Navigating the 18-n+m Isomers of PdSn2: Chemical Pressure Relief through Isolobal Bonds and Main Group Clustering.

The 18-n electron-counting rule provides structural guidelines for electronically feasible transition metal (T)-main group (E) phases, contributing toward the goal of material design. However, the availability of numerous potential structure types at any electron count creates a challenge for the prediction of the preferred structures of specific compounds, as is illustrated by the concept of 18-n+m isomerism. In this Article, we explore the driving forces stabilizing one 18-n+m isomer over another with an analysis of the structure of PdSn2, a layered intergrowth of the fluorite and CuAl2 structure types. The DFT-reversed approximation Molecular Orbital (DFT-raMO) method reveals that PdSn2 and its hypothetical parent structures all adhere to bonding schemes approximating the electronic configurations expected from the 18-n rule, with various degrees of isolobal Pd-Pd bonding and Sn clustering. However, partial electron transfer between the Pd 5p orbitals to the Sn 5s orbitals contributes to the absence of convincing electronic pseudogaps near their Fermi energies. As such, there is no clear electronically driven preference among the structure types. This situation allows for atomic packing effects to prevail: DFT-Chemical Pressure (DFT-CP) analysis illustrates that in the fluorite-type parent structure, positive Pd-Sn CPs lead to overcompression of the Pd atoms and a stretching of the relatively open Sn sublattice. In contrast, in the CuAl2-type parent structure, Sn atoms cluster into tetrahedra, opening space for an expanded Pd environment and the formation of Pd-Pd interactions. However, the tetrahedral packing of the Sn atoms here leads to frustration between negative and positive Sn-Sn CPs. Through the development of the angular CP correlation function (CPcor+) as a tool to quantify frustration among interatomic interactions, we demonstrate how the observed PdSn2 structure balances these effects by tuning the degree of Sn-Sn clustering and expansion of the Pd environment. These observations point to generalizations for most 18-n+m isomers, where increased main group ligand clustering (+m) and isolobal bonds (+n) can accommodate compositions with different T and E atomic sizes.

Entropic Control of Bonding, Guided by Chemical Pressure: Phase Transitions and 18-n+m Isomerism of IrIn3.

As with other electron counting rules, the 18-n rule of transition metal-main group (T-E) intermetallics offers a variety of potential interatomic connectivity patterns for any given electron count. What leads a compound to prefer one structure over others that satisfy this rule? Herein, we investigate this question as it relates to the two polymorphs of IrIn3: the high-temperature CoGa3-type and the low-temperature IrIn3-type forms. DFT-reversed approximation Molecular Orbital analysis reveals that both structures can be interpreted in terms of the 18-n rule but with different electron configurations. In the IrIn3 type, the Ir atoms obtain largely independent 18-electron configurations, while in the CoGa3 type, Ir-Ir isolobal bonds form as 1 electron/Ir atom is transferred to In-In interactions. The presence of a deep pseudogap for the CoGa3 type, but not for the IrIn3 type, suggests that it is electronically preferred. DFT-Chemical Pressure (CP) analysis shows that atomic packing provides another distinction between the structures. While both involve tensions between positive Ir-In CPs and negative In-In CPs, which call for the expansion and contraction of the structures, respectively, their distinct spatial arrangements create very different situations. In the CoGa3 type, the positive CPs create a framework that holds open large void spaces for In-based electrons (a scenario suitable for relatively small T atoms), while in the IrIn3 type the pressures are more homogenously distributed (a better solution for relatively large T atoms). The open spaces in the CoGa3 type result in quadrupolar CP features, a hallmark of low-frequency phonon modes and suggestive of higher vibrational entropy. Indeed, phonon band structure calculations for the two IrIn3 polymorphs indicate that the phase transition between them can largely be attributed to the entropic stabilization of the CoGa3-type phase due to soft motions associated with its CP quadrupoles. These CP-driven effects illustrate how the competition between global and local packing can shape how a structure realizes the 18-n rule and how the temperature can influence this balance.

Ligilactobacillus ubinensis sp. nov., a novel species isolated from the wild ferment of a durian fruit (Durio zibethinus).

A Gram-stain-positive, rod-shaped, non-spore-forming, catalase-negative, urease-negative, homofermentative and facultatively anaerobic strain, named WILCCON 0076T, was isolated from a wild ferment of pieces of a 'Kampung' durian fruit collected on the island of Ubin (Pulau Ubin), Singapore. The durian had fallen to the ground from a durian tree (Durio zibethinus), on which a group of long-tailed macaques had been observed picking and eating the fruits. Comparative analyses of 16S rRNA gene sequences indicated that WILCCON 0076T potentially represented a novel species within the genus Ligilactobacillus, with the most closely related type strain being Ligilactobacillus agilis DSM 20509T (16S rRNA gene sequence similarity of 97.2 %). Average nucleotide identity and digital DNA-DNA hybridization prediction values were only 86.0% and 18.9 %, respectively. On the basis of the results of a polyphasic approach that included phylogenomic, chemotaxonomic and morphological analyses, we propose a novel species with the name Ligilactobacillus ubinensis sp. nov. (type strain WILCCON 0076T=DSM 114293T=LMG 32698T).

Emergent Transitions: Discord between Electronic and Chemical Pressure Effects in the REAl3 (RE = Sc, Y, Lanthanides) Series.

Atomic packing and electronic structure are key factors underlying the crystal structures adopted by solid-state compounds. In cases where these factors conflict, structural complexity often arises. Such is born in the series of REAl3 (RE = Sc, Y, lanthanides), which adopt structures with varied stacking patterns of face-centered cubic close packed (FCC, AuCu3 type) and hexagonal close packed (HCP, Ni3Sn type) layers. The percentage of the hexagonal stacking in the structures is correlated with the size of the rare earth atom, but the mechanism by which changes in atomic size drive these large-scale shifts is unclear. In this Article, we reveal this mechanism through DFT-Chemical Pressure (CP) and reversed approximation Molecular Orbital (raMO) analyses. CP analysis illustrates that the Ni3Sn structure type is preferable from the viewpoint of atomic packing as it offers relief to packing issues in the AuCu3 type by consolidating Al octahedra into columns, which shortens Al-Al contacts while simultaneously expanding the RE atom's coordination environment. On the other hand, the AuCu3 type offers more electronic stability with an 18-n closed-shell configuration that is not available in the Ni3Sn type (due to electron transfer from the RE dz2 atomic orbitals into Al-based states). Based on these results, we then turn to a schematic analysis of how the energetic contributions from atomic packing and the electronic structure vary as a function of the ratio of FCC and HCP stacking configurations within the structure and the RE atomic radius. The minima on the atomic packing and electronic surfaces are non-overlapping, creating frustration. However, when their contributions are added, new minima can emerge from their combination for specific RE radii representing intergrowth structures in the REAl3 series. Based on this picture, we propose the concept of emergent transitions, within the framework of the Frustrated and Allowed Structural Transitions principle, for tracing the connection between competing energetic factors and complexity in intermetallic structures.

Perspectives on frailty screening, management and its implementation among acute care providers in Singapore: a qualitative study.

BACKGROUND: COVID-19 pandemic has reminded how older adults with frailty are particularly exposed to adverse outcomes. In the acute care setting, consideration of evidence-based practice related to frailty screening and management is needed to improve the care provided to aging populations. It is important to assess for frailty in acute care so as to establish treatment priorities and goals for the individual. Our study explored understanding on frailty and practice of frailty screening among different acute care professionals in Singapore, and identify barriers and facilitators concerning frailty screening and its implementation. METHODS: A qualitative study using focus group discussion among nurses and individual interviews among physicians from four departments (Accident & Emergency, Anesthesia, General Surgery, Orthopedics) in three acute hospitals from the three public health clusters in Singapore. Participants were recruited through purposive sampling of specific clinicians seeing a high proportion of older patients at the hospitals. Thematic analysis of the data was performed using NVIVO 12.0. RESULTS: Frailty was mainly but inadequately understood as a physical and age-related concept. Screening for frailty in acute care was considered important to identify high risk patients, to implement targeted treatment and care, and to support decision making and prognosis estimation. Specific issues related to screening, management and implementation were identified: cooperation from patient/caregivers, acceptance from healthcare workers/hospital managers, need for dedicated resources, guidelines for follow-up management and consensus on the scope of measurement for different specialties. CONCLUSION: Our findings indicated the need for 1) frailty-related education program for patients/care givers and stakeholders 2) inter-professional collaboration to develop integrated approach for screening and management of hospital patients with frailty and 3) hospital-wide consensus to adopt a common frailty screening tool.

Decreased lymphatic HIF-2α accentuates lymphatic remodeling in lymphedema.

Pathologic lymphatic remodeling in lymphedema evolves during periods of tissue inflammation and hypoxia through poorly defined processes. In human and mouse lymphedema, there is a significant increase of hypoxia inducible factor 1 α (HIF-1α), but a reduction of HIF-2α protein expression in lymphatic endothelial cells (LECs). We questioned whether dysregulated expression of these transcription factors contributes to disease pathogenesis and found that LEC-specific deletion of Hif2α exacerbated lymphedema pathology. Even without lymphatic vascular injury, the loss of LEC-specific Hif2α caused anatomic pathology and a functional decline in fetal and adult mice. These findings suggest that HIF-2α is an important mediator of lymphatic health. HIF-2α promoted protective phosphorylated TIE2 (p-TIE2) signaling in LECs, a process also replicated by upregulating TIE2 signaling through adenovirus-mediated angiopoietin-1 (Angpt1) gene therapy. Our study suggests that HIF-2α normally promotes healthy lymphatic homeostasis and raises the exciting possibility that restoring HIF-2α pathways in lymphedema could mitigate long-term pathology and disability.