The Journal of Physical Chemistry B最新文献

Neutral fats in living organisms are stored in lipid droplets, intracellular organelles enveloped by a phospholipid monolayer. The fusion of these lipid droplets is vital for numerous physiological functions and is regulated by specific proteins and lipids. Dysregulation of this process, leading to excessive droplet growth, is associated with various pathological conditions. Notably, changes in the lipid composition of the boundary monolayers can significantly influence the fusion rate, mirroring fusion dynamics of membranous compartments surrounded by lipid bilayers. In this study, we conducted a theoretical and computational analysis of monolayer fusion, extending the established bilayer fusion model to this context. We characterize the energy trajectory associated with monolayer fusion, tracing the process from the initial unperturbed state to the formation of physical contact between monolayers, and subsequently to the expansion of this structure, which we refer to as the monolayer stalk, analogous to bilayer fusion. Unlike bilayer fusion, monolayer fusion features a single energy barrier, determining the process efficiency. Once this barrier is overcome, further droplet merging occurs spontaneously, highlighting the dynamic nature of lipid droplet interactions. We analyze how lipid composition influences this energy barrier and explore the effects of factors such as Gaussian curvature and hydration-induced repulsion on the energy landscape. Our calculations reveal that Gaussian curvature energy significantly contributes to barrier height. An increase in the proportion of lipids exhibiting large negative spontaneous curvature, which enhances fusion likelihood, can substantially decrease this barrier. Our findings are consistent with existing experimental data and allow us to quantify the barrier height as a function of lipid composition. Specifically, we demonstrate that incorporating 50 mol % of dioleoylphosphatidylethanolamine (DOPE) into pure dioleoylphosphatidylcholine (DOPC) monolayers reduces the energy barrier height by approximately 16 k_BT - half of this reduction attributed to changes in spontaneous curvature, with the other half due to modification in hydration repulsion parameters. These findings provide quantitative insights into lipid droplet fusion mechanisms, advancing our understanding of lipid metabolism and its physiological regulation.

Molecular dynamics was utilized to investigate the dissociation process of the 1-hexyl-3-methylimidazolium chloride ionic liquid ([HMIM][Cl] IL). To further study the mechanism at the molecular scale, the local microstructure variation in the mixtures with the increase of water content was analyzed in detail. The simulation results show that there are still 35.89% of free ions in pure ILs. With the increase in water content, water molecules preferentially bind to free ions. When the water content is greater than 0.8, the water molecules gradually insert the anion and cation from the periphery of the cation-anion pair and finally almost replace the anion around the cation. The analysis of spatial distribution function, solvent accessible area, and ion diffusion coefficient further confirmed this conclusion. These quantitative ion pairing and dissociation mechanisms shed light on the rational design of the IL aqueous toward their applications in the chemical-related fields and provide key parameters for the modeling of IL aqueous solution.

Density functional theory calculations of 0D (zero-dimensional) metal oxide nanomaterials and protein amino acids have been used to evaluate the disease progression for biosensing applications. In this study, the interaction of glycine with ZnO clusters was evaluated, incorporating a van der Waals correction. Glycine was rotated to interact with the nanoparticles at different active sites. Binding and cohesion energies, the density of states, and charge transfer were calculated for each system. The results indicate that glycine interacting with the ZnO(3) cluster in the XZ-plane exhibits greater stability due to higher binding and cohesion energies. A higher charge transfer was also observed for this interaction. Furthermore, the density of state analysis shows a significant decrease in all band gaps, indicating a reduction in the cluster's semiconductive behavior. To experimentally validate this interaction, atomic force microscopy (AFM) was performed as a proof of concept. A silicon contact tip in pinpoint mode was used with ZnO nanoparticles and a functionalized silicon wafer containing glycine. The AFM results confirm the binding affinity between glycine and ZnO nanoparticles.

Insulin aspart, a biomacromolecule essential for diabetes treatment, is known to interact with polymer-based drug delivery systems. Plasticized poly(vinyl chloride) (PVC) materials, widely used in medical infusion tubing, contribute significantly to insulin aspart loss due to adsorption. However, experimental studies alone cannot distinguish the individual contributions of plasticizers and the PVC matrix in this process. To address this, we employed coarse-grained molecular dynamics (Martini 3) simulations to investigate protein-surface interactions over extended time scales, providing deeper insights into adsorption mechanisms. Our results revealed a strong preference for insulin aspart adsorption onto PVC regions rather than plasticizers, explaining the experimentally observed lack of adsorption differences between plasticized and nonplasticized PVC surfaces. Additionally, we explored the formation of the insulin aspart adsorption layer for both monomeric and hexameric forms, further characterizing the thermodynamics of the adsorption process.