VCU Department of Physics Colloquia: Spring 2019

 

Linking Morphology Dependent Resonances to Plasmonic Resonance Geometries using Dielectric Aqueous Dimers

Bobby Cox 

Department of Physics 

Virginia Commonwealth University

Friday, April 26 at 4:00 pm in 701 W. Grace St., Room 2310

One of the hurdles to LSPR (localized Surface Plasmon Resonance) systems is predicting how certain nanoparticle morphologies will effect enhancement field geometry. Theoretical predictions can lack simple analytical solutions, requiring simulation software to find numerical solutions, and experimental trial and error can result in wasted resources in trying to find ideal morphologies for the problem at hand. Recent research from Trent University’s Khattak et. al. have found a connection between the morphology dependent resonance (MDR) of microwaves inside of dielectric aqueous dimers (such as the famous ‘grape plasma’ produced in microwave ovens), and the enhanced field geometry of LSPR ‘hot spots’. This talk will go over the results from Kahattak et. al., the pros and cons of using microwave MDRs as an experimental test for LSPR, and a discussion on where researchers could go next to further test this hypothesis.

 

 

Catalytic Mechanism and Dynamics of Cytochrome P45019A1

at the Membrane Interface

Prof. John Hackett

Department of Physiology and Biophysics and The Massey Cancer Center

Virginia Commonwealth University

Canceled Due to Inclement Weather!

Friday, April 19 at 4:00 pm in 701 W. Grace St., Room 2310

Cytochrome P450 19A1 (CYP19A1, aromatase) required for the synthesis of estrogens from androgens, is among the key targets for treatment of estrogen-dependent cancers. It is representative of other steroidogenic CYPs (i.e. 11A1 ,11B2, 17A1, 51) insofar as it also catalyzes a sequential oxidation and shares structural features at the putative substrate recognition interface. It is one of the few enzymes known to construct an aromatic ring with a controversial mechanism. How steroidogenic CYPs, including CYP19A1, recognize, and in some cases discriminate between very similar substrates remain salient unanswered questions in the field. Little effort has been made to elucidate substrate recognition and discrimination mechanisms of the highly-selective endobiotic-metabolizing CYPs. This colloquium will provide an update on the current state of knowledge of the CYP19A1 catalytic mechanism and summarize our recent efforts to integrate experimental and computational approaches to glean novel insight into the functional dynamics of CYP19A1 in a native-like membrane environment.  

 

 

Azido-substituted Nucleosides as Radiation Damage Enhancement Agents

Prof. Amitava Adhikary

Department of Chemistry,

Oakland University 

Friday, April 12 at 4:00 pm in 701 W. Grace St., Room 2310

   The aminyl radical, RNH•, is extremely important towards understanding the chemistry of biological molecules since amine groups are common to DNA bases, amino acids and other biomolecules. Irradiation followed by ESR studies in homogeneous glassy solutions of DNA-bases, nucleosides, and nucleotides as well as X-ray irradiation of single crystals of DNA-models at low temperatures have established that DNA-heteroatom centered radicals, such as, RNH are produced via deprotonation of the purine or pyrimidine base cation radicals (or holes). This conclusion is well-supported by pulse radiolysis as well as flash photolysis studies in aqueous solutions at ambient temperature. Studies in our laboratory have established that RNH• plays an important role in the prototropic equilibria of DNA-base π-cation radicals (such as, guanine cation radical, cytosine cation radical, adenine cation radical). Apart from RNH• formation via deprotonation of base cation radicals, pulse radiolysis and product analyses studies have established that hydroxyl radical (•OH) can also produce RNH• in purines, predominantly via •OH addition to the C4=C5 double bond of the purine ring along with subsequent water elimination and via H-atom abstraction from the exocyclic amine group. We have recently observed that in azido-substituted nucleosides, e.g., in 3′-azidothymidine (3′-AZT), radiation-mediated electrons lead to neutral aminyl radical (RNH) production at the C3′-site of sugar moiety at 77 K. Formation of nitrene anion radical (RN•¯) occurs via prompt N2 loss from the highly unstable azide anion radical (RN3•¯). Subsequently, rapid protonation of RN•¯ leads to RNHformation (scheme 1). In 3′-AZT, RNH• undergoes a bimolecular H-atom abstraction either from the methyl group at C5 in a thymine base to give dUCH2• or from the C5′-atom to give C5′• of a proximate 3′-AZT (scheme 1). Unlike 3′-AZT, 3′-azido-2′,3′-dideoxyguanosine (3′-AZ-2′,3′-ddG)-RNH• at 77 K resulted in thermally activated one-electron oxidation of a proximate guanine base to give G(N1-H)• (scheme 1). We have extended our work to azidopentofuranoses, and on various pyrimidine nucleosides with azido modification at the C5-site of the pyrimidine base, e.g., C5-azidomethyl-2’-deoxyuridine (5-AZmdU) and our results prove that radiation-produced electrons can be converted to highly damaging RNH• at 77 K. However, RNH• formation is not observed upon radiation-produced electron addition at 77 K from C4-azido pyrimidine nucleosides or C2-azido purine nucleosides. It is well-established that radiation-induced strand breaks, particularly double strand breaks play a very important role in causing radiation-induced cell death, mutation, aging, and cancer. To date, there is no evidence that radiation-produced aqueous (or solvated) and prehydrated electrons cause strand breaks. However, our work on azido-DNA-models show that radiation-produced electrons can be converted to highly damaging RNH• which cause strand breaks and unaltered base release. A direct correlation between cell death and micronuclei-induction was obtained in HeLa cells exposed at increasing doses of γ-irradiation in the presence of an aqueous solution (0.1mM) of 3′-AZT. Moreover, 3′-AZT causes significant radiosensitization in irradiated human colon cancer cells, in irradiated human larynx squamous carcinoma cells, and in irradiated human malignant glioma cells. In addition, our very recent studies employing a number of C5-azidomethyl and C5-azidovinyl pyrimidine nucleosides show that 5-AZmdU caused significant radiosensitization against EMT-6 breast cancer cells. Therefore, these results offer an opportunity to investigate the potential use of azido-DNA-models as site-specific radiation sensitizers. Supported by the NIH NCI via grant R01 CA045424.

 

 

Toward the next quantum revolution:

controlling physical systems and taming decoherence

Prof. Edwin Barnes

Department of Physics,

Virginia Tech  

Friday, April 5 at 4:00 pm in 701 W. Grace St., Room 2310

   Recent years have witnessed enormous progress toward harnessing the power of quantum mechanics and integrating it into novel technologies capable of performing tasks far beyond present-day capabilities. Future technologies such as quantum computing, sensing and communication demand the ability to control microscopic quantum systems with unprecedented accuracy. This task is particularly daunting due to unwanted and unavoidable interactions with noisy environments that destroy quantum information in a process known as decoherence. I will present recent progress in understanding and modeling the effects of noise on the dynamics of a quantum bit and show how this can be used to develop new ways to slow down decoherence. I will then describe a new general theory for dynamically combating decoherence by driving quantum bits in such a way that noise effects destructively interfere and cancel out, enabling the high level of control needed to realize quantum information technologies. 

 

Electron Microscopy, cryoEM and two real-life examples

Dr. Montserrat Samso

Department of Physiology and Biophysics,

Virginia Commonwealth University 

Friday, March 29 at 4:00 pm in 701 W. Grace St., Room 2310

Most tasks within the cell are carried out by specialized proteins carrying out a variety of functions. In biological electron microscopy (EM), the high-energy electrons of the microscope interact with the atoms of the proteins rendering highly magnified images. “Single-particle” image processing programs can then be used to obtain the 3D reconstruction of the protein being studied.  Such 3D structures have helped enormously to figure out how these small molecular machines work. Furthermore, cryogens (cryoEM) can be used to see the proteins in their native hydrated state and since ~2015, the implementation of direct electron detectors gives an unprecedented high level of detail and thus the near-atomic structure of a much larger number of proteins is being determined. These concepts will be illustrated with two  examples based on the ryanodine receptor, a large calcium channel that plays a major role in excitable cells. RyRs self-assemble in clusters, and here we determined several forms of planar arrangement. In addition, we determined how RyRs can sense different cations in the environment and how they respond to these signals.

 

The journey to a new science frontier at Jefferson Lab, from 12 GeV to the Electron-Ion Collider

Rolf Ent

Jefferson Lab 

Friday, March 22 at 4:00 pm in 701 W. Grace St., Room 2310

The understanding of the structure of matter at the level of atoms and molecules is a cornerstone of the technical achievements of the modern civilization; everything from modern medicine to communication infrastructure depend on this knowledge. The current understanding of the internal structure of nucleons – protons and neutrons - and nuclei, however, are at a comparatively primitive level.  While we know the interior landscape of nucleons includes a strong-force driven sea of quarks, antiquarks and gluons, with a net surplus of a few ever-present valence quarks, we have very little idea how the macro-properties and structure of nucleons and nuclear matter emerge from their strong dynamics.  This lack of understanding has been due both to the difficulty of the theory of Quantum Chromodynamics (QCD) that govern quarks and gluons, and experimental limitations.  Advances in the theoretical understanding of QCD in the past decades, however, have led to a framework that enables to precisely image the gluons and quarks, and to understand the role they and their interactions play in nucleons and nuclei. The Jefferson Lab 12-GeV accelerator uses electrons to initiate this “nuclear femtography” program to image the quark and gluon structure of nucleons and nuclei. Ultimately, a new accelerator facility is required to understand the role of the gluons that bind us all, the Electron-Ion Collider. This would be the world's first polarized electron-proton collider, and the world's first e-A collider.

Rational Design of Materials for a Clean Energy Future

Prof. Puru Jena

Department of Physics, Virginia Commonwealth University

Friday, February 22 at 4:00 pm in 701 W. Grace St., Room 2310

Clean, abundant, and sustainable energy is undoubtedly one of the greatest challenges in the 21st century. Fossil fuels that account for more than 80% of the world’s current energy needs are not only limited, but also are harmful to the environment. While renewable energy sources such as solar and hydrogen together can meet this need, considerable material challenges remain before they can reduce our dependence on fossil fuels. In addition, efficient batteries have to be developed to store this energy. This talk will deal with some of the material challenges in energy harvesting and storage, with particular emphasis on Li- and Na-ion batteries, and perovskite-based solar cells. A common feature of all these materials is that they are complex salts where their negative ion components can be identified as super-halogen clusters mimicking the chemistry of halogens, but with electron affinities that far exceed that of any halogen atom. This realization has made it possible to use the vast advances in cluster science to design novel materials for energy applications. I will discuss how a rational design of clusters can lead to the synthesis of halogen-free electrolytes in metal-ion batteries, anti-perovskites for superionic conductors, and organic hybrid perovskites for solar cells. Experimental evidence will be provided to establish the predictive capability of our theory.

Topological Quantum Materials for Battery Anode Applications

Prof. Qiang Sun

Peking University, Beijing, China 

Friday, February 15 at 4:00 pm in 701 W. Grace St., Room 2310

Battery science and technology are of current interest. While the specific capacity of the commercially used graphite anode for lithium battery is limited to 372 mAh/g. Extensive efforts have been devoted to improve the performance but not much progress was made during the past 25 years. Inspired by the 2016 Nobel Prize in Physics for topological state and phases of materials, we have explored the possibility of using topological semimetal materials (TSMs) for metal-ion battery anode having the merits of intrinsic high electronic conductivity and ordered porosity for metal ions transport. In this talk, we will focus on all carbon based porous topological semimetal for Li-ion battery anode, all silicon based porous topological semimetal for Na-ion battery anode, and high-pressure-assisted design of porous topological semimetal carbon, which range from synthesis simulation to property predictions, bridging quantum materials physics and battery technology. We will show that topological quantum materials are promising for ion battery anode applications with the merits of high capacity, fast kinetics and good stability going beyond the conventional anode materials.

 

“Building from Nature” - Bioinspired materials for the fabrication of functional devices

Dr. Vamsi Yadavalli

Department of Chemical and Life Science Engineering, Virginia Commonwealth University

Friday, February 8 at 4:00 pm in 701 W. Grace St., Room 2310

Biomimetic composites of naturally derived and synthetic polymers provide exciting opportunities to develop soft, flexible, biocompatible, and physiologically compliant devices for diverse applications in healthcare. Bioinspired materials can serve not only as the structural, but also as the functional components of such devices. This poses material-specific functionalization and fabrication related challenges in the design and fabrication of these systems. Natural silk protein biopolymers show tremendous promise in this regard due to intrinsic properties of mechanical performance, optical transparency, biocompatibility, biodegradability, processability, and the ability to stabilize biomolecules. The exceptional ensemble of properties provides opportunities to employ silk proteins for numerous applications.

This talk will discuss some of the recent work from our group in transitioning from the silk cocoon to protein based biocomposites that can be used as biosensors, electrodes, biophotonic elements, drug delivery vehicles, and energy storage devices. By integrating microfabrication tools with natural materials, we show how high resolution, high fidelity structures can be patterned in both rigid and flexible formats in two and three dimensions. Composites with materials such as conducting polymers provide added functionality as opto-electronic architectures. The ease of fabrication, biochemical functionalization, biocompatibility, as well as tunable mechanical properties and biodegradation of these biomaterials provide unique possibilities as sustainable, bioresorbable protein microdevices. 

 

Adventures in Carbon Cluster Chemistry Using Helium Droplet Methods

Dr. William K. Lewis

Senior Research Chemist, Fuel and Energy Branch, Air Force Research Laboratory

Friday, February 1 at 4:00 pm in 701 W. Grace St., Room 2310

  

Carbon is a fascinating element with a rich chemistry to explore.  In the bulk, it adopts the familiar graphite and diamond allotropes; on the nanoscale, it produces fullerenes, graphenes, and nanotubes; and with only a few atoms, it forms clusters with linear, cyclic, and cage structures.  The many forms of carbon find application in a wide variety of fields, from materials science to combustion to astrochemistry.  We are using helium droplet methods to assemble small neutral carbon clusters from-the-ground-up, and to examine their structure, energetics, and interaction with other molecules of interest.  In this talk we will discuss assembly processes to produce carbon clusters in a systematic way, measurements of binding energies and structures, and results from rovibrational spectroscopy of the C3-H2O complex.

 

 

Metallic Clusters Supported on Graphene as Efficient Materials for Hydrogen Storage

J. Ulises Reveles

Department of Physics, Virginia Commonwealth University

Friday, January 25 at 4:00 pm in 701 W. Grace St., Room 2310

  

Recent studies suggest that graphene decorated with transition and light metal atoms is a feasible alternative for the design of the next generation of hydrogen storage systems, that is, materials which require a gravimetric content of at least 7.5 wt%, and an adsorption energy of 0.2–0.6 eV per H2.

We present a first principles study of hydrogen adsorption in palladium (Pdx), titanium (Tix), nickel (Nix), and bimetallic TixAly clusters supported on graphene. Our results show that selected clusters present an enhanced hydrogen gravimetric content up to 3.2–3.6 wt%, and support the hypothesis controlled introduction of small metal clusters to graphene is a feasible way to enhance its hydrogen gravimetric content. Furthermore, our study ­­opens up the possibility of investigating other binary TMx–Ay (TM = transition metal and A = main group) clusters supported on graphene as promising candidates for hydrogen storage.

 

 

 

Strong-Field Chemistry of Ions and Radicals: Ultrafast Dynamics and Nanomaterial Synthesis

Katharine Tibbetts

Department of Chemistry, Virginia Commonwealth University

Friday, January 18 at 4:00 pm in 701 W. Grace St., Room 2310

   Ionizing radiation can be destructive when it causes damage to DNA, but also can be constructive when used to synthesize novel nanomaterials without toxic chemicals. High-intensity, ultrashort (picosecond-femtosecond) laser pulses can mimic many properties of ionizing radiation such as X-rays, using visible or infrared wavelengths instead. This talk will highlight recent recent results in our laboratory using strong-field femtosecond laser pulses to induce ion chemistry. First, we will present ultrafast dynamics measurements of organophosphorus and nitrotoluene radical cations using pump-probe techniques. The organophosphorus molecules dimethyl methylphosphonate (DMMP) and trimethyl phosphate (TMP) model the DNA sugar-phosphate backbone, so their radical cation dynamics can provide insight into reaction pathways occurring in DNA upon removal of an electron from the phosphate group. The nitrotoluenes model explosives such as TNT, making their dissociation dynamics relevant to energetic material development. The ionization-induced coherent vibrational dynamics in both families of molecules will be discussed. The second part of the talk will discuss applications to nanomaterials synthesis of high-density plasmas consisting of free electrons and OH• radicals formed by focusing femtosecond laser pulses in aqueous solution. The plasma electrons can reduce metal ions in solution to form metal nanoparticles, and the hydroxyl radicals can result in accelerated particle growth or back-oxidation, depending on the target metal. We will discuss the mechanisms leading to the conversion of tetrachloroaurate ([AuCl4]-), silver nitrate (AgNO3), and copper acetate (Cu(OAc)2) to Au, Ag and Cu nanoparticles both in aqueous solution and in the presence of a silicon wafer. When silicon is present, the metal nanoparticles can be isolated in a silica matrix, which prevents their aggregation and yields ultrasmall ~2 nm particles.

 

 

VCU Department of Physics Colloquia: Fall 2018

 

Applications of Lithium-Ion Batteries in Electric Drive Vehicles

Tien Quang Duong 

Vehicle Technologies Office, U.S. Department of Energy

Friday, November 30 at 4:00 pm in 701 W. Grace St., Room 2310

Supathorn (Supy) Phongikaroon, PH.D., P.E.

Department of Mechanical and Nuclear Engineering, VCU

Friday, November 16 at 4:00 pm in 701 W. Grace St., Room 2310

 

 

 

A rapid overview of high-speed atomic force microscopy: it's impact and applications.

Dr. Loren Picco

Department of Physics, VCU

Friday, November 9 at 4:00 pm in 701 W. Grace St., Room 2310

I will provide an introduction to my research into scanning probe microscope development and instrumentation. I will go over some of the high-impact areas of research that it has been used for and then round off with some highlights of my most recent work and plans now that I am establishing my lab at VCU.

 

 

A look into the fabrication,characterization and applications of 2D hemetene.

Tyler Selden

PhD candidate in Nanoscience

VCU Department of Physics

Friday, November 2 at 4:00 pm in 701 W. Grace St., Room 2310

 

 

Personalizing cancer therapy with nanoscience tools

Graeme F. Murray

MD/PhD candidate in Nanoscience

VCU School of Medicine and Department of Physics

Friday, October 26 at 4:00 pm in 701 W. Grace St., Room 2310

Dr. Magdalena K. Morgan

VCU Innovation Gateway 

Friday, October 5 at 4:00 pm in 701 W. Grace St., Room 2310

Dr. Morgan will explain how the Innovation Gateway is helping students, faculty and researchers commercialize their inventions and creative work. She works with a team of technical professionals, business developers and administrators to guide and support VCU faculty, staff and trainees in the process of technology transfer to industry. Her talk will discuss how the Innovation Gateway conducts intellectual property evaluation and protection, technology marketing, start-up creation, and new programs to promote a culture of innovation here at VCU.

Modified Dark Matter: Relating Dark Energy, Dark Matter, and Baryonic Matter

Dr. Doug Edmonds

Department of Physics, Penn State-Hazelton 

Friday, September 28 at 4:00 pm in 701 W. Grace St., Room 2310

Modified dark matter (MDM) is a phenomenological model of dark matter, inspired by gravitational thermodynamics. For an accelerating Universe with positive cosmological constant ($\Lambda$), such phenomenological considerations lead to the emergence of a critical acceleration parameter related to $\Lambda$. Such a critical acceleration is an effective phenomenological manifestation of MDM, and is found in tight correlations between dark matter and baryonic matter in galaxy rotation curves, the so-called Mass Discrepancy Acceleration Relation (MDAR). The resulting MDM mass profiles are consistent with observational data at both the galactic and cluster scales.

Synthetic Strategies of some Nanostructured Materials

Dr. Tarek M. Abdel-Fattah

Department of Chemistry and Applied Research Center at Thomas Jefferson National Accelerator Facility and Department of Molecular Biology and Chemistry at Christopher Newport University

Friday, September 21 at 4:00 pm in 701 W. Grace St., Room 2310

Nanotechnology deals with materials with dimensions in the range of 1 nm to 100 nm. Materials in that range (1-100 nm) possess novel properties and characteristics different from bulk materials.  Therefore, nanotechnology has been of increasing interest in the last decade and used as catalysts, sensors, solar cells and in water decontamination systems. We will present the detailed insights into two synthetic strategies, bottom-up and top-down, for nanomaterials fabrication. In addition, we will report the synthesis and assembly of highly ordered multiple tube-in-tube nanostructures within porous materials.