The Journal of Physical Chemistry B最新文献

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.

This study explores the thermodynamic and structural behaviors of linker peptides, short polypeptide segments that often bridge protein domains. We are focusing on three prototypical classes─glycine-serine (GS), glycine-glycine (GG), and alanine-proline (AP)─and exploring their conformational dynamics as isolated entities outside a multidomain protein context. Using extensive molecular dynamics (MD) simulations and free energy perturbation (FEP) analyses, we characterize the free energy landscapes, entropic properties, and solvation energetics of 20 representative linkers. Our results reveal a pronounced linear relationship between linker length and key thermodynamic contributions, including zero-point vibrational energy (ZPVE), potential energy, and entropy. Notably, vibrational entropy emerges as a dominant stabilizing term. We also found that AP linkers display more rigid, yet extended conformations compared to the highly flexible GS and moderately flexible GG linkers. These findings underscore the nuanced role of linker composition in contributing to multidomain protein architecture and dynamics, and highlight how thermodynamic forces shape linker conformational behavior. Collectively, our work enhances the mechanistic understanding of protein linkers, offering valuable insights for the rational design of peptide-based systems and informing future efforts to modulate interdomain flexibility and stability in multidomain proteins.

This study explores the thermodynamic and structural behaviors of linker peptides, short polypeptide segments that often bridge protein domains. We are focusing on three prototypical classes─glycine-serine (GS), glycine–glycine (GG), and alanine-proline (AP)─and exploring their conformational dynamics as isolated entities outside a multidomain protein context. Using extensive molecular dynamics (MD) simulations and free energy perturbation (FEP) analyses, we characterize the free energy landscapes, entropic properties, and solvation energetics of 20 representative linkers. Our results reveal a pronounced linear relationship between linker length and key thermodynamic contributions, including zero-point vibrational energy (ZPVE), potential energy, and entropy. Notably, vibrational entropy emerges as a dominant stabilizing term. We also found that AP linkers display more rigid, yet extended conformations compared to the highly flexible GS and moderately flexible GG linkers. These findings underscore the nuanced role of linker composition in contributing to multidomain protein architecture and dynamics, and highlight how thermodynamic forces shape linker conformational behavior. Collectively, our work enhances the mechanistic understanding of protein linkers, offering valuable insights for the rational design of peptide-based systems and informing future efforts to modulate interdomain flexibility and stability in multidomain proteins.

The von Willebrand factor (VWF), a multimeric plasma glycoprotein, binds to the platelet glycoprotein (GPIbα) to initiate the process of primary hemostasis as a response to blood flow alteration in the site of vascular injury. The GPIbα binding site located on the A1 domain of VWF is exposed during the activation of the VWF multimer when it changes from a coiled form to a thread-like, extended form. Though experimental studies have demonstrated that the autoinhibitory module (AIM) connected to the N-/C-termini of the A1 domain is a regulator of VWF activity, the molecular mechanism underlying the regulation of A1–GPIbα binding remains unclear. We modeled the structures of the A1 domain having full-length N-terminal AIM (NAIM) and C-terminal AIM (CAIM) with different types of O-linked glycans. The conventional and steered molecular dynamics simulations were conducted to investigate the dynamics of the AIM and O-glycans under different conditions and elucidate how they affect the binding of GPIbα. Our results indicate that the NAIM alone with no glycan is sufficient to shield the GPIbα binding site under static conditions. However, when the AIM is unfolded with external forces applied, the O-glycans on both NAIM and CAIM increase the shielding of the binding site. These findings suggest a potential mechanism by which the AIM and O-glycans regulate the interaction of the VWF A1 domain and GPIbα.

The rapid development of the natural gas hydrate industry has put forward higher requirements for hydrate promotion technology. The exploration of methods that can simultaneously enhance both the hydrate formation rate and the final gas and water conversion efficiency has become a critical research focus. This study systematically investigated the synergistic effects of electric field (EF) signals, including three distinct waveforms (square, sine, ramp wave) at six different voltage levels, combined with four concentration gradients of the cationic surfactant called hexadecyl trimethylammonium bromide (CTAB) on the CH₄ hydrate formation process. Experimental results demonstrated that the application of external EF significantly enhanced the gas storage capacity of hydrate, with different waveforms exhibiting varying degrees of promotional effects. Notably, square wave and ramp wave, which allow for instantaneous changes in the EF direction, exhibited superior performance in improving hydrate formation rates and gas and water conversion efficiency and enhancing hydrate fluidity. Furthermore, a kinetic model for hydrate formation was developed, which showed excellent agreement with the observed results. These findings not only advance the theoretical framework of EF-assisted hydrate formation but also provide valuable insights and practical guidance for the development of natural gas hydrate technologies.

The von Willebrand factor (VWF), a multimeric plasma glycoprotein, binds to the platelet glycoprotein (GPIbα) to initiate the process of primary hemostasis as a response to blood flow alteration in the site of vascular injury. The GPIbα binding site located on the A1 domain of VWF is exposed during the activation of the VWF multimer when it changes from a coiled form to a thread-like, extended form. Though experimental studies have demonstrated that the autoinhibitory module (AIM) connected to the N-/C-termini of the A1 domain is a regulator of VWF activity, the molecular mechanism underlying the regulation of A1-GPIbα binding remains unclear. We modeled the structures of the A1 domain having full-length N-terminal AIM (NAIM) and C-terminal AIM (CAIM) with different types of O-linked glycans. The conventional and steered molecular dynamics simulations were conducted to investigate the dynamics of the AIM and O-glycans under different conditions and elucidate how they affect the binding of GPIbα. Our results indicate that the NAIM alone with no glycan is sufficient to shield the GPIbα binding site under static conditions. However, when the AIM is unfolded with external forces applied, the O-glycans on both NAIM and CAIM increase the shielding of the binding site. These findings suggest a potential mechanism by which the AIM and O-glycans regulate the interaction of the VWF A1 domain and GPIbα.

The rapid development of the natural gas hydrate industry has put forward higher requirements for hydrate promotion technology. The exploration of methods that can simultaneously enhance both the hydrate formation rate and the final gas and water conversion efficiency has become a critical research focus. This study systematically investigated the synergistic effects of electric field (EF) signals, including three distinct waveforms (square, sine, ramp wave) at six different voltage levels, combined with four concentration gradients of the cationic surfactant called hexadecyl trimethylammonium bromide (CTAB) on the CH₄ hydrate formation process. Experimental results demonstrated that the application of external EF significantly enhanced the gas storage capacity of hydrate, with different waveforms exhibiting varying degrees of promotional effects. Notably, square wave and ramp wave, which allow for instantaneous changes in the EF direction, exhibited superior performance in improving hydrate formation rates and gas and water conversion efficiency and enhancing hydrate fluidity. Furthermore, a kinetic model for hydrate formation was developed, which showed excellent agreement with the observed results. These findings not only advance the theoretical framework of EF-assisted hydrate formation but also provide valuable insights and practical guidance for the development of natural gas hydrate technologies.

Hydrogen bonds and metal-ligand interactions catalyze the epoxy-amine cross-linking reactions. Through a detailed quantum chemical study, it was demonstrated that water, through hydrogen bond formations, acts as a better catalyst than amines in the epoxy-amine cross-linking reactions. The presence of various solvated metal cations (Na⁺, Mg²⁺, and Al³⁺) results in the formation of metal-ligand interactions with both epoxy and amine moieties. A comprehensive investigation of these interactions has been performed in the study to demonstrate that the presence of these cations in small quantities effectively catalyzes the epoxy-amine reactions. The energetic analysis of different metal-epoxy-amine complexes suggests the inhibitory nature of Al³⁺ toward the extent of cross-linking.

Poly(vinyl alcohol) (PVA) films have been widely used as flexible matrixes in advanced optical materials. Most studies concern the rigidification strategy of PVA films, while the physicochemical properties of inside bound water are ignored. In this study, we have employed lumichrome as the fluorescent probe to explore the acid-base property of bound water, which was demonstrated to exhibit an enhanced proton-accepting ability than bulk water, evidenced by the promoted deprotonation of lumichrome in the ground state. Decreasing the water content in a PVA film is demonstrated to further improve the proton-accepting ability. Different from that in bulk solution, a selective prototropism of lumichrome is determined in PVA films, which is induced by the formation of an anchored lumichrome-PVA complex through three hydrogen bonds. This work first points out the enhanced proton-accepting ability of bound water in PVA films, opening a new avenue for the development of flexible optical materials based on proton transfer.

The hydrophilicity of two-dimensional (2D) transition-metal carbides, carbonitrides, and nitrides (MXene) nanochannels plays a critical role in water transport during filtration, yet its specific effects on MXene membranes remain inadequately understood. Herein, we systematically investigated water transport through Ti₃C₂T_X MXene nanochannels using molecular dynamics simulations coupled with experimental validation, addressing a significant knowledge gap in MXene-based separation membranes. Our simulations demonstrated that strong interactions between water molecules and hydrophilic nanochannel MXene surfaces (Ti₃C₂(OH)₂ MXene or Ti₃C₂(NH)₂ MXene) facilitated the formation of ordered molecular arrangements, substantially improving water permeability. Conversely, hydrophobic nanochannels (Ti₃C₂O₂ MXene or Ti₃C₂F₂ MXene) exhibited disordered water molecule distributions, leading to reduced permeability. Experimental validation corroborated these simulation results, demonstrating a direct correlation between the hydrophilicity of the Ti₃C₂T_X surface and the water flux. The highly hydrophilic Ti₃C₂(OH)₂ MXenes exhibited water flux maximum, whereas the more hydrophobic Ti₃C₂F₂ MXenes had the lowest water flux. By integrating molecular dynamics simulations with experimental analyses, we gained comprehensive insights into the influence of nanochannel hydrophilicity on water transport mechanisms in MXene membranes. These findings provide critical guidelines for designing high-performance MXene-based membranes for advanced water treatment and separation applications.