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Despite the central role of aromaticity in the chemistry of expanded porphyrins, the evaluation of aromaticity remains difficult for these extended macrocycles. The presence of multiple conjugation pathways and different planar and nonplanar π-conjugation topologies makes the quantification of global and local aromaticity even more challenging. In neutral expanded porphyrins, the predominance of the aromatic conjugation pathway passing through the imine-type nitrogens and circumventing the amino NH groups is established. However, for charged macrocycles, the question about the main conjugation circuit remains open. Accordingly, different conjugation pathways in a set of neutral, anionic, and cationic expanded porphyrins were investigated by means of several aromaticity indices rooted in the structural, magnetic, and electronic criteria. Overall, our results reveal the predominance of the conjugation pathway that passes through all nitrogen atoms to describe the aromaticity of deprotonated expanded porphyrins, while the outer pathway through the perimeter carbon atoms becomes the most aromatic in protonated macrocycles. In nonplanar and charged macrocycles, a discrepancy between electronic and magnetic descriptors is observed. Nevertheless, our work demonstrates AVmin remains the best tool to determine the main conjugation pathway of expanded porphyrins. M.A. and I.C.R. wish to acknowledge the VUB for a Strategic Research Program awarded to ALGC. The resources and services used in this work were provided by the Flemish Supercomputer Center (VSC), funded by the Research Foundation - Flanders (FWO), and the Flemish Government. I.C.R. acknowledges co-funding from the European Union′s Horizon 2020 research and innovation Maria Skłodowska-Curie Actions, under grant agreement number 945380. It has been also supported by grants from the Spanish government MICINN (PGC2018-098212-B-C21, PID2019-104772GB, PID2019-105488GB-I00, and PCI2019-103657), Diputación Foral de Gipuzkoa (2019-CIEN-000092-01), Gobierno Vasco (IT1346-19, IT1254-19, and PIBA19-0004), and the DIPC (DIPC_INV_003132). Open Access funding provided by University of Basque Country.

Herein, a library of trifluoroethyl substituted aminomaleimide derivatives are reported with small size and enhanced emissions in both solution and solid-state. A diCH2CF3 substituted aminochloromaleimide exhibits the most efficient dual-state emission (Φf >50 % in solution and solid-state), with reduced quenching from protic solvents. This is attributed to the reduction of electron density on the maleimide ring and suppressed π-π stacking in the solid-state. This mechanism was explored in-depth by crystallographic analysis, and modelling of the electronic distribution of HOMO-LUMO isosurfaces and NCI plots. Hence, these dual-state dyes overcome the limitations of single-state luminescence and will serve as an important step forward for this rapidly developing nascent field. The authors thank the Ministerio de Economia y Competitividad (MINECO) of Spain (project: PID2019-104772GB-I00) and the Basque Government (project IT1346-19), and the Leverhulme Trust (RPG-2016-452). Dr. Thomas R. Wilks and Dr. Yujie Xie are thanked for helpful discussions and Chi Tsang (University of Birmingham) for high resolution mass spectroscopy analysis. The authors acknowledge the computational resources, and technical and human support provided by the DIPC.

A recent article by Anderson and co-workers challenges our conclusions on the aromaticity of the four oxidation states of a butadyine-linked six-porphyrin nanoring, based on the experimental

Fluorescent dyes that exhibit high solid state quantum yields and sensitivity to the mechanical properties of their local environment are useful for a wide variety of applications, but are limited in chemical diversity. We report a trityl-functionalised maleimide that displays rigidochromic behaviour, becoming highly fluorescent when immobilised in a solid matrix, while displaying negligible fluorescence in solution. Furthermore, the dye's quantum yield is shown to be sensitive to the nature of the surrounding matrix. Computational studies reveal that this behaviour arises from the precise tuning of inter- and intramolecular noncovalent interactions. This work expands the diversity of molecules exhibiting solid state environment sensitivity, and provides important fundamental insights into their design., In this study, by systematic tuning of imide substituent a maleimides dye with sensitivity to its solid-state environment was investigated.

In the oriented external electric-field-driven catalysis, the reaction rates and the selectivity of chemical reactions can be tuned at will. The activation barriers of chemical reactions within external electric fields of several strengths and directions can be computationally modeled. However, the calculation of all of the required field-dependent transition states and reactants is computationally demanding, especially for large systems. Herein, we present a method based on the Taylor expansion of the field-dependent energy of the reactants and transition states in terms of their field-free dipole moments and electrical (hyper)polarizabilities. This approach, called field-dependent energy barrier (FDBβ), allows systematic one-dimensional (1D), two-dimensional (2D), and three-dimensional (3D) representations of the activation energy barriers for any strength and direction of the external electric field. The calculation of the field-dependent FDBβ energy barriers has a computational cost several orders of magnitude lower than the explicit electric field optimizations, and the errors of the FDBβ barriers are within the range of only 1-2 kcal·mol-1. The achieved accuracy is sufficient for a fast-screening tool to study and predict potential electric-field-induced catalysis, regioselectivity, and stereoselectivity. As illustrative examples, four cycloadditions (1,3-dipolar and Diels-Alder) are studied This work was supported with funds from the Ministerio de Economía y Competitividad (MINECO) of Spain (project CTQ2017-85341-P to M.S.), the Spanish government MICINN (projects PGC2018-098212-B-C22 to J.M.L, PID2020-113711GB-I00 to M.S., and PID2019-104772GBI00 to M.T.S.), the Generalitat de Catalunya (project 2017SGR39 to M.S. and J.M.L.), and Gobierno Vasco (project IT1346-19 to M.T.S.). The authors thank the Spanish government for the predoctoral grant to P.B.-S. (FPU17/ 02058)

Large conjugated rings with persistent currents are novel promising structures in molecular-scale electronics. A six-porphyrin nanoring structure that allegedly sustained an aromatic ring current involving 78π electrons was recently synthesized. We provide here compelling evidence that this molecule is not aromatic, contrary to what was inferred from the analysis of 1H-NMR data and computational calculations that suffer from large delocalization errors. The main reason behind the absence of an aromatic ring current in these nanorings is the low delocalization in the transition from the porphyrins to the bridging butadiyne linkers, which disrupts the overall conjugated circuit. These results highlight the importance of choosing a suitable computational method to study large conjugated molecules and the appropriate aromaticity descriptors to identify the part of the molecule responsible for the loss of aromaticity., This work has been supported by grants from the Spanish government MICINN (PGC2018-098212-B-C21, PID2019-104772GB-I00, EUR2019-103825, PID2019-105488GB-I00, and PCI2019-103657), Diputación Foral de Gipuzkoa (2019-CIEN-000092-01), and Gobierno Vasco (IT1346-19, IT1254-19, PRE_2016_1_0159, and PIBA19-0004). E.R.C. acknowledges funding from the Juan de la Cierva program IJCI-2017-34658.

Fluorescent barcoding is a pivotal technique for the investigation of the microscale world, from information storage to the monitoring of dynamic biochemical processes. Using fluorescence lifetime as the readout modality offers more reproducible and quantitative outputs compared to conventional fluorescent barcoding, being independent of sample concentration and measurement methods. However, the use of fluorescence lifetime in this area has been limited by the lack of strategies that provide spatiotemporal manipulation of the coding process. In this study, we design a two-component photo-switchable nanogel that exhibits variable fluorescence lifetime upon photoisomerization-induced energy transfer processes through light irradiation. This remotely manipulated fluorescence lifetime property could be visually mapped using fluorescence lifetime imaging microscopy (FLIM), allowing selective storage and display of information at the microscale. Most importantly, the reversibility of this system further provides a strategy for minimizing the background influence in fluorescence lifetime imaging of live cells and sub-cellular organelles., Using fluorescence lifetime as the readout modality offers more reproducible and quantitative outputs compared to conventional fluorescent barcoding, being independent of sample concentration and measurement methods. Here, the authors design a photo-switchable nanogel exhibiting variable fluorescence lifetime, and demonstrate visual mapping by using fluorescence lifetime imaging microscopy on a sub-cellular scale.

The zero-point static vibrational averaging (ZPVA) correction to the (hyper)polarizability is written in first-order as the sum of two contributions, one involving electric field derivatives, and the other a sum over normal coordinate derivatives of the zero point energy. It is shown that the sum over 3N-6 normal modes can be replaced by a single term using field-induced coordinates (FICs). A computational strategy that takes advantage of this simplification is presented and applied to a typical push-pull polyene NH2-(CH=CH)3-NO2. From the dependence of the first-order ZPVA on the field-dependent equilibrium geometry we also obtain other loworder static and dynamic vibrational curvature contributions to the (hyper)polarizabilities. The entire set of electronic and vibrational terms is partitioned into two different sequences, each of which exhibits rapid initial convergence for NH2(CH=CH)3NO2 at the Hartree-Fock/6-31G+p level. Including electron correlation at the MP2 level and the frequency-dependence of the ZPVA correction is discussed Support for this work under Grant PB98- 0457-C02-01 from the Dirección General de Enseñanza Superior e Investigación Científica y Técnica (MEC-Spain) is acknowledged

The mechanism of the cyclopropanation of alkenes with diazocompounds catalyzed by ClFeIII–porphyrin, [ClFeII–porphyrin]−, and FeII–porphyrin has been investigated by density functional theory calcu...

Designed repeat proteins catalyze the 1,3-dipolar reaction between an imine and a π-deficient dipolarophile in THF solution to form unnatural nitroproline esters, a reaction that no enzyme can catalyze. NMR studies and mutation experiments show that both acidic and basic residues can catalyze the reaction. The diastereocontrol of the reaction depends on the flexibility of the protein and on the number and location of the active lysine and glutamate residues, which can participate independently or forming dyads that promote the formation of unusual diastereomeric cycloadducts. QM/MM calculations permit one to rationalize the origins of this

In this work, we studied computationally the N-demethylation reaction of methylamine, dimethylamine, and trimethylamine as archetypal examples of primary, secondary, and tertiary amines catalyzed by high-field low-spin Fe-containing enzymes such as cytochromes P450. Using DFT calculations, we found that the expected C-H hydroxylation process was achieved for trimethylamine. When dimethylamine and methylamine were studied, two different reaction mechanisms (C-H hydroxylation and a double hydrogen atom transfer) were computed to be energetically accessible and both are equally preferred. Both processes led to the formation of formaldehyde and the N-demethylated substrate. Finally, as an illustrative example, the relative contribution of the three primary oxidation routes of tamoxifen was rationalized through energetic barriers obtained from density functional calculations and docking experiments involving CYP3A4 and CYP2D6 isoforms. We found that the N-demethylation process was the intrinsically favored one, whereas other oxidation reactions required most likely preorganization imposed by the residues close to the active sites.

We herein present a simple methodology to systematically expand the scope of maleimide-based dyes and also provide an insight into the relationship between substitution pattern and optical properties., A series of maleimide derivatives were systematically designed and synthesized with tunable fluorescent properties. The facile modifications herein provide a simple methodology to expand the scope of maleimide-based dyes and also provide insight into the relationship between substitution pattern and optical properties.

The macrocyclic ring of expanded porphyrins presents a conformational versatility that leads to original structural motifs and generates unique Hückel-to-Möbius topological switches. These systems can act as optoelectronic materials, and their range of applicability depends on the high values of the nonlinear optical properties (NLOPs) and the large differences between the Hückel and Möbius structures. With the aim to design new topological switches with the optimum NLOPs, we have performed a DFT computational study on the effect of three different geometric and electronic factors of the meso-substituents: (i) their electron-withdrawing and -releasing character; (ii) their distribution along the porphyrin ring; and (iii) the length of the conjugation path. In this work, we report the electronic and vibrational contributions to static and dynamic NLOPs of the Hückel and Möbius conformations of 18 meso-substituted [28]-hexaphyrins. These systems can achieve first and second hyperpolarizability values around 1 × 10^5 and 2 × 10^7 au, respectively, and differences between the Möbius and Hückel conformations around 4 × 10^4 and 5 × 10^6 au, respectively. From our results, we conclude that efficient NLOP topological switches can be obtained from push-pull porphyrins with a π-conjugated spacer and strong electron-withdrawing and -releasing groups located on opposite sides of the skeleton ring Financial support was provided by the Ministerio de Economía y Competitividad (MINECO) of Spain and FEDER (projects CTQ2016-80375-P and CTQ2014-52525-P) and the Generalitat de Catalunya (Grant 2014SGR139)

In a very recent article (Chem.-Eur. J. 2014, 20, 6636), Olson et al. performed a theoretical study of the low-lying isomers of Li3N3 and found that two of the most stable structures show a novel N3(3-) molecular motif, which possesses structural and chemical bonding features similar to ozone. We explore a first application of these new Li3N3 species as a captor of carbon dioxide. Our results conclude that this is a very exothermic and exoergic process (the capture of one and two carbon dioxide molecules on Li3N3 releases, respectively, 42 and 70 kcal mol(-1) in relative free energy values evaluated at the CCSD(T)/aug-cc-pVTZ//B3LYP/aug-cc-pVTZ level of theory), which apparently occurs without any energy barrier but requires a nonlinear N3(3-) molecular motif.

Meso‐aryl expanded porphyrins present a structural versatility that allows them to achieve different topologies with distinct aromaticities. Several studies appeared in the literature studying these topological switches from an experimental and theoretical point of view. Most of these publications include density functional theory calculations, being the B3LYP the most used methodology. In this work, we show that the selection of the functional has a critical role on the geometric, energetic, and magnetic results of these expanded porphyrins, and that the use of an inadequate methodology can even generate spurious stationary points on the potential energy surface. To illustrate these aspects, in this article we have studied different molecular distortions of two expanded porphyrins, [32]‐heptaphyrin and [26]‐hexaphyrin using 11 DFT functionals and performing single point energy calculations at the local pair natural orbital coupled cluster DLPNO‐CCSD(T) method, which have been carried out for benchmarking purposes. For some selected functionals, the dispersion effects have also been evaluated using the D3‐Grimme's dispersion correction with Becke–Johnson damping. Our results let us to conclude that the CAM‐B3LYP, M05‐2X, and M06‐2X functionals are the methodologies that provide a more consistent description of these topological switches, while other methods, such as B3LYP, BPE, and BP86, show a biased description., Ministerio de Economía y Competitividad of Spain . Grant Numbers: CTQ2016‐80375‐P , CTQ2014‐52525‐P , CTQ2014‐51912‐REDC -Universidad del País Vasco ‐ Euskal Herriko Unibertsitatea (UPV/EHU) . Grant Number: UFI11/22 QOSYC -Basque Government . Grant Number: IT673‐13 -Generalitat de Catalunya . Grant Number: 2014SGR139

International audience; The role of aromaticity in porphyrinoids is a current subject of debate due to the intricate structure of these macrocycles, which in some cases adopt Hückel, Möbius and even figure-eight conformers. One of the main challenges in these large π-conjugated structures is identifying the most conjugated pathway because, among aromaticity descriptors, there are very few that can be applied coherently to this variety of conformers. In this paper, we have investigated the conjugated pathways in nine porphyrinoid compounds using several aromaticity descriptors, including BLA, BOA, FLU and HOMA, as well as the recently introduced AV1245 and AVmin indices. All the indices agree on the general features of these compounds, such as the fulfillment of Hückel's rule or which compounds should be more or less aromatic from the series. However, our results evince the difficulty in finding the most aromatic pathway in the macrocycle for large porphyrinoids. In fact, only AVmin is capable of recognizing the annulene pathway as the most aromatic one in the nine studied structures. Finally, we study the effect of the exchange in DFT functionals on the description of the aromaticity of the porphyrinoids. The amount of exact exchange quantitatively changes the picture for most aromaticity descriptors, AVmin being the only exception that shows the same qualitative results in all cases.

Attosecond time-resolved photoemission spectroscopy reveals that photoemission from solids is not yet fully understood. The relative emission delays between four photoemission channels measured for the van der Waals crystal tungsten diselenide (WSe) can only be explained by accounting for both propagation and intra-atomic delays. The intra-atomic delay depends on the angular momentum of the initial localized state and is determined by intra-atomic interactions. For the studied case of WSe, the photoemission events are time ordered with rising initial-state angular momentum. Including intra-atomic electron-electron interaction and angular momentum of the initial localized state yields excellent agreement between theory and experiment. This has required a revision of existing models for solid-state photoemission, and thus, attosecond time-resolved photoemission from solids provides important benchmarks for improved future photoemission models., This work was supported by the German Research Foundation (DFG) within the Collaborative Research Center (SFB) 613 (F.S., P.B., W.P., and U.H.), the Priority Programs SPP 1931 (C.S., M.H., and W.P.), and SPP 1840 (St.F., S.N., and W.P.); the Basque Government (grant IT-756-13 UPV/EHU) (V.M.S., E.E.K., R.D.M., P.M.E., and A.K.K.); and the Spanish Ministerio de Economía y Competitividad (grants FIS2016-76617-P and FIS2016-76471-P) (V.M.S., E.E.K., R.D.M., P.M.E., and A.K.K.) and Fondo Europeo de Desarrollo Regional (FEDER) (CTQ2016- 80375-P) (M.T.-S.). N.M.K. acknowledges hospitality and financial support from the theory group in cooperation with the small quantum systems (SQS) research group of European XFEL.

Expanded porphyrins have emerged as a new promising class of molecules for the creation of new Hückel-to-Möbius topological switches with distinct aromaticities and magnetic and electric properties. In this work, we report a theoretical investigation of the conformational switch between the Hückel planar and the singly twisted Möbius structure for eight different meso-substituted [28]-hexaphyrins (with different steric effects and electron-withdrawing and -releasing character). Our results show how a change in the nature of the meso-substituent is able to turn an endothermic interconversion process with a high energy barrier into an exothermic and almost barrierless Hückel-Möbius transition. We also provide a thorough analysis of the main factors (aromaticity, intramolecular hydrogen bonds, ring strain, and steric effects) that play a role in this interconversion process. Overall, these results are very relevant to find new ways to control the thermochemistry and kinetics of these topological switches and even "freeze" the switch in the desired Möbius or Hückel conformation.

The N-demethylation reactions of N,N,N-trimethylpropan-1-ammonium and N,N-dimethyl-, and N-methylpropan-1-aminium cations in the presence of (AcO)2(imidazole)2(H2O)Fe=O complex have been studied by density functional theory. These transformations are suitable models for the N-demethylation of tri-, di-, and monomethylated lysine residues of histones in the presence of Jumonji-C containing histone demethylases. It has been found that the N-demethylation reaction is stepwise and occurs on triplet and quintet potential energy hypersurfaces. Both spin states are nearly degenerated and quantum jump from one state to another has a transition probability close to one. The preferred intrinsic mechanism depends upon the methylation degree. For trimethylated residues the mechanism consists of a proton abstraction from a methyl group followed by a formation of a hydroxymethylaminium intermediate. This mechanism also occurs when dimethylated residues are able to orientate one methyl group towards the Fe=O group of the catalytic site. In contrast, when is a N-H group of the substrate close enough to the Fe=O group, the intrinsically preferred N-demethylation reaction leads to the formation of an iminium intermediate that can be hydrolyzed to form the corresponding N-demethylated product.

The microwave-assisted imidazole-catalyzed transformation of propargyl vinyl ethers (PVEs) into multisubstituted salicylaldehydes is described. The reaction is instrumentally simple, scalable, and tolerates a diverse degree of substitution at the propargylic position of the starting PVE. The generated salicylaldehyde motifs incorporate a broad range of topologies, spanning from simple aromatic monocycles to complex fused polycyclic systems. The reaction is highly regioselective and takes place under symmetry-breaking conditions. The preparative power of this reaction was demonstrated in the first total synthesis of morintrifolin B, a benzophenone metabolite isolated from the small tree Morinda citrifolia L. A DFT study of the reaction was performed with full agreement between calculated values and experimental results. The theoretically calculated values support a domino mechanism comprising a propargyl Claisen rearrangement, a [1,3]-H shift, a [1,7]-H shift (enolization), a 6π electrocyclization, and an aromatization reaction.

The effect of a single water molecule on the reaction between H(2)O(2) and HO has been investigated by employing MP2 and CCSD(T) theoretical approaches in connection with the aug-cc-PVDZ, aug-cc-PVTZ, and aug-cc-PVQZ basis sets and extrapolation to an ∞ basis set. The reaction without water has two elementary reaction paths that differ from each other in the orientation of the hydrogen atom of the hydroxyl radical moiety. Our computed rate constant, at 298 K, is 1.56 × 10(-12) cm(3) molecule(-1) s(-1), in excellent agreement with the suggested value by the NASA/JPL evaluation. The influence of water vapor has been investigated by considering either that H(2)O(2) first forms a complex with water that reacts with hydroxyl radical or that H(2)O(2) reacts with a previously formed H(2)O·OH complex. With the addition of water, the reaction mechanism becomes much more complex, yielding four different reaction paths. Two pathways do not undergo the oxidation reaction but an exchange reaction where there is an interchange between H(2)O(2)·H(2)O and H(2)O·OH complexes. The other two pathways oxidize H(2)O(2), with a computed total rate constant of 4.09 × 10(-12) cm(3) molecule(-1) s(-1) at 298 K, 2.6 times the value of the rate constant of the unassisted reaction. However, the true effect of water vapor requires taking into account the concentration of the prereactive bimolecular complex, namely, H(2)O(2)·H(2)O. With this consideration, water can actually slow down the oxidation of H(2)O(2) by OH between 1840 and 20.5 times in the 240-425 K temperature range. This is an example that demonstrates how water could be a catalyst in an atmospheric reaction in the laboratory but is slow under atmospheric conditions.

Recently, much attention has been focused on the design and synthesis of molecules with aromatic Möbius topology. One of the most promising applications is the manufacture of Hückel-to-Möbius topological optical switches with high nonlinear optical properties. In this work, we evaluate the electronic and vibrational contributions to static and dynamic nonlinear optical properties of the CS Hückel and C2 Möbius topologies synthesized by Herges and co-workers (Ajami, D. et al. Nature2003, 426, 819). Calculations are performed at the HF, B3LYP, BHandHLYP, BMK, M052X, CAM-B3LYP, and MP2 levels with the 6-31+G(d) basis set. Our results conclude that the BHandHLYP, M052X, and CAM-B3LYP methods correctly reproduce the X-ray crystal structure and provide similar nonlinear optical properties.

The infrared anharmonic spectra for the H(+)(H2O)3, H(+)(H2O)4, and H(+)(H2O)21 water clusters have been reported using vibrational second-order perturbation theory at the B3LYP level with 6-31+G(d) and 6-311++G(3df,3pd) basis sets. The anharmonicity results crucial for the evaluation of the protonated water clusters and the anharmonic corrections can be larger than 500 cm(-1), resulting in a shift of the H3O(+) asymmetric stretchings near the region of 2000 cm(-1).

The reaction between the HO radical and (H2O)n (n = 1, 3) clusters has been investigated employing high-level quantum mechanical calculations using DFT-BH&HLYP, QCISD, and CCSD(T) theoretical approaches in connection with the 6-311 + G(2df,2p), aug-cc-pVTZ, and aug-cc-pVQZ basis sets. The rate constants have also been calculated and the tunneling effects have been studied by means of time–dependent wavepacket calculations, performed using the Quantum–Reaction Path Hamiltonian method. According to the findings of previously reported theoretical works, the reaction between HO and H2O begins with the formation of a pre-reactive complex that is formed before the transition state, the formation of a post-reactive complex, and the release of the products. The reaction between HO and (H2O)2 also begins with the formation of a pre-reactive complex, which dissociates into H2O…HO + H2O. The reaction between HO and (H2O)3 is much more complex. The hydroxyl radical adds to the water trimer, and then it occurs a geometrical rearrangement in the pre-reactive hydrogen-bonded complex region, before the transition state. The reaction between hydroxyl radical and water trimer is computed to be much faster than the reaction between hydroxyl radical and a single water molecule, and, in both cases, the tunneling effects are very important mainly at low temperatures. A prediction of the atmospheric concentration of the hydrogen-bonded complexes studied in this work is also reported.

International audience; We examine the use of nucleus independent chemical shifts (NICS) as a tool for analysis of pristine and fluorinated finite-length carbon nanotubes. The introduction of both variable molecule length and different nanotube curvatures introduces additional subtleties to NICS analysis not present in analysis of more conventional 2D molecules. Notably the precise length of tube segment considered can strongly influence calculated NICS values. We provide specific examples using (6,6) and (7, 7) nanotube segments under fluorination. Although care should be taken when comparing systems of different length or curvature, important chemical information can still be retrieved from the local aromaticity patterns. In particular, local aromaticity is observed to play a relevant role in the orientation towards the ideal C4F addition pattern for fluorinated carbon nanotubes.

The microwave-assisted imidazole-catalyzed transformation of propargyl vinyl ethers (PVEs) into multisubstituted salicylaldehydes is described. The reaction is instrumentally simple, scalable, and tolerates a diverse degree of substitution at the propargylic position of the starting PVE. The generated salicylaldehyde motifs incorporate a broad range of topologies, spanning from simple aromatic monocycles to complex fused polycyclic systems. The reaction is highly regioselective and takes place under symmetry-breaking conditions. The preparative power of this reaction was demonstrated in the first total synthesis of morintrifolin B, a benzophenone metabolite isolated from the small tree Morinda citrifolia L. A DFT study of the reaction was performed with full agreement between calculated values and experimental results. The theoretically calculated values support a domino mechanism comprising a propargyl Claisen rearrangement, a [1,3]-H shift, a [1,7]-H shift (enolization), a 6π electrocyclization, and an aromatization reaction., This research was supported by the Spanish Ministerio de Economía y Competitividad (MINECO) and the European Regional Development Fund (CTQ2011-28417-C02-02 and CTQ2013-45415-P), the UPV/EHU (UFI11/22 QOSYC), and the Basque Government (GV/EJ, grant IT-324-07). L.C. thanks Spanish MEC for a FPI grant and D.M.A. thanks CSIC for a JAE-intro grant. M.T.-S., M.O.-G., and F.P.C. thank the SGI/IZO- SGIker UPV/EHU and the DIPC for generous allocation of computational resources.

The rotational barriers and conformational properties of the hydroxyl and mercapto groups attached to the alpha and beta positions of cyclohexa-2,5-dione and cyclohexa-2,5-dienthione have been studied at the B3LYP/ 6-311++G(d,p) level of theory. The results show that the conformational preferences of these studied systems are the result of a subtle interplay between different competing effects (conjugation, hyperconjugation, and steric repulsions). The applicability of the density functional theory reactivity indices and the maximum hardness principle for the present systems has been analyzed.

Hardness profiles are calculated for the hydrogen bond interchange in the hydrogen fluoride dimer; the study is carried out at the Hartree-Fock and second- order Moller-Plesset (MP2) levels of theory with three different basis sets. The basis set superposition error (BSSE) is corrected by means of the chemical Hamiltonian approach (CHA). Uncorrected and BSSE-corrected energy and hardness profiles are compared. Their analysis shows that hardness profiles do not lead to spurious minima as energy profiles do in various cases. The CHA methodology is shown to be valuable in the analysis of intermolecular interactions, with BSSE observed to carry smaller modifications on hardness profiles than on energy curves. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem 106: 2910 -2919, 2006

A simplified model of the hardness kernel, η ( r → , r → ′ ) ≅ δ ( r → − r → ′ ) , has been evaluated for the calculation of the global hardness in a series of Lewis acids and bases using the MP2 method. It is found that this simple model yields the appropriate ordering of the molecules according to their hardness values when compared to experimental available results.

In the present work, we have computed the energy and hardness profiles for a series of inter and intramolecular conformational changes at several levels of calculation. All processes studied have in common the fact that the choice of a weak methodology or a poor basis set results in the presence of spurious stationary points in the energy profile. At variance with the energy profiles, the hardness profiles calculated as the difference between the vertical ionization potential and electron affinity always show the correct number of stationary points independently of the basis set and methodology used. For this reason, we have concluded that hardness profiles can be used to check the reliability of the energy profiles for those chemical systems that, because of their size, cannot be treated with high level ab initio methods.

We have studied how the calculation of electronic and vibrational contributions to nonlinear optical properties of three representative π-conjugated organic molecules is affected by the choice of basis set and the inclusion of electron correlation effects. The 6-31G basis does not always provide even qualitative accuracy. For semiquantitative accuracy a 6-31+G(d) basis is sufficient. Although, as compared to QCISD, a second-order Moller–Plesset (MP2) treatment often yields a substantial fraction of the electron correlation contribution, our MP2 results for the separate electronic and vibrational terms are not consistently of semiquantitative accuracy. Nevertheless, at the MP2 level the ratio between the vibrational and electronic contributions is satisfactorily reproduced.

Two simplified models of the hardness kernel, η(r,r‘) ≅ 1/|r − r‘| and η(r,r‘) ≅ δ(r − r‘), have been tested to calculate the global hardness for a set of 18 molecules using the hybrid B3LYP functional. It is found that the simplest model, η(r,r‘) ≅ δ(r − r‘), yields the best ordering of the systems by hardness when compared to experimentally available hardnesses. However, it is worth noting that this approximation provides correct estimates of global hardnesses only after empirical corrections. Finally, it is also shown that the B3LYP method gives results close to conventional ab initio correlated methods.

In earlier work, the present authors have shown that hardness profiles are less dependent on the level of calculation than energy profiles for potential energy surfaces (PESs) having pathological b e- haviors. At variance with energy profiles, hardness profi les always show the correct number of stationary points. This characteristic has been used to indicate the existence of spurious stationary points on the PESs. In the present work, we apply this methodology to the hydrogen fluoride dimer, a classical diffi cult case for the density functional theory methods.

Exceptions to the generalized maximum hardness principle (MHP) for nitrogen heterocycles, along non-totally symmetric vibrations (bond-length alternating modes), are caused by pseudo-Jahn-Teller (PJT) coupling between the ground and the excited state along those modes. Thus, the PJT effect causes an increase of the energy gap between the ground and the excited state, and this is reflected in an increase of hardness. This relationship is based on the assumption that the hardness (defined as difference between ionization potential and electron affinity) is approximately equal to the HOMO-LUMO gap (Koopmans' approximation), and this is in turn assumed to be approximately equal to the energy difference between ground and excited state. The analogy is valid here because the excited state and the relevant vibration have the same symmetry, and the geometry and force constants of the optimized minima for the two coupled states are reasonably similar Support for this work under Grants No. BQU2002-04112-C02-02 and BQU2002-03334 from the Dirección General de Enseñanza Superior e Investigación Científica y Técnica (MEC-Spain) is acknowledged. L. B. is financed by the Ramón y Cajal program from the Spanish Ministerio de Ciencia y Tecnología. M. T.-S. is financed through CIRIT Project No. FI/01- 000699 from the Generalitat de Catalunya. M. S. thanks the DURSI (Generalitat de Catalunya) for financial support through the Distinguished University Research Promotion, 2001

The conformational flexibility of the expanded porphyrins allows them to achieve different topologies with distinct aromaticities and nonlinear optical properties (NLOP). For instance, it is possible to switch between Möbius and Hückel topologies applying only small changes in the external conditions or in the structure of the ring. In this work, we evaluate the electronic and vibrational contributions to static and dynamic NLOP of the Hückel and Möbius conformers of A,D-di-pbenzi[28] hexaphyrin (1.1.1.1.1.1) synthesized by Latos-Gra˙zy´nski and co-workers [Angew. Chem., Int. Ed. 46, 7869 (2007)]. Calculations are performed at the HF, M052X, and CAM-B3LYP levels using the 6-31G, 6-311G(d), and 6-31+G(d) basis sets. Our results conclude that M052X/6-31G and CAM-B3LYP/6-31G methods provide a correct qualitative description of the electronic and vibrational contributions for the NLOP of expanded porphyrins. The studied systems show high NLOP with large differences between the Möbius and Hückel conformations (around 1 × 106 a.u. for γ¯ ). The obtained results indicate that the expanded porphyrins are promising systems to manufacture Hückel-to-Möbius topological switches This research has been supported by the Spanish Direccion General de Investigacion Cientifica y Tecnica (DGYCIT, Grant Nos. CTQ2011-27812/BQU and CTQ2011-23156/BQU), the Generalitat de Catalunya (Grant Nos. 2009SGR01472 and 2009SGR637), and the Research Executive Agency (Grant Agreement No. PERG05-GA-2009-249310). The calculations described in this work were carried out at the Centre de Supercomputacio de Catalunya (CESCA). M. T-S. acknowledges the CSIC for the JAE-DOC contract

The expanded porphyrins have become a useful tool to synthesize new Hückel-to-Möbius topological switches. Only applying small changes in the external conditions (temperature, solvent, redox potential) or in the structure of the ring allows the expanded porphyrins to achieve Hückel and Möbius topologies with distinct aromaticities and magnetic and electric properties. In this work, we report a theoretical investigation of the reaction mechanism of the conformational switch between the Hückel planar and the singly twisted Möbius structures for two different meso-substituted [28]hexaphyrins(1.1.1.1.1.1); that is, the meso-substituents are the hydrogen atoms and pentafluorophenyls. Calculations are performed with the B3LYP, BH&HLYP, CAM-B3LYP, M05-2X, and MP2 methodologies along with the 6-31G and 6-311G(d,p) basis sets. For benchmarking purposes, single-point energies are calculated at the CCSD(T)/6-31G level. Our results conclude that, in overall, CAM-B3LYP and M05-2X are the methods that provide the most equilibrated results for the different steps of the topological switch. In addition, we point out that the ring strain and the steric effect of the meso-substituents play a relevant role in the thermochemistry and kinetics of the Hückel-to-Möbius topological switches., This research has been supported by the Research Executive Agency (Grant Agreement no. PERG05-GA-2009-249310) and by the Generalitat de Catalunya (Grant 2009SGR01472). The calculations described in this work were carried out at the Centre de Supercomputació de Catalunya (CESCA). M.T-S. acknowledges the CSIC for the JAE-DOC contract, and E.M. acknowledges a contract under the PERG05-GA-2009-249310 grant. We are grateful to Ramon Crehuet for his help in the NEB calculations

The role of the HO(4)(-) anion in atmospheric chemistry and biology is a matter of debate, because it can be formed from, or be in equilibrium with, key species such as O(3) + HO(-) or HO(2) + O(2) (-). The determination of the stability of HO(4)(-) in water therefore has the greatest relevance for better understanding the mechanism associated with oxidative cascades in aqueous solution. However, experiments are difficult to perform because of the short-lived character of this species, and in this work we have employed DFT, CCSD(T) complete basis set (CBS), MRCI/aug-cc-pVTZ, and combined quantum mechanics/molecular mechanics (QM/MM) calculations to investigate this topic. We show that the HO(4)(-) anion has a planar structure in the gas phase, with a very large HOO-OO bond length (1.823 A). In contrast, HO(4)(-) adopts a nonplanar configuration in aqueous solution, with huge geometrical changes (up to 0.232 A for the HOO-OO bond length) with a very small energy cost. The formation of the HO(4)(-) anion is predicted to be endergonic by 5.53±1.44 and 2.14±0.37 kcal mol(-1) with respect to the O(3) + HO(-) and HO(2) + O(2)(-) channels, respectively. Moreover, the combination of theoretical calculations with experimental free energies of solvation has allowed us to obtain accurate free energies for the main reactions involved in the aqueous decomposition of ozone. Thus, the oxygen transfer reaction (O(3) + OH(-) → HO(2) + O(2)(-)) is endergonic by 3.39±1.80 kcal mol(-1), the electron transfer process (O(3) + O(2)(-) → O(3)(-) + O(2)) is exergonic by 31.53±1.05 kcal mol(-1), supporting the chain-carrier role of the superoxide ion, and the reaction O(3) + HO(2)(-) → OH + O(2)(-) + O(2) is exergonic by 12.78±1.15 kcal mol(-1), which is consistent with the fact that the addition of small amounts of HO(2)(-) (through H(2)O(2)) accelerates ozone decomposition in water. The combination of our results with previously reported thermokinetic data provides some insights into the potentially important role of the HO(4)(-) anion as a key reaction intermediate.

Sulfuric acid can act as a catalyst of its own formation. We have carried out a computational investigation on the gas-phase formation of H 2SO4 by hydrolysis of SO3 involving one and two water molecules, and also in the presence of sulfuric acid and its complexes with one and two water molecules. The hydrolysis of SO3 requires the concurrence of two water molecules, one of them acting as a catalyzer, and our results predict an important catalytic effect, ranging between 3 and 11 kcal·mol-1 when the catalytic water molecule is substituted by a sulfuric acid molecule or one of its hydrates. In these cases, the reaction products are either bare sulfuric acid dimer or sulfuric acid dimer complexed with a water molecule. There are broad implications from these new findings. The results of the present investigation show that the catalytic effect of sulfuric acid in the SO3 hydrolysis can be important in the Earth's stratosphere, in the heterogeneous formation of sulfuric acid and in the formation of aerosols, in H2SO4 formation by aircraft engines, and also in understanding the formation of sulfuric acid in the atmosphere of Venus. © 2012 American Chemical Society., This work was supported by the Spanish DGYCIT (CTQ2011-27812) and the Generalitat de Catalunya (Grant 2009SGR01472). The calculations described in this work were carried out at the Centre de Supercomputació de Catalunya (CESCA) and at CTI-CSIC. M.T.-S. acknowledges the CSIC for a JAE-Doc contract. We also thank the reviewers for their comments and suggestions regarding this work.

In a very recent article (Chem. Eur. J. 14, 8652-8660 (2008)), the present author has shown that the picture of the local softness and local hardness is incomplete and that the understanding of these reactivity indices must be "redefined". In fact, the local softness and hardness contain the "same potential" information and they have to be considered as "local abundance" or "concentration" of their corresponding properties. In this contribution, we will analyze the implications in the applicability of the local version of the HSAB principle.

The reactions between fifteen carbonyl oxides and water have been investigated with the aim of contributing to a better understanding of the effects of the substituents in the reactivity of carbonyl oxides. We have employed density functional theory and large scale ab initio methods (CCSD(T), CASSCF, and CASPT2), combined with transition state theory, to investigate the addition of water to carbonyl oxide and, for those carbonyl oxides having a methyl substituent in syn, the hydrogen transfer from the methyl group to the terminal oxygen of carbonyl oxide. In this case, the water acts as a catalyst and this reaction can contribute to the atmospheric formation of a hydroxyl radical. Carbonyl oxides with electron withdrawing substituents and zwitterionic character have low energy barriers and react fast, whereas carbonyl oxides with electron releasing substituents have high energy barriers and react slowly. The position of the substituents plays also an important role and carbonyl oxides having a hydrogen atom substituent in syn react faster than carbonyl oxides having a hydrogen atom substituent in anti. The differences in the reactivity of different substituted carbonyl oxides raise up to ten orders of magnitude and the branching ratios for the two different reactions investigated are also reported.

The level of ab initio theory which is necessary to compute reliable values for the static and dynamic (hyper)polarizabilities of three medium size π-conjugated organic nonlinear optical (NLO) molecules is investigated. With the employment of field-induced coordinates in combination with a finite field procedure, the calculations were made possible. It is stated that to obtain reasonable values for the various individual contributions to the (hyper)polarizability, it is necessary to include electron correlation. Based on the results, the convergence of the usual perturbation treatment for vibrational anharmonicity was examined Support for this work under Grant Nos. BQU2002-04112-C02-02 and PB98-0457-C02-01 from the Dirección General de Enseñanza Superior e Investigación Científica y Técnica -MEC--Spain is acknowledged. One of us M.T. thanks the Generalitat of Catalunya for financial help through CIRIT Project No. FI/01-00699