Probing the oxyferrous and catalytically active ferryl states of Amphitrite ornata dehaloperoxidase by cryoreduction and EPR/ENDOR spectroscopy. Detection of compound I

Dehaloperoxidase (DHP) from Amphitrite ornata is a heme protein that can function both as a hemoglobin and as a peroxidase. This report describes the use of 77 K cryoreduction EPR/ENDOR techniques to study both functions of DHP. Cryoreduced oxyferrous [Fe(II)-O(2)] DHP exhibits two EPR signals characteristic of a peroxoferric [Fe(III)-O(2)(2-)] heme species, reflecting the presence of conformational substates in the oxyferrous precursor. (1)H ENDOR spectroscopy of the cryogenerated substates shows that H-bonding interactions between His N(ε)H and heme-bound O(2) in these conformers are similar to those in the β-chain of oxyferrous hemoglobin A (HbA) and oxyferrous myoglobin, respectively. Decay of cryogenerated peroxoferric heme DHP intermediates upon annealing at temperatures above 180 K is accompanied by the appearance of a new paramagnetic species with an axial EPR signal with g(⊥) = 3.75 and g(∥) = 1.96, characteristic of an S = 3/2 spin state. This species is assigned to Compound I (Cpd I), in which a porphyrin π-cation radical is ferromagnetically coupled with an S = 1 ferryl [Fe(IV)═O] ion. This species was also trapped by rapid freeze-quench of the ambient-temperature reaction mixture of ferric [Fe(III)] DHP and H(2)O(2). However, in the latter case Cpd I is reduced very rapidly by a nearby tyrosine to form Cpd ES [(Fe(IV)═O)(porphyrin)/Tyr(?)]. Addition of the substrate analogue 2,4,6-trifluorophenol (F(3)PhOH) suppresses formation of the Cpd I intermediate during annealing of cryoreduced oxyferrous DHP at 190 K but has no effect on the spectroscopic properties of the remaining cryoreduced oxyferrous DHP intermediates and kinetics of their decay. These observations indicate that substrate (i) binds to oxyferrous DHP outside of the distal pocket and (ii) can reduce Cpd I to Cpd II [Fe(IV)═O]. These assumptions are also supported by the observation that F(3)PhOH has only a small effect on the EPR properties of radiolytically cryooxidized and cryoreduced ferrous [Fe(II)] DHP. EPR spectra of cryoreduced ferrous DHP disclose the multiconformational nature of the ferrous DHP precursor. The observation and characterization of Cpds I, II, and ES in the absence and in the presence of F(3)PhOH provides definitive evidence of a mechanism involving consecutive one-electron steps and clarifies the role of all intermediates formed during turnover.     

A study on the effect of starting material phase on the production of trititanate nanotubes

Mixed phase TiO₂ powders of different composition and particle size were subjected to the hydrothermal reaction with 10 M NaOH. It was found that the anatase phase component of the starting material is easily converted to trititanate nanotubes at 140 °C. At this temperature the rutile phase remains unreacted, however at 170 °C it reacts to form trititanate plates and belts. When the reaction time is increased to 7 days, all the TiO₂ is converted to trititanate and the morphology is exclusively nanoplates and belts, with the tube phase destroyed. Many researchers have observed some heterogeneity in their reaction products, but have mainly focussed on the nanotubes. We observed that the tubes are only prepared from the anatase phase component of a TiO₂ precursor, whereas the rutile component produces trititanate plates and sheets, irrespective of the reaction length. The particle size affects the rate of reaction, resulting in the phase transition being more easily visible in the reactions starting with the larger TiO₂ particle size.     

Adaptive hierarchic transformations for dynamically p-enriched slope-limiting over discontinuous Galerkin systems of generalized equations

We study a family of generalized slope limiters in two dimensions for Runge–Kutta discontinuous Galerkin (RKDG) solutions of advection-diffusion systems. We analyze the numerical behavior of these limiters applied to a pair of model problems, comparing the error of the approximate solutions, and discuss each limiter’s advantages and disadvantages. We then introduce a series of coupled p-enrichment schemes that may be used as standalone dynamic p-enrichment strategies, or may be augmented via any in the family of variable-in-p slope limiters presented.     

Cascading of liquid crystal elastomer photomechanical optical devices

Photomechanical actuation is demonstrated in two coupled liquid crystal elastomer photomechanical optical devices (PODs) acting in series. The response function of an individual POD is characterized and used to predict the temporal response of the coupled system. The predicted coupled-system response agrees with the experiment for several waveforms and frequencies, suggesting that large-scale integration of photomechanical devices is possible.     

In vitro evaluation of cytotoxic and inflammatory properties of silica nanoparticles of different sizes in murine RAW 264.7 macrophages

The biological response to four well-characterized amorphous silica nanoparticles was investigated in RAW 264.7 macrophages in view of their potential application as drug carriers to sites of inflammation. All silica nanoparticles-induced cell membrane damage, reduced metabolic activity, generated ROS and released various cytokines, but to different extents. Two silica nanoparticles of 34 nm (A and B) with different zetapotentials were more cytotoxic than (aggregated) 11 and 248 nm nanoparticles, while cytokines were mostly induced by the (aggregated) 11 nm and only one of the 34 nm nanoparticles (34A). The results indicate that specific silica nanoparticles may have counterproductive effects, for example when used as carriers of anti-inflammatory drugs. The physicochemical properties determining the response of nanoparticles vary for different responses, implying that a screening approach for the safe development of nanoparticles needs to consider the role of combinations of (dynamic) physicochemical properties and needs to include multiple toxicity endpoints.     

Scalar potential without cubic term in 3-3-1 models without exotic electric charges

A detailed study of the criteria for stability of the scalar potential, and the proper electroweak symmetry breaking pattern in some 3-3-1 models without exotic electric charges is presented. In this paper we concentrate in a scalar sector with three Higgs scalar triplets, with a potential that does not include the cubic term, due to the presence of a discrete symmetry. For the analysis we use, and improve, a method previously developed to study the scalar potential in the two-Higgs-doublet extension of the standard model. Our main result is to show the consistency of those 3-3-1 models without exotic electric charges.     

InGaN micro-pixellated light-emitting diodes with nano-textured surfaces and modified emission profiles

We present the fabrication details and performance characteristics of InGaN light-emitting diodes (LEDs) consisting of arrays of interconnected micro-pixels where each micro-pixel is nano-textured via nano-imprinting. We have taken the further step of embodying the pixels in a rhomboidal geometry. It is found that the power output of these nano-textured micro-LEDs with rhomboidal geometries is 57% higher than that of conventional square-shaped broad-area reference LEDs. The series resistance of the textured LEDs is reduced, owing to the multi-finger electrodes introduced. Furthermore, these LEDs can sustain higher operation current of up to 500 mA without encapsulation, suggesting improved thermal dissipation capability. Finally, the combined effects of surface texturing, micro-LED configuration, and geometric shaping on the light extraction are analyzed. It is found that the power enhancement by surface texturing, micro-pixellating and the rhomboidal geometry are 32%, 16%, and 9%, respectively, implying that surface texturing is the most effective contribution to increasing the light extraction efficiency in our design. The angular dependent far-field beam profile is also remarkably changed, compared with the standard Lambertian emission pattern of the conventional square-shaped LEDs. Substantial increase in the EL intensity is evident from both the top surface and the sidewall.     

High sensitivity (1 ppm) hydrogen detection using an unconventional Pd/n-InP Schottky device

Hydrogen is detected using a Pd/n-InP Schottky diode in which the elongated, very thin Pd electrode is of greater resistance than the underlying semiconductor substrate. Four-probe measurements of the device resistance, as a function of hydrogen concentration, are made by contacting only the Pd electrode, with a sensitivity of 1 ppm being achieved. On hydrogen exposure the device resistance drops from an initial high value, characteristic of the Pd electrode alone, to a lower value due to a hydrogen-induced lowering of the Schottky barrier that opens up the InP substrate as a parallel current carrying channel.     

Tricritical point in heterogeneous k-core percolation

k-core percolation is an extension of the concept of classical percolation and is particularly relevant to understanding the resilience of complex networks under random damage. A new analytical formalism has been recently proposed to deal with heterogeneous k-cores, where each vertex is assigned a local threshold k(i). In this Letter we identify a binary mixture of heterogeneous k-cores which exhibits a tricritical point. We investigate the new scaling scenario and calculate the relevant critical exponents, by analytical and computational methods, for Erd?s-Rényi networks and 2D square lattices.     

Weighted inequalities for some integral operators with rough kernels

In this paper we study integral operators with kernels $$K(x,y) = k_1 (x - A_1 y) \cdots k_m \left( {x - A_m y} \right),$$ $k_i \left( x \right) = {{\Omega _i \left( x \right)} \mathord{\left/ {\vphantom {{\Omega _i \left( x \right)} {\left| x \right|}}} \right. \kern-0em} {\left| x \right|}}^{{n \mathord{\left/ {\vphantom {n {q_i }}} \right. \kern-0em} {q_i }}}$ where Ω _i : ? ⁿ → ? are homogeneous functions of degree zero, satisfying a size and a Dini condition, A _i are certain invertible matrices, and n/q ₁ +…+n/q _m = n?α, 0 ≤ α < n. We obtain the appropriate weighted L ^p -L ^q estimate, the weighted BMO and weak type estimates for certain weights in A(p, q). We also give a Coifman type estimate for these operators.