Type V deep eutectic solvents (DESs) are composed exclusively of nonionic molecular species, in contrast to type I-IV DESs, which contain at least one ionic component. In the absence of ionic constituents, the cohesive energy of type V DESs is governed primarily by hydrogen bonding and van der Waals interactions. Such an intermolecular framework imparts distinct physicochemical properties, such as increased hydrophobicity and relatively low viscosity (compared to their ionic counterparts), substantially broadening the application potential of DESs. Owing to their fundamental distinction from ionic DESs and ionic liquids (ILs), it is imperative to understand how the nonionic nature of type V DESs influences their microstructure and dynamic behavior for their rational and strategic utilization. To address this, we examined the microenvironment of a thymol/camphor-based type V DES using three molecular probes: Coumarin-153, a neutral benchmark probe widely employed for investigating dynamics in solutions, and two fluorescent molecular rotors, Thioflavin T and Auramine O, whose fluorescence quantum yield is sensitive to the microviscosity of the local environment. Absorption and steady-state fluorescence measurements reveal that the local micropolarity experienced by Coumarin-153 in the DES is comparable to that of acetonitrile. A slight red-edge excitation shift observed in the steady-state fluorescence spectra with varying excitation wavelengths points to the presence of subtle spatial heterogeneity within the solvent. Time-resolved emission spectra (TRES) were recorded over the temperature range of 278-333 K and used to construct the solvent correlation function, which describes the solvent's reorganization in the excited state following the electronic excitation of Coumarin-153. The solvation dynamics were found to be bimodal, with a dominant, markedly slow component indicative of a highly sluggish solvent response. Correlating the solvation dynamics with the shear viscosity of the solvent reveals significant decoupling (p ≈ 0.62, where p is the decoupling parameter), suggesting decoupling of the solvation dynamics from the viscosity of the medium. Furthermore, a dynamic crossover was observed at approximately 308 K or 35 °C, showing temperature-dependent modulation in the structural features of the thymol/camphor-based DES. In contrast, the rotational dynamics of Coumarin-153 closely follow the Stokes-Einstein-Debye hydrodynamic model (p ≈ 0.8), indicating that despite heterogeneity, Coumarin-153 experiences an effectively homogeneous local environment. In the thymol/camphor-based DES, the temperature-dependent evolution of fluorescence quantum yield for both Thioflavin T and Auramine O reveals a nonuniform response across the studied range, manifesting as two distinct friction regimes separated by a well-defined crossover at 308 K. Microviscosity determination of both probes reveals decoupling of the torsional relaxation from the bulk viscosity of the solvent, which is complemented by the disparity in the activation energy values of viscous flow and nonradiative transition obtained by utilizing Arrhenius-type curves. This observation suggests that the photophysical behavior of molecular rotors like Thioflavin T and Auramine O is not governed solely by the bulk viscosity of the DES; rather, the local microstructure of the solvent plays a dominant role. These findings underscore how variations in local polarity and specific solute-solvent interactions drive preferential solvation, revealing the presence of microscopically heterogeneous domains within the nonionic, hydrogen-bonded framework of the DES.
Solution viscosities of poly((3-(acrylamido)propyl)trimethylammonium chloride) (PAPTMAC-Cl 7.8) and of poly(styrenesulfonate sodium) (PSS-Na 75.6) were measured in water containing different amounts of NaCl at 25 °C; the numbers after the abbreviation of the polymers state their M w in kDa. The intrinsic viscosity of the polycation in water amounts to 4460 mL/g and is about three times larger than that of the polyanion, despite the fact that its mass is only one tenth that of the polyanion. At low salinities the shear-overlap parameters Σ as a function of composition c (mass per volume) pass maxima for PAPTMAC-Cl 7.8, but exhibit points of inflection for PSS-Na 75.6. At sufficiently large salinities these dependencies become linear in both cases. Points of inflection in Σ (c) indicate crossover condition and separate the solvent dominated from the solute dominated flow regimes. For the polycation, the Σcrov values are always larger than for the polyanion. The analysis of these results in the light of the HSAB (Hard Soft Acid Base) approach of Pearson yields strong indications that the observed dissimilarities between the two types of polyelectrolytes are not caused by the opposite charges attached to the macromolecules, but result from the combination of the soft NR4+ with the hard Cl- ions in the case of PAPTMAC-Cl 7.8 and of the hard RSO3- with the hard Na+ ions in the case of PSS-Na 75.6. This insight opens up new opportunities for the tailoring of rheological properties for polyelectrolytes in saline solutions.
The effect of inorganic salts on the local structure of N,N-dimethylformamide (DMF), known to be of vital importance in applications, e.g., electrospinning, is investigated by molecular dynamics computer simulations. Four salts, i.e., LiCl, LiBr, MgCl2, and CaCl2, are considered in various concentrations covering the entire range of their solubilities. The performance of several interaction models was assessed. It is found that when proper charge scaling of the ions is performed, all models considered are able to reasonably reproduce the known experimental properties of these solutions, including their densities, the measurement of which is also reported here. The only exception in this respect is the solubility of the salts: as only the AMBER model is found to be able to simultaneously reproduce the good solubility of all four salts considered, this is the model of our choice in this study. We find that the structure of these salt solutions is primarily determined by the cation-DMF interaction, which is found to be an order of magnitude stronger than the anion-DMF interaction and which clearly destroys the weak, CH-donated hydrogen-bonding structure of neat DMF. Solvation shell DMF molecules turn by their O atom to the cation, but within this constraint, their N atom also approaches it as closely as possible. The average lifetime of cation-DMF contacts is found to be on the order of 1 ns for Li+ and Ca2+, while for Mg2+, it turns out to be many orders of magnitude longer than the entire length of our simulated equilibrium trajectories of 50 ns. Further, the interaction energy of contact Mg2+-DMF pairs falls in the order of covalent chemical bonds, the coordination number results in exactly 6.00 in every case, and the first solvation shell itself is exceptionally well ordered. All these findings strongly suggest (yet do not prove) the formation of the [Mg(DMF)6]2+ hexacomplex by a Mg2+ ion and its six first-shell DMF neighbors.
This study investigates the impact of dehydration on the molecular structure and spin dynamics of both the organic protein matrix and the inorganic hydroxyapatite components of bone. A comprehensive comparison between natural and dehydrated bovine cortical bones is conducted to elucidate the role of water in maintaining bone structure and dynamics. The organic protein components and inorganic hydroxyapatite are monitored separately using a combination of solid-state NMR techniques: wPMLG-detected 1H MAS, 13C CP-MAS, 13C 2D PASS CP-MASS, 1H-13C HETCOR, and 13C relaxometry for the organic (mainly type I collagens) and 31P MAS, 31P 2D PASS, and 31P relaxometry for hydroxyapatite. Our findings highlight a significant and previously overlooked effect of dehydration on the inorganic hydroxyapatite components of bone. Dehydration induces more pronounced changes in the spinning CSA sideband pattern of 31P nuclei residing on the inorganic hydroxyapatite components rather than the 13C spinning CSA sideband pattern of the organic matrix. There is no substantial change in the 13C chemical shift anisotropy (CSA) parameter, which suggests that dehydration does not lead to the decomposition of the organic matrix. The spin-lattice relaxation time is getting elongated in the dehydrated bone compared to the intact bone, suggesting that the motional degrees of freedom of the collagenous matrix are being affected due to the removal of free water from the surface of collagen. The remarkable alteration of the motional dynamics of 31P nuclei is demonstrated by quantitative measurements of the 31P spin-lattice relaxation time. The T1 values increase by approximately 80% for the amorphous surface layer and by 40% for the crystalline apatite core upon dehydration. These experimental findings suggest that 31P 2D PASS NMR and 31P spin-lattice relaxation measurements serve as highly sensitive indicators of structural and dynamical changes in the hydroxyapatite phase, with potential implications for the early detection of pathological conditions such as osteoporosis. Collectively, this work addresses critical gaps in understanding how dehydration influences the molecular structure and nuclear spin dynamics in organic protein components and inorganic hydroxyapatite components of bone. Additionally, this detailed information about the local electronic environment and nuclear spin dynamics of carbon and phosphorus nuclei will illuminate the path to designing biomimetic bone-like materials.
In the present work, the effect of 1,2-propylene glycol (1,2-PG) or 1,3-butylene glycol (1,3-BG) incorporation on the self-assembling behaviors of polyoxyethylene oleyl ethers in dilute aqueous solutions is extensively investigated. This study aims to elucidate the mechanism by which the short-chain diol introduction contributes to preventing the phase separation occurring in aqueous makeup cleansing products under high temperatures. The critical micellization concentration and standard free energy of micellization of polyoxyethylene oleyl ethers in 1,2-PG-water mixed solvents steadily increase with increasing concentration of 1,2-PG in water, indicating that the addition to water of 1,2-PG disfavors micelle formation. Additionally, the introduction of 1,2-PG resulted in a significant increase in the effective surface area demand per molecule of polyoxyethylene oleyl ether, pointing to a reduction in the packing tightness of the surfactant molecules. Results of SAXS experiments indirectly demonstrate that the effective critical packing parameter of polyoxyethylene oleyl ethers in the aqueous solution of 1,2-PG decreases with increasing 1,2-PG concentration, which corresponds well with the changes in the cloud point of amphiphiles. NMR measurements confirm that these observations may be related to the swelling of the hydrophilic chain induced by excessive water penetration into the palisade layer, which helps counteract the dehydration of the POE (polyoxyethylene) segments induced by elevated temperatures. Furthermore, 1,3-BG exhibits effects similar to those of 1,2-PG but with a notably stronger intensity.
The synthesis and photophysical properties of four [Re(R-NI-phen)(CO)3Cl] complexes (Re-R), where NI = 1,8-naphthalimide and phen = 1,10-phenanthroline, are reported. The R-NI chromophores were substituted at their 4-positions with R = H (Re-H), ethynyl benzene (Re-EB), ethynyl thiophene (Re-ES), ethynyl trimethylsilane (Re-ET), yielding a series of metal-organic bichromophores. The R-NI-phen organic chromophores were investigated in parallel to better understand the photophysical properties exhibited in the Re-R complexes. The excited-state processes of these molecules were studied by transient absorption and time-resolved infrared spectroscopies, to unravel the kinetics of the energy transfer processes occurring in the Re-R series. Namely, the interplay between the singlet ligand-centered (1LC), the triplet metal-to-ligand charge-transfer (3MLCT), and the triplet ligand-centered (3LC) excited states were studied using these time-resolved spectroscopic techniques, supported by quantum chemical calculations, to monitor the changing excited-state dynamics in the Re-R series. These studies reveal that the thermal equilibrium between the 3MLCT and 3LC excited states present in Re-H is modulated in favor of the 3LC excited state in the remaining Re-R series, giving rise to increasingly ligand-like photophysics as the electron-donating strength of the R-group increases.
Boron complexes derived from aniline-imine or salicylaldimine ligands (Boranils) exhibit attractive photophysical characteristics, including strong absorption, dual-state emission, and synthetic accessibility. Despite these advantages, their potential as two-photon (TP) photosensitizers for photodynamic therapy (TP-PDT) remains largely unexplored, and the role of the substitution position in modulating their TP activity has not been systematically investigated. In this work, we present a comprehensive computational study on the substitution-dependent photophysical properties of Boranil derivatives relevant to TP-PDT. A library of 48 substituted Boranil systems was designed by introducing iodine, dimethylamine, and six polar substituents at ten distinct positions on the Boranil core. The key photophysical processes governing TP-PDT performance─including TP absorption (TPA), intersystem crossing (ISC), and singlet oxygen (1O2) generation capability─were analyzed using state-of-the-art RI-CC2 and time-dependent density functional theory calculations. The results reveal that both the nature and the position of substitution play a critical role in tuning the TPA response and the excited-state dynamics of Boranil derivatives, with several designed systems exhibiting substantially enhanced TPA strengths compared to the parent framework. To assess their potential biological compatibility, interactions of the most promising candidates with human serum albumin were further examined through molecular docking and molecular dynamics simulations, which indicate stable binding and favorable binding free energies. Overall, these results reveal a clear structure-photophysics relationship in which substitution at specific positions of the Boranil core modulates charge-transfer interactions and transition dipole alignment, leading to significant enhancement of TPA.
The spatial distribution of the temperature of aqueous solutions under the conditions of laser trapping for molecular assembly was systematically evaluated. Recent studies have revealed that laser trapping (also called optical tweezers) is a powerful tool not only for manipulating micro/nanoparticles but also for controlling molecular assembly, such as crystallization. However, laser trapping for molecular assembly usually requires focused laser irradiation with a power of ∼1.0 W, which should cause a higher temperature elevation in a larger region compared to that for conventional optical tweezers (<0.1 W). In this work, the ratio metric measurement of thermoresponsive fluorescent protein revealed the actual spatial distribution of temperature rise in a relatively wide field of view (∼100 μm) and a wide range of irradiation time (seconds to minutes) at the laser power of 0.1-1.0 W, highlighting the impact of temperature elevation on molecular assembly over the laser focal spot size (∼1 μm). We also found the confinement of photothermally generated clusters by laser trapping at the laser focus, which indicates a synergistic interplay of laser trapping and photothermal effects on the aggregation of thermoresponsive polymers above the lower critical solution temperature. We foresee that the photothermal effects on molecular assembly studied in this work should enhance the understanding of the underlying mechanisms of molecular accumulation/aggregation induced by laser trapping.
Accelerating the discovery of high-performance ionic liquids (ILs) for hydrogen sulfide (H2S) capture is hindered by the prohibitive cost of experimental screening and the limited generalization capability of purely data-driven machine learning models, which often lack thermodynamic consistency and fail in complex chemical extrapolation tasks. To address these challenges, this study introduces a physics-informed hybrid artificial neural network (hybrid ANN) that integrates the van't Hoff equation directly into the model architecture. This approach preserves the data-driven flexibility of machine learning while enforcing fundamental thermodynamic constraints, ensuring that predictions remain physically consistent across unexplored chemical spaces. The hybrid ANN demonstrated exceptional predictive accuracy, achieving a coefficient of determination (R2) exceeding 0.9987 on a conventional test set. More critically, in a rigorous generalization test involving unseen cation-anion combinations, the purely data-driven ANN model suffered a catastrophic performance collapse, with R2 plummeting from 0.9990 to 0.8215, whereas the hybrid ANN maintained robust performance with an R2 of 0.9925. This highlights the essential role of embedded physical knowledge in safeguarding model reliability under data-sparse conditions. Interpretability analysis using SHAP revealed that structural features, particularly the imidazolium cation and alkyl chain substituents, exert a stronger influence on H2S solubility than operational pressure, underscoring the dominance of molecular design over process parameters. The model further captured smooth, continuous nonlinear interactions among cations, anions, and side chains, providing actionable insights for the rational design of next-generation IL-based H2S capture solvents. This work establishes a paradigm for integrating domain knowledge with deep learning to enable reliable, interpretable, and generalizable predictive modeling in complex chemical systems.
Electrolytes serve as critical components in batteries and electrolytic cells. This study proposes a framework to assess the contributions of clusters to electric conductivity. Within this framework, clusters are first identified, and their molarities are calculated by integrating excess infrared spectroscopy with density functional theory (DFT). Subsequently, the self-diffusion coefficients of these clusters are estimated through the Stokes-Einstein relation. Finally, the conductivities of charged clusters are evaluated using the Nernst-Einstein equation. By combining these steps, the percentage contribution of charged clusters to overall electric conductivity is quantitatively determined. Taking the binary system of sodium trifluoromethanesulfonate (NaOTf) and 1,2-dimethoxyethane (DME) as a model electrolyte, liquid clusters, namely, Na+(DME)3, Na+(DME)2, OTf-(DME)4, Na(OTf)2-(DME)4, (Na)2OTf+(DME)4, NaOTf(DME)2, NaOTf(DME)3, as well as DME monomer, dimer, trimer, and tetramer, were identified in the binary mixtures. Contributions from charged clusters to the overall conductivity at each experimental concentration were derived. It was found that, at low salt concentrations, Na+(DME)3 plays the dominant role, while at high concentrations, the biggest contributor is OTf-(DME)4. Together with other techniques including nuclear magnetic resonance and molecular dynamics, DME was found to interact strongly with Na+, in a mode of bidentate to make a coordination number of six. On the contrary, the interaction between DME and OTf- is weak, with negligible hydrogen bonds. The present work addresses the conductivity properties of electrolytes at the cluster level, providing physical insights into the concerned topic. It may also shed light on the design of new electrolytes to meet the needs of vigorously developing battery industries.
As lithium-ion batteries advance toward higher voltages and energy densities, traditional carbonate-based electrolytes not only undergo oxidative decomposition under high pressure but also induce structural degradation of cathode materials and destabilization of the electrode-electrolyte interface (CEI), severely limiting battery cycle life and safety. To address these challenges, this study designed 18 nitrile ether derivatives (EDD series) featuring varying numbers and positions of cyano substituents, using ethylene glycol bis(propionitrile)ether (DENE) as the molecular backbone. A multiscale approach combining density functional theory calculations and molecular dynamics simulations was employed to systematically investigate their performance regulation mechanisms. Theoretical calculations reveal that increasing the number of cyano substituents significantly enhances the redox potential of the molecules. Among these, terminal cyano groups exhibit the most pronounced effect on reducing the reduction potential, while symmetrically distributed cyano substituents are more conducive to broadening the electrochemical stability window. Frontier molecular orbital analysis indicates that cyano substitution primarily lowers the LUMO energy level of the molecules, thereby enhancing their reduction activity. Molecular dynamics simulations further demonstrate that nitrile-ether molecules effectively modulate solvation structures through strong cyanide-Li+ coordination, significantly reducing carbonate solvents' proportion in the primary solvation shell. This regulates lithium ion desolvation processes and transport properties like migration number. Based on a comprehensive evaluation of these multidimensional properties, this study identifies molecule 110011 as a candidate additive suitable for high-voltage cathode interface protection and molecule 102001 as a functional additive prioritized for anode interface film formation. Both exhibit optimal comprehensive performance in terms of interface stability and ion transport efficiency, respectively. This study aims to enhance the electrochemical performance of high-voltage lithium-ion batteries, providing multifaceted theoretical foundations for the rational design of electrolyte additives in high-voltage lithium-ion batteries.
We present a thermodynamically consistent framework to model adsorption in flexible nanoporous materials by coupling three-dimensional classical density functional theory (cDFT) based on the SAFT-VR-Mie equation of state with the osmotic ensemble formalism. This approach enables the treatment of fluid adsorption in deformable frameworks, overcoming the rigid-host limitation of conventional cDFT descriptions. The methodology is first validated on a simplified MIL-53-type model, where adsorption isotherms and grand potential trends are shown to be in good agreement with molecular simulation data. The analysis highlights how breathing transitions and hysteresis emerge from the interplay between the fluid grand potential and the host free-energy landscape, emphasizing the critical role of the relative stability of narrow- and large-pore states and of the associated energy barriers. The framework is then applied to methane adsorption in the flexible metal-organic framework MIL-53. After minimal calibration of the fluid-framework cross-interactions, the model reproduces experimental adsorption isotherms at 300 and 213 K and captures adsorption-induced structural transitions within the osmotic description. While quantitative prediction of hysteresis remains sensitive to the assumed host free-energy profile, the present osmotic SAFT-cDFT approach provides a computationally efficient and predictive tool for investigating adsorption-deformation coupling in responsive porous materials, opening perspectives for the screening and thermodynamic analysis of flexible metal-organic frameworks.
Symmetry-breaking charge transfer in photoexcited donor-acceptor octupolar molecules is a critical phenomenon for molecular electronics, yet a unified understanding of its driving forces remains to be fully understood. While symmetry-breaking charge transfer in symmetric octupolar molecules is driven by solvation, the intramolecular charge transfer dynamics is additionally modulated by the Jahn-Teller effect, which is intrinsic to such systems. Usually, these two types of interaction are analyzed independently, overlooking their possible synergy. A unified theoretical model of the combined influence of the Jahn-Teller effect and solute-solvent interactions on symmetry-breaking charge transfer in excited octupolar molecules with C3 symmetry is developed. The key finding is the additivity of the effects of these two distinct interactions on symmetry-breaking charge transfer. This synergy is quantified by a single effective parameter, enabling an accurate prediction of the emergent dipole moment. One consequence of this additivity is that, when the Jahn-Teller effect is strong, the degree of symmetry breaking may depend weakly on the polarity of the solvent. The scope of the identified regularities extends beyond the bounds of donor-acceptor compounds, encompassing mixed-valence complexes as well. Our results provide a fundamental predictive tool for the rational design of octupolar materials, where the internal structure and the external environment can be cooperatively tuned to achieve desired charge-separated states for applications in nonlinear optics and molecular electronics.
The electrostatic interactions of phosphate groups and counterions critically affect the structure, function, and reactivity of DNA or RNA. We present a joint experimental-theoretical investigation of dimethyl phosphate (DMP-) in aqueous solution, an established model system of the sugar-phosphate backbone. 31P NMR spectroscopy, as a probe of phosphate-ion association, reveals a systematic shielding of the 31P chemical shift (δiso(31P)) with variations of Mg2+ and Ca2+ content and moderate temperature dependence. Enhanced sampling molecular dynamics (MD) and ab initio (GIAO-DF-LMP2) level of theory are used to reveal the microscopic mechanism. Simulations are performed for a configurational ensemble of DMP--ion geometries and their first solvation shells, demonstrating (i) the spatial convergence of changes of the nuclear shielding constant σiso(31P), (ii) the intramolecular geometric origin of short-time scale σiso(31P) fluctuations, and (iii) an average shift of σiso(31P) of about 3-8 ppm upon contact ion pair formation with Mg2+ or Ca2+ ions. A quantitative analysis of δiso(31P) for varying ion content and temperature allows us to extract the temperature-dependent fraction of the contact ion pair species, indicating that solvent-separated or free ion pairs are the energetically preferred species. The results impose boundary conditions for improvements of phosphate ion force fields and establish the interactions underlying the changes of δiso(31P).
Electrostatic interactions between charged amino acid side chains play an important role for the stability of α-helices. The strength of these interactions depends on the protonation state of the residues, which is determined by the pH of the environment. Force fields used for molecular dynamics (MD) simulations of such systems should therefore accurately model charged interactions and their dependence on the protonation state. We performed MD simulations for two distinct protonation states on a set of helical peptides known to exhibit various degrees of pH-dependence in experiments and compared two recommended combinations of AMBER protein force field and water model: ff14SB + TIP3P and ff19SB + OPC. While both combinations model similar side chain interactions for the helical states of the peptides, they showed some differences in the overall helical content and the stability of the hydrogen bonds. Nevertheless, both combinations were capable of detecting protonation-dependent structural changes in the peptides. This could be useful for identifying pH-sensitive sites in helical peptides or for designing pH-dependent switches.
UV-induced polymerization is a widely adopted technique in materials science, valued for its rapid curing, low energy consumption, and ability to produce polymers with tunable properties. Central to this process are photoinitiators that generate free radicals upon exposure to UV light to initiate polymerization. This study investigates the effect of varying 2,2-dimethoxy-2-phenylacetophenone (DMPA) concentrations on the polymerization kinetics, grafting efficiency, grafting yield, and final properties of a polymer synthesized by grafting ethylene glycol methyl ether acrylate (EGMEA) onto 25% mole epoxidized natural rubber (ENR), forming P(EGMEA3-g-ENR1). The polymerization process and kinetics were monitored in real time using in situ Raman spectroscopy, enabling precise tracking of chemical changes, initiation points, curing time, and the overall progress of grafting. Thermal properties and degradation behavior were analyzed by using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The results revealed that an optimal DMPA concentration of 1.5 mol % yielded the highest grafting efficiency and grafting yield. Excessive concentrations of photoinitiators led to premature chain termination and grafting yield, while insufficient DMPA concentrations hindered monomer conversion, lowering grafting efficiency and compromising polymer integrity. These findings underscore the importance of optimizing photoinitiator concentrations for achieving the desired material properties and enhancing the efficiency of UV-induced graft polymerization. Importantly, this work aims to improve the performance and processability of natural-rubber-based polymers for energy-storage applications. By optimizing the UV-grafting process and tailoring polymer properties, the study supports the development of rubber-derived materials suitable for use in battery components, particularly as binders or solid polymer matrices in lithium-ion and solid-state batteries.This work addresses a significant knowledge gap, as similar studies on rubber-based polymers have not been previously reported.
We extend the multi-input linear correction (MILC) framework to the energy representation (ER) theory to improve the accuracy and robustness of solvation free energy (SFE) predictions. While ER theory offers a computationally efficient route to SFE from solute-solvent pair interaction distributions, its standard functionals often suffer from systematic biases. Although the truncated hypernetted chain (tHNC) functional was developed to reduce these errors, it relies on an empirical truncation parameter that is temperature-dependent and difficult to define for mixed solvents. To overcome these limitations, we propose the MILC-ER scheme, which utilizes a combination of descriptors─approximate SFEs for fully charged and zero-charge states, and the average interaction energy─to capture both electrostatic and excluded-volume effects without empirical truncation. Our model achieves exceptional accuracy on the FreeSolv database (excluding carboxylic acids), yielding a mean absolute deviation (MAD) of 0.35 kcal/mol relative to Bennett acceptance ratio (BAR) values. Critically, we employ a nested cross-validation protocol to provide an unbiased assessment of the model's generalization capability. The results demonstrate that simple linear models consistently outperform complex nonlinear machine learning algorithms, such as Random Forests, confirming that the systematic errors in ER functionals scale linearly with the chosen physical descriptors. This linear framework is not only statistically robust and well-conditioned for small-data regimes but also physically interpretable as a generalized extension of conventional correction schemes. Furthermore, the MILC-ER coefficients remain transferable across different temperatures and successfully generalize to mixed-solvent environments, as demonstrated for ethanol-water systems. These findings establish MILC-ER as a high-precision, computationally efficient, and transferable tool for large-scale solvation studies.
The GAAA tetraloop-receptor (TL-R) interaction is a ubiquitous tertiary interaction in RNA structures. Using the P4-P6 domain in the Tetrahymena thermophila group I intron as a model system, we studied the mechanism of TL-R formation using computer simulations. We show that the intron folds via a multistep pathway, populating seven states with distinct tertiary contacts. Under physiological Mg2+ concentrations ([Mg2+]), the loop-bulge-P4 tertiary interaction is essential to stabilize the docked TL-R complex, whereas in high [Mg2+], the TL-R complex is stable by itself. The solvated Mg2+ ions modulate the TL-R docking-undocking dynamics and stabilize non-native intermediate states. The condensation of Mg2+ in the major grooves of the TL and R helices is critical for them to attain a specific stiffness essential for their facile docking. The results highlight the critical role of Mg2+ ions in facilitating the formation of TL-R interactions that stabilize long-range tertiary contacts in the RNA structures.
We present X-ray emission (XES) and absorption (XAS) spectra of the F- ion in aqueous solution, along with a theoretical analysis using combined ab initio quantum chemistry spectral calculations and quantum molecular dynamics simulations. The spectra are predicted to have a significantly different dependence on the distance between the anion and the oxygen atoms of water molecules in the first solvation shell. The XES spectrum shows a strong reconfiguration of emission line intensities, while the excitation energy of a resonance in the XAS spectrum is highly sensitive to this distance. Comparisons with the recorded XES and XAS spectra yield predicted F-O distances that agree with 2.7 Å. Two weak features in the XES spectrum are identified as being due to interatomic radiative decay (IRD), thus proving a negative ion counterpart to the recently identified IRD process for the Na+ and Mg2+ cations in aqueous solution, with the difference that the IRD feature appears on opposite sides of the main ion emission in the two cases. Arguments are provided that the combination of X-ray emission and absorption, together with quantum spectral and molecular dynamics calculations, has much to offer for future studies of the structure and electronic properties of anionic solutions.
In the context of energy applications for salts and, more specifically, in the case of molten salt reactors, the solvation of corrosion species, the nature and behavior of radiation-produced excess electrons, transient radicals, and molecular gas species all depend on the Lewis acid-base behavior of the constituent salt melt. Speciation of dissolved species and their transport properties are also influenced by the ability of the melt to form networks. This article focuses on the structural properties of melts composed of alkaline earth metal ions coupled with the Cl- anion, and the quantum mechanical behavior of Cl2, a typical product of the reaction of radiation-produced chlorine radicals in Cl--based molten salts. We explore the effect of M2+ Lewis acidity on chlorobasicity, seen in this work as the availability of Cl- ions to chemically react with Cl2 to produce Cl3-.