The Journal of Physical Chemistry B最新文献

Noncovalent interactions, particularly hydrogen bonding, play a pivotal role in determining the structural stability and functional properties of molecules, including bioactive compounds like resveratrol. This study focuses on the hydrogen-bonding behavior and other noncovalent interactions in gas-phase resveratrol-ethanol (EtOH) and resveratrol-methanol (MtOH) complexes, referred to as System 1 and System 2, respectively. These systems were optimized using the ωB97XD functional and cc-pVDZ basis set, providing a detailed picture of their stability and intermolecular interactions. By employing advanced methods such as Domain-Based Local Pair Natural Orbital Coupled Cluster (DLPNO-CCSD)(T) for energy decomposition, natural bond orbital (NBO) for charge analysis, atoms in molecule (AIM) for electron density topology, and noncovalent interaction (NCI) techniques, we decompose interaction energies into meaningful components like electrostatic, dispersion, and exchange-repulsion. The findings indicate that, while hydrogen bonding contributes to the stability of these complexes, London dispersion and other attractive interactions are substantial factors as well. The resveratrol-EtOH and resveratrol-MtOH systems demonstrate a robust electronic environment with significant contributions from various intermolecular forces, underscoring the importance of noncovalent interactions in stabilizing bioactive compounds. This study adds to our understanding of molecular interactions in resveratrol complexes, with potential implications for medicinal chemistry and material science, particularly where solvation effects are critical.

Molecular-level interactions among lipids, cholesterol, and water dictate the nanoscale membrane organization of lipid bilayers into liquid-ordered (Lo) and liquid-disordered (Ld) phases, characterized by different polarities and orders. Generally, solvatochromic dyes easily discriminate polarity difference between Lo and Ld phases, whereas molecular flippers and rotors show distinct photophysics depending on the membrane order. Despite progress in single-molecule spectral imaging and single-molecule orientation mapping, direct experimental proof linking polarity with microviscosity sensed by the same probe eludes us. Here, we demonstrate spectrally resolved single-molecule orientation localization microscopy to connect nanoscopic localization of a probe on a bilayer membrane with its emission spectra, three-dimensional dipole orientation, and rotational constraint offered by the local microenvironment and highlight the excellent correspondence between the polarity and order experienced by the same probe. This technique has the potential to address nanoscale heterogeneity and dynamics, especially in biology and material sciences.

In this study, the synergistic behavior of aqueous binary mixtures of 1,2-dimethoxyethane (DME), 2-methoxyethanol (2ME), and ethylene glycol (EG) was investigated using three solvatochromic dyes: coumarin 461 (C461), 4-aminophthalimide (4AP), and para-nitroaniline (pNA) through steady-state UV-visible spectroscopy and fluorescence emission spectroscopy. The absorption maxima of the dyes exhibited extensive bathochromic shifts with varying solvent mixture compositions. In the water-rich region of the mixtures, the absorption maxima displayed significantly larger bathochromic shifts compared with those in pure water. A clear case of synergistic solvation was observed, indicating that the polarity of mixtures exceeds that of pure water. The synergistic effect was pronounced in the water-DME and water-2ME mixtures, while it was weaker in the water-EG mixture. This "hyper-polarity" was analyzed from the molar transition energy variation using a generalized Bosch solvation model. In the water-DME and water-2ME mixtures, the equilibrium constant for synergistic solvation was significantly greater than that for preferential solvation, whereas in the water-EG mixture, the values were comparable. This behavior stemmed from the intermolecular hydrogen bonding between water and cosolvents. The mole fraction of synergistic solvation suggested microheterogeneity around the solute within the mixtures. Notably, the variation in emission maxima of the probes showed no synergistic behavior, implying that solvent reorientation in the excited state disrupts the synergistic effect. IR spectroscopy was also employed to investigate the hydrogen-bonded structures in the binary mixtures. Analytical modeling of -OH and -CH stretching frequency was established, and it revealed that the formation of water-DME and water-2ME hydrogen-bonded aggregates is responsible for the observed synergistic "hyper-polarity" effect.

There is sufficient evidence to prove that microemulsions can be formed by two immiscible liquids (generally called oil and water components) in the presence of an amphi-solvent rather than traditional surfactants, but how to explain such surfactant-free microemulsions (SFMEs) with thermodynamics is still a challenge. In this work, based on the Flory-Huggins theory, a general thermodynamic principle for SFMEs was established, by assuming SFMEs to be a pseudobinary system consisting of the water-rich and oil-rich components (i.e., the water-rich and oil-rich phases) and considering the curvature dependence of the enthalpy of dispersion between the two pseudocomponents. A new parameter, called the two-phase interaction parameter, was introduced. The thermodynamic model can predict the SFME region in the ternary phase diagram as well as the droplet size and type of SFMEs formed. The formation and stability of SFMEs are attributed to the balance between the entropy and enthalpy of dispersion of the two phases. The rationality of the thermodynamic principle suggested here was confirmed by the experimental results of the ternary mixture of n-butanol (oil), ethanol (amphi-solvent), and water. This work provides a thermodynamic explanation for SFMEs, which can deepen our understanding of the nature of SFMEs.

Since the advent of time-resolved spectroscopy based on precision frequency technology of laser sources, it has been considered an alternative way to study dynamic processes in photochemical systems. This Perspective introduces asynchronous and interferometric nonlinear spectroscopy (AI-NS), a spectroscopic technique that combines asynchronously generated laser pulses and interferometric detection, offering an unprecedented temporal dynamic range with high spectral resolution and rapid data acquisition capabilities. By eliminating the need for mechanical delay stages, AI-NS facilitates the rapid collection of time-resolved data on dynamics ranging from femtoseconds to nanoseconds while simultaneously distinguishing frequency-dependent responses. Here, we detail the technical methodology of AI-NS and explore its applications to the studies of various systems, including semiconductors and biological systems. Additionally, we highlight prospective advancements, such as integration with multidimensional spectroscopy techniques. AI-NS not only expands the scope of spectroscopic analysis but also opens new avenues for the exploration of diverse materials and molecular systems.

The global health crisis triggered by the SARS-CoV-2 virus has highlighted the urgent need for effective treatments. As existing drugs are not specifically targeted at this virus, there is a growing interest in exploring natural antimicrobial peptides such as defensin as potential therapeutic options. Human β defensin type 2 (hBD-2), which is a cationic cysteine-rich peptide, serves as the initial barrier against bacterial and fungal invaders in mammals. It can bind with Spike-RBD and occupy the same site as the ACE2 receptor, thereby hindering viral entry into cells expressing ACE2. To explore the effect of different point mutations on the binding of hBD-2 with RBD, the binding dynamics and interactions between hBD-2 point mutants with RBD were studied and compared with that of RBD&hBD-2 wild-type complex. In total, 247 hBD-2 point mutants were built with the mutation sites at the binding region of hBD-2 (RES18-30) with the RBD of CoV-2. All-atom molecular dynamics simulations were carried out on RBD binding with hBD-2 point mutants. Analysis based on root-mean-square deviation (RMSD), hydrogen bonds analysis, and binding free energy using the MM/PBSA method revealed that many point mutants of hBD-2 exhibit weaker binding with RBD compared to the wild type; however, a subset of mutants, including C20I, C20K, R22W, R23H, R23L, Y24L, K25F, K25H, G28Y, T29R, and C30K, displayed enhanced binding with RBD. The findings can offer insights designing hBD-2-based novel drugs to combat SARS-CoV-2 in the long term.

Due to their distinctive optical, electrical, and catalytic characteristics, gold nanoparticles (AuNPs) have found increasing use for a wide range of applications, including biomedicine and catalysis. Inherent agglomeration propensities impair their functional qualities, stability, and biocompatibility. This work investigates the potential applications of the cataractous eye protein isolate (CEPI), a waste product rich in proteins from cataract surgery, as a novel AuNP stabilizing agent. It was found that CEPI can successfully stabilize AuNPs under a variety of situations, preventing ethanol-induced aggregation and preserving their structural integrity. Using spectroscopic and analytical techniques, including UV-Vis spectroscopy, dynamic light scattering (DLS), circular dichroism (CD) spectroscopy, and fluorescence quenching studies, we confirmed the successful binding of CEPI to AuNPs and the enhanced stability of the conjugates. A shift in the localized surface plasmon resonance (LSPR) peak and modifications to the secondary structure of the CEPI were indicative of strong binding and protective effects between CEPI and AuNPs. These findings suggest that CEPI, an underutilized biomaterial, can serve as an effective and biocompatible stabilizer for AuNPs, with potential applications in biomedical and therapeutic fields.

Nanoaperture optical tweezers allow for trapping single proteins and detecting their conformational changes without modifying the protein, i.e., being free from labels or tethers. While past works have used laser heating as a way to vary the local temperature, this does not allow for probing of lower temperature values. Here we investigate the lower temperature dynamics of individual Bovine Serum Albumin (BSA) proteins with the help of a custom Peltier cooling stage. The BSA transitions between the normal (N) and fast (F) states. The normal form of BSA has a maximum occupancy at 21 ± 1 °C, which is interpreted as its maximum stability point for the compact N form with respect to the F form. In this way, it is possible to find the relative thermodynamic parameters of single proteins without requiring any modifications to the intrinsic structure.

Molar conductivities are one of the fundamental transport properties of electrolytes that reflect the complex and dynamic interactions between ions and solvents comprehensively. The quantitative accuracy of experimental input-free simulations of molar conductivities is strongly influenced by the underlying interaction parameters employed in the model. When validated with experimental molar conductivities, the developed model could be used to reveal further atomistic level details about the solvation structures and correlated ion pair formation, providing in-depth knowledge about solution physical chemistry and shedding light on electrolyte-solvent system design rules. Divalent cations are more challenging to model than monovalent cations due to their higher charge densities and stronger interactions with the environment. Yet, they started attracting significant attention for next-generation energy storage purposes. In this work, we focus on two earth-abundant divalent cation electrolytes, Mg(TFSI)₂ and Ca(TFSI)₂ in a dimethylacetamide-tetrahydrofuran (DMA-THF) cosolvent system. We used quantum mechanical cluster models to optimize the force field parameters (including the pairwise nonbonded interaction parameters and atomic charges) to be applied in classical simulations. With the reliable force field model, we discussed the importance of including ion correlation explicitly in predicting the molar conductivities via the Onsager formalism and showed that the conventional Nernst-Einstein formula overestimates ionic mobilities due to its intrinsic independent and uncorrelated particle assumption. Further, we investigated the solvation structures and ion pair formations. We concluded that the suitability of the interaction potentials utilized in a classical model for particular systems needs to be assessed not solely by directly comparing the simulated molar conductivities with the measured ones but, more importantly, by using the correct formalism (Onsager) to deduce the simulated result from dynamics trajectories.

Cryopreservation is the preservation and storage of biomaterials using low temperatures. There are several approaches to cryopreservation, and these often include the use of cryoprotectants, which are solutes used to lower the freezing point of water. Isochoric (constant-volume) cryopreservation is a form of cryopreservation that has been gaining interest over the past 18 years. This method utilizes the anomalous nature of water in that it expands as it freezes. The expansion of ice on freezing is used to induce a pressure in the system that limits ice growth. In this work, we use Gibbsian thermodynamics, the Elliott et al. multisolute osmotic virial equation, the Feistel and Wagner correlation for ice Ih, and the Grenke and Elliott correlation for the thermodynamic properties of liquid water at low temperatures and high pressures to predict how the pressure, volume fraction of ice, and solute concentration in the unfrozen fraction change as the solution is cooled isochorically. We then verified our model by predicting experimental results for saline solutions and ternary aqueous solutions containing NaCl and organic compounds commonly used as cryoprotectants: glycerol, ethylene glycol, propylene glycol, and dimethyl sulfoxide. We found that our model accurately predicts experimental data that were collected for cryoprotectant concentrations as high as 5 M, and temperatures as low as -25 °C. Since we have shown that our liquid water correlation, on which this work was based, makes accurate predictions to -70 °C, as long as the pressure is not higher than 400 MPa, we anticipate that the prediction methods presented in this work will be accurate down to -70 °C. In this work we also modeled how sealing the isochoric chamber at room temperature versus at the nucleation temperature impacts isochoric freezing. The prediction methods developed in this work can be used in the future design of isochoric cryopreservation experiments and protocols.