Abstracts

Keynote Session Abstracts#

Lester Andrews Graduate Research Symposium Keynote

Selective, Catalytic Functionalization of C-H Bonds

Dr. John F. Hartwig
University of California, Berkeley, CA 94720 (USA)
Division of Chemical Sciences, and Lawrence Berkeley National Laboratories, Berkeley, CA.

The selective introduction or modification of functional groups in complex molecules has been a longstanding challenge in catalysis. Our group has developed practical methods for the catalytic functionalization of C-H bonds with main group reagents, which led us to a general strategy to use one C-H bond functionalization process to form a range of products. We have also sought developed methods for the selective amination of C-H bonds in complex molecules and oxidation of C-H bonds in light alkanes. Selected examples of such processes with an emphasis on the fundamental mechanistic issues will be presented.

In addition to developing reactions of small-molecule catalysts, we have sought to combine the reactivity of catalysts based on noble metals with the selectivity and evolutionary potential of enzymes. To do so, we have created artificial heme enzymes in which the iron of the heme has been replaced with noble metals to create catalysts for reactions that have not been catalyzed by natural or mutant heme enzymes.

This lecture will present recent directions of research in our group toward discovering selective reactions of organic molecules with noble metal complexes and noble-metal enzymes. The design and selection, as well as the intimate mechanism, of catalysts and catalytic reactions for these selective functionalization processes will be presented.

Oral Presentation Abstracts#

Session 1#

Synthesis of Monosilylated 1,4-Diketones, Substituted Pyrroles and Tetrahydroindoles via Silyloxyallyl Cation Intermediacy

Joshua A. Malone, Rendy G. Kartika
Department of Chemistry, Louisiana State University

The relevance of pyrroles, tetrahydroindoles and indoles in various natural products and pharmaceutical relevant motifs, provide important synthetic targets in organic synthesis. We showcase a methodology for nucleophilic capture of unsymmetrical silyloxyallyl cations with various silylenol ethers to afford differentiated 1,4-diketones in a regioselective manner. Following nucleophilic capture, condensation with various amines affording a variety of substituted pyrroles and tetrahydroindoles.

Dehydration of Tertiary Alcohol with Triphosgene-DMAP under Mild Conditions

Moshood O. Ganiu, Alexander H. Cleveland, and Rendy Kartika
Department of Chemistry, Louisiana State University, 232 Choppin Hall, Baton Rouge, Louisiana 70803, United States

The synthesis of alkenes via the dehydration of alcohol represents one of the well-known and oldest synthetic method. While there exist various methods for the elimination of alcohol to generate alkene, many of them make use of strong acid, produce various side products, and are neither regio nor stereoselective. Herein, we report a benign, regioselective and stereoselective method for the elimination of tertiary alcohols. This fascinating transformation was achieved via the action of Triphosgene and DMAP at room temperature. Most substrates explored using this methodology produce CO₂ as the only side product. However, some substrates produce the competing chlorination as a minor side product which can easily be separated upon purification using flash chromatography.

Development of a Novel Pentafluorobenzylisothiocyanate for Use as a Chiral Derivatizing Agent

Emily B. Crull and Matthew G. Donahue
Department of Chemistry and Biochemistry, University of Southern Mississippi

A chiral, non-racemic compound’s absolute configuration directly influences its chemical, physical, biological, and pharmaceutical properties. The use of nuclear magnetic resonance spectroscopy in the determination of absolute configuration is an appealing prospect due to its wide spread availability and ease of use. One method of accomplishing this is through the use of chiral derivatizing agents (CDAs) that form a covalent bond with the chiral substrate. We have developed a pentafluorobenzene CDA that has no aromatic protons thereby allowing for simpler proton NMR interpretation. A novel chiral, non-racemic C₆F₅ benzylisothiocyanate has been synthesized over four-steps from pentafluorobenzaldehyde. The reaction of this isothiocyanate with chiral amines results in the production of diastereomeric thioureas. This new chiral adduct causes a change in the electronic structure inducing ¹H, ¹³C, and ¹⁹F NMR signals for the chiral compound to shift. The electron withdrawing properties of the pentafluorophenyl ring allows for the two enantiomers of each amine to be differentiated by ¹H, ¹³C, and ¹⁹F NMR. Comparison of the observed chemical shifts with those calculated at the B3LYP 6-31G* level has served as the basis for a predictive model for determining enantiomeric excess by NMR.

Session 2#

Strategic Development of a Synthetic Route for the Preparation of a Tri-Substituted Quinoline as a Potential Treatment for HIV-1 by Allosteric Integrase Inhibition

Jared Hume, Nicholas Jentsch, Alison Hart, Jian Sun, Julie Pigza, Jacques Kessl, Matthew Donahue
Department of Chemistry and Biochemistry, University of Southern Mississippi

The human immunodeficiency virus (HIV) is a retrovirus that is known to develop resistance to treatments. This requires a large array of medications that can be easily exchanged and target various stages of the virion’s life cycle. Recent developments have shown quinoline derivatives to be capable of allosteric noncovalent bonding with recombinant HIV integrase. This is significant because all three approved HIV integrase medications on the market inhibit HIV integrase by binding to the enzyme’s active site. The creation of a more varied medication regime is important for when resistance to treatment arises. HIV integrase is an essential viral enzyme in the replication of the virus and is an ideal clinical target. The heterocyclic quinoline derivatives are synthesized in an eight-step sequence from commercially available materials. Over the course of this campaign, a particularly challenging aryl-aryl bond formation was encountered. Specifically, 4-chloro-3-iodo-2-methylquinoline underwent metalation with isopropylmagnesium chloride and copper bromide dimethylsulfide followed by a quench with ethyl chlorooxoacetate. The resulting α-ketoester was then carried forward through three additional steps to a common intermediate to be derivatized at the 4-position of the quinoline scaffold using a palladium-catalyzed Suzuki coupling reaction. This presentation will focus on the development of the synthetic route used to make these compounds and the challenges that occurred during scale-up and purification of the late stage intermediates. The assay results to inhibit HIV-1 integrase will also be discussed.

Novel catalyst assessment for CO₂ reduction efficiency

Ekta Goel, David O Wipf
Department of Chemistry, Mississippi State University

Excess CO₂ emissions are the leading cause of global warming. Plants reduce CO₂ while producing life-sustaining O₂ but reproducing this process still evades scientists. Thus, developing efficient and scalable methods for electrochemical conversion of CO2 to value added products is a major focus area in Green Chemistry.

This work assesses two novel catalysts to perform homogeneous CO₂ reduction. Catalyst performance is evaluated against a Ni(cyclam) complex as a standard. A small volume three electrode cell is used with glassy carbon working electrode, a platinum mesh counter electrode, and Ag/Ag⁺ reference electrode. Controlled potential electrolysis of the catalyst dissolved in a CO₂ saturated solution generates CO and H₂ (due to water splitting) which are quantified by gas chromatography equipped with TCD(thermal conductivity detector) and FID (Flame ionization detector). This information gives the faradaic efficiency of the system and provides an estimate of the catalyst’s feasibility for CO₂ reduction.

Synthesis and Evaluation of Ruthenium Complexes with Cytotoxicity Against Cancer Cells.

Ambar B. Shrestha, Jessica L. Gray, Fengrui Qu, Seungjo Park, Yonghyun Kim, Elizabeth T. Papish
Department of Chemistry and Biochemistry, The University of Alabama, Tuscaloosa, AL 35487

Metal based non-porphyrin anticancer drugs have been studied for decades as potential cytotoxic agents following the debut of cis-platin as a clinical drug for the treatment of various neoplastic diseases. However, life threatening side effects of cis-platin made researchers seek alternatives for use in photodynamic therapy (PDT) with photosensitizers as well as photo-activated chemotherapy (PACT). Several ruthenium based complexes of the type [(N,N)₂Ru(6,6'-dhbp)]²⁺ (6,6'-dhbp = 6,6'-dihydroxybipyridine) have been synthesized in our group and studied for their selective cytotoxicity towards cancer cells (Inorg. Chem. 2017, 56, 7519). Here we report our efforts to synthesize two new ruthenium complexes that extend the conjugation of the aromatic spectator ligands. Light triggered photodissociation, singlet oxygen production, and cytotoxicity will be studied.

Session 3#

Surface modified ground rubber tire (GRT) for the removal of lead from contaminated water

Achala S. Liyanage, Suranga M. Rajapaksha, Zoe Beckworth, Dennis W. Smith Jr. and Todd Mlsna
Department of Chemistry, Mississippi State University

The disposal of waste tire rubber has become a major environmental issue that poses a serious threat to natural environments around the world. Hence, the management and disposal of waste tires is a matter of concern. In this study, recycled ground rubber tire (GRT) particles were modified to remediate contaminated water. Chitosan-modified GRT was synthesized as a potential low-cost adsorbent for the removal of lead from waste water systems. The surface chemistry and composition of the raw GRT and chitosan-modified adsorbents were examined by attenuated total reflection Fourier transform infrared spectroscopy, scanning electron microscopy, scanning electron microscopy/energy dispersive X-ray spectroscopy, thermal gravimetric analysis, and surface area measurements. These characterizations confirm successful grafting of chitosan onto GRT. Batch sorption studies were carried out at 298 K, pH values from 2 to 6, with different contact time up to 24 h, and with different initial adsorbent concentrations. Remediated solutions were then analyzed using atomic absorption spectroscopy. Kinetic data were fitted using pseudo-first-order and pseudo-second-order models. Results indicate that pseudo-second-order equations provide the best correlation for the adsorption data. Results show that chitosan coating on GRT can improve its performance as an adsorbent and therefore suggest that chitosan modified GRT can be used as an effective and low-cost adsorbent for metal ion remediation from contaminated water systems.

Quantitative Study of Fluorophore Assembly and Disassembly Using Combination of UV-vis, Fluorescence, and Polarized Resonance Synchronous Spectroscopy

Buddhini C. Nugaduwa Vithanage and Dongmao Zhang
Department of Chemistry, Mississippi State University

Persistent intense interest into the assembly and disassembly of molecular aggregations are stimulated by their importance in biological machineries, as well as their potential applications in photonics. However, understanding of optical properties of the assembled molecular fluorophores is challenging because of the complexity of the interplay of the photon absorption, scattering, and emission that can concurrently occur in sample containing aggregated fluorophores. With their unique photochemical properties, Porphyrins have remained a central research topics for decades for their applications ranging from chemistry, biology, medicine, and photovoltaic. Porphyrin can self-assemble into a tubular structures at acidic pHs. However, possibility of the disassembly of the aggregated porphyrin has not been investigated. Using meso- tetrakis (4-sulfonato phenyl) porphyrin (TPPS) as the model molecule, reported herein is combined UV-vis extinction, Stokes-shifted fluorescence, and polarized resonance synchronous spectroscopic (PRS2) study of porphyrin assembly and disassembly at acidic solutions. Series of optical constants including photon absorption and scattering cross-sections as well as fluorescence and light scattering depolarizations has been quantified. The sharp difference in the fluorescence depolarization of the monomer and assembled porphyrin highlights the effectiveness of PRS2 for monitoring the fluorophore assembly. Kinetics studies revealed that porphyrin assembly and disassembly is an extraordinarily slow processes, lasting at least for two months’ sample incubation period. Besides providing a series of new insights to the porphyrin assembly and disassembly, the methodology described in this work should be directly applicable for quantitative understanding of the optical properties of self-assembled materials including molecular aggregates and supramolecular species.

Phase Transferable Polymer Encapsulated Bimetallic Nanoparticles

Matthew Confer^1,2, Dr. Shane Street^1
1Department of Chemistry and Biochemistry, University of Alabama
²Department of Chemical and Biological Engineering, University of Alabama

Polymer encapsulated nanoparticles (NPs) have potential applications in devices, biomedical nanotechnology, and as catalysts. It is known that such particles retain their catalytic activity in solution as pseudo-homogeneous catalysts, effectively bridging homogeneous and heterogeneous catalysis. Here, a method to separate NP catalysts from a reaction mixture is demonstrated which involves making the encapsulating polymer phase transferable between immiscible organic and aqueous phases. Polyethyleneimine, a water soluble cationic polymer, was modified to be soluble in a water immiscible organic phase (hexane) via partial monoalkylation by reductive amination of terminal amines using aldehydes. The product has secondary amines which are protonatable to allow for shuttling between phases. A “one pot” co-reduction of modified polyethyleneimine encapsulated CuPt bimetallic NPs was used to produce phase transferable catalysts. The structure and activity of the NPs encapsulated in the polymer substrate are dependent of their mechanism of formation, including solvent environment. These particles can catalyze both aqueous phase reactions (e.g. dehydrogenation of ammonia borane) and organic phase reactions (e.g. Suzuki coupling). The polymer encapsulated bimetallic NPs have been evaluated for activity, separation efficiency, and reuse in reactions in either phase.

Chromium ion removal from aqueous media by aluminum and magnesium impregnated biochar

Amali Herath, Cody Layne, Griffin Burk, Todd Mlsna
Department of Chemistry, Mississippi State University

Heavy metal contamination of water bodies by anthropogenic activities is inevitable. Therefore, the development of a cost effective and efficient treatment method is immensely important. Biochar is a promising candidate for the removal of heavy metal contaminants and has received great attention in the scientific community due to its inherent low cost of production and high absorption capacity. Douglas fir biochar (DFBC) produced from fast pyrolysis was impregnated with 5% aluminum sulfate and magnesium chloride. The resulting biochar was characterized by point of zero charge, thermogravimetric analysis, scanning electron microscopy, and transmission electron microscopy. The BET surface area reduced from 535 m²/mg to 316 m²/mg following the metal ion loading. Energy Dispersive X-ray spectroscopy provided evidence for the facile impregnation of Al and Mg into the biochar. Batch sorption investigation of chromium solution on Al/Mg biochar was carried out at pH values ranging from 2 to 10 while the adsorbate concentration varied from 5 to 300 mg/L. The sorption of chromium was monitored by UV-visible spectroscopy at 370 nm. The effect of temperature on sorption was studied at 25, 35 and 45 °C and adsorption isotherms were analyzed at different temperatures, ranging from 25-45 °C using Langmuir, Freundlich, Redlich-Peterson, Toth, and Sips isotherm models. Langmuir adsorption isotherms give a maximum adsorption capacity of 80 mg/g at pH 6.5 and at 45 °C. It can be concluded that Al/Mg Douglas fir biochar is a more effective adsorbent for chromium ion removal compared to untreated Douglas fir biochar.

Graphene coated pine wood biochar to decontaminate Cu (II) from aqueous solutions

Hasara Samaraweera, Dr. Todd Mlsna
Department of Chemistry, Mississippi State University

Biochar-based nano-composites are emerging materials used for application in metal decontamination. The introduction of biochar functionalized with nanomaterials enhances the removal efficiency of biochar. In this study, pine wood waste was pretreated with ~1% Graphene suspension, followed by slow pyrolysis under Nitrogen at 600 °C for 1 h. This produced a highly porous novel Graphene coated pine wood biochar (GPBC) and was used for the removal of Cu (II) from aqueous solutions. Only a small percentage of Graphene was incorporated (weight percentage, ~1%) into the pine wood feedstock. Copper(II) removal efficiency of GPBC increases by 53% compare to unmodified biochar (PBC). Langmuir maximum adsorption capacities and BET surface area of GPBC and PBC are 12.4 mg/g, 608 m²/g and 8.9 mg/g, 483 m²/g respectively. Both GPBC and PBC were characterized by determining point of zero charge (PZC), thermo gravimetric Analysis (TGA), Fourier Transform Infrared spectroscopy (FTIR), X ray diffraction Spectroscopy (XRD), BET isotherm, scanning and transmission electron Microscopies (SEM and TEM) and energy dispersive X-ray spectroscopy (EDS). Cu (II) sorption equilibrium was attained after 6 h for GPBC, whereas for PBC removal was equilibrated after 14 h (0.05 g of adsorbent dose, 20 mL of 25 ppm Cu (II) solution). Pseudo second order kinetic model provides the best correlation of the experimental data for both adsorbents. Batch sorption studies were carried out for both PBC and GPBC, at pH values starting from 2 to 6 since Cu(II) starts to precipitate at pH 6.2. Maximum Cu (II) uptake occurs at pH 5.5. Also, Cu(II) adsorption capacity increases with the increasing metal ion concentration, pH, contact temperature as well as the contact time.

Session 4#

A Transition State “Trapped”? QM-cluster Models of Engineered Threonyl-tRNA Synthetase

Thomas J. Summers, Qianyi Cheng and Nathan J. DeYonker
Department of Chemistry, University of Memphis

In a recent study by the Peter Schultz lab, protein engineering was used to design a core within the threonyl-tRNA synthetase enzyme (ThrRS) capable of stabilizing the coplanar transition state conformation of an inserted non-canonical p-biphenylalanine (BiPhe) residue. To examine the energetics between BiPhe and interacting residues, fully quantum mechanical cluster models were derived from the X-ray crystal structures of the preliminary (Protein Data Bank entries 4S02, 4S0J, 4S0L, 4S0I, and 4S0K) and final (PDB entry 4S03) ThrRS proteins. Density functional theory computations were performed to investigate the energetic profiles of BiPhe dihedral rotation within the ThrRS models. Near-coplanar BiPhe side chain transition states were found for the 4S0I and 4S0K models, though they are not expected to be persistent on any observable timescale. For the 4S03 model, the results indicate steric and hydrophobic forces of residues surrounding BiPhe eliminate the coplanar transition state from the energy landscape. The central dihedral angle for the BiPhe rings thermally fluctuates within the ThrRS protein models with an approximate range of 17° – 26° at 310K. BiPhe-residue interaction counts (RICs) and other methods are used to quantify the interaction differences among the different ThrRS cores. Through these techniques, the iterative ThrRS structures are shown to compress the BiPhe side chain, leading to the experimentally observed “trapped” coplanar transition state analogue within the 4S03 core.

Insights into the Mechanism of the HER Catalyzed by (py-NHC-p-CF₃Ph)W(CO)₄

Robert W. Lamb,¹ Aron J. Huckaba,² Hunter Shirley,² Steve Guertin,³ Shane Autry,² Hammad Cheema,² Kallol Talukdar,² Tanya Jones,² Jonah W. Jurss,² Amala Dass,² Nathan I. Hammer,² Russell H. Schmehl,³ Jared H. Delcamp², Charles Edwin Webster^1
1Department of Chemistry, Mississippi State University, Mississippi State, Mississippi
²Department of Chemistry and Biochemistry, University of Mississippi, University, Mississippi
³Department of Chemistry, Tulane University, New Orleans, Louisiana

A hydrogen economy can be achieved if an efficient means of H2 production is realized via the hydrogen evolution reaction (HER), 2H⁺ (aq) + 2e^– → H₂ (g). Herein, we report a computational investigation of the catalysis and spectroscopy of a novel W–NHC complex that can catalyze HER both electrochemically and photochemically without the use of a photosensitizer. A mechanistic proposal will be presented.

Artificial Neural Network Predictions of Carbonyl Reactivity and Spectroscopic Properties from a Database of Charge Density Descriptors

Kiran K Donthula, Preston J MacDougall
Department of Chemistry, Middle Tennessee State University, Murfreesboro, Tennessee

Carbonyl compounds are important to study because of their biological and industrial significance. A database of descriptors has been created for a range of aldehydes, ketones, imides, and amides. It is based on topological properties of the electron density, specifically for the carbonyl carbon’s bond critical points and the maxima/minima in its valence-shell charge concentration. For each critical point, the database contains values of electron density (ρ), Laplacian (∇²ρ), Hessian eigenvalues (λ₃, λ₂, λ₁), as well as radii from the enveloped carbon nucleus. In 2009, Balabin and Lomakina used three-layer feed forward artificial neural networks, with back-propagation, to predict interaction energy values. These studies, and others, indicate that data-mining techniques, used in conjunction with neural networks, can be productively applied in the prediction of properties that would otherwise be expensive and time-consuming to calculate. The training set has 200 molecules, with each molecule containing 48 descriptors. The artificial neural network (ANN) were trained to predict the experimental values of C13 chemical shifts and C=O stretching frequencies for molecules containing a carbonyl group. Additional properties, such as intermolecular interaction energies with nucleophiles, were calculated via ab initio methods, and the ANN was also trained to estimate these energies. Predictions are made using Laplacian critical point data, as well as bond critical point data, both separately and combined. Mean Absolute Percent Errors (MAPE) are compared between these three data sets. The calculated MAPE for neural network predictions of C13 shifts, C=O stretching frequency, and interaction energies are 1.23, 0.73, and 16.2 respectively. All molecular wave functions are generated using Gaussian 09, and electron density analysis is done using AIMAll and DenProp. For a “stretch-test” we chose the E. coli enzyme D-fructose-6-phosphate aldolase (FSA), which catalyzes a nucleophilic addition reaction of a carbon nucleophile (ketone) to a carbon electrophile (aldehyde). The covalent interaction energy between a nucleophile and an electrophile within the binding pocket of an enzyme (FSA) is predicted by our ANN with an error of –3.2 kcal/mol (13.5 % error).

DFT Investigation of Mechanistic Pathways for Pummerer-type Heteroallene Rearrangements

Nicholas Jentsch¹, Dr. Dean Tantillo², Dr. Matthew Donahue^1
1Department of Chemistry and Biochemistry, University of Southern Mississippi
²Department of Chemistry, University of California, Davis

The vicinal diamine substructure which is found within a wide variety of natural products, is shown to have antibiotic, anti-cancer and neurologic therapeutic indications. Therefore, the development of efficient reaction methodologies targeting this vicinal diamine substructure are essential for further drug development. We have been investigating a new synthetic tool for the creation of carbon-nitrogen bonds to afford 1,2-diamines as the protected cyclic urea. Our hypothesis is that an electron deficient heteroallene, such as a carbodiimide, will engage the nucleophilic oxygen of a vinyl sulfoxide resulting in a zwitterionic species. This species is proposed to undergo a [3,3]-sigmatropic rearrangement to produce an electrophilic thionium ion intermediate. Subsequently, an intramolecular 5-exo-trig cyclization will yield the cyclic urea. This presentation will discuss the use of DFT calculations to study the mechanistic characteristics of heteroallene rearrangements. First, synthetic inspiration derived from a previously reported Pummerer-type rearrangement of phenyl vinyl sulfoxide and dichloroketene to produce γ-lactones was studied. Results revealed the presence of a post-transition state bifurcation leading to an alternative [2+2] cycloaddition product. The second system examined involved the reaction of symmetric carbodiimides and phenyl vinyl sulfoxide. Initial engagement of the sulfoxide oxygen with dimethylcarbodiimide revealed an energy barrier of 45 kcal/mol, supporting the necessity for carbodiimide activation via exogenous acid.

Session 5#

Synthesis and Characterization of Novel Bio-Based Poly(ether-amide)s (PEA)s*

Guery Saenz, Colleen Scott
Department of Chemistry, Mississippi State University

The worldwide consumption of plastic between the years 2014 and 2020 is predicted to increase by 29%. This in-crease in consumption of plastics is problematic in two ways: it causes a demand on the mining of fossil for raw materials notwithstanding an ongoing awareness of the limited source and volatile cost of petroleum; the products produced from these raw materials are non-biodegradable thus resulting in environmental pollution. Subsequently, the continued production of these products from petrochemicals comes with cost volatility in addition to waste disposal. As a result, bio-based polymers are being pursued as a sustainable and environmentally friendly alternative to the non-renewable fossil fuel. In this work, we described the synthesis and thermal properties of two novel poly(ether amide)s (PEAs) by melt polycondensation as alternative thermoplastics. The starting monoaromatic materials used were methyl 4-hydroxy-3-methoxybenzoate (methyl vanillate) and methyl 4-hydroxybenzoate de-rived from lignin, which is a cheap and sustainable raw material. The thermal properties of the new PEAs show that the glass transition temperature (Tg), and the highest temperature for 50% mass loss are approximately 100 °C and 350 °C, respectively. The polymer produced from methyl 4-hydroxybenzoate has higher thermal stability compared to the polymer produced from methyl 4-hydroxy-3-methyoxybenzoate. The range in which the thermal properties suggest that these new and promising PEAs could be used as replacements for commodities common thermoplastics derived from petroleum.

Synthesis of novel water-soluble semiconducting polyrhodamine

Ranganath Wahalathantrige Don and Colleen Scott
Department of Chemistry, Mississippi State University

Conjugated polymers (CP) play a leading role in the field of developing organic semiconducting materials. These polymers have great electronic, thermal, and optical properties. In addition, they also have better solubility, low temperature processability, and mechanical properties when compared to conventional semiconductors. These characteristics are very important in applications such as display backpanels, sensors and active/passive matrix devices. Still the real-life applications of CP are limited due to major drawbacks, such as poor solubility in polar solvents and low reversibility of the redox reaction.

This work describes the synthesis, chemical and redox stability, in addition to processability, and sensory properties of a novel soluble electrical semiconducting polymer. The polymer was synthesized by a Buchwald/Hartwig cross-coupling reaction between fluorescein ditriflate and p-phenylenediamine. According to the UV-visible spectroscopic studies, the material showed very good chemical stability towards extremely acidic and basic conditions, even after several cycles back and forth. Furthermore, under acidic conditions, the wavelength of maximum absorbance (λ_max) of the diluted polymer solution was blue shifted from 510 nm to 488 nm when it was exposed to hydrogen peroxide (H₂O₂). On the contrary, the basified polymer became colorless in the presence of H₂O₂. When doped with polyprotic acids such as polystyrene sulfonic acid, p-phenylene sulfonic acid and sulfuric acid, the material acted as an electrical semiconductor, and the cyclic voltammetry (CV) studies showed good redox stability with reversible redox potentials. The results obtained indicate that this polymer could be a building block for a sensory or energy storing material.

Synthesis of 1,2-disulfonyl-1,2-diazetidine which acts as a suitable slow imine releaser and demonstrates diverse reactivity toward different unactivated styrene derivatives

Hetti Handi Chaminda Lakmal, Hui Zhou, Jonathan Baine, Xin Cui
Department of Chemistry, Mississippi State University, Mississippi State, MS 39762

1,2-diazetidine is the second smallest possible ring with two nitrogen atoms and it has unique features such as good stability at ambient storage conditions, being able to exist as a white color powder and being easy to handle. It is a four membered ring with two adjacent nitrogen atoms and it consists of different types of bonds including C-C, C-N and N-N bonds. According to the previous studies synthetic strategies for 1,2-diazetidine include a [2+2] cycloaddition of an alkene and an azo compound as the classical method as well as an intermolecular ring closing methodology that was recently reported. We are reporting an intramolecular cyclization between 1,2-disulfonyl hydrazine and dihaloethane via disubstitution reaction.

1,2-sulfonyl-1,2-diazetidine undergoes a Lewis acid catalyzed C-C and N-N bond cleavage as a retro [2+2] reaction and slowly releases highly reactive formaldimine in a controlled manner. Therefore, it gives a greater opportunity to study the reactivity of the unstable formaldimine. Constructing a saturated six membered ring with formaldimine and an olefin is a challenging synthesis. It can undergo Lewis acid catalyzed [2+2+2] cyclization with two molecules of unactivated styrene and one molecule of formaldimine released by 1,2-diazetine to give pharmaceutically important piperidine, a six membered ring as a product. In addition to that 1,2-sulfonyl-1,2-diazetidene shows different reactivity towards α-methylstyrene. It undergoes a Lewis acid catalyzed tandem imino ene and aza prins reaction with one molecule of α-methylstyrene and two molecules of formaldime which is followed by an elimination of sulfonyl amine to give 4-phenyl-1-sulfonyl-1,2,3,6-tetrahydropyridines as product.

Session 6#

Synthesis and Preliminary Biological Evaluation of Peracetylated β-D-glucopyranosyl Aurones and Aurone Glucosides

Arjun Kafl¹, Shrijana Bhattarai¹, Scott T. Handy^1,2
1Molecular Bioscience Program, Middle Tennessee State University
²Department of Chemistry, Middle Tennessee State University

Aurones are categorized as a minor sub-class of the large flavonoid family based on their low abundance in the nature compared with other flavonoids. They are widespread among the plant kingdom. Along with their primary function of imparting color to flowering plants, thereby attracting pollinators for seed dispersal, they have been reported to exhibit a phytoalexin role against various pathogenic infections in plants. Beyond plants, these secondary metabolites have been reported to exhibit a wide range of bioactivity making them a promising therapeutic heterocyclic scaffold in the field of drug discovery. Their broad spectrum of bioactivity, including antimicrobial, anti-inflammatory, antioxidant, antiviral, and anticancer properties have been widely explored. Various substituted glycosylated aurones have also been isolated from plant sources, including aurisidin and sulfuretin-6-O-glucosidses. To date, the study of glycosylated derivatives has been limited to only a few naturally occurring ones and no syntheses have been reported. Inspired by this gap, a series of peracetylated glycosyl derivatives of aurones and their corresponding glucosides were synthesized and subjected to various biological screening to study the effect of the glycosyl moiety on the biological activity of aurones.

Studies of cooperative binding in boronic acid modified PAMAM dendrimers

Xiaoli Liang, Marco Bonizzoni
Department of Chemistry and Biochemistry, The University of Alabama

Cooperativity in molecular binding process of macromolecules with multiple binding sites is interesting and pervasive, yet poorly understood. We studied the binding cooperativity in systems with multiple interaction sites to develop general models of these interactions. Poly(amidoamine) (PAMAM) dendrimers containing multiple terminal amine groups are ideal for these studies. We decorated the surface of G3 and G5 PAMAM with 3-formylphenylboronic acids to turn them into receptors with multiple boronic acid binding sites. We prepared a series of receptors with variable extents of surface decoration to evaluate the effect of receptor density on the surface of the globular dendrimer. This gave us access to a series of receptors with varying degrees of cooperativity. Cis-diol groups reversibly bind to boronic acids, so we used pyrogallol red (PG), a dye with two cis-diol groups, as a binding probe. As the boronated PAMAM receptors were titrated into PG, the binding was monitored via UV-Vis absorption and fluorescence emission. The binding isotherms for all G3 boronated PAMAM receptors revealed significant positive cooperativity. We observed a more interesting behavior in the case of the G5-based receptors: in this case, low-density receptors displayed no cooperativity, but an affinity enhancement was observed as the density of boronic acid binding sites increased. Appropriate control experiments confirmed that this effect was due to positive cooperativity among adjacent receptors. Models for these complex interacting systems are being evaluated for quantitative determination of the cooperative effect.

Discrimination and quantitation for carboxylate anions in neutral water

Yifei Xu, Marco Bonizzoni
Department of Chemistry and Biochemistry, The University of Alabama, Tuscaloosa, AL 35487-0336

Citric acid cycle intermediates are interesting targets for chemical detection because they are involved in energy generation, biosynthesis, and biological signaling cycles. Their levels in bodily fluid are related to critical diseases. However, these analytes have very similar structures and are thus difficult to differentiate using typical chemoselective receptors.

Our group has had success in using poly(amidoamine) (PAMAM) dendrimers as supramolecular hosts in carboxylates sensing applications by establishing electrostatic and H-bonding interactions between the host and anion guests. We became interested in exploiting these interactions for the detection of carboxylate analytes in water through simple optical spectroscopy. However, such interactions are hard to use analytically because neither the carboxylates nor the PAMAM receptors have detectable signals in the non-interfering visible region of the spectrum.

In this study, we circumvented this problem by utilizing a dye-displacement assay based on PAMAM-dye complexes. A calcein-PAMAM complex was formed in neutral aqueous HEPES buffer, then the calcein dye was displaced by the introduction of carboxylate anion. The interactions were monitored through absorbance and fluorescence techniques. Analytical data obtained was interpreted using pattern recognition algorithms to recover discriminatory power. Linear discriminant analysis (LDA) was used for data interpretation, to discriminate among these carboxylate analytes. Finally, with fluorescence anisotropy measurements, followed by Principal Component Analysis (PCA), we were able to identify unknown samples with a 100% accuracy and quantify their concentration with a limit of detection of 2.0 mM.

Session 7#

A Metabolomics Study using NMR to Understand Biochar’s Effects on Escherichia coli

Rebecca A. Hill, John Hunt, Emily Sanders, Melanie Tran, Griffin A. Burk, Todd E. Mlsna, and Nicholas C. Fitzkee
Department of Chemistry, Mississippi State University

Biochar is used as a soil amendment in agricultural applications due to its adsorptive properties, porous surface, and inexpensive cost. The chemical features allow biochar to adsorb and remove waste, as well as retain nutrients and increase soil fertility. However, the effects of biochar on bacteria present in the soil remain poorly understood. The microbial metabolome, or the set of chemical pathways that bacteria utilize to process metabolites, was examined to understand the effects of biochar on bacteria. In our study, Escherichia coli (E. coli) was grown in a complex, well-defined media (RPMI) as a model to gain an understanding of how concentrations of metabolites change over time. The concentrations of metabolites in the media, after treatment with biochar or activated carbon, were quantified at several time points using a 1D NMR method. Several metabolites in RPMI media were adsorbed by biochar and activated carbon, including L-asparagine, L-glutamine, and L-arginine. However, activated carbon adsorbed more of these compounds than biochar. Some metabolites in RPMI media were adsorbed by activated carbon but not biochar, including cis-4-hydroxy-L-proline, L-proline, and L-valine. Over time, E. coli exhibits a slower growth rate in biochar- or activated carbon-treated media compared to untreated media. Principal Component Analysis (PCA) was used to examine the statistical variance in metabolic concentrations. This analysis suggests that biochar was less disruptive than activated carbon, providing benefits for soil amendment while minimizing the impact on bacterial viability. Although future work is needed to characterize how this response may change in soil (vs. liquid media), this work suggests that biochar could have practical utility for the microbiological aspect of soil conditioning.

Student-Centered, Active Learning Pedagogy Improves Undergraduate General Chemistry Students’ Academic Performance, Success, Attitudes and Retention in STEM Disciplines*

Viveka L. Perera and Debra A. Mlsna
Department of Chemistry, Mississippi State University

A four-semester pilot program was instituted at Mississippi State University to incorporate student-centered active-learning, content-focused recitation session into the General Chemistry I (CH 1213) course. We studied the impact of recitation sessions with the large-enrollment sections of general chemistry I course on student achievement, success rate, student enthusiasm, and retention in STEM discipline. In order to assess the influence of implementing recitations, we studied departmental final (standardized ACS) exam scores, DFW rates, and success of students in next chemistry (CH1223) courses. We found that the students’ performance in departmental ACS standardized final examination was significantly enhanced with recitation group problem-solving classes. In fact, though student scores were greater in Spring 2016, the semester in which recitation was incorporated into the CH1213 course for the first time the improvement in students’ performance was not statistically significant. Because students in chemistry I was not sufficiently enhanced, the teaching model for recitation was subsequently changed in fall 2016. The rise of exam scores with recitation learning impacted equally on all the individuals irrespective of their general characteristics of gender, knowledge level (as measured by Math ACT score) or ethnicity except for black or African American students. Nevertheless, the pass/fail rates did not alter much with recitation, many more students were successful with earning grades of “A”. Addressing broader impacts, we observed the success of students in subsequent general chemistry II (CH1223) course, which may translate into confidence and continuation in STEM majors leading to improved graduation and retention rates in STEM disciplines.

Mapping Structure–Activity Relationships for Oxygen Reduction Reaction at Coinage Metal Pseudo–Single–Crystal–Electrodes

Timothy J. Dowell and David O. Wipf
Department of Chemistry, Mississippi State University

The electrochemical reduction of molecular oxygen (ORR) is the key bottleneck to developing next generation energy storage technologies (e.g. low temperature fuel cells and metal‒air batteries) due to its sluggish reaction kinetics, high overpotentials, and lack of suitable catalyst. Significant effort has been devoted to elucidating the underlying mechanism of ORR and developing novel ORR catalyst‒materials over the years. However, ORR activity at various catalysts (e.g. polycrystalline, nanoparticle, and single-crystal electrodes) has revealed that their “structures” have significant impact on the ORR kinetics and mechanism. Furthermore, methods capable of interrogating these structure‒activity relationships are scarce; leading to difficulties in determining active sites at heterogeneous ORR‒catalysts (i.e. comprised of high‒index surfaces, kinks, atomic steps, and grain boundaries).

Herein, we show the correlation of surface structures at pseudo‒single‒crystal electrodes of coinage metals (Au, Ag, Cu) and their activity for ORR in alkaline media. Pseudo-Single-Crystal–Electrodes (PSCE) are prepared by carefully polishing and etching annealed polycrystalline electrodes to expose well-defined and randomly oriented crystallites. Scanning electrochemical microscopy (SECM) combined with electron backscatter diffraction (EBSD) has been employed to interrogate the crystallographic orientation dependence on ORR activity for these materials. Using Tip‒generation substrate‒collection (TG‒SC) mode of SECM, the localized electrochemical activities of various surface features (i.e. crystallographic orientations and boundaries) have been mapped during ORR. To illustrate, mapping experiments of gold PSCEs reveals clear differences in ORR activity based on crystallographic orientation. Our work demonstrates a promising approach to rapid interrogation of surface‒activity relationships for ORR catalysts.

Poster Presentation Abstracts#

Synthesis and characterization of zinc (II) bis(pyrrole)phenylenediamine complexes

Jacob Mayhugh
Department of Chemistry and Biochemistry, Auburn University, Auburn, AL 36830

The synthesis and characterization of Schiff base bis(pyrrole)phenylenediamine (H₂L) and its Zn(II) complexes are described. The ligands were synthesized with isomers of phenylenediamine and 2-formyl-1H-pyrrole. Spectral studies reveal the ligand has coordination through the Schiff base and pyrrole nitrogen atoms. Furthermore, x-ray structures indicate unique binding patterns exhibited by the para and ortho-phenylenediamine complex derivatives, resulting in a tetranuclear coplanar structure (Zn₄L₄) and dinuclear double-stranded helical structure (Zn₂L₂), respectively. These observations may provide insight into the steric effects of peripheral substituents on metallosupramolecular self-assembly.

Propargylic C-H oxidation using a Cu(II) 2-quinoxalinol salen catalyst and tert-butyl hydroperoxide

Clayton C. Black. Anne E. V. Gorden
Department of Chemistry and Biochemistry, Auburn University, Auburn, AL 36830

The synthesis of α,β-acetylenic ketones is of wide interest due to their use as starting materials for the synthesis of heterocycles, nucleosides, aromatic compounds, anticancer agents, and other versatile compounds. While several examples of C-H oxidation reactions exist, very few examples of propargylic oxidations have been reported. Examples reported previously include the use of expensive transition metals such as rhodium, much higher catalyst loading, long reaction times (24 hours), or they may use multiple additives in addition to the catalyst. Herein, we report the oxidation of alkynes to α,β-acetylenic carbonyls using only 1 mol % of an inexpensive Cu(II) 2-quinoxalinol salen catalyst with tert-butyl hydroperoxide in 4 hours. These reactions proceed under mild conditions (70 °C) with excellent selectivity, producing yields as high as 78%. The optimized conditions were used on a variety of alkyne substrates to produce the desired α,β-acetylenic ketones. Also, we report the ability to run these reactions in water using a sulfonated version of the 2-quinoxalinol salen with good yields, reducing the need for volatile organic solvents and promoting the concept of “green chemistry”.

Using Salphenazine-type Imidazoles in Chemosensing for Detection of [UO₂]²⁺ and other Metal Ions

Ethan A. Hiti, Charmaine D. Tutson, Emily E. Hardy, William R. Yates, Branson A. Maynard, Anne E. V. Gorden
Department of Chemistry and Biochemistry, Auburn University, Auburn, AL 36830

As the need for renewable and more carbon neutral energy increases, the need and interest in nuclear power is growing simultaneously. A major concern with nuclear power is the generation of radioactive waste and the possibility of the radioactive material being released into the environment. To combat this issue, fast and in-the-field detection of radioactive material is needed for faster response and clean up if a spill should occur. One method for detecting radioactive by-products is by using a chemical sensor, or chemosensor, that can selectively bind or give a distinct response when bound to uranyl (UO₂²⁺), the most biologically relevant species of uranium. The rational design of such a species can be quite challenging. Schiff base ligands with the N-C-C-C-O binding motif have been used previously for this purpose. The Schiff base ligand, 2-(1H-imidazo[4,5b]-phenazin-2-yl) and derivatives thereof, are formed from a condensation reaction followed by an intramolecular cyclization of an array of salicylaldehydes and 2,3-diaminophenazine. These ligands are examined here for their efficiency as chemosensors for uranyl and Copper (II) . The shift in UV-visible spectrum upon metal binding was observed and allows for sensing of these metal ions. Tuning the electronics of the ligand through substituent effects and of the binding affinity to these metal ions is also discussed.

Solvent-dependent ligand structures and conformations on gold and silver nanoparticles

Maleesha De Silva, Dongmao Zhang
Department of Chemistry, Mississippi State University

Nanoparticle interfacial interaction has emerged as one of the most active area of research. However, most of the studies have focused on the ligand binding to nanoparticle in individual solvents. Potential solvent effect on the ligand structure and composition has to our knowledge, not been systematically investigated. Discussed herein is the solvent dependent of the ligand structure and conformation on plasmonic gold nanoparticle (AuNP) and silver (AgNP) nanoparticle surfaces. Several classes of model molecules have been employed in this study that include thioamide (mercaptobenzimidazole, thioguanine), aromatic mono- and dithiols (methylbenzenethiol and benzene dithiols), aliphatic mono- and dithiol (ethanethiol and ethanedithiol), and nonspecific ligand (adenine). The solvent effects were studied using two approaches. The first is performed by first mixing ligand in water/ethanol mixture solvent with AuNPs, then washing ligand-containing AuNP/AgNP aggregates using the targeted solvents. The second is by first aggregating the AuNPs and AgNPs using KNO₃ then adding the ligand in targeted solvents. The model solvents including water, tetrahydrofuaran, carbon tetrachloride, and dichloromethane. The experimental results are analyzed in combination with computational modeling. The data obtained with these two solvent dependent studies shed a series of new insights to the mass transfer and chemical reactivity of ligands trapped on the junction of the aggregated AuNPs and AgNPs.

Reactive Ag⁺ Adsorption

Sumudu Athukorale¹, Ganganath S. Perera¹, Manuel Gadogbe¹, Felio Perez², and Dongmao Zhang^1,3
1Department of Chemistry, Mississippi State University, Mississippi State, Mississippi 39762, United States ²Integrated Microscopy Center, University of Memphis, Memphis, Tennessee 38152, United States ³Department of Chemistry, Xihua University, Chengdu, 610039, China

Proposed mechanisms of monolayer silver formation on gold nanoparticle (AuNP) include AuNP-facilitated under-potential reduction and antigalvanic reduction in which the gold reduces Ag⁺ into metallic atoms Ag(0). Reported herein is the spontaneous reactive Ag⁺ adsorption onto gold substrates that include both as-obtained and butanethiol-functionalized citrate- and NaBH4-reduced gold nanoparticles (AuNPs), commercial high-purity gold foil, and gold film sputter-coated onto silicon. The silver adsorption invariably leads to proton releasing to the solution. The nominal saturation packing density of silver on AuNPs varies from 2.8 ± 0.3 nmol/cm² for the AuNPs preaggregated with KNO3 to 4.3 ± 0.2 nmol/cm² for the AuNPs prefunctionalized with butanethiol (BuT). The apparent Langmuir binding constant of the Ag⁺ with the preaggregated AuNPs and BuT-functionalized AuNPs are 4.0 × 10³ M^–1 and 2.1 × 10⁵ M^–1, respectively. The silver adsorption has drastic effects on the structure, conformation, and stability of the organothiols on the AuNPs. It converts disordered BuT on AuNPs into highly ordered trans conformers but induces near complete desorption of sodium 2-mercaptoethanesulfonate and sodium 3-mercapto-1-propyl sulfonate from AuNPs. Mechanically, the Ag⁺ adsorption on AuNPs most likely proceeds by reacting with molecules preadsorbed on the AuNP surfaces or chemical species in the solutions, and the silver remains as silver ion in these reaction products. This insight and methodology presented in this work are important for studying interfacial interactions of metallic species with gold and for postpreparation modulation of the organothiol structure and conformation on AuNP surfaces.

Colorimetric High-throughput Screening Ligand and Gold Nanoparticle Interaction

Niroshani S. Abeynayake, Dongmao Zhang
Department of Chemistry, Mississippi State University

Understanding the ligand interaction with gold nanoparticles (AuNPs) is important for biosensing, gold catalytic activity, drug synthesis and delivery. Despite the availability of many instrument-based methods to monitor the ligand interactions such as; UV-vis, fluorescence, surface enhanced Raman spectroscopy (SERS), and dynamic light scattering, there is lack of rapid, high-throughput non-instrument-based screening method. Hence, this method enables us to minimize the cost of instrumentation and the expertise needed for handling and analyzing the data, making it highly facile and cost-effective technique. Potassium cyanide is used as the probe to screen the ligand interactions. Cyanide-induced gold dissolution has been used for a series of applications including cyanide quantification. Furthermore, it is significant to understand metal dissolution process in order to govern the stability in different chemical environment depending on the concentration, and types of ligand functionalized. Effect of ligand functionalized on the AuNP is investigated with spherical AuNPs by functionalizing the NPs with polymer, protein, thiolated polyethylene glycol (PEG) and small organothiols. The finding is important for understanding not only the ligand interaction of the multicomponent-functionalized AuNPs, but also AuNP dissolution processes. Moreover, once the colorimetric screening is established, we can use other techniques too such as SERS to monitor the dissolution process.

Sequential Multi-modal Raman Spectral Acquisitions on Reflective Background-free Raman Substrates

Prakash C. Khanal, Joanna Xu, Timothy Dowell, and Dongmao Zhang
Department of Chemistry, Mississippi State University

Raman spectroscopy has become increasingly popular for chemical, biological, and forensic analysis due to the decreasing instrument cost and increased availability of the miniaturized field-deployable device. One significant challenge in Raman application is however, the difficulty in obtaining quality Raman spectra for samples in their given forms. Demonstrated herein is a convenient Raman sampling technique that enables rapid screening the effectiveness of six different sample preparation and spectral acquisition methods for solid samples. This includes four normal Raman sampling methods with the as-obtained sample powder, solvent-dispersed powder, dissolved sample solution, and drop-dried deposits, as well as two surface enhanced Raman spectra (SERS) that uses gold and silver nanoparticles are the SERS substrates. All the measurements are conducted sequentially with a miniscule amount of sample powder deposited on background-free reflective Raman substrates. The general applicability of the technique is demonstrated with broad range of chemicals including carbohydrates, amino acids, polymers, proteins, proteins, fluorescent dyes, and a few other organic and inorganic compounds. Only a few samples that is amenable to with every sampling techniques. However, for every sample at least one of the sampling techniques is applicable for obtaining high quality Raman spectrum. This multimodal sampling method can be readily implemented in both research lab and in field. It should be significance for a wide range of Raman spectroscopic applications including chemical identifications, molecular interfacial interactions with gold and silver molecules, and crystal identifications.

Synthesis, Characterization, and Structure of a [(phen)₂Cu(OTf)]OTf Complex; An Efficient Nitrogen Transfer Pre-catalyst

Henry U. Valle, Kathleen M. Riley, Dylan E. Russell Daniel K. Wolgemuth, C. Flannery Voges-Haupt, T. Alexander Rogers, Shanterell L. Redd, Dr. Sean L. Stokes and Dr. Joseph P. Emerson
Department of Chemistry, Mississippi State University

Aziridines are valued as important building blocks for the synthesis of a wide range of active compounds. The development of efficient, cost effective catalysts for nitrene transfer reactions to olefins is a continuing area of research in modern chemistry. There are a number of transition metal complexes that are known to catalyse the aziridination of olefins, however most require expensive transition metal ions. Herein we report our efforts to generate aziridines using a copper(II) complex that offers high efficiency at generating aziridines from olefins and N-transfer agents.

Enantioselective N-transfer Reactions for Aziridination and Amination in Water using DNA Templating; Efforts Toward Sustainable Catalysis

Sydnee D. Elmore, Daniel K. Wolegemuth, Henry U. Valle, and Joseph P. Emerson
Department of Chemistry, Mississippi State University

Small heterocyclic molecules, such as aziridines, are important precursors for a wide range of valuable products in medicinal chemistry. Although catalysts capable of performing nitrogen atom transfer reactions with olefins are a prominent area of research, they often require the use of expensive or harmful transition metals and organic solvents. Most often, catalysts for asymmetric transformations must contain chiral centers in order yield the desired enantioselective products, but with the use of DNA templating, many transition metal complexes show promise for asymmetric selectivity. Herein, we report our efforts towards sustainable catalysis, which utilize DNA templating to drive enantioselective N-transfer reactions for aziridination and amination of olefins in water.

Non-Heme Copper(II) Complexes: Efficient Carbon and Nitrogen Atom Transfer Catalyst

Dylan E. Russell, Henry U. Valle, Zhenyu Zhu, Sydnee D. Elmore, Daniel K. Wolgemuth, Dr. Sean L. Stokes and Dr. Joseph P. Emerson
Department of Chemistry, Mississippi State University

Aziridines and cyclopropanes are valued as important building blocks for the synthesis of a wide range of active compounds. The development for more efficient and cost effective catalysts for the atom transfer reaction with olefins is a continuing area of research in both organic and inorganic chemistry. Transition metal complexes which catalyze reactions of olefins with nitrenes and carbenes are very well developed efficient approaches to the direct synthesis of aziridines, and cyclopropanes. As part of our efforts in the catalytic formation of C-N and C-C bonds, here- in we show the development of an efficient copper(II) catalysts that exhibits high reactivity toward olefins.

Self-Initiated Functionalization of Waste Tire Rubber Networks And New Composite Applications

Eugene B. Caldona¹, Tom Rosenmayer², Ganesh Naranayan¹, Dennis W. Smith, Jr.^{1 1}Department of Chemistry, Mississippi State University, Mississippi State, MS 39762, United States ²Lehigh Technologies, Tucker, GA 30084, United States

Due to their low-cost, chemical resistance, and thermal stability, ground rubber tires (GRT) prepared via cryogenic grinding, have found application as functional fillers in polymer composites, asphalt formulations, and raw chemical and fuel source. Self-initiated functionalization via free radical polymerization provides enhanced compatibility with matrix resins for new applications feedstocks for biomass and biochar products, and possibly new proppant and related components in fracturing technologies for oil and gas recovery. Self-initiated surface grafting of GRT via acrylic acid bulk polymerization without the use of initiator affords composites with improved bonding and variable rheological properties. For instance, asphalt/GRT composites display reduced reflective cracking in overlays, improved cracking, skid, and rutting resistance, longer pavement life, and decreased noise level. Surface functionalization with polyacrylic acid gave useful applications for epoxy composites with enhanced mechanical properties. This presentation will give an overview of the rubber projects in our laboratory, which includes GRT surface modification, hydrosilylation of used tire rubber, fluorination of GRT particles, and other recycled rubber materials and rubber/polymer blends and composites.

A Modular Approach to Semi-Fluorinated Aromatic Ether Polymers via Step-Growth Polymerization of Fluoroalkenes

Ketki Eknath Shelar, Behzad Farajidizaji, Andrzej Sygula and Dennis W. Smith, Jr.
Department of Chemistry, Mississippi State University, Mississippi State, MS 39762

Our research laboratories have successfully demonstrated the synthesis of semi-fluorinated aryl ether polymers which include perflourocyclobutyl (PFCB) aryl ether polymers prepared via [2+2] radical mediated thermal cyclodimerization of trifluorovinyl ethers (TFVE). PFCBs have been widely used in high performance passive optics, electro-optics, polymer light-emitting diodes (PLEDs), space survivability, and polymeric fuel cell membranes (PEMs), high use temperature fluorosilicones, POSS composites, liquid crystalline polymers, and exhibit similar advantages as their fully fluorinated analogs. We have also demonstrated the nucleophilic addition of bisphenols to TFVEs to form fluoro-arylene vinylene ether (FAVE) polymers. Moreover, we have successfully synthesized poly(perfluorocycloalkyenyl aryl ether) homopolymers and copolymers in one step via nucleophilic addition/elimination with bisphenols and perfluorocycloalkenes (PFCAs). We are currently working on a project to attach TFVEs to corannulene or other buckybowls (curved-surface polycyclic aromatic hydrocarbons) and introduce a novel functional group aspect to these materials. This presentation will overview the projects currently ongoing in our laboratory including three fluoropolymer platforms and new strategies to fluoro-functional corannulenes.

Modular Design and Synthesis of a New Type of Ru(II) Half Sandwich Complexes

Jonathan Baine, Heiti Handi Chaminda Lakmal, Xiaolin Quan, Mojtaba Hajiloo and Xin Cui
Department of Chemistry, Mississippi State University, Mississippi State, MS 39762

Numerous examples of ruthenium catalyzed C-H activation and asymmetric C-C bond formations have recently been reported. Similar to Pd catalyzed cross-coupling, this new area promises to replace several existing classical methods. In this work we report a modular design and synthesis resulting in several difunctional Ru(II) complexes. These complexes are expected to serve as Ru(II) catalysts for C-H activation and asymmetric C-C bond formation. These complexes require an 8-step synthesis involving several Pd couplings and consist of a three-ring backbone with two attached amide groups and a phosphine. These amides are designed to act as directing groups for C-H activation and asymmetric C-C bond formation. Herein we report the synthesis and characterization of a range of these complexes.

DFT Investigation of Mechanistic Pathways for Pummerer-type Heteroallene Rearrangements

Binod Nepal
Department of Chemistry, Louisiana State University

The development of new reactions that construct stereocenter-containing organonitrogen compounds are highly valued due to the ubiquity of nitrogen atoms in bioactive molecules, such as natural products and pharmaceuticals. In recent years, a particular problem that has gamered attention is the catyalic enantioselective synthesis of functionalized enamides at the beta-carbon, approached via conjugate addition to alpha, beta-unsaturated imides. Herein, we present a novel enantioconvergent approach to functionalize enamides at the beta-carbon with indoles, enabled by strategic tautomerization of 2-amidoallyl to 1-amidoallyl cations. These reactive species were produced via ionization of racemic starting materials with a chiral Brønsted acid, which concomitantly provide asymmetric induction in the ensuing nucleophilic addition.

Synthesis and Reactivity Studies of Bio-inspired Mononuclear Cu (II) Complexes

Niharika Botcha, Nirupama Singh, Anusree Mukherjee
Department of Chemistry, The University of Alabama in Huntsville

The constantly increasing demand for energy and fuel resources requires the development of new energy solutions that are more sustainable and address the need for energy efficiency and conservation. Coordination complexes of late transition metals bound by nitrogen rich ligands are very important because of their pivotal roles in catalytic applications. Tetradenatate ligands from the bispicen family with amine and pyridine functionalities (N2/Py2) have also received significant attention for their role in hydrocarbon oxidation with high selectivity. These ligands are also attractive candidates for designing homogeneous catalysts as ease of synthesis allows systematic investigation of structural-functional relationship of the catalysts. They efficiently catalyze most of the organic transformations occurs in living systems under mild conditions with nontoxic oxidants such as O₂ or H₂O₂ to oxidize a wide range of molecules, usually in a very selective manner. Thus, we can take inspiration from these natural phenomenon’s and attempt to develop new catalysts that will ideally oxidize a wide array of organic molecules using cheap and environmentally benign oxidants. In our group synthetic mononuclear copper (II) metal containing model complexes were synthesized and characterized using different spectroscopic techniques.

An Unorthodox Approach to Creating Lab Partnerships: Evaluating Psychological Responses That Arises from the Feeling of Uncertainty to Promote Leadership and Independence, and Increase Communication and Productivity in Chemistry Undergraduate Laboratories

Jarquees Williams
Department of Chemistry, Mississippi State University, Mississippi State, MS 39762

To approach the subject of student laboratory success is to understand the many factors that contribute to each individual student’s comfortability and preparedness. It has always been theorized that factors such as gender, and personality have contributed to the comfort level of the individual. This is directly related to the leadership and independence attributes of the student, thus, effecting productivity and understanding of the various tasks that must be comprehended to complete an experiment.

Traditional methods of assigning lab partnerships have shown to promote the dependency of one lab partner on another over time. This dependency impedes effective subject matter conversations, which negatively affect productivity in the laboratory. In this presentation, data will be presented that supports a new approach to assigning lab partnerships. Each student’s lab partner was unbeknownst to them until the beginning of lab. The psychological response of the student body was observed and analyzed by the instructor and collated with student survey data collection over a period of four weeks. Based on the thorough observations and student surveys, results indicate that majority of the students favor the new approach of creating lab partnerships compared to the tradition approaches. Also, student responses indicated that the new approach heavily promotes independence by forcing students to increase preparation for each laboratory experiment. This decreases the cognitive load of the students and increases constructivism which facilitates student and instructor duties. Furthermore, the information presented supports the promotion of student independence and class communication.

Evaluation of the impact of Student Laboratory Partnerships in an Undergraduate General Chemistry Laboratory on Their Study Group Interactions Outside the Classroom

Dulani Samarasekara and Deb Mlsna
Department of Chemistry, Mississippi State University, Mississippi State, MS 39762

The purpose of this study was to evaluate the effects of the five different laboratory partnerships established in General Chemistry laboratories and students’ study group interactions outside the classroom on their social interactions and the perceived quality of their Chemistry learning. The evaluation addressed two areas of academic and psychological (satisfaction) outcomes. Five different laboratory partnerships were designed and implemented for both first and second year general Chemistry students (N = 4550) for four consecutive semesters. Chemistry lab sections were randomly designated into one of the five different laboratory partnerships; (1) free choice- Students find their own partner (no assignment), (2) Random assignment- lab partners were assigned randomly, (3) Side-to-side assignment – kept Math ACT score constant among student pairs (4) High-low assignment- kept Math ACT score variable among student pairs (Some of the student pairs had small ACT discrepancy while other pairs have large ACT discrepancy) (5) Assigned based on lecture section-students paired with partner in same lecture section; if same lecture section not available, then pairs were kept with same professor. In General Chemistry lectures, students were encouraged to involve in study groups outside the classroom with their laboratory partners and student contact information was provided. In this study, student lecture grades and survey findings were used to measure students’ Chemistry performance and their attitudes about their lab partners and study group partners. Analysis of effective student interactions and success within the chemistry environment will be discussed.