The kinetics of chemical aging in most commercial plastics have remained long debated, since the nature of dense polymeric solids inhibits the in situ experimental investigation of complex degradation paths, while traditional computational techniques fail to reach the time scales associated with slow-progressing degradative reactions. In this work, a novel mechanistic framework is introduced in which the infrequent reaction events that govern the long-time-scale evolution of the chemistry of any amorphous solid are described as successive elementary transitions of the atomistic configuration between local minima on its energy landscape. For each elementary reaction event, the corresponding transition state is identified, allowing the estimation of the free-energy barrier and, thereby, of the transition rate constant by means of transition state theory. The result is a network of states populated by the stationary states that are visited by the system along chemical paths. We demonstrate the applicability of the presented approach for the study of complex reaction schemes by applying it to the study of the autoxidation of glassy polystyrene. The introduction of an appropriately trained reactive force field, ReaxFF-lg/CHOpox, tailored for the accurate description of the reactions propagating polymer oxidation, i.e., peroxy radical and hydroperoxide formation, in the glassy state, allows the large-scale sampling of potential reaction paths in situ. From the created network of states, we extracted the energetics and rates of the elementary reactions in the glassy state. For both reactions, the broad distribution of free-energy barriers, spanning over many orders of magnitude, is indicative of the significant impact that the local dense environment has on reaction kinetics and highlights the importance of studying solid-state reactions in situ.
Utilizing redox mediators (RMs) in aprotic Li-O2 batteries as catalysts provides promising solutions to several challenges, including high overpotential, cathode passivation, and electrolyte instability, while enabling the solution-phase catalysis. Despite these advantages, the fundamental origin of their electrochemical activity and how it governs the solution-phase pathway remain poorly understood. To bridge this gap, we systematically explored the stability of reactive intermediates and their influence on solution-phase Li2O2 formation using a series of anthraquinone-based RMs: anthraquinone (AQ), 1-nitroanthraquinone (MNAQ), 1,5-dinitroanthraquinone (1,5-DNAQ), and 1,8-dinitroanthraquinone (1,8-DNAQ). All the studied RMs facilitate the formation of stable intermediate complexes with Li+, O2•-, and LiO2•, thereby promoting the solution-phase Li2O2 formation pathway. Among them, 1,8-DNAQ exhibits the enhanced coordination with Li+ through cooperative participation of carbonyl and nitro oxygens, highlighting the role of the NO2 functional group in dual-site binding. The introduction of electron-withdrawing NO2 groups systematically raises the reduction potential (AQ < MNAQ < 1,5-DNAQ < 1,8-DNAQ), approaching the ideal value of 2.96 V, which is consistent with experimental observations. A correlation is observed between the NO2 substitution, reduction potential, and the LUMO energy, unveiling the underlying origin of the potential shift. Interestingly, the rise in reduction potential is not solely dictated by LUMO energy tuning through functional group modification but also by the thermodynamic stabilization of the reduced species. The involvement of the NO2 group enables electron delocalization, which stabilizes the reduced species and results in an enhanced redox performance compared to the unsubstituted AQ. The following study establishes a structure-property relationship linking the electronic structure, stability of reduced species, and redox activity. It demonstrates how NO2 functionalization correlates with the tuning of reduction potential. These insights provide design principles for developing redox mediators to enhance the catalytic activity and reversibility in next-generation Li-O2 batteries.
We report a joint study of photoelectron imaging spectroscopy and density functional theory (DFT) calculation for aluminum-doped silver cluster anions, AgnAl- (n = 4-17). To explore their electronic and geometric structures, we measured size-dependent photoelectron spectra at a photon energy of 3.87 eV and compared them with simulated spectra for DFT-optimized structures. It is found that the Al atom is exposed on the cluster surface at 4 ≤ n ≤ 15, whereas it is fully encapsulated at n = 16 and 17; a highly symmetric framework similar to the Frank-Kasper-type tetrahedron is obtained as the most stable structure for n = 16. For n = 15, DFT calculations suggest the coexistence of endohedral forms; however, no clear experimental signatures supporting this prediction were obtained. Also found is that the vertical detachment energies of AgnAl- with n = odd are lower than those for the neighboring sizes. Since the total number of the valence electrons of AgnAl- is n + 4, this observation indicates that the outermost orbitals of the odd-numbered clusters are singly occupied. The present DFT calculation confirms that their spin multiplicities are indeed doublet, whereas those of the even-numbered clusters are singlet. Photoelectron angular distribution from the outermost orbital for n = 15 exhibits a large positive anisotropy with respect to the laser polarization, which manifests a 1S21P61D102S1 electronic configuration as observed in valence isoelectronic systems of Ag18- and Ag15Sc-. While all sizes exhibit electronic shell structures similar to those observed in undoped silver clusters, the energy ordering of the discrete levels in the endohedrally doped clusters, Al@Agn- (n = 16 and 17), is not as predicted by the spherical jellium model; 2S-like orbitals are located in the manifold of 1D-like orbitals.
The present work investigates theoretically the conformational preferences for complexes between a series of donor alcohols MeChH, where Ch = O, S, Se, and Te, and a common acceptor molecule acetophenone (APh). The latter is characterized by two distinct regions of negative electrostatic potential: the directed lone pair electrons on the carbonyl oxygen and the diffuse electronic cloud on its π-ring. It is predicted that when MeOH is the donor, O-H···O hydrogen bonding (H-bonding) to the carbonyl oxygen of APh gives rise to the most preferred APh-MeOH conformer, while H-bonding to its π-cloud is less favored. However, such binding preferences alter remarkably when the heavier alcohols act as the donor. Electronic structure calculations, including those at the CCSD(T)/CBS limit, predict highest stability for conformers bound by a combination of π-hole and σ-hole interactions, both involving the heavy chalcogen atom. The former involves the interaction of its lone pair with the electron-deficient region above the carbonyl group of APh, while the latter involves a chalcogen-bond (Ch-bond) with the π-cloud of APh (Ch···π interaction). Also, the ChH···π H-bonded interactions involving the SH/SeH/TeH donor and the π-cloud on APh become increasingly stable as compared to their carbonyl-bound ChH···O H-bonded counterparts as we move down the group. A chalcogen-chalcogen (Ch···Ch) interaction with the carbonyl oxygen of APh is stabilized only for MeTeH, leading to a Te···O Ch-bond. The important role of heavy atom substitution in biomolecular recognition is thus highlighted. Observed modulations in binding preferences and in the very nature of the nonbonded interactions are attributable to a delicate interplay of electrostatic and dispersion interactions.
The electronic absorption spectrum of the brominated benzene derivative 1,2-dibromobenzene (1,2-DBB) is studied using synchrotron radiation. Absolute absorption cross sections are measured in the ultraviolet (UV) and vacuum ultraviolet (VUV) regions 1200-2900 Å (34,500-83,300 cm-1); the VUV spectrum in the 1200-1700 Å (∼58,800-83,300 cm-1) region is reported for the first time. A detailed spectral analysis is performed, supported by time-dependent density functional theory (TDDFT) calculations. The S0-S1 transition in the UV region shows extensive vibrational structure, typical of benzene derivatives, tentatively assigned to ring deformation modes using calculated excited-state vibrational frequencies. The intensity profile of this band, simulated using Franck-Condon Herzberg-Teller simulations, shows a good agreement with the experimental spectrum. The VUV absorption spectrum is dominated by strong valence bands with weak and diffuse Rydberg transitions superimposed on the intensity profiles of the valence bands. Rydberg series converging to the first three ionization potentials of 1,2-DBB are assigned using quantum defect analysis. Vertical excitation energies calculated at the TDDFT/CAM-B3LYP/aug-cc-pVTZ level of theory help in corroborating the Rydberg assignments and assigning valence transitions and charge transfer transitions. Simulations of excited-state potential energy curves along the CBr bond provide some insights into the photodissociation dynamics of 1,2-DBB. The measured UV absorption cross-section data helps in estimating photolysis lifetimes of 1,2- and 1,3-DBB with respect to CBr bond breaking at different altitudes from the Earth's surface, thus providing valuable inputs toward modeling the ozone depletion processes in the upper atmosphere.
Coupled-cluster theory provides an accurate description of electronic ground and excited states. While it has been rigorously established that the coupled-cluster ground state energy is size extensive and local excitations are size intensive in the thermodynamic limit, the separability of other properties in coupled-cluster theory is subject to known limitations. In particular, it was shown [Stanton, J. Chem. Phys. 1994, 101, 8928-8937] that multicenter two-particle density matrices are not asymptotically separable in general. In the present work, an analogous analysis is applied to the excitonic coupling of local excitations of two separate molecules, using both the equation-of-motion (EOM) and linear-response (LR) formalism. It is shown that for both formalisms the two-electron transition density associated with the excitonic coupling does not exactly separate into a product of local one-electron transition densities. Numerical examples are provided for Ne2, (CO)2, and (C2H4)2, using coupled-cluster expansions up to single, double, triple, and quadruple excitations (CCSDTQ). Small but noticeable deviations on the order of 5-10% are reported for approximations like CCSD and its second-order approximate variant CC2. As soon as triple excitations are included, the separability error becomes significantly smaller. Exploratory computations for the coupling of larger chromophores such as perylene or cumarine dyes using the CC2 method indicate that the separability error can grow up to orders of 20%. While these deviations are typically below the error margin of this method, the separability error could be of relevance in the design and benchmarking of local coupled-cluster approaches for excited states.
The rational design of fluorescent organic molecules is central to the development of advanced linear and nonlinear photonic materials. Purine-based compounds have emerged as promise candidates for several photonics applications due to their structural similarity to biological nucleobases synthetic versatility and favorable photophysical properties. However, their optical characterization typically generates large and complex data sets that are difficult to interpret, particularly when multiple compounds are analyzed simultaneously. Here, we apply principal component analysis (PCA) to a series of purine derivatives to systematically investigate the relationships between molecular descriptors and photophysical performance. The PCA model applied in the optical properties of the set captures 76.8% of the total variance within the first two principal components, enabling clear clustering of molecules according to their electronic structure. Importantly, by applying PCA directly to one- and two-photon absorption spectra, we achieve effective spectral deconvolution with 91.87% and 94.51%, respectively, isolating contributions associated with intensity, spectral shifts, and bandwidth. The robustness of this approach is validated through accurate spectral reconstruction. To extend the analysis toward predictive modeling, multiple linear regression (MLR) was employed to correlate PCA-derived features from one-photon absorption data with the transition dipole moment (μ01). The proposed PCA-MLR framework effectively captures the intrinsic relationships within the spectra of the studied group, minimizing the need for extensive experimental trials. The resulting model exhibits excellent predictive performance (R2 = 0.9728) and accurately estimating the μ01 = 7.07D of an external validation molecule with a deviation of approximately 2.5%. Overall, this PCA-MLR framework provides a powerful and efficient strategy for interpreting complex photophysical data sets and accelerating the design and optimization of organic molecules for linear and nonlinear photonic applications.
Organic thermally activated delayed fluorescence (TADF) emitters have attracted considerable attention in organic light-emitting diode (OLED) applications, owing to their potential for 100% exciton utilization. Among them, multiple-resonance (MR) TADF compounds have emerged as a particularly promising class of emitters, offering superior color purity and high photoluminescence quantum yields (PLQYs) compared to conventional donor-acceptor-type TADF materials. With the increasing demand for ultrahigh-definition display technologies, exemplified by the BT.2020 color gamut standard, the development of MR-TADF materials featuring narrowband emission and high efficiency has become a key research priority. In this study, we systematically assessed the predictive capabilities of density functional theory (DFT) and machine learning (ML) methods in determining the luminescence properties of MR-TADF materials. While ML models offer rapid prediction capabilities, their generalization ability remains limited, primarily constrained by the quality and size of the available training data set. In contrast, DFT-based approaches, although more computationally demanding, exhibit reliable accuracy and generalization performance when calibrated using appropriate regression models. Using a B3LYP-based calibration model, we further predicted the optical properties of the designed MR-TADF molecules and identified a promising candidate exhibiting deep-blue emission. Overall, the findings underscore the complementary roles of DFT and ML approaches in MR-TADF research and provide valuable theoretical guidance for the rational design of high-performance MR-TADF emitters tailored to next-generation OLED applications.
Trifluorodimethyl sulfide (CH3SCF3) has been proposed to be a potential alternative refrigerant based on various rigorous quantum chemistry calculations. It is revealed that the half F-substitution is capable of tuning the stability and reactivity of dimethyl sulfide (CH3SCH3) significantly. The strength of both S-C bonds is enhanced. The bond dissociation energies increase by 5-6 kcal/mol with respect to CH3SCH3, and decomposition temperature of CH3SCF3 is predicted to be 875 K. Meanwhile, the existence of CH3 group keeps the good reactivity of CH3SCF3 toward OH radicals in the troposphere. Complex-forming H-abstraction to produce H2O and CF3SCH2 radicals is the predominant mechanism accompanied by minor S-O association/elimination pathways. The atmospheric lifetime and radiative efficiency of CH3SCF3 is 0.2-1 years and 0.25 Wm2-ppb-1, respectively, leading to a global warming potential of 9-90 for a 100-year time horizon. The possible degradation products of CH3SCF3 in the atmosphere include both radicals, e.g., CF3SCH2OO, CF3SCH2OONO, CF3SCH2OONO2, CF3SCH2O, CF3S, and molecules, e.g., (CF3SCH2OO)2, CF3SCH2OOH, CH2O, and CH3S(O)CF3. The present computational work not only provides interesting insights into the dramatic impact of the partial fluorination on stability and reactivity of sulfides but also demonstrates that CH3SCF3 should be a viable refrigerant replacement for hydrofluorocarbons and even hydrofluoroolefins with excellent thermal stability and environmental sustainability.
The propargyl radical (C3H3) is the simplest resonance-stabilized free radical (RSFR), but how does stepwise methyl substitution in the alkene reactant affect its dynamics of their formation? We report a crossed molecular beam study of the reactions of atomic carbon (C, 3Pj) with four butene isomers (C4H8) under single-collision conditions at a collision energy of 28 ± 2 kJ mol-1. Barrierless addition of atomic carbon to the alkene C═C bond triggers ring opening to substituted triplet allenes─a de facto insertion mechanism─followed by unimolecular decomposition via atomic hydrogen (H), methyl (CH3), or ethyl (C2H5) loss, yielding a family of propargyl-type RSFRs. RRKM calculations reveal that the branching ratios are highly sensitive to the alkene structure. While the methyl loss channel, affording 1-methylpropargyl, dominates for 2-butenes (80-90%), the predicted hydrogen-atom loss channel (≈10%), leading to 1,3-dimethylpropargyl is identified experimentally by comparison with theoretical energetics. For isobutene, near-equal competition is observed, with the reaction producing 3-methylpropargyl (≈50%) and 1,1-dimethylpropargyl (≈40%), along with 2-vinylallyl (≈5%), whose formation is supported by experimental data. Most notably, the reaction with 1-butene uniquely favors an enthalpically driven hydrogen shift, eventually producing 1-vinylallyl (≈38%), which is assigned based on the excellent agreement between the measured and calculated reaction exothermicity. Rapid entropically favored fragmentation channels yield ≈40% of propargyl-type species (propargyl, 1- and 3-ethylpropargyls), slightly outcompeting the allyl-type product. These results establish a systematic progression from C2H4 via C3H6 to C4H8, where the increasing alkyl substitution unlocks new fragmentation channels, providing a versatile gas-phase route to alkylated RSFRs─key intermediates in the growth of methylated and ethylated PAHs and aliphatic chains in combustion and cold interstellar environments (molecular clouds).
Exhaust gas recirculation (EGR) technology creates opportunities for chemical interactions between transportation fuels and NOx. In this study, 2-ethylfuran (2EF), a representative component of furan-based biofuels, was selected to systematically investigate its reaction kinetic characteristics with those of NO2. Rate constants over a wide temperature range of 298-2400 K were calculated using multistructural canonical variational transition-state theory (MS-VTST) combined with a multidimensional tunneling correction method. The results show that the reaction rate exhibits a strong temperature dependence across the entire temperature range. This dependence is determined not only by the structure of fuel molecules but also by whether O-atom or N-atom attack occurs. In the low-temperature range (298-800 K), the combined effects of multistructural torsional anharmonicity, variational effects, and tunneling effects do not outweigh the influence of energy barrier height on reaction rates, causing the order of the rate constants to still follow the energy barrier height trend. In both NO2-addition and H-abstraction mechanisms, the reactions involving N-atom attack on 2EF are kinetically dominant. Notably, the tunneling effect plays a significant role in H-abstraction reactions in the low temperature range (T ⩽ 500K). This study identifies key kinetic factors governing the reaction of furan-based biofuels with NO2, thereby providing crucial theoretical support for refining the interaction mechanism between oxygenated furan biofuels and NOX under EGR conditions.
Understanding the ligand effects of organic ligand-protected copper clusters toward CO2 is a prerequisite for improving their rational design for CO2 capture and conversion. In this work, the regulatory roles of pyridine ligands on the structure of Cu3O+ in Cu3OPyn+ (n = 0-3) clusters and their reactivity toward CO2 were investigated through a combination of mass spectrometry and density functional theory (DFT) calculations. Experimental results reveal that pyridine ligands significantly modulate CO2 adsorption capacity and rate: the Cu3O+ cluster adsorbs up to three CO2 molecules; Cu3OPy+ and Cu3OPy2+ adsorb a maximum of two and one, respectively; and Cu3OPy3+ shows no adsorption. Notably, the pyridine-ligated Cu3OPy1-2+ clusters exhibit reactivity approximately 2 orders of magnitude higher than the bare Cu3O+ cation, with Cu3OPy+ being the most reactive one among all four Cu3OPy0-3+ clusters. DFT calculations indicate that the ligand-induced enhanced reactivity originates from the increased polarity, enlarged effective collision cross section (CCS), and added vibrational degrees of freedom (DOF) rather than CO2 adsorption energy or charge transfer. These conclusions were further supported by reactions between CuPy0-3+ clusters and CO2. This study revealed the ligand effects on the structures and reactivity of copper-based clusters toward CO2 at the atomic level, providing useful insights for the design of efficient ligand-protected cluster catalysts for CO2 capture and conversion.
A complex cyclic polypeptide antibiotic, thiostrepton, is made by two large macrocyclic rings: a 26-membered ring associated with a thiazoline moiety and a 27-membered ring accompanied by a quinaldic acid unit, a dehydropiperidine ring, and a flexible bis-dehydroalanine tail. The site-specific local structure and nuclear-spin dynamics of this polypeptide antibiotic is determined by using 2D solution NMR (1H-13C HSQC, 1H-13C HMBC, 1H-1H COSY, 1H-1H TOCSY, and 1H-1H NOESY) and solid-state NMR methods (13C CP-MAS 2D PASS, 1H-13C HETCOR, and site-specific 13C spin-lattice relaxation measurements). The combined 1H-13C HETCOR and 1H-1H NOESY data demonstrate that the quinaldic acid residue is positioned in close spatial proximity to multiple structural elements, including the thiazoline and piperidine rings, isoleucine-valine chain, butyrine, thiostreptin residue, dehydroalanine units, threonine, and thiazole. These interactions generate a compact hydrophobic core that stabilizes the conformation of the bis-dehydroalanine tail. The flexible side chains of both macrocyclic rings, together with the tail region, accommodate themselves within the interface of ribosomal protein L11 and the 23S rRNA, thereby perturbing the 70S ribosomal subunit. The dynamics of these flexible segments are quantified by employing NMR relaxometry. Therefore, although functional activity is not examined directly, the integrated solution- and solid-state NMR results deliver site-specific structural information and local nuclear spin dynamics at individual carbon sites of this cyclic polypeptide antibiotic. These characteristics are associated with the functional state of thiostrepton and offer a foundation for the rational design of next-generation polypeptide antibiotics.
Bond dissociation energies (BDEs) have been calculated for the set of actinide halides AnX with An = Ac, Pa, and Np-Lr and X = F-I. Two composite thermochemistry methods based on the Feller-Peterson-Dixon (FPD) approach have been utilized, one involving spinor-based relativistic CCSD(T) calculations where spin-orbit (SO) was included at the orbital level and another using scalar relativistic CCSD(T) with a posteriori SO contributions based on 2-component multireference configuration interaction calculations. The method that was chosen for a given actinide halide was based on which representation yielded the best single determinant reference determinant for the coupled cluster calculation. The spinor-based method was chosen for all cases except for AmX, CmX, and BkX. Both composite approaches included contributions accounting for basis set truncation, outer-core correlation, the Gaunt interaction, and QED. The scalar FPD results, as well as the spinor-based calculations for AcF, also included higher order electron correlation up through CCSDT(Q). In addition to BDEs, CCSD(T) equilibrium bond lengths, harmonic frequencies, and vibrational anharmonicity constants are reported for all species. Last, the FPD BDEs for the fluorides were used to confirm the trend across the actinide series previously predicted by Gibson using bonding models based atomic promotion energies that provide a single 6d electron for bonding. In particular the local minimum in the BDEs at AmF is confirmed in the present calculations. The BDEs for LrX are predicted to be slightly larger than those of AcX, making them the largest in the actinide halide series.
The kinetics of the reaction between I+ and the methyl halides CH3X (X = F, Cl, Br, I) are measured at temperatures ranging from 300 to 600 K using a selected-ion flow tube apparatus. Exothermic product channels for X = F, Cl, Br forming CH2I+ + HX or CH2X+ + HI require an intersystem crossing, making the series a model system for the kinetics involving consistently large spin-orbit coupling. The reaction efficiencies relative to capture rates increase steeply along the series (X = F: 0.07, Cl: 0.22, Br: 0.67, I: 0.95); however, this is shown not to be a function of the halide mass or increasing coupling. Nonadiabatic transition state theory was applied to reaction coordinates calculated using density functional theory by treating minimum energy crossing points between singlet and triplet surfaces as proxies for the adiabatic transition states. This quantitatively reproduced both the magnitude and temperature dependence of the X = F, Cl, and Br reactions. The reaction efficiencies are controlled by the energy of the adiabatic transition state as the incident I+ approaches a hydrogen atom, leading to abstraction. The energies of those transition states are, in turn, a function of the entrance well depth of the triplet I+(H3CX) complexes, which are electrostatically bound and scale with the polarizabilities of the methyl halides. Charge transfer processes (dominating the X = I reaction and a minor product for X = Br) behave nonstatistically.
Molecular photoswitches are chemical systems that can undergo reversible chemical transformations following the absorption of light. Such systems find potential application in modern technologies such as molecular electronics, optical data storage, exploitation of solar energy, and much more. In this paper, we present ab initio nonadiabatic molecular dynamics of the dicyano phenyl-substituted dihydroazulene/vinylheptafulvene (DHA/VHF) system using ab initio multiple spawning in combination with state-averaged α-complete active space self-consistent field theory to study the photoinduced electrocyclic ring opening reaction that converts DHA to VHF. Scrutinizing the mechanism of the photoinduced ring opening reaction is crucial to be able to design new derivatives with improved properties and to design experiments that can probe the photoswitching of such systems. Our simulations show that this DHA system photoswitches with a 41% quantum yield on a sub-picosecond time scale. In addition to that, we simulate the time-resolved photoelectron spectrum, which, by comparison to the experimental equivalent, shows that our dynamics reproduce the experiments with high precision. Furthermore, we simulate the (hitherto unmeasured) elastic ultrafast electron diffraction signal and show that it contains significant features directly related to the nuclear dynamics of the photoswitching event. Our atomistic simulations thus identify ultrafast electron diffraction as an excellent technique for studying the photoswitching of DHA/VHF derivatives and that this could aid in the design and development of new related compounds with optimized switching quantum yields.
Pyruvate is frequently found in aged sea salt aerosols. To test the influence of the salt environment on the photochemistry of pyruvate, small model clusters were generated from sodium pyruvate salt using electrospray ionization. These clusters were studied using Fourier-Transform Ion Cyclotron Resonance mass spectrometry (FT-ICR MS). UV/vis spectra were recorded using a tunable optical parametric oscillator (OPO) system. Additionally, photokinetics as well as sustained off-resonance irradiation (SORI) collision-induced dissociation (CID) experiments help to further understand the mechanisms responsible for the fragmentation of the studied systems. Quantum chemical calculations allow assignment of the transitions responsible for the absorptions. The clusters mainly fragment by losing sodium pyruvate units, NamPyrm, resulting in Nan-mPyrn-m-1+ fragments. Photodissociation cross sections for nonstoichiometric fragmentation are around 2 orders of magnitude lower. We found that the formation of these fragments starts with the C-C bond photolysis of a pyruvate anion and can lead to several secondary fragments. For the two larger cluster sizes, neutral CH3COCOO is lost, presumably in the form of a CH3CO radical, followed by CO2 elimination. The electron is transferred to a second pyruvate molecule in the cluster, resulting in a radical dianion, CH3COCOO2-. For the smallest cluster size, a variety of secondary fragments was observed, including CO2- stabilized by two Na+ ions in the cluster.
Long-chain alkanes are key intermediate volatility organic compounds (IVOCs) in the atmosphere and recognized as significant precursors to the formation of secondary organic aerosol (SOA). C12-C14 n-alkylcyclohexanes are representative IVOCs that undergo oxidation by both OH radicals and Cl atoms. In this work, the initial hydrogen abstraction and subsequent multigeneration oxidation mechanisms of C12-C14 n-alkylcyclohexanes initiated by Cl atoms and OH radicals were systematically investigated using quantum chemical methods. The results show that both Cl atoms and OH radicals preferentially abstract a hydrogen atom from the tertiary carbon of the cyclohexane ring, proceeding via low-energy barriers. The formed alkyl radicals undergo barrierless additions to O2 subsequently and reactions with NO, forming alkoxy radicals (C12H23O, C13H25O, and C14H27O) that are consistent with experimentally observed products. The calculated rate constants for the reactions with Cl atoms and OH radicals at 298 K are in the ranges of 1.59-2.17 × 10-9 and 1.55-3.75 × 10-11 cm3 molecule-1 s-1, respectively, showing a slight increasing trend with carbon-chain length. Notably, the presence of a single water molecule was found to significantly increase the energy barriers for H-abstraction, indicating that water vapor exerts a negative catalytic effect on these atmospheric oxidation reactions. This finding suggests that under high-humidity conditions, the gas-phase oxidation of such IVOCs may be slower than currently predicted, with potential implications for SOA formation estimates. By elucidating the mechanistic details and kinetic parameters for this important class of IVOCs, this work provides a theoretical foundation for improving chemical mechanisms in atmospheric models.
Photoactive yellow protein (PYP), a prototypical photoreceptor responsible for the photophobic response of the Halorhodospira halophila bacterium to harmful ultraviolet (UV) radiation, is known to undergo photooxidation in aqueous solution. However, the vertical detachment energy and electronic structure of the deprotonated chromophore that lies at the heart of PYP have not been measured in aqueous solution. Here, we use X-ray, extreme ultraviolet (EUV), and multiphoton UV liquid-microjet photoelectron spectroscopy, supported by high-level quantum chemistry calculations, to map out the electronic structure of the deprotonated PYP chromophore in aqueous solution. The vertical and adiabatic electron detachment energies are found to be 6.8 ± 0.1 eV and around 5.9 eV, respectively. Multiphoton UV photoelectron spectroscopy measurements confirm the existence of a high-lying two-photon resonance close to the detachment threshold that could be responsible for UV photooxidation, and they reveal the existence of a three-photon resonance in the detachment continuum. This work demonstrates the power of combining X-ray, EUV, and UV liquid-microjet photoelectron spectroscopy to unravel the electronic structure of weakly soluble organic chromophores, paving the way for deeper insights into their roles in photobiological processes.
The growing energy demand of global information technologies motivates the development of sustainable materials capable of retaining and processing information at the atomic scale. Resolving the site- and orbital-specific origins of magnetic anisotropy energy (MAE) is key to establishing the physical principles required for the rational design of tailored atomic-scale magnets. However, these contributions remain obscured in the output of noncollinear density functional theory calculations incorporating spin-orbit coupling. We present the Palacký OptoElectronic Toolkit (POET), an open-access suite that decomposes complex simulation data into intuitive graphical representations that map electronic reorganization onto atomic and orbital contributions and elucidates the interplay between bonding and magnetic anisotropy. To demonstrate its utility, we investigate two complementary strategies for achieving electric-field tunable MAE in transition-metal-functionalized graphene on various substrates. We show that iodination of Pt adatoms on nitrogen-decorated single-vacancy graphene on MgO creates strong, field-tunable in-plane anisotropy, while OsPt and OsPd heterodimers yield exceptional perpendicular MAE of ∼150 meV. The microscopic insights enabled by POET facilitate the rational control of magnetic anisotropy through chemical engineering, paving the way for energy-efficient information storage and processing at the atomic limit.