Department of chemistry - Posters in the Hall
End of Year Annual Event - 2011
Undergraduate and Graduate Students Present their Research
Undergraduates Student Presenters
Zach Arnold
Fadwa Constandinidis
Andria Fortney
Ashley Hoang
Miyong Hughes
Tai Lam
Allie Meyerhoefer
Sarah Slate
Triet Truong1– Judged Best Undergraduate Research Poster
Triet Truong2
Graduate Student Presenters
Amanda Balaguer– Judged Best Graduate Research PosterAndrew M. Beauchamp
Jeffrey D. Fogle
Dennis Lennaerts
Rachel Sayers
Michael E. Smith
Abstracts
DETERMINATION OF THE KINETIC PARAMETERS OF BB’B’ MONOMERS UTILIZED TO PREPARE HYPERBRANCHED POLY(ARYLENE ETHER)S
Ashley Hoang, Shravanthi Raghavapuram, and Eric Fossum, Ph.D.
Wright State University, Dept. of Chemistry,
Dayton, Ohio
The degree of branching in hyperbranched poly(arylene ether)s prepared from 3,5,4’-trifluorodiphenyl sulfone, 1, or 3,5,4’-trifluorobenzophenone, 2, can be tailored via reaction temperature. 13C and 19F NMR spectroscopic analysis of 1 and 2 indicated that the 4’- site was the most reactive and that displacement of the first meta fluorine resulted in a considerable decrease in the reactivity of the second. To better understand and control the overall polymerization process it is crucial to determine the activation energy of each reactive site in the BB’B” monomers. Thus, a series of kinetic studies were performed, employing 2 equivalents of m-cresol, as the nucleophile. Initial kinetic studies were carried out on the corresponding BB’ monomer, 3,5-difluorodiphenyl sulfone. Reaction temperatures of 75 ˚C, 100 ˚C, 125 ˚C, and 150 ˚C were utilized and the aliquots removed from the reaction mixture were analyzed via a combination of GC/MS and NMR spectroscopy.
ESTIMATING THE ANALYTICAL AND SURFACE ENHANCEMENT FACTORS IN SERS: A NOVEL PHYSICAL CHEMISTRY AND NANOTECHNOLOGY LABORATORY EXPERIMENT
Joshua D. Baker, Khadijeh S. Alnajjar, Jennifer L. Monahan, Adam C. Stahler, Nora E. Hunter, Kent M. Weaver , Allie J. Meyerhoefer, David A. Dolson, and Ioana E. Pavel, Ph.D.
Wright State University, Dept. of Chemistry, Dayton, Oh
Surface-enhanced Raman spectroscopy (SERS) is an embodiment of Raman spectroscopy that has all molecular fingerprint capabilities of Raman and extremely high sensitivity. Theory predicted and experiments confirmed that exceptionally large Raman cross-section increases (i.e., single-molecule detection events) are associated with targeted molecules located in the nano–sized interstitial sites of aggregates of interacting silver nanoparticles (AgNPs). Recently, a novel laboratory experiment was successfully implemented for undergraduate and graduate students in physical chemistry and nanotechnology classes. The main scientific goal of this experiment was to demonstrate the SERS-based sensing capabilities of colloidal AgNPs by estimating the analytical (AEF) and surface (SEF) enhancement factors. AEF and SEF are the most important values for characterizing the SERS effect. Additionally, most SERS-based cutting-edge applications (e.g., cellular imaging, protein and DNA detection, quality control in both chemical and pharmaceutical industries, etc.) require an accurate determination of the magnitude of the signal enhancement. To achieve this, students synthesized a Creighton colloid and characterized its optical properties by UV-VIS absorption spectrophotometry. A rhodamine 6G fluorescent dye (R6G) was added to the colloidal AgNPs to determine the AgNP enhancement efficiency. Raman, SERS and fluorescence measurements were then performed to estimate the AEF (7.4 × 104) and SEF (5.2 × 101) values. Although these factors do not correspond to single-molecule detection events (maximum enhancement of 105 and 7 × 109 for colloids), the R6G concentration (1.0 × 10-6 M) was three orders of magnitude less than in previous laboratory experiments and facilitated the rapid acquisition of SERS spectra with very good signal–to–noise ratio. This laboratory experiment successfully introduced students to the fundamentals of SERS spectroscopy and to concepts related to light scattering, surface chemistry and resonance effects. Furthermore, students acquired new instrumental and nanotechnology–related skills that will benefit them in technologically-demanding careers.
ELECTROANALYSIS OF NADH AND L-DOPA USING A CONDUCTING POLYMER CARBON MODIFIED ELECTRODE
Urmi Chaudhuri, Sarah Slate, and Suzanne K. Lunsford, Ph.D.
Wright State University, Dept. of Chemistry, Dayton, Oh
The electrochemical oxidation of dihydronicotinamide adenine dinucelotide (NADH) in aqueous solution has been an increase interest since it plays a role in the generation of ATP, the body’s energy currency, and has been found to be deficient in several age related degenerative diseases. Therefore, NADH/NAD+ redox enzymes are of extreme importance in biological systems as well as the common neurotransmitter such as L-DOPA (3,4-dihydroxyphenylalanine). The NADH and L-DOPA have been found to be beneficial for patients suffering from Parkinson’s disease, Alzheimer’s disease and depression. Over the past few decades, conducting polymers play a critical role in the development of biosensors. These chemically modified polymer electrodes was developed to meet the needs for controlling the reactivity, selectivity and sensitivity of the electrode reactions. The main use for such conducting polymers as poly(2,2-bithiophene) implemented on modified electrodes is centered on the optimization of the electrocatalytic processes and electrocatalysis. The employment of cyclic voltammetry (CV) has been used across many fields of chemistry to study redox states and will be carried out to analyze the redox reactions of NADH and L-DOPA in this study at pH values around neutral. CV enables a wide range to be rapidly scanned for reducible or oxidizable species. We will discuss and present the voltammetric studies of NADH and L-DOPA at a poly(2,2-bithiophene) modified carbon electrode.
ADSORPTION AND DESORPTION OF BARIUM TO HEMATITE (µ-Fe2O3) IN ARTIFICIAL SEAWATER
Dennis Lennaerts and Steven R. Higgins, Ph.D.,
Wright State University, Department of Chemistry, Dayton, Ohio
Barite (BaSO4sub>) is a widely studied mineral that forms in the ocean by precipitation. To correctly interpret the results of barite studies it is important to know how and where the precipitation takes place. One of the suggested ways is the adsorption of barium to iron oxides at shallow depth followed by sinking of the iron oxides and release of the barium at deeper depth (Sternberg et al. 2005). This adsorption/desorption is driven by the pH difference at different depths. This research focuses on the adsorption/desorption of barium to hematite (α-Fe2O3 in artificial seawater. The adsorption is studied at various pH levels to simulate the varying pH at depth in the ocean. The barium concentration in artificial seawater is measured with ICP-OES at various time intervals in order to calculate the kinetics of the adsorption. Experiments were conducted as a function of time, solution pH and initial Ba concentration in synthetic seawater and the results and interpretation of these investigations will be presented.
SIMULTANEOUS DETERMINATION OF CATECHOL AND ASCORBIC ACID WITH CTAB MODIFIED CARBON PASTE ELECTRODE
Miyong Hughes and Suzanne K. Lunsford, Ph.D.
Wright State University, Dept. of Chemistry, Dayton, Ohio
Catechol is a common neurotransmitter involved in neurological diseases such as Parkinson’s, Alzheimer’s disease, and Schizoprenia. Selective determination of catechol in the presence of ascorbic acid (AA) has gained considerable attention over the years. The concentration of catechol and AA and other neurotransmitters in biological samples vary from species to species, in a wide range, from 10-7 M to 10-2
M. Hence, selectivity and sensitivity are important in the development of any procedure for the determination of catechol in the presence of common interferents such as AA. Several electrochemical techniques and electrode materials have been explored for the analytical determination of the neurotransmitters. Electrochemical analysis of unmodified electrodes such as glassy carbon (bare carbon paste electrodes) has the disadvantage of a lack of selectivity due to overlapping oxidation potentials of catechol and AA. This poster presentation will discuss the use of a cation surfactant Cetyltrimethylammonium Bromide (CTAB) modified carbon paste electrode. This hand built CTAB carbon paste electrode was fabricated and applied to simultaneous determination of catechol and AA. The modified CTAB electrode resolved the overlapped voltammetric responses of catechol and AA without the need of prior separation techniques which will be illustrated.
TAILORING THE SOLUBILITY AND THERMAL CHARACTERISTICS OF POLY(ETHER ETHER KETONE)S
Andria Fortney, and Eric Fossum, Ph.D.
Wright State University, Dept. of Chemistry, Dayton, Ohio
The solubility and thermal properties of poly(ether ether ketone) (PEEK) have been modified by incorporating various ratios of a comonomer, 3,5-difluorobenzophenone. 1. Since 1 is simply the geometric isomer of 4,4’-difluorobenzophenone, 2, which is traditionally utilized to synthesize PEEK, the resulting polymers have the same chemical composition, allowing for very accurate structure-property relationships to be determined. In addition, the use of monomer 1 affords PEEK systems that carry pendant benzoyl groups, which provide a versatile site for the introduction of functional groups. The thermal properties were investigated by a combination of thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The ratio of monomer 2 to monomer 1 had a dramatic influence on the thermal properties and solubility characteristics of PEEK. At lower ratios, 50:50 and 75:25, the PEEK derivatives were completely amorphous and soluble in N-methylpryrrolidinone (NMP), while at higher ratios, 80:20, 85:15, and 90:10, the materials became semi-crystalline and their solubility in NMP decreased significantly. TGA analysis indicated excellent thermal stability as all of the materials 5 % weight loss temperatures (Td5%) in excess of 450°C.
METAL TRIFLATE CATALYSTS IN FRIEDEL-CRAFT ACYLATIONS OF SYDNONES
Amanda Balaguer, Ryan Selhorst, and Kenneth Turnbull, Ph.D.,
Wright State University, Dept. of Chemistry, Dayton, Ohio
In a comparative study, various homogeneous metal triflates have been used as catalysts in the acylation of 3-phenylsydnone with acetic anhydride. Reactions were performed initially under thermal conditions overnight and monitored by thin layer chromatography for completion. When optimal conditions were achieved, these predetermined parameters were employed for “scaled-up” reactions, with the modification that they were performed under microwave irradiation, which gave better yields of the acylated product in shorter amounts of time. Thermal reactions took overnight to react while microwave reactions took 30 minutes. Future work includes testing the efficiency of other metal triflate catalysts, expanding the study to different parent sydnones, and utilizing various other anhydrides. The scope and limitations of the present findings will be enumerated.
5-ALKOXY-1,4-DICARBOETHOXY-2,3-DIPHENYLBENZENES
Rachel Sayers and William A. Feld, Ph.D.
Wright State University, Department of Chemistry, Dayton, Ohio
A series of alkoxy, phenylated terephthlates has been synthesized as monomer precursors to the corresponding poly(phenylene vinylene)s (PPV). The hydroxy terephthalate was synthesized via 1) a Diels-Alder cycloaddition between an ethynyl boronic ester and a cyclopentadienone and 2) hydrolysis/oxidation of the boronate ester. The synthesis, characterization and subsequent manipulation of the unique terephthalate as PPV precursors will be presented.
RESTRICTED ROTATION IN ORTHO-FLUOROPHENYL SUBSTITUTED DERIVATIVES
Jeffrey D. Fogle and William A. Feld, Ph.D.
Wright State University, Department of Chemistry, Dayton, OHIO
Various 2,3-bis(2-fluorophenyl)benzene derivatives were synthesized with various R groups in the 1,4-position and hexyl substituent in the 5 postion. The various R groups include: CO2Et, CH2OH, CH2Cl, COOH and COCl. The 1H, 13C and 19F NMR spectra show the occurrence of “cis” and “trans” diastereomers due to the restricted rotation caused by the ortho-substituted fluorine. The asymmetric derivatives give rise to four enantiomers (two for cis and two for trans) which has signals visible in some spectra corresponding to all four isomers. The degree of restriction is shown to be affected by the R groups in the 1,4-position.
R = CO2Et, CH2OH, CH2Cl, COOH, COCl
SOLUTE-CONTROLLED DISSOLUTION THRESHOLDING AT NEAR-EQUILIBRIUM CALCITE-WATER INTERFACES
Man Xu, Ph.D.,1 Kevin G. Knauss, Ph.D.,2 Steven R. Higgins, Ph.D.1
1Wright State University, Department of Chemistry, Dayton, Ohio
2Lawrence Berkeley National Laboratory, Earth Sciences Division, Berkeley, CA
Direct measurements at the aqueous solution-calcite (
) interface were performed using in situ atomic force microscopy (AFM) at 50-70 °C to reveal the influence of solution saturation state and magnesium concentration on calcite dissolution kinetics and surface morphology. Under near-equilibrium conditions, time-sequential AFM images demonstrated a linear relationship between step speed and solution saturation state, Ωcalcite. Dissolved Mg2+ brought negligible inhibitory effects on calcite dissolution at [Mg2+] ≤ 10-4 molal. Upon the introduction of 10-3 molal Mg2+, however, Ωcalcite acted as a “switch” for magnesium inhibition. That is, no significant changes in step kinetics were observed at Ωcalcite ≤ 0.1, whereas a sudden inhibition from Mg2+ was activated at Ωcalcite ≥ 0.2. The presence of the Ω-switch in dissolution kinetics indicates the presence of critical undersaturation in accordance with thermodynamic principles. Etch pits formed in Mg-free near-equilibrium solutions exhibited a nearly-triangle shape, while in the presence 10-3 molal Mg2+ the etch pits displayed a unique distorted rhombic profile, different from those formed under far-from-equilibrium conditions. Such inconsistency in calcite step morphologies may be associated with the increased influence of the backward reaction and the anisotropy in net kink detachment rates. The calcite dissolution results presented in this work demonstrate a need to consider fundamental surface interactions that may lead to highly nonlinear near-equilibrium behavior and serve as a foundation for the development of robust geochemical models for the prediction of long-term calcite dissolution kinetics in natural water systems.
SYNTHESIS OF ALKYL ALKOXY AMMONIUM COMPOUNDS FOR USE IN EXCHANGE REACTIONS
Andrew M. Beauchamp, and William A. Feld, Ph.D.
Wright State University, Department of Chemistry Dayton, OHIO
Multiple alkyl alkoxy ammonium ionic liquids were synthesized by quaternization reactions with tris[2-(2-methoxyethoxy)ethyl]amine and alkyl halides. These compounds were used in cation exchange reactions with dilithium phthalocyanine. The ether functionalized cations were used in an effort to improve ion conductivity while reducing electronic conductivity by taking advantage of the characteristics used in current electrolytes such as polyethylene oxide. The products were found to be low melting solids that may have use in new electronics technology.
SPECTROSCOPIC INVESTIGATIONS OF SUBLETHAL DOSES OF PLATINUM GROUP METALS ON CHICK EMBRYO BONE DEVELOPMENT
Tai Lam, Adam Stahlera, Jennifer Monahana, Marjorie Markopoulosa, Jessica Daghera, Joshua Bakera, Zofia Gagnon, Ph.D.b, and Ioana Pavel, Ph.D. a
aWright State University, Department of Chemistry,
Dayton, OHIO
bMarist College, Department of Environmental Science and Policy, Poughkeepsie, NY
Platinum group metals (PGMs) are found at pollutant levels in the environment and are known to bioaccumulate in various plant and animal tissues. Our previous studies showed that chick embryos exposed to PGMs concentrations of 5.0 ppm (LD50) and higher presented skeletal deformities. In this study, the effects of PGMs on the skeleton formation of developing chick embryo tibiotarsi were investigated at sublethal doses through the use of various spectroscopic methods. Chick embryos were injected with 1.0 mL of 1.0 ppm Pd(II), Pt(IV), Rh(III) aqueous salt solutions and a PGM mixture on the 7th and 14th day of incubation. Control groups with no‐injection and 1.0 mL injections of saline solutions were included. Embryos were sacrificed on the 20th day and tibiotarsi were harvested. Micro‐Raman imaging of the paraffin embedded cross–sections of tibiotarsi revealed anomalous calcium inclusions within the bone marrow for the PGM mixture treatment. Hyperspectral Raman data were analyzed using in house–written codes within MatLab v. 7.11.0 R2010b. Raman univariate chemical maps were created using the baseline–corrected intensity of the n1(PO43–) stretching mode. Significant changes (one–way ANOVA, p ≤ 0.001) in the average mineralization age of tibiotarsi were found in all treatments when compared to controls. More exactly, the Integrated area of n1(CO32–)/ Integrated area of n1(PO43–) was 0.101 ± 0.074, 0.099 ± 0.076, 0.047 ± 0.035, 0.057 ± 0.038, 0.085 ± 0.061 and 0.074 ± 0.049 for the no injection control, the saline vehicle control, Pd, Pt, Rh, and the PGM mixture treatments, respectively. Flame atomic absorption spectroscopy revealed ~50% change in the percent calcium content for the Pd and Pt treatments with respect to the no‐injection control (17.05% calcium). PGM concentrations in all tibiotarsi were below inductively–coupled–plasma optical–emission spectroscopy detection levels. Overall, spectroscopic results show sublethal doses of PGMs negatively impact bone development.
EFFECT OF CRYSTAL ORIENTATION ON THE DISSOLUTION KINETICS OF CALCITE SURFACES BY AN ATOMIC EMISSION SPECTROSCOPIC AND INTERFEROMETRIC APPROACH
Michael E. Smith,a Steven R. Higgins, Ph.D.,a and Kevin G. Knauss, Ph.D.b
aWright State University, Department of Chemistry, Columbus, OHIO
bLawrence Berkeley National Laboratory, Earth Sciences Division, Berkeley, CA
Geologic CO2 sequestration has emerged as a technology to reduce greenhouse gas emissions by injecting CO2 into subsurface mineral reservoirs consisting predominately of cementing carbonate minerals, e.g. calcite. However, geochemical reactions between subsurface minerals and CO2 containing fluids can potentially alter the porosity and permeability of subsurface minerals which can ultimately cause undesirable leakage of CO2 from sequestration reservoirs back to the atmosphere. In the present work, we’ve examined the effects of polished crystal-surface orientation and degree of solution undersaturation on the dissolution kinetics of calcite as a means of improving our understanding of fundamental reactions that may influence the efficacy of CO2 sequestration in geological formations. Surface orientations of interest included ~ 1 cm2 areas of both the (104) crystallographic plane of natural calcite specimens, consisting of flat terraces with few steps, as well as fully kinked surfaces created by sectioning approximately parallel to the (001) plane. Dissolution reactions were carried out by exposing polished calcite surfaces to experimental solutions with compositions similar to sequestration environments. Instantaneous dissolution rates of calcite were determined from solution analyses using atomic emission spectroscopy. Images of post-reacted samples taken with a vertical scanning interferometer (VSI) facilitated a second, independent calculation of absolute dissolution rates for the calcite surface-orientations of interest. The results from these investigations may lead to the development of relatively simple models for mineral grain shape evolution during dissolution, a process that impacts pore sizes and shapes in subsurface environments.
DNA BARCODING OF SEA TURTLE LEECHES (OZOBRANCHUS SPP.) IN FLORIDA COASTAL WATERS
Triet Truong and Audrey E. McGowin, Ph.D.
Wright State University, Department of Chemistry, Dayton, OHIO
The etiological agent of Fibropapillomatosis (FP), a neoplastic disease originally identified only on green sea turtles (Chelonia mydas), is still unknown. Studies have shown an association between FP and the fibropapilloma-associated turtle herpesvirus (FPTHV), but not all turtles with FPTHV develop FP. Recently, high viral loads of FPTHV were detected in marine turtle leeches (Ozobranchus spp.) from a green sea turtle, but the study failed to identify the species of marine leech. Leeches may transmit or activate FPTHV but are impossible to identify at all life stages using taxonomic practices. In this study, character-based DNA barcoding using mitochondrial cytochrome c oxidase I (COI) gene as a molecular marker was employed successfully to identify both species of Ozobranchus spp. (Ozobranchus branchiatus and Ozobranchus margoi) at all stages of development from eight different sites in Florida (Daytona Beach to Key West). Genetic sequences for O. branchiatus and O. margoi were submitted to the National Center for Biotechnology Information GenBank with O. branchiatus added as a new species to the database. The spread of FP to other species of turtles combined with the discovery of a new turtle host for the O. branchiatus leech suggests the vector organism involvement behind FP maybe species specific. However, further sampling and genetic analyses must be conducted in order to confirm whether the separate haplotypes identified for O. branchiatus on a loggerhead are indeed haplotypes of the same species and not the discovery of cryptic specimens.
IDENTIFYING NEW HAPLOTYPES AND POTENTIAL CRYPTIC SPECIES FOR MARINE LEECHES (OZOBRANCHUS SPP.) FROM HAWAIIAN AND FLORIDA SEA TURTLES BASED ON MOLECULAR DATA
Triet Truonga and Audrey E. McGowin, Ph.D. ,a Philip Lavretsky,b and Jeffrey L. Peters, Ph.D.b
Wright State University, Department of Chemistrya & Department of Biological Sciencesb, Dayton, OHIO
Character-based DNA barcoding using mitochondrial cytochrome c oxidase I (COI) gene as a molecular marker was employed to identify both species of Ozobranchus spp. (Ozobranchus branchiatus and Ozobranchus margoi) at all stages of development from different Florida and Hawaiian locations. The COI barcode for O. branchiatus reveals multiple fixed polymorphisms between specimens collected on C. mydas (green turtles) in Florida and Hawaii. Phylogenetic analysis of O.spp at other genes (18S rDNA, 28S rDNA, and Histone H3) is being used to establish whether O. branchiatus specimens from Hawaii and Florida are distinct species. Interestingly, the separate COI haplotypes identified for O. branchiatus on Florida green turtles share closer genetic similarities to O. branchiatus found on Hawaiian green turtles, raising the possibility the specimens found on a Florida Caretta caretta (loggerhead) might actually be a cryptic species or subspecies of O. branchiatus. Extensive molecular analysis at different loci will help elucidate whether the O. branchiatus leeches collected from a loggerhead are haplotypes of the same species or a cryptic species. New primers were developed to sequence the Histone H3. Prior to this study, only genetic data for the COI gene of Florida O. branchiatus was available in the National Center for Biotechnology Information (NCBI) Genbank. This is also the first study to sequence the nuclear ribosomal gene 28S rDNA and the nuclear protein coding-gene Histone H3 for O. margoi.
Comparative cytotoxicity study of ionic silver and silver nanoparticles
using an MTT bioassay
Zach S. Arnolda, Alice Changa, Nora E. Hunterb, Marjorie M. Markopoulosc, Sesha Lakshmi A. Palurid, John C. Trefryc, Dawn P. Wooleyc, and Ioana E. Pavela-d
aDepartment of Chemistry, Wright State University, Dayton, Ohio
bEnvironmental Sciences Ph.D. Program, Wright State University, Dayton, Ohio
cBiomedical Sciences Ph.D. Program, Wright State University, Dayton, Ohio
dDepartment of Pharmacology and Toxicology, Wright State University, Dayton, Ohio
The development and deployment of nanomaterials for consumer applications is underway. In fact, 54% of the nanomaterials in commercial use contain silver due to its antimicrobial and antiviral properties. Yet, little is known about the cytotoxicity of silver nanomaterials, in particular silver nanoparticles (AgNPs). In this study, non-ionic AgNPs were synthesized, characterized, and size-selected for use in comparative toxicological studies. Colloidal AgNPs were produced using a modified Creighton method by the reduction of silver nitrate with sodium borohydride. The physicochemical properties of AgNPs were characterized to confirm the size and shape distribution (TEM, UV-Vis absorption spectrophotometry), surface functionalization and charge (reaction mechanism), aggregation state (TEM), concentration (flame atomic absorption spectrophotometry), and purity (Raman spectroscopy). The U.S. Environmental Protection Agency and other organizations have recently established these parameters as being critical for the comparison between various cytotoxicity studies. Tangential flow ultrafiltration was employed to size-select AgNPs (20 nm diameter and smaller) and to concentrate them (larger than 10-fold) in a small volume of water with minimal aggregation for cellular dosage. Monkey kidney cells (Vero 76) and murine long osteocytic bone cells (MLO-Y4) were exposed to varying concentrations of ionic silver (Ag+) and nonionic AgNPs ranging from 0 to 512 ppm. MTT, an in vitro bioassay, was used to measure the cell metabolic function and to determine the median lethal dose (LD50) of silver ionic and nonionic AgNPs. LD50 of silver ionic was calculated at 29 ppm (VERO 76) and 26 ppm (MLO-Y4) using the Kärber and the Reed-Muench formula. The LD50 values obtained using the two methods were found to agree very well with each other. Preliminary results obtained for the Vero 76 and MLO-Y4 cells indicated AgNPs as being at least 10-fold less cytotoxic than the ionic silver (LD50 in the 64-512 ppm range).
POLY(ARYLENE ETHER)S DERIVED FROM 3,5-DIFLUOROBENZOTRIFLUORIDE
Fadwa Constandinidis and Eric Fossum, Ph.D.
Wright State University, Department of Chemistry, Dayton, OHIO
The characterization and polymerization behavior of a B2 monomer, 3,5-difluorobenzotrifluoride, 1, designed for nucleophilic aromatic substitution, NAS, reactions have been studied. As determined by a combination of NMR spectroscopy and model reactions, the electrophilic sites present at the 3 and 5 positions in monomer 1 were sufficiently activated by the presence of the trifluoromethyl group, located in the meta position, to allow displacement reactions to occur under relatively mild conditions. Reaction with a variety of bis-phenolates provided the corresponding poly(arylene ether)s, PAEs, which carried a pendant trifluoromethyl group. Unfortunately, the polymerization process was also accompanied by a competing cyclization process, which led to cylic oligomers. In order to limit the formation of oligomers, the initial concentration of A2 monomer was varied from 80-100%. GPC traces indicated a clear increase in molecular weight and a reduction of cyclic species when the initial A2 concentration was reduced. The resulting materials were completely amorphous as indicated by the presence of only a glass transition temperature in their DSC traces. They were soluble in a wide variety of organic solvents. The 5% decomposition temperatures obtained from thermogravimetic analysis indicated that they possessed excellent thermal stability.
