Characterization of surface functional groups present on laboratory-generated and ambient aerosol particles by means of heterogeneous titration reactions

A Knudsen flow reactor has been used to quantify surface functional groups on aerosols collected in the field. This technique is based on a heterogeneous titration reaction between a probe gas and a specific functional group on the particle surface. In the first part of this work, the reactivity of different probe gases on laboratory-generated aerosols (limonene SOA, Pb(NO3)2, Cd(NO3)2) and diesel reference soot (SRM 2975) has been studied. Five probe gases have been selected for the quantitative determination of important functional groups: N(CH3)3 (for the titration of acidic sites), NH2OH (for carbonyl functions), CF3COOH and HCl (for basic sites of different strength), and O3 (for oxidizable groups). The second part describes a field campaign that has been undertaken in several bus depots in Switzerland, where ambient fine and ultrafine particles were collected on suitable filters and quantitatively investigated using the Knudsen flow reactor. Results point to important differences in the surface reactivity of ambient particles, depending on the sampling site and season. The particle surface appears to be multi-functional, with the simultaneous presence of antagonistic functional groups which do not undergo internal chemical reactions, such as acid-base neutralization. Results also indicate that the surface of ambient particles was characterized by a high density of carbonyl functions (reactivity towards NH2OH probe in the range 0.26-6 formal molecular monolayers) and a low density of acidic sites (reactivity towards N(CH3)3 probe in the range 0.01-0.20 formal molecular monolayer). Kinetic parameters point to fast redox reactions (uptake coefficient ?0>10-3 for O3 probe) and slow acid-base reactions (?0<10-4 for N(CH3)3 probe) on the particle surface. [Authors]

The use of heterogeneous chemistry for the characterization of functional groups at the gas/particle interface of soot and TiO(2) nanoparticles

Six gases (N((CH3)3), NH2OH, CF3COOH, HCl, NO2, O3) were selected to probe the surface of seven combustion aerosol (amorphous carbon, flame soot) and three types of TiO2 nanoparticles using heterogeneous, that is gas-surface reactions. The gas uptake to saturation of the probes was measured under molecular flow conditions in a Knudsen flow reactor and expressed as a density of surface functional groups on a particular aerosol, namely acidic (carboxylic) and basic (conjugated oxides such as pyrones, N-heterocycles) sites, carbonyl (R1-C(O)-R2) and oxidizable (olefinic, -OH) groups. The limit of detection was generally well below 1% of a formal monolayer of adsorbed probe gas. With few exceptions most investigated aerosol samples interacted with all probe gases which points to the coexistence of different functional groups on the same aerosol surface such as acidic and basic groups. Generally, the carbonaceous particles displayed significant differences in surface group density: Printex 60 amorphous carbon had the lowest density of surface functional groups throughout, whereas Diesel soot recovered from a Diesel particulate filter had the largest. The presence of basic oxides on carbonaceous aerosol particles was inferred from the ratio of uptakes of CF3COOH and HCl owing to the larger stability of the acetate compared to the chloride counterion in the resulting pyrylium salt. Both soots generated from a rich and a lean hexane diffusion flame had a large density of oxidizable groups similar to amorphous carbon FS 101. TiO2 15 had the lowest density of functional groups among the three studied TiO2 nanoparticles for all probe gases despite the smallest size of its primary particles. The used technique enabled the measurement of the uptake probability of the probe gases on the various supported aerosol samples. The initial uptake probability, g0, of the probe gas onto the supported nanoparticles differed significantly among the various investigated aerosol samples but was roughly correlated with the density of surface groups, as expected. [Authors]

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A Knudsen flow reactor has been used to quantify functional groups on the surface of seven different types of combustion particle samples: 3 amorphous carbons (FS 101, Printex 60, FW 2), 2 flame soots (hexane soot generated from a rich and a lean diffusion flame), and 2 Diesel particles (SRM 2975, Diesel soot recovered from a Diesel particulate filter). The technique is based on a heterogeneous titration reaction between a probe gas and a specific functional group on the particle surface. Six probe gases have been selected for the quantification of important functional groups: N(CH3)3 for the titration of acidic sites, NH2OH for carbonyl functions of aldehydes and ketones, CF3COOH and HCl for basic sites of different strength, O3 and NO2 for oxidizable groups. The limit of detection was generally well below 1% of a formal monolayer of adsorbed probe gas. Results obtained with N(CH3)3 were higher for the FW 2 amorphous carbon (post-oxidized sample, according to the manufacturer) and the Diesel particles (between 5.2·10 13 and 5.8·10 13 molecule/cm2), indicating a higher state of oxidation than for the other samples (between 1.3·10 12 and 3.7·10 12 molecule/cm2). The ratio of uptakes of CF3COOH and HCl inferred the presence of basic oxides on the particle surface, owing to the larger stability of the acetate compared to the chloride counter ion in the resulting pyrylium salt. The reactivity of the FS 101 amorphous carbon (3.7·10 15 molecule/cm2) and the hexane flame soot (between 1.9·10 15 and 2.7·10 15 molecule/cm2) towards O3 was very high, indicating the presence of a huge amount of oxidizable or reduced groups on the surface of these samples. Besides the quantification of surface functional groups, the kinetics of reactions between particles and probe gases has also been studied. The uptake coefficient γ0 was roughly correlated with the amount of probe gas taken up by the samples. Indeed, the presence of a high density of functional groups led to fast uptake of the probe gas. These different findings indicate that the particle surface appeared multi-functional, with the simultaneous presence of antagonistic functional groups which do not undergo internal chemical reactions, such as acid-base neutralization. Results also point to important differences in the surface reactivity of the samples, depending on the combustion conditions. The relative distribution of the surface functional groups may be a useful indicator for the state of oxidation and the reactivity of the particle surface.

Assessment of diesel exhaust particulate exposure and surface characteristics in association with levels of oxidative stress biomarkers

Exposure to PM10 and PM2.5 (particulate matter with aerodynamic diameter smaller than 10 μm and 2.5 μm, respectively) is associated with a range of adverse health effects, including cancer, pulmonary and cardiovascular diseases. Surface characteristics (chemical reactivity, surface area) are considered of prime importance to understand the mechanisms which lead to harmful effects. A hypothetical mechanism to explain these adverse effects is the ability of components (organics, metal ions) adsorbed on these particles to generate Reactive Oxygen Species (ROS), and thereby to cause oxidative stress in biological systems (Donaldson et al., 2003). ROS can attack almost any cellular structure, like DNA or cellular membrane, leading to the formation of a wide variety of degradation products which can be used as a biomarker of oxidative stress. The aim of the present research project is to test whether there is a correlation between the exposure to Diesel Exhaust Particulate (DEP) and the oxidative stress status. For that purpose, a survey has been conducted in real occupational situations where workers were exposed to DEP (bus depots). Different exposure variables have been considered: - particulate number, size distribution and surface area (SMPS); - particulate mass - PM2.5 and PM4 (gravimetry); - elemental and organic carbon (coulometry); - total adsorbed heavy metals - iron, copper, manganese (atomic adsorption); - surface functional groups present on aerosols (Knudsen flow reactor). (Demirdjian et al., 2005). Several biomarkers of oxidative stress (8-hydroxy-2'-deoxyguanosine and several aldehydes) have been determined either in urine or serum of volunteers. Results obtained during the sampling campaign in several bus depots indicated that the occupational exposure to particulates in these places was rather low (40-50 μg/m3 for PM4). Size distributions indicated that particles are within the nanometric range. Surface characteristics of sampled particles varied strongly, depending on the bus depot. They were usually characterized by high carbonyl and low acidic sites content. Among the different biomarkers which have been analyzed within the framework of this study, mean levels of 8- hydroxy-2'-deoxyguanosine and several aldehydes (hexanal, heptanal, octanal, nonanal) increased during two consecutive days of exposure for non-smokers. In order to bring some insight into the relation between the particulate characteristics and the formation of ROS by-products, biomarkers levels will be discussed in relation with exposure variables.

Functionally and phylogenetically diverse plant communities key to soil biota

Recent studies assessing the role of biological diversity for ecosystem functioning indicate that the diversity of functional traits and the evolutionary history of species in a community, not the number of taxonomic units, ultimately drives the biodiversity-ecosystem-function relationship. Here, we simultaneously assessed the importance of plant functional trait and phylogenetic diversity as predictors of major trophic groups of soil biota (abundance and diversity), six years from the onset of a grassland biodiversity experiment. Plant functional and phylogenetic diversity were generally better predictors of soil biota than the traditionally used species or functional group richness. Functional diversity was a reliable predictor for most biota, with the exception of soil microorganisms, which were better predicted by phylogenetic diversity. These results provide empirical support for the idea that the diversity of plant functional traits and the diversity of evolutionary lineages in a community are important for maintaining higher abundances and diversity of soil communities.

Ethical issues in nutrition support of severely disabled elderly persons: a guide for health professionals.

Providing or withholding nutrition in severely disabled elderly persons is a challenging dilemma for families, health professionals, and institutions. Despite limited evidence that nutrition support improves functional status in vulnerable older persons, especially those suffering from dementia, the issue of nutrition support in this population is strongly debated. Nutrition might be considered a basic need that not only sustains life but provides comfort as well by patients and their families. Consequently, the decision to provide or withhold nutrition support during medical care is often complex and involves clinical, legal, and ethical considerations. This article proposes a guide for health professionals to appraise ethical issues related to nutrition support in severely disabled older persons. This guide is based on an 8-step process to identify the components of a situation, analyze conflicting values that result in the ethical dilemma, and eventually reach a consensus for the most relevant plan of care to implement in a specific clinical situation. A vignette is presented to illustrate the use of this guide when analyzing a clinical situation.

Assessment of diesel exhaust particulate exposure and surface characteristics in association with levels of oxidative stress biomarkers

Exposure to PM10 and PM2.5 (particulate matter with aerodynamic diameter smaller than 10 μm and 2.5 μm, respectively) is associated with a range of adverse health effects, including cancer, pulmonary and cardiovascular diseases. Surface characteristics (chemical reactivity, surface area) are considered of prime importance to understand the mechanisms which lead to harmful effects. A hypothetical mechanism to explain these adverse effects is the ability of components (organics, metal ions) adsorbed on these particles to generate Reactive Oxygen Species (ROS), and thereby to cause oxidative stress in biological systems (Donaldson et al., 2003). ROS can attack almost any cellular structure, like DNA or cellular membrane, leading to the formation of a wide variety of degradation products which can be used as a biomarker of oxidative stress. The aim of the present research project is to test whether there is a correlation between the exposure to Diesel Exhaust Particulate (DEP) and the oxidative stress status. For that purpose, a survey has been conducted in real occupational situations where workers were exposed to DEP (bus depots). Different exposure variables have been considered: - particulate number, size distribution and surface area (SMPS); - particulate mass - PM2.5 and PM4 (gravimetry); - elemental and organic carbon (coulometry); - total adsorbed heavy metals - iron, copper, manganese (atomic adsorption); - surface functional groups present on aerosols (Knudsen flow reactor). Several biomarkers of oxidative stress (8-hydroxy-2'-deoxyguanosine and several aldehydes) have been determined either in urine or serum of volunteers. Results obtained during the sampling campaign in several bus depots indicated that the occupational exposure to particulates in these places was rather low (40-50 μg/m3 for PM4). Bimodal size distributions were generally observed (5 μm and <1 μm). Surface characteristics of PM4 varied strongly, depending on the bus depot. They were usually characterized by high carbonyl and low acidic sites content. Among the different biomarkers which have been analyzed within the framework of this study, mean urinary levels of 8-hydroxy-2'-deoxyguanosine increased significantly (p<0.05) during two consecutive days of exposure for non-smoker workers. On the other hand, no statistically significant differences were observed for serum levels of hexanal, nonanal and 4- hydroxy-nonenal (p>0.05). Biomarkers levels will be compared to exposure variables to gain a better understanding of the relation between the particulate characteristics and the formation of ROS by-products. This project is financed by the Swiss State Secretariat for Education and Research. It is conducted within the framework of the COST Action 633 "Particulate Matter - Properties Related to Health Effects".

Probing functional groups at the gas-aerosol interface using heterogeneous titration reactions: a tool for predicting aerosol health effects?

The complex chemical and physical nature of combustion and secondary organic aerosols (SOAs) in general precludes the complete characterization of both bulk and interfacial components. The bulk composition reveals the history of the growth process and therefore the source region, whereas the interface controls--to a large extent--the interaction with gases, biological membranes, and solid supports. We summarize the development of a soft interrogation technique, using heterogeneous chemistry, for the interfacial functional groups of selected probe gases [N(CH(3))(3), NH(2)OH, CF(3)COOH, HCl, O(3), NO(2)] of different reactivity. The technique reveals the identity and density of surface functional groups. Examples include acidic and basic sites, olefinic and polycyclic aromatic hydrocarbon (PAH) sites, and partially and completely oxidized surface sites. We report on the surface composition and oxidation states of laboratory-generated aerosols and of aerosols sampled in several bus depots. In the latter case, the biomarker 8-hydroxy-2'-deoxyguanosine, signaling oxidative stress caused by aerosol exposure, was isolated. The increase in biomarker levels over a working day is correlated with the surface density N(i)(O3) of olefinic and/or PAH sites obtained from O(3) uptakes as well as with the initial uptake coefficient, γ(0), of five probe gases used in the field. This correlation with γ(0) suggests the idea of competing pathways occurring at the interface of the aerosol particles between the generation of reactive oxygen species (ROS) responsible for oxidative stress and cellular antioxidants.

Effects of polymer-coated multi-wall carbon nanotubes on mouse RAW 264.7 macrophages

Surface characteristics (area, chemical reactivity) play an important role in cell response to nanomaterials. The aim of this study was to evaluate the oxidative and inflammatory effects of multi−wall carbon nanotubes (MWCNT) uncoated (P0) or coated with carboxylic polyacid or polystyrene polybutadiene polymetacrylate of methyl polymers (P1 and P2 respectively) on murine macrophages (RAW 264.7 cell line). Carbon black nanoparticles (CB, diameter 95 nm) and crocidolite fibers (diameter: 80 nm, length: < 10 μm) were used as controls. Surface functional groups present on MWCNTs were analyzed by Knudsen flow reactor. The amount of acidic sites was P1> P0> P2, for basic sites was P0> P1>> P2 and for oxidizable sites was P0> P2> P1. In contact with cells, P2 formed smaller aggregates than P0 and P1, which were of similar size. Optical microscopy showed the formation of vacuoles after exposure only to P0, P1 and crocidolite. Incubation of cells with P0, P1 and crocidolite fibers induced a significant and similar decrease in metabolic activity, whereas P2 and CB had no effect. Cell number and membrane permeability were unmodified by incubation with the different particles. Incubation of macrophages with P0, P1 and crocidolite induced a dose− and time−dependent increase in mRNA expression of oxidative stress marker (HO−1, GPX1) and inflammatory mediators (TNF−a, MIP−2). No such responses were observed with P2 and CB. In conclusion, MWCNT coated with a carboxylic polyacid polymer exerted similar oxidative and inflammatory effects to uncoated MWCNT. By contrast, no such effects were observed with MWCNT coated with a polystyrene−based polymer. This kind of coating could be useful to decrease MWCNT toxicity.

Paralysis of ventilated newborn babies does not influence resistance of the total respiratory system.

Paralysis with pancuronium bromide is used in newborn infants to facilitate ventilatory support during respiratory failure. Changes in lung mechanics have been attributed to paralysis. The aim of this study was to examine whether or not paralysis per se has an influence on the passive respiratory mechanics, resistance (Rrs) and compliance (Crs) of the respiratory system in newborn infants. In 30 infants with acute respiratory failure, Rrs was measured during paralysis with pancuronium bromide and after stopping pancuronium bromide (group A). Rrs was also measured in an additional 10 ventilated infants in a reversed fashion (group B): Rrs was measured first in nonparalysed infants and then they were paralysed, mainly for diagnostic procedures, and the Rrs measurement repeated. As Rrs is highly dependent on lung volume, several parameters, that depend directly on lung volume were recorded: inspiratory oxygen fraction (FI,O2), arterial oxygen tension/alveolar oxygen tension (a/A) ratio and volume above functional residual capacity (FRC). In group A, the Rrs was not different during (0.236+/-0.09 cmH2O x s x mL(-1)) and after (0.237+/-0.07 cmH2O x s x mL(-1)) paralysis. Also, in group B, Rrs did not change (0.207+/-0.046 versus 0.221+/-0.046 cm x s x mL(-1) without versus with pancuronium bromide). FI,O2, a/A ratio and volume above FRC remained constant during paralysis. These data demonstrate that paralysis does not influence the resistance of the total respiratory system in ventilated term and preterm infants when measured at comparable lung volumes.

MFGE8 does not influence chorio-retinal homeostasis or choroidal neovascularization in vivo.

PURPOSE: Milk fat globule-epidermal growth factor-factor VIII (MFGE8) is necessary for diurnal outer segment phagocytosis and promotes VEGF-dependent neovascularization. The prevalence of two single nucleotide polymorphisms (SNP) in MFGE8 was studied in two exsudative or "wet" Age-related Macular Degeneration (AMD) groups and two corresponding control groups. We studied the effect of MFGE8 deficiency on retinal homeostasis with age and on choroidal neovascularization (CNV) in mice. METHODS: The distribution of the SNP (rs4945 and rs1878326) of MFGE8 was analyzed in two groups of patients with "wet" AMD and their age-matched controls from Germany and France. MFGE8-expressing cells were identified in Mfge8(+/-) mice expressing ß-galactosidase. Aged Mfge8(+/-) and Mfge8(-/-) mice were studied by funduscopy, histology, electron microscopy, scanning electron microscopy of vascular corrosion casts of the choroid, and after laser-induced CNV. RESULTS: rs1878326 was associated with AMD in the French and German group. The Mfge8 promoter is highly active in photoreceptors but not in retinal pigment epithelium cells. Mfge8(-/-) mice did not differ from controls in terms of fundus appearance, photoreceptor cell layers, choroidal architecture or laser-induced CNV. In contrast, the Bruch's membrane (BM) was slightly but significantly thicker in Mfge8(-/-) mice as compared to controls. CONCLUSIONS: Despite a reproducible minor increase of rs1878326 in AMD patients and a very modest increase in BM in Mfge8(-/-) mice, our data suggests that MFGE8 dysfunction does not play a critical role in the pathogenesis of AMD.

Expression of a functional single chain antibody on the surface of extracellular enveloped vaccinia virus as a step towards selective tumour cell targeting.

Recombinant vaccinia virus with tumour cell specificity may provide a versatile tool either for direct lysis of cancer cells or for the targeted transfer of genes encoding immunomodulatory molecules. We report the expression of a single chain antibody on the surface of extracellular enveloped vaccinia virus. The wild-type haemagglutinin, an envelope glycoprotein which is not required for viral infection and replication, was replaced by haemagglutinin fusion molecules carrying a single chain antibody directed against the tumour-associated antigen ErbB2. ErbB2 is an epidermal growth factor receptor-related tyrosine kinase overexpressed in a high percentage of human adenocarcinomas. Two fusion proteins carrying the single chain antibody at different NH2-terminal positions were expressed and exposed at the envelope of the corresponding recombinant viruses. The construct containing the antibody at the site of the immunoglobulin-like loop of the haemagglutinin was able to bind solubilized ErbB2. This is the first report of replacement of a vaccinia virus envelope protein by a specific recognition structure and represents a first step towards modifying the host cell tropism of the virus.

Cell surface expression of a functional rubella virus E1 glycoprotein by addition of a GPI anchor.

Rubella virus (RV) envelope glycoproteins E1 and E2 are targeted to the Golgi as heterodimers. While E2 contains a transmembrane Golgi retention signal, E1 is arrested in a pre-Golgi compartment in the absence of E2, and appears to require heterodimerization in order to reach the Golgi. Various forms of E1 with deletions in the ectodomain or lacking the cytoplasmic (CT) and transmembrane (TM) domains, as well as the 29 C-terminal amino acid residues of the ectodomain were also retained intracellularly. We therefore investigated the possibility of targetting E1 to the plasma membrane by addition of a glycosylphosphatidylinositol (GPI) anchor. We found that E1GPI was transported to the cell surface where it retained the hemadsorption activity characteristic of the wild-type E1/E2 heterodimer. Furthermore, coexpression of a mammalian GPI-specific phospholipase D (GPI-PLD) resulted in the release of E1GPI and in constitutive expression of a soluble form of E1. This study thus demonstrates that the GPI anchor has a dominant effect over the E1 pre-Golgi retention signal and that E1 is sufficient for hemadsorption.

Socioeconomic status, structural and functional measures of social support, and mortality: The British Whitehall II Cohort Study, 1985-2009.

The authors examined the associations of social support with socioeconomic status (SES) and with mortality, as well as how SES differences in social support might account for SES differences in mortality. Analyses were based on 9,333 participants from the British Whitehall II Study cohort, a longitudinal cohort established in 1985 among London-based civil servants who were 35-55 years of age at baseline. SES was assessed using participant's employment grades at baseline. Social support was assessed 3 times in the 24.4-year period during which participants were monitored for death. In men, marital status, and to a lesser extent network score (but not low perceived support or high negative aspects of close relationships), predicted both all-cause and cardiovascular mortality. Measures of social support were not associated with cancer mortality. Men in the lowest SES category had an increased risk of death compared with those in the highest category (for all-cause mortality, hazard ratio = 1.59, 95% confidence interval: 1.21, 2.08; for cardiovascular mortality, hazard ratio = 2.48, 95% confidence interval: 1.55, 3.92). Network score and marital status combined explained 27% (95% confidence interval: 14, 43) and 29% (95% confidence interval: 17, 52) of the associations between SES and all-cause and cardiovascular mortality, respectively. In women, there was no consistent association between social support indicators and mortality. The present study suggests that in men, social isolation is not only an important risk factor for mortality but is also likely to contribute to differences in mortality by SES.