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The Story of Black Scientists Born in the 19th Century
No full textThe technological innovations developed in Africa have an important place in the history of invention and date back to the ancient world. Africans had a knowledge of astronomy, agricultural science, engineering, and medicine based on natural plant products. Although this knowledge was often more developed in Africa than anywhere else in the world, African contributions were mostly ignored by the rest of the world. Many contributions of Blacks to modern technology are still not widely known. In 1913 alone, more than a thousand inventions were patented by African Americans who were fortunate enough to be accepted at the patent office. Many other black inventors discovered medicines as well as laborsaving devices, but were not allowed to patent them in their own names; others who controlled their labor stole credit, authorship, and profit for their discoveries. In this article, we hope to inspire young people of all colors by telling the stories of black scientists who developed products, medicines, and systems that changed lives. All scientists presented here were born before the 20th century, when Blacks were up against severe forms of oppression and inhumanity. Black people faced unparalleled obstacles in accessing both primary and higher education, and the few educational facilities that were available to Blacks were inadequate compared to those available to whites. Additionally, black people could not obtain housing or jobs, and they were not recognized or included as members of society. Despite these challenges, some of the greatest scientific discoveries were made by black people. The black scientists highlighted here did not have equal access to education during their lifetime, and it was only through perseverance that they were able to overcome obstacles and earn educational degrees. We highlight the scientific discoveries made by some of the most brilliant black scientists during this era, depicting how racist laws and practices affected them, and we discuss them chronologically by their date of birth to identify the social changes that occurred over the years
Dual-Band Electrochromic Devices Utilizing Niobium Oxide Nanocrystals
No full textIn this study we realize functioning electrochromic devices based on colloidal niobium oxide nanocrystals which show dual-band electrochromic behavior, with spectral
selectivity between near-infrared and visible wavelengths. Minimally coloring vanadium
oxide counter electrodes allow for full electrochromic devices that embody the dual-band
electrochromic behavior of the niobium oxide component. The devices are fabricated
using solution processing on both glass and flexible substrates, demonstrating that our
platform has potential for the development of low-cost dual-band electrochromic devices
for dynamic solar control in a variety of form factors and applications
A Physics-Aware Neural Network for Protein-Ligand Interactions with Quantum Chemical Accuracy
No full textQuantifying intermolecular interactions with quantum chemistry (QC) is useful for many chemical problems, including understanding the nature of protein-ligand interactions. Unfortunately, QC computations on protein-ligand systems are too computationally expensive for most use cases. The flourishing field of machine-learned (ML) potentials is a promising solution, but it is limited by an in- ability to easily capture long range, non-local interactions. In this work we develop an atomic-pairwise neural network (AP-Net) specialized for modeling intermolecular interactions. This model benefits from a number of physical constraints, including a two-component equivariant message passing neural network architecture that predicts interaction energies via an intermediate prediction of monomer electron densities. The AP-Net model also benefits from a comprehensive training dataset com- posed of paired ligand and protein fragments. This model accurately predicts QC-quality interaction energies of protein-ligand systems at a computational cost reduced by orders of magnitude
Reducing Ohmic Resistances in Membrane Capacitive Deionization Using Micropatterned Ion-exchange Membranes, Ionomer Infiltrated Electrodes and Ionomer Coated Nylon Meshes
No full textMembrane capacitive deionization (MCDI) is an emerging water desalination platform that is compact, electrified, and does not require high pressure piping. In this work, we micropatterned highly conductive poly(phenylene alkylene) ion-exchange membranes (IEMs) with different surface geometries for MCDI. The micropatterned membranes increase the interfacial area with the liquid stream leading to a 700 mV reduction in cell voltage when operating at constant current (2 mA cm-2; 2000 ppm NaCl feed) and improved the energy normalized adsorbed salt (ENAS) value, increasing it by 1.4 times. Combining the micropatterned poly(phenylene alkylene) IEMs with poly(phenylene alkylene) ionomer filled electrodes reduced the cell voltage by 1000 mV improved the ENAS values by 2.3 times relative to the base case. This reduction in cell voltage allowed for higher current density operation (i.e., 3 to 4 mA cm-2) without the occurrence of significant parasitic reactions. Finally, we implemented porous ionic conductors into the spacer channel with flat and micropatterned IEM configurations and ionomer infiltrated electrodes. For the configuration with flat IEMs, the porous ionic conductor improved ENAS values across the current density regime (2 to 4 mA cm-2). The porous ionic conductors combined with micropatterned IEMs and porous ionic conductors only improved ENAS when operating the cell at 4 mA cm-2. The latter observation motivates future work to design integrated patterned IEMs with porous ionic conductor materials for improving MCDI energy efficiency over a wide current density range and with varying NaCl feed concentrations
Quantum chemical and molecular modeling studies of twenty therapeutic nucleosides and nucleoside analogues
No full textNaturally occurring and synthetic, chemically modified nucleosides and nucleoside analogues are suggested to be effective therapeutic agents against different diseases, especially viral diseases, and cancer. Theoretical studies including molecular dynamics simulations are often necessary for the determination of the stability, conformational characteristics, binding efficiency, etc. of such residues. Here, we report AMBER force field parameters and topologies, including glycosidic torsion parameters and partial atomic charges for a set of twenty therapeutically important nucleosides/nucleoside analogues most of which are known/potential antiviral and antitumor agents. These parameter sets would be useful for future simulation studies involving these residues and for further improvements. We also report molecular properties observed from quantum mechanical calculations and conformational characteristics extracted from molecular dynamics simulations of these residues using the newly derived parameter sets. Our results would enrich the understanding of their functional characteristics, activity, and efficacy as therapeutic agents and possibly for their repurposing against other similar diseases
The mechanism of amyloid fibril growth from Φ-value analysis
No full textAmyloid fibrils are highly stable misfolded protein assemblies playing an important role
in several neurodegenerative and systemic diseases. While structural information of the
amyloid state is now abundant, mechanistic details about the misfolding process remain
elusive. Here we present a Φ-value inspired approach and apply it to PI3K-SH3 amyloid
fibrils to examine the rate-limiting step for fibril elongation. We use experimental Φvalues as constraints in biased MD-simulations to provide the first view of the transition
state of a protein misfolding reaction. The resulting framework is generally applicaple and
provides mechanistic insight into the misfolding reaction comparable to the breakthroughs
previously achieved for protein folding. While protein folding proceeds on funnel-shaped
landscapes, we find that the misfolding reaction energy landscape consists of a large ’golf
course’ region, defined by a single energy barrier and transition state, accessing a sharply
funneled region. Thus, misfolding occurs by numerous unsuccesful binding attempts
and rare successful monomer-fibril end collisions which rapidly anneals to the final state.
Taken together, these insights enable, the first quantitative and highly resolved description
of a protein misfolding reaction
Influence of crystallization kinetics and flow behavior on structural inhomogeneities in 3D printed parts made from semi-crystalline polymers
No full textWe report the results of a study focusing on the influence of crystallization kinetics and the flow behavior on structural inhomogeneities in 3D printed parts made from polyamide 12 (PA12) and poly (lactic acid) (PLA) by Dynamic Mechanical Analysis (DMA), Differential Scanning Calorimetry (DSC), Fast Scanning Calorimetry (FSC) and Wide-Angle X-ray Diffraction (WAXD). Temperature-dependent WAXD measurements on the neat PLA filament reveal that PLA forms a single orthorhombic α phase
during slow cooling and subsequent 2nd heating. The PA12 filament shows a well pronounced polymorphism with a reversible solid-solid phase transition between the
(pseudo)hexagonal γ phase near room temperature and the monoclinic α′ phase above the Brill transition temperature TB = 140 °C. The influence of the print bed temperature Tb on structure formation, polymorphic state, and the degree of crystallinity χc of the 3D printed parts is investigated by height and depth dependent WAXD scans and compared with that of 3D printed single layers, used as a reference. It is found that the heat transferred from successive layers has a strong influence on the polymorphic state of PA12 since a superimposed mixture of γ and α phase is present in the 3D printed parts. In case of PLA a single α phase is formed. The print bed temperature has, in comparison to PA12, a major influence on the degree of crystallinity χc and
thus the homogeneity of the 3D printed parts, especially close to the print bed. By comparing the obtained results from WAXD, DMA, DSC and FSC measurements with relevant printing times, guidelines for 3D printed parts with a homogeneous structure are derived
Analytic gradients for the electrostatic embedding QM/MM in periodic boundary conditions using particle-mesh Ewald sums and electrostatic potential fitted charge operators
No full textLong-range electrostatic effects are fundamental for describing chemical reactivity in the condensed phase. Here, we present the methodology of an efficient quantum mechanical/molecular mechanical (QM/MM) model in periodic boundary conditions (PBC) compatible with QM/MM boundaries at chemical bonds. The method combines electrostatic potential fitted (ESPF) charge operators and electrostatic potentials derived from the smooth particle-mesh Ewald (PME) sum approach. The total energy and its analytic first derivatives with respect to QM, MM and lattice vectors allow QM/MM molecular dynamics (MD) in the most common thermodynamic ensembles. We demonstrate the robustness of the method by performing a QM/MM MD equilibration of methanol in water. We simulate the cis/trans isomerization free energy profiles in water of proline amino acid and a proline-containing oligopeptide, showing a correct description of the reaction barrier. Our PBC-compatible QM/MM model can efficiently be used to study chemical reactivity in condensed phase and enzymatic catalysis
Pinched Tube Method for Gas Sample Transfers
No full textWhen transferring small volumes of gas samples between laboratories, cold welded, pinched copper tubes offer an
inexpensive and convenient solution. In this paper, we outline the preparation, loading, transfer, and analysis methods used in a multi-campus, collaborative study under the United States Department of Energy. This gas transfer method has been utilized on samples from novel nuclear reactions, where the presence of low-mass gas isotopes is often used as an indicator of a successful reaction. Low-mass isotopic gas analysis requires careful preparation and handling to mitigate contamination, primarily resulting from air intrusion. The pinched tubes were found to be hermetic until punctured using a saddle valve prior to gas analysis with an analytical instrument. The integrity of this transfer method was proven using a Fourier Transform Ion Cyclotron Resonance (FT-ICR) mass spectrometer. We also discuss hermiticity measurements during the tube puncturing process
Angle-Dependent Electrocatalytic Activity of Twisted Bilayer Graphene for Hydrogen Evolution Reaction
No full textTwo-dimensional (2D) materials are attractive for their unique electronic structures and catalytic properties. In this work, we propose to use the twist angle as a knob to tune the catalytic properties of 2D materials. As proof of concept, we investigate the effects of twist angle on the electrocatalytic properties of twisted bilayer graphene (tBLG). We predict the activity of tBLG with the twist angle of 13.174° and 21.787° for hydrogenation evolution reaction (HER) using the density functional theory (DFT) calculation and computational hydrogen electrode (CHE) approach. We calculate the hydrogen adsorption energy (ΔGH*) at various sites on tBLG and examine their angle-dependency. By comparing the GH* for different active sites of untwisted bilayer graphene (BLG) and tBLG, we find that the GH* decreases with the increase of twist angle. As a result, the thermodynamic limiting potential for HER increases with the twist angle. Furthermore, the ΔGH* shows a correlation with the layer distance and the site location on the 2D plane. Detailed analysis reveals that the twist of bilayer graphene could increase the z height (dz) of active sites as a function of their distance to the symmetry centers, alter the local geometry of active sites, and therefore modify the ΔGH*. These results indicate that the twist angle can be effectively used as a knob to fine-tune the electrocatalytic properties of 2D materials, promising a whole new family of twisted 2D catalysts