Abstract Predicting nanocrystal (nanoparticle) assembly into ordered arrays (superlattices) is a grand challenge in materials chemistry that has largely resisted first-principles theories. Here, we extend MOLT-CF, a classical density functional theory, to multicomponent nanocrystal systems and subject it to a rigorous validation by comparing against nearly 300 experiments spanning two decades of literature. We use MOLT-CF to predict stability and phase diagrams for binary superlattices of nanocrystals with linear hydrocarbon ligands, as well as many other fine structural details, for example, lattice constants, packing fractions, ligand structure, and, in the case of (cubic) perovskite nanocrystals, orientation. Significant discrepancies from experiments are noted only for the Li3Bi and Cu3Au superlattices. In the former, we predict that this lattice is stabilized by particle fractionalization, which is supported by a reexamination of experimental data in the literature. In the case of Cu3Au (for which MOLT-CF predicts thermodynamic instability against phase separation into single-component lattices), we propose two alternative candidate structures that reconcile theory with experimental observations. These results establish MOLT-CF as a rigorous platform for the computational design of next-generation functional nanoparticle materials.
Abstract Metal oxyhalides are versatile materials, exhibiting properties relevant to photocatalysis, solid-state battery systems, ferromagnetism, multiferroics, and nonlinear optics. Here, mixed-metal oxyhalide intergrowths, layered materials formed by intercalating SrBi3O4Cl3 and Bi2GdO4Cl blocks along the c direction within a crystal, are reported. They are synthesized through a flux-based approach in which the SrBi3O4Cl3-to-Bi2GdO4Cl ratio can be precisely controlled. Despite the structural and compositional flexibility of such intergrowths, there is no general framework for predicting which local structural arrangements are preferred. Density functional theory combined with Bader charge analysis shows that preferred stacking sequences are those that minimize charge disproportionation across distinct chlorine environments, consistent with Pauling’s fifth rule, and we support this bonding-based framework through computational cation substitution that shifts the ionic-covalent balance of the metal–chloride bonding. With the preferred stacking arrangement established, this same system further reveals that intergrowth layering and Sr/Bi site occupancy modulate the interaction between the Bi3+ lone pair and anion p orbitals. Density functional theory calculations reveal that intergrowth formation destabilizes the O-2p orbitals, raising the valence band maximum for visible-light absorption, with the lone-pair interaction and layering-driven internal electrostatic field acting as competing effects on the resulting band gap. Significantly, this experimental-computational study establishes a transferable, bonding-based framework for stacking-sequence stability in layered oxyhalide intergrowths, while also clarifying how the same structural levers used to control stability can be tuned to engineer band structure.
Abstract We report that the Na+ ion within the calcium–sodium–calcium (Ca–Na–Ca) metal triad in two thermostable bacterial α-amylases (ca. 58 kDa) can be directly detected by 23Na (I = 3/2) quadrupole-central-transition (QCT) NMR spectroscopy in aqueous solution. We show that 23Na QCT NMR signals from hyperthermostable Bacillus licheniformis α-amylase (BLA) and its mesophilic homologue, Bacillus amyloliquefaciens α-amylase (BAA), exhibit remarkable subppm spectral resolution, which is unprecedented in NMR studies of quadrupolar nuclei in proteins. Using this new 23Na QCT NMR methodology, we examine the pH-dependent unfolding, melting temperatures (Tm), long-term thermal inactivation profiles, and chemical denaturing of BAA and BLA. We also use 23Na QCT NMR to monitor EDTA titration experiments, which yielded the apparent binding constants of the Na+ ion to BAA and BLA to be (0.3 ± 0.1) × 109 and (0.6 ± 0.1) × 109 M–1, respectively. Because the Ca–Na–Ca metal triad is located in the vicinity of the active cleft, the subppm spectral resolution of 23Na QCT NMR makes it possible to detect subtle changes of the enzyme structure caused by the presence of inhibitors such as acarbose and quercetin. This work represents the first time that Na+ ions tightly bound to an enzyme are directly observed by 23Na QCT NMR in aqueous solution. This new 23Na QCT NMR approach can potentially be extended to detection of other metal ions with quadrupolar nuclei such as K+, Mg2+, and Zn2+ in metalloenzymes in their native aqueous environment.
Abstract Particulate methane monooxygenase (pMMO) and its homolog ammonia monooxygenase (AMO), central enzymes in the global carbon and nitrogen cycles, contain three highly conserved mononuclear copper centers, denoted CuB, CuC, and CuD. While these sites have been well characterized structurally and spectroscopically, with recent studies identifying CuD as the active site, their reduction potentials have not been measured. This knowledge gap has hindered efforts to determine how the two electrons and two protons required for substrate oxidation are sourced and delivered. Here, we have elucidated the redox properties of each copper center in pMMO/AMO by protein film voltammetry using samples with copper occupancies known from cryoelectron microscopy (cryoEM) structures. The reduction potential of the CuB site, −72 to −139 mV, is significantly lower than the ∼400 mV measured for the CuD site, with consistent values determined for pMMOs and AMO from different species. Mutation of a residue in the second sphere of CuB, Glu35, alters the redox potential and impairs cell growth and pMMO activity, indicating that redox chemistry at CuB might be functionally relevant. Finally, a Pourbaix diagram constructed for the CuBII/I and CuDII/I half-reactions suggests that a proton-coupled electron transfer (PCET) process occurs at the CuD site but not at the CuB site. Thermochemical analysis of this proposed PCET process is compatible with electron delivery by a quinol reductant. These results provide new context for future investigations of the pMMO and AMO reaction mechanisms.
Abstract Photolabile linkers (PLLs) enable spatiotemporal control over substrate release but often suffer from slow photorelease kinetics, low quantum yields, or limited functionalization options. Here, we report a family of heterobifunctional PLLs based on (3-hydroxy-5-alkoxynaphthalen-2-yl)methyl (NQMP) chromophores that combine rapid, high-yielding photochemical cleavage with orthogonal conjugation chemistries for efficient substrate immobilization and light-triggered release. Six heterobifunctional NQMP-based linkers bearing terminal acetylene, cyclooctyne, amine, carboxyl, allyl, and biotin groups were synthesized and employed for the immobilization of fluorescent dyes, acetylsalicylic acid, biotin, avidin, and doxorubicin on silica microspheres and mesoporous silica nanoparticles. Mild UV-A irradiation resulted in efficient release of the attached payloads while preserving the integrity of the solid support. Mesoporous silica nanoparticles provide high loading capacity and are suitable for light-controlled drug delivery. The modular design, excellent photochemical efficiency, orthogonal conjugation chemistries, and compatibility with diverse substrates make NQMP-based PLLs versatile tools for reversible surface functionalization, controlled cargo release, affinity capture, and photoresponsive drug delivery applications.
