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Metal–ligand cooperation is an important aspect in earth-abundant metal catalysis. Utilizing ligands as electron reservoirs to supplement the redox chemistry of the metal has resulted in many new exciting discoveries. Here, we demonstrate that iron bipyridine-diimine (BDI) complexes exhibit an extensive electron-transfer series that spans a total of five oxidation states, ranging from the trication [Fe(BDI)]3+ to the monoanion [Fe(BDI]−1. Structural characterization by X-ray crystallography revealed the multifaceted redox noninnocence of the BDI ligand, while spectroscopic (e.g., 57Fe Mössbauer and EPR spectroscopy) and computational studies were employed to elucidate the electronic structure of the isolated complexes, which are further discussed in this report., In this study, the multifaceted electrochemistry of a bis(imino)bipyridine iron(II) complex is described. Spectroscopic studies demonstrate that throughout the various reduction processes, the oxidation state on the metal center remains constant (Fe(II); S = 1), whereas the ligand accesses four distinct oxidation states: [BDI]0 ⇄ [BDI]3−. The observed redox noninnocence of the ligand was investigated by computational methods, which is further discussed in this report.

We evaluate the performance of ten common carbon force fields for the interaction energies in double and triple layered carbon onions. In particular, we consider the C20@C60, C20@C80, C20@C180, C80@C240, C60@C240 and C240@C540 double-layer carbon onions and C60@C240@C540 and C80@C240@C540 triple-layered carbon onions. We consider the following carbon force fields: Tersoff, REBO-II, AIREBO, AIREBO-M, screened versions of Tersoff and REBO-II, LCBOP-I, 2015 and 2020 versions of ReaxFF, and the machine-learning GAP force field. We show that the ReaxFF force fields give the best performance for the interaction energies of the cabon onions relative to density functional theory interaction energies obtained at the PBE0-D3/def2-TZVP level of theory. We proceed to use the ReaxFF-15 force field to explore the interaction energies in a giant ten-layered carbon onion with a C60 core and show that the interaction energy between the outer layer and the inner layers increases linearly with the number of layers in the carbon onion (with a squared correlation coefficient of R2 = 0.9996). This linear increase in the stabilization energy with each consecutive layer may have important thermodynamic consequences for describing the formation and growth of large carbon onions.

We have examined the use of systematic bond-separation reactions and purposely constructed chemistry-preserving isodesmic reactions for the thermochemical calculation of aromatic hydrocarbon species. The bond-separation approach yields somewhat disappointing accuracy even when the reaction energies are obtained with generally robust composite and double-hybrid (DH) density functional theory (DFT) methods. In contrast, for the purposely constructed reactions, we find a dramatic improvement in the accuracy for energies calculated with all methods examined. Notably, for medium-sized aromatic hydrocarbons, we find that an effective approach for formulating a well-balanced reaction is to split the target species into two halves with an aromatic overlapping region. Overall, the G4(MP2)-XK, MPW2PLYP, MN15, PBE, and DC-DFTB3 methods are reasonable within their respective classes of methods for the calculation of bond-separation as well as chemistry-preserving isodesmic reactions. We have further computed per-carbon atomization energy (AE) for a series of D6h benzene-type molecules, and thus obtained a formula for extrapolation to the graphene limit [AEn = 711.5 × (1 − 1/n0.640) kJ mol−1, where n = number of carbons]. It suggests that nano-graphene with a length larger than 10 nm would resemble properties of bulk graphene, and conversely, downsizing a nano-graphene beyond this point may lead to considerably altered properties from the bulk.

Perylene bisimide (PBI) cyclophanes have been shown to form ideal hosts for large aromatic molecules, offering rigid cavities and ideal monomer spacing for π–π stacking interactions between the host and guest. Here, we show computationally that these characteristics also make PBI cyclophanes ideal receptors for the planar transition structures of a number of representative stereoinversion processes. The observed catalytic effect can hereby be explained using two fundamental concepts: transition state stabilization due to shape-complementarity between cyclophane and the transition structures and, to a smaller extent, ground state destabilization due to non-complementarity between cyclophane and equilibrium structures. Energy decomposition analyses of the noncovalent interactions between the host and guest structures reveal that dispersion and electrostatic interactions make the largest contributions to stabilizations and thus suggest that catalysis in this system is mainly driven by π–π stacking interactions.

The need for sustainable and large-scale energy supply has led to significant development of renewable energy and energy storage technologies. Divalent metal ion (Mg, Ca, and Zn) batteries are promising energy storage technologies for the sustainable energy future, but the need for suitable electrode materials have limited their commercial development. This paper investigates, at the atomic scale, the adsorption and migration of Mg, Ca, and Zn on pristine and defective graphene surfaces, to bring insight into the metal storage and mobility in graphene and carbon-based anodes for divalent metal ion batteries. Such atomistic studies can help address the challenges facing the development of novel divalent metal battery technologies, and to understand the storage differences between divalent and monovalent metal-ion batteries. The adsorption of Ca on the graphene-based system is shown to be more energetically favorable than the adsorption of both Mg and Zn, with Ca showing adsorption behavior similar to the monovalent ions (Li, Na, and K). This was further investigated in terms of metal migration on the graphene surface, with much higher migration energy barriers for Ca than for Mg and Zn on the graphene systems, leading to the trapping of Ca at defect sites to a larger extent.

Inverse vulcanization provides dynamic and responsive materials made from elemental sulfur and unsaturated cross-linkers. These polymers have been used in a variety of applications such as energy storage, infrared optics, repairable materials, environmental remediation, and precision fertilizers. In spite of these advances, there is a need for methods to recycle and reprocess these polymers. In this study, polymers prepared by inverse vulcanization are shown to undergo reactive compression molding. In this process, the reactive interfaces of sulfur polymers are brought into contact by mechanical compression. Upon heating these molds at relatively low temperatures (≈100 °C), chemical bonding occurs at the polymer interfaces by S-S metathesis. This method of processing is distinct from previous studies on inverse vulcanization because the polymers examined in this study do not form a liquid phase when heated. Neither compression nor heating alone was sufficient to mold these polymers into new architectures, so this is a new concept in the manipulation of sulfur polymers. Additionally, high-level ab initio calculations revealed that the weakest S-S bond in organic polysulfides decreases linearly in strength from a sulfur rank of 2 to 4, but then remains constant at about 100 kJ mol-1 for higher sulfur rank. This is critical information in engineering these polymers for S-S metathesis. Guided by this insight, polymer repair, recycling, and repurposing into new composites was demonstrated.

Eleven isomers of SiC4H2 lying within 50 kcal mol-1 have been theoretically investigated using density functional theory and high-level coupled-cluster methods. Among them, four isomers, 1-ethynyl-3-silacycloprop-1(2)-en-3-ylidene (1), diethynylsilylidene (2), 1-sila-1,2,3,4-pentatetraenylidene (4), and 1,3-butadiynylsilylidene (5), have already been identified in the laboratory. The current investigation reports three low-lying ( 1 eV) silylidenes [2-sila-(didehydrovinylidene)cyclopropene (8), an isomer with a planar tetracoordinate carbon (ptC) atom (10), and 1-ethynyl-1-silapropadienylidene (11)], which remain elusive in the laboratory to date. Isomer 9 also contains a ptC atom, which turned out to be a transition state at all levels. Though all isomers are polar (μ ≠ 0), rotational spectrum is available only for 4. Using matrix isolation, three isomers (1, 2, and 5) have been trapped in the laboratory at 10 K. Considering the astrochemical relevance of silicon-carbide clusters in the interstellar medium, the current theoretical data demand new molecular spectroscopic studies on SiC4H2. Surprisingly, unlike the isovalent C5H2 isomers, where the bent carbenes are yet to be identified in the laboratory, the bent silylidenes (2 and 5) have been trapped in the case of SiC4H2. In both the cases, molecules with transannular C-C and/or Si-C bonds remain elusive, though they lie in the low-lying region. Using suitable precursors, whether these peculiar geometries (especially 3 and 6) would be identified or not in the laboratory needs to be addressed by molecular spectroscopists. The present investigation documents structural and spectroscopic information of SiC4H2 isomers, which may compliment future molecular spectroscopic observations including radioastronomical searches.

Stable equilibrium compounds containing a planar antiaromatic cyclooctatetraene (COT) ring are promising candidates for organic electronic devices such as organic semiconductor transistors. The planarization of COT by incorporation into rigid planar π-systems, as well as by oxidation or reduction has attracted considerable attention in recent years. Using dispersion-corrected density functional theory calculations, we explore an alternative approach of planarizing COT derivatives by adsorption onto graphene. We show that strong π-π stacking interactions between graphene and COT derivatives induce a planar structure with an antiaromatic central COT ring. In addition to being reversible, this strategy provides a novel approach for planarizing COT without the need for incorporation into a rigid structure, atomic substitution, oxidation, or reduction.

Reactions involving Criegee intermediates (CIs, R1 R2 COO) are important in atmospheric ozonolysis models. In recent years, density functional theory (DFT) and CCSD(T)-based ab initio methods are increasingly being used for modeling reaction profiles involving CIs. We obtain highly accurate CCSDT(Q)/CBS reaction energies and barrier heights for ring-closing reactions involving atmospherically important CIs (R1 /R2 = H, Me, OH, OMe, F, CN, cyclopropene, ethylene, acetaldehyde, and acrolein). We use this benchmark data to evaluate the performance of DFT, double-hybrid DFT (DHDFT), and ab initio methods for the kinetics and thermodynamics of these reactions. We find that reaction energies are more challenging for approximate theoretical procedures than barrier heights. Overall, taking both reaction energies and barrier heights into account, only one of the 58 considered DFT methods (the meta-GGA MN12-L) attains near chemical accuracy, with root-mean-square deviations (RMSDs) of 3.5 (barrier heights) and 4.7 (reaction energies) kJ mol-1 . Therefore, MN12-L is recommended for investigations where CCSD(T)-based methods are not computationally feasible. For reaction barrier heights performance does not strictly follow Jacob's Ladder, for example, DHDFT methods do not perform better than conventional DFT methods. Of the ab initio methods, the cost-effective CCSD(T)/CBS(MP2) approach gives the best performance for both reaction energies and barrier heights, with RMSDs of 1.7 and 1.4 kJ mol-1 , respectively. All the considered Gaussian-n methods show good performance with RMSDs below the threshold of chemical accuracy for both reaction energies and barrier heights, where G4(MP2) shows the best overall performance with RMSDs of 2.9 and 1.5 kJ mol-1 , respectively. © 2019 Wiley Periodicals, Inc.

Inspired by the promise of hydrogen (H2) as a clean alternate to the existing energy sources, we have employed spin-polarized density functional theory calculations on a recently designed two-dimensional C 4 N monolayer as a promising H 2 storage material. By means of first principles DFT calculations, we have comprehensively studied the geometric and electronic properties of pristine, defected and metal-doped C 4 N nanosheets and further explored their H 2 storage properties. We found that light metal dopants such as Li, Na, K, Mg, and Ca bind strongly to defects on a C 4 N nanosheet with binding energies of 3–4 eV per dopant. These binding energies are sufficiently strong to surpass metal clustering. Thermal stability of the metal-doped C 4 N nanosheets has been further verified by means of ab initio molecular dynamics simulations. The bonding nature of the metal dopants with the C 4 N nanosheet has been studied through Bader analysis and Roby-Gould methods and the electronic properties were studied through density of states. We found that each dopant in the metal-doped C 4 N nanosheet can bind up to five H 2 molecules with adsorption energies ranging between 0.15 and 0.60 eV/ H 2 , which results in optimal H 2 storage capacities. Finally, we employed thermodynamic analysis to investigate the H 2 adsorption/desorption mechanism under practical operating conditions.

Based on spin-polarized DFT calculations, we have studied the interaction mechanism of recently synthesized blue phosphorene (BlueP) monolayers towards selected key volatile organic compounds (VOCs) such as acetone, ethanol and propanal. Our binding energy analysis shows that pristine BlueP weakly binds the VOCs and that this binding does not appreciably change the electronic properties of the monolayer – a prerequisite for any sensing material. However, mono, di, and tri-vacancy defects and Si/S-substitutional doping significantly enhance the binding energies with VOCs. Density of state (DOS) calculations show that upon adsorption of VOCs, mono-vacancy and S-substituted BlueP monolayers undergo a major change in electronic structure, which make them potential candidates for VOCs sensing materials. By contrast, binding of VOCs to di- and tri-vacancy and Si-substitution sites does not alter the electronic structure of BlueP monolayers drastically, therefore, are not qualified for VOCs sensing applications.

The ability to accurately calculate reaction barrier heights is of central importance to many areas of chemistry. We report an extensive study examining the basis set convergence of post-CCSD(T) contributions (up to CCSDT(Q)) for a diverse set of 28 reaction barrier heights. In contrast to previous studies, we focus here on larger transition structures (TSs) involving 4-7 non-hydrogen atoms. The set of reaction barrier heights includes pericyclic, bipolar cycloaddition, cycloreversion, and multiple-proton transfer reactions. We find that in most cases post-CCSD(T) contributions converge rapidly toward the basis set limit, such that even double-ζ and truncated double-ζ basis sets provide useful estimates of the T-(T) and (Q) contributions, respectively. In addition, we find that due to the tendency of these small basis sets to systematically underestimate the T-(T) and (Q) components, scaling is an effective approach for improving performance. For example, scaling the T-(T)/cc-pVDZ contribution by 1.25 results in an RMSD of merely 0.4 kJ mol

The equilibrium geometries and spectroscopic properties of two key singlet carbenes, buta-1,3-diynylcarbene (6) and 2-methylenebicyclo[1.1.0]but-1(3)-en-4-ylidene (9), which have not been experimentally observed to date, are investigated using high-level coupled-cluster (CC) methods. The current theoretical study necessitates new experimental data on C5H2 isomers considering the relevance of these molecules to interstellar chemistry. Bent-pentadiynylidene (4) has been missing in the laboratory and the prime focus of our earlier theoretical work. The present theoretical study indicates that isomers 6 and 9 are also viable experimental targets. Apart from ethynylcyclopropenylidene (2), pentatetraenylidene (3), ethynylpropadienylidene (5), and 3-(didehydrovinylidene)cyclopropene (8), which are identified by Fourier transform microwave spectroscopy, the dipole moments of elusive 4, 6, and 9 are also nonzero (μ ≠ 0). The relative energies of these isomers, calculated at the CCSDT(Q)/CBS level of theory, with respect to linear triplet pentadiynylidene (1) reveal that they all lie within 25.1 kcal mol-1. Therefore, geometric, energetic, aromatic, and spectroscopic parameters are reported here, which may assist the efforts of molecular spectroscopists in the future. Anharmonic vibrational calculations on isomers 6 and 9 indicate that the former is loosely bound and would be challenging to be detected experimentally. Among the undetected carbenes, 9 may be considered as a potential target molecule considering its higher polarity and aromatic nature.

International audience; Nitrogen Monoxide (NO) is observed in the gas phase of molecular clouds. It may accrete on dust grains and there its hydrogenation should lead to hydroxylamine (NH 2 OH), the same way that CO is transformed in methanol (CH 3 OH) on the surface dust grains. NO hydrogenation has been said barrier-less, whereas CO hydrogenation proceed through quantum tunneling, and is thus slower. However, CH 3 OH is widely observed and is considered as a proxy of complex organic molecules while hydroxy-lamine remains undetected. We aim at studying, analyzing, and understanding the 1 chemical network of NO hydrogenation on cold surfaces. Experiments are carried out using a new Ultra-Hight Vacuum (UHV) setup named VENUS. NO molecules and H atoms are co-deposited on a golden mirror at different temperatures. Infrared spectroscopy as well as Temperature Programmed Desorption (TPD) are used to follow the NO reactivity, with both H and D, and in presence or absence of water substrate. Quantum calculations on water ice cluster models are computed separately. During the hydrogenation of NO, 10 reactions proceed concurrently. They are identified and constrained by changing physical conditions in experiments or in calculations. Among them, we demonstrate that the HNO+H addition reaction has a barrier which is probably crossed via quantum tunneling at 10 K. Moreover, abstraction reactions are occurring although they are limited by H and O bonding with their environment. Chemical desorption should occur especially in absence of water which enhances the total production of hydroxylamine. The chemical network of the hydrogenation of NO has been re-investigated. Each of the 10 reactions are sorted by efficiency. We exclude the possibility of a chemical loop between NO and HNO, especially in presence of water. Therefore hydroxylamine remains the main product of the hydrogenation of NO on grains and the question of its non-detection in ices or in the gas phase, specifically in shocked regions where ice mantles should be sputtered, is still open.

The enthalpies of formation and isomerization energies of P4Sn molecular cages are not experimentally (or theoretically) well known. We obtain accurate enthalpies of formation and isomerization energies for P4Sn cages (n = 3, 4, 5, 6, and 10) by means of explicitly correlated high-level thermochemical procedures approximating the CCSD(T) and CCSDT(Q) energies at the complete basis set (CBS) limit. The atomization reactions have very significant contribution from post-CCSD(T) correlation effects and, due to the presence of many second-row atoms, the CCSD and (T) correlation energies converge exceedingly slowly with the size of the one-particle basis set. As a result, these cage structures are challenging targets for thermochemical procedures approximating the CCSD(T) energy (e.g., W1-F12 and G4). Our best enthalpies of formation at 298 K (∆fH°298) are obtained from thermochemical cycles in which the P4Sn cages are broken down into P2S2 and S2 fragments for which highly accurate ∆fH°298 values are available from W4 theory. For the smaller P4S3 and P4S4 cages, the reaction energies are calculated at the CCSDT(Q)/CBS level and for the larger P4S5, P4S6, and P4S10 cages, they are obtained at the CCSD(T)/CBS level. Our best ∆fH°298 values are − 94.5 (P4S3), − 108.4 (α-P4S4), − 98.7 (β-P4S4), − 126.2 (α-P4S5), − 126.1 (β-P4S5), − 112.7 (γ-P4S5), − 144.7 (α-P4S6), − 153.9 (β-P4S6), − 134.4 (γ-P4S6), − 136.3 (δ-P4S6), − 118.7 (e-P4S6), and − 215.4 (P4S10) kJ mol−1. Interestingly, we find a linear correlation (R2 = 0.992) between the enthalpies of formation of the most stable isomers of each molecular formula and the number of atoms in the P4Sn cages. We use our best ∆fH°298 values to assess the performance of a number of lower-cost composite ab initio methods. For absolute enthalpies of formation, G4(MP2) and G3(MP2)B3 result in the best overall performance with root-mean-square deviations (RMSDs) of 10.6 and 12.9 kJ mol−1, respectively, whereas G3, G3B3, and CBS-QB3 result in the worst performance with RMSDs of 27.0–38.8 kJ mol−1. In contrast to absolute enthalpies of formation, all of the considered composite procedures give a good-to-excellent performance for the isomerization energies with RMSDs below the 5 kJ mol−1 mark.

Nitroxide radicals have previously been successfully used as electrodes in all-organic radical batteries. However, one drawback of these batteries is significantly reduced redox potentials, in comparison to that of widely used lithium-ion batteries, making their energy-producing capacity rather small for use as a primary battery. In addition, strong propensity of nitroxide radicals to engage in side reactions with traditional electrolytes based on molecular solvents give rise to a series of undesirable and irreversible byproducts, thus significantly reducing the life of nitroxide batteries. Ionic liquids (ILs) have previously demonstrated their ability to reduce the reactivity of radicals through strong intermolecular interactions. In this study, we investigate the use of ILs as electrolytes with the view of increasing redox potentials of nitroxide radicals. A series of imidazolium, phosphonium, and pyrrolidinium-based ILs coupled with widely used anions were chosen to predict redox potentials of the 2,2,...

Hypochlorous acid (HOCl) is a highly reactive, toxic species generated by neutrophils via the action of myeloperoxidase in order to destroy invading pathogens. However, when HOCl is produced inappropriately, it can damage host tissue and proteins and plays a role in the initiation and progression of disease. Carnosine, a peptide of β-alanine and histidine, has been shown to react rapidly with HOCl yielding monochloramines and can undergo intramolecular transchlorination. The current study examines the kinetics and pH dependence of the reactions of carnosine and novel structural derivatives with HOCl and the occurrence of intra- and intermolecular transchlorination processes. We demonstrate that the transchlorination reactions of carnosine are pH dependent, with intramolecular transfer favored at higher pH. Carcinine, having a structure identical to carnosine though lacking the carboxylic acid group of the histidine residue, reacts with HOCl and forms monochloramines though intramolecular transfer reactions are not observed, and this is supported by computational modeling. Novel analogues with one (carnosine+1) and two (carnosine+2) methylene groups in the alkyl chain of the β-alanine react with HOCl to yield monochloramines that undergo transchlorinations to yield a mixture of mono- and dichloramines. The latter are stable over 24 h. The ability of carnosine and derivatives to react rapidly with HOCl to give long-lived, poorly reactive, species may prevent damage to proteins and other targets at sites of inflammation.

Polymers are an attractive anchoring platform for the synthesis of radioimmunoconjugates. They enable independent control over the amount of radioisotope loading and antibody attachment, which is pivotal in developing tailorable formulations for personalised medicine. Herein, we report the synthesis of p(HEMA-ran-GMA) for the conjugation of lutetium ions and rituximab as a functional platform for radioimmunotherapy. We demonstrate the suitability of this platform using non-Hodgkin's lymphoma cells.

Perylenequinones are a class of aromatic polyketides characterised by a highly conjugated pentacyclic core, which confers them with potent light-induced bioactivities and unique photophysical properties. Despite the biosynthetic gene clusters for the perylenequinones elsinochrome A (1), cercosporin (4) and hypocrellin A (6) being recently identified, key biosynthetic aspects remain elusive. Here, we first expressed the intact elc gene cluster encoding 1 from the wheat pathogen Parastagonospora nodorum heterologously in Aspergillus nidulans on a yeast-fungal artificial chromosome (YFAC). This led to the identification of a novel flavin-dependent monooxygenase, ElcH, responsible for oxidative enolate coupling of a perylenequinone intermediate to the hexacyclic dihydrobenzo(ghi)perylenequinone in 1. In the absence of ElcH, the perylenequione intermediate formed a hexacyclic cyclohepta(ghi)perylenequinone system via an intramolecular aldol reaction resulting in 6 and a novel hypocrellin 12 with opposite helicity to 1. Theoretical calculations supported that 6 and 12 resulted from atropisomerisation upon formation of the 7-membered ring. Using a bottom-up pathway reconstruction approach on a tripartite YFAC system developed in this study, we uncovered that both a berberine bridge enzyme-like oxidase ElcE and a laccase-like multicopper oxidase ElcG are involved in the double coupling of two naphthol intermediates to form the perylenequinone core. Gene swapping with the homologs from the biosynthetic pathway of 4 showed that cognate pairing of the two classes of oxidases is required for the formation of the perylenequinone core, suggesting the involvement of protein–protein interactions.

Herein we demonstrated that the shape and phase of colloidal ZnSe nanocrystals can be spontaneously tuned through tailoring the selenium precursor reactivity in a phosphine-free reaction system. Selenium species with diverse reaction activities, i.e. Se22− or Se2−, were produced by the addition of different volumes of reductant superhydride (lithium triethylborohydride). Theoretical calculation of ΔGr indicates that superhydride-reduced Se22− is less active than Se2− for the reaction with a Zn precursor. Nanoparticle growth using Se22− produces wurtzite ZnSe nanorods whereas the reaction of more reactive Se2− with the zinc precursor leads to the formation of spherical zinc blende ZnSe nanodots. This work not only provides a facile synthetic approach for the preparation of high quality ZnSe nanocrystals but also gives insights into the shape and phase control of other colloidal nanocrystals.

The mechanism for the semipinacol rearrangement in cis-fused β-lactam diols has been examined using highly accurate double-hybrid density functional theory methods. This reaction involves a competition between two possible migrating groups (alkyl and acyl), which can undergo a 1,2 C–C bond migration. We find that acyl migration is both kinetically and thermodynamically more favorable. These results are consistent with experimental observations and are rationalized based on conformational, structural, and orbital interaction analysis. We proceed to investigate the semipinacol rearrangement in trans-fused β-lactam diol and propose that this system undergoes a reversed selectivity which favors the alkyl migration.

The ability to accurately calculate relative energies of fullerenes is important in many areas of computational nanotechnology. Because of the large size of fullerenes, their relative energies cann...

Using hydrogen as an energy carrier requires new technological solutions for its onboard storage. The exploration of two-dimensional (2D) materials for hydrogen storage technologies has been motivated by their open structures, which facilitates fast hydrogen kinetics. Herein, the hydrogen storage properties of lightweight metal functionalized r57 haeckelite sheets are studied using density functional theory (DFT) calculations. H2 molecules are adsorbed on pristine r57 via physisorption. The hydrogen storage capacity of r57 is improved by decorating it with alkali and alkaline-earth metals. In addition, the in-plane substitution of r57 carbons with boron atoms (B@r57) both prevents the clustering of metals on the surface of 2D material and increases the hydrogen storage capacity by improving the adsorption thermodynamics of hydrogen molecules. Among the studied compounds, B@r57-Li4, with its 10.0 wt% H2 content and 0.16 eV/H2 hydrogen binding energy, is a promising candidate for hydrogen storage applications. A further investigation, as based on the calculated electron localization functions, atomic charges, and electronic density of states, confirm the electrostatic nature of interactions between the H2 molecules and the protruding metal atoms on 2D haeckelite sheets. All in all, this work contributes to a better understanding of pure carbon and B-doped haeckelites for hydrogen storage.

We present a systematic assessment of the density functional tight binding (DFTB) method for calculating heats of formation of fullerenes with isodesmic-type reaction schemes. We show that DFTB3-D/3ob can accurately predict Δf H values of the 1812 structural isomers of C60 , reproduce subtle trends in Δf H values for 24 isolated pentagon rule (IPR) isomers of C84 , and predict Δf H values of giant fullerenes that are in effectively exact agreement with benchmark DSD-PBEP86/def2-QZVPP calculations. For fullerenes up to C320 , DFTB Δf H values are within 1.0 kJ mol-1 of DSD-PBEP86/def2-QZVPP values per carbon atom, and on a per carbon atom basis DFTB3-D/3ob yields exactly the same numerical trend of (Δf H [per carbon] = 722n-0.72 + 5.2 kJ mol-1 ). DFTB3-D/3ob is therefore an accurate replacement for high-level DHDFT and composite thermochemical methods in predicting of thermochemical stabilities of giant fullerenes and analogous nanocarbon architectures.

Noncovalent interactions are an integral part of the modern catalysis toolbox. Although stronger noncovalent interactions such as hydrogen bonding are commonly the main driving force of catalysis, π-π interactions typically provide smaller additional stabilizations, for example, to afford selectivity enhancements. Here, it is shown computationally that pristine graphene flakes may efficiently catalyze the skeletal inversions of various benzannulated cyclooctatetraene derivatives, providing an example of a catalytic process driven solely by π-π stacking interactions. Hereby, the catalytic effect results from disproportionate shape complementarity between catalyst and transition structure compared with catalyst and reactant. An energy decomposition analysis reveals electrostatic and, especially with increasing system size, to a larger extent, dispersion interactions as the origin of stabilization.

Shape complementarity between catalyst and transition state structure is one of the cornerstones of chemical catalysis. Likewise, noncovalent interactions play a major role in catalysis. It has been predicted computationally and recently confirmed experimentally [Kroeger, A. A.; Hooper, J. F.; Karton, A. ChemPhysChem, 2020, 21, 1675-1681] that pristine graphene can efficiently catalyze chemical processes via π-interactions and shape complementarity. Here we show that other two-dimensional materials with different electronic structures and chemical compositions (h-BN and graphane) can also catalyze chemical processes that proceed via planar transition state structures. These include the bowl-to-bowl inversions in corannulene and sumanene and the rotation about the C-C bond in substituted biphenyls. This catalytic activity is achieved through shape complementarity between planar nanomaterial and planar transition state structure, enabling disproportionate stabilization of the transition state structures over the nonplanar reactants and products. A DFT-based energy decomposition analysis shows that this catalytic activity is mainly driven by dispersion and electrostatic forces, which together outweigh the Pauli repulsion term. These findings enrich and expand the concept of catalysis by pristine 2D materials.

11 pags., 8 figs., 1 tab., The relatively weak London dispersion forces are the only interactions that could cause aggregation between simple aromatic molecules. The use of molecular dynamics and high-levelab initiocomputer simulations has been used to describe the aggregation and interactions between molecular systems containing benzene, naphthalene and anthracene. Mixtures containing one type of molecule (homogenous) and more than one type of molecule (heterogenous) were considered. Our results indicate that as molecular weight increases so does the temperature at which aggregation will occur. In all simulations, the mechanism of aggregation is through small clusters coalescing into larger clusters. The structural analysis of the molecules within the clusters reveals that benzene will orient itself in T-shaped and parallel displaced configurations. Molecules of anthracene prefer to orient themselves in a similar manner to a bulk crystal with no T-shaped configuration observed. The aggregation of these aromatic molecules is discussed in the context of astrochemistry with particular reference to the dust formation region around stars., NAMD was developed by the Theoretical and Computational Biophysics Group in the Beckman Institute for Advanced Science and Technology at the University of Illinois at UrbanaChampaign. This work was in part supported by resources provided by the Pawsey Supercomputing Centre with funding from the Australian Government and the Government of Western Australia, with the assistance of computational resources from the Pople high-performance computing cluster of the Faculty of Science at the University of Western Australia and with the assistance of resources from the National Computational Infrastructure (NCI), which is supported by the Australian Government. AK gratefully acknowledges an Australian Research Council (ARC) Future Fellowship (Project No. FT170100373). I. S. M. fellowship is funded by Australian Research Council (No. FT140100191). I. C. acknowledges funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007– 2013)/ERC2013-SyG, Grant Agreement No. 610256 NANOCOSMOS. DT acknowledges MEAE and MESRI for the financial support.

Inverse vulcanization is a copolymerization of elemental sulfur and alkenes that provides unique materials with high sulfur content (typically ≥50% sulfur by mass). These polymers contain a dynamic and reactive polysulfide network that creates many opportunities for processing, assembly, and repair that are not possible with traditional plastics, rubbers and thermosets. In this study, we demonstrate that two surfaces of these sulfur polymers can be chemically joined at room temperature through a phosphine or amine-catalyzed exchange of the S–S bonds in the polymer. When the nucleophile is pyridine or triethylamine, we show that S–S metathesis only occurs at room temperature for a sulfur rank > 2—an important discovery for the design of polymers made by inverse vulcanization. This mechanistic understanding of the S–S metathesis was further supported with small molecule crossover experiments in addition to computational studies. Applications of this chemistry in latent adhesives, additive manufacturing, polymer repair, and recycling are also presented.

Despite versatile applications of functionalized graphene in catalysis, applications of pure, unfunctionalized graphene in catalysis are in their infancy. This work uses both computational and experimental approaches to show that single-layer graphene can efficiently catalyze the racemization of axially chiral BINOL in solution. Using double-hybrid density functional theory (DHDFT) we calculate the uncatalyzed and catalyzed Gibbs free reaction barrier heights in a number of representative solvents of varying polarity: benzene, diphenyl ether, dimethylformamide (DMF), and water. These calculations show that (i) graphene can achieve significant catalytic efficiencies (▵▵G≠cat ) varying between 47.2 (in diphenyl ether) and 60.7 (in DMF) kJ mol-1 . An energy decomposition analysis reveals that this catalytic activity is driven by electrostatic and dispersion interactions. Based on these computational results, we explore the graphene-catalyzed racemization of axially chiral BINOL experimentally and show that single-layer graphene can efficiently catalyze this process. Whilst the uncatalyzed racemization requires high temperatures of over 200 °C, a pristine single-layer graphene catalyst makes it accessible at 60 °C.

Green phosphorus and its monolayer variant, green phosphorene (GreenP), are the recent members of two-dimensional (2D) phosphorus polymorphs. The new polymorph possesses the high stability, tunable direct bandgap, exceptional electronic transport, and directionally anisotropic properties. All these unique features could reinforce it the new contender in a variety of electronic, optical, and sensing devices. Herein, we present gas-sensing characteristics of pristine and defected GreenP towards major environmental gases (i. e., NH3, NO, NO2, CO, CO2, and H2O) using combination of the density functional theory, statistical thermodynamic modeling, and the non-equilibrium Green's function approach (NEGF). The calculated adsorption energies, density of states (DOS), charge transfer, and Crystal Orbital Hamiltonian Population (COHP) reveal that NO, NO2, CO, CO2 are adsorbed on GreenP, stronger than both NH3 and H2O, which are weakly physisorbed via van der Waals interactions. Furthermore, substitutional doping by sulfur can selectively intensify the adsorption towards crucial NO2 gas because of the enhanced charge transfer between p orbitals of the dopant and the analyte. The statistical estimation of macroscopic measurable adsorption densities manifests that the significant amount of NO2 molecules can be practically adsorbed at ambient temperature even at the ultra-low concentration of part per billion (ppb). In addition, the current-voltage (I-V) characteristics of S-doped GreenP exhibit a variation upon NO2 exposure, indicating the superior sensitivity in sensing devices. Our work sheds light on the promising application of the novel GreenP as promising chemical gas sensors.

Polymeric carbon nitride materials have been used in numerous light‐to‐energy conversion applications ranging from photocatalysis to optoelectronics. For a new application and modelling, we first refined the crystal structure of potassium poly(heptazine imide) (K‐PHI)—a benchmark carbon nitride material in photocatalysis—by means of X‐ray powder diffraction and transmission electron microscopy. Using the crystal structure of K‐PHI, periodic DFT calculations were performed to calculate the density‐of‐states (DOS) and localize intra band states (IBS). IBS were found to be responsible for the enhanced K‐PHI absorption in the near IR region, to serve as electron traps, and to be useful in energy transfer reactions. Once excited with visible light, carbon nitrides, in addition to the direct recombination, can also undergo singlet–triplet intersystem crossing. We utilized the K‐PHI centered triplet excited states to trigger a cascade of energy transfer reactions and, in turn, to sensitize, for example, singlet oxygen (1O2) as a starting point to synthesis up to 25 different N‐rich heterocycles., The triplet excited states of the new heterogeneous triplet sensitizer, potassium poly(heptazine imide),can be used to trigger a cascade of energy‐transfer reactions and, in turn, to sensitize, for example, singlet oxygen (1O2), as a starting point to synthesize N‐rich heterocycles. In this way aldoximes can be converted into 1,2,4‐oxadiazoles under visible light irradiation.

The equilibrium geometry of the singlet ground electronic state of the bent isomer of C5H2, bent-pentadiynylidene (4; X ∼ 1 A 1 ; C 2 v ), has been theoretically investigated by means of the highly accurate W3-F12 thermochemical protocol. Five isomers of C5H2, namely linear-pentadiynylidene (1; X ∼ 3 Σ g - ; D ∞ h ), ethynylcyclopropenylidene (2; X ∼ 1 A ′ ; C s ), pentatetraenylidene (3; X ∼ 1 A 1 ; C 2 v ), ethynylpropadienylidene (5; X ∼ 1 A ′ ; C s ), and 3-(didehydrovinylidene)cyclopropene (6; X ∼ 1 A 1 ; C 2 v ) had already been identified in the laboratory. With respect to 1, the relative energy difference calculated at the CCSDT(Q)/CBS level of theory including zero-point vibrational energy corrections are: 0.66 (2), 13.53 (3), 14.12 (4), 15.40 (5), and 20.01 (6) kcal mol−1, respectively. Isomers 2–6 are associated with a non-zero dipole moment ( μ ≠ 0 ), however, except 4, all the other four isomers were identified by Fourier Transform Microwave spectroscopy, including 5 and 6 which lie higher in energy. Isomer 4 remains elusive to date. We believe that the theoretical data such as, optimal geometry, dipole moment, rotational and centrifugal distortion constants, harmonic vibrational frequencies, infra-red intensities, and isotopic shifts (12C–13C) in harmonic vibrational frequencies presented here would assist experimentalists in the identification of this elusive molecule (4).

In this work, we use high-level ab initio procedures to show that the high-energy isomers of C7H2 with a planar tetracoordinate carbon (ptC) atom serve as reactive intermediate leading to the forma...

Crotonaldehyde, a common environmental pollutant and product of endogenous lipid peroxidation, reacts with guanine to form DNA adducts with pronounced genotoxicity and mutagenicity. Here, we explore the molecular mechanism of this adduct formation using double-hybrid density functional theory methods. The reaction can be envisaged to occur in a two-step fashion via an aza-Michael addition leading to an intermediate ring-open adduct followed by a cyclization reaction giving the mutagenic ring-closed adduct. We find that (i) a 1,2-type addition is favored over a 1,4-type addition for the aza-Michael addition, and (ii) an initial tautomerization of the guanine moiety in the resulting ring-open adduct significantly reduces the barrier toward cyclization compared to the direct cyclization of the ring-open adduct in its keto-form. Overall, the aza-Michael addition is found to be rate-determining. We further find that participation of a catalytic water molecule significantly reduces the energy barriers of both the addition and cyclization reaction. © 2018 Wiley Periodicals, Inc.

The potent antioxidant α-tocopherol is known to trap two hydroxyl radicals leading to the formation of the experimentally observed α-tocopherylquinone product. Based on double-hybrid density functional theory calculations, we propose for the first time, a reaction mechanism for the conversion of α-tocopherol to α-tocopherylquinone. We find that a water-catalysed ring-opening reaction plays a key role in this conversion. The water catalysts act as proton shuttles facilitating the proton transfers and reducing the ring strain in the cyclic transition structures. On the basis of the proposed reaction mechanism, we proceed to design an antioxidant with potentially enhanced antioxidant properties.

Efficient chemical gas detection is of great importance for various functionalities (such as leakage detection of hazardous and explosive gases in industrial safety systems). The recent discovery of 2D black phosphorene (BlackP) has created intensive interests toward nanosensors because of its maximized surface-to-volume ratio and exceptional carrier mobility that potentially deliver the superior performance than the conventional transition-metal oxides sensors. In this work, we have performed first-principles DFT calculations coupled with the statistical analysis to unravel the structural, electronic, and gas-sensing characteristics of pristine, defected, and metal-substituted BlackP toward toxic H2S and SO2 gas molecules. Our findings have revealed that pristine BlackP weakly interacts with both H2S and SO2 by van der Waals (vdW) forces characterized by the small binding energies. The analysis of electronic properties via the density of states (DOS) indicates that there is a negligible change in DOS aft...

Simultaneous loading of hydrophobic and hydrophilic drugs into a drug delivery system is a difficult task and challenges still remain due to opposite nature of drugs. So far, most of the drug delivery systems have been designed based on liposomes, dual emulsions or porous nano-silica cavities. The application of Graphene and its oxidized derivatives as nanocarriers (NCs) have grown rapidly in the past few years. The first part of this study, using molecular modeling methods, provides details on the possibility and the mechanism of simultaneous loading of two hydrophobic and hydrophilic drugs, Rifampicin and Isoniazid, into graphene oxide (GO). The results confirmed the possibility of simultaneous loading of drugs in GO. The binding energies, calculated at the B3LYP-D3/6-31G(d) level of theory, are: −46.5 and −14.0 kJ mol−1 for Isoniazid and Rifampicin, respectively. Drugs loading, as also evidenced in the second part of study experimentally. The drug-loaded NCs were coated with biopolymers of Chitosan and Gum Tragacanth. SEM results confirmed that GO-NCs have produced with a diameter

Accurate double-hybrid density functional theory and isodesmic-type reaction schemes are utilized to report accurate estimates of the heats of formation (ΔfH) for all 24 isolated-pentagon-rule isomers of the third most abundant fullerene, C84. Kinetic stabilities of these C84 isomers are also considered via C–C bond cleavage rates (Pcleav) calculated using density functional theory. Our results show that the relative abundance of C84 fullerene isomers observed in arc discharge synthesis is the result of both thermochemical and kinetic factors. This provides timely insight regarding the characterization of several C84 isomers that have been obtained experimentally to date. For instance, the established assignments of C84 isomers of (using the Fowler–Manolopoulos numbering scheme) 22 [D2(IV)], 23 [D2d(II)], 19 [D3d], 24 [D6h], 11 [C2(IV)], and 4 [D2d(I)] are consistent with the relative ΔfH and Pcleav values for these structures. However, our thermochemical and kinetic stabilities of Cs isomers 14, 15, and ...

Cholesterol oxidase (ChOx), a member of the glucose-methanol-choline (GMC) family, catalyzes the oxidation of the substrate via a hydride transfer mechanism and concomitant reduction of the FAD cofactor. Unlike other GMC enzymes, the conserved His447 is not the catalytic base that deprotonates the substrate in ChOx. Our QM/MM MD simulations indicate that the Glu361 residue acts as a catalytic base facilitating the hydride transfer from the substrate to the cofactor. We find that two rationally chosen point mutations (His447Gln and His447Asn) cause notable decreases in the catalytic activity. The binding free energy calculations show that the Glu361 and His447 residues are important in substrate binding. We also performed high-level double-hybrid density functional theory simulations using small model systems, which support the QM/MM MD results. Our work provides a basis for unraveling the substrate oxidation mechanism in GMC enzymes in which the conserved histidine does not act as a base.

Smart regulation of substance permeability through porous membranes is highly desirable for membrane applications. Inspired by the stomatal closure feature of plant leaves at relatively high temperature, here we report a nano-gating membrane with a negative temperature-response coefficient that is capable of tunable water gating and precise small molecule separation. The membrane is composed of poly(N-isopropylacrylamide) covalently bound to graphene oxide via free-radical polymerization. By virtue of the temperature tunable lamellar spaces of the graphene oxide nanosheets, the water permeance of the membrane could be reversibly regulated with a high gating ratio. Moreover, the space tunability endows the membrane with the capability of gradually separating multiple molecules of different sizes. This nano-gating membrane expands the scope of temperature-responsive membranes and has great potential applications in smart gating systems and molecular separation., The smart regulation of substance permeability is highly desirable for membrane separation technologies. Here, the authors design a poly(N-isopropylacrylamide)-grafted graphene oxide membrane with temperature tunable lamellar spaces, allowing for water gating and size-variable molecular separations.

We evaluate the performance of carbon force fields for 1811 C60 PW6B95-D3/Def2-QZVP isomerization energies. Several force fields (most notably the machine-learning GAP-20 potential) exhibit a high statistical correlation with the DFT isomerization energies. Therefore, linear scaling of the isomerization energies can significantly improve the accuracy. The best scaled force fields attain mean-absolute deviations of 8.5 (GAP-20), 12.3 (LCBOP-I and REBO-II), and 13.3 (ABOP) kcal mol−1, which translate to mean-absolute relative deviations of 4.7% (GAP-20), 6.5% (LCBOP-I), 6.6% (REBO-II) and 7.1% (ABOP). Therefore, these force fields offer a computationally economical way for exploring the relative energies of fullerenes.

We calculate the CCSD(T)/CBS complexation energies of C6X6⋯C2Xn complexes (X = F, Cl; n = 2, 4) by means of the W1-F12 and CCSD(T)/MP2(CBS) procedures. These complexes involve π–π stacking, charge-transfer, and van der Waals interactions and their complexation energies range between 11.1 (C6F6⋯C2F2) and 34.0 (C6Cl6⋯C2Cl4) kJ mol−1. We use our best CCSD(T)/CBS data to assess the performance of DFT, double-hybrid DFT (DHDFT), and standard/composite ab initio methods. The G4 and G4(MP2) composite methods show relatively poor performance with root-mean-square deviations (RMSDs) of 8.7 and 6.3 kJ mol−1, respectively. With the main exception of the Minnesota functionals, DFT functionals without a dispersion correction do not predict binding in these complexes. Most of the conventional DFT procedures attain RMSDs above the ‘chemical accuracy’ threshold. The best performing functionals with RMSDs ≤2.0 kJ mol−1 are: B3LYP-D3, PW6B95-D3, LC-ωPBE-D3, PWPB95-D3, B2GP-PLYP-D3, and B2-PLYP-D3.

We examine the reaction of ethanol with glyoxal to form hemiacetal by means of the high-level G4(MP2) procedure. In this reaction, an intermolecular proton transfer is coupled with the formation of a covalent C O bond between the two molecules. We find a novel catalytic reaction mechanism in which an H 2 SO 4 catalyst reduces the barrier height from ∆ H ‡ 298 = 140.2 to 16.3 kJ mol −1 . It is well established that H 2 SO 4 can effectively catalyse intramolecular proton transfers. This letter shows that H 2 SO 4 can catalyse an intermolecular proton transfer that is coupled with a covalent bond formation.