Friday May 5th – Presentations

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Quantum Size Effects in Optically Pumped NMR in Strained GaAs/AlGaAs Quantum Wells

John T. Tokarski III, 1 Stephen A. McGill,2 Gary Sanders,3 Chris Stanton,3 John L. Reno,4 and Clifford R. Bowers1

1University of Florida, Department of Chemistry, Gainesville, FL, 32611, USA
2National High Magnetic Field Laboratory, Tallahassee, FL, 32360, USA
3University of Florida, Department of Physics, Gainesville, FL, 32611, USA
4Sandia National Laboratories, Albuquerque, NM, 87123, USA

10:15 AM
to 10:35 AM
Physical Chemistry

Recently we reported the effects of elastic interactions and resulting bowing moments on strain in bulk GaAs/Si composites1 using optically pumped nuclear magnetic resonance (OPNMR).2 We have also reported the effects of strain in GaAs/AlGaAs quantum wells, where the heavy-hole/light-hole energy splitting was affected by both strain and quantum confinement.3 In that 30 nm wide GaAs well, our calculations show that only modest quantum confinement effects were present, and strain effects dominated the modifications of the electronic band structure, optical absorption, and OPNMR action spectrum. Here we present our progress-to-date on an OPNMR study of a series of GaAs/AlGaAs quantum wells where the well-width is varied. In collaboration with Sandia National Laboratories, a series of quantum well arrays (QWA) with widths of 28, 14, 7, and 4 nm were grown via molecular beam epitaxy.  By comparing the photon energy dependences of the OPNMR, magneto-optical absorption and photoluminescence spectra to electronic band structure calculations, we expect a more complete understanding of the OPNMR photo-physics to emerge. The QWA films were epoxy-bonded to a transparent, single crystal sapphire wafer, and the sacrificial GaAs substrate was etched down to the stop-etch layer using selective wet chemical etching. Magneto-photoluminescence experiments ensured the complete removal of the bulk GaAs growth substrate. The exploitation of strain, quantum confinement, and magnetic field to enhance and control the optically pumped nuclear spin hyperpolarization could have applications to nuclear spin electronics and quantum computing.

 

 

[1] Wood, R.M.; Tokarski III, J.T.; McCarthy, L.A.; Stanton, C.J; Bowers, C.R., Characterization of elastic interactions in GaAs/Si composites by optically pumped nuclear magnetic resonance, Journal of Applied Physics, 2016, 120, 085104.

[2] Kuhns, P. L.; Kleinhammes, A.; Schmiedel, T.; Moulton, W. G.; Chabrier, P.; Sloan, S.; Hughes, E.; Bowers, C. R., Magnetic-field dependence of the optical Overhauser effect in GaAs, Physical Review B, 1997, 55, 7824-7830.

[3] Wood, R. M.; Saha, D.; McCarthy, L. A.; Tokarski, J. T.; Sanders, G. D.; Kuhns, P. L.; McGill, S. A.; Reyes, A. P.; Reno, J. L.; Stanton, C. J.; Bowers, C. R., Effects of strain and quantum confinement in optically pumped nuclear magnetic resonance in GaAs: Interpretation guided by spin-dependent band structure calculations. Physical Review B, 2014, 90 155317.

Molecular insight into allosteric modulation of Potassium Channel Interacting Protein 3

Jaroslava Miksovska

Florida International University

10:35 AM
to 10:55 AM
Biophysical

Downstream regulatory antagonist modulator also known as K+ channel interacting protein 3 (DREAM/KChIP3) is a calcium sensing protein that co-assembles with Kv4 potassium channels in the brain and heart as well as with DNA in the nucleus where it regulates gene expression. The interaction of DREAM/KChIP3 with A-type Kv4 channels and DNA has been shown to regulate neuronal signaling, pain sensing and memory retention. Previous results have shown a Ca2+ dependent interaction between DREAM/KChIP3 and Kv4/DNA which involves interactions at the N-terminus. However, the mechanism by which Ca2+ binding at the C-terminus of DREAM/KChIP3 induces structural changes at the N-terminus remains unknown. We have identified a highly conserved network of aromatic residues that modulate protein dynamics and the pathways of signal transduction on DREAM/KChIP3. Using molecular dynamics simulations, site directed mutagenesis and fluorescence spectroscopy we provide strong evidence in support of a highly dynamic mechanism of signal transduction and regulation. We have identified that Trp169, Phe171, and Tyr174 at the entering helix of EF-hand 3 function as key amino acids involved in propagation of Ca2+ induced structural changes. The observed structural motions provide insight into the mechanism mediating the calcium dependent Kv4 and DNA binding. Together, the work presented here provides the first mechanism of intramolecular signal transduction in a Ca2+ binding protein of the NCS family.

KINETIC PRODUCTS IN FLUX-DERIVED F-ELEMENT BORATES, INCLUDING THE THIRD AND FOURTH AMERICIUM BORATES

Alexander T. Chemey and Thomas E. Albrecht-Schmitt

Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, USA

10:35 AM
to 10:55 AM
Inorganic Chemistry

Boric acid flux reactions with lanthanide and actinide trichlorides have yielded new structures and insights into the kinetic products of the f-borates. These reactions proceeded at significantly lower temperatures than previous experiments and for a much shorter duration. We have determined that the first neodymium kinetic product is a previously-reported acentric tetraborate chloride. The second kinetic product is a neodymium hexaborate chloride which is analogous to a series of lanthanide hexaborate bromides. An isomorphous americium hexaborate chloride has been obtained as the first kinetic product in the americium chloride-boric acid system. The second americium borate phase is isomorphous with a known samarium borate, and is notable for excluding all chlorides which were present in the starting material. These americium borates were obtained under identical reaction conditions, suggesting a small thermodynamic difference. This presentation will discuss the new structures and the order in which the neodymium, plutonium, and americium borates form.

ON THE ROLE OF CORE-SHELL SYNERGY IN NANOTECHNOLOGY

Gang Chen

Department of Chemistry, University of Central Florida, Orlando FL 32816, USA

10:35 AM
to 10:55 AM
Materials Chemisry

The core-shell type nanostructure, which can be broadly defined as an inner nanoparticle (core) encapsulated inside an outer layer material (shell), is one of the simplest but most important motifs in multi-component systems. Here, I will describe the utilization of core-shell synergy for exploring new and complex nanomaterials. Our studies have unveiled the diverse interactions between core and shell: (1) shell can protect the integrity of the core, and retain its surface ligands, which is essential in the following separations, mechanistic studies and other practical applications; (2) shell coverage of the core is controllable through tuning the core-shell interfacial free energy, which breaks the uniformity of surface properties and makes the site-specific coding on core surface feasible; (3) the shell growth is templated on the core nanoparticle, and this in turn reshapes the core nanoparticle via core-shell synergistic effects.  Our current studies have improved our understanding of how these core-shell interactions operate. Eventually, with these knowledge, greater control of nanomaterials can be achieved, in terms of synthesis, processing and application.

ANTI-MRSA NATURAL PRODUCTS FROM AN EPIGENETIC MODIFIED FLORIDIAN MANGROVE-ASSOCIATED FUNGUS

Sylvia Soldatou1, 2, Renee Fleeman3, Lindsey N. Shaw3, Bill J. Baker1, 2

1 School of Chemistry, National University of Ireland, Galway, Ireland
2 Department of Chemistry, Center for Drug Discovery and Innovation (CDDI), University of South Florida, Tampa, USA
3 Department of Cell Biology, Microbiology and Molecular Biology, University of South Florida, Tampa, USA

10:35 AM
to 10:55 AM
Natural Products

The ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) are responsible for the majority of nosocomial infections and are resistant to most antibacterial agents. We focus on mangrove-associated microorganisms which have been found to be a great source of chemically diverse and biologically active metabolites. Moreover, we are interested in enhancing the bioactivity of these secondary metabolites by epigenetic regulation of the fungi using HDAC and DNMT inhibitors.

During the course of this work, a suite of new and known compounds with anti-MRSA activity have been uncovered from a Floridian red mangrove-associated fungus. Using an enhanced rice medium, the fungus was cultured under the regulation of an HDAC inhibitor. After a 21-day incubation period the fungal culture was extracted in organic solvents. Following the anti-MRSA activity, the EtOAc partition was active against MRSA at 5 µg/ml and was subjected to MPLC. All bioactive MPLC fractions were purified through several rounds of HPLC which led to the isolation of at least four new and know compounds, exhibiting moderate activity against MRSA. The structures of the pure compounds which belong to the benzopyrone and benzofuran families were elucidated by 1D and 2D NMR spectroscopy.

MAGNETIC RESONANCE INVESTIGATION OF BONDING BETWEEN FIRST ROW TRANSITION METALS

Samuel M. Greer1,2, Kathryn Gramigna3, Sebastian A. Stoian1,2, Johannes McKay1, Christine Thomas3, Stephen Hill1,4

1 National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310, USA.
2 Department of Chemistry, Florida State University, Tallahassee, FL 32306, USA.
3 Department of Chemistry, Brandeis University, Waltham, MA 02453, USA.
4 Department of Physics, Florida State University, Tallahassee, FL 32306, USA.

10:35 AM
to 10:55 AM
Physical Chemistry

Tuning magnetic interactions between multiple spin carrying metals, to illicit desired magnetic/electronic properties, has long been a goal in molecular magnetism research. A great deal of this work has focused on exchange coupled clusters where the magnetic ions are weakly coupled through a bridging group. Here, we report on our efforts to understand the relationship between structure and physical properties of multi-metallic compounds with a direct metal-metal bond. To this end, we have performed a combined electron paramagnetic resonance and 57Fe Mössbauer spectroscopic investigation of several such compounds with varying spin states and coordination environments. We have rationalized the observed spectroscopic parameters in terms of ligand field theory and quantum chemical calculations.

Enhancements of the Psi4 Electronic Structure Package for Research, Education, and Development

Lori A. Burns and C. David Sherrill

Georgia Institute of Technology

10:40 AM
to 11:05 AM
Computational Chemistry

Psi4 is an open-source and freely available electronic structure package written in C++ for speed and Python for ease of interaction. It includes most common methods including density functional theory, many-body-perturbation theory, coupled-cluster theory, complete active space SCF, and configuration interaction. Enhancements to the top-level driver enable automatic basis-set extrapolations for optimizations, easily-specified composite methods, and n-body counterpoise-correction wrappers. Through transparent interfacing with external libraries, Psi4 gains capabilities in dispersion correction, PCM solvation, density-matrix renormalization group, effective fragment potentials (EFP), and relativistic corrections. After extensive infrastructure changes made over the past year, Psi4 is easier to obtain, extend, and interface. While retaining the ability to run as an executable with the simple text Psithon syntax, Psi4 gains a new mechanism of importing as a module into python `python -c "import psi4"` and thus ease of calling quantum chemistry operations from a Python script or Jupyter notebook. How to interact with Psi4 for research, education, and development will be discussed.

INVESTIGATION OF THE ORTHO-PYRIDINONE METHIDE REACTIVITY OF VITAMIN B6 

Gregory R. Boyce

Florida Gulf Coast University

10:40 AM
to 11:05 AM
Organic Chemistry

Our laboratory is dedicated to the development of new reactions for the synthesis of complex biologically active targets. This presentation will describe our progress in exploring the ortho-pyridinone methide reactivity of vitamers of vitamin B6. While ortho-quinone methide reactivity that has been well-studied; the analogous reactivity with 3-pyridinols has received little attention. Two vitamers of vitamin B6, pyridoxine and pyridoxal, serve as inexpensive, non-toxic, and readily available 3-pyridinols from which we can investigate this reactivity. Additionally, functionalization of these vitamers is of interest due to the broad range of biological activity (anti-SARS, anti-HIV, anti-diabetic, gram-negative antibiotic) displayed by their derivatives. We have utilized ortho-pyridinone methide reactivity to generate novel ether, amino, furopyridine and tricyclic derivatives with high regioselectivity. The scope, limitations, mechanistic insights, and reactivity trends for these operationally-simple methodologies will be presented. Efforts to utilize these specific derivatives as water-triggered pro-substances to deliver molecules of importance will also be discussed.

INTERACTION MECHANISMS OF MEMBRANE ACTIVE MOLECULES

Jianjun Pan

Department of Physics, University of South Florida, Tampa, FL 33620, USA

10:55 AM
to 11:30 AM
Biophysical

Cell membranes provide an efficient mechanism of compartmentalizing cellular contents from the surrounding while allowing selective transportation of essential molecules across the hydrophobic barrier. It is not surprising that many small amphipathic peptides can threaten bacteria by directly interacting with their membrane envelopes. Identifying the interaction mechanism of those small peptides will help us develop antimicrobial compounds with better potency. We are interested in elucidating the impacts of natural and synthesized peptides on physical properties of model lipid membranes. Our main experimental tools include atomic force microscopy, force spectroscopy, Raman spectroscopy, electron paramagnetic spectroscopy, and fluoresce microscopy. The second topic of membrane interaction centers on misfolded protein aggregates. In particular, we have obtained several interesting aspects of membrane perturbation caused by oligomeric and fibrillar aggregates formed by a polyglutamine peptide. Lastly, I will briefly cover how simple lipid mixtures can give rise to the fascinating heterogeneous organization in lipid membranes.

Ultrafast Spectroscopy of New Photonic Materials for Solar Energy Conversion

Dr. Amy M. Scott

University of Miami

10:55 AM
to 11:30 AM
Materials Chemisry

Harnessing sunlight as an alternative energy resource continues to stimulate material science research for the design and synthesis of new photonic materials.  Hybrid organic – inorganic materials have been increasingly studied in the material science community in order to create new materials with unique features.  For the past three years, our group has been focusing on the fundamental light harvesting and photophysics of organic liquid crystals, single crystal and thin film perovskites, and gold nanocluster-quantum dot systems.  In this talk, I will highlight each of these projects and how ultrafast transient absorption plays a vital role for developing structure-property relationships with the aim to develop a mechanistic understanding of exciton and electron/hole dynamics. These studies help establish a fundamental understanding of the photophysical processes in new photonic materials to ultimately guide the design of new materials with targeted ultrafast dynamics and optoelectronic properties.

Biosynthesis of deep-sea marine natural products: genes, enzymes, and pathways

Guojun Wang

 

Harbor Branch Oceanographic Institute, Florida Atlantic University
5600 US 1 North, Fort Pierce, FL, 34946

10:55 AM
to 11:30 AM
Natural Products

Among marine organisms, sponges are the most prolific producers of marine natural products (MNPs) which are recently becoming an attractive source of drug discovery. One probable reason is the huge amount of diverse microorganisms symbiotically living inside a sponge provide an extremely rich reservoir of natural product biosynthetic genes. However, the supply of a potent MNP is often the major issue banning it from further clinical studies. My laboratory focuses on the biosynthesis of MNPs from deep-sea sponges to identify biosynthetic origin and pathways and ultimately to develop sustainable supplies for them.
Leiodermatolide (LDM), isolated from the sponge Leiodermatium sp. (sampled at ~400 m), is a trans-AT (acyl transferase) type-I polyketide, in which AT domains are encoded by separate genes, instead of generally integrated into the architecture of polyketide synthases (PKSs). LDM is a potent mitosis-targeting agent and shows strong in vitro inhibitory activity against cancer cell proliferation. Notably, LDM is potent against the leukemia cell line HEL92.1.7 with a GI50 of 1.0 nM; this cell line contains the Pgp efflux transporter which is a major cause of drug resistance in chemotherapy. The in vivo antitumor activity of LDM was recently confirmed in a mouse model of metastatic pancreatic cancer. LDM arrests cell division at the G2/M phase. Notably, LDM employs a distinct mode of action that fundamentally differs from current anti-mitotic drugs including taxanes and vinca alkaloids. LDM doesn’t bind to tubulin, nor does it induce or inhibit tubulin polymerization in vitro. LDM also causes an immediate block of microtubule elongation.
A fosmid library of LDM-producing sponge Leiodermatium was constructed. The library is being screened by primers specifically targeting the highly conversed KS (ketosynthase) domains of trans-AT type I PKSs and other specific structural features. A set of fosmids were obtained. Cloning, sequencing, and restriction analysis indicated that those fosmids share common sequences but each with a unique restriction pattern. A 24-kb DNA sequence was identified, which are likely involved in the biosynthesis of a trans-AT type I polyketide. Domains such as KS, ACP (acyl carrier protein), KR (keto-reductase) and DH (dehydrogenase) were identified, but lacing AT domains. Sequencing of additional fosmids is in the process.

High-Nuclearity 3d/4f-Metal Complexes with Aesthetically-Pleasing Structures and Single-Molecule Magnetism Properties

Dimitris I. Alexandropoulos,1 Luis Cunha-Silva,2 George Christou3 and Theocharis C. Stamatatos*,1

1. Department of Chemistry, 1812 Sir Isaac Brock Way, Brock University, L2S 3A1 St. Catharines, Ontario, Canada
2. REQUIMTE-LAQV & Department of Chemistry and Biochemistry, Faculty of Sciences, University of Porto, 4169-007 Porto, Portugal
3. Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200, USA

10:55 AM
to 11:30 AM
Inorganic Chemistry

The search for polynuclear metal complexes (or clusters) with new structural motifs and interesting properties, such as magnetic, optical and catalytic, continues to attract the interest of the academic community for a number of reasons. These include, but are not limited to: (i) the synthesis of nanoscale molecular materials with large nuclearities and unique structures, (ii) the isolation of high-spin molecules and single-molecule magnets (SMMs) with large spin ground state values (S) and energy barriers (U) for the magnetization reversal, and (iii) the synthesis of molecular magnetic refrigerants with enhanced magnetocaloric properties as alternatives to low-temperature cooling applications. Highly anisotropic systems resulting from the presence of metal ions with unquenched orbital angular momenta, i.e., 4f-metal ions such as DyIII and TbIII, may lead to prominent SMMs with large blocking temperatures and U values. In this work, we have decided to combine lanthanides (Ln) with various 3d-metal ions, under different reaction conditions, as a means of obtaining high-nuclearity heterometallic 3d/4f-metal clusters with unique structures, large S values and interesting SMM properties. To this end, several new families of {M6Ln6} (M2+ = divalent metal ions), {Cu6Ln12}, {Mn6Ln4} will be discussed in detail.

Structural Photonics Examined Using Ultrafast and Magneto-Optical Spectroscopy

Kenneth L. Knappenberger, Jr. 

Florida State University, Tallahassee, FL USA

10:55 AM
to 11:30 AM
Physical Chemistry

Monolayer-protected clusters (MPCs) are an emerging class of photonic materials that can be synthesized and isolated with atomic precision. Control over MPC composition results, in part, from electron filling of Superatom orbitals,  yielding colloidal metal nanoparticles of specific magic sizes. These synthetic advances overcome many limitations of inherently heterogeneous colloidal metal nanoparticle syntheses. Recently, post-synthetic electrochemical methods for manipulating the oxidation state of stable MPCs have been demonstrated. Here, femtosecond time-resolved and magneto-optical spectroscopy studies of a family of MPCs in the 1-2 nm size range will be presented. These results show that the optical, electronic and magnetic properties of MPCs are extremely sensitive to the electronic configuration of Superatom orbitals. For example, the magnetic properties of Au25(SR)18, where SR represents an alkanethiol, can be switched reversibly by oxidative opening of the eight-electron Superatom P orbital. Collective interactions between assembled MPCs also exhibit spin-dependent magnetic phenomena not present in the isolated building blocks. Magnetic Circular Dichroism and time-dependent spectroscopy on dimerized 20-atom MPCs reveal inter-particle spin-dependent dynamics not observed for the monomer. Importantly, these results indicate that the magnetic properties of gold MPCs result from the electronic configuration of metal-based Superatom orbitals

The Quartic Force Field for More Than Just Highly-Accurate Predictions of Rovibrational Spectral Features

Ryan C. Fortenberry

Department of Chemistry & Biochemistry, Georgia Southern University, Statesboro, GA 30460

11:05 AM
to 11:30 AM
Computational Chemistry

The quartic force field (QFF) is a minimal potential energy surface that defines the potential portion of the internuclear Hamiltonian as a fourth-order Taylor series expansion. By utilizing a composite approach based on the CCSD(T) method with complete basis set extrapolation, core correlation, and scalar relativistic considerations, exceptional accuracies can be achieved. Vibrational frequencies comparing to as good as 1 cm-1 can be produced and rotational constants within a few dozen MHz are also possible. Furthermore, combinations of QFFs for different electronic states, charges, or reaction minima can produce exceptionally accurate electronic spectra, photoionization energies, and reaction schema. Recent successes will be discussed including the photoelectron spectrum of CP- and C2P-, energetics for the formation/destruction of the ArHAr+ proton-bound complex, and the rotational constants of HPSi. Furthermore, predictions for such species related to as-of-yet unobserved properties will also reported.

Gold Redox Catalysis with Diazonium Salts

Xiaodong Shi

Department of Chemistry, University of South Florida, Tampa, FL 33620, USA

11:05 AM
to 11:30 AM
Organic Chemistry

Gold redox catalysis has received far less attention compared to the well established regime of carbophilic Au(I) Lewis acid catalysis. This can be attributed to the high oxidation potential between Au(I) and Au(III), which creates a reliance on strong oxidants such as selectfluor or hypervalent iodine.

The discovery of photo-assisted diazonium activation toward gold(I) oxidation greatly extended the scope of gold redox catalysis by avoiding the use of a strong oxidant. Some practical issues that limit the application of this new type of chemistry are the relative low efficiency (long reaction time and low conversion) and the strict reaction condition control that is necessary (degassing and inert reaction environment). Herein, an alternative photo-free condition has been developed through base induced diazonium activation.

We have reported a Gold-catalyzed cross-coupling strategy using aryldiazonium salts as the oxidant. By forming an alkynyl or aryl gold complex in situ, oxidation of AuI to AuIII with diazonium salt, sp2-sp2 and sp-sp2 cross coupling was achieved. By using this strategy, Gold-catalyzed C-heteroatom (C–X) coupling reactions are also evaluated. By accelerating the reaction rate to outcompete C–C homo-coupling or diazonium dediazoniation, gold-catalyzed Sandmeyer reactions were achieved with different nucleophiles, forming C–Br, C–S and C–P bonds in high yields and selectivity.

In combination with Na2CO3 and diazonium salts, a Au(III) intermediate could be generated. The efficient activation of various substrates including alkyne, alkene, allene and cyclopropanol wcould then be achieved. A rapid Au(III) reductive elimination allows access to C-C coupling products in good to excellent yields. Challenging substrates such as cyclopropanol and electron rich/neutral allenes, which could not be activated under the photo condition (<5% yield), could be activated to subsequently yield the desired coupling products in good to excellent yield.