2012 Spring Seminar Series

• 2011 Fall
• 2011 Spring

Tuesday, January 31, 2012

Molecular Insights into Amyloid Oligomers and their Interactions with Model Membranes

Prof. Jie Zhang University of Akron Department of Chemical and Biomolecular Engineering 11:00 AM Tuesday, January 31, 2012 CEB 218 (810 South Clinton Street)

The aggregation of monomeric proteins/peptides to form ordered amyloid oligomers/fibrils is a pathogenic hallmark of many degenerative diseases including Alzheimer's, Parkinson's, and prion diseases. Despite of significant progress, oligomeric structures and associated toxicity at the very early stage of aggregation remain unclear. Structural knowledge of these oligomers is essential for understanding the pathology of amyloidoses and for the rational design of drugs against amyloid diseases. This talk will cover our recent works in three aspects. (i) We identify a series of atomic structures of amyloid oligomers with different sequences (ABeta;, hIAPP, GNNQQNY, and K3) and structural morphologies (micelles, annulars, triangulars, globulomers, and linears), delineate several common features in amyloid structures, and illustrate aggregation driving forces that stabilize these oligomeric structures. (ii) More importantly, we further examine the interactions of amyloid oligomers with lipid bilayers to examine membrane-damage mechanisms by varying oligomeric morphology, lipid compositions, cholesterol contents, and position and orientation of ABeta; relative to lipid bilayers. Two postulated mechanisms of membrane damage (membrane thinning vs. ion channel) associated with amyloid toxicity are discussed. (iii) In addition, due to the complex nature of cell membranes, we also alternatively employ self-assembled monolayers (SAMs) as model systems to study the aggregation and conformational changes of ABeta; peptides using an integrated simulation and experimental approach. The complementary results from simulations and experiments reveal different ABeta; adsorption, structural transition, and aggregation scenarios on the SAMs, providing parallel insights into the understanding of ABeta; structure and aggregation on cell membrane.

Friday, January 27, 2012

Free Surface Electrospinning from a Wire Electrode

Dr. Keith Forward Massachusetts Institute of Technology Department of Chemical Engineering 12:00 PM Thursday, January 27, 2012 CEB 218 (810 South Clinton Street)

The needle or nozzle-based electrospinning process has long been explored for its capability to produce unique nanofiber materials with desirable properties such as high surface area and high porosity. These materials are of interest in a wide range of fields such as textiles, filtration, tissue engineering, drug delivery systems, nanocomposites, and alternative-energy generation systems such as solar cells, fuel cells, and energy storage devices. However, one of the perceived drawbacks of the method for industrial purposes is its low production rate. A typical production rate from a single spinneret is 0.1 -1 g of fiber per hour, depending on the solution properties and operating parameters. To overcome the low productivity of nozzle-based electrospinning, we consider “free surface electrospinning” (also referred to as “needleless electrospinning”) where electrohydrodynamic jets self-organize spontaneously on a free liquid surface. It has been estimated that the concentration of the jets can be increased by an order of magnitude or more compared to conventional electrospinning by employing free surface electrospinning. A bench-top apparatus was analyzed where free surface electrospinning occurs from a thin wire electrode. In this process, metal wire electrodes mounted on a spindle are drawn through an electrified liquid bath in a direction perpendicular to the wire axes. As a wire moves through the fluid/air interface, liquid is entrained on the wire, resulting in a thin film of liquid coating the wire. Due to a Plateau-Rayleigh instability, the coating breaks up into individual droplets of charged liquid on the metal wire. At sufficiently high local electric field, the individual drops deform and jets are produced from the droplets, giving rise to a form of free surface electrospinning. As the spindle rotates, electrospinning continues to occur until the supply of liquid is exhausted or the required electric field conditions are no longer met. By mounting several wires on a rotating spindle, the process of immersion, entrainment, dewetting and jetting can be performed repeatedly in a simple manner. The processes of charging, entrainment, droplet breakup, and jetting are all coupled in this process. We examine how the liquid properties (i.e. surface tension, viscosity, density, concentration) and wire electrode rotation rate affect liquid entrainment and droplet breakup. Applied potential and rotation rate of the spindle are varied to study the effects of these operating parameters. A model for the productivity of the process is presented to account for liquid properties and operating parameters. Based upon the presented productivity model, a small pilot-plant scale apparatus was designed and built. The apparatus has the capability of producing 200 g of fiber per hour, depending on liquid properties and operating parameters. This study shows the ease of scaling up free surface electrospinning, and the capability of industrializing electrospinning.

Thursday, January 26, 2012

Self-assembly and Crystallization of Mesostructured Zeolites

Prof. Brad Chmelka University of California at Santa Barbara Department of Chemical Engineering 11:00 AM Thursday, January 26, 2012 CEB 218 (810 South Clinton Street)

Mesoporous zeolites represent a new and technologically important class of materials that exhibit improved transport, catalytic, and adsorption properties compared to conventional zeolites with sub-nanometer pore dimensions. During their syntheses, the transient development(s) of mesoscopic and crystalline order are closely coupled and difficult to control. Such processes are important to monitor and understand to optimize the compositions, structures, and properties of mesostructured zeolites. In particular, solid-state nuclear magnetic resonance (NMR) spectroscopy, in conjunction with small-angle X-ray scattering (SAXS), transmission electron microscopy (TEM), and adsorption/reaction measurements, establish new molecular-level insights on the local interactions and distributions of complicated organic structure-directing agents with respect to crystallizing inorganic frameworks and their resulting catalytic reaction properties. The analyses reveal the formation of intermediate framework configurations, which subsequently transform into zeolitic structures with novel combinations of both nano- and mesoscale porosities. Such materials are shown to result from competition between simultaneous and coupled surfactant self-assembly and inorganic crystallization processes, the interplay between which governs the onset and development of framework structural order on the different length scales. The results provide criteria for rational design strategies aimed at synthesizing hierarchically porous zeolites with different framework morphologies and improved transport, catalytic, and adsorption properties.

Friday, January 20, 2012

Efficient Membranes through Polymer Engineering

Dr. Ayse Asatekin Massachusetts Institute of Technology Department of Chemical Engineering 11:00 AM Friday, January 20, 2012 CEB 218 (810 South Clinton Street)

Water scarcity affects one in three people across the globe, limiting access to safe water for drinking, sanitation, and agriculture. This number is expected to grow significantly as fresh water resources are depleted, and water pollution affects larger areas. Preserving our water resources and generating fresh, safe water relies on the development of new technologies. Membranes that remove contaminants from water are a key to energy-efficient and effective water treatment. However, their wide-spread use is limited by low permeability, poor selectivity, and membrane fouling. Rational design of polymeric membrane systems to control key factors such as morphology, surface chemistry, and nanostructure can significantly improve these performance parameters, and make affordable, effective and efficient water treatment systems possible. This presentation focuses on the development of ultrafiltration (UF) membranes with exceptional fouling resistance manufactured without additional processing steps, making use of the self-organizing properties of amphiphilic comb copolymers. Polyacrylonitrile¬-graft¬-poly(ethylene oxide) (PAN-g-PEO), an amphiphilic comb copolymer with a hydrophobic polyacrylonitrile (PAN) backbone and hydrophilic poly(ethylene oxide) (PEO) side chains, is used as an additive in the manufacture of novel PAN UF membranes. During casting, the PAN-g-PEO additive segregates to form a PEO brush layer on all membrane surfaces, including internal pores. This creates a hydrophilic membrane surface that resists adsorption of feed components. The resultant membranes resist adsorptive fouling completely, and recover initial performance with a water-only rinse or backwash, eliminating the need for harsh chemical cleanings. They also have significantly higher fluxes compared with membranes cast from PAN only. We have investigated the performance of these membranes in a wide range of applications, including oil well produced water, refinery wastewater, shale gas field wastewater, and membrane bioreactors for treating domestic wastewater. Due to their ability to resist adsorptive fouling, these membranes can sustain higher fluxes, require less frequent backwashes, eliminate the need for chemical cleanings, and achieve longer membrane lifetimes, translating to reduced energy consumption during operation and better process economics. This can mean cheaper methods to provide clean water and to protect our water resources.

Tuesday, January 17, 2012

Third Generation Photovoltaics: Harnessing the heat or "hot" electrons

Dr. Prashant Nagpal Los Alamos National Lab Center for Solar Photophysics 11:00 AM Tuesday, January 17, 2012 CEB 218 (810 South Clinton Street)

The sun produces 150,000 TW of incident radiation on earth which can easily provide us with a carbon neutral source of renewable energy to meet our current needs (~15 TW). However, energetically broad distribution of the emitted electromagnetic radiation from the sun poses significant scientific challenges to harvest this energy economically. Conventionally, a semiconductor photocell absorbs this incident radiation generating electron-hole pairs across its energy bandgap, which are then collected at different electrodes to get useful electric power. However, material challenges of collecting these charge carriers before they recombine, along with fundamental challenges of utilizing the excess energy from “hot” carriers (generated by photons with energy higher than semiconductor bandgap), need to be addressed to develop clean energy sources., I will discuss my recent results on progress made in developing efficient thermophotovoltaic emitters and infrared photocells to achieve above mentioned goals. Thermophotovoltaics (TPV) is a less-studied alternative to the photovoltaic (PV), or light-to-electric, energy conversion method described above. In TPV, a secondary emitter re-emits all the incident power as an energetically narrow beam of infrared light matched to the photocell bandgap. This incident light can then be converted efficiently into electricity without incurring losses from hot-carriers. However, emission from real materials has impeded study in this area. I will show how refractory materials, like tungsten, can be easily molded into desired nanophotonic or plasmonic metamaterials to selectively tailor the glow and directionality of the emitted light. Moreover, this energy-conversion process requires using this tailored light source (or incident sunlight for PV) to generate electricity using a cheap photocell module. I will discuss my recent results in understanding charge transport and tuning recombination dynamics in thin film semiconductor devices, specifically semiconductor nanocrystals, for development of solution processable, inexpensive, infrared photocell modules. I will also discuss some fundamental advances made in thin-film plasmonics which can be beneficial not only for development of thinner solar cells, but also for developing next-generation of medical sensors, faster computer chips.

Friday, January 13, 2012

Alternative Solvent Systems for Green and Sustainable Processes

Dr. Elizabeth Biddinger Georgia Institute of Technology Department of Chemical and Biomolecular Engineering 1:30 PM Friday, January 13, 2012 CEB 218 (810 South Clinton Street)

Solvents are typically the largest component in a chemical synthesis and separation process. The energy usage and waste generation from the use of these solvents contributes significantly to the overall energy consumption and waste generation in a process. By developing and implementing alternative solvent systems, greener chemical processes can be established. Alternative solvents can be used to improve reaction and separation efficiencies, and reduce energy consumption and waste generation. There are multiple classes of alternative solvents including tunable solvents, switchable solvents and ionic liquids. Each class has its own advantages, which play a significant part in the selection of an alternative solvent system. Tunable solvents have properties than can be changed (“tuned”) in a continuous manner with the application of heat, pressure or another external stimulus. Conversely, switchable solvents have drastic step-changes in their properties (ionic strength, volatility, hydrophilicity, etc.) in response to some impetus such as the temperature, pressure, pH, absorption of light or introduction of a chemical “switch.” Traditional ionic liquids are organic salts that are liquids below 100°C. Traditional ionic liquids do not change properties with an external stimulus, though are touted for their non-volatility and ionic strength. Several examples of these alternative solvent systems will be presented including tunable solvents for combining homogeneous reactions with heterogeneous separations, and switchable solvents known as reversible ionic liquids. Examples of reversible ionic liquid use for CO2 capture and nanoparticle synthesis will be given.