Coordination Polymer Heterostructures, More than the Sum of the Parts
Daniel R. Talham
Department of Chemistry, University of Florida
Assembled from molecular precursors, coordination polymer solids offer the ability to alter behavior through molecular synthesis, an advantage often attributed to molecular materials or organic polymers, yet they can possess physical properties more commonly associated with the inorganic solid state. While coordination polymer materials were a relatively late addition to the nanoscience revolution, even more recent is a focus on nanoscale and mesoscale heterostructures of coordination polymer solids. At the mesoscale, surfaces and interfaces play key, sometimes dominant roles in dictating properties. Using primarily cyanometallate coordination polymers, this presentation will look at some examples for which new behavior is seen in submicron heterostructures, properties that are different from those observed in the bulk or in smaller nanoparticles. Examples include studies of magnetism and light-switchable magnetism, structural phase transitions, and alkali-ion storage for battery applications.
A Reassessment of the Electronic Structure of Cr(VI) Sites Supported on Amorphous Silica and Implications for Cr Coordination Number.
Nathan Peek, Albert Stiegman, David B. Jeffcoat, Susannah L. Scott, §, Cristina Moisii, Lambertus van de Burgt, Salvatore Profeta
Florida State University
The electronic structure of isolated Cr(VI) sites supported on silica was re-investigated using multiple, complementary electronic spectroscopies applied to transparent xerogel monoliths. The absorption spectrum exhibits three previously reported peaks, at 22,800, 29,100 and 41,500 cm-1, as well as a previously unresolved band at ca. 36,900 cm-1. The emission is a long-lived red luminescence with λmax = 13,600 cm-1, emanating from the lowest excited state. Assignment of the excited states was facilitated using time-dependent density functional theory (TD-DFT) calculations performed on cluster models. All of the observed electronic transitions and their energies are accounted for by dioxoCr(VI) sites. Small variations in site symmetry at Cr result principally in inhomogeneous broadening of the spectral bands, as well as a red-edge effect in the photoemission spectrum. Recently, it has been proposed that there are two monomeric sites present on the surface: the well-established four coordinate dioxo site and a five-coordinate mono-oxo site. The results of this study find no compelling evidence for a significant contribution from a mono-oxoCr(VI) sites.
Investigation Of Z/E Configurational Isomerization In Dicyanorhodanine-Functionalized Oligothiophenes
Lei Li,1 Asmerom O. Weldeab,1 Cory T. Kornman,1 and Ronald K. Castellano1
1 Department of Chemistry, University of Florida, P.O. Box 117200, Gainesville, FL 32611-7200, USA
Oligothiophenes functionalized with the dicyanorhodanine acceptor have been widely used as electron donor materials in organic solar cells, where they have led to state-of-the-art device performance. Surprisingly, there are no reports in this literature that has considered potential configurational isomerization (Z to E) within the acceptor portion that could potentially alter electronics, conformational preferences, or molecular packing. Reported here is the preliminary investigation of Z/E configurational isomerization in a homologous series of oligothiophenes terminated with the dicyanorhodanine group. The structures of the two configurational isomers were first confirmed by 2D NMR (gHMBC and EXSIDE), and their gas-phase stabilities were studied through DFT calculation. The origin of the isomerization and the consequences of the structural change on optical properties have been explored. By varying the π-conjugation length, solubilizing groups, solvent, and photon source, some of the factors that influence the Z/E configurational isomerization have been identified. The kinetics of the processes and consequences of the isomerization on thin film processing and structure are currently being evaluated.
Photoreversible Covalent Hydrogels for Soft-Matter Additive Manufacturing
Christopher P. Kabb,† Christopher S. O’Bryan,§ Christopher C. Deng,† Thomas E. Angelini,§, ‡,⊥ and Brent S. Sumerlin*,†
†George & Josephine Butler Polymer Research Laboratory, Center for Macromolecular Science & Engineering, Department of Chemistry, University of Florida, Gainesville, FL 32611, USA.
§Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611, USA.
‡J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL 32611, USA.
⊥Institute for Cell and Regenerative Medicine, University of Florida, Gainesville, FL 32611, USA.
Reversible-covalent chemistry provides access to robust materials with the ability to be degraded and reformed upon exposure
to an appropriate stimulus. Photoresponsive units are attractive for this purpose, as the spatial and temporal application of light is easily controlled.
Coumarin derivatives undergo a [2+2] cycloaddition upon exposure to long-wave UV irradiation (365 nm), and this process can be
reversed using short-wave UV light (254 nm). Therefore, polymers crosslinked by coumarin groups are excellent candidates as reversiblecovalent
gels. In this work, copolymerization of coumarin-containing monomers with the hydrophilic comonomer N,N-dimethylacrylamide
yielded water-soluble, linear polymers that could be cured with long-wave UV light into free-standing hydrogels, even in the absence of a photoinitiator.
Importantly, the gels were reverted back to soluble copolymers upon short-wave UV irradiation. This process could be cycled,
allowing for recycling and remolding of the hydrogel into additional shapes. Further, this hydrogel can be imprinted with patterns through a
mask-based, post-gelation photoetching method. Traditional limitations of this technique, such as the requirement for uniform etching in one
direction, have been overcome by combining these materials with a soft-matter additive manufacturing methodology. In a representative
application of this approach, we printed solid structures in which the interior coumarin-crosslinked gel is surrounded by a nondegradable gel.
Upon exposure to short-wave UV irradiation, the coumarin-crosslinked gel was reverted to soluble prepolymers that were washed away to
yield hollow hydrogel objects.
Novel nitric oxide (NO) releasing polymers to combat thrombosis and infection
Elizabeth J. Brisbois
University of Central Florida
Blood-contacting devices, such as catheters and complex extracorporeal artificial organs, suffer from two major clinical problems: 1) platelet activation leading to thrombosis, and 2) infection. One approach to improving the hemocompatibility of blood-contacting devices is to develop materials that release nitric oxide (NO). Nitric oxide is an endogenous gas molecule produced by nitric oxide synthase (NOS) enzymes that has several key biological roles. Healthy endothelial cells exhibit a NO surface flux of 0.5 – 4.0 x10-10 mol cm-2 min-1 that inhibits platelet adhesion and activation. Macrophages also release NO that acts as a potent natural antimicrobial agent. Polymeric materials that mimic this NO release are expected to have similar antithrombotic and antimicrobial properties. In this presentation, examples of incorporating NO donor molecules such as diazeniumdiolates (NONOates) or S-nitrosothiols (RSNOs) in biomedical grade polymers will be discussed, including new methods to modify existing polymeric medical devices (e.g., catheters) with NO donor molecules via a solvent swelling technique. These new materials are used to fabricate “prototype” intravascular catheters and extracorporeal circuits, and further evaluated for the hemocompatibility and antimicrobial activity via short-term (4 h) and long-term (1-2 weeks) in vivo experiments using clinically relevant animal models.
Reaction mechanisms and rate constants of PAH growth in astrophysical environments
Alexander M. Mebel
Florida International University
The presentation will overview results of quantum chemical calculations of potential energy surfaces combined with RRKM-Master Equation calculations of reaction rate constants, carried out in order to unravel reaction mechanisms of the growth of polycyclic aromatic hydrocarbons (PAHs) at temperatures and pressures relevant to the interstellar medium or to carbon-rich circumstellar environments. We will describe our recent efforts directed toward the development of a comprehensive mechanism of PAH growth and consider possible formation routes to two-ring PAHs, naphthalene and indene, as well as the Hydrogen Abstraction aCetylene Addition (HACA) and Hydrogen Abstraction Vinylacetylene Addition (HAVA) growth mechanisms of larger PAHs. The computational results will be compared with the experimental findings by R. Kaiser’s (University of Hawaii at Manoa) and M. Ahmed’s (LBL) groups utilizing a pyrolytic chemical reactor and product identification by means of photoionization spectroscopy using the quasi-continuous tunable vacuum ultraviolet light from the Advanced Light Source. In particular, we will describe the C6H5 + C4H4 and C10H7 (1-/2-naphthyl) + C4H4 reactions and show that they can form naphthalene, phenathrene, and anthracene even at very low temperatures in the interstellar medium. Alternatively, the HACA mechanism is feasible only in high-temperature circumstellar environments. We will consider prototype C2H2 addition steps as well as formation of phenanthrene from a biphenylyl radical and formation of pyrene from a phenanthryl radical. The complementary nature of the HACA and HAVA mechanisms and their role in the build-up of two-dimensional graphene-type nanostructures and three-dimensional carbonaceous nanostructures holding corannulene units through the incorporation of five-membered rings will be discussed.
Characterization of plasma- and laser-based ambient ionization techniques for forensic analysis
Kenyon Evans-Nguyen, Gaston Merideth II, Abigail Smola, and Kelsey May
The University of Tampa, Tampa, FL
Ambient ionization mass spectrometry is a powerful technology for forensic analysis, particularly for drugs and explosives. Given the simple and rapid nature of the technique, it is promising for on-site analysis of explosive devices. Most efforts in ambient ionization focus on organic analysis. While many high explosives are organic, more common explosives are inorganic. This talk will focus on the development of ambient ionization techniques amenable to organic and inorganic analysis, as well as elemental analysis with application to explosives. The suitability of Direct Analysis in Real Time (DART), Low Temperature Plasma (LTP), and microwave jet plasmas for organic, inorganic, and elemental analysis is being characterized. Additionally, the use of lasers in concert with these techniques to enhance surface desorption is being studied. Model explosive mixtures are being analyzed as well as "thermometer" ions, which provide insight into the energy being imparted by ionization. The data yielded by thermometer ion spectra can help to predict the expected extent of fragmentation that can be expected for the labile bonds in explosives.
Geochemical impacts from Hurricane Irma to a west Florida blackwater estuary
Jordon Beckler-1,2, Emily Buckley-2, Diane Santioanni-2, Sean Jones-2, Arielle O’Brien-2, Emily Hall-2, Elizabeth Yanuskiewicz-2, Martial Taillefert-3, Eric Milbrandt-4
1- FAU Harbor Branch Oceanographic Institute, 2 -Mote Marine Laboratory, 3- Georgia Tech, 4-Sanibel Captiva Conservation Foundation
With the recent passing of Hurricane Irma over southwest Florida, the Caloosahatchee Estuary and San Carlos Bay system experienced extremely low salinities, decreased water clarity, and severe hypoxia – an event unprecedented in both duration, extent, and areal coverage since continuous monitoring began in 2007. Coincidentally, we led a week-long geochemical field campaign that began on Sep. 25th 2017 and was the wet-season complement to a previous dry-season (low-flow) sampling effort in Dec. 2016. On several full estuary transects, we quantified the size partitioning of iron, nutrients, and carbon in surface and bottom waters, as well as the solid phase organic carbon and reactive iron hydroxide content in surface sediments. Further, sediment respiratory processes and flux rates were elucidated from sediment cores using Hg/Au voltammetric microelectrode profiling and core separation and wet-chemical analyses.
Conditions after the storm were drastically different than under low flow conditions. For example, surface water dissolved iron concentrations were an order of magnitude higher (~ 8 mM) than under low flow conditions. While organically-complexed iron(III) concentrations exceeded 5 mM, the sediment-derived diffusive fluxes, which dominated under low-flow conditions, were negligible after the hurricane. Indeed, an excess of organic carbon in sediments relative to reactive iron hydroxides favored sulfate reduction (and sulfide production) in lieu of dissimilatory iron reduction, sequestering pore water iron and the resulting sediment-derived iron flux. However, an additional >3 mM of surface water iron was observed in the reduced (+II) form, with concentration profiles indicating a complementary source from the upriver drainage basin or Lake Okeechobee. Interestingly, the Fe(II) was relatively less stable in the lower estuary, either because of flocculation processes or oxidation as hypoxic conditions lessened.
I finally speculate on potential links to a local sustained bloom of the Florida red tide species K. brevis that began a few weeks after the storm, as well as the potential resilience of this system and other Florida blackwater river estuaries to extreme weather events expected to increase in the future.
Aha1 stimulates tau aggregation
Lindsey B. Shelton, Jeremy D. Baker, Dali Zheng, Brian S.J. Blagg, and Laura J. Blair
Department of Molecular Medicine and USF Health Byrd Institute, University of South Florida, Tampa, Florida
Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana
The microtubule associated protein tau pathologically accumulates inside neurons in Alzheimer’s disease (AD) and other tauopathies. Chaperones, such as heat shock protein 90kDa (Hsp90), have been shown to preserve pathological tau. Inhibition of the ATPase activity of the abundantly expressed 90kDa heat shock protein (Hsp90) reduces tau levels in vivo. This ATPase activity is also regulated by a diverse set of Hsp90 co-chaperones. In particular, the activator of Hsp90 ATPase homolog 1 (Aha1) is the only known stimulator of this ATPase activity. However, the effects of Aha1 on Hsp90-mediated tau fibrilization have not been well-characterized. Since it is known that Hsp90 promotes tau fibrilization, we hypothesized that Aha1 would further stimulate tau aggregation through stimulation of Hsp90 ATP hydrolysis. We have now found Aha1 is co-localized and co-immunoprecipitates with pathogenic tau in AD brain tissue. In recombinant and cell models, Aha1 coordinated with Hsp90 to accelerate insoluble tau accumulation, which was prevented by an Aha1 mutation that reduces Hsp90 interaction. In vivo, Over-expression of Aha1 in the hippocampus of rTg4510 tau transgenic mice increased oligomeric and insoluble tau, concomitant with reduced neuronal viability. Recently, we have determined that ablation of Aha1 levels or activity slowed the accumulation of pathogenic tau. Overall, these data suggest that Hsp90 ATP hydrolysis promotes tau oligomer and fibril formation, and small molecule inhibitors of Aha1 may be beneficial for the prevention or treatment of tau-related diseases.
Material Systems for Nano-Scale 3D Printing by Multi-Photon Lithography
Stephen M. Kuebler
Department of Chemistry and CREOL, The College of Optics and Photonics, University of Central Florida
Multi-Photon Lithography is a flexible method for single-step fabrication of 3D structures with feature sizes well below 1 micron. A wide range of material systems has been investigated for multiphoton lithography, including photoresists, chalcogenide glasses, hybrid pre-ceramics, and metals. Post-printing processes have also been developed for transforming polymeric 3D structures into other materials, either by conformal deposition, pyrolysis, structure inversion, or other means. This presentation will give an overview of material systems for multiphoton lithography and show examples of functional 3D nano-scale devices that have been created with these material systems.
David M. Rogers
University of South Florida
Spin-Labeling Magnetic Resonance Applications in the Glycine Riboswitch
Gail E. Fanucci, Michelle Ehrenberger, Jacqueline M. Esquiaqui.
Department of Chemistry, University of Florida
Our lab utilizes site-directed spin labeling magnetic resonance (SLMR) to characterize motion and flexibility associated with function and malfunction. Here we will discuss our latest activates related to strategies to characterize conformational changes in the glycine riboswitch with particular focus on the leader-linker region compared to the glycine binding region of the second aptamer. We are able to show that different regions of this large dynamic RNA are pre-formed in solution and stabilized by either monovalent or divalent ions. To date, it appears that the riboswitch regions preform prior to binding glycine, possibly indicating that a truncated riboswitch that does not contain the expression platform does not completely recapitulate the true conformational landscape of the in vivo messenger RNA species.
Insight on the surface chemistry of bimetallic nanostars: capping agents and stability
Chiara Deriu, MS; Asier Bracho; Alejandro Rizo; Bruce McCord, PhD
Department of Chemistry and Biochemistry, Florida International University, Miami, FL
Anisotropic nanoparticles represent the state-of-the-art substrates for surface-enhanced Raman spectroscopy (SERS), and there is great interest in the development of facile synthetic strategies that achieve these morphologies in a seedless, one-pot, and surfactant-free manner. However, the absence of surfactants as shape directors poses challenges in maintaining the stability of the colloid, and detergents such as CTAB are generally added post-synthesis as stabilizers. This hinders the SERS signal via the formation of a bilayer that prevents a close contact between analyte and metal surface. Ideal capping agents for SERS substrates, on the other hand, should ensure a shelf-life to the colloid without interfering with the SERS measurement. A published protocol for the surfactant-free synthesis of poorly capped bimetallic Au/Ag nanostars was selected as a basis to study alternatives to CTAB as stabilizing agent to be added post-synthesis. DLVO theory of colloid stability was used as a criterion for the selection of candidate stabilizing agents, and UV/Vis spectroscopy was used to evaluate the stability of the colloidal preparations over time. XPS, Zeta potential measurements, and infrared spectroscopy were used to investigate the surface chemistry of the nanostars, and the interaction modes of the candidate stabilizers. Preliminary results obtained from decay studies indicate a pattern of increased capping efficacy for candidate agents bearing carboxylate functions, suggesting that the driving force in the capping process is not purely electrostatic in nature.
The Preparation of High-Nuclearity Heterometallic Pb-Mn Clusters
Elly Earlywine, Khalil A. Abboud, and George Christou
Department of Chemistry, University of Florida, Gainesville FL 32611-7200
Intense research activity continues in the development of high-nuclearity metal-oxo clusters because of their relevance to various areas of chemistry, physics, and material science. Recently, some of these clusters have also attracted great interest because they can structurally be considered small molecular pieces of the bulk metal oxides. In our group, the use of manganese with its various stable paramagnetic oxidation states (II-IV) in metal-oxo-carboxylate chemistry has led to numerous clusters with fascinating structural features and intriguing physical properties (e.g., magnetism). Although considerable effort has also been made in the development of heterometallic manganese clusters, few clusters have been reported that contain both manganese and a heavy main group element such as bismuth or lead. Additionally, several of them are low-nuclearity (eight or fewer metal centers). New Pb/Mn clusters also have the possibility of showing their own interesting physical properties, such as multiferroism. Hence, we have initiated a study into the preparation of high-nuclearity, heterometallic heavy metal Mn-oxo clusters, with the focus of this talk being on the discovery of new Pb-Mn-oxo clusters.
Preliminary Characterization of Sexual Assault Lubricants: Comparison Between DART-TOFMS, GC-MS, and FT-IR
Caterina R. Vadell-Orsini, Brooke R. Baumgarten, Mark Maric, Candice M. Bridge
National Center for Forensic Science, University of Central Florida
Unfortunately, sexual assaults are a reality in today's society. Increasing use of condoms reduces potential of recovering DNA evidence, and a novel approach for the analysis of other trace evidence is required. The characterization and classification of lubricants is a relatively new approach for analyzing unknown trace evidence that could be collected from the crime scene or the victim.
In this study, 20 samples from different sexual lubricant manufacturing types were tested: water-based, silicone-based, oil-based, and organic/edible lubricants, and personal hygiene products which could also be used in sexual assaults. Instrumental methods were developed for direct analysis in real time-time of flight mass spectrometry (DART-TOFMS), gas chromatography-mass spectrometry (GC-MS) and Fourier transform infrared spectroscopy (FTIR). Analytical protocols were designed to increase the identification of unique components in these lubricants to develop a classification scheme for unknown samples.
Neat lubricants, as well as solvent extracts, were analyzed in both positive and negative ionization modes using DART-TOFMS in replicates of five. Neat lubricants and extracts were also analyzed via FTIR in triplicate, and extracts were analyzed by GC-MS in triplicate. Multivariate statistical techniques were used to identify unique markers that describe each class within the larger dataset. Classification schemes were developed for each instrument individually.
The outcomes of the classification schemes are expected to separate the different manufacturing types into groups, and sub-classes within each manufacturing type. The classification schemes developed from this preliminary study will affect the forensic trace evidence community by aiding in future exploitation of evidence found at a crime scene based on the data, thus providing investigative leads and innovative techniques in the analysis of trace evidence.
Can a Catalytic Process for oxidation of N2 or N2O to nitrate be developed?
Elena V. Rybak-Akimova1, Taryn D. Palluccio1, Christopher C. Cummins2, Steven P. Nolan3, Catherine S. J. Cazin3, Manuel Temprado4, Jack Davis5, Leonardo F. Serafim5, Burjor Captain5, Carl D. Hoff5
1. Tufts University, 2. Massachusetts Institute of Technology, 3. University of Ghent, 4. University of Alcala, 5. University of Miami.
Production of ammonia in the Haber process is one of the largest industrial users of hydrogen gas, due to the large demand of NH3 by the fertilizer industry. Close to half of the ammonia produced is combusted in the Ostwald process to form HNO3. During that process N2O and NOx are produced as waste gases which are removed by the BASF DeNOx process. Nitrous oxide in particular is a potent greenhouse gas, approximately three hundred times more potent in infrared absorption than isoelectronic CO2. Energetic savings in both of these processes can in principle be achieved by development of new technologies and catalysts.
Thermochemical calculations of Lewis in the 1920’s showed that production of dilute HNO3 directly from N2, O2, and H2O was marginally favorable at ambient temperatures. Addition of a base can readily be calculated to yield a strong driving force as shown in reactions (1) and (2). The feedstock for these processes do not involve energy costs comparable to current technologies.
N2(g) + 2.5 O2 + Na2O(s) --> NaNO3(s) ) dG300 = -76 kcal/mol (1)
N2O(g) + 2 O2 + Na2O(s) --> NaNO3(s) dGo300 = -109 kcal/mol (2)
Development of a catalyst for reaction (1) has not been extensively studied in spite of the fact that it could represent a significant reduction in H2 to produce NH3 which is later combusted in the Ostwald process. In the BASF DeNOx process NH3 is added to the flue gas stream to reduce N2O to N2 by NH3. This also corresponds to a loss in H2 equivalents in the emerging hydrogen economy. Development of a catalyst for reaction (1) presents greater kinetic barriers than does reaction (2) making it more challenging but also more rewarding. In this presentation studies of binding and activation of O2, N2, and NxOy will be discussed together with relevant literature reports to analyze the prospects for developing better methods to clean up the waste gas stream from the Ostwald process as a first step toward the long range goal of replacing it.
Fabrication of Triboluminescence Sensors via Additive Manufacturing
Tawakalt Mayowa Akintola, Jolie Breaux Frketic, Roy Madhuparna, Phong Tran, Tarik Dickens
Department of Industrial and Manufacturing Engineering, FAMU-FSU College of Engineering, 2525 Pottsdamer St., Tallahassee, Florida 32310 United States
High-Performance Materials Institute, 2005 Levy Ave, Tallahassee, Florida 32310 United States
In this presentation, functional 3D printing parts were produced using ZnS:Mn powder/Polystyrene (PS) composites. ZnS:Mn is a triboluminescence (TL) material which produces light emission under mechanical loads such as impact, stress, and fracture.
By combining TL materials with additive manufacturing, we can achieve unique TL structures that once restrained by conventional methods. Additionally, 3D printing of TL materials will allow us to strategically embed functionalized material for self-sensing in applications for damage detection and monitoring. The processing-performance relationship has been investigated by TGA, DSC and SEM to understand the effect of TL crystal sizes and distribution on the performance of TL printed parts.
Flexural testing beams were 3D printed and their fracture/deformation energy emission was estimated via J-integral
analysis of three-point bend test.
Modular functionalization of polymeric β-ketoesters via dynamic enamine chemistry
Michael B. Sims, Jacob J. Lessard, Lian Bai, Brent S. Sumerlin
The George & Josephine Butler Polymer Research Laboratory, University of Florida
Post-polymerization modification has emerged as a powerful tool for functional polymer synthesis, complementing the suite of controlled polymerization techniques. The recent development of highly rapid, efficient, and mild functionalization reactions has greatly improved the diversity of readily accessible macromolecular structures, and there remains significant interest in further expanding the synthetic toolbox available to polymer chemists. In this work, we outline the utility of the reaction between primary amines and β-ketoesters for post-polymerization modification via the formation of robust enamine linkages. Commercially available 2-(acetoacetoxy)ethyl methacrylate (AAEMA) was polymerized under RAFT conditions to yield well-defined polymers bearing pendent β-ketoester moieties. These polymers could then rapidly functionalized with a variety of primary amines under very mild conditions, and the structure of the attached functionality was found to strongly influence the physical properties of the resultant polymers. In a representative example, the functionalization of polyAAEMA with benzylamine resulted in an increase of the glass transition temperature from 11 °C to 50 °C. As enamines are dynamic-covalent linkages, we furthermore investigated the conditions that would enable the exchange of one functionality for another, enabling dynamic modification of the polymers’ physical and chemical properties.
Using theory and experiment to elucidate the origin of product specificity in protein arginine methyltransferases
Orlando Acevedo1, Abhishek Thakur1, Tamar B. Caceres2, Owen M. Price2, Joan M. Hevel2
1 Department of Chemistry, University of Miami, Coral Gables, FL 33146.
2 Department of Chemistry and Biochemistry, Utah State University, Logan, UT 84322.
Protein arginine methyltransferases (PRMTs) play pivotal roles in signaling networks that control all aspects of central dogma, metabolism, and signal transduction. As the major arginine methylation enzyme, protein arginine methyltransferase 1 (PRMT1) strictly generates monomethylated arginine (MMA) and asymmetric dimethylated arginine (ADMA), but not symmetric dimethylated arginine (SDMA). However, it remains unclear how PRMT1 product specificity is regulated, an important exploit since PRMTs have been implicated in many human diseases. In our joint theoretical and experimental study, it was discovered for the first time that a single amino acid mutation (Met48 to Phe) in the PRMT1 active site enabled PRMT1 to generate MMA, ADMA, and a limited amount of SDMA. A double mutant H293S-M48F-PRMT1 produced SMDA as the major product with limited amounts of MMA and ADMA. Intriguingly, protein arginine methyltransferase 7 (PRMT7) is unique within the PRMT family in that is capable of only forming MMA. Our recent efforts determined that a mutation of Phe71 to Ile in PRMT7 allowed a second turnover to occur, similar to PRMT1. This seminar will highlight our efforts integrating biochemical, biophysical, computational, and structural approaches to provide mechanistic understanding of how the PRMT isoforms establish the strict product specificity that is required for the desired biological effect.
The Zebrafish as a Toxicological Model for Assessing Toxic Potential of Cyanobacteria in the Environment
John P. Berry
Department of Chemistry and Biochemistry, Florida International University
As ubiquitous components of marine, freshwater and coastal systems, and owing to their recognized production of a diversity of toxic or otherwise biologically active secondary metabolites, cyanobacteria (or "blue-green algae") are emerging as major environmental concerns with respect to human, animal and ecosystem health. In order to understand their contribution - as "toxins" - to environmental health concerns we have employed the zebrafish (Danio rerio), and particularly embryonic and larval stages of the species, as a toxicological model to identify, isolate and characterize bioactive metabolites from cyanobacteria. As a means of identifying possibly relevant cyanobacterial toxins, the zebrafish embryo has been used to screen a wide array of cyanobacterial isolates (i.e., cultures) and compounds, and has consequently identified numerous lead to possibly novel toxins. In turn, the model system has been used to both isolate and subsequently characterize several bioactive metabolites in relation to their possible role as environmental toxicants. Subsequently, and most recently, we have adapted state-of-the-art techniques based on nuclear magnetic resonance (NMR), and particularly, high-resolution magic angle spinning (HRMAS) NMR, to investigate in vivo effects of these toxic metabolites on metabolic profiles in the intact ebrafish embryo model toward understanding both pathways of toxicity, and possible biomarkers of toxin exposure. This approach will be specifically illustrated in reference to examples of both previously established toxins, and possibly emerging/novel toxins identified through this strategy.
Computational Study of alkene reduction using Old Yellow Enzyme
Sunidhi Lenka, M. Pilar Buteler, Robert W. Powell, III, Jon D. Stewart, Adrian E. Roitberg
University of Florida
Old Yellow Enzymes (OYE) are a class of enzymes known for reduction of electron deficient alkenes with high stereoselectivity, leading to generation of synthetic intermediates for flurbiprofen (non-steroidal anti-inflammatory drugs) and pregabalin etc. The potential of OYE to generate chiral centers has led to various protein engineering approaches to obtain high yield of stereoselective products.
The present research focuses on OYE 1 and OYE 3, which are different homologs of the old yellow enzymes having high sequence identity. Previous experimental studies of OYE 1 indicated a change in stereoselectivity of product, by mutation of Trp 116 for substrate (S)- carvone and (R)- carvone. Further studies showed that OYE 3 produced different enantiomeric excess products for some substrates compared to OYE 1. Comparing the active site of both proteins, the only difference was found at position 296, with Phe for OYE 1 and Ser for OYE 3. This residue is present in loop 6 (289-309) which plays a significant role in reactant accommodation. Hence, studying the dynamic properties of this loop and its effect on stereoselectivities would provide a deeper perspective of the enzyme properties.
Molecular dynamics simulations using the AMBER GPU suite has been used to rationalize the difference in stereoselectivities and develop specific protein engineering methodology to generate products. The system has been studied along a specific reaction coordinate using umbrella sampling, in order to sample different binding orientations of the substrate. It has been found that, loop 6 is much more flexible and solvent exposed for OYE 3 than OYE 1. Hence, it provides more freedom for the substrate to orient in the active site. The results from our group are consistent with the experimental data leading us to further investigate the catalytic properties of the active site.
Membrane-Active Hydantoin Derivatives as Antibiotic Agents
Ma Su, Donglin Xia, Peng Teng,Alekhya Nimmagadda, Chao Zhang,Timothy Odom,
Annie Cao,Yong Hu, and Jianfeng Cai
University of South Florida
Hydantoin (imidazolidinedione) derivatives such as nitrofurantoin are small molecules that have aroused considerable interest recently due to
their low rate of bacterial resistance. However, their moderate antimicrobial activity may hamper their application combating antibiotic resistance in the long run. Herein, we report the design of bacterial membrane-active hydantoin derivatives, from which we identified compounds that show much more potent antimicrobial activity than nitrofurantoin against a panel of clinically relevant Gram-positive and Gram-negative bacterial strains. These compounds are able to act on bacterial membranes, analogous to natural host-defense peptides. Additionally, these hydantoin compounds not only kill bacterial pathogens rapidly but also prevent the development of methicillin resistant Staphylococcus aureus (MRSA) bacterial resistance under the tested conditions. More intriguingly, the lead compound exhibited in vivo efficacy that is much superior to vancomycin by eradicating bacteria and suppressing inflammation caused by MRSA-induced pneumonia in a rat model, demonstrating its promising therapeutic potential.
Iodine catalyzed diazo activation to access radical reactivity
Chiyu Wei, Pan Li, Xiaodong Shi*
Univerisity of South Florida
An unprecedented iodine catalyzed diazo activation is disclosed herein under either photo- or thermal-initiated conditions. The mechanistic studies revealed the formation of an iodo-substituted alkyl radical as the key intermediate, which represents a novel approach to enable diazo radical reactivity. This metal-free diazo-activation strategy was successfully applied to olefin cyclopropanation with excellent yields. A further extension to substituted pyrrole synthesis under thermal-initiated conditions demonstrates the unique reactivity using this method over typical metal-catalyzed conditions.
Organic Acid and Carbonyl Formation from γ-Ketohydroperoxide Decomposition in n-Butane Oxidation
Denisia M. Popolan-Vaida,[a],[b] Arkke J. Eskola,[c] Brandon Rotavera,[c] Jessica F. Lockyear,[b] Zhandong Wang,[d] S. Mani Sarathy,[d] Arnas Lucassen,[c] Kai Moshammer,[c] Philippe Dagaut,[e] Nils Hansen,[c] Stephen R. Leone,[b] and Craig A. Taatjes[c]
[a] Department of Chemistry, University of Central Florida, Orlando, Florida 32816, USA
[b] Department of Chemistry, University of California, Berkeley, and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
[c] Combustion Research Facility, Sandia National Laboratories, Livermore, California 94551 USA
[d] King Abdullah University of Science and Technology, Clean Combustion Research Center, Thuwal 23955-6900, Saudi Arabia
[e] Centre National de la Recherche Scientifique, INSIS, 45071 Orléans Cedex 2, France
Autoignition of hydrocarbon-air mixtures plays a crucial role in the development of new low-emission, high efficiency engine technologies and relies on chain-branching reactions. A key chain-branching step in autoignition is the decomposition of ketohydroperoxides to form an oxy radical and OH. Other pathways compete with chain-branching, such as “Korcek” dissociation of γ-ketohydroperoxide to a carbonyl and an acid. A high temperature (500-1100 K) jet-stirred reactor in conjunction with a high-resolution tunable synchrotron photoionization time-of-flight mass spectrometer offers a unique experimental approach to monitor chemical transformations of key intermediates in well-defined conditions comparable to those in combustion engines. This experimental arrangement was used to reveal new insights into the mechanism of n-butane low temperature oxidation reaction. In addition to corroborating the observations of the ketohydroperoxide species in the oxidation of butane, the use of partially deuterated butane provides evidence for the Korcek mechanism of decomposition of the intermediate ketohydroperoxide species into acid, ketone and aldehyde pairs, through the observation of the partially deuterated acetone and formic acid Korcek pair. It was found that the Korcek decomposition mechanism of γ-ketohydroperoxide is a substantial fraction of the organic acid production, but it is unlikely to be a significant perturbation on the autoignition process. The results provide experimental bounds that enable the construction of more realistic and accurate kinetic mechanisms for autoignition chemistry.
Structural characterization of the Rous Sarcoma Virus capsid protein in its tubular assembly and simulations of the self-assemblies of the HIV capsid protein
Jaekyun Jeon, Ivan Hung, Alok K. Mitra, Ambroise Desfosses, Xin Qiao, Daniel Huang, Peter L. Gor’kov, Rebecca C. Craven, Richard L. Kingston, Zhehong Gan, Fangqiang Zhu, and Bo Chen
Department of Physics, University of Central Florida
The capsid proteins (CAs) of ortho-retroviruses share a common tertiary fold but form distinct capsids. They are promising antiviral drug targets and templates for versatile nano-assemblies. However, they are tough to characterize due to the strong polymorphism. In this work, solid state NMR was applied to characterize the CA tubular assembly of Rous sarcoma (RSV), a prototype of retrovirus. A novel resonance assignment strategy was developed that exploits the well-resolved NCACX spectra to facilitate the assignment of congested NCOCX spectra, which led to a nearly complete assignment (234 residue out of the 237-residue protein). Based on this, site-specific dynamics and secondary structural information were determined. Combining with constraints from cryo-EM, we established an atomic resolution model of the tubular assembly by molecular dynamics flexible fitting. Our model shows that significant structural rearrangements take place at flexible loops and the 310 helix regions, while the rest of the protein retains its structure upon assembly. The analyses of our model suggests the assembly polymorphism is attributed to the disorder of the trimer interface between C-terminal domains. In addition, the different contact angles between helices at assembly interfaces of tubular and planar assemblies for HIV and RSV CA. Based on simulations of our novel coarse grain model, it suggests the two systems undergo different assembly pathways.