Chemistry, Volume 2, Issue 4 (December 2020) – 10 articles

Catalytic nitrobenzene reduction is crucial for the synthesis of 4,4-methylene diphenyl diisocyanate, which is used to produce polyurethane foams, thermoplastic elastomers, and adhesives. The stability and activity of nanoparticle catalysts are affected by surface ligands and stabilizers. We established the complete composition of 7.0 ± 1.1 nm iridium oxide nanoparticles that were stabilized by polyvinylpyrrolidone (PVP[Ir]). PVP[Ir] and its surface stabilizers were characterized using elemental analysis (EA), high-resolution X-ray photoelectron spectroscopy (XPS), powder X-ray diffraction (PXRD), FT-IR, and UV-vis spectroscopy. Notably, PVP[Ir] contained 33.8 ± 0.4% Ir. XPS binding energy analyses suggest that 7% of the Ir is Ir(0) and 93% is IrO₂. Using formic acid as the source of hydrogen, PVP[Ir] catalyzed the selective hydrogenation of nitrobenzene to give aniline as the only product in 66% yield in 1 h at 160 °C in a high-pressure metal reactor. Less than 1% of the side products (azobenzene and azoxybenzene) were detected. In contrast, using alcohol as the hydrogen source led to a low yield and a poor selectivity for aniline. Full article

Bis(diphenylphosphino)methane dioxide (dppmO₂) forms eight-coordinate cations [M(dppmO₂)₄]Cl₃ (M = La, Ce, Pr, Nd, Sm, Eu, Gd) on reaction in a 4:1 molar ratio with the appropriate LnCl₃ in ethanol. Similar reaction in a 3:1 ratio produced seven-coordinate [M(dppmO₂)₃Cl]Cl₂ (M = Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb), whilst LuCl₃ alone produced six-coordinate [Lu(dppmO₂)₂Cl₂]Cl. The complexes have been characterised by IR, ¹H and ³¹P{¹H}-NMR spectroscopy. X-ray structures show that [M(dppmO₂)₄]Cl₃ (M = Ce, Sm, Gd) contain square antiprismatic cations, whilst [M(dppmO₂)₃Cl]Cl₂ (M = Yb, Dy, Lu) have distorted pentagonal bipyramidal structures with apical Cl. The [Lu(dppmO₂)₂Cl₂]Cl has a cis octahedral cation. The structure of [Yb(dppmO₂)₃(H₂O)]Cl₃·dppmO₂ is also reported. The change in coordination numbers and geometry along the series is driven by the decreasing lanthanide cation radii, but the chloride counter anions also play a role. Full article

Wollastonite (CaSiO₃) is an important mineral that is widely used in ceramics and polymer industries. Defect energetics, diffusion of Ca ions and a solution of dopants are studied using atomistic-scale simulation based on the classical pair potentials. The energetically favourable defect process is calculated to be the Ca-Si anti-site defect cluster in which both Ca and Si swap their atomic positions simultaneously. It is calculated that the Ca ion migrates in the ab plane with an activation energy of 1.59 eV, inferring its slow diffusion. Favourable isovalent dopants on the Ca and Si sites are Sr²⁺ and Ge⁴⁺, respectively. Subvalent doping by Al on the Si site is a favourable process to incorporate additional Ca in the form of interstitials in CaSiO₃. This engineering strategy would increase the capacity of this material. Full article

A model for the survival of the amino acid content in micrometeorites and its possible transformations upon atmospheric entry is described. Since any organic species released in the atmosphere at high altitudes would exhibit a limited lifetime with respect to the typical timescale for atmospheric mixing (due to the substantial radiation field of the early Sun), only the organic content inside the meteorites could have contributed to prebiotic chemistry. It is thus important to determine both the amino acid loss from meteorites, due to both degassing and chemical degradation, and the extent of the chemical transformation of amino acids subjected to the increased temperature due to friction with the atmosphere. According to the interplay between the potential energy barrier and the pre-exponential factor in rate coefficients, either diffusion or chemical processing might be the dominant process following the rising temperature upon atmospheric entry. The possibility of the elimination of water from glycine to form aminoketene, or ${\mathrm{CO}}_2$ to form methylamine, ultimately driven by gravitational energy, was examined along with the more conventional formation of a peptide bond between two glycine units to afford Gly–Gly. While retention, degassing, and decarboxylation are the fastest processes, each dominating in different ranges of the initial velocity and radius, the formation of either Gly–Gly from bimolecular water elimination or aminoketene from unimolecular water elimination appears to be negligible. Full article

The synthesis and corrosion inhibition performance of poly(butylene-succinate)-L-proline (PBSLP) prepared by solution polymerization are reported. PBSLP was characterized by FTIR, XRD, and SEM/energy dispersive X-ray (EDX). PBSLP was used to protect mild steel in 1 M hydrochloric acid. An SEM and an atomic force microscope (AFM) were used to characterize the surface morphology of the mild steel coupons. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were used to characterize the inhibition mechanism of PBSLP, and the inhibitor was a mixed-type corrosion inhibitor with a maximum corrosion inhibition efficiency of 93.0%. Adsorption studies revealed the adsorption of PBSLP to be a monolayer process and therefore, obeyed the Langmuir isotherm model. Full article

Traditional organic antimicrobials mainly act on specific biochemical processes such as replication, transcription and translation. However, the emergence and wide spread of microbial resistance is a growing threat for human beings. Therefore, it is highly necessary to design strategies for the development of new drugs in order to target multiple cellular processes that should improve their efficiency against several microorganisms, including bacteria, viruses or fungi. The present review is focused on recent advances and findings of new antimicrobial strategies based on metal complexes. Recent studies indicate that some metal ions cause different types of damages to microbial cells as a result of membrane degradation, protein dysfunction and oxidative stress. These unique modes of action, combined with the wide range of three-dimensional geometries that metal complexes can adopt, make them suitable for the development of new antimicrobial drugs. Full article

The large originator pharmaceutical companies need more and more new compounds for their molecule banks, because high throughput screening (HTS) is still a widely used method to find new hits in the course of the lead discovery. In the design and synthesis of a new compound library, important points are in focus nowadays: Lipinski’s rule of five (RO5); the high Fsp³ character; the use of bioisosteric heterocycles instead of aromatic rings. With said aim in mind, we have synthesized a small compound library of new spiro[cycloalkane-pyridazinones] with 36 members. The compounds with this new scaffold may be useful in various drug discovery projects. Full article

This work establishes the ‘click’ nature of the base-catalyzed oxirane ring opening reaction by the selenolate nucleophile. The ‘click’-generated ß-hydroxy selenide can be alkylated to afford cationic selenium species. Hemolytic studies suggest that selenonium cations do not lyse red blood cells even at high concentrations. Overall, these results indicate the future applicability of the developed organo-selenium chemistry in the preparation of a new class of cationic materials based on the seleno-ether motif. Full article

The crystal structures of inorganic hydroborates (salts and coordination compounds with anions containing hydrogen bonded to boron) except for the simplest anion, borohydride BH₄⁻, are analyzed regarding their structural prototypes found in the inorganic databases such as Pearson’s Crystal Data [Villars and Cenzual (2015), Pearson’s Crystal Data. Crystal Structure Database for Inorganic Compounds, Release 2019/2020, ASM International, Materials Park, Ohio, USA]. Only the compounds with hydroborate as the only type of anion are reviewed, although including compounds gathering more than one different hydroborate (mixed anion). Carbaborane anions and partly halogenated hydroborates are included. Hydroborates containing anions other than hydroborate or neutral molecules such as NH₃ are not discussed. The coordination polyhedra around the cations, including complex cations, and the hydroborate anions are determined and constitute the basis of the structural systematics underlying hydroborates chemistry in various variants of anionic packing. The latter is determined from anion–anion coordination with the help of topology analysis using the program TOPOS [Blatov (2006), IUCr CompComm. Newsl. 7, 4–38]. The Pauling rules for ionic crystals apply only to smaller cations with the observed coordination number within 2–4. For bigger cations, the predictive power of the first Pauling rule is very poor. All non-molecular hydroborate crystal structures can be derived by simple deformation of the close-packed anionic lattices, i.e., cubic close packing (ccp) and hexagonal close packing (hcp), or body-centered cubic (bcc), by filling tetrahedral or octahedral sites. This review on the crystal chemistry of hydroborates is a contribution that should serve as a roadmap for materials engineers to design new materials, synthetic chemists in their search for promising compounds to be prepared, and materials scientists in understanding the properties of novel materials. Full article

The Flack Parameter is now almost universally reported for all chiral materials characterized by X-ray crystallography. Its elegant simplicity was an inspired development by Howard Flack, and although the original algorithm for its computation has been strengthened by other workers, it remains an essential outcome for any crystallographic structure determination. As with any one-parameter metric, it needs to be interpreted in the context of its standard uncertainty. Full article