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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
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DOE OSTI2024

Access to Advanced Functional Materials through Postmodification of Biomimetic Assemblies via Click Chemistry

The design, synthesis, and fabrication of functional nanomaterials with specific properties remain a long-standing goal for many scientific fields. The self-assembly of sequence-defined biomimetic synthetic polymers presents a fundamental strategy to explore the chemical space beyond biological systems to create advanced nanomaterials. Moreover, subsequent chemical modification of existing nanostructures is a unique approach for accessing increasingly complex nanostructures and introducing functionalities. Of these modifications, covalent conjugation chemistries, such as the click reactions, have been the cornerstone for chemists and materials scientists. Herein, we highlight some recent advances that have successfully employed click chemistries for the postmodification of assembled one-dimensional (1D) and two-dimensional (2D) nanostructures to achieve applications in molecular recognition, mineralization, and optoelectronics. Specifically, biomimetic nanomaterials assembled from sequence-defined macromolecules such as peptides and peptoids are described.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Rietveld Refinement for Macromolecular Powder Diffraction

Powder X-ray diffraction (PXRD) has been employed extensively for the structural characterization of materials, quantitative analysis of multicomponent mixtures, phase identification, texture, and microstructural analysis. At the heart of all those lies the Rietveld method, which has revolutionized the use of powder diffraction for materials studies. Initially applied to minerals and inorganics, the Rietveld method has progressively been used for more complex materials, for instance, zeolites and pharmaceuticals. A major advance of the method came some 20 years ago, when the first protein structure was successfully refined. Because of the sheer complexity of macromolecules, several new approaches and algorithms had to be pioneered or adapted from macromolecular single-crystal diffraction experiments, thus constituting macromolecular PXRD a quite unique field of study. This review aims to provide necessary elements of theory and application of structure solution and refinement via the Rietveld method for macromolecular PXRD data. Here, practical explanations and highlighted case studies are also presented.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Reversal of Catalytic Material Substrate Selectivity through Partitioning of Polymers in Hierarchically Ordered Virus-like Particle Frameworks

Control over the selectivity of catalytic materials is a topic of growing interest. Virus-like particle (VLP) based materials such as protein macromolecular frameworks (PMFs) are promising for catalytic applications due to their ease of assembly, modular ability to encapsulate a variety of enzymes, and ease of separation from a reaction mixture. Here we demonstrate the reversal of the initially negative material charge through the titration of a positively charged polymer into the material, causing the reversal of guest molecule uptake and enzymatic activity of PMFs. The charge-inverse material partitions a charged enzyme substrate to concentrate the substrate near an enzyme incorporated within the material, generating up to 5.9-fold increases in enzyme activity toward the partitioned substrate over the excluded substrate. Here we also show that the polymer distributes heterogeneously through the material up to a point of saturation and the effects of guest macromolecules on the lattice parameters of PMFs.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Rational Design of Novel Biomimetic Sequence-Defined Polymers for Mineralization Applications

Silica biomineralization is a naturally occurring process, wherein organisms use proteins and other biological structures to direct the formation of complex, hierarchical nanostructures. Discovery and characterization of such proteins and their underlying mechanisms spurred significant efforts to identify routes for biomimetic mineralization that reproduce the exquisite shapes and size selectivities found in nature. A common strategy has been the use of short peptide sequences with chemistry mimicking those found in natural systems, such as the use of the silaffin-derived R5 peptide. While progress has been made using this approach, there are many limitations that have prevented breakthroughs in biomimicry. To advance our ability to use charged macromolecules for silica formation, we propose to use sequence-defined synthetic polymers known as peptoids, or N-substituted polyglycines, which present significant capability for the precise tuning of sequence and structure beyond what can often be achieved with peptides alone. This study presents a computationally predicted design of these polymers that leads to the controlled formation of silica nanomaterials. We investigate surface adsorption and the mineralization process through analysis of binding mechanisms and energetics of the R5 system. Next, we synthesized two R5-inspired peptoids and validated our prediction in the design of mineralization polymers through characterization using surface plasmon resonance and electron microscopy. Here, this computationally guided study holds great promise for designing new sequences with unprecedented control of the placement of chemical functional groups, thus allowing for further unraveling of silicification mechanisms and the eventual design of sequence-defined synthetic polymers leading to the predictive synthesis of nanostructured functional materials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Using Data-Science Approaches to Unravel Insights for Enhanced Transport of Lithium Ions in Single-Ion Conducting Polymer Electrolytes

Solid polymer electrolytes have yet to achieve the desired ionic conductivity (>1 mS/cm) near room temperature required for many applications. This target implies the need to reduce the effective energy barriers for ion transport in polymer electrolytes to around 20 kJ/mol. In this work, we combine information extracted from existing experimental results with theoretical calculations to provide insights into ion transport in single-ion conductors (SICs) with a focus on lithium ion SICs. Through the analysis of temperature-dependent ionic conductivity data obtained from the literature, we evaluate different methods of extracting energy barriers for lithium transport. The traditional Arrhenius fit to the temperature-dependent ionic conductivity data indicates that the Meyer–Neldel rule holds for SICs. However, the values of the fitting parameters remain unphysical. Our modified approach based on recent work (Macromolecules 2023, 56, 15, 6051), which incorporates a fixed pre-exponential factor, reveals that the energy barriers exhibit temperature dependence over a wide range of temperatures. Using this approach, we identify anions leading to the energy barriers <30 kJ/mol, which include trifluoromethane sulfonimide (TFSI), fluoromethane sulfonimide (FSI), and boron-based organic anions. In our efforts to design the next generation of anions, which can exhibit the energy barriers <20 kJ/mol, we have performed density functional theory (DFT) based calculations to connect the chemical structures of boron-based anions via the binding energy of cation (lithium)-anion pairs with the experimentally derived effective energy barriers for ion hopping. Not only have we identified a correlation between the binding energy and the energy barriers, but we also propose a strategy to design new boron-based anions by using the correlation. This combined approach involving experiments and theoretical calculations is capable of facilitating the identification of promising new anions, which can exhibit ionic conductivity >1 mS/cm near room temperature, thereby expediting the development of novel superionic single-ion conducting polymer electrolytes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Hierarchical Materials from High Information Content Macromolecular Building Blocks: Construction, Dynamic Interventions, and Prediction

Hierarchical materials that exhibit order over multiple length scales are ubiquitous in nature. Because hierarchy gives rise to unique properties and functions, many have sought inspiration from nature when designing and fabricating hierarchical matter. More and more, however, nature’s own high-information content building blocks, proteins, peptides, and peptidomimetics, are being coopted to build hierarchy because the information that determines structure, function, and interfacial interactions can be readily encoded in these versatile macromolecules. Here, we take stock of recent progress in the rational design and characterization of hierarchical materials produced from high-information content blocks with a focus on stimuli-responsive and “smart” architectures. We also review advances in the use of computational simulations and data-driven predictions to shed light on how the side chain chemistry and conformational flexibility of macromolecular blocks drive the emergence of order and the acquisition of hierarchy and also on how ionic, solvent, and surface effects influence the outcomes of assembly. Furthermore, continued progress in the above areas will ultimately usher in an era where an understanding of designed interactions, surface effects, and solution conditions can be harnessed to achieve predictive materials synthesis across scale and drive emergent phenomena in the self-assembly and reconfiguration of high-information content building blocks.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Process-Specific Effects of Sulfate on CaCO 3 Formation in Environmentally Relevant Systems

Additives, such as ions, small molecules, and macromolecules, have been found to regulate the formation of CaCO 3 and control its morphologies and properties. However, a single additive usually affects dominantly one process in CaCO 3 's formation and is seldom found to significantly affect multiple CaCO 3 formation processes. In this work, we used in situ grazing incidence X-ray techniques to observe the heterogeneous formation of CaCO 3 and found that a series of formation processes (i.e., nucleation, growth, and Ostwald ripening) were modulated by sulfate. In the nucleation process, increased interfacial free energy and bulk free energy cooperatively increased the nucleation barrier and decreased nucleation rates. In the growth process, sulfate reduced the electrostatic repulsion between CaCO 3 precursors and nuclei, promoting CaCO 3 growth. This influence on the growth counteracted the inhibition effect in the nucleation process, causing a nearly 100% increase in the volume of heterogeneously formed CaCO 3 . Meanwhile, adsorbed sulfate on CaCO 3 nuclei may poison the surface of smaller CaCO 3 nuclei, inhibiting Ostwald ripening. These revealed sulfate's active roles in controlling CaCO 3 formation advance our understanding of sulfate-incorporated biomineralization and scaling phenomena in natural and engineered aquatic environments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Pseudomonas sp. Strain 273 Incorporates Organofluorine into the Lipid Bilayer during Growth with Fluorinated Alkanes

Anthropogenic organofluorine compounds are recalcitrant, globally distributed, and a human health concern. Although rare, natural processes synthesize fluorinated compounds, and some bacteria have evolved mechanisms to metabolize organofluorine compounds. Pseudomonas sp. strain 273 grows with 1-fluorodecane (FD) and 1,10-difluorodecane (DFD) as carbon sources, but inorganic fluoride release was not stoichiometric. Metabolome studies revealed that this bacterium produces fluorinated anabolites and phospholipids. Mass spectrometric fatty acid profiling detected fluorinated long-chain (i.e., C 12 –C 19 ) fatty acids in strain 273 cells grown with FD or DFD, and lipidomic profiling determined that 7.5 ± 0.2 and 82.0 ± 1.0% of the total phospholipids in strain 273 grown with FD or DFD, respectively, were fluorinated. The detection of the fluorinated metabolites and macromolecules represents a heretofore unrecognized sink for organofluorine, an observation with consequences for the environmental fate and transport of fluorinated aliphatic compounds.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

InteraChem: Virtual Reality Visualizer for Reactive Interactive Molecular Dynamics

Interactive molecular dynamics in virtual reality (IMD-VR) simulations provide a digital molecular playground for students as an alternative or complement to traditional molecular modeling kits or 2D illustrations. Previous IMD-VR studies have used molecular mechanics to enable simulations of macromolecules such as proteins and nanostructures for the classroom setting with considerable success. Here, we present the InteraChem molecular visualizer, intended for reactive IMD-VR simulation using semiempirical and ab initio methods. InteraChem visualizes not only the molecular geometry but also (1) isosurfaces such as molecular orbitals and electrostatic potentials and (2) two-dimensional graphs of time-varying simulation quantities such as kinetic/potential energy, internal coordinates, and user-applied force. Additionally, InteraChem employs speech recognition to facilitate user interaction and introduces a novel “atom happiness” visualization using emojis to indicate the energetic feasibility of a particular bonding arrangement. Furthermore, we include a set of accompanying exercises that we have used to teach chemical reactivity in small molecular systems.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Building a Simplistic Automatic Extruder: Instrument Development Opportunities for the Laboratory

This work presents an automatic extruder as a research experience for undergraduate students. The system offers a user-friendly approach to preparing vesicles, such as liposomes or polymersomes, with a defined size and polydispersity properties crucial for research in biology and macromolecules. It comprises two syringe pumps connected by a membrane filter. The setup is controlled by software. Compared to manual extrusion, this automated system provides advantages, such as precisely controlled variables. The project describes a tool to enhance undergraduate learning in science and engineering laboratories. Building an automatic extruder serves as a simplified model of a complex industrial process. It offers a clear advantage: automating a well-understood manual extrusion process. To make this project accessible, it is broken down into three manageable tasks: software development, hardware assembly, and testing procedures. This breakdown describes the software created, the hardware components used, and the testing procedures conducted for this project. All project data, including software code, testing data, and procedures, are freely available online. This allows undergraduate students to not only begin their own projects but also contribute to this educational instrument’s ongoing development.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Folding Coarse-Grained Oligomer Models with PyRosetta

Non-biological foldamers are a promising class of macromolecules that share similarities to classical biopolymers such as proteins and nucleic acids. Currently, designing novel foldamers is a non-trivial process, often involving many iterations of trial synthesis and characterization until folded structures are observed. In this work, we aim to tackle these foldamer design challenges using computational modeling techniques. We developed CG PyRosetta, an extension to the popular protein folding python package, PyRosetta, which introduces coarse-grained (CG) residues into PyRosetta, enabling the folding of toy CG foldamer models. Although these models are simplified, they can help explore overarching physical hypotheses about how oligomers can form. Through systematic variation of CG parameters in these models, we can investigate various folding hypotheses at the CG scale to inform the design process of new foldamer chemistries. In this study, we demonstrate CG PyRosetta’s ability to identify minimum energy structures with a diverse structural search over a range of simple models, as well as two hypothesis-driven parameter scans investigating the effects of side-chain size and internal backbone angle on secondary structures. We are able to identify several types of secondary structures from single- and double-helices to sheet-like and knot-like structures. Here, we show how side-chain size and backbone bond angle both play an important role in the structure and energetics of these toy models. Optimal side-chain sizes promote favorable packing of side chains, while specific backbone bond angles influence the specific helix type found in folded structures.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Studying the Collective Functional Response of a Receptor in Alchemical Ligand Binding Free Energy Simulations with Accelerated Solvation Layer Dynamics

Ligand binding free energy simulations (LB-FES) that involve sampling of protein functional conformations have been longstanding challenges in research on molecular recognition. Particularly, modeling of the conformational transition pathway and design of the heuristic biasing mechanism are severe bottlenecks for the existing enhanced configurational sampling (ECS) methods. Inspired by the key role of hydration in regulating conformational dynamics of macromolecules, this report proposes a novel ECS approach that facilitates binding-associated structural dynamics by accelerated hydration transitions in combination with the lambda-exchange of free energy perturbation (FEP). Further, two challenging protein-ligand binding processes involving large configurational transitions of the receptor are studied, with hydration transitions at binding sites accelerated by Hamiltonian-simulated annealing of the hydration layer. Without the need for pathway analysis or ad hoc barrier flattening potential, LB-FES were performed with FEP/lambda-exchange molecular dynamics simulation at a minor overhead for annealing of the hydration layer. The LB-FES studies showed that the accelerated rehydration significantly enhances the collective conformational transitions of the receptor, and convergence of binding affinity calculations is obtained at a sweet-spot simulation time scale. Alchemical LB-FES with the proposed ECS strategy is free from the effort of trial and error for the setup and realizes efficient on-the-fly sampling for the collective functional response of the receptor and bound water and therefore presents a practical approach to high-throughput screening in drug discovery.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Connecting Hindered Transport in Porous Media across Length Scales: From Single-Pore to Macroscopic

Hindered mass transport is widely observed in various porous media, including filtration membranes and porous rocks. However, there is no universal model capable of predicting transport in porous media due to the heterogeneity of porous structures and the complexity of the underlying microscopic mechanisms, including electrostatic and hydrodynamic effects. Here, we used a highly ordered porous medium (i.e. a silica inverse opal film) as a model system to directly explore the effects of geometric parameters (i.e. pore size, pore throat size and tracer particle size) and microscopic interaction parameters (e.g. controlled by ionic strength) on nanoparticle transport in porous environments using three-dimensional single-particle tracking. We found a linear scaling relation between the macroscopic diffusion coefficient and microscopic diffusion behaviors and a combination of parameters associated with microscopic features and phenomena, including both geometric effects and particle-level interactions. The proportionality coefficient relating micro and macro behaviors was complex and related to the connectivity of the matrix and pore-size variation, which could lead to tortuous diffusion pathways, hindering macroscopic transport. Furthermore, these findings provide important insights into nanoparticles and macromolecules transport in various porous media.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Discrete Orientations of Interfacial Waters Direct Crystallization of Mica-Binding Proteins

Understanding the basis of templated molecular assembly on a solid surface requires a fundamental comprehension of both short- and long-range aqueous response to the surface under a variety of solution conditions. Herein we provide a detailed picture of how the molecular-scale response to different mica surfaces yields distinct solvent orientations that produce quasi-static directional potentials onto which macromolecules can adsorb. We connect this directionality to observed (a)symmetric epitaxial alignment of designed proteins onto these surfaces, corroborate our findings with 3D atomic force microscopy experiments, and identify slight differences in surface structure as the origin of this effect. Furthermore, our work provides a detailed picture of the intrinsic electrolyte response in the vicinity of mineral interfaces, with clear predictions for experiment, and highlights the role of solvent on the predictive assembly of hierarchical materials on mineral surfaces.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

New Perspective on Electron Transfer through Molecules

Motivated by experiments which display unusual length and temperature effects for electron transfer in the nanometer length regime, we propose a new approach for describing long range electron transfer (ET) processes through molecules. We posit that the electron reorganization in the molecules (e.g., the electronic polarization of a macromolecule or organic film by an applied electric potential, or the injected charge generating a dipole moment) should be included in the description. We numerically solve a one-dimensional model for the electron transport, which includes electron-electron interactions explicitly; and we show that it generates a power law distance dependence for electron similar to that observed in experiments. The model does not include vibrations explicitly and should be consistent with the weak temperature dependences observed experimentally. This approach emphasizes the need to treat the electronic changes in the molecule(s) more explicitly to understand the behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Polyethylene Glycol Crowder’s Effect on Enzyme Aggregation, Thermal Stability, and Residual Catalytic Activity

Protein stability and performance in various natural and artificial systems incorporating many other macromolecules for therapeutic, diagnostic, sensor, and biotechnological applications attract increasing interest with the expansion of these technologies. Here we address the catalytic activity of lysozyme protein (LYZ) in the presence of a polyethylene glycol (PEG) crowder in a broad range of concentrations and temperatures in aqueous solutions of two different molecular mass PEG samples (Mw = 3350 and 10000 g/mol). The phase behavior of PEG–protein solutions is examined by using dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS), while the enzyme denaturing is monitored by using an activity assay (AS) and circular dichroism (CD) spectroscopy. Molecular dynamic (MD) simulations are used to illustrate the effect of PEG concentration on protein stability at high temperatures. The results demonstrate that LYZ residual activity after 1 h incubation at 80 °C is improved from 15% up to 55% with the addition of PEG. The improvement is attributed to two underlying mechanisms. (i) Primarily, the stabilizing effect is due to the suppression of the enzyme aggregation because of the stronger PEG–protein interactions caused by the increased hydrophobicity of PEG and lysozyme at elevated temperatures. (ii) The MD simulations showed that the addition of PEG to some degree stabilizes the secondary structures of the enzyme by delaying unfolding at elevated temperatures. The more pronounced effect is observed with an increase in PEG concentration. This trend is consistent with CD and AS experimental results, where the thermal stability is strengthened with increasing of PEG concentration and molecular mass. Overall, the results show that the highest stabilizing effect is approached at the critical overlap concentration of PEG.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

On the Interfacial Behavior of Catenated Poly(l-lactide) at the Air–Water Interface

Interfacial properties of polymeric materials are significantly influenced by their architectural structures and spatial features, while such a study of topologically interesting macromolecules is rarely reported. Here, we reported, for the first time, the interfacial behavior of catenated poly(l-lactide) (C-PLA) at the air–water interface and compared it with its linear analogue (L-PLA). The isotherms of surface pressure–area per repeating unit showed significant interfacial behavioral differences between the two polymers with different topologies. Isobaric creep experiments and compression–expansion cycles also showed that C-PLA demonstrated higher stability at the air–water interface. Interestingly, when the films at different surface pressures were transferred via the Langmuir–Blodgett method, successive atomic force microscopy imaging displayed distinct nanomorphologies, in which the surface of C-PLA exhibited nanofibrous structures, while that of the L-PLA revealed a smoother topology with less fiber-like structures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Ultrastructure of Critical-Gel-like Polyzwitterion–Polyoxometalate Complex Coacervates: Effects of Temperature, Salt Concentration, and Shear

The structure of unconventional complex coacervates, such as polymer-nonpolymer complex coacervates, remains less investigated than that of the conventional coacervates formed between oppositely charged polyelectrolytes with symmetric charge species. Yet, their microscopic structural organization is important to further elucidate the mechanism of liquid-liquid-phase separation processes upon complexation. In this work, we characterize the microstructural organization of complex coacervates formed between inorganic polyoxometalate (POM) and polyzwitterion by small-angle X-ray scattering (SAXS) with in situ temperature and shear control. Furthermore, despite the apparent transparent and homogeneous morphology of dense coacervates as observed by optical microscopy, our previous results (Macromolecules 2018, 51, 22, 9405-9411) suggest that dense polyzwitterion-POM coacervates exhibit critical-gel-like networks containing both complex-poor region (mesh pore) and complex-rich region (connective network). SAXS results as reported in this work support that the complex-rich region is actually in the form of loosely packed POM aggregates linked by polyzwitterion, designated as complex particles. The structure of aggregating complex particles is further examined against varied composition and salt concentrations, temperature, and shear, thanks to the high X-ray scattering contrast of POMs from that of other components in the coacervates. The complex particles in the dense coacervates appear to grow with more tightly packed POM aggregates with increasing POM-to-polyzwitterion concentration ratio, in contrast to more loosely packed POM aggregates with decreasing salt concentration. Conversely, increasing temperature could result in smaller complex particles containing more loosely packed POM aggregates, consistent with temperature-dependent viscoelasticity of dense coacervates. Furthermore, such POM-based hybrid dense coacervates exhibit intriguing strain-hardening behavior, resulting from shear-enhanced POM packing inside the complex particles. Distinct from the shear-thinning behavior of most conventional crosslinked polymeric networks, the strain-hardening property combined with thermal- and salt-responsive characteristics of polyzwitterion-POM coacervates could broaden the applications of hybrid organic-inorganic macroion coacervates as smart functional materials working under extreme environmental conditions.

36 MATERIALS SCIENCE↗