Saturday May 5th – Presentations

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Materials Science and Engineering Research Perspective within the Functional Materials and Manufacturing Institute REU Program at University of South Florida

John N Kuhn

Venkat Bhethanabotla

University of South Florida

03:20 PM
Chemistry Education

Functional materials are prevalent throughout the modern world and are constant reminders of advances from engineering. Thus, functional materials research with a mindset toward application/manufacturing is an outstanding topic to engage emerging researchers such as high school students, undergrads, and K12 teachers. This is exactly what is done at the Functional Materials and Manufacturing Institute (FMMI) at University of South Florida (USF) through the Research Experience for High School Students, Undergraduates and Teachers (REHSS, REU, and RET) programs. Materials science and engineering itself is in the process transitioning from the past ways of separate topics (e.g., metallurgy, ceramics, etc) to a modern mindset that includes emphases on hard and soft matter, bio-materials, and nano-materials, unified by an atomistic-level materials perspective. With this mindset, we postulate that materials research is entering discipline unspecific mindset. That is, researchers on materials science and engineering projects self-select based on interests which are independent of academic training. This hypothesis will be tested by analyzing the correlation between academic major and department of the research advisor for ~ 150 applicants to the NSF-site REU program at the USF FMMI. REU applicants are mainly from science (chemistry and physics) and engineering (chemical, mechanical, biomedical, materials, and electrical) disciplines, and are asked to rank three projects of interest among the potential projects proposed by faculty in similar fields. In this paper, the trends between disciplines for the top and top three ranked projects of the applicants will be discussed. Case studies for REU participants will be discussed for illustrations in which the disciplines between REU and faculty are similar and dissimilar.

Evidence of Ferrimagnetism in II-VI Dilute Magnetic Quantum Dots

Jasleen K. Bindra1,2, Lavrenty Gutsev1, Sebastian A. Stoian1,2, Johan van Tol2, Kedar Singh3, Geoffrey F. Strouse1, Naresh S Dalal1,2*

 

1Department of Chemistry and Biochemistry, Florida State University, Tallahassee, Florida 32306, USA
2National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA
3School of Physical Sciences, Jawaharlal Nehru University, New Delhi 110067, India
4Department of Physics, Institute of Science, Banaras Hindu University, Varanasi 221005, India

09:05 AM
Materials Chemisry

The onset of spin frustration with increasing iron incorporation into wurtzite ZnSe is computationally predicted and experimentally tested. Density functional theory (DFT) models indicate magnetic spin frustration arises due to formation of local Fe-Fe spin lattices within the ZnSe lattice. Comparison of the DFT-GGA spin models to the experimentally prepared 1.8 nm Fe0.1Zn0.9Se QD reveal the predicted spin frustration within the QD is observed by comparison to field and temperature dependent Mossbauer and magnetic susceptibility measurements. The use of computational methods that can anticipate the onset of desirable properties apriori in QDs prior to the synthetic preparation will enhance the toolset of the experimentalist when searching for specific magnetic properties.

Fabric Phase Sorptive Extraction: a Unique Integration of Solid Phase Extraction (SPE) and Solid Phase Microextraction (SPME)

 

Abuzar Kabir and Kenneth G. furton

Florida International University

09:25 AM
Analytical Chemistry

Sample preparation remains as the bottleneck in the analytical workflow. As such, the significant improvements in chromatographic separation and mass-spectrometric detection in recent years have not been fully exploited. Among the conventional sample preparation techniques, SPE utilizes exhaustive extraction principle and generally employed small ligands such as C8, C18 bonded to silica particles. SPME, on the other hand, utilizes equilibrium driven extraction principle and primarily employs long-chain organic polymers, immobilized on a fused silica fiber. Although, SPE and SPME are different in principle and applications, both require sample pretreatment processes such as filtration, centrifugation, protein precipitation etc., prior to analyte extraction. These extra steps are laborious, time consuming, and often results in significant analyte loss.

Fabric sorptive extraction (FPSE) is developed to prepare samples containing high volume of interferents without any sample pretreatment. The FPSE device utilizes a piece of fabric as the substrate to chemically bind polymeric sorbent via sol-gel reaction. The sol-gel sorbent provides unique selectivity, sponge-like porous sorbent allows rapid mass transfer of the analyte for analyte-sorbent interaction and the fabric substrate acts as a bait via hydrophilic interactions to lure the target analyte(s). As a result, FPSE provides a near exhaustive extraction in a relatively short period.

After the extraction, the device is exposed to a small volume of organic solvent for analyte back-extraction. Finally, the sample can be injected simultaneously into LC/GC/CE for complementary information. Several recent applications of FPSE for extracting a number of important analytes from different sample matrices will be presented.

 

Extraterrestrial Contributions to the Prebiotic Inventory of the Early Earth from Meteorites

Chris J. Bennett1,2,3, Amy LeBlue-DeBartola1, Brandon Wilson1, Claire Pirim2, Jennifer Noble2, Laurene Tetard1, Alfons Schulte1, Dan Britt1, Andrew Saydjari4, Aaron McKee3, Jay Forsythe3,5, Eric Parker3,6, Ramanarayanan Krishnamurthy7, Facundo Fernandez3, Thomas Orlando3, Nicholas Hud3

1 – University of Central Florida, FL 32816
2 - Université des Sciences et Technologies de Lille, Lille, France
3 – Georgia Institute of Technology, Atlanta, GA 30332
4 – Yale University, New Haven, CT 06520
5 – College of Charleston, Charleston SC 29424
6 – NASA Goddard Space Flight Center, Greenbelt MD 20771
7 – The Scripps Research Institute, La Jolla, CA 92037

09:25 AM
Physical Chemistry

Meteorites, in particular the 4% of carbonaceous chondrites that fall to the Earth, represent some of the most primitive and unaltered bodies in the solar system that we are able to study, and could have contributed an extraterrestrial source of organics to the prebiotic Earth. Of particular interest is the presence of amino acids and related compounds which could have yielded active length peptides within the primordial environment either directly or by production within the heated environment. The amino acids and associated species are found to be in high abundance within certain types of carbonaceous chondrites (specifically CM2 and CR2 groups), presenting an opportunity to try to answer some key questions, such as: i) Are amino acids incorporated into meteorites or formed within them? ii) To what extent are these species present as free acids vs. polymeric forms within the meteorite? iii) Are there spatial associations between acids or polymer abundances with the mineral/metal components found within meteorites? And iv) Does the temperature and history of the meteorite parent body play a role in their abundances and play a role in their production/destruction mechanisms?

Here, we present some recent work investigating the process of the polymerization process on mineral surfaces as well as looking for evidences of these processes by looking at the Murchison (CM2), Allende (CV3), Jbilet Winselwan (CM2), and Tagish Lake (C2?) meteorites. A correlated approach is outlined whereby techniques including Raman and FTIR microscopy, TEM, ToF-SIMS, and some preliminary work using ESI-MS and nanoIR are helping to shed light on some of these questions.

Dechlorination comparison of PCB 153 with ball-milled ZVMg with and without activated carbon

Shannon D. Prendergast, Adibah M. Almutairi, Cherie L. Yestrebsky

University of Central Florida

02:25 PM
Environmental

Polychlorinated biphenyls (PCBs) are a class of man-made halogenated organic compounds that were used in many commercial and industrial applications. PCBs are currently a source of contamination due to leaching into surrounding areas. High toxicity and strict regulations create an urgent need to remediate PCBs in an economical way. In this project, our main objective is to dechlorinate PCBs by using ball-milled zero-valent magnesium (ZVMg), with and without activated carbon, in the presence of acidified ethanol and ethyl lactate (EtOH/EL). The completed experiments showed promising results on the degradation of PCB-153. Degradation-rate constants for both systems in EtOH/EL were calculated. There was a significant difference in the rate of reaction containing activated carbon, as opposed to just using ball-milled ZVMg. A detailed study of the byproducts formed in the dechlorination processes and degradation pathway are presented in this work.

Closing Remarks and Discussion

Deborah Bromfield Lee

Florida Southern College

03:45 PM
Chemistry Education

In this session, we will wrap up the papers with an invitation for discussion and call for collaborations.

Polymer coated lanthanide based nanoparticles as potential PARACEST MRI contrast agents

Pratik Roy, Daniel R. Talham

Department of Chemistry, University of Florida

09:25 AM
Materials Chemisry

Lanthanide based Paramagnetic Chemical Exchange Saturation Transfer (PARACEST) agents offer an alternative to T1 and T2 contrast agents. These systems rely on dynamic chemical exchange of labile protons with bulk water and lead to a decrease in magnetization giving negative contrast in MRI. The major advantage is that one can turn ‘on’ and ‘off’ the image contrast by the application of an external radiofrequency pulse. All published examples of PARACEST agents are single molecule systems, although there are potential advantages to particle-based systems. The interaction of double-hydrophilic block copolymers, containing a poly (acrylic acid) block with europium ions in water leads to the spontaneous formation of polymer-coated nanoparticles, with an average diameter near 20 nm. Saturation transfer experiments with these assemblies show a significant decrease in intensity of the bulk water signal, suggesting it’s potential application as a PARACEST agent.

Development of Complex v2RDM Driven Relativistic CASSCF Methods

Run R. Li and A. Eugene DePrince III

Florida State University

09:20 AM
Computational Chemistry

In order to use ab initio methods to correctly predict the properties of chemical systems containing heavy elements, one must account for both correlation and relativistic effects, including spin-orbit coupling. The complete active space self-consistent-field method (CASSCF) provides a reliable description of nondynamical correlation effects, but the steep scaling of configuration interaction (CI)-based CASSCF precludes its application to large systems. The variational two-electron reduced-density-matrix (v2RDM) driven methods provide a computationally efficient alternative to CI-based approaches. Both scalar relativistic and spin-orbit coupling effects can be captured within an exact two component (X2C) extension of v2RDM-driven CASSCF.  We have developed a complex generalized implementation of the v2RDM approach for X2C-v2RDM-CASSCF computations.  Our preliminary investigations indicate that the complex generalized v2RDM approach has some surprising numerical properties.  For example, in atomic systems, constraints on the expectation values of the square of the total orbital angular momentum and its projection on the z-axis yield quite different results for a given L and different ml values.  It appears that v2RDM computations corresponding to the maximal orbital angular momentum projection provides the best agreement with CI-based computations.

Manganese Dioxide Nanoparticle Formation and Electrochemical Characterization

Juliette Experton, Xiaojian Wu, Gelan Wang, Charles R. Martin

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

10:15 AM
Analytical Chemistry

Manganese dioxide is an environmentally abundant material that shows considerable interest for energy-related applications, such as supercapacitor and cathode material in batteries. However, its use is currently limited by its poor cyclability and its low ionic and electronic conductivities. To overcome these limitations, many strategies have been centered on the design of MnO2 nanoparticles to reduce the diffusion distance for the insertion cations. We have developed a method to grow MnO2 nanoparticles on gold nanotubes in the absence of a direct electrical contact. This method entails using gold nanotubes as bipolar electrode. A voltage of 2 V is applied across a gold nanotube membrane to generate redox reactions, one cathodic and one anodic, at either end of the tubes. The anodic reaction is chosen such that it forms MnO2 nanoparticles at one opening of the nanotubes. We describe here the mechanism of electrodeposition of these MnO2 nanoparticles. Furthermore, electrochemical measurements of conductivity and permselectivity are presented to address the performance of MnO2 as a cathode material in lithium-ion batteries.

Zero-Valent Iron (ZVI) Activation of Persulfate (PS) for Oxidation of 3,5,6-Trichloro-2-Pyridinol

Roaa Mogharbel and Cherie Yestrebsky

University of Central Florida

03:00 PM
Environmental

3,5,6-trichloro-2-pyridinol (TCPy) is the main hydrolytic product of chlorpyrifos, a broad-spectrum organophosphorous insecticide, widely used in agriculture. The USEPA has been listed TCPy as a persistent and mobile pollutant. TCPy is more water soluble than its parent compound, which significantly increases its ability to leach into surface water and groundwater, causing widespread contamination in soils and the aquatic environment. Because of this hazard, the EPA issued a proposal in 2015 recommending that chlorpyrifos use be completely ceased. In this study, the degradation of TCPy by sulfate radicals was evaluated using zero-valent iron (ZVI) activated persulfate (PS) in aqueous media. The reaction kinetics were examined as functions of ZVI concentration, PS dose, and pH. Results show that ZVI-activated persulfate can effectively degrade TCPy in water. Increasing initial concentration of persulfate or ZVI significantly enhances degradation efficiency. ZVI-activated persulfate appeared to be a cost-effective method for treatment of TCPy.

New Approaches for Overcoming Ensemble Mismatches in QM/MM Free Energy Simulations

Phillip S. Hudson, Fiona L. Kearns, Stefan Boresch, H. Lee Woodcock

University of South Florida
University of Vienna

10:15 AM
Computational Chemistry

The hybrid quantum mechanical / molecular mechanical (QM/MM) framework is the current tool of choice when accurate computations of macromolecular systems are essential. However, when carrying out alchemical free energy simulations (FES) with QM/MM, technical and computational challenges necessitate taking an "indirect" approach, i.e., introducing a thermodynamic cycle and using a "low" level of theory (typically MM) to perform the alchemical transformation. This leaves computing the free energy between low and high levels of theory as the main challenge. While this may seem like a straight-forward task, it is fraught with problems. The chief amongst these is the fact that low and high levels of theory often lead to vastly different ensembles; methods to connect these via FES, in an affordable, robust way are essentially non-existent. Herein, we will present new methods that greatly improve both the accuracy and efficiency of computing free energies between MM and QM levels of theory. These include the development, implementation, and validation of both more robust FES techniques as well as new schemes for modifying "low level" potentials to facilitate overcoming disparate ensembles.

Supermolecular Building Layer (SBL) Approach to MOFs for Biomedical Applications

Jarrod F. Eubank, Christian Beauchemin, Eric Alonso, and Juan Garcia

Florida Southern College

10:15 AM
Materials Chemisry

The necessity for materials with targeted functions for various applications has driven scientists to pursue rational synthetic strategies toward design. The relatively recent development of a class of inorganic-organic hybrid materials known as metal-organic frameworks (MOFs) has significantly aided in the advancement of modern synthetic strategies toward functional materials due to their ease of construction and exceptional tenability. Efforts began with the use of simple molecular building blocks (MBBs, resulting in geometric moieties having multi-connectedness (i.e., greater than 2-connected)) and advanced to more hierarchically complex, and thereby more selective, design strategies like the supermolecular building block (SBB) and, more recent, supermolecular building layer (SBL) techniques. These exclusive approaches have opened avenues to materials with unprecedented or previously difficult to attain properties, such as pores lined with free carboxyl groups. Here, we focus on the SBL approach to target materials for biomedical applications. Preliminary work indicates the ability to design and utilize carboxyl-functionalized MOFs for drug delivery applications. In addition, the construction of MOFs via the incorporation of bioactive molecules suggests potential for additional biomedical applications.

Avoiding misidentification of phosphopeptides: Exploring the factors that enhance and inhibit phosphate scrambling in peptide sequencing

Laura S. Baileya, Melanie Alvasb, Nicolas Galyc, Amanda L. Patricka, Nicolas C. Polfera

a University of Florida, Department of Chemistry, Gainesville, FL, USA
b Sorbonne Université, Paris, France
c Université Paul Sabatier, Toulouse, France

10:35 AM
Analytical Chemistry

Phosphorylation is one of the most ubiquitous post-translational modifications (PTM) in proteins, and thus plays a critical factor in many regulatory mechanisms. Although this PTM is most commonly found on serine (90%), threonine (10%), and tyrosine (0.05%), it has also been found on histidine and arginine (mainly in eukaryotes) [1]. Mass spectrometry-based sequencing is the key technology for peptide/protein identification, as well as identification of any PTMs. This typically involves peptide fragmentation via collision-induced dissociation (CID). However, the high lability of PTMs often leads to uninformative fragmentation, such as loss of these groups. Even more worryingly, phosphate groups may be subject to intramolecular transfer—often referred to as sequence “scrambling”— which may result in incorrect sequencing [2]. In a systematic study, we aim to determine the mechanism behind phosphate scrambling and if this transfer can be minimized.

Our template sequence G[B]AXDAAPAAXAPAA[B]AAR (where XD is phosphorylated donor tyrosine or serine residue, XA is a non-phosphorylated acceptor residue, and [B] represents where a basic residue may be added) was simplified from Cui and Reid’s work. The most scrambled Reid sequence, GRApSpSPVPAPSSGLHAAVR, showed an average rearrangement of 42.3% (defined as the number of scrambled fragments verses the sum of scrambled and un-scrambled fragments), and similar sequences showed scrambling ratios ranging from 10% to 50% [3]; however, our simplified alanine version only showed 2% scrambling. In a systematic study of 13 sequences, we investigated how several parameters affected phosphate scrambling, including the phosphate donor and acceptor identity (tyrosine vs. serine), the number of donors and acceptors (1:1, 1:2, and 2:2 donor:acceptor ratios), the contribution of basic residues, and the position of the basic residue near either the carboxy- or amino-terminus. While the number and identity of donors and acceptors had little effect on scrambling (scrambling ratios of 0.1-5%), higher scrambling ratios were observed when a basic residue was added near the carboxy-terminus (14% for arginine and 30% for histidine).

Secondly, we sought to inhibit the intramolecular transfer, thereby eliminating the appearance of scrambled fragments. Towards this end, appearance of scrambled fragments was investigated based on the timescale of activation (i.e., slow vs. fast), location of fragmentation (i.e., trap vs. collision cell), and charge state. Fast activation nearly eliminated scrambling in the histidine sequence (2% scrambling). Further, increasing the charge state decreased the appearance of scrambled fragments from 30% ([y11+HPO3]+1) for a charge state of +2 to 15% ([y10+HPO3]+2) for the +3 charge state and 5% ([y7+HPO3]+2) for the +4 charge state. Therefore, while histidine appears necessary for the transfer of phosphate, the specificity of conditions (especially the protonation of the mediating residue) would indicate it’s an uncommon occurrence in proteomics.

 

[1] Proteomics 2013, 13 (6), 910–931.

[2] J. Mass Spectrom. 2009, 44 (6), 861–878.

[3] Proteomics 2013, 13 (6), 964–973.

In situ treatment systems for remediation of polychlorinated biphenyl-contaminated building materials

Adibah Almutairi, Charles G. Lewis, Christian Clausen, Cherie Yestrebsky.

University of Central Florida

03:20 PM
Environmental

Poly-Chlorinated Biphenyls (PCBs) are a family of synthetic organohalides comprising 209 congeners which were used historically as additives in paint over a span of many years. Even though the production of PCBs in the USA has been banned since the late 1970s due to their carcinogenic nature, their former prevalence and widespread use means many structures are still coated with PCB-laden paints. This results in an urgent need for development of a cost-effective method to extract and degrade PCBs from contaminated materials. Experiments employing reductive dehalogenation through the use of zero-valent magnesium (ZVMg) ball-milled with activated carbon (AC) in an acidified solvent system have shown that PCBs can be broken down. This research describes the development of two delivery systems for effective deployment of this treatment reaction to field samples. Two treatment systems formulated in this process, the Non-Metal Treatment System (NTMS) and the Activated Metal Treatment System (AMTS), are capable of extracting or extracting and degrading, respectively. In the development of NMTS and AMTS, an acidified dual system of ethanol/ethyl lactate and an acidified 2-BOE were used as solvents while ZVMg over activated carbon is used in the AMTS. After development, applications of the systems extended to laboratory prepared PCB-laden paint as well as field samples received from Seattle. PCBs were degraded significantly below their starting concentrations with removal efficiency greater than 99% for all samples after treatment. The use of acidified 2-BOE and ZVMg permitted the extraction and destruction of PCBs from contaminated building materials in a one-step treatment.

Embedded cluster density approximation for exchange-correlation energy

Chen Huang

Department of Scientific Computing, Florida State University

10:40 AM
Computational Chemistry

Accurate, large-scale electronic structure simulations are essential for understanding the properties of materials and molecules at the nanoscale. Kohn-Sham density functional theory (KS-DFT) is widely used for large-scale material simulations, however, its accuracy is limited by the accuracy of the exchange-correlation (XC) functionals. As we are improving the accuracy of XC functionals, KS-DFT starts to lose its computational efficiency. In this presentation, we discuss our effort on developing the embedded cluster density approximation (ECDA) method for scaling up high-level KS-DFT simulations in large systems. In ECDA, for each atom (called central atom) its nearby atoms are selected as its buffer atoms. The central atom and its buffer atoms form the cluster. The rest atoms define the environment. The system’s electron density is partitioned among the cluster and its environment based on the finite-temperature density functional embedding theory. The obtained cluster is embedded in the system and is a small Kohn-Sham system whose XC energy density is calculated using a high-level XC functional. System’s XC energy is constructed by patching these locally computed, high-level XC energy densities over the entire system in an atom-by-atom manner. A key step is to efficiently compute the system's XC potential for the patched XC energy. We directly take the functional derivative of the patched XC energy with respect to the electron density without invoking the system's unoccupied orbitals, therefore making ECDA computationally efficient for investigating large systems. Since ECDA is a variational method, forces can be efficiently calculated based on the Hellmann-Feynman theorem. The accuracy of ECDA is investigated by patching the random phase approximation correlation energy in one-dimensional hydrogen chains, and by patching the exact exchange energy in molecules.

Fe3Se4 Phase Stabilized by Transition Metal Doping

Luis A. Saucedo, David Hardy, Geoffrey F. Strouse, Michael Shatruk

Florida State University

10:35 AM
Materials Chemisry

With a growing interest in rare-earth free magnetic materials, Fe3Se4 is a promising material, being composed of earth-abundant elements and showing ferrimagnetic ordering at 340 K.  In a common synthesis of this material, elemental selenium is used as a precursor, resulting in long reaction times and the presence of ferrimagnetic Fe7Se8 or superconducting FeSe impurity. Herein we show a synthetic route using molecular precursors, which allow not only for shorter reaction times, but also for stabilization of the Fe3Se4 phase by doping with small concentrations of 3d transition metals (e.g., V, Cr, Mn). The synthesis, characterization and magnetic studies of these materials will be discussed.

Triumphs and Tribulations in the Molecular Modeling of Porous Materials

Brian Space

University of South Florida

11:05 AM
Computational Chemistry

Highly accurate molecular models for gas sorption in MOF's have been extensively applied to both hydrogen and carbon dioxide – critical comparisons between models are considered. Calculated observables such as isosteric heats, sorption isotherms and compressibilities are objectively compared with experimental measurements and found to be in excellent agreement. A series of MOF structures have been examined from non-polar to polar and open to confined to assess the what topologies and associated potential energy interactions are responsible for increased sorption. Polarization interactions are shown to be essentially many body in nature and non-negligible considering MOF”s that are promising soprtion candiates for multiple applications as the interactions are tunable. Widely used models for other sorbates are found to be unpredictable in fidelity and unreliable, yet continue to see wide acceptance. This has troubling implications for biological simulations as well, where poorly constructed force fields are ramapant.

Revisiting Bond Breaking and Making in the Solid State: Where are the Electrons?

Xiaoyan Tan,1 Alexander A. Yaroslavtsev,2 Vincent Yannello, Zachary P. Tener,1 Daniel Haskel,3 Francois Guillou,4 Andrey Rogalev,4 Michael Shatruk1

1 Department of Chemistry and Biochemistry, Florida State University, Tallahassee, FL 32306, USA
2 European XFEL GmbH, 22869 Schenefeld, Germany
3 Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA
4 European Synchrotron Radiation Facility, 71 Avenue des Martyrs, CS40220, Grenoble, France

10:55 AM
Materials Chemisry

More than 30 years ago, a seminar paper by Hoffmann and Zheng [1] addressed the chemical aspects of first-order phase transitions in ThCr2Si2-type structures. They suggested that the breaking and making of the X–X bonds between the [T2X2] layers (X = group 13-16 element; T = transition metal), separated by layers of alkali, alkali-earth, or rare-earth metal atoms (A), correlates with the filling of the electronic d-band of the transition metal. Such correlations have been the focus of many studies on structural, electronic, and magnetic phase transitions in this class of materials.

The structural phase transitions in the ThCr2Si2-type materials involve the collapse or expansion of the structure along the tetragonal c axis, i.e. in the direction parallel to the interlayer X–X bonds. Despite many examples of such transitions being known, the direct experimental assessment of changes in the electron density redistribution between the A and [T2X2] layers upon the formation and breaking of the X–X bonding interactions is largely lacking. Earlier studies by us [2] and other groups [3] have revealed fascinating pressure-induced transitions in EuCo2Pn2 (Pn = P, As) which are accompanied by the change in the Eu oxidation state and the transition from the localized (4f) magnetism to itinerant (3d) magnetism. In the present contribution, we demonstrate that the changes in the electron concentration in the [Co2Pn2] layer defy the formal electron-counting rules that are often used for Zintl-like phases. X-ray absorption measurements offer the direct insight into the changes in the Eu oxidation state and magnetism and the associated redistribution of the electron density in the [Co2Pn2] layer.

The research reported in this presentation has been supported by the National Science Foundation under Award DMR-1507233.

1. Hoffman, R.; Zheng, C. J. Phys. Chem. 1985, 89, 4175–4181.
2. Tan, X.; Fabbris, G.; Haskel, D.; Yaroslavtsev, A. A.; Cao, H.;  Thompson, C. M.; Kovnir, K.; Menushenkov, A. P.; Chernikov, R. V.; Garlea, V. O.; Shatruk, M. J. Am. Chem. Soc. 2016, 138, 2724-2731.
3. Chefki, M.; Abd-Elmeguid, M. M.; Micklitz, H.; Huhnt, C.; Schlabitz, W.; Reehuis, M.; Jeitschko, W. Phys. Rev. Lett. 1998, 80, 802-805.

Surface Enhanced/Quenched Fluorescence near a nanorod

Shengli Zou and Yadong Zhou

University of Central Florida

01:30 PM
Computational Chemistry

Using a developed model, we showed that surface enhanced fluorescence for molecules or quantum dots near a cylindrical nanorod can not be predicted using the conventional method. We studied the position dependence of the emitter near the nanorod and also investigated the emission wavelength and incident polarization dependence of the enhanced fluorescence signals. The model was also verified by comparing the calculated the enhancement factors of surface enhanced Raman scattering with those measured in the experiments.

Tuning the Selectivity Between C2H2 and CO2 in Molecular Porous Materials

Tony Pham,1 Katherine A. Forrest,1 Kai-Jie Chen,2 Douglas M. Franz,1 Michael J. Zaworotko,2 and Brian Space1

 

1.) Department of Chemistry, University of South Florida, 4202 East Fowler Avenue, CHE205, Tampa, FL 33620-5250, United States
2.) Department of Chemical & Environmental Sciences, University of Limerick, Limerick, Republic of Ireland

01:30 PM
Materials Chemisry

Experimental and theoretical C2H2 and CO2 adsorption studies were performed in MPM-1-Cl and MPM-1-TIFSIX, two robust molecular porous materials (MPMs) with the empirical formula [Cu2(adenine)4Cl2]Cl2 and [Cu2(adenine)4(TiF6)2], respectively. Both MPMs consist of a hydrogen-bonding network that is self-assembled by dinuclear copper–adenine paddlewheel complexes. The difference between the two structures is simply the axial ligand. Experimental measurements revealed that MPM-1-Cl displays higher low-pressure uptake, isosteric heat of adsorption (Qst), and selectivity for C2H2 than CO2, whereas the opposite is true for MPM-1-TIFSIX. Dynamic breakthrough experiments and modeling studies confirmed that MPM-1-Cl is more selective toward C2H2, while MPM-1-TIFSIX is more selective toward CO2. Molecular simulations revealed that both MPMs display a greater preference for C2H2 within their large channels. However, MPM-1-TIFSIX contains a small accessible channel in the structure that is not present in MPM-1-Cl; this channel represents the primary binding site in the material. Calculation of the classical MPM–adsorbate interaction energies and diffusion barriers about the primary binding site in MPM-1-TIFSIX revealed that this site is more favorable for CO2 than C2H2, thus explaining why the selectivity in this MPM is inverted relative to MPM-1-Cl.

Development of electronic unsaturation in transition metal cluster complexes: Addition of Pt(IPr) groupings as sterically demanding ligands

Vincent J Zollo Jr, Sedigheh Etezadi, Burjor Captain

University of Miami

08:45 AM
Inorganic Chemistry

Nature has utilized catalytic properties of transition metals all throughout time seen electron transport in oxidative and reductive pathways and the centers of enzymes found in every form of life. On the lab bench, we try to mimic the action through analogous species using a synthetic approach. The development of electronic unsaturation in transition metal complexes has been widely studied for its role in small molecule activation and catalysis. The 14 electron compound Pt(SnBut3)(IPr)(H), 1 [IPr = N,N’-bis-(2,6-(diisopropyl) phenyl)imidazole-2-ylidene] was reacted with transition metal carbonyl cluster complexes. This yielded numerous mixed-metal cluster compounds structurally determined by single crystal x-ray diffraction, mass and NMR spectroscopy. The reaction between 1 and Ru56-C)(CO)15 resulted in three mixed-metal clusters: PtRu56-C)(IPr)(CO)15, 2 Pt2Ru56-C)(IPr)2(CO)15 , 3 H2PtRu55-C)(IPr)(CO)14 it was shown 2 was able to activate H2, while 3 showed dynamic activity in solution. The progression of the development of unsaturated complexes was furthered using M3(CO)12 (M = Fe, Ru, Os) starting reagents. Seven new mixed-metal cluster complexes were synthesized. Working under the assumption each metal obeys the 18 e- rule, unsaturation was found amongst most species. Moving down the triad, the reaction of 1 with Fe3(CO)12 afforded triangular Fe-Pt complexes: PtFe2(IPr)(CO)9, 4 and Pt2Fe(IPr)2(CO)6, 5. The reaction of 1 with Ru3(CO)12 resulted with a trigonal bipyramid structure Pt2Ru3(IPr)2(CO)12, 6.  The reaction of Os3(CO)12 with 1 is the most interesting. This gave mono and bis Pt(IPr) equatorial adducts: PtOs3(IPr)(CO)12, 7 and Pt2Os3(IPr)2(CO)12, 8 and a dihydride Pt(IPr) adduct, (µ-H)2PtOs3(IPr)(CO)10, 9. Most notable formed is the asymmetric raft, PtOs4(IPr)2(CO)12, 10 as well as its carbonyl substitution product PtOs4(IPr)(CO)13, 11 . This increased development of unsaturated species serves as a platform for prominent pre-cursor catalysts to those found in nature.  The synthesis, characterization, and application will be further discussed with insight to the complex bonding of sterically demanding ligands.

Small molecule modulation of the 14-3-3 interactome

James H. Frederich

Florida State University

01:30 PM
Biochemistry / Chem Bio.

14-3-3 proteins are an abundant family of adapter molecules that regulate the activity of several hundred cellular client proteins by forming transient protein-protein interactions (PPIs). Many of these PPIs are involved in phosphorylation-dependent signaling pathways that govern cellular homeostasis. Consequently, 14-3-3 PPIs are attractive targets for drug discovery; however, the development of a small-molecule that can selectively target one 14-3-3 PPI among several hundred has been a major challenge. Herein, we present our efforts to craft selective 14-3-3 PPI stabilizers from the natural product fusicoccin A.

Exploring (R)-9bMS, a small molecular inhibitor of ACK1-AR epigenetic circuitry in Triple Negative Breast Cancer

Mithila Sawant, Nupam Mahajan

Moffitt Cancer Center, 12902 Magnolia Drive, Tampa, FL 33612, USA
Department of Oncological Sciences, University of South Florida, Tampa, FL 33612, USA

02:05 PM
Biochemistry / Chem Bio.

The highly aggressive Triple Negative Breast Cancers (TNBCs) constitute approximately 20% of total breast cancers. The unavailability of a genuine target in TNBCs, unlike ER/HER2 positive cancers restricts their treatment modalities. Recent studied in our lab have identified ACK1 (also known as TNK2) non-receptor tyrosine kinase as a critical contributing factor towards the aggressiveness and invasive capacity of TNBCs. A positive correlation between the expression of ACK1 and high proliferation rate, invasion and colony forming potential of TNBCs was observed, which could be abolished by genetic ablation of ACK1. In addition, recent studies from our lab have established the existence of positive feedback circuit wherein ACK1 directly phosphorylated histone H4 at Tyr88 residue, upstream of AR gene locus. This novel epigenetic role of ACK1 in regulating AR expression was shown to be crucial for developing drug-resistance in Castration resistant prostate cancer cells (CRPCs). Numerous recent reports have emphasized on the emerging role of Androgen Receptor (AR) as a prospective target in breast cancer. Thus exploring ACK1 and its downstream effector AR as plausible hits to circumvent the problem of lack of expression of targetable receptors may provide clinical benefits in TNBCs. We have designed a small molecular inhibitor of ACK1, (R)-9bMS, which has shown to be potent inhibitor of prostate cancer and TNBCs. (R)-9bMS stalled the cell proliferation of high ACK1 and AR expressing TNBC cell lines. (R)-9bMS was successful in not only diminishing the ACK1 expression, but also exerted an epigenetic shutting-down of AR transcription, reflected in loss of TNBC xenograft tumor growth. Our data strengthens the candidature of (R)-9bMS as potent anti-cancer agent and accentuates that abolishing the ACK1 addiction of TNBCs using ACK1 small molecular inhibitors could serve as a potential therapeutic intervention

A molecular simulation investigation of PEGDA nanogels

Shalini J. Rukmani1, Ping Lin2, Coray M. Colina1,2

1. Department of Materials Science and Engineering, University of Florida, Gainesville, 32611, USA
2. Department of Chemistry, University of Florida, Gainesville, 32611, USA

01:55 PM
Computational Chemistry

PEG (polyethylene glycol) based nanogels have been widely used in biomedical applications due to several attractive properties including biocompatibility and versatile end group chemistry. In this work, we studied the effect of varying cross-linking densities and topological features on the structural properties of PEGDA (PEG-diacrylate) nanogels using atomistic molecular dynamics simulations. Topology diagrams were constructed to study the distribution of cross-linked junctions and meshes formed in these networks. It was found that the radius of gyration, average mesh sizes and hydrophilicity decreased as a function of the cross-linking density. The shapes of these nanogels for different topologies were characterized by calculating the aspect ratios based on the gyration tensor. Nanogel structures with higher cross-linking densities showed a globular shape while structures with lower cross-linking density showed shape anisotropy. The connectivity and distribution of the cross-linked junctions played a major role in determining the size, shape anisotropy and hydrophilicity of PEGDA nanogels.

Unusual Magnetic Behavior of σ-Dimerizing Organic Radicals

Alina Dragulescu-Andrasi, Hoa Phan, Xiang Li, Yan-Yan Hu, Eugene DePrince, Minyoung Jo, Michael Shatruk

Florida State University, Department of Chemistry and Biochemistry

08:30 AM
Organic Chemistry

Many stable organic radicals are well-known to undergo Peierls dimerization in their π-π stacked solid-state structures. Recently, we demonstrated that certain π-radicals, which σ-dimerize upon cooling, can undergo light-induced splitting into the pair of π-radicals in the solid state. The photo-generated paramagnetic structure exhibits remarkable thermal stability, which allows one to interrogated its physical properties using conventional static methods, such as X-ray crystallography, UV-visible spectroscopy, or magnetometry. In this contribution, we report another unconventional phenomenon that leads to abrupt and hysteretic switching between paramagnetic π-radical and diamagnetic σ-dimer states. The switching effect is based on the transition between the plastic-crystal phase with dynamic rotational disorder and a normal crystalline phase in the dimerized form. A comprehensive investigation of this phenomenon with experimental and theoretical methods will be reported.