An official website of the United States government
Abstract Here, the observation of spin‐polarized emission for the Au25(SC8H9)18monolayer‐protected cluster (MPC) is reported. Variable‐temperature variable‐field magnetic circular photoluminescence (VTV‐MCPL) measurements are combined with VT‐PL spectroscopy to provide state‐resolved characterization of the transient electronic structure and spin‐polarized electron‐hole recombination dynamics of Au25(SC8H9)18. Through analysis of VTV‐MCPL measurements, a low energy (1.64 eV) emission peak is assigned to intraband relaxation between core‐metal‐localized superatom‐D to ‐P orbitals. Two higher energy interband components (1.78 eV, 1.94 eV) are assigned to relaxation from superatom‐D orbitals to states localized to the inorganic semirings. For both intraband superatom‐based or interband relaxation mechanisms, the extent of spin‐polarization, quantified as the degree of circular polarization (DOCP), is determined by state‐specific electron‐vibration coupling strengths and energy separations of bright and dark electronic fine‐structure levels. At low temperatures (<60 K), metal–metal superatom‐based intraband transitions dominate the global PL emission. At higher temperatures (>60 K), interband ligand‐based emission is dominant. In the low‐temperature PL regime, increased sample temperature results in larger global PL intensity. In the high‐temperature regime, increased temperature quenches interband radiative recombination. The relative intensity for each PL mechanism is discussed in terms of state‐specific electronic‐vibrational coupling strengths and related to the total angular momentum, quantified by Landég‐factors.
more »
« less
Thermoresponsive polymer assemblies via variable temperature liquid-phase transmission electron microscopy and small angle X-ray scattering
Abstract Herein, phase transitions of a class of thermally-responsive polymers, namely a homopolymer, diblock, and triblock copolymer, were studied to gain mechanistic insight into nanoscale assembly dynamics via variable temperature liquid-cell transmission electron microscopy (VT-LCTEM) correlated with variable temperature small angle X-ray scattering (VT-SAXS). We study thermoresponsive poly(diethylene glycol methyl ether methacrylate) (PDEGMA)-based block copolymers and mitigate sample damage by screening electron flux and solvent conditions during LCTEM and by evaluating polymer survival viapost-mortemmatrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS). Our multimodal approach, utilizing VT-LCTEM with MS validation and VT-SAXS, is generalizable across polymeric systems and can be used to directly image solvated nanoscale structures and thermally-induced transitions. Our strategy of correlating VT-SAXS with VT-LCTEM provided direct insight into transient nanoscale intermediates formed during the thermally-triggered morphological transformation of a PDEGMA-based triblock. Notably, we observed the temperature-triggered formation and slow relaxation of core-shell particles with complex microphase separation in the core by both VT-SAXS and VT-LCTEM.
more »
« less
- Award ID(s):
- 1905270
- PAR ID:
- 10305678
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 12
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Directing polymer self-assembly through noncovalent interactions is a powerful way to control the structure and function of nanoengineered materials. Dynamic hydrogen bonds are particularly useful for materials with structures that change over time or in response to specific stimuli. In the present work, we use the supramolecular association of urea moieties to manipulate the morphology, thermal response, and mechanical properties of soft polymeric hydrogels. Urea-terminated poly(isopropyl glycidyl ether)- b -poly(ethylene oxide)- b -poly(isopropyl glycidyl ether) ABA triblock copolymers were synthesized using controlled, anionic ring-opening polymerization and subsequent chain-end functionalization. Triblock copolymers with hydroxy end-groups were incapable of hydrogelation, while polymers terminated with meta -bis-urea motifs formed robust gels at room temperature. Rheometric analysis of the bulk gels, variable-temperature infrared spectroscopy (VT-IR), differential scanning calorimetry (DSC), and small-angle X-ray scattering (SAXS) confirmed the formation of structured hydrogels via association of the meta -bis-urea end-groups. Monourea end-groups did not result in the same regular structure as the meta -bis-urea. In future, the reported hydrogels could be useful for elastomeric, shape-morphing 3D-printed constructs, or as biomimetic scaffolds with precisely tailored porosity and mechanical properties.more » « less
-
Abstract Polymer‐protein hybrids can be deployed to improve protein solubility and stability in denaturing environments. While previous work used robotics and active machine learning to inform new designs, further biophysical information is required to ascertain structure–function behavior. Here, we show the value of tandem small‐angle x‐ray scattering (SAXS) and quartz crystal microbalance with dissipation (QCMD) experiments to reveal detailed polymer‐protein interactions with horseradish peroxidase (HRP) as a test case. Of particular interest was the process of polymer‐protein complex formation under thermal stress whereby SAXS monitors formation in solution while QCMD follows these dynamics at an interface. The radius of gyration (Rg) of the protein as measured by SAXS does not change significantly in the presence of polymer under denaturing conditions, but thickness and dissipation changes were observed in QCMD data. SAXS data with and without thermal stress were utilized to create bead models of the potential complexes and denatured enzyme, and each model fit provided insight into the degree of interactions. Additionally, QCMD data demonstrated that HRP deforms by spreading upon surface adsorption at low concentration as shown by longer adsorption times and smaller frequency shifts. In contrast, thermally stressed and highly inactive HRP had faster adsorption kinetics. The combination of SAXS and QCMD serves as a framework for biophysical characterization of interactions between proteins and polymers which could be useful in designing polymer‐protein hybrids.more » « less
-
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.more » « less
-
Metal nanoparticles are attracting interest for their light-absorption properties, but such materials are known to dynamically evolve under the action of chemical and physical perturbations, resulting in changes in their structure and composition. Using a transmission electron microscope equipped for optical excitation of the specimen, the structural evolution of Cu-based nanoparticles under simultaneous electron beam irradiation and plasmonic excitation was investigated with high spatiotemporal resolution. These nanoparticles initially have a Cu core–Cu2O oxide shell structure, but over the course of imaging, they undergo hollowing via the nanoscale Kirkendall effect. We captured the nucleation of a void within the core, which then rapidly grows along specific crystallographic directions until the core is hollowed out. Hollowing is triggered by electron-beam irradiation; plasmonic excitation enhances the kinetics of the transformation likely by the effect of photothermal heating.more » « less
