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Selected Works

Iowa State University

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Articles 1 - 30 of 31

Full-Text Articles in Biochemical and Biomolecular Engineering

Probing The Enzymatic Activity Of Alkaline Phosphatase Within Quantum Dot Bioconjugates, Jonathan C. Claussen, Anthony Malanoski, Joyce C. Breger, Eunkeu Oh, Scott A. Walper, Kimihiro Susumu, Ramasis Goswami, Jeffrey R. Deschamps, Igor L. Medintz Jan 2015

Probing The Enzymatic Activity Of Alkaline Phosphatase Within Quantum Dot Bioconjugates, Jonathan C. Claussen, Anthony Malanoski, Joyce C. Breger, Eunkeu Oh, Scott A. Walper, Kimihiro Susumu, Ramasis Goswami, Jeffrey R. Deschamps, Igor L. Medintz

Jonathan C. Claussen

Enzymes provide the critical means by which to catalyze almost all biological reactions in a controlled manner. Methods to harness and exploit their properties are of strong current interest to the growing field of biotechnology. In contrast to depending upon recombinant genetic approaches, a growing body of evidence suggests that apparent enzymatic activity can be enhanced when located at a nanoparticle interface. We use semiconductor quantum dots (QDs) as a well-defined and easily bioconjugated nanoparticle along with Escherichia coli-derived alkaline phosphatase (AP) as a prototypical enzyme to seek evidence for this process in a de novo model system. We began …

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Complex Logic Functions Implemented With Quantum Dot Bionanophotonic Circuits, Jonathan C. Claussen, Niko Hildebrandt, Kimihiro Susumu, Mario G. Ancona, Igor L. Medintz Jan 2014

Complex Logic Functions Implemented With Quantum Dot Bionanophotonic Circuits, Jonathan C. Claussen, Niko Hildebrandt, Kimihiro Susumu, Mario G. Ancona, Igor L. Medintz

Jonathan C. Claussen

We combine quantum dots (QDs) with long-lifetime terbium complexes (Tb), a near-IR Alexa Fluor dye (A647), and self-assembling peptides to demonstrate combinatorial and sequential bionanophotonic logic devices that function by time-gated Förster resonance energy transfer (FRET). Upon excitation, the Tb-QD-A647 FRET-complex produces time-dependent photoluminescent signatures from multi-FRET pathways enabled by the capacitor-like behavior of the Tb. The unique photoluminescent signatures are manipulated by ratiometrically varying dye/Tb inputs and collection time. Fluorescent output is converted into Boolean logic states to create complex arithmetic circuits including the half-adder/half-subtractor, 2:1 multiplexer/1:2 demultiplexer, and a 3-digit, 16-combination keypad lock.

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Exploiting Issatchenkia Orientalis Sd108 For Succinic Acid Production, Han Xiao, Zengyi Shao, Yu Jiang, Sudhanshu Dole, Huimin Zhao Jan 2014

Exploiting Issatchenkia Orientalis Sd108 For Succinic Acid Production, Han Xiao, Zengyi Shao, Yu Jiang, Sudhanshu Dole, Huimin Zhao

Zengyi Shao

Background: Recent advances in synthesizing valuable chemicals such as organic acids from low-cost renewable biomass through microbial fermentation have attracted great attention. However, the toxicity of organic acids presents a key challenge to the development of an economically viable fermentation process. Therefore, a platform organism that not only produces organic acids but also tolerates the associated toxicity is highly desirable. Results: Here we report the discovery, characterization, and engineering of a yeast strain, Issatchenkia orientalis SD108, that is tolerant to low pH and high concentration of organic acids. This strain demonstrated a higher tolerance compared to I. orientalis ATCC 24210 …

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Nanomaterial-Mediated Biosensors For Monitoring Glucose, Eric S. Mclamore, Masashige Taguchi, Andre Ptitsyn, Jonathan C. Claussen Jan 2014

Nanomaterial-Mediated Biosensors For Monitoring Glucose, Eric S. Mclamore, Masashige Taguchi, Andre Ptitsyn, Jonathan C. Claussen

Jonathan C. Claussen

Real-time monitoring of physiological glucose transport is crucial for gaining new understanding of diabetes. Many techniques and equipment currently exist for measuring glucose, but these techniques are limited by complexity of the measurement, requirement of bulky equipment, and low temporal/spatial resolution. The development of various types of biosensors (eg, electrochemical, optical sensors) for laboratory and/or clinical applications will provide new insights into the cause(s) and possible treatments of diabetes. State-of-the-art biosensors are improved by incorporating catalytic nanomaterials such as carbon nanotubes, graphene, electrospun nanofibers, and quantum dots. These nanomaterials greatly enhance biosensor performance, namely sensitivity, response time, and limit of …

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Biophotonic Logic Devices Based On Quantum Dots And Temporally-Staggered Forster Energy Transfer Relays, Jonathan C. Claussen, W. Russ Algar, Niko Hildebrandt, Kimihiro Susumu, Mario G. Ancona, Igor L. Medintz Jan 2013

Biophotonic Logic Devices Based On Quantum Dots And Temporally-Staggered Forster Energy Transfer Relays, Jonathan C. Claussen, W. Russ Algar, Niko Hildebrandt, Kimihiro Susumu, Mario G. Ancona, Igor L. Medintz

Jonathan C. Claussen

Integrating photonic inputs/outputs into unimolecular logic devices can provide significantly increased functional complexity and the ability to expand the repertoire of available operations. Here, we build upon a system previously utilized for biosensing to assemble and prototype several increasingly sophisticated biophotonic logic devices that function based upon multistep Förster resonance energy transfer (FRET) relays. The core system combines a central semiconductor quantum dot (QD) nanoplatform with a long-lifetime Tb complex FRET donor and a near-IR organic fluorophore acceptor; the latter acts as two unique inputs for the QD-based device. The Tb complex allows for a form of temporal memory by …

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Yttrium(Iii) Oxomolybdates(Vi) As Potential Host Materials For Luminescence Applications: An Investigation Of Eu3+-Doped Y2[Moo4]3 And Y2[Moo4]2[Mo2o7], Sonja Laufer, Sabine Strobel, Thomas Schleid, Joanna Cybinska, Anja V. Mudring, Ingo Hartenbach Jan 2013

Yttrium(Iii) Oxomolybdates(Vi) As Potential Host Materials For Luminescence Applications: An Investigation Of Eu3+-Doped Y2[Moo4]3 And Y2[Moo4]2[Mo2o7], Sonja Laufer, Sabine Strobel, Thomas Schleid, Joanna Cybinska, Anja V. Mudring, Ingo Hartenbach

Anja V. Mudring

Two ternary yttrium(III) oxomolybdates(VI) are investigated, both structurally and spectroscopically. The crystal structure of Y2[MoO4]3 was solved at room temperature in the orthorhombic space group Pba2 (a = 1030.21(3), b = 1032.41(3), c = 1057.25(3) pm, Z = 4). In the unit cell, three discrete ortho-oxomolybdate(VI) units [MoO4]2− and two Y3+ cations, both with CN = 7 featuring a monocapped trigonal-prismatic oxygen environment, can be distinguished. Y2[MoO4]2[Mo2O7] crystallizes monoclinically in the space group P21/c (a = 681.85(2), b = 959.13(3), c = 1052.99(3) pm, β = 105.586(2)°) with two formula units per unit cell. In this compound the anionic environment …

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Refactoring The Silent Spectinabilin Gene Cluster Using A Plug-And-Play Scaffold, Zengyi Shao, Guodong Rao, Chun Li, Zhanar Abil, Yunzi Luo, Huimin Zhao Jan 2013

Refactoring The Silent Spectinabilin Gene Cluster Using A Plug-And-Play Scaffold, Zengyi Shao, Guodong Rao, Chun Li, Zhanar Abil, Yunzi Luo, Huimin Zhao

Zengyi Shao

Natural products (secondary metabolites) are a rich source of compounds with important biological activities. Eliciting pathway expression is always challenging but extremely important in natural product discovery because an individual pathway is tightly controlled through a unique regulation mechanism and hence often remains silent under the routine culturing conditions. To overcome the drawbacks of the traditional approaches that lack general applicability, we developed a simple synthetic biology approach that decouples pathway expression from complex native regulations. Briefly, the entire silent biosynthetic pathway is refactored using a plug-and-play scaffold and a set of heterologous promoters that are functional in a heterologous …

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Activation And Characterization Of A Cryptic Polycyclic Tetramate Macrolactam Biosynthetic Gene Cluster, Yunzi Luo, Hua Huang, Jing Liang, Meng Wang, Lu Lu, Zengyi Shao, Ryan E. Cobb, Huimin Zhao Jan 2013

Activation And Characterization Of A Cryptic Polycyclic Tetramate Macrolactam Biosynthetic Gene Cluster, Yunzi Luo, Hua Huang, Jing Liang, Meng Wang, Lu Lu, Zengyi Shao, Ryan E. Cobb, Huimin Zhao

Zengyi Shao

Polycyclic tetramate macrolactams (PTMs) are a widely distributed class of natural products with important biological activities. However, many of these PTMs have not been characterized. Here we apply a plug-and-play synthetic biology strategy to activate a cryptic PTM biosynthetic gene cluster SGR810-815 from Streptomyces griseus and discover three new PTMs. This gene cluster is highly conserved in phylogenetically diverse bacterial strains and contains an unusual hybrid polyketide synthase-nonribosomal peptide synthetase, which resembles iterative polyketide synthases known in fungi. To further characterize this gene cluster, we use the same synthetic biology approach to create a series of gene deletion constructs and …

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Structure, Stability, And Electronic Interactions Of Polyoxometalates On Functionalized Graphene Sheets, Jean-Philippe Tessonnier, Stephanie Goubert-Renaudin, Shaun Alia, Yushan Yan, Mark A. Barteau Jan 2013

Structure, Stability, And Electronic Interactions Of Polyoxometalates On Functionalized Graphene Sheets, Jean-Philippe Tessonnier, Stephanie Goubert-Renaudin, Shaun Alia, Yushan Yan, Mark A. Barteau

Jean-Philippe Tessonnier

Polyoxometalates (H3PMo12O40, H 3PW12O40, H4PMo11VO 40) supported on oxygen- and alkyl-functionalized graphene sheets were investigated. Discrete molecular species were directly observed by electron microscopy at loadings below 20 wt.%. The interaction between the polyoxometalates and the graphene surface was found to significantly impact their vibrational spectra and a linear correlation between the frequency of the M-Oc-M vibration and the dispersion was evidenced by FTIR. While bulk-like electronic properties were observed for small aggregates (2-5 nm), UV-vis spectroscopy and cyclic voltammetry revealed changes in the electronic structure of isolated molecular species as a result of their interaction with graphene. Because of …

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Materials For Diabetes Therapeutics, Kaitlin M. Bratlie, Roger L. York, Michael A. Invernale, Robert Langer, Daniel G. Anderson Jan 2012

Materials For Diabetes Therapeutics, Kaitlin M. Bratlie, Roger L. York, Michael A. Invernale, Robert Langer, Daniel G. Anderson

Kaitlin M. Bratlie

This review is focused on the materials and methods used to fabricate closedloop systems for type 1 diabetes therapy. Herein, we give a brief overview of current methods used for patient care and discuss two types of possible treatments and the materials used for these therapies-(i) artificial pancreases, comprised of insulin producing cells embedded in a polymeric biomaterial, and (ii) totally synthetic pancreases formulated by integrating continuous glucose monitors with controlled insulin release through degradable polymers and glucose-responsive polymer systems. Both the artificial and the completely synthetic pancreas have two major design requirements: the device must be both biocompatible and …

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Dispersion Of Alkyl-Chain-Functionalized Reduced Graphene Oxide Sheets In Nonpolar Solvents, Jean-Philippe Tessonnier, Mark A. Barteau Jan 2012

Dispersion Of Alkyl-Chain-Functionalized Reduced Graphene Oxide Sheets In Nonpolar Solvents, Jean-Philippe Tessonnier, Mark A. Barteau

Jean-Philippe Tessonnier

Alkyl chains were grafted onto reduced graphene oxide sheets to allow their dispersion in toluene, a common and representative nonpolar solvent. The grafting occurred on a variety of oxygen-containing functionalities already present on reduced graphene oxide, such as hydroxyl and epoxide groups. The structure and the defect density of the sheets were not significantly altered during the synthesis. When dispersed in water-toluene mixtures, phase transfer from the aqueous to the organic phase was observed upon grafting. In addition, the dry powder obtained readily disperses in common organic solvents without the assistance of any sonication treatment.

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Electrochemical Glutamate Biosensing With Nanocube And Nanosphere Augmented Single-Walled Carbon Nanotube Networks: A Comparative Study, Jonathan C. Claussen, Mayra S. Artiles, Eric S. Mclamore, Subhashree Mohanty, Jin Shi, Jenna L. Rickus, Timothy S. Fisher, D. Marshall Porterfield Jan 2011

Electrochemical Glutamate Biosensing With Nanocube And Nanosphere Augmented Single-Walled Carbon Nanotube Networks: A Comparative Study, Jonathan C. Claussen, Mayra S. Artiles, Eric S. Mclamore, Subhashree Mohanty, Jin Shi, Jenna L. Rickus, Timothy S. Fisher, D. Marshall Porterfield

Jonathan C. Claussen

We describe two hybrid nanomaterial biosensor platforms, based on networks of single-walled carbon nanotubes (SWCNTs) enhanced with Pd nanocubes and Pt nanospheres and grown in situ from a porous anodic alumina (PAA) template. These nanocube and nanosphere SWCNT networks are converted into glutamate biosensors by immobilizing the enzyme glutamate oxidase (cross-linked with gluteraldehyde) onto the electrode surface. The Pt nanosphere/SWCNT biosensor outperformed the Pd nanocube/SWCNT biosensor and previously reported similar nanomaterial-based biosensors by amperometrically monitoring glutamate concentrations with a wide linear sensing range (50 nM to 1.6 mM) and a small detection limit (4.6 nM, 3s). These results combined with …

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Effects Of Carbon Nanotube-Tethered Nanosphere Density On Amperometric Biosensing: Simulation And Experiment, Jonathan C. Claussen, James B. Hengenius, Monique M. Wickner, Timothy S. Fisher, David M. Umulis, D. Marshall Porterfield Jan 2011

Effects Of Carbon Nanotube-Tethered Nanosphere Density On Amperometric Biosensing: Simulation And Experiment, Jonathan C. Claussen, James B. Hengenius, Monique M. Wickner, Timothy S. Fisher, David M. Umulis, D. Marshall Porterfield

Jonathan C. Claussen

Nascent nanofabrication approaches are being applied to reduce electrode feature dimensions from the microscale to the nanoscale, creating biosensors that are capable of working more efficiently at the biomolecular level. The development of nanoscale biosensors has been driven largely by experimental empiricism to date. Consequently, the precise positioning of nanoscale electrode elements is typically neglected, and its impact on biosensor performance is subsequently overlooked. Herein, we present a bottom-up nanoelectrode array fabrication approach that utilizes low-density and horizontally oriented single-walled carbon nanotubes (SWCNTs) as a template for the growth and precise positioning of Pt nanospheres. We further develop a computational …

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Spatiotemporal Effects Of A Controlled-Release Anti-Inflammatory Drug On The Cellular Dynamics Of Host Response, Tram T. Dang, Kaitlin M. Bratlie, Said R. Bogatyrev, Xiao Chen, Robert Langer, Daniel G. Anderson Jan 2011

Spatiotemporal Effects Of A Controlled-Release Anti-Inflammatory Drug On The Cellular Dynamics Of Host Response, Tram T. Dang, Kaitlin M. Bratlie, Said R. Bogatyrev, Xiao Chen, Robert Langer, Daniel G. Anderson

Kaitlin M. Bratlie

In general, biomaterials induce a non-specific host response when implanted in the body. This reaction has the potential to interfere with the function of the implanted materials. One method for controlling the host response is through local, controlled-release of anti-inflammatory agents. Herein, we investigate the spatial and temporal effects of an anti-inflammatory drug on the cellular dynamics of the innate immune response to subcutaneously implanted poly(lactic-co-glycolic) microparticles. Noninvasive fluorescence imaging was used to investigate the influence of dexamethasone drug loading and release kinetics on the local and systemic inhibition of inflammatory cellular activities. Temporal monitoring of host response showed that …

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Rapid Characterization And Engineering Of Natural Product Biosynthetic Pathways Via Dna Assembler, Zengyi Shao, Yunzi Luo, Huimin Zhao Jan 2011

Rapid Characterization And Engineering Of Natural Product Biosynthetic Pathways Via Dna Assembler, Zengyi Shao, Yunzi Luo, Huimin Zhao

Zengyi Shao

We report a synthetic biology strategy for rapid genetic manipulation of natural product biosynthetic pathways. Based on DNA assembler, this method synthesizes the entire expression vector containing the target biosynthetic pathway and the genetic elements required for DNA maintenance and replication in various hosts in a single-step manner through yeast homologous recombination, offering unprecedented flexibility and versatility in pathway manipulations.

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Dead Zones In Porous Catalysts: Concentration Profiles And Efficiency Factors, Roger L. York, Kaitlin M. Bratlie, Lloyd R. Hile, Larry K. Jang Jan 2011

Dead Zones In Porous Catalysts: Concentration Profiles And Efficiency Factors, Roger L. York, Kaitlin M. Bratlie, Lloyd R. Hile, Larry K. Jang

Kaitlin M. Bratlie

This paper examines the conditions under which a dead zone, or a portion of the catalyst devoid of reactant, can form in a porous catalyst in which simultaneous reaction and diffusion are occurring. The condition that allows for the existence of a dead zone is defined by a critical Thiele modulus. When the Thiele modulus - the ratio of chemical reaction to diffusion - is greater than the critical Thiele modulus, a dead zone exists. This dead zone can be mathematically defined by a change of boundary conditions. We examine nth order reactions in isothermal infinite slabs, infinite cylinders, and …

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Development Of Cationic Polymer Coatings To Regulate Foreign-Body Responses, Minglin Ma, Wendy F. Liu, Paulina S. Hill, Kaitlin M. Bratlie, Daniel J. Siegwart, Justin Chin, Miri Park, Joao Guerreiro, Daniel G. Anderson Jan 2011

Development Of Cationic Polymer Coatings To Regulate Foreign-Body Responses, Minglin Ma, Wendy F. Liu, Paulina S. Hill, Kaitlin M. Bratlie, Daniel J. Siegwart, Justin Chin, Miri Park, Joao Guerreiro, Daniel G. Anderson

Kaitlin M. Bratlie

A library of cationic polymers, poly(beta-amino alcohols) with a great chemical diversity are synthesized using combinatorial polymerization. These polymers, when immobilized on a surface, drastically affect the behavior of monocyte/macrophage cells in vitro and early inflammatory reactions in vivo. Certain polymers are found capable of mitigating the foreign-body responses.

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Real-Time In Vivo Detection Of Biomaterial-Induced Reactive Oxygen Species, Minglin Ma, Wendy F. Liu, Kaitlin M. Bratlie, Tram Dang, Robert Langer, Daniel G. Anderson Jan 2011

Real-Time In Vivo Detection Of Biomaterial-Induced Reactive Oxygen Species, Minglin Ma, Wendy F. Liu, Kaitlin M. Bratlie, Tram Dang, Robert Langer, Daniel G. Anderson

Kaitlin M. Bratlie

The non-specific host response to implanted biomaterials is often a key challenge of medical device design. To evaluate biocompatibility, measuring the release of reactive oxygen species (ROS) produced by inflammatory cells in response to biomaterial surfaces is a well-established method. However, the detection of ROS in response to materials implanted in vivo has not yet been demonstrated. Here, we develop a bioluminescence whole animal imaging approach to observe ROS released in response to subcutaneously-implanted materials in live animals. We compared the real-time generation of ROS in response to two representative materials, polystyrene and alginate, over the course of 28 days. …

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Reversible Addition - Fragmentation Chain Transfer In Microemulsions: Effect Of Chain Transfer Agent Aqueous Solubility, Jennifer M. O'Donnell, Eric W. Kaler Jan 2010

Reversible Addition - Fragmentation Chain Transfer In Microemulsions: Effect Of Chain Transfer Agent Aqueous Solubility, Jennifer M. O'Donnell, Eric W. Kaler

Jennifer M. Heinen

Microemulsion polymerizations are attractive for investigating compartmentalization effects in heterogeneous reversible addition - fragmentation chain transfer (RAFT) polymerizations because the propagating radicals are segregated into surfactant stabilized polymer particles, which drastically reduces the effects of biradical termination, Also, microemulsion polymerizations do not involve the large monomer droplets that are present in emulsion and miniemulsion polymerizations. RAFT microemulsion polymerizations of butyl aery late with a high water solubility chain transfer agent, methyl-2-(O-ethylxanthyl)propionate (MOEP), and a low water solubility chain transfer agent, methyl-2-(O-dodecylxanthyl)propionate (MODP), were investigated to determine the effect of chain transfer agent compartmentalization on the control of the polymerization. The …

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Cloning And Heterologous Expression Of The Spectinabilin Biosynthetic Gene Cluster From Streptomyces Spectabilis, Zengyi Shao Jan 2010

Cloning And Heterologous Expression Of The Spectinabilin Biosynthetic Gene Cluster From Streptomyces Spectabilis, Zengyi Shao

Zengyi Shao

Spectinabilin is a rare nitrophenyl-substituted polyketide metabolite. Here we report the cloning and heterologous expression of the spectinabilin gene cluster from Streptomyces spectabilis. Unexpectedly, this gene cluster is evolutionarily closer to the aureothin gene cluster than to the spectinabilin gene cluster from Streptomyces orinoci. Moreover, the two nearly identical spectinabilin gene clusters use a distinctly different regulation mechanism.

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Dna Assembler, An In Vivo Genetic Method For Rapid Construction Of Biochemical Pathways, Zengyi Shao, Hua Zhao, Huimin Zhao Jan 2009

Dna Assembler, An In Vivo Genetic Method For Rapid Construction Of Biochemical Pathways, Zengyi Shao, Hua Zhao, Huimin Zhao

Zengyi Shao

The assembly of large recombinant DNA encoding a whole biochemical pathway or genome represents a significant challenge. Here, we report a new method, DNA assembler, which allows the assembly of an entire biochemical pathway in a single step via in vivo homologous recombination in Saccharomyces cerevisiae. We show that DNA assembler can rapidly assemble a functional d-xylose utilization pathway (∼9 kb DNA consisting of three genes), a functional zeaxanthin biosynthesis pathway (∼11 kb DNA consisting of five genes) and a functional combined d-xylose utilization and zeaxanthin biosynthesis pathway (∼19 kb consisting of eight genes) with high efficiencies (70 - 100%) …

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Microfabrication Of Homogenous, Asymmetric Cell-Laden Hydrogel Capsules, Qiaobing Xu, Tram T. Dang, Kaitlin M. Bratlie, Ivy Chen, Robert Langer, Daniel G. Anderson Jan 2009

Microfabrication Of Homogenous, Asymmetric Cell-Laden Hydrogel Capsules, Qiaobing Xu, Tram T. Dang, Kaitlin M. Bratlie, Ivy Chen, Robert Langer, Daniel G. Anderson

Kaitlin M. Bratlie

Cell encapsulation has been broadly investigated as a technology to provide immunoprotection for transplanted endocrine cells. Here we develop a new fabrication method that allows for rapid, homogenous microencapsulation of insulin-secreting cells with varying microscale geometries and asymmetrically modified surfaces. Micromolding systems were developed using polypropylene mesh, and the material/surface properties associated with efficient encapsulation were identified. Cells encapsulated using these methods maintain desirable viability and preserve their ability to proliferate and secrete insulin in a glucose-responsive manner. This new cell encapsulation approach enables a practical route to an inexpensive and convenient process for the generation of cell-laden microcapsules without …

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Understanding The Dielectric Properties Of Heat-Treated Carbon Nanofibers At Terahertz Frequencies: A New Perspective On The Catalytic Activity Of Structured Carbonaceous Materials, Edward P.J. Parrott, J. Axel Zeitler, James Mcgregor, Shu-Pei Oei, Husnu Emrah Unalan, Swee-Ching Tan, William I. Milne, Jean-Philippe Tessonnier, Robert Schlogl, Lynn F. Gladden Jan 2009

Understanding The Dielectric Properties Of Heat-Treated Carbon Nanofibers At Terahertz Frequencies: A New Perspective On The Catalytic Activity Of Structured Carbonaceous Materials, Edward P.J. Parrott, J. Axel Zeitler, James Mcgregor, Shu-Pei Oei, Husnu Emrah Unalan, Swee-Ching Tan, William I. Milne, Jean-Philippe Tessonnier, Robert Schlogl, Lynn F. Gladden

Jean-Philippe Tessonnier

Terahertz time domain spectroscopy (THz-TDS) has been used to study the electrical and optical properties of a series of carbon nanofibers (CNFs) that have undergone different heat treatments. The high-temperature heat-treated (HHT) sample displayed increased absorption and real refractive indices across the range 0.3-3.5 THz when compared to the low-temperature heat-treated (LHT) and pyrolitically stripped (PS) samples. The experimental results were fitted by using a Drude-Lorentz model and an effective medium approximation to yield the electrical parameters of the sample such as the plasma frequency, phonon mode frequency, and oscillator strength. These parameters were used to rationalize the differences as …

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Microstructure Evolution And Monomer Partitioning In Reversible Addition - Fragmentation Chain Transfer Microemulsion Polymerization, Jennifer M. O'Donnell, Eric W. Kaler Jan 2008

Microstructure Evolution And Monomer Partitioning In Reversible Addition - Fragmentation Chain Transfer Microemulsion Polymerization, Jennifer M. O'Donnell, Eric W. Kaler

Jennifer M. Heinen

Small-angle neutron scattering (SANS) studies of reversible addition - fragmentation chain transfer (RAFT) microemulsion polymerizations of butyl acrylate and 2-ethylhexyl acrylate with the RAFT agent methyl-2-(O-ethylxanthyl) propionate (MOEP) allow the observed rate retardation to be attributed to slow fragmentation of the macro-RAFT radical. Microemulsion polymerization allows the RAFT mechanism to be investigated in the absence of termination reactions so that the cause of the rate retardation frequently observed in both homogeneous and heterogeneous polymerizations may be isolated. However, the concentration of monomer at the locus of polymerization (Cmon(part)) must be known as a function of conversion before a mechanistic study …

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Determination Of The Escherichia Coli S-Nitrosoglutathione Response Network Using Integrated Biochemical And Systems Analysis, Laura R. Jarboe, Daniel R. Hyduke, Linh M. Tran, Katherine J.Y. Chou, James C. Liao Jan 2008

Determination Of The Escherichia Coli S-Nitrosoglutathione Response Network Using Integrated Biochemical And Systems Analysis, Laura R. Jarboe, Daniel R. Hyduke, Linh M. Tran, Katherine J.Y. Chou, James C. Liao

Laura R. Jarboe

During infection or denitrification, bacteria encounter reactive nitrogen species. Although the molecular targets of and defensive response against nitric oxide (NO) in Escherichia coli are well studied, the response elements specific to S-nitrosothiols are less clear. Previously, we employed an integrated systems biology approach to unravel the E. coli NO-response network. Here we use a similar approach to confirm that S-nitrosoglutathione (GSNO) primarily impacts the metabolic and regulatory programs of E. coli in minimal medium by reaction with homocysteine and cysteine and subsequent disruption of the methionine biosynthesis pathway. Targeting of homocysteine and cysteine results in altered regulatory activity of …

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A Reactive Oxide Overlayer On Rhodium Nanoparticles During Co Oxidation And Its Size Dependence Studied By In Situ Ambient-Pressure X-Ray Photoelectron Spectroscopy, Michael E. Grass, Hendrik Bluhm, Yawen Zhang, Derek Butcher, Jeong Y. Park, Yimin Li, Kaitlin M. Bratlie, Tianfu Zhang, Gabor A. Somorjai Jan 2008

A Reactive Oxide Overlayer On Rhodium Nanoparticles During Co Oxidation And Its Size Dependence Studied By In Situ Ambient-Pressure X-Ray Photoelectron Spectroscopy, Michael E. Grass, Hendrik Bluhm, Yawen Zhang, Derek Butcher, Jeong Y. Park, Yimin Li, Kaitlin M. Bratlie, Tianfu Zhang, Gabor A. Somorjai

Kaitlin M. Bratlie

The smaller, the better: In situ synchrotron ambient pressure X-ray photoelectron spectroscopy allows examination of the oxidation state of the surface of the rhodium nanoparticles (NPs) during CO oxidation in an O2 atmosphere. 2 nm NPs oxidize to a larger extent than 7 nm NPs during reaction at 150-200°C, which correlates with a fivefold increase in turnover frequency for the smaller nanoparticles.

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Quantitative Elucidation Of A Distinct Spatial Gradient-Sensing Mechanism In Fibroblasts, Ian C. Schneider, Jason M. Haugh Dec 2005

Quantitative Elucidation Of A Distinct Spatial Gradient-Sensing Mechanism In Fibroblasts, Ian C. Schneider, Jason M. Haugh

Ian C. Schneider

Migration of eukaryotic cells toward a chemoattractant often relies on their ability to distinguish receptor-mediated signaling at different subcellular locations, a phenomenon known as spatial sensing. A prominent example that is seen during wound healing is fibroblast migration in platelet-derived growth factor (PDGF) gradients. As in the well-characterized chemotactic cells Dictyostelium discoideum and neutrophils, signaling to the cytoskeleton via the phosphoinositide 3-kinase pathway in fibroblasts is spatially polarized by a PDGF gradient; however, the sensitivity of this process and how it is regulated are unknown. Through a quantitative analysis of mathematical models and live cell total internal reflection fluorescence microscopy …

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Spatial Analysis Of 3′ Phosphoinositide Signaling In Living Fibroblasts, Iii: Influence Of Cell Morphology And Morphological Polarity, Ian C. Schneider, Elizabeth M. Parrish, Jason M. Haugh Aug 2005

Spatial Analysis Of 3′ Phosphoinositide Signaling In Living Fibroblasts, Iii: Influence Of Cell Morphology And Morphological Polarity, Ian C. Schneider, Elizabeth M. Parrish, Jason M. Haugh

Ian C. Schneider

Activation of phosphoinositide (PI) 3-kinase is a required signaling pathway in fibroblast migration directed by platelet-derived growth factor. The pattern of 3′ PI lipids in the plasma membrane, integrating local Pl 3-kinase activity as well as 3′ PI diffusion and turnover, influences the spatiotemporal regulation of the cytoskeleton. In fibroblasts stimulated uniformly with platelet-derived growth factor, visualized using total internal reflection fluorescence microscopy, we consistently observed localized regions with significantly higher or lower 3′ PI levels than adjacent regions (hot and cold spots, respectively). A typical cell contained multiple hot spots, coinciding with apparent leading edge structures, and at most …

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Rational Pathway Engineering Of Type I Fatty Acid Synthase Allows The Biosynthesis Of Triacetic Acid Lactone From D-Glucose In Vivo, Wenjuan Zha, Zengyi Shao, John W. Frost, Huimin Zhao Jan 2004

Rational Pathway Engineering Of Type I Fatty Acid Synthase Allows The Biosynthesis Of Triacetic Acid Lactone From D-Glucose In Vivo, Wenjuan Zha, Zengyi Shao, John W. Frost, Huimin Zhao

Zengyi Shao

Metabolic pathway engineering is a powerful tool to synthesize structurally diverse and complex chemicals via genetic manipulation of multistep catalytic systems involved in cell metabolism. Here, we report the rational design of a fatty acid biosynthetic pathway, Brevibacterium ammoniagenes fatty acid synthase B (FAS-B), that allows the microbial synthesis of triacetic acid lactone (TAL) from an inexpensive feedstock, D-glucose. TAL can be chemically converted to phloroglucinol, which is a core structure for the synthesis of various high value bioactive compounds and energetic compounds such as 1,3,5-triamino-2,4,6-trinitrobenzene (TATB). Synthesis of phloroglucinol from d-glucose using this combined biological and chemical synthesis may …

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Spatial Analysis Of 3′ Phosphoinositide Signaling In Living Fibroblasts: Ii. Parameter Estimates For Individual Cells From Experiments, Ian C. Schneider, Jason M. Haugh Jan 2004

Spatial Analysis Of 3′ Phosphoinositide Signaling In Living Fibroblasts: Ii. Parameter Estimates For Individual Cells From Experiments, Ian C. Schneider, Jason M. Haugh

Ian C. Schneider

Fibroblast migration is directed by gradients of platelet-derived growth factor (PDGF) during wound healing. As in other chemotactic systems, it has been shown recently that localized stimulation of intracellular phosphoinositide (PI) 3-kinase activity and production of 3′ PI lipids in the plasma membrane are important events in the signaling of spatially biased motility processes. In turn, 3′ PI localization depends on the effective diffusion coefficient, D, and turnover rate constant, k, of these lipids. Here we present a systematic and direct comparison of mathematical model calculations and experimental measurements to estimate the values of the effective 3′ PI diffusion coefficient, …

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