Search Results (1,164)

Voltage-sensitive ion channels are glycoprotein macromolecules that carry ion currents across membranes of nerve and muscle fibers. The hypothesis presented helps explain the changes that convert an insulating ion channel into an ion conductor, stating that it undergoes a structural transformation on threshold reduction in the voltage across the membrane. Experimental data show that the excitable membrane is a ferroelectric liquid crystal. The Channel Activation by Electrostatic Repulsion hypothesis proposes the following: electrical attractions between boundary surface charges compress the polar channel into a compact smectic phase with induced dipoles. Critical depolarization eliminates surface charges and dipoles, decreasing the dielectric permittivity of the ion channel. This increases the repulsive electrostatic forces between positively charged residues in the four S4 segments. These forces form a selectivity filter dome and cause a proteinquake to a chiral nematic phase. The selectivity filter allows ions to enter as it strips their hydration waters. The permeant ions occupy hydrogen bonds of ion-conducting helices, displacing protons. Disordered regions between adjacent helices form liquid line defects. In the thermal chaos of physiological temperature, a line defect occasionally connects the inner and outer surfaces, forming a transient ion pathway that carries unpredictable surges of permeant ion currents, as observed in experiments. Tests for this hypothesis are proposed. Full article

Photosynthetic water oxidation is catalyzed by the Mn4CaO5 oxygen-evolving complex (OEC) of photosystem II (PSII), where hydrogen-bonding and ion-binding networks regulate proton transfer, substrate-water delivery, and S-state advancement. Acetate binding inhibits oxygen evolution, competes with chloride, and stabilizes the $S=5/2$ spin isomer of the S${}_2$ state, but its donor-side binding site remains unresolved. Here, we combine EPR spectroscopy, pH-dependent oxygen-evolution measurements, mutagenesis, and QM/MM calculations to support a donor-side acetate-binding model and determine how acetate perturbs the OEC environment. Acetate increases the ratio of the $g=4.1$ to $g=2$ S${}_2$-state EPR signals in spinach PSII membranes and cyanobacterial PSII core complexes, with stronger stabilization persisting to higher pH in spinach PSII. The D1-N87A Synechocystis PSII variant exhibits spinach-like acetate sensitivity and pH-dependent oxygen-evolution behavior, with an effective acidic $p{K}_a$ of approximately 5.3, versus 4.2 for wild-type cyanobacterial PSII, implicating long-range perturbations of the narrow-channel hydrogen-bonding network. QM/MM calculations support acetate binding near the D1-D61/W1 region, where the acetate-bound $S=5/2$ isomer is only 1.0 kcal mol${}^{-1}$ higher in free energy than the $S=1/2$ isomer, consistent with the observed spin-isomer equilibrium shift. These results reveal how acetate perturbs proton-transfer and chloride-binding processes in PSII. Full article

We investigate the ultrafast dynamics of a visible-light-driven salicylaldehyde Schiff base-functionalized molecular motor using non-adiabatic molecular dynamics (NAMD) at the orthogonalization-corrected method 2 and the multireference configuration interaction (OM2/MRCI) level. Results reveal a dynamic competitive interplay between E → Z photoisomerization and excited-state intramolecular proton transfer (ESIPT). Importantly, we reveal a direct coupling mechanism between double-bond rotation and proton transfer: within a critical 500–900 fs window, ESIPT transiently stalls rotor rotation while modulating the central double-bond order. The S₁ state lifetime is ~1677 fs. Time-resolved fluorescence analysis further predicts rapid fluorescence quenching within ~37 fs accompanied by a pronounced spectral red-shift, indicating that the system quickly enters a dark state with negligible oscillator strength. This study provides atomistic insights into the relaxation pathways of visible-light-driven motors, offering a theoretical basis for designing efficient long-wavelength responsive molecular machines. Full article

The oxygen-evolving center (OEC) in photosynthesis is a unique biological Mn₄CaO₅-cluster that splits water into electrons, protons, and dioxygen. It is a great challenge for chemists to develop a robust and precise mimic of the OEC in the laboratory. Herein, we report the formation of a rare-earth-element-containing Mn₄YO₄-cluster that represents an excellent and robust model of the OEC. The key synthetic precursor, the Mn₃YO₂-cluster, is reported for the first time, which possesses an identical mixed-valence Mn^III₂Mn^IV metal core and a hydrogen-bonding network coordination sphere. This precursor is very reactive and can convert into various compounds in solution. Importantly, it has been found that the presence of organic bases significantly influences the distribution of intermediates and promotes the formation of the Mn₄YO₄-cluster. Meanwhile, two Mn₄YO₄-clusters are described, which closely mimic the main metal-oxide core and peripheral ligands, as well as the oxidation states of the four Mn ions in the OEC, revealing that both the terminal ligands and a bridging carboxylate are variable. This new Mn₄YO₄-cluster displays a remarkable stability in the presence of water in acetonitrile solution. These findings shed new light on the synthesis of rare-earth-element-containing clusters and the rational design of robust artificial water-splitting catalysts, and provide chemical insights into the dynamic structural changes of both biological and artificial clusters. Full article

Proton Exchange Membrane Fuel Cells (PEMFCs) have emerged as promising clean-energy-conversion devices for various applications, including transportation and stationary power generation. The accurate modeling and parameter estimation of PEMFCs are fundamental to optimizing their performance, extending their operational lifespan, and facilitating their widespread commercialization. However, their inherent nonlinear characteristics and complex electrochemical processes present significant challenges in developing accurate mathematical models and reliable parameter-estimation methods. This review systematically examines the state of the art in PEMFC parameter estimation and modeling, with particular emphasis on the critical challenges posed by nonlinearities, the evolution of analytical and computational methods, and the role of sensitivity analysis in model refinement. The paper synthesizes findings from recent studies employing evolutionary algorithms, metaheuristic techniques, reinforcement learning, and hybrid approaches, evaluating their relative merits in terms of accuracy, convergence speed, and robustness. Furthermore, it explores how sensitivity analysis provides valuable insights into parameter influence under varying operational conditions, guiding model optimization efforts. The review identifies persistent gaps in current methodologies, particularly regarding generalizability across different fuel cell types and real-time applicability, while highlighting promising directions for future research, including hybrid algorithms and advanced data-preprocessing techniques. Full article

Sulfonamides are a fundamental class of compounds with diverse pharmacological applications. Here, two benzene-1,3-disulfonamide-containing cycloalkyne compounds were designed to demonstrate the strained conformations due to the 11-membered ring. Their structures were experimentally analyzed using single-crystal X-ray crystallography and nuclear magnetic resonance (NMR) spectroscopy. The molecules exhibit flexible sulfonamide conformations together with characteristic distortions of the benzene and alkyne moieties. Comparing the compound data obtained, the proton NMR chemical shift of hydrogen at the 2-position of the benzene ring shows a correlation of a dihedral angle involving the benzene ring and sulfonamide sulfur, and the carbon NMR shift suggests an angle distortion of the alkyne. The conformations of the crystal structure and the solution state in DMSO are supported by NOESY spectra and DFT calculations. The relative chemical shift differences were quantitatively reproduced by DFT calculations. We believe this fundamental research will contribute to the design and development of sulfonamide–alkyne–benzene-based medium-sized heterocyclic molecules with detailed conformation predictions. Full article

Single-electron emission from the coronene (C₂₄H₁₂) molecule induced by the impact of 100 keV H⁺ projectiles is investigated using the continuum distorted wave–eikonal initial state approximation within a semi-classical impact-parameter framework. Multi-center orbitals in the initial channel are derived using the Gaussian quantum chemistry software package, while wave functions of the emitted electron in the exit channel are evaluated using a spherically averaged static potential of the molecular core. The evaluated total ionization cross sections and probabilities are compared and discussed with results obtained from a simplified description of the molecule in which the molecular geometry is ignored. The ionization cross sections of the molecular orbitals generally increase monotonically with decreasing binding energy; however, several deviations from this overall trend are observed. Both the overall trend and the deviations are interpreted in terms of information-theoretical quantities. Full article

We propose a lattice structure and space group symmetry, Pmmm (No. 47), for the QCD condensate ground state, whose Wyckoff positions are occupied by the four light quarks and antiquarks $u$, $d$, $\tilde{u}$, $\tilde{d}$. These serve as the fundamental building blocks of both the condensate lattice ground state and the baryonic and leptonic particle excitations embedded within it as topological defects of the nominal Wyckoff occupation, offering a more structured alternative to the QCD instanton liquid picture. Building on Bloch quark wave solutions of a tight-binding Hamiltonian defined on this lattice, we propose a generalization of Einstein’s Equivalence Principle: composite particles embedded in the lattice and propagating by tunnelling cannot distinguish acceleration by gravity, the strong, weak, or electromagnetic forces, or curvature of the lattice itself, arising from local variation in unit cell shape. We derive an eight-by-eight tight-binding Hamiltonian that decouples into two four-by-four blocks separating the quark and antiquark sectors. Electrons, positrons, protons, neutrons, deuterons, and α-particles are embedded in the lattice as defect-induced deviations from the nominal Wyckoff occupation, with their spin and helicity emerging structurally from this picture. We further propose that the lattice’s unit cells carry a small nonzero rest mass, whose collective gravitational effect across a galactic halo may account for the discrepancy between visible mass and rotation curves, identifying the Pmmm condensate as a dark matter candidate. Finally, we outline a mechanism near black hole horizons by which local melting of the condensate lattice followed by quark reactions that conserve the number and flavor of the quarks could yield a new route to baryon asymmetry. We propose a framework that goes several steps beyond the Standard Model by introducing a Pmmm space group unit cell for the QCD condensate ground state, built from the four light quarks and antiquarks $u$, $d$, $\tilde{u}$, $\tilde{d}$. We further propose that topological defects of the Pmmm condensate lattice are the geometric origin of particle excitations. Full article

Graphene oxide (GO) membranes present a compelling alternative to the permeability-selectivity trade-off inherent in conventional polymer membranes. However, the incomplete mechanistic understanding and the absence of scalable, defect-controlled fabrication processes continue to hinder their practical deployment. This review synthesizes and integrates transport mechanisms, computational modeling, fabrication, and translational constraints across graphene-based membrane architectures into a comprehensive design-oriented framework. Five key aspects of this synthesis are highlighted. Firstly, the available evidence supports a three-regime transport model, which unifies viscous near-frictionless flow, activated molecular hopping, and solution–diffusion. This reframes selectivity as a tunable function of the C/O ratio and interlayer chemistry. Secondly, a quantitative parity analysis of literature data reveals that classical molecular dynamics tends to overestimate GO laminate water permeance by a representative factor of approximately 3–8× across the matched comparisons examined. This discrepancy can be corrected using a tortuosity–porosity factor derived from wet-state XRD. Machine-learning force fields (GAP, MACE), while still in an early stage of development with limited reported applications, narrow the residual discrepancy to within 1.5–2× in the studies reviewed. Thirdly, a tiered computational roadmap identifies nuclear quantum effects as critical for proton-transport applications but unresolved for water permeance in GO laminate geometry. Fourthly, performance across water nanofiltration, gas separation, ion recovery, and osmotic energy harvesting is benchmarked against commercial references, with explicit caveats regarding the heterogeneity of testing conditions across cited studies, alongside a technology readiness assessment. Lastly, a standardized 500-h hydraulic stability protocol is proposed to facilitate cross-laboratory comparison. Collectively, this synthesis provides a structured, albeit not exhaustively validated, basis for the discussion of next-generation membrane design. Full article

Hydrogen is increasingly recognised as one of the leading pathways for decarbonising the maritime sector. Proton exchange membrane fuel cell (PEMFC) hybrid propulsion is emerging as a promising low-emission technology; however, its safe deployment depends on marine engineers being trained to interpret and manage coupled hydrogen, fuel cell, battery, and electric propulsion systems. However, a critical training gap remains. Alternative fuel guidance identifies hazards and safety barriers, but does not consistently translate hydrogen PEMFC–LFP operation into observable competence assessment evidence and implementation pathways. This paper develops a demonstrator-anchored and regulatory-grounded competency framework for marine engineers operating compressed hydrogen PEMFC-lithium iron phosphate (LFP) battery–electric propulsion systems. A structured purposive narrative synthesis combined prototype vessel testing evidence with regulatory safety training, and competency framework literature. The experimental operational data, including compressed hydrogen supply, pressure regulation, PEMFC charging, battery buffering, propulsion current demand, voltage sag, state-of-charge response, monitoring tasks, alarms, and emergency isolation, were used as operational anchors rather than calibrated performance validation evidence. The analysis identified six competency domains. Compared with IGF/LNG model course training, the largest hydrogen-specific competence gaps concerned compressed hydrogen handling, PEMFC purge and shutdown logic, battery-buffered propulsion monitoring, integrated emergency shutdown, and communication during abnormal operation. These findings were translated into assessable learning outcomes, a provisional 40 h training module, instructor prerequisites, practical assessment evidence, a proposed digital twin/VR supplement, and a staged implementation roadmap. The proposed framework provides a structured pilot pathway. It translates operational testing evidence into assessable maritime education and training. It also establishes a foundation for future competency development and certification for commercial vessels. Full article

The electrocatalytic nitrate reduction reaction (NO₃RR) enables sustainable ammonia synthesis from nitrate waste, yet its complex mechanism and severe competition from the hydrogen evolution reaction (HER) demand precise control over interfacial electronic structures. This review provides a mechanistic overview of interfacial electron engineering for NO₃RR via charge transfer, d-band center modulation, and d-p orbital coupling. We propose a reverse-engineering framework that starts from the three kinetic bottlenecks of NO₃RR (nitrate activation, *H supply, and intermediate poisoning) and back-extracts the required electronic effects (charge transfer, d-band shift, and d-p orbital coupling). From this perspective, we cover the construction of built-in electric fields (BIEFs) in heterojunctions, engineering atomic-scale active sites (e.g., single-atom and dual-atom catalysts), and exploiting hydrogen spillover and reverse spillover for cross-spatial proton delivery. Given that rational interfaces dynamically evolve under operating conditions, we highlight that in situ/operando characterization captures the dynamic restructuring of valence states, coordination environments, and morphologies, establishing clear structure–electron–activity relationships. Finally, we discuss key challenges and outline future directions, including machine learning-accelerated screening, dynamic interface regulation, and synergistic integration of multiple electronic effects. This review offers a comprehensive framework for interfacial electron engineering, guiding rational design of next-generation NO₃RR electrocatalysts. Full article

Harmalol is a β-carboline alkaloid exhibiting promising antioxidant properties; however, a comprehensive understanding of its radical scavenging mechanisms in aqueous media across a wide pH range remains limited. In this study, the antioxidant activity of harmalol toward hydroperoxyl radicals was investigated theoretically at the M06-2X/6-311+G(d,p)/PCM(water) level by combining thermodynamic and kinetic analyses over the pH range 2–13. The calculations revealed that the antioxidant behavior of harmalol strongly depends on its protonation state, tautomeric form, and the surrounding pH. Under physiological conditions, the monocationic form predominates, with a smaller contribution from the neutral/zwitterionic I and II species, and radical scavenging proceeds predominantly via proton-coupled electron transfer (PCET)-type hydrogen-transfer reactions involving the monocationic, neutral and zwitterionic I forms as well as radical adduct formation (RAF) mechanism involving zwitterion I. Analysis of SOMO distributions, spin densities, and atomic charges confirmed that the hydrogen transfer reactions for monocationic, neutral and zwitterionic I forms do not follow a classical hydrogen atom transfer (HAT) mechanism. The zwitterion I and neutral forms of harmalol exhibited significantly higher apparent rate constants for the PCET reaction than the monocationic species. Under alkaline conditions, the monoanionic forms exhibit the most favorable thermodynamic parameters toward radical scavenging via formal hydrogen transfer mechanism. Relaxed potential energy surface scans suggest that hydrogen transfer from both monoanionic forms may proceed through a barrierless pathway, while radical adduct formation can also contribute to the antioxidant activity under strongly basic conditions. In addition, monoanion II efficiently participates in single-electron transfer (SET) reactions characterized by very high apparent rate constants. Overall, the results demonstrate that the antioxidant efficiency of harmalol increases with increasing pH and provide detailed insight into the pH-dependent radical scavenging mechanisms of β-carboline derivatives in aqueous environments. Full article

Electrochemical CO₂ reduction to ethanol is a promising route for circular carbon fuel and chemical production, but practical implementation remains limited by coupled membrane, catalyst, transport, and system integration constraints. This Communication reassesses anion-exchange membranes (AEMs) and bipolar membranes (BPMs) for CO₂-to-ethanol electroreduction by integrating recent 2024–2026 advances with foundational membrane and CO₂RR literature. The central argument is that membrane selection is not a passive separation choice; instead, it actively controls local pH, charge carriers, CO₂ availability, carbonate formation, water activity, proton/cation delivery, product crossover, and downstream techno-economic assessment (TEA) and life-cycle assessment (LCA) burdens. AEM operation can create alkaline cathodic microenvironments that favor C–C coupling, but bicarbonate/carbonate formation imposes carbon-loss, salt-management, and CO₂-recovery penalties. BPM operation can improve pH separation and carbon management through water dissociation and bicarbonate acidification, but its viability depends on water-dissociation efficiency, co-ion exclusion, junction stability, hydration management, and voltage control. Recent ethanol-selective catalyst studies further show that copper oxidation state, grain boundaries, subsurface dopants, ionomers, interfacial wettability, and dynamic operation interact strongly with membrane-imposed microenvironments. This Communication proposes a membrane-centered decision framework linking AEM/BPM selection with ethanol selectivity, single-pass carbon utilization, energy efficiency, durability, TEA/LCA boundaries, and future reactor design. Full article

Decarbonizing heavy-duty logistics requires powertrains that integrate novel topology design, degradation-aware optimization, and robust dynamic performance under real-world operational loads. While solid oxide fuel cells offer high efficiency, their application in transportation is hindered by thermal fatigue. This study proposes a novel hybrid powertrain topology integrating a metal-supported solid oxide fuel cell (SOFC), a micro gas turbine (MGT), and an aluminum–silicon phase change material (PCM) thermal buffer. A high-fidelity dynamic model is developed and coupled with a multi-objective optimization framework to size the PCM buffer and battery pack, balancing capital expenditure and system lifetime. Furthermore, a degradation-aware energy management strategy based on a thermal state-of-charge metric is introduced. Simulations over a 10 h dynamic drive cycle indicate that the optimal configuration (120 kg PCM, 80 kWh battery) extends the SOFC’s simulated remaining useful life to 38,400 h, a 2.5-fold improvement over unbuffered systems. Concurrently, the proposed energy management strategy reduces the MGT mechanical wear index by 98% compared to conventional load-following strategies. The system demonstrates robust performance across ambient temperatures from −20 °C to +45 °C and achieves a 22% reduction in projected capital expenditure compared to standard proton exchange membrane fuel cell powertrains. This topology offers a highly durable and economically viable pathway for next-generation zero-emission heavy-duty vehicles. This work addresses a critical gap in the literature: the lack of integrated thermal buffering and degradation-aware control strategies for high-temperature fuel cell systems in dynamic vehicular applications. By coupling a physical latent heat buffer with a novel Thermal-SOC-proportional Energy Management Strategy, the proposed architecture directly targets the primary degradation mechanisms that have historically impeded SOFC commercialization in heavy-duty transport. Full article

The hyperfine structure of the hydrogen atom provides a clean, experimentally relevant two-qubit platform in which the coupled electron and proton spins exhibit rich quantum behavior. We investigate the open-system dynamics of this system under the simultaneous influence of the intrinsic hyperfine coupling, an external static magnetic field (via the Zeeman interaction), and local Markovian dephasing noise. Employing the Lindblad master equation, we derive the exact time evolution of the density matrix for general X-shaped initial states and focus on two complementary measures of quantum coherence—the $L_1$-norm coherence $C_L\left(t\right)$ and the relative entropy of coherence $C_R\left(t\right)$—together with the state purity $P\left(t\right)$. Numerical results reveal that all three quantities display characteristic damped oscillatory evolution. For a vanishing magnetic field, the decay is relatively rapid and smooth, whereas increasing the proton magnetic parameter markedly raises the oscillation frequency and slows the overall envelope of both coherence and purity. Even under stronger dephasing rates, a suitably chosen external field can substantially postpone the loss of quantum features, acting effectively as a control knob that reshapes the coherent unitary dynamics to counteract dissipative effects. These findings underscore the delicate competition between intrinsic atomic interactions and environmental noise, while offering a practical route for protecting quantum resources in spin-based systems. Our work bridges fundamental atomic physics with resource-theoretic concepts and highlights promising strategies for coherence preservation in realistic, controllable quantum platforms. Full article