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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 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Triplet-pair spin signatures from macroscopically aligned heteroacenes in an oriented single crystal

The photo-driven process of singlet fission generates coupled triplet pairs (TT) with fundamentally intriguing and potentially useful properties. The quintet 5 TT 0 sublevel is particularly interesting for quantum information because it is highly entangled, is addressable with microwave pulses, and could be detected using optical techniques. Previous theoretical work on a model Hamiltonian and nonadiabatic transition theory, called the JDE model, has determined that this sublevel can be selectively populated if certain conditions are met. Among the most challenging, the molecules within the dimer undergoing singlet fission must have their principal magnetic axes parallel to one another and to an applied Zeeman field. Here, we present time-resolved electron paramagnetic resonance (TR-EPR) spectroscopy of a single crystal sample of a tetracenethiophene compound featuring arrays of dimers aligned in this manner, which were mounted so that the orientation of the field relative to the molecular axes could be controlled. The observed spin sublevel populations in the paired TT and unpaired (T+T) triplets are consistent with predictions from the JDE model, including preferential 5 TT 0 formation at z ‖ B 0 , with one caveat—two 5 TT spin sublevels have little to no population. This may be due to crossings between the 5 TT and 3 TT manifolds in the field range investigated by TR-EPR, consistent with the intertriplet exchange energy determined by monitoring photoluminescence at varying magnetic fields.

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

Exploring the Effects of Intersubunit Interface Mutations on Virus-Like Particle Structure and Stability

Virus-like particles (VLPs) from bacteriophage MS2 provide a platform to study protein self-assembly and create engineered systems for drug delivery. Here, we aim to understand the impact of intersubunit interface mutations on the local and global structure and function of MS2-based VLPs. In previous work, our lab identified locally supercharged double mutants [T71K/G73R] that concentrate positive charge at capsid pores, enhancing uptake into mammalian cells. To study the effects of particle size on cellular internalization, we combined these double mutants with a single point mutation [S37P] that was previously reported to switch particle geometry from T = 3 to T = 1 icosahedral symmetry. These new variants retained their enhanced cellular uptake activity and could deliver small-molecule drugs with efficacy levels similar to our first-generation capsids. Surprisingly, these engineered triple mutants exhibit increased thermostability and unexpected geometry, producing T = 3 particles instead of the anticipated T = 1 assemblies. Transmission electron microscopy revealed various capsid assembly states, including wild-type (T = 3), T = 1, and rod-like particles, that could be accessed using different combinations of these point mutations. Molecular dynamics experiments recapitulated the structural rationale in silico for the single point mutation [S37P] forming a T = 1 virus-like particle and showed that this assembly state was not favored when combined with mutations that favor rod-like architectures. Through this work, we investigated how interdimer interface dynamics influence VLP size and morphology and how these properties affect particle function in applications such as drug delivery.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2021

Two-dimensional phase cartography for high-harmonic spectroscopy

Extremely nonlinear spectroscopy based on high-order-harmonic generation has become a powerful investigation method for attosecond dynamics in gas and solid targets. In particular, the phase of harmonic emission was shown to carry profound insight into atomic and molecular structure and dynamics. However, current techniques offer phase measurements only along specific directions, thus providing partial characterization. Here we report on a new approach combining optical and quantum interferometers measuring along two dimensions the intensity and phase of harmonic emission from aligned molecules in the exact same experimental conditions. This two-dimensional cartography technique measures the phase with no arbitrary offset and no uncertainty on its sign. Measurements along different dimensions can be combined in two ways: either a single mapping or a redundant mapping allowing high-precision phase recovery using a Shack–Hartmann-like algorithm. We demonstrate both methods in a nitrogen test case, which allows disentangling structural and dynamical effects. Two-dimensional phase cartography paves the way to high-resolution high-harmonic spectroscopy for applications such as quantum orbital tomography and attosecond charge migration in molecules.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Streptomyces umbrella toxin particles block hyphal growth of competing species

Abstract Streptomycesare a genus of ubiquitous soil bacteria from which the majority of clinically utilized antibiotics derive 1 . The production of these antibacterial molecules reflects the relentless competitionStreptomycesengage in with other bacteria, including otherStreptomycesspecies 1,2 . Here we show that in addition to small-molecule antibiotics,Streptomycesproduce and secrete antibacterial protein complexes that feature a large, degenerate repeat-containing polymorphic toxin protein. A cryo-electron microscopy structure of these particles reveals an extended stalk topped by a ringed crown comprising the toxin repeats scaffolding five lectin-tipped spokes, which led us to name them umbrella particles.Streptomyces coelicolorencodes three umbrella particles with distinct toxin and lectin composition. Notably, supernatant containing these toxins specifically and potently inhibits the growth of selectStreptomycesspecies from among a diverse collection of bacteria screened. For one target,Streptomyces griseus, inhibition relies on a single toxin and that intoxication manifests as rapid cessation of vegetative hyphal growth. Our data show thatStreptomycesumbrella particles mediate competition among vegetative mycelia of related species, a function distinct from small-molecule antibiotics, which are produced at the onset of reproductive growth and act broadly 3,4 . Sequence analyses suggest that this role of umbrella particles extends beyondStreptomyces, as we identified umbrella loci in nearly 1,000 species across Actinobacteria.

Science & Technology - Other Topics↗
DOE OSTI2021

Dynamic Nuclear Polarization Enhanced Nuclear Spin Optical Rotation

Here, nuclear spin optical rotation (NSOR) has been investigated as a magneto-optical effect, which holds the potential for applications, including hybrid optical-nuclear magnetic resonance (NMR) spectroscopy and gradientless imaging. The intrinsic nature of NSOR renders its detection relatively insensitive, which has prevented it moving from a proof of concept to a method supporting chemical characterizations. In this work, the dissolution dynamic nuclear polarization technique is introduced to provide nuclear spin polarization, increasing the signal-to-noise ratio by several thousand times. NSOR signals of 1 H and 19 F nuclei are observed in a single scan for diluted compounds, which has made this effect suitable for the determination of electronic transitions from a specific nucleus in a large molecule.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗
DOE OSTI2022

Improved Syntheses of 4'-Vinylbenzo-3 n -Crown- n Ethers ( n = 5–7)

We report a convenient, high-yielding, and scalable synthetic approach to the construction of crown ether monomers has been developed. Using this method, a wide-ranging class of polymerizable crown ethers can be efficiently obtained. The identity of the crown ethers was further established using single-crystal X-ray diffraction studies. Two of the vinylbenzocrown ethers crystallize with water, affording infinite supramolecular assemblies containing hydrogen-bonded water molecules. The crown ethers described in this manuscript will be used as host molecules in separation science.

36 MATERIALS SCIENCE↗
DOE OSTI2026

A Ce 4+ Aluminum Hydride Complex

Complexes of reducing hydride ligands by high-oxidation state cerium are unknown due to the fundamental mismatch in their redox chemistry. Herein we report the synthesis, characterization, and reactivity of the first example of a Ce 4+ aluminum hydride complex. Synthetic strategies adapted from the preparation of Ce 4+ alkyl complexes facilitated the isolation of [Ce 4+ (κ 2 -H 3 AlC(TMS) 3 )(NP( t Bu) 3 ) 3 ] (CeHAl). The bonding and structure of this complex is characterized by single-crystal XRD, NMR, and UV–vis–NIR spectroscopy, and DFT computations. The fundamental reactivity profile is evaluated by cyclic voltammetry and small-molecule reactions.

anions↗
DOE OSTI2023

CO electroreduction on single-atom copper

Electroreduction of carbon dioxide (CO 2 ) or carbon monoxide (CO) toward C 2+ hydrocarbons such as ethylene, ethanol, acetate and propanol represents a promising approach toward carbon-negative electrosynthesis of chemicals. Fundamental understanding of the carbon–carbon (C-C) coupling mechanisms in these electrocatalytic processes is the key to the design and development of electrochemical systems at high energy and carbon conversion efficiencies. Here, we report the investigation of CO electreduction on single-atom copper (Cu) electrocatalysts. Atomically dispersed Cu is coordinated on a carbon nitride substrate to form high-density copper–nitrogen moieties. Chemisorption, electrocatalytic, and computational studies are combined to probe the catalytic mechanisms. Unlike the Langmuir-Hinshelwood mechanism known for copper metal surfaces, the confinement of CO adsorption on the single-copper-atom sites enables an Eley-Rideal type of C-C coupling between adsorbed (*CO) and gaseous [CO(g)] carbon moxide molecules. The isolated Cu sites also selectively stabilize the key reaction intermediates determining the bifurcation of reaction pathways toward different C 2+ products.

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

Materials Data on H4C7 by Materials Project

C7H4 crystallizes in the monoclinic P2_1 space group. The structure is zero-dimensional and consists of two 1,1'-(1,8-naphthylene)bispyrene molecules. there are forty-two inequivalent C+0.57- sites. In the first C+0.57- site, C+0.57- is bonded in a distorted single-bond geometry to two C+0.57- and one H1+ atom. There is one shorter (1.37 Å) and one longer (1.44 Å) C–C bond length. The C–H bond length is 1.09 Å. In the second C+0.57- site, C+0.57- is bonded in a trigonal planar geometry to three C+0.57- atoms. There is one shorter (1.42 Å) and one longer (1.44 Å) C–C bond length. In the third C+0.57- site, C+0.57- is bonded in a trigonal planar geometry to three C+0.57- atoms. There are a spread of C–C bond distances ranging from 1.39–1.50 Å. In the fourth C+0.57- site, C+0.57- is bonded in a distorted single-bond geometry to one C+0.57- and one H1+ atom. The C–H bond length is 1.09 Å. In the fifth C+0.57- site, C+0.57- is bonded in a distorted single-bond geometry to one C+0.57- and one H1+ atom. The C–C bond length is 1.37 Å. The C–H bond length is 1.09 Å. In the sixth C+0.57- site, C+0.57- is bonded in a distorted trigonal planar geometry to two C+0.57- and one H1+ atom. The C–C bond length is 1.42 Å. The C–H bond length is 1.09 Å. In the seventh C+0.57- site, C+0.57- is bonded in a trigonal planar geometry to three C+0.57- atoms. There is one shorter (1.42 Å) and one longer (1.45 Å) C–C bond length. In the eighth C+0.57- site, C+0.57- is bonded in a distorted trigonal planar geometry to two C+0.57- and one H1+ atom. The C–C bond length is 1.37 Å. The C–H bond length is 1.09 Å. In the ninth C+0.57- site, C+0.57- is bonded in a distorted trigonal planar geometry to two C+0.57- and one H1+ atom. The C–C bond length is 1.41 Å. The C–H bond length is 1.09 Å. In the tenth C+0.57- site, C+0.57- is bonded in a distorted trigonal planar geometry to two C+0.57- and one H1+ atom. The C–C bond length is 1.39 Å. The C–H bond length is 1.09 Å. In the eleventh C+0.57- site, C+0.57- is bonded in a trigonal planar geometry to three C+0.57- atoms. There is one shorter (1.45 Å) and one longer (1.50 Å) C–C bond length. In the twelfth C+0.57- site, C+0.57- is bonded in a trigonal planar geometry to three C+0.57- atoms. In the thirteenth C+0.57- site, C+0.57- is bonded in a trigonal planar geometry to three C+0.57- atoms. There is one shorter (1.40 Å) and one longer (1.42 Å) C–C bond length. In the fourteenth C+0.57- site, C+0.57- is bonded in a distorted single-bond geometry to one C+0.57- and one H1+ atom. The C–H bond length is 1.09 Å. In the fifteenth C+0.57- site, C+0.57- is bonded in a distorted single-bond geometry to one C+0.57- and one H1+ atom. The C–C bond length is 1.40 Å. The C–H bond length is 1.09 Å. In the sixteenth C+0.57- site, C+0.57- is bonded in a trigonal planar geometry to three C+0.57- atoms. There is one shorter (1.43 Å) and one longer (1.44 Å) C–C bond length. In the seventeenth C+0.57- site, C+0.57- is bonded in a trigonal planar geometry to three C+0.57- atoms. There is one shorter (1.43 Å) and one longer (1.44 Å) C–C bond length. In the eighteenth C+0.57- site, C+0.57- is bonded in a distorted single-bond geometry to one C+0.57- and one H1+ atom. The C–H bond length is 1.09 Å. In the nineteenth C+0.57- site, C+0.57- is bonded in a distorted single-bond geometry to one C+0.57- and one H1+ atom. The C–C bond length is 1.43 Å. The C–H bond length is 1.09 Å. In the twentieth C+0.57- site, C+0.57- is bonded in a trigonal planar geometry to three C+0.57- atoms. There is one shorter (1.41 Å) and one longer (1.43 Å) C–C bond length. In the twenty-first C+0.57- site, C+0.57- is bonded in a trigonal planar geometry to three C+0.57- atoms. The C–C bond length is 1.43 Å. In the twenty-second C+0.57- site, C+0.57- is bonded in a distorted trigonal planar geometry to two C+0.57- and one H1+ atom. The C–C bond length is 1.40 Å. The C–H bond length is 1.09 Å. In the twenty-third C+0.57- site, C+0.57- is bonded in a distorted single-bond geometry to one C+0.57- and one H1+ atom. The C–H bond length is 1.09 Å. In the twenty-fourth C+0.57- site, C+0.57- is bonded in a distorted single-bond geometry to one C+0.57- and one H1+ atom. The C–C bond length is 1.41 Å. The C–H bond length is 1.09 Å. In the twenty-fifth C+0.57- site, C+0.57- is bonded in a trigonal planar geometry to three C+0.57- atoms. The C–C bond length is 1.43 Å. In the twenty-sixth C+0.57- site, C+0.57- is bonded in a distorted single-bond geometry to one C+0.57- and one H1+ atom. The C–H bond length is 1.09 Å. In the twenty-seventh C+0.57- site, C+0.57- is bonded in a distorted single-bond geometry to one C+0.57- and one H1+ atom. The C–C bond length is 1.44 Å. The C–H bond length is 1.09 Å. In the twenty-eighth C+0.57- site, C+0.57- is bonded in a trigonal planar geometry to three C+0.57- atoms. In the twenty-ninth C+0.57- site, C+0.57- is bonded in a trigonal planar geometry to three C+0.57- atoms. The C–C bond length is 1.40 Å. In the thirtieth C+0.57- site, C+0.57- is bonded in a distorted single-bond geometry to two C+0.57- and one H1+ atom. The C–C bond length is 1.39 Å. The C–H bond length is 1.09 Å. In the thirty-first C+0.57- site, C+0.57- is bonded in a distorted trigonal planar geometry to two C+0.57- and one H1+ atom. The C–C bond length is 1.40 Å. The C–H bond length is 1.09 Å. In the thirty-second C+0.57- site, C+0.57- is bonded in a trigonal planar geometry to three C+0.57- atoms. Both C–C bond lengths are 1.43 Å. In the thirty-third C+0.57- site, C+0.57- is bonded in a trigonal planar geometry to three C+0.57- atoms. The C–C bond length is 1.43 Å. In the thirty-fourth C+0.57- site, C+0.57- is bonded in a distorted single-bond geometry to two C+0.57- and one H1+ atom. The C–C bond length is 1.37 Å. The C–H bond length is 1.09 Å. In the thirty-fifth C+0.57- site, C+0.57- is bonded in a distorted trigonal planar geometry to two C+0.57- and one H1+ atom. The C–C bond length is 1.43 Å. The C–H bond length is 1.09 Å. In the thirty-sixth C+0.57- site, C+0.57- is bonded in a trigonal planar geometry to three C+0.57- atoms. There is one shorter (1.41 Å) and one longer (1.43 Å) C–C bond length. In the thirty-seventh C+0.57- site, C+0.57- is bonded in a trigonal planar geometry to three C+0.57- atoms. The C–C bond length is 1.43 Å. In the thirty-eighth C+0.57- site, C+0.57- is bonded in a distorted trigonal planar geometry to two C+0.57- and one H1+ atom. The C–C bond length is 1.40 Å. The C–H bond length is 1.09 Å. In the thirty-ninth C+0.57- site, C+0.57- is bonded in a distorted single-bond geometry to one C+0.57- and one H1+ atom. The C–H bond length is 1.09 Å. In the fortieth C+0.57- site, C+0.57- is bonded in a distorted single-bond geometry to one C+0.57- and one H1+ atom. The C–C bond length is 1.41 Å. The C–H bond length is 1.09 Å. In the forty-first C+0.57- site, C+0.57- is bonded in a trigonal planar geometry to three C+0.57- atoms. The C–C bond length is 1.43 Å. In the forty-second C+0.57- site, C+0.57- is bonded in a distorted trigonal planar geometry to two C+0.57- and one H1+ atom. The C–H bond length is 1.09 Å. There are twenty-four inequivalent H1+ sites. In the first H1+ site, H1+ is bonded in a single-bond geometry to one C+0.57- atom. In the second H1+ site, H1+ is bonded in a single-bond geometry to one C+0.57- atom. In the third H1+ site, H1+ is bonded in a single-bond geometry to one C+0.57- atom. In the fourth H1+ site, H1+ is bonded in a single-bond geometry to one C+0.57- atom. In the fifth H1+ site, H1+ is bonded in a single-bond geometry to one C+0.57- atom. In the sixth H1+ site, H1+ is bonded in a single-bond geometry to one C+0.57- atom. In the seventh H1+ site, H1+ is bonded in a single-bond geometry to one C+0.57- atom. In the eighth H1+ site, H1+ is bonded in a single-bond geometry to one C+0.57- atom. In the ninth H1+ site, H1+ is bonded in a single-bond geometry to one C+0.57- atom. In the tenth H1+ site, H1+ is bonded in a single-bond geometry to one C+0.57- atom. In the eleventh H1+ site, H1+ is bonded in a single-bond geometry to one C+0.57- atom. In the twelfth H1+ site, H1+ is bonded in a single-bond geometry to one C+0.57- atom. In the thirteenth H1+ site, H1+ is bonded in a single-bond geometry to one C+0.57- atom. In the fourteenth H1+ site, H1+ is bonded in a single-bond geometry to one C+0.57- atom. In the fifteenth H1+ site, H1+ is bonded in a single-bond geometry to one C+0.57- atom. In the sixteenth H1+ site, H1+ is bonded in a single-bond geometry to one C+0.57- atom. In the seventeenth H1+ site, H1+ is bonded in a single-bond geometry to one C+0.57- atom. In the eighteenth H1+ site, H1+ is bonded in a single-bond geometry to one C+0.57- atom. In the nineteenth H1+ site, H1+ is bonded in a single-bond geometry to one C+0.57- atom. In the twentieth H1+ site, H1+ is bonded in a single-bond geometry to one C+0.57- atom. In the twenty-first H1+ site, H1+ is bonded in a single-bond geometry to one C+0.57- atom. In the twenty-second H1+ site, H1+ is bonded in a single-bond geometry to one C+0.57- atom. In the twenty-third H1+ site, H1+ is bonded in a single-bond geometry to one C+0.57- atom. In the twenty-fourth H1+ site, H1+ is bonded in a single-bond geometry to one C+0.57- atom.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Hyperspectral Detection of the Fluorescence Shift between Chirality-Sorted Empty and Water-Filled Single-Wall Carbon Nanotube Enantiomers

Single-wall carbon nanotubes (SWCNTs) have extraordinary electronic and optical properties that depend strongly on their exact chiral structure and their interaction with their inner and outer environment. The fluorescence (PL) of semiconducting SWCNTs, for instance, will shift depending on the molecules with which the SWCNT’s hollow core is filled. These interaction-induced shifts are challenging to resolve on the ensemble level in samples containing a mixture of different filling contents due to the relatively large inhomogeneous line width of the ensemble SWCNT PL compared to the size of these shifts. To circumvent this inhomogeneous broadening, single-tube spectroscopy and hyperspectral imaging are often applied, which until now required time-consuming statistical studies. Here, we present hyperspectral PL microscopy combined with automated SWCNT segmenting based on either principal component analysis or a convolutional neural network, capable of both spatially and spectrally resolving the PL along the length of many individual SWCNTs at the same time and automatically fitting peak positions and line widths of individual SWCNTs. The methodology is demonstrated by accurately determining the emission shifts and line widths of thousands of left- and right-handed empty and water-filled SWCNTs coated with a chiral surfactant, resulting in four statistical distributions which cannot be resolved in ensemble spectroscopy of unsorted samples. The results demonstrate a robust method to quickly probe ensemble properties with single-enantiomer spectral resolution. Moreover, it promises to be an absolute quantitative method to characterize the relative abundances of SWCNTs with different handedness or filling content in macroscopic samples, simply by counting individual species.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Hole-Transport Layer for High Current Density and Stability of Sn-Pb Perovskites and All-Perovskite Tandem Solar Cells

Sn-Pb perovskites are essential for achieving efficient single-junction solar cells and all-perovskite tandem solar cells (APTSCs). Although Sn oxidation and defective surfaces were once major limitations, recent advances in intrinsic material quality have largely mitigated these issues. As a result, the HTL-related interface is now regarded as the primary bottleneck for device performance. To address the intrinsic drawbacks of PEDOT:PSS, chemical surface modification and additive strategies have been widely applied, and alternative HTLs, like polymeric, inorganic, or small-molecule HTLs, have also gained attention. These approaches offer improved energy-level alignment, high transparency, and enhanced chemical durability, leading to higher short-circuit current density and longer operational lifetime in both single-junction and tandem devices. In this Perspective, we highlight the key criteria and practical effects of HTL materials suitable for Sn-Pb perovskites.

14 SOLAR ENERGY↗
DOE OSTI2021

Isolated copper single sites for high-performance electroreduction of carbon monoxide to multicarbon products

Electrochemical carbon monoxide reduction is a promising strategy for the production of value-added multicarbon compounds, albeit yielding diverse products with low selectivities and Faradaic efficiencies. Here, copper single atoms anchored to Ti 3 C 2 T x MXene nanosheets are firstly demonstrated as effective and robust catalysts for electrochemical carbon monoxide reduction, achieving an ultrahigh selectivity of 98% for the formation of multicarbon products. Particularly, it exhibits a high Faradaic efficiency of 71% towards ethylene at -0.7 V versus the reversible hydrogen electrode, superior to the previously reported copper-based catalysts. Besides, it shows a stable activity during the 68-h electrolysis. Theoretical simulations reveal that atomically dispersed Cu–O 3 sites favor the C–C coupling of carbon monoxide molecules to generate the key *CO-CHO species, and then induce the decreased free energy barrier of the potential-determining step, thus accounting for the high activity and selectivity of copper single atoms for carbon monoxide reduction.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Cross-Platform Classifier of Chemical Stability for Charged Redoxmers

The development of new redox flow battery chemistries is hampered by time-consuming organic syntheses and electrochemical characterization of candidate redoxmer molecules. Here, we use Sure Independence Screening and Sparsifying Operator (SISSO) to demonstrate a cross-platform classifier for chemical stability of charged redoxmers in electrolyte solutions. This SISSO model yields a single formula to separate positively charged dialkoxyarene catholytes and negatively charged pyridinium anolytes into stable and unstable species in acetonitrile-based electrolytes as probed through cyclic voltammetry measurements. Using such classifiers, the stability of new compounds across different synthetic platforms can be rapidly assessed.

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

Novel Hydrogen Clathrate Hydrate

We report a new hydrogen clathrate hydrate synthesized at 1.2 GPa and 298 K documented by single-crystal x-ray diffraction, Raman spectroscopy, and first-principles calculations. The oxygen sublattice of the new clathrate hydrate matches that of ice II, while hydrogen molecules are in the ring cavities, which results in the trigonal R3c or R¯3c space group (proton ordered or disordered, respectively) and the composition of ( H 2 O) 6 H 2 . Raman spectroscopy and theoretical calculations reveal a hydrogen disordered nature of the new phase $C$$^{'}_{1}$, distinct from the well-known ordered C 1 clathrate, to which this new structure transforms upon compression and/or cooling. Furthermore, this new clathrate phase can be viewed as a realization of a disordered ice II, unobserved before, in contrast to all other ordered ice structures.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Precise transcript targeting by CRISPR-Csm complexes

Robust and precise transcript targeting in mammalian cells remains a difficult challenge using existing approaches due to inefficiency, imprecision and subcellular compartmentalization. Here we show that the clustered regularly interspaced short palindromic repeats (CRISPR)-Csm complex, a multiprotein effector from type III CRISPR immune systems in prokaryotes, provides surgical RNA ablation of both nuclear and cytoplasmic transcripts. As part of the most widely occurring CRISPR adaptive immune pathway, CRISPR-Csm uses a programmable RNA-guided mechanism to find and degrade target RNA molecules without inducing indiscriminate trans-cleavage of cellular RNAs, giving it an important advantage over the CRISPR-Cas13 family of enzymes. Using single-vector delivery of the Streptococcus thermophilus Csm complex, we observe high-efficiency RNA knockdown (90–99%) and minimal off-target effects in human cells, outperforming existing technologies including short hairpin RNA- and Cas13-mediated knockdown. We also find that catalytically inactivated Csm achieves specific and durable RNA binding, a property we harness for live-cell RNA imaging. These results establish the feasibility and efficacy of multiprotein CRISPR-Cas effector complexes as RNA-targeting tools in eukaryotes.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Cryo2StructData: A Large Labeled Cryo-EM Density Map Dataset for AI-based Modeling of Protein Structures

The advent of single-particle cryo-electron microscopy (cryo-EM) has brought forth a new era of structural biology, enabling the routine determination of large biological molecules and their complexes at atomic resolution. The high-resolution structures of biological macromolecules and their complexes significantly expedite biomedical research and drug discovery. However, automatically and accurately building atomic models from high-resolution cryo-EM density maps is still time-consuming and challenging when template-based models are unavailable. Artificial intelligence (AI) methods such as deep learning trained on limited amount of labeled cryo-EM density maps generate inaccurate atomic models. To address this issue, we created a dataset called Cryo2StructData consisting of 7,600 preprocessed cryo-EM density maps whose voxels are labelled according to their corresponding known atomic structures for training and testing AI methods to build atomic models from cryo-EM density maps. Cryo2StructData is larger than existing, publicly available datasets for training AI methods to build atomic protein structures from cryo-EM density maps. We trained and tested deep learning models on Cryo2StructData to validate its quality showing that it is ready for being used to train and test AI methods for building atomic models.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2024

Control of work functions of nanophotonic components

Work function is an essential material’s property playing important roles in electronics, photovoltaics, and more recently, in nanophotonics. We have studied effects of organic, and inorganic dielectric materials on work functions of Au films in single layered, and multilayered structures. We found that measured work function of metallic surfaces can be affected by dielectric materials situated 10–100 nm away from the metallic surface. We have found that, (i) the glass underneath ~ 50 nm gold slab reduces the work function of gold, (ii) Rh590:PMMA increases the work function of a gold film deposited on top of the polymer, and (iii) reduces it if Rh590:PMMA is deposited on top of Au. (iv) With increase of the Rh590 concentration in PMMA, n, the work function first decreases (at n < 64 g/l), and then increases (at n > 64 g/l). (v) The work function of a Fabry–Perot cavity or an MIM waveguide is almost the same as that of single Au films of comparable thickness. The experimental results can be qualitatively explained in terms of a simple model taking into account adhesion of charged molecules to a metallic surface, and formation of a double layer of charges accelerating or decelerating electrons exiting the metal and decreasing or increasing the work function.

36 MATERIALS SCIENCE↗