our methodology and results should be highly relevant for diagnosing and treating diarrheal infections and have important applications in public health.

Escherichia coli is a leading contributor to infectious diarrhea and child mortality worldwide, but it remains unknown how alterations in the gut microbiome vary for distinct E. coli pathotype infections and whether these signatures can be used for diagnostic purposes. Further, the majority of enteric diarrheal infections are not diagnosed with respect to their etiological agent(s) due to technical challenges. To address these issues, we devised a novel approach that combined traditional, isolate-based and molecular-biology techniques with metagenomics analysis of stool samples and epidemiological data. Application of this pipeline to children enrolled in a case-control study of diarrhea in Ecuador showed that, in about half of the cases where an E. coli pathotype was detected by culture and PCR, E. coli was likely not the causative agent based on the metagenome-derived low relative abundance, the level of clonality, and/or the virulence gene content. Our results also showed that diffuse adherent E. coli (DAEC), a pathotype that is generally underrepresented in previous studies of diarrhea and thus, thought not to be highly virulent, caused several small-scale diarrheal outbreaks across a rural to urban gradient in Ecuador. DAEC infections were uniquely accompanied by coelution of large amounts of human DNA and conferred significant shifts in the gut microbiome composition relative to controls or infections caused by other E. coli pathotypes. Our study shows that diarrheal infections can be efficiently diagnosed for their etiological agent and categorized based on their effects on the gut microbiome using metagenomic tools, which opens new possibilities for diagnostics and treatment. IMPORTANCE E. coli infectious diarrhea is an important contributor to child mortality worldwide. However, diagnosing and thus treating E. coli infections remain challenging due to technical and other reasons associated with the limitations of the traditional culture-based techniques and the requirement to apply Koch’s postulates. In this study, we integrated traditional microbiology techniques with metagenomics and epidemiological data in order to identify cases of diarrhea where E. coli was most likely the causative disease agent and evaluate specific signatures in the disease-state gut microbiome that distinguish between diffuse adherent, enterotoxigenic, and enteropathogenic E. coli pathotypes. Therefore, our methodology and results should be highly relevant for diagnosing and treating diarrheal infections and have important applications in public health.

Silanol type hybrid polymers modified with silver nanoparticles encapsulated with SiO2 for biocorrosion protection of 2024-T3 aluminum alloy were studied through electrochemical characterization and surface analysis techniques. Two different encapsulated silver nanoparticles were synthesized using tetraethoxysilane as a core shell. The hybrid polymer was prepared by the sol–gel technique by mixing tetraethoxysilane and triethyl(octyl)silane in 1-propanol, followed by the incorporation of silver nanoparticles or encapsulated silver nanoparticles. Relatively uniform coatings were observed by a scanning electron microscopy analysis. Transmission electron microscopy and dynamic light scattering results indicated that the diameter of the silver nanoparticles was around 20 nm, whereas the encapsulated silver nanoparticles presented diameters between 24 and 30 nm. The viability results showed that polymers modified with encapsulated nanoparticles exhibit higher antibacterial properties than the polymer modified with free silver nanoparticles. This fact may be associated with a higher hydrophobicity of the coatings modified with silver encapsulated nanoparticles. Additionally, impedance measurements revealed a protective effect of all synthesized coatings for 2024-T3 aluminum alloy in chloride media inoculated with Pseudomonas aeruginosa. Keywords: Hybrid polymers, Silver nanoparticles, SiO2 nanocapsules, Biocorrosion, Pseudomonas aeruginosa

We have examined the electrocatalytic activity for the oxidation of glutathione of a wide variety of molecular catalysts: FeN4 complexes (MN4 = metal porphyrins and metal phthalocyanines) confined on the surface of graphite electrodes in order to establish reactivity descriptors for these catalysts for this reaction. We have conducted these studies mainly in alkaline media (pH = 13). The reaction order in OH− is 1 for pH values lower than 8. For higher pH values, the reaction becomes pH independent. The reaction order in glutathione is close to 1 in the concentration range examined (10−3–10−2 M). The activity of the surface-confined MN4 complexes is related to the Fe(II)/(I) and the Fe(III)/(II) redox transitions of the immobilized FeN4 complexes. The catalysts are active only in the potential range where the Fe(II) state predominates. The activity as (log j) E versus the Fe(II)/(I) formal potential varies in a non-linear fashion giving a volcano correlation as previously observed for the oxidation of L-cysteine and many other reactions catalyzed by MN4 complexes. A plot of (E)logj versus the Fe(II)/(I) formal potential gives also an asymmetrical volcano, with one of the branches with a slope close to unity. These volcano correlations clearly shows that the Fe(II)/(I) redox potential needs to be tuned to a certain potential to obtain a maximum activity for the oxidation of glutathione. Most Fe porphyrins show low activity because the metal center Fe(III) is in the wrong oxidation state in the potential range studied.

Bond nature of carboxylic groups can play an important role in Ag(I)-carboxylate compounds because light and thermal stability are important requirements for future applications such as antibacterial additives. A linear correlation between bond character and light stability of silver carboxylate complexes has been predicted by a direct relationship of infrared and 13C NMR spectroscopic data. This correlation is in agreement with the thermogravimetric analysis and provides a new approach to explore the interaction and the physical properties of metal-carboxylate bonds.

Objectives The importance of mother-child interaction in early infancy on child development has been well documented. The purpose of this study was to assess the feasibility of using the Still Face Paradigm to measure mother interactive style, infant affect and emotional regulation in a rural Ecuador setting. Methods Infant’s emotional regulation and the quality of mother’s interaction were measured with the Still Face Paradigm at 4 months of age (±15 days). Twenty-four infants and their mothers were assessed in their home. Mother interactive style was coded for attention seeking and contingent responding. Emotional regulation was described by change in infant affect between Still Face episodes. Results A significant difference was found for infant affect between the five Still Face episodes (F1,118 = 9.185, p = 0.003). A significant negative correlation was found for infant affect between episode 3 and 2 with attention seeking mother interactive style during episode 3 (rho = −0.44, p = 0.03), indicating that mothers using more contingent-responding interactions had infants with more positive affect. Conversely, a significant positive association was found for infant affect between episode 3 and 2 and contingent responding mother interactive style during episode 3 (rho = 0.46, p = 0.02), indicating that mothers who used more attention seeking play had infants who showed less positive affect. Conclusion for Practice Study results demonstrate feasibility in using the Still Face Paradigm in working populations residing in a rural region in Ecuadorian highlands and may be feasible in other similar populations in Latin America, and as a successful approach to measuring maternal-child interactions within a field-based epidemiological study design.

Nitrogen doped carbon nanotubes (N-CNTs) were synthesized by the chemical vapor deposition technique (CVD) using ferrocene and iron (II) phthalocyanine as carbon precursors and ethylendiamine as the carbon and nitrogen source. Fe2O3 nanoparticles, Co nanoparticles and MoO3 were supported on a sol–gel polymer and were used as catalyst and seed growth of the N-CNTs. The influence of the metal transition used as catalyst and the amount of ethylendiamine were studied in N-CNTs for oxygen reduction reaction (ORR) in alkaline media. The morphology of the N-CNTs was studied using scanning electron microscopy (SEM) revealing that de N-CNTs were multiwalled with averages of diameters ranging between 40 and 70 nm. The presence and type of nitrogen in the graphene grid was analyzed by means of Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The obtained results indicated that N-CNTs catalyzed by MoO3 presented the highest content of pyridinic-type nitrogen (around 39%). The electrocatalytic activity of N-CNTs for the ORR was evaluated by rotating disk electrode (RDE) technique in 0.2 M NaOH. The electrochemical results showed that N-CNTs catalyzed with 0.2 wt.% MoO3 and synthesized with 19.5 wt.% of ethylendiamine exhibited higher activity for ORR than N-CNTs catalyzed with Co nanoparticles or Fe2O3 nanoparticles.

Common alloys used for the manufacture of aircrafts are subject to different forms of environmental deterioration. A major one is corrosion, and there is a strong body of evidence suggesting that environmental microorganisms initiate and accelerate it. The development of an appropriate strategy to reduce this process depends on the knowledge concerning the factors involved in corrosion. In this work, a biofilm forming bacterial consortium was extracted in situ from the corrosion products formed in an aircraft exposed to Antarctic media. Two thermophilic bacteria, an Anoxybacillus and a Staphylococcus strain, were successfully isolated from this consortium. Two extracellular enzymes previously speculated to participate in corrosion, catalase and peroxidase, were detected in the extracellular fraction of the consortium. Additionally, we assessed the individual contribution of those thermophilic microorganisms on the corrosion process of 7075-T6 aluminum alloy, which is widely used in aeronautical industry, through electrochemical methods and surface analysis techniques.

In this work, the effect of porosity on Ti–6Al–4V alloy was studied by using the Archimedes method, BET analysis, ultrasound method, micro-hardness, surface analysis, such as scanning electron microscopy, X-ray powder diffraction and X-ray photoelectron spectroscopy, and electrochemical measurements, such as open circuit potential curves, electrochemical impedance spectroscopy and linear swept voltammetry. Apparent porosity of porous electrodes was close to 31% and 42%, which decreased significantly the elastic modulus. BET analysis revealed that the primary porosity for the porous electrodes was macro-porosity and that the micro- and meso-porosity was increased slightly by exposure. Surface analysis revealed the presence of α-phase and β-phase prior to exposure for bulk and porous electrodes. The impedance response for bulk and porous electrodes were completely different. For bulk electrodes, two time-constants were observed in high and low frequencies ranges, being associated with the formation of an oxide layer and the oxygen reduction reaction taking place at the electrolyte/oxide interface. Whereas the porous electrodes showed a De Levie behavior that was not influenced by porosity and exposure time. Anodic current was not modified by exposure.

Objectives Diarrhoea is a common and well-studied cause of illness afflicting international travellers. However, traveller's diarrhoea can also result from travel between high and low disease transmission regions within a country, which is the focus of this study. Methods We recruited participants for a case-control study of diarrhoea at four sites along an urban-rural gradient in Northern Ecuador: Quito, Esmeraldas, Borbon and rural communities outside of Borbon. At each of these sites, approximately 100 subjects with diarrhoea (cases) were recruited from Ministry of Health clinics and were age-matched with subjects visiting the same clinics for other complaints (controls). Results Travellers to urban destinations had higher risk of diarrhoea and diarrhoeagenic Escherichia coli (DEC) infections. Travel to Quito was associated with diarrhoea (aOR = 2.01, 95% CI = 1.10-3.68) and travel to Guayaquil (another urban centre in Ecuador) was associated with Diffuse Adherent E. coli infection (OR = 2.09, 95% CI = 1.01-4.33). Compared to those not travelling, urban origins were also associated with greater risk of diarrhoea in Esmeraldas (aOR = 2.28, 95% CI = 1.20-4.41), and with higher risk of diarrhoeagenic E. coli infections in Quito (aOR = 2.61, 95% CI = 1.16-5.86), with >50% of travel from Quito and Esmeraldas specified to another urban destination. Conclusions This study suggests that individuals travelling from lower-transmission regions (rural areas) to higher transmission regions (urban centres) within a single country are at a greater risk of acquiring a diarrhoea-related illness. Investments to improve water, sanitation and hygiene conditions in urban areas could have impacts on outlying rural areas within a given country.

An experimental protocol was studied to improve the adhesion of a polymeric poly(methyl methacrylate) coating that was modified with silver nanoparticles to an aluminum alloy, AA2024. The nanoparticles were incorporated into the polymeric matrix to add the property of inhibiting biofilm formation to the anticorrosive characteristics of the film, thus also making the coating antibiocorrosive. The protocol consists of functionalizing the surface through a pseudotransesterification treatment using a methyl methacrylate monomer that bonds covalently to the surface and leaves a terminal double bond that promotes and directs the polymerization reaction that takes place in the process that follows immediately after. This results in more compact and thicker poly(methyl methacrylate) (PMMA) coatings than those obtained without pseudotransesterification. The poly(methyl methacrylate) matrix modified with nanoparticles was obtained by incorporating both the nanoparticles and the methyl methacrylate in the reactor. The in situ polymerization involved combining the pretreated AA2024 specimens combined with the methyl methacrylate monomer and AgNps. The antibiofilm capacity of the coating was evaluated against P. aeruginosa, with an excellent response. Not only did the presence of bacteria decrease, but the formation of the exopolymer subunits was 99.99% lower than on the uncoated aluminum alloy or the alloy coated with unmodified poly(methyl methacrylate). As well and significantly, the potentiodynamic polarization measurements indicate that the PMMA-Ag coating has a good anticorrosive property in a 0.1-M NaCl medium.

The use of implants carries on a series of problems, among them infections, poor biocompatibility, high levels of cytotoxicity, and significant mechanical differences between implants and host organs that promote stress shielding effects. These problems indicate that the materials used to make implants must meet essential requirements and high standards for implantations to be successful. In this work, we present the synthesis, characterization and evaluation of the antibiofilm, mechanical, and thermal properties, and cytotoxic effect of a nanocomposite-based scaffold on polyurethane (PU) and gold nanoparticles (AuNPs) for soft tissue applications. The effect of the quantity of AuNPs on the antibacterial activity of nanocomposite scaffolds was evaluated against Staphylococcus epidermidis and Klebsiella spp., with a resulting 99.99% inhibition of both bacteria using a small quantity of nanoparticles. Cytotoxicity was evaluated with the T10 1/2 test against fibroblast cells. The results demonstrated that porous nanogold/PU scaffolds have no toxic effects on fibroblast cells to the 5 day exposition. With respect to mechanical properties, stress-strain curves showed that the compressive modulus and yield strength of PU scaffolds were significantly enhanced by AuNPs (by at least 10 times). This is due to changes in the arrangement of hard segments of PU, which increase the stiffness of the polymer. Thermogravimetric analysis showed that the degradation onset temperature rises with an increase in the quantity of AuNPs. These properties and characteristics demonstrate that porous nanogold/PU scaffolds are suitable material for use in soft tissue implants.

Few studies have detailed the prenatal pesticide exposure levels of women employed in or residing near large-scale agricultural industries. This study reports pesticide metabolite levels during and shortly after pregnancy in a pilot study of workers in Ecuador. Urine samples were collected for 16 rose workers and 10 nonagricultural workers enrolled into the study in early pregnancy. We measured six nonspecific organophosphatedialkylphosphate (DAP) pesticide metabolites, two alkylenebis-dithiocarbamate pesticide metabolites [ethylene thiourea (ETU) and propylene thiourea (PTU)], 3,5,6-trichloro-2-pyridinol (TCPy), malathion dicarboxylic acid, and two pyrethroid metabolites (2,2-dimethylcyclo propanecarboxylic acid and 3-phenooxybenzoic acid). We collected 141 urine samples (mean: 5.4 per woman). We observed high detection frequencies for five DAP metabolites and ETU, PTU, and TCPy. We report elevated levels of ETU in the entire sample (median 4.24 ng/mL, IQR 2.23, 7.18), suggesting other possible non-occupational pathways of exposure. We found no statistical differences in pesticide levels by current employment status, although the highest pesticide levels were among rose workers. We observed within-woman correlation in TCPy and PTU levels, but not in ETU or DAP levels. The present study is the first to characterize prenatal pesticide exposure levels among working women in Ecuador. Limitations include a small sample size and use of a convenience sample. Strengths include a longitudinal design and multiple urine samples per woman. Results provide an initial characterization of prenatal pesticide exposure levels and how these levels vary over pregnancy in a community impacted by agricultural industry and will inform further studies in the region.

The recently introduced new electroanalytical protocol of stripping voltammetry microprobe (SPV) has been considerably improved with respect to analytical performance. The determination of the silver ions is shown to be possible by the precipitation of a solution of silver drops on an electrode surface, which is previously moistened with a solution of NaCl. The electrode thus modified, i.e., with the silver chloride precipitate on the surface, is introduced into a chloride electrolyte and is negatively polarized to reduce the silver salt to metallic silver. Whereas this reduction process produces only a broad signal, the following electrochemical oxidation of the silver metal back to AgCl provides a highly sensitive and narrow signal, which lends itself for analysis. The linear range for determination of silver ions following this protocol is 1.4 × 10 −7 to 7.4 × 10 −4 mol L −1 and the detection limit is 4.6 × 10 −8 mol L −1 .

Since ancient times, silver ions have been known to be effective against a broad range of micro-organisms but in the last decade, this metal has been greatly studied because of their antimicrobial capability against a wide range of bacteria, viruses, and fungi. For the same reason, it is the most extensively studied metal with antibacterial applications in medicine. Besides applications, the antimicrobial activity is associated with high effectiveness, low toxicity, and virtually no resistance of micro-organisms to the presence of this metal. The appearance of new bacterial strains resistant to antibiotics is a serious health problem; so, there is a strong incentive to develop new bactericides. This makes current research in bactericidal silver complexes particularly important. This review summarizes the most important aspect related to coordination chemistry of Ag(I) carboxylate complexes and their influence as antibacterial agents.

This paper describes how electrochemical trace analysis can be performed in micro samples based on the precipitation of a sparingly soluble compound and its immobilization on an electrode surface. Precipitation is performed in a solution droplet put on the electrode in an upside-down position in air. The solvent of the droplet is then evaporated and the immobilized residue is subjected to a voltammetric measurement after introducing the electrode to an electrolyte solution. This methodology can be used for the quantification of dissolved ions (after precipitation) as well as for that of dispersed solids. As example, here the quantification of silver ions following precipitation as AgCl is described. Keywords: Stripping voltammetry, Precipitation, Immobilization, Electrochemistry, Microanalysis

International audience; Surface based on polyelectrolytes functionalized with amino acids onto amino-terminated solid surfaces of silicon wafers was prepared, with the purpose of evaluate the chemical functionality of the polyelectrolyte films in adsorption and catalytic activity of an enzyme. In this work, the adsorption of the enzyme glucose 6-phosphate dehydrogenase from Leuconostoc mesenteroides (LmG6PD) was studied as model. The polyelectrolytes were obtained from poly (maleic anhydride-alt-vinylpyrrolidone) [poly(MA-alt-VP)] and functionalized with amino acids of different hydropathy index: glutamine (Gln), tyrosine (Tyr) and methionine (Met). The polyelectrolytes were adsorbed onto the amino-terminated silicon wafer at pH 3.5 and 4.5 and at low and high ionic strength. At low ionic strength and pH 3.5, the largest quantity of adsorbed polyelectrolyte was on the films containing glutamine moiety as the most hydrophilic amino acid in the side chain of polymer chain (5.88 mg/m 2), whereas at high ionic strength and pH 4.5, the lowest quantity was in films containing tyrosine moiety in the side chain (1.88 mg/m 2). The films were characterized by ellipsometry, contact angle measurements and atomic force microscopy (AFM). The polyelectrolyte films showed a moderate degree of hydrophobicity, the methionine derivative being the most hydrophobic film. With the aim of evaluate the effect of the amino acid moieties on the ability of the surface to adsorb enzymes, we study the activity of the enzyme on these surfaces. We observed that the polarity of the side chain of the amino acid in the polyelectrolyte affected the quantity of LmG6PD adsorbed, as well as its specific activity, showing that films prepared from poly(MA-alt-VP) functionalized with Met provide the best enzymatic performance. The results obtained demonstrated that the surfaces prepared from polyelectrolytes functionalized with amino acids could be an attractive and simple platform for the im-mobilization of enzymes, which could be of interest for biocatalysis applications.

Silver nanofibers (Ag-Nfbs) ~ 80 nm in diameter were synthesized by hydrothermal treatment. The nanofibers (3 and 5 wt%) were added in the initial feed together with the catalytic system. Polymerizations in an ethylene atmosphere were performed, yielding PE nanocomposites in situ with 3 and 5 wt% content of Ag-Nfbs. The antibacterial effect of the silver-nanofiber composites was evaluated after incubation of Escherichia coli ATCC 25923 for 8 h on their surface. Bacterial viability tests showed that the silver-nanofiber composites inhibited the growth of Escherichia coli ATCC 25923 by 88 and 56%. This behavior is attributed to increased silver ions release from the nanocomposite. TEM analysis showed that the antibacterial effect is associated with membrane disruption but not with changes in shape.

The development of polymer nanocomposites with antimicrobial properties has been a key factor for controlling or inhibiting the growth of microorganisms and preventing foodborne diseases and nosocomial infections. Commercially available antibacterial products based on silver-polymer are the most widely used despite the fact that copper is considerably less expensive. The incorporation of copper nanoparticles as antibacterial agents in polymeric matrices to generate copper-polymer nanocomposites have presented excellent results in inhibiting the growth of a broad spectrum of microorganisms. The potential applications in food packaging, medical devices, textiles and pharmaceuticals and water treatment have generated an increasing number of investigations on preparing copper based nanocomposites and alternative polymeric matrices, as potential hosts of nano-modifiers. This review presents a comprehensive compilation of previous published work on the subject, mainly related to the antimicrobial activity of copper polymer nanocomposites. Within all the phenomenology associated to antibacterial effects we highlight the possible mechanisms of action. We discuss the differences in the susceptibility of Gram negative and positive bacteria to the antibacterial activity of nanocomposites, and influencing factors. As well, the main applications of copper polymer-metal nanocomposites are described, considering their physical and chemical characteristics. Finally, some commercially available copper-polymer nanocomposites are described.

The antimicrobial effect of incorporating silver nanoparticles (AgNps) into zirconia matrix–polyether glycol was studied. AgNps of 4–6 nm in size were synthesized using the inverse micelles method, and different doses of metallic nanoparticles were incorporated into zirconia–polyether glycol mixtures during the ageing procedure. Atomic force microscopy (AFM) of the modified hybrid film showed a homogenous distribution of 20–80 nm diameter AgNps, indicating agglomeration of these structures during film modification; such agglomerations were greater when increasing the dosage of the colloidal system. The AgNps-hybrid films showed higher antimicrobial activity against Gram-positive bacteria than for Gram-negative bacteria. Hybrid films prepared with dioctyl sodium sulfosuccinate (AOT) stabilized AgNps presented enhanced antibacterial activity compared to that obtained through the addition of a high AgNO3 concentration (0.3 wt%).

FT-IR spectroscopy of carboxylic groups and viability tests were useful to understand the antibacterial properties of six highly efficient silver(I) pyridinecarboxylate (nicotinic, picolinic and isonicotinic acids) and bipiridinecarboxylate (pyridine-2,3-dicarboxylic, pyridine-2,4-dicarboxylic and pyridine-2,5-dicarboxylic acids) complexes with AgO and AgN bonds against E. coli (ATCC 25922) and Streptococcus agalactiae (ISP 329-09). The results show a tendency between the nature of AgX (X=oxygen and nitrogen) bonds and the rate or efficiency of antibacterial behavior.

A new hybrid sol–gel type film, composed of tetraethylorthosilicate (TEOS) and tetraocthylorthosilicate (TEOCS), and modified with different nanoparticle systems, has been investigated as a coating for protection of AA-2024-T3 aluminium alloy. The nanoparticle systems considered were either ZrO2 or CeO2 or their combination. The zirconia nanoparticles were prepared from a Zr (IV) propoxide sol (TPOZ), using an organic stabilizer, and the CeO2 nanoparticles were developed spontaneously after adding cerium nitrate solution to the hybrid sol. The chemical composition and the structure of the hybrid sol–gel films were examined by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The corrosion resistance of the coated AA-2024 alloy was examined by potentiodynamic polarization. The results revealed that, for short exposure times in the electrolyte, incorporation of ZrO2 or CeO2 nanoparticles in the hybrid film does not provide an increase in the corrosion resistance of the coated AA-2024 alloy. Further, the resistance was significantly reduced by increasing the nanoparticle content. Conversely, by incorporating both nanoparticles (ZrO2 and CeO2), the corrosion resistance of the resulting hybrid films increased slightly. The behavior changed significantly when the coated alloy was exposed to the electrolyte for 5 days. The corrosion resistance of the coatings, unmodified and modified with CeO2 or ZrO2 nanoparticles, decreased by two or three orders of magnitude, while the film modified with both nanoparticles (CrO2 and ZrO2) showed a relatively high corrosion resistance and responsiveness to activation processes during anodic polarization.

Polyethylene nanocomposites containing silver nanoparticles with antimicrobial properties were produced via in situ polymerization. The silver nanoparticles were added together with the catalytic system (metallocene catalyst and methylaluminoxane, MAO, as cocatalyst) directly to the reactor. The polymerization activity did not present significant changes with the incorporation of the silver nanoparticles in comparison to the homopolymerization without filler. The effect of various silver nanoparticle contents on silver ion release and antimicrobial efficacy against Escherichia Coli were studied. Nanocomposites containing higher nanosilver concentrations (5 wt.%) showed the highest silver ion release, and after 24 h reached 99.99% of efficacy against the bacteria compared with the neat PE. Transmission electron microscopy (TEM) images showed that the nanospheres were well dispersed throughout the polyethylene matrix.

We have revisited correlations between catalytic activity and formal potentials of MN4 catalysts for the reduction of O2 (ORR). When comparing the activities of Cr, Mn, Co and Fe MN4 complexes for ORR as a plot of (log i/n)E versus the M(III)/(II) formal potential of the catalyst (n = number of electrons involved in the ORR), two linear correlations are obtained: one for Cr, Mn and Fe complexes and another for Co complexes. Mn and Fe are 4-electron reduction catalysts and Cr and Co are 2-electron reduction catalysts for ORR in alkaline media. We show that instead of plotting the formal potential E°′ of the catalyst but the difference between this parameter and the reversible potential Erev of the corresponding catalytic reaction (O2/OH−) or (O2/HO2−), as (E°′ − Erev) and using the Co(II)/(I) formal potential for cobalt macrocyclics, instead of the Co(III)/(II) redox couple, all data points merge into one single linear correlation of slope +0.170 V/decade. It is possible that when (E°′ − Erev) approaches zero, the maximum activity could be achieved and this is especially important for 4-electron catalysts and the linear correlation might be part of an incomplete volcano correlation. Keywords: Linear correlations, Phthalocyanines, Fe porphine, O2 reduction catalyst, Redox potentials

The antibacterial effects against Staphylococcus epidermidis of five silver carboxylate complexes with anti-inflammatory ligands were studied in order to analyze and compare them in terms of stability (in solution and after exposure to UV light), and their antibacterial and morphological differences. Four effects of the Ag-complexes were evidenced by transmission electronic microscopy (TEM) and scanning electronic microscopy (SEM): DNA condensation, membrane disruption, shedding of cytoplasmic material and silver compound microcrystal penetration of bacteria. 5-Chlorosalicylic acid (5Cl) and sodium 4-aminosalicylate (4A) were the most effective ligands for synthesizing silver complexes with high levels of antibacterial activity. However, Ag-5Cl was the most stable against exposure UV light (365 nm). Cytotoxic effects were tested against two kinds of eukaryotic cells: murine fibroblast cells (T10 1/2) and human epithelial ovarian cancer cells (A2780). The main objective was to identify changes in their antibacterial properties associated with potential decomposition and the implications for clinical applications.

We have investigated the electrocatalytic activity of tetraphenyl porphyrin, of substituted tetraphenyl porphyrins and of vitamin B 12 for the electro-oxidation of 2-aminoethanethiol, with the catalysts confined on graphite electrodes. Several N4-macrocyclic were used in order to have a great variety of formal potentials of the catalysts and compare this parameter with the catalytic activity. The electrocatalytic activity, measured as current at constant potential, increases with the formal potential of the catalysts as follows: Co-pentafluorotetraphenylporphyrin 12 . Vitamin B 12 exhibits the maximum activity. A correlation of log I (at constant potential) vs. the formal potential E ′ of the catalysts gives a volcano correlation when data of Co-phthalocyanines studied in previous work is included in the comparison. This clearly shows that the search for better catalysts for this reaction point to those N 4 -macrocyclic complexes with Co(II)/(I) formal potentials close to −1.0 V vs. SCE which corresponds to an optimum situation for the interaction of the thiol with the active site. When comparing reactivity trends of similar catalysts for the oxidation of other thiols ( l -cysteine, mercaptoacetate and 2-mercaptoethanol) E ′ max correlates linearly with the p K a of the thiol.

The effect of zirconia and zirconia-polyester glycol hybrid coatings on the corrosion resistance of mechanically polished or anodized AISI 316 stainless steel (316L), was studied by potentiodynamic polarization and electrochemical impedance spectroscopy in 0.1 M NaCl and scanning electron microscope and atomic force microscopy examinations. The deposition of zirconia coatings was achieved by the sol–gel technique by immersing the samples in either the inorganic polymer or the organic–inorganic polymer mixture. From potentiodynamic and impedance measurements, the grade of protection is reduced with the exposure time to the electrolyte, which is mainly associated with lost of film adhesion and, consequently, detachment from the metal substrate. However, the uncoated anodized sample revealed an unexpected corrosion behavior; the anodic film formed during anodizing readily increased the corrosion resistance of the 316L stainless steel in 0.1 M NaCl, revealing a considerable reduction in the corrosion current density and an increase in the pitting potential.

We have investigated the electrocatalytic activity of several substituted and unsubstituted cobalt–phthalocyanines of substituted tetraphenyl porphyrins and of vitamin B12, for the electro-oxidation of 2-mercaptoacetate, with the complexes pre-adsorbed on a pyrolytic graphite electrode. Several N4-macrocyclic were used to have a wide variety of Co(II)/(I) formal potentials. The electrocatalytic activity, measured as current at constant potential, increases with the Co(II)/(I) redox potential for porphyrins as Co–pentafluorotetraphenylporphyrin Co–octamethoxyphthalocyanine > Co–tetranitrophthalocyanine Co–tetraaminophthalocyanine > Co–unsubstituted phthalocyanine > Co–tetrasulfonatophthalocyanine > Co–perfluorinated phthalocyanine. Vitamin B12 exhibits the maximum activity. A correlation of log I (at constant potential) versus the Co(II)/(I) formal potential of the catalysts gives a volcano curve. This clearly shows that the search for better catalysts for this reaction point to those N4-macrocyclic complexes with Co(II)/(I) formal potentials close to −0.84 V versus SCE, which correspond to an optimum situation for the interaction of the thiol with the active site.

The aim of this study is to examine chitosan, which is a good film former, as a corrosion protective coating for AA-2024-T3 aluminium alloy. The aluminium samples were first anodized to increase adhesion of the subsequently dip coated film from a chitosan-acetic acid solution. To further increase the protective ability of the chitosan coating, the coated samples were immersed in a copper ion solution for 24 h. The copper salts used were sulphate and acetate. The chitosan membranes exposed to copper ion solutions revealed a reduced permeability in comparison with the unexposed samples, and an increase in stability in aqueous solutions, as revealed by a steady state and a high open circuit potential in borax solution. From UV-Vis spectroscopic measurement of the film on ITO glasses, the reduction in permeability of the chitosan film modified by copper ions appears to be associated with copper cross linking within the chitosan structure.

The hydrazine oxidation by iron(II) phthalocyanine (Fe(II)Pc) has been studied using an energy profile framework through quantum chemistry theoretical models calculated in the gas phase at the density functional theory B3LYP/LACVP(d) level. We applied two models of charge-transfer mechanisms previously reported (J. Phys. Chem. A 2005, 109, 1196) for the hydrazine oxidation mediated by Co(II)Pc. Model 1 consists of an alternated loss of one electron and one proton, involving anionic and neutral species. Model 2 considers an alternated loss of two electrons and two protons and includes anionic, neutral, and cationic species. Both applied models describe how the charge-transfer process occurs. In contrast with the obtained results for Co(II)Pc, we found that the hydrazine oxidation mediated by Fe(II)Pc is a fully through-bond charge-transfer mechanism. On the other hand, the use of different charge-transfer descriptors (spin density, electronic population, condensed Fukui function) showed a major contribution of the iron atom in comparison with the cobalt atom in the above-mentioned process. These results could explain the higher catalytic activity observed experimentally for Fe(II)Pc in comparison with Co(II)Pc. The applied theoretical models are a good starting point to rationalize the charge-transfer process of hydrazine oxidation mediated by Fe(II)Pc.