LaCNS Seminars Spring 2019
- Friday, January 18, 2019, 12:30 pm, 206 Williams Hall (joint LaCNS – Macromolecular
Dr. Leah Broussard (Wigner Fellow, Oak Ridge National Laboratory), host Gerald Schneider
"The Nab Experiment: A Laboratory for Neutron Beta Decay"
Abstract: The neutron has been recognized as an excellent target to search for new clues that can lead to an explanation for the lack of antimatter in the universe, insight on the nature of dark matter, and a more complete understanding of the laws and symmetries of nature. When removed from the nucleus, the free neutron is unstable, decaying with a lifetime of about 15 minutes. The kinematic properties of its decay provide a wealth of information about the weak force. The Nab experiment will provide one of the most precise tests of our understanding of the weak interaction by measuring correlations in unpolarized neutron beta decay. The experiment features a 7 m tall magnetic spectrometer that captures the electron and proton resulting from the decay, and silicon-detector based detection systems that allow reconstruction of the momenta of the decay particles. This presentation will introduce you to the unique features of the neutron and why it is important to particle physics, and describe how Nab, now commissioning at the Spallation Neutron Source at Oak Ridge National Laboratory, will study the properties of its decay with the best precision yet.
- Friday, February 8, 2019, 12:30 pm, 206 Williams Hall (joint LaCNS – Macromolecular seminar)
Dr. Flora Meilleur (North Carolina State University/Oak Ridge National Laboratory), host Gerald Schneider
"Cellulose degrading oxidative enzymes: structural insights from neutron diffraction and scattering"
Abstract: Sensitivity to hydrogen/deuterium and lack of observable radiation damage make cold neutrons an ideal probe for structural studies of redox enzymes. Neutron protein crystallography (NPC) is a powerful tool for investigating protein chemistry because it directly locates hydrogen atom positions [1,2]. Small-angle scattering (SAS) provides low resolution information on protein dimensions. Combined with contrast variation techniques and modeling, small angle neutron scattering (SANS) further allows the structural investigation of individual components within protein-protein complexes. I will first introduce the neutron facilities at ORNL before presenting recent results from my lab.
My lab focuses on metallo-enzymes with a specific interest in cellulose degrading oxidative enzymes. Fungal lytic polysaccharide monooxygenases (LPMOs) are copper containing metallo-enzymes involved in biomass oxidation. LPMO-catalyzed monooxygenation requires input of two electrons from LPMO redox partners, the cellobiose dehydrogenase enzymes (CDHs), and of one oxygen molecule to achieve hydroxylation of one carbon in the glycosidic bond . I will discuss our recent X-ray and neutron crystallographic studies that provide new insight into the LPMO monooxygenation mechanism [4,5]. Redox complexes such as the LPMO-CDH complex, are often transient, and their structural characterization can be challenging. We are using SANS to characterize the interaction between CDH and LPMO .
 O’Dell W.B., Bodenheimer A.M., Meilleur F. (2016) Neutron protein crystallography: A complementary tool for locating hydrogens in proteins. Arch. Biochem. Biophys. 602:48-60
 Schroder G.C., O’Dell W.B., Myles D.A., Kovalevsky A., Meilleur F. (2018) IMAGINE: neutrons reveal enzyme chemistry. Acta Cryst. D74:778-786
 Bodenheimer A.M., O’Dell W.B., Stanley C.B, Meilleur F. (2017) Structural studies of Neurospora crassa LPMO9D and redox partner CDHIIA using neutron crystallography and small-angle scattering. Carbohydr Res. 448:200-204
 O’Dell W.B., Swartz P.D., Weiss K.L., Meilleur F. (2017) Crystallization of a fungal lytic polysaccharide monooxygenase expressed from glycoengineered Pichia pastoris for X-ray and neutron diffraction Acta Cryst. F73:70-78
 O’Dell W. D., Aggarwal P., Meilleur F. (2017) Oxygen Activation at the Active Site of a Fungal Lytic Polysaccharide Monooxygenase. Angew. Chem. Int. Ed. 56:767-770
 Bodenheimer A.M., O’Dell W.B., Stanley C.B, Meilleur F. (2017) Structural studies of Neurospora crassa LPMO9D and redox partner CDHIIA using neutron crystallography and small-angle scattering. Carbohydr. Res. 448:200-204
- Monday, February 11, 2019, 3:00 pm, 1008B Digital Media Center
Dr. Jonathan Nickels (Assistant Professor, Chemical and Environmental Engineering, University of Cincinnati), host Gerald Schneider
"Using neutron scattering to study nanoscale structure and motion in biomolecules"
Abstract: Neutron scattering is a powerful technique for the characterization of biomolecules, providing unique information about the structure and dynamics of biological systems on multiple time and length scales. The sensitivity of the neutron to hydrogen and its isotope deuterium is a uniquely useful tool because of the abundance of hydrogen in biological materials, and draws a clear contrast to x-ray scattering methods in which there is only a weak sensitivity to hydrogen. Because of this, neutrons have proven useful in our research into the nature of water interactions with proteins and other biopolymers and into the properties of self-assembled lipid bilayers. In this discussion, I will focus on this latter project, specifically on how neutron scattering methods have helped to understand the physical basis of lateral lipid organization in cell membrane, covering my experiments with both model lipid bilayers and living cell membranes. The existence and role of lateral lipid organization in biological membranes has been studied and contested for more than 30 years. Lateral lipid domains, or rafts, are hypothesized as scalable compartments in biological membranes, providing appropriate physical environments to their resident membrane proteins. This implies that lateral lipid organization is associated with a range of biological functions, such as protein co-localization, membrane trafficking, and cell signaling, to name just a few. Moreover, we have recently suggested that lipid rafts may also act to buffer membrane physical properties from changes in temperature and environmental perturbations.
Our experiments have provided direct observations of cell membrane transverse and lateral structure in the Bacillus subtilis cell membrane. Neutron contrast from isotopic labeling was the key enabling tool to detect ~40nm lipid rafts via laterally heterogeneous distribution of labeled fatty acids. Using membrane mimics, we have also utilized other neutron to isolate the structure and dynamics of lipid domains in greater detail to interrogate potential mechanisms of raft formation. Finally, I will touch upon ongoing work which utilizes neutron scattering methods to demonstrate the proposed buffering effect of bilayer physical properties, suggesting a physically based function for these biological structures.
- Monday, March 11, 2019, 3:00 pm, 1008B Digital Media Center
Dr. Eric Stinaff (Associate Professor, Physics and Astronomy, Ohio University), host Rongying Jin
"Opto-electronic studies of semiconductor nanostructures and 2D materials"
Abstract: Our group investigates the optical and electronic properties of novel semiconductor nanomaterials, nanostructures and nanostructure-based devices. I will first present our work on quantum dots (QDs), nanoscale crystals whose dimensions are on the order of the size of the charge carriers (e.g. electrons). These have proven to be remarkably flexible tools for probing fundamental quantum mechanical properties and have received considerable attention as a candidate for physical implementations for quantum information processing. As individual QDs are brought together the discrete energy levels begin to display molecular behavior, forming bonding and antibonding orbitals. This new class of coupled nanostructures has already shown unique properties such as tunable g-factors and the formation of anti-bonding ground states. I will describe results from our research into these artificial molecules including optical studies of single spins, tunable luminescence lifetime effects, and the ability to control processes such as the electron-hole exchange interaction.
The second area of our research revolves around two-dimensional (2D) materials. We have developed a novel growth process based on the complementary growth of 2D semiconductors on, and around, bulk metal/metal-oxide patterns. This scalable process results in as-grown, naturally contacted, 2D materials-based devices. The technique has the added potential of producing self-contacted heterostructured devices as well as controllable doping of the 2D material using alloyed metallic contacts. The materials display strong luminescence, monolayer Raman signatures, and relatively large crystal domains. Measurements of first-generation metal-semiconductor-metal photodiodes, without any optimization and at standard temperature and pressure, typically show responsivities on the order of 1 to 10 A/W and a time response on the order of 2 µs, an order of magnitude faster than the best reported result. Since the material grows controllably around the lithographically defined patterns, complex device structures and wafer scale circuits can be envisioned.
- **CANCELLED** (to be rescheduled)
Dr. Joshua Sangoro (Assistant Professor, Chemical and Biomolecular Engineering, University of Tennessee, Knoxville), host Gerald Schneider
Mesoscale Organization and Dynamics in Ionic Liquids"
Abstract: The impact of mesoscale organization on transport and dynamics in ionic liquids is investigated by broadband dielectric spectroscopy and dynamic mechanical spectroscopy as well as x-ray and neutron scattering techniques, complemented by computational approaches. Signatures of slow, sub-α dynamics are identified in the dynamic-mechanical and dielectric spectra and employed to probe lifetimes and dynamics of mesoscale aggregates in ionic liquids. It is found that the dynamics of mesoscale aggregates dominate many physicochemical properties such as the static dielectric permittivity and viscosity. By using mixtures of ionic liquids to tune composition-dependent evolution of the morphology, it becomes possible to realize ionic liquids with enhanced physicochemical properties that are otherwise inaccessible in neat systems. This talk will discuss the role of mesoscale organization and dynamics on macroscopic physical properties of ionic liquids.
- Monday, March 25, 2019, 3:00 pm, 1008B Digital Media Center
Dr. Lilo Pozzo (The Weyerhaeuser Endowed Associate Professor of Chemical Engineering, University of Washington), host Bhuvnesh Bharti
"Structure and Dynamics of Conjugated Polymers from Neutron Scattering and MD Simulations"
Abstract: Conjugated polymer films, nanofibers, and networks can be ideal materials for the design of efficient photovoltaic devices, batteries, thermoelectric cells, light emitting diodes and many emerging energy technologies. It is also recognized that the structure and dynamics of organic semiconductor materials correlates strongly with large changes in optical, electronic and mechanical properties so that their control and manipulation is essential to advancing the field. This presentation outlines the use of neutron scattering techniques in the development of structure-property relationships for conjugated polymer nanomaterials. It also highlights recent results on the use of neutron and x-ray scattering techniques for improvements in molecular simulation force fields specifically produced for conjugated polymers. Quasi-elastic neutron scattering (QENS) experiments are used along with computationally efficient MD simulations to understand the nature of important nanoscale motions. X-ray and polarized neutron diffraction are also used to correlate experimental and model-generated polymer structures. QENS validation of MD force fields presents a unique opportunity to increase the accuracy of highly uncertain parameters used in simulation of conjugated polymers and other complex macromolecules. These parameters are currently estimated from quantum mechanical calculations such as density functional theory but, unlike many force fields for small molecules, they are not parameterized to available experimental data. Moreover, high variability is observed in parameters for the small number of force fields that have been proposed in the literature.
- **RESCHEDULED** Tuesday, April 9, 2019, 3:00 pm, 1008B Digital Media Center
Dr. Ted Cremer (Chief Scientist, Adelphi Technology), host Leslie Butler
“Fast and Moderated DD and DT Neutron Sources, Applications, and Neutron Optical Instruments”Abstract: Presented are fast (2.5 MeV DD and 14 MeV DT) fusion-based, Adelphi neutron generators and their applications, including Prompt Gamma Neutron Activation Analysis (PGNAA), radiographic-tomographic imaging, and 14 MeV DT-based Associated Particle Imaging (API), as well as a person-carried, field-deployable DT neutron generator, developed under a Defense Advanced Research Projects Agency (DARPA) grant.
Also presented are Adelphi moderated fast neutron sources, such as (1) epithermal neutrons for applications such as boron neutron capture therapy (BNCT) cancer treatment, and (2) thermal neutron sources for thermal neutron activation analysis (TNA), radiography-tomography, powder diffractometry, and residual stress analysis.
Briefly surveyed are slow neutron optics, including cold neutron spin echo devices, developed by the Pynn Group at Indiana University (commercialized by Adelphi), as well as Adelphi material (CRLs) and magnetic compound refractive lenses (MCRLs) for slow neutron microscopy, and compound refractive magnetic prisms (MCRPs) to offset gravity droop in small angle neutron scatter (SANS).
Presented are results of focusing and microscope-imaging experiments with MCRLs on pf2 VCN (very cold neutron) and D33 SANS (cold neutron) beam lines at Institüt Laue-Langevin (ILL) in Grenoble, France.
- Monday, April 29, 2019, 3:00 pm, 1008B Digital Media Center
Dr. Xi Dai (Professor, The Hong Kong University of Science and Technology), host Jiandi Zhang
Chiral magnetic effect and collective modes in topological semimetals
Abstract: Quasi-particles and collective modes are two fundamental aspects that characterize a quantum matter in addition to its ground state features. For example, the low energy physics for Fermi liquid phase in He-III was featured not only by Fermionic quasi-particles near the chemical potential, but also by fruitful collective modes in the long wave length limit, including several different sound waves that can propagate through it under different circumstances. On the other hand, it is very difficult for sound waves to be carried by the electron liquid in ordinary metals, due to the fact that long range Coulomb interaction among electrons will generate plasmon gap for ordinary electron density waves and thus prohibits the propagation of sound waves through the electron liquid. In the present paper, we propose a unique type of acoustic collective modes formed by Weyl fermions under the magnetic field, which is called chiral zero sound (CZS). The CZS only exists and propagates along an external magnetic field for Weyl semi-metal systems containing multiple-pairs of Weyl points. The sound velocity of CZS is proportional to the field strength in the weak field limit, whereas it oscillates dramatically in the strong field limit generating completely new mechanism for quantum oscillations through the dynamics of neutral Bosonic excitation, which may manifest itself in the thermal conductivity measurements under magnetic field.
- Monday, May 6, 2019, 3:00 pm, 1008B Digital Media Center
Dr. Geoffrey Bothun (Professor, Chemical Engineering, University of Rhode Island), host Bhuvnesh Bharti
Lessons from nature: Engineered nanoparticles as proteins in lipid bilayers"
Abstract: How engineered nanoparticles interact with biological membranes plays an important role in nanotoxicology and nanomedicine. These interactions can either stabilize or destabilize a membrane, which are comprised of a self-assembled lipid bilayer scaffold, depending on the size, shape, and surface chemistry of the nanoparticle. Proteins exhibit analogous behavior and are known to modulate membrane structure and function – this is involved in many cellular processes including endocytosis. Taking a lesson from nature, insight can be gained from our understanding of protein-membrane interactions to design nanoparticles with properties that allow us to control the membrane. For example, theories describing lateral capillarity and changes in lipid phase behavior caused by hydrophobic proteins may be extended to small hydrophobic nanoparticles embedded within lipid bilayers to control transmembrane permeability. Furthermore, if the nanoparticles are responsive to external electromagnetic fields, the structure and function of a membrane may be selected on demand. This seminar will describe collaborative work that has been ongoing in our group for over a decade to create a variety of “nature-inspired” hybrid liposome structures, as well as recent work using neutron scattering techniques to directly examine how nanoparticles alter the physical and mechanical properties of membranes.
Dr. Zhili Xiao (Argonne National Laboratory/Northern Illinois University), host Rongying Jin