Role of SiNx Barrier Layer on the Performances of Polyimide Ga2O3-doped ZnO p-i-n Hydrogenated Amorphous Silicon Thin Film Solar Cells

In this study, silicon nitride (SiN_x) thin films were deposited on polyimide (PI) substrates as barrier layers by a plasma enhanced chemical vapor deposition (PECVD) system. The gallium-doped zinc oxide (GZO) thin films were deposited on PI and SiN_x/PI substrates at room temperature (RT), 100 and 200 °C by radio frequency (RF) magnetron sputtering. The thicknesses of the GZO and SiN_x thin films were controlled at around 160 ± 12 nm and 150 ± 10 nm, respectively. The optimal deposition parameters for the SiN_x thin films were a working pressure of 800 × 10⁻³ Torr, a deposition power of 20 W, a deposition temperature of 200 °C, and gas flowing rates of SiH₄ = 20 sccm and NH₃ = 210 sccm, respectively. For the GZO/PI and GZO-SiN_x/PI structures we had found that the GZO thin films deposited at 100 and 200 °C had higher crystallinity, higher electron mobility, larger carrier concentration, smaller resistivity, and higher optical transmittance ratio. For that, the GZO thin films deposited at 100 and 200 °C on PI and SiN_x/PI substrates with thickness of ~000 nm were used to fabricate p-i-n hydrogenated amorphous silicon (α-Si) thin film solar cells. 0.5% HCl solution was used to etch the surfaces of the GZO/PI and GZO-SiN_x/PI substrates. Finally, PECVD system was used to deposit α-Si thin film onto the etched surfaces of the GZO/PI and GZO-SiN_x/PI substrates to fabricate α-Si thin film solar cells, and the solar cells’ properties were also investigated. We had found that substrates to get the optimally solar cells’ efficiency were 200 °C-deposited GZO-SiN_x/PI.     

Synthesis,Crystal Structure and Luminescent Property of Cd (II) Complex with N-Benzenesulphonyl-L-leucine

A new trinuclear Cd (II) complex [Cd₃(L)₆(2,2-bipyridine)₃] [L = N-phenylsulfonyl-L-leucinato] has been synthesized and characterized by elemental analysis, IR and X-ray single crystal diffraction analysis. The results show that the complex belongs to the orthorhombic, space group P2₁2₁2₁ with a = 16.877(3) Å, b = 22.875(5) Å, c = 29.495(6) Å, α = β = γ = 90°, V = 11387(4) ų, Z = 4, D_c= 1.416 μg·m⁻³, μ = 0.737 mm⁻¹, F (000) = 4992, and final R₁ = 0.0390, ωR₂ = 0.0989. The complex comprises two seven-coordinated Cd (II) atoms, with a N₂O₅ distorted pengonal bipyramidal coordination environment and a six-coordinated Cd (II) atom, with a N₂O₄ distorted octahedral coordination environment. The molecules form one dimensional chain structure by the interaction of bridged carboxylato groups, hydrogen bonds and π-π interaction of 2,2-bipyridine. The luminescent properties of the Cd (II) complex and N-Benzenesulphonyl-L-leucine in solid and in CH₃OH solution also have been investigated.     

SAXS Studies of the Endoglucanase Cel12A from Gloeophyllum trabeum Show Its Monomeric Structure and Reveal the Influence of Temperature on the Structural Stability of the Enzyme

Endoglucanases are key enzymes applied to the conversion of biomass aiming for second generation biofuel production. In the present study we obtained the small angle X-ray scattering (SAXS) structure of the G. trabeum endo-1,4-β-glucanase Cel12A and investigated the influence of an important parameter, temperature, on both secondary and tertiary structure of the enzyme and its activity. The CD analysis for GtCel12A revealed that changes in the CD spectra starts at 55 °C and the T_m calculated from the experimental CD sigmoid curve using the Boltzmann function was 60.2 ± 0.6 °C. SAXS data showed that GtCel12A forms monomers in solution and has an elongated form with a maximum diameter of 60 ± 5 Å and a gyration radius of 19.4 ± 0.1 Å as calculated from the distance distribution function. Kratky analysis revealed that 60 °C is the critical temperature above which we observed clear indications of denaturation. Our results showed the influence of temperature on the stability and activity of enzymes and revealed novel structural features of GtCel12A.     

Synthesis,Crystal Structure and Luminescent Property of Mg(II) Complex with N-Benzenesulphonyl-L-Leucine and 1,10-Phenanthroline

A new complex [Mg(L)₂(phen)(H₂O)₂](phen)(H₂O)₂ [L= N-benzenesulphonyl-L-leucine] was synthesized by the reaction of magnesium chloride hexahydrate with N-benzenesulphonyl-L-leucine and 1,10-phenanthroline in the CH₃CH₂OH/H₂O (v:v = 5:1). It was characterized by elemental analysis, IR and X-ray single crystal diffraction analysis. The crystal of the title complex [Mg(L)₂(phen)(H₂O)₂](phen)(H₂O)₂ belongs to triclinic, space group P-1 with a = 0.72772(15) nm, b = 1.4279(3) nm, c = 1.4418(3) nm, α = 63.53(3)°, β = 79.75(3)°, γ = 81.83(3)°, V = 1.3163(5) nm³, Z =1, D_c= 1.258 μg·m⁻³, μ = 0.177 mm⁻¹, F(000) = 526, and final R₁ = 0.0506, ωR₂ = 0.1328. The complex comprises a six-coordinated magnesium(II) center, with a N₂O₄ distorted octahedron coordination environment. The molecules are connected by hydrogen bonds and π-π stacking to form one dimensional chain structure. The luminescent property of the Mg(II) complex has been investigated in solid.     

TiB2-Based Composites for Ultra-High-Temperature Devices,Fabricated by SHS,Combining Strong and Weak Exothermic Reactions

TiB₂-based ceramic matrix composites (CMCs) were fabricated using elemental powders of Ti, B and C. The self-propagating high temperature synthesis (SHS) was carried out for the highly exothermic “in situ” reaction of TiB₂ formation and the “tailing” synthesis of boron carbide characterized by weak exothermicity. Two series of samples were fabricated, one of them being prepared with additional milling of raw materials. The effects of TiB₂ vol fraction as well as grain size of reactant were investigated. The results revealed that combustion was not successful for a TiB₂:B₄C molar ratio of 0.96, which corresponds to 40 vol% of TiB₂ in the composite, however the SHS reaction was initiated and self-propagated for the intended TiB₂:B₄C molar ratio of 2.16 or above. Finally B₁₃C₂ was formed as the matrix phase in each composite. Significant importance of the grain size of the C precursor with regard to the reaction completeness, which affected the microstructure homogeneity and hardness of investigated composites, was proved in this study. The grain size of Ti powder did not influence the microstructure of TiB₂ grains. The best properties (HV = 25.5 GPa, average grain size of 9 μm and homogenous microstructure), were obtained for material containing 80 vol% of TiB₂, fabricated using a graphite precursor of 2 μm.     

Synthesis and Hydrolytic Degradation of Substituted Poly(DL-Lactic Acid)s

Non-substituted racemic poly(DL-lactic acid) (PLA) and substituted racemic poly(DL-lactic acid)s or poly(DL-2-hydroxyalkanoic acid)s with different side-chain lengths, i.e., poly(DL-2-hydroxybutanoic acid) (PBA), poly(DL-2-hydroxyhexanoic acid) (PHA), and poly(DL-2-hydroxydecanoic acid) (PDA) were synthesized by acid-catalyzed polycondensation of DL-lactic acid (LA), DL-2-hydroxybutanoic acid (BA), DL-2-hydroxyhexanoic acid (HA), and DL-2-hydroxydecanoic acid (DA), respectively. The hydrolytic degradation behavior was investigated in phosphate-buffered solution at 80 and 37 °C by gravimetry and gel permeation chromatography. It was found that the reactivity of monomers during polycondensation as monitored by the degree of polymerization (DP) decreased in the following order: LA > DA > BA > HA. The hydrolytic degradation rate traced by DP and weight loss at 80 °C decreased in the following order: PLA > PDA > PHA > PBA and that monitored by DP at 37 °C decreased in the following order: PLA > PDA > PBA > PHA. LA and PLA had the highest reactivity during polymerization and hydrolytic degradation rate, respectively, and were followed by DA and PDA. BA, HA, PBA, and PHA had the lowest reactivity during polymerization and hydrolytic degradation rate. The findings of the present study strongly suggest that inter-chain interactions play a major role in the reactivity of non-substituted and substituted LA monomers and degradation rate of the non-substituted and substituted PLA, along with steric hindrance of the side chains as can be expected.     

Bio-Control of Salmonella Enteritidis in Foods Using Bacteriophages

Two lytic phages, vB_SenM-PA13076 (PA13076) and vB_SenM-PC2184 (PC2184), were isolated from chicken sewage and characterized with host strains Salmonella Enteritidis (SE) ATCC13076 and CVCC2184, respectively. Transmission electron microscopy revealed that they belonged to the family Myoviridae. The lytic abilities of these two phages in liquid culture showed 10⁴ multiplicity of infection (MOI) was the best in inhibiting bacteria, with PC2184 exhibiting more activity than PA13076. The two phages exhibited broad host range within the genus Salmonella. Phage PA13076 and PC2184 had a lytic effect on 222 (71.4%) and 298 (95.8%) of the 311 epidemic Salmonella isolates, respectively. We tested the effectiveness of phage PA13076 and PC2184 as well as a cocktail combination of both in three different foods (chicken breast, pasteurized whole milk and Chinese cabbage) contaminated with SE. Samples were spiked with 1 × 10⁴ CFU individual SE or a mixture of strains (ATCC13076 and CVCC2184), then treated with 1 × 10⁸ PFU individual phage or a two phage cocktail, and incubated at 4 °C or 25 °C for 5 h. In general, the inhibitory effect of phage and phage cocktail was better at 4 °C than that at 25 °C, whereas the opposite result was observed in Chinese cabbage, and phage cocktail was better than either single phage. A significant reduction in bacterial numbers (1.5–4 log CFU/sample, p < 0.05) was observed in all tested foods. The two phages on the three food samples were relatively stable, especially at 4 °C, with the phages exhibiting the greatest stability in milk. Our research shows that our phages have potential effectiveness as a bio-control agent of Salmonella in foods.     

Three-dimensional label-free visualization and quantification of polyhydroxyalkanoates in individual bacterial cell in its native state

Polyhydroxyalkanoates (PHAs) are biodegradable polyesters that are intracellularly accumulated as distinct insoluble granules by various microorganisms. PHAs have attracted much attention as sustainable substitutes for petroleum-based plastics. However, the formation of PHA granules and their characteristics, such as localization, volume, weight, and density of granules, in an individual live bacterial cell are not well understood. Here, we report the results of three-dimensional (3D) quantitative label-free analysis of PHA granules in individual live bacterial cells through measuring the refractive index distributions by optical diffraction tomography (ODT). The formation and growth of PHA granules in the cells of Cupriavidus necator, the best-studied native PHA producer, and recombinant Escherichia coli harboring C. necator poly(3-hydroxybutyrate) (PHB) biosynthesis pathway are comparatively examined. Through the statistical ODT analyses of the bacterial cells, the distinctive characteristics for density and localization of PHB granules in vivo could be observed. The PHB granules in recombinant E. coli show higher density and localization polarity compared with those of C. necator, indicating that polymer chains are more densely packed and granules tend to be located at the cell poles, respectively. The cells were investigated in more detail through real-time 3D analyses, showing how differently PHA granules are processed in relation to the cell division process in native and nonnative PHA-producing strains. We also show that PHA granule–associated protein PhaM of C. necator plays a key role in making these differences between C. necator and recombinant E. coli strains. This study provides spatiotemporal insights into PHA accumulation inside the native and recombinant bacterial cells.

Due to our increasing concerns on the accumulation of nondegradable plastic wastes, polyhydroxyalkanoates (PHAs), a family of bacterial polyesters, have emerged as a promising alternative to synthetic plastics. PHAs have been attracting much attention because they are biodegradable and possess material properties that are comparable to those of popular synthetic plastics, such as polypropylene and polyethylene (1–4).PHAs are synthesized by numerous bacteria as an energy, carbon, and redox storage material under unbalanced growth conditions in the presence of an excess carbon source. PHAs exist in the form of insoluble granules in the cytoplasm. PHA granules in vivo are amorphous polymers bound by several different enzymes and proteins, such as PHA synthase, PHA depolymerase, regulatory proteins, and other granule-associated proteins, known as phasin and PhaM (5, 6). Through the actions of these enzymes and proteins, microorganisms synthesize and degrade PHAs in response to the environmental condition. For example, Cupriavidus necator (also known as Ralstonia eutropha), which is the model organism for studying poly(3-hydroxybutyrate) (PHB) biosynthesis, accumulates PHB under an unfavorable growth condition, such as a nitrogen- or phosphorus-deficient condition, to store the excess carbon sources inside cells (1, 2). Cells degrade PHB and utilize it for growth and maintenance when needed under balanced growth conditions (1, 2).It has always been amazing to observe cells accumulating such large amounts of polymers inside the cells. Several techniques have been used to observe the dynamic behavior and characteristics of PHA granules in vivo. Fluorescence microscopy (7–9), transmission electron microscopy (TEM) (10, 11), and electron cryotomography (12) have provided information on the shape and localization of PHA granules in bacteria, such as C. necator, Rhodospirillum rubrum, and recombinant Escherichia coli expressing the heterologous PHA biosynthesis genes, under various conditions. However, these studies have provided only two-dimensional image information and/or showed a nonnative state of the cells and PHA granules due to the pretreatment process used (more explanations are provided in SI Appendix, Text S1). Although several models for granule formation have been proposed based on these observations (6, 12–14), many of the details for the formation and characteristics of in vivo PHA granules are still unknown.Here, we present the results of three-dimensional (3D) quantitative analyses for PHA granules in individual live bacterial cells by measuring the refractive index (RI) distribution using optical diffraction tomography (ODT). Formation of PHB granules in the cells of C. necator and recombinant E. coli harboring C. necator PHB biosynthesis genes was monitored with culture time to understand the spatiotemporal formation, growth, and distribution of PHB granules during cell growth. Based on the reconstructed 3D RI, the volumes and weights of cells and PHB granules, PHB content, and PHB granule density could be quantified at a single-cell level. Also, the variations of PHB formation in the individual cells could be obtained through statistical analyses. In addition, we present real-time movies of PHB accumulation in living C. necator and recombinant E. coli cells. These results reveal the distinctive characteristics of in vivo PHA granule formation and distribution in native and nonnative PHA producers.     

Gravitational field of a charged mass point

Adopting, with Schwarzschild, the Einstein gauge (|_μν| = -1), a solution of Einstein's field equations for a charged mass point of mass M and charge Q is derived, which differs from the Reissner-Nordstrøm solution only in that the variable r is replaced by R = (r³ + a³)^⅓, where a is a constant. The Newtonian gravitational potential ψ (2/c²)(1 - g₀₀) obeys exactly the Poisson equation (in the R variable), with the mass density equal to (E²/4πc²), E denoting the electric field. ψ also obeys a second linear equation in which the operator on ψ is the square root of the Laplacian operator. The electrostatic potential Φ (= Q/R), ψ, and all the components of the curvature tensor remain finite at the origin of coordinates. The electromagnetic energy of the point charge is finite and equal to (Q²/a). The charge Q defines a pivotal mass M^* = (Q/G^½). If M < M^*, then the whole mass is electromagnetic. If M > M^*, the electromagnetic part of the mass M_em equals [M - (M² - M^*2)^½], whereas the material part of the mass M_mat equals (M² - M^*2)^½. When M > M^*, the constant a is determined, following Schwarzschild, by shrinking the “Schwarzschild radius” to zero. When M < M^*, a is determined so as to make the gravitational acceleration vanish at the origin.     

Microstructure and Wear Properties of Laser Cladding WC/Ni-Based Composite Layer on Al–Si Alloy

The microstructural and wear properties of laser-cladding WC/Ni-based layer on Al–Si alloy were investigated by scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and wear-testing. The results show that, compared with the original specimen, the microhardness and wear resistance of the cladding layer on an Al–Si alloy were remarkably improved, wherein the microhardness of the layer achieved 1100 HV and the average friction coefficient of the layer was barely 0.14. The mainly contributor to such significant improvement was the generation of a WC/Ni-composite layer of Al–Si alloy during laser cladding. Two types of carbides, identified as M₇C₃ and M₂₃C₆, were found in the layer. The wear rate of the layer first increased and then decreased with the increase in load; when the load was 20 N, 60 N and 80 N, the wear rate of layer was1.89 × 10⁻³ mm³·m⁻¹, 3.73 × 10⁻³ mm³·m⁻¹ and 2.63 × 10⁻³ mm³·m⁻¹, respectively, and the average friction coefficient (0.14) was the smallest when the load was 60 N.     

Inexpensive Ipomoea aquatica Biomass-Modified Carbon Black as an Active Pt-Free Electrocatalyst for Oxygen Reduction Reaction in an Alkaline Medium

The development of inexpensive and active Pt-free catalysts as an alternative to Pt-based catalysts for oxygen reduction reaction (ORR) is an essential prerequisite for fuel cell commercialization. In this paper, we report a strategy for the design of a new Fe–N/C electrocatalyst derived from the co-pyrolysis of Ipomoea aquatica biomass, carbon black (Vulcan XC-72R) and FeCl₃·6H₂O at 900 °C under nitrogen atmosphere. Electrochemical results show that the Fe–N/C catalyst exhibits higher electrocatalytic activity for ORR, longer durability and higher tolerance to methanol compared to a commercial Pt/C catalyst (40 wt %) in an alkaline medium. In particular, Fe–N/C presents an onset potential of 0.05 V (vs. Hg/HgO) for ORR in an alkaline medium, with an electron transfer number (n) of ~3.90, which is close to that of Pt/C. Our results confirm that the catalyst derived from I. aquatica and carbon black is a promising non-noble metal catalyst as an alternative to commercial Pt/C catalysts.     

Estimating Hantavirus Risk in Southern Argentina: A GIS-Based Approach Combining Human Cases and Host Distribution

We use a Species Distribution Modeling (SDM) approach along with Geographic Information Systems (GIS) techniques to examine the potential distribution of hantavirus pulmonary syndrome (HPS) caused by Andes virus (ANDV) in southern Argentina and, more precisely, define and estimate the area with the highest infection probability for humans, through the combination with the distribution map for the competent rodent host (Oligoryzomys longicaudatus). Sites with confirmed cases of HPS in the period 1995–2009 were mostly concentrated in a narrow strip (~90 km × 900 km) along the Andes range from northern Neuquén to central Chubut province. This area is characterized by high mean annual precipitation (~1,000 mm on average), but dry summers (less than 100 mm), very low percentages of bare soil (~10% on average) and low temperatures in the coldest month (minimum average temperature −1.5 °C), as compared to the HPS-free areas, features that coincide with sub-Antarctic forests and shrublands (especially those dominated by the invasive plant Rosa rubiginosa), where rodent host abundances and ANDV prevalences are known to be the highest. Through the combination of predictive distribution maps of the reservoir host and disease cases, we found that the area with the highest probability for HPS to occur overlaps only 28% with the most suitable habitat for O. longicaudatus. With this approach, we made a step forward in the understanding of the risk factors that need to be considered in the forecasting and mapping of risk at the regional/national scale. We propose the implementation and use of thematic maps, such as the one built here, as a basic tool allowing public health authorities to focus surveillance efforts and normally scarce resources for prevention and control actions in vast areas like southern Argentina.     

Characterization of double-stranded-RNA-activated kinase that phosphorylates α subunit of eukaryotic initiation factor 2 (eIF-2α) in reticulocyte lysates

Incubation of reticulocyte lysates with low levels of double-stranded (ds) RNA (1-20 ng/ml) activates a cAMP-independent protein kinase (dsI) that phosphorylates the α-subunit (M_r 38,000) of initiation factor 2 (eIF-2) and produces an inhibition of protein chain initiation similar to that caused by heme deficiency. Activation of dsI from its latent precursor takes place on the ribosomes and requires ATP. dsI can also be activated in ribosomal salt washes and in partially purified preparations of the latent precursor of dsI. In all preparations, activation is accompanied by the ds RNA-dependent phosphorylation of a polypeptide doublet that migrates as bands of 67 and 68.5 kilodaltons (67/68.5) in NaDodSO₄/acrylamide gels. The rate of phosphorylation of these components in a ribosome salt wash is more rapid than the ds RNA-dependent phosphorylation of eIF-2α. Other polypeptides in the salt wash also undergo ds RNA-dependent phosphorylation, but their significance is not clear. All of these phosphorylations are prevented by high concentrations of poly(I)·poly(C)(20 μg/ml), but not by an antiserum specific for the heme-regulated eIF-2α kinase. Both the latent and activated forms of dsI have been partially purified from a 0.5 M KCl wash of reticulocyte ribosomes. The two species have similar M_rs (≈120,000) and sedimentation coefficients (≈3.75 S), which suggests that activation of dsI probably does not involve extensive changes. By comparison, the heme-regulated eIF-2α kinase has an M_r of ≈160,000 and sediments at ≈6.6 S. However, in vitro, dsI and HRI both phosphorylate the same site(s) of eIF-2α. Purified dsI inhibits protein synthesis in hemin-supplemented lysates with the same kinetics induced by the addition of ds RNA; both inhibitions are reversed by eIF-2. dsI that has been activated in the salt wash and then purified does not require ds RNA for expression and no longer displays phosphorylation of the 68.5/67 doublet, which appears to occur only during activation. The data support the view that this component(s) may be the eIF-2α kinase activated by ds RNA.     

Evaluation of hepatoprotective effect of methanolic extract of Clitoria ternatea (Linn.) flower against acetaminophen-induced liver damage

Objective

To evaluate the hepatoprotective and antioxidant activity of Clitoria ternatea (C. ternatea) flower extract against acetaminophen-induced liver toxicity.

Methods

The antioxidant property of C. ternatea flower extract was investigated by employing established in vitro antioxidant assay. The C. ternatea flower extract was studied in this work for its hepatoprotective effect against acetaminophen-induced liver toxicity in mice. Activity was measured by monitoring the levels of aspartate aminotransferase, alanine aminotransferase, billirubin and glutathione with histopathological analysis.

Results

The amount of total phenolics and flavonoids were estimated to be 105.40±2.47 mg/g gallic acid equivalent and 72.21±0.05 mg/g catechin equivalent respectively. The antioxidant activity of C. ternatea flower extract was 68.9% at a concentration of 1 mg/mL and was also concentration dependant, with an IC₅₀ value of 327.00 µg/mL. The results of acetaminophen-induced liver toxicity experiment showed that mice treated with the extract (200 mg/kg) showed a significant decrease in alanine aminotransferase, aspartate aminotransferase, and bilirubin levels, which were all elevated in the paracetamol group (P<0.05). Meanwhile, the level of glutathione was found to be restored in extract treated animals compared to the groups treated with acetaminophen alone (P<0.05). Therapy of extract also showed its protective effect on histopathological alterations and supported the biochemical finding.

Conclusion

The present work confirmed the hepatoprotective effect of C. ternatea flower against model hepatotoxicant acetaminophen.     

Sol-Gel Synthesis and Antioxidant Properties of Yttrium Oxide Nanocrystallites Incorporating P-123

Yttrium oxide (Y₂O₃) nanocrystallites were synthesized by mean of a sol-gel method using two different precursors. Raw materials used were yttrium nitrate and yttrium chloride, in methanol. In order to promote oxygen vacancies, P-123 poloxamer was incorporated. Synthesized systems were heat-treated at temperatures from 700 °C to 900 °C. Systems at 900 °C were prepared in the presence and absence of P-123 using different molar ratios (P-123:Y = 1:1 and 2:1). Fourier transform infrared spectroscopy (FTIR) results revealed a characteristic absorption band of Y–O vibrations typical of Y₂O₃ matrix. The structural phase was analyzed by X-ray diffraction (XRD), showing the characteristic cubic phase in all systems. The diffraction peak that presented the major intensity corresponded to the sample prepared from yttrium chloride incorporating P-123 in a molar ratio of P-123:Y = 2:1 at 900 °C. Crystallites sizes were determined by Scherrer equation as between 21 nm and 32 nm. Antioxidant properties were estimated by 2,2-diphenyl-1-picrylhydrazyl (DPPH•) assays; the results are discussed.     

Organic particulate material levels in the atmosphere: Conditions favoring sensitivity to varying relative humidity and temperature

This study examines the sensitivity in predicted levels of atmospheric organic particulate matter (M_o, μg m^-3) as those levels may potentially be affected by changes in relative humidity and temperature. In a given system, for each partitioning compound, f_g and f_p represent the gaseous and particulate fractions (f_g + f_p = 1). Sensitivity in the M_o levels becomes dampened as the compounds contributing significantly to M_o are increasingly found in the particle phase (f_p → 1). Thus, although local maxima in sensitivity can be encountered as M_o levels increase, because as M_o increases each f_p → 1, then increasing M_o levels generally tend to reduce sensitivity in M_o levels to changes in relative humidity and temperature. Experiments designed to elucidate the potential magnitudes of the effects of relative humidity and temperature on M_o levels must be carried out at M_o levels that are relevant for the ambient atmosphere: The f_p values for the important partitioning compounds must not be elevated above ambient-relevant values. Systems in which M_o levels are low (e.g., 1–2 μg m^-3) and/or composed of unaged secondary organic aerosol are the ones most likely to show sensitivity to changing relative humidity and temperature. Results from two published chamber studies are examined in the above regard: [Warren B, et al. (2009) Atmos Environ 43:1789–1795] and [Prisle NL, et al. (2010) Geophys Res Lett 37:L01802].The effects of varying relative humidity (RH) on ambient aerosol particles composed of inorganic materials such as NaCl and NH₄HSO₄ are well understood (1). In contrast, the understanding of the effects of varying RH on aerosol organic particulate matter (OPM) is less perfect, though it can be said that as with inorganic materials, a range of hygroscopicities can be expected: Particles composed of cuticular plant wax compounds are minimally hygroscopic, whereas aged/oxidized secondary organic aerosol (SOA) particles can be at least moderately hygroscopic.Mechanism I: When OPM exhibits hygroscopic properties, increasing the RH will lead to uptake of water into the particles and the aerosol mass concentration will increase. And, if the organic compounds capable of contributing significantly to the particle phase (i.e., those with low enough vapor pressures) are not already mostly in the particle phase, there is the potential that the increasing aerosol mass concentration can draw significantly more condensable organic mass into the particle phase. The end result can be simultaneous increases in the water and organic portions of the aerosol mass concentration, represented here as M_w (μg m^-3) and M_o (μg m^-3), respectively.Mechanism II: When M_o is considerably below 100% of the total mass concentration of condensable compounds (e.g., ∼5% condensed) so that the system is capable of a significant percentage increase in condensation (e.g., ∼5% to ∼10% condensed), increases in RH can cause significant increases in M_o even when the condensing OPM is minimally hygroscopic. As discussed by Chang and Pankow (2) and Pankow and Chang (3), under such threshold conditions even a small increase in the water content of the OPM can cause a sufficient decrease in the mean molecular weight of that phase so that the values of the relevant gas/particle partitioning constants K_p increase enough to double or even triple M_o. On the other hand, there can be little effect of RH on M_o whenever the majority of the condensable organic compounds are already mostly condensed. The design of any experimental study to discern the effects of RH (or temperature) on M_o levels must take these facts into consideration.     

INAUGURAL ARTICLE by a Recently Elected Academy Member:In vitro evolution of horse heart myoglobin to increase peroxidase activity

Random mutagenesis and screening for enzymatic activity has been used to engineer horse heart myoglobin to enhance its intrinsic peroxidase activity. A chemically synthesized gene encoding horse heart myoglobin was subjected to successive cycles of PCR random mutagenesis. The mutated myoglobin gene was expressed in Escherichia coli LE392, and the variants were screened for peroxidase activity with a plate assay. Four cycles of mutagenesis and screening produced a series of single, double, triple, and quadruple variants with enhanced peroxidase activity. Steady-state kinetics analysis demonstrated that the quadruple variant T39I/K45D/F46L/I107F exhibits peroxidase activity significantly greater than that of the wild-type protein with k₁ (for H₂O₂ oxidation of metmyoglobin) of 1.34 × 10⁴ M⁻¹ s⁻¹ (≈25-fold that of wild-type myoglobin) and k₃ [for reducing the substrate (2, 2′-azino-di-(3-ethyl)benzthiazoline-6-sulfonic acid] of 1.4 × 10⁶ M⁻¹ s⁻¹ (1.6-fold that of wild-type myoglobin). Thermal stability of these variants as measured with circular dichroism spectroscopy demonstrated that the T_m of the quadruple variant is decreased only slightly compared with wild-type (74.1°C vs. 76.5°C). The rate constants for binding of dioxygen exhibited by the quadruple variant are identical to the those observed for wild-type myoglobin (k_on, 22.2 × 10⁻⁶ M⁻¹ s⁻¹ vs. 22.3 × 10⁻⁶ M⁻¹ s⁻¹; k_off, 24.3 s⁻¹ vs. 24.2 s⁻¹; K_O2, 0.91 × 10⁻⁶ M⁻¹ vs. 0.92 × 10⁻⁶ M⁻¹). The affinity of the quadruple variant for CO is increased slightly (k_on, 0.90 × 10⁻⁶ M⁻¹s⁻¹ vs. 0.51 × 10⁻⁶ M⁻¹s⁻¹; k_off, 5.08 s⁻¹ vs. 3.51 s⁻¹; K_CO, 1.77 × 10⁻⁷ M⁻¹ vs. 1.45 × 10⁻⁷ M⁻¹). All four substitutions are in the heme pocket and within 5 Å of the heme group.