Some Mo‐oxo complexes bearing pyridine rings have the capability for dihydrogen production from water. However, energy barrier and overall energy vary depending on the effect exerted by several ...substituent groups located at different positions around one or more pyridine rings which are ligands of these compounds. Based on the Karunadasa and coworkers investigation where the para‐position was experimentally tested in compounds derivatised from the 2,6‐bis1,1‐bis(2‐pyridil)ethyl‐pyridine oxo‐molybdenum complex synthesized (Karunadasa et al., Nature, 2010, 464, 1329), we tested the combined effect of electron‐withdrawing and electron‐donating groups simulated as perturbations represented by point‐charges. Then, we used the density polarization concept, δρ(r), a local reactivity descriptor corresponding to the partially integrated linear response function, χ(r, r′) (a non‐local reactivity descriptor), which is able to reveal different displacements of π‐electrons on molecular structures. We perturbed the para‐positions in the pentadentate ligand 2,6‐bis1,1‐bis(2‐pyridil)ethyl‐pyridine in the Mo‐based complex by means of point‐charges. They were located in three different configurations of the organic ligand (trans, geminal, and cis) which could help to explain energy barriers and overall energy of reactions catalyzed by this type of Mo‐complexes. Our results indicate that the trans configuration of point‐charges induces the most amount of fraction of electron shifted on the complex. A Mo‐based complex bearing the same trans configuration for electron‐withdrawing and electron‐donating substituent groups (cyano and amino, respectively), leads to a kinetically more favorable H2 release than the cis or geminal configuration of the substituent groups aforementioned.
The mesomeric effect is visualized by means of 3D pictures of the density polarization δρ(r) independently of the substituent group nature since it is represented as a perturbation on the external potential, δυ(r). When the linear response function χ(r, r′), a non‐local reactivity descriptor, is integrated with respect to r′ (coordinates of the perturbation), we obtain the δρ(r) a local reactivity descriptor that quantifies the fraction of electron shifted on the whole molecular structure.
The main purpose of this study is to elucidate some discrepancies already observed in the catalytic activity values of some zirconocene methyl cations. The EDA‐NOCV scheme was employed for a ...theoretical description of the interactions between an ethylene molecule and five catalysts of zirconocene methyl cation. The nature of the chemical interactions has been elucidated through the QTAIM topological analysis. The steric hindrance due to the ligands was evaluated qualitatively by means of an IRI‐based analysis and quantitively through Fisher information. The findings prove that the indenyl ligand seems to favor the orbital interaction between the ethylene molecule and the metal centre of zirconocene methyl cation. Both electrostatic and orbital contributions play a crucial role in stabilising the studied complexes. Based on the NOCV deformation density contributions, the strongest orbital interaction is reached with the bis(indenyl)methyl zirconium cation, which is the only one exhibiting covalent interactions. Especially, the strong contribution of π‐back donation (occurring from the occupied orbitals of the zirconium atom to the π* anti‐bonding orbital of ethylene) may be a key to understand why this catalyst has a higher polymerisation yield than the other studied catalysts. This work suggests a perspective for predicting values of catalytic activity when theoretically designing novel catalysts of zirconocene type.
When covalent interactions predominate over non covalent interactions, the catalytic activity increases significantly which was concluded through the combined analysis given by energy decomposition analysis, natural orbitals of chemical valence and quantum theory of atoms in molecules.
In the current work, the authors analyzed and compared the chemical behavior of some (anti)aromatic compounds. The species selected are benzene and cyclobutadiene as the aromatic and antiaromatic ...classical examples, respectively. Next, the anion Al42−, which is the first all‐metal molecule catalogued as aromatic and its non‐metallic isoelectronic analog, B42− were also analyzed. The antiaromatic clusters Al44− and B44− were studied in form of lithium salts. And the end, the non‐planar B12 boron cluster and its isoelectronic analogs (B11Be− and B11C+) were considered for being analyzed under the same criterium. The analysis was realized employing the following descriptors: molecular electrostatic potential and local hyper‐softness to get insights concerning local reactivity when facing reagents leading to ionic or covalent interactions. The results show that all the molecules analyzed presented some specific variations in their respective local reactivity despite being labeled as aromatic compounds. This analysis provides a notion that the local reactivity is more based on the nature of the atoms and the molecular geometry than the aromatic character by itself.
Through the use of the local hyper‐softness, s2r, we found that, despite being B12, B11C+, and B11Be+ isoelectronic aromatic molecules, C+ distorts the local reactivity more than Be− does, thus revealing the capability of s2r to distinguish effects caused by the different nature of the substituent atomic ions aforementioned. Consequently, the two resulting species, B11C+ and B11Be−, are still aromatic molecules like B12, but differ in their local reactivities.
The reason why the local softness (LS) and the local hyper-softness (LHS) allow comparisons of local reactivities among molecular systems of similar or different sizes is analyzed. We evidenced this ...scaling behavior on these functions by means of their working formulae. This feature bases on the scaling capacity of LS and LHS according to the molecular size. The Fukui function (FF), and the dual descriptor (DD) do not satisfy that property.
The dual descriptor potential Martínez-Araya, Jorge I.
Journal of mathematical chemistry,
05/2024, Volume:
62, Issue:
5
Journal Article
Peer reviewed
The dual descriptor potential (DDP) has appeared in several papers, It is proposed as a local reactivity descriptor within the framework of the Conceptual Density Functional Theory and as a ...complementary tool of the molecular electrostatic potential (MEP) rather than the dual descriptor (DD). DDP provides information concerning the most energetically favorable sites to undergo nucleophilic and electrophilic attacks. Unlike the dual descriptor, DDP is directly related with energy. Furthermore, the DDP seems to depure the scalar field, allowing us to unveil the predominance of nucleophilic and electrophilic regions on a molecule. This is in stark contrast to the dual descriptor, which tends to scatter around the molecule, hindering the interpretation of the local reactivity on regions that exceed the atomic volume. To the best of our knowledge, this is the first time that DDP is represented as a 3D picture. To assess its capability to describe interaction among molecules, DDP was tested on some molecular systems, along with MEP. Results show that the joint use of these tools helps in the understanding of certain experimental evidences, serving as an alternative to the molecular orbital theory.
The electron density depletion associated with π-hole at the ring center typical of energetic compounds was clearly revealed by the molecular electrostatic potential (ESP). In addition, the spatial ...arrangement of NO2 groups appears to affect the ESP value in the ring center, and therefore sensitivity to detonation. Indeed, for monocyclic nitrobenzene compounds with the same number of NO2 groups, the ESP value in the ring center decreases as the NO2 groups are more closely spaced. As expected, the central rings become less aromatic as NO2 groups are added. The MCI, PDI, PLR, NICSzz(1), FLU indices are all strongly correlated with the ESP values observed in the ring center of the set of nitrobenzenes. Aromaticity indices based on electron delocalization criteria appear to be very sensitive to small variations in aromaticity. Among magnetic-based indices, only NICSzz(1) is capable to predict small changes in aromaticity. The PLR index derived from conceptual DFT is quite relevant for predicting small variations in aromaticity. According to our results, the most suitable aromaticity index is not based on a single criterion, and that selecting it is more subtle. Therefore, it is important to combine information from several criteria to obtain a more complete description of the aromaticity of the studied compounds.
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•Spatial arrangements of NO2 groups affect the ESP value at the ring center.•ESP value at the ring center decreases as the NO2 groups are closely spaced.•Central rings become less aromatic as NO2 groups are added.•NICSzz(1) is capable of properly predicting small changes in aromaticity.•Delocalization-based indices are sensitive to slight changes in aromaticity.
The necessity of the human hippocampus for remote autobiographical recall remains fiercely debated. The standard model of consolidation predicts a time-limited role for the hippocampus, but the ...competing multiple trace/trace transformation theories posit indefinite involvement. Lesion evidence remains inconclusive, and the inferences one can draw from functional MRI (fMRI) have been limited by reliance on covert (silent) recall, which obscures dynamic, moment-to-moment content of retrieved memories. Here, we capitalized on advances in fMRI denoising to employ overtly spoken recall. Forty participants retrieved recent and remote memories, describing each for approximately 2 min. Details associated with each memory were identified and modeled in the fMRI time-series data using a variant of the Autobiographical Interview procedure, and activity associated with the recall of recent and remote memories was then compared. Posterior hippocampal regions exhibited temporally graded activity patterns (recent events > remote events), as did several regions of frontal and parietal cortex. Consistent with predictions of the standard model, recall-related hippocampal activity differed from a non-autobiographical control task only for recent, and not remote, events. Task-based connectivity between posterior hippocampal regions and others associated with mental scene construction also exhibited a temporal gradient, with greater connectivity accompanying the recall of recent events. These findings support predictions of the standard model of consolidation and demonstrate the potential benefits of overt recall in neuroimaging experiments.
Searching for adequate and effective compounds displaying antimicrobial activities, especially against Gram-positive bacteria, is an important research area due to the high hospitalization and ...mortality rates of these bacterial infections in both the human and veterinary fields. In this work, we explored (
)-4-amino-3-((3,5-di-
-butyl-2-hydroxybenzylidene)amino) benzoic acid (SB-1, harboring an intramolecular hydrogen bond) and (
)-2-((4-nitrobenzilidene)amino)aniline (SB-2), two Schiff bases derivatives. Results demonstrated that SB-1 showed an antibacterial activity determined by the minimal inhibitory concentration (MIC) against
,
, and
(Gram-positive bacteria involved in human and animal diseases such as skin infections, pneumonia, diarrheal syndrome, and urinary tract infections, among others), which was similar to that shown by the classical antibiotic chloramphenicol. By contrast, this compound showed no effect against Gram-negative bacteria (
,
, and
). Furthermore, we provide a comprehensive physicochemical and theoretical characterization of SB-1 (as well as several analyses for SB-2), including elemental analysis, ESMS,
H and
C NMR (assigned by 1D and 2D techniques), DEPT, UV-Vis, FTIR, and cyclic voltammetry. We also performed a computational study through the DFT theory level, including geometry optimization, TD-DFT, NBO, and global and local reactivity analyses.
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