The Journal of Physical Chemistry B最新文献

A Morita-Baylis-Hillman adduct (MBHA) derivative bearing a triphenylamine (TPA) moiety was previously found to react with Nα-acetyl-l-lysine methyl ester with the formation of the corresponding diadduct derivative as the major reaction product and a monoadduct as the minor one. The characterization of photochemical features of the diadduct bearing two triphenylaminocinnamic (TPAC) fluorophores suggested that this compound shows the tendency to undergo the [2 + 2] photocycloaddition reaction. This hypothesis was evaluated in the present study in both the diadduct derivatives obtained with Nα-acetyl-l-lysine methyl ester and Nα-acetyl-l-lysine. The hypothesis was confirmed in the case of the diadduct derivative obtained from Nα-acetyl-l-lysine methyl ester, whereas the UV-A irradiation of the diadduct derivative obtained from Nα-acetyl-l-lysine led to the formation of a strongly emissive (QY = 69%, λ_em = 460 nm) symmetric dimer.

Flavocytochrome c sulfide dehydrogenase (FCC) is an important enzyme of sulfur metabolism in sulfur-oxidizing bacteria, and its catalytic properties have been extensively studied. However, the ultrafast dynamics of FCC is not well understood. We present ultrafast transient absorption and fluorescence spectroscopy measurements to unravel the early events upon excitation of the heme and flavin chromophores embedded in the flavocytochrome c (FccAB) from the bacterium Thiocapsa roseopersicina. The fluorescence kinetics of FccAB suggests that the majority of the photoexcited species decay nonradiatively within the first few picoseconds. Transient absorption spectroscopy supports these findings by suggesting two major dynamic processes in FccAB, internal conversion occurring in about 400 fs and the vibrational cooling occurring in about 4 ps, mostly affecting the heme moiety.

This study investigates the photoreaction mechanism of a hydroxy-substituted oxindole photoswitch using femtosecond transient absorption, fluorescence up-conversion, and computational chemistry. Deprotonation of the hydroxyl group enhances the push–pull character in the molecule, allowing tuning of the photoisomerization mechanism from a precessional to an axial motion. The neutral form of the switch exhibits longer excited-state lifetimes, while the anionic form decays rapidly within 200 fs. Computational models show that deprotonation increases the charge transfer and accessibility to conical intersections. This work highlights how varying the electron-donating strength of a substituent in a push–pull photoswitch tunes the photoreaction mechanism in designing photoswitches.

This study investigates the photoreaction mechanism of a hydroxy-substituted oxindole photoswitch using femtosecond transient absorption, fluorescence up-conversion, and computational chemistry. Deprotonation of the hydroxyl group enhances the push-pull character in the molecule, allowing tuning of the photoisomerization mechanism from a precessional to an axial motion. The neutral form of the switch exhibits longer excited-state lifetimes, while the anionic form decays rapidly within 200 fs. Computational models show that deprotonation increases the charge transfer and accessibility to conical intersections. This work highlights how varying the electron-donating strength of a substituent in a push-pull photoswitch tunes the photoreaction mechanism in designing photoswitches.

Strong interactions of polyelectrolytes (PEs) with water have been used to control many technological applications of PEs in cryopreservation as well as in anti-icing or lubricating coatings. In all of these cases, knowledge of the phase diagrams of PE with water is important, particularly at low temperatures, where the ice phase is more stable. In this work, we study the phase diagrams of negatively and positively-charged PEs by using infrared spectroscopy (IR) and differential scanning calorimetry (DSC). The results show a coexistence curve of the ice phase in equilibrium with the PE-rich phase in water. The phase diagrams for positively- and negatively-charged PEs were similar, and a nearly 40% volume fraction of water to polymer remains unfrozen. Comparison of the collected data with the predictions from a theoretical model based on the Gibbs-Thomson and Flory-Huggins models reveals that the concentrated PE-water phase has closely associated counterions, and the entropy of the counterions does not play a dominant role. This finding is surprising since PEs are expected to have strongly dissociated charges under these conditions. Interestingly, we also found evidence of a stable unfrozen water PE phase that does not change upon further cooling to -100 °C. These observations are important for applications where controlling the formation of ice is critical.

The potential application of gas hydrates in storing clean energy has increased the interest in studying clathrate hydrates of gases like methane, CO₂, and hydrogen. In this work, we conduct large-scale molecular studies of methane hydrate growth and visualize the simulation results using mixed reality (MR) headsets and regular two-dimensional snapshots of the simulation domain. The results show the novel molecular observation of the trapping of gas nanobubbles within the growing solid hydrate. Our first-of-a-kind visualization of the internal hydrate structures in mixed reality enabled the length measurements of the simulation domain and nanobubble sizes, which showed that the gas nanobubbles were up to 9 nm in diameter. This is bigger than the simulation domain commonly used in atomistic gas hydrate studies, which explains why this is the first observation of the trapping of methane gas nanobubbles within a growing hydrate. Furthermore, our estimates of the increased storage due to the trapping of the nanobubbles indicate a 37% increase in the weight percentage of methane stored. Although this work focused on nanobubble-enhanced methane storage in hydrates, the idea, methods, and tools developed can be leveraged to enhance the storage of other gases, like hydrogen and CO₂. This study also revealed that the presence of gas nanobubbles accelerates the rate of hydrate formation, which is consistent with experimental observations. Finally, we expect our workflow for MR visualization of gas hydrate structures to facilitate other novel observations and insights from molecular dynamics (MD) studies of gas hydrates.

The potential application of gas hydrates in storing clean energy has increased the interest in studying clathrate hydrates of gases like methane, CO₂, and hydrogen. In this work, we conduct large-scale molecular studies of methane hydrate growth and visualize the simulation results using mixed reality (MR) headsets and regular two-dimensional snapshots of the simulation domain. The results show the novel molecular observation of the trapping of gas nanobubbles within the growing solid hydrate. Our first-of-a-kind visualization of the internal hydrate structures in mixed reality enabled the length measurements of the simulation domain and nanobubble sizes, which showed that the gas nanobubbles were up to 9 nm in diameter. This is bigger than the simulation domain commonly used in atomistic gas hydrate studies, which explains why this is the first observation of the trapping of methane gas nanobubbles within a growing hydrate. Furthermore, our estimates of the increased storage due to the trapping of the nanobubbles indicate a 37% increase in the weight percentage of methane stored. Although this work focused on nanobubble-enhanced methane storage in hydrates, the idea, methods, and tools developed can be leveraged to enhance the storage of other gases, like hydrogen and CO₂. This study also revealed that the presence of gas nanobubbles accelerates the rate of hydrate formation, which is consistent with experimental observations. Finally, we expect our workflow for MR visualization of gas hydrate structures to facilitate other novel observations and insights from molecular dynamics (MD) studies of gas hydrates.

Vapor-deposited organic semiconductor glasses exhibit distinct molecular anisotropy and exceptional kinetic and thermodynamic stability, distinguishing them from the inherently isotropic and poorly stable glasses formed through liquid cooling. In this study, we exploit these unique properties to examine local changes in surface potential as the stable glass transitions to a supercooled liquid upon heating above the glass transition temperature (T_g). Vapor deposited glasses of organic molecules with permanent dipole moments can generate a measurable surface potential due to their anisotropic molecular orientation. We use local electrostatic force microscopy and Kelvin probe force microscopy to provide insights into the dynamics of the phase transformation occurring above T_g. We demonstrate that changes in polarization upon conversion to the isotropic liquid serve as an effective proxy for tracking this transition and highlight their potential for evaluating the thermal stability of organic devices under diverse thermal conditions.

Bacterial viruses infect bacterial cells and stimulate the production of holin proteins that accumulate in the cellular membranes. When the number of such proteins reaches a threshold, the membrane permeabilizes and the cell is destroyed in the process known as cell lysis. Experimental studies indicate that cell lysis occurs at specific times, although the underlying molecular mechanisms of such precise timing remain not well understood. Recently, a theoretical framework has been introduced to explain these phenomena as a coupling between stochastic processes of holins accumulation in the membrane and breaking the membrane that leads to threshold behavior. However, this approach does not account for many biologically important processes in cell lysis. In this work, we investigated the role of transcriptional bursting and mRNA production on the dynamics of cell lysis. The original stochastic framework is extended, allowing us to evaluate the cell lysis dynamics under more realistic biological conditions using analytical calculations and Monte Carlo computer simulations. It is shown explicitly that the random processes of transcription bursting and mRNA production do not affect the threshold-like dynamics of cell lysis, although they influence the absolute values of the maximal thresholds and their distributions. It is also found that the effect of mRNA production is generally stronger than the effect due to transcriptional bursting. Physical-chemical arguments to explain these observations are presented. Thus, our theoretical analysis suggests that the precise timing of cell lysis is a robust phenomenon despite involving multiple random biochemical processes. Our theoretical approach clarifies some important mechanistic aspects of complex biological processes of cell lysis.

Bacterial viruses infect bacterial cells and stimulate the production of holin proteins that accumulate in the cellular membranes. When the number of such proteins reaches a threshold, the membrane permeabilizes and the cell is destroyed in the process known as cell lysis. Experimental studies indicate that cell lysis occurs at specific times, although the underlying molecular mechanisms of such precise timing remain not well understood. Recently, a theoretical framework has been introduced to explain these phenomena as a coupling between stochastic processes of holins accumulation in the membrane and breaking the membrane that leads to threshold behavior. However, this approach does not account for many biologically important processes in cell lysis. In this work, we investigated the role of transcriptional bursting and mRNA production on the dynamics of cell lysis. The original stochastic framework is extended, allowing us to evaluate the cell lysis dynamics under more realistic biological conditions using analytical calculations and Monte Carlo computer simulations. It is shown explicitly that the random processes of transcription bursting and mRNA production do not affect the threshold-like dynamics of cell lysis, although they influence the absolute values of the maximal thresholds and their distributions. It is also found that the effect of mRNA production is generally stronger than the effect due to transcriptional bursting. Physical-chemical arguments to explain these observations are presented. Thus, our theoretical analysis suggests that the precise timing of cell lysis is a robust phenomenon despite involving multiple random biochemical processes. Our theoretical approach clarifies some important mechanistic aspects of complex biological processes of cell lysis.