Structural and functional characterization of the colibactin resistance gene clbS
Prabhanshu Tripathi, Steven D. Bruner
Department of Chemistry, University of Florida, Gainesville, FL 32611, USA
Colibactin is an uncharacterized secondary metabolite produced by certain strains of E. coli present in the human gut. It induces double-stranded DNA breaks in eukaryotic cells promoting colorectal cancer and tumor formation under host inflammatory conditions. The colibactin biosynthetic pathway has been studied extensively by various groups since its discovery nearly a decade ago. The biosynthetic gene cluster consists of several NRPS, PKS, hybrid NRPS/PKS genes, a transporter and a resistance gene. The biosynthesis involves a prodrug-like resistance strategy where the inactive genotoxin is transported to the periplasm, cleaved and processed to the active form. Two genes clbM and clbQ from this pks island have already been structurally characterized in our laboratory. The ClbM structure was recently solved and was identified as a colibactin MATE transporter. Here, we report the X-ray structure of the colibactin resistance gene clbS, whose gene product protects the host bacteria from the genotoxic effects of colibactin. The structure was solved to 2.0 Å and reveals ClbS as a DNA-binding protein.
Gold Nanoparticle-Based, Paper Devices for Rapid and Sensitive Colorimetric and Electrochemical Biosensing
Pingping Liang, Bhargav Guntupalli, Haixiang Yu and Yi Xiao*
Department of Chemistry and Biochemistry, Florida International University, 11200 SW 8th Street, Miami, FL, 33199. *Corresponding author: firstname.lastname@example.org
Paper-based devices are an attractive option for colorimetric and electrochemical detection of small-molecule targets onsite for a number of reasons: (1) they are low-cost, lightweight, portable, disposable and user-friendly; (2) they can be manufactured with excellent reproducibility; (3) they require smaller volumes of sample and reagents. We have developed a paper-based device that consists of mixed cellulose ester paper supporting a wax-encircled, gold nanoparticle (AuNP)-coated film atop a cotton absorbent layer, sandwiched between two plastic cover layers. This paper-based device makes it possible to monitor NAD+-driven biochemical processes in the presence or absence of selective dehydrogenase inhibitors, with a readout that can be interpreted by naked-eye observation within 4 min in a 25 µL sample volume. In parallel, we have established an ambient filtration method that provides a simple and novel way to rapidly generate porous thin gold films (thickness ~40 nm) atop a layer of carbon nanotubes (CNTs) on paper for use as disposable electrodes, without the need for sophisticated instruments, clean-room environments, or any post-growth process. We have used these paper-based electrodes to achieve specific and simultaneous detection of dopamine and serotonin. Clearly, these hybrid films exhibit fast electron transfer and excellent electrocatalytic properties that are similar to purchased gold films, but with a larger electroactive surface that lends itself to more sensitive analyte detection.
Simulations of gas sorption in rht-MOF-9
Douglas Franz, Tony Pham, Katherine Forrest, Zac Dyott, Brian Space
University of South Florida, Dept. of Chemistry
Metal-organic frameworks are highly porous crystalline materials well-suited for computer simulation (primarily because of periodicity of structure). Grand-canonical (constant μ,V,T) Monte Carlo (a method mostly known for random perturbations which are accepted or rejected by a Boltzmann probability) simulations of hydrogen (77 and 87K), carbon dioxide, methane, acetylene, ethylene, and ethane gas (298K) sorption in rht-MOF-9 were performed using Massively Parallel Monte Carlo (MPMC), a statistical-mechanical molecular simulation code developed by our lab. Gas uptake (storage) isotherms and Qst (heat of adsorption) were calculated, and efforts were made to discover the primary binding-sites of the gases via radial distribution calculations and simulated annealing. rht-MOF-9 is a copper based MOF with 3 distinct cages. Theoretical results were compared to experimental data.
MANIPULATION OF ELECTRON TRANSFER RATES IN MOLECULES WITH SHORT MID INFRARED PULSES
Igor V. Rubtsov
Department of Chemistry, Tulane University, New Orleans LA 70118, USA
It was recently proposed theoretically by D. Beratan and co-workers that electron transfer rate in donor-bridge-acceptor molecules can be changed by manipulating interferences of inelastic pathways through the bridge. Experimental attempts to accomplishing this goal by exciting vibrational modes at the bridge with a mid-IR radiation are discussed. Several molecular systems were interrogated featuring bridges of different types, including hydrogen bonded bridges and bridges involving coordination bonds. The results show that vibrational excitation may increase or reduce the rate of electron transfer. It is demonstrated that vibrational excitation of the bridge modes could reduce the electron transfer rate while heat accelerates it.
Sex determination of human remains using LAMP amplified Amelogenin gene and a deoxyribozyme sensor
Alexandra L. Smith
Dmitry M. Kolpashchikov
University of Central Florida
Sex identification of unknown remains is crucial to personal identification of human remains in anthropology and forensics. When conventional methods, such as metric or morphological analyses, are not an option due to the fragmented or prepubescent remains, molecular diagnostics are needed. The amelogenin gene, found on sex (X and Y) chromosomes, is the most common molecular marker used for sex determination because it exhibits sexual dimorphism in size and sequence. We develop a new method for fluorescent analysis of amelogenin gene for sex identification. In this assay, human DNA is amplified during a period of 15 min to 30 min by isothermal loop mediated amplification (LAMP) followed by analysis by binary deoxyribozyme sensors (BiDZ) for 60 min. High selectivity of the amelogenin sequences of X and Y chromosome was demonstrated. The assay promises to simplify molecular-based sex determination of human remains.
Conformation plasticity of the N-terminal intrinsically disordered region of ChiZ memrbane protein
Cristian A. Escobar1,2 and Timothy A. Cross1,2
1 Institute of Molecular Biophysics, Florida State University, Tallahassee, FL, USA
2 National High Magnetic Field Laboratory, Tallahassee, FL, USA
ChiZ is a transmembrane protein from Mycobacterium tuberculosis involved in cell division regulation. It was proposed that the N-terminal cytoplasmic domain is essential for cellular activity even though it is intrinsically disordered. Using solution NMR, it was possible to identify two regions in the N-terminal domain with different dynamics, amide proton exchange rates and tendencies to form compact structure. Interestingly, one of these regions is conserved, which suggests these differences are important for function. To assess the relevance of these differences, the N-terminal domain was studied in the presence of liposomes and in the full length protein using a combination of solution and solid state NMR. The N-terminal domain is able to bind liposomes, but it remains highly dynamic, even in the reconstituted full length protein. Paramagnetic relaxation enhancement experiments showed that the N-terminal domain interaction with lipids is mediated by electrostatic interactions between arginine side chains and lipid head groups. However, the conserved region has a lower tendency to interact with lipids. This data suggests that the loose binding of the N-terminal region to lipids may facilitate the sampling of conformations that may be required for function. Speculation as to this function in the cytoplasm will be presented.
Nucloephile assisted activation of diazonium salt for gold oxidation chemistry
S. Hosseyni, X. Shi,
University of South Floirda
The discovery of photo-assisted diazonium activation toward gold(I) oxidation greatly extended the scope of gold redox catalysis by avoiding the use of strong oxidant. Some practical issues that limit the applications of this new type of chemistry are the relative low efficiency (long reaction time and low conversion) and the strict reaction conditions control (degassing and inert reaction environment). An alternative, photo-free condition is developed through Lewis base activated diazonium activation. With this method, simple PPh3AuCl catalyst was used with the combination of NaHCO3 and diazonium salts to produce gold(III) intermediate. Effective activations of various substrates, including alkyne, alkene and allene have been achieved followed by gold(III) reductive elimination, giving the C-C bond coupling products with good to excellent yields
Reversible-covalent hydrogels linked by photosensitive coumarin dimers
Christopher P. Kabb1, Christopher S. O'Bryan2, W. Gregory Sawyer2, Thomas E. Angelini2, Brent S. Sumerlin1
1. George & Josephine Butler Polymer Research Laboratory, Center for Macromolecular Science & Engineering, Department of Chemistry, University of Florida
2. Department of Mechanical and Aerospace Engineering, University of Florida
Coumarin derivatives undergo a [2+2] cyclization upon exposure to long-wave UV irradiation (365 nm). This process can be reversed using short-wave UV light (254 nm) to revert the dimers to their monomeric form. Therefore, networks crosslinked by coumarin groups are an ideal candidate as reversible-covalent gels. In this work, copolymerization of coumarin-containing monomers with a hydrophilic comonomer resulted in water soluble, linear polymers. These “prepolymers” were irradiated with long-wave UV in the absence of a photoinitiator to yield free-standing hydrogels. Importantly, the gels were reverted back to soluble copolymers upon short-wave UV irradiation. This material provides an opportunity for preparing patterned hydrogels through a 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 3D soft matter printing methodology. We have printed cylinders in which the interior coumarin gel is surrounded by a nondegradable gel, and upon exposure of these cylinders to short-wave UV irradiation, the coumarin gel is reverted to soluble prepolymers and washed away to yield a thin, hollow hydrogel tube.
Quantum Thermodynamics by Repeated Measurement
David M. Rogers
Univ. South Florida
Modeling and understanding quantum heat engines and photochemical energy harvesting processes requires an extension of traditional thermodynamical models. They are challenging both because net flows of energy are only possible out of equilibrium and also because quantum systems do not stay diagonal under these conditions. This talk derives a consistent thermodynamics for quantum nonequilibrium processes when repeated measurement of some part of the system is possible. Its limit under a slow rate of measurement results in well-understood weak-coupling expressions for energy and entropy. Using the example of a molecular dipole emitting light into an empty room, we show that under fast measurement, the emission process displays damped oscillatory behavior. Moreover, full measurement of the emitted light leads to a non-Boltzmann steady-state for the dipole.
THIENYL-PYRIDYL BASED FUNCTIONAL OLIGOMERS: DESIGN, SYNTHESIS, AND POTENTIAL APPLICATIONS AS SENSORS
Lei Li,1 Asmerom O. Weldeab,1 Seda Cekli,1 Kirk S. Schanze,1,2 and Ronald K. Castellano1
1 Department of Chemistry, University of Florida, P.O. Box 117200, Gainesville, FL 32611-7200, USA
2 Department of Chemistry, University of Texas at San Antonio, One UTSA Way, San Antonio, TX 78249, USA
Owing to their outstanding electronic and optical properties, π-conjugated oligomers containing the thienyl-pyridyl unit are promising candidates for optoelectronic applications. Reported here is the first chemical and photophysical evaluation of this unit in the context of extended Donor-Acceptor-Donor (D-A-D) π-conjugated oligomers. Two families with different internal electron acceptor structures (either isoindigo or diketopyrrolopyrrole) have been designed and synthesized, each featuring pyridine linked in its 4-position at the termini. The consequences of pyridyl protonation (i.e., the addition of trifluoroacetic acid) and metalation (i.e., the addition of Pd2+/Cu2+) on photophysical properties have been evaluated by UV-Vis and fluorescence spectroscopy using both the D-A-D oligomers and simplified model compounds. Additionally, 1H NMR studies have been carried out to assign the protonation and metalation positions.
Next-Generation Oil Dispersants from Hollow Amphiphilic Nanocapsules
a) George & Josephine Butler Polymer Research Laboratory, Center for Macromolecular Science & Engineering, Department of Chemistry, University of Florida, Gainesville, FL, USA
b) Tulane University, Chemistry Department, New Orleans, LA, USA. E
Hollow amphiphilic crosslinked nanocapsules were synthesized by sequential grafting-from of crosslinked hydrophobic polycaprolactone (PCL) via ring-opening polymerization and grafting-to of hydrophilic poly(ethylene glycol) (PEG) onto 70 nm silica nanoparticles, followed by removal of the silica core. To accomplish the crosslinking of the PCL layer a bis-caprolactone monomer was used. The effects on the brush properties of PCL grafted silica nanoparticles with crosslinker were investigated. Incorporation of only 0.25 mol% crosslinker in the bulk grafting reaction resulted in dramatic effects, such as significantly enhanced brush length and high chain molecular weight dispersities. Hollow PCL nanocapsules were synthesized by performing the grafting reaciton of PCL with 2.5 mol% crosslinker under dilute conditions. Upon removal of the silica core, a significant increase in hydrodynamic radius was observed due to the relief of constrain of surface tethered chain ends and swelling in a good solvent. PEG was then coupled to particles grafted with crosslinked PCL to yield amphiphilic block polymer grafted silica nanoparticles, which displayed excellent dispersibility in water, and resulted in a contraction of the PCL layer, as determined by dynamic light scattering. Core removal of the amphiphilic block polymer grafted silica nanoparticles gave hollow amphiphilic crosslinked nanocapsules which displayed significant swelling in good, non-selective solvent conditions, and a collapsed hydrophobic core block in aqueous conditions. Finally, the amphiphilic materials, both before and after core removal, were determined to be effective at stabilizing hydrocarbons in water, with the hollow nanocapsules having ca. 15 times greater uptake capacity.
A Distributive ATP Grasp Ligase Macrolactonizes Multiple Microviridin Core Peptides within a Single Substrate
Yi Zhang,1 Kunhua Li,2 Guang Yang,1 Joshua L McBride,1 Steven D Bruner2 and Yousong Ding1
1Department of Medicinal Chemistry, Center for Natural Products, Drug Discovery and Development, College of Pharmacy, University of Florida, Gainesville, Florida, 32610, USA.
2Department of Chemistry, University of Florida, Gainesville, Florida, 32611, USA.
Microviridins are a distinct type of ribosomally synthesized and post-translationally modified peptides (RiPPs) with a cage-like architecture and are potent inhibitors of therapeutically-relevant serine proteases. Their biosynthesis requires the sequential installation of two ester and one amide linkages by two ATP grasp ligases. Functionally diverse enzymes contribute to astonishing chemical and functional richness of RiPPs and therefore offer opportunities to produce new analogs and to discover new enzymology. Of particular, enzymes that process multiple core peptides within a single precursor peptide are invaluable to investigate the combination of enzyme specificity and promiscuity. However, such enzymes have been known only in one example. Here we report in vitro characterization of an ATP grasp ligase AMdnC in a silent microviridin pathway of Anabaena sp. PCC7120, whose precursor peptide AMdnA contains three core peptides. AMdnC catalyzed an unprecedented multi-site macrolactonization on AMdnA. Its catalysis occurred in a distributive fashion and followed an unstrict N-to-C overall directionality. Furthermore, AMdnC processed engineered precursor peptides with one to four core peptides. Collectively, these results disclose the second example of enzyme with novel catalytic properties in processing multiple core peptides and suggest that highly organized synthetic biology modules exist in nature.
The dock-and-coalesce mechanism for the association of a WASP disordered region with the Cdc42 GTPase
Li Ou, Megan Matthews, Xiaodong Pang, and Huan-Xiang Zhou
Department of Physics and Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA
Intrinsically disordered proteins (IDPs) play key roles in signaling and regulation. Many IDPs undergo folding upon binding to their targets. We have proposed that coupled folding and binding of IDPs generally follow a dock-and-coalesce mechanism, whereby a segment of the IDP, through diffusion, docks to its cognate subsite and, subsequently, the remaining segments coalesce around their subsites. Here, by a combination of experiment and computation, we determined the precise form of dock-and-coalesce operating in the association between the intrinsically disordered GTPase binding domain (GBD) of the Wiskott-Aldrich Syndrome protein (WASP) and the Cdc42 GTPase. The association rate constants (ka) were measured by stopped-flow fluorescence under various solvent conditions. ka reached 107 M-1s-1 at physiological ionic strength and had a strong salt dependence, suggesting that an electrostatically enhanced, diffusion-controlled docking step may be rate-limiting. Our computation, based on the transient-complex theory, identified the N-terminal basic region of the GBD as the docking segment. However, several other changes in solvent conditions provided strong evidence that the coalescing step also contributed to determining the magnitude of ka. Addition of glucose and TFE and an increase in temperature all produced ka values much higher than expected from the effects on the docking rate alone. Conversely, addition of urea led to ka values much lower than expected if only the docking rate was affected. These results all pointed to ka being approximately two thirds of the docking rate constant under physiological solvent conditions. The dock-and-coalesce mechanism allows WASP and other IDPs to code electrostatic complementarity into the docking segment to gain binding speed and use additional interactions formed by the coalescing segments to reinforce binding affinity.
U-Turn Electron Transfer: A New Strategy to Control Photo-triggered Energy Conversion Reactions of Coordination Compounds
Nicholas F. Polizzi, Ting Jiang, David N. Beratan, and Michael J. Therien
Department of Chemistry, French Family Science Center, 124 Science Drive, Duke University, Durham, North Carolina 27708, USA
Efficient energy conversion requires quantitative, light-driven formation of high-energy, charge-separated states. Conventional artificial photosystem designs seek to promote electron transfer (ET) by polarizing excited donor electron density toward the acceptor (“one-way” ET). Enigmatically, the excited donor of the archetypal R. sphaeroides reaction center polarizes its electron density away from its electron acceptor: light absorption by the reaction center thus triggers a “U-turn” ET event. Whatever mechanistic importance lies behind this biological U-turn ET has been obscured by the inability to experimentally reverse donor excited-state polarization within the reaction center. We describe how U-turn ET produces a strikingly larger yield of high-energy photo-products compared to a conventional one-way ET scheme, by minimizing intersystem crossing to the donor triplet state. We directly compare one-way vs. U-turn ET strategies via linked donor-acceptor (DA) assemblies based on highly conjugated (porphinato)metal-(polypyridyl)metal constructs, in which selective optical excitation produces donor excited states polarized either toward or away from the acceptor. Ultrafast spectroscopic studies of these DA assemblies pinpoint the importance of realizing donor singlet and triplet excited states that have opposite electronic polarizations to shut down intersystem crossing, a scheme exploited by the reaction center of R. sphaeroides. These results offer an unexpected U-turn design principle, heralded by Nature, that averts intersystem crossing and dramatically increases the yield of high-energy photo-products critical for light-driven energy conversion reactions.
Calculating Optical Properties of Plasmonic Crystals for Applications in Spectroscopy and Sensing
Alec Bigness1, Alfred J. Baca2, and Jason M. Montgomery1
1. Department of Chemistry, Florida Southern College, Lakeland, FL 33801, USA
2. US NAVY NAVAIR-NAWCWD, Research and Intelligence Department, Chemistry Branch, China Lake CA 93555, USA
Plasmonic crystals are periodic arrays of metallic nanostructures that support surface plasmons, or collective oscillations of conducting electrons at the interface between a metal and a dielectric. Surface plasmons can exhibit unique optical properties, such as enhanced absorption, scattering and field confinement of light at the resonance frequency. This so called surface plasmon resonance (SPR) is sensitive to the size, shape, and dielectric environment of a plasmonic crystal and is therefore tunable for particular applications. Such properties make plasmonic crystals attractive for spectroscopy based sensing applications. Here we present a survey of work that involves two types of plasmonic crystals composed of metal coated, square arrays of either nanowell or nanopost structures formed via soft nanoimprinting as Surface Enhanced Raman Scattering (SERS) substrates and refractive index sensors. Such crystals can exhibit SERS enhancement factors of 105 to 106 over large areas and with sufficiently high levels of uniformity for precise two-dimensional Raman mapping of surface bound monolayers. Three-dimensional finite-difference time-domain (3D FDTD) simulations qualitatively capture the key features of these systems and suggests a route to the fabrication of optimized, highly efficient SERS substrates or refractive index sensors in silco. Collectively, the ease of fabrication together with the high sensitivities and spatial resolution that can be achieved suggests an attractive route to the design and optimization SERS substrates and sensors for portable chemical warfare agent detection, environmental monitors, noninvasive imaging of biomolecules, and other applications.
Design principles for crystalline polymers: packing, polymerization mechanism and applications to energy conversion
Jose L. Mendoza-Cortes
†Department of Chemical & Biomedical Engineering, FAMU-FSU College of Engineering and
‡Scientific Computing Department, Materials Science and Engineering Program, High Performance Material Institute, Condensed Matter Theory-National High Magnetic Field Laboratory, Florida State University, Tallahassee Florida 32310, United States
Computational chemistry and materials science algorithms are now powerful enough that they can predict many properties of materials and molecules before they are synthesized. This new tool has allow us to start designing crystalline polymers. In the first part of the talk, I will discuss some principles we have been using to design the packing of crystalline polymers, then we will discuss the polymerization mechanism of a classic polymeric reaction and finally, we will discuss the application of several of these new materials to energy storage (hydrogen storage) and energy conversion (thermoelectrics).
Gold Redox Catalysis through Base Initiated Diazonium Decomposition toward Alkene, Alkyne, Allene and Cyclopropanol Activation
Boliang Dong, Haihui Peng, Seyedmorteza Hosseyni, Stephen E. Motika, Abiola A. Jimoh and Xiaodong Shi*
University of South Florida
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 had been developed through Lewis base induced diazonium activation. With this method, a unreactive Au(I) catalyst was used in combination with Na2CO3 and diazonium salts to produce a Au(III) intermediate. The efficient activation of various substrates, including alkyne, alkene, allene and cyclopropanol were achieved, followed by rapid Au(III) reductive elimination, which yielded the C-C bond coupling products with good to excellent yields. Relative to the previously reported photo-activation method, our approach offered a higher efficiency through faster reaction rates and provided significantly broader reaction scope.
INTERPLAY OF HYDROGEN BONDING AND ELECTRONIC STRUCTURE ON THE OPTOELECTRONIC PROPERTIES OF GUANINE-TERMINATED OLIGOMERS
Danielle E. Fagnani,1 Dylan E. Holst,1 Daken J. Starkenburg,2 Jiangeng Xue,2 and Ronald K. Castellano1
1 Department of Chemistry, University of Florida, P.O. Box 117200, Gainesville FL 32611-7200, USA
2 Department of Materials Science and Engineering, University of Florida, P.O. Box 116400, Gainesville, FL 32611-6400, USA
Semiconducting, π-conjugated organic molecules are attractive for many modern optoelectronic applications. While the relationship between molecular structure and intrinsic optical and electronic properties is well understood, the effect of supramolecular packing on solid-state properties in thin films, and consequences on performance in applied settings, has yet to be rigorously established. We are currently using a hierarchical self-assembly approach to investigate this relationship; nanoscale to mesoscale order in thin films can be achieved by equipping conventional π-systems with robust hydrogen bonding units. In this particular work, we are constructing a set of linear π-conjugated oligomers covalently linked to guanine (G), one of the DNA nucleobases, or a protected guanine (PG) comparator at each terminus. Guanine is known to form tetramers (known as the “G-quartet” in biology) that have the ability to template highly ordered 2-D π-conjugated frameworks in thin films and further encourage 3-D order via π-π stacking; these capabilities are weakened for PG derivatives. The goal of this work is to understand how the molecular recognition capabilities of these guanine-containing π-conjugated oligomers (via hydrogen-bonding) manifest in the solid-state thin films and may systematically affect the bulk properties of π-conjugated materials in diagnostic devices.
A Comprehensive Analytical Approach for Characterizing the Impacts of Climate Change on Carbon Sequestration in Peatlands
Bill Cooper#, Suzanne Hodgkins#, Rachel Wilson*, Kelsey Rogers*, Jeff Chanton*
#Department of Chemistry & Biochemistry, Florida State University
*Department of Earth, Ocean and Atmospheric Science, Florida State University
Peatlands represent the largest stores of sequestered carbon on earth. The majority of global peatlands are found in boreal regions, where low temperatures and saturated soils preserve organic matter. Nonetheless, peat deposits exist at subtropical and tropical latitudes, where much warmer temperatures would be expected to promote rapid decomposition and thus inhibit peat accumulation. Mechanisms that protect natural organic matter (NOM) from microbial decomposition and release to the atmosphere as carbon dioxide and methane are not well understood, particularly the relationships between NOM composition and microbial enzyme expression. Of particular concern is how these mechanisms will be altered as global warming proceeds. In this presentation we will summarize results of comprehensive analytical characterization of NOM in peatlands across a hemispheric latitudinal gradient ranging from sub-arctic Sweden to tropical Borneo. Characteristics of solid phase organic matter (SOM) were identified by Fourier transform infrared spectroscopy (FTIR) and solid state 13C NMR (SS-NMR), while dissolved organic matter (DOM) in soil porewaters was characterized by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) and excitation-emission matrix spectroscopy coupled with parallel factor analysis (EEM-PARAFAC). Results to date suggest strong correlations between preservation of NOM and its composition, as well as the microbial enzymes being expressed. These data further indicate that remineralization of peatland NOM to CO2 and CH4 may be more complicated than originally thought.
TRIIRON CLUSTERS CONTAINING MIXED BRIDGING LIGANDS FOR THE STUDY OF DINITROGEN REDUCTION
Ricardo B. Ferreira and Leslie J. Murray
Center for Catalysis, Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200, United States
Biological systems employ polynuclear clusters for the biological activation of small molecule substrates in a way to promote multi-electron redox reactions. For instance, biological N2 fixation is a process that involves a six-electron reduction and it is catalyzed by a family of metalloenzymes called nitrogenases. The most abundant nitrogenase is the molybdenum-dependent nitrogenase found in diazotrophs that contains the iron-molybdenum cofactor (FeMoco) in its active site – a cluster composed of seven Fe and one Mo atoms bound through bridging sulfides. There are evidences for the presence of hydride bridges in the FeMoco during the N2 reduction and such ligands are believed to act as sites for storage of electron and proton equivalents, having an essential role in the N2-binding and reduction. For these reasons, we are investigating the synthesis and reactivity of bromide- and sulfide-bridged triiron clusters and specifically, that of mixed sulfide-hydride systems. In this work, we will discuss our ongoing efforts to synthesize and examine the reactivity of such clusters.
Carmen Gauthier1 and Michael Mury2
1. Florida Southern College, Lakeland, FL 33801
2. All Saints Academy, Winter Haven, FL 33800
In this session we will review the topics that will be discussed during the Chemical Education sessions here at FAME. We will discuss our hopes for building the chemical education community in Florida through integration and collaboration between secondary and post-secondary faculty.
Direct Patching Exchange-Correlation Potential in Density Functional Theory
Department of Scientific Computing, Florida State University
To obtain accurate electronic structures in large systems, we need to scale up high-level electronic structure calculations. Kohn-Sham density functional theory (DFT) is exact with the exact exchange-correlation (XC) potential. We developed a simple, yet effective method to direct construct accurate XC potentials in a system. The method consists of two steps: (a) the system partitioning and (b) the XC potential patching. We developed two schemes to partition the system: (1) partition the system’s density and (2) partition the system’s density matrix. Once the partitioning is finished, an embedded cluster is defined and its XC potential can be computed by inverting its electron density with advanced, orbital-based XC functionals, or correlated-wave function methods. The cluster’s XC potential is projected to its central atom, and the system’s XC potential is obtained by patching it atom by atom. We demonstrate the performance of this exchange-correlation potential patching (XCPP) method of patching the potential of a fully nonlocal XC functional: the exact-exchange (EX) and the correlation based on the random phase approximation (RPA). XCPP-RPA is applied to two one-dimensional systems: a H20 chain and a H10Li8 chain. In both tests, XCPP-RPA results converge to the benchmark as we increase the cluster sizes. We observed an effective error cancellation between the patched EX and RPA energies when the density partitioning is employed. The patched EX+RPA potentials agree well with the benchmarks. This work serves the first step toward self-consistent RPA simulations of large systems within the framework of XCPP.
Induced chirality of phenylene-based conjugated polymers complexed with polysaccharides
Prakash Manandhar, Tereza Vokata, and Joong Ho Moon
Department of Chemistry & Biochemistry, Biomolecular Sciences Institute, Florida International University, 11200 SW 8th St., Miami, Florida 33199, United States
Understanding the structure-function relationship of conjugated polymers (CPs) interacting with various biologically active materials is pivotal for designing functional materials for biological sensing, labeling, and delivery. The physical and biophysical properties of functional materials are closely related to the functional groups of CPs and natures of self-assembly in an aqueous environment. In this presentation, we report substantial self-assembly differences of a set of four CPs containing the same positively charged side chains, which only different in the backbone chemical structure and connectivity, upon complexation with linear polyanion, glycosaminoglycan (GAG). Electronic spectroscopic data including induced circular dichroism (ICD) reveal that CP/GAG form unique helixes depending on the nature of backbone and the type of GAG. The structure-property relationships can be useful for fabrication of highly ordered macromolecular materials for broad electronic or biological applications.
DEVELOPMENT AND APPLICATION OF VARIOUS KNOEVENAGEL α,γ-DIFUNCTIONALIZATION METHODOLOGIES
Primali V. Navaratne , Alexander J. Grenning
Department of Chemistry, University of Florida, Gainesville FL32611-7200
We are investigating, developing and applying Knoevenagel adducts as a platform for multifunctionalization and complex molecular synthesis. Initial results revealed that Knoevenagel adducts can act as trimethylenemethane (TMM) dipole surrogates where intermolecular α,γ-difunctionalization is possible. Along with that, a route to 1-aryl tetralin lignans by Knoevenagel adducts via deconjugative α-alkylation/intramolecular 6-endo-trig Heck cyclization was developed. This demonstrated the intramolecular version of α,γ-difunctionalization of Knoevenagel adducts. Recent advancement on α,γ-difunctionalization of Knoevenagel adducts include a simple, tunable synthetic plan to convene an array of galiellactone and analogues, utilizing deconjugative α-alkylation/decarboxylative-Saegusa oxidation methodology.
Strategies for Success in STEM Majors – Implementation and Evaluation of a Pilot Course
Emily C. Heider, Jamil Johnson
University of Central Florida
Demand for a highly-trained STEM workforce is garnering increasingly urgent notice, and national efforts call on the development of talent from all sectors, including underrepresented minorities. According to the National Research Council (NRC) panel, the ingredients for inclusive success in STEM are the “acquisition of knowledge, skills, and habits of mind; opportunities to put these into practice; a developing sense of competence and progress; motivation to be in, a sense of belonging to, or self-identification with the field; and information about stages, requirements, and opportunities.” Addressing these requirements for freshmen STEM majors in a first-year experience course has potential to staunch the outflow of students from STEM fields. Strategies for Success (SLS 1501) is 3-credit elective cours, with the focus on helping students transition to collegiate life. Recently, a pilot section of SLS-1501 was offered exclusively to STEM majors to focus more narrowly on strategies for success in STEM majors and aimed to achieve the goals set by the NRC for inclusive success in STEM. The focus of this research is to evaluate the merit of the course – through analysis of the scientific reasoning exams administered in the course, surveys of the students who completed the course, and through following the progress of the students in their chosen majors over time.