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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Optical Activity of Chiral Excitons

Recent activity in the area of chiroptical phenomena has been focused on the connection between structural asymmetry, electron spin configuration and light/matter interactions in chiral semiconductors. In these systems, spin‐splitting phenomena emerge due to inversion symmetry breaking and the presence of extended electronic states, yet the connection to chiroptical phenomena is lacking. Here, in this study, we develop an analytical effective mass model of chiral excitons, parameterized by density functional theory. The model accounts for parity mixing of the band edge Bloch functions resulting from polar distortions, resulting in allowed magnetic dipole transitions. Through the study of a prototypical chiral 2D hybrid perovskite semiconductor, we show that circular dichroism of the chiral exciton and its interband continuum emerges from spin‐splitting via cross‐coupling of Rashba‐like and chiral/helical spin‐texture components. To demonstrate the generality of our approach, and as a counterpoint, we apply our model to describe chiroptical properties of three‐dimensionally confined excitons in perovskite nanocrystals that occur without chiral lattice distortions.

14 SOLAR ENERGY↗
DOE OSTI2025

Shear–Mediated Stabilization of Spin Spiral Order in Multiferroic NiI 2

Type-II multiferroicity from non-collinear spin order is recently explored in the van der Waals material NiI 2 . Despite the importance for improper ferroelectricity, the microscopic mechanism of the helimagnetic order remains poorly understood. Here, the magneto-structural phases of NiI 2 are investigated using resonant magnetic X-ray scattering (RXS) and X-ray diffraction. Two competing magnetic phases are identified. Below 60 K, an incommensurate magnetic reflection (q ≈ [0.143,0,1.49] reciprocal lattice units) is observed which exhibits finite circular dichroism in RXS, signaling the inversion symmetry-breaking helimagnetic ground state. At elevated temperature, in the non-polar phase (60 K < T < 75 K), a distinct q ≈ [0.087,0.087,1.5] magnetic order is observed, attributed to a collinear incommensurate (CI) state. The first-order CI-helix transition is concomitant with a structural transition characterized by a significant interlayer shear, which drives the helimagnetic ground state as evidenced by a mean-field Heisenberg model including interlayer exchange and its coupling to the structural distortion. Furthermore, these findings identify interlayer magneto-structural coupling as the key driver behind multiferroicity in NiI 2 .

36 MATERIALS SCIENCE↗
DOE OSTI2022

Two–Photon Printing of Shape–Memory Microstructures and Metasurfaces via Radical–Mediated Thiol–Vinyl Hydrothiolation

Shape-memory resists capable of high-resolution curing into arbitrarily designed structures are increasingly demanded for soft robotics, optical sensors, microscale manufacturing, and biomedicine. Amorphous, shape-memory thiol-vinyl networks were printed using two-photon polymerization (2PP) curing of a simple resin formulated with commercially available reagents. The ability to print high-resolution feature sizes down to 200 nm is attributed to the use of radicalmediated, thiol-vinyl step-growth polymerization that quickly crosslinks the resin, limiting diffusive transport. The thermomechanical behavior of the 2PP-cured material analyzed in compression, tension and three-point bending is similar to the behavior of the UV-polymerized samples. To demonstrate the ability to design, field, and test 4D responsive microstructures, an array of nine springs with coil diameters of 330 μm was printed. Following compressive shapefixing, printed arrays can release 11 μJ of stored elastic strain energy when reheated. Further, a new concept of dichroic-memory of a metamaterial device is demonstrated by printing a twisted woodpile structure with circular dichroism as characterized by Mueller Matrix ellipsometry. Furthermore, our results demonstrate how combining high-resolution 2PP curing with stimuli-responsive molecular architectures can further the engineering of responsive microstructures and metamaterials.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Chiral Perovskite Nanoplatelets with Tunable Circularly Polarized Luminescence in the Strong Confinement Regime

Chiral perovskite nanocrystals have emerged as an interesting chiral excitonic platform that combines both structural flexibility and superior optoelectronic properties. Despite several recent demonstrations of optical activity in various chiral perovskite nanocrystals, efficient circularly polarized luminescence (CPL) with tunable energies remains a challenge. The chirality imprinting mechanism as a function of perovskite nanocrystal dimensionality remains elusive. Here, in this study, atomically thin inorganic perovskite nanoplatelets (NPLs) are synthesized with precise control of layer thickness and are functionalized by chiral surface ligands, serving as a unique platform to probe the chirality transfer mechanism at the organic/perovskite interface. It is found that chirality is successfully imprinted into mono-, bi-, and tri-layer inorganic perovskite NPLs, exhibiting tunable circular dichroism (CD) and CPL responses. However, chirality transfer decreases in thicker NPLs, resulting in decreased CD and CPL dissymmetry factors for thicker NPLs. Aided by large-scale first-principles calculations, it is proposed that chirality transfer is mainly mediated through a surface distortion rather than a hybridization of electronic states, giving rise to symmetry breaking in the perovskite lattice and spin-split conduction bands. The findings described here provide an in-depth understanding of chirality transfer and design principles for distorted-surface perovskites for chiral photonic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Infrared Optical Anisotropy in Quasi‐1D Hexagonal Chalcogenide BaTiSe 3

Polarimetric infrared (IR) detection bolsters IR thermography by leveraging the polarization of light. Optical anisotropy, i.e., birefringence and dichroism, can be leveraged to achieve polarimetric detection. Recently, giant optical anisotropy is discovered in quasi-1D narrow-bandgap hexagonal perovskite sulfides, A 1+x TiS 3 , specifically BaTiS 3 and Sr 9/8 TiS 3 . In these materials, the critical role of atomic-scale structure modulations in the unconventional electrical, optical, and thermal properties raises the broader question of the nature of other materials that belong to this family. To address this issue, for the first time, high-quality single crystals of a largely unexplored member of the A 1+x TiX 3 (X = S, Se) family, BaTiSe 3 are synthesized. Single-crystal X-ray diffraction determined the room-temperature structure with the P31c space group, which is a superstructure of the earlier reported P6 3 /mmc structure. The crystal structure of BaTiSe 3 features antiparallel c-axis displacements similar to but of lower symmetry than BaTiS 3 , verified by the polarization dependent Raman spectroscopy. Fourier transform infrared (FTIR) spectroscopy is used to characterize the optical anisotropy of BaTiSe 3 , whose refractive index along the ordinary (E ⊥ c) and extraordinary (E ‖ c) optical axes is quantitatively determined by combining ellipsometry studies with FTIR. With a giant birefringence Δn ∼ 0.9, BaTiSe 3 emerges as a new candidate for miniaturized birefringent optics for mid-wave infrared to long-wave infrared imaging.

optical anisotropy↗
DOE OSTI2024

Enhancing Chiroptoelectronic Activity in Chiral 2D Perovskites via Chiral–Achiral Cation Mixing

Rational design of chiral two-dimensional hybrid organic–inorganic perovskites is crucial to achieve chiroptoelecronic, spintronic, and ferroelectric applications. Here, in this study, an efficient way to manipulate the chiroptoelectronic activity of 2D lead iodide perovskites is reported by forming mixed chiral (R- or S-methylbenzylammonium (R-MBA + or S-MBA + )) and achiral (n-butylammonium (nBA + )) cations in the organic layer. The strongest and flipped circular dichroism signals are observed in (R/S-MBA 0.5 nBA 0.5 ) 2 PbI 4 films compared to (R/S-MBA) 2 PbI 4 . Moreover, the (R/S-MBA 0.5 nBA 0.5 ) 2 PbI 4 films exhibit pseudo-symmetric, unchanged circularly polarized photoluminescence peak as temperature increases. First-principles calculations reveal that mixed chiral–achiral cations enhance the asymmetric hydrogen-bonding interaction between the organic and inorganic layers, causing more structural distortion, thus, larger spin-polarized band-splitting than pure chiral cations. Temperature-dependent powder X-ray diffraction and pair distribution function structure studies show the compressed intralayer lattice with enlarged interlayer spacing and increased local ordering. Overall, this work demonstrates a new method to tune chiral and chiroptoelectronic properties and reveals their atomic scale structural origins.

2D perovskites↗
DOE OSTI2025

Revealing Robust Room Temperature Ferromagnetism in Gd‐Doped Few‐Layered MoS 2 Thin Films

2D MoS 2 holds great promise for spintronics, yet is limited by intrinsic diamagnetism. This study demonstrates inducing ferromagnetic behavior in MoS 2 films doped with 0.47% Gd, achieving an ultrahigh saturation magnetization of 454 emu/cm 3 in a few‐layered film over 11‐times higher than bulk films (40 nm). Raman spectroscopy, X‐ray photoelectron spectroscopy, X‐ray magnetic circular dichroism, and density functional theory (DFT) calculations reveal an interplay between Gd dopants and Mo, S vacancies (V 1Mo+2S ), leading to the formation of bound magnetic polarons (BMPs) that drive ferromagnetic ordering. H 2 S annealing and DFT calculations reveal that defect healing reduces the saturation magnetization by 83%. High sulfur migration barrier in few‐layered films helps preserve BMPs, thereby sustaining ferromagnetism, whereas lower migration barriers in bulk films lead to suppression. These findings highlight the synergy between Gd doping and defect engineering in achieving ultrahigh room‐temperature ferromagnetism, offering a scalable strategy for developing high‐performance 2D magnetic materials for spintronic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Self‐Assembly of Helical Nanofibrous Chiral Covalent Organic Frameworks

Abstract Despite significant progress on the design and synthesis of covalent organic frameworks (COFs), precise control over microstructures of such materials remains challenging. Herein, two chiral COFs with well‐defined one‐handed double‐helical nanofibrous morphologies were constructed via an unprecedented template‐free method, capitalizing on the diastereoselective formation of aminal linkages. Detailed time‐dependent experiments reveal the spontaneous transformation of initial rod‐like aggregates into the double‐helical microstructures. We have further demonstrated that the helical chirality and circular dichroism signal can be facilely inversed by simply adjusting the amount of acetic acid during synthesis. Moreover, by transferring chirality to achiral fluorescent molecular adsorbents, the helical COF nanostructures can effectively induce circularly polarized luminescence with the highest luminescent asymmetric factor ( g lum ) up to ≈0.01.

Tang, Xihao↗
DOE OSTI2023

Genetic Fusion of Thermoresponsive Polypeptides with UCST‐type Behavior Mediates 1D Assembly of Coiled‐Coil Bundlemers

Abstract Thermoresponsive resilin‐like polypeptides (RLPs) of various lengths were genetically fused to two different computationally designed coiled coil‐forming peptides with distinct thermal stability, to develop new strategies to assemble coiled coil peptides via temperature‐triggered phase separation of the RLP units. Their successful production in bacterial expression hosts was verified via gel electrophoresis, mass spectrometry, and amino acid analysis. Circular dichroism (CD) spectroscopy, ultraviolet‐visible (UV/Vis) turbidimetry, and dynamic light scattering (DLS) measurements confirmed the stability of the coiled coils and showed that the thermosensitive phase behavior of the RLPs was preserved in the genetically fused hybrid polypeptides. Cryogenic‐transmission electron microscopy and coarse‐grained modeling revealed that functionalizing the coiled coils with thermoresponsive RLPs leads to their thermally triggered noncovalent assembly into nanofibrillar assemblies.

Patkar, Sai S.↗
DOE OSTI2024

Self‐Standing Chiral Covalent Organic Framework Thin Films with Full‐Color Tunable Guest‐Induced Circularly Polarized Luminescence

Abstract Exploring self‐standing chiral covalent organic framework (COF) thin films with controllable circularly polarized luminescence (CPL) is of paramount significance but remains a challenging task. Herein, we demonstrate the first example of self‐standing chiral COF films employing a polymerization‐dispersion‐filtration strategy. Pristine, low‐quality chiral COF films were produced by interfacial polymerization and then re‐dispersed into COF colloidal solutions. Via vacuum assisted assembly, these COF colloids were densely stacked and assembled into self‐standing, pure chiral COF films ( L‐ / D‐ CCOF‐F) that were transparent, smooth, crack‐free and highly crystalline. These films were tunable in thicknesses, areas, and roughness, along with strong diffuse reflectance circular dichroism (DRCD) and cyan CPL signals, showing an intrinsic luminescence asymmetric factor ( g lum ) of ~4.3×10 −3 . Furthermore, these COF films served as host adsorbents to load various achiral organic dye guests through adsorption. The effective chiral transfer and energy transfer between CCOF‐F and achiral fluorescent dyes endowed the dyes with strong chirality and tunable DRCD, resulting in intense, full‐color‐tunable solid‐state CPL. Notably, the ordered arrangement of dye guest molecules within the preferentially oriented chiral pores of CCOF‐F contributed to an amplified | g lum | factor of up to 7.2×10 −2 , which is state‐of‐the‐art for COF‐based CPL materials. This work provides new insights into the design and fabrication of self‐standing chiral COF films, demonstrating their great potential for chiroptical applications.

Tang, Xihao↗
DOE OSTI2022

Self-Assembly of Helical Nanofibrous Chiral Covalent Organic Frameworks

Despite significant progress on the design and synthesis of covalent organic frameworks (COFs), precise control over microstructures of such materials remains challenging. Herein, two chiral COFs with well-defined one-handed double-helical nanofibrous morphologies were constructed via an unprecedented template-free method, capitalizing on the diastereoselective formation of aminal linkages. Detailed time-dependent experiments reveal the spontaneous transformation of initial rod-like aggregates into the double-helical microstructures. Impoirtantly, we have further demonstrated that the helical chirality and circular dichroism signal can be facilely inversed by simply adjusting the amount of acetic acid during synthesis. Moreover, by transferring chirality to achiral fluorescent molecular adsorbents, the helical COF nanostructures can effectively induce circularly polarized luminescence with the highest luminescent asymmetric factor (g lum ) up to ≈0.01.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Genetic Fusion of Thermoresponsive Polypeptides with UCST–type Behavior Mediates 1D Assembly of Coiled–Coil Bundlemers

Thermoresponsive resilin-like polypeptides (RLPs) of various lengths were genetically fused to two different computationally designed coiled coil-forming peptides with distinct thermal stability, to develop new strategies to assemble coiled coil peptides via temperature-triggered phase separation of the RLP units. Furthermore, their successful production in bacterial expression hosts was verified via gel electrophoresis, mass spectrometry, and amino acid analysis. Circular dichroism (CD) spectroscopy, ultraviolet-visible (UV/Vis) turbidimetry, and dynamic light scattering (DLS) measurements confirmed the stability of the coiled coils and showed that the thermosensitive phase behavior of the RLPs was preserved in the genetically fused hybrid polypeptides. Cryogenic-transmission electron microscopy and coarse-grained modeling revealed that functionalizing the coiled coils with thermoresponsive RLPs leads to their thermally triggered noncovalent assembly into nanofibrillar assemblies.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Macrocyclic β‐Sheets Stabilized by Hydrogen Bond Surrogates

Abstract Mimics of protein secondary and tertiary structure offer rationally‐designed inhibitors of biomolecular interactions. β‐Sheet mimics have a storied history in bioorganic chemistry and are typically designed with synthetic or natural turn segments. We hypothesized that replacement of terminal inter‐β‐strand hydrogen bonds with hydrogen bond surrogates (HBS) may lead to conformationally‐defined macrocyclic β‐sheets without the requirement for natural or synthetic β‐turns, thereby providing a minimal mimic of a protein β‐sheet. To access turn‐less antiparallel β‐sheet mimics, we developed a facile solid phase synthesis protocol. We surveyed a dataset of protein β‐sheets for naturally observed interstrand side chain interactions. This bioinformatics survey highlighted an over‐abundance of aromatic–aromatic, cation‐π and ionic interactions in β‐sheets. In correspondence with natural β‐sheets, we find that minimal HBS mimics show robust β‐sheet formation when specific amino acid residue pairings are incorporated. In isolated β‐sheets, aromatic interactions endow superior conformational stability over ionic or cation‐π interactions. Circular dichroism and NMR spectroscopies, along with high‐resolution X‐ray crystallography, support our design principles.

Chemistry↗
DOE OSTI2024

Chiral Teropyrenes: Synthesis, Structure, and Spectroscopic Studies

Abstract We present the inaugural synthesis of a chiral teropyrene achieved through a four‐fold alkyne benzannulation catalyzed by InCl 3 , resulting in good yields. The product underwent thorough characterization using FT‐Raman and FT‐IR spectroscopies, demonstrating a close agreement with calculated spectra. X‐ray crystallographic analysis unveiled a notable twist in the molecule‘s backbone, with an end‐to‐end twist angle of 51°, consistent with computational predictions. Experimentally determined enantiomeric inversion barriers revealed a significant energy barrier of 23 kcal/mol, facilitating the isolation of enantiomers for analysis by circular dichroism (CD) and circularly polarized luminescence (CPL) spectroscopies. These findings mark significant strides in the synthesis and characterization of chiral teropyrenes, offering insights into their structural and spectroscopic properties.

Chemistry↗
DOE OSTI2025

De Novo Design of High‐Affinity Miniprotein Binders Targeting Francisella Tularensis Virulence Factor

Abstract Francisella tularensis poses considerable public health risk due to its high infectivity and potential for bioterrorism. Francisella‐like lipoprotein (Flpp3), a key virulence factor unique to Francisella, plays critical roles in infection and immune evasion, making it a promising target for therapeutic development. However, the lack of well‐defined binding pockets and structural information on native interactions has hindered structure‐guided ligand discovery against Flpp3. Here, we used a combination of physics‐based and deep‐learning methods to design high‐affinity miniprotein binders targeting two distinct sites on Flpp3. We identified four binders for site I with binding affinities ranging between 24–110 nM. For the second site, an initial binder showed a dissociation constant ( K D ) of 81 nM, and subsequent site saturation mutagenesis yielded variants with sub‐nanomolar affinities. Circular dichroism confirmed the topology of designed miniproteins. The X‐ray crystal structure of Flpp3 in complex with a site I binder is nearly identical to the design model (Cα root‐mean‐square deviation (RMSD): 0.9 Å). These designed miniproteins provide research tools to explore the roles of Flpp3 in tularemia and should enable the development of new therapeutic candidates.

Gokce‐Alpkilic, Gizem [Molecular Engineering and S↗
DOE OSTI2020

Experimental and theoretical rationalization for the base pairing abilities of inosine, guanosine, adenosine, and their corresponding 8-oxo -7,8-dihydropurine, and 8-bromopurine analogues within A-form duplexes of RNA

Inosine is an important RNA modification, furthermore RNA oxidation has gained interest due, in part, to its potential role in the development/progression of disease as well as on its impact on RNA structure and function. In this report we established the base pairing abilities of purine nucleobases G, I, A, as well as their corresponding, 8-oxo-7,8-dihydropurine (common products of oxidation at the C8-position of purines), and 8-bromopurine (as probes to explore conformational changes), derivatives, namely 8-oxoG, 8-oxoI, 8-oxoA, 8-BrG, and 8-BrI. Dodecamers of RNA were obtained using standard phosphoramidite chemistry via solid-phase synthesis, and used as models to establish the impact that each of these nucleobases have on the thermal stability of duplexes, when base pairing to canonical and noncanonical nucleobases. Thermal stabilities were obtained from thermal denaturation transition (Tm) measurements, via circular dichroism (CD). The results were then rationalized using models of base pairs between two monomers, via density functional theory (DFT), that allowed us to better understand potential contributions from H-bonding patterns arising from distinct conformations. Overall, some of the important results indicate that: (a) an anti-I:syn-A base pair provides thermal stability, due to the absence of the exocyclic amine; (b) 8-oxoG base pairs like U, and does not induce destabilization within the duplex when compared to the pyrimidine ring; (c) a U:G wobble-pair is only stabilized by G; and (d) 8-oxoA displays an inherited base pairing promiscuity in this sequence context. Gaining a better understanding of how this oxidatively generated lesions potentially base pair with other nucleobases will be useful to predict various biological outcomes, as well as in the design of biomaterials and/or nucleotide derivatives with biological potential.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Improving the bioaccessibility of lipophilic ingredient in its oral intestinal delivery by ultrasound and biological cross‐linker

Abstract BACKGROUND Great efforts have been made to improve the oral bioaccessibility of lipophilic ingredients with multi‐functionalities. Achieving intestinal delivery of lipophilic ingredients and their encapsulation in micelles composed of bile salts and lipid hydrolysates (i.e. fatty acids) is critical for improving oral bioaccessibility. Therefore, oil‐core microcapsules are considered ideal carriers of lipophilic ingredients. Previous studies have reported oil‐core/zein‐shell microcapsules constructed by a one‐step anti‐solvent process. Still, its efficacy as an intestinal delivery system was limited because if the porous shell structure. RESULTS Zein solution was pretreated with ultrasound and tannic acid (TA) cross‐linking. Composite oil‐core microcapsule (COM) with a compact shell structure was successfully prepared by using modified zein solution in the anti‐solvent process. Fourier‐transform infrared spectroscopy and circular dichroism analyses indicated that ultrasound and TA synergistically promote the conformational transition of zein from α‐helix to β‐sheet and enhance the hydrophobic interactions among protein chains. The above changes contribute to the strengthen of shell zein network. Correspondingly, COM presents superior encapsulation efficiency and environmental stability over the simple oil‐core microcapsule (SOM) prepared without the use of ultrasound and TA. Furthermore, antioxidant activity of β‐carotene was well retained during the encapsulation process. In vitro studies indicated that COM was more resistant to digestibility and acid‐induced swelling. More than 87% of β‐carotene could be released in the intestine in a sustainable way. The controllable release behavior thus promoted a significant increase in bioaccessibility of β‐carotene encapsulated in COM compared to SOM (85.9% versus 48.5%). CONCLUSION The COM generated here shows potential for bioaccessibility improvement of lipophilic ingredients. © 2022 Society of Chemical Industry.

Wei, Yun‐Shan↗
DOE OSTI2023

The N‐terminal intrinsically disordered region of Ncb5or docks with the cytochrome b 5 core to form a helical motif that is of ancient origin

Abstract NADH cytochromeb 5 oxidoreductase (Ncb5or) is a cytosolic ferric reductase implicated in diabetes and neurological conditions. Ncb5or comprises cytochromeb 5 (b 5 ) and cytochromeb 5 reductase (b 5 R) domains separated by a CHORD‐Sgt1 (CS) linker domain. Ncb5or redox activity depends on proper inter‐domain interactions to mediate electron transfer from NADH or NADPH via FAD to heme. While full‐length human Ncb5or has proven resistant to crystallization, we have succeeded in obtaining high‐resolution atomic structures of theb 5 domain and a construct containing the CS andb 5 R domains (CS/b 5 R). Ncb5or also contains an N‐terminal intrinsically disordered region of 50 residues that has no homologs in other protein families in animals but features a distinctive, conserved L 34 MDWIRL 40 motif also present in reduced lateral root formation (RLF) protein in rice and increased recombination center 21 in baker's yeast, all attaching to ab 5 domain. After unsuccessful attempts at crystallizing a human Ncb5or construct comprising the N‐terminal region naturally fused to theb 5 domain, we were able to obtain a high‐resolution atomic structure of a recombinant rice RLF construct corresponding to residues 25–129 of human Ncb5or (52% sequence identity; 74% similarity). The structure reveals Trp 120 (corresponding to invariant Trp 37 in Ncb5or) to be part of an 11‐residue α‐helix (S 116 QMDWLKLTRT 126 ) packing against two of the four helices in theb 5 domain that surround heme (α2 and α5). The Trp 120 side chain forms a network of interactions with the side chains of four highly conserved residues corresponding to Tyr 85 and Tyr 88 (α2), Cys 124 (α5), and Leu 47 in Ncb5or. Circular dichroism measurements of human Ncb5or fragments further support a key role of Trp 37 in nucleating the formation of the N‐terminal helix, whose location in the N/b 5 module suggests a role in regulating the function of this multi‐domain redox enzyme. This study revealed for the first time an ancient origin of a helical motif in the N/b 5 module as reflected by its existence in a class of cytochromeb 5 proteins from three kingdoms among eukaryotes.

Biochemistry & Molecular Biology↗