Towards a unified fold-cusp model for bond polarity scaling: electron rearrangements in the pyrolytic isomerization of cubane to cyclooctatetraene.

Context: This study meticulously examines the criteria for assigning electron rearrangements along the intrinsic reaction coordinate (IRC) leading to bond formation and breaking processes during the pyrolytic isomerization of cubane (CUB) to 1,3,5,7-cyclooctatetraene (COT) from both thermochemical and bonding perspectives. Notably, no cusp-type function was detected in the initial thermal conversion step of CUB to bicyclo[4.2.

Synergizing Machine Learning, Conceptual Density Functional Theory, and Biochemistry: No-Code Explainable Predictive Models for Mutagenicity in Aromatic Amines.

This study synergizes machine learning (ML) with conceptual density functional theory (CDFT) to develop OECD-compliant predictive models for the mutagenic activity of aromatic amines (AAs) with a fully No-Code methodology using a comprehensive data set of 251 AAs, Leave-One-Out-Cross-Validation (LOOCV), and three distinct data splits. Our research employs the GFN2-xTB method, known for its robustness and speed, to compute descriptors for procarcinogens and their activated metabolites in vacuum and aqueous phases. We evaluate the effectiveness of different theoretical definitions of electrophilicity within CDFT, namely, PSL, GCV, and CDP schemes, and the newly introduced Log QP descriptor to approximate Log P information.

Formulating Reduced Density Gradient Approaches for Noncovalent Interactions.

This work elucidates several forms of reduced electron density gradient (RDG) to describe noncovalent interactions (NCIs). By interpreting the RDG as a local moment function, we systematically leveraged Weizacker's and Fermi's local moments. This resulted in high-fidelity RDG representations consistent with the NCI analysis.

Revisiting the bonding evolution theory: a fresh perspective on the ammonia pyramidal inversion and bond dissociations in ethane and borazane.

This work offers a comprehensive and fresh perspective on the bonding evolution theory (BET) framework, originally proposed by Silvi and collaborators [X. Krokidis, S. Noury and B.

A simple topology-based model for predicting the activation barriers of reactive processes at 0 K.

This work reveals an underlying correlation between the topology and energetic features of matter configurations/rearrangements by exploiting two topological concepts, namely, structural stability and persistency, leading thus to a model capable of predicting activation energies at 0 K. This finding provides some answers to the difficulties of applying Thom's functions for extracting energetic information of rate processes, which has been a limitation for exact, biological, and technological sciences. A linear relationship between the experimental barriers of 17 chemical reactions and both concepts was found by studying these systems' topography along the intrinsic reaction coordinate.

On the Notation of Catastrophes in the Framework of Bonding Evolution Theory: Case of Normal and Inverse Electron Demand Diels-Alder Reactions.

This paper generalizes very recent and unexpected findings [J. Phys. Chem.

Photochemically Induced 1,3-Butadiene Ring-Closure from the Topological Analysis of the Electron Localization Function Viewpoint.

The electronic rearrangement featuring the photochemically-induced 1,3-cis-butadiene is discussed within a bonding evolution theory (BET) perspective based on the topological analysis of the electron localization function and Thom's catastrophe theory. The process involves the vertical singlet-singlet excitation S →S , and the subsequent deactivation implying the S /S and S /S conical intersection regions. BET results reveal that the new CC bond is finally formed on the S surface, as also recently found in the photochemical addition of two ethylenes [Phys.

Introduction to celebrating Latin American talent in chemistry.

In celebration of the excellence and breadth of Latin American research achievements across the chemical sciences, we are delighted to present an introduction to the themed collection, Celebrating Latin American talent in chemistry.

Machine learning predictive classification models for the carcinogenic activity of activated metabolites derived from aromatic amines and nitroaromatics.

A 3D-QSAR study based on DFT descriptors and machine learning calculations is presented in this work. Our goal has been to build predictive models for classifying the carcinogenic activity of a set of aromatic amines (AA) and nitroaromatic (NA) compounds. As the main result, we stress that calculations must consider both the activated metabolites (derived from AA and NA species) and the water solvent to obtain reliable predictive classification models.

On Electron Pair Rearrangements in Photochemical Reactions: 1,3-Cyclohexadiene Ring Opening.

1,3-Cyclohexadiene ring opening has been studied within the bonding evolution theory (BET) framework. We have focused on describing for the first time the electron pair rearrangements leading to the -1,3,5-hexatriene (HT) product from CHD. The nature of bonding in this process begins with the weakening of the double bonds in the Franck-Condon region.

Unraveling the Bonding Nature Along the Photochemically Activated Paterno-Büchi Reaction Mechanism.

The photochemically activated Paterno-Büchi reaction mechanism following the singlet excited-state reaction path was analyzed based on a bonding evolution framework. The electronic rearrangements, which describe the mechanism of oxetane formation via carbon-oxygen attack (C-O), comprises of the electronic activation of formaldehyde and accumulation of pairing density on the O once the reaction system is approaching the conical intersection point. Our theoretical evidence based on the ELF topology shows that the C-O bond is formed in the ground-state surface (via C-O attack) returning from the S surface accompanied by 1,4-singlet diradical formation.

On the nature of bonding in the photochemical addition of two ethylenes: C-C bond formation in the excited state?

In this work, the 2s + 2s (face-to-face) prototypical example of a photochemical reaction has been re-examined to characterize the evolution of chemical bonding. The analysis of the electron localization function (as an indirect measure of the Pauli principle) along the minimum energy path provides strong evidence supporting that CC bond formation occurs not in the excited state but in the ground electronic state after crossing the rhombohedral S/S conical intersection.

A physiologic rise in cytoplasmic calcium ion signal increases pannexin1 channel activity via a C-terminus phosphorylation by CaMKII.

Pannexin1 (Panx1) channels are ubiquitously expressed in vertebrate cells and are widely accepted as adenosine triphosphate (ATP)-releasing membrane channels. Activation of Panx1 has been associated with phosphorylation in a specific tyrosine residue or cleavage of its C-terminal domains. In the present work, we identified a residue (S394) as a putative phosphorylation site by Ca/calmodulin-dependent kinase II (CaMKII).

Are There Only Fold Catastrophes in the Diels-Alder Reaction Between Ethylene and 1,3-Butadiene?

This work revisits the topological characterization of the Diels-Alder reaction between 1,3-butadiene and ethylene. In contrast to the currently accepted rationalization, we here provide strong evidence in support of a representation in terms of seven structural stability domains separated by a sequence of 10 elementary catastrophes, but all are only of the fold type (F and F), that is, CH + CH:1-7-[FF]F[FF][FF][]F-0: CH. Such an unexpected finding provides fundamental new insights opening simplifying perspectives concerning the rationalization of the CC bond formation in pericyclic reactions in terms of the simplest Thom's elementary catastrophe, namely, the one-(state) variable, one-(control) parameter function.

A Close Look to the Oxaphosphetane Formation along the Wittig Reaction: A [2+2] Cycloaddition?

The Wittig reaction between triphenylphosphine methylide and benzaldehyde has been studied both from conceptual and computational approaches. The supernucleophilic character of ylide accounts for the feasibility of the initial nucleophilic attack. The nature of bonding driving the formation of the first oxaphosphetane (OPA) intermediate in such a domino reaction is examined within a topological-based bonding evolution theory perspective.

Are one-step aromatic nucleophilic substitutions of non-activated benzenes concerted processes?

Aromatic nucleophilic substitution (SAr) reactions of non-electrophilically activated benzenes have been studied within the Molecular Electron Density Theory (MEDT) at the B3LYP/6-311+G(d) computational level. These reactions, taking place through a one-step mechanism, present a high activation Gibbs free energy, ΔG = 31.0 kcal mol, which decreases to 22.

On the electron flow sequence driving the hydrometallation of acetylene by lithium hydride.

The sequence of the electronic flow driving the hydrometallation of acetylene by lithium hydride (and that of the opposite β-hydride elimination reaction from the alkenyl metal intermediate), was examined within the perspective provided by the bonding evolution theory (BET). The analysis was based on the application of catastrophe theory to the changes of the electron localization function topology along the intrinsic reaction coordinate. The description of the electronic processes occurring on the process was represented in terms of topological structural stability domains (SSDs) and the associated elementary bifurcation catastrophes.

Reaction Electronic Flux Perspective on the Mechanism of the Zimmerman Di-π-methane Rearrangement.

The reaction electronic flux (REF) offers a powerful tool in the analysis of reaction mechanisms. Noteworthy, the relationship between aromaticity and REF can eventually reveal subtle electronic events associated with reactivity in aromatic systems. In this work, this relationship was studied for the triplet Zimmerman di-π-methane rearrangement.

Understanding the Highly Varying pKa of Arylamines. A Perspective from the Average Local Ionization Condensed-to-Atom Framework.

The highly varying experimental pKa values for 36 arylamines spanning 7 orders of magnitude is carefully examined. Within this framework, a valence condensed-to-atom model for the average ionization energy is introduced and tested. The theoretical approach is connected to orbital Fukui functions directly mapped into semilocal or regional site-specific responses.

Dual Emission of a Novel (P,N) Re(I) Complex: A Computational and Experimental Study on [P,N-{(C6H5)2(C5H4N)P}Re(CO)3Br].

The spectroscopic, electrochemical, and photophysical properties of the new complex [P,N-{(C6H5)2(C5H4N)P}Re(CO)3Br] are reported. The UV-vis spectrum in dichloromethane shows an absorption maximum centered at 315 nm and a shoulder at 350 nm. These absorption bands have been characterized to have MLCT character.

A computational and conceptual DFT study on the mechanism of hydrogen activation by novel frustrated Lewis pairs.

A computational and conceptual density functional theory (DFT) study on the mechanism of molecular hydrogen activation by a set of three frustrated Lewis pairs (FLPs) was performed at the ωB97X-D/6-311G(d,p) level of theory. A reduced model and other two prototypes derived from experimental data, based on the donor nitrogen and acceptor boron atoms, were used. Analysis based on the energy results, geometries and the global electron density transfer at the TSs made it possible to obtain some interesting conclusions: (i) despite the well-known very low reactivity of molecular hydrogen, the catalytic effectiveness of the three FLPs produces reactions with almost unappreciable activation energies; (ii) the reactions, being exothermic, follow a one-step mechanism via polarised TSs; (iii) there are neither substituent effects on the kinetics nor on the thermodynamics of these reactions; (iv) the activation of molecular hydrogen seems to be attained when the N-B distance in the FLP derivatives is around 2.

On the intrinsic reactivity index for electrophilicity/nucleophilicity responses.

We present a critical discussion related to the recent definition of the intrinsic reactivity index, IRI, (Tetrahedron Lett. 2013, 54, 339-342; Tetrahedron 2013, 69, 4247-4258) formulated to describe both, electrophilicity (charge acceptance) and nucleophilicity (charge donation) reactivities. We here stress that such an IRI model, based on the quantity μ/η, should be properly related to theoretical approximations associated to the change in the global electronic energy of a given chemical system under interaction with a suitable electron bath (Gazquez JL et al.

Understanding the thermal [1s,5s] hydrogen shift isomerization of ocimene.

α-Ocimene, β-ocimenes and alloocimenes are isomeric monoterpenes occurring naturally as oils within several plants and fruits. These thermally unstable compounds are employed in the pharmaceutical and fine-chemicals industries due to their natural plant defense properties and pleasant odors. In this work, and in the context of a recent revival in attention on the subject, we provide new theoretical insights concerning the nature of the electronic reorganization driving the decomposition of cis-β-ocimene to alloocimene.

Theoretical investigation of the selectivity in intramolecular cyclizations of some 2'-aminochalcones to dihydroquinolin-8-ones and indolin-3-ones.

The selectivity of the intramolecular cyclizations of a series of 2'-aminochalcones was investigated with an approach that combines spin-polarized conceptual density functional theory and energy calculations. To that aim, condensed-to-atoms electrophilic Fukui functions, f NN (+) (r), were utilized as descriptors of the proclivity for nucleophilic attack of the NH2 group on the unsaturated α and β carbons. The results of our model are in excellent agreement with the experimental available evidence permitting us in all cases to predict when the cyclization processes led to the formation of 5-exo and 6-endo products.