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Previous experimental results on the free radical-scavenging properties of boldine, one of the most potent natural antioxidants, suggested that the benzylic hydrogen, neighboring a nitrogen lone electron pair, might be the key to its protective and antioxidant effect, in contrast to the usually assumed labile phenolic hydrogen atoms. Our computations suggest that both boldine and glaucine can undergo two successive hydrogen transfers under attack by an oxidizing radical (from C-6a-H and C-7-H). The hydroxyl groups of boldine could also participate via the HAT mechanism, although to a lesser extent. In the case of quaternary N-methylated derivatives, the sharing of the nitrogen lone pair makes the transfer of the C-6a hydrogen energetically unfeasible, supporting the earlier proposal based on experimental evidence. The hydroxyl groups of boldine and its derivatives could contribute to antioxidant activity via the sequential proton loss electron transfer mechanism, although this would only be relevant at higher pH values. [ABSTRACT FROM AUTHOR]

In the context of the design and study of new materials for hydrogen storage, in this work structural, compositional, thermodynamic and kinetic-mechanistic factors for the desorption/absorption of a hydrogen molecule in the M3AlH10−xNa (M = Be or Mg; x = 0 or 2) hydrides are evaluated. The results show that the mechanisms of hydrogen detachment/attachment are energetically more favorable when the two involved hydrogen atoms are related to different metals in each system. The hydrogenation of M3AlH8Na occurs very easily at relatively low temperatures. The most convenient values of temperature and rate constants for thermal dehydrogenation are reached for the Be3AlH10Na system in tetrahedral geometry. These factors, together with the fact that this structure is quite symmetrical, make the tetrahedral Be3AlH10Na a good candidate as an assembly unit for suprastructures. However, our results indicate that the dehydrogenation temperature is rather high; so, future studies about ways to facilitate Be3AlH10Na dehydrogenation, such as its catalysis or its support on some surface, are necessary for energy-based uses. [ABSTRACT FROM AUTHOR]

A simple and chemically intuitive approach is used to design ptC-containing E–C clusters (E = Si–Pb). This approach consists in replacing three or two consecutive protons from an aromatic hydrocarbon by one E24+ or one E2+ fragment, respectively. In the model, electrons from E are removed from the pz orbitals, emptying them. Si–Pb favors the formation of a 3c-2e (E–C–E) σ-bond, which involves the ptC. Additionally, the π-electronic cloud is delocalized through the E-pz orbitals allowing the E atoms to effectively take part in the electronic delocalization, preserving the 4n + 2 Hückel's rule from the parent hydrocarbon. Two aromatic monocycles and one aromatic bicycle – benzene (C6H6), cyclopentadienyl anion (C5H5−) and pentalene dianion (C8H62−) – have been transformed into C–E systems. After an extensive exploration of their potential energy surfaces, four new global minima with ptC are identified, resulting from the substitution of the protons by Si and Ge cations in C5H5− and C8H62− (E3C5 and E4C8). The analysis of both the chemical bonding and the magnetic response to an external magnetic field confirms the aromatic character of these species. [ABSTRACT FROM AUTHOR]

The internal isomerization, MNC ↑ MCN (M = Cu, Ag, Au), is investigated through quantum chemical computations. CuNC and AgNC are shown to be neither thermochemically nor kinetically stable against transformation to MCN. The free energy barrier (ΔG‡) for AuNC is somewhat considerable (7.1 kcal mol−1), indicating its viability, particularly at low temperature. Further, the Ng inserted analogues, MNgCN (M = Cu, Ag, Au; Ng = Xe, Rn) turn out to be thermochemically stable with respect to all possible dissociation channels but for two two-body dissociation channels, viz., MNgCN → Ng + MCN and MNgCN → Ng + MNC, which are connected to the internal isomerization processes, MNgCN → NgMCN and MNgCN → NgMNC, respectively. However, they are kinetically protected by substantial ΔG‡ values (11.8–15.4 kcal mol−1 for Cu, 9.8–13.6 kcal mol−1 for Ag, and 19.7–24.7 kcal mol−1 for Au). The pathways for such internal conversion are explored in detail. A thorough inspection of the bonding situation of the studied molecules, employing natural bond order, electron density, adaptive natural density partitioning, and energy decomposition analyses indicates that the M–Ng bonds in MNgCN and Ng–C bonds in AuNgCN can be represented as an electron-shared covalent bond. For the other Ng–C bonds, although an ionic description is better suited, the degree of covalent character is also substantial therein. [ABSTRACT FROM AUTHOR]

Viable planar pentacoordinate carbon (ppC) systems with a ppC bonded to a transition metal and embedded in a metallocene framework are reported. Our detailed global minima search shows that CAl4MX2 (M = Zr and Hf; X = F–I and C5H5) clusters with ppCs are appropriate candidates for experimental realization in the gas phase. The fulfillment of the 18 electron rule and electron delocalization is found to be crucial for the stabilization of these ppC arrangements. [ABSTRACT FROM AUTHOR]

Computational prediction and design of sandwich structures have drawn a lot of attention because of their interesting bond characteristics and broad applications. Most studies focus on the thermodynamic stability. In this study, we performed a series of Born–Oppenheimer molecular dynamics (BO-MD) simulations to investigate the dynamic stability of the well-known sandwich structure CrB24. The aim was to find at which temperature the sandwich structure is stable. The MD results showed that the sandwich structure has an extremely poor dynamic stability. Additionally, one highly symmetric endohedral structure with a chromium atom at the center of a B24 cage was found. As a demonstration, we attempted to point out the importance of dynamics studies on the future design of sandwich structures. [ABSTRACT FROM AUTHOR]

In this paper, we provide solid evidence to show that among an overwhelming structural diversity, alkaline earth metals (Ca, Sr, Ba) have the ability to form inverted sandwich compounds with C6H6, C7H7+, and C8H82+ of Dnh symmetry and general formula [E–(CnHn)–E]n−6 (n = 6–8) with planar 10-π-electron aromatic cores by virtue of transferring two electrons per metal atom to the ring. However, the origin of the orbital interaction between the metals and the carbon ring is quite different; while [E–(C6H6)–E] complexes are dominated by δ-interactions, both π- and δ-interactions are important in [E–(C7H7)–E]+ and [E–(C8H8)–E]2+ complexes. [ABSTRACT FROM AUTHOR]

The potential energy surfaces of a series of clusters with the formula CAl3E (E = P, As, Sb, Bi) are systematically explored using density functional theory and high level ab initio calculations. The global minimum structure of these clusters contains a planar tetracoordinate carbon atom. The presence of a C=E double bond is supported by the Wiberg bond indices, the adaptive natural density partitioning analysis, and the magnetic response. Our results show that these planar tetracoordinate carbon clusters are both thermodynamically and kinetically viable species in the gas phase. [ABSTRACT FROM AUTHOR]

A quasi-planar member of the so-called 'Wankel motor' family, B182-, is found. This boron cluster is an electronically stable dianion and a concentric doubly σ- and π-aromatic system. The inner B6 unit in B182- undergoes quasi-free rotation inside the perimeter of the B12 ring. The absence of any localized σ-bond between the inner ring and the peripheral boron atoms makes the system fluxional. [ABSTRACT FROM AUTHOR]

New experimental and theoretical data show that the previously reported planar tetracoordinate Sn complexes [Sn(Ph2P(Se)N(Se)PPh2)2] (1-sq) and [Sn(iPr2P(Se)N(Se)PiPr2)2] (2-sq) were not isolated and rather confused with the selenium complexes [Se(Ph2P(Se)N(Se)PPh2)2] (3-sq) and [Se(iPr2P(Se)N(Se)PiPr2)2] (4-sq), respectively. [ABSTRACT FROM AUTHOR]

The B19- anion and other boron species have been dubbed 'Wankel motors' for the almost barrierless rotation of inner and outer concentric rings relative to each other in these compounds. A single substitution in B19- is shown to shut down the well-established fluxionality in the anion. A carbon atom substituted in the structure to give a neutral CB18 species is shown computationally to enforce bond localization. [ABSTRACT FROM AUTHOR]

The effectiveness of our proposed approach to stabilize a planar tetracoordinate carbon (ptC) in cyclic aromatic hydrocarbons, introduced in the title article, is unquestionable as our exhaustive searches on the singlet and triplet potential energy surfaces of the new ptC molecules identified as viable species are reproducible. Besides, the T1 diagnostic value for the Si2C5H2 system reported in the comment seems to be the T1 amplitudes. We recomputed the T1 diagnostic value using different software (Gaussian and ORCA), which gave similar values to that reported in our communication. Additionally, a multiconfigurational (complete active space SCF) calculation fully confirms the mono-configurational character of the questioned Si2C5H2 ptC structure. We accept that the linear isomer for the C7H2 system, in the triplet electronic state, is competitive with the isomer reported in our article, in the singlet electronic state, as mentioned in the title comment. However, this is a minor correction that does not affect the primary goal and main conclusions of our communication. [ABSTRACT FROM AUTHOR]

The increase in and concern about neurodegenerative diseases continue to grow in an increasingly long-lived world population. Therefore, the search for new drugs continues to be a priority for medicinal chemistry. We present here the synthesis of a series of compounds with acetamide nuclei. Their structures were established using UV-Visible, NMR, HRMS and IR techniques. Furthermore, we report the crystal structures that were obtained from compounds 5a-5d by X-ray diffraction. The compounds were evaluated as potential inhibitors of the monoxidase enzymes; A (MAO-A) and B (MAO-B), and cholinesterases; acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) through in silico studies using the induced fit docking (IFD) method and binding free energy (Δ G bind ) calculations by the MMGBSA method. Interestingly, compounds 5b, 5c and 5d showed much better Δ G bind than the reference drug Zonisamide. Compound 5c is the best in the series, which indicates a potential selective affinity of our compounds against MAO-B, which could be a promising finding in the search for new drugs for Parkinson's disease treatment. The acetamide crystal exhibits moderate NLO properties suggesting that it could be considered a potential candidate for application in nonlinear optical devices., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (This journal is © The Royal Society of Chemistry.)

A single crystal of a piperonal chalcone derivative was obtained, fully characterized, and crystallized by a slow evaporation technique. The synthesized compound was characterized by UV-Visible, FT-IR, HRMS, 1 H NMR, and 13 C NMR spectroscopic studies and X-ray crystallography, revealing that the crystal belongs to a triclinic crystal system with a P 1̄ space group, Z = 2. In the present work, we focus on molecular modeling studies such as Hirshfeld surface analysis, energy framework calculations, frontier molecular orbital analysis, natural bond orbital analysis, and NLO properties of a π-conjugate system combining the chalcone and the pyrazole[3,4- b ]pyridine scaffolds to describe the in-depth structural analysis thereof. Good agreement was found between the calculated results and experimental data. In addition, Hirshfeld surface analysis of the crystal structure showed that the intermolecular stabilization in the crystal packing comes mainly from H⋯H bond interactions. The chalcone crystal exhibits significant NLO properties suggesting that it could be considered a potential candidate for application in nonlinear optical devices., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Viable planar pentacoordinate carbon (ppC) systems with a ppC bonded to a transition metal and embedded in a metallocene framework are reported. Our detailed global minima search shows that CAl 4 MX 2 (M = Zr and Hf; X = F-I and C 5 H 5 ) clusters with ppCs are appropriate candidates for experimental realization in the gas phase. The fulfillment of the 18 electron rule and electron delocalization is found to be crucial for the stabilization of these ppC arrangements.

Computational prediction and design of sandwich structures have drawn a lot of attention because of their interesting bond characteristics and broad applications. Most studies focus on the thermodynamic stability. In this study, we performed a series of Born-Oppenheimer molecular dynamics (BO-MD) simulations to investigate the dynamic stability of the well-known sandwich structure CrB24. The aim was to find at which temperature the sandwich structure is stable. The MD results showed that the sandwich structure has an extremely poor dynamic stability. Additionally, one highly symmetric endohedral structure with a chromium atom at the center of a B24 cage was found. As a demonstration, we attempted to point out the importance of dynamics studies on the future design of sandwich structures.

In this paper, we provide solid evidence to show that among an overwhelming structural diversity, alkaline earth metals (Ca, Sr, Ba) have the ability to form inverted sandwich compounds with C6H6, C7H7(+), and C8H8(2+) of Dnh symmetry and general formula [E-(CnHn)-E](n-6) (n = 6-8) with planar 10-π-electron aromatic cores by virtue of transferring two electrons per metal atom to the ring. However, the origin of the orbital interaction between the metals and the carbon ring is quite different; while [E-(C6H6)-E] complexes are dominated by δ-interactions, both π- and δ-interactions are important in [E-(C7H7)-E](+) and [E-(C8H8)-E](2+) complexes.

The potential energy surfaces of a series of clusters with the formula CAl3E (E = P, As, Sb, Bi) are systematically explored using density functional theory and high level ab initio calculations. The global minimum structure of these clusters contains a planar tetracoordinate carbon atom. The presence of a C=E double bond is supported by the Wiberg bond indices, the adaptive natural density partitioning analysis, and the magnetic response. Our results show that these planar tetracoordinate carbon clusters are both thermodynamically and kinetically viable species in the gas phase.

The B19(-) anion and other boron species have been dubbed 'Wankel motors' for the almost barrierless rotation of inner and outer concentric rings relative to each other in these compounds. A single substitution in B19(-) is shown to shut down the well-established fluxionality in the anion. A carbon atom substituted in the structure to give a neutral CB18 species is shown computationally to enforce bond localization.

A quasi-planar member of the so-called 'Wankel motor' family, B18(2-), is found. This boron cluster is an electronically stable dianion and a concentric doubly σ- and π-aromatic system. The inner B6 unit in B18(2-) undergoes quasi-free rotation inside the perimeter of the B12 ring. The absence of any localized σ-bond between the inner ring and the peripheral boron atoms makes the system fluxional.

We explore in detail the potential energy surfaces of the Al(x)Mg(y) (x, y = 1-4) systems as case studies to test the utility and limitations of simple rules based on electron counts and the phenomenological shell model (PSM) for bimetallic clusters. We find that it is feasible to design stable structures that are members of this set of small Al-Mg binary clusters, using simple electron count rules, including the classical 4n + 2 Hückel model, and the most recently proposed PSM. The thermodynamic stability of the title compounds has been evaluated using several different descriptors, including the fragmentation energies and the electronic structure of the systems. Three stable systems emerge from the analysis: the Al(4)Mg, Al(2)Mg(2) and Al(4)Mg(4) clusters. The relative stability of Al(4)Mg is explained by the stability of the Al(4)(2-) subunit to which the Mg atom donates its electrons. Here the Mg(2+) sits above the aromatic 10 π-electron Al(4)(2-) planar ring. The Al(2)Mg(2) and Al(4)Mg(4) clusters present more complicated 3D structures, and their stabilities are rationalized as a consequence of their closed shell nature in the PSM, with 10 and 20 itinerant electrons, respectively.

The potential energy surfaces of the Na(Si(5-n)(BH)(n))(-) and Si(5-n)(BH)(n)(2-) (n = 0-5) systems have been explored in detail. We established that all the global minimum structures of anionic and dianionic systems can be obtained by substitution of one or more silicon atoms of the global minima of NaSi(5)(-) and Si(5)(2-) for B-H units. The conservation of the overall structure upon isoelectronic substitution was shown to be due to the preservation of the chemical bonding pattern. Theoretical VDEs were calculated for all of the sodiated Na(Si(5-n)(BH)(n))(-) (n = 0-5) systems to facilitate their experimental detection.