The ORCA quantum chemistry program package

Alkyl effects on charge recombination in copper electrolyte-based dye-sensitized solar cells: Insights for targeted molecular design towards high performance

Two quinoxaline dyes utilized in copper-electrolyte-based dye-sensitized solar cells (Cu-DSSCs) are theoretically investigated to analyze the impact of alkyl chains on dye performance. The investigation shows that ZS4, known for its record efficiency of up to 13.2 %, exhibits higher electron coupling and fewer binding sites for dye-[Cu(tmby)2]2+ interaction compared to ZS5. Contrary to common belief, alkyl chains are found to not only provide shielding but also hinder the interaction between dye and [Cu(tmby)2]2+ by influencing the optimal conformation of dyes, thereby impeding the charge recombination process. It is crucial to consider the influence of alkyl chains on dye conformation when discussing the relationship between dye structure and performance, rather than oversimplifying it as often done traditionally. Building on these findings, eight dyes are strategically designed by adjusting the position of the alkyl chain to further decrease charge recombination compared to ZS4. Theoretical evaluation of these dyes reveals that changing the alkyl chain on the nitrogen atom from 2-ethylhexyl (ZS4) to 1-hexylheptyl (D3-2) not only reduces the charge recombination rate but also enhances light harvesting ability. Therefore, D3-2 shows potential as a candidate for experimental synthesis of high-performance Cu-DSSCs with improved efficiency.

Avian cryptochrome 4 binds superoxide

Flavin-binding cryptochromes are blue-light sensitive photoreceptors that have been implicated with magnetoreception in some species. The photocycle involves an intra-protein photo-reduction of the flavin cofactor, generating a magnetosensitive radical pair, and its subsequent re-oxidation. Superoxide (O2 • - ) is generated in the re-oxidation with molecular oxygen. The resulting O2 • - -containing radical pairs have also been hypothesised to underpin various magnetosensitive traits, but due to fast spin relaxation when tumbling in solution would require immobilisation. We here describe our insights in the binding of superoxide to cryptochrome 4 from C. livia based on extensive all-atom molecular dynamics studies and density-functional theory calculations. The positively charged "crypt" region that leads to the flavin binding pocket transiently binds O2 • - at 5 flexible binding sites centred on arginine residues. Typical binding times amounted to tens of nanoseconds, but exceptional binding events extended to several hundreds of nanoseconds and slowed the rotational diffusion, thereby realising rotational correlation times as large as 1 ns. The binding sites are particularly efficient in scavenging superoxide escaping from a putative generation site close to the flavin-cofactor, possibly implying a functional relevance. We discuss our findings in view of a potential magnetosensitivity of biological flavin semiquinone/superoxide radical pairs.

Unraveling the molecular basis for effective regulation of integrin α5β1 for enhanced therapeutic interventions

Cell attachment to the extracellular matrix significantly impacts the integrity of tissues and human health. The integrin α5β1 is a heterodimer of α5 and β1 subunits and has been identified as a crucial modulator in several human carcinomas. Integrin α5β1 significantly regulates cell proliferation, angiogenesis, inflammation, tumor metastasis, and invasion. This regulatory role of integrin α5β1 in tumor metastasis makes it an appealing target for cancer therapy. The majority of the drugs targeting integrin α5β1 are limited only to clinical trials. In our study, we have performed 94287 compounds screening to determine potential drugs against α5β1 integrin. We have used ATN-161 as a reference and employed combined bioinformatic methodologies, including molecular modelling, virtual screening, MM-GBSA, cell-line cytotoxicity prediction, ADMET, Density Functional Theory (DFT), Non-covalent Interactions (NCI) and molecular simulation, to identify putative integrin α5β1 inhibitors. We found Taxifolin, PD133053, and Acebutolol that possess inhibitory activity against α5β1 integrin and could act as effective drug for the cancer treatment. Taxifolin, PD133053, and Acebutolol exhibited excellent binding to the druggable pocket of integrin α5β1, and also maintained a unique binding mechanism with extra hydrophobic contacts at molecular level. Overall, our study gives new pharmacological candidates that may act as a potential drug against integrin α5β1.

The structure of Mn(II)-bound Rubisco from Spinacia oleracea

The rate of photosynthesis and, thus, CO2 fixation, is limited by the rate of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). Not only does Rubisco have a relatively low catalytic rate, but it also is promiscuous regarding the metal identity in the active site of the large subunit. In Nature, Rubisco binds either Mg(II) or Mn(II), depending on the chloroplastic ratio of these metal ions; most studies performed with Rubisco have focused on Mg-bound Rubisco. Herein, we report the first crystal structure of a Mn-bound Rubisco, and we compare its structural properties to those of its Mg-bound analogues.

Deciphering Spectroscopic Signatures of Competing Ca2+ - Peptide Interactions

Calcium-protein interactions are of paramount importance in biochemistry. They are a key element in a number of biological processes, such as neuronal signaling. Therefore, an understanding of the interaction at the molecular level is highly desirable. Here, we study the zwitterionic model peptide l-alanyl-l-alanine (2Ala), which has two distinct and competing binding sites for Ca2+: The carbonyl of the peptide bond and the C-terminus, the carboxylate group. We perform linear and two-dimensional IR spectroscopy experiments and find that the spectroscopic signatures of both moieties in the IR spectra change in amplitude and peak position upon the addition of CaCl2: A blueshift of the asymmetric carboxylate band and a redshift for the amide I mode. Ab initio molecular dynamics simulations confirm the direct interaction of the Ca2+ ion at both the carboxylate and the amide CO site leading to different spectral responses. The blueshift of the asymmetric carboxylate band is caused by a localization of the charge, leading to a decoupling of the CO stretching modes of the carboxylate group. The slight redshift of the amide I mode of 2Ala upon the addition of CaCl2 contrasts the blueshift that has been observed for isolated amide motifs, such as N-methylacetamide (NMA). This difference is caused by the smaller number of water molecules being replaced by the Ca2+ ion for 2Ala's amide compared to less sterically hindered, isolated amide carbonyls, in conjunction with vibrational Stark effects. Our results highlight the importance of considering potential competing binding sites, such as the amide CO backbone, the termini and residues, as well as the nature of the hydration of both peptide and ion, when exploring ions' interacting with small peptides and larger proteins.

Study of the Energy Crossing Between Excited States Affected by the Electronegativity of Substituents for Three 4-Azido-1,8-naphthalimide Derivatives

Rapid detection of H2S is crucial for human physiological health and natural ecosystems. In this study, the fluorescent sensing mechanisms of three 4-azido-1,8-naphthalimide-based fluorescent probes to monitor H2S were theoretically investigated by density functional theory and time-dependent density functional theory. The potential energy curve of the charge transfer (CT) state has a crossover with that of the locally excited (LE) state proved by the constructed linear interpolating internal coordinate pathway. Thus, the transform takes place from the LE state to the CT state causing the fluorescence quenching of the probes from a nonradiative transition process of the CT state. The distance between the Franck-Condon point and the minimal energy conical intersection becomes larger with the increase of the electronegativity of substituents on the 1,8-naphthalimide fluorophore. In addition, the degree of charge separation is closely related to the energy difference between the CT and the LE states which are also essentially affected by the electronegativity of the substituents. Since the electronegativity of the substituents has proved important for the probes, our work lays a certain theoretical foundation for the design and synthesis of more sensitive 4-azido-1,8-naphthalimide-based fluorescent probes.

Exceptionally Short Tetracoordinated Carbon-Halogen Bonds in Hexafluorodihalocubanes

Molecules that contain bonds whose length significantly deviates from the average are of interest in the context of understanding the nature and limits of the chemical bonds. However, it is difficult to disentangle the individual contributions of the multiple factors that give rise to such bond-length deviations as reports on such molecules remain scarce. In the present study, we have succeeded in synthesizing hexafluorodihalocubanes of the type C8F6X2 (2) (X = Cl (2Cl), Br (2Br), I (2I)), which represent a new series of molecules with unusual C(sp3)-halogen bonds. The C(sp3)-halogen bonds of 2Cl, 2Br, and 2I, determined via single-crystal X-ray diffraction analysis, are approximately 0.07-0.09 Å shorter than typical C(sp3)-halogen bonds. In particular, the carbon-iodine bonds of 2I are the shortest C(sp3)-I bonds reported to date. The solution-state structures and electronic states of the C(sp3)-halogen bonds in these hexafluorodihalocubanes were analyzed by X-ray absorption spectroscopy, which revealed detailed information on the length of these C(sp3)-halogen bonds in solution and the solid state as well as on the electron-deficient nature of 2. Detailed theoretical calculations and a comparison with halotrinitromethanes (1), which represent another series of molecules with shortened C(sp3)-halogen bonds, revealed that the factors responsible for the shortening of the C(sp3)-halogen bond vary among the different C(sp3)-halogen bonds, i.e., for C(sp3)-Cl and C(sp3)-Br, the s-character and hyperconjugation effects predominate, whereas for C(sp3)-I, the interatomic Coulombic interaction effect prevails.

Antimicrobial Potency of Nor-Pyochelin Analogues and Their Cation Complexes against Multidrug-Resistant Pathogens

The opportunistic pathogen Pseudomonas aeruginosa develops increasing resistance toward even the most potent antibiotics. Like other bacteria, the pathogen produces a number of virulence factors including metallophores, which constitute an important group. Pseudomonads produce the iron-chelating metallophore (siderophore) pyochelin, which, in addition to its iron-scavenging ability, is an effector for the transcriptional regulator PchR in its FeIII-bound form (ferripyochelin). In the present study, docking studies predicted a major ferripyochelin binding site in PchR, which prompted the exploration of nor-pyochelin analogues to produce tight binding to PchR, and thereby upregulation of the pyochelin metabolism. In addition, we investigated the effects of using the analogues to bind the antimicrobial cations GaIII and InIII. Selected analogues of nor-pyochelin were synthesized, and their GaIII- and InIII-based complexes were assessed for antimicrobial activity. The results indicate that the GaIII complexes inhibit the pathogens under iron-limited conditions, while the InIII-based systems are more effective in iron-rich media. Several of the GaIII complexes were shown to be highly effective against a multidrug-resistant P. aeruginosa clinical isolate, with minimum inhibitory concentrations (MICs) of ≤1 μg/mL. Similarly, two of the InIII-based systems were particularly effective against the isolate, with an MIC of 8 μg/mL. These results show high promise in comparison with other, traditionally potent antibiotics, as the compounds generally indicated low cytotoxicity toward mammalian cells. Preliminary mechanistic investigations using pseudomonal transposon mutants suggested that the inhibitory effects of the InIII-based systems could be due to acute iron deficiency as a result of InIII-bound bacterioferritin.

In silico validation of allosteric inhibitors targeting Zika virus NS2B-NS3 protease

The Zika virus (ZIKV), a member of the Flaviviridae family, poses a major threat to human health because of the lack of effective antiviral drugs. Although the NS2B-NS3 protease of ZIKV (NS2B-NS3pro) is regarded as a major target for antiviral inhibitors, viral mutations can lead to ineffective competitive inhibitors. Allosteric inhibitors bind to highly conserved nonprotease active sites, induce conformational changes in the protease active site, and prevent substrate binding. Currently, no molecular simulation techniques are available for accurately predicting and analysing conformational changes in the protease catalytic domain. In this study, we developed a combined approach that involves blind docking, Gaussian accelerated molecular dynamics, two-dimensional potential of mean force profiling, density functional theory (DFT) calculations, and interaction region indicator (IRI) analysis and employed it to examine the allosteric inhibitor-01 molecule and its interaction with ZIKV NS2B-NS3pro. Our results indicated that the binding of inhibitor-01 to NS2B-NS3pro resulted in two major conformational states, state I and state II, which in turn changed the volume of the protease active site from 1014 Å3 to 710 and 820 Å3, respectively. These two states had an inactive catalytic domain (residues His116, Asp140, and Ser200). DFT and IRI analyses revealed that, in state I, Lys138 and Gln139 formed hydrogen bonds with inhibitor-01, whereas Lys138, Leu214, Asn217, Val220, and Ile221 engaged in van der Waals interactions with inhibitor-01. Advancements in computational techniques and power are expected to facilitate further progress in overcoming challenges associated with designing allosteric inhibitors for viral proteases.

RadicalPy: A Tool for Spin Dynamics Simulations

Radical pairs (electron-hole pairs, polaron pairs) are transient reaction intermediates that are found and exploited in all areas of science, from the hard realm of physics in the form of organic semiconductors, spintronics, quantum computing, and solar cells to the soft domain of chemistry and biology under the guise of chemical reactions in solution, biomimetic systems, and quantum biology. Quantitative analysis of radical pair phenomena has historically been successful by a few select groups. With this in mind, we present an intuitive open-source framework in the Python programming language that provides classical, semiclassical, and quantum simulation methodologies. A radical pair kinetic rate equation solver, Monte Carlo-based spin dephasing rate estimations, and molecule database functionalities are implemented. We introduce the kine-quantum method, a new approach that amalgamates classical rate equations, semiclassical, and quantum techniques. This method resolves the prohibitively large memory requirement issues of quantum approaches while achieving higher accuracy, and it also offers wavelength-resolved simulations, producing time- and wavelength-resolved magnetic field effect simulations. Model examples illustrate the versatility and ease of use of the software, including the new approach applied to the magnetosensitive absorption and fluorescence of flavin adenine dinucleotide photochemistry, spin-spin interaction estimation from molecular dynamics simulations on radical pairs inside reverse micelles, radical pair anisotropy inside proteins, and triplet exciton pairs in anthracene crystals. The intuitive interface also allows this software to be used as a teaching or learning aid for those interested in the field of spin chemistry. Furthermore, the software aims to be modular and extensible, with the aim to standardize how spin dynamics simulations are performed.

Effect of weak intermolecular interactions on the ionization of benzene derivatives dimers

The interactions between π-systems in dimers of aromatic molecules lead to particularly stable conformations within the relative orientations of the monomers. Extensive research has been conducted on the properties of these complexes in the neutral state. However, in recent decades, there has been a significant surge in applications harnessing these structures for electrical purposes. Therefore, this study places particular emphasis on a deeper understanding of the redox properties of these compounds and how to modify them. To achieve this, we have focused on modeling the effect of a wide range of functional groups on the redox properties of benzene derivatives, observing a correlation between these properties and the change in the molecular dipole moment. Then, we investigated the effect of π-stacking interactions on these properties in dimers formed by either identical or different monomers. In both cases, there is an enhancement of the reducing character of the systems due to these interactions. Upon oxidation, the charge is distributed proportionally to the redox potential of each monomer. Therefore, if there is heterogeneity in these potentials, the properties of the complete cationic system will be influenced by the monomer with a greater tendency to undergo oxidation. The considered models serve as an excellent example for studying the behavior of nucleobases in DNA or aromatic amino acids, among others.

Accelerating Small Electron Polaron Dissociation and Hole Transfer at Solid-Liquid Interface for Enhanced Heterogeneous Photoreaction

In a photocatalysis process, quick charge recombination induced by small electron polarons in a photocatalyst and sluggish kinetics of hole transfer at the solid-liquid interface have greatly limited photocatalytic efficiency. Herein, we demonstrate hydrated transition metal ions as mediators that can simultaneously accelerate small electron polaron dissociation (via metal ion reduction) and hole transfer (through high-valence metal production) at the solid-liquid interface for improved photocatalytic pollutant degradation. Fe3+, by virtue of its excellent redox ability as a homogeneous mediator, enables the BiVO4 photocatalyst to achieve drastically increased photocatalytic degradation performance, up to 684 times that without Fe3+. The enhanced performance results from Fe(IV) species production (via Fe3+ oxidation) induced by dissociation of small electron polarons (via Fe3+ reduction), featuring an extremely low kinetic barrier (5.4 kJ mol-1) for oxygen atom transfer thanks to the donor-acceptor orbital interaction between Fe(IV) and organic pollutants. This work constructs a high-efficiency artificial photosynthetic system through synergistically eliminating electron localization and breaking hole transfer limitation at the solid-liquid interface for constructing high-efficiency artificial photosynthetic systems.

Comparing coupled cluster and composite quantum chemical methods for computing activation energies and reaction enthalpies of radical propagation reactions

Accurate determination of activation energies and reaction enthalpies is essential for understanding the propagation step in free radical polymerization, as it significantly affects polymer chain length and structure. In this study, we compare DLPNO-CCSD(T) to canonical CCSD(T) for 17 radical addition activation energies and 18 reaction enthalpies from Radom and Fischer's test set. Additionally, we compare the computationally efficient composite methods G3(MP2)-RAD and CBS-RAD against CCSD(T)/aug-cc-pVTZ and DLPNO-CCSD(T)/CBS methods. Compared to the CCSD(T)/aug-cc-pVTZ reference, our results indicate that DLPNO-CCSD(T)/CBS with unrestricted Hartree-Fock (UHF) or UB3LYP reference orbitals and NormalPNO parameters consistently achieves chemical accuracy, with mean absolute deviations of 3.5 kJ mol-1 for activation energies and 1.5 kJ mol-1 for reaction enthalpies. Comparing the two composite methods shows that CBS-RAD agrees most closely with coupled cluster reaction enthalpies, while G3(MP2)-RAD tracks the activation energies most closely.

Theoretical mechanistic insights on the thermal and acid-catalyzed rearrangements of N-methyl-N-nitroanilines

The thermal and acid-catalyzed rearrangement mechanisms of N-methyl-N-nitroanilines were theoretically investigated via density functional theory (DFT) calculations for all possible proposed mechanisms. The results indicate that the thermal rearrangement of N-methyl-N-nitroanilines undergoes a radical pair complex mechanism through the homolysis of their N-N bond to generate a radical pair complex and the recombination of the radical pairs followed by aromatization. For the acid-catalyzed rearrangements, N-methyl-N-nitroanilines are first protonated on the nitrogen atom of their aniline moiety and then generate protonated N-methyl-O-nitroso-N-phenylhydroxylamines through a three-membered spirocyclic oxadiaziridine transition state. The N-protonated N-methyl-O-nitroso-N-phenylhydroxylamines favor homolytic dissociation to generate N-methylaniline cationic radical and nitrogen dioxide complexes, which further combine together and aromatize to afford protonated N-methyl-o-nitroanilines and N-methyl-p-nitroanilines, respectively. The radical pair complexes are more stable than the corresponding solvent-caged radical pairs. The thermal rearrangements require higher activation energy than the corresponding acid-catalyzed rearrangements.

Exploring the potential energy surface of B4H42-: an exception of the Wade-Mingos rules

An analysis of the potential energy surface of B4H42- which, according to Wade-Mingos rules should have a tetrahedral structure, is presented. Our results indicate that the global minimum has a planar diamond-like boron skeleton and that the nearest local minimum lies 7.8 kcal mol-1 above it. This isomer corresponds to a Jahn-Teller distorted tetrahedral B4H4 structure as a result of the gain of two electrons. Furthermore, the analysis of the bonding pattern using the Adaptive Natural Density Partitioning method indicates a double σ and π delocalization providing high stability. These results show that B4H42- is an exception to the Wade-Mingos rules and open the door to future experimental characterization of this compound.

Probing the Molecular Interactions of Electrochemically Reduced Vitamin B2 with CO2

The electrochemical reduction of riboflavin (vitamin B2) in a dimethyl sulfoxide solvent was examined under a CO2 atmosphere and compared with results under an argon atmosphere. Variable-scan-rate cyclic voltammetry combined with controlled potential electrolysis (CPE) and analysis by UV-vis and EPR spectroscopies provided insights into the nature of interactions of reduced flavins with dissolved CO2. Reductive exhaustive CPE experiments under CO2 indicated an overall two-electron stoichiometry, compared to one-electron reduction under an argon atmosphere, due to the lowering of the formal one-electron reduction potential of the flavin radical anion to form the dianion, which can be rationalized by riboflavin-CO2 molecular interactions. UV-vis spectroscopic measurements confirmed complete chemical reversibility of the redox transformations over extended time scales. Digital simulation modeling of the voltammetric data enabled extraction of thermodynamic and kinetic parameters for the proposed mechanism, comprising multiple proton-coupled electron transfer steps, diamagnetic anions, radical anions, and neutral radical intermediates enroute to the fully reduced state, as well as evidence of a long-lived solution phase complex of the reduced riboflavin with CO2.

Photophysical, thermal and imaging studies on vancomycin functional branched poly(N-isopropyl acrylamide) of differing degrees of branching containing nile red for detection of Gram-positive bacteria

Highly branched poly(N-isopropyl acrylamide) additives chain end functionalised with vancomycin have been designed to agglutinate and report on targetted Gram-positive strains of bacteria (S. aureus). These branched systems selectively desolvate with temperature or binding interactions depending on their chain architecture. We have prepared samples with three different degrees of branching which have incorporated Nile red acrylate as a low concentration of co-monomer to report upon their solution properties. A linear analogue polymer functionalised with vancomycin along the chain instead of the termini is presented as a control which does not bind to targeted bacteria. These samples were analysed by diffusion NMR spectrometry (DOSY), calorimetry, fluorescence lifetime measurements, optical microscopy and scanning electron microscopy to gain a full understanding of their solution properties. The branched polymers are shown conclusively to have a core-shell structure, where the chain ends are expressed from the desolvated globule even above the lower critical solution temperature - as demonstrated by NMR measurements. The level of desolvation is critically dependent on the degree of branching, and as a result we have found intermediate structures provide optimal body temperature bacterial sensing as a consequence of the Nile red reporting dye.

Reductive Elimination From Tetra-Alkyl Cuprates [MenCu(CF3)4-n]- (n=0-4): Beyond Simple Oxidation States

In recent years, the electronic structures of organocuprates in general and the complex [Cu(CF3)4]- in particular have attracted significant interest. A possible key indicator in this context is the reactivity of these species. Nonetheless, this aspect has received only limited attention. Here, we systematically study the series of tetra-alkyl cuprates [MenCu(CF3)4-n]- and their unimolecular reactivity in the gas phase, which includes concerted formal reductive eliminations as well as radical losses. Through computational studies, we characterize the electronic structures of the complexes and show how these are connected to their reactivity. We find that all [MenCu(CF3)4-n]- ions feature inverted ligand fields and that the distinct reactivity patterns of the individual complexes arise from the interplay of different effects.

Decomposition and Growth Pathways for Ammonium Nitrate Clusters and Nanoparticles

Understanding the formation and decomposition mechanisms of aerosolized ammonium nitrate species will lead to improvements in modeling the thermodynamics and kinetics of aerosol haze formation. Studying the sputtered mass spectra of cation and anion ammonium nitrate clusters can provide insights as to which growth and evaporation pathways are favored in the earliest stages of nucleation and thereby guide the development and use of accurate models for intermolecular forces for these systems. Simulated annealing Monte Carlo optimization followed by density functional theory optimizations can be used reliably to predict minimum-energy structures and interaction energies for the cation and anion clusters observed in mass spectra as well as for neutral nanoparticles. A combination of translational and rotational mag-walking and sawtooth simulated annealing methods was used to find optimum structures of the various heterogeneous clusters identifiable in the mass spectra. Following these optimizations with ωB97X-D3 density functional theory calculations made it possible to rationalize the pattern of peaks in the mass spectra through computation of the binding energies of clusters involved in various growth and dissociation pathways. Testing these calculations against CCSD(T) and MP2 predictions of the structures and binding energies for small clusters demonstrates the accuracy of the chosen model chemistry. For the first time, the peaks corresponding with all detectable species in both the positive and negative ion mass spectra of ammonium nitrate are identified with their corresponding structures. Thermodynamic control of particle growth and decomposition of ions due to loss of ammonia or nitric acid molecules is indicated. Structures and interaction energies for larger (NH4NO3)n nanoparticles are also presented, including the prediction of new particle morphologies with trigonal pyramidal character.

Uncovering the Crucial Role of Chelating Structures in Cyano-Alkyl-Phosphate Electrolytes for High-Voltage Lithium Metal Batteries

The inferior oxidative stability of commercial carbonate electrolytes and overgrowth of the electrode-electrolyte interphase (EEI) have largely hindered the development of high-voltage lithium metal batteries. In this study, these challenges are addressed by designing Li+-solvent chelating solvation structures to inhibit solvent decomposition using cyano-alkyl-phosphate as a demonstration. Theoretical and experimental studies confirm that the -P═O and -C≡N groups within diethyl (2-cyanethyl) phosphonate exhibit a comparable ability to coordinate with Li+, facilitating the formation of seven-membered chelating structures. This unique solvation structure contributes to the formation of anion-derived inorganic-rich EEI with high stability and robustness, hindering the further decomposition of the electrolyte. Additionally, the cyano group has a strong complexation with the transition metal (TM) in the cathode to inhibit TM dissolution, thereby ensuring the structural stability of the cathode particle. Utilizing this special chelating structure, the designed electrolyte demonstrates favorable Li plating/stripping reversibility and promising oxidative stability in high-voltage batteries. Consequently, the LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode exhibits a high capacity retention (90%) after operating 300 cycles. Under harsh testing conditions, the 4.6 V Li||NCM811 pouch cell with a capacity of 1.4 Ah (∼295 Wh kg-1 based on the total mass of the cell) retains 70% capacity after 80 cycles. This work provides new insights into the correlation between the solvation structure and oxidative stability of electrolytes, contributing significantly to the advancement of high-voltage lithium metal batteries.

Aromatic stabilization energies in excited states at the multiconfigurational level: assessment in archetypal organic rings

In this study, the excited state (anti)aromaticity of archetypal rings: benzene, cyclobutadiene, and cyclooctatetraene, was investigated using the energetic criterion by calculating aromatic stabilization energies. Calculations were performed at the multiconfigurational level, including dynamic correlation effect corrections using the N-electron valence state perturbation theory (NEVPT2) method. Results were compared with previously published data based on the magnetic and delocalization criteria. Aromaticity was assessed for the ground state, singlet excited states (S1, S2, and S3), and triplet excited states (T1, T2, T3, and T4). (Anti)aromaticity assignments using the energetic criterion demonstrate both agreement and discrepancies with the other criteria, particularly for higher energy electronic states demonstrating the complexity of aromaticity assignment beyond the ground state. Finally, an approximate equation is proposed for the calculation of aromatic stabilization energies in excited states using experimental data such as formation enthalpies and well-resolved absorption spectra.

A bis-Phenolate Carbene-Supported bis-μ-Oxo Iron(IV/IV) Complex with a [FeIV(μ-O)2FeIV] Diamond Core Derived from Dioxygen Activation

The diiron(II) complex, [(OCO)Fe(MeCN)]2 (1, MeCN = acetonitrile), supported by the bis-phenolate carbene pincer ligand, 1,3-bis(3,5-di-tert-butyl-2-hydroxyphenyl)benzimidazolin-2-ylidene (OCO), was synthesized and characterized by single-crystal X-ray diffraction, 1H nuclear magnetic resonance, infrared (IR) vibrational, ultraviolet/visible/near-infrared (UV/vis/NIR) electronic absorption, 57Fe Mössbauer, X-band electron paramagnetic resonance (EPR) and SQUID magnetization measurements. Complex 1 activates dioxygen to yield the diferric, μ-oxo-bridged complex [(OCO)Fe(py)(μ-O)Fe(O(C═O)O)(py)] (2) that was isolated and fully characterized. In 2, one of the iron-carbene bonds was oxidized to give a urea motif, resulting in an O(CNHC═O)O binding site, while the other Fe(OCO) unit remained unchanged. When the reaction is performed at -80 °C, an intensively colored, purple intermediate is observed (INT, λmax = 570 nm; ε = 5600 mol L-1 cm-1). INT acts as a sluggish oxidant, reacting only with easily oxidizable substrates, such as PPh3 or 2-phenylpropionic aldehyde (2-PPA). The identity of INT can be best described as a dinuclear complex containing a closed diamond core motif [(OCO)FeIV(μ-O)2FeIV(OCO)]. This proposal is based on extensive spectroscopic [UV/vis/NIR electronic absorption, 57Fe Mössbauer, X-band EPR, resonance Raman (rRaman), X-ray absorption, and nuclear resonance vibrational (NRVS)] and computational studies. The conversion of the diiron(II) complex 1 to the oxo diiron(IV) intermediate INT is reminiscent of the O2 activation process in soluble methane monooxygenases (sMMO). Most importantly, the low reactivity of INT supports the consensus that the [FeIV(μ-O)2FeIV] diamond core in sMMO is kinetically inert and needs to open up to terminal FeIV═O cores to react with the strong C-H bonds of methane.

Unraveling the Source of Self-Induced Diastereomeric Anisochronism in Chiral Dipeptides

Mastering of analytical methods for accurate quantitative determinations of enantiomeric excess is a crucial aspect in asymmetric catalysis, chiral synthesis, and pharmaceutical applications. In this context, the phenomenon of Self-Induced Diastereomeric Anisochronism (SIDA) can be exploited in NMR spectroscopy for accurate determinations of enantiomeric composition, without using a chiral auxiliary that could interfere with the spectroscopic investigation. This phenomenon can be particularly useful for improving the quantitative analysis of mixtures with low enantiomeric excesses, where direct integration of signals can be tricky. Here, we describe a novel analysis protocol to correctly determine the enantiomeric composition of scalemic mixtures and investigate the thermodynamic and stereochemical features at the basis of SIDA. Dipeptide derivatives were chosen as substrates for this study, given their central role in drug design. By integrating the experiments with a conformational stochastic search that includes entropic contributions, we provide valuable information on the dimerization thermodynamics, the nature of non-covalent interactions leading to self-association, and the differences in the chemical environment responsible for the anisochronism, highlighting the importance of different stereochemical arrangement and tight association for the distinction between homochiral and heterochiral adducts. An important role played by the counterion was pointed out by computational studies.

Distinct Adjacent Substrate Binding Pocket Regulates the Activity of a Decameric Feruloyl Esterase from Bacteroides thetaiotaomicron

Understanding how the human gut microbiota contribute to the metabolism of dietary carbohydrates is of great interest, particularly those with ferulic acid (FA) decorations that have manifold health benefits. Here, we report the crystal structure of a decameric feruloyl esterase (BtFae) from Bacteroides thetaiotaomicron in complex with methyl ferulate (MFA), revealing that MFA is situated in a noncatalytic substrate binding pocket adjacent to the catalytic pocket. Molecular docking and mutagenesis studies further demonstrated that the adjacent pocket affects substrate binding in the active site and negatively regulates the BtFae activity on both synthetic and natural xylan substrates. Additionally, quantum mechanics (QM) calculations were employed to investigate the catalytic process of BtFae from substrate binding to product release, and identified TS_2 in the acylation step is rate-limiting. Collectively, this study unmasks a novel regulatory mechanism of FAE activity, which may contribute to further investigation of FA-conjugated polysaccharides metabolism in the human gut.

Chemically Transferable Electronic Coarse Graining for Polythiophenes

Recent advances in machine-learning-based electronic coarse graining (ECG) methods have demonstrated the potential to enable electronic predictions in soft materials at mesoscopic length scales. However, previous ECG models have yet to confront the issue of chemical transferability. In this study, we develop chemically transferable ECG models for polythiophenes using graph neural networks. Our models are trained on a data set that samples over the conformational space of random polythiophene sequences generated with 15 different monomer chemistries and three different degrees of polymerization. We systematically explore the impact of coarse-grained representation on ECG accuracy, highlighting the significance of preserving the C-β coordinates in thiophene. We also find that integrating unique polymer sequences into training enhances the model performance more efficiently than augmenting conformational sampling for sequences already in the training data set. Moreover, our ECG models, developed initially for one property and one level of quantum chemical theory, can be efficiently transferred to related properties and higher levels of theory with minimal additional data. The chemically transferable ECG model introduced in this work will serve as a foundation model for new classes of chemically transferable ECG predictions across chemical space.

Conformational isomerism breaks the electrolyte solubility limit and stabilizes 4.9 V Ni-rich layered cathodes

By simply increasing the concentration of electrolytes, both aqueous and non-aqueous batteries deliver technical superiority in various properties such as high-voltage operation, electrode stability and safety performance. However, the development of this strategy has encountered a bottleneck due to the limitation of the intrinsic solubility, and its comprehensive performance has reached its limit. Here we demonstrate that the conformational isomerism of the solvent would significantly affect the solubility of electrolytes. By transforming the configuration of solvent from cis-cis to cis-trans upon thermal triggering, we successfully break the solubility limit, and a beyond concentrated electrolyte with the lowest solvent-to-salt molar ratio of 0.70 is constructed. Transitions between cis-cis and cis-trans conformers are observed through Nuclear Magnetic Resonance (NMR) testing. The electrolyte consists entirely of anion-mediated solvation structures and promotes the formation of robust inorganic-dominated cathode electrolyte interphase. As a result, it enables stable cycling of 4.9 V-class LiNi0.8Co0.1Mn0.1O2 positive electrodes. Moreover, a high capacity of 151.2 mAh g-1 can be maintained after 1000 cycles at cut-off voltage of 4.8 V. This work provides a chemical pathway to build new concept electrolytes working under harsh conditions.

Exploring the material basis and molecular targets of Changma Xifeng tablet in treating Tourette syndrome: an integrative approach of network pharmacology and miRNA analysis

This study was to investigate the mechanism of Changma Xifeng tablet, a traditional Chinese medicine in the treatment of Tourette syndrome. Network pharmacology was utilized to pinpoint blood-entering constituents of Changma Xifeng and explore their potential targets. Additionally, differential microRNA expression analysis was conducted to predict Tourette syndrome-associated targets, complemented by molecular docking and dynamics simulations to support the interactions of the active compounds with these targets. The study identified 98 common targets between Changma Xifeng and Tourette syndrome, which may be involved in the treatment process. A protein-protein interaction network and a drug-active ingredient-disease target network highlighted the formulation's multi-component, multi-target therapeutic approach. Eight pivotal targets-AR, GRM5, MET, RORA, HTR2A, CNR1, PDE4B, and TOP1-were identified at the intersection of microRNA and drug targets. Molecular docking revealed 12 complexes with favorable binding energies below - 7 kcal/mol, specifically: AR with Alfacalcidol, TOP1 with Albiflorin, GRM5 with Arachidic Acid, GRM5 with Palmitic Acid, AR with Arachidic Acid, AR with 2-Hydroxyoctadecanoic Acid, RORA with Pinellic Acid, RORA with Palmitic Acid, AR with Acoronene, AR with Epiacoronene, AR with 4,4'-Methylenediphenol, and HTR2A with Calycosin. Our molecular docking and molecular dynamics simulations suggest potential stable interactions between the formulation's active components and target proteins. These computational methods provide a preliminary theoretical framework that will guide our future experimental work. The study provides a scientific rationale for the use of traditional Chinese medicine in Tourette syndrome management and offers new insights for drug development.

Metallicious: Automated Force-Field Parameterization of Covalently Bound Metals for Supramolecular Structures

Metal ions play a central, functional, and structural role in many molecular structures, from small catalysts to metal-organic frameworks (MOFs) and proteins. Computational studies of these systems typically employ classical or quantum mechanical approaches or a combination of both. Among classical models, only the covalent metal model reproduces both geometries and charge transfer effects but requires time-consuming parameterization, especially for supramolecular systems containing repetitive units. To streamline this process, we introduce metallicious, a Python tool designed for efficient force-field parameterization of supramolecular structures. Metallicious has been tested on diverse systems including supramolecular cages, knots, and MOFs. Our benchmarks demonstrate that parameters accurately reproduce the reference properties obtained from quantum calculations and crystal structures. Molecular dynamics simulations of the generated structures consistently yield stable simulations in explicit solvent, in contrast to similar simulations performed with nonbonded and cationic dummy models. Overall, metallicious facilitates the atomistic modeling of supramolecular systems, key for understanding their dynamic properties and host-guest interactions. The tool is freely available on GitHub (https://github.com/duartegroup/metallicious).

Dicitrinols A-C: Citrinin Derivatives from Hydrothermal Vent-Associated Fungus Penicillium citrinum TW132-59

Three new unusual citrinin derivatives with a unique 6/5/7/5 core, dicitrinols A-C (1-3, respectively), were isolated via the fermentation of hydrothermal vent-associated fungus Penicillium citrinum TW132-59. Their structures were unambiguously determined by nuclear magnetic resonance, mass spectrometry, and electronic circular dichroism calculations. Dicitrinols A-C represent a novel cage carbon skeleton with a decahydro-5,9,4-(epipropane[1,1,3]triyl)cycloocta[b]furan ring system. Dicitrinols A-C showed moderate antifungal activity against Candida albicans, Cryptococcus neoformans, and Fusarium oxysporum and antibacterial activity against Staphylococcus aureus, Pseudomonas aeruginosa, and Acinetobacter baumannii with minimum inhibitory concentrations ranging from 4 to 16 μg/mL.

Singlet and triplet excited states of a series of BODIPY dyes as calculated by TDDFT and DLPNO-STEOM-CCSD methods

The singlet and triplet excited states of three iodine substituted BODIPY dyes differing by their substituents (-phenyl, -phenylOH and -phenylNO2) at the meso position of the BODIPY core (BOD) are investigated using (TDA)-TDDFT and DLPNO-STEOM-CCSD calculations. An assessment of hybrid (B3LYP and MN15) and double hybrid (SOS-PBE-QIDH and SOS-ωPBEPP86) exchange-correlation functionals is performed with respect to the DLPNO-STEOM-CCSD method for four types of transitions, namely , , and . It is found that MN15 and SOS-PBE-QIDH provide a balanced description of the excited state energies when compared to the DLPNO-STEOM-CCSD results. An investigation of the effects of the solvent (dichloromethane), of the substituent and of geometrical relaxation in the excited states is then performed. In particular, the study discusses the possibility of populating charge transfer states ( and ) following photoexcitation in the first and second absorption bands in these systems.

Ab Initio Kinetics of Electrochemical Reactions Using the Computational Fc0/Fc+ Electrode

The current state-of-the-art electron-transfer modeling primarily focuses on the kinetics of charge transfer between an electroactive species and an inert electrode. Experimental studies have revealed that the existing Butler-Volmer model fails to satisfactorily replicate experimental voltammetry results for both solution-based and surface-bound redox couples. Consequently, experimentalists lack an accurate tool for predicting electron-transfer kinetics. In response to this challenge, we developed a density functional theory-based approach for accurately predicting current peak potentials by using the Marcus-Hush model. Through extensive cyclic voltammetry simulations, we conducted a thorough exploration that offers valuable insights for conducting well-informed studies in the field of electrochemistry.

Reaction pathways leading to HPALD intermediates in the OH-initiated oxidation of isoprene

In this study, we revisited the mechanism of isoprene oxidation by OH radicals, focusing on the formation of hydroperoxyaldehydes (HPALDs) in the reactions following O2-addition at the α-position to Z,Z'-OH-allyl radical products of the 1,6-H shift of the 1st-generation Z-δ-OH-isoprenylperoxy radicals. Utilizing high-level ab initio quantum chemical calculations and a master equation approach, we provide theoretical confirmation that the formation of δ-HPALDs dominates by far and show that production of β-HPALDs by the mechanism proposed by Wennberg et al. (Chem. Rev., 2018, 118, 3337-3390) is negligible. Besides the dominance of the δ-HPALD formation channel, our investigation also reveals a novel though minor reaction channel resulting in the formation of an allylic δ-hydroperoxy acid and OH radical. Of primary importance for the assessment of the respective channels is the identification of a chemically activated mechanism driving the δ-HPALD formation process under atmospheric conditions. Different from traditional thermally activated pathways, we found that the rovibrationally hot peroxy radicals resulting from O2 addition to Z,Z'-OH-allyl radicals undergo prompt rearrangement and decomposition at a rate faster than their collisional relaxation, predominantly yielding δ-HPALDs in a chemically activated manner with high efficiency under atmospheric conditions.

Electron Spin Dynamics of the Intersystem Crossing in Aminoanthraquinone Derivatives: The Spectral Telltale of Short Triplet Excited States

We studied the excited state dynamics of two bis-amino substituted anthraquinone (AQ) derivatives, with absorption in the visible spectral region, which results from the attachment of a electron-donating group to the electron-deficient AQ chromophore. Femtosecond transient absorption spectra show that intersystem crossing (ISC) takes place in 190-320 ps, and nanosecond transient absorption spectra demonstrated an unusually short triplet state lifetime (2.06-5.43 μs) for the two AQ derivatives. Pulsed laser-excited time-resolved electron paramagnetic resonance (TREPR) spectra show an inversion of the electron spin polarization (ESP) phase pattern of the triplet state at a longer delay time after laser flash. Spectral simulations show faster decay of the Ty sublevel than the other two sublevels (τx = 15.0 μs, τy = 1.50 μs, τz = 15.0 μs); theoretical computation predicts initial overpopulation of the Ty sublevel, and rationalizes the short T1 state lifetime and the ESP inversion. Theoretical computations taking into account the electron-vibrational coupling, i.e., the Herzberg-Teller effect, successfully rationalize the TREPR experimental observations.

Substituted fullerenes as a promising capping ligand towards stabilization of exohedral Dy(III) based single-ion magnets: a theoretical study

Organometallic dysprosocenium-based molecular magnets are the forefront runners in offering giant magnetic anisotropy and blocking temperatures close to the boiling point of liquid nitrogen. Attaining linearity in the organometallic dysprosocenium complexes is the key to generating giant magnetic anisotropy and blocking barriers. In the present study, we have unravelled the coordination ability of the substituted fullerene (C55X5)- (where X = CCH3, B, and N) generated by fencing around the five-membered ring of fullerene towards stabilizing a new family of exohedral dysprosium organometallic complexes showcasing giant magnetic anisotropy and blockade barriers. Eight exohedral mononuclear dysprosium organometallic complexes, namely [Dy(η5-C55X5)(η4-C4H4)] (1), [Dy(η5-C55X5)(η5-Cp)]+ (2), [Dy(η5-C55X5)(η5-Cp*)]+ (3), [Dy(η5-C55X5)(η6-C6H6)]2+ (4), [Dy(η5-C55X5)(η8-C8H8)] (5), [Dy(η5-C55X5)2]+ (6) (where X = CCH3), [Dy(η5-C55B5)2]+ (7) and [Dy(η5-C55N5)2]+ (8), were studied using scalar relativistic density functional theory (SR-DFT) and the complete active space self-consistent field (CASSCF) methodology to shed light on the structure, stability, bonding and single-ion magnetic properties. SR-DFT calculations predict complexes 1-8 to be highly stable, with a strictly linear geometry around the Dy(III) ion in complexes 6-8. Energy Decomposition Analysis (EDA) predicts the following order for interaction energy (ΔEint value): 5 > 1 > 2 ≈ 3 > 6 > 7 > 8 > 4, with sizable 4f-ligand covalency in all the complexes. CASSCF calculations on complexes 1-8 predict stabilization of mJ |±15/2〉 as the ground state for all the complexes except for 5, with the following trend in the Ucal values: 6 (1573 cm-1) ≈ 3 (1569 cm-1) > 1 (1538 cm-1) > 8 (1347 cm-1) > 2 (1305 cm-1) > 7 (1284 cm-1) > 4 (1125 cm-1) > 5 (108 cm-1). Ab initio ligand field theory (AILFT) analysis provides a rationale for Ucal ordering, where π-type 4f-ligand interactions in complexes 1-4 and 6-8 offer giant barrier height while the large (C8H8)2- rings generate δ-type interaction in 5, which diminishes the axiality in the ligand field. Our detailed finding suggests that the exohedral organometallic dysprosocenium complexes are more linear compared to bent [DyCp*2]+ cations and display a giant barrier height exceeding 1500 cm-1 with negligible quantum tunnelling of magnetization (QTM) - a new approach to design highly anisotropic dysprosium organometallic complexes.

Enhanced detection of aromatic oxidation products using NO3 - chemical ionization mass spectrometry with limited nitric acid

Nitrate ion-based chemical ionization mass spectrometry (NO3 --CIMS) is widely used for detection of highly oxygenated organic molecules (HOMs). HOMs are known to participate in molecular clustering and new particle formation and growth, and hence understanding the formation pathways and amounts of these compounds in the atmosphere is essential. However, the absence of analytical standards prevents robust quantification of HOM concentrations. In addition, nitrate-based ionization is usually very selective towards the most oxygenated molecules and blind to less oxygenated compounds hindering the investigation of molecular formation pathways. Here, we explore varying concentrations of nitric acid reagent gas in the sheath flow of a chemical ionization inlet as a method for detecting a wider range of oxidation products in laboratory-simulated oxidation of benzene and naphthalene. When the concentration of reagent nitric acid is reduced, we observe an increase in signals of many oxidation products for both precursors suggesting that they are not detected at the collision limit. The sensitivity of naphthalene oxidation products is enhanced to a larger extent than that of benzene products. This enhancement in sensitivity has a negative relationship with molecular oxygen content, the oxygen-to-carbon ratio, the oxidation state of carbon, and lowered volatility. In addition, the sensitivity enhancement is lower for species that contain more exchangeable H-atoms, particularly for accretion products. While more experimental investigations are needed for providing the relationship between enhancement ratios and instrumental sensitivities, we suggest this method as a tool for routine check of collision-limited sensitivities and enhanced detection of lower-oxygenated species.

The impact of acyl-CoA:cholesterol transferase (ACAT) inhibitors on biophysical membrane properties depends on membrane lipid composition

Acyl-coenzyme A: cholesterol acyltransferases are enzymes which are involved in the homeostasis of cholesterol. Impaired enzyme activity is associated with the occurrence of various diseases like Alzheimer's disease, atherosclerosis, and cancers. At present, mitotane is the only inhibitor of this class of enzymes in clinical use for the treatment of adrenocortical carcinoma but associated with common and severe adverse effects. The therapeutic effect of mitotane depends on its interaction with cellular membranes. The search for less toxic but equally effective compounds is hampered by an incomplete understanding of these biophysical properties. In the present study, the interaction of the three ACAT inhibitors nevanimibe, Sandoz 58-035, and AZD 3988 with membranes has been investigated using lipid model membranes in conjunction with biophysical experimental (NMR, ESR, fluorescence) and theoretical (MD simulations) approaches. The data show, that the drugs (i) incorporate into lipid membranes, (ii) differently influence the structure of lipid membranes; (iii) affect membrane structure depending on the lipid composition; and (iv) do not cause hemolysis of red blood cells. The results are discussed with regard to the use of the drugs, in particular to better understand their efficacy and possible side effects.

Catalytic prenyl conjugate additions for synthesis of enantiomerically enriched PPAPs

Polycyclic polyprenylated acylphloroglucinols (PPAPs) are a class of >400 natural products with a broad spectrum of bioactivity, ranging from antidepressant and antimicrobial to anti-obesity and anticancer activity. Here, we present a scalable, regio-, site-, and enantioselective catalytic method for synthesis of cyclic β-prenyl ketones, compounds that can be used for efficient syntheses of many PPAPs in high enantiomeric purity. The transformation is prenyl conjugate addition to cyclic β-ketoesters promoted by a readily accessible chiral copper catalyst and involving an easy-to-prepare and isolable organoborate reagent. Reactions reach completion in just a few minutes at room temperature. The importance of this advance is highlighted by the enantioselective preparation of intermediates previously used to generate racemic PPAPs. We also present the enantioselective synthesis of nemorosonol (14 steps, 20% yield) and its one-step conversion to another PPAP, garcibracteatone (52% yield).

Resonance Effects from Substituents on L-Type Ligands Mediate Synthetic Control of Gold Nanocluster Frontier Orbital Energies

The ligands of metal nanoclusters can be used to control their properties and reactivity, but a framework guiding their use remains elusive. Hammett studies of Au8(PPh3)72+ and Au9(PPh3)83+ nanoclusters with para- and meta-methyl and -methoxy groups indicate that resonance effects, not inductive effects, yield quantitative shifts of the HOMO-LUMO transitions involving orbitals local to the cluster core. Individual ligand exchanges reveal that these shifts are caused by only four of seven ligands, inconsistent with inductive effects. Quantum chemical calculations predict no trend in Au atom charges with respect to Hammett parameter but do predict bond length trends expected for a resonance structure that includes the Au atoms. Computed orbitals show contributions from specific para-OMe oxygen lone pairs to the HOMO, indicating delocalization from the core to specific ligands. These results suggest that resonance structures could be drawn including Au and ligands, guiding efforts to modulate nanocluster electronic structure and energy transfer.

Parallel Implementation of the Density Matrix Renormalization Group Method Achieving a Quarter petaFLOPS Performance on a Single DGX-H100 GPU Node

We report cutting edge performance results on a single node hybrid CPU-multi-GPU implementation of the spin adapted ab initio Density Matrix Renormalization Group (DMRG) method on current state-of-the-art NVIDIA DGX-H100 architectures. We evaluate the performance of the DMRG electronic structure calculations for the active compounds of the FeMoco, the primary cofactor of nitrogenase, and cytochrome P450 (CYP) enzymes with complete active space (CAS) sizes of up to 113 electrons in 76 orbitals [CAS(113, 76)] and 63 electrons in 58 orbitals [CAS(63, 58)], respectively. We achieve 246 teraFLOPS of sustained performance, an improvement of more than 2.5× compared to the performance achieved on the DGX-A100 architectures and an 80× acceleration compared to an OpenMP parallelized implementation on a 128-core CPU architecture. Our work highlights the ability of tensor network algorithms to efficiently utilize high-performance multi-GPU hardware and shows that the combination of tensor networks with modern large-scale GPU accelerators can pave the way toward solving some of the most challenging problems in quantum chemistry and beyond.

Modulation of the magnetic properties of mononuclear Dy(III) complexes by tuning the coordination geometry and local symmetry

Precise control of the crystal field and local symmetry around the paramagnetic spin center is crucial for the design and synthesis of single-molecule magnets (SMMs). Herein, three mononuclear Dy(III)-based complexes, [Dy(LN6)(CH3COO)2](BPh4)(CH2Cl2) (1), [Dy(LN6)(2,6-Cl-4-NO2-PhO)(H2O)2]2(PF6)2(H2O)(2,6-Cl-4-NO2-PhO)2 (2) and [Dy(LN6)(2,6-Cl-4-NO2-PhO)2](BPh4)(CH2Cl2)2 (3) (LN6 = N6-hexagonal plane accomplished by a neutral Schiff base ligand formed from 2,6-diacetylpyridine and ethylenediamine), are successfully isolated. In these complexes, the Dy(III) centers are coordinated with six neutral N atoms from a nonrigid equatorial ligand, while different oxygen-bearing ligands are arranged at the axial positions of the central ions by gradual regularization of the axial ligands. As a result, Dy(III) ions in the three complexes exhibit various coordination geometries, forming a ten-coordinate tetradecahedron for 1, a nine-coordinate muffin configuration for 2 and a distorted eight-coordinate hexagonal bipyramid for 3. Magnetic studies reveal that all complexes exhibit no SIM behaviour under zero dc field, due to the predominant quantum tunneling of magnetization (QTM), which can be effectively suppressed by additional dc fields. Experiments, coupled with theoretical calculations, demonstrate that varying local symmetries and coordination geometries are synergistically responsible for the disparities of QTM and uniaxial anisotropy, resulting in notably different magnetic properties.

Quantum tunnelling effect in the cis-trans isomerization of uranyl tetrahydroxide

The role of quantum tunnelling (QT) in the proton transfer kinetics of the uranyl tetrahydroxide (UTH, [UO2(OH)4]2-) cis to trans isomerization was computationally studied under three possible reaction pathways. The first pathway involved a direct proton transfer from the hydroxide ligand to the oxo atom. In the other two pathways, one or two water molecules were added to the second sphere. The first H2O, bound by hydrogen bonds to the ligands, acts as a bridge enabling a proton shuttling, a concerted hopping of a proton from the hydroxide to the oxo atom similar to the Grotthuss mechanism. In the third pathway, the second water molecule does not participate in the H-transfer chain, but works as an anchor for the first water molecule, limiting its movement and therefore enhancing the QT. Since experimentally the reaction occurs in water, the first two pathways (no water or one H2O) serve only as models of the gas phase behaviour, while the third pathway will always be thermodynamically and kinetically preferred. The effects were investigated in the gas phase as well as in a continuum aqueous model, including the H/D Kinetic Isotope Effect (KIE). The results indicate that at very low temperatures, QT is the only mechanism that permits the reaction kinetics, consistent with the large computed KIE. At higher temperatures, thermally activated tunnelling competes with the classical crossing over the potential barrier.

Probing the protonation and reduction of heptavalent neptunium with computational guidance

Influence of pH on the speciation and stability of heptavalent neptunium is poorly understood although it is frequently invoked in the literature to explain experimental observations. The present study employs Density Functional Theory (DFT) methodology to assess the thermodynamic feasibility of protonation reactions for the Np(VII) anion complex and the impact on its reduction to Np(VI). This theoretical framework is then explored experimentally through the titration and systematic protonation of Np(VII) in solution and solid-state samples while monitoring them spectroscopically. Computational results reveal that protonation reactions with the axial OH- ligands of the Np(VII) anionic complex, [NpO4(OH)2]3-, are more thermodynamically favorable than the equatorial oxo ligands. In addition, DFT studies indicated that up to four sequential protonation reactions may be feasible before reduction becomes thermodynamically favorable. Experimental results also uncover that protonation leads to distinct changes in the observable vibrational signals and UV-Vis absorption features. Overall, we observed that the protonation of [NpO4(OH)2]3- in solution and in the solid-state occurs before reduction to the Np(VI)O22+ species.

Synthesis of Amorphous and Various Phase-Pure Nanoparticles of Nickel Phosphide with Uniform Sizes via a Trioctylphosphine-Mediated Pathway

Nickel phosphides are of particular interest because they are highly active and stable catalysts for petroleum/biorefinery and hydrogen production. Despite their significant catalytic potential, synthesizing various phase-pure nickel phosphide nanoparticles of uniform size remains a challenge. In this work, we develop a robust trioctylphosphine (TOP)-mediated route to make highly uniform phase-pure Ni12P5, Ni2P, and Ni5P4 nanoparticles. The synthetic route forms amorphous Ni70P30 nanoparticle intermediates. The reactions can be stopped at the amorphous stage when amorphous particles are desired. The amount of P incorporation can be controlled by varying the ratio of TOP to Ni(II). The mechanism for composition control involves the competition of the kinetics of two processes: the addition of the reduced Ni and the incorporation of P into Ni. Uniform Ni70P30 amorphous nanoparticles can be generated at a high TOP-to-Ni(II) ratio, where the P incorporation kinetics is made to dominate. Ni70P30 can later be transformed into phase-pure Ni12P5, Ni2P, and Ni5P4 nanocrystals of uniform size. The transformation can be controlled precisely by modulating the temperature. A UV-vis study coupled with theoretical modeling reveals Ni(0)-TOPx complexes along the synthetic path. This approach may be expanded to create other metal compounds, potentially enabling the synthesis of uniform nanoparticles of a greater variety.

Synthesis of a mixed-linker Ce-UiO-67 metal-organic framework

Ce-based metal-organic frameworks (MOFs) have recently gained scientific interest, since Ce is the most abundant rare-earth element in the Earth's crust and since their synthesis has some advantages, including first of all their redox activity, the high porosity of these crystalline materials, and Ce availability. In particular, Ce(iv)-based MOFs, such as Ce-UiO-66 and Ce-UiO-67, are synthesised under mild conditions. For most applications, the presence of functional groups in the frameworks is needed; in this context, linkers containing N-functionalities have been highlighted, as they allow for the incorporation of a large variety of metal cations. In order to insert N-functionalities for the sake of successive metal-functionalization of materials as Ce-UiO-67, we have successfully synthesised a mixed-linker version of this MOF, by incorporating 2,2'-bipyridine-5,5'-dicarboxylic acid together with the conventional biphenyl-4,4'-dicarboxylic acid linker; we have worked on a reproducible and upscalable procedure using benzoic acid as the modulator, without altering the original framework topology. Mixed-linker Ce-UiO-67 MOFs exhibit good thermal stability, high Brunauer-Emmett-Teller (BET) SSAs and microporosity. The pristine samples are highly stable if stored in a desiccator, as demonstrated by the preservation of their high crystallinity for at least 18 months.

High pressure-derived nonsymmetrical [Cu2O]2+ core for room-temperature methane hydroxylation

Nonsymmetrical oxygen-bridged binuclear copper centers have been proposed and modeled as intermediates and transition states in several C─H oxidation pathways, leading to the postulation that structural dissymmetry enhances the reactivity of the bridging oxygen. However, experimentally characterizing the structure and reactivity of these transient species is remarkably challenging. Here, we report the high-pressure synthesis of a metastable nonsymmetrical dicopper-μ-oxo compound with exceptional reactivity toward the mono-oxygenation of aliphatic C─H bonds. The nonequivalent coordination environment of copper stabilizes localized mixed valency and greatly enhances the hydrogen atom abstraction activity of the bridging oxygen, enabling room-temperature hydroxylation of methane under pressure. These findings highlight the role of dissymmetry in the reactivity of binuclear copper centers and demonstrate precise control of molecular structures by mechanical means.

AtmoSpec-A Tool to Calculate Photoabsorption Cross-Sections for Atmospheric Volatile Organic Compounds

Characterizing the photolysis processes undergone by transient volatile organic compounds (VOCs) in the troposphere requires the knowledge of their photoabsorption cross-section-quantities often challenging to determine experimentally, particularly due to the reactivity of these molecules. We present a computational tool coined AtmoSpec, which can predict a quantitative photoabsorption cross-section for volatile organic compounds by using computational photochemistry. The user enters the molecule of interest as a SMILES code and, after selecting a level of theory for the electronic structure (and waiting for the calculations to take place), is presented with a photoabsorption cross-section for the low-energy conformers and an estimate of the photolysis rate coefficient for different standardized actinic fluxes. More specifically, AtmoSpec is an automated workflow for the nuclear ensemble approach, an efficient technique to approximate the absolute intensities and excitation wavelengths of a photoabsorption cross-section for a molecule in the gas phase of interest in atmospheric chemistry and astrochemistry. This work provides background information on the nuclear ensemble approach, a guided example of a typical AtmoSpec calculation, details about the architecture of the code, and the current limitations and future developments of this tool.

Atmospheric Degradation Mechanism of Isoamyl Acetate Initiated by OH Radicals and Cl Atoms Revealed by Quantum Chemical Calculations and Kinetic Modeling

Isoamyl acetate is one of the volatile organic compound class molecules relevant to agricultural and industrial applications. With the growing interest in isoamyl acetate applications in industry, the atmospheric fate of isoamyl acetate must be considered. Reaction mechanisms, potential energy profiles, and rate constants of isoamyl acetate reaction with atmospheric relevant oxidant OH radicals and Cl atoms have been obtained from the quantum chemical calculations and kinetic modeling. The geometry optimizations were conducted using M06-2X/6-311++G(3df,3pd) followed by single point-energy calculations at the DLPNO-CCSD(T) method with an extrapolated complete basis set. The rate constants were calculated by solving the master equation. A hydrogen-abstraction reaction dominates the first step of isoamyl acetate degradation, while the addition-substitution reaction plays a small role in the degradation products. The kinetic study was conducted to evaluate the rate constants within a temperature range of 200-400 K. The total rate constants for the isoamyl acetate degradation reactions initiated by the OH radical and Cl atom were determined to be 6.96 × 10-12 and 1.27 × 10-10 cm3 molecule-1 s-1, respectively, under standard temperature and pressure conditions. The product degradation mechanism, ozone formation potential, and atmospheric impacts were discussed.

Chevalierlin: A spirocyclic alkaloid from a hydrothermal vent associated fungus Aspergillus chevalieri TW132-65

A previously undescribed spirodiketopiperazine-indole alkaloid, chevalierlin (1), two pairs of previously undescribed dihydroisocoumarin enantiomers eurotiumides H-I (2-3), as well as six related known compounds (4-9) were isolated from the culture of a hydrothermal vent associated fungus Aspergillus chevalieri TW132-65. Their structures were unambiguously determined by NMR, mass spectrometry, and ECD calculations. Chevalierlin (1) exhibits moderate cytotoxic activities with IC50 values of 6.20 ± 0.05 μM and 7.68 ± 0.01 μM against Namalwa and Raji cell lines.

Nonflammable Ether and Phosphate-Based Liquid Electrolytes for Sodium-Ion Batteries

This study investigates a group of electrolytes containing NaPF6 or NaBF4 salts in phosphate- and ether-based solvents for high-mass loading sodium-ion batteries. It explores physicochemical properties such as ionic conductivity, dynamic viscosities, and nonflammability. The combination of experimental with computational studies reveals detailed insights into the physicochemical properties of the nonflammable liquid electrolytes. Diglyme-based electrolytes become nonflammable with 50 vol % phosphate solvents, while tetraglyme-based electrolytes require 70 vol %. The solvation structure has been investigated using NMR and is combined with computational studies to provide information about properties such as solvation structure, ionic conductivity, and viscosity. The molecular dynamic simulations confirm the enhanced solvation in diglyme-based liquid electrolytes observed experimentally by 23Na-NMR. Despite lacking sufficient electrochemical stability, this work provides a fundamental understanding of the solvation structure and physicochemical properties of a novel electrolyte system. This is an important contribution to be applied in future electrolyte design rationale.

A new approach for endowing photocatalytic performance to biochar based on peryleneimide: Emphasizing the achievement of highly efficient degradation to RhB

Having unique structural characteristics of biochar contributes great potential in photocatalysis, the preparation process complexity is still a great challenge for biochar-based photocatalysts. Based on this, this study proposes a new, simple, efficient, and flexible approach to preparing biochar-based photocatalysts by perylene diimide (GPC/PDI). The results showed that the hybridization between GPC and PDI was achieved by π-π stacking, which was reduced with increasing pyrolysis temperature, increased first and then decreased with increasing PDI content, and improved with enhanced solvent polarity. When the pyrolysis temperature was 400 °C, the PDI addition was 0.05 mg, and the reaction solvent was water, the degradation of 200 mg/L rhodamine B (RhB) by GPC400/PDI0.5 was 94%, and the reaction rate constant was 10 and 4 times higher than GPC400 and PDI, which were also effective in simulating actual wastewater treatment. This was attributed to the efficient electron-hole separation and migration along the π-π stacking direction due to the hybridization of GPC and PDI, which in turn reacts to produce reactive oxygen species (1O2, •O2-, •OH), facilitating the photocatalytic degradation process.