UV-Vis quantification of hydroxyl radical concentration and dose using principal component analysis.

Hydroxyl radicals (∙OH) are powerful oxidizing species formed naturally in the environment or artificially produced to destroy contaminants in water treatment facilities. Their short lifetime and high reactivity, however, present a significant challenge to quantifying their concentration in solution. Herein, we developed a novel method to accurately measure the steady-state ∙OH concentration and total ∙OH dose produced during the UV photolysis of hydrogen peroxide (H2O2) by monitoring the loss of salicylic acid (SA). This information can be acquired using only benchtop UV-Vis spectroscopy, thus expanding measurement capabilities of resource-limited laboratories by eliminating the need for sophisticated instrumentation. To improve the precision with which the rate of SA loss was measured compared to previous methods, we applied principal component analysis (PCA) to fit the UV-Vis spectra collected during SA exposure to ∙OH. For our experimental conditions consisting of 12 mL solutions composed of ≤ 100 mM H2O2 and 0.07 mM SA, the steady-state ∙OH concentration throughout the complete photolysis of H2O2 was 1.33 × 10-11 M ± 1.14 × 10-12 M. This represents more than a ten-fold improvement in reducing the uncertainty of the measurement, with respect to narrowing the 95 % confidence interval, compared to a previous method that employed matrix analysis to process the spectra. Furthermore, the variance of the measured ∙OH concentrations was reduced by a factor of 100 compared to previous methods. Using PCA, the limit-of-detection and limit-of-quantitation for ∙OH are 5.33 × 10-13 M and 1.23 × 10-12 M, respectively. By developing quantitative relationships among ∙OH concentration, H2O2 concentration, and UV exposure time, we also show how to calculate the equivalent exposure to ∙OH generated in natural aquatic environments by indirect photolysis. Finally, we use this methodology to demonstrate that the presence of suspended carbonaceous nanoparticles at concentrations as high as 300 ppm does not affect ∙OH concentration.

The State-of-the-Art of Sensors and Environmental Monitoring Technologies in Buildings.

Building energy consumption accounts for 30%-45% of the global energy demand. With an ever-increasing world population, it has now become essential to minimize the energy consumption for the future of the environment. One of the most crucial aspects in this regard is the utilization of sensing and environmental monitoring technologies in buildings as these technologies provide stakeholders, such as owners, designers, managers, and occupants, with important information regarding the energy performance, safety and cost-effectiveness of the building. With the global sensors market value predicted to exceed $190 billion by 2021 and the number of sensors deployed worldwide forecasted to reach the '1 Trillion' mark by 2025, a state-of-the-art review of various commercially-viable sensor devices and the wide range of communication technologies that complement them is highly desirable. This paper provides an insight into various sensing and environmental monitoring technologies commonly deployed in buildings by surveying different sensor technologies, wired and wireless communication technologies, and the key selection parameters and strategies for optimal sensor placement. In addition, we review the key characteristics and limitations of the most prominent battery technologies in use today, different energy harvesting sources and commercial off-the-shelf solutions, and various challenges and future perspectives associated with the application of sensing and environmental monitoring technologies within buildings.

The role of the dihedral angle and excited cation states in ionization and dissociation of mono-halogenated biphenyls; a combined experimental and theoretical coupled cluster study.

We present a combined theoretical and experimental study on the ionization and primary fragmentation channels of the mono-halogenated biphenyls; 2-chlorobiphenyl, 2-bromobiphenyl and 2-iodobiphenyl. The ionization energies (IEs) of the 2-halobiphenyls and the appearance energies (AEs) of the principal fragments are determined through electron impact ionization, while quantum mechanical calculations at the coupled cluster level of theory are used to elucidate the observed processes and the associated dynamics. The primary fragmentation channels are the direct loss of the halogen upon ionization, the loss of the respective hydrogen halides (HX) as well as loss of the hydrogen halide and an additional hydrogen. We find that the dihedral angle strongly influences the relative potential energy of the neutral and the cation on their respective ground state surfaces, an effect caused by the strong influence of the nuclear motion on the conjugation between the phenyl rings. For the principal dissociative ionization channels from the mono-halogenated biphenyls we reason that these can not be described as statistical decay from the ground state cation, but must rather be understood as direct, state-selective processes from specific excited cationic states characterized through local ionization of either the halogenated or the non-substituted phenyl ring.

Amplified cross-linking efficiency of self-assembled monolayers through targeted dissociative electron attachment for the production of carbon nanomembranes.

The determination of the negative ion yield of 2'-chloro-1,1'-biphenyl (2-Cl-BP), 2'-bromo-1,1'-biphenyl (2-Br-BP) and 2'-iodo-1,1'-biphenyl (2-I-BP) upon dissociative electron attachment (DEA) at an electron energy of 0 eV revealed cross section values that were more than ten times higher for iodide loss from 2-I-BP than for the other halogenides from the respective biphenyls (BPs). Comparison with dissociative ionization mass spectra shows that the ratio of the efficiency of electron impact ionization induced fragmentation of 2-I-BP, 2-Br-BP, and 2-Cl-BP amounts to approximately 1:0.7:0.6. Inspired by these results, self-assembled monolayers (SAMs) of the respective biphenyl-4-thiols, 2-Cl-BPT, 2-Br-BPT, 2-I-BPT as well as BPT, were grown on a Au(111) substrate and exposed to 50 eV electrons. The effect of electron irradiation was investigated by X-ray photoelectron spectroscopy (XPS), to determine whether the high relative DEA cross section for iodide loss from 2-I-BPT as compared to 2-Br-BP and 2-Cl-BP is reflected in the cross-linking efficiency of SAMs made from these materials. Such sensitization could reduce the electron dose needed for the cross-linking process and may thus lead to a significantly faster conversion of the respective SAMs into carbon nanomembranes (CNMs) without the need for an increased current density. XPS data support the notation that DEA sensitization may be used to achieve more efficient electron-induced cross-linking of SAMs, revealing more than ten times faster cross-linking of 2-I-BPT SAMs compared to those made from the other halogenated biphenyls or from native BPT at the same current density. Furthermore, the transfer of a freestanding membrane onto a TEM grid and the subsequent investigation by helium ion microscopy (HIM) verified the existence of a mechanically stable CNM created from 2-I-BPT after exposure to an electron dose as low as 1.8 mC/cm2. In contrast, SAMs made from BPT, 2-Cl-BPT and 2-Br-BPT did not form stable CNMs after a significantly higher electron dose of 9 mC/cm2.

Comparing postdeposition reactions of electrons and radicals with Pt nanostructures created by focused electron beam induced deposition.

The ability of electrons and atomic hydrogen (AH) to remove residual chlorine from PtCl2 deposits created from cis-Pt(CO)2Cl2 by focused electron beam induced deposition (FEBID) is evaluated. Auger electron spectroscopy (AES) and energy-dispersive X-ray spectroscopy (EDS) measurements as well as thermodynamics calculations support the idea that electrons can remove chlorine from PtCl2 structures via an electron-stimulated desorption (ESD) process. It was found that the effectiveness of electrons to purify deposits greater than a few nanometers in height is compromised by the limited escape depth of the chloride ions generated in the purification step. In contrast, chlorine atoms can be efficiently and completely removed from PtCl2 deposits using AH, regardless of the thickness of the deposit. Although AH was found to be extremely effective at chemically purifying PtCl2 deposits, its viability as a FEBID purification strategy is compromised by the mobility of transient Pt-H species formed during the purification process. Scanning electron microscopy data show that this results in the formation of porous structures and can even cause the deposit to lose structural integrity. However, this phenomenon suggests that the use of AH may be a useful strategy to create high surface area Pt catalysts and may reverse the effects of sintering. In marked contrast to the effect observed with AH, densification of the structure was observed during the postdeposition purification of PtC x deposits created from MeCpPtMe3 using atomic oxygen (AO), although the limited penetration depth of AO restricts its effectiveness as a purification strategy to relatively small nanostructures.

Protein degradation rate is the dominant mechanism accounting for the differences in protein abundance of basal p53 in a human breast and colorectal cancer cell line.

We determine p53 protein abundances and cell to cell variation in two human cancer cell lines with single cell resolution, and show that the fractional width of the distributions is the same in both cases despite a large difference in average protein copy number. We developed a computational framework to identify dominant mechanisms controlling the variation of protein abundance in a simple model of gene expression from the summary statistics of single cell steady state protein expression distributions. Our results, based on single cell data analysed in a Bayesian framework, lends strong support to a model in which variation in the basal p53 protein abundance may be best explained by variations in the rate of p53 protein degradation. This is supported by measurements of the relative average levels of mRNA which are very similar despite large variation in the level of protein.

Oxygen-promoted catalyst sintering influences number density, alignment, and wall number of vertically aligned carbon nanotubes.

A lack of synthetic control and reproducibility during vertically aligned carbon nanotube (CNT) synthesis has stifled many promising applications of organic nanomaterials. Oxygen-containing species are particularly precarious in that they have both beneficial and deleterious effects and are notoriously difficult to control. Here, we demonstrated diatomic oxygen's ability, independent of water, to tune oxide-supported catalyst thin film dewetting and influence nanoscale (diameter and wall number) and macro-scale (alignment and density) properties for as-grown vertically aligned CNTs. In particular, single- or few-walled CNT forests were achieved at very low oxygen loading, with single-to-multi-walled CNT diameters ranging from 4.8 ± 1.3 nm to 6.4 ± 1.1 nm over 0-800 ppm O2, and an expected variation in alignment, where both were related to the annealed catalyst morphology. Morphological differences were not the result of subsurface diffusion, but instead occurred via Ostwald ripening under several hundred ppm O2, and this effect was mitigated by high H2 concentrations and not due to water vapor (as confirmed in O2-free water addition experiments), supporting the importance of O2 specifically. Further characterization of the interface between the Fe catalyst and Al2O3 support revealed that either oxygen-deficit metal oxide or oxygen-adsorption on metals could be functional mechanisms for the observed catalyst nanoparticle evolution. Taken as a whole, our results suggest that the impacts of O2 and H2 on the catalyst evolution have been underappreciated and underleveraged in CNT synthesis, and these could present a route toward facile manipulation of CNT forest morphology through control of the reactive gaseous atmosphere alone.

Cardiac changes in anorexia nervosa.

UNLABELLED: Introduction Anorexia nervosa is an eating disorder, which is associated with many different medical complications as a result of the weight loss and malnutrition that characterise this illness. It has the highest mortality rate of any psychiatric disorder. A large portion of deaths are attributable to the cardiac abnormalities that ensue as a result of the malnutrition associated with anorexia nervosa. In this review, the cardiac complications of anorexia nervosa will be discussed. METHODS: A comprehensive literature review on cardiac changes in anorexia nervosa was carried out. RESULTS: There are structural, functional, and rhythm-type changes that occur in patients with anorexia nervosa. These become progressively significant as ongoing weight loss occurs. CONCLUSION: Cardiac changes are inherent to anorexia nervosa and they become more life-threatening and serious as the anorexia nervosa becomes increasingly severe. Weight restoration and attention to these cardiac changes are crucial for a successful treatment outcome.

Electron induced surface reactions of organometallic metal(hfac)2 precursors and deposit purification.

The elementary processes associated with electron beam-induced deposition (EBID) and post-deposition treatment of structures created from three metal(II)(hfac)2 organometallic precursors (metal = Pt, Pd, Cu; hfac = CF3C(O)CHC(O)CF3) have been studied using surface analytical techniques. Electron induced reactions of adsorbed metal(II)(hfac)2 molecules proceeds in two stages. For comparatively low electron doses (doses <1 × 10(17) e(-)/cm(2)) decomposition of the parent molecules leads to loss of carbon and oxygen, principally through the formation of carbon monoxide. Fluorine and hydrogen atoms are also lost by electron stimulated C-F and C-H bond cleavage, respectively. Collectively, these processes are responsible for the loss of a significant fraction (≥ 50%) of the oxygen and fluorine atoms, although most (>80%) of the carbon atoms remain. As a result of these various transformations the reduced metal atoms become encased in an organic matrix that is stabilized toward further electron stimulated carbon or oxygen loss, although fluorine and hydrogen can still desorb in the second stage of the reaction under the influence of sustained electron irradiation as a result of C-F and C-H bond cleavage, respectively. This reaction sequence explains why EBID structures created from metal(II)(hfac)2 precursors in electron microscopes contain reduced metal atoms embedded within an oxygen-containing carbonaceous matrix. Except for the formation of copper fluoride from Cu(II)(hfac)2, because of secondary reactions between partially reduced copper atoms and fluoride ions, the chemical composition of EBID films and behavior of metal(II)(hfac)2 precursors was independent of the transition metal's chemical identity. Annealing studies of EBID structures created from Pt(II)(hfac)2 suggest that the metallic character of deposited Pt atoms could be increased by using post deposition annealing or elevated substrate temperatures (>25 °C) during deposition. By exposing EBID structures created from Cu(II)(hfac)2 to atomic oxygen followed by atomic hydrogen, organic contaminants could be abated without annealing.

Absolute quantification of protein copy number using a single-molecule-sensitive microarray.

We report the use of a microfluidic microarray incorporating single molecule detection for the absolute quantification of protein copy number in solution. In this paper we demonstrate protocols which enable calibration free detection for two protein detection assays. An EGFP protein assay has a limit of detection of <30 EGFP proteins in a microfluidic analysis chamber (limited by non-specific background binding), with a measured limit of linearity of approximately 6 × 10(6) molecules of analyte in the analysis chamber and a dynamic range of >5 orders of magnitude in protein concentration. An antibody sandwich assay was used to detect unlabelled human tumour suppressor protein p53 with a limit of detection of approximately 21 p53 proteins and a dynamic range of >3 orders of magnitude. We show that these protocols can be used to calibrate data retrospectively to determine the absolute protein copy number at the single cell level in two human cancer cell lines.

Scaling advantages and constraints in miniaturized capture assays for single cell protein analysis.

Measuring protein expression in single cells is the basis of single cell proteomics. The sensitivity and dynamic range of a single cell immunoassay should ideally be such that proteins that are expressed between 1-10(6) copies per cell can be detected and counted. We have investigated the effect of miniaturizing antibody microarrays by reducing capture spot sizes from 100 µm to 15 µm using dip-pen nanolithography. We demonstrate that protocols developed for printing and passivating antibody capture spots using conventional pin-based contact printing can be directly transferred to dip-pen lithography whilst retaining the capture activity per unit area. Using a simple kinetic model, we highlight how the limit of detection and dynamic range of a sandwich immunoassay, respectively, increase and decrease when spot size is reduced. However, we show that reducing spot size is more effective than increasing assay chamber volume when seeking to multiplex such a microfluidic immunoassay. Although we make particular reference to single cell microfluidic immunoassays, the topics discussed here are applicable to capture assays in general.

Electron induced reactions of surface adsorbed tungsten hexacarbonyl (W(CO)6).

Tungsten hexacarbonyl (W(CO)(6)) is frequently used as an organometallic precursor to create metal-containing nanostructures in electron beam induced deposition (EBID). However, the fundamental electron stimulated reactions responsible for both tungsten deposition and the incorporation of carbon and oxygen atom impurities remain unclear. To address this issue we have studied the effect of 500 eV incident electrons on nanometer thick films of W(CO)(6) under Ultra-High Vacuum (UHV) conditions. Results from X-ray Photoelectron Spectroscopy, Mass Spectrometry, and Infrared Spectroscopy reveal that the initial step involves electron stimulated desorption of multiple CO ligands from parent W(CO)(6) molecules and the formation of partially decarbonylated tungsten species (W(x)(CO)(y)). Subsequent electron interactions with these W(x)(CO)(y) species lead to ligand decomposition rather than further CO desorption, ultimately producing oxidized tungsten atoms incorporated in a carbonaceous matrix. The presence of co-adsorbed water during electron irradiation increased the extent of tungsten oxidation. The electron stimulated deposition cross-section of W(CO)(6) at an incident electron energy of 500 eV was calculated to be 6.50 × 10(-16) cm(-2). When considered collectively with findings from previous precursors (MeCpPtMe(3) and Pt(PF(3))(4)), results from the present study are consistent with the idea that the electron induced reactions in EBID are initiated by low energy secondary electrons generated by primary beam-substrate interactions, rather than by the primary beam itself.

Ultraviolet photofragmentation spectroscopy of alkaline earth dication complexes with pyridine and 4-picoline (4-methyl pyridine).

A detailed experimental and theoretical study has been undertaken of the UV photofragmentation spectroscopy of the alkaline earth metal dications Mg(2+), Ca(2+), and Sr(2+) complexed with pyridine and 4-methyl pyridine (4-picoline). The ion complexes have been prepared using the pick-up technique and held in an ion trap where their internal temperature has been reduced to <150 K. Exposure of the trapped ions to tunable UV laser radiation leads to the appearance of photofragments with intensities that show significant variation as a function of wavelength. For all three metal dications, the resultant spectra show evidence of resolved features. Time-dependent density functional theory (TDDFT) has been used to identify possible electronic transitions that might be present in the [M(pyridine)(4)](2+) complexes (M = Mg, Ca, and Sr) within the wavelength range studied. These calculations show that the spectra are dominated by strong π* ← π and weaker π* ← n transitions localized on the pyridine ligands. The calculations correctly identify those regions of the experimental spectra where UV transitions begin to occur in the complexes and also the wavelengths at which absorption maxima are reached; however, more subtle features of the spectra are difficult to assign with confidence.