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cis-2-tert-Butyl-5-(tert-butylsulfonyl)-1,3-dioxane (cis-1) exhibits a high degree of eclipsing in the H–C5–S–C segment in the solid state, the origin of which remains unexplained. The eclipsed conformation that corresponds to an energetic minimum in the solid state practically corresponds to a rotational transition state in solution, which allows an approach to understand transitions states. The difference in the enthalpy of sublimation ΔsubH between cis-1 and the more stable trans-1 is 8.40 kcal mol−1, lets to consider that the intermolecular interactions in the crystalline structure must be responsible for the conformational effect observed in the solid state. The study of the experimental electron density of cis-1 in solid state allowed to establish that CH⋯O＝S intermolecular interaction is the main contribution to the observed eclipsing. The charge density analysis was also performed using the quantum theory of atoms in molecules to evaluate the nature and relevance of the intermolecular interactions in the crystal structure. [ABSTRACT FROM AUTHOR]

Phosphate ester hydrolysis is an important reaction that plays a major role in both enzymatic and non-enzymatic processes, including DNA and pesticide breaking. Although it is a widely studied reaction, the precise mechanistic details, especially for copper complexes, remain under discussion. To contribute to the debate, we present the catalyzed hydrolysis of phosphomono-, di- and tri-esters mediated by the [Cu(II)(1,10-phenanthroline)] complex. The reaction coordinates for several substrates were explored through the metadynamics formalism. Thus, we found that for mono- and di-substituted ester phosphates a concerted mechanism is observed, where a coordinated hydroxyl group attacks the phosphorus atom at the same side as the leaving group, along with a proton transfer. In contrast, tri-substituted phosphate remains coordinated with the metal, and the nucleophile acts independently following an addition–elimination process. That is, the metallic complex achieves a specific nucleophile-phosphate interaction that produces a concerted transition state in the phosphoester hydrolysis process. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel approach to track the origin of the metal complex structure from the topology of the α and β spin densities as an extension of the Linnett–Gillespie model. Usually, the theories that explain the metal–ligand interactions consider the disposition and the relative energies of the empty or occupied set of d orbitals, ignoring the spin contribution explicitly. Our quantum topological approach considers the spatial distribution of the α and β spin valence shells, and the energy interaction between them. We used the properties of the atomic graph, a topological object that summarises the charge concentrations and depletions on the valence shell of an atom in a molecule, and the interacting quantum atoms (IQA) energy partition scheme. Unlike the Linnett–Gillespie model, which is based on electron–electron repulsion, our approach states that the ligands provoke a redistribution of the electron density to maximize the nuclear–electron interactions in each spin valence shell to bypass the concentration of electron–electron interactions, resulting in a polarization pattern which determines the position of the ligands. [ABSTRACT FROM AUTHOR]

Quantum Chemical Topology (QCT) is a well established structural theoretical approach, but the development of its reactivity component is still a challenge. The hypothesis of this work is that the reactivity of an atom within a molecule is a function of its electronic population, its delocalization in the rest of the molecule, and the way it polarizes within an atomic domain. In this paper, we present a topological reactivity predictor for cabonyl additions, κ. It is a measure of the polarization of the electron density with the carbonyl functional group. κ is a model obtained from a QSAR procedure, using quantum-topological atomic descriptors and reported hydration equilibrium constants of carbonyl compounds. To validate the predictive capability of κ, we applied it to organic reactions, including a multicomponent reaction. κ was the only property that predicts the reactivity in each reaction step. The shape of κ can be interpreted as the change between two electrophilic states of a functional group, reactive and non-reactive. [ABSTRACT FROM AUTHOR]

We investigated two important unresolved issues on excited state intramolecular proton transfer (ESIPT) reactions, i.e., their driving force and the charge state of the transferred species by means of quantum chemical topology. We related changes in the aromaticity of a molecule after electron excitation to reaction dynamics in an excited state. Additionally, we found that the conveyed particle has a charge intermediate between that of a bare proton and a neutral hydrogen atom. We anticipate that the analysis presented in this communication will yield valuable insights into ESIPT and other similar photochemical reactions. [ABSTRACT FROM AUTHOR]

A novel and alternative explanation of the rotational barrier of ethane and several hexasubstituted derivatives, CX3CX3 (X = H, F, CH3, Cl, Br), is suggested based on the evaluation of the properties of the electron distribution. The forces exerted on the electron density of the topological atoms making up a molecule, the Ehrenfest forces, are analyzed and, with the help of the virial theorem, they are used to explain the experimental rotational barriers. According to this approach, the barrier is mainly a consequence of the decrease of the always attractive Ehrenfest forces (EFs) linking the two C atoms. In addition, the behavior of the EFs is related to a decrease of stability of the central C atoms, which is not compensated by the stabilization of the substituents. Also, during rotation from the staggered to the equilibrium conformation, the electron density at the C–C bond critical point and the electron delocalization between C atoms decrease and are accompanied by an increase of electron delocalization between the substituents. According to the analysis of the EF field lines and to the behavior of the integrated forces, the rotational barrier cannot be explained as a result of any repulsive forces acting on the electron density, although a possible interpretation of the quantum force that balances the EF in stationary states as a measure of traditional Pauli repulsions is also examined. [ABSTRACT FROM AUTHOR]

Casiopeínas® are copper complexes with the general formula [Cu(N–N)(N–O)]NO3and [Cu(N–N)(O–O)]NO3where N–N denotes a substituted bipyridine or phenanthroline, N–O indicates α-aminoacidate or peptide and O–O represents acetylacetonate or salicylaldehyde. This family of compounds has been evaluated in vitroand in vivoshowing cytotoxic, genotoxic, and antineoplastic activity. The action mechanism is still not completely elucidated, but the possibility exists that these compounds interact with DNA by intercalation due to the aromatic moiety. In this work we found, using the properties of the electron density of a π-complex model base–Casiopeína®–base, that the stacking mechanism between Casiopeínas® and DNA bases is due to an electron density deficiency of the ligand of the Casiopeína® which is compensated for by an electron transfer from adenines by a π–π interaction. [ABSTRACT FROM AUTHOR]

The conformational preference in normal and reverse anomeric effects is analyzed by taking advantage of the known additivity and transferability of functional group energies defined by the gradient of the electron density. As the anomeric effect has an energetic origin and every change in the electron density produces an energetic change, an explanation of this phenomenon should be based on the density changes taking place in a conformational equilibrium. The total energy of substituted cyclohexanoids is partitioned into ring and substituent contributions and the preferred conformation is the result of a balance between them. This new alternative approach allows understanding of the anomeric effect in terms of group energy contributions. In general, the most stable conformer in both the anomeric and reverse anomeric effects is that where the ring transfers charge to the heteroatom in the substituent during the process. [ABSTRACT FROM AUTHOR]