Friday May 4th – Presentations

In by admin

Machine learning approaches to evaluate correlation patterns in allosteric signaling: a case study of the PDZ2 domain

Mohsen Botlani, Ahnaf Siddiqui, Sameer Varma

University of South Florida

06:10 PM
Computational Chemistry

Many proteins are regulated by dynamic allostery wherein regulator-induced changes in structure are comparable with thermal fluctuations. Consequently, understanding their mechanisms requires assessment of relationships between and within conformational ensembles of different states. Here we show how machine learning based approaches can be used to simplify this high-dimensional data mining task and also obtain mechanistic insight. In particular, we use these approaches to investigate two fundamental questions in dynamic allostery. Firstly, how do regulators modify inter-site correlations in conformational fluctuations ($C_{ij}$)? Secondly, how are regulator-induced shifts in conformational ensembles at two different sites in a protein related to each other? We address these questions in the context of the human PTP1E's PDZ2 domain, which is a model protein for studying dynamic allostery. We use molecular dynamics to generate conformational ensembles of the PDZ2 domain in both the regulator-bound and regulator-free states. The employed protocol reproduces methyl deuterium order parameters from NMR. Results from unsupervised clustering of $C_{ij}$ combined with flow analyses of weighted graphs of $C_{ij}$ show that regulator binding significantly alters the global signaling network in the protein; however, not by altering the spatial arrangement of strongly interacting amino acid clusters, but by modifying the connectivity between clusters. Additionally, we find that regulator-induced shifts in conformational ensembles, which we evaluate by repartitioning ensembles using supervised learning, are, in fact, correlated. This correlation $\Delta_{ij}$ is less extensive compared to $C_{ij}$, but in contrast to $C_{ij}$, $\Delta_{ij}$ depends inversely on the distance from the regulator binding site. Assuming that $\Delta_{ij}$ is an indicator of the transduction of the regulatory signal leads to the conclusion that the regulatory signal weakens with distance from the regulatory site. Overall, this work provides new approaches to analyze high-dimensional molecular simulation data, and also presents applications that yield new insight into dynamic allostery.

Green Methods for the Synthesis of Anti-Cancer Resveratrol Analogues

Daniel H. Paull

Florida Gulf Coast University

10:15 AM
Organic Chemistry

Resveratrol analogues have been widely tested in all kinds of aging-related disorders in the last decade, and their use has only increased because of successes in several diverse areas, including anti-inflammatory, cardioprotective, and anti-cancer. Likewise, we need an ever-expanding library of synthetic methods for their production, especially ones that are easy, quick, efficient, and clean. These green principles guide our method development, and we have three distinct methods to present.

The products we synthesize are tested against various breast cancer cell lines, and we have found several that are active against, and induce metastasis-inhibiting morphological changes in, triple-negative breast cancer cell lines. We are currently designing and synthesizing a second, more focused set of compounds for testing. This application will be presented along with the advantages of each green method for these syntheses.

Experimentally Correlating the Spatial Distribution of Fluorine to the Growth of Anatase TiO2 Crystal Facets

Justin R. Mulcahy, Shuai He, Decarle S. Jin, Wenxiao Guo, Sarah Arteta, Esdras Lopez, Zihua Zhu, and Wei David Wei

Department of Chemistry and Center for Catalysis, University of Florida, Gainesville, Florida 32611, United States
Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99354, United States

06:05 PM
Materials Chemisry

Although the capability of fluorine to selectively stabilize anatase titanium dioxide (TiO2) crystal facets has been recognized, resolving its physical distribution remains empirically elusive. Here, we provide direct experimental evidence to reveal the spatial location of fluorine on the surface of anatase TiO2 truncated bipyramid (TB) single crystals using nanoscale secondary ion mass spectrometry (NanoSIMS). Fluorine was found to preferentially adsorb on the (001) facet over the (101) facet of TBs. Moreover, NanoSIMS depth profiling exhibited a significantly different fluorine distribution between these two facets in the near-surface region, which correlates the essential role of lattice fluorine doping with the anisotropic crystal growth of TBs.

Giant Molecules: Exploring Synthetic Parameters on the Path to New Mn-O Torus-like Clusters

Ashlyn Hale, Khalil A. Abboud, George Christou*

Department of Chemistry, University of Florida, PO Box 117200 Gainesville, FL 32611-7200, USA

10:35 AM
Inorganic Chemistry

The discovery of fascinating giant molecular clusters of paramagnetic metal ions (metal nuclearity of 30 or greater, and diameters up to 4.3 nm) has garnered immense interest due to their relevance to chemistry, physics, and materials science. The allure of diverse giant clusters is rooted in their fantastic features, such as their aesthetically-pleasing architectures, nanoscale size regime, and phenomenal physical properties. These features uniquely position giant clusters at the interface between the classical and quantum realms. Mn-O clusters are at the forefront of 3d transition metal giant clusters, owing to the relevance of Mn to molecular magnetism, especially single-molecule magnets (SMMs). The largest homometallic Mn-O cluster and SMM to date was synthesized by our group over a decade ago: the Mn84­ torus is a SMM and with a diameter of ~4.3 nm, it truly straddles the classical-quantum interface. Over a decade later, our group reported a second member in the family, the Mn­70 torus, the second largest SMM and Mn-O cluster to date. Herein, we present the revitalized and systematic investigation into this family of giant torus-like clusters, in order to further deduce which synthetic and structural parameters dictate the curvature and thus the nuclearity of the product, paving the way for targeted syntheses and the discovery of new giant Mn-O clusters.


Michael E. Sigman and Mary R. Williams

National Center for Forensic Science, University of Central Florida, PO Box 162367, Orlando, FL 32816.

10:55 AM
Analytical Chemistry

Detecting an ignitable liquid residue in fire debris is a challenging data analysis problem. Partial combustion and pyrolysis of substrate materials in a fire produce many chemical compounds also found in commercial ignitable liquids. The fire often leads to partial evaporation of the ignitable liquid, resulting in a modified chromatographic profile. The highly varied background signal and evaporation effects of the fire combine to enhance the data analysis challenge.  The ASTM E1618 standard method facilitates the classification of unevaporated ignitable liquids into a set of classes and categories based on chemical composition, product use, production method, or miscellaneous. However, fire debris data analysis methods based on ASTM E1618 that rely on visual pattern recognition are subjective and lead to categorical decisions and statements devoid of any reference to evidential value. Computational methods, such as support vector machines, discriminant analysis, k-nearest neighbors and others, can be used to identify ignitable liquid residues in the presence of a highly varied background signal. These methods can also provide a measure of the strength of the evidence. Research results on the use of computational pattern recognition methods for the detection of ignitable liquid residue in fire debris samples will be presented. The computational results will be evaluated by performance metrics, including receiver operating characteristic analysis, detection error tradeoff, Tippett plots and empirical cross entropy. Calculation and reporting of likelihood ratios will be discussed based on the computational methods.

Origins of Life: Prebiotic Chemistry in Simulated Hydrothermal Vent Environments via Calcium Carbonate, Barium Carbonate and Iron Sulfide Chemical Garden Catalysis.

Arthur P. Omran and Oliver Steinbock

Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390, USA

10:55 AM
Physical Chemistry

Hydrothermal environments could be the setting for where life originated. Hydrothermal vent chimneys such as black and white smokers can be simulated in the lab using pump injected chemical garden tubes. The hydrothermal vent chimneys are examples of chemical gardens themselves. To simulate white smoker hydrothermal vents, we have synthesized calcium carbonate and barium carbonate chemical garden tubes, by injecting calcium chloride and barium chloride respectively, into sodium silicate solution. To simulate black smoker hydrothermal vents, we have synthesized iron (II) sulfide chemical garden tubes, by injecting iron (II) chloride into sodium silicate solution containing sodium sulfide. We have characterized these precipitation products spectroscopically and with x-ray diffraction. We then expose these tubes to hydrothermal conditions and added formaldehyde. We found that these tubes act as a heterogeneous catalyst for the formose reaction and produce various sugars associated with the reaction. Furthermore, we found that at lower starting pH values for our system the calcite tubes act as a catalyst for the Cannizzaro reaction producing formic acid and methanol. We verified the products of these reactions using 1H NMR. Moreover, the presence of organic species in the system does not inhibit the precipitation formation of the chemical garden tubes. Finally, we demonstrate that the carbonate tubes evolve a bicarbonate buffer. We believe that synthesis and transport in a hydrothermal environment could form, and subsequently protect via buffering, biomonomers setting the stage for further chemical evolution.

Bacterial large subunit ribosome assembly

Riley Gentry, Jared Childs, Eda Koculi

University of Central Florida

10:55 AM
Biochemistry / Chem Bio.

The ribosome is the protein-RNA complex responsible for protein production in every known organism. While the structure of bacterial ribosome is known from crystallographic studies, the knowledge of the intermediates’ structures and compositions remains largely unknown. Because ribosome assembly in bacteria is a very fast and efficient process, the intermediates in ribosome assembly do not accumulate in cell in quantities sufficient to perform biophysical investigation. To increase the amount of intermediates accumulated during large subunit ribosome assembly, we expressed in Escherichia coli the helicase inactive R331A DbpA protein. Expression of R331A DbpA produces the accumulation of three large subunit intermediates. Our experiments demonstrate that the intermediates belong to three different stages of the large subunit ribosome assembly and that they rearrange to form the 50S large subunit via three parallel pathways. This is the first time that the existence of multiple pathways of large subunit ribosome assembly was observed experimentally. The ribosomal RNA is extensively modified in bacteria, and the modifications are shown to influence both the structure of the ribosome and its function. Using Next Generation Sequencing we determined that most of the modifications occur in the early stages of large subunit ribosome assembly. Lastly, our chemical modification experiments combined with Next Generation Sequencing demonstrate that the maturation of the peptidyltransferase center is the last step of large subunit ribosome assembly, preventing in this way the formation of malfunctioning ribosomes. This conclusion agrees with the data previously gathered on the bacterial and mitochondrial ribosomes.


Advances in 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

04:55 PM
Additive Manufacturing

Multi-Photon Lithography is an emerging technique for creating functional nano-scale 3D structures and devices.  The method relies on the combination of chemical and optical nonlinearity to achieve strong spatial confinement of the writing beam within a photoactive medium.  In this presentation we will briefly discuss how the technique works and how it has been used to create optically functional photonic crystals and other nanophotonic devices.

Copper Cycling in Sediments of Lakes Treated with Copper-Based Pesticides

Mohrah F. Albalawi and Melanie J. Beazley

University of Central Florida

06:25 PM

Copper-based algaecides and herbicides are commonly used in aquatic systems to control problematic algae and weeds leading to concerns of copper accumulation at application sites. In spite of this accumulation, algaecides and herbicides are still routinely applied throughout the year and, therefore, create an environmental concern. Excessive amounts of copper are toxic to fish and other aquatic organisms as well as affect microbial metabolic activities in aquatic sediments. For this study, water and sediment were collected from two central Florida lakes that have had monthly treatments of copper-based pesticides for the past seven years. Control samples were collected at an untreated lake. Speciation experiments determined that copper was primarily associated with the organic fraction. Copper was also present in the adsorbed and precipitated fractions, confirming thermodynamic models of copper speciation. In contrast, control lake sediments contained lower total copper concentrations and did not exhibit changes in depth. The results of this study will help elucidate the fate of copper from pesticides in aquatic environmental systems.

ANI strikes again. New results from a grown-up Machine learning method for organic systems.

Adrian E. Roitberg

University of Florida

06:35 PM
Computational Chemistry

In the theoretical study of molecular systems, a compromise between speed and accuracy is required to study the energetics of chemical systems. Quantum mechanical (QM) methods allow accurate energies and forces to be calculated but require substantial computational effort. Classical force fields are fast but only accurate near equilibrium and are generally unable to be used in reactivity studies due to their restrictive functional form.

Machine learning methods such as artificial neural networks have been used to develop neural network potentials (NNP), which are fitted to QM reference energies, though few have shown to be size extensible. Through the continued development of our methodology and data set, known as ANAKIN-ME (or ANI for short), we developed a new class of NNP, which are size extensible and chemically accurate. Specifically, we develop the ANI-1 potential for organic molecules containing H, C, N, and O. Through extensive benchmarks, case studies, and molecular dynamics simulations, we will provide evidence that the ANI method produces chemically accurate and size extensible potentials.

We will also show that active learning techniques allows these networks to learn new chemistry with very small amounts of new data, and that chemical reactions can then be studied with high accuracy.

As the results clearly show, these types of methods are a potential game changer for molecular simulations. The ANI method continues to bring a new, highly efficient, and accurate method for the development of NNPs into the realm of reality, and opens the door for the next generation of “out-of-the-box” general purpose potentials.

Synthesis and Biological Evaluation of Spirastrellolide A analogues

Jagadeesh Nagendra Manda, Barry B. Butler Jr, and Aaron Aponick

University of Florida

10:45 AM
Organic Chemistry

Spirastrellolide A is a marine macrolide first isolated by the Anderson group from the Caribbean marine sponge Spirastrella coccinea in 2003. Due to its novel antimitotic potency (IC50 = 100 ng/mL) and selective inhibition of protein phosphatase 2A (IC50 = 1 nM), Spirastrellolide A is potentially a lead compound for anti-cancer therapeutics. However, further evaluation of its biological potency was hindered by inadequate supplies. This issue could be circumvented by developing structurally simplified analogues of Spirastrellolide A that could retain the biological activity. A convergent synthesis of southern hemisphere of spirastrellolide A which involved two key intermediates including a tetrahydropyran and a [6,6]-spiroketal was designed. Two gold-catalyzed cyclization methods developed in our group were employed in the synthesis, namely 1) Gold-catalyzed dehydrative cyclization of monoallylic diols for the synthesis of the tetrahydropyran, and 2) Regioselective gold-catalyzed spiroketalization for the efficient generation of the [6,6]-spiroketal. Progress towards the synthesis of Spirastrellolide A analogues will be presented.

Expanding Cu-ligated multilayers for use in hybrid lithographic strategies

Alexandra M. Patron1, Daniel F. Santavicca2, Corey P. Causey1, Thomas J. Mullen1

1 - University of North Florida, Department of Chemistry
2 - University of North Florida, Department of Physics

06:25 PM
Materials Chemisry

The development of hybrid-lithographic strategies to fabricate nanoscale features with tailored chemical functionalities has garnered tremendous interest in recent years for applications such as nanoelectronic and sensor fabrication. The molecular-ruler process shows great utility for this purpose as it combines top-down lithography for the creation of complex architectures over large areas in conjunction with molecular self-assembly, which enables precise control over the physical and chemical properties of small local features to employed to produce registered nanogaps between metal features. The solution deposition of mercaptoalkanoic acids and metal ions are commonly used to generate the metal-ligated multilayers employed in the molecular-ruler process; however, few studies have explored molecules with varied chemical functionalities. Here, we explore the solution and vapor deposition of alkanethiol molecules as the terminating layer of metal-ligated SAMs. We observe that the solution deposition of alkanethiol molecules resulted in islands of low surface coverages with features that varied in height. Unlike solution deposition, islands produced via vapor deposition exhibit markedly higher surface coverages of uniform heights. To illustrate the applicability of the vapor deposition approach, metal-ligated multilayers, both with and without a vapor-deposited alkanethiol layer as the terminating layer, are utilized to create nanogaps between Au features using the molecular ruler process. Expansion of the molecular-ruler process to include molecules with other chemical functionalities and tailored deposition conditions has the potential to improve the overall versatility, and thus the utility, of this process.

Creating New Coordination Environments for Spin-Crossover Complexes: Data Mining and Chemical Intuition

Jeremy J. Hrudka, Hoa Phan, Alina Dragulescu-Andrasi, Sandugash Yergeshbayeva, Michael Shatruk

Florida State University, Department of Chemistry and Biochemistry

10:55 AM
Inorganic Chemistry

The design of transition metal complexes that exhibit switching between the low-spin and high-spin electronic configurations (spin crossover, SCO) usually involves some a priori knowledge of typical ligand coordination environments which are conducive to the occurrence of SCO for a specific metal ion. For example, the octahedral coordination of the Fe(II) ions by six N-donor atoms is known to often furnish SCO behavior. In this contribution, we demonstrate that effective prediction of the possibility of spin-state switching in homoleptic Fe(II) complexes with chelating diimines can be achieved on a very simple principle that takes into account the separate between the N-donor sites of the chelating ligand. We further use this principle to analyze the ligand field strength and modify the SCO temperature of heteroleptic complexes. Among these, especially noteworthy are the complexes with the {N4S2} ligand set, which provides a new coordination environment for the design of SCO Fe(II) complexes.

N-Acyltransferases and Fatty Acid Amides

Brian G. O'Flynn, Ryan L. Anderson, Gabriela Suarez, Dylan Wallis, and David J. Merkler

Department of Chemistry
University of South Florida

04:00 PM
Biochemistry / Chem Bio.

Fatty acid amides are a family of cell signaling lipids with the general structure of R-CO-NH-Y. This structural simplicity belies a wealth of diversity amongst this lipid family as the R-group is derived from fatty acids (R-COOH) and the Y-group is derived from biogenic amines (H2N-Y). The fatty acid amide family is divided into classes, defined by parent amines. Examples include the N-acylethanolamines (NAEs, R-CO-NH-CH2-CH2OH) and the N-acylglycines (NAGs,
R-CO-NH-CH2-COOH). Other classes of fatty acid amides are known. The best known fatty acid amide is N-arachidonoylethanolamine (anandamide), a fatty acid amide found in the human brain that binds to the cannabinoid receptors.

We have a long interest in the enzymes of fatty acid amide biosynthesis. We identified an enzyme that oxidizes the NAGs to the to the primary fatty acid amides and showed that inhibiting this enzyme led to the cellular accumulation of the NAGs. We have characterized a number of insect N-acyltransferases (from D. melanogaster, B. mori, and T. castaneum) that catalyze the acyl-CoA-dependent formation of fatty acid amides from an amine acyl-acceptor substrate. Knock-out experiments in D. melanogaster validate our in vitro substrate specificity studies demonstrating that one novel N-acyltransferases, arylalkyl N-acyltransferase-like 2 (AANATL2), does catalyze the formation of N-acyldopamines in vivo. We developed a straightforward platform technology to rapidly identify substrates for our panel of uncharacterized insect N-acyltransferases. Our application of this technology lead to identification of an enzyme in D. melanogaster, agmatine N-acetyltransferase (AgmNAT), which catalyzes the formation of N-acetylagmatine, a virtually unknown metabolite. We have determined the X-ray structure of AgmNAT. Our work on AgmNAT hints at an unknown reaction in arginine metabolism and points to a novel class on fatty acid amides, the N-acylagmatines. The presentation will also include our results on the kinetic and chemical mechanisms of the novel N-acyltransferases.

Direct Digital Manufacturing Processes for Electronics and Biology

Kenneth Church

nScrypt, Inc

05:45 PM
Additive Manufacturing

This talk will cover 3D printing and supplemental processes to enable a more complete device.  Printed structures are typically a single material and tools that have multi-material capabilities typically print one type of material.  Functional devices are comprised of diverse materials with diverse properties.  To accommodate this, nScrypt has developed a system with multiple tools and processes integrated on a single platform.  This enables printing functional devices such as RF antenna systems, as opposed to printed antennas.  This also enables biological prints and multiple processes will be required to reach the holy grail of a printed organ.  In electronics and biology, functioning parts are not single material and multi-material requires multi-processes.  These processes include heat, cooling, milling, polishing, pick and place and a wide variety of printing techniques.  Examples of printed electronic structures will be covered and demonstrated.  In addition, the transition from electronics to biology and the similarities in printing.

Single-molecule magnets, their oligomers and polymers: their structure, magnetic properties at ambient and high pressures, and high-field EPR spectroscopy

Christos Lampropoulos

Department of Chemistry, University of North Florida, Jacksonville FL 32226

04:00 PM
Inorganic Chemistry

Single molecule magnets (SMMs) are molecular materials, namely zero-dimensional, which exhibit both classical (magnetization hysteresis) and quantum properties (i.e. quantum tunneling, quantum phase interference, entanglement and others). SMMs are typically studied as the monomers, but it is unclear what happens if we have polymeric arrays of them or oligomers. In this work, the archetypical Mn12 SMM was used as a building block in order to synthesize polymers and oligomers. In this talk, our work on 1D / 2D / 3D polymers as well as oligomers of Mn12 SMMs will be discussed. These materials were thoroughly characterized with single-crystal x-ray crystallography, SQUID magnetometry at both ambient and elevated pressures, along with high-field high-frequency EPR spectroscopy.

Catalytic Activation of Diazonium and Diazo Compounds: New Chemistry from Unexpected Results

Xiaodong Shi

Department of Chemistry, University of South Florida

11:05 AM
Organic Chemistry

Activation and transformations of organic compounds is the main goal for organic chemists.  Various activation strategy might give different intermediate, leading to distinct transformations. Dazonium and diazo compounds were active motifs containing two nitrogen atoms.  Releasing of nitrogen gas is an entropic gaining and irreversible process which makes dazonium and diazo compounds wildly used in organic synthesis.

By utilizing gold catalyst, our group developed a diazoester decomposition forming a carbophilic carbocation for Friedel–Crafts alkylation.  With this result, we further wanted to merge photoredox and gold catalyst together to activate diazonium salt.  Surprisingly, photoredox catalyst was not necessary in the transformation, which suggested that gold catalyst itself could also serve as a redox catalyst between Au(I) and Au (III).  Unexpectedly, we developed iodide activation of diazo compounds to form iodocaboradical.

Biological N–N bond formation: From the nitrogen cycle to microbial natural products

Jonathan D. Caranto

University of Central Florida

04:35 PM
Biochemistry / Chem Bio.

Nitrous oxide (N2O) participates in ozone layer depletion and is a potent greenhouse gas, with a global warming potential 300 times greater than that of carbon dioxide. The atmospheric N2O concentration has surged 120% since the pre-industrial era largely due to increased fertilizer use. An estimated 60–75% of this gas is emitted as a by-product of microbial biochemical pathways that mediate the nitrogen cycle. Designing inhibitors for N2O-producing enzymes in these pathways could decrease N2O emissions, but this approach requires knowledge of the enzymatic mechanisms.

Agricultural N2O is largely a by-product of nitrification and denitrification that are mediated by nitrifying and denitrifying microorganisms, respectively. Nitrification oxidizes ammonia to nitrite or nitrate while denitrification reduces nitrate to dinitrogen or N2O. In denitrification, N2O is an obligate intermediate or the final product of the pathway that is generated from the two-electron reduction of two molecules of nitric oxide (NO). Occasionally, this N2O escapes the microorganism and is released into the environment. By contrast, N2O is not an obligate intermediate of nitrification. However, recent work provided evidence for NO as an obligate intermediate of nitrification. Nitrifying microorganisms frequently possess enzymatic machinery for nitrifier denitrification, which includes a respiratory NO reductase that can reduce NO to N2O. In addition to this NO reduction pathway, an alternate oxidative N2O-generating pathway was recently characterized, for which hydroxylamine (NH2OH) is oxidized to N2O.

This presentation will survey metalloenzyme intermediates that have been characterized along the reaction pathways of N2O-producing enzymes. Bacterial respiratory NO reductases found in denitrification and nitrifer denitrification pathways are mixed heme/non-heme diiron enzymes. By contrast, the NO reductases found in fungal denitrifiers contain mononuclear cytochrome P450 active sites. NO reductase activity has been characterized in a third class of metalloenzyme known as flavo-diiron proteins (FDPs) that contain a non-heme diiron center. Finally, cytochrome P460 exhibits a covalently modified c-heme enzyme that generates N2O by oxidation of NH2OH instead of NO reduction. For each of these enzymes, the mechanisms and iron-nitrosyl intermediates leading to N–N bond formation and the subsequent generation of N2O will be discussed. In addition, the application of these studies to a new research direction—N–N bond formation in microbial natural product biosynthesis—will also be discussed.

Mechanical Instabilities in Contracting 3D Printed Microtissues

Thomas E. Angelini

University of Florida

06:10 PM
Additive Manufacturing

Living cells are often dispersed in extracellular matrix (ECM) gels like collagen and Matrigel as minimal tissue models. Generally, large-scale contraction of these constructs is observed, in which the degree of contraction and compaction of the entire system correlates with cell density and ECM concentration. The freedom to perform diverse mechanical experiments on these contracting constructs is limited by the challenges of handling and supporting these delicate samples. Here, we present a method to create simple cell-ECM constructs that can be manipulated with significantly reduced experimental limitations. We 3D print mixtures of cells and ECM (collagen-I) into a 3D growth medium made from jammed microgels. With this approach, we design microtissues with controlled dimensions, composition, and material properties. We also control the elastic modulus and yield stress of the jammed microgel medium that envelops these microtissues. Similar to well-established bulk contraction assays, our 3D printed tissues contract. By contrast, the ability to create high aspect ratio objects with controlled composition and boundary conditions allows us to drive these microtissues into different regimes of physical instability. For example, a contracting tissue can be made to buckle as a whole or break up into pieces, depending on composition, size, and shape. These new instabilities may be employed in tissue engineering applications to anticipate the physical evolution of tissue constructs under the forces generated by the cells within.

Precise Formation of concise G-Octamer for Construction of Noncovalent and Covalent “Molecular Cube” with enhanced stability

Ying He, Yanbin Zhang, Xiaodong Shi

University of South Florida

04:00 PM
Organic Chemistry

Both non-covalent and covalent “molecular cube” was constructed through self-assembly of designated guanosine derivatives, which were characterized by X-ray, NMR and MS.  The key design was the analysis of the key steric factors that control G-quartet stacking.  With the introduction of 8-aryl and sterically hindered protecting group on ribose, interdigitation of sugar between G-quartet layers was prevented successfully and a concise, discrete self-assembled guanosine octamer was achieved with enhanced stability and unique property on Rb+ recognition.

Cobalt-Manganese-Oxide Clusters as Potential Water Oxidation Catalysts (WOCs)

Preet Mahalay, Khalil A. Abboud and George Christou

Department of Chemistry, University of Florida, Gainesville, FL 32611

04:35 PM
Inorganic Chemistry

The ability of Nature to achieve high-efficiency catalytic water oxidation in plants and cyanobacteria using the earth-abundant metals Mn and Ca is unmatched in any of the artificial systems known to date. Most of the latter rely on 4d and 5d metals such as Ru, Ir, etc. Thus, efficient catalytic oxidation of water using 3d metals such as Mn, Co and Cu remains a long-standing challenge for synthetic chemists. Homometallic, high oxidation state Mn and Co systems have been extensively researched as WOCs over the past 20 years, but only recently has an efficient water oxidation catalyst of Mn been reported – the very recent report of water oxidation electrocatalysis with a remarkably low overpotential of only 0.33 V by a member of the well-known [Mn12O12(O2CR)16(H2O)4] family of clusters. While very active, the catalyst begins to decay within a few hours and is assigned to slow decomposition of the Mn12 cluster. Since several robust Co/O clusters containing kinetically-inert CoIII have also been reported in the literature and shown to be good WOCs, we have initiated a program seeking to amalgamate the benefits of the two areas by developing mixed-metal Co/Mn/O/RCO2- clusters. In this presentation will be described the development of a synthetic route to a new family of high oxidation state CoIII/MnIV/O clusters and their characterization by X-ray crystallography, magnetic studies, and other techniques.

Manumycin-A is a potent inhibitor of mammalian thioredoxin reductase

Anupama Tuladhar; Kathleen Rein

Department of Chemistry and Biochemistry, Florida International University, Miami, Fl, 33199.

04:55 PM
Biochemistry / Chem Bio.

The thioredoxin system is the major cellular reductant system present in the cell, whose role is to maintain cellular redox homeostasis. The system controls many cellular processes such as DNA synthesis and also act as an antioxidant. The thioredoxin system is comprised of thioredoxin reductase (TrxR) and thioredoxin (Trx) which reduces target protein disulfide bridges by thiol-disulfide exchange. Because it is a regulator of numerous critical cellular functions, TrxR is also a common target for many cancer drugs including cisplatin and auranofin. Recently we have shown that the Florida red tide toxin, brevetoxin can inhibit mammalian TrxR which explains the oxidative stress observed in marine organisms exposed to red tide. We have discovered several compounds which are similar to brevetoxin in size and functionality that have a similar effect on TrxR. One of these compound is manumycin A (man-A). Unlike PbTx-2, man-A a known farnesyl transferase inhibitor, inhibits both DTNB and insulin reduction which implies that the potential binding site of man-A is C-terminal selenocysteine. Inhibition of TrxR at the C-terminal tail produces a pro-oxidant known as SecTRAP (Selenium Compromised Thioredoxin Reductase-derived Apoptotic Proteins), which produces superoxide radical anion. This might explain the observed burst of ROS in cells exposed to man-A. We have also tried to characterize the molecular mechanism of action by using site-specific mutant enzymes which allow us to determine the specific site of interactions between enzyme and man-A. The result with the mutant enzymes have revealed that man-A interacts in very different ways with mitochondrial and cytoplasmic TrxRs. This study will thus identify a novel mechanism of action of man-A and thus will contribute to develop a new drug to treat cancer.

3D Bioprinting and Efforts to Biofabricate Bioficial Organs

Stuart K. Williams, Ph.D.

Director, Bioficial Organs Program
University of Louisville

06:35 PM
Additive Manufacturing

The disparity between available donor organs and patients in need of a transplant has been the impetus to create human tissues and organs for transplantation.  Efforts to biofabricate replacement organs has evolved over several decades and has included advancements in cell biology, tissue culture, tissue engineering and regenerative medicine.  Further evolution toward a totally biologic organ replacement has included the technology known as 3D Bioprinting.   Progress toward the fabrication of a Total Bioficial Heart using 3D Bioprinting will be discussed including the source of autologous cells to create components of the heart.  Examples of other Bioficial Organs that are being 3D Bioprinted and the clinical readiness of this technology will also be presented.  Finally,  we are now exploring the use of regenerative medicine and 3D Bioprinting in space with a hope to bring these technologies to support long-term space exploration.

Unleashing bacterial biosynthetic pathways to expand diketopiperazine chemical diversity

Amy L. Lane

University of North Florida

04:20 PM
Organic Chemistry

Natural products with 2,5-diketopiperazine (DKP) scaffolds offer a broad range of bioactivities and chemical structures. The functional and structural diversity of these cyclodipeptides arises via enzyme-catalyzed construction from a variety of amino acids as well as tailoring of DKP cores. For many years, nonribosomal peptide synthetases (NRPSs) were the only enzymes recognized as catalysts for DKP assembly. Cyclodipeptide synthases (CDPSs), employing two aminoacyl-tRNAs as substrates for DKP assembly, were first reported in 2009. Aminoacyl-tRNAs are uncommon players in natural product assembly, making CDPSs intriguing members of Nature’s biosynthetic repertoire. Biochemical and bioinformatics analyses support that CDPSs are found from at least six bacterial phyla and some animals, yet biosynthetic pathways with CDPSs remain understudied relative to pathways featuring NRPSs or other common biosynthetic enzymes.  Through studies of bacterial pathways that include CDPSs, my group has unveiled novel biosynthetic capabilities and developed tools for the engineered biosynthesis of DKPs. This presentation will highlight our strategies for the characterization of these pathways to discover uniquely functionalized DKPs and our development of a platform for the CDPS-catalyzed assembly of novel DKPs from unnatural aminoacyl-tRNA precursors. Our results establish the catalytic promise of CDPSs beyond natural cellular aminoacyl-tRNAs, and showcase the utility of biosynthetic strategies for expanding the breadth of chemical space provided natural products.

Conducting Charge Transfer Salts of Fe(II) Complexes with Organic TCNQ Radicals

Ökten Üngör, Hoa Phan, Michael Shatruk

Florida State University, Department of Chemistry & Biochemistry

04:55 PM
Inorganic Chemistry

Fe(II) complexes with ligands of an intermediate ligand field strength often show magnetic bistability, i.e. switching between the high-spin (HS) and low-spin electronic configurations driven by changes in temperature, pressure, or photoexcitation. This control by external stimuli makes spin crossover (SCO) complexes promising materials for applications. We are interested in designing multifunctional materials that exhibit both SCO and conductivity by combining Fe(II) centers and organic TCNQ-type acceptors. In such complexes, TCNQ radical anions are arranged in stacks that provide conducting pathways. The stacking distance can be affected by structural changes induced by SCO, and thus the synergy between the SCO and conductivity can be achieved. The synthesis of such materials can be achieved in two ways: first, by coordinating TCNQ ligands directly to the Fe(II) center, which is partially protected by blocking ligands that limit the growth of extended structures; second, by co-crystallizing completely blocked Fe(II) centers with free TCNQ radicals. We will discuss several complexes, in which Fe(II) cations have been co-crystallized with fractionally charged TCNQ radical anions to result in hybrid semiconducting materials.