Abstract One of the unresolved aspects of cellulose-based liquid crystalline phases is their chirality. Although cellulose is intrinsically chiral, both left-handed (LH) and right-handed (RH) chiral nematic phases are reported in cellulose derivatives under different conditions. The origin of these discrepancies?and whether LH and RH twisted structures coexist within a single material?has remained unclear. Here, the first direct evidence of hierarchical LH and RH twisted structures coexisting in a solvent-free, thermotropic cellulose derivative at room temperature is provided. Free-standing cholesteric films exhibit distinct LH and RH twisted domains, whose pitches respond oppositely to uniaxial mechanical strain: the LH pitch increases, while the RH pitch decreases with increasing strain. This contrasting response results from the coexistence of intertwined LH and RH twisted structures, whose optical axes are oriented differently relative to the strain direction. Notably, after stretching beyond their elastic limit, the films spontaneously recover their original shape within minutes. During this recovery, circular dichroism (CD) measurements reveal an increase in RH pitch and a decrease in LH pitch, evidencing reversible, strain-responsive behavior. Multiscale structural characterization confirms the hierarchical chiral organization and its mechanoresponsive nature, providing new insights into the origin of chirality in cellulose-based liquid crystalline materials.

Electroactive bacteria mediate electron exchange with external compounds through a process known as extracellular electron transfer (EET). A key step in EET is the transfer of electrons from the menaquinone pool to inner membrane-associated quinol-cytochrome c oxidoreductase complexes, which subsequently relay electrons to periplasmic redox partners. Gene-knockout and proteomic analyses have identified several critical components involved in EET in Geobacter sulfurreducens, including six inner membrane oxidoreductase gene clusters. Of these, three - CbcL, ImcH, and CbcBA - have been linked to specific respiratory pathways depending on the redox potential of the terminal electron acceptor. Cbc4 is one of the other inner membrane oxidoreductase complexes and is composed by three subunits: a membrane-anchored tetraheme c-type cytochrome (CbcS), an iron–sulfur protein containing four [4Fe-4S] clusters (CbcT), and an integral membrane protein (CbcU). In this study, the sequence and AlphaFold model of CbcS were analyzed and its cytochrome domain was produced, and structurally and functionally characterized using Nuclear Magnetic Resonance spectroscopy. CbcS has four bis-histidine low-spin hemes and the structure of its hemecore is homologous to CymA and NrfH from Shewanella and Desulfovibrio species, respectively, despite differences on its axial ligands. Potentiometric titrations showed that the redox active window of CbcS overlaps with those of the triheme periplasmic cytochrome family (PpcA-E), its putative redox partners. Nevertheless, NMR-monitored electron transfer experiments revealed that CbcS transfers electrons to PpcA through the heme group closer to the C-terminal (heme IV). Together, these findings provide insights on a putative new respiratory pathway in G. sulfurreducens.

The global transition to electric vehicles and renewable energy systems has heightened the demand for lithium-ion batteries (LIBs), creating an urgent need for sustainable battery recycling methods to recover critical raw materials, including lithium. Lithium-selective cation-exchange polymeric membranes are one of the emerging options to achieve such lithium recycling. To make this change even greener, instead of using traditional fossil-origin polymers to produce membranes, this research employed bacterial cellulose acetate (BCA), a bio-derived and eco-friendly polymer. By adding 5 wt% N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (PP13–TFSI), an ionic liquid (IL) which is a plasticizer and lithium-ion conductor, and 20 wt% hydrogen manganese oxide (HMO), which is a lithium-selective inorganic filler, four BCA-based membranes (BCA, BCA-IL, BCA-HMO and BCA-IL-HMO) were prepared. The membranes were extensively characterized for their morphology, thermal stability, chemical, and mechanical properties. Subsequently, they were tested in diffusion cells (without applying any external driving force) for ionic conductivity, lithium selectivity, and lithium flux using binary salt mixtures and synthetic LIB leachate. The BCA-IL membrane outperformed other BCA-based membranes in terms of separation factors, achieving values of 10.50 (Li+/Mn2+), 11.75 (Li+/Ni2+), and 10.95 (Li+/Co2+) with a lithium flux of 0.12 mol m−2 h−1 when processing synthetic LIB leachate. Under the same conditions, the BCA-HMO membranes exhibited a higher lithium flux (0.51 mol m−2 h−1) but with lower separation factor values of 3.39 (Li+/Mn2+), 3.62 (Li+/Ni2+), and 3.36 (Li+/Co2+). The use of plant-derived cellulose acetate (CA) as an alternative to BCA was also assessed; however, despite promising ideal lithium selectivity values (for example, 112 for Li+/Ni2+ in the case of CA-HMO membrane), their conductivity was up to two orders of magnitude lower than that of BCA-based membranes. All these findings highlight the promising potential of BCA-based membranes for lithium recovery from lithium-ion battery leachates.

The rising lithium-ion battery market drives lithium demand and requires efficient and selective lithium recovery methods from aqueous sources. Membrane technologies can address environmental and inherent efficiency issues in conventional lithium extraction methods. This study presents the synthesis of novel lithium-selective mixed matrix membranes (MMMs) by integrating 0–30 wt% of a lithium selective filler named hydrogen manganese oxide (HMO) into a sulfonated polyethersulfone (SPES)-Nafion polymer matrix. The membranes were produced by casting and thoroughly examined to assess their chemical, physical, morphological, thermal, and mechanical characteristics. The transport of lithium across membranes was evaluated in diffusion and electro-diffusion studies. The membrane containing 20 wt% of HMO exhibited the highest ideal selectivity values, which were 1.05 for Li+/K+, 1.20 for Li+/Na+, and 13.36 for Li+/Mg2+; and more than 97% increase in lithium-ion conductivity when compared with the control membrane without HMO. In diffusion experiments, the binary separation factors for Li+/K+, Li+/Na+, and Li+/Mg2+ were 0.71, 1.52, and 11.83, respectively, while under electro-diffusion conditions, the corresponding values were 0.82, 1.55, and 9.88. Above 20 wt% of HMO, membranes lose their separation capacity as HMO aggregates inside the membrane structure. The higher selectivity of membranes towards Li+ in the presence of Mg2+ is due to magnesium's larger hydrated radius and higher hydration energy compared to lithium. Overall, the prepared membranes demonstrated a promising potential for green lithium recovery. This study facilitates the advancement of sustainable lithium-selective MMM synthesis.

The goal of miniaturization in microelectronics catalyzes the evolution of field‐effect transistors (FETs), transitioning from classical scaling approaches to innovative architectures like gate‐all‐around FETs. Among these advancements, nanowire field‐effect transistors (NW‐FETs) emerge as a promising solution to the limitations of traditional FET designs, offering improved electrostatic control, reduction of short‐channel effects, and better overall device performance metrics. Metal oxide nanowires (NWs) provide high mobility, excellent optical transparency, mechanical flexibility, and compatibility with thin‐film technology, making them ideal candidates to be the pillar of a new wave of transparent and flexible electronics with unprecedented integration levels. This review highlights the different configurations of NW‐FETs, exploring their fabrication techniques and different advantages, as well as state‐of‐the‐art progress in metal oxide NW‐FETs, such as zinc oxide (ZnO), indium oxide (In 2 O 3 ), tin oxide (SnO 2 ), and multicomponent materials. To further improve NW‐FET performance, recent developments in doping, surface passivation methods, and post‐fabrication treatments are examined, as well as emerging fabrication methodologies. By addressing material limitations and integrating innovative design strategies, metal oxide NW‐FETs are set to play a pivotal role in sustaining Moore's Law and shaping the future of nanoelectronics.

Metal oxide nanostructures have recently gained high attention due to advances in their synthesis, particularly hydrothermal techniques, which allow precise control over their morphology, composition, and crystallinity, as well as integration into devices. Zinc-tin oxide (ZTO) nanostructures, in particular, are notable for their sustainability and multifunctional applications, including catalysis, electronics, sensors, and energy harvesting. Their ternary oxide nature supports a broad range of functionalities. The use of seed layers during synthesis has proven to be beneficial, particularly for binary systems such as ZnO, as it not only impacts the growth of nanostructures but is also advantageous for applications requiring nanostructures supported on substrates, such as in photocatalysis and sensor technologies. This work investigates the effect of various seed layers (e.g., Cu, stainless steel, Cr, Ni) on the hydrothermal synthesis of ZTO nanostructures. Compared to seed layer free methods under similar conditions, the presence of seed layers significantly influenced the resulting structures. The study produced diverse morphologies, including ZnSnO₃ nanowires and Zn₂SnO₄ nanoparticles, octahedrons, and nanowires. Findings suggest a relationship between the seed layer's phase and the resulting nanostructure phase. Furthermore, shorter synthesis durations favored discrete nanostructures, while longer durations facilitated the formation of thin films with nanostructured surfaces. These observations underscore the dual role of seed layers in influencing both the structural phase and growth kinetics of ZTO nanostructures.

Summary Mammalian aldehyde oxidases (AOXs) are complex enzymes dependent on a molybdopterin-active site (Moco), two [2Fe?2S] spectroscopically distinct centers, and one flavin adenine dinucleotide (FAD) cofactor. AOXs belong to the xanthine oxidase (XO) family of mononuclear molybdenum enzymes. AOXs and XO share a high degree of structural similarity forming homodimers that encompass in each subunit a chain of redox centers involved in the transfer of reducing equivalents from substrate oxidation (Moco ? [2Fe?2S] I ? [2Fe?2S] II? FAD) to molecular oxygen. However, AOXs and XO differ in substrate specificity and, while XO has a clear role in the last steps of purine catabolism, AOXs are very promiscuous enzymes. They catalyze a wide diversity of reactions, accept diverse substrates, and play an important role in drug and xenobiotic metabolism. Despite numerous studies, the physiological substrates of AOX and its physiological relevance are still unclear.

Metal-dependent formate dehydrogenases (FDHs) catalyze, under mild conditions, the reversible reduction of CO2 to formate, a versatile C1 feedstock that can contribute to a carbon-neutral economy. Metal-dependent FDHs are the most widespread selenoproteins found in bacteria, and around 44% of them include selenocysteine (Sec) as a ligand to the Mo/W active site. In the sulfate-reducer Nitratidesulfovibrio vulgaris Hildenborough, the main FDH responsible for CO2 reduction is the W/Sec-dependent FdhAB, which is among the most active CO2 reductases reported so far. In contrast to most metal-dependent FDHs, this enzyme is relatively O2-tolerant and can be purified aerobically. In this work, we evaluated the role of Sec in the catalytic and stability properties of the W/Sec-FdhAB. For that, a Sec-to-Cys variant (U192C) was created, its catalytic and spectroscopic properties were characterized, and its crystal structure was determined. Sec substitution by Cys strongly affects activity, decreases the KM for formate, and increases susceptibility to O2. While Sec-to-Cys replacement induces only weak changes of the WV EPR signals, using 77Se-labeled enzyme, we could show that Sec undoubtedly coordinates the W metal in the WV redox state. The crystal structure of U192C confirmed previous findings on the redox switch mechanism of activation and protection of FdhAB, while revealing a putative catalytic intermediate of FdhAB with Arg441 orienting a CO2 substrate analog (probably SO2) in the active site. Overall, the results indicate that Sec plays a critical role in the high activity displayed by W/Sec-FdhAB, and that it may also be involved in or modulate the proton transfer to and from the active site.Metal-dependent formate dehydrogenases (FDHs) catalyze, under mild conditions, the reversible reduction of CO2 to formate, a versatile C1 feedstock that can contribute to a carbon-neutral economy. Metal-dependent FDHs are the most widespread selenoproteins found in bacteria, and around 44% of them include selenocysteine (Sec) as a ligand to the Mo/W active site. In the sulfate-reducer Nitratidesulfovibrio vulgaris Hildenborough, the main FDH responsible for CO2 reduction is the W/Sec-dependent FdhAB, which is among the most active CO2 reductases reported so far. In contrast to most metal-dependent FDHs, this enzyme is relatively O2-tolerant and can be purified aerobically. In this work, we evaluated the role of Sec in the catalytic and stability properties of the W/Sec-FdhAB. For that, a Sec-to-Cys variant (U192C) was created, its catalytic and spectroscopic properties were characterized, and its crystal structure was determined. Sec substitution by Cys strongly affects activity, decreases the KM for formate, and increases susceptibility to O2. While Sec-to-Cys replacement induces only weak changes of the WV EPR signals, using 77Se-labeled enzyme, we could show that Sec undoubtedly coordinates the W metal in the WV redox state. The crystal structure of U192C confirmed previous findings on the redox switch mechanism of activation and protection of FdhAB, while revealing a putative catalytic intermediate of FdhAB with Arg441 orienting a CO2 substrate analog (probably SO2) in the active site. Overall, the results indicate that Sec plays a critical role in the high activity displayed by W/Sec-FdhAB, and that it may also be involved in or modulate the proton transfer to and from the active site.

Polysaccharides in plant cell walls serve as a rich carbon and energy source, yet their structural complexity presents a barrier to efficient degradation. To address this, anaerobic microorganisms like R. flavefaciens have developed sophisticated multi-enzyme complexes known as cellulosomes, which enable the efficient breakdown of these recalcitrant polysaccharides. These complexes are assembled through high-affinity interactions between cohesin (Coh) modules in scaffoldin proteins and dockerin (Doc) modules in cellulosomal enzymes. R. flavefaciens FD-1 harbors one of the most intricate cellulosomes described to date, comprising over 200 Doc-containing proteins encoded in its genome. Despite substantial research on this cellulosome, the role of a group of truncated but functional dockerins, known as group-2 Docs, remains unclear. In this study, we present a detailed structural and binding analysis of a Coh-Doc complex involving the cohesin from the cell-anchoring scaffoldin ScaE and a group-2 Doc that bears only one of the two Ca+2-coordinating loops that characterise the canonical Docs. Our findings reveal a novel tripartite binding mechanism, in which the cohesin can simultaneously bind two distinct dockerin units in three alternative conformations. This discovery provides new insights into the modular versatility of the R. flavefaciens cellulosome and sheds light on the mechanisms that enhance its efficiency in polysaccharide degradation.

The bacterium Geotalea uraniireducens, commonly found in uranium-contaminated environments, plays a key role in bioremediation strategies by converting the soluble hexavalent form of uranium (UVI) into less soluble forms (e.g. UIV.). While most of the reduction and concomitant precipitation of uranium occur outside the cells, there have been reports of important reduction processes taking place in the periplasm. In any case, the triheme periplasmic cytochromes are crucial players, either by ensuring an effective interface between the cell´s interior and exterior or by directly participating in the reduction of the metal. Therefore, understanding the functional mechanism of the highly abundant G. uraniireducens’ triheme cytochromes is crucial to assist the elucidation on the respiratory pathways in this bacterium. In this work, a detailed functional characterization of the triheme cytochromes PpcA and PpcB from G. uraniireducens was conducted using NMR and visible spectroscopy techniques. Despite sharing high amino acid sequence and structural homology with their counterparts from G. sulfurreducens, the results obtained showed that the heme reduction potential values are less negative, the order of oxidation of the hemes is distinct, and the redox and redox-Bohr network of interactions revealed unprecedented functional mechanisms of the G. uraniireducens cytochromes. In these cytochromes, the reduction potential values of the three heme groups are much more similar, hence covering a narrow range of values, features that facilitate the directional electron flow from the inner membrane, thereby favouring the optimal reduction of uranium.

Flow electrode capacitive deionization (FCDI) is a desalination technology employing flowable carbon slurries to remove salt from an influent through the electro-sorption of ions at the surface of pores of activated carbon particles. This study presents an extensive morphological, electrochemical and rheological analysis of flow electrodes prepared using commercial (YP50F, YP80F, Norit, PAC) and lab-synthesized (KUA, PAC-OX) activated carbons. Simultaneous optimization of particle size, surface area, and surface chemistry of activated carbons is essential to enhance desalination efficiency in FCDI applications. The lab-made highly microporous activated carbon (KUA), prepared from a Spanish anthracite, exhibited a remarkably high specific surface area ( 2800 m2/g) but required first a particle size reduction through ball milling (from 56 μm to 12 μm) for the respective flow electrodes to achieve flowability. The slurry of milled fine KUA (designated as KUAF) shows a specific capacitance of 55 F/g, a 38-fold increase compared to its pristine form. The KUA-F flow electrode also achieved a maximum salt adsorption capacity of 185 mg/g, outperforming the leading commercial alternative (YP80F) by 26 %. The FCDI cell with the KUA-F flow electrode exhibited a desalination efficiency of 79 % at 15 wt% loading, surpassing YP80F by 29 %. In contrast, using PAC-OX (oxidized form of PAC), despite increasing oxygen functional groups and with relatively higher specific surface area, led only to a 2 % improvement in desalination performance, highlighting that oxidation alone at larger particle sizes and broader distribution is insufficient.

As billions of people suffer from water scarcity, finding sustainable water resources is imperative. Flow capacitive deionization (FCDI) is a highly promising desalination process that can produce clean water from saline streams such as brackish and seawater. Conventional FCDI systems employ Computerised Numerical Control (CNC)-milled graphite plates that serve as current collectors and flow electrode channels. However, they have drawbacks such as high manufacturing costs, waste generation, and the difficulty of producing complex geometries required for efficient flow electrode mixing. Here, we successfully demonstrate that 3D-printed flow electrode gaskets, made of non-conductive polyethylene terephthalate glycol (PET-G) or a carbon black-infused conductive polylactic acid (PLA), are viable alternatives to traditional graphite plates. In specific cases, the desalination and energy efficiency in FCDI cells with 3D-printed conductive gaskets were even 25 % and 10 % higher, respectively, compared to traditional CNC-milled current collectors. The transition to 3D printing offers notable benefits, such as the competence to fabricate complex designs that enhance internal mixing and charge percolation. This innovation represents a change of paradigm in the way FCDI cells should be designed and manufactured, using additive manufacturing, which represents an efficient, scalable, and cost-effective substitute for the conventional approach, contributing therefore for the advancement of FCDI desalination technology.

This study pioneers the application of deep eutectic solvents (DES) as electrolytes in flow electrode capacitive deionisation (FCDI) desalination systems, providing a novel and improved alternative to aqueous flow electrodes. The deep eutectic solvent, choline chloride-urea (ChCl-U), was selected for its wide electrochemical stability window, allowing voltages exceeding 1.23 V, which is the limit for aqueous flow electrodes. The effect of water doping on the viscosity and performance of the DES flow electrodes was also investigated. Cyclic voltammetry confirmed the electrochemical stability, while rheological and electrochemical impedance spectroscopy revealed that the addition of water reduced the viscosity and enhanced the conductivity of ChCl-U, making it suitable for use as an electrolyte in FCDI. Desalination experiments were performed within a potential range of up to 2.2 V. The ChCl-U flow electrode, containing 20 wt% water and 10 wt% activated carbon, achieved the best balance between desalination efficiency (83 %), desalination rate (0.17 mg/cm2.min), and effluent quality. Furthermore, 1H NMR analysis confirmed the absence of traces of the deep eutectic solvent in the dilute stream. The results highlight the potential of DES flow electrodes to enhance desalination processes by enabling higher operational voltages and improved performance, thereby paving the way for more efficient FCDI desalination systems.

Electromembrane processes are employed in critical applications such as desalination, lithium recovery, and salinity gradient energy conversion. However, issues like fouling and concentration polarisation may limit their effectiveness. Profiled ion-exchange membranes offer several advantages over flat membranes, including improved fluid mixing, enhanced mass transfer, lower pressure drop (thus, lower energy consumption), and elimination of the spacer’s shadow effect. Nonetheless, their preparation is considerably more complex than that of flat membranes. In this study, we pioneered the use of solvent-free fused deposition modelling (FDM) 3D printing to fabricate flat and profiled (chevron and stripe) cation-exchange membranes (CEMs). The functionalisation of the 3D-printed membranes into CEMs was achieved via sulfonation. The optimised electrical resistance and permselectivity of the prepared membranes were 10.7 ± 4 Ωcm2 and 97.3 ± 4 %, respectively, after 14 h of sulfonation, closely matching commercial alternatives (e.g., FUMASEP FKB-PK-130, 9.7 ± 3 Ωcm2 and 96.7 ± 1 %). Sulfonation durations exceeding 14 h increased the membranes’ electrical resistance due to the formation of sulfone cross-bridges that do not participate in cations’ exchange. Since FDM 3D printing is a solvent-free and additive manufacturing method, it significantly reduces waste during membrane fabrication, resulting in an E-factor value of 1.5. Therefore, this work opens a path toward customisable, scalable, and greener CEM production for electrochemical applications ranging from the recovery of critical raw materials and water desalination to renewable energy conversion.

Flow electrode capacitive deionization (FCDI) is an emerging desalination technology that utilises flowable electrodes and can be operated in diverse configuration modes. This study provides a systematic assessment of the three main configuration arrangements under a voltage range between 0.8 and 2.0 V: isolated closed-cycle (ICC), short-circuited closed-cycle (SCC), and single-cycle with separate concentrate chamber (SCSC). The ICC mode shows the highest specific energy consumption (up to 72.02 Wh/mol of NaCl at 2.0 V) and low operational stability manifested by extreme alteration of pH in the electrode compartments (anode compartment pH down to 2.17; cathode compartment pH up to 12.08), which leads to the need for frequent electrode regeneration or replacement. In comparison to the ICC mode, the SCC mode exhibited superior performance, with a 44.3 % increase in salt removal and up to 3.95 % higher current efficiency at 2.0 V, due to the regeneration of electrodes through short-circuiting, as it reduces the electrical resistance and minimises the side reactions. The SCSC mode emerged as the most stable and reliable among the three, with uniform current and conductivity profiles, as well as minimal pH fluctuations, which is critical to produce treated water within desired quality standards. These findings highlight the promising potential of SCSC mode as an optimal configuration for scalable, continuous and energy-efficient FCDI systems, providing a balanced solution for long-term desalination with reduced operational complexity and costs.