USF Human Donation Program: Experimental Research in Decomposition
Erin H. Kimmerle, Ph.D.
Florida Institute for Forensic Anthropology and Applied Science, University of South Florida
In 2016, USF initiated a human donation program for experimental research in forensic anthropology, outdoor crime scenes, legal medicine, and related forensic sciences. The 3.5-acre Adam Kennedy Memorial Forensic Field, established for outdoor research utilizes donors for research in forensic anthropology, geochemistry, geophysics, biochemistry, ecology, and forensic art. Currently, numerous projects investigating human decomposition, the effects of scavenging, geochemical analysis for human identification, and various methods of remote sensing for locating and documenting clandestine graves are underway. There have been 21 donors and more than 75 pre-donors register. The establishment of this program and the preliminary areas of research will be discussed. More specifically, the research on progressive decomposition to establish baseline rates in Florida shows that the effects of vulture and opossum scavenging on remains plays a significant role in the rate of decomposition, more than any other variable. The scavengers can also cause skeletal fractures and damage that mimics trauma and unexpected alterations to the body and scene.
Deborah Bromfield Lee
Florida Southern College
In this session I will review the topics that will be discussed during the Chemical Education sessions here at FAME. I introduce the breath of talks in this session but also the opportunity for questions and discussion at the end of each talk and especially at the end of the day. I hope this starts discussions of collaborations to strengthens the efforts of chemical educators.
Implementing a Gradual Release of Responsibility teaching model in a large enrollment chemistry course
Nicole Lapeyrouse and Cherie Yestrebsky
University of Central Florida
Collaborative learning has shown to increase students’ participation and attitude towards a given subject area. The following study was designed to increase students’ attitude, engagement, and responsibility in a large enrollment chemistry course by utilizing a modified Gradual Release of Responsibility (GRR) model. GRR progressively transfers responsibility from instructor to the student and allows students to be more independent and help them address atypical problems. This method was implemented by initially placing all of the responsibility on the instructor using focused learning and guided instruction. As the course progressed students gradually shifted from lecture based learning to group work and collaboration, then finally, independent tasks. Students were assessed by the use of clickers to monitor their understanding and engagement, as well as surveys to determine their perception and attitudes on this specific style of teaching. Undergraduate peer mentors were utilized to help guide students throughout the lecture and during group work. This experience also simulated a smaller classroom style by allowing the students to interact with undergraduate teaching assistants (UTAs) to help guide them and clarify any misunderstandings. The ACS cumulative exam was used as a metric to measure the effectiveness of the GRR model compared to previous semesters that utilized a traditional teaching method.
Investigating the use of a mixed-reality teaching simulator to analyze changes in GTA discourse decisions
Erin K. H. Saitta1, DangQuang Nguyen1, Constance M. Doty2, Jacquelyn J. Chini2
(we have two presenting authors and two authors who will not bet presenting)
1University of Central Florida, Department of Chemistry
2University of Central Florida, Department of Physics
National shifts in research-based STEM instruction has led to more departments incorporating active learning into introductory courses and laboratories thereby increasing the frequency with which graduate teaching assistants (GTAs) are expected to implement student-centered instruction. We have incorporated a mixed-reality teaching simulator into GTA professional development to create an immersive environment in which GTAs can practice the skills necessary to facilitate student-centered instruction. This presentation will discuss how the simulator, TeachLivETM, was used to investigate changes in graduate teaching assistant discourse choices while leading a class discussion. Descriptions of the types of data collected and the methodology driving the data analysis will be presented.
Using the Universal Design for Learning framework to design curricula that supports all learners
University of Central Florida
The chemistry education community has focused on student-centered, active learning strategies to develop research-based practices to support student learning. However, some sub-groups of learners have not been fully incorporated in the development of and research on such teaching practices. Universal Design for Learning (UDL) provides a framework for developing flexible teaching strategies and materials that supports learners at all ends of the ability spectrum. This framework provides a set of three guiding principles and thirty-one checkpoints for designing courses to be supportive of, and accessible to, all learners. This presentation will outline how the UDL framework can be used to design and/or modify classroom activities and assessments to improve accessibility. Specifically, multiple means of representation, multiple means of action and expression, and multiple means of engagement. Federal legislation requires equitable access to education for all students. One manner in which we can support individuals with disabilities is by considering the broad range of needs for all learners. By modifying or redesigning existing class activities, we can better address all students' needs.
Catalytic Synthesis of Cyclic Polymers
Zhihui Miao, Weijia Niu, Tomohiro Kubo, Vineet Jhakar, Kyle Vents, Daniel A. Savin, Brent S. Sumerlin, Adam S. Veige
University of Florida
This presentation will include a discussion on aspects of catalysis design for the synthesis of novel cyclic polymers. Four distinct transition metal catalysts that polymerize monomers via ring expansion will be presented. Polymer characterization techniques include SEC, DLS, viscosity, NMR, and preliminary rheology. Conclusions to be drawn from this work are: 1) we are now able to synthesis pure cyclic polymers on a bulk scale efficiently from readily available monomers, and 2) stereoregular cyclic polymers can now be synthesized via ring expansion metathesis polymerization (REMP).
Structural and Functional Versatility of Interferon-Inducible Gtpases
Sayantan Roy, Bing Wang, and Qian Yin
Florida State University
GTP triphosphatases (GTPases) have been meticulously documented for their roles to regulate multiple cellular processes spanning from cell mobility, membrane fusion and fission, to cytokinesis and vesicle transport. Interferon (IFN)-inducible GTPases, consisting of more than forty members in human and mice, are among the most highly expressed interferon stimulated genes (ISGs), sometimes accounting for twenty percent of all proteins induced by IFN-γ. Recent genetic and cell studies start to reveal the important roles of IFN-inducible GTPases in restriction and elimination of pathogens, yet the molecular mechanisms are largely unclear. Using a combination of biochemical, biophysical, and structural tools, we start to understand the functional forms of two IFN-inducible GTPases, GBP2 and IRGM, and the mechanisms governing their activation. We characterized their oligomeric status, enzymatic activity, and their interactions with potential binding partners.
Engineering Polyelectrolyte Complex Micelles with Solid or Liquid Cores
University of Central Florida
Polyelectrolyte complexes form by mixing oppositely charged polymers in solution. The resultant complex phase separates from solution into either irregularly shaped solids (or rather glasses), called precipitates, or micron sized liquid droplets that can coalesce into a distinct phase, called a coacervate. Using oppositely charged polypeptides, one can tune between solid and liquid complexes by manipulating the chirality of the polyelectrolyte. Homochiral complexes form precipitates with hydrogen bonded b-strand structure. In contrast, if one or more polypeptide is composed of both L and D monomers, coacervates are formed with no secondary structure. This inability to form secondary structure is attributed to steric hindrance of the racemic polypeptide impeding hydrogen bond formation. Therefore, since both types of complexes are formed using weak polyelectrolytes, the ability of the homochiral molecules to hydrogen bond causes the difference in phase. Using oppositely charged block-copolyelectrolytes that contain neutral blocks covalently linked to charged blocks allows the phase separation to be stabilized on the nanoscale, creating self-assembled micellar structures in dilute solutions. These polyelectrolyte complexes micelles can be used as drug and gene delivery vehicles for charged therapeutics like nucleic acids and proteins. Using diblock copolypeptides of varying chirality the resulting micellar structure can have both solid and liquid polyelectrolyte cores. This presentation will focus on characterization of polypeptide based polyelectrolyte complex micelles using scattering techniques (light, x-rays, neutrons), circular dichroism, and electron microscopy to reveal structural differences of solid and liquid micellar cores. Insight will be provided as to how differences in solid and liquid cores influence the design of drug delivery vehicles. If time permits, investigations into related micelles with dynamic coronas will be discussed.
Understanding How CRISPR-CAS9 Controls DNA Specificity
Travis Hand1, Anuska Das1, and Hong Li1,2
1Institute of Molecular Biophysics, 2Department of Chemistry and Biochemistry
Cas9 is an RNA-guided DNA cleavage enzyme being actively developed for genome editing and gene regulation. To be cleaved by Cas9, a double stranded DNA, or the protospacer, must be complementary to the Cas9-bound guide RNA and adjacent to a short Cas9-specific element called Protospacer Adjacent Motif (PAM). Understanding the correct juxtaposition in time and space of the protospacer- and PAM-interaction with Cas9 will enable development of versatile and safe Cas9-based technology. We report identification and biochemical characterization of Cas9 from thermophile Acidothermus cellulolyticus (AceCas9). Acidothermus cellulolyticus has been used for producing the enzyme endo-1, 4-β-glucanase (E1) which is used for the commercial hydrolysis of cellulose into glucose. Genome editing in A. cellulylyticus could impact its utilization in bioenergy development. We found that AceCas9 depends strictly on a 5’-NNNCC-3’ PAM and is more efficient in cleaving negative supercoils than relaxed DNA. We further characterized the dependence of AceCas9 on temperature, guide length, divalent metal ions, and mismatches to the guide RNA. The thermostability, cytosine-specific and DNA topology-sensitive properties of the AceCas9 maybe explored for specific genome editing applications.
Initial Results Correlating Atmospheric Composition to Students' Progression Through the Learning Process
Brian Butts, Taylor Duffy, Stephanie Rodriguez, Michael Hampton
Department of Chemistry, University of Central Florida
This presentation will cover the initial results from a study relating changes in atmospheric composition in a lecture hall during class to the progression of students through the learning process. The learning process includes a number of steps that involve various emotions. By definition, emotions cause activation of the autonomic nervous system that, in turn, will cause changes in metabolism. As a result, the concentrations and identities of the volatile compounds emitted by the students should be altered. The composition of the classroom’s atmosphere was determined by placing CO2 and total volatile organic compound (VOC) sensors at the air return vent, and the events occurring throughout the lecture were recorded. Short-term variations in CO2 and VOC concentrations were observed and correlations between those changes and particular events in class have been identified.
Moving Commodity Plastics Forward Utilizing Bio-Cycles
Gabriel N. Short, Haley Donow, Ha T. H. Nguyen, Patricia I. Scheurle, Stephen A. Miller
University of Florida
Society utilized polymers at an ever increasing rate. This increase leads to two problems, source of monomers and ultimate fate of the polymers. With most commodity plastics made from fossil fuels, there is a finite future for these polymers. These petroleum based polymers do not degrade which has led to a build-up in natural environments. Monomers synthesized from biorenewable starting materials are the future. Sources include ferulic acid, citric acid, succinic acid, amino acids, and a range of renewable diols. To increase usable of these biorenewable starting materials, cyclization to form bio-cycles are used in the synthesis to increase glass transition temperature and subsequent range of application. A succinic acid based poly(ethylene terephthalate) mimic has been successfully synthesized with thermal properties above that of some commodity plastics, showing this is a viable future route.
Implementing a Circular Economy Paradigm: Sustainable Introductory Laboratories
Dr. Scott L. Wallen, Laura Wemple, Brent Collins, Troy Kelly and Cole Rittenhouse
Florida Polytechnic University
The design of laboratory experiments in a typical general chemistry laboratory curriculum is not based on sustainable practices, such as using renewable starting materials and reusing any hazardous wastes generated. Using a circular economy paradigm we have designed a laboratory that maintains the pedagogical requirements for engineers and scientists taking introductory chemistry while at the same time integrating experiments where the products/wastes of one experiment are the starting materials for another experiment. This not only reduces costs and waste generated but provides a valuable opportunity to teach aspiring engineers and scientists a sustainable approach in what is often their first laboratory experience. The talk will focus on this concept that won the Campus Safety, Health and Environmental Management Association’s (CSHEMA) Innovation award in 2016. Specific experiments and reuse of materials in nanotechnology laboratory experiments that have been designed considering sustainable practices, green chemistry and based on the circular economy paradigm will be presented.
The Effect of Li+ Binding on Secondary and Tertiary Structure, Hydrophobicity, Thermodynamics, and Interactions with Interacting Partners of DREAM.
Samiol Azam* and Jaroslava Miksovska.
Florida International University, Miami, FL, United States.
Li+ is widely used for the treatment of manic-depressive illness. Studies on neuronal calcium sensor protein 1 (NCS-1) have found that Li+ can inhibit the interaction between NCS-1 and inositol 1,4,5-triphosphate receptor protein, alleviating hyperarousal of insomnia patient. Li+ can have neuroprotective or neurotoxic effects depending on the concentration. In a rat model, chronic exposure of Li+ has shown a significant decrease in membrane-associated protein kinase C (PKC) in the hippocampus, suggesting potential clinical relevance. Here, we show that Li+ binds to a neuronal calcium sensor protein named Downstream Element Antagonist Modulator (DREAM), a protein expressed in the hippocampus region of the brain. Li+ association results in a decrease in the emission intensity of tryptophan, suggesting rearrangements of the tertiary structure of the protein. Li+ binding also exposes hydrophobic cavity of the protein as evidenced by binding of the hydrophobic molecule 1,8-ANS. CD data reveals that Li+ binding increases the rigidity of the protein. Tryptophan emission and CD data are further supported by lifetime data. Thermodynamics parameters of Li+ association to DREAM have been obtained through isothermal titration calorimetry (ITC) measurements. Li+-bound DREAM interactions with binding partners have been obtained by titrating FITC-tagged presenilin-1 and potassium channel against Li+-bound DREAM. Findings of this project suggest potentials for the Li+ compound in the animal model to investigate if acute and chronic exposure of Li+ has any effect on the expression level of DREAM and if Li+-based compounds influence interactions between DREAM and intracellular partners.
The Novel Disaggregase Activity of Protein Disulfide Isomerase
Albert Serrano,1 Michael Taylor,1 Helen Burress,1 Xin Qiao,2 Lucia Cilenti,1 Lauren Farley,1 Jason O. Matos,1 Bo Chen,2 Suren A. Tatulian,2 and Ken Teter1
1 Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, FL 32826, USA
2 Department of Physics, University of Central Florida, Orlando, FL 32816, USA
Protein disulfide isomerase (PDI) exhibits linked but independent functions as an oxidoreductase and chaperone. We have identified a unique property of PDI that is related to its chaperone activity. Using isotope-edited Fourier transform infrared spectroscopy, we have shown that PDI partially unfolds upon contact with the catalytic A1 subunit of cholera toxin, aggregated alpha-synuclein, or aggregated amyloid beta peptide. The substrate-induced unfolding of PDI allows it to act as a disaggregase to break apart the multimeric cholera toxin and to both prevent and reverse amyloid formation at a 1:10 molar ratio of PDI:substrate (alpha-synuclein or amyloid beta peptide). Chaperones that function through conditional disorder and chaperones that function as a disaggregase have been described, but neither property has been attributed to PDI. Furthermore, no disaggregase is known to act by conditional disorder. Our observations thus provide a conceptual advance to understand the chaperone activity of PDI and its neuroprotective function.
Redox-Assisted Self-Assembly of π-Conjugated Chromophores Provides Function-Enhanced Superstructures
Kaixuan Liu, Adam Levy, Chuan Liu, Jean-Hubert Oliver
Department of Chemistry, Cox Science Center, 1301 Memorial Drive, University of Miami, Florida 33124
While nature has mastered the art of engineering non-equilibrium structures that enable energy capture, conversion, and storage with unrivaled efficiency, this level of structural control over synthetic materials with dimensions spanning the nano- to mesoscale remains elusive. Consequently, current technology exploits equilibrium-based strategies to construct organic electronic materials for which molecular interactions and macroscopic organization are neither structurally nor electronically configured for maximum efficiency. Redox-assisted self-assembly of water-soluble perylene diimide will be presented as a new tool to access out-of-equilibrium intermediates through which to navigate the aggregation free energy landscapes and engineer supramolecular assemblies kinetically trapped in local energy minimum. Investigating the electronic properties of these off-equilibrium superstructures using ground-state electronic absorption spectroscopy indicates a 30% enhancement of the exciton bandwidth when compared to equilibrium-constructed architectures. Such modification of nanoscale-object electronic properties exclusively provided by redox-assisted self-assembly originates from a reconfiguration of the superstructure conformation. Examination of the solid-state morphology of assemblies produced through electronically perturbed out-of-equilibrium intermediates reveals complex hierarchical architectures that feature micrometer-long anisotropic domains. To conclude, a preliminary molecular road map to regulate redox-assisted self-assembly will be introduced. The ability to modulate nanoscale-object electronic structure, used in conjunction with facile hierarchical organization offers exceptional promises for the development of optoelectronic materials.
Reductive dechlorination of chlorinated compounds by zero-valent iron with Vitamin B12
Nicole Lapeyrouse, Dr. Greg Booth, Dr. Cherie Yestrebsky
University of Central Florida
During the 1970’s chlorinated organic solvents, such as 1,2-dichlorpropane (DCP), were used heavily as degreasers, paint strippers, chemical intermediates, and soil fumigants. Within the last 30 years, use of these solvents has steadily declined due to their adverse health effects and now are primarily used as chemical intermediates. DCP is classified as a probable human carcinogen and has been shown to cause damage to kidneys, blood cells, liver, respiratory and reproductive systems, and prolonged exposure to high concentrations can lead to death. Due to these hazards and contamination in the environment, DCP has secured a place on the EPA Priority Pollutants List. DCP is a recalcitrant compound and current remediation methods that employ zero-valent iron (ZVI) are unable to remediate it making its elimination urgent and necessary. Researchers at UCF’s Industrial and Environmental Lab have employed a novel method for the remediation of DCP by the utilization ZVI and vitamin B12 as an electron shuttle. Batch reactions were performed in order to determine a kinetic model for this degradation mechanism. In addition, varying concentration of vitamin B12 were tested to determine degradation parameters. Dechlorination byproducts of DCP were confirmed by gas chromatography mass spectrometry (GC-MS) couple to a purge and trap. Experiments were conducted over a 3-week period and more than 95% degradation was observed for DCP. The primary degradation product was propene. Based on these results the proposed mechanism follows a SN2 like reaction with the formation of a cobalt alkyl intermediate yielding the release of a single chloride. In a subsequent step the cobalt complex undergoes an elimination reaction forming propene and releasing the second chloride. Future work aims to utilize this technology to aid in the dechlorination of other recalcitrant organic compounds such as 1,2,3-trichloropropane (TCP) and 1,2-dichloroethane. Preliminary studies have shown the complete degradation of TCP using the same reaction scheme.
Development of Metal-Organic Frameworks as a Versatile Platform for Heterogeneous Catalysis
University of South Florida
Metal–organic frameworks (MOFs) represent a new class of materials, and one of their striking features lies in the tunable, designable, and functionalizable nanospace. The nanospace within MOFs allows designed incorporation of different functionalities for targeted applications, such as gas storage/separation, sensing, drug delivery; and it has also provided plenty of opportunities for heterogeneous catalysis application. We will illustrate different approaches to develop MOFs as versatile platform for heterogeneous catalysis.
Control and Stabilization of Human Galectin-3 with Polymer Conjugation
Amanda Pritzlaff, Dominic Rucco, and Daniel Savin
University of Florida
The human signaling protein galectin-3 (gal3) is being investigated as a polymer conjugate partner in order to control and study gal3 function. Gal3 contains a large disordered N-terminal domain (NTD) which is thought to mediate aggregation and therefore regulate the biological function of the protein. This region also makes the protein difficult to isolate and study due to its propensity to precipitate, so modification with soluble polymers is anticipated to have a stabilizing effect. Variants of the protein were created including a gal3 S7C mutant with a cysteine replacing the seventh serine in the unstructured NTD. Mutants were then conjugated to poly ethylene oxide (PEO) acrylate or methacrylate (500 g/mol PEO methacrylate, 2000 and 5000 g/mol PEO acrylate) through a thiol-Michael addition at the mutated cysteine.
Fermi resonance in CO2: Exploring the vibrational structure of the carbon dioxide dimer
Olaseni Sode,1 Murat Keçeli,2 and Samuel Maystrovsky1
1. The University of Tampa, Department of Chemistry, Biochemistry and Physics, Tampa, FL, 33606.
2. Argonne National Laboratory, Computational Science Division, Argonne, IL, 60439.
The vibrational structure of the carbon dioxide monomer and dimer are explored using a flexible-monomer two-body potential energy function. This recently developed potential [O. Sode and J. N. Cherry, J. Comput. Chem., (2017)] is fit to the electronic energies at the CCSD(T)-F12b/aug-cc-pVTZ level of theory and integrated into vibrational structure programs, such as MaVi, NITROGEN and SINDO, to determine anharmonic corrections to the harmonic frequencies. Vibrational correlation approaches were employed, and the vibrational configuration interaction (VCI) results agree to within a few wavenumbers of the experimentally determined peaks, especially in the intramolecular region. While the dimer intermolecular vibrations in THz region are difficult to explore experimentally, we identify fundamental, overtone and combination bands with our computational approach. Our results suggest Fermi resonance in this low-frequency region due to mixing between the overtone and fundamental bands..
Laser-ablation for the analysis of anthropological evidence
Mauro Martinez, Matthieu Baudelet
National Center for Forensic Science and Chemistry Department, University of Central Florida
The study of anthropological evidence has seen a new dimension with elemental analysis. For a long time, it relied on XRF and/or ICP-MS. The introduction of laser-ablation has given the opportunity to reduce sample preparation while having full access to the whole periodic table with limits of detection from ppb’s to %. This talk will show the use of Laser-Induced Breakdown Spectroscopy (LIBS) and Laser-Ablation ICP-MS (LA-ICP-MS) for anthropological materials, from the cultural to the forensic point of view. We consider anthropological evidence in a general sense (not only bones but also hair and teeth).
Bone analysis has mainly relied on osteology and is based on the practitioner’s experience, or consist in the use with empirical mathematical formulas and comparison in databases. This talk will present new approaches for the use of LIBS and results that extend the capability of elemental analysis for forensic analysis.
Teeth are great indicators in the human body for growth, evolution of diet and even geographical movements. This information can be extracted from LA-ICP-MS elemental maps. Information on the history and cultural distribution of an archaeological population will be discussed.
DNA is not easy to recover from hair, preventing sex determination in some cases. Using LIBS on the hair, we identified different minor elements of interest that can reflect the metabolism change in the body that can be different between male and female individuals. This study substantiates the potential of the elemental analysis of hair as a proxy for human sex determination.
Incorporating Peer-reviewed Research Journal Articles into Organic and Biochemistry Classes
Rose Mary Stiffin, PhD
Florida Memorial University
The benefit of introducing undergraduate students to research has been reported in a plethora of education and scientific journals. Although the integration of research with teaching at a teaching institution is beneficial to both the faculty member and the student, often the faculty member may be overburdened with teaching loads. How then can research be introduced as a means of developing the skills mentioned, such as hypothesis formation, data/statistical analysis, and methodology?
The purpose of this presentation is to introduce students to scientific research in two courses, namely Organic (I and II) and Biochemistry. We do this by acquiring peer-reviewed scientific journal articles from any of the Free Access journals, in any biochemical/biological area of study. The choices are limited only to accessibility of article and number of students per class.
An assessment tool is used as well as allowing extra points during the Q&A period of other classmates’ presentations to determine their final grade for the paper presentation. Thus, the use of peer-reviewed articles in scientific journals provide students exposure to research, which leads to their developing a deeper understanding of the nature of scientific knowledge. The PowerPoint presentation will also show that the presentations provide a low-barrier and unattainable laboratory resource gateway for students to enter research (seeking and obtaining internships, Senior Projects, and entrance into graduate school in the science-related disciplines).
The mechanism and kinetics of oxidation of cyclopentadienyl radical in combustion flames: A theoretical view
A. R. Ghildina,1 A. D. Oleinikov, G. R. Galimova,1 V. N. Azyazov,1 and A. M. Mebel2
1 - Samara National Research University, Samara 443086, Russian Federation
2 - Florida International University, Miami, Florida 33199, USA
We will report a detailed theoretical investigation of the oxidation mechanism of the cyclopentadienyl radical with the main oxidants present in combustion flames, including O, OH, and O2. Ab initio calculations of potential energy surfaces in conjunction with the RRKM-Master Equation theoretical approach have been employed to evaluate temperature- and pressure-dependent total and product specific rate constants and product branching ratios for these and related reactions. The C5H5 + O reaction is shown to proceed by barrierless oxygen addition to the ring followed by fast H migration, ring opening, and dissociation to C4H5 + CO. The C5H5 + O rate constant is calculated to be close to 1.0x10-10 cm3 molecule-1 s-1 and to be pressure-independent and nearly independent of temperature. The C5H5 + OH reaction is shown to proceed either by well-skipping pathways without stabilization of C5H6O intermediates leading to the bimolecular products ortho-C5H5O + H, C5H4OH (hydroxycyclopentadienyl) + H, and C4H6 (1,3-butadiene) + CO, or via stabilization of the C5H6O intermediates, which then undergo unimolecular thermal decomposition to ortho-C5H5O + H and C4H6 + CO. The well-skipping and stabilization/dissociation pathways compete depending on the reaction conditions; higher pressures favor the stabilization/dissociation and higher temperature favor the well-skipping channels. For the C5H5 + O2 reaction, the results show that at low temperatures from 500 to 800-1250 K (depending on pressure), the reaction predominantly forms a collisionally-stabilized C5H5-OO complex and then, the thermalized complex rapidly decomposes back to the reactants establishing a C5H5 + O2/C5H5-OO equilibrium. At higher temperatures, typically above 1000 K, the mechanism is different and the C5H5 + O2 reaction proceeds to form various bimolecular products. Cyclopentadienone C5H4O + OH are predicted to be the predominant product, whereas relatively minor products include H2CCHCHC(H)O + CO, vinylketene + HCO, and highly endothermic C5H5O + O produced directly by the O-O bond cleavage in the initial complex. Overall, the rate constant of the C5H5 + O2 reaction at combustion-relevant temperatures is predicted to be very slow, 10-16-10-15 cm3 molecule-1 s-1, that is typically ~5 orders of magnitude lower than those for the oxidation reactions of cyclopentadienyl with OH and O(3P).
Kandinsky Circles: Nested Supramolecular Hexagons with High Antibacterial Activity
University of South Florida
Nested concentric structures widely exist in nature and designed systems with circles, polygons, polyhedra, and spheres sharing the same center or axis. In art field, concentric rings are also known as Kandinsky circles named after Wassily Kandinsky, a pioneer in abstract art, because of his prominent and profound painting Color Study; Squares with Concentric Circles.2 In addition to art and mathematics study, chemists have been fascinated by nested architectures with discovery and/or creation of a significant number of 2D and 3D systems that display nested layer and shell arrangements of atoms, molecules and materials. It still remains challenging to construct discrete nested architecture at (supra)molecular level. Herein, three generations (G2−G4) of giant nested supramolecules, or Kandinsky circles have been designed and assembled with molecular weight 17,964, 27,713 and 38,352 Da, respectively. In the ligand preparation, consecutive condensation between precursors with primary amines and pyrylium salts was applied to modularize the synthesis. These discrete nested supramolecules were prone to assemble into tubular nanostructures through hierarchical self-assembly. Furthermore, nested supramolecules displayed high antimicrobial activity against Gram-positive pathogen methicillin-resistant Staphylococcus aureus (MRSA), and negligible toxicity to eukaryotic cells, while the corresponding ligands didn’t show potent antimicrobial activity. The membrane-activity of these supramolecules was confirmed via electrophysiology study of planar lipid bilayer, subcellular localization by 3D deconvolution fluorescence microscopy, and bacterial morphology by TEM. We believe that those 2D multi-layered supramolecules were able to assemble into channels with multi-layered structure and distinct pore size inside the bacterial membrane and thus, lead to enhanced leakage of cytoplasmic components and cell death. Our endeavors will shed light into both antibiotics and supramolecular chemistry field and pave a new avenue into the development and application of antimicrobial agents.
Electronic structure and reactivity of atmospheric ions
Kai Lister, Jennifer E. Ruliffson, Melanie White, Rachael Mizrahi, and Joshua J. Melko
University of North Florida
In atmospheric chemistry it is vital to be able to control for energetics and environment to accurately model reaction pathways and kinetics of compounds that behave differently across the atmospheric layers. Nowhere is this more evident than in the context of nitrogen oxides and isoprene. In the troposphere nitrogen oxides may react with volatile organic compounds (of which isoprene is a major contributor) to form ozone creating significant health impacts. As these compounds rise to the stratosphere nitrogen oxides are implicated in the depletion of the ozone layer and isoprene is thought to be a possible intermediate in the formation of secondary organic aerosols. Our group proposes two methods used for controlling/determining temperature and composition of gas phase nitric oxide and isoprene.
Photoelectron spectroscopy experiments in conjunction with computational methods are used to map part of the potential energy surface of nitric oxide. Nitric oxide anions are created using electron ionization and isolated via mass spectrometry, and photoelectron spectra are captured via velocity map imaging. Theoretical spectra are produced at various ion temperatures using ezSpectrum software, which calculates the Franck-Condon factors using Gaussian09 optimizations of equilibrium geometry, harmonic frequencies, and normal mode vectors.
Through the use of a mixing tank and helium damping gas, reaction pathways of isoprene were mapped by varying source conditions to control the extent of fragmentation and clustering of reaction products. This experiment allows for future work studying the formation of secondary organic aerosols to better understand the origins of cloud formation.
Mass Selection of Van der Waals-Tagged Ions within a Cryogenic Linear Ion Trap
Larry Tesler; Nicolas C. Polfer
University of Florida, Department of Chemistry
Infrared ion spectroscopy has the potential to become a gold standard technique for molecular identification in mass spectrometry;1 however, the low duty cycle of the technique, where only one analyte is probed at one laser wavelength at one time, imposes a significant impediment for analytical applications. Prior work showed that using a cryogenic linear ion trap (cryoLIT), multiple solvent-tagged ions can be mass-isolated, irradiated, and mass detected in a multiplexed manner and thus significantly improving throughput;2,3 however, the solvent-tagged ions require multiple photons to lose their tags leading to band broadening and shifting, and the polar solvent molecules will perturb the IR spectrum of the analyte4. Tagging the analyte ions, through van der Waals interactions, with an inert gas (i.e. N2) is preferable as it is in principle a more innocent tag that only requires a single photon to evaporate off the analyte.3 With that in mind, N2-tagged infrared photodissociation will be the focus of this talk.
The cryoLIT is a cryogenic linear ion trap extension to a custom mass spectrometer (ESI-QMF-QIT-TOF).2 The cryoLIT is cooled by a temperature-controlled cryostat with the temperature monitored at the coldfinger and one of the DC endplates. Tagging and collisional-cooling gas is introduced into the trap via a solenoid pulse valve. Tagged ions are mass selected via a stored waveform inverse Fourier Transform (SWIFT) excitation, followed by irradiation with a tunable optical parametric oscillator (OPO) light source (LaserVision) from 2000 to 4000 cm-1 to induce infrared photodissociation (IRPD), which manifests itself by loss of the tag. The relative populations of untagged and tagged ions are detected through a resonant mass instability scan.
As of now, N2-tagged ions have been observed for several ion species; when obtaining a mass spectrum of loperamide (m/z 477), the singly (m/z 505) and doubly (m/z 535) tagged ions are observed with a singly tagged efficiency of 11% at trap temperature of 23K. Using a SWIFT waveform, the singly tagged loperamide ion was mass isolated from the untagged and doubly tagged ions, demonstrating that IRPD experiments are possible with N2-tagged ions. N2-tagging has also been observed for tryptophan (m/z 205), and an IRPD spectrum of the N2-tagged molecule has been reported.3 Further investigation of N2-tagging within the cryoLIT will be done by looking at N2-tagging of RRL4G (polypeptide) and its fragments; tagging yields will be analyzed to determine how N2-tagging behaves as a function of trap temperature and molecular properties (i.e. mass, charge, collisional cross-section).
(1) J. Am. Soc. Mass Spectrom., 27, 757 (2016)
(2) J. Mass Spectrom., 52, 720 (2017)
(3) Analyst, 143, 1615 (2018)
(4) M. R. Bell, W. D. Vinicius, A. P. Cismesia, L. F. Tesler, A. E. Roitberg and N. C. Polfer, In Preparation.