Surface Engineering of the Mechanical Properties of Molecular Crystals via an Atomistic Model for Computing the Facet Stress Response of Solids.

Invited for the cover of this issue are Mubarak Almehairbi, Vikram C. Joshi, Changquan Calvin Sun and Sharmarke Mohamed. The image depicts the digital exploration of the mechanical properties of crystals on specific facets that may be of interest for materials applications by "dialing-in" their stress response. Read the full text of the article at 10.1002/chem.202400779.

Surface Engineering of the Mechanical Properties of Molecular Crystals via an Atomistic Model for Computing the Facet Stress Response of Solids.

Dynamic molecular crystals are an emerging class of crystalline materials that can respond to mechanical stress by dissipating internal strain in a number of ways. Given the serendipitous nature of the discovery of such crystals, progress in the field requires advances in computational methods for the accurate and high-throughput computation of the nanomechanical properties of crystals on specific facets which are exposed to mechanical stress. Here, we develop and apply a new atomistic model for computing the surface elastic moduli of crystals on any set of facets of interest using dispersion-corrected density functional theory (DFT-D) methods. The model was benchmarked against a total of 24 reported nanoindentation measurements from a diverse set of molecular crystals and was found to be generally reliable. Using only the experimental crystal structure of the dietary supplement, L-aspartic acid, the model was subsequently applied under blind test conditions, to correctly predict the growth morphology, facet and nanomechanical properties of L-aspartic acid to within the accuracy of the measured elastic stiffness of the crystal, 24.53±0.56 GPa. This work paves the way for the computational design and experimental realization of other functional molecular crystals with tailor-made mechanical properties.

Exsolution of Co-Fe Alloy Nanoparticles on the PrBaFeCoO5+δ Layered Perovskite Monitored by Neutron Powder Diffraction and Catalytic Effect on Dry Reforming of Methane.

Reversible exsolution and dissolution of metal nanoparticles (NPs) in complex oxides have been investigated as an efficient strategy to improve the performance and durability of the catalysts for thermal and electrochemical energy conversion. Here, in situ exsolution of Co-Fe alloy NPs from the layered perovskite PrBaFeCoO5+δ (PBFC) and their dissolution back into the oxide host have been monitored for the first time by in situ neutron powder diffraction and confirmed by X-ray diffraction and electron microscopy. Catalytic tests for dry reforming of methane showed stable operation over ∼100 h at 800 °C with negligible carbon deposition (<0.3 mg/gcat h). The CO2 and CH4 conversions are among the highest achieved by layered double perovskites. The cyclability of the PBFC catalyst and the potential to improve the catalytic activity by adjusting the composition, size, and the NP distribution would pave the way for highly efficient energy conversion applications.

Exsolution of Ni Nanoparticles from A-Site-Deficient Layered Double Perovskites for Dry Reforming of Methane and as an Anode Material for a Solid Oxide Fuel Cell.

Exsolution is a promising technique to design metal nanoparticles for electrocatalysis and renewable energy. In this work, Ni-doped perovskites, (Pr0.5Ba0.5)1-x/2Mn1-x/2Nix/2O3-δ with x = 0, 0.05, 0.1, and 0.2 (S-PBMNx), were prepared to design exsolution systems as solid oxide fuel cell anodes and for catalysis applications. X-ray diffraction and transmission electron microscopy (TEM) analyses demonstrated that correlating A-site deficiency with Ni content can effectively induce exsolution of all Ni under H2 atmosphere at T ∼ 875 °C, yielding the reduced (exsolved) R-PBMNx materials. On heating the exsolution systems in air, metal incorporation in the oxide lattice did not occur; instead, the Ni nanoparticles oxidized to NiO on the layered perovskite surface. The lowest area-specific resistance (ASR) under wet 5% H2/N2 in symmetrical cells was observed for R-PBMN0.2 anode (ASR ∼ 0.64 Ω cm2 at 850 °C) due to the highest Ni particle density in the R-PBMNx series. The best performance for dry reforming of methane (DRM) was also obtained for R-PBMN0.2, with CH4 and CO2 conversion rates at 11 and 32%, respectively, and the highest production of H2 (37%). The DRM activity of R-PBMN0.2 starts at 800 °C and is sustained for up to at least 5 h operation with little carbon deposition (0.017 g·gcat-1·h-1). These results clearly demonstrate that varying Ni-doping in layered double perovskite oxides is an effective strategy to manipulate the electrochemical performance and catalytic activity for energy conversion purposes.

C-demethylation and 1, 2-amino shift in (E)-2-(1-(3-aminophenyl) ethylidene)hydrazinecarboxamide to (E)-2-(2-aminobenzylidene)hydrazinecarboxamide and their applications.

A Novel (E)-2-(1-(3-aminophenyl)ethylidene)hydrazinecarboxamide 1 was synthesized by traditional method and converted to (E)-2-(2-aminobenzylidene)hydrazinecarboxamide 2 by single step in DMSO at room temperature. Synthesized compound 1 was analysed by spectroscopy (NMR and LC-MS) techniques and molecule 2 was characterized using single crystal X-ray diffraction and spectroscopy (NMR and GC-MS) techniques. These analytical technique results revealed that, C-demethylation and 1, 2 amino shift in phenyl ring of compound 1 gives molecule 2. DNA binding studies of compounds 1 and 2 was carried out by electronic absorption spectroscopy. This result revealed that, compounds 1 and 2 showed hyperchromism with bathochromic shift. Anticancer activity of compounds 1 and 2 is carried out by molecular docking with five receptors.Computer aided virtual screening demonstrated that the synthesized molecules possess ideal drug likeliness, pharmacokinetics features, toxicity profile for structure based drug discovery. The molecular docking studies revealed that the synthesized molecules are significant binding with the five selected cancer receptors with minimum binding energy (kcal/mol), number of hydrogen bonds, weak interaction, docking score and cluster RMS. The docking studies also suggested that the molecules showed interactions with DNA and the theoretical values of the binding are comparable with that of the experimental values. Hirshfeld surface analysis was used to analyze and quantify the intermolecular interactions in the crystal structure of compound 2.

Microwave assisted synthesis of coumarin-purine derivatives: An approach to in vitro anti-oxidant, DNA cleavage, crystal structure, DFT studies and Hirshfeld surface analysis.

An easy and efficient microwave-assisted protocol has been developed for the synthesis of coumarin-purine hybrids (3a-3j). The newly constructed 1,3-dimethyl-7-((substituted)-2-oxo-2H-chromen-4-yl)methyl)-1H-purine-2,6(3H,7H)-dione derivatives were evaluated for their in vitro antioxidant activity by DPPH free radical-scavenging ability assay and DNA cleavage by using calf thymus. The compound 3i, shows the most excellent DPPH scavenging activity with a -OH substitution at C7 of coumarin ring. In addition, the structure of compound 3f, has been elucidated using single crystal X-ray diffraction technique. Theoretical calculations (DFT) were carried out using Gaussian09 program package and B3LYP correlation function. Full geometry optimization were carried out using 6-311G++(d, p) basis set and the frontier orbital energy were presented. Hirshfeld surface analysis was used for the intermolecular interactions in the crystal structure. The experimental result of the compound 3f has been compared with the theoretical results and it was found that the experimental data are in a good agreement with the calculated values.