The Journal of Physical Chemistry B最新文献

Lipid membrane phase separation, which is a thermodynamic physical process, has attracted attention as a dynamic function of cellular interfaces. As membrane tension influences the phase separation of cellular membranes under isothermal conditions, it is essential to clarify the physicochemical mechanism involved. Living cells contain numerous macromolecules that can generate osmotic pressure across the membrane due to the semipermeable nature of the lipid bilayer. In this research, we examined how macromolecular surroundings and the transmembrane osmotic pressure influence membrane phase separation, utilizing model membranes like giant lipid vesicles. We generated osmotic pressure across the membrane using dextran (molecular weights 40,000 and 200,000) and polyethylene glycol (molecular weight 6,000) as model macromolecules. Microscopic observations represented the changes in the percentage of phase-separated vesicles and miscibility temperature caused by osmotic tension, indicating that macromolecular surroundings tend to suppress membrane phase separation, while macromolecular osmotic pressure across the membrane markedly induces phase separation. Lipid membrane phase separation can be regulated by the macromolecular concentration and osmotic pressure across the membrane. This finding offers new insights into the formation and regulation of membrane domains within the macromolecularly crowded environments of living cells.

In this study, we have investigated the concentration-dependent intermolecular dynamics of aqueous solutions of aniline hydrochloride, sodium phenoxide, and 4-methylpyridine using femtosecond Raman-induced Kerr effect spectroscopy at 298 K. The densities, viscosities, and surface tensions of the aqueous solutions were also measured at 298 K. Quantum chemistry calculations of the target aromatics and their clusters with water molecule(s) or a counterion were performed to obtain their optimized structures and cluster interaction energies. In the difference low-frequency Kerr spectra (<250 cm^-1) of the aqueous aromatic solutions and neat water, the first moment (M₁) of the intermolecular vibrational band, which mainly originated from the aromatic ring, showed that the librations of the anilinium cation and phenoxide anion were higher in frequency than that of 4-methylpydine. Furthermore, the libration of the phenoxide anion was also higher in frequency than that of the anilinium cation. Quantum chemistry calculations indicated that the strong hydrogen bonding and compact hydration structure resulting from the negatively charged aromatic ring led to higher-frequency libration of the phenoxide anion than the anilinium cation. In addition, the M₁ increased with increasing concentration. The concentration sensitivities were stronger in aqueous solutions of aniline hydrochloride and sodium phenoxide than in aqueous solutions of 4-methylpyridine. Based on the quantum chemistry calculation results, we conclude that strong aromatic-water and aromatic-counterion interactions lead to a higher-frequency libration of aromatics with charged side groups. The collective orientational relaxation times of the aqueous aromatic solutions showed the fractional Stokes-Einstein-Debye behavior.

The α7-nicotinic acetylcholine receptor (α7-nAChR) is a cation-selective Cys-loop receptor involved in diverse physiological processes and is an important therapeutic target. Multiple cryo-EM structures of putative open states are now available, and their functional relevance is under active investigation. Here, we combined single-channel patch-clamp recordings with atomistic molecular dynamics (MD) simulations to assess the conductive properties of several α7-nAChR structures solved with different ligands. Simulations restrained to the respective cryo-EM structures produced only modest ion flux for all models, inconsistent with experiment, whereas fully unrestrained simulations revealed marked differences in their ability to relax into physiologically conductive ensembles. Two structures, 7KOX and ligand-bound 8V82, consistently stabilized into conductive states whose permeation properties agreed with our measured inward single-channel conductance. The conduction of 8V82 nearly stopped upon removing the ligands resolved in the PDB structures. 8V80 showed only intermittent conduction with ligands, and remained nonconductive without them. 7EKT collapsed into a nonconductive conformation upon relaxation, irrespective of whether the modeled ligands were retained or removed. 9LH5, despite having a transmembrane pore nearly identical to 7KOX's, exhibited approximately 2-fold higher conductance, likely due to a widened extracellular vestibule. Across models, permeation events followed Poissonian statistics with a characteristic entry lag captured by a double-Poisson model. Simulations of outward currents consistently overestimated the conductance compared to experiments, perhaps reflecting the absence of the full intracellular domain in available structural models and/or the presence of current-blocking concentrations of cytosolic Mg²⁺ in patch-clamp cell-attached recordings. These results identify the conformations most compatible with the physiological open state and underscore the importance of unrestrained MD, ligand stabilization, and extracellular-vestibule geometry in shaping α7-nAChR conduction.

Triplet photosensitizers are essential in photocatalytic hydrogen production and photoredox organic transformations, relying on efficient light absorption, intersystem crossing, and subsequent electron or energy transfer processes. Recent developments have focused on transition metal complexes with favorable electronic configurations, such as Cu(I) complexes, which feature extended excited-state lifetimes and reduced nonradiative decay. In contrast, Zn(II) complexes, despite being isoelectronic with Cu(I), are generally dismissed as photosensitizers because they predominantly exhibit ligand-centered emission, and MLCT states, when observed, are short-lived and poorly suited for photocatalysis. Nonetheless, their tunable coordination chemistry, low toxicity, and catalytic potential make them promising candidates. In this work, we demonstrate that Zn(II) complexes can be deliberately engineered to act as efficient triplet photosensitizers by exploiting intraligand charge transfer (ILCT) rather than MLCT. We report a comparative study of Zn(II) complexes supported by redox-noninnocent tridentate pincer ligands bearing different aryl substituents, revealing pronounced differences in triplet-state behavior. Structural analysis shows that coplanarity between the aryl-azo and phenanthroline moieties is essential for efficient ILCT and long-lived triplet emission. To elucidate the role of the metal center, a structurally analogous Cd(II) complex was examined, which exhibits photophysical behavior nearly identical to its Zn(II) counterpart, confirming that the metal primarily enforces ligand geometry rather than participating electronically in the excited state. Both Zn(II) and Cd(II) complexes function as effective photosensitizers for singlet-oxygen-mediated oxidation, achieving photocatalytic efficiencies of approximately 50%. Although this efficiency is lower than that of certain Ir-based systems, this work establishes a design strategy in which unfavorable metal-centered electronic interactions are intentionally bypassed, and the metal serves chiefly as a structural anchor. These findings position Zn(II) complexes as sustainable, earth-abundant photosensitizers and provide a new framework for designing triplet photosensitizers based on closed-shell metal ions.

Ether-based electrolytes have gained increasing attention for energy storage based on their utility as solvate ionic liquids at high concentration and their role in forming effective cointercalation complexes at graphite electrodes. While transferrable atomistic models have been proposed to describe glyme ether solutions at varying concentration and backbone chain lengths, coarse-grained models have not been extensively explored. The need for coarse-grained descriptions is emphasized by the formation of potentially mesoscale aggregate structures which enable efficient ion transport. Herein we describe a simple approach to developing such models using a combination of a charge smearing for long-ranged electrostatics and Boltzmann Inversion to develop short-ranged tabulated potentials. The impact of long-ranged interactions on electrolyte structure and the ingredients to the coarse-grained models are discussed along with the importance of system selection for training the short-ranged portion. Overall, the final model shows good transferability for diglyme and monoglyme, which share an emphasis on ion association, but fails to capture the solvent separated ionic structure of triglyme electrolytes.

Post-translational modifications (PTMs) such as phosphorylation, acetylation, and methylation critically expand proteome function by regulating protein structure and interactions. Hydropathy changes serve as a main driving force; however, a quantitative, mechanistic understanding of how their distinct chemical changes alter local protein hydropathy remains limited. To bridge this gap, we extend the Protocol for Assigning a Residue's Character on a Hydropathy (PARCH) scale, a residue-level hydropathy scale, to systematically evaluate PTM-induced physicochemical changes. By applying this method, we quantify the effect and magnitude of hydropathy shifts at modification sites and map how these perturbations influence the local protein environment. Our analysis reveals that phosphorylation exerts a strong, consistent hydrophilic effect, significantly increasing PARCH values due to the introduction of a large, charged phosphate group. In contrast, N-lysine acetylation, which neutralizes charge, shows context-dependent effects, predominantly increasing the hydrophobicity but occasionally enhancing the local hydrophilicity. Methylation presents the most complex signature, with no uniform trend, where increased side chain bulk can paradoxically increase water exposure despite the modification's nonpolar nature. This study establishes the PARCH scale as a powerful quantitative tool for deciphering how PTMs regulate the local hydropathy landscape of proteins, providing a predictive foundation for understanding their structural, hydropathy, and functional consequences.

We introduce a novel series of excited state intramolecular proton transfer (ESIPT)-active 2-phenylbenzimidazole fluorophores (1-3) as highly selective turn-on probes for insulin amyloid aggregates (IAAs). Synthesized via an eco-friendly, metal-free route, these probes show high specificity for IAAs over native insulin and Thioflavin-T (ThT). Density functional theory (DFT) calculations confirm the intrinsic ESIPT mechanism, while photophysical studies reveal that a specific binding mode restricts molecular motion, enhancing quantum yield and fluorescence lifetime. Crucially, the lead compound (3) binds to a unique site distinct from ThT, as proven by competitive binding and Förster Resonance Energy Transfer (FRET) assays. It also exhibits superior affinity, a low detection limit, the ability to modulate aggregation kinetics, and excellent biocompatibility. This work moves beyond ThT, positioning the ESIPT-active 2-phenylbenzimidazole scaffold as a promising theranostic tool for amyloid-related pathologies such as Type-2 diabetes.

We demonstrate that classical density functional theory (DFT) based on the PC-SAFT equation of state is a fast, accurate, and predictive model to predict multicomponent adsorption in porous materials, which is an essential step toward the design of next-generation adsorbents for relevant applications. Using GPU acceleration, adsorption isotherms and adsorption enthalpies can be obtained in a matter of seconds, which is several orders of magnitude faster than grand canonical Monte Carlo (GCMC) simulations. Using metal-organic frameworks as adsorbents and non- or weakly polar molecules as adsorbates, we validate our approach by performing GCMC simulations for binary, ternary, and quaternary mixtures with practically relevant applications, such as noble gas separations (Kr/Xe, Ar/Kr/Xe), direct dry air capture (CO₂/N₂), hydrogen enrichment (CH₄/H₂, CH₄/H₂/N₂) and adsorbed natural gas (CH₄/C₃H₈, CH₄/C₂H₆/C₃H₈, CH₄/C₂H₆/C₃H₈/N₂). Classical DFT reproduces loadings and adsorption enthalpies of the mixtures in close agreement with results from GCMC simulations. Thus, classical DFT expands our toolbox for studying multicomponent adsorption.

Cryptochromes act as flavin-binding photoreceptors in many organisms. The green alga Chlamydomonas reinhardtii contains both a plant cryptochrome (pCRY) and an animal-like cryptochrome (aCRY) with very distinct photochemistry. pCRY functions as a blue light receptor, whereas dual-function aCRY acts as a (6-4) photolyase and as a photoreceptor up to 680 nm. aCRY additionally uses 8-hydroxy-5-deazaflavin (8-HDF, F0) as a light-harvesting pigment. The proton donor to flavin in pCRY, an aspartic acid, is replaced by an asparagine in aCRY. Here, the effects of the exchange in aCRY-N395D are studied with and without 8-HDF using nanosecond time-resolved UV-vis and FTIR difference spectroscopy. We show that the exchange of a single amino acid transforms both the photochemistry and the conformational response, even to the level of functionality, by slower photoactivation for DNA repair. Proton transfer from D395 to flavin and hypsochromic shifts occur in aCRY-N395D as in pCRY but with ultrafast kinetics. The flavin neutral radical is formed before 100 ns as opposed to microseconds in pCRY and milliseconds in aCRY. Hallmarks of conformational changes of plant cryptochromes are initiated in aCRY-N395D highlighting the importance of aspartate for signaling. These insights strongly improve our understanding of the differentiation of protein functions within the cryptochrome/photolyase superfamily.

Molten chloride fast reactors (MCFRs) are emerging as a promising class of molten salt reactor (MSR) designs due to their ability to dissolve large amounts of major actinides while keeping low melting points and sustaining a hard neutron spectrum. In this context, understanding the transport properties of molten salts─such as viscosity and self-diffusivity─is essential for the design and optimization of MSRs with efficient heat transfer. However, an important gap remains in the literature regarding the transport properties in molten chlorides. In this work, we performed classical molecular dynamics (MD) simulations with the polarizable ion model (PIM) to evaluate the viscosities and self-diffusion coefficients of molten NaCl-MgCl₂-LaCl₃, which was used in our previous work as a simulant for the ARAMIS-A reactor fuel. To validate the accuracy of our approach, calculated transport properties for the NaCl-LaCl₃ binary system were benchmarked against capillary viscometry measurements from the literature and our own pulsed-field gradient nuclear magnetic resonance (PFG-NMR) experiments. Our study compares the roles of NaCl and MgCl₂ on the transport properties of MCFR fuels. Interestingly, we observe that MgCl₂ does not affect LaCl₃-poor and LaCl₃-rich melts in the same way due to the competition between multivalent ions for chloride ions in their first coordination shells and their ability to form cluster species.