Does the S-H Bond Always Break after Adsorption of an Alkylthiol on Au(111)?

The reaction mechanism for the formation of alkyl thiol self-assembled monolayers (SAM) on Au(111) is still not clearly understood. Especially, the role of defects on the chemisorption process is an important goal to be addressed. In this work, different minimum energy reaction paths for R-SH dissociation of thiols (with long and short chains and dithiol species) adsorbed on gold adatom are calculated by using periodic density functional theory (DFT). Our results show a lower energy barrier for the RS-H bond dissociation when two thiols are adsorbed per adatom. In addition, in contrast with the formation of an adatom at the Au(111) which has been shown to depend on the alkyl chain length, the activation energy of the RS-H bond dissociation of thiols adsorbed on an adatom was shown to be independent of the alkyl chain length. The presented results and derived hypothesis support the model that thiols with long alkyl chain thiols mainly adsorb molecularly on Au(111), while for short alkyl chain thiols the S-H bond breaks. This result is explained by the fact that short-chain thiols have lower interchain interaction energies and are thus more mobile compared to the long alkyl chain thiols on the Au(111) surface. This feature enables the short chains to reach adequate geometries, driven by entropy, which could deform the Au(111) more drastically and probably pull Au atoms out from surface to form adatoms. With these results a new mechanism is proposed for the formation of alkyl chain thiols on Au(111).

Prenatal exposure to bisphenol A and phthalates and childhood respiratory tract infections and allergy.

BACKGROUND: There is growing concern that prenatal exposure to bisphenol A (BPA) and phthalates, which are widely used in consumer products, might affect susceptibility to infections and the development of allergy and asthma in children, but there are currently very few prospective studies. OBJECTIVE: We sought to evaluate whether prenatal exposure to BPA and phthalates increases the risk of respiratory and allergic outcomes in children at various ages from birth to 7 years. METHODS: We measured BPA and metabolites of high-molecular-weight phthalates, 4 di-(2-ethylhexyl) phthalate (DEHP) metabolites (Σ4DEHP) and mono-benzyl phthalate (MBzP), and 3 low-molecular-weight phthalate (LMWP) metabolites (Σ3LMWP) in urine samples collected during the first and third trimesters in pregnant women participating in the Infancia y Medio Ambiente-Sabadell birth cohort study. The occurrence of chest infections, bronchitis, wheeze, and eczema in children was assessed at ages 6 and 14 months and 4 and 7 years through questionnaires given to the mothers. Atopy (specific IgE measurement) and asthma (questionnaire) were assessed at ages 4 and 7 years, respectively. RESULTS: The relative risks (RRs) of wheeze (RR, 1.20; 95% CI, 1.03-1.40; P = .02), chest infections (RR, 1.15; 95% CI, 1.00-1.32; P = .05), and bronchitis (RR, 1.18; 95% CI, 1.01-1.37; P = .04) at any age increased for each doubling in concentration of maternal urinary BPA. Σ4DEHP metabolites were associated with the same outcomes (wheeze: RR, 1.25; 95% CI, 1.04-1.50, P = .02; chest infections: RR, 1.15; 95% CI, 0.97-1.35; P = .11; bronchitis: RR, 1.20; 95% CI, 1.01-1.43; P = .04). MBzP was associated with higher risk of wheeze (RR, 1.15; 95% CI, 1.00-1.33; P = .05). The risk of asthma at age 7 years was also increased with increasing prenatal BPA, Σ4DEHP, and MBzP exposure. There were no other exposure-outcome associations. CONCLUSIONS: Prenatal exposure to BPA and high-molecular-weight phthalates might increase the risk of asthma symptoms and respiratory tract infections throughout childhood.

Exposure to bisphenol A during pregnancy and child neuropsychological development in the INMA-Sabadell cohort.

BACKGROUND: Bisphenol A (BPA) may be a neurodevelopmental toxicant, but evidence is not consistent in terms of the sex-specific patterns of the associations and the specific behavioral or cognitive domains most affected. OBJECTIVE: To examine the effects of prenatal BPA exposure on cognitive, psychomotor, and behavioral development in 438 children at 1, 4 and 7 years of age. METHODS: BPA was measured in spot urine samples collected in trimester 1 and 3 of pregnancy from women participating in the INMA-Sabadell birth cohort study. Cognitive and psychomotor development was assessed at 1 and 4 years using psychologist-based scales. Attention deficit hyperactivity disorder (ADHD) symptoms and other behavioral problems were assessed at 4 years by teachers and at 7 years by parents using questionnaire-based rating scales. RESULTS: Geometric mean creatinine-adjusted BPA concentration of the averaged samples was 2.6 µg/g creatinine. BPA exposure was not associated with the cognitive scores or their subscales at 1 and 4 years of age. At 1 year of age, exposure in the highest tertile of BPA concentrations was associated with a reduction of psychomotor scores (T3 vs T1 ß=-4.28 points, 95% CI: -8.15, -0.41), but there was no association with psychomotor outcomes at 4 years. At 4 years, BPA exposure was associated with an increased risk of ADHD-hyperactivity symptoms (Incidence Rate Ratio (IRR) per log10 µg BPA/g creatinine increase=1.72; 1.08, 2.73) and this association was stronger in boys than in girls. Further, boys had an increased risk of ADHD-inattention symptoms whereas girls showed a reduced risk (p for interaction <0.1). At 7 years, these associations were not statistically significant nor were any other behavioral problems. CONCLUSIONS: These results suggest that prenatal BPA exposure does not affect cognitive development up to age 4 years. Associations are observed with psychomotor development and ADHD-related symptoms at early ages, but these do not appear to persist until later ages.

Characterization of two-dimensional chiral self-assemblies L- and D-methionine on Au(111).

A combination of XPS, in situ RAIRS, LEED, and STM experiments together with ab initio DFT calculations were used to elucidate the self-assembly properties at the atomic level, and enabled the interpretation of the expression of surface chirality upon adsorption of both enantiomers of methionine on a clean Au(111) surface under UHV conditions. The combination of experimental results, in particular, LEED and STM data with quantum chemical calculations is shown to be a successful setup strategy for addressing this challenge. It was found that the methionine molecular self-assembly consists of the first molecule lying parallel to the gold surface and the second interacting with the first methionine through a 2D H-bond network. The interaction with the gold surface is weak. The stability of the assembly is mainly due to the presence of intermolecular H bonds, resulting in the formation of ziplike dimer rows on the Au(111) surface. The methionine molecules interact with each other via their amino acid functional groups. The assembly shows an asymmetric pattern due to a slightly different orientation of the methionine molecules with respect to the surface. Simulations of the STM image of methionine assemblies were consistent with the experimental STM image. The present study shows another example of Au(111) stabilizing a self-assembled biological layer, which is not chemically perturbed by the surface.

Mapping the affinity of aluminum(III) for biophosphates: interaction mode and binding affinity in 1 : 1 complexes.

The interaction of aluminum with biomolecular building blocks is a topic of interest as a first step to understand the potential toxic effects of aluminum in biosystems. Among the different molecules that aluminum can bind in a biological environment, phosphates are the most likely ones, due to their negatively charged nature. In the present paper, we combined DFT quantum mechanical calculations with the implicit solvent effect in order to characterize the interaction of Al(III) with these molecules. An extended set composed of a total of 59 structures was investigated, which includes various types of phosphates (monoester, diester, triester-phosphates) and various phosphate units (mono-, di- and tri-phosphate), considering various charge and protonation states, and different binding modes. The goal is to unveil the preferential interaction mode of Al(III) with phosphates in 1 : 1 complexes. Our results reveal that Al(III) prefers to form dicoordinated complexes with two phosphates, in which the interaction with each of the phosphates is of monodentate character. Our results also suggest a high affinity for binding basic phosphate groups, pointing to ATP, phosphorylated peptides, and basic diphosphates (such as 2,3-DPG) as strong aluminum chelators.

Prenatal bisphenol a urine concentrations and early rapid growth and overweight risk in the offspring.

BACKGROUND: Increasing experimental evidence suggests that prenatal bisphenol A (BPA) exposure induces offspring weight gain, but these effects remain largely unexplored in humans. We examined the effects of prenatal BPA exposure on postnatal growth and obesity. METHODS: BPA concentrations were measured in two spot-urine samples collected in the 1st and 3rd trimesters of pregnancy from mothers in a Spanish birth cohort study (n = 402). We used the average of the two creatinine-adjusted BPA concentrations as the exposure variable. Rapid child growth was defined as a weight gain Z score >0.67 in the first 6 months of life. Age- and sex-specific Z scores for body mass index (BMI) were calculated at age 14 months and 4 years, based on the World Health Organization referent; overweight was defined as a BMI Z score greater than or equal to the 85th percentile. Age- and sex-specific waist circumference Z scores were calculated at age 14 months and 4 years using the analysis population mean. RESULTS: Twenty-six percent of children were rapid growers; 25% were overweight at 14 months and 21% at 4 years. Geometric mean BPA concentrations were 2.6 µg/g creatinine (standard deviation = 2.3) in 1st trimester and 2.0 (2.3) in 3rd trimester samples (Pearson r = 0.13). At 4 years, BPA exposure was associated with increased waist circumference (ß per log10 µg/g = 0.28 [95% confidence interval = 0.01 to 0.57]) and BMI (ß = 0.28 [-0.06 to 0.63]). BPA was not associated with obesity-related outcomes at earlier ages. CONCLUSIONS: This study provides some evidence for an association between prenatal BPA exposure and obesity-related outcomes in childhood, although not in infancy. The large uncertainties in BPA exposure assessment require that findings be interpreted with caution.

Chlorine-enhanced surface mobility of Au(100).

Motivated by experimental studies of two-dimensional Ostwald ripening on Au(100) electrodes in chlorine-containing electrolytes, we have studied diffusion processes using density functional theory. We find that chlorine has a propensity to temporary form AuCl complexes, which diffuse significantly faster than gold adatoms. With and without chlorine, the lowest activation energy is found for the exchange mechanism. Chlorine furthermore reduces the activation energy for the detachment from kink sites. Kinetic Monte Carlo simulations were performed on the basis of extensive density functional theory calculations. The island-decay rate obtained from these Monte Carlo simulations, as well as the decay rate obtained from the theoretical activation energies and frequency factors when inserted into analytical solutions for Ostwald ripening, are in agreement with experimental island-decay rates in chlorine-containing electrolytes.

Effect of coverage and defects on the adsorption of propanethiol on Au(111) surface: a theoretical study.

Periodic density functional calculations have been carried out to investigate both the thiol adsorption on Au(111) surface and the reaction mechanism for the formation of the self-assembled monolayers, taking propanethiol as a representative example. The effect of coverage and surface defects (adatoms and vacancies) has been analyzed. It is found that the most stable physisorption (undissociated) site is an adatom site, whereas the chemisorption site for the thiol is a vacancy site or protrusion consisting of a pair of adatoms, followed by one adatom site. The results point out that the thiolate self-assembled monolayer adsorption process occurs preferentially on step edges.

Exposure to Bisphenol A and Phthalates during Pregnancy and Ultrasound Measures of Fetal Growth in the INMA-Sabadell Cohort.

BACKGROUND: Prenatal exposure to bisphenol A (BPA) and phthalates may affect fetal growth; however, previous findings are inconsistent and based on few studies. OBJECTIVES: We assessed whether prenatal exposure to BPA and phthalates was associated with fetal growth in a Spanish birth cohort of 488 mother-child pairs. METHODS: We measured BPA and eight phthalates [four di(2-ethylhexyl) phthalate metabolites (DEHPm), mono-benzyl phthalate (MBzP), and three low-molecular-weight phthalate metabolites (LMWPm)] in two spot-urine samples collected during the first and third trimester of pregnancy. We estimated growth curves for femur length (FL), head circumference (HC), abdominal circumference (AC), biparietal diameter (BPD), and estimated fetal weight (EFW) during pregnancy (weeks 12-20 and 20-34), and for birth weight, birth length, head circumference at birth, and placental weight. RESULTS: Overall, results did not support associations of exposure to BPA or DEHPm during pregnancy with fetal growth parameters. Prenatal MBzP exposure was positively associated with FL at 20-34 weeks, resulting in an increase of 3.70% of the average FL (95% CI: 0.75, 6.63%) per doubling of MBzP concentration. MBzP was positively associated with birth weight among boys (48 g; 95% CI: 6, 90) but not in girls (-27 g; 95% CI: -79, 25) (interaction p-value = 0.04). The LMWPm mono-n-butyl phthalate (MnBP) was negatively associated with HC at 12-20 pregnancy weeks [-4.88% of HC average (95% CI: -8.36, -1.36%)]. CONCLUSIONS: This study, one of the first to combine repeat exposure biomarker measurements and multiple growth measures during pregnancy, finds little evidence of associations of BPA or phthalate exposures with fetal growth. Phthalate metabolites MBzP and MnBP were associated with some fetal growth parameters, but these findings require replication. CITATION: Casas M, Valvi D, Ballesteros-Gomez A, Gascon M, Fernández MF, Garcia-Esteban R, Iñiguez C, Martínez D, Murcia M, Monfort N, Luque N, Rubio S, Ventura R, Sunyer J, Vrijheid M. 2016. Exposure to bisphenol A and phthalates during pregnancy and ultrasound measures of fetal growth in the INMA-Sabadell cohort. Environ Health Perspect 124:521-528; http://dx.doi.org/10.1289/ehp.1409190.

Stability of benzalkonium surfactants on hemimicelle-based solid-phase extraction cartridges.

The capability of hemimicelle-based solid-phase extraction cartridges for the preservation of organic compounds after their concentration from water samples was investigated for the first time. The approach is illustrated by studying the stability of benzalkonium homologue (C12, C14 and C16) surfactants (BAS) on monolayers of dodecyl sulphate (SDS) hemimicelles formed on alumina. The stability study included storage of cartridges at room temperature, at 4 and -20 degrees C, during a period of up to 3 months. The influence of water matrix components was also investigated from parallel experiments using spiked distilled, river and wastewater samples. Complete recovery of BAS was obtained for all storage conditions tested. Recoveries were independent on the alkyl chain length of BAS homologues and water matrix. The SPE of BAS on the SDS hemimicelles had a strong stabilizing effect for the target compounds and their analysis can be accomplished after at least 3 months without the necessity of special storage conditions for cartridges. Because of the lack of data, an additional stability study was carried out for BAS in an aqueous matrix using traditional preservation methods such as acidification (pH 2)/refrigeration, addition of formaldehyde (5%)/refrigeration, and freezing (-20 degrees C). Only combination of chemical addition (e.g. nitric acid or formaldehyde)/refrigeration was found effective to preserve BAS in the short term (e.g. for a week), then losses up to 40% were observed for these target compounds after a month.

Dietary and sociodemographic determinants of bisphenol A urine concentrations in pregnant women and children.

Bisphenol A (BPA) exposure during early life may have endocrine-disrupting effects, but the dietary and sociodemographic predictors of BPA exposure during pregnancy and childhood remain unclear. Our aim was to evaluate the correlations between, and sociodemographic and dietary predictors of, serial urinary BPA concentrations measured during pregnancy and childhood in a Spanish birth cohort study. BPA was measured in two spot urine samples collected from 479 women during the first and third trimester of pregnancy and in one urine sample from their 4-year old children (n=130). Average dietary intakes were reported in food frequency questionnaires during the first and third pregnancy trimester and at age 4years. Multivariate mixed models and linear regression models were used to estimate associations between sociodemographic and dietary factors and BPA concentrations. A small, but statistically significant correlation was found between serial maternal BPA concentrations measured during pregnancy (r=0.17). Pregnant women who were younger, less-educated, smoked, and who were exposed to second-hand tobacco smoke (SHS) had higher BPA concentrations than others. BPA concentrations were also higher in children exposed to SHS. High consumption of canned fish during pregnancy was associated with 21% [GM ratio=1.21; 95%CI 1.02, 1.44] and 25% [GM ratio=1.25; 95%CI 1.05, 1.49] higher urinary BPA concentrations in the first and third pregnancy trimester, respectively, compared to the lowest consumption group. This study suggests that canned fish may be a major source of BPA during pregnancy in Spain, a country of high canned fish consumption. Further evaluation of specific BPA exposure sources in the sociodemographic group of younger women who smoke, are exposed to SHS, and have a low educational level is needed. Studies identifying sources of exposure would benefit from repeat BPA measurements and questionnaires specifically focused on dietary and packaging sources.

Extraction and stability of pesticide multiresidues from natural water on a mixed-mode admicellar sorbent.

The suitability of a mixed-mode sorbent made up of admicelles of sodium dodecyl sulphate (SDS) and tetrabutylammonium (TBA) to extract and preserve pesticides from river and underground water was assessed. Pesticides belonging to different structural groups (i.e. triazines, carbamates, phenylureas, anilides, chloroacetanilides, organophosphorus and phenoxyacids), most of them well known by their instability, were selected for this purpose. Extraction of pesticides with the admicellar sorbent was optimized. Percolation of 250 mL of sample through the SPE cartridge, elution with 1 mL of methanol (neutral and basic pesticides) or 2 mL of 0.3M NaOH:methanol (90:10, v/v) (acidic pesticides) and direct analysis of the extract by liquid chromatography/UV detection, permitted to obtain method detection limits in the range 2-60 ng L(-1). Their degradation on the SPE cartridges after sample percolation was investigated under a variety of experimental conditions, namely darkness, natural illumination and different temperatures (room temperature, 4 °C and -20 °C) for 3 months. Under darkness, most of pesticides were stable for 1 month at room temperature and 3 months at 4 °C. Only atriazine and clorfenvinfos did not follow this general behaviour. No influence of matrix components on the stabilization of pesticides in the admicellar sorbent was observed. The stabilizing capability of surfactant aggregates surpassed that of C18 and black carbon and was similar to that obtained in some polymeric materials, which have the disadvantage of requiring large volumes of solvents for analyte elution. The stabilization of pesticides on the admicellar sorbent was long enough to permit easy shipping and storage of the cartridges in monitorization campaigns.

A simple and rapid extraction method for sensitive determination of perfluoroalkyl substances in blood serum suitable for exposure evaluation.

In this work, we propose a microextraction method based on a new supramolecular solvent (SUPRAS) made up of reverse aggregates of hexanoic acid, combined with liquid chromatography/triple quadrupole mass spectrometry (LC/QQQ MS-MS) for the determination of the perfluoroalkyl substances (PFASs) in blood serum. A SUPRAS is a nano-structured liquid made up of surfactant aggregates synthesized through a self-assembly process. The method involved the acidification of 765 µL of blood serum (600 µmol of hydrochloric acid per mL of serum) followed by the addition of hexanoic acid (97 µL) and tetrahydrofuran (THF) (600 µL), conditions under which the supramolecular solvent (∼360 µL) formed in situ after vortex-shaking and centrifugation. Parameters affecting extraction efficiency and concentration factors were studied. The overall sample treatment took only 20 min and several samples (20-30) can be simultaneously analyzed using conventional lab equipments, making additional investments unnecessary. Recoveries for the internal standards in samples ranged from 75 to 89% with relative standard deviations between 1 and 15%. Calibration was based on the use of internal standards. The method was very sensitive with detection limits ranging from 2 to 20 pg mL(-1) for PFASs. The approach developed was successfully applied to the determination of PFASs in different blood serum samples. The concentration of PFASs found in samples of animal origin ranged between 17 and 197.3 pg mL(-1) and between 84 and 5168 pg mL(-1) in samples of human origin. Both the analytical and operational features of this method make it suitable for the evaluation of exposure to PFASs.

Analysis of perfluorinated compounds in biota by microextraction with tetrahydrofuran and liquid chromatography/ion isolation-based ion-trap mass spectrometry.

An analytical method combining both a simple, fast and efficient solvent microextraction and a sensitive and selective monitoring mode, based on ion isolation ion-trap mass spectrometry (MS), was developed for analysis of perfluorinated compounds (PFCs) in biota. The method involved the vortex-shaking of 0.2g of tissue sample and 800microL of tetrahydrofuran (THF):water (75:25, v/v) for 7min, subsequent centrifugation for 13min and direct quantitation of PFCs in the extract against solvent-based calibration curves. Selection of solvent composition was based on Hildebrand solubility parameters and their components (i.e. dispersion, dipole-dipole and hydrogen bonding forces). Recoveries in samples for PFCs with hydrocarbon chain lengths between C(4) and C(14) ranged from 85 to 111%, with relative standard deviations between 1 and 11%. The ion isolation monitoring mode, proposed for the first time for ion-trap-MS quantitation, proved to be effective in avoiding space-charge effects caused by co-eluting matrix components while keeping the sensitivity of full scan MS operation. Detection limits of the method were in the range 0.8-6ngg(-1) for perfluoroalkyl carboxylates (PFACs) and 0.4-0.8ngg(-1) for perfluoroalkyl sulfonates (PFASs) in wet weight samples. The method was validated using a reference material made up of flounder muscle and by comparison with triple quadrupole MS measurements and it was applied to the determination of PFCs in liver and muscle samples from sea birds and fishes. Only PFASs were found in samples at quantifiable levels (2.9 and 13.1ngg(-1)) while PFACs were below the respective quantitation limits. This method allows quick and simple microextraction of PFCs with minimal solvent consumption, while delivering accurate and precise data.

Spontaneous nanoripple formation on metallic templates.

Nanoripple structures spontaneously formed at room temperature during chemical and electrochemical deposition of metals, semiconductors, and alloys on gold and copper templates, patterned with nanocavities, have been studied by atomic force microscopy (AFM) and scanning tunneling microscopy (STM). Annealing the templates at approximately equal to 373 K also results in ripple formation. Both experimental results and modeling, including anisotropic surface diffusion, demonstrate that nanocavity size in the template determines the ripple wavelength and amplitude, prior to a final stage of coarsening. Therefore, an ordered array of "nanodefects" introduced in the substrate is able to guide the self-organization of these nanofeatures during their growth, creating the possibility for nanofabrication of parallel interconnections with adjustable periodicity. Ripples are robust nanostructures that can in turn be used as templates for the preparation of hybrid nanostructured surfaces with specific physical properties.

Use of coacervates for the on-site extraction/preservation of polycyclic aromatic hydrocarbons and benzalkonium surfactants.

The suitability of coacervates for the preservation of organic pollutants after their extraction from water samples was investigated for the first time. Acid-induced sodium dodecanesulfonic acid (SDSA) micelle-based coacervates were selected for this purpose. Their capacity to preserve benzalkonium homologue (C(12), C(14) and C(16)) surfactants (BASs) and different polycyclic aromatic hydrocarbons (PAHs) [benzo(a)pyrene (BaP), benzo(b)fluoranthene (BbF), benzo(k)fluoranthene (BkF), benzo(ghi)perylene (BghiP), benzo(a)anthracene (BaA) and indene(1,2,3-c-d)pyrene (IP)] was investigated. BASs and PAHs were efficiently extracted by the coacervate by formation of mixed aggregates and hydrophobic interactions, respectively. Their stability into the coacervate was investigated under three temperature conditions (room temperature, 4 degrees C and -20 degrees C) and two hydrochloric acid concentrations (3.75 M and 4.2 M), which was used to induce coacervation. No losses were observed during at least 3 months at the different experimental conditions tested. The increase of the temperature up to 35 degrees C for a month did not affect the stability of the target compounds. No influence of the water matrix (distilled, river or wastewater) on the stabilization of BASs and PAHs was observed. The high-stabilizing capacity of the coacervate for the target compounds and its low volume make easy the transport and storage of analytes.