Abstract The W/SeCys-FdhAB formate dehydrogenase from Desulfovibrio vulgaris Hildenborough is a dimeric periplasmic enzyme that catalyzes the reversible oxidation of formate and reduction of CO2. It belongs to the group of metal-dependent FDHs, with a tungsten at the active site coordinated by two pyranopterin guanine dinucleotides, a selenocysteine, and one labile sulfur atom. FdhAB has a remarkably high activity and unusual tolerance to oxygen, making it an ideal model system to study biological CO2 reduction.

Indium oxide (In2O3)-based transparent conducting oxides (TCOs) have been widely used and studied for a variety of applications, such as optoelectronic devices. However, some of the more promising dopants (zirconium, hafnium, and tantalum) for this oxide have not received much attention, as studies have mainly focused on tin and zinc, and even fewer have been explored by solution processes. This work focuses on developing solution-combustion-processed hafnium (Hf)-doped In2O3 thin films and evaluating different annealing parameters on TCO’s properties using a low environmental impact solvent. Optimized TCOs were achieved for 0.5 M% Hf-doped In2O3 when produced at 400 °C, showing high transparency in the visible range of the spectrum, a bulk resistivity of 5.73 × 10−2 Ω.cm, a mobility of 6.65 cm2/V.s, and a carrier concentration of 1.72 × 1019 cm−3. Then, these results were improved by using rapid thermal annealing (RTA) for 10 min at 600 °C, reaching a bulk resistivity of 3.95 × 10 −3 Ω.cm, a mobility of 21 cm2/V.s, and a carrier concentration of 7.98 × 1019 cm−3, in air. The present work brings solution-based TCOs a step closer to low-cost optoelectronic applications.

Solution-based memristors are emergent devices, due to their potential in electrical performance for neuromorphic computing combined with simple and cheap fabrication processes.

Extracellular electron transfer is a key metabolic process of many organismsthat enables them to exchange electrons with extracellular electrondonors/acceptors. The discovery of organisms with these abilities and theunderstanding of their electron transfer processes has become a priority for thescientific and industrial community, given the growing interest on the use ofthese organisms in sustainable biotechnological processes. For example, inbioelectrochemical systems electrochemical active organisms can exchangeelectrons with an electrode, allowing the production of energy and added-valuecompounds, among other processes. In these systems, electrochemical activeorganisms exchange electrons with an electrode through direct or indirectmechanisms, using, in most cases, multiheme cytochromes. In numerouselectroactive organisms, these proteins form a conductive pathway that allowselectrons produced from cellular metabolism to be transferred across the cellsurface for the reduction of an electrode, or vice-versa. Here, the mechanisms bywhich the most promising electroactive bacteria perform extracellular electrontransfer will be reviewed, emphasizing the proteins involved in these pathways.The ability of some of the organisms to perform bidirectional electron transferand the pathways used will also be highlighted.

Stimuli-responsive supramolecular receptors are important building blocks for the construction of self-assembled functional materials. We report the design and synthesis of a pH and light-responsive 2-hydroxychalcone-beta-cyclodextrin conjugate (1-Ct) and its characterization by spectroscopic and computational methods. 1-Ct follows the typical reaction network of trans-chalcone-flavylium photoswitches. Upon light irradiation, 1-Ct can be photochemically converted into the cis-chalcone/hemiketal forms (1-Cc/1-B) under neutral pH conditions or to the flavylium cation (1-AH+) at acidic pH values. This stimuli-responsive beta-cyclodextrin host, 1Ct, was found to form stronger intramolecular self-inclusion complexes (Kintra = 14) than 1-AH+ (Kintra = 3) and weaker than 1-Cc/1-B (overall Kintra = 179), allowing control over their stability and binding properties by combinations of pH and light stimuli.

Abstract Vanadium compounds have frequently been proposed as therapeutics, but their application has been hampered by the lack of information on the different V-containing species that may form and how these interact with blood and cell proteins, and with enzymes. Herein, we report several resolved crystal structures of lysozyme with bound VIVO2+ and VIVOL2+, where L=2,2?-bipyridine or 1,10-phenanthroline (phen), and of trypsin with VIVO(picolinato)2 and VVO2(phen)+ moieties. Computational studies complete the refinement and shed light on the relevant role of hydrophobic interactions, hydrogen bonds, and microsolvation in stabilizating the structure. Noteworthy is that the trypsin?VVO2(phen) and trypsin?VIVO(OH)(phen) adducts correspond to similar energies, thus suggesting a possible interconversion under physiological/biological conditions. The obtained data support the relevance of hydrolysis of VIV and VV complexes in the several types of binding established with proteins and the formation of different adducts that might contribute to their pharmacological action, and significantly widen our knowledge of vanadium?protein interactions.

Metal-dependent formate dehydrogenases are important enzymes due to their activity of CO2 reduction to formate. The tungsten-containing FdhAB formate dehydrogenase from Desulfovibrio vulgaris Hildenborough is a good example displaying high activity, simple composition, and a notable structural and catalytic robustness. Here, we report the first spectroscopic redox characterization of FdhAB metal centers by EPR. Titration with dithionite or formate leads to reduction of three [4Fe–4S]1+ clusters, and full reduction requires Ti(III)–citrate. The redox potentials of the four [4Fe–4S]1+ centers range between −250 and −530 mV. Two distinct WV signals were detected, WDV and WFV, which differ in only the g2-value. This difference can be explained by small variations in the twist angle of the two pyranopterins, as determined through DFT calculations of model compounds. The redox potential of WVI/V was determined to be −370 mV when reduced by dithionite and −340 mV when reduced by formate. The crystal structure of dithionite-reduced FdhAB was determined at high resolution (1.5 Å), revealing the same structural alterations as reported for the formate-reduced structure. These results corroborate a stable six-ligand W coordination in the catalytic intermediate WV state of FdhAB.Metal-dependent formate dehydrogenases are important enzymes due to their activity of CO2 reduction to formate. The tungsten-containing FdhAB formate dehydrogenase from Desulfovibrio vulgaris Hildenborough is a good example displaying high activity, simple composition, and a notable structural and catalytic robustness. Here, we report the first spectroscopic redox characterization of FdhAB metal centers by EPR. Titration with dithionite or formate leads to reduction of three [4Fe–4S]1+ clusters, and full reduction requires Ti(III)–citrate. The redox potentials of the four [4Fe–4S]1+ centers range between −250 and −530 mV. Two distinct WV signals were detected, WDV and WFV, which differ in only the g2-value. This difference can be explained by small variations in the twist angle of the two pyranopterins, as determined through DFT calculations of model compounds. The redox potential of WVI/V was determined to be −370 mV when reduced by dithionite and −340 mV when reduced by formate. The crystal structure of dithionite-reduced FdhAB was determined at high resolution (1.5 Å), revealing the same structural alterations as reported for the formate-reduced structure. These results corroborate a stable six-ligand W coordination in the catalytic intermediate WV state of FdhAB.

{Cytochromes are electron transfer proteins essential in various biological systems, playing crucial roles in the respiratory chains of bacteria. These proteins are particularly abundant in electrogenic microorganisms and are responsible for the efficient delivery of electrons to the cells’ exterior. The capability of sending electron outside the cells open new avenues to be explored for emerging biotechnological applications in bioremediation, microbial electrosynthesis and bioenergy fields. To develop these applications, it is critical to identify the different redox partners and elucidate the stepwise electron transfer along the respiratory paths. However, investigating direct electron transfer events between proteins with identical features in nearly all spectroscopic techniques is extremely challenging. NMR spectroscopy offers the possibility to overcome this difficulty by analysing the alterations of the spectral signatures of each protein caused by electron exchange events. The uncrowded NMR spectral regions containing the heme resonances of the cytochromes display unique and distinct signatures in the reduced and oxidized states, which can be explored to monitor electron transfer within the redox complex. In this study, we present a strategy for a fast and straightforward monitorization of electron transfer between c-type cytochromes, using as model a triheme periplasmic cytochrome (PpcA) and a membrane associated monoheme cytochrome (OmcF) from the electrogenic bacterium Geobacter sulfurreducens. The comparison between the 1D 1H NMR spectra obtained for samples containing the two cytochromes and for samples containing the individual proteins clearly demonstrated a unidirectional electron transfer within the redox complex. This strategy provides a simple and straightforward means to elucidate complex biologic respiratory electron transfer chains.}

Reinforced concrete flat slabs are used worldwide in multi-story buildings. In these slabs, the design is often governed by punching shear and serviceability. The mitigation of these issues during design usually leads to increased raw material consumption and costs. Previous studies have shown that using Fiber Reinforced Concrete (FRC) or High-Strength Concrete (HSC) only at the vicinity of the column, while casting the rest of the slab with Normal Strength Concrete (NSC), can lead to an improved behavior under gravity loads in terms of both serviceability and ultimate capacity. Motivated by these results and the scarcity of previous tests, the present paper experimentally investigates the applicability of High-Performance Fiber Reinforced Concrete (HPFRC) as an alternative material that can be seen as an improvement over FRC and HSC, allowing a combination of ductility and strength. In addition, the HPFRC used in this paper is self-compacting, thus reducing the labor costs associated with concrete vibration. Five 150 mm thick flat slabs were tested under monotonically increasing punching load. The experimental variables were the flexural reinforcement ratio and the extent of the HPFRC zone. One of the specimens was cast only with NSC and served as a reference slab. Results show that the solution was effective for both flexural reinforcement ratios considered. Cracking load, maximum load, as well as the displacement capacity were increased significantly, even for a small extent of HPFRC (1.5 times the effective depth from the face of the column). Regarding the ultimate load capacity, it was observed an increase of 44% to 58% for the specimens with lower reinforcement ratio (0.64%) and between 15%–21% for the specimens with higher reinforcement ratio (0.96%). The results indicate that the use of HPFRC is a promising solution regarding both serviceability and ultimate limit state design of reinforced concrete flat slabs under gravity loading, with obvious advantages in material savings and labor costs.

Abstract The colloidal suspensions of aqueous cellulose nanocrystals (CNCs) are known to form liquid crystalline systems above certain critical concentrations. From an isotropic phase; tactoid formation; growth; and sedimentation have been determined as the genesis of a high-density cholesteric phase; which after drying; originates solid iridescent films. Herein; we report the coexistence of a liquid crystal upper phase and an isotropic bottom phase in CNC aqueous suspensions at isotropic-nematic phase separation for the first time. Furthermore; isotropic spindle-like domains are observed in the low-density liquid crystalline phase; and high-density liquid crystalline phases are also prepared. The CNCs isolated from the low- and high-density liquid crystalline phases are found to have similar average lengths; diameters; and surface charges. The existence of a liquid crystalline low-density phase is explained by the presence of air dissolved in the water present within the CNCs. The air dissolves out when the water solidifies into ice and remains within the CNCs. The self-adjustment of the cellulose chain conformation enables the entrapment of air within the CNCs and CNC buoyancy in aqueous suspensions. This article is protected by copyright. All rights reserved