Submitted Poster Presentations (Listed in alphabetical order of advisor [Benderskii through Goodson])
| Advisor: | Alex Benderskii |
| Authors: | The Benderskii Group |
| Title: | Nonlinear Optical Probes of Bio- and Material Interfaces |
| Abstract: | This poster will review research directions in Prof. Alex Benderskii's group (Physical/Analytical divisions). The general theme is understanding molecular structure, dynamics, and morphology of condensed phase interfaces, including biomembranes, biomimetic surfaces used in bioengineering, and novel organic semiconductor materials. Second order nonlinear optical (NLO) spectroscopies, an array of novel noninvasive probe techniques, are being developed for the purpose of characterizing these buried interfaces with molecular level of detail. Principles, advantages, and applications will be discussed, including: Vibrational (IR) and electronic (UV-vis) spectroscopies of interfacial molecules, implemented using SFG (Sum Frequency Generation, wIR+wvis) and SHG (Second Harmonic Generation, 2wvis). Coupled NLO spectroscopy-microscopy (in particular, vibrational SFG microscopy in the fingerprint mid-IR spectral range), a powerful technique that allows to relate molecular structure with morphology of heterogeneous samples, e.g. biomembranes. Ultrafast time-resolved spectroscopy which enables observation of the chemical dynamics and short-lived structures such as hydrogen bonding network at interfaces. Electric field induced NLO response, used to measure local electric fields at interfaces and imaging of cross-membrane potential in live cells. |
| Advisor: | David E. Benson |
| Authors: | Marinella Sandros, De Gao, and David E. Benson |
| Title: | Nanometer Scale Biosensors |
| Abstract: | The union of biology and nanotechnology has generated a new field in science known as nanobiotechnology. Within this field, assembly reactions of nanoparticles to produce ligand dependent signals have been the major focus of many research groups. Our goal is to synthesize biomolecular nanoparticle assemblies that couple the molecular recognition of proteins with nanoparticle electronic properties using ligand gated electron transfer. This strategy will provide a significant advance in the nanobiotechnology field. We have prepared water-soluble CdSe nanoparticles from CdO. Exchange of the initial trioctylphosphine oxide capping groups with 16-thiolhexadecanoic acid formed water soluble CdSe nanoparticles that are air and moisture stable for up to two weeks. Standard recombinant DNA techniques have been used to produce maltose binding proteins with cysteine rich domains that can bind to the surface of CdSe nanoparticles. Exchanging the capping groups 16-thiolhexadecanoic acid of the water- soluble CdSe nanoparticles with the cysteine-rich domains of the maltose binding protein changed the nanoparticle charge/size ratio and electronic properties. By selectively placing Ru-polypyridyl complexes on the surface of these proteins, we hope to utilize the protein hinge-bending motion to modify the distance and the electron transfer rate between the metal polypyridyl complex and the nanoparticle surface. This work should provide a ligand dependent change in CdSe fluorescence intensity that will eventually produce nanometer scale biosensors. |
| Advisor: | David E. Benson |
| Authors: | Vivekanand Shete and David E. Benson |
| Title: | Design of Metallohydrogenase |
| Abstract: | The ability to rationally design any protein structure and function has practical applications. Introduction of metal centers in proteins provides a starting point for such design. Such designs can be generated using Dezymer, an automated design algorithm. Therefore, using the Dezymer algorithm, we will introduce coordination spheres such as Rh(III)Cys2Met2X2 into proteins of known three-dimensional structure. These mononuclear centers mimic the coordination sphere of ruthenium and rhodium homogeneous hydrogenation catalysts that contain thioether and thiolate ligands, using an octahedral RhCys2Met2(CO)H coordination sphere. The ability of these de novo hydrogenase functional mimetic proteins to bind and activate small diatomic ligands such as H2, CO, and C2H4 will then be experimentally examined. This work presents a modular strategy to catalyze biological reactions in order to extend the scope of biocatalysis for asymmetric transformation and green chemistry. |
| Advisor: | David E. Benson |
| Authors: | Cagil Gokdemir and David E. Benson |
| Title: | Protein Stability on Material Surfaces: Enhancing Medical Implants |
| Abstract: | With the improvements in medicine and chemistry, medical implants can easily be coated with proteins to increase biocompatibility of medical implants. Proteins that coat these materials are typically in the denatured conformation and increase the chance of material recognition and rejection. Our goal is to produce a protein coated inorganic surface where the protein is still in a native conformation. For our studies, we selected a domain of tenascin due to the high stability and cytoskeletal function. We have confirmed the thermal stability of this domain in bulk solution and are currently modifying the tenascin to study protein stability at silica-water interfaces. To understand the stability of the protein on the inorganic surface, we will be using a combination of two different methods, total internal reflected fluorescence (TIRF) and fluorescence resonance energy transfer (FRET). Once a detailed understanding of protein stability on surfaces is achieved, we hope to produce protein coated materials that have dramatically increased biocompatibility that will enhance medical implant technology. |
| Advisor: | David E. Benson |
| Authors: | Marla Swain and David E. Benson |
| Title: | Rational Design of Galactose Oxidase Mimetic Proteins |
| Abstract: | A variety of enzymes achieve catalytic activity through the use of crosslinked amino acid cofactors (CAACs) formed by intramolecular posttranslational modification of endogenous amino acids in the enzyme. In galactose oxidase (GAO), new bond-forming reactions result in the formation of a tyrosine-cysteine crosslink that is involved in a two- electron oxidation of primary alcohols to the corresponding aldehydes. Though crystallographic and electrophoretic analysis have provided some mechanistic data, little is known about the dominant mechanisms governing formation of the CAAC in GAO. In order to predict amino acid mutations that can form these CAACs, the Dezymer biomolecular modeling package was used to survey a library of 500 known high-resolution protein structures that do not contain CAACs. Rat intestinal fatty acid binding protein (IFABP) was selected for experimental analysis due to its rather high tendency for CAACs. Five of the sites predicted by Dezymer to geometrically accommodate Y-C cofactor formation were selected for experimental analysis. Using recombinant DNA methods, these sites will be constructed in IFABP. The generated mutant IFABPs will be used to study factors that control Y-C cofactor biogenesis and experimentally confirm geometrically driven predictions. |
| Advisor: | Ashok S. Bhagwat |
| Authors: | Joanna Klapacz, Anjum Sohail, and Ashok Bhagwat |
| Title: | Transcription-Dependent Increase in Multiple Classes of Base Substitution Mutations in E. coli |
| Abstract: | All organisms sustain a certain number of mutations as a result of
normal cellular processes or interactions with the environment. Base pairing
protects bases from the attacks of endogenous and exogenous agents. We have
shown that active transcription increases the frequency of C-to-T mutations
up to 10-fold if the cytosine is in the non-transcribed strand. Transcription also increases non-C-to-T mutations in DNA repair-proficient cells by a factor of 3. Sequence analysis revealed that the G to T transversions dominate the spectrum of non-C-to-T mutations in E. coli. |
| Advisor: | Ashok S. Bhagwat |
| Authors: | Mala Samaranayake, Jason McLellan, Asad Ullah, Joanna Klapacz, Todd Roy, Anjum Sohail, and Ashok S. Bhagwat |
| Title: | Human Activation-Induced Cytidine Deaminase (AID) and it's Role in Mutation Spectrum |
| Abstract: | In response to antigen, B cells undergo a series of specialized genetic events to produce the "ideal" population of antibodies. The events of somatic hypermutation, gene conversion and class-switch recombination have been recognized for many years, but many of the enzymes involved have remained elusive. The exact mechanisms behind these events are still not fully understood. The recent discovery of Activation-Induced cytidine Deaminase (AID) has led to propose new models for these genetic events. The goal of this project is to elucidate the role of AID protein in mutation spectrum and understand the molecular and biochemical mechanisms that lead to antibody diversification. |
| Advisor: | Stephanie L. Brock |
| Authors: | The Brock Group |
| Title: | Research in the Brock Group: Solid State Chemistry in Zero to Three Dimensions |
| Abstract: | Solid state inorganic materials form the basis of a number of
important technologies including energy storage and conversion (batteries,
solar panels), computing (silicon chips), and data storage (hard drives).
These materials are typically characterized by 3-D linked structures, and
the properties are a collective function of this extended framework
(delocalized). Recently, it has been shown that when the size of the
particles or crystallites is on the order of 1-100 nm, the physical
properties are different than those found in materials composed of larger
(micron-sized) particles. The miniaturization of electronic and magnetic
devices is beginning to extend in to this nanometer regime, thus
providing an impetus to understand the impact of size reduction on
physical properties (device performance) and to develop preparation
techniques for small features/particles.
Despite this recent interest in nanoscale materials, there is still much to discover among traditional solids. The increasing complexity of properties demanded by a single material provide motivation to develop and study solids with increasing complexity. Therefore, research in the Brock group spans a range of materials from 3-dimensional (extended solids) to 0- dimensional (nanoparticles), with a focus on the synthesis of new materials and developing an understanding of structure, size, and physical property correlations. Accordingly, a brief overview will be provided of our efforts to prepare and study nanoparticles of transition metal phosphides, structures based on 1-D covalent linkages of Group 15 elements, intermediate dimensionality polymers based on oxide or chalcogenide frameworks, and 3-D diamond like semiconductors. |
| Advisor: | Stephanie L. Brock |
| Authors: | Susanthri Perera, Petru S. Fodor, Lowell Wenger, and Stephanie L. Brock |
| Title: | Synthesis and Characterization of Discrete MP (M = Fe, Mn) Nanoparticles |
| Abstract: | Particles with sizes in the range of 1-100 nm have been demonstrated to exhibit size dependant physical properties that differ from bulk materials (non nanoparticulate). Despite considerable interest in nanoparticles of the semiconducting main group pnictides (Pnictogen = group 15 element) such as GaAs and InP, transition metal (TM) analogs have remained essentially unexplored. This is surprising since bulk materials of TM pnictides show a number of magnetic properties of significant interest including ferromagnetism, magnetooptical and magnetoelastic properties. Accordingly, novel size dependent magnetic and electronic properties are expected from nanoparticle TM pnictide systems, and these materials may have attractive prospects in the design of new devices. We have developed a procedure based on the reaction of TM salts or TM carbonyl complexes with phosphines to create TM phosphide nanoparticles with good control of particle size and degree of polydispersity. The application of this method to the synthesis of Fe and Mn phosphide nanoparticles and the physical properties of the resultant materials will be discussed in light of structure and particle size. |
| Advisor: | Stephanie L. Brock |
| Authors: | Buddhimathie Jayasekera, Jennifer A. Aitken, Mary Jane Heeg, and Stephanie L. Brock |
| Title: | Towards an Arsenic Analog of Hittorf's Phosphorus: Mixed Pnictogen Chains in Cu2P3-XAsXI2 (X<0.5) |
| Abstract: | Transition metal pnictogen halides (pnictogen = Group 15 element) are a small class of relatively unexplored materials in solid-state chemistry. To date, compounds are limited to Cu-P-X (X = I, Br, Cl) phases, and these can be classified as having neutral or anionic phosphorus networks. The compound Cu2P3I2 contains neutral, infinite phosphorus chains, similar to those found in Hittorf's modification of phosphorus. The phosphorus chains consist of fused four- and five-membered rings and between the chains are columns of CuI in which Cu ions are distributed over multiple sites. We are interested in exploring the effects of pnictogen substitution on the structure and physical properties of these materials. We have successfully synthesized several mixed Cu2P3-XAsXI2 phases in which x < 0.5. These materials have been characterized by a combination of single crystal and powder diffraction techniques. The stability and physical properties of these materials will be discussed in light of the preferential ordering of As within the chains, and the increased disorder in the Cu lattice. |
| Advisor: | Stephanie L. Brock |
| Authors: | Kanchana Somaskandan and Stephanie L. Brock |
| Title: | Synthesis and Characterization of III-V based Diluted Magnetic Semiconductor Nanoparticles |
| Abstract: | The focus of our research is to develop a synthetic strategy to prepare III-V based diluted magnetic semiconductor (DMS) nanoparticles. Nanoparticles have sizes ranging from 1-100 nm and are of interest because they exhibit size dependent electronic, magnetic, and optical properties. DMS's, on the other hand, are solid solutions in which magnetic ions, typically Mn(II) are dissolved into a semiconductor matrices. So far only II-VI based DMS nanoparticles have been studied, since the introduction of Mn2+ is relatively easy in these materials. Resultant nanoparticles exhibit sharp luminescence and giant Faraday rotations and have a net antiferromagnetic coupling. In contrast, spin introduction in III-V systems creates holes in the semiconductor band and results in a ferromagnetic material. The simultaneous presence of ferromagnetic and semiconducting properties may permit application in dual-purpose devices that can both store and process information. Our initial target is Fe or Mn-doped indium phosphide DMS nanoparticles. The synthesis consists of indium(III) chloride, tris-(trimethylsilyl) phosphine, and iron or manganese salts/precursors combined in trioctylphosphine/trioctylphosphine oxide and heated to 100-260° C. Particles are isolated by size selective precipitation and characterized by UV/Visible spectroscopy, X-ray powder diffraction, transmission electron microscopy, and SQUID magnetometry. Strategies for transition metal ion incorporation will be discussed, along with the influence of the dopant and particle size on structure and properties. |
| Advisor: | Christine S. Chow |
| Authors: | Jean-Paul Desaulniers, Helen M.P. Chui, Christine S. Chow |
| Title: | Synthetic Approaches Towards Selective 15N-Labelling of Pseudouridines in Helix 69 of 23S rRNA of E. coli |
| Abstract: | Pseudouridine is natural modified nucleoside found abundantly in nature. Its capacity to hydrogen bond in a unique fashion has prompted many researchers to study the structure and function of this nucleoside within the context of RNA. A particular region of interest includes helix 69 from 23S rRNA in Escherichia coli, as this hairpin region contains two pseudouridines, at positions 1911 and 1917, and a 3-methylated pseudouridine derivative at position 1915. A recent synthetic methodology has been developed in this lab for the synthesis of 3-methylpseudouridine phosphoramidite. Using a modified version of this methodology, a route for the synthesis of 3-15N-methylpseudouridine has been established. Future applications include the synthesis of 3-15N-methylpseudouridine phosphoramidite, as well as 15N3 and 15N1-labeled pseudouridine and their corresponding amidites, as this would allow researchers to better understand the structural and dynamic effects that the N1 and N3 positions play within the context of a specific RNA region by using 2D NMR techniques. |
| Advisor: | Christine S. Chow |
| Authors: | Jason Walter Kieltyka, Lew M. Hryhorczuk, and Christine S. Chow |
| Title: | Elucidating the Mechanism of RNA Strand Scission by Transition Metal Polypyridyl Complexes |
| Abstract: | RNAs are wonderfully diverse macromolecules that can have a myriad of secondary and tertiary structures. The use of inorganic complexes as chemical probes of structure offers an approach for rapid screening and the ability to examine very large (~3,000 nucleotides) RNAs. The model hairpins studied in this project, the 790 loop and the 1920 loop, occur in the E. coli 16S and 23S rRNAs, respectively. These sites are important in the ribosomal protein synthesis. It is possible to elucidate the binding sites of the inorganic complexes because they induce RNA strand scission. The goals of this project are to observe cleavage and to elucidate the mechanism of cleavage by using mass spectrometry. The development of electrospray ionization mass spectrometry (ESI-MS) has allowed scientists to observe noncovalent interactions between biomolecules and small molecules, and through the use of CID and MS/MS experiments it may also be possible to observe strand scission of nucleic acids. The goal of the preliminary work was to first determine the binding stoichiometry of tris(4,7-diphenyl-1,10-phenanthroline)rhodium(III) (Rh(DIP)33+) for its various targets. Through such experiments we can determine if each binding site leads to cleavage or if a single Rh(DIP)33+ can induce cleavage at multiple sites. The next goals involve the calculation of binding constants and their comparison to the solution state binding constants as well as the use of MS/MS experiments to map the binding sites in order to determine whether cleavage occurs directly at the binding site or at a remote site. Finally, we hope to be able to elucidate the mechanism of strand scission caused by the Rh(DIP)33+ and then compare it to novel compounds. |
| Advisor: | John F. Endicott |
| Authors: | Konrad Szaciłowski, Manawadevi Y. Udugala-Ganehenege and John F. Endicott |
| Title: | Electron-Transfer Parameters for di-Nickel and di-Copper Complexes from Metal-to-Metal Charge-Transfer (MMCT) Spectra based on a Three-Center Perturbation-Theory Model |
| Abstract: | The electronic
coupling between ds-donor
and ds-acceptor
metal centers mediated by a bridging halide has long been presumed to be
very efficient and to be a major factor in very facile inner-sphere
electron transfer reaction pathways. However, the coupling of transition
metal donor-acceptor complexes through s-networks
has received much less systematic attention than the coupling through p-networks.
An approach to the synthesis of appropriate model complexes is to link the
metal complexes through the peripheral atoms of their ligands. This
approach has been used in constructing complexes with a s-bridging
ligand between a transition metal donor and acceptor by utilizing a xylene
linkage between carbon atoms of two tetraaza-macrocyclic ligands.
The
synthesis and donor-acceptor properties of some novel, halo-bridged
dinickel(II) and dicopper(II) complexes of a,a’-bis
(5,7-dimethyl-1,4,8,11-tetraazacyclotetradeca-4,7-diene-6-yl)-o-xylene and
a,a’-bis
(5,7-dimethyl-1,4,8,11-tetraazacyclotetradecane-6-yl)-o-xylene are
reported. These complexes were characterized by both spectroscopic and
electrochemical techniques. The non-halo-bridged complexes have
significant affinity for halides (Kf
~ 104
M–1).
A bridging-ligand mediated superexchange model is used to treat the
magnetic and electron transfer coupling in the MII(X–)MII
complexes. Three-centered perturbation theory arguments are used to
interrrelate the spectroscopic, magnetic and electrochemical properties of
the halide-bridged complexes. It is inferred that bridging halide
mediated, ds/ps/ds
metal-metal coupling
significantly alters the chemical properties of the bimetallic complexes
only when the donor and acceptor orbitals are coaxial with the bridging
ligand. In such a limit, the coupling takes the form of a three-center
bonding contribution. |
| Advisor: | Theodore Goodson III |
| Authors: | Mahinda I Ranasinghe and Theodore Goodson III |
| Title: | Investigation of Optical excitations in Novel Dendrimers Using Ultra Fast Anisotropy Measurements |
| Abstract: | Dendrimers believed to have potential applications in areas such as light harvesting, light emitting devices and medicine etc. The search for a model that can be used to describe the optical excitation migration in homogeneous dendrimers has attracted great attention. In most cases in a dendrimer the conjugation is disrupted at the branching point, however the excitation is delocalized. The strength of interactions among neighboring chromophores plays a key role in determining the energy migration mechanism. Conversely, having many identical chromophores held tightly together in an ordered macromolecular architecture will allow for many dipoles to be accessible for optical excitation. Therefore, the relative orientation of dipoles will be important in determining the mechanism of energy migration. In our dendrimer systems (as seen below) a collection of oriented dipoles are excited by polarized light, and the distribution of the optical excitation among the dipoles leads to depolarization of the emission. Through our investigation we have found that the anisotropy measurement is a very powerful tool for investigating energy migration in such branched dendritic architectures. We investigated excitation migration dynamics in dendrimers in which nitrogen at the branching point. The energy migration processes in the dendrimers were investigated utilizing ultra fast time resolved fluorescence anisotropy measurements. The fluorescence anisotropy of all three dendrimers decayed to a residual value within ~100 fs. This fluorescence anisotropy decay showed a general trend in decreasing with increasing dendrimer generation. The residual anisotropy value also showed a gradual decrease with an increase in the dendrimer generation. This fast energy depolarization is discussed through a coherent excitonic mechanism among dipoles oriented in different directions. We believe formation of coherent domains leads to fast energy migration extending over a large part of the dendrimer. |
| Advisor: | Theodore Goodson III |
| Authors: | Ying Wang, Palaniappan Arumugan,Oleg Varnavski, and Theodore Goodson III |
| Title: | Photophysical studies on dye functionalized poly(Amidoamine) dendrimer-encapsulated gold nanoparticles |
| Abstract: | Nano-scale materials are now important for the variety of applications including catalysis, medicine and novel optical effects. New materials with tailored capabilities for light emission as well as quenching behavior may be realized through novel dendrimer metal nano-composites. In this presentation, the optical properties of dendrimer metal nano- composites functionalized with two different chromophores on the surface will be presented. Both dansylated and Lissamine Rhodamine B- sulfoaminated poly(amidoamine) dendrimer G2 have been used as templates for encapsulation gold nanoparticles. The functionalization of G2 by Lissamine Rhodamine B-sulfonyl chloride is first report. The preparation. of nanoparticles is relied on literature. For the case of the dansylated system there is evidence of ground-state complexation and fluorescence quenching through interactions of chromophore-G2-gold system. Time- resolved fluorescence measurements were carried out near the surface- plasmon resonance. The dynamic seemed to be unaffected by the presence of the metal nanoparticles. However, for the rhodamine-G2-gold system, time-resolved fluorescence measurements show strong dynamic difference in the absence and presence of metal nanoparticles. The difference of two systems will be discussed in detail. This presentation will give the first results of chromophore-metal interaction in an organic dendrimer. |