Toughening Of Aromatic Epoxy Polymers For Fiber Reinforced Composite Matrices Via Aliphatic Epoxy Copolymers
Authors: Markus A. Downey; Lawrence T. Drzal
Abstract: Epoxy polymers play an important role in many modern day applications. Their high strength-to-weight ratio and corrosion resistance make them especially desirable materials for high-performance structural applications in a fiber-reinforced composite (FRP). A significant limitation with epoxy polymers is their inherent low toughness due to the lack of a crack arresting mechanism. While toughening bulk epoxies can be achieved through numerous mechanisms, in order to make the toughening useful for FRP properties such as strength, modulus and glass transition temperature cannot be detrimentally affected. Additionally, the proposed toughening mechanism needs to be compatible with current manufacturing processes, such as resin transfer molding.
In this work, the addition of aliphatic epoxy copolymers to the aromatic epoxy was investigated. Both epoxies undergo the same amine reaction to form a highly cross-linked network. The more flexible aliphatic chain of the aliphatic epoxy absorbs more energy prior to fracturing while the stiffer aromatic chain provided high modulus. The resulting aromatic/aliphatic epoxy polymer showed substantially increased impact toughness without major losses in flexural properties. At these low concentrations of aliphatic epoxy, the glass transition temperature is also only slightly reduced. Since these two epoxies form a miscible system, this approach to increasing the toughness should be applicable for FRP produced with all current manufacturing processes and represents an important building block as the matrix for fiber-reinforced composites
This work was supported in part by General Electric Aviation
Composition Dependence Of Glucose Oxidation At Mediated Glucose Oxidase Bioanodes
Authors: Yira Feliciano; Scott Calabrase Barton
Abstract: Research in Enzymatic biofuel cells holds significant technological promise for sustainable energy generation by combining renewable catalysts with fuel flexibility. In the past decade, research interest has grown due to potential applications such as biosensors, portable electronics, and implantable power. However, the limitations of enzymatic biofuel cells for such applications are low stability of the electrode and low current density.
Our previous work describes the optimization of mediator redox potential for a laccase-catalyzed oxygen reduction electrode. This result leads us to our current research, focused on composition dependence of the electrode structure, in terms of the balance between loadings of enzyme and mediator.
The electrode under study is a modified with a film consisting of glucose oxidase with poly(N-VI12[Os(bpy)2Cl]+/2+. An optimum glucose conversion current density is found at 40 wt% GOx, where the catalytic and electron transport properties are balanced. A mathematical model is used to estimate the limits of current density. This model incorporate film thickness, which is one of the important parameter that affects the performance of the redox polymer mediated enzyme electrodes by affecting the mobility of the redox active centers and the species transport. The outcome of this study will be improved quantitative understanding of mediated enzyme electrode behavior, applicable to engineering of biofuel cells.
This work was supported in part by The authors thank Sloan and U.S. Dept. of Education for partial support of this work through a Graduate Assistantship in Areas of National Need (GAANN) fellowship for YF.
Correlating Surface Properties To Nonspecific Binding: GFP As A Tag In Lignocellulosic Biofuel Production
Authors: Carolyn Haarmeyer; Tim Whitehead
Abstract: The deconstruction of lignocellulosic plant matter into fuels like alcohols is an important area of renewable energy research. To produce fuels from plant mass, lignocellulosic biofuel production includes pretreatment, which breaks down plant cell walls, enzymatic hydrolysis, which uses enzymes to convert carbohydrates into simple sugars, fermentation, which converts these sugars into alcohols, and downstream purifications. Lignocellulosic biofuel production can be made more cost efficient by increasing the recyclability of the cellulases that hydrolyze cellulose into sugar. These cellulases nonspecifically adsorb to lignin, a biological polymer that reinforces plant cell walls. This adsorption step irreversibly inactivates these cellulases. To understand why this nonspecific binding occurs, we will correlate a quantifiable surface property of proteins (like these cellulases) to lignin binding. As a model system, we have chosen to use enhanced green fluorescent protein (eGFP) as a proxy for these cellulases, as eGFP readily adsorbs to lignin, and it can readily be quantified in solution by visible fluorescence. Mutable surface residues on eGFP have been determined computationally and small libraries have been designed to give full coverage of the biologically relevant ranges for the net charge and charge density of eGFP. Mutant eGFP variants from these libraries will be selected based on surface properties and will be characterized for their binding affinity to lignin. Comparisons of experimental results to theoretical predictions like DLVO theory will be made. This unprecedented wealth of information will be used to design new cellulases that resist lignin-mediated inactivation.
This work was supported in part by National Science Foundation
Graphene Nanoplatelet Based Polymeric Nanocomposites With Enhanced Barrier Properties
Authors: T. Honaker-Schroeder; F. Vautard; L. Drzal; L. Sui
Abstract: Polymer matrix nanocomposites are gaining increased interest because of their ability to add or enhance a variety of different properties when compared to the base polymer matrix, including mechanical, electrical, thermal, and barrier properties. A particular nanoparticle that shows promise in enhancing all four of those properties at a low concentration is a Graphene nanoPlatelet (GnP). GnP can be produced with diameters ranging from 0.3 to 25 microns, and thicknesses between 2 and 6 nanometers. If GnP is added to a cost effective polymer matrix such as high density polyethylene (HDPE), the large aspect ratio of the GnP can form a tortuous path that is impermeable to the transport of small molecules. This GnP nano-composite could be used for the manufacture of structures such as gas tanks and fuel lines in motor vehicles, also potentially reducing the weight of the vehicles.
In this study, concentrations of GnP from 0.2 to 15 percent weight in HDPE have been investigated for three different nanoplatelet diameters between 0.3 and 15 microns. Additionally, two processing methods have been employed, melt mixing and microlayer co-extrusion. It was found that the addition of GnP greatly improved the barrier properties of HDPE, along with increasing the stiffness of the material. While the ultimate strength remained similar for all concentrations, the impact resistance decreased with increasing GnP concentration. The thermal stability of the composite was also improved but the percolation threshold was not achieved due to limited dispersion of the platelets yielding no increase in electrical conductivity.
This work was supported in part by Hyundai-Kia America
Nano-Scale Homogenization Of Bio-Based PLA/Cellulose Composites In One-Step Emulsion Process
Authors: Shaowen Ji; Jue Lu; Ankush Gokhale; Anna Song; Jason M. Thompson; Ilsoon Lee
Abstract: Cellulose fibers from renewable bioresources have been widely studied as one of the natural-organic fillers for the development of bio-based polymer composites, due to their impressive physical and mechanical properties as well as the biodegradable nature. In the green composite field, the use of nano-sized fillers is gradually replacing for traditional micro-sized ones, which leads to significant improvement of final properties. The major obstacle for the fabrication of these bio-composites is the difficult dispersion and poor interfacial adhesion of hydrophilic nanomaterials from renewable bioresources in the organic solvent or hydrophobic polymer matrix. Our technology has been developed to improve the production of bio-based polymer composites (e.g. PLA) with the uniform dispersion of hydrophilic nanomaterials and enhanced performance in the nano-scale by manipulating the old fashioned emulsion process. The key is to form water-in-oil-in-water type multiple emulsions instead of conventional oil-in-water ones via a fast dynamic nano-mixing process based on the single emulsion method. By utilizing the inner aqueous space, hydrophilic nanoparticles or molecules can be encapsulated in the polymer matrix. The production of PLA micro/nano-particles with controlled size and shape can be well achieved by this technology in a much reduced time of up to 2 min and mild operation conditions. The emulsion method is one of the oldest industrial processes and abundant experience for scale-up and commercialization can be used for reference from existing manufacturing productions.
This work was supported in part by MIIE, URC
Interlaminar Reinforcement Of Glass Fiber/Epoxy Composites With Graphene Nanoplatelets (GnP)
Authors: Nicholas T. Kamar; Mohammad Hossain; Al Loos; Lawrence T. Drzal
Abstract: Incorporation of carbonaceous nanomaterials into fiber-reinforced/epoxy composites (FR/EP) has been shown to improve a variety of intralaminar mechanical properties. Our research investigated the ability of graphene nanoplatelets (GnP) to improve the interlaminar properties of glass reinforced multilayer composites. We developed a novel method for the inclusion of GnPs into plain-weave glass fabric fiber-reinforced/epoxy composites processed with vacuum assisted resin transfer molding (VARTM). Pristine GnPs are dispersed in a solvent solution of diglycidyl ether of bisphenol A epoxy resin and then uniformly coated onto the surface of glass fabrics at different concentrations prior to laminate stacking. The sizing/GnP combination adheres to the glass fabric and allows full resin infusion using a conventional VARTM processing method. Subsequently, four-point bending test results on the cured laminate produces a 29% improvement in flexural strength with the addition of only 0.25 wt% GnP compared to the pristine glass FR/EP. At the same loading, mode-I fracture toughness testing revealed a 25% improvement. Significant improvements were also obtained in low velocity drop-weight impact properties. Analysis of the composite samples after impact testing with ultrasonic c-scans and dye penetration tests showed less damage resulted in the composite. The c-scan images revealed that both interfacial and through-the-thickness damage decreased with addition of GnP contents. Interestingly, dye penetration tests indicated that impacted surface damage decreased, but back surface damage increased with addition of GnPs. The mechanisms by which the GnP improves the impact properties of the multilayer composites will be discussed.
High-Resolution Sequence Function Mapping Of Full Length Proteins
Authors: Caitlin A. Kowalsky; Justin R. Klesmith; Tim A. Whitehead
Abstract: Comprehensive sequence-function mapping can be used to optimize enzyme catalysis and protein binding. Next-generation sequencing of mutant libraries provides millions of sequencing reads. Comparing how often a given mutant appears before and after selection provides a measure of that mutant's fitness. This method has previously been limited to mapping short stretches of amino acid sequence . Here we extend this method to allow mapping of entire protein sequences through the use of a modular, universal PCR amplification method. We have extended the deep sequencing derived sequence-function maps to proteins of arbitrary size. Both growth and yeast display systems can be used to select for mutants with enhanced functionality. Analytical solutions to normalize data over separate populations allows for the multiple mutant protein libraries to be independently selected. Because of this, we can map the sequence-function space for proteins 800 residues using a single 150 bp PE MiSeq sequencing reaction. We are no longer limited by the length of the protein but rather by the amount of sequencing data we can obtain.
 Whitehead, T. A. et al. (2012). Nature Biotechnology, 30(6), 543-8
This work was supported in part by National Science Foundation under award No. CBET-1254238
Modeling Of Non-Precious Metal Cathode For Proton Exchange Membrane Fuel Cell
Authors: Nathaniel Leonard; Selvarani Ganesan; Scott Calabrese Barton
Abstract: Proton exchange membrane fuel cells (PEMFCs) have long been thought of as an alternative to internal combustion engines in the transportation industry, but cost, particularly of precious metal catalysts, has impeded commercialization. Catalysts based on pyrolyzed metal/nitrogen/carbon (MNC) compounds are one less expensive alternative. These non-precious metal catalysts generally require higher mass and volume loadings. In this work we explore the impact of these higher loadings by modeling key transport phenomena within the cathode catalyst layer of a PEMFC with a non-PGM catalyst.
A gas/liquid transport system that takes into account hydrophobicity, porosity, and evaporation is coupled with kinetics and conductivity to model the transport phenomena within the cathode. The gas/liquid transport system is treated via a two-phase porosity model that calculates saturation, liquid permeability, and effective diffusivity as a function of liquid pressure and constituent fluxes within the cathode. The combination of the various transport phenomena impact the kinetics via a Tafel model, and the various impacts of water, oxygen, proton, and electron transport on performance can be calculated. The model captures key experimental parameters that have been shown to influence electrode performance, and will be used to explain experimental observation and guide further optimization.
This work was supported in part by We gratefully acknowledge the partial financial support from the U.S. Department of Energy (EERE), under a Non PGM Catalyst development effort (Contract no EE 0000459) lead by Northeastern University (Sanjeev Mukerjee, P.I.).
Catalytic Oxidative Pretreatment Of Woody Biomass At Mild Reaction Conditions And Enzymatic Conversion To Fermentable Hydrolysate
Authors: Zhenglun Li; Namita Bansal; Yaoping Zhang; Trey K. Sato; Charles H. Chen; Li Hinchman; Ramin Vismeh; Alexander Toulokhonov; Eric L. Hegg; David B. Hodge
Abstract: We previously developed the alkaline peroxide pretreatment catalyzed by copper-diimine complexes, which significantly increases the enzymatic digestibility of a range of herbaceous and woody feedstocks including switchgrass, prairie cordgrass as well as hybrid poplar. Under mild operation conditions (room temperature and ambient pressure), the maximum efficacy of the pretreatment can be achieved with less than one hour of reaction time. Mechanistic studies of the catalytic oxidation reveal disruption of cell wall layers, which is associated with lignin removal and cellulose oxidation. We optimized the key parameters during pretreatment and enzymatic hydrolysis, which produces hydrolysate from recalcitrant hammer-milled hybrid poplar with >80% yield of monomeric sugars.
Fermentation studies indicate that the hydrolysate from hybrid poplar can easily be fermented to ethanol, regardless of the toxicity from the residual copper catalyst in the hydrolysate. The severity of the toxicity can be alleviated by a simple process of catalyst recovery prior to fermentation, or by using lower amount of an improved less-toxic catalyst during pretreatment. LCMS analysis of the hybrid poplar hydrolysate has demonstrated the presence of monomeric lignin fragments including vanillin, syringic acid and p-hydroxybenzoic acid, which as aromatic by-products add to the overall profitability of the biorefinery process. Further investigations of the lignotoxins in the hydrolysate have provided more important information on hydrolysate toxicity as well as valuable guidance for the future optimization of yeast strains.
This work was supported in part by Department of Energy Great Lakes Bioenergy Research Center (DOE BER Office of Science DE-FC02-07ER64494)
Effect Of Static Pre-Stretch Induced Surface Anisotropy On Orientation Of Mesenchymal Stem Cells
Authors: Chun Liu; Jungsil Kim; Seungik Baek; Christina Chan
Abstract: Mechanical cues in the cellular environment play important roles in guiding various cell behaviors, such as cell alignment, migration, proliferation, and differentiation. Numerous studies have shown that mechanical cyclic stretch can induce cells to align perpendicular to the stretch direction, while relatively fewer studies focus on static stretch. However, almost all of the previous studies of static stretch were post-stretch, which means the cells were first seeded to allow attachment and then the substrate subsequently stretched. In contrast, we create a static pre-stretched anisotropic surface in which the cells are seeded after the substrate is stretched. The results show that cells align in the direction of pre-stretch, which is induced by the anisotropy that can be predicted by the theory of finite elasticity.
The experimental results agreed with a "Cell mechano-active sensing" model, which suggests that the cells can sense and respond to surface anisotropy by orienting in the direction of maximal effective stiffness. In this study we employed a theory of "small deformation superimposed on large" to predict the anisotropy induced by the uniaxial pre-stretch. After a 10% uniaxial pre-stretch, the effective stiffness that the cells sense in the stretched direction is 1.33 times of that in the perpendicular direction. Next, we explored the impact of pre-stretch magnitude on cell orientation angle distribution. Cells (mesenchymal stem cells or primary neurons) seeded on poly-L-lysine coated PDMS membrane surfaces with 10%, 20%, or 30% pre-stretch were quantified after 4 days of culture for their cell orientation angles. The results showed that the ratio of cells that orient parallel (within ±10°) increased with the magnitude of the stretch.
In summary, we demonstrated that cells aligned on static pre-stretched anisotropic surface, and the number of cells that aligned in parallel orientation increased with the pre-stretch magnitude. Besides alignment of MSCs, we investigated the impact of pre-stretched surface on axonal growth and orientation. The results showed that axonal alignment also increased with the pre-stretch magnitude and a larger pre-stretch can promote thicker and longer axonal growth.
This work was supported in part by This study was supported in part by the National Science Foundation (CBET 0941055), the National Institute of Health (R01GM079688, R01GM089866).
Separation Of Perchlorate Ions By Polyelectrolyte Multilayer Membranes
Authors: Oishi Sanyal; Anna Sommerfeld; Ilsoon Lee
Abstract: Perchlorate ion has been recently identified as a harmful contaminant in drinking water. It competes with Iodine ion during its uptake by the thyroid gland thereby inhibiting the formation of thyroid hormone. In average its maximum allowable concentration is 6 ppb. Being a monovalent ion the most effective membrane operation which is suitable for its rejection is reverse osmosis (RO). A major disadvantage of desalination processes is the extreme high pressure requirement which is due to the inherent low flux offered by such membranes. We therefore modify a nanofiltration (NF) membrane such that its rejection is similar to that of desalination membrane but the flux remains higher than the latter. The surface modification technique used is called the layer-by-layer (LbL) assembly. This technique involves the deposition of alternately charged polyelectrolytes on a surface to form polyelectrolyte multilayers and allows the formation of nanothin films. Layering of such nanothin films on the surface of NF membrane helps in reduction of porosity of the membrane which in turn leads to size-based exclusion of ions. The performance of the modified membrane has been tested against a commercial RO membrane under cross flow conditions. The perchlorate concentration of the feed and permeate samples are measured using LC-MS/MS technique in order to evaluate the membrane rejection. The effects of various conditions on these membranes which include transmembrane pressure and cross flow velocity are currently being tested. This work is primarily focused on perchlorate ion but it can be extended to several other monovalent ions.
This work was supported in part by DOD SERDP
Investigation Of Na2/3[Ni1/3Ti2/3]O2 As A Layered Electrode Material For Na-ion Batteries And The Effect Of Manganese Substitution On The Electrochemical Properties
Authors: Rengarajan Shanmugam; Wei Lai
Abstract: Na-ion batteries have emerged as promising low cost, alternative rechargeable battery chemistry, currently being targeted towards large-scale electrical energy storage that is critical for increased penetration of renewable energy sources and stabilizing the power grid. Na-ion batteries essentially work on the principle of storing charge by ion intercalation into host materials, like Li-ion batteries. Sodium chemistry is more attractive because of wide availability of inexpensive sodium mineral resources. We have demonstrated the reversible sodium intercalation/de-intercalation in a new class of layered oxide materials with composition Na2/3[Ni1/3Ti2/3]O2 using a non-aqueous electrolyte. This material can be used as a bi-functional electrode using Ni2+/3+ and Ti4+/3+ redox couples that have average Eo values of 3.6 and 0.7 V, respectively. Studies are underway to investigate the effect of partial manganese substitution, in the ‘2a’ sites of the transition metal layer, on the intrinsic electronic conduction and the electrochemical properties.
Influences On Hemicellulose Dissolution And Enzymatic Hydrolysis Yield After The Soda Pulping Of Hardwoods
Authors: Ryan J. Stoklosa; David Hodge
Abstract: The development of an economical and sustainable biomass conversion industry is inherently tied to the transportation logistics of the feedstocks, capital equipment costs for processes, and high titer yields of sugar for conversion. As a way to decrease the costs associated with commercialization, the pulp and paper industry can offer an already developed infrastructure with regards to feedstock transportation and process equipment. This research evaluated alkali impregnation followed by soda pulping of three hardwoods and the associated effect on the dissolution of hemicellulose, and the yields of monomeric sugars from enzymatic hydrolysis after pulping. Soda pulping trials were conducted in a pressurized digester at 170°C for one hour for all three hardwoods. The severity of the pulping trial was quantified with the H-factor relationship where time and temperature are combined into a single variable to express the rate of delignification. Two other severity conditions were applied to a hybrid poplar feedstock (Populus nigra x maximowiczii cv. NM6) to see if temperature or time during pulping can contribute to higher sugar yields from enzymatic hydrolysis. The dissolution of hemicellulose increased during the heat up phase of the pulping trial, but at the start of the constant temperature phase the hemicellulose amount decreased; this was attributed to polysaccharide degradation to saccharinic acids. High yields of glucose (> 80%) were achieved after enzymatic hydrolysis for all pulped feedstocks. Sugar yields were also compared based upon enzyme loading and particle size of the pulped substrate.
This work was supported in part by Northeast Sun Grant Initiative
Engineering Delivery Vehicles For SiRNA Therapeutics
Authors: Daniel Vocelle; Georgina A. Comiskey; Olivia Chesniak; Stephen Lindeman; Sean Norton; Amanda Phillips; Christina Chan; S. Patrick Walton; Milton R. Smith
Abstract: Given the limitations of small molecule and protein based drugs, new therapeutic approaches are needed for treating disease-associated proteins. One potential candidate, short interfering RNA (siRNA) therapeutics, is capable of highly specific targeting for a wide range of proteins. With the assistance of target specific delivery vehicles, siRNAs are transported from an extracellular environment into the cytoplasm of eukaryotic cells. Utilizing the RNA Interference (RNAi) pathway, siRNA degrades sequence specific messenger RNA (mRNA) and reduces target protein expression. siRNA therapeutics have been developed for cancers, genetic disorders, and infectious diseases, but currently are still awaiting FDA approval.
siRNA therapeutics are currently limited by their dependency on inefficient delivery vehicles. Within in vivo models, vehicles are restricted by poor delivery, in addition to issues of toxicity and immunogenicity. While many types of delivery vehicles have been developed, there is little consensus regarding the mechanisms or characteristics essential for delivery. Using silica nanoparticles, delivery criteria can be investigated among four main categories: siRNA binding affinity, membrane translocation, biodistribution, and protein suppression. Wherein, the effects of vehicle size, structure, charge, and functionalized surface can be characterized.
Our current data indicates an optimal binding affinity and the presence of dextran facilitates active silencing. Particle endocytosis exhibits preferential accumulation within the lysosome, causing complex dissociation, particle degradation, and eventually exocytosis. While achieving silencing comparable to those of commercially available reagents, dextran functionalized silica nanoparticles have an increased rate and onset of silencing, a 10 fold increase in the amount of siRNA delivered to the cell, and no observable toxicity.
This work was supported in part by Financial support for this work was provided in part by the National Institutes of Health (#GM079688, #RR024439, and #GM089866), MSU Foundation, National Science Foundation (CBET 0941055), MUCI, and the Center for Systems Biology
Cell Wall Hydrophilicity Impacts On Enzymatic Digestibility For Alkaline Hydrogen Peroxide Pretreated Grasses
Authors: Dan Williams; David Hodge
Abstract: Treatment of biomass with alkaline hydrogen peroxide (AHP) can be used as a chemical pretreatment or alternatively as a post-treatment. This work will present research results of AHP pretreatment used as a post-treatment for liquid hot water (LHW) pretreatment as a delignifying step. The effect of AHP on the carbohydrate and lignin compositional changes after pretreatment and fiber swelling behavior of corn stover and switchgrass will be shown as a function of hydrogen peroxide loading as well as the formation of potential fermentation inhibitors. We hypothesize that the digestibility improvement resulting from AHP pretreatment may be attributed to mild oxidation or solubilization of the lignin remaining in the cell wall and, for grasses, destruction of ferulate crosslinks between cell wall polymers which would have the net effect of increasing the hydrophilicity to allow improved water and enzyme penetration into the cell wall. To test this hypothesis, we will correlate the hydrophilicity of the cell wall as measured indirectly by lignin and cell wall carboxylic acid content to water swelling capacity, water activity at limiting free water, and digestibility.
This work was supported in part by Department of Energy; Great Lakes Bioenergy Research Center
Controlled Release Of Novel Anti-Biofilm Compounds From Porous Multilayer Films
Authors: Jing Yu; Alessandra Hunt; Andrew Izbicki; Chris Waters; Ilsoon Lee
Abstract: Biofilms are notorious for their strong immune defense, high tolerance to antibiotic treatment and difficulty in clearance. It has been found that biofilms are responsible for about 65% of infections happened in hospital, leading to more than 500,000 deaths, 17million infections and $94 billion medical expense annually in the United States alone. Recently, a series of novel benzimidazole molecules have been developed as anti-biofilm compounds (ABCs). Thus, new types of anti-biofilm coatings can be designed with the incorporation of ABCs. Polyelectrolyte multilayers (PEMs) have been considered as a versatile platform for antibacterial surface design. In order to create anti-biofilm coatings and achieve controlled release, porous poly(acrylic acid) (PAA)/poly(allylamine hydrochloride) (PAH) multilayers have been fabricated. 5-methoxy-2-[(4-methylbenzyl)sulfanyl]-1H-benzimidazole (named ABC-1) molecules were incorporated into the porous multilayers via evaporation method since ABC-1 can be dissolved in ethanol. During the evaporation, ABC-1 molecules were condensed and diffused into the porous multilayers at the same time, leading to an optimization of ABC-1 loading. The porous structure of the multilayer is critical to the amount of ABC-1 incorporated and the release profile. Completely different porous structures can be achieved by adjusting pH for porous treatment, using different cross-linking methods, and changing molecule weight of PAH. By tuning the porous structure, the release of ABC-1 can be controlled. It has already been found about 99% of V. cholerae biofilm formation was suppressed by this type of anti-biofilm coatings.
Functional And Stability Assessment Of A Cobalt(III)-oxo Cubane Cluster Water Oxidation Catalyst Immobilized On ITO
Authors: Hao Yuan; Richard Lunt; Robert Ofoli
Abstract: Producing hydrogen by using sunlight to split water has long been regarded as a promising route to abundant clean energy. In our research, we are trying to mimic the natural photosynthetic oxygen evolution center (OEC) to make catalysts that can effectively catalyze the water oxidation process. We have synthesized a cobalt(III) oxo cubane water oxidation catalyst which is a structural mimic of the natural oxygen-evolving center. We immobilized it on indium tin oxide (ITO) to promote recycling and reusability. Fourier transform-infrared (FTIR) and surface FTIR spectroscopies were used before and after deposition, respectively, to detect the organic ligands around the core. Scanning electron microscopy (SEM) was used to characterize the structure of the immobilized catalyst, and energy dispersive x-ray spectroscopy (EDS) the composition. Finally, cyclic voltammetry was employed to assess functionality, stability, and recyclability. The results showed that this catalyst can be successfully immobilized on ITO, and that the complex functions in the same manner as the free catalyst in solution. We also believe the separation of synthesis and immobilization has great potential for optimizing catalytic complexes.
This work was supported in part by This study was funded by the US Army through the Engineering Research and Development Center (ERDC) in Champaign, IL
Transparent Luminescent Solar Concentrators Employing UV And NIR Selective Absorbers
Authors: Yimu Zhao; Richard Lunt
Abstract: Luminescent solar concentrators are regaining attention as low-cost solar harvesting systems around the building envelope. However, the visible absorption and emission of previously demonstrated chromophores result in highly colored systems that hamper their widespread adoptability in many applications including solar windows. Here, we demonstrate transparent luminescent solar concentrators (TLSC) that employ ultraviolet (UV) or near-infrared (NIR) absorbing luminophores for selective light harvesting that creates an entirely new paradigm for power-producing transparent surfaces. In the first configuration, we have designed systems composed of metal halide phosphorescent luminophore blends; these nanoclusters enable selective harvesting of UV photons with absorption cutoff positioned at the edge of visible spectrum (430nm) and massive-downconverted emission in the near-infrared (800nm) with quantum yields for luminescence of 75%. Through experiment and modeling, we show that this architecture can be scaled up to areas > 1 m2 with a power conversion efficiency of 1-2% due to the massive luminescent downconversion. We have also developed transparent luminescent solar concentrators employing fluorescent organic salts with both efficient NIR absorption and emission that allow for efficiencies > 4-5%. The moderately low Stokes shift of these systems is overcome by embedding spatially segmented solar cell arrays throughout the waveguide, leading to minimal reabsorption losses. We will discuss the photophysical properties of both classes of luminophores, the impact of ligand-host control, and optimization of the TLSC architectures.
This work was supported in part by National Science Foundation (CAREER award, CBET-1254662).
Engineering siRNA Asymmetry
Authors: Phillip Angart; S. Patrick Walton
Abstract: Short interfering RNAs (siRNAs) provide a method of post-transcriptional, targeted gene knockdown that is of interest as a therapeutic strategy for the treatment of a variety of diseases. Gene knockdown or silencing occurs through interactions of the siRNA with the native eukaryotic RNA interference (RNAi) pathway. siRNA specificity derives from the Watson-Crick base pairing interactions between the bases of the siRNA and its complementary target. The active silencing complex, known as RISC, operates as a multiple turnover enzymatic complex capable of decreasing target transcript levels sufficiently to initiate the therapeutic effect. However, siRNA activity can vary greatly depending upon its sequence and the reasons for this variability are not completely understood. Structurally, siRNAs are double-stranded RNAs with 19 central base pairs, two-nucleotide 3’ overhangs, and 5’ phosphates. Central to the function of siRNAs is the ability of the RNAi pathway to discriminate which strand of the structurally symmetric siRNA is to be active (guide strand) and which strand is to be degraded (passenger strand). Failure to incorporate the correct strand can cause both off-target effects as well as competition for the protein Argonaute 2, the core protein of RISC. This loading step represents a significant event in the success of an siRNA and must occur properly for maximal siRNA function. We are investigating the contributing factors that lead to siRNA strand selection and its influence on siRNA activity.
This work was supported in
part by National Institutes of Health (#GM079688, #RR024439, and #GM089866), MSU Foundation, National Science Foundation (CBET 0941055), MUCI, and the Center for Systems Biology.