Publications

A library of 36 L-amino acid anilides, which are potential selectors for chiral HPLC, was synthesized in solution and attached to functionalized macroporous polymer beads. The best selector from the library was identified by a deconvolution process using the HPLC separation of several racemic N-(3,5-dinitrobenzoyl)-alpha-amino acid alkylamides as a probe. In each deconvolution step, a series of chiral stationary phases (CSPs) containing a subset of the amino acid anilide selector library was screened for enantioselectivity. After the best CSP was chosen, the library was further deconvoluted until the single best selector was found. The highest selectivity was obtained with a L-proline-1-indananilide that exhibited alpha values up to 23 under normal-phase HPLC conditions. In addition, six CSPs were prepared using individual selectors from the library, and screening results indicate that the deconvolution process indeed led to the most selective receptor.

Artificial intelligence for scientific discovery has recently generated significant interest within the machine learning and scientific communities, particularly in the domains of chemistry, biology, and material discovery. For these scientific problems, molecules serve as the fundamental building blocks, and machine learning has emerged as a highly effective and powerful tool for modeling their geometric structures. Nevertheless, due to the rapidly evolving process of the field and the knowledge gap between science (e.g., physics, chemistry, & biology) and machine learning communities, a benchmarking study on geometrical representation for such data has not been conducted. To address such an issue, in this paper, we first provide a unified view of the current symmetry-informed geometric methods, classifying them into three main categories: invariance, equivariance with spherical frame basis, and equivariance with vector frame basis. Then we propose a platform, coined Geom3D, which enables benchmarking the effectiveness of geometric strategies. Geom3D contains 16 advanced symmetry-informed geometric representation models and 14 geometric pretraining methods over 46 diverse datasets, including small molecules, proteins, and crystalline materials. We hope that Geom3D can, on the one hand, eliminate barriers for machine learning researchers interested in exploring scientific problems; and, on the other hand, provide valuable guidance for researchers in computational chemistry, structural biology, and materials science, aiding in the informed selection of representation techniques for specific applications.

Carbon aerogels are distinguished by a series of remarkable qualities, including ultralow density, low thermal conductivity, and high specific surface area; however, their low strength and inherent brittleness present a problem that severely constrains their application. Here a design strategy is proposed to overcome these shortcomings by synergistically carbonizing flexible organic fibers and aerogel matrix while elaborately engineering their interfacial bonding; the result is the creation of an ultra-strong, damage-tolerant carbon aerogel composite. The material exhibits a nanoporous carbon aerogel matrix reinforced by in situ-formed carbon fibers, featuring low residual stress and gradient atomic-scale bonding between the fibers and matrix. This structure imparts ultrahigh strength, with high specific strength normalized by density, all surpassing the benchmark properties of existing aerogels; it also displays exceptional fracture toughness with unprecedented stability in crack propagation. These attributes are further combined with excellent thermal stability and insulation, high-temperature mechanical properties, good machinability, and ease of large-scale production.

For the original paper see ibid., vol. 47, no. 11, p. 2059-2074 (1999). In the aforementioned paper the authors used a jar of water as a substitute for a human's head and then made a statement that the dielectric constant of water is similar to most human tissues. The commenter disagrees with this statement. In reply the authors also disagree with the comments, pointing out that while a jug of water and a human head may differ significantly in function, they differ little in form from the perspective of an electromagnetic field, and the substitution of one for the other offers simple insight into antenna performance near a high-dielectric lossy mass. They concede that the dielectric constant of water is roughly 1.5 times that of average human tissue. However, they believe that this neither invalidates their observation that antenna performance is significantly affected by the presence of a watery mass, nor their statement that one may expect similar degradation of performance near a human head.

Background Adverse life experiences require a broader range of adaptive behavioral strategies to cope with related stressors. The association between intensity, duration, type of stress and impacts on mental health is important for effective programming aimed at increasing resilience in the face of stress. This study examines adverse life experiences, coping strategies, and associations with mental health outcomes among very young adolescent orphans.Methods The analytic sample was collected between January and March of 2019 and included 350 adolescent orphans ages 10–15 years old from three districts in Tanzania. Participants completed survey interviews, 75–90 minutes in length, that measured adverse life experiences, stigma, coping strategies, and psychological symptoms.Results A four-factor dimensional structure of the KidCope survey fits these data and distinguished between distraction and resignation coping strategies. Use of distraction as a coping dimension was the most frequently used coping dimension and was associated with lower reported symptoms of depression, anxiety, and externalizing behaviors. Resignation was positively associated with adverse life experiences including emotional abuse, emotional neglect, and physical neglect. Problem-focused coping was not associated with study outcomes and social support coping was associated with externalizing behaviors only.Conclusion Results from adolescent orphans in a low-resource context suggest that distraction coping strategies may be adaptive in response to stress. Implications for intervention programming that aims to target acquisition of coping skills and mindsets among vulnerable populations are discussed.

Mn-rich disordered rocksalt (DRX) cathode materials exhibit a phase transformation from a disordered to a partially disordered spinel-like structure ($δ$-phase) during electrochemical cycling. In this computational study, we used charge-informed molecular dynamics with a fine-tuned CHGNet foundation potential to investigate the phase transformation in Li$_{x}$Mn$_{0.8}$Ti$_{0.1}$O$_{1.9}$F$_{0.1}$. Our results indicate that transition metal migration occurs and reorders to form the spinel-like ordering in an FCC anion framework. The transformed structure contains a higher concentration of non-transition metal (0-TM) face-sharing channels, which are known to improve Li transport kinetics. Analysis of the Mn valence distribution suggests that the appearance of tetrahedral Mn$^{2+}$ is a consequence of spinel-like ordering, rather than the trigger for cation migration as previously suggested. Calculated equilibrium intercalation voltage profiles demonstrate that the $δ$-phase, unlike the ordered spinel, exhibits solid-solution signatures at low voltage. A higher Li capacity is obtained than in the DRX phase. This study provides atomic insights into solid-state phase transformation and its relation to experimental electrochemistry, highlighting the potential of machine learning interatomic potentials for understanding complex oxide materials.

Abstract The successful synthesis and structural characterization of molecules that represent segments of extended solids is a valuable strategy for learning metric and stereochemical characteristics of those solids. This approach has been useful in cases in which the solids are particularly difficult to crystallize and thus their atomic connectivity and overall structures become difficult to deduce with X‐ray diffraction techniques. One such class of materials is the covalently linked C x N y extended solids, where molecular analogues remain largely absent. In particular, structures of C 3 N 4 solids are controversial. This report illustrates the utility of a simple molecule, N(C 3 N 3 ) 3 Cl 6 , in answering the question of whether triazine based C 3 N 4 phases are layered or instead they adopt 3D structures. Here, we present density functional calculations that clearly demonstrate the lower stability of graphitic C 3 N 4 relative to 3D analogues.

In the original version of this article, when equations were referenced within the main text, the numbering was offset by 2. For instance, when eq 1 was referenced, it was incorrectly referred to as eq 3. When eq 16 was referenced, it was incorrectly referenced as eq 18, and so on and so forth for all other references to the equations in the main text. The correct equation referencing is shown below for all instances:n.