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In the search for new nonlinear optical (NLO) switching devices, expanded porphyrins have emerged as ideal candidates thanks to their tunable chemical and photophysical properties. Introducing meso-substituents to these macrocycles is a successful strategy to enhance the NLO contrasts. Despite its potential, the influence of meso-substitution on their structural and geometrical properties has been scarcely investigated. In this work, we pursue to grasp the underlying pivotal concepts for the fine-tuning of the NLO contrasts of hexaphyrin-based molecular switches, with a particular focus on the first hyperpolarizability related to the hyper-Rayleigh scattering (βHRS). Building further on these concepts, we also aim to develop a rational design protocol. Starting from the (un)substituted hexaphyrins with various π-conjugation topologies and redox states, structure-property relationships are established linking aromaticity, photophysical properties and βHRS responses. Ultimately, inverse molecular design using the best-first search algorithm is applied on the most favorable switches with the aim to further explore the combinatorial chemical compound space of meso-substituted hexaphyrins in search of high-contrast NLO switches. Two definitions of the figure-of-merit of the switch performance were used as target objectives in the optimization problem. Several meso-substitution patterns and their underlying characteristics are identified, uncovering molecular symmetry and the electronic nature of the substituents as the key players for fine-tuning the βHRS values and NLO contrasts of hexaphyrin-based switches.

This work evaluated the potential of a synthesized faujasite-type zeolite Y as an adsorbent for the removal of relevant heavy metals such as silver (Ag+), copper (Cu2+), and cobalt (Co2+). The adsorption data of Ag+, Cu2+, and Co2+ ions were determined experimentally at pH 6 and temperatures of 298, 308, and 318 K. Two theoretical approaches have been applied based on statistical physics modeling and density functional theory (DFT) to understand and characterize the ion exchanges involved in the removal of all metals. Results showed that this zeolite was more efficient for the adsorption of Ag+ via cation-exchange. Based on the physical modelling, the removal of heavy metals on this zeolite was mono and multi-ionic (simple and multi-interactions), where the ions interacted via one and two adsorption sites. It was also noted that the temperature increment generated more available functional groups of the zeolite, facilitating the access to the smaller cavities and the interactions with the adsorbent. Adsorption energies for removing these metals with tested zeolite were slightly endothermic and were consistent with the typical values reported for ion exchange systems of heavy metals + zeolites. DFT results demonstrated that these cationic exchange energies depend on the nature of precursor salt, but with the same ranking. Both statistical and DFT approaches agreed that exchange Ag+ in zeolite Y was easier than Cu2+ and Co2+. Overall, the application of both theoretical approaches provided a reliable interpretation of the adsorption mechanism.

This work evaluated the potential of a synthesized faujasite-type zeolite Y as an adsorbent for the removal of relevant heavy metals such as silver (Ag+), copper (Cu2+), and cobalt (Co2+). The adsorption data of Ag+, Cu2+, and Co2+ ions were determined experimentally at pH 6 and temperatures of 298, 308, and 318 K. Two theoretical approaches have been applied based on statistical physics modeling and density functional theory (DFT) to understand and characterize the ion exchanges involved in the removal of all metals. Results showed that this zeolite was more efficient for the adsorption of Ag+ via cation-exchange. Based on the physical modelling, the removal of heavy metals on this zeolite was mono and multi-ionic (simple and multi-interactions), where the ions interacted via one and two adsorption sites. It was also noted that the temperature increment generated more available functional groups of the zeolite, facilitating the access to the smaller cavities and the interactions with the adsorbent. Adsorption energies for removing these metals with tested zeolite were slightly endothermic and were consistent with the typical values reported for ion exchange systems of heavy metals + zeolites. DFT results demonstrated that these cationic exchange energies depend on the nature of precursor salt, but with the same ranking. Both statistical and DFT approaches agreed that exchange Ag+ in zeolite Y was easier than Cu2+ and Co2+. Overall, the application of both theoretical approaches provided a reliable interpretation of the adsorption mechanism.

The spectroscopic study of pathological calcifications (including kidney stones) is extremely rich and helps to improve the understanding of the physical and chemical processes associated with their formation. While Fourier transform infrared (FTIR) imaging and optical/electron microscopies are routine techniques in hospitals, there has been a dearth of solid-state NMR studies introduced into this area of medical research, probably due to the scarcity of this analytical technique in hospital facilities. This work introduces effective multinuclear and multidimensional solid-state NMR methodologies to study the complex chemical and structural properties characterizing kidney stone composition. As a basis for comparison, three hydrates (n=1, 2 and 3) of calcium oxalate are examined along with nine representative kidney stones. The multinuclear magic angle spinning (MAS) NMR approach adopted investigates the 1H, 13C, 31P and 31P nuclei, with the 1H and 13C MAS NMR data able to be readily deconvoluted into the constituent elements associated with the different oxalates and organics present. For the first time, the full interpretation of highly resolved 1H NMR spectra is presented for the three hydrates, based on the structure and local dynamics. The corresponding 31P MAS NMR data indicates the presence oflow-level inorganic phosphate species; however, the complexity of these data make the precise identification of the phases difficult to assign. This work provides physicians, urologists and nephrologists with additional avenues of spectroscopic investigation to interrogate this complex medical dilemma that requires real, multitechnique approaches to generate effective outcomes.

The spectroscopic study of pathological calcifications (including kidney stones) is extremely rich and helps to improve the understanding of the physical and chemical processes associated with their formation. While FTIR imaging and optical/electron microscopies are routine techniques in hospitals, there has been a dearth of solid state NMR studies introduced into this area of medical research, probably due to the scarcity of this analytical technique in hospital facilities. This work introduces effective multinuclear and multi-dimensional solid state NMR methodologies to study the complex chemical and structural properties characterising kidney stone composition. As a basis for comparison three hydrates (n = 1, 2 and 3) of calcium oxalate are examined along with nine representative kidney stones. The multinuclear MAS NMR approach adopted investigates the 1H, 13C, 31P and 43Ca nuclei, with the 1H and 13C MAS NMR data able to be readily deconvoluted into the constituent elements associated with the different oxalates and organics present. For the first time, the full interpretation of highly resolved 1H NMR spectra is presented for the three hydrates, based on structure and local dynamics. The corresponding 31P MAS NMR data indicates the presence of low-level inorganic phosphate species, however the complexity of these data make the precise identification of the phases difficult to assign. This work provides physicians, urologists and nephrologists with additional avenues of spectroscopic investigation to interrogate this complex medical dilemma that requires real multi technique approaches to generate effective outcomes.

Supramolecular gels form a class of soft materials that has been heavily explored by the chemical community in the past 20 years. While a multitude of experimental techniques has demonstrated its usefulness when characterizing these materials, the potential value of computational techniques has received much less attention. This review aims to provide a complete overview of studies that employ computational tools to obtain a better fundamental understanding of the self-assembly behavior of supramolecular gels or to accelerate their development by means of prediction. As such, we hope to stimulate researchers to consider using computational tools when investigating these intriguing materials. In the concluding remarks, we address future challenges faced by the field and formulate our vision on how computational methods could help overcoming them. ispartof: Gels vol:7 issue:3 pages:1-18 ispartof: location:Switzerland status: Published online

International audience; Introduction: The therapy to reduce urinary oxalate excretion in primary hyperoxaluria type 1 is still required. Case presentation: A 37-year-old hemodialyzed man suffered from systemic oxalosis secondary to primary hyperoxaluria type 1 exhibited a drastic plasma oxalate decrease from 110 to 22 µmol/L two months after adjunction of lanthanum carbonate to classical treatment (intensive hemodialysis with pyridoxine). A 34-year-old woman with normal kidney function presented 10 years of bilateral kidney stones due to primary hyperoxaluria type 1 [hyperoxaluria (109.2 mg/24 h), plasma oxalate (56.0 µmol/L)]. The oxalate level remained uncontrolled despite of low oxalate-normal calcium diet, pyridoxine and increased water intake though the lanthanum carbonate adjunction resulted in significant decrease in plasma oxalate and oxaluria. Conclusion: We report the lanthanum efficacy in reducing circulating and urinary oxalate levels in type 1 primary hyperoxaluria. Possible mechanism of observed falls in oxalate concentration would be a decrease in the intestinal absorption of oxalate.

We present here a versatile computational code named "elecTric fIeld generaTion And maNipulation (TITAN)," capable of generating various types of external electric fields, as well as quantifying the local (or intrinsic) electric fields present in proteins and other biological systems according to Coulomb's Law. The generated electric fields can be coupled with quantum mechanics (QM), molecular mechanics (MM), QM/MM, and molecular dynamics calculations in most available software packages. The capabilities of the TITAN code are illustrated throughout the text with the help of examples. We end by presenting an application, in which the effects of the local electric field on the hydrogen transfer reaction in cytochrome P450 OleTJE enzyme and the modifications induced by the application of an oriented external electric field are examined. We find that the protein matrix in P450 OleTJE acts as a moderate catalyst and that orienting an external electric field along the Fe─O bond of compound I has the biggest impact on the reaction barrier. The induced catalysis/inhibition correlates with the calculated spin density on the O-atom. © 2019 Wiley Periodicals, Inc.

Expanded porphyrins are currently recognized as the ideal test bed to explore the correlation between molecular properties and (anti)aromaticity since they can adopt different π-conjugation topologies and change easily the number of π-electrons along the conjugation pathway. From recent studies, aromaticity indeed emerges as the guiding concept to rationalize the spectroscopic features and the two-photon absorption cross sections in expanded porphyrins. However, from the theoretical point of view, the complex structure-property relationship between aromaticity, π-conjugation topology, and photophysical properties is not fully understood yet. To unravel such structure-property relationships, we focused on octaphyrin(1.1.1.1.1.1.1.1) macrocycles since they are flexible enough to provide twisted-Hückel, Möbius, and Hückel untwisted topologies with distinct aromaticity character. In this work, the (anti)aromaticity of the different states was first quantified using different aromaticity criteria. Second, the fingerprints of aromaticity on UV/vis spectra were elucidated. Importantly, we found that the absorption spectra of certain antiaromatic Hückel structures are characterized by more intense absorption bands than its aromatic homologues, contrary to the general statement that antiaromatic expanded porphyrins exhibit significantly attenuated absorption bands compared to aromatic ones. Finally, the role of aromaticity and π-conjugation topology on linear and nonlinear optical properties was scrutinized and our results pinpoint the importance of molecular topology and symmetry on the first and second hyperpolarizabilities. Overall, we demonstrate that expanded porphyrins upon topology interconversions can act as efficient nonlinear optical switches. ©

In molecular mechanochemistry, the chemical properties of a reactant system are modified through the absorption of mechanical energy at the single molecular level, as opposed to thermochemistry (heat), electrochemistry (electrical current) and photochemistry (light). In this proof-of-concept paper, we present a theoretical approach to rationalize and predict the change in chemical properties and concepts when an external stretching force, Fext, is applied to a chemical bond. By considering perturbations to the total molecular energy due to Fext, a series of mechanochemical response indices are obtained within the framework of conceptual density functional theory (DFT). Trends in these indices monitoring the change in hardness and electrophilicity among others, were rationalized for a number of diatomic molecules in terms of the ground-state geometry and the frontier molecular orbitals of the molecule. Finally, we present a set of rules that can be easily adopted for polyatomic molecules to predict the changing chemical reactivity of single molecules when subjected to an external force.

In this work, we report a systematic study on the global and local aromaticity of acenes using a series of model structures from 2-acene to 11-acene. A recently developed ansatz, an information-theoretic approach coached into density functional reactivity theory has been employed, which essentially provides different density functionals characterizing the molecular electron density distribution. Based on the correlation analysis of six conventional aromaticity indices with eight information-theoretic quantities, we examined the aromaticity of acenes from both global and local perspectives. From the global aromaticity viewpoint, our results suggest that different descriptors based on various physicochemical properties are intrinsically dependent. A novel laminated feature ruling local aromaticity of acenes has been unveiled, from which we found that the distance from the terminal rings plays the critical role. Based on the shape of the correlation plots between the conventional aromaticity indices and information-theoretic quantities, the latter could be separated into three subgroups. The seemingly contradictory results from global and local aromaticity perspectives not only present us the uniqueness of the acene systems but all demonstrate the effectiveness of the information-theoretic approach from density functional reactivity theory. Besides strengthening the validity of a series of new aromaticity descriptors, our results should lead to more clear insights into the chemical significance of the information-theoretic quantities.

Objective Hospitalization is generally accompanied by changes in food intake. Patients typically receive hospital meals upon personal preference within the framework of the food administration services of the hospital. In the present study, we assessed food provision and actual food and snack consumption in older patients admitted for elective hip or knee arthroplasty. Design A prospective observational study. Setting Orthopedic nursing ward of the Maastricht University Medical Centre+. Participants In the present study, n=101 patients (age: 67±10 y; hospital stay: 6.1±1.8 d) were monitored during hospitalization following elective hip or knee arthroplasty. Measurements Energy and protein provided by self-selected hospital meals and snacks, and actual energy and protein (amount, distribution, and source) consumed by patients was weighed and recorded throughout 1–6 days. Results Self-selected meals provided 6.5±1.5 MJ·d-1, with 16, 48, and 34 En% provided as protein, carbohydrate, and fat, respectively. Self-selected hospital meals provided 0.75±0.16 and 0.79±0.21 g·kg-1·d-1 protein in males and females, respectively. Actual protein consumption averaged merely 0.59±0.18 and 0.50±0.21 g·kg-1·d-1, respectively. Protein consumption at breakfast, lunch, and dinner averaged 16±8, 18±9, and 20±6 g per meal, respectively. Conclusions Though self-selected hospital meals provide patients with ∼0.8 g·kg-1·d-1 protein during short-term hospitalization, actual protein consumption falls well below 0.6 g·kg-1·d-1 with a large proportion (∼32%) of the provided food being discarded. Alternative strategies are required to ensure maintenance of habitual protein intake in older patients admitted for elective orthopedic surgery. Electronic Supplementary Material Supplementary material is available for this article at 10.1007/s12603-019-1157-2 and is accessible for authorized users.

International audience; The adsorption of GLY-PRO-GLU tripeptide on Au(110) is investigated within the frame of all atom classical mechanics simulations and Density Functional Theory, focusing on the surface reconstruction. It is shown that the tripeptide adsorption reorganizes and restructures the Au(110) surface. A mechanism for the surface restructuration is proposed for both the neutral and zwitterionic form of the peptide at room temperature in Ultra High Vacuum. Diverse residues may be involved in the Au atoms displacement, and in particular glutamic acid, triggering a double proton transfer and the formation of a zwitter ionic state, is found to be responsible for the triggering of the surface reconstruction.

In recent years, a considerable interest has grown in the design of molecular nanowires with an increasing conductance with length. The development of such nanowires is highly desirable because they could play an important role in future molecular-scale circuitry. Whereas the first experimental observation of this nonclassical behavior still has to be realized, a growing number of candidate wires have been proposed theoretically. In this Letter, we point out that all the wires with an anti-Ohmic increasing conductance with length proposed so far share a common characteristic: their diradical character increases with length. The conceptual connection between diradical character and conductance enables a systematic design of such anti-Ohmic wires and explains the difficulty in their syntheses. A strategy is proposed to balance the stability and conductance so that this nonclassical phenomenon can be observed.

In this work, we explore the design of so-called "reversible bithermoelectric switches", molecules which can be switched reversibly between a positive and negative Seebeck coefficient through the application of external stimuli. We focus on heptaphyrins, a class of expanded porphyrins that can be shifted between a Hückel and Möbius topology, and demonstrate that these molecules are promising candidates for such an electronic function. Our calculations lead to the conclusion that the molecular switch between these two π-conjugation topologies causes the thermopower to change considerably from +50 μV/K to -40 μV/K, respectively. We address some of the limitations of our approach and expect that this behavior will be retrieved experimentally as well, although chemical modifications of the molecules and/or electrodes might be required. Bithermoelectric switches could potentially constitute an entirely new class of molecular switches which, instead of switching between an ON and an OFF state (the modus operandi ofmost molecular switches so far), revert the direction of the heat and/or charge transport. This could potentially lead to a wide range of novel technological applications.

A hitherto unexplored class of molecules for molecular force probe applications are expanded porphyrins. This work proves that mechanical force is an effective stimulus to trigger the interconversion between Hückel and Möbius topologies in [28]hexaphyrin, making these expanded porphyrins suitable to act as conformational mechanophores operating at mild (sub‐1 nn) force conditions. A straightforward approach based on distance matrices is proposed for the selection of pulling scenarios that promote either the planar Hückel topology or the three lowest lying Möbius topologies. This approach is supported by quantum mechanochemical calculations. Force distribution analyses reveal that [28]hexaphyrin selectively allocates the external mechanical energy to molecular regions that trigger Hückel–Möbius interconversions, explaining why certain pulling scenarios favor the Hückel two‐sided topology and others favor Möbius single‐sided topologies. The meso‐substitution pattern on [28]hexaphyrin determines whether the energy difference between the different topologies can be overcome by mechanical activation., Use the force: The Hückel and Möbius topology of [28]hexaphyrin can be mechanically locked by applying an external pulling force to different meso positions in a sub‐nano‐Newton force regime. The mechanical energy is distributed to a specific region in the molecule to trigger the interconversion.

The extension of the E = E[N, v] functional for exploring chemical reactivity in a conceptual DFT context to include external electric fields is discussed. Concentrating on the case of a homogeneous field the corresponding response functions are identified and integrated, together with the conventional response functions such as permanent dipole moment and polarizability, in an extended response function tree associated with the E = E[N, v, ϵ] functional. In a case study on the dihalogens F2, Cl2, Br2, I2 the sensitivity of condensed atomic charges (∂q/∂ϵ) is linked to the polarizability of the halogen atoms. The non-integrated (∂ρ(r)/∂ϵ) response function, directly related to the field induced density change, is at the basis of these features. It reveals symmetry breaking for a perpendicular field, not detectable in its atom condensed counterpart, and accounts for the induced dipole moment directly related to the molecular polarizability. The much higher sensitivity of the electronic chemical potential/electronegativity as compared to the chemical hardness is highlighted. The response of the condensed Fukui functions to a parallel electric field increases when going down in the periodic table and is interpreted in terms of the extension of the outer contours in the non-condensed Fukui function. In the case of a perpendicular field the (∂f(r)/∂ϵ) response function hints at stereoselectivity with a preferential side of attack which is not retrieved in its condensed form. In an application the nucleophilic attack on the carbonyl group in H2CO is discussed. Similar to the dihalogens, stereoselectivity is displayed in the Fukui function for nucleophilic attack (f+) in the case of a perpendicular electric field, and opposite to the one that would arise based on the induced density. Disentangling the expression for the evolution of the Fukui function in the presence of an electric field reveals that this difference can be traced back to local differences in the polarization or induced density between the anionic and the neutral system. This difference may be exploited, e.g. for an appropriately substituted H2CO, to generate enantioselectivity. This journal is

Non-covalent interactions involving aromatic rings play a central role in many areas of modern chemistry. In medicinal and bioorganic chemistry, the intermolecular interactions between the aromatic side chains of amino acids, such as phenylalanine and tyrosine, are of great interest. To enhance the affinity between such aromatic side chains, halogenation is a promising modification strategy. In the current work, the nature and strength of halogenated p-p stacked phenylalanine (Phe) dimers have been investigated using density functional theory, energy decomposition analyses and the non-covalent interaction (NCI) method. Our analysis shows that increasing the degree of halogenation enhances the strength of the stacking interactions and, moreover, the heavier halides (Cl, Br and I) lead to stronger interactions compared to the lighter F. This effect was traced back to local secondary interactions of the halide with the aliphatic C-H bonds of the phenylalanine side chain. Based on the computational findings, a set of peptide hydrogelators was synthesized, and the resulting hydrogel properties were further investigated via dynamic rheometry. Experimental observations can be correlated to the trends found in the theoretical analysis, suggesting that local interactions indeed play a noticeable role in enhancing peptide-based hydrogel strength. This journal is

Density Functional Theory has made the study of biomaterials feasible in the past years leading to better understanding of causes and possible treatments of related pathologies. Although it has been successfully applied in many fields, it has not yet consistently found its way into the field of pathological calcifications. An overview will be given of the studies where this technique has been applied in order to outline the important contributions that it can bring in the field of biomineralization.More specifically, studies on DFT calcifications from calciumoxalates and calcium phosphates, with relevance to bone formation and kidney stones, will be reviewed. Finally, a short outlook on silica mineralization will be presented as well.

Metabolomics is recognized as a crucial scientific domain, promising to advance our understanding of cell biology, physiology and medicine. Tandem mass spectrometry (MS/MS) has strong potential to elucidate the metabolites in complex biological samples and to become a standard tool complementing established techniques. However, despite its potential for answering many key questions, a major challenge in the use of tandem mass spectrometry for characterizing metabolites lies in a lack of computational tools for accurate annotation and structure identification allowing us to turn complex data into molecular knowledge. Chemo-informatics and related machine-learning in silico fragmentation tools have already been established and used for different classes of metabolites. For the classes of metabolites where existing chemo-informatics approaches produce insufficiently accurate predictions a supervised machine learning based strategy can be used to predict possible molecular structures from “unassigned” experimental tandem MS data. Here, we propose a new innovative in silico approach employing quantum mechanical (QM) methods in order to predict ion formation and subsequent fragmentation patterns of arbitrary small molecules and validate putative annotations of tandem mass spectrometry (MS) data. The focus is on the evaluation of a new conceptual density functional theory (CDFT) nuclear reactivity descriptor of the nuclear Fukui function type, that characterizes the forces that the atomic nuclei experience due to proton attachment and captures the onset of the change in the nuclear positions induced by it. A series of test compounds for which high quality experimental data exist and that were investigated before in a more approximate theoretical framework have been examined. The output of these calculations provides a list of the most probable molecular structures predicted to match the experimental tandem MS spectrum (“de novo metabolite identification”).

International audience; Dans cette contribution, nous étudions les calculs rénaux contenant la whitlockite (Wk). En premier lieu, la présence du fer dans la formule stœchiométrique de la Wk est discutée grâce à la fluorescence X. Puis, nous abordons la relation à l’infection à l’aide d’observations au Microscope électronique à balayage (MEB) aptes à mettre en évidence de possibles empreintes de bactéries. Elles montrent que le processus infectieux est établi pour des teneurs supérieures à 20%, ceux-ci ne pouvant toutefois pas être écartés en dessous de cette teneur. Finalement, l’étude de relation entre la taille des cristaux de Wk et l’infection par DRX ne permet pas de l’établir. Le message pour le clinicien est le suivant : pour un patient asymptomatique, si le calcul ne contient ni struvite, ni apatite carbonatée et moins de 20% de Wk, il convient d’observer par MEB les calculs rénaux afin de pouvoir écarter ou non un processus infectieux.

International audience; Single-atom alloys (SAAs) are emerging materials containing isolated metal atoms dispersed on host metal surfaces, exhibiting unique reactivity compared with the corresponding monometallic counterparts. However, the stability of the isolated atoms in the host metal has hardly been studied, although, metal segregation has been commonly observed in bimetallic nanoparticles under reaction conditions. In this work we focus on single-atom Pt anchored on various metallic support surfaces. Density Functional Theory (DFT) calculations coupled with environmental segregation energy analysis are performed to map the segregation trends of 22 different Pt-SAA surfaces under various hydrogen conditions. The results show the high stability of single-atom Pt in Ni, Co, Rh and Ir host metallic surfaces while no stability is predicted on Au and Ag surfaces. For Pd and Cu host supports, the single-atom Pt is found to be stable on specific surface facets and within definite temperature and pressure conditions. This work brings an important understanding of SAA systems through the prediction of of surface atomic ordering changes under operating conditions which related to the reactivity will ultimately allow the design of more efficient catalysts.

Interpreting the interaction between the amorphous silica surface and water is a key step to understand its physicochemical properties. However, due to the flexibility of the structure and the distribution of types and geometries of the silanols one can obtain a broad range of interaction energies, as was already shown in former studies. This time we were able to investigate the distribution of silanols in relation with the calculated interaction energies, and thus designate those different silanols sites. Different dispersion-correction PBE-D (PBE + D2, D3, D3-BJ, TS, TS-HI, MBD, and FI-MBD) and meta-GGA SCAN methods has been used to quantify the interactions between water and defined silanols sites of the surface. All the methods give similar interaction energies, showing equivalent performances of SCAN and PBE-D methods to describe week interactions in our system. Following various routes, we identified a protocol of calculation in order to compute the interaction energies more accurately, taking into consideration the van der Waals (vdW) forces. Once different silanols are correctly described within the calculation level, it is clear that the geometry and environment determine its chemistry. Furthermore, the possible deformation of the silica surface affected by the water interaction is studied. The quantification of the interaction energies is important in order to correctly scale the results and confront with the experiments. With this information in mind, one can think about synthesis techniques that modify the silanols distribution of the silica surface in a way to tune its hydrophobicity and acidity.

Silver based-nanoparticles (Ag NPs) have been recently shown to be promising catalysts for the degradation of toxic organic dyes in wastewater despite the challenges of recycling. In this paper, self-supported Ag NPs were obtained at the surface of AgTi2(PO4)3 NASICON-type phosphates through in situ chemical reduction by sodium borohydride (NaBH4). The adopted approach enables the self-growth of zero-valent Ag NPs on the NASICON matrix, and concomitantly leads to the formation of Ag1−xNaxTi2(PO4)3. The crystalline structure, morphology and phase composition of the Ag nanocomposite has been characterized by several techniques. The catalytic performance of the as-fabricated Ag NPs/Ag1−xNaxTi2(PO4)3 has then been verified in the reduction of methylene blue (MB) and methyl orange (MO) dyes, chosen as target pollutants. Our findings reveal a good catalytic activity with an efficiency and time of reaction of respectively ∼ 96.30% and 320 s in the case of the MB reduction and ∼ 94.60% and 270 s in the case of the MOreduction. Additionally, the initial AgTi2(PO4)3 phase can be regenerated via simple calcination route and recycled up to five times with no appreciable loss of catalytic activity.

The focus of this short review is directed towards investigations of the dynamics of nanostructured metallic heterogeneous catalysts and the evolution of interfaces during reaction—namely, the metal–gas, metal–liquid, and metal–support interfaces. Indeed, it is of considerable interest to know how a metal catalyst surface responds to gas or liquid adsorption under reaction conditions, and how its structure and catalytic properties evolve as a function of its interaction with the support. This short review aims to offer the reader a birds-eye view of state-of-the-art methods that enable more realistic simulation of dynamical phenomena at nanostructured interfaces by exploiting resource-efficient methods and/or the development of computational hardware and software.

International audience; Monohydrated and dihydrated calcium oxalates have been widely studied in the literature because of their role in urolithiasis, a mammal pathology responsible for the formation of stones in the kidney. It is clear that the physicochemical environment plays a crucial role in the crystal growth and the resulting morphologies of calcium oxalates. To study these processes, reliable models for the calcium oxalates’ faces, exposed to water and potential additives, are needed. Here, we have used a total surface energy minimization approach to predict the crystal morphology of the calcium oxalate monohydrate and dihydrate phases. Surface energies were calculated at density functional theory level, taking into account surface relaxation and the effect of solvation. An excellent agreement was found between theoretically predicted morphologies and their experimental counterparts obtained by SEM, clearly demonstrating the importance of the inclusion of water in the model for the prediction of morphologies.

When and how do external electric fields (EEFs) lead to catalysis in the presence of a (polar or nonpolar) solvent? This is the question that is addressed here using a combination of molecular dynamics (MD) simulations, quantum mechanical/molecular mechanical calculations with EEF, and quantum mechanical/(local) electric field calculations. The paper focuses on a model reaction, the Menshutkin reaction between CH3I and pyridine in three solvents of varying polarity. Using MD simulations, we find that the EEF causes the solvent to undergo organization; the solvent molecules gradually align with the applied field as the field strength increases. The collective orientation of the solvent molecules modifies the electrostatic environment around the Menshutkin species and induces a global electric field pointing in the opposite direction of the applied EEF. The combination of these two entangled effects leads to partial or complete screening of the EEF, with the extent of screening being proportional to the polarity/polarizability of the solvent. Nevertheless, we find that catalysis of the Menshutkin reaction inevitably emerges once the EEF exceeds the opposing field of the organizing solvent, i.e., once polarization of the Menshutkin complex is observed to set in. Overall, our analysis provides a lucid and pictorial interpretation of the behavior of solutions in the presence of EEFs and indicates that EEF-mediated catalysis should, in principle, be feasible in bulk setups, especially for nonpolar and mildly polar solvents. By application of the charge-transfer paradigm, it is shown that the emergence of OEEF catalysis in solution can be generalized to other reactions as well.

The nature of isolated tungsten oxide (WOx) sites in the dispersed phase on the surface of a β-cristobalite (β-SiO2) support in undoped and Na-or Mn-doped WOx/SiO2 model catalysts used for the oxidative coupling of methane (OCM) has not been explored previously. This work provides a computational model for isolated surface WOx sites (doped and undoped) supported on β-cristobalite (β-SiO2) and computationally explores their molecular structure, degree of hydration, and energetics over a wide range of OCM-relevant temperatures from 500 to 1300 K. Ab initio thermodynamic analysis showed that the most stable molecular configuration of the surface sites in all cases (WOx, Na-WOx, Mn-WOx) was the digrafted, dioxo pseudotetrahedral WO4. The thermal stability of the surface WO4 sites was in the order Na-WO4 ≫ WO4 > Mn-WO4 in the OCM-relevant temperature range of 850-1300 K. A spin analysis of an Mn-WO4 isolated surface site indicates a paramagnetic high-spin Mn2+-O-W6+ electronic state, in line with literature reports. The computed frequencies for isolated surface WO4 sites agree well with the experimental in situ Raman spectra of the corresponding model catalysts, proving their existence. Finally, steady-state OCM studies showed that the C2 selectivity was highest for Na-WO4 sites, followed by Mn-WO4 and WO4, a trend mimicking the degree of distortion in the molecular geometry of each site. Na-WO4 exhibited the lowest reactivity toward CH4 and the highest degree of Wâ• O bond elongation.

The nature of isolated tungsten oxide (WOx) sites in the dispersed phase on the surface of a β-cristobalite (β-SiO2) support in undoped and Na-or Mn-doped WOx/SiO2 model catalysts used for the oxidative coupling of methane (OCM) has not been explored previously. This work provides a computational model for isolated surface WOx sites (doped and undoped) supported on β-cristobalite (β-SiO2) and computationally explores their molecular structure, degree of hydration, and energetics over a wide range of OCM-relevant temperatures from 500 to 1300 K. Ab initio thermodynamic analysis showed that the most stable molecular configuration of the surface sites in all cases (WOx, Na-WOx, Mn-WOx) was the digrafted, dioxo pseudotetrahedral WO4. The thermal stability of the surface WO4 sites was in the order Na-WO4 ≫ WO4 > Mn-WO4 in the OCM-relevant temperature range of 850-1300 K. A spin analysis of an Mn-WO4 isolated surface site indicates a paramagnetic high-spin Mn2+-O-W6+ electronic state, in line with literature reports. The computed frequencies for isolated surface WO4 sites agree well with the experimental in situ Raman spectra of the corresponding model catalysts, proving their existence. Finally, steady-state OCM studies showed that the C2 selectivity was highest for Na-WO4 sites, followed by Mn-WO4 and WO4, a trend mimicking the degree of distortion in the molecular geometry of each site. Na-WO4 exhibited the lowest reactivity toward CH4 and the highest degree of Wâ• O bond elongation.

Judiciously applied oriented external electric fields (OEEFs) exert catalytic effects on the kinetics and improve the thermodynamics of chemical reactions. Herein, we examine the ability of OEEFs to assist catalysts and show that the rate of oxidative addition between palladium catalysts and alkyl/aryl electrophiles can be controlled by an OEEF applied along the direction of electron reorganization (the "reaction axis"). The concerted mechanism of oxidative addition proceeds through a transition state with moderate charge transfer character. We demonstrate that OEEFs along the reaction axis can control this charge transfer and impart electrostatic catalysis. When the applied field exceeds a certain critical value (∼0.15 V/Å), we observed a mechanistic crossover from the concerted to a dissociative CSNAr type of reactivity for aryl electrophiles. To our surprise, alkyl electrophiles follow a hitherto unexplored SN2 pathway for the reaction with large transition state stabilization at relatively low OEEFs. A valence-bond state correlation diagram (VBSCD) is employed to comprehend the results. Finally, although the catalytic effect of salt additives in oxidative addition is known, its mechanism is still under debate. Our findings further show evidence that salt additives exert electric-field effects on the rate of cross-coupling reactions, and their cocatalytic effects can be judiciously reproduced by applied external electric fields. As such, we propose that the use of additives (anionic or cationic) is an experimentally viable strategy to implement external electric-field effects in routinely used oxidative addition catalysis.

This paper results from a round table discussion at the CCTC2018 Conference in Changsha City, Hunan, China, in December 2018. It presents a report on the status, prospects, and issues of conceptual density functional theory (CDFT). After a short exposition on the history of CDFT, its fundamentals, philosophy, and successes are highlighted. Then ten issues for reflection on the future of conceptual DFT are formulated and discussed, ending with one or more summarizing statements on the present status of various concepts/principles/practices and proposed directions for future research. The issues include the further analysis of the energy functional, E[N,v], extended to include effects of temperature, solvent, and mechanical forces, basic requirements for physically acceptable response functions as reactivity descriptors, the use of the grand canonical ensemble, the relevance of CDFT for chemical kinetics and thermodynamics, the domain of validity of CDFT-based principles, the combination of CDFT with reaction path calculations, information-theoretic descriptors, and the treatment of excited states and time dependence. The final issue advocates the transition of CDFT from an interpretative to a predictive mode; we believe this is of utmost importance for promoting CDFT as a viable alternative to wave function-based methods for the practicing chemist, a separate issue treated in the final section.

This contribution follows the recent remarkable catalysis observed by Groves et al. in hydrogen-abstraction reactions by a) an oxoferryl porphyrin radical-cation complex [Por⋅+ FeIV (O)Lax ] and b) a hydroxoiron porphyrazine ferric complex [PyPzFeIII (OH)Lax ], both of which involve positively charged substituents on the outer circumference of the respective macrocyclic ligands. These charge-coronated complexes are analogues of the biologically important Compound I (Cpd I) and synthetic hydroxoferric species, respectively. We demonstrate that the observed enhancement of the H-abstraction catalysis for these systems is a purely electrostatic effect, elicited by the local charges embedded on the peripheries of the respective macrocyclic ligands. Our findings provide new insights into how electrostatics can be employed to tune the catalytic activity of metalloenzymes and can thus contribute to the future design of new and highly efficient hydrogen-abstraction catalysts.

This review sets out to understand the reactivity of diradicals and how that may differ from monoradicals. In the first part of the review, we delineate the electronic structure of a diradical with its two degenerate or nearly degenerate molecular orbitals, occupied by two electrons. A classification of diradicals based on whether or not the two SOMOs can be located on different sites of the molecule is useful in determining the ground state spin. Important is a delocalized to localized orbital transformation that interchanges "closed-shell" to "open-shell" descriptions. The resulting duality is useful in understanding the dual reactivity of singlet diradicals. In the second part of the review, we examine, with a consistent level of theory, activation energies of prototypical radical reactions (dimerization, hydrogen abstraction, and addition to ethylene) for representative organic diradicals and diradicaloids in their two lowest spin states. Differences and similarities in reactivity of diradicals vs monoradicals, based on either a localized or delocalized view, whichever is suitable, are then discussed. The last part of this review begins with an extensive, comparative, and critical survey of available measures of diradical character and ends with an analysis of the consequences of diradical character for selected diradicaloids.

Sodium and lithium hexatitanates (A2B6O13, where A = Li or Na, B = Ti or Sn) have been considered as anode materials in batteries. In this work, the Li- and Na-ion migration energies of Li2Ti6O13, Li2Sn6O13 and Na2Ti6O13 are explored using atomistic simulations. Alkali-ion transport is explored using a validated forcefield with nudged elastic band and synchronous transition state calculations. The results show that Li-ion migration exhibits activation energies of 0.47 and 0.52 eV for Li2Ti6O13 and Li2Sn6O13, respectively. In addition, Na-ion migration in Na2Ti6O13 has the lowest activation energy of 0.17 eV. Sodium and lithium can also be accommodated into the Li2Ti6O13, Li2Sn6O13 and Na2Ti6O13 structures. Li-ion migration through the channel of Na2Ti6O13 has an activation energy of 0.39 eV, while Na-ion migration in Li2Sn6O13 and Li2Ti6O13 has values of 0.95 and 1.16 eV, respectively. The Li-ion migration barrier in Na2Ti6O13 is lower than that for Li2Sn6O13 and Li2Ti6O13 because of the lower electrostatic interactions in the NaO8 channels. The presence of quasi-transition state structures for the diffusion path impacts on the reduction of the energy barrier to reach the transition state structure, providing the low barriers for Na and Li ions in Na2Ti6O13 lattice structure. The calculated defect energetics reveal that there is a viable incorporation mechanism, without the involvement of Ti4+ to Ti3+ reduction, as reported in the literature, which describes the defect behavior and the reversible insertion of Li+ and Na+ ions in these tunnel structures.

Alchemical derivatives have been used in recent years to obtain essentially qualitative information about transformations in which the number of electrons is unchanged. Within the context of Conceptual DFT, we present a systematic approach for combining changes in both the number of electrons and the nuclear charge so that for example one can navigate from one neutral atom to another. A general formalism is presented for transformations involving changes both in or , where Parr's parabolic approach for the dependence is considered as one particular case and the ensemble description in the 0 K limit as the second case. The B3LYP functional in its CAMB3LYP version combined with the aug-cc-pCVQZ basis has been chosen to perform Coupled Perturbed Kohn Sham calculations of the alchemical derivatives. The monotonic behaviour of the alchemical potential is scrutinised. The order of magnitude analysis of the derivatives preludes convergence at third order. These results are injected in two strategies for obtaining transmutation energies from neutral atoms to a neighbouring neutral atom: one road moving along the diagonal, the other one walking along a pure alchemical road after ionisation or electron attachment. Roads involving the anion of the reference atom are much less successful than those involving its cation. The transmutation energy for the cationic pathway displays chemical accuracy when the procedure is carried at third order in . The difficulties inherent to an accurate description of the anion and its response functions are responsible for the shortcomings along the anionic paths. As a direct application Ionization Energies (IE) and Electron Affinities (EA) are evaluated showing an almost perfect agreement with the direct evaluation and a difference with experimental values less than 0.5 eV for the IE. For the first EA reasonable agreement is obtained with direct and experimental values whereas the second EAs for atoms with stable mono-anions show a remarkable agreement with literature data. Besides proof of concept that with the information content of an atom one can get accurate energetics of its neighbours, the results indicate that alchemical derivatives are capable to yield quantitative information when navigating through Chemical Compound Space.

Expanded porphyrins have been recently identified as promising candidates for conductance switching based on aromaticity and molecular topology changes. However, the factors that control electron transport switching across the metal-molecule-metal junction still need to be elucidated. For this reason, the transport properties of Hückel/Möbius (anti)aromatic compounds are investigated thoroughly in this work to gain qualitative understanding into the conductivity of these unique macrocycles. Starting from a polyene model, a simple counting rule is developed to predict the occurrence of quantum interference around the Fermi level at the Hückel level of theory. Next, the different approximations of Hückel theory are lifted, enabling the exploration of the influence of each of these approximations on the transport properties of expanded porphyrins. Along the way, a detailed study on the relationship between the conductance and aromaticity/topology has been undertaken. Even though it has been proposed that the π-conjugated systems of expanded porphyrins can be approximated as polyene macrocycles based on the "annulene model", it turns out that the distortion induced by the pyrrole rings to the electronic structure of the expanded porphyrins causes the simple counting rule for the prediction of quantum interference developed for polyenes to fail in some specific situations. Nevertheless, our back-of-the-envelope approach enables an intuitive rationalization of most of the transport properties of expanded porphyrins. Our conclusions cast further doubt on the proposed negative relationship between conductance and aromaticity and highlight the importance of the connectivity on determining the shape of the transmission functions of the different states. We hope that the new insights provided here will offer experimentalists a road map toward the design of functional, multidimensional electronic switches based on expanded porphyrins.

With the idea of using alchemical derivatives to explore in an efficient, computer- and cost-effective way Chemical Space was launched several years ago. In the context of Conceptual DFT response functions, these energies vs nuclear charge derivatives permit the estimatation of the energy of transmutants of a given starting or reference molecule showing different nuclear compositions. After an explorative study on small and planar molecules (Balawender et al. J. Chem. Theory Comput. 2013, 9, 5327) by the present authors of this paper, the present study fully exploits the computational advantages of the alchemical derivatives in larger three-dimensional systems. Starting from a single reference calculation on C60, the complete BN substitution pattern, from single substituted C58BN via the belt (C20(BN)20 and the ball C12(BN)24 structures to the fully substituted (BN)30, is explored. Successive and simultaneous substitution strategies are followed and compared, indicating that both techniques yield identical results up to 13 substitutions but that for higher substitutions the simultaneous approach needs to be taken. Due to the cost-efficiency of the algorithm this path can indeed be followed as opposed to earlier work in the literature where for each step a full SCF calculation was at stake leading to prohibitively large computational demands for adopting the simultaneous approach. Previously formulated rules governing the substitution pattern by Kar and co-workers are scrutinized in this context and reformulated giving chemical insight in the gradual substitution process and the relative energies of the isomers. In its present form the method offers an interesting venue to study BN substitution patterns in higher fullerenes and graphene and in general paves the way for more efficient exploration of the Chemical Space.

The first example of the OCPPCO ligand, diisophosphaethynolate, is reported via reductive coupling of a Sc-OCP precursor. Upon reduction with KC8 , isolation of the dinuclear complex, namely [K(OEt2 )]2 [(nacnac)Sc(OAr)]2 (OCPPCO), is observed, leading to a unique motif [OCPPCO]4- , stabilized by two scandium centers. Detailed NMR spectra of all complexes as well as IR and single crystal X-ray studies were obtained to fully elucidate the nature of these complexes in solution as well as in the solid state. Theory is combined to probe the electronic structure and orbitals responsible for the bonding interactions in the Sc-OCPPCO-Sc skeleton but also to compare to the linear mode observed in the precursor.

We explore a new strategy to tune the conductivity of molecular electronic devices: captodative substitution. We demonstrate that a careful design of such substitution schemes on a benzene parental structure can enhance the conductivity by almost an order of magnitude under small bias. Once this new strategy has been established, we apply it to molecular wires and demonstrate that it enables the unprecedented anti-Ohmic design of wires whose conductivity increases with the length. Overall, the captodative substitution approach provides a very promising pathway toward full chemical control of the conductivity of molecules which opens up the possibility to design molecular switches with an improved on/off ratio among others.

In the last decade, halogen bonds, noncovalent interactions formed between positive regions in the electrostatic potential on halogen atoms, often referred to as sigma-holes, and electron-rich sites, have gained a lot of interest. Recently, this interest has been expanded towards interactions with GroupV and GroupVI elements, giving rise to pnicogen and chalcogen bonds. Although chalcogen bonds have already shown some promising results for applications in crystallography and catalysis, experimental results characterising these noncovalent interactions remain scarce. In this combined experimental and theoretical study, original data allowing the characterization of SO chalcogen bonds is obtained by studying the 1:1 molecular complexes between 2,2,4,4-tetrafluoro-1,3-dithiethane (C2F4S2) and dimethyl ether (DME). Ab initio calculations of the C2F4S2DME dimer yield two stable chalcogen-bonded isomers, the difference being the presence or absence of secondary FH interactions. Liquid-krypton solutions containing C2F4S2 and DME were studied using FTIR and Raman spectroscopy. Upon subtraction of rescaled monomer spectra, clear complex bands are observed. The observed complexation shifts agree favourably with the ab initio calculated shifts of the chalcogen-bonded complexes. The 1:1 stoichiometry of the complex is confirmed and a complexation enthalpy of -13.5(1)kJmol(-1) is found, which is in good agreement with the calculated values. A Ziegler-Rauk energy decomposition analysis revealed that electrostatic interactions prominently dominate over orbital interactions. Nevertheless, significant charge transfer occurs from the oxygen in DME to one of the sulfur atoms in C2F4S2 and the carbon along the extension of the chalcogen bond.

Using a set of state-of-the-art quantum chemical techniques we scrutinized the characteristically different reactivity of frustrated and classical Lewis pairs towards molecular hydrogen. The mechanisms and reaction profiles computed for the H2 splitting reaction of various Lewis pairs are in good agreement with the experimentally observed feasibility of H2 activation. More importantly, the analysis of activation parameters unambiguously revealed the existence of two reaction pathways through a low-energy and a high-energy transition state. An exhaustive scrutiny of these transition states, including their stability, geometry and electronic structure, reflects that the electronic rearrangement in low-energy transition states is fundamentally different from that of high-energy transition states. Our findings reveal that the widespread consensus mechanism of H2 splitting characterizes activation processes corresponding to high-energy transition states and, accordingly, is not operative for H2-activating systems. One of the criteria of H2-activation, actually, is the availability of a low-energy transition state that represents a different H2 splitting mechanism, in which the electrostatic field generated in the cavity of Lewis pair plays a critical role: to induce a strong polarization of H2 that facilities an efficient end-on acid-H2 interaction and to stabilize the charge separated “H+–H−” moiety in the transition state.

The synthesis of the monomeric organogermanium(II) hydrides {(LGeH)M(CO)5} (M = Cr (4), W (5)) utilizing the C,N-chelated ligand L (L is [2-(CH2NEt2)-4,6-tBu2-C6H2]-) is reported. The stabilization of the GeH terminal bond in 4 and 5 is accompanied by the combination of the electronic and steric protection of the ligand L. The reactivity of the GeH terminal bond was also investigated and attempts to reduce the polar C≡N bond in tBuNC provided unexpected N-C bond cleavage reaction yielding organogermanium(II) cyanides {(LGeCN)M(CO)5} (M = Cr (6), W (7)) instead of hydrogermylation reaction

The reduction of N,C,N-chelated antimony(III) chlorides [C 6H 3-2,6-(CH=NR) 2]SbCl 2(R=Ph (1), tBu (2), Dip (3); Dip=2,6-iPr 2C 6H 3) with an appropriate amount of KC 8or Li[AlH 4] resulted in the formation of rare examples of monomeric stibinidenes [C 6H 3-2,6-(CH=NR) 2]Sb (R=Ph (4), tBu (5), Dip (6)). Similarly, the reduction of compounds 1 or 2 by two equivalents of K[B(sBu) 3H] led to the stibinidenes 4 and 5. In contrast, the analogous reaction of compound 3 resulted in the formation of an unprecedented stibinidene [C 6H 3-2-(CH=NR)-6-(CH 2NHR)]Sb (7) (R=Dip), in which the hydrogen atoms that come from the K[B(sBu) 3H] are incorporated into the ligand backbone. To gain further insight into this intriguing reactivity with K[B(sBu) 3H] and to assess the influence of the substitution at both the antimony atom and pendant substituents, we prepared compounds [C 6H 3-2-(CH=NDip)]Sb(Ph)Cl (8) and [C 6H 2-2-(CH=NDip)-4,6-(tBu) 2]SbCl 2(9). The treatment of compound 8 with K[B(sBu) 3H] smoothly led to the 1-Ph-2-Dip-1H-2,1-benzazastibole (11), whereas the reaction of compound 9 with K[B(sBu) 3H] resulted in either tBu-substituted 1-Cl-2-Dip-1H-2,1-benzazastibole (13) or the formation of unprecedented Sb−Sb dimer bis(2-Dip-1H-2,1-benzazastibole) (12) depending on the reaction stoichiometry. The miscellaneous reactivity of antimony(III) precursors with reducing agents together with the structure and bonding of the resulting products has also been investigated from a theoretical point of view.

N,C,N-Chelated pnictinidenes ArE [where E = As (1), Sb (2) or Bi (3); Ar = C 6H 3-2,6-(CH=Nt-Bu) 2] were used as ligands for the coordination of transition metal carbonyls. Thus, the reaction of 1-3 with [M(CO) 5THF] (where M = Cr, W) or [Mo(CO) 5(Me 3N)] gave complexes [(ArE)M(CO) 5] [where E = As and M = Cr (1a), Mo (1b), W (1c); E = Sb and M = Cr (2a), Mo (2b), W (2c); E = Bi and M = Cr (3a), Mo (3b), W (3c)]. Analogously, the treatment of 1-3 with [Fe 2(CO) 9] resulted in the formation of the complexes [(ArE)Fe(CO) 4] [where E = As (1d), Sb (2d) or Bi (3d)]. All compounds were characterized by 1H and 13C NMR spectroscopy, Raman, IR and UV-Vis spectroscopy. The molecular structures of the majority of the compounds (except 1b and 1c) were also determined by the single-crystal X-ray diffraction analysis. Furthermore, the structure and bondingof the title compounds have also been thoroughly investigated using a computational approach.

In this contribution we present reactivity studies of a rare example of a titanium salt, in the form of [μ 2-K(OEt 2)] 2[(PN) 2Ti≡N] 2 (1) (PN - = N-(2-(diisopropylphosphino)-4-methylphenyl)-2,4,6-trimethylanilide) to produce a series of imide moieties including rare examples such as methylimido, borylimido, phosphonylimido, and a parent imido. For the latter, using various weak acids allowed us to narrow the pK a range of the NH group in (PN) 2Ti≡NH to be between 26-36. Complex 1 could be produced by a reductively promoted elimination of N 2 from the azide precursor (PN) 2TiN 3, whereas reductive splitting of N 2 could not be achieved using the complex (PN) 2Ti=N=N=Ti(PN) 2 (2) and a strong reductant. Complete N-atom transfer reactions could also be observed when 1 was treated with ClC(O) tBu and OCCPh2 to form NC tBu and KNCCPh 2, respectively, along with the terminal oxo complex (PN) 2Ti≡O, which was also characterized. A combination of solid state 15N NMR (MAS) and theoretical studies allowed us to understand the shielding effect of the counter cation in dimer 1, the monomer [K(18-crown-6)][(PN) 2Ti≡N], and the discrete salt [K(2,2,2-Kryptofix)][(PN) 2Ti≡N] as well as the origin of the highly downfield 15N NMR resonance when shifting from dimer to monomer to a terminal nitride (discrete salt). The upfield shift of 15N nitride resonance in the 15N NMR spectrum was found to be linked to the K + induced electronic structural change of the titanium-nitride functionality by using a combination of MO analysis and quantum chemical analysis of the corresponding shielding tensors.

In recent years, external electric fields (EEFs) have captured some spotlight as novel effectors of chemical change. EEFs directly impact the structure of molecular systems. For example, aligning an electric field along a specific bond-axis leads to either shortening or elongation of the bond (and ultimately bond breaking). Furthermore, EEFs enable unprecedented control over chemical reactivity. Orienting an electric field along the so-called “reaction-axis,” the direction in which the electrons reorganize during the conversion from reactant to product, leads to catalysis or inhibition and can induce mechanistic crossover from concerted to stepwise reactions. Off-reaction-axis orientation enables control over the stereoselectivity of reactions and disables forbidden–orbital mixing. Two-directional fields enable control over both reactivity and selectivity. In this advanced review, we offer an overview of this rapidly evolving research field with a focus on the valence bond modeling of EEF effects and the insight it offers. A wide variety of examples will be considered and a link to the experiment will be made throughout. We end by offering some perspectives in which we postulate that, as experimental techniques continue to mature, EEFs could potentially become a generally applicable “zapping” tool to facilitate elaborate chemical syntheses. This article is categorized under:. Structure and Mechanism > Reaction Mechanisms and Catalysis.