化学•材料最新文献

We report on new donor-chromophore-acceptor triads BDX-ANI-NDI and BDX-ANI-xy-NDI where the BDX donor is 2,2,6,6-tetramethylbenzo[1,2-d;4,5-d]bis[1,3]dioxole, the ANI chromophore is 4-(N-piperidinyl)naphthalene-1,8-dicarboximide, the NDI acceptor is naphthalene-1,8:4,5-bis(dicarboximide), and xy is a 2,5-xylyl spacer. The results on these compounds are compared to the analogous derivatives having a p-methoxyaniline (MeOAn) as the donor. BDX^•+ has no nitrogen atoms and only a single hydrogen atom coupled to its unpaired electron spin, and therefore has significantly decreased hyperfine interactions compared to MeOAn^•+. We use femtosecond transient absorption (fsTA) and nanosecond TA (nsTA) spectroscopies, the latter with an applied static magnetic field, to study the charge transfer dynamics and determine the spin-spin exchange interaction (J) for BDX^•+-ANI-NDI^•- and BDX^•+-ANI-xy-NDI^•- at both ambient and cryogenic temperatures. Time-resolved electron paramagnetic resonance (EPR) and pulse-EPR measurements on these spin-correlated radical pairs (SCRPs) were used to probe their spin dynamics. We demonstrate that BDX^•+-ANI-xy-NDI^•- has an unusually long lifetime of ∼550 μs in glassy butyronitrile (PrCN) at 85 K, which makes it useful for pulse-EPR studies that target quantum information science (QIS) applications. We also show that rotation of the BDX group about the single bond linking it to the neighboring phenyl group has a significant impact on the spin dynamics, and in particular the magnitude of J. By comparing the results on these compounds to the analogous MeOAn series, insights into design principles for creating improved spin-correlated radical pair systems for QIS studies are obtained.

Taylor-Aris (T-A) dispersion of a solute in a flowing solvent is a fundamental phenomenon in most mass-transfer processes. Despite its significance and numerous applications in microreactors, colloidal transport in confined media, chromatographic separation, and transport in biological tissues, the effect of the slip length and the topology of surface potential landscapes on T-A dispersion in nanostructured channels has not been studied in detail. We propose a novel methodology for molecular dynamics (MD) simulation of T-A dispersion in such systems, derive an analytical expression for the dispersion coefficient in them, and report on the results of extensive MD simulations of the phenomenon in carbon nanotubes and hexagonal carbon nanochannels. By broadening the topology of the surface energy landscape, we vary the slip lengths, making it possible to distinguish between the effects of confinement, the topology of the energy landscape, and the slip length on the T-A dispersion coefficient. It is demonstrated that measuring the T-A dispersion coefficient in laminar flow is a straightforward and reliable approach for estimating the slip length in nanotubes and other nanostructured materials.

In this study, the AEO_nBO₂ series of block polyoxybutenol ethers was synthesized by combining the AEO series of polyoxyethylene and preparing 1,2-epoxybutane (BO) block polyether using a semicontinuous method. The synthesis was performed by HPLC, MALDI-TOF-MS, FT-IR, and ¹H NMR for structural analysis. The interaction parameters and surface tension of the systems before and after synthesis were studied using surface tension meter. The diffusion process of the systems before and after synthesis was studied using a KRÜSS bubble pressure tensiometer. The surfactant properties of AEO_n and AEO_nBO₂ were evaluated by static and dynamic surface tension measurements. Each system formed a saturated adsorption layer in a water solution. The critical micelle concentration decreased dramatically after the introduction of BO groups, and the diffusion-adsorption process was consistent with the kinetic mechanism of hybrid diffusion. The microscopic self-assembled aggregate micellar behavior of all the systems was investigated using DLS, TEM, and SEM. The micellization process in all systems was spontaneous and enthalpy-driven, forming spherical aggregates, with the BO block reducing the aggregate diameter of the feedstock from 220.06 nm to about one-third of 80.02 nm. In addition, the dynamic contact angle, application, and physicochemical properties such as foaming and foam stabilization of each system were investigated. The contact angle was reduced from 70 to 50° at 120 s of stabilization, with a foam volume of 80 mL in all systems at 200 s. However, the AEO_nBO₂ showed accelerated foam decay at 500 s, with an increase in the contact angle from 70 to 50° at 200 s, but the AEO_nBO₂ showed accelerated foam decay at 500 s, with a decrease in the contact angle from 70 to 50° at 120 s stabilization. At 200 s, the foam volume of all systems was 80 mL, but AEO_nBO₂ showed an accelerated foam decay process, which shows that the BO group can accelerate the foam decay, and the comparative results show that the BO group can also optimize other application properties and physicochemical properties.

Actin is a major cytoskeletal system that mediates the intricate organization of macromolecules within cells. The bacterial cytoskeletal protein MreB is a prokaryotic actin-like protein governing the cell shape and intracellular organization in many rod-shaped bacteria, including pathogens. MreB stands as a target for antibiotic development, and compounds like A22 and its analogue, MP265, are identified as potent inhibitors of MreB. The bacterial actin MreB shares structural homology with eukaryotic actin despite lacking sequence similarity. It is currently not clear whether small molecules that inhibit MreB can act on eukaryotic actin due to their structural similarity. In this study, we investigate the molecular interactions between A22 and its analogue MP265 with MreB and eukaryotic actin through a molecular dynamics approach. Employing MD simulations and free energy calculations with an all-atom model, we unveil the robust interaction of A22 and MP265 with MreB, and substantial binding affinity is observed for A22 and MP265 with eukaryotic actin. Experimental assays reveal A22's toxicity to eukaryotic cells, including yeast and human glioblastoma cells. Microscopy analysis demonstrates the profound effects of A22 on actin organization in human glioblastoma cells. This integrative computational and experimental study provides new insights into A22's mode of action, highlighting its potential as a versatile tool for probing the dynamics of both prokaryotic and eukaryotic actins.

Diphenylamine (DPL) has been widely utilized in industrial chemicals, but its degradation by HO^• radicals in the environment has not been fully studied yet. The present study uses quantum chemical calculations to evaluate the reaction of DPL with HO^• radicals in atmospheric and aqueous environments. The results showed that, in the atmosphere, the diphenylamine reacted with the HO^• radical rapidly, with an overall rate constant of 9.24 × 10¹¹ to 1.34 × 10¹¹ M^-1 s^-1 and a lifetime of 0.17 to 1.55 h at 253-323 K. The calculated overall rate constant in water (k_overall = 1.95 × 10¹⁰ M^-1 s^-1, pH = 3-14) is in excellent agreement with the experimental value (k_overall = 1.00 × 10¹⁰-1.36 × 10¹⁰ M^-1 s^-1). The HO^• + DPL reaction in water could occur following the hydrogen transfer (15.4%), single electron transfer (41.6%), and radical adduct formation (41.7%) mechanisms, clarifying that addition products were not exclusive products. Nevertheless, variations in temperature and pH within aqueous environments had an impact on the mechanisms, kinetics, and degradation products of the reaction of DPL with HO^• radicals.

Selected molecular species containing the disulfide bond, RSSR, have been considered, these ranging from hydrogen disulfide, H₂S₂ (R = H), to diphenyl disulfide with R = C₆H₅. The aim of this work is two-fold: (i) to investigate different computational approaches in order to derive accurate equilibrium structures at an affordable cost, (ii) to employ the results from the first goal in order to benchmark cheaper methodologies rooted in the density functional theory. Among the strategies used for the accurate geometrical determinations, the semiexperimental approach has been exploited in combination with a reduced-dimensionality VPT2 model, without however obtaining satisfactory results. Instead, the so-called "Lego brick" approach turned out to be very effective despite the flexibility of the systems investigated. Concerning the second target of this work, the focus was mainly on the S-S bond and the structural parameters related to it. Among those tested, PBE0(-D3BJ), M06-2X(-D3) and DSD-PBEP86-D3BJ have been found to be the best-performing functionals.

N-terminal disulfide bond oxidoreductase (nDsbD_Ox/Red) proteins display divergent substrate binding mechanisms depending on the conformational changes to the Phe₇₀ cap, which is also dependent on the disulfide redox state. In nDsbD_Ox, the cap dynamics is complex (shows both open/closed Phe₇₀ cap conformations), resulting in an active site that is highly flexible. So the system's active site is conformationally selective (the active site adapts before substrate binding) toward its substrate. In nDsbD_Red, the cap is generally closed, resulting in induced fit-type binding (adapts after substrate approach). Recent studies predict Tyr₄₀ and Tyr₄₂ residues to act as internal nucleophiles (Tyr_40/42O^-) for disulfide association/dissociation in nDsbD_Ox/Red, supplementing the electron transfer channel. From this perspective, we investigate the cap dynamics and the subsequent substrate binding modes in these proteins. Our molecular dynamics simulations show that the cap opening eliminates Tyr₄₂O^- electrostatic interactions irrespective of the disulfide redox state. The active site becomes highly flexible, and the conformational selection mechanism governs. However, Tyr₄₀O^- formation does not alter the chemical environment; the cap remains mostly closed and plausibly follows the induced fit mechanism. Thus, it is apparent that mostly Tyr₄₂O^- facilitates the internal nucleophile-mediated self-preparation of nDsbD_Ox/Red proteins for binding.

It has been reported that the self-assembly pattern of light levitating droplet clusters above the hot gas-liquid interface is dependent on the quantity of droplets. However, the already-reported theoretical explanation of the quantity-dependent self-assembly pattern cannot work well when the quantity of the light levitating droplet exceeds 15. Herein, we propose a new theoretical perspective to understand the self-assembly of a light levitating droplet cluster by referring to the classical densest packing problem of identical rigid circles in a larger circle with the introduction of the minimum total potential energy principle. Amazingly, the theoretical results obtained by this new approach agree well with experimental results, even though the quantity of the light levitating droplet is up to 142. This study deepens our understanding of the quantity-dependent self-assembly pattern of the light levitating droplet clusters and provides significant inspiration for other analogous self-assembly phenomena.

Organosulfates (OS, ROSO₃^-), ubiquitous constituents of atmospheric particulate matter (PM), influence both the physicochemical and climatic properties of PM. Although the formation pathways of OS have been extensively researched, only a few studies have investigated the atmospheric fate of this class of compounds. Here, to better understand the reactivity and transformation of OS under cloudwater- and aerosol-relevant conditions, we investigate the hydroxyl radical (OH) oxidation bimolecular rate constants (k_OS+OH^II) and products of five atmospherically relevant OS as a function of pH and ionic strength: methyl sulfate (MeS), ethyl sulfate (EtS), propyl sulfate (PrS), hydroxyacetone sulfate (HaS) and phenyl sulfate (PhS). Our results show that OS are oxidized by OH with k_OS+OH^II between 10⁸ - 10⁹ M^-1 s^-1, which corresponds to atmospheric lifetimes of minutes in aqueous aerosol to days in cloudwater. We find that k_OS+OH^II increases with carbon chain length (MeS < EtS < PrS) and aromaticity (PrS < PhS), but does not depend on solution pH (2, 9). In addition, we find that whereas the OH reactivity of the aliphatic OS studied here decreases by ∼2× with increasing ionic strength (0-15 M), the reactivity of PhS decreases by ∼10×. The oxidation of EtS and PrS produced organic peroxides (ROOH) as first-generation oxidation products, which subsequently photolyzed; the oxidation of PhS resulted in hydroxylated aromatic products. These results highlight the need for inclusion of OS loss pathways in atmospheric models, and suggest caution in using ambient OS concentration measurements alone to estimate their production rates.