MacLeod Carey, Desmond

Context. Formaldehyde H2CO was the first organic polyatomic molecule discovered in the interstellar medium to have been detected in a variety of sources. However, pathways to synthesize this molecule under interstellar conditions have yet to be discussed. Aims. We carried out a systematic study to analyze the chemical processes that can explain the H2CO formation mechanism toward a decamer of methanol (CH3OH)10 as target material to mimic an ice mantle bombarded by an OH+ cation. Methods. We performed Born-Oppenheimer (ab initio) molecular dynamics simulations to obtain the formation mechanisms of complex organic molecules (COMs) such as formaldehyde H2CO and its HCOH isomer. Results. We found that CH2OH+ and CH2(OH)2 are the main precursors to form H2CO and HCOH. We discuss its formation mechanisms and the astrophysical implications in star-forming regions. These processes are likely relevant to the production of COMs.

The use of different N-heterocyclic carbene (NHC) as dative ligands benefits from their capabilities ranging from strong to weak σ-donor according to the Tolman electronic parameter (TEP), well spread in the formation of monometallic complexes, and recently extended to metallic nanocluster and surfaces. Here, we set to explore the role of relativistic effects in determining the stabilization of the dative carbon–metal bond on coinage metal complexes given by NHC-MCl species (M = Cu, Ag, Au), by quantifying their contribution to the different terms related to the bond formation by comparing scalar relativistic and non-relativistic DFT calculations. Our results show a strong contribution to the stabilization of the NHC-M bond, increasing along with the group, from the lighter Cu atom (7.9%) to Ag (15.3%), and most notoriously for the heavier member, Au (39.9%). This observation is similar along the different stabilizing terms related to the C-M bond, where the acceptor character of the metal center is affected, resulting in a stronger σ-donor interaction from the involved ligand. Thus, the theoretical evaluation of carbon–metal bonds requires the equal footing treatment of relativistic effects along with the group, which is beneficial for the theoretical evaluation of ligand capabilities prior to the engaging exploration of the efficient formation of related complexes involving lighter to heavy metallic centers.

The search for new antibacterial agents that could decrease bacterial resistance is a subject in continuous development. Gram-negative and Gram-positive bacteria possess a group of metalloproteins belonging to the MEROPS peptidase (M4) family, which is the main virulence factor of these bacteria. In this work, we used the previous results of a computational biochemistry protocol of a series of ligands designed in silico using thermolysin as a model for the search of antihypertensive agents. Here, thermolysin from Bacillus thermoproteolyticus, a metalloprotein of the M4 family, was used to determine the most promising candidate as an antibacterial agent. Our results from docking, molecular dynamics simulation, molecular mechanics Poisson-Boltzmann (MM-PBSA) method, ligand efficiency, and ADME-Tox properties (Absorption, Distribution, Metabolism, Excretion, and Toxicity) indicate that the designed ligands were adequately oriented in the thermolysin active site. The Lig783, Lig2177, and Lig3444 compounds showed the best dynamic behavior; however, from the ADME-Tox calculated properties, Lig783 was selected as the unique antibacterial agent candidate amongst the designed ligands.

Relevant virulence traits in Candida spp. are associated with dimorphic change and biofilm formation, which became an important target to reduce antifungal resistance. In this work, Co(II) complexes containing a benzotriazole derivative ligand showed a promising capacity of reducing these virulence traits. These complexes exhibited higher antifungal activities than the free ligands against all the Candida albicans and non-albicans strains tested, where compounds 2 and 4 showed minimum inhibitory concentration values between 15.62 and 125 μg mL−1. Moreover, four complexes (2–5) of Co(II) and Cu(II) with benzotriazole ligand were synthesized. These compounds were obtained as air-stable solids and characterized by melting point, thermogravimetric analysis, infrared, Raman and ultraviolet/visible spectroscopy. The analysis of the characterization data allowed us to identify that all the complexes had 1:1 (M:L) stoichiometries. Additionally, Density Functional Theory calculations were carried out for 2 and 3 to propose a probable geometry of both compounds. The conformer Da of 2 was the most stable conformer according to the Energy Decomposition Analysis; while the conformers of 3 have a fluxional behavior in this analysis that did not allow us to determine the most probable conformer. These results provide an important platform for the design of new compounds with antifungal activities and the capacity to attack other target of relevance to reduce antimicrobial resistance. © 2023, Springer Nature Switzerland AG.

Spatial race under low oxygen conditions requires solid mild propellants to be used. Therefore, we study the catalytic effect of the previously reported [trans-Cu(μ-OH)(μ-dmpz)]6 complex on the thermal decomposition of ammonium perchlorate by a differential scanning calorimetry (DSC) technique. The copper compound causes a decrease of ammonium perchlorate's decomposition temperature to 372.5 °C, consequently increasing the heat release by 576 J·g−1, when used in a 5 wt% as burning rate (BR) catalyst. It must be remarked that, the [trans-Cu(μ-OH)(μ-dmpz)]6 complex presents a superior performance as BR catalyst when compared to nano-metallic oxides. This Cu(II) compound modifies the decomposition mechanism of ammonium perchlorate, providing the necessary O2 to accelerate the overall burning process paving the way to the study of copper pyrazolate complexes as BR catalysts.

The hydrogen storage properties of Ti-doped Bn ((Formula presented.)) clusters are investigated by using the “diatomic deposition method” with further evaluation by density functional theory computations. The results show that TiBn ((Formula presented.)) clusters possess the ability to storage up to four H2 molecules, reaching a mass fraction of 6.12%. Further, the hydrogen release temperature is analyzed by molecular dynamics simulations with a variable temperature. It turns out that the TiB7 and TiB9 clusters release the H2 molecules at T ≲ 700 K, while TiB8 requires higher temperature due to stronger interactions with the H2 molecules, confirmed by the electronic density of states. The size-dependent properties and odd–even nuclearity on the clusters can be useful for applications with controlled temperature. These results serve for further design of novel materials with reversible and controlled hydrogen storage properties based on TiB7/TiB9 motifs. Additionally, new lower-energy isomers for TiB4 and TiB9 clusters were found within the accuracy of the all-electron triple-ζ Slater [slater type orbital (STO)-Triple-zeta basis set(TZP)] basis set.

Recently, P. V. Nhatet al., have discussed and commented on our article (DOI: 10.1039/D0CP04018E) for the case of the most stable structure of Ag15. They have found a new most stable structure (labeled as 15-1) in comparison to the putative global minimum reported by us, which is a four layered 1-4-6-4 stacking structure with aC2vpoint group (15-2). In this reply, we have performed a larger structure search which allowed us to confirm the results of Nhatet al.The results show the existence of multiple isoenergetic isomers with similar structure motifs for the Ag15system, increasing the problem complexity to locate the global minimum. The results in regard to the structure and electronic properties of the new lowest energy structure are discussed.

A new structure for spherical fullerene is evaluated involving sixty phenylene rings, replacing every C-vertex from C60, which is based on the isolated-pentagon-rule (IPR) motif based on a cyclo‐meta‐phenylene derivatives reported by Isobe group, resulting in superstructures mimicking C60 (1). Density functional theory calculation shows its stability and properties, also predicting a related C70 counterpart (2), and nano-onions incorporating C60 and C70 inside 1 and 2. These species are attractive targets of 0D-covalent organic frameworks (0D-COF) related to hollow fullerenes, which can be extended to other sp (Taylor et al., 1990) [2]-based species. The obtained structures show increased redox potentials in a larger π-surface area in comparison to C60 and C70, which are of relevance for photovoltaic applications. © 2020 Elsevier Ltd.