Abstracts

Keynote Session Abstracts#

Lester Andrews Graduate Research Symposium Keynote

Beyond Li-Ion: The Lithium/Sulfur Cell

Elton J. Cairns
University of California, Berkeley, and Lawrence Berkeley National Laboratory

The lithium/sulfur cell is widely regarded as the next-generation high specific energy rechargeable cell. This is true because of its very high theoretical specific energy (~2600 Wh of energy stored per kg of reactants) compared to that of the lithium ion cell (~600 Wh/kg). In spite of the very attractive specific energy, the development of the Li/S cell has been slow and difficult due to the facts that sulfur and its reaction product Li2S are both electronically non-conductive, sulfur is dissolved as polysulfides into most organic solvent based electrolytes (resulting in capacity loss), and the soluble polysulfides can react chemically at the lithium electrode. During the last few years, we have been successful in ameliorating the above problems, resulting in laboratory coin cells with very high sulfur utilization (~1400 mAh/gS) and very long cycle lives (1500 deep cycles) for two different versions of sulfur electrode formulations. We are now in the process of developing electrode structures and formulations that will be useful in commercial Li/S cells. Our recent advances will be reviewed and discussed. If the commercialization of our technology is successful, it will be feasible to have electric automobiles with a range of at least 300 miles per charge.

Mississippi Regional Biophysical Consortium Keynote

The coordinated action of RPA and DNA primase at the replication fork

Walter J. Chazin
Departments of Biochemistry and Chemistry, and Center for Structural Biology, Vanderbilt University, Nashville, TN

Faithful copying of our genome requires the coordinated action of multi-domain proteins operating within dynamic multi-protein machines that operate at the replication fork. Replication Protein A (RPA) is the primary ssDNA-binding protein in eukaryotes. Beyond protecting and organizing the ssDNA, it serves as an essential scaffold in virtually all DNA transactions. During replication, RPA and DNA primase together play a central role in the transition from unwinding the duplex to initiating synthesis on both the leading and lagging strand templates. In this presentation, I will introduce the unique characteristics of multi-domain proteins and multi-protein machinery and new perspectives on structural biology that are required for such complex dynamic systems. The concept of remodeling of protein architecture will be defined. I will then describe how X-ray crystallography, NMR, X-ray scattering and computation modeling have been used to build a picture of how RPA and primase function in the transition from duplex unwinding to template priming. I will also present provocative new data suggesting that DNA charge transport driven by the 4Fe-S cluster of primase can be used as a molecular switching mechanism to control primer length counting and hand off to DNA polymerase α for primer extension.

Oral Presentation Abstracts#

Session 1#

Nanoscale Patterning of Proteins: Toward Biosensor Development

Zachary L. Highland, Leegwater, Cody N., and Jayne C. Garno
Department of Chemistry, Louisiana State University

Protein patterning at the nanoscale can be used to for the development of biosensors as well as for research studies of immunochemistry. Controlling the placement and the orientation of proteins is challenging, because the chemistry procedures need to preserve the bioactivity and binding affinity of relatively fragile molecules. Particle lithography offers advantages to pattern proteins, requiring small amounts of dilute reagents in buffered reagents with few chemical steps to prevent denaturation. By changing the diameter of the mesospheres that are used as a surface mask, the surface packing density can be selected according to the size of the protein. When particle lithography is used in conjunction with organosilane chemistry, many different silicon surfaces can be tailored for the binding of proteins in selective regions. A substrate with mesospheres patterned on the surface can be placed in a dilute solution of methyl terminated silane which will resist protein binding. Once the spheres are removed, the active silane can then be bound to the bare substrate that was protected by the mesosphere. Using two different methods developed in our lab, fibronectin and green fluorescent protein were covalently bound to polished Si(111) and glass cover slides respectively. Fibronectin is an important protein in the extracellular matrix and its many process in cell development and growth. In moving towards a biochip for fluorescent detection of protein, green fluorescent protein was chosen for its fluorescent properties in addition to its wide use in research.

Comparing the Structures of PEI/DNA and PEI/siRNA Gene Delivery Complexes using Multiscale Modeling

Dennis Kennetz, Jesse Ziebarth, Yongmei Wang
University of Memphis

Complexes consisting of polyethyleneimine (PEI) and DNA or siRNA have received extensive attention because of their potential use in gene delivery, but their physicochemical properties remain poorly understood. For example, PEI/DNA complexes are known to be more stable than PEI/siRNA complexes, but the factors that underlie this difference have not been fully described. Thus, we performed atomistic and coarse-grained simulations of complexation between PEI and DNA or siRNA to identify differences in the respective complex structures. Atomistic simulations revealed that the large majority of direct interactions in both PEI/DNA and PEI/siRNA complexes were between PEI and the nucleic acid phosphate groups, with interactions between PEI and groove sites being rare for both nucleic acids. However, the greater distance between phosphate groups in DNA allowed for a larger number of charged PEI amine groups to interact with phosphate groups in DNA than in corresponding siRNA complexes. Coarse-grained simulations of the complexation between relatively rigid polyanion chains (DNA/siRNA) and flexible polycation chains (PEI) showed that the relative lengths of the polyelectrolyte chains had a profound impact on complex structure. Simulations of long polyanions and short polycations, a model for PEI/DNA complexation, resulted in the formation of stable aggregates of polyanion chains that were held tightly together by the polycations. In contrast, the polyanion chains in simulations of long polycations and short polyanions, representing PEI/siRNA complexation, did not aggregate and were more exposed to the solution.

Selection of mRNA Cap Aptamers for Applications in Synthetic mRNA Expression-based stem Cell Differentiation

Krishna Sapkota and Faqing Huang
Department of Chemistry and Biochemistry, The University of Southern Mississippi

Direct introduction of synthetic messenger RNA (mRNA) is a safer and efficient approach for exogenous gene expression in the cell. The mRNA Expression in the cell requires the synthetic mRNA to contain a 7-methylguanosine (m⁷G) cap bound to the first transcribed nucleotide at 5’ end by an inverted 5’-5’ triphosphate linkage. The current method of mRNA preparation by in vitro transcription in the presence of a cap generates a mixture of m⁷G capped mRNA and uncapped triphosphate mRNA, which not only lowers the expression efficiency but can also trigger a strong innate immune response by activating cytosolic RNA sensors. The unavailability of Cap-mRNA purification method inspired us to select the high affinity Cap-aptamers which can then be used for the affinity purification of cap-mRNA. Currently we are focusing on a high efficient approach for cap analog (m⁷GpppA) synthesis by enhancing the hydrophobicity of both constituent nucleosides. The cap analog m7GpppA will be immobilized on a solid support and used to select the Cap aptamers by in vitro evolution technique. The isolated aptamers will be used to prepare affinity column for m7G capped mRNA transcripts encoding MyoD. The purified Cap-mRNA transcripts will then be transfected into the cell to express MyoD that promotes stem cell differentiation into myocytes.

Photochemical Reduction of CHCl₃ Initiated by SPEEK Systems Using Solutions and Swollen Films

Md S Islam and G. Mills
Department of Chemistry and Biochemistry, Auburn University, Alabama, 36849, United States

Illumination of aqueous systems containing sulfonated poly(ether etherketone), SPEEK, together with sodium formate have been found to effectively reduce chloroform to dichloromethane both in the presence or absence of air. The polyketone acted as a sensitizer whereas HCO₂^– served as H-atom donor; the photoreduction process involves polymeric α–hydroxyl (SPEEK•) and CO₂^– radicals. For air-free SPEEK/HCO₂^– aqueous solution, r(Cl^–) increased slightly with light intensity (I₀) whereas the quantum yields of Cl^– generation, 𝜙(Cl^–), decreased with increasing I₀. Analogous kinetic results were obtained using SPEEK/PVA blends to initiate the photoreduction of CHCl₃. The photoreduction was also initiated effectively using swollen SPEEK/PVA films, which could be reused numerous times as sensitizers. For all systems, the highest values of (Cl^–) were determined at 6 ≤ pH ≤ 8, coinciding with the range where SPEEK• is most efficiently photogenerated. However, a sharp maximum of (Cl^–) was determined at a pH of 7.3; DSC results suggest that changes of the polyelectrolyte under such conditions may influence the photoreaction. GC-MS analysis performed on illuminated solutions confirmed that CH₂Cl₂ was the main organic product but traces of C₂H₂Cl₄ were also detected.

Session 2#

Graphite-coated Fe₃C/α-Fe-derived iron oxide nanosheets and pulse-electrodeposited Ni-Co-S interconnected-nanoflake array for high-performance hybrid rechargeable charge storage applications

Hadi Khani, David O. Wipf
Department of Chemistry, Mississippi State University

Nanostructured nickel cobalt sulfide (Ni_4.5Co_4.5S₈) and graphite coated iron carbide/α-Fe (g-Fe₃C/Fe) derived iron oxide nanosheets at hollow graphite shells (Fe₃O₄@g-Shells) have been selectively prepared through a single step pulse-electrodepositon and facile two step annealing/electrochemical cycling process, respectively. The electrochemical characterization of the Ni_4.5Co_4.5S₈ and g-Fe₃C/Fe starting materials showed that both have high specific capacitances (1480 F g^–1 and 482 F g^–1 at 1 A g^–1) and excellent rate capabilities (≈95% and ̴ 83% retention at 20 A^–1, respectively). To demonstrate the advantageous pairing of these high rate materials, asymmetric supercapacitors (ASC) were assembled with Ni_4.5Co_4.5S₈ and g-Fe₃C/Fe as the positive and negative electrodes, respectively. The (Ni_4.5Co_4.5S₈ //g-Fe₃C/Fe) asymmetric capacitor with optimized mass loading could be reversibly operated in the 0.0V–1.6V potential window, delivering an impressive energy density of 64 Wh kg^–1 at 0.8 kW kg^–1 and a remarkable rate performance of 53 Wh kg^–1 at the very high power density of 16 kW kg^–1. Additionally, the asymmetric cell assembly exhibits a remarkable cycling stability retaining after the hundreds of cycles.

Nanocomposites of Silver Telluride and Naphthalene-Diimide–Bithiophene Co-Polymer Films for Electrical Property Enhancement

Tabitha Sutch¹, Luke Presson², Greg Szulczewski^1
1Department of Chemistry, University of Alabama
²Department of Chemistry, Centre College

Thermoelectric materials convert thermal energy into electrical power by extracting electrons from an n-type layer and holes from a p-type layer. Thermoelectric materials must be good electrical conductors and poor thermal conductors. Furthermore, the voltage generated across the hot and cold ends of the materials must be large, which is called the Seebeck coefficient. These parameters are difficult to optimize in a single-phase material. Thus, composite materials of inorganic nanostructures with high Seebeck coefficients and conducting polymers with low thermal conductivity are considered for thermoelectric devices. The majority of these composite materials are p-type semiconductors. As a result, this work focused on the development of n-type composites. In this study, we synthesized silver telluride from a tellurium precursor. Tellurium nanowires were synthesized by reducing tellurium dioxide with ascorbic acid in diethelyene glycol. The tellurium nanowires were stirred in water with excess silver nitrate and converted into silver telluride. Transmission electron microscopy (TEM) was used to characterize the tellurium nanowires and silver telluride whiskers. X-ray photoelectron spectroscopy (XPS) was used to determine if oxidation was present on the silver telluride whiskers. Silver telluride was mixed into poly{[N ,N′ -bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis-(dicarboximide)-2,6-diyl]-alt -5,5′ -(2,2′ -bithiophene)} or P(NDI2OD-T2), a well-known n-type conducting polymer. The goal of this work was to increase the electrical conductivity of the composite films. We found the best electrical responses in composites of silver telluride and P(NDI2OD-T2) dissolved in dichlorobenzene with subsequent thermal annealing. Absorption and fluorescence spectroscopy were used to assess the degree of P(NDI2OD-T2) packing and orientation.

Quantitative Comparison of a Laser and Light-Emitting Diode for Fluorescence Detection with Capillary Electrophoresis

Thu H. Nguyen and S. Douglass Gilman
Department of Chemistry, Louisiana State University, Baton Rouge, LA 70803

Signal-to-noise ratios were quantitatively compared for capillary electrophoretic separation and fluorescence detection of fluorophores using a blue LED and Argon-ion laser lines as excitation sources. Three fluorophores used for this study were rhodamine 123, fluorescein, and 5-carboxyfluorescein. An LED with the nominal wavelength of 470 nm, and argon-ion laser lines at 465 nm, 472 nm, and 488 nm were coupled to optical fibers for use in a commercial instrument, so the collimation of the LED relative to the laser is not an issue for comparison of the sources. The signal-to-noise ratios were determined for all three fluorophores at several excitation intensities of the two sources tested. Fluorophore excitation and emission spectra, source spectra, and spectra of the notch and emission filters were all taken into account in analysis and comparison of S/N ratios for different sources. For the laser and LED sources studied in this work at the same excitation intensity, the laser lines provided S/N ratios 2-4 times higher than those with the LED. Limits of detection for the three fluorophores were 3-20 times lower with laser lines relative to the LED. It is important to recognize that the noise and spectral characteristics of the laser source, LED, and fluorophores as well as the detector design all impact the relative performance for fluorescence detection. Simplistic, general statements about the superiority of laser or LED sources for CE fluorescence detection should be considered with caution.

Session 3#

The Synthesis Towards α-methylselenocysteine

Robert Wehrle and Dr. Douglas Masterson
Department of Chemistry and Biochemistry, University of Southern Mississippi

Selenocysteine (Sec) is considered to be the 21st proteinogenic amino acid and is how elemental selenium is assimilated in the biological systems. Laboratory synthesis and incorporation into synthetic peptides can be challenging owing to selenium’s reactivity to atmospheric oxygen when compared to the lower chalcogen species such as oxygen or sulfur. Once Sec is initially oxidized, the hydrogen at the α-position of the amino acid allows for facile elimination of the selenium as selenium oxide leaving dehydroalanine. Once dehydroalanine is formed, reverting back to Sec is highly improbable, however having a methyl at the α-position instead of a hydrogen could shut down this elimination. Typically, Sec is synthesized from serine, however the synthesis become exceptionally difficult forming α-methylSec due to the neopentyl substitution site present at the α-position. The rate of substitution to a neopentyl site is approximately 1000-fold slower compared to the typical isobutyl site if the reaction even progresses at all. To aid in the substitution at this site with a selenating reagent the leaving group can be made into a more readily removable group, such as OTs, OMs, or OTf. With these modified leaving groups, α-methylSec or its diselenide dimer should be obtainable.

An Angularly Fused Pentacene as a Precursor for the Bis-corannulene Molecular Receptors with Polar Tethers

K. G. Upul R. Kumarasinghe¹, Frank R. Fronczek², Henry U. Valle¹, Andrzej Sygula^1
1Department of Chemistry, Mississippi State University
²Department of Chemistry, Louisiana State University

A novel angularly fused pentacene, bis-corannulenoanthracene (C₅₀H₂₂), was prepared by the Diels-Alder cycloaddition of isocorannulenofuran to a bis-benzyne precursor, followed by deoxygenation of the endoxide adducts. The highly insoluble C₅₀H₂₂ was characterized by UV-Vis, Fluorescence, IR and HRMS. While the hydrocarbon is stable enough to be isolated and stored, its pentacene core allows for a facile cycloaddition of maleic anhydride to the central ring, producing bis-benzocorannulenebarrelene which was fully characterized by spectroscopic methods and by X-ray crystal structure determination. ¹HNMR titration of bis-benzocorannulenebarrelene shows the formation of both 1:1 and 2:1 inclusion complexes with C₆₀ with in chlorobenzene-d₅. The determined association constants K₁ and K₂ are 3,610 ± 20 and 2,000 ± 120 M^–1, respectively. The presence of the polar “anchors” on the tether of this receptor allows for its deposition on a solid support like silica gel.

A Non-invasive Fluorescence-based Oxygen Sensor and Platform for Studying Cell Responses to Metabolic Agents in Real-Time

Koutilya R. Buchapudi^1,2, William Johnston^2,3, Sven E. Eklund^1,2
1Department of Biomedical Engineering, Louisiana Tech University, Ruston, LA, 71272, USA.
²Chemistry Program, Louisiana Tech University, Ruston, LA, 71272, USA.
³School of Biological Sciences, Louisiana Tech University, Ruston, LA, 71272, USA

A fluorescence-based sensor in a transverse flow/stop measurement platform has been developed to determine real-time changes in oxygen consumption rates for cell metabolic studies. The oxygen sensitive fluorophore platinum octaethylporphyrin (PtOEP) was embedded in a cellulose acetate matrix and affixed to a fiber optic bundle, which provided for transmission of the excitation and emission wavelengths of the film. The fiber optic bundle was sealed in a sensor head that can be used in standard 24-well plates common to research labs. The utility of the sensor and sensing platform were determined by measuring the changes in oxygen consumption rates of Candida albicans during 90/30 s flow/stop cycles. Exposure of the cells to fluoride and glucose showed the expected decrease and increase in oxygen consumption rates respectively in real time. The robustness of the fluorophore film was demonstrated by exposure to different media and analyte conditions in the absence of cells. For stop cycle time intervals less than 1 minute the sensor exhibited a rapid and fairly linear change in fluorescence intensity to changing oxygen concentrations in the measurement chamber. Future work will include development of the instrument into a multianalyte microphysiometer. The sensor head can be modified to include sensors for additional analytes such as glucose, pH and potassium. Other directions for study include decreasing the fiber optic cable footprint to maximize the number of sensors and decreasing the size of the instrument so that it could be used in a wider variety of experimental designs.

Conservative Reduction of Esters to Ethers via an Oxonium Ion Intermediate

Alison Hart and Julie A. Pigza
Organic Chemistry, Department of Chemistry and Biochemistry

The ether functional group is extremely useful in natural product synthesis due to its lack of reactivity and overall general compatibility. The development of a tunable ester to ether reduction is highly desired, as conventional methods such as the Williamson ether synthesis do not work with bulky alkyl halides, and the acid catalyzed condensation of alcohols is limited to making symmetric ethers. In the current literature, the reduction of esters to ethers has been explored, however their broad applicability has been hindered, especially for one-step conversions. Therefore we are interested in developing a general and tunable two-step method for the reduction of esters to ethers via an oxonium ion intermediate which is susceptible to nucleophilic attack producing the desired ether or α-substituted ether products. A significant ester reduction substrate scope, including both aromatic and non-aromatic esters, will be conducted using ReactIR for in situ reaction monitoring. The completion of the ester reduction will be observed by the loss of the carbonyl peak, allowing for the shortest possible reaction times for specific substituent classes. A brief outline of our results using our ester model substrate will be given, along with progress towards developing an overall tunable one-pot methodology.

Session 4#

Lester Andrews and Biophysical Joint Session

Near Infrared Spectroscopy and Chemometrics can be used to Determine Physiological Status in the Endangered Snow Leopard (Panthera uncia)

Kristen Counsell¹, Beth Roberts², Brandie Balkenbusch², Andrew Kouba³, Scott Willard¹, Carrie Vance^1
1Department of Biochemistry, Molecular Biology, Entomology and Plant Pathology, Mississippi State University
²Research and Conservation, Memphis Zoo, Memphis, TN
³Department of Wildlife, Fisheries and Aquaculture, Mississippi State University

Aquaphotomics is the study of changes in patterns of water H-bonding structure with near infrared spectroscopy (NIRS). Water band coordinates in the first overtone of the O-H stretching band (1300-1600nm) act as solute biomarkers; specific wavelength shifts correspond to the solute’s physical properties and concentration. We used aquaphotomics to evaluate steroid and non-steroid reproductive hormones in urine of snow leopards to detect pregnancy and parturition. This study measures NIR efficacy in distinguishing and quantifying the hormones estradiol (E₁G), progesterone (P₄) and prostaglandin (PGFM) as a rapid and non-destructive assay for estrus, pregnancy and parturition, respectively. Triplicate sampling of standards and snow leopard urine (37 °C) had NIR spectra (1 nm resolution) collected using a quartz l=0.1 cm cuvette and ADS-FieldSpec^®3 fiber-optic system. Chemometric analysis (Grams AI/IQ 9.1) using mean centering and 2^nd derivative GAP spectral pre-processing revealed unique water spectral patterns corresponding to each hormone. NIR water coordinates were determined for E1G (1380nm, 1414nm, 1448nm, 1492nm), P₄ (1418nm, 1440nm, 1478nm) and PGFM (1442nm, 1450nm, 1510nm) standards. Quantitative calibration of NIR water signatures reflecting E1G (0-4000 pg/ml), P₄ (0-3 pg/ml) and PGFM (100-1600pg/ml) levels were R²=0.92, 0.99 and 0.97, respectively. In the samples of urine from a pregnant snow leopard, spectral shifts of the water O-H stretch occurred over the course of three days as P₄ values dropped to baseline, and concurrently, PGFM levels increased from 708 pg/ml to 1625 pg/ml, signaling parturition. These spectral shifts demonstrate NIR has the ability to detect steroid and non-steroid hormones in urine for reproductive analysis.

The thermodynamics of metal and substrate binding with an taurine/α-ketoglutarate-dependent oxygenase (TauD)

Mingjie Li¹, Kate L Henderson^1,2 Salette Martinez³ Robert P Hausinger,³ and Joseph P Emerson^{1 1}Department of Chemistry, Mississippi State University
²Department of Biochemistry, University of Wisconsin
³Department of Biochemistry and Molecular Biology, Michigan State University

The biochemistry of iron has been studied for the last 80+ years, however, little has been done to characterize how iron(II) is mediated throughout living systems, and more importantly how iron(II) coordination impacts biomolecule stability. Here we have focused our efforts on a nonheme iron(II) oxygenase, TauD. TauD is a taurine and α-ketoglutarate (αKG) dependent metalloenzyme, which catalyzes the hydroxylation of taurine leading to its decomposition into aminoacetaldehyde and sulfite; where sulfite is a key metabolite in E. coli.. Here, we explore the thermodynamic properties and global stability of TauD and a variety of TauD complexes using a combination of circular dichroism spectroscopy and calorimetry techniques. The results show a general increase of the melting temperature as substrate and cofactors are added to TauD. However there are interesting discrepancies in the spectroscopically measured change in enthalpy (ΔH_VF) versus the calorimetric enthalpy (ΔH_DSC), which could suggest that denaturing these metalloenzymes costs more than just the energy needed to unfold the protein. Additionally, the thermodynamic associated with of bioavailable, divalent metal ions (including Fe, Co and Mn) binding with TauD are elucidated.

Typical and Atypical Prion-like Propagation of Neurotoxic Amyloid-β Oligomers

Dexter N. Dean¹, Kayla M. Pate², Pradipta K. Das³, Sarah E. Morgan³, Melissa A. Moss^2,4, and Vijayaraghavan Rangachari^1
1Department of Chemistry and Biochemistry and ³School of Polymers and High Performance Materials, The University of Southern Mississippi
²Biomedical Engineering Program and ⁴Department of Chemical Engineering, The University of South Carolina

Soluble oligomers of the amyloid-β (Aβ) peptide have emerged as the primary neurotoxic agents in Alzheimer disease (AD). Recent evidence from animal models also implicates aggregates of Aβ to undergo prion-like propagation towards seed-specific fibril deposition. However, dearth in a molecular understanding of Aβ oligomers has confounded the insights into propagation and dissemination of toxic amyloid aggregates. Our recent reports on a distinct 12-24mer oligomer of Aβ, called large fatty acid-derived oligomers (LFAOs), have opened doors in investigating this elusive mechanism. We have previously established that LFAOs undergo replication upon interacting with monomers to form quantitative amounts of identical oligomers. Here, we sought to investigate the concentration-dependent dynamics of LFAOs to reveal how such transitions manifest in their ability to replicate and induce neuronal apoptosis. We have also investigated the ability of LFAOs to undergo prototypical prion-like propagation, where LFAOs grow as distinct repeating units leading to morphologically unique fibrils. We discovered that LFAOs undergo a concentration-dependent transition between 12mers and disperse 12-24mers, which correlates with their ability to replicate and induce apoptosis. At low concentrations (sub-µM), LFAOs exist as 12mers and undergo atypical prion-like propagation (replication) upon interaction with Aβ monomers. While at high concentrations (> 10 µM), LFAOs exist as disperse 12-24mers and propagate towards morphologically unique fibrils in typical prion-like fashion. The observations reported here may have profound significance in deciphering the emerging roles of Aβ oligomer phenotypes in prion-like propagation and dissemination of toxicity in AD.

Session 5#

The Effect of Functionalized Cellulose on the Thermal Stability of ABS and HIPS-Reinforced Composites

Chemar J. Huntley¹, Kristy D. Crews¹, and Dr. Michael L. Curry^1,2
1Department of Materials Science and Engineering, Tuskegee University, Tuskegee, AL 36088 ²Department of Chemistry, Tuskegee University, Tuskegee, AL 36088

Interest in cellulose as a reinforcement filler in composites has increased over the years. Cellulose is abundant in nature, possesses a high specific strength, and is biodegradable. Due to its biodegradability, cellulose is ideal for composite applications to increase sustainability and recyclability. In this research, CreaTech cellulose was oxidized using the Albright-Goldman methodology to increase its hydrophobicity and uniform distribution within a thermoplastic-polymer matrix. The polymorphic structure and crystallinity percentage of the cellulose was determined using XRD analysis, while the surface characteristics were examined with SEM. Also, FTIR analysis ensured the introduction of carbonyl-functional groups on the cellulosic structure. After chemical functionalization, the cellulose was incorporated into ABS- and HIPS-matrix composites, where the thermal properties were observed with DSC and TGA analyses. Future research includes determining the cellulose weight percentages that produce the optimal properties for composite materials.

Funder Acknowledgements: The authors gratefully acknowledge the National Science Foundation under Grant Nos. NSF EPS-1158862, NSF HRD-1137681, NSF IGERT on Sustainable Electronics DGE-1144843, and AGEP HRD-1433005 for support of this research.

A cross-reactive sensor array for qualitative and quantitative metal ion detection in aqueous solution

Michael Ihde and Marco Bonizzoni
Department of Chemistry, University of Alabama

We are currently investigating the qualitative and quantitative detection of divalent metal ions in water using array sensing techniques. By exposing an array of dyes to multiple analytes in a single experiment, we have been able to obtain a data set that can be reduced with minimal loss of information using a mathematical transformation known as linear discriminant analysis (LDA). Our cross-reactive array consists of just two commercially available dyes (xylenol orange and methylthymol blue) and is able to detect eleven divalent metal ions qualitatively, including metals that have significant health and environmental impact. Furthermore, we have used the same array to map metal ion concentrations of four environmentally relevant divalent metal ions (Hg(II), Pb(II), Cd(II), and Cu(II)) quantitatively at concentrations as low as 1 µM in neutral water.

Construction of Solid State Nanoreactor for the Synthesis and Characterization of Large Scale Metallic Nanoparticles

Aiesha L. Ethridge¹, Demetrius A. Finley², Michael L. Curry^1,3
1Department of Materials Science and Engineering, Tuskegee University
²Department of Materials Science and Engineering, REU Site, Tuskegee University
³Department of Chemistry, Tuskegee University

The current state of nanoparticles fabrication via polymer or solid state means is limited by the instability of the formed nanoparticles against self-aggregation and the ability to produce monodispersed nanoparticles on the macro-scale. Hence, motivation for this project is to construct a solid state nanoreactor that uses multifunctional reduction methods (chemical reduction and photoreduction) to produce technologically relevant monometallic and multimetallic nanoparticles with controllable shapes and sizes and with specific designed cores and shell compositions at the macroscale “gram scale”. In particular, this design will take advantage of polymeric means (Dendrimers and high temperature polymers such as PPI) to control the growth modes of CuNi, CoPt, and CuNiCo particles during formation. The resulting morphologies and structures of the formed nanoparticles will be characterized by UV-vis, SEM, TEM, and XPS. Furthermore, future tests will be conducted to establish the influence of the particle’s composition and structure on its bioaccumulation in the environment, its solubility in water and in various buffer solutions, and measure free ions by ICP after sitting in water for various periods of times and its effect on other biological systems.

Session 6#

Sugar Sensing Using Boronic Acid-Modified Poly(amidoamine) Dendrimers

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

Boronic acids can be used as receptors in chemical sensors for sugars. However, their binding affinity and solubility are usually poor in H₂O. We improved these parameters by covalently connecting boronic acid moieties to the surface of third-generation poly(amido)amine (PAMAM) dendrimers, to form PAMAM-boronic acid receptors (PAMAMba). We first monitored the interaction of these receptors with dyes such as 4 methylesculetin and alizarin Red S that contain diol moieties by absorbance and fluorescence spectroscopy. We then studied the interaction of the PAMAMba receptor with sugars by setting up an indicator displacement assay based on these results. Addition of monosaccharides (e.g. fructose, glucose, galactose and ribose) and disaccharides (e.g. lactose, maltose, sucrose and trehalose) to the [PAMAMba●(dye)_n] complexes allowed us to study their complexation to PAMAMba by following the displacement of the bound dyes. Finally, we demonstrated the use of these polymer-based sensors in a multivariate array sensing platform for the discrimination of common mono- and disaccharides in water as a proof of principle towards their broader applicability in physiologically and environmentally relevant conditions.

Small-Molecule Models of Poly(amidoamine) Dendrimers

Nicholas J White and Marco Bonizzoni
The Department of Chemistry, The University of Alabama, Tuscaloosa, Alabama

Amine-terminated poly(amidoamine) dendrimers (PAMAM) are hyperbranched polyelectrolytes which can bind to small anionic molecules through non-covalent interactions. To determine the individual contribution, cooperativity, and multivalency of these interactions in water, we have preparing a series of model molecules. The intact model, K₀, contains all key functional groups present in PAMAM dendrimers: a sterically hindered tertiary amine, an amide functional group, and a primary amine. Additional molecules have also been synthesized; these “knockouts” (K_n) are missing individual moieties that may be involved in the binding process. K₁ omits the tertiary amine while K₂ and K₃ omit the primary amine. The K₁-K₃ series will provide insight into electrostatic effects and afford a comparison of the relative importance of protonation of the primary and tertiary amines. K₄ is a pH-independent protonation probe that will allow us to study the effect of changing pH without affecting the charge state of the probe.

Comparison of the binding properties of these model compounds with those of the intact model, and of the full dendrimers, will allow us to explore the effects of each target interaction, as well as of cooperativity among these interactions. This will be carried out using ¹H NMR spectroscopy. Additionally, thermodynamic parameters of binding will be studied using isothermal calorimetry.

Visible light generation of high-valent iron(V)-oxo-porphyrin and manganese(V)-oxo-corrole

Ka Wai Kwong, Jonathan Malone, Mike Winchester, and Rui Zhang
Department of Chemistry, Western Kentucky University, 1906 College Heights Blvd. Bowling Green, KY 42101

High-valent transition metal-oxo intermediates are of fundamental importance because of their central roles as active oxidizing species in enzymatic and synthetic catalytic oxidations.

In this presentation, new photochemical methods to generate high-valent iron-oxo porphyrin and manganese-oxo corroles will be presented. Visible-light irradiation of photo-labile bromate porphyrin-iron(III) salts gave iron(IV)–oxo porphyrin radical cations (compound I model) or the neutral iron(IV)–oxo porphyrin (compound II model), depending on the electronic structure of porphyrin ligands. Similar approach was extended to produce two manganese(V)-oxo corrole in different electronic environment. Our spectrum and kinetic studies discovered that the rate constants of corrole-mangnaese(V)-oxo species were remarkably affected by the nature of corrole ligand and solvent that will be discussed.

Session 7#

Pd(PNp₃)₂ Catalyzed Buchwald-Hartwig Amination Reaction Rate and Kinetic Study

Huaiyuan Hu, and Kevin. Shaughnessy
Department of Chemistry, University of Alabama

The Buchwald-Hartwald amination is a well-know Pd catalyzed cross coupling reaction that displays a variety of applications. The catalyst system based on Pd₂(dba)₃ and trineopentylphosphine (PNp₃) displayed high catalytic activity as well as functional group tolerance for a wide scope of sterically demanding arylbromides and aryl chlorides with sterically hindered aniline derivatives. Kinetic study was performed for further exploration of the reaction mechanism because the reaction rate showed some interesting correlation with the halide identity and substrate steric in the initial studies. Oxidative addition of haloarenes to trineuropentylphosphine Pd(0) was found to be the rate limiting step in the whole Pd-catalyzed coupling reaction. For arylbromides, the steric of the arybromides didn’t affect much on the reaction rate because the rate of dissociation of PNP₃ from Pd(PNP₃)₂ was much slower than that of the oxidative addition step. Moreover, it was surprisingly to see the reaction rate is actually increased within the first 30 minutes. Conversely, the steric of arylchlorides had an obviously negative effect on the reaction rate, and the reaction rate was observed to slowly decrease corresponding to time.

Donicity of Meridional Tridentate Ligands: ¹⁹⁵Pt NMR of CCC-NHC Pt Pincer Square Planar Complexes

Min Zhang, Eric Van Dornshuld, Xiaofei Zhang, T. Keith Hollis, Charles Edwin Webster
Department of Chemistry, Mississippi State University, Mississippi State, Mississippi 39762, United States

Pincer (tridentate-mer) ligands have drawn much interest in recent years due to their entropically enhanced stability and versatility which allows fine tuning of ligand steric hinderance, electron donating strength, bite angles, and chirality. The tridentate pincers ligands have found a niche in the production of organometallic catalysts applicable in a variety of bond forming reactions, such as C-C, C-N, and olefin metathesis. These useful properties stem from the inherent donor ability of these pincer scaffolds. While the advancement of this area of research is paramount, a systematic approach to measuring the donicity of these planar complexes could be very useful. Tolman electronic parameter (TEP) is one of the most facile and effective methods for determining ligand donor ability by measuring the A₁ C-O stretching frequency (ν(CO)) of a carbonyl complex by IR. However, the trans-ligand exerts considerable control over the ν(CO), and the cis-ligand plays a negligible role in a meridional tridentate complex. Another method to determine the ligand donor ability is by direct measurement of NMR chemical shift of a ligated metal center, for example, ¹⁹⁵Pt NMR. All orbital contributions could be effectively analyzed, regardless of denticity or orbital interactions. ¹⁹⁵Pt is much more sensitive than C-O stretching frequency. CCC-NHC Pt pincer square planar complexes with different backbones and ligands were synthesized, and their ¹⁹⁵Pt NMR shifts were obtained using sodium hexachloroplatinate(IV) as an external standard ([PtCl₆]^2–, 0 ppm). The result of ¹⁹⁵Pt NMR shifts indicates that a complex with an electron-deficient substituent on backbones or ligands has a low-field chemical shift.

Solvent Effects on the Reduction of a Palladium(II) Precatalyst for Suzuki Cross Coupling

Kerry Barnett and Kevin Shaughnessy
Department of Chemistry, The University of Alabama, Tuscaloosa, AL 35487-0336

Palladium cross-coupling reactions are widely used in synthesis for the production of new compounds, such as pharmaceuticals. Over the years, research in the field has progressed to develop efficient catalyst systems that perform under optimal conditions. The active catalyst species contains palladium with a zero charge oxidation state. However, some catalyst precursors used in cross-coupling reactions contain palladium in the +2 oxidation state. Palladium(II) precatalysts must undergo reduction to palladium(0) to generate the active catalyst. The mono-ligated palladium(II) precatalyst, [(DTBNpP)PdCl₂]₂ (DTBNpP = di-tert-butylneopentylphosphine), was prepared and used for the Suzuki coupling of aryl bromides with aryl boronic acids. It was hypothesized that the palladium(II) precatalyst undergoes a known reduction pathway involving two subsequent transmetallations of the aryl boronic acid followed by reductive elimination of the aryl substituents to generate the active mono-ligated palladium(0) species. ³¹P-NMR spectroscopy was used to determine the mechanism of reduction under the optimized reaction conditions. The ³¹P-NMR spectra obtained provide evidence of a side reaction to produce a catalytically inactive palladacycle species. Further analysis suggests that the rate of palladacycle formation varies with solvent. Studies were conducted in various solvents and catalyst loadings using NMR spectroscopy and gas chromatography to probe the change in reaction behavior as a function of solvent.

Poster Presentation Abstracts#

Electrochemical Studies of Nickel/H2SO4 Oscillating Systems and the Preparation and Testing of Copper Coupled Microelectrode Array Sensors

David Clark and David Wipf
Mississippi State University

Nickel is one of the most important passive metals used for electrodeposition processes in the world (1). Over 150 metric tons of Ni is consumed yearly for electroplating (2). Nickel is well known for its highly lustrous finish and corrosion resistant properties. Although Ni is very resistant to corrosion, it is not completely resistant. Nickel has been known to corrode in acidic medium such as sulfuric acid. The corrosion of Ni in Ni/H2SO4 produce periodic states of oscillations as a potential is applied or a current is passed through the system (3)-(5). Studies on these types of oscillatory states have been performed since 1950.

Traditionally, Ni electrochemical studies on Ni/H₂SO₄ oscillating systems have been performed by applying external forcing techniques through variations of applied potential or current during the electrodissolution (corrosion) of Ni single wire electrodes in high concentrations of H₂SO₄ solutions (1 M, 3 M, and 4.5 M). External forcing is the process in which perturbations are applied to a system by an external source and have helped to provide a better understanding of Ni/H₂SO₄ oscillating systems. However, little attention has been given to performing electrochemical studies on Ni/H₂SO₄ oscillating systems in low concentrations of H₂SO₄ solutions (0.3 M - 0.9 M) and no attention has been given to the possibility for the external forcing of these unique systems via concentration change at the Ni electrode surface until now (for example, Figure (1).

Although electrochemical studies on Ni single wire electrodes provided a significant amount of information about self-organization and periodic oscillations, an in depth analysis of the Ni/H2SO4 oscillating system was not possible because of the lack of adequate technology (6). In order to overcome this issue, coupled microelectrode array sensors (CMAS) have been recently developed. CMAS are integrated devices with multiple electrodes that are connected externally in a circuit, and all of the electrodes on the CMAS have the same amount of potential applied or current passing through them during experiments.

CMAS can be used for studying self-organization and periodic oscillations via external forcing (7)-(8). CMAS have also been used for real-time corrosion monitoring in cooling water systems, simulated seawater, and concrete (9). CMAS are useful devices because they are capable of simulating single wire electrodes of the same size (5)-(6), (9). During the last six decades, many electrochemical studies have been performed by using CMAS; however, there is little published detailed descriptions of CMAS fabrication.

The work presented here shows that periodic oscillations were successfully controlled by changing the concentration of the proton concentration at the Ni electrode surface via external forcing. This work will outline the steps in which the CMAS were fabricated. The steps in which the CMAS was modified via electrodeposition of Ni will be shown. This work will also show the results that were collected from CV experiments performed on the modified CMAS.

Human Scent Profiling via Active SPME GCMS for Determination of Odor Reduction

Glenn B Crisler II, Shamitha Dissanayake¹, Todd Mlsna¹, Christopher Vanlangenberg², Bronson Strickland³, Steve Demarais^3
1Department of Chemistry, Mississippi State University
²Department of Mathematics & Statistics, University of North Carolina
³Department of Wildlife, Fisheries, & Aquaculture, Mississippi State University

The human scent profile contains numerous volatile organic compounds (VOCs). The VOC profile from each person is a fingerprint that allows insight into the individual’s dietary habits, biochemistry, and certain environmental factors. This has been formally observed 2500 years ago by Hippocrates, who noticed that certain diseases cause their sufferers to have certain distinctive odors. Removal of the entire VOC profile is impossible by scent elimination products because of the body’s constant production of these compounds. This study targets the major components of the human VOC profile and quantifies the effectiveness of 4 different scent control products. In this study 65 subjects were tested, and samples were processed using active SPME GCMS technique. The effectiveness of each product and mechanisms of scent control were analyzed.

Synthesis of α-FeOOH and CoPi Thin Films for use as Catalysts in Electrochemical Water Oxidation and Efficiency Comparison to Known Effective Catalysts

Jeremy Hitt, Dusty Trotman, and Shanlin Pan
Department of Chemistry, The University of Alabama

As the world looks to develop new forms of clean, renewable energy, water oxidation by electrolysis appears very promising. Electrolysis is used to produce hydrogen and oxygen gas which is combusted in fuels cells to make electricity. The most important factor affecting the efficiency of electrolysis cells is the electrode surface that is in contact with the water. Here we synthesize, test, and compare two newer types of catalysts for water splitting that can perform at near neutral pH. These two catalysts, α-FeOOH and CoP_i, are grown on conductive glass surfaces by electrodeposition and compared with two previously known catalysts (IrO_x nano-particle thin film and NanoCOT). The samples are used to split water in an electrochemical cell using linear sweep voltammetry, and their efficiencies are calculated and compared graphically to assess their effectiveness for large scale hydrogen production.

Fabrication and Characterization of a Metal Organic Framework and Zirconium (IV) Hydroxide Thin Films for the Detection of Explosive Vapors

Jennifer E. Shankwitz¹, Greg Szulczewski¹, Adam Hauser^2
1Department of Chemistry, The University of Alabama
²Department of Physics, The University of Alabama

There exists a significant need for low-cost, lightweight, and robust point detection of explosives and chemical warfare agents. Frequency-dependent electrical impedance is a promising avenue for low-cost detectors via electrical circuits. Our goal is to create a device that can detect such substances in real time in order to help minimize the damage caused to our troops and citizens. Active layers were formed by ultrasonic spray deposition of metal organic framework compound or zirconium (IV) hydroxide thin films onto lithographic electrodes. The films were characterized by atomic force microscopy, scanning electron microscopy, and energy-dispersive x-ray spectroscopy to determine the thickness, morphology, and areal coverage of each candidate film. The next step in our project is to measure the electrical behavior of the modified electrodes when exposed to known quantities of explosive vapors.

This project has been funded under Army Research Office STIR award #W911F-15-1-0104.

Determination of the leaf level emissions of volatile organic compounds from chestnut tree species by gas chromatography-mass spectrometry and chemometrics

Jinyan She¹, Mary King¹, Richard Baird², and Todd Mlsna^1
1Department of Chemistry, Mississippi State University
²Department of Biochemistry, Molecular Biology, Entomology, and Plant Pathology

American chestnut tree (Castanea dentata) is ecological and economic significance. However, it was nearly devastated by chestnut blight fungus. Many methods have been developed to restore the American chestnut trees back to natural. Breeding the blight-resistance chestnuts by crossing Chinese chestnuts with the American species via “backcrossing” is one method in use. However, to determine the resistance of one generation of breeding specie takes at least five years and the complete test requires a minimum of six generations. Researches showed that volatile organic compounds (VOCs) produced by tree leaves have a role in defense mechanisms to pathogens. Herein, we are developing a resistance test method by discriminating the VOCs profiles emitted from BC3F2, B3F3 generations, American, and Chinese chestnut tree leaves using Headspace Solid Phase Microextraction (HS-SPME) coupled with Gas Chromatography-Mass Spectrometry (GC-MS) and the pattern recognition assisted with chemometrics. Further works are including dynamic headspace pre-concentration extraction method development and application of current statistical model to field samples.