Electron transfer in tetrahemic cytochromes c3: spectroelectrochemical evidence for a conformational change triggered by heme IV reduction

Electron transfer in tetrahemic cytochromes c3 from Desulfovibrio vulgaris Hildenborough (D.v.H.) and Desulfovibrio desulfuricans Norway (D.d.N.) strains has been investigated by thin layer spectroelectrochemistry with visible absorption, CD, and resonance Raman (RR) monitoring. The observed splitting of the isosbestic point in the Soret absorption band indicates that the electron transfer from the (FeIII)4 state to the (FeII)4 state proceeds via an intermediate species, which corresponds to 25 and 50% reduction for the D.v.H. cyt.c3 and the D.d.N. cyt.c3, respectively. For the latter, a specific CD signal is observed at half-reduction. RR monitoring of the redox process does not reveal multiple splitting of the high-frequency RR bands, at variance with previously published results on the enzymatic reduction of cyt.c3 from Desulfovibrio vulgaris Miyazaki, a cytochrome highly homologous to D.v.H. cyt.c3 [Verma, A.L., Kimura, A., Nakamura, A., Yagi, T., Inoguchi, H., & Kitagawa, T. (1988) J. Am. Chem. Soc. 110, 6617-6623]. The low-frequency RR spectra of the intermediate species differ significantly from the ones calculated from a linear combination of the all-ferric and all-ferrous states, for the same reduction ratio. Frequency shifts of the bending modes of the cysteine and propionate heme substituents are observed, as well as changes specific to each cytochrome; most notable is the activation of two torsional modes in the case of D.d.N. cyt.c3. Comparison of the results obtained for the two cytochromes leads to the conclusion that reduction of heme IV triggers the observed conformational change. This conclusion is supported by the spectroelectrochemical investigation of the mutant D.v.H. cyt.c3 H25M, in which the sixth ligand of heme III, histidine, is replaced by a methionine.     

Experimental investigation of liquid water formation and transport in a transparent single-serpentine PEM fuel cell

Liquid water formation and transport were investigated by direct experimental visualization in an operational transparent single-serpentine PEM fuel cell. We examined the effectiveness of various gas diffusion layer (GDL) materials in removing water away from the cathode and through the flow field over a range of operating conditions. Complete polarization curves as well as time evolution studies after step changes in current draw were obtained with simultaneous liquid water visualization within the transparent cell. The level of cathode flow field flooding, under the same operating conditions and cell current, was recognized as a criterion for the water removal capacity of the GDL materials. When compared at the same current density (i.e. water production rate), higher amount of liquid water in the cathode channel indicated that water had been efficiently removed from the catalyst layer.

Visualization of the anode channel was used to investigate the influence of the microporous layer (MPL) on water transport. No liquid water was observed in the anode flow field unless cathode GDLs had an MPL. MPL on the cathode side creates a pressure barrier for water produced at the catalyst layer. Water is pushed across the membrane to the anode side, resulting in anode flow field flooding close to the H₂ exit.     

A nanoporous interferometric micro-sensor for biomedical detection of volatile sulphur compounds

A simple one-step NaCl-assisted microwave-solvothermal method has been developed for the preparation of monodisperse α-Fe₂O₃ mesoporous microspheres. In this approach, Fe(NO₃)₃ · 9H₂O is used as the iron source, and polyvinylpyrrolidone (PVP) acts as a surfactant in the presence of NaCl in mixed solvents of H₂O and ethanol. Under the present experimental conditions, monodisperse α-Fe₂O₃ mesoporous microspheres can form via oriented attachment of α-Fe₂O₃ nanocrystals. One of the advantages of this method is that the size of α-Fe₂O₃ mesoporous microspheres can be adjusted in the range from ca. 170 to ca. 260 nm by changing the experimental parameters. High photocatalytic activities in the degradation of salicylic acid are observed for α-Fe₂O₃ mesoporous microspheres with different specific surface areas.     

Mechanical response of reaction phases of the TiAl/steel brazed joint under a tensile load

This article offers a study of a mechanical response of the TiAl/Steel brazed joint. The (i) intermetallic reaction layer’s phases, (ii) the residue filler, and the (iii) base metals constitute the complex structure considered. The study features TiAl and 42CrMo steel brazed with an AgCuTi filler metal. The analysis includes the microstructural study and an evaluation of mechanical properties of the brazed joint. In addition, the fracture behavior of the joint under a tensile loading in situ is studied in the context of the impact that reaction phases may have on the joint properties. The results of the study indicate that the complex joint structure is due to the presence of a ternary intermetallic reaction layer, as well as the presence of intermetallics in the filler residue. The multilayered structure includes Ti₃Al+AlCuTi+AlCu₂Ti ternary intermetallic reaction layer, Ag(Cu) residue filler, AlCu₂Ti intermetallic dispersed in the residue braze and TiC layer. The hardness sequence of the structure has been established. The crack initiation, its propagation, and an ultimate fracture are associated primarily with Ti₃Al+AlCuTi+AlCu₂Ti ternary intermetalics layer.     

Functionalized diatom silica microparticles for removal of mercury ions

Diatom silica microparticles were chemically modified with self-assembled monolayers of 3-mercaptopropyl-trimethoxysilane (MPTMS), 3-aminopropyl-trimethoxysilane (APTES) and n-(2-aminoethyl)-3-aminopropyl-trimethoxysilane (AEAPTMS), and their application for the adsorption of mercury ions (Hg(II)) is demonstrated. Fourier transform infrared spectroscopy and x-ray photoelectron spectroscopy analyses revealed that the functional groups (–SH or –NH₂) were successfully grafted onto the diatom silica surface. The kinetics and efficiency of Hg(II) adsorption were markedly improved by the chemical functionalization of diatom microparticles. The relationship among the type of functional groups, pH and adsorption efficiency of mercury ions was established. The Hg(II) adsorption reached equilibrium within 60 min with maximum adsorption capacities of 185.2, 131.7 and 169.5 mg g⁻¹ for particles functionalized with MPTMS, APTES and AEAPTMS, respectively. The adsorption behavior followed a pseudo-second-order reaction model and Langmuirian isotherm. These results show that mercapto- or amino-functionalized diatom microparticles are promising natural, cost-effective and environmentally benign adsorbents suitable for the removal of mercury ions from aqueous solutions.     

Complementary variational principles with fractional derivatives

Complementary variational principles for a class of fractional boundary value problems are formulated. They are used for the error estimates of solutions for a general mechanical problems, first Painlevé equation also given in the form with fractional derivatives and in the task of image regularization.     

Preliminary management and optimization of a gas reservoir in central Serbia

Management of hydrocarbon reservoirs is a dynamic, continuous and complex process. It is applied from reservoir discovery to its abandonment, with the objective of achieving maximum profitability by using a recovery process with minimum capital investments and operation costs.The goals of modern system-engineer' approach to hydrocarbon reservoir management are: managing efficiency; adequate and on time decision making; increasing reserves, and oil and gas recovery factor; production increment; risk reduction; investment efficiency; minimizing costs and environmental protection.The gas reservoir “M” is the gas reservoir discovered in central part of Serbia. It was not put in production yet, so it is important to apply reservoir management concepts from the beginning of the production process.Based on production characteristics, this reservoir belongs to a group of smaller gas reservoirs that characterizes most often the Serbian exploitation area. Also, this reservoir fullfils most of criteria for using it as an underground gas storage reservoir. Thus, the analysis of possibilities for conversion into the underground gas storage after certain production period was also considered.The management of gas reservoir “M” has been analyzed by two different approaches. The first one refers to the management of the reservoir as a gas producer during the whole reservoir life. The second management approach considers gas production for a certain period of time, followed by underground gas storage (UGS). In this paper, economic and financial evaluation results are given for the presented options of gas reservoir management.A decision analysis has been applied to select an optimized gas reservoir management approach.Adequate management of this gas reservoir would contribute to further development and reform of Serbia's gas energy sector that is characterized by great dependence on natural gas imports, and a lack of underground gas storage.     

Electrochemical synthesis of nickel hexacyanoferrate nanoarrays with dots, rods and nanotubes morphology using a porous alumina template

Transition metal hexacyanoferrate (MeHCF) have attracted extensive attention because of their outstanding properties including, electrocatalysis, molecular magnetism, biosensing and ion-exchange. This paper describes an approach for fabrication of ordered nanoarrays of Ni hexacyanoferrate (NiHCF) structures with different morphologies such as dots, rods and tubes in order to advance their properties and applications. The method is based on the conversion of Ni into NiHCF nanostructures by electrochemical oxidation in the presence of hexacyanoferrate ions, using nanoporous anodic alumina oxide (AAO) as a template. The structure and morphology of formed Ni and NiHCF nanoarrays were confirmed by scanning electron microscopy (SEM), showing agreement with the pore structures of the AAO template. The electrocatalytic activity of NiHCF nanorod array electrodes showed high catalytic properties for the detection of hydrogen peroxide and the potential to be used as a platform for direct biosensing applications. The ion-exchange ability of fabricated NiHCF nanostructures (nanorods and nanotubes) toward alkali cations such as Na⁺ has been successfully confirmed.     

Pore architecture of diatom frustules: potential nanostructured membranes for molecular and particle separations

Diatoms produce diverse three-dimensional regular silica structures with nanometer to micrometer dimensions and hold considerable promise for biological and biomimetic fabrication of nanostructured materials and devices. In the present work, we describe the ultrastructural characterization of porous structures in diatom biosilica and discuss their potential as membrane filters for diffusion based separations. The frustules of two centric diatom species, Coscinodiscus sp. and Thalassiosira eccentrica, were investigated using scanning electron microscopy and atomic force microscopy. Their morphological features, including pore size, shape, porosity, and pore organization, are described. We observed that although pore organization in frustules of Thalassiosira eccentrica and Coscinodiscus sp. is in reverse order, a striking commonality is the size range of the smallest pores in both species (around 40 nm). The consensus lower pore size suggests that frustule valves have a common function at this size of excluding viruses or other deleterious particles, and the pore size and organization is optimized for this purpose. We suggest and implement an experimental approach to study the potential of diatom frustules for diffusive separation of molecular or nanoparticular components in microfluidic or lab-on-a-chip environments.     

Graphene-Based Sorbents for Multipollutants Removal in Water: A Review of Recent Progress

The coexistence of multiple toxic water pollutants (heavy metals, organic dyes, oils, and organic solvents) limits the sustainable supply of clean water worldwide and urges the development of advanced water purification technology that can remove these contaminants simultaneously. Since its discovery, graphene-based materials have gained substantial attention toward development of new-generation sorbents for water purification. Despite several recently published reviews on water purification technology using graphene and its derivatives, there is still a gap in the review considering multiple water-pollutant remediation using advanced graphene materials. In this review, in the first instance, a comparative structure–function–performance relationship between graphene-based sorbents and the multipollutants in water is established. A fundamental correlation is made between the sorption performance for diverse pollutants in water with the more specific adsorption properties (surface area, pore size, type of functional groups, C/O, C/N, and C/S atomic ratio) of advanced graphene sorbents. Second, the underlying interaction mechanisms are uncovered between different classes of water pollutants using single graphene-based sorbents. Third, the rational design of advanced multipollutant sorbents based on graphene is elaborated. The reality, challenges, and opportunities of advanced graphene materials as emerging sorbents for sustainable water purification technology are finally presented in the last section.