EMBARGOED FOR RELEASE: Monday, Sept. 9, 2013, 8:30 a.m. Eastern Time Note to journalists: Please report that this research was presented at a meeting of the American Chemical Society. A press conference on this topic will be held Monday, Sept. 9, at 3 p.m. in the ACS Press Center, Room 211, in the Indiana Convention Center. Reporters can attend in person or access live audio and video of the event and ask questions at www.ustream.tv/channel/acslive.
Newswise — INDIANAPOLIS, Sept. 9, 2013 — The amazingly efficient lungs of birds and the swim bladders of fish have become the inspiration for a new filtering system to remove carbon dioxide from electric power station smokestacks before the main greenhouse gas can billow into the atmosphere and contribute to global climate change.
A report on the new technology, more efficient than some alternatives, is on the agenda today at the 246th National Meeting & Exposition of the American Chemical Society (ACS), the world’s largest scientific society. The meeting, which features almost 7,000 presentations on new advances in science and other topics, continues here through Thursday in the Indiana Convention Center and downtown hotels.
With climate change now a major concern, many power plants rely on CO2 capture and sequestration methods to reduce their greenhouse gas emissions. Speaking at a symposium, “CO2 Separation and Capture,” Aaron P. Esser-Kahn, Ph.D., said he envisions new CO2-capture units with arrays of tubes made from porous membranes fitted side-by-side, much like blood vessels in a natural lung. Once fabricated to be highly efficient and scalable to various sizes by repeating units, these units can then be “plugged” into power plants and vehicles, not unlike catalytic converters, he explained. To capture the most CO2, the Esser-Kahn group from the University of California, Irvine, first had to figure out the best pattern to pack two sets of different-sized tubes –– one for waste emissions and the other a CO2-absorbing liquid –– into the unit. “The goal is to cram as much surface area into the smallest space possible,” said Esser-Kahn. They studied the way blood vessels are packed in the avian lung and the fish swim bladder. Birds need to exchange CO2 for oxygen rapidly, as they burn a lot of energy in flight, while fish need to control the amount of gas in their swim bladder effectively to move up and down in the water. “We’re trying to learn from nature,” said Esser-Kahn, adding that the avian lung and fish swim bladder are biologically well-suited systems for exchanging gases. But the blood vessels in the avian lung and fish swim bladder are packed in different patterns. The avian lung consists of a hexagonal pattern where three large tubes form the vertices of a triangle and a small tube sits in the gap, while the fish swim bladder has a squarer pattern where a large and small tube alternate between vertices of a square. It turned out that this tube-packing challenge is a well-studied mathematical problem with nine unique solutions, or patterns, Esser-Kahn said. The team used computer simulations to predict how efficient gas exchange would be for each pattern. Four were predicted to be highly efficient, including the avian lung’s hexagonal pattern and the fish swim bladder’s squarer pattern. However, the most efficient pattern was actually one not found in nature: the double-squarer pattern, similar to the squarer one in the fish swim bladder, but with two small tubes alternating with a large tube. Esser-Kahn’s team then synthesized miniature units up to a centimeter long and confirmed experimentally that the double-squarer pattern was the most efficient, outperforming the avian lung and fish swim bladder by almost 50 percent. Now, scientists can conduct further research to improve CO2-capture units’ efficiencies by adjusting the sizes of the tubes, thicknesses of the tube walls and membrane materials that make up the tube walls. “Biological systems spent an incredible amount of time and effort moving towards optimization,” said Esser-Kahn. “What we have is the first step in a longer process.” Other presentations at the symposium included:
- Novel carbon capture and sequestration: Biomimetic solid sorbents and gas shale analysis
- Process and thermodynamics considerations of CO2 capture from post-combustion flue gases
- Improving the regeneration of CO2-binding organic liquids with a polarity change
The American Chemical Society is a nonprofit organization chartered by the U.S. Congress. With more than 163,000 members, ACS is the world’s largest scientific society and a global leader in providing access to chemistry-related research through its multiple databases, peer-reviewed journals and scientific conferences. Its main offices are in Washington, D.C., and Columbus, Ohio. To automatically receive news releases from the American Chemical Society, contact firstname.lastname@example.org.
Microvascular materials for mass and energy transport
Work into synthesizing microvascular materials has recently taken a step forward in the form of a new synthetic process VaSC (Vaporization of a Sacrificial Component) that enables the formation of 3D microstructures that are meters in length. We report on our recent advances in using VaSC to create three-dimensional gas exchange units modeled on the design of avian lungs and vascular systems for heat distribution. We are focused on mass transfer applications for the capture of CO2. We will report on recent research into creating high surface area micro-structures and the use of two phase flow systems to release gas from capture solutions.
New directions in the synthesis of oxacalixarenes and related oxacyclophanes
Our research has focused on two areas of oxacyclophane synthesis which are discussed in this talk. The first area involves a new approach towards the synthesis of oxacalixarenes. Traditionally, halogens are utilized as leaving groups in the nucleophilic aromatic substitution reaction to make oxacalixarenes; however our approach utilizes a two-step process of activation followed by substitution to allow for the use of hydroxyl groups (i.e., phenols) as leaving groups. Our other area of focus is in the synthesis of a new class of redox active oxacyclophanes that contain p-benzoquinones.
Developments in the synthesis of small and large molecules using olefin metathesis catalysts
Olefin metathesis is an established technique for making and breaking carbon-carbon double bonds, and has been adapted in applications that range from total synthesis to high performance plastics. Over the past several decades, efforts have been directed toward the development of catalysts that display enhanced functional group tolerance or increased selectivity as compared to their precursors, or facilitate access to small and macromolecules with unique structures and functions. In this presentation, we will describe previous and recent efforts aimed at designing and accessing new classes of olefin metathesis catalysts as well as our efforts toward using catalysts in hand in various applications.
Self-healing polymer design via noncovalent and dynamic covalent interactions
The development of polymers that can spontaneously repair themselves after mechanical damage would significantly improve the safety, lifetime, energy efficiency, and environmental impact of manmade materials. Our laboratory has recently succeeded in developing self-healing polymers via either noncovalent or dynamic covalent bonding interactions. For noncovalent mechanism, we developed multiphase supramolecular thermoplastic elastomers that combine high modulus and toughness with spontaneous healing capability (Nature Chemistry 2012, 4, 467; Angew. Chem., Int. Ed. 2012, 51, 10561). In contrast to previous self-healing polymers, our systems spontaneously self-heals as a single-component solid material at ambient conditions without the need of any external stimulus, healing agent, plasticizer, or solvent.
Oxidative de-polymerization and the flex fuel generator: An ideal context based learning tool
The basic concepts within math and science are best learned and retained when the joy of connecting the dots between cause and effect relationships can be drawn within the context of iterative hands-on experimentation. The foundational concepts of reaction kinetics, catalysis, thermodynamics, ideal gas laws, stoichiometry, viscosity, radical reactions, and chain length dependent material properties are topics usually first encountered in the classroom in the absence of an experiential context. To best prepare the next generation of creative problem solvers and innovators we must reintroduce i) useful context and ii) the joy of real time hands-on discovery into the learning process. An inexpensive method and apparatus (Flex Fuel Generator) capable of achieving both of these goals will be introduced and discussed.
Controlled catalyst transfer polycondensation of a p-phenyleneethynylene-based monomer: Surface-initiated polymerizations and other applications
Conjugated polymers, such as the poly(p-phenyleneethylene)s (PPEs), hold promise for use in organic light-emitting diodes, molecular wires, and many other applications. The aforementioned polymers are typically synthesized from A2+ B2 or A-B type monomers using Sonogashira-type cross coupling chemistry or alkyne metathesis. Since these methodologies grow polymer in a step-growth fashion, it can be difficult to access high molecular weight materials with low polydispersity or prepare relatively sophisticated materials, such as block copolymers or surface-grafted polymer brushes. We envisioned that the drawbacks intrinsic to the step-growth polymerization of phenyleneethynylene-based monomers may be overcome through the development of a chain-growth catalyst transfer polycondensation (CTP) method. While CTPs have been successfully utilized to prepare various conjugated homo- and copolymers, including poly(thiophene)s, poly(fluorene)s, and poly(phenylenes), the first synthesis of a PPE via chain-growth CTP will be described in this presentation. Ongoing and future efforts involing the use of CTP based methods to prepare well-defined macromolecular structures containing PPEs, such as block copolymers, surface-grafted polymers, and other materials capable of self-assembling into well-ordered structures on the nanoscale will also be discussed.
Development of chain-growth condensation polymerization since coming back from Jeff's group
I stayed Jeff's group for a year in 1997-98 as a visiting scientist. Before that we had set up research on chain-growth condensation polymerization (CGCP), but our landmark JACS paper about CGCP in solid-liquid phase was published in 1999 when I came back to Japan. In this paper, I would like to talk about development of CGCP.
Conventional condensation polymerization proceeds in step-growth polymerization mechanism, but the mechanism can be converted to chain-growth by enhancement of the reactivity of the polymer end group; the monomer reacts only with the initiator and the polymer end group. The approaches we have adopted are (1) change of substituent effect induced by bond formation of the monomer with the polymer end group, and (2) selective transfer of catalysts to the polymer end group in coupling polymerization with a transition metal catalyst.
In the first case, we have attained CGCP for the synthesis of well-defined poly(p-benzamide)s, poly(m-benzamide)s, aromatic polyethers, poly(ether sulfone), and aromatic polyesters. Taking advantage of the living polymerization nature, we synthesized a variety of condensation polymer-containing architectures such as block copolymers, star polymers, graft copolymers, and hyperbranched polymers.
The second case of CGCP with a metal catalyst has been independently found by us and McCullough et al. in the synthesis of poly(hexylthiophene). We have developed this polymerization to the precision synthesis of poly(p-phenylene), polyfluorene, poly(N-alkylpyrrole), and poly(pyridine-3,5-diyl). Block copolymers of different π-conjugated polymers were also synthesized by successive catalyst-transfer condensation polymerization in one pot.
Brief discussion on water treatment solutions of GE waters and process technologies
Dr. Ashok Shetty has lead the Chemical Synthesis team at GE Water & Process Technologies (GEWPT). GEWPT, a part of GE Power and Water, provides water treatment, wastewater treatment and process systems solutions. Its goal is to help solve complex challenges related to water availability and quality, to increase productivity, reduce costs and help our customers meet environmental regulations. This presentation will be focused on GE's Water Treatment Solutions that include Cooling water, Boiler and Waste Water Treatments.
Synthesis and analysis of redox shuttles for overcharge protection in lithium-ion batteries
Hundreds of compounds have been tested as redox shuttle additives for overcharge protection in lithium-ion batteries, a condition that shortens battery lifetimes, yet only a few compounds have proven effective for ³100 overcharge cycles. Identifying new redox shuttles with improved solubilities, oxidation potentials that match specific battery cathodes, and retaining or increasing shuttle lifetimes has been a challenge for this field.Determining the efficacy of redox shuttles can be a slow process, especially if shuttles are successful at overcharge protection; each cycle takes ~20 hours, so researchers may wait months or longer for their batteries to fail. Driven by the desire to obtain faster experimental results, we developed a new screening method to identify promising redox shuttle candidates. We compared reported battery cycling results to those from our own laboratory using cyclic voltammetry of neutral molecules and UV-vis and EPR analysis of radical cations generated by chemical oxidation. We found that UV-vis and EPR spectroscopies were both more effective at predicting overcharge performance, and testing requires only a few hours. Using this method, we can weed out poor candidates and focus on further testing of redox shuttles whose radical cations slow rates of decay. Our method requires no battery electrolyte - just the redox shuttle candidate, chemical oxidant, dry solvent, and a UV-vis or EPR instrument to record the intensity of the radical cation spectra vs time. This presentation will focus on results concerning commercially available redox shuttles and those synthesized in our laboratory, including derivatives of 1,4-dimethoxybenzene and phenothiazine.
Hybrid functional materials by surface modification: Applications in catalysis and adsorption
Research in the Notestein group focuses on the development of novel hybrid or inorganic materials and understanding how extended surfaces alter the properties of reactive sites for applications primarily in catalysis and adsorption. This talk will emphasize our work on hybrid materials, including grafted inorganic catalysts and novel materials derived from oligomeric aromatic structures grafted onto and grown from oxide surfaces. The latter work was strongly influenced by time spent under Professor Jeffrey Moore's direction.
Development and applications of 3D covalent organic polyhedrons (COPs) and porous polymer frameworks (PPFs) through dynamic covalent chemistry
Dynamic covalent chemistry (DCC) has been strongly integrated into diverse research fields, and has enabled easy access to a variety of combinatorial libraries, 2-D shape-persistent macrocycles, and 3-D molecular cages that target many important applications, such as drug discovery, biotechnology, molecular separation, light harvesting, etc. This presentation will focus on the efficient synthesis of shape-persistent, structure-tunable 3-D covalent organic polyhedrons (COPs) as well as porous polymer frameworks (PPFs) via reversible metathesis reactions. The framework materials and the well-defined discrete COPs have shown great potential in carbon capture, fullerene separation, biomedical diagnostics, etc. These results illustrate how the thermodynamically controlled DCC can be utilized to construct target-specific nanomaterials and enable their practical applications.
Tuning sol-gel-sol transitions of moderately concentrated aqueous solutions of thermosensitive hydrophilic block copolymers
A unique strategy has been developed for tuning sol-gel/gel-sol transitions of moderately concentrated aqueous solutions of thermosensitive hydrophilic block copolymers, which are usually fixed at a specific concentration. Our method is to statistically incorporate a small amount of stimuli-responsive groups into the thermosensitive block of block copolymers such that the lower critical solution temperature can be modified via an external stimulus. Using "living"/controlled radical polymerization techniques, we have synthesized a series of doubly responsive hydrophilic block copolymers through the incorporation of various stimuli-responsive groups into the thermosensitive block(s), and demonstrated the tuning of thermally-induced sol-to-gel and/or gel-to-sol transitions of their moderately concentrated aqueous solutions by applying external stimuli.
Self-healing materials technology: A new approach to improving corrosion resistance in coatings
Introduction to the Concept of Self-Healing Materials
Self-Healing materials are a class of smart materials that are capable of repairing themselves, when they are damaged, at ambient temperature, without any external intervention.[1,2] Given this definition of self-healing technology, not all technologies commonly referred to as self-healing are truly self-healing. With this in mind, materials healing technologies can broadly be classified as autonomic and non-autonomic healing technologies. The focus of this talk will be on autonomic healing technologies facilitated by microencapsulated healing agents for application in protective coatings.
Life Extension in Coatings
A coating with the capability to repair itself when damaged, will last longer in its specific application. The implication of such self-healing functionality is that maintenance cycles on major assets can be lengthened, significantly reducing costs associated with materials, labor and downtimes. Many of the most critical applications of coatings are for protection of metal substrates in harsh environments where frequent inspection is difficult or costly. These applications stand to benefit the most from the potential of lifetime extension afforded by self-healing technologies.
In this talk, I will discuss various considerations in designing self-healing systems for protective coatings and examples of such systems based on a variety of chemistries.
1. Blaiszik, B. J.; Kramer, S. L. B.; Olugebefola, S. C.; Moore, J. S.; Sottos, N. R.; White, S. R. Annu. Rev. Mater. Res.2010 , 40, 179 – 211.
2. Wilson, G. O.; Andersson, H. M.; White, S. R.; Sottos, N. R.; Moore, J. S.; Braun, P. V. 2010. Self-Healing Polymers. Encyclopedia of Polymer Science and Technology.
Helical folding dynamics in association with intermolecular aggregation
We have been studying a number of conjugated oligomers to probe their various aspects of properties, including supramolecular assembly, semiconducting and opto-electronic capabilities. Monodispersed synthetic oligomers capable of manifesting tailored chain conformations, i.e., foldamers, have also been designed to emulate and assist better understanding the higher-order structures formation by biological macromolecules, as the folding of both synthetic and natural systems are dictated by non-covalent forces of similar chemical nature. In this presentation, a specific example will be discussed, elucidating important information about the folding dynamics of a phenylene ethynylene oligomer, which is believed to aggregate intermolecularly under both folded and unfolded conformations. Specifically, foldamers of sufficient chain lengths comprising alternating ortho- and para-phenyleneethynylene units in the backbone were proven to assume a helical conformation, driven by intramolecular aromatic stacking interactions. Such chain molecules bearing different side chains exhibited the same helical structure in varied, respectively suitable solvents, in accordance to the polarity of side chains.Different folding dynamics were manifested when the solvophobic and aromatic stacking interactions were intensified by varying the solvation conditions. The observed folding stability and unique folding dynamics is believed to be related to the competition of intermolecular aggregations in the folded and unfolded states.
Small-molecule detection using DNA assembly-driven reactions
The molecular recognition and self-assembly capabilities of nucleic acids are a key driving force behind nearly all of the chemical processes that make life possible. The ability of nucleic acids to selectively recognize other nucleic acids, as well as small molecules and proteins, has been refined by billions of years of evolution. Realizing the tremendous potential of these exquisite recognition and assembly capabilities, researchers have harnessed these properties in the laboratory with the goal of redirecting DNA and RNA to perform tasks outside of their canonical biological roles.
One example of this is the development of DNA split aptamers, which are comprised of two nucleic acid strands that only assemble in the presence of a specific small-molecule or protein target. We have explored the use of split aptamers as a recognition element to transduce the presence of a small-molecule into the output of DNA ligation. Reactive groups are appended to the termini of the split aptamer fragments. If the target small molecule is present, it directs assembly of the aptamer, bringing the reactive groups into close proximity and thus promoting ligation of the DNA strands. This ligation event can be detected using an enzyme-linked output or in the format of a lateral flow sensor. Additionally, we have demonstrated that the increased effective molarity provided by DNA assembly is sufficient to enable the use of non-bioorthogonal chemistry in complex biological fluids.
Molecular and cellular recognition in engineering protein hydrogels
This lecture will explore strategies for the use of molecular recognition in the design of protein hydrogels. Control of gel structure, dynamics and physical properties will be examined, and opportunities for control of cellular behavior will be described.
Synthetic molecules that bind anions and transport them across a lipid membrane
By mimicking the hydrogen-bonding mode found in a ClC chloride channel, an anion receptor was prepared with a binding site that contains four hydrogen bonding donors, two NHs and two OHs. Systematic modification yielded an effective synthetic molecule capable of transporting an anion, e.g. chloride, across a POPC lipid membrane. Then, the study has been further extended to develop a synthetic anion transporter that works only in the presence of external stimulation such as light and chemical inputs.
Overview of polymer science utilized for the development of a stable micelle for oncology applications
Polymer micelles have been enticing candidates for drug delivery vehicles since the mid 1970's. Despite the large volume of research performed in this field over 40 years, successful clinical application of this technology remains elusive. A key hurdle to the clinical use of a micelle-based therapeutic is the stability of the micelle following dilution in biological media. We will describe our methodology in developing a polymer micelle system containing reversible stabilization, based upon metal-acetate chemistry, for use in oncology applications. A brief synopsis of synthesis, characterization, formulation, and in vivo results will be presented.
Supramolecular polymers interfacing with proteins and cells
Supramolecular chemistry has primarily found its inspiration in biomolecules, such as proteins, DNA, lipids, and their interactions. Currently the supramolecular assembly of designed compounds can be controlled to great extent. This provides the opportunity to combine synthetic supramolecular materials with biomolecules to modulate biological phenomena.Self-assembling supramolecular architectures provide attractive scaffolds for the organized display of biological ligands. Their dynamic nature allows for simple non-covalent synthesis of multivalent structures and for the introduction of multiple different functionalities. As an example, columnar and spherical supramolecular polymers can be decorated with biological ligands such as sugars and peptides for the assembly of proteins along the supramolecular framework or for the recognition and entry of cells.
High-resolution secondary ion mass spectrometry for imaging cell membrane organization
The plasma membranes of mammalian cells are compartmentalized into domains of differing protein and lipid composition that are believed to be required for proper cell function. The distributions of specific proteins on the cell surface have been established through the use of immunolabels that can be detected with various microscopy techniques. The distributions of distinct lipid species in the plasma membrane, however, remain poorly characterized due to an inability to directly visualize them without using labels that may induce lipid clustering. In collaboration with Peter Weber (Lawrence Livermore National Laboratory) and Joshua Zimmerberg (National Institutes of Health), we have addressed this challenge by using high-resolution secondary ion mass spectrometry (SIMS) to image metabolically incorporated isotope-labeled lipids in the plasma membrane. In this approach, we metabolically incorporate distinct stable isotopes (i.e., 15N and 18O) into the cellular lipid species of interest (i.e., sphingolipids and cholesterol). Then we use high-resolution SIMS, which is performed on a Cameca NanoSIMS 50, to map the lipid-specific isotope distribution on the cell surface. The results of these studies will be discussed.
Self-assembly of amphiphilic organic dyes and photochemical properties
Amphiphilic diarylethene (DE) derivatives that show photochromism and amphiphilic cyanobisbiphenylethene (CNBE) derivatives that show aggregate-induced enhanced emission were synthesized and their photochemical properties were investigated. These dyes possessing hydrophobic core and hydrophilic oligo(ethylene glycol) side chains self-assembled in water by solvophobic effect.
For DE derivatives with asymmetric unit, induced circular dichroism (ICD) was observed upon UV irradiation in water. This ICD was explained by the difference in the self-assembling behavior between the open- and the closed-ring isomers. It was suggested that the closed-ring isomers assembled into a chiral nanostructure. DE derivatives having different lengths and numbers of oligo(ethylene glycol) side chains were also synthesized. The intensity of the ICD signal was the largest for the molecule having two hexaethylene glycol side chains. Meanwhile, the compound showed lower critical solution temperature (LCST) behavior and the clouding was controlled by irradiation with appropriate wavelength of light, which originates from the different cloud-point temperatures between the open- and the closed-ring isomers.
CNBE derivatives showed AIEE in water and in the solid state. The fluorescence quantum yield got larger with the rigidity of the aggregates (i.e. in ethyl acetate < in water < in the solid state). Judging from the measurement of fluorescence spectrum, fluorescence quantum yield, and fluorescence lifetime, a key factor for the enhanced emission is suppression of the nonradiative decay process (knr) arising from the restriction of molecular motion. Additionally, the difference in the emission rate constant (kf) is not negligible to explain the difference in fluorescence quantum yield between in water and in the solid state.
Manipulating the electronic properties of arylene ethynylenes via transition metal coordination
Interest in arylene ethynylene oligomers and polymers is often fueled by the desirable electronic properties associated with these types of conjugated molecules. Two factors can explain the fact that para-arylene ethynylenes are much more sought after for these purposes than their isomeric ortho and meta relatives. First, para conjugation pathways offer enhanced electron delocalization compared to ortho and meta counterparts. Second, ortho- and meta-arylene ethynylenes have the ability to fold into helices that distort the π-system from planarity, decreasing the effective conjugation of these oligomers.
Current research efforts are directed toward addressing this second limitation in ortho-arylene ethynylene structures. Specifically, when pyrazine and pyridine rings are strategically placed throughout the arylene ethynylene molecule, the conjugated backbone can act as a ligand for appropriately sized transition metals. Metal cations with preferences for square planar (Pd (II)) and linear (Ag (I)) coordination environments can enforce planarity in the organic structure. This coordination-driven planarization can increase the effective conjugation of the backbone, making ortho-arylene ethynylenes more attractive targets for the development of organic electronic devices.
Folding of ortho-phenylenes
Although formally conjugated, steric interactions force the ortho-phenylenes into highly twisted conformations exhibiting limited delocalization. Recently, however, it has been shown that this twisting results in well-defined helices both in solution and in the solid state; o-phenylenes have therefore been proposed as a new class of chiroptical materials. The actual reasons for this folding behavior are not clear, however: the role of specific arene–arene interactions is not obvious, and common methods of computational chemistry fail to predict the relative stabilities of the various conformers. We have prepared a series of oligomers with varying substitution. The substituent effect on conformer distributions was used, in combination with dispersion-corrected DFT calculations, to evaluate the role of aromatic stacking in determining their folding. From these results, a simple model has been developed which explains several aspects of their behavior, including the sensitivity of their conformational preferences to small changes in the strengths of aromatic interactions. Efforts to use this model to design o-phenylenes with increased folding propensities will also be discussed.
Cis conformational preference of N-alkylated aromatic amide and urea bonds: Construction of aromatic foldamers with unique structures
Aromatic secondary amides such as benzanilide exist in trans form, whereas N-alkylated benzanilides exist in cis form in the crystal and predominantly in cis form in solution. The cis conformational preference is also observed in aromaticN,N'-dialkylated ureas, such as N,N'-dimethyl-N,N'-diphenylurea. The folded structures of these cis-amide and urea derivatives can be applied to construct the aromatic foldamers with unique conformational properties, including helical, aromatic multi-layered, and chiral cyclic structures. The cis conformational preference of the amide bond was also observed in the aromatic heterocycles such as pyrroles and imidazoles. The oligomers that benzamide and pyrroleamide are linked alternately were synthesized and their structures were investigated. The oligomers 1 with chiral substituents showed significant CD signals in CH3CN. Aromatic multi-layered oligoureas 2 showed the helical structure in the crystal. The helical properties of the oilgoureas in solution have been studied systematically by synthesis and conformational analysis of the derivatives with chiral substituents. The utilities of cis-amides and ureas in developing unique aromatic foldamers will be discussed.
Model dynamic networks from metallo-supramolecular crosslinked polymers
We report the synthesis and characterization of a random copolymer consisting of n-butyl acrylate backbone functionalized with side chain ligands of 2,6-bis-(1' methyl benzimidazoyl) pyridine. The polymer was prepared in a controlled fashion via reversible addition-fragmentation chain transfer (RAFT) polymerization providing a well-defined model dynamic acrylic polymer. The ligands tethered along the polymer backbone are capable of binding to a variety of metal ions with a range of binding strengths resulting in a tunable, reversible crosslinked network under appropriate conditions. The nature of the metal-ligand bonds was explored both in solution and the solid state across a range of binding strengths with numerous characterization techniques. Solution viscosities as well as bulk mechanical properties such as modulus, ultimate tensile strength, and resistance to creep are easily tuned simply by varying the metal ligand combination.
Biotemplated synthesis of novel materials
To meet the ever-growing challenges we face in the next century, especially those in the biomedical and energy fields, organic and materials chemists must design new ways of making more complex materials from simple components. Self-assembly is a powerful tool for accomplishing these goals as it allows for the fabrication of complex arrays of small molecules that can easily become much greater than the sum of their parts. This research presentation will cover the use of bioconjugate materials developed to template the formation of inorganic and organic nanostructures.
Surface chemistry on organic semiconductor crystals: The Diels-Alder reaction
While the bulk structure of organic crystals such as tetracene (lower symmetry, weak intermolecular forces) is very different than the typical substrates used in surface reactions (e.g. gold in gold-thiol monolayers), we have recently demonstrated that Diels-Alder chemistry can be used to functionalize the surface of tetracene and rubrene with a high degree of control and specificity including selective functionalization of faces. The chemistry is tolerant to a wide variety of functional groups, and generic to the acene class of organic semiconductors. This talk outlines spectroscopic evidence for Diels-Alder adducts at the surface, the implications of performing organic chemistry on reactants that are confined in the surface of the crystal, and the potential effects on device performance of organic field effect transistors.
Molecular origami: Folding phenylene ethynylene macrocycles into nanotube segments via cycloadditions
The synthesis of discrete carbon nanotube segments of well-defined diameter, length and chiral vector remains a synthetic challenge, and the creation of such materials could provide starting materials for the synthesis of monodisperse samples of carbon nanotubes for a host of applications. We describe the synthetic strategy to use shape-persistent phenylene ethynylene macrocycles which can be "folded" to create the nascent walls of the tube by making use of cycloadditions to the alkyne moieties of these macrocycles. Several macrocycles have been synthesized, which are potential precursors to armchair, zigzag and chiral nanotubes. Modeling of the cycloadditions reveals that the products should be accessible. Progress using Diels-Alder cycloadditions of the macrocyclic alkynes with cyclopentadienones as well as benzopyryliums formed by alkynylbenzaldehydes will be discussed.
Self-association and its steric control of cationic oligothiophenes
Cationic oligothiophenes have played a key role in the study of conduction mechanism of p-doped polythiophene and radical cations of oligothiophenes, which were made persistent with appropriate substituents, have been shown to undergo self-association, so-called π-dimer formation, in the condensed phase. We designed and synthesized series of oligothiophenes annelated with bicyclo[2.2.2]octene units to investigate the driving forces of π-dimerization and the structure–property relationships of the π-dimers of oligothiophene radical cations. Combined with the results of DFT calculations, SOMO–SOMO interaction was found to be the most important factor affecting π-dimerization enthalpy when comparing oligothiophenes with the same chain length. By applying this finding, we are trying to construct redox-responsible oligothiophene-networks based on the π-dimer formation and some results will also be presented.
Conjugated polymers copolymerized with flexible chains: A platform to create highly ordered polymer nanostructures
This presentation will survey recent examples from our lab in which we have created conjugated polymers (CPs) composed of alternating oligo(phenylene vinylene)s and flexible segments. Our synthetic strategy utilized a Sonogashira cross-coupling polymerization to join pre-synthesized, and therefore structurally uniform, oligo(phenylene vinylenes) of 3, 5, and 7 repeat units with a tetraethylene glycol containing linker. We utilized polarization modulation fluorescence microscopy to interrogate individual polymer molecules for their conformation and electronic properties, and have found a direct link between the chromophore size and the resulting anisotropy of the polymer nanostructures.
Polymer nanoparticle assemblies
Nanoscale structures and morphologies impart desired function to many polymer-based materials. Thus far, amazing arrays of structures, morphologies and materials have been created using molecular self-assembly. Yet, there are structures or morphologies that are difficult to create using known strategies or in materials of choice. We have been pursuing the use of polymer nanoparticles and the concept of sphere packing to create nanoscale assemblies. Our approache has following advantages: (a) obtain stable nanoscale structures in a single step, through self-assembly from any two or more spherical moieties; (b) independently pre-assemble the polymer domains with the required molecular assembly within the particle and domain size; (c) systematically alter the packing of the polymer through changes in the radii of the nanoparticles or interparticle interactions or both: and (d) ability to use multiple polymer components in the assembly. The concept of spherical packing is a powerful bottom-up approach that provides control and tunabilty in each step of the self-assembly process to reliably obtain stable nanoscale morphologies. This talk will focus on the protocols for the fabrication of polymer nanoparticles and self-assembly of nanoparticles . The talk will also discuss the charge transport properties in assemblies created from conjugated molecules and polymers.
Rethinking how we teach general chemistry in the world of Google, the internet, and smartphones
As technology has become a larger part of our culture the way students search for information has changed. For most people the days of looking up information in a bound copy of an encyclopedia are long gone. When searching for information most people “Google it” first, and then go to various other resources on the internet. Using a smartphone or other mobile device answers to questions can be found almost instantaneously any place a phone can be used! Does this mean books and other traditional methods of transferring information (such as lecture) are no longer valuable? No! But it is important for teachers to carefully consider how a students' time is used both in, and outside of the lecture hall or classroom. Technology increasingly can, and often should, be used to improve the learning experience a student has when working with a given subject material. Technology also offers novel methods for the assessment of student learning. Advances in online course homework and testing systems allow instant feedback, customizable remediation, and a far larger bank of questions than is typically possible with a traditional text book. This talk will discuss how general chemistry classes at the University of Illinois at Urbana-Champaign have changed to take advantage of the technology available to students today.
Chemistry professors: Discipline-rich and ready for chemistry education
It is both common and unfortunate, within some communities, to caricaturize professors from top tier departments and institutions as unsupportive, disinterested, and even disdainful of undergraduate education. For about 15 years, at the University of Michigan, the department has experimented with broadening the familiar intergenerational research group model to support faculty work in instructional development, while at the same time enriching the experience for our students who wish to become faculty members. This design has become integrated into the fabric of the chemistry program and is now simply a part of the way we think about our work. As of Fall 2013, the experiment is over: we have recently budgeted internal support mechanisms for undergraduates, graduate students, and post-doctoral associates who want to get involved, and we have created a new Associate Chair position to oversee this aspect of the department's program.
Main thing is to keep the main thing the main thing: Reflections on 13 years teaching and learning organic chemistry at a PUI
Many chemical educators at the start of their careers are unaware of how just much they will learn from their students. While the old adage “To master a subject, teach it” still rings true, technical expertise is only one facet of a successful career. Faculty recognition of his or her status as a professional student can lead to unexpected professional and personal growth. This is especially true at primarily undergraduate institutions (PUIs), where teaching in the information age has accelerated the rate of change in all areas of education, even year-to-year and day-to-day. This talk aims to extract focus from the collective teachings of over 1,300 undergraduate students over 13 years at a PUI institution in Detroit, MI. The author will report on reflections made in the adolescence of his career, including the use of research as a teaching tool for undergrads, integration of writing/presentation skills into lab courses, the value of new assessment strategies for student success in theory courses and the frustration/joy of academic advising.
To infinity and beyond: The online organic chemistry story
In the summer of 2008, Jeff Moore and I embarked on a journey to teach organic chemistry completely online. Armed with an idea, hope, enthusiasm, and naiveté, 37 students from across the state of Illinois learned organic chemistry, and we learned a lot about learning. After scaling up to 180, 320, and then 750 students by the fall of 2009, including with students from Lahore University of Management Sciences in Pakistan and Peking University in Beijing, we had grown faster than we had ever imagined. We have learned much in the experience, and the enterprise is still thriving today. This presentation will give a brief history and discuss the many things I have learned from the experience. Also, future directions and challenges will be addressed.
Autonomy in the laboratory and learning in the classroom
An evolution of research projects in the Moore group will be presented, highlighting examples of coworker-initiated discoveries. Parallelisms will be drawn between laboratory discovery and classroom learning. I'll conclude with a discussion of how my own teaching philosophy has evolved from direct observations of the power of autonomy.