Pentlandite (Fe, Ni)₉S₈ is an important accessory mineral on asteroidal surfaces. It has been identified in returned regolith samples from asteroids Itokawa, Ryugu, and Bennu. Currently, systematic studies to understand the response of this mineral phase under space weathering conditions are lacking. In this work, we performed pulsed laser irradiation to simulate micrometeoroid impacts, and ion irradiation with 1 keV H⁺ and 4 keV He⁺ to simulate solar wind exposure for pentlandite. To understand the chemical, microstructural, and spectral alterations resulting from simulated space weathering, we conducted X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and reflectance spectroscopy across the visible to near-infrared wavelengths. Our results reveal S depletion and a change in the Fe:Ni ratio at the sample surface with continuing ion irradiation. Ion irradiation also created compositionally distinct rims in the pentlandite samples, while laser irradiation produced a surface melt. Additionally, we identified hillocks protruding from the pentlandite rim after He⁺ irradiation. Our findings also show that laser and H⁺-irradiation cause the sample to brighten, while He⁺ ion irradiation causes darkening. The change in spectral slope for samples irradiated with the laser and He⁺ is minimal, while H⁺ causes the sample to redden slightly. This work will enable the identification of space weathering signatures on pentlandite grains present in the recently returned samples from asteroids Ryugu and Bennu.

Carbon fiber is a critical material in a wide range of industries, where it is highly valued for its high specific strength/stiffness, excellent wear resistance, efficient electrical and thermal transport properties, chemical resistance, and low coefficient of thermal expansion. The properties of a specific carbon fiber are closely tied to its structural characteristics at all length scales. In this work, we applied wide-angle x-ray diffraction to a set of heat-treated mesophase pitch-based carbon fibers, with the goal of elucidating the crystalline structures as a function of fiber orientation. To assist with analysis and interpretation of the experimental data, we employed diffraction pattern simulations using the scalar and vector forms of the Debye scattering equation to determine the influence of basal plane orientation, crystalline ordering (turbostratic-graphitic), and basal plane asymmetry on the diffraction patterns. The results presented here suggest that growth of the transverse crystallites in mesophase pitch-based carbon fiber is fixed until graphitization temperatures are reached. The work completed here provides a framework for the analysis of carbon fiber and other oriented carbon-based materials via diffraction.

Stereocomplexation, or stereochemistry-directed complexation between complementary stereoregular macromolecules such as polymers and peptides, brings about remarkable changes in the thermomechanical properties and stability of materials. Peptide stereocomplexes tie together these merits of stereocomplexation with the vast compositional space and biological function of peptides, and therefore are compelling building blocks of highly tunable, functional materials. In this work, we introduce peptide stereocomplexes as cross-links in polymer hydrogels. Attaching either L- or D-peptides to 4-arm PEG furnishes conjugates that are soluble in aqueous buffer, while their 1 : 1 blends form hydrogels at or above 7.5% (w/v). Increasing conjugate concentration increases both shear storage modulus (G′) and the intensity of the characteristic β-sheet infrared absorption at 1630 cm⁻¹, highlighting the importance of peptide secondary structure for gelation. These gels, having peptide stereocomplexes as cross-links, strain stiffen up to nearly 50% strain, then soften at higher strains. Despite the crystalline nature of stereocomplexes, these gels display dynamic behavior: after application and removal of high strain, the gels recover partially, with 10–50% recovery of G′ after the first cycle and 50–70% in subsequent cycles. Moreover, the peptide stereocomplex cross-links imbue proteolytic stability, with nearly 80% of conjugates remaining intact after a 1 h incubation with Proteinase K, compared to just ∼40% of the L-conjugates. We anticipate that the material platform and combination of characterization methods presented here will readily extend to studying other peptides sequences, so as to leverage the full range of peptide design space and accelerate the development and implementation of peptide stereocomplexes to control hydrogel properties, function, and lifetime.

Hafnium oxide-based thin films, in particular hafnium zirconium oxide (HZO), have potential for applications in nonvolatile memory and energy harvesting. Atomic layer deposition (ALD) is the most widely used method for HZO deposition due to its precise thickness control and ability to provide conformal coverage. Previous studies have shown the effects of different metal precursors, oxidizer precursors, and process temperatures on the ferroelectric properties of HZO. However, no mechanism has been identified to describe the different phase stabilities as the metal precursor purge time varies. This study investigates how varying the metal precursor purge time during plasma-enhanced ALD (PE-ALD) influences the phases and properties of the HZO thin films. Grazing incidence X-ray diffraction, Fourier transform infrared spectroscopy, and scanning transmission electron microscopy are used to study the changes in phase of HZO with variation of the metal precursor purge time during the PE-ALD process. The phases observed are correlated with polarization and relative permittivity responses under an electric field, including wake-up and endurance effects. The resulting phases and properties are linked to changes in composition, as measured using time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy. It is shown that short metal precursor purge times result in increased carbon and nitrogen impurities and stabilization of the antipolar Pbca phase. Long purge times lead to films comprising predominantly the ferroelectric Pca2₁ phase.

Boron–phosphorus (B–P) frustrated Lewis pairs (FLPs) are an important class of compounds for activating various small molecules. Utilizing the ring expansion reactivity of 9-chloro-9-borafluorene, a borinine-based FLP was synthesized. Various five-membered main-group element heterocycles were obtained via the reaction of the FLP with Me₃NO, S₈, and Se. Subsequent reduction of these species yielded the ring-expanded compounds, each featuring bridging B–E–B (E = O, S, Se) bonds. Similarly, halide abstraction from the FLP with AgNTf₂ led to the formation of a cationic ring-expanded compound with a bridging B–Cl–B motif. This motif constitutes one of the first examples of a boron-stabilized chloronium ion, as verified using in-depth bonding analysis methods. Mechanistic pathways for the reduction- and halide abstraction-mediated ring expansion reactions are proposed with the aid of density functional theory. Electronic structure computations were performed to determine the best representation of bonding interactions in each compound, suggesting phosophorus(V)–chalcogen double bonding and chalcogen–boron(III) dative interactions within the heterocycles.

The bis-acetate complexes (SbQ₃)Pt(OAc)₂ (1) and (SbQ₂Ph)Pt(OAc)₂ (2) (Q = 8-quinolinyl) were used to study C–Cl acetoxylation of 1,2-dichloroethane (DCE) to generate 2-chloroethyl acetate and the complexes (SbQ₃)PtCl₂ (1b) and (SbQ₂Ph)PtCl₂ (2b), respectively. The first acetoxylation step produced the intermediates (SbQ₃)Pt(Cl)(OAc) (1a) and (SbQ₂Ph)Pt(Cl)(OAc) (2a). The reaction was studied using pseudo first order kinetics (excess DCE) in order to compare the rates of reaction of 1 and 2, which revealed that k_obs = 2.44(6) × 10^–4 s^–1 for 1 and 0.51(2) × 10^–4 s^–1 for 2. The intermediate 1a was synthesized independently, and the solid-state structure was determined using single crystal X-ray diffraction. A non-Sb containing control complex, (^tbpy)Pt(OAc)₂ (3) (^tbpy = 4,4′-di-tert-butyl-2,2′bipyridine), was studied for the acetoxylation of DCE to form (^tbpy)Pt(Cl)(OAc) with k_obs = 0.46(1) × 10^–4 s^–1. Density Functional Theory (DFT) calculations were used to examine possible Pt-mediated mechanisms for the reactions of 1, 2, or 3 with DCE. The lowest energy calculated substitution mechanism occurs with nucleophilic attack by the Pt center on the C−Cl bond followed acetate reaction with the Pt−C bond. However, close in energy and potentially also a viable mechanism is a direct substitution mechanism where the coordinated acetate anion directly reacts with the C−Cl bond of DCE. In addition, the rate of acetoxylation for complex 1 in heated dichloromethane-d₂ and chloroform-d was determined (0.43(1) × 10^–4 s^–1 for dichloromethane-d₂ and 0.37(1) × 10^–4 s^–1 for chloroform-d) and compared to the rate of acetoxylation of DCE.

Reaction of copper(II) bromide with 3,5-di­chloro­pyridine (3,5-Cl₂py) or 3,5-di­methyl­pyridine (3,5-Me₂py) led to the isolation of the coordination polymers catena-poly[[bis­(3,5-di­chloro­pyridine)­copper(II)]-di-μ-bromido], [CuBr₂(C₅H₃Cl₂N)₂]_n or [CuBr₂(3,5-Cl₂py)₂]_n (1), and catena-poly[[bis­(3,5-di­methyl­pyridine)­copper(II)]-di-μ-bromido], [CuBr₂(C₇H₉N)₂]_n or [CuBr₂(3,5-Me₂py)₂]_n (2), respectively. The structures are characterized by bibromide-bridged chains [d(av.)_Cu⋯Cu = 3.93 (9) Å]. In 1, the chains are linked perpendicular to the a axis by non-classical hydrogen bonds and halogen bonds, while in 2, only non-classical hydrogen bonds are observed.

The reaction of CAAC-CS₂ betaine (1; CAAC = cyclic(alkyl)(amino)carbene) and alkali metal reductants under ambient conditions yields carbene-stabilized carbon disulfide radical anions as crystalline alkali metal salts. The radicals 3–5 form multinuclear clusters featuring diverse metal sulfide and disulfide interactions, which promote unusual reductive coupling and cyclization of adjacent CS₂ units to C₂S₃ heterocycles (6). The addition of crown ethers to 3–5 sequesters the alkali cations and facilitates disulfide cleavage to yield stable [CAAC-CS₂]^·– monomers (7 and 8). Calculated natural atomic spin populations suggest that the spin densities in the clustered and monomeric species are comparable and evenly distributed between the CAAC and CS₂ subunits. Subsequent reductions afford [CAAC-CS₂]^2– dianions (9–12), which can be reoxidized to radicals by comproportionation reactions with 1. The radicals are, in turn, oxidized to betaine 1 through salt elimination reactions with transition metals. Cyclic voltammograms of 1 feature reversible 1/1^·–/1^2– couples with a small separation between the events (ΔΔG = 11.1 kcal mol^–1). All isolated compounds were characterized by a combination of electron paramagnetic resonance spectroscopy, heteronuclear NMR spectroscopy, infrared spectroscopy, and single-crystal X-ray diffraction. Insights into their electronic structure are supported by density functional theory calculations.

Two-dimensional hybrid organic–inorganic perovskites (HOIPs) have emerged as promising materials for light-emitting diode applications. In this study, by using time-of-flight neutron spectroscopy we identified and quantitatively separated the lattice vibrational and molecular rotational dynamics of two perovskites, butylammonium lead iodide (BA)₂PbI₄ and phenethyl-ammonium lead iodide (PEA)₂PbI₄. By examining the corresponding temperature dependence, we found that the lattice vibrations, as evidenced by neutron spectra, are consistent with the lattice dynamics obtained from Raman scattering. We revealed that the rotational dynamics of organic molecules in these materials tend to suppress their photoluminescence quantum yield (PLQY) while the vibrational dynamics did not show predominant correlations with the same. Additionally, we observed photoluminescence emission peak splitting for both systems, which becomes prominent above certain critical temperatures where the suppression of PLQY begins. This study suggests that the rotational motions of polarized molecules may lead to a reduction in exciton binding energy or the breaking of degeneracy in exciton binding energy levels, enhancing non-radiative recombination rates, and consequently reducing photoluminescence yield. These findings offer a deeper understanding of fundamental interactions in 2D HOIPs and could guide the design of more efficient light-emitting materials for advanced technological applications.