Influence of the bath Gas on the mobility separation and stability of common explosives
Alan McKenzie-Coe1, Francisco Fernandez-Lima1,2
1 Department of Chemistry and Biochemistry, Florida International University, Miami, USA
2 Biomolecular Science Institute, Florida International University, Miami, USA
In a previous work, we showed the potential of Trapped Ion Mobility Spectrometry Mass Spectrometry for the separation and characterization of common explosives in air. In particular, we showed that adduct complexes of explosives can undergo exponential losses in their ion abundance due to interactions with the residual gas molecules. In the present work, a systematic study was performed in other to evaluate the stability and reactivity of common explosives as a function of the bath gas composition. Theoretical calculations were performed to study the effect of residual gas molecules on the reaction landscape of the explosive complexes. In addition, dopant gases were introduced to TIMS-MS operation to tailor the interactions using methanol, 2-propanol, and acetone as gas modifiers. Preliminary results show that gas modifiers can significantly affect the separation and mobility of common explosive complexes during a TIMS-MS experiment.
Family of Mn-Ce Clusters from Reductive Aggregation: Unusual Long Range Coupling through Ce(IV)
Sayak Das Gupta, Shreya Mukherjee, Khalil A. Abboud, and George Christou
Department of Chemistry, University of Florida, Gainesville FL 32611-7200, USA
Developing new synthetic routes to high nuclearity MnIII,IV clusters has been an integral part of the research in our group. Several years ago we reported a new synthetic method involving ‘reductive aggregation’ of MnO4- ions in the presence of excess RCO2H in MeOH. This approach gave several new Mn12 and Mn16 clusters. However, to date reductive aggregation has not been employed for the synthesis of heterometallic Mn clusters, and this has stimulated our present interest in extending this method to Mn-Ce chemistry. Using reductive aggregation, we have now obtained a family of related Mn-Ce clusters. This presentation will describe their structures and magnetic properties, including the identification of unusual long-range coupling between Mn ions separated by diamagnetic Ce(IV).
Analyzing the Speed of Sound in Methane and Propane Using a Ruben’s Tube
Madeline Greenberg and Bridget Alligood DePrince
Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306-4390
The Ruben’s tube is a commonly-used physics demonstration that uses fire to visualize longitudinal acoustic standing waves. We report on extended applications of this classic demonstration that offer a relatively inexpensive (and exciting!) means by which advanced physical chemistry topics can be explored. One application involves the analysis of speed of sound in both methane and propane, the results of which qualitatively agree with the expected relative speed of sound within the two gases. We will report on our findings, as well as our work involved in better understanding the quantitative data obtained in the experiments. This work is part of the larger STACT (Science and Technical Arts Collaborative Teaching) project, an initiative encouraging collaborations between science and technical arts teachers in Florida’s secondary school system.
A Systematic Investigation of the Synthetic Utility of a Leucine Hydroxylase in the Preparation of Nonproteinogenic Amino Acids
Christian R. Zwick, Hans Renata
The Scripps Research Institute
Noncanonical amino acids (ncAAs) are highly valuable building blocks for the preparation of active pharmaceutical ingredients. De novo chemical synthesis of ncAAs, however, is still a tedious endeavor and often requires non-trivial methods to provide high enantioenrichment for the desired products. A biocatalytic, direct functionalization of existing amino acids offers an alternative strategy that could potentially streamline synthetic approaches towards this class of molecules. This talk will describe our efforts in characterizing a highly proficient leucine hydroxylase with relaxed substrate specificity, allowing for the regio- and enantioselective hydroxylation of a range of aliphatic amino acids. In addition, applications of this transformation in the synthesis of bioactive peptide building blocks and an alkaloid natural product will be discussed.
STEP-WISE SELF-ASSEMBLY OF GIANT SUPRAMOLECULAR FRACTALS
Department of Chemistry, University of South Florida, Tampa FL 33620, USA
Self-assembly as a powerful bottom-up approach has been extensively used by nature to create complex biological systems. Synthetic supramolecular chemistry aims to use the principles of biological self-assembly to construct artificial nanostructures using molecular building blocks with desired functions and properties. The corresponding abiological assemblies, however, still suffered from a lack of complexity and thus were unable to reach the high degrees of functionality found in natural systems. With the goal of increasing the complexity of metallo-supramolecules, we designed and assembled a series of giant supramolecular architectures with fractal geometry using 2,2’:6’,2”-terpyridine ligands in a step-wise manner. This strategy allows us to harness strong and weak binding metal ions, e.g., Ru(II) with Fe(II), Zn(II) or Cd(II) through self-assembly, in which stable Ru(II)-organic ligand was assembled or synthesized for the subsequent self-assembly with metal ions with low binding strength and high reversibility to construct heteroleptic metallo-supramolecules. It is expected that this step-wise self-assembly approach will advance terpyridine-based supramolecular chemistry into a new level of sophistication through constructing supramolecular fractals with increasing complexity.
Anisotropy of B-DNA groove bending
Ning Ma and Arjan van der Vaart
USF Department of Chemistry
DNA bending is critical for DNA packaging, recognition, and repair. Bending occurs toward either the major or minor groove; since the grooves are not equivalent, the energetics will depend on the direction. Here we quantify the anisotropy for the first time by assessing the free energy cost of major and minor groove bending from computer simulations. The simulations show that bending toward the major groove is generally preferred. We also show that the preference for major groove bending is not due to electrostatics or sterics, but originates from solvation effects.
Predicting and refining crystal structures with NMR data
James Harper, Keyton Kalakewich, Luther Wang
University of Central Florida, Department of Chemistry
Theoretical crystal structure predictions (CSP) usually ranks candidates by lattice energy. Despite significant recent progress, the consistent selection of a correct structure remains challenging and is largely limited to rigid structures. This presentation explores an alternative in which NMR parameters are calculated for candidate structures then compared with experimental data to obtain rankings. This approach is demonstrated to eliminate approximately 90% of CSP candidates when carbon-13 data are employed and lattice effects are ignored. Inclusion of lattice fields significantly improves selectivity and allows a single correct structure to be consistently chosen. An important component of these studies is the discovery that an ab initio refinement of geometry is required in to ensure accurately selection. Surprisingly, most published crystal structures can also be improved by a lattice-including refinement. Several NMR parameters are able to track and guide these refinements, but they are largely undetectable by conventional diffraction methods. This “NMR crystallography” approach to refining and improving certain crystal structures is illustrated using lauric acid and other small organic structures. Harper, J. K. and Grant, D. M. (2006). Cryst. Growth Des., 6, 2315–2321.  Kalakewich, K. et al.(2013) Cryst. Growth Des. 13, 5391–5396.  Harper, J. K. et al. (2013) CrystEngComm, 15, 8693–8704.
Multi-Iron Clusters as Functional Models for FeMo Cofactor: Exploring the Reactivity of Triiron-Hydride Clusters and Expanding the Ligand Toolbox
Brian Knight, Kevin J. Anderson, and Leslie J. Murray*
University of Florida
As a means to interrogating the fundamental chemical transformations effected by the iron-molybdenum cofactor (FeMoco), we have explored the development of novel ligands designed to generate multiiron compounds and the reactivity profiles of the resultant complexes. In particular, our reported triiron(II) tri(μ-hydride) species provides a platform to understand the reactivity of hydrides bound to high spin iron clusters. To that end, recent results on reductive elimination and oxidative addition, hydride transfer reactivity, and bond activation will be discussed. Notably, these reactivity manifolds are commonly invoked in catalytic cycles for biological metal cluster cofactors.
Task-Specific Design and Functionalization of Advanced Porous Organic Polymers
University of South Florida
Porous organic polymers (POPs) represent an emerging class of nanoporous materials, and they feature robust covalent framework structures with high water and chemical stability. This, together with their high surface areas and tunable pore sizes, makes them hold promise for a variety of applications. We will demonstrate how POPs can be task-specific designed and functionalized via either de novel synthesis or stepwise post-synthetic modification for applications in environmental remediation such as oil spill cleanup, heavy metal removal, ion exchange, nuclear waste treatment.
BRINGING STEM TO SPED: BUILDING BLOCKS AND MOLECULAR MODELS FOR STUDENTS WHO ARE PHYSICALLY IMPAIRED
Kiyoshi Casey,1 Melissa Diaco,3 Scott M. Ames,2 Krystal Blackmon-Rhodes,3 and Kenneth A. Goldsby1
1Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306; 2Agricultural Science Program, Ransom Middle School, Pensacola, FL 32533; 3Escambia Westgate School, 10050 Ashton Brosnanham Road, Pensacola, FL 32533
Long before “hands-on/minds-on” became a cliché, it was generally recognized that learning is a tactile process. We can lament the inexorable migration of science teaching from the laboratory to the computer screen, but consider how technology has improved education for students who are physically impaired. There is no doubt that touch screens and specialized software helped make great strides in SPecial EDucation (SPED), but at what cost in the STEM fields where modeling scientific relationships often starts with building physical models, and equipment is constructed to test scientific constructs. We will describe a grassroots approach to designing, building, and testing “building blocks” specifically for SPED students. The potential for using these blocks as simple molecular models will also be discussed, including broader implications and caveats for the simple models generally used to illustrate molecular structure in introductory chemistry courses.
Synthesis and Biological Studies of GPI-Anchored Peptides and Proteins
Department of Chemistry, University of Florida, Gainesville, FL 32611
Many surface proteins are anchored to the cell membrane through glycosylphosphatidylinositols (GPIs), a class of complex glycolipids. GPI-anchored proteins have their polypeptide C-termini linked to a fixed position of the highly conserved core structure of GPI anchors. GPI-anchored proteins play a pivotal role in various biological and pathological processes. To study these events, it is necessary to have access to GPI-anchored peptides and proteins, as well as other GPI conjugates, in homogeneous and structurally defined forms. The aims of this project are to develop methods for the synthesis of these important biomolecules and use synthetic GPI conjugates to investigate GPI biology. In this regard, we have established several methods for GPI-anchored peptide, glycopeptide, and protein synthesis. These methods include chemical synthesis based upon regioselective chemical ligation of peptides or glycopeptides with GPI anchors and chemoenzymatic synthesis that used enzymes, such as bacterial sortase, to couple synthetic peptides and glycopeptides or recombinant proteins with GPI anchors. The synthesized GPIs and GPI conjugates have been employed to explore problems such as bacterial toxin-GPI interactions, GPI organization on the cell surface, GPI-anchored proteomics, etc.
Atomistic modeling of protein liquid-liquid phase separation
Sanbo Qin and Huan-Xiang Zhou
Department of Physics and Institute of Molecular Biophysics, Florida State University, Tallahassee, FL 32306, USA
Intracellular membraneless organelles, formed by liquid-liquid phase separation (LLPS) of mixtures of proteins and possibly RNA, mediate myriad cellular functions. Cells use a variety of biochemical signals such as expression level and posttranslational modification to regulate the formation and dissolution of membraneless organelles during functional processes. We have developed a powerful computational method called FMAP [1,2] for determining the thermodynamic conditions for LLPS, where proteins separate into a low-concentration (“dissolved”) phase and a high-concentration (“droplet”) phase. FMAP involves calculating the excess chemical potentials of protein molecules over a wide range of concentrations. By using fast Fourier transform to efficiently evaluate protein-protein interactions, FMAP enables an atomistic representation of the protein molecules. Here we applied FMAP to three homologues of g-crystalin to elucidate why minor changes in amino-acid sequence can lead to drastic differences in critical temperature (Tc, the highest temperature at which LLPS exists). Our calculations reproduce the experimental observation that gB and gD have similar Tc but gF has a much higher Tc. The calculations further reveal that weak intermolecular binding through the ridge between the two domains of g-crystalin drives droplet formation. A single residue at position 130, a Ser in both gB and gD but a Trp in gF, that lines the inter-domain ridge makes a prominent contribution to the disparity in Tc. Our study opens the door to quantitative modeling of the regulation of membraneless organelle formation by biochemical signals.
- S. Qin and H.-X. Zhou (2014). Further development of the FFT-based method for atomistic modeling of protein folding and binding under crowding: optimization of accuracy and speed. J. Chem. Theory Comput. 10, 2824-2835.
- S. Qin and H.-X. Zhou (2016). Fast method for computing chemical potentials and liquid-liquid phase equilibria of macromolecular solutions. J. Phys. Chem. B. 120, 8164-8174.
Electronic Processes in Well-Defined Nanoscale objects that Feature Single-Walled Carbon Nanotubes Wrapped by Semiconducting Polymers
Jean-Hubert Olivier,1 Michael Therien,2 Jaehong Park,2 Yusong Bai,2 George Bullard2
1 Department of Chemistry, University of Miami, Coral Gables FL 33124-0431, USA
2 Department of Chemistry, Duke University, Durham NC, 27708-0346, USA
Highly charged semiconducting polymers that feature a 2,2’-(1,3-benzyloxy)-bridged (b)-1,1’-bi-2-naphthol unit have been shown to single-chain wrap the nanotube surface with fixed helical chirality and pitch length. We demonstrate that chiral anionic semiconducting polymers that feature a perylene diimide (PDI) electron acceptor as an integral part of the polymer repeat unit provides polymer-SWNT superstructures for light-driven energy conversion reactions. Femtosecond pump-probe transient absorption spectroscopic experiments show that excitation into the SWNT E11 transition generates SWNT hole polaron [(6,5) SWNT(•+)n] and PDI radical anion (PDI−•) states. These studies demonstrate for the first time a photoinduced electron transfer process involving a SWNT and a semiconducting polymer in which: (i) the charge-separated products, and (ii) photoinduced charge separation and thermal charge recombination dynamics, are fully characterized. To fully exploit these polymer-SWNT hybrids in energy conversion applications, we have developed solution-based processes to structure dense, highly aligned arrays of these nano-objects on solid substrates. We show that ionic self-assembly approaches provide solid-state SWNT-based materials from solution that feature aligned, individualized nanotubes at high mass fraction per unit volume. The ability to modulate polymer electronic structure by design, used in conjunction with facile hierarchical organization, offers exceptional promise for the development of new types of optoelectronic nanomaterials.