Many residues within proteins adopt conformations that appear to be stabilized by interactions between an amide N–H and the amide N of the previous residue. To explore whether these interactions constitute hydrogen bonds, we characterized the IR stretching frequencies of deuterated variants of proline and the corresponding carbamate, as well as the four proline residues of an Src homology 3 domain protein. The CδD2 stretching frequencies are shifted to lower energies due to hyperconjugation with N i electron density, and engaging this density via protonation or the formation of the N i+1–H···N i interaction ablates this hyperconjugation and thus induces an otherwise difficult to explain blue shift in the C–D absorptions. Along with density functional theory calculations, the data reveal that the N i+1–H···N i interactions constitute H-bonds and suggest that they may play an important and previously underappreciated role in protein folding, structure, and function.

This article describes a graduate student-led effort to develop a climate survey to assess, advocate for, and improve the well-being and mental health of graduate students and postdocs in the Department of Chemistry at the University of Wisconsin−Madison. Graduate students have an increased incidence of depression relative to the general population, and given the transient nature of the student population, understanding and addressing mental health concerns can be challenging. The goal of this article is to illustrate how students, with the support of departmental faculty, staff, and existing on-campus mental health resources, can take the lead to investigate and assess issues related to the challenging graduate school environment. We describe the student-led development and implementation of and the subsequent follow-up to a department-wide survey aimed at destigmatizing the subject of mental health and fostering a more supportive community. This article serves as a framework to assist other interested and motivated graduate students who, with the support of local faculty, wish to develop and initiate a similar process in their own departments. We demonstrate that student-led actions can effectively tackle department-level problems and encourage other interested students to initiate a similar effort.

A multistep phase sequence following the crystallization of amorphous Al2O3 via solid-phase epitaxy (SPE) points to methods to create low-defect-density thin films of the metastable cubic γ-Al2O3 polymorph. An amorphous Al2O3 thin film on a (0001) α-Al2O3 sapphire substrate initially transforms upon heating to form epitaxial γ-Al2O3, followed by a transformation to monoclinic θ-Al2O3, and eventually to α-Al2O3. Epitaxial γ-Al2O3 layers with low mosaic widths in X-ray rocking curves can be formed via SPE by crystallizing the γ-Al2O3 phase from amorphous Al2O3 and avoiding the microstructural inhomogeneity arising from the spatially inhomogeneous transformation to θ-Al2O3. A complementary molecular dynamics (MD) simulation indicates that the amorphous layer and γ-Al2O3 have similar Al coordination geometry, suggesting that γ-Al2O3 forms in part because it involves the minimum rearrangement of the initially amorphous configuration. The lattice parameters of γ-Al2O3 are consistent with a structure in which the majority of the Al vacancies in the spinel structure occupy sites with tetrahedral coordination, consistent with the MD results. The formation of Al vacancies at tetrahedral spinel sites in epitaxial γ-Al2O3 can minimize the epitaxial elastic deformation of γ-Al2O3 during crystallization.

The crystallization of amorphous solids impacts fields ranging from inorganic crystal growth to biophysics. Promoting or inhibiting nanoscale epitaxial crystallization and selecting its final products underpins applications in cryopreservation, semiconductor devices, oxide electronics, quantum electronics, structural and functional ceramics, and advanced glasses. As precursors for crystallization, amorphous solids are distinguished from liquids and gases by the comparatively long relaxation times for perturbations of the mechanical stress and for variations in composition or bonding. These factors allow experimentally controllable parameters to influence crystallization processes and to drive materials towards specific outcomes. For example, amorphous precursors can be employed to form crystalline phases, such as polymorphs of Al2O3, VO2, and other complex oxides, that are not readily accessible via crystallization from a liquid or through vapor-phase epitaxy. Crystallization of amorphous solids can further be guided to produce a desired polymorph, nanoscale shape, microstructure, and orientation of the resulting crystals. These effects can enable advances in applications in electronics, magnetic devices, optics, and catalysis. Directions for the future development of the chemical physics of crystallization from amorphous solids can be drawn from the impact of structurally complex and non-equilibrium atomic arrangements in liquids and the atomic-scale structure of liquid-solid interfaces.

π-interactions are an important motif in chemical and biochemical systems. However, due to their anisotropic electron densities and complex balance of intermolecular interactions, aromatic molecules represent an ongoing challenge for accurate and transferable force field development. Historically, ab initio force fields for aromatics have not exhibited good accuracy with respect to bulk properties or have only been used to study gas-phase dimers. Using benzene as a proof of concept, herein we show how our own ab initio MASTIFF force field incorporates an atomically anisotropic description of intermolecular interactions to yield an accurate and robust model for aromatic interactions irrespective of phase. Compared to existing models, the MASTIFF benzene force field not only is accurate for liquid phase properties but also offers transferability to the gas and solid phases. Additionally, we introduce a computationally efficient OpenMM plugin which enables customizable anisotropic intermolecular functional forms and which can be generically used in any MD simulation where a model for nonspherical atomic features is required. Overall, our results demonstrate the importance of atomic-level anisotropy in enabling next-generation ab initio force field development.