Tiny but mighty! N,N-dimethyl-4-(5-nitrothiophen-2-yl)aniline, a push-pull fluorescent dye for lipid droplet imaging

Lipid droplets (LDs) are ubiquitous cellular organelles with a neutral lipid core containing triacylglycerols and cholesteryl esters surrounded by phospholipids. Recent findings indicate that LDs are intricately linked to diseases, such as cancer and neurological disorders, in addition to their roles in cellular senescence and immune responses. Herein, we describe a simple yet robust push-pull molecule, N,N-dimethyl-4-(5-nitrothiophen-2-yl)aniline (NiTA), as a versatile LD fluorescent probe. NiTA showed an absorption spectrum with a substantial bathochromic shift and a fluorescence spectrum with excellent solvatochromism. Leveraging the remarkable photophysical features of NiTA, we stained LDs in major immune cells, including T and B cells, and macrophages, and monitored the changes in LDs under oxidative and starvation conditions. Furthermore, we demonstrated the applicability of NiTA for visualizing the organization of medaka fish (Oryzias latipes) embryos during development. We expect the small yet powerful NiTA to be utilized in various applications, including fluorescence mapping to observe LD numbers, morphology, and polarity changes in animals and cells.

Comprehensive analysis of Syzygium cumini L. pomace extract as an α-amylase inhibitor: In vitro inhibition, kinetics, and computational studies

Type 2 diabetes mellitus (T2DM) is a widespread metabolic disorder characterized by impaired regulation of blood glucose levels. Jamun (Syzygium cumini L.) fruits and seeds have been traditionally used in Ayurveda to manage diabetes. While fruit and seed extracts have been extensively studied for their anti-α-amylase properties, pomace, a byproduct of juice extraction, remains under explored. This study investigated the α-amylase inhibitory potential of jamun pomace (JP) extract by using in vitro and in silico methods. Enzyme inhibition assays revealed an half-maximal inhibitory concentration (IC₅₀) value of 85.68 ± 5.22 μg/mL for the JP extract, comparable to acarbose (64.28 ± 7.15 μg/mL). The extract exhibited mixed-mode inhibition, whereas acarbose showed competitive mode inhibition. At 10 μg/mL, the Vmax of JP extract was half that of acarbose, demonstrating significant inhibition. GC-MS analysis identified 11 volatile compounds (R1-R11) in the JP extract. Density Functional Theory (DFT) and ADMET analyses confirmed the chemical reactivity of the volatiles, drug-like properties, and low toxicity. Molecular docking revealed a high binding score for R11 (-8.0 kcal/mol), similar to acarbose (-8.2 kcal/mol). Molecular dynamics simulations further demonstrated the stability of α-amylase complexes with R11, R3, and R8, with R11 showing the lowest binding energy (-28.75 ± 6.25 kcal/mol). These findings suggest that R11 and JP extracts hold promise as anti-diabetic agents. Utilizing JP extract as a nutraceutical offers the dual benefit of diabetes management and sustainable waste valorization in jamun juice production.

Deciphering Zn(II)-Carboxylic Acid Interactions: Tailoring Oil/Water Interfaces and Surfactant Efficiency

This study elucidates the synergistic interactions between dodecanoic acid (C12) and zinc ions (Zn2+) at oil/water interfaces, a critical phenomenon for understanding the intricate dynamics of surfactant systems. Interfacial tension (IFT) measurements, performed via pendant drop tensiometry, reveal that the pronounced affinity of C12 for the oil/water interface causes an approximate 35% reduction in the IFT (from 50 to about 32 mN/m). However, introducing Zn2+ ions with C12 created an IFT decrease to approximately 22 mN/m, representing an overall reduction of nearly 55%, indicative of their interactions that substantially enhance interfacial adsorption and promote molecular ordering. The stoichiometric relationship between C12 and Zn2+ exhibits a marked concentration dependency. This phenomenon underscores the complex nature of the involved interfacial assembly and the dual role of both C12 and Zn2+ in modulating the physicochemical properties of the interface, which has been supported by the complementary density functional theory (DFT) and COSMO-RS calculations. Moreover, vibrational sum frequency generation (VSFG) spectroscopy corroborates the experimental findings by detecting high-order alkane chain arrangements induced by the Zn2+ ions. These integrated methodologies demonstrate that the Zn2+ ion's role varies, depending on the surface coverage by C12, and causes a more ordered interfacial film under controlled conditions, optimizing the reduction of IFT. Our research introduces a promising approach for creating advanced surfactant systems, emphasizing the intricate role of metal cations like Zn2+ at interfaces in various chemical engineering and environmental management applications.applications.

Theoretical prediction of pressure-stabilized all-nitrogen N12 molecular crystals with π-π stacking

All-nitrogen compounds are ideal high-energy-density materials as they decompose into environmentally friendly nitrogen gas (N2). However, achieving structural stability often conflicts with high-energy performance. In this study, we demonstrated that two aromatic pentazole rings can be linked via an -NN- bond with sp2 orbital hybridization, resulting in a planar π-conjugated compound known as N12. Computational analyses, including the electron localization function and isochemical shielding surface calculations, demonstrated that the pentazole anion in N12 maintained electron delocalization and exhibited aromaticity. Interestingly, under high pressure, the N12 molecule formed a super π-π stacking crystalline structure. The thermodynamic and dynamic stabilities of crystalline N12 were verified using phonon spectrum and ab initio molecular dynamics calculations. Electronic structure calculations revealed that the N12 crystal exhibited semiconducting properties with a large bandgap and was comparable to stable CHON energetic materials. Unlike other all-nitrogen compounds, π-π stacking in the N12 crystalline structure contributed to a high mass density and resulted in a large decomposition barrier, which was crucial for achieving high energy performance and high structural stability. Therefore, further evaluations of detonation performance revealed that the N12 crystalline possessed excellent detonation velocity and pressure among the known all-nitrogen molecular crystals. This work enhances the understanding of nitrogen chemistry and provides new insights into the stabilization of all-nitrogen compounds through π-π stacking.

Impact of Derivative Observations on Gaussian Process Machine Learning Potentials: A Direct Comparison of Three Modeling Approaches

Machine learning (ML) potentials have become a well-established tool for providing inexpensive, yet quantum-mechanically accurate, atomistic simulations. Here, we extend our current modeling procedure, based on Gaussian process regression, to include derivative observations into the ML models. We directly compare three system-energy modeling approaches based on quantum mechanically derived quantities: (i) atomic energies, (ii) total system energy, and (iii) total system energy with derivative observations. We find that modeling the total energy with derivative observations has the best performance across the board, achieving chemical accuracy with fewer training data. In addition, both energy and force errors are around an order of magnitude lower when derivative observations are added to the models in some cases. We follow up with a discussion on the multiple advantages the proposed method of modeling brings, such as improved data set availability and the ability to easily include dispersion interactions. Additionally, we discuss the use cases of the new modeling approach in the ML force field FFLUX.

FC2DES: Modeling 2D Electronic Spectroscopy for Harmonic Hamiltonians

Two-dimensional electronic spectroscopy (2DES) can provide detailed insight into the energy transfer and relaxation dynamics of chromophores by directly measuring the nonlinear response function of the system. However, experiments are often difficult to interpret, and the development of computationally affordable approaches to simulate experimental signals is desirable. For linear spectroscopy, optical spectra of small to medium-sized molecules can be efficiently calculated in the Franck-Condon approach. Approximating the nuclear degrees of freedom as harmonic around the ground- and excited-state minima, closed-form expressions for the exact finite-temperature linear response function can be derived using known solutions for the propagation operator between normal mode coordinate sets, fully accounting for Duschinsky mode-mixing effects. In the present work, we demonstrate that a similar approach can be utilized to yield analogous closed-form expression for the finite-temperature nonlinear (third-order) response function of harmonic nuclear Hamiltonians. The resulting approach, named FC2DES, is implemented on graphics processing units, allowing efficient computations of 2DES signals for medium-sized molecules containing hundreds of normal modes. Benchmark comparisons against the widely used cumulant method for computing 2DES signals are performed on small model systems, as well as the nile red molecule. We highlight the advantages of the FC2DES approach, especially in systems with moderate Duschinsky mode mixing and for long delay times in the nonlinear response function, where low-order cumulant approximations are shown to fail.

Toward Chemical Accuracy in Biomolecular Simulations through Data-Driven Many-Body Potentials: I. Polyalanine in the Gas Phase

A predictive understanding of how proteins fold, misfold, and stabilize requires accurate molecular-level insights into the thermodynamic and kinetic forces shaping their backbones. While empirical force fields remain the workhorse of biomolecular simulations, their limited functional forms often fall short in capturing the complex many-body interactions that govern protein dynamics. Quantum-mechanical methods, on the other hand, offer high accuracy but are prohibitively expensive for large biomolecules. In this work, we introduce a generalized, intramolecular formulation of the data-driven many-body MB-nrg formalism that approaches "gold standard" coupled cluster accuracy in simulating polyalanine chains in the gas phase. By decomposing polyalanines into chemically intuitive building blocks, we develop modular and transferable potential energy functions that accurately reproduce reference energies, normal-mode harmonic frequencies, and conformational free-energy landscapes. Compared to empirical force fields commonly used in biosimulations, the MB-nrg potential energy function yields a smoother and more physically grounded free-energy surface, captures transient structural motifs under-represented by empirical force fields, and enables flexible sampling of secondary structure transitions in longer peptides. This work establishes a foundation for extending coupled-cluster-level modeling to larger biomolecular systems under physiologically relevant conditions, while highlighting the methodological challenges that remain in achieving consistent accuracy at scale.

PHAST-MBD: Implementing Many-Body Dispersion in the PHAST 2.0 Potential, Results for Noble Gases

A recently published empirical force field (herein PHAST or PHAST 2.0) is employed in its many-body dispersion-corrected form (PHAST-MBD) to examine the effects of collective dispersion interactions. Rare gases are used as a systematic way to test increasing importance of van der Waals attractions in systems dominated by repulsion-dispersion that are a challenge to extant force fields. The effects of many-body dispersion were studied for liquid and supercritical fluid regime for the series Neon, Argon, Krypton and Xenon. The PHAST force field is a condensed phase atomistic molecular modeling potential that includes contributions from repulsion-dispersion, permanent electrostatics, and many-body polarization. Each of these pieces is physics based and seeks to mimic their constituent first-principles counterparts with as few fitting parameters as possible. Critically, it is built to reproduce accurate gas phase pair interactions. This facilitates the efficacy of mixing rules for unlike interactions while many-body effects are added via explicit polarization and dispersion models. The effectiveness of PHAST-MBD is demonstrated calculating rare gas densities as compared to experiment over a wide pressure range. Pair potentials fail systematically at high pressure and density as dispersion grows while PHAST-MBD reproduces experiment in all regimes. This is strong evidence in favor of the PHAST 2.0 paradigm of physically motivated empirical potentials that reproduce gas phase interactions and facilitate accurate mixing rules with many-body effects included explicitly. This work suggests a hybrid future approach that will be adopted in PHAST-MBD that keeps the accurate PHAST pair interactions and only includes many-body terms via the coupled dipole method (CDM); such an approach avoids the issues identified here that the CDM many body van der Waals (MBVDWs) formalism has reasonable but nonoptimal implicit mixing rules and can alter pair potentials.

Aerosol Measurements and Decadal Changes: The Role of Climatic Changes and How It Reflects in Respiratory Allergies and Asthma

The causative agents of respiratory allergies are bioaerosols, such as house dust mite feces, pollen grains, and fungal spores. Climate change and urbanization are considered to lead to an increase in the load of allergenic bioaerosols due to impacts on plant phenophases and allergenicity. Continuous and efficient monitoring of the atmospheric composition worldwide is essential, given the major changes involved and their impact on climate change. The complexity of the exposome, evolving from single to multiple complex exposures, is explored in this work. Acquiring information from interdisciplinary scientific disciplines, such as aerobiology (for airborne particles of biological origin), aerosol science (for airborne particles of chemical or inorganic material), and integrating this with the actual reactome of patients with respiratory diseases, we aim to provide evidence of the multifactorial nature of this interaction in real life. The objective of this review is to present how we can monitor aerosols and mostly monitor the exposome, especially the biological one, i.e., pollen and fungal spores, and what their impact is, or could be, on respiratory allergies. A huge technological advancement has been required, as traditional methods of particle collection and identification have been based on tedious laboratory procedures, with delays of more than a week. This has limited their practical use to allergic patients and their treating physicians. Automation, real-time high temporal resolution, and the use of artificial intelligence are being increasingly used in medicine. Likewise, this overview summarizes the current aerosol measurement and modeling capabilities and discusses the classification of various aerosol particles and their impact on respiratory allergies. Satellite remote sensing is highlighted as a solution to the gaps in global aerosol representation by examining aerosol load in the atmospheric column in major cities worldwide. We also discuss potential novel threats, such as pioneer bioaerosols and the respiratory epithelial barrier, as well as future insights into the impact of climate change on allergy and asthma. We conclude with a discussion of emerging co-exposures and co-diseases resulting from the ongoing climate change.

Mid-infrared acetone gas sensors using substrate-integrated hollow waveguides augmented by advanced preconcentrators

The identification of volatile organic compounds (VOC) such as acetone, a relevant biomarker for diabetes mellitus in exhaled human breath has become essential for early disease diagnostics, prognosis, and monitoring of metabolic responses to pharmacological interventions. Gas chromatography coupled with mass spectrometry (GC-MS) is considered as the gold standard for breath analysis. However, its inability to offer point-of-care monitoring limits its applicability in clinical environments. Optical techniques based on absorption in the mid-infrared range (2.5 to 25 μm) appear as promising alternatives due to their inherent selectivity, potential for miniaturization, portability, and direct analysis with rapid response. Relevant biomarkers present in exhaled breath, are usually observed in the ppb to ppm (v/v) concentration regime. For sensitivity enhancement of optical sensing techniques, appropriate preconcentration schemes are required prior to the optical detection. The present study describes a method combining a multi-channel substrate-integrated preconcentration module (a.k.a., muciPRECON) for enhancing and optimizing the detection of acetone via a mid-infrared photonic sensing system. The sensor system comprises a compact Fourier Transform Infrared (FTIR) spectrometer, a technique that enables detailed infrared spectral analysis, coupled to a substrate-integrated hollow waveguide (iHWG) simultaneously acting as a gas cell and as a photon conduit. Preconcentation experiments were from acetone/nitrogen gas mixtures in the concentration range of 5-100 ppm at - 10 °C followed by desorption at a temperature of 100 °C and direct injection into the IR sensing system Thus obtained acetone spectra were quantified evaluating a molecule-specific vibrational absorption peak area in the spectral window 1260-1170 cm-1. After extensive screening, Tenax was identified as superior sorbent material providing an enrichment factor of up to 153-times, a limit of detection (LOD) of 0.118 ppm, and a limit of quantification (LOQ) of 0.393 ppm. These results are indeed promising for practical applications, especially since acetone concentrations usually vary between 0.3 and 0.9 ppmv within the exhaled breath of healthy individuals, and in individuals with diabetes, acetone concentrations are typically around 1.7 to 3.0 ppmv. Consequently, the developed systems have the necessary sensitivity and accuracy to detect acetone levels that are in the relevant physiological range indicating their potential use in future real-world scenarios.

Real-time tracking of energy flow in cluster formation

Femtosecond time-resolved spectroscopy has shaped our understanding of light-matter interaction at the atomic level. However, the photoinduced formation of chemical bonds, especially for larger aggregates, has evaded observation due to difficulties to prepare reactants at well-defined initial conditions. Here, we overcome this hurdle by taking advantage of the exceptional solvation properties of superfluid helium, which allow us to stabilize atoms in a metastable, foam-like configuration with 10 Å interatomic distance. We apply photoexcitation with a femtosecond laser pulse to collapse such a dilute metastable aggregate of Mg atoms formed inside a nanometer-sized He droplet, and track cluster formation at a characteristic time of (450 ± 180) fs through photoionization with a time-delayed second pulse. We find that energy pooling collisions of electronically excited Mg atoms occur during cluster formation, leading to transient population of highly-excited Mg atoms, up to 3 eV above the excitation photon energy. Relaxation and conversion to nuclear kinetic energy drives cluster fragmentation and ejection of ionic fragments from the droplet. Our results demonstrate the potential of He droplets for bond formation studies, and for revealing involved energy- and charge transfer dynamics, like photon energy upconversion.

Predicting accurate binding energies and vibrational spectroscopic features of interstellar icy species. A quantum mechanical study

In the coldest, densest regions of the interstellar medium (ISM), dust grains are covered by thick ice mantles dominated mainly by water. Although more than 300 species have been detected in the gas phase of the ISM by their rotational emission lines within the radio frequency range, only a few were found in interstellar ices, e.g. CO, CO2, NH3, CH3OH, CH4 and OCS, by means of infrared (IR) spectroscopy. Observations of ices require a background-illuminating source for absorption, constraining the available sight lines for investigation. Further challenges arise when comparing with laboratory spectra due to the influence of temperature, ice structure and the presence of other species. In the era of IR observations provided by the James Webb space telescope (JWST), it is crucial to provide reference spectral data confirming JWST's assigned features. For this purpose, this study addresses the adsorption of the aforementioned species on water ice surfaces and their IR features by means of quantum chemical computations grounded on the density functional theory (DFT) hybrid B3LYP-D3(BJ) functional, known to give reliable results for binding energy and vibrational frequency calculations, including IR spectra simulation. The calculated binding energies and IR spectral data are presented in the context of experimental spectra of ices and the new findings from the JWST, which have already proven to be insightful thanks to its unmatched sensitivity. We show that quantum chemistry is a powerful tool for accurate frequency calculations of ISM ice interfaces, providing unprecedented insights into their IR signatures.

Quantum Nature of Ubiquitous Vibrational Features Revealed for Ethylene Glycol

Vibrational properties of molecules are of widespread interest and importance in chemistry and biochemistry. The reliability of widely employed approximate computational methods is questioned here against the complex experimental spectrum of ethylene glycol. Comparisons between quantum vibrational self-consistent field and virtual-state configuration interaction (VSCF/VCI), adiabatically switched semiclassical initial value representation (AS-SCIVR), and thermostatted ring polymer molecular dynamics (TRPMD) calculations are made using a full-dimensional, machine-learned potential energy surface. Calculations are done for five low-lying conformers and compared with the experiment, with a focus on the high-frequency, OH-stretches, and CH-stretches, part of the spectrum. Fermi resonances are found in the analysis of VSCF/VCI eigenstates belonging to the CH-stretching band. Results of comparable accuracy, quality, and level of detail are obtained by means of AS SCIVR. The current VSCF/VCI and AS-SCIVR power spectra largely close the gaps between the experiment and TRPMD and classical MD calculations. Analysis of these results provides guidance on what level of accuracy to expect from TRPMD and classical MD calculations of the vibrational spectra for ubiquitous CH- and OH-stretching bands. This work shows that even general vibrational features require a proper quantum treatment, usually not achievable by the most popular theoretical approaches.

Computing Excited States of Molecules Using Normalizing Flows

Calculations of highly excited and delocalized molecular vibrational states are computationally challenging tasks, which strongly depend on the choice of coordinates for describing vibrational motions. We introduce a new method that leverages normalizing flows, i.e, parametrized invertible functions, to learn optimal vibrational coordinates that satisfy the variational principle. This approach produces coordinates tailored to the vibrational problem at hand, significantly increasing the accuracy and enhancing the basis set convergence of the calculated energy spectrum. The efficiency of the method is demonstrated in calculations of the 100 lowest excited vibrational states of H2S, H2CO, and HCN/HNC. The method effectively captures the essential vibrational behavior of molecules by enhancing the separability of the Hamiltonian and hence allows for an effective assignment of approximate quantum numbers. We demonstrate that the optimized coordinates are transferable across different levels of basis set truncation, enabling a cost-efficient protocol for computing vibrational spectra of high-dimensional systems.

Development of a Transferable Density-Functional Tight-Binding Model for Organic Molecules at the Water/Platinum Interface

A computationally efficient and transferable approach for modeling reactions at metal/water interfaces could significantly accelerate our understanding and ultimately the development of new catalytic transformations, particularly in the context of the emerging field of biomass conversion. Here, we present a parametrization of Pt-X (X = H, O, C) density-functional tight-binding (DFTB) for addressing this need. We first constructed Pt-H, Pt-O, and Pt-C repulsive potential splines. These pairwise parameters were then augmented to include many-body interactions using the Chebyshev Interaction Model for Efficient Simulation (ChIMES). We compare the geometrical and energetic performances of both DFTB and DFTB/ChIMES methods with DFT reference data across a variety of organic molecules at the platinum surface from nanoparticles to single-crystal surfaces. DFTB shows limited transferability between extended crystal surfaces and small nanoparticles. This transferability is significantly improved through the introduction of three-body interactions with Pt in DFTB/ChIMES, which provides consistent results across various systems, with reductions in the RMSD from around 30 kcal/mol in DFTB to around 10 kcal/mol. We demonstrate the stability and reliability of the obtained parameters by performing metadynamic simulations for the adsorption of phenol on Pt(111). We observe that DFTB itself is undersolvating the surface, leading to only one or two chemisorbed water molecules in a c(4 × 6) unit cell. In contrast, DFTB/ChIMES leads to a coverage of about 0.5 ML and successfully captures the chemisorbed mode of phenol at both the solid/liquid and the solid/gas interfaces. Furthermore, in agreement with experimental measurements, the adsorption at the solid/liquid interface is significantly weaker than that at the solid/gas interface. Furthermore, we highlight that even with DFTB, where we can accumulate dynamics for more than 1 ns for a given system, the simulations are not fully converged.

Orientational Geometry, Surface Density, and Binding Free Energy of Intermediates as Full Descriptors for Electrochemical CO2 Reduction at Metal Surfaces

Metal catalysts for the electrochemical CO2 reduction reaction (CO2RR) have attracted widespread attention due to their high catalytic efficiency, stability, broad product diversity, and ease of preparation. Studies show that the product distribution and yield of the electrochemical CO2RR on metal surfaces result from the metal's binding energy of an intermediate adsorbed CO (*CO). However, reaction pathways could be manipulated by other thermodynamic parameters, such as orientation and surface density. In this work, the CO2RR on Au electrode surfaces was comprehensively analyzed using high-performance in situ electrochemical sum-frequency generation (EC-SFG) spectroscopy. The improved signal intensities allowed the reaction to be monitored with a fast time resolution, extracting key thermodynamic and kinetic features from the experiments. Our EC-SFG spectrometer allowed the comprehensive analysis of the potential-dependent polarized SFG signal, allowing us to quantify *CO orientation at the Au electrode surface as a function of applied potential. These experimental results were then used to determine the maximum surface density and binding energies of the *CO intermediate in a self-contained analysis. These EC-SFG experiments enabled us to quantify the reaction rate constant for the system. We then discuss how the binding energy, orientation angle, and absolute surface density of an intermediate should be fully considered in understanding its thermodynamic behaviors in the CO2RR. This work demonstrates the potential of high-efficiency EC-SFG spectroscopy to provide an all-inclusive analysis of the CO2RR on metal surfaces and opens the door for other catalysts to be investigated using this technique to determine the best system for efficient electrocatalysis.

First principles potentials for reactions on molecular crystals: modelling the interstellar H + CO reaction

The potential energy barriers for successive hydrogenation of carbon monoxide mean that the observed interstellar abundances of small hydrogenated carbon molecules such as formaldehyde cannot be accounted for by gas phase hydrogenation reactions. Consequently these reactions are thought to occur on the surface of ice grains in the interstellar medium. Aspects of the interaction of hydrogen atoms with cold CO ice surfaces are examined here by means of molecular dynamics calculations. In order to undertake these calculations a new and flexible approach to developing potential energy surfaces for gas-surface processes (including with ions as reactants) on finite temperature molecular crystals is developed. Interaction energies are calculated by a deep learned potential from electronic structure theory calculations incorporating extended CO ice structures, including under periodic boundary conditions. Direct hydrogenation on the CO ice surface requires energies higher than those typically available in the interstellar medium. Hydrogen atoms are readily adsorbed onto ice surfaces to feed catalytic hydrogenation processes within and on the icy grain, but do not directly reflect the temperature dependence of reactivity observed experimentally.

Fundamental invariant-neural network as a correction to the intramolecular force field illustrated for the full-dimensional potential energy surface of propane

As a highly effective approach for constructing potential energy surfaces (PESs) with both precision and efficiency, Δ-machine learning has been widely used in PES development. Inspired by the Δ-machine learning framework, we develop a combined model of fundamental invariant-neural network (FI-NN) and force field. Fitting the difference between the force field and ab initio energy by the FI-NN method is able to improve the accuracy of the force field. We demonstrate this enhanced methodology through the development of an intramolecular force field for propane, where CCSD(T)-F12a/AVTZ energies are initially approximated by the force field and subsequently refined using the FI-NN approach. Compared to the PES fitted by FI-NN, this combined method reduces the root mean square error (RMSE) by 50%.

Electric-Field-Dependent Covalent Interactions between H+ and Surface O Atoms Promote the Structural Disintegration of Montmorillonite

The structural stability of clay minerals is an important geochemical process. However, a long-standing challenge is to understand the surface reaction mechanisms for mineral structure stability. Quantum mechanical analysis indicates that a strong surface reaction, electric-field-dependent covalent interactions between H+ and basal oxygen (O) atoms of montmorillonite (MMT) surface, occurs in hydrothermal experiments. The covalent interactions strongly depend on the orbital hybridization of siloxane atoms at the MMT surface and increase with increasing acid concentration and temperature. The electric-field-dependent covalent interactions between H+ and surface O atoms weaken the Si-O bonding energy in MMT crystals, consequently contributing to the structural disintegration. A critical adsorption pressure of H+ at the MMT surface for complete disintegration was estimated to be -241.6 MPa. For example, the transformation rate of MMT is 34.7% at an adsorption pressure of -203.5 MPa, while it reaches up to 97.4% when adsorption pressures are below -241.6 MPa. Our findings will enhance the understanding and awareness of mineral weathering and soil acidification, which depend on the clay mineral structure.

Chalcogen-Bonding-Enabled, Light-Driven Decarboxylative Oxygenation of Amino Acid Derivatives and Short Peptides Using O2

Here we report a photocatalytic method for the decarboxylative oxygenation of amino acid derivatives and short peptides using dioxygen as a green oxidant. A reverse catalytic strategy utilizing Lewis basic diphenyl diselenide as a Lewis acid catalyst to activate carboxylic acid via chalcogen bonding interaction is the key to this work. This synthetic method is tolerant of functionalities present in both natural and non-proteinogenic amino acids, enabling the efficient synthesis of C-terminal amides or imides. Mechanistic studies suggest there is a dual noncovalent interaction between diphenyl diselenide and carboxylic acid, which allows radical decarboxylation through photoinduced intermolecular electron transfer. This new activation mode of carboxylic acids will add a new dimension to classical decarboxylative reactions.

Deconstructing 1H NMR Chemical Shifts in Strong Hydrogen Bonds: A Computational Investigation of Solvation, Dynamics, and Nuclear Delocalization Effects

This study provides the first quantitative dissection of the factors influencing 1H NMR chemical shifts δH in strong hydrogen-bonded systems, focusing on solvation, nuclear dynamics, and nuclear delocalization. A novel computational framework was developed, combining static quantum chemical calculations (nonrelativistic and relativistic), ab initio molecular dynamics (AIMD), and three-dimensional numerical solutions of the Schrödinger equation. This multiscale approach was applied to three model systems: the bifluoride anion (FHF)-, the Zundel cation (H5O2)+, and the pyridine-pyridinium cation (PyHPy)+. Our results reveal that nuclear dynamics and delocalization are the dominant factors determining δH in complexes with short, strong hydrogen bonds. Solvation effects, while critical for defining the hydrogen-bonding environment, play a secondary role. By isolating the contributions of each factor, we demonstrate that traditional methods often underestimate the quantum mechanical nature of the proton. The application of three-dimensional Schrödinger equation solutions represents a significant methodological advancement, enabling deeper insights into proton behavior in hydrogen bonds. This work not only enhances our understanding of NMR parameters in challenging systems but also establishes a robust framework for modeling complex interactions in chemical and biological environments.

Computational investigation of stigmasterol as a potential therapeutic agent for cervical cancer: insights from density functional theory (DFT) and molecular docking studies

Cervical cancer an appalling disease common amongst women worldwide, caused by human papillomavirus (HPV) with 80% increasing cases in developing countries, is reported to be persistent despite the various treatment measures. Hence, this research explores the properties of stigmasterol (SML), a biological active compound derived from Costus afer plant, as a drug agent for treatment of cervical cancer via density functional theory (DFT) studies and molecular docking investigation. Here, five key proteins were selected (for 4LEO, 7X8O, 5N2F, 4P7U and 2N5R) for in silico molecular docking study with SML. The DFT at ωB97XD/6-311++G (2d, 2p) level of theory was utilized and optimization of the compound was carried out in four different solvent phases, viz; acetone, ethanol, water, and gas to ascertain the level of reactivity and stability of the compound. The HOMO-LUMO energy gaps exhibited by acetone, ethanol, gas, and water were: 9.4128 eV, 9.4134 eV, 9.3140 eV, and 9.4164 eV, respectively. Interestingly, the resulting binding affinities for SML-protein interaction for 4LEO, 7X8O, 5N2F, 4P7U and 2N5R showed notable binding affinities of - 7.6 kcal/mol, - 5.2 kcal/mol, - 6.1 kcal/mol, - 5.2 kcal/mol and - 5.0 kcal/mol, respectively, as compared to the binding affinities (- 5.2 to - 7.6 kcal/mol) recorded for proteins-standard drugs interaction. The Non-covalent interactions (NCI) analysis showed predominately, van der Waals interactions in all the phases. This investigation suggest that SML can be used in the treatment and management of cervical cancer and requires further investigation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40203-025-00361-1.

Effect of Hydrogen Bonding on Ultrafast Intersystem Crossing in 7-Diethylaminothiocoumarin

Thiocarbonyls exhibit unique photophysical properties, characterized by rapid intersystem crossing (ISC) due to favorable singlet-triplet energetics and enhanced spin-orbit coupling. However, the role of hydrogen bonding in modulating the ISC remains underexplored. This study investigates the effect of solvent-solute hydrogen bonding on the ISC dynamics of 7-(diethylamino)-4-methyl-2-sulfanylidene-2H-chromen-2-one (thiocoumarin 1, TC1) using steady-state and time-resolved spectroscopy, complemented by theoretical calculations. Experimental data reveal that in methanol, hydrogen bonding leads to increased fluorescence quantum yield, prolonged singlet-state lifetime, and reduced triplet yield compared to aprotic acetonitrile. Time-resolved spectroscopy identifies an additional long-lived emissive singlet state in methanol, attributed to a hydrogen-bonded state, which slows ISC. Theoretical calculations demonstrate that hydrogen bonding alters the electronic structure and constrains ISC along key nuclear coordinates, including the C═S bond vibration and dihedral angles, leading to decreased triplet formation. These findings provide mechanistic insights into hydrogen-bonding-mediated control of ISC in thiocoumarins, with implications for designing functional materials with tunable photophysical properties.

Real-space observation of the dissociation of a transition metal complex and its concurrent energy redistribution

Mechanistic insights into photodissociation dynamics of transition metal carbonyls, like Fe(CO)5, are fundamental for understanding active catalytic intermediates. Although extensively studied, the structural dynamics of these systems remain elusive. Using ultrafast X-ray scattering, we uncover the photochemistry of Fe(CO)5 in real space and time, observing synchronous oscillations in atomic pair distances, followed by a prompt rotating CO release preferentially in the axial direction. This behavior aligns with simulations, reflecting the interplay between the axial Fe-C distances' potential energy landscape and non-adiabatic transitions between metal-to-ligand charge-transfer states. Additionally, we characterize a secondary delayed CO release associated with a reduction of Fe-C steady state distances and structural dynamics of the formed Fe(CO)4. Our results quantify energy redistribution across vibration, rotation, and translation degrees of freedom, offering a microscopic view of complex structural dynamics, enhancing our grasp on Fe(CO)5 photodissociation, and advancing our understanding of transition metal catalytic systems.

Probing Host-Guest Interactions of the Dual Anion Receptor Harmane with Halide and HSO4- Anions

Harmane is a polycyclic amine that can recognize F- and HSO4- via the ═N-H or ≡N binding site. The active binding site depends on whether the solvent is protic or aprotic, but the underlying molecular mechanism remains unclear. As a first step toward obtaining such mechanisms in solutions, we investigated the interactions of harmane with halide anions (F-, Cl-, Br-, and I-) and HSO4- in the gas phase using negative ion photoelectron spectroscopy combined with theoretical calculations. The adiabatic/vertical detachment energies for deprotonated harmane and harmane·X- (X = F, Cl, Br, I, and HSO4) were determined to be 2.72/2.79, 3.25/3.38, 4.19/4.43, 4.35/4.40, 3.93/3.99, and 4.49/4.75 eV, respectively, with an uncertainty of ±0.05 eV. All the X- anions were found to form hydrogen bonds with harmane through the ═N-H site. A nearly complete proton transfer was observed within the harmane·F- complex anion. Larger halide anions in other harmane-halide complexes remain relatively intact. Four closely lying isomers of harmane·HSO4- were identified. The photodetachment locations of the harmane complex anions were also revealed by electronic state calculations and molecular orbital analyses. The current work lays out a foundation for future work on microsolvated clusters to probe how solvent molecules influence the harmane-anion binding motif.

Low to near-zero CO2 production of hydrogen from fossil fuels: critical role of microwave-initiated catalysis

Presently, there is no single, clear route for the near-term production of the huge volumes of CO2-free hydrogen necessary for the global transition to any type of hydrogen economy. All conventional routes to produce hydrogen from hydrocarbon fossil fuels (notably natural gas) involve the production-and hence the emission-of CO2, most notably in the steam methane reforming (SMR) process. Our recent studies have highlighted another route; namely, the critical role played by the microwave-initiated catalytic pyrolysis, decomposition or deconstruction of fossil hydrocarbon fuels to produce hydrogen with low to near-zero CO2 emissions together with high-value solid nanoscale carbonaceous materials. These innovations have been applied, firstly to wax, then methane, crude oil, diesel, then biomass and most recently Saudi Arabian light crude oil, as well as plastics waste. Microwave catalysis has therefore now emerged as a highly effective route for the rapid and effective production of hydrogen and high-value carbon nanomaterials co-products, in many cases accompanied by low to near-zero CO2 emissions. Underpinning all of these advances has been the important concept from solid state physics of the so-called Size-Induced-Metal-Insulator Transition (SIMIT) in mesoscale or mesoscopic particles of catalysts. The mesoscale refers to a range of physical scale in-between the micro- and the macro-scale of matter (Huang W, Li J and Edwards PP, 2018, Mesoscience: exploring the common principle at mesoscale, Natl. Sci. Rev. 5, 321-326 (doi:10.1093/nsr/nwx083)). We highlight here that the actual physical size of the mesoscopic catalyst particles, located close to the SIMIT, is the primary cause of their enhanced microwave absorption and rapid heating of particles to initiate the catalytic-and highly selective-breaking of carbon-hydrogen bonds in fossil hydrocarbons and plastics to produce clean hydrogen and nanoscale carbonaceous materials. Importantly, also, since the surrounding 'bath' of hydrocarbons is cooler than the microwave-heated catalytic particles themselves, the produced neutral hydrogen molecule can quickly diffuse from the active sites. This important feature of microwave heating thereby minimizes undesirable side reactions, a common feature of conventional thermal heating in heterogeneous catalysis. The low to near-zero CO2 production of hydrogen via microwave-initiated decomposition or cracking of abundant hydrocarbon fossil fuels may be an interim, viable alternative to the conventional, widely-used SMR, that a highly efficient process, but unfortunately associated with the emission of vast quantities of CO2. Microwave-initiated catalytic decomposition also opens up the intriguing possibility of using distributed methane in the current natural gas structure to produce hydrogen and high-value solid carbon at either central or distributed sites. That approach will lessen many of the safety and environmental concerns associated with transporting hydrogen using the existing natural gas infrastructure. When completely optimized, microwave-initiated catalytic decomposition of methane (and indeed all hydrocarbon sources) will produce no aerial carbon (CO2), and only solid carbon as a co-product. Furthermore, reaction conditions can surely be optimized to target the production of high-quality synthetic graphite as the major carbon-product; that material of considerable importance as the anode material for lithium-ion batteries. Even without aiming for such products derived from the solid carbon co-product, it is of course far easier to capture solid carbon rather than capturing gaseous CO2 at either the central or distributed sites. Through microwave-initiated catalytic pyrolysis, this decarbonization of fossil fuels can now become the potent source of sustainable hydrogen and high-value carbon nanomaterials.This article is part of the discussion meeting issue 'Microwave science in sustainability'.

Enhanced Bioactivity of Natural Products by Halogenation: A Database Survey and Quantum Chemistry Calculation Study

Natural products (NPs) have long been the cornerstone of drug discovery. Halogenated organic NPs are limited, while around one-fourth of approved chemical drugs are organohalogens. This suggests that the introduction of halogens into NPs may enhance their potential for transformation into drugs. In this study, we utilized a matched molecular pair (MMP) approach alongside a database survey to investigate the impact of halogenation on this transformation. The study revealed that halogenation increased the bioactivity of 70.3% of NPs, with 50.3% exhibiting at least a 2-fold enhancement. Halogen bonds (XBs) are prevalent between organohalogens and their targets. To explore whether halogenated NPs could form XBs with their targets, computational studies were performed and demonstrated that halogenated NPs or NP-derived drugs formed strong XBs with their targets, resulting in improved binding affinities. This study highlights the considerable potential of introducing halogens into NPs as a strategic approach for enhancing bioactivity and facilitating the development of drugs.

Large-Scale Non-Adiabatic Dynamics Simulation Based on Machine Learning Hamiltonian and Force Field: The Case of Charge Transport in Monolayer MoS2

We present an efficient and reliable large-scale non-adiabatic dynamics simulation method based on machine learning Hamiltonian and force field. The quasi-diabatic Hamiltonian network (DHNet) is trained in the Wannier basis based on well-designed translation and rotation invariant structural descriptors, which can effectively capture both local and nonlocal environmental information. Using the representative two-dimensional transition metal dichalcogenide MoS2 as an illustration, we show that density functional theory (DFT) calculations of only ten structures are sufficient to generate the training set for DHNet due to the high efficiency of Wannier analysis and orbital classification in sampling the interorbital couplings. DHNet demonstrates good transferability, thus enabling direct construction of the electronic Hamiltonian matrices for large systems. Compared with direct DFT calculations, DHNet significantly reduces the computational cost by about 5 orders of magnitude. By combining DHNet with the DeePMD machine learning force field, we successfully simulate electron transport in monolayer MoS2 with up to 3675 atoms and 13475 electronic levels by using a state-of-the-art surface hopping method. The electron mobility is calculated to be 110 cm2/(V s), which is in good agreement with the extensive experimental results in the range of 3-200 cm2/(V s) during 2013-2023. Due to the high performance, the proposed DHNet and large-scale non-adiabatic dynamics methods have great potential to be applied to study charge carrier dynamics in a wide range of material systems.

OH Roaming as a Key Pathway in the Anti-CH3CHOO + H2O Reaction Yielding CH3COOH and H2O

The reaction of anti-CH3CHOO with H2O is a crucial atmospheric process, resulting in the end products CH3COOH + H2O through the dissociation of the intermediate hydroxyethyl hydroperoxide (CH3CH(HO)OOH, HEHP). Based on an accurate full-dimensional PES, we have obtained detailed dynamics information for this reaction through quasi-classical trajectory simulations. We report two reaction mechanisms for the CH3COOH + H2O product channel: one involving a direct mechanism through the transition state and the other an intriguing OH roaming mechanism. The roaming pathway proceeds via the dissociation of HEHP into OH and the hydroxyethoxy radical (CH3CH(HO)O, HEO), where the OH radical roams near HEO and abstracts a hydrogen atom, subsequently forming H2O and CH3COOH. The presence of this roaming pathway significantly increases the yield of CH3COOH + H2O. This work provides new dynamical support for the study of the anti-CH3CHOO + H2O reaction and enriches our understanding of atmospheric chemistry.

Room Temperature Gas-Phase Detection and Formation Gibbs Energy of the Water Dimethyl Ether Bimolecular Complex

Hydrated complexes are of general interest for understanding nucleation processes in the atmosphere, where water is abundant, especially as the role of whether water enhances or inhibits nucleation is still uncertain. We have recorded the Fourier transform infrared absorption spectrum of the water dimethyl ether bimolecular complex in the gas phase at room temperature. Four distinct bands are observed and assigned. The equilibrium constant of complex formation is determined from the experimental integrated absorbance of the bands and the corresponding calculated intensities. The calculated band intensities are obtained with a 9D reduced-dimensional variational local mode model with the CCSD(T)-F12a/cc-pVDZ-F12 potential energy and dipole moment surfaces. A similar equilibrium constant for a majority of the observed bands is obtained, with an average value of 0.042 ± 0.003 at T = 298 K. The water dimethyl ether complex studied here is similar to the water dimer, and our determined equilibrium constant may serve as a reasonable estimate for that of water dimer, which is especially relevant in atmospheric chemistry.

OH-stretching dynamics in trimethylamine monohydrate: what can we learn from three different direct absorption spectra?

The hydrogen-bonded binary complex between water and trimethylamine is characterised in jet expansions, in the room temperature gas phase and in frozen argon matrices via its OH-stretching fundamental. The spectral comparison reveals two bracketing resonance partners with weak environmental dependence of their wavenumber. They correspond to the water bending overtone alone and in combination with a stretching motion of the monomers relative to each other. The environment-sensitive OH-stretching mode moves from the combination band location at room temperature all the way down to the pure water bending overtone in cryomatrix isolation, sharing its infrared intensity in proportion to the spectral vicinity and coupling strength. The intermediate jet-cooled spectrum largely removes thermal excitation and embedding effects. It thus provides the easiest entry point for theoretical modelling. Chemical and isotope substitutions at the amine support the robustness of the assignment, whereas a switch from water to methanol removes the bending-based resonance opportunities. After correction for the resonances, the OH-stretching positions of the water complex follow those of the methanol complex quite closely. This shows that methanol and water undergo similar hydrogen bond interactions with the amine. Previous contradicting spectral interpretations of water trimethylamine mixtures in supersonic jets and in argon matrices are discussed and discouraged. For the dihydrate of trimethylamine, both hydrogen-bonded OH stretching vibrations are characterised in the jet expansion.

Theoretical study on the structures and vibrational spectra of (H2O-Arn)+, n = 1, 2: formation of a hemi-bond of water radical cation

The possible existence of a hemi-bond in the cationic complex of water and Ar has been actively debated in the literature. We simulated vibrational spectra of low-energy conformers of H2O+-Arn (n = 1, 2) in the mid- and near-infrared regions based on ab initio anharmonic algorithms with potential energy at CCSD/aug-cc-pVTZ quality. Decent agreements between experimental data and spectra simulated with four types of normal modes, intermolecular translation, H-O-H bending, and O-H stretching, validate our computational algorithms. By cross-examination of the available experimental data and our simulations, we believe that both the hydrogen-bond and hemi-bond conformers of H2O+-Ar2 should coexist under the experimental conditions. Our simulated spectra of hemi-bond conformers of H2O+-Ar2 further suggest that spectral features in the under-explored part of the near-infrared region may provide additional spectral features to double check the existence of the hemi-bond conformer.

Intramolecular proton bonding in aliphatic dicarboxylate anions: dynamic conformational landscapes and spectral signatures

Carboxylate moieties are central to organic chemistry and a main driving force of biomolecular recognition. Their diffuse anionic structure is prone to building proton-mediated supramolecular bonds with a marked delocalization of charge, a chemical motif that is key to processes of proton storage and transfer. We investigate intramolecular proton bonding interactions in benchmark aliphatic dicarboxylate anions of the form HOOC(CH2)n-2COO- (n = 4-8), hence succinate, glutarate, adipate, pimelate and suberate. Infrared ion spectroscopy is employed to expose the vibrational fingerprints of the mass-selected anions isolated at room temperature. Ab initio molecular dynamics calculations are applied to rationalize the fluxional character of the shared proton and its impact on the cyclic structure adopted by the anion. Our findings indicate that anions with shorter alkyl chains are constrained to symmetrically share protons in anti-anti configurations of the carboxylate moieties. Longer chain lengths increase the conformational flexibility of the alkyl backbone and stabilize anti-syn configurations with asymmetric proton sharing. As a result, the vibrational spectrum evolves towards progressively more differentiated carboxylic and carboxylate stretching modes. In all systems, the dynamic character of the proton bond can be recognized through a characteristic broad O-H stretching band that narrows down and blue shifts as proton delocalization is reduced in the larger anions.

Molecular dynamics simulations of atmospherically relevant molecular clusters: a case study of nitrate ion complexes

The formation and decomposition of complexes of ions with atmospheric analyte molecules are key processes in chemical ionization mass spectrometry (CIMS) instruments, as well as in atmospheric new particle formation (NPF). In this study, we conduct extensive molecular dynamics (MD) simulations of the decomposition of already-formed molecular complexes with nitrate ions (NO3-). We study purely thermal decomposition in vacuo and in the presence of nitrogen gas, as well as the decomposition driven by electric-field induced collisions with nitrogen gas. Our findings are relevant to improving the understanding of basic processes taking place in CIMS as well as in other MS instruments more generally.

Structural and FTIR spectroscopic studies of matrix-isolated 3-thio-1,2,4-triazole complexes with carbon dioxide. The UV-induced formation of thiol⋯CO2 complexes

Matrix isolation FTIR spectroscopy was combined with quantum chemical calculations to characterize complexes of 3-thio-1,2,4-triazole (ST) with carbon dioxide. Geometries of the possible 1 : 1 and 1 : 2 complexes were optimized at the DFT (B3LYPD3) level of theory with the 6-311++G(3df,3pd) basis set. The computational results show that ST interacts specifically with carbon dioxide through different hydrogen bond and van der Waals interactions. For the 1 : 1 complexes of the most abundant ST thione tautomer, four stable minima, STn⋯CO2, have been located on the potential energy surface. In contrast, for the ST thiol tautomer, three STl⋯CO2 structures were optimized. Experimentally, the two most stable 1 : 1 complexes of STn with CO2, characterized by the presence of the N-H⋯O hydrogen bridge and an additional S6⋯C10 interaction, were identified in solid argon upon deposition. Annealing of the matrix at 32 K proved that one 1 : 2 structure is also present, resulting from the addition of a second CO2 molecule to the 1 : 1 complexes. The laser irradiation at λ = 270 nm, apart from generating the thiol tautomer of ST, also leads to the formation of three thiol⋯CO2 complexes. Furthermore, the presence of CO2 in the argon matrix was found to influence the efficiency of the UV-induced thione-thiol tautomerization, though to a lesser extent than nitrogen. This suggests that while CO2 forms stronger intermolecular interactions with ST, its impact on tautomerization kinetics is less pronounced, highlighting the nuanced role of specific gas-phase interactions in modulating photochemical transformations in low-temperature matrices. The findings presented in this work not only enhance the fundamental understanding of weak intermolecular interactions but also provide new insights into the role of CO2-specific effects in photochemical and structural transformations of heterocycles.

Isomer-selective dissociation dynamics of 1,2-dibromoethene ionised by femtosecond-laser radiation

We study the isomer-specific photoionisation and photofragmentation of 1,2-dibromoethene (DBE) under strong-field fs-laser irradiation in the gas phase complementing previous studies utilising ns- and ps-laser excitation. Our findings are compatible with a dissociative multiphoton-ionisation mechanism producing a variety of ionic photofragments. Using both Stark deflection and chemical separation of the two isomers, pronounced isomer-specific photofragmentation dynamics could be observed for different product channels. While for Br+ formation, the isomer specificity appears to originate from different photoexcitation efficiencies, for the C2H2Br+ channel it is more likely caused by differences in the coupling to the exit channel. By contrast, the formation of the C2H2+ photofragment does not seem to exhibit a pronounced isomeric dependence under the present conditions. The present work underlines the importance of isomeric effects in photochemistry even in small polyatomics like the present system as well as their pronounced dependence on the photoexcitation conditions.

Three-Dimensional Atomic-Level Structure of an Amorphous Glucagon-Like Peptide-1 Receptor Agonist

Amorphous formulations are increasingly used in the pharmaceutical industry due to their increased solubility, but their structural characterization at atomic-level resolution remains extremely challenging. Here, we characterize the complete atomic-level structure of an amorphous glucagon-like peptide-1 receptor (GLP-1R) agonist using chemical shift driven NMR crystallography. The structure is determined from measured chemical shift distributions for 17 of the 32 carbon atoms and 16 of the 31 hydrogen atoms in the molecule. The chemical shifts are able to provide a detailed picture of the atomic-level conformations and interactions, and we identify the structural motifs that play a major role in stabilization of the amorphous form. In particular, hydrogen bonding of the carboxylic acid proton is strongly promoted, although no carboxylic acid dimer is formed. Two orientations of the benzodioxole ring are promoted in the NMR structure, corresponding to a significant stabilization mechanism. Our observation that inclusion of water leads to stabilization of the carboxylic acid group might be used as a strategy in future formulations where hydrogen bonding between neighboring molecules may otherwise be hindered by sterics.

Accurate vibrational hydrogen-bond shift predictions with multicomponent DFT

In this work we explore the use of multicomponent methods for the computational simulation of anharmonic OH vibrational shifts. Multicomponent methodologies have become popular over the last years, but still are limited in their application range. However, by enabling the simultaneous quantum treatment of protonic and electronic wave functions/densities, they hold promise for the treatment of anharmonic effects and proton vibrations in general. This potential has only been probed but not fully realized so far. This study investigates the performance of Nuclear-Electronic Orbital Density Functional Theory (NEO-DFT) in the prediction of water OH shifts upon complexation with organic molecules. We make use of the HyDRA database, expanded to 35 hydrogen-bonded monohydrates of small organic molecules, and evaluate a range of DFT functionals, both hybrid and double-hybrid. We introduce a robust prediction strategy based on common ingredients available when running conventional DFT and NEO-DFT calculations, which for the first time reduces the root mean square deviation (RMSD) values below 10 cm-1 for the set. Double-hybrid functionals in combination with a DFT treatment of the proton of interest is found to be particularly promising. The new systems added to the HyDRA dataset are presented and used as an extra test to the methodology.

The evolution of machine learning potentials for molecules, reactions and materials

Recent years have witnessed the fast development of machine learning potentials (MLPs) and their widespread applications in chemistry, physics, and material science. By fitting discrete ab initio data faithfully to continuous and symmetry-preserving mathematical forms, MLPs have enabled accurate and efficient atomistic simulations in a large scale from first principles. In this review, we provide an overview of the evolution of MLPs in the past two decades and focus on the state-of-the-art MLPs proposed in the last a few years for molecules, reactions, and materials. We discuss some representative applications of MLPs and the trend of developing universal potentials across a variety of systems. Finally, we outline a list of open challenges and opportunities in the development and applications of MLPs.

Rotational orientation control of a ground state ortho-H2 dissociation on a metal surface

When hydrogen molecules collide with a surface, they can either scatter away from the surface or undergo dissociative chemisorption. The relative probabilities of these different outcomes could depend on the rotational orientation of the impinging molecules, however, due to the lack of steric control techniques for ground state hydrogen, they could not be measured directly. Here, we demonstrate that magnetic field manipulation can be used to control the rotational orientation of H2 molecules colliding with a nickel surface and change the balance between reactive and scattering collision events. Our measurements show that molecules which approach the surface while rotating within a plane parallel to the surface are less likely to undergo specular scattering than those rotating within a perpendicular plane. An opposite trend was measured for the likelihood of dissociative chemisorption. A possible link between these two findings, and its potential impact on the interpretation of dissociation mechanisms is discussed.

Photoelectron Spectroscopy of Fulvenallenyl and Fluorine-Substituted Fulvenallenyl Anions

The anion photoelectron spectra of C7H5-, C7H4F- and C7H3F2- generated in a photoemission anion source with the benzene, fluorobenzene, and p-difluorobenzene precursors, respectively, are presented and analyzed with supporting density functional theory calculations. Patterns in the mass spectra recorded for these three separate precursors suggest that the anions may be formed through C or C- addition to the benzene or fluorobenzene rings. The spectrum of C7H5- can be definitively assigned to the anion of the fulvenallenyl radical, which is the most stable structural isomer of both C7H5- and •C7H5. The spectra of C7H4F- and C7H3F2- are also consistent with fulvenallenyl structures. Assignment to a specific regioisomer of the fluorofulvenallenyl or difluorofulvenallenyl anion is less certain, though we eliminate the possibility of structures featuring a -C≡C-F group. The electron affinities of the radicals trend upward with fluorination, but only modestly, a result of delocalization of the SOMO of the neutral radical (HOMO of the anion) over the entire molecule. Computational results on the electronic and molecular structures of these species are explored.

Ternary CaBe2B7- Cluster: A Turning Nanoclock

Boron-based alloy clusters have unique structural and electronic properties, exotic chemical bonding, and intriguing dynamic fluxionality. Based on global structural searches and electronic structure calculations, we report on the rational design of a ternary CaBe2B7- cluster. This boron-based alloy cluster turns out to adopt a quasi-triple-layered structure, which demonstrates dynamic structural fluxionality, analogous to a turning clock at the subnanoscale. The intramolecular rotation barrier is merely 0.08 kcal mol-1 at the single-point CCSD(T) level. Chemical bonding analysis suggests that the ternary system features double 6π/6σ aromaticity, which underlies its thermodynamic stability and dynamic structural fluxionality. This work also highlights the potential to explore a heptagonal [B7]5- ring as inorganic ligand in chemistry.

Design and applications of photochromic compounds for quantitative chemical analysis and sensing

Photochromic compounds, capable of reversibly switching between distinct molecular states upon light irradiation, have emerged as powerful tools for quantitative chemical analysis and sensing. This feature reviews recent advancements in this developing field, focusing on the design principles and applications of photoswitchable sensors. We begin with a concise overview of the fundamental photophysics and photochromism of key compound classes, and then discuss the mechanisms of analyte recognition and signal transduction, showcasing how light-induced isomerization modulates analyte binding and enhances signal contrast compared to conventional optical sensors. The unique sensitivity of the photoswitching process to the microenvironment is also explored. Finally, we outline future research directions and challenges for realizing the full potential of photochromic compounds in analytical chemistry related fields, including diagnostics, environmental monitoring, and materials science.

Synthesis and Characterization of Bio-Composite Based on Urea-Formaldehyde Resin and Hydrochar: Inherent Thermal Stability and Decomposition Kinetics

This work reports a study on the structural characterization, evaluation of thermal stability, and non-isothermal decomposition kinetics of urea-formaldehyde (UF) resin modified with hydrochar (obtained by the hydrothermal carbonization of spent mushroom substrate (SMS)) (UF-HC). The structural characterization of UF-HC, performed by scanning electron microscopy (SEM), Fourier transform infrared (FTIR), and X-ray diffraction analyses, showed that UF-HC consists of a large number of spheroidal particles, which are joined, thus forming clusters. It constitutes agglomerates, which are composed of crystals that have curved plate-like forms, including crystalline UF structure and graphite lattices with an oxidized face (graphene oxide, GO). The measurement of inherent thermal stability and non-isothermal decomposition kinetic analysis was carried out using simultaneous thermogravimetric-differential thermal analyses (TGA-DTA) at various heating rates. Parameters that are obtained from thermal stability assessment have indicated the significant thermal stability of UF-HC. Substantial variation in activation energy and the pre-exponential factor with the advancement of decomposition process verifies the multi-step reaction pathway. The decomposition process takes place through three independent single-step reactions and one consecutive reactions step. The consecutive stage represents a path to the industrial production of valuable heterocyclic organic compounds (furan) and N-heterocyclic compounds (pyrroles), building a green-protocol trail. It was found that a high heating rate stimulates a high production of furan from cellulose degradation via the ring opening step, while a low heating rate favors the production of urea compounds (methylolurea hemiformal (HFn)) by means of methylene ether bridges breaking.

Material characterization methods for investigating charge storage processes in 2D and layered materials-based batteries and supercapacitors

Two-dimensional (2D) materials offer distinct advantages for electrochemical energy storage (EES) compared to bulk materials, including a high surface-to-volume ratio, tunable interlayer spacing, and excellent in-plane conductivity, making them highly attractive for applications in batteries and supercapacitors. Gaining a fundamental understanding of the energy storage processes in 2D material-based EES devices is essential for optimizing their chemical composition, surface chemistry, morphology, and interlayer structure to enhance ion transport, promote redox reactions, suppress side reactions, and ultimately improve overall performance. This review provides a comprehensive overview of the characterization techniques employed to probe charge storage mechanisms in 2D and thin-layered material-based EES systems, covering optical spectroscopy, imaging techniques, X-ray and neutron-based methods, mechanical probing, and nuclear magnetic resonance spectroscopy. We specifically highlight the application of these techniques in elucidating ion transport dynamics, tracking redox processes, identifying degradation pathways, and detecting interphase formation. Furthermore, we discuss the limitations, challenges, and potential pitfalls associated with each method, as well as future directions for advancing characterization techniques to better understand and optimize 2D material-based electrodes.

Introduction to Relativistic Electronic Structure Calculations

It is important to include relativistic effects in electronic structure calculations for many important chemical problems, including heavy-element chemistry, intersystem crossing, and zero-field splitting. The subject is old, but recent developments have been rapid. The specialized literature can be daunting for nonspecialists, and this article is intended to provide an entry to that literature, especially for the modern treatment of molecules. There are only five equations. We include discussion of the relations between four-component, two-component, and one-component treatments, the distinction between scalar relativistic effects and angular-momentum-dependent effects, approximate treatments of spin-orbit coupling, including the molecular mean-field approximations, the inclusion of electron correlation in relativistic wave functions, and zero-field splitting.

Complex-Variable Equation-of-Motion Coupled-Cluster Singles and Doubles Theory with the Resolution-of-the-Identity Approximation

We present an implementation of complex-variable equation-of-motion coupled-cluster singles and doubles (EOM-CCSD) theory with the resolution-of-the-identity (RI) approximation. Complex-variable methods are used in the framework of non-Hermitian quantum chemistry to treat electronic resonances. As test cases, we study different types of resonances of N2 and CO, namely, temporary anions, Stark resonances, autoionizing Rydberg states, and core-ionized states that decay by the Auger-Meitner effect. Temporary anions are treated with the complex basis function (CBF) method and different variants of the complex absorbing potential method. The other resonances are treated only with CBFs. The memory requirements of our implementation are significantly lower than those of canonical EOM-CCSD. We demonstrate that the RI error is smaller than the basis set error for all types of resonances. However, when the size of the decay width approaches the magnitude of the RI error, the width is qualitatively wrong with the RI approximation. In addition, when an adequate auxiliary basis set is not available, i.e., for autoionizing Rydberg states and for core-ionized states, the RI error in the total decay width increases by a factor 10.

Mechanistic Foundations of the Sequential Activation of Methane by Ta+: Oxidative Addition, Ring-Opening σ-Bond Metathesis, and C-C Bond Formation

The kinetics of Ta+ + CH4 and related reactions TaCnHm+ + CH4 (n = 2-4, m = n, 2n, 3n) are measured from 300-600 K using a selected-ion flow tube apparatus. Complicated kinetics are analyzed through a novel bootstrapping methodology, and rate constants for 38 unimolecular, bimolecular, and ternary processes are reported at each of the four temperatures. As has been well-established, Ta+ efficiently dehydrogenates methane through a non-spin-conserved process. Sequential chemistry leads to the dehydrogenation of up to four methane molecules per tantalum center through the competing processes of TaCnHm+ + CH4 → TaCn+1Hm+2+ + H2 (dehydrogenation) and TaCn+1Hm+4+ (association). Supported by density functional theory calculations, the distinct mechanisms and product structures of the sequential reactions are derived. The activation energy for oxidative insertion of Ta into a C-H bond is well-predicted by a simple heuristic: whether or not the reactant tantalum atom possesses unbound valence electrons of opposite spin. TaCH2+ is predicted to have a small activation energy for oxidative insertion but can only proceed to dehydrogenation of methane via carbon-carbon bond formation, enabled by three separate intersystem crossing events. The product is determined to be the tantalapropene dihydride cation, not the more intuitive tantalapropane cation, via comparison of measured and calculated thermal dissociation rates. The TaC2H4+ tantalapropene dihydride has a prohibitive barrier to oxidative insertion. It proceeds instead through a ring-opening insertion of the entire tantalapropene moiety into a C-H bond via σ-bond metathesis; the unbroken metallacycle bond acts as a tether, preventing the activated products from separating and allowing for further isomerization, leading to dehydrogenation. This and subsequent dehydrogenation processes occur without carbon-carbon bond formation; no evidence of a tantalabutane or larger metallacycle is found.

Heterogeneous Adsorption of Volatile Organic Compounds to Aerosol Particle Surfaces Probed with In Situ Surface Vibrational Sum Frequency Scattering

Vibrational sum frequency scattering (VSFS) has shown great utility in monitoring organics at sub-micrometer droplet surfaces, but the adsorbates were present upon generation. Herein, we present the first direct observation of heterogeneous gas-phase adsorption to droplet surfaces using in situ VSFS spectroscopy. This marks a significant development in the VSFS technique by allowing direct observation of heterogeneous adsorption to droplet surfaces in situ under ambient conditions, not relying on bulk removal or uptake. Using a flow tube system, we investigated formic acid vapor adsorption under different interaction times, concentrations, and physical environments. VSFS was used to compare adsorption to droplet surfaces from the gas phase and the underlying bulk at different interaction times. We then quantified the adsorption free energies for the different adsorption processes and found no significant difference between adsorption from the aqueous particle phase and that from the gas phase to the particle surface, with similar results at depressed relative humidity.

Photophysics of a Methylated GFP Chromophore Anion in Vacuo

The photophysical properties of the isolated chromophore anion from the green fluorescent protein have been extensively studied over the years to understand the factors influencing transition energies, excited-state lifetimes, and fluorescence. A commonly used model for the protein chromophore is 4'-hydroxybenzylidene-2,3-dimethyl-imidazolinone (p-HBDI). In this work, we have spectroscopically characterized a derivative, brMe-p-HBDI, which features methylation on the carbon bridging the phenol and imidazolinone rings. Experiments were conducted on the anionic form in the gas phase and at cryogenic temperatures using the SAPHIRA ion-storage ring and the LUNA2 fluorescence mass spectrometer, both located in Aarhus. Photoinduced action spectra reveal that brMe-p-HBDI- cooled to about 20-30 K exhibits maximum absorption at 496.0 ± 0.5 nm. Vibrationally resolved bands appear at shorter wavelengths, while a featureless absorption tail extends toward longer wavelengths, up to approximately 520 nm. The methyl substituent induces a clear redshift (75 meV) in absorption as p-HBDI- absorbs maximally at 481.51 ± 0.15 nm. The excited-state lifetime of brMe-p-HBDI- is determined to be 51 ± 3 ps following 495 nm photoexcitation and probing at 800 nm, which is significantly shorter than the nanosecond lifetime previously reported for p-HBDI-. Consistent with this, no fluorescence was detected from brMe-p-HBDI- at 100 K, in contrast to p-HBDI- that is strongly fluorescent according to recent work. These findings are corroborated by (time-dependent) density-functional theory calculations: A methyl substituent at the bridge carbon is predicted to cause a redshift of 77 meV, in excellent agreement with the experimental shift. We find that brMe-p-HBDI- is planar in the ground state (S0) but undergoes a twist motion in the S1 state, leading to a lower-energy nonplanar form where the angle between the two rings is 90°. Our work reveals that even a minor alteration in molecular structure can have a significant impact on the photophysics.