The Effect of Steric Crowding on Photosiomerization
Dr. William Brittain (Texas State), Dr. Gabriel Lopez (Duke) & Dr. Jan Genzer (NCSU). The photoisomerization and steady state adsorption spectra of spiropyrans are sensitive to local environment. The adsorption maximum of these chromophores is a sensitive probe of microenvironment polarity. The process is also sensitive to pH, ions, and heat. To date, studies have not clearly distinguished the influence of steric crowding near the chromophore. We will study photoisomerization kinetics of spiropyran and other chromophores that are surface-immobilized; surface depositions will be systematically altered to produce samples with different grafting densitites. The relationship between surface grafting density of photoisomerization rate will probe the effect of crowding on molecular rearrangements.
Use of Photoisomerization to Study Self-Assembly
Dr. William Brittain (Texas State) & Dr. Stefan Zauscher (Duke). Programmed assembly of peptide-nucleotide syntactomer micelles will be monitored and potentially controlled by covalently attached chromophores. Click chemistry will be used to couple alkyne-modified spiropyran with polynucleotides containing azide-functionalized nucleotides. The photoisomerization rate is related to the microenvironment and thus can provide data on self-assembly or aggregation rates. The colored photoisomer is zwitterionic and thus, may also influence the assembly process. We will study how the concentration of covalently attached chromophore alters the assembly of polynucleotides.
Spiropyran Photoisomerization during Phase Separation of Elastin-Like Polypeptides (ELP)
Dr. William Brittain (Texas State) & Dr. Ashtosh Chillkoti (Duke). The photoisomerization of spiropyran produces a colored, zwitterionic merocyanine; this process is solvochromatic and can provide information about the microenvironment surround the chromophore. Syntactomers are macromolecules with a regularity of repeat unit structure that is intermediate between random, synthetic polymers and proteins with repeating sequences of multiple monomer units. These materials exhibit aqueous lower critical solution temperatures (LCST) that correspond to the temperature for coalescence. This coalescence event will be studied using spiropyran molecules to provide information about the ELP microenvironment and to photochemically induce changes. UV/Vis spectroscopy will be used to study normal LCST behavior of modified ELP followed simultaneous irradiation of the sample to study the effect of the merocyanine isomer on the LCST. The proposed work plan includes spiropyran synthesis and UV/Vis studies of LCST at the Texas State PREM, and peptide modification/characterization at MRSEC partner Duke University.
Assembly of Amyloid Nanostructures from Hybrid Peptide-Polymer Molecules
Dr. Tania Betancourt (Texas State) & Dr. Carol Hall (NCSU). In recent years there has been an increased interest on the study of the properties of amyloid fibril materials. Understanding the formation of disease-related amyloids is not only critical for understanding the onset and progression of amyloid associated diseases or for the design of additives for protein pharmaceuticals, but also because the very unique properties of fibril materials offer a number of interesting possibilities for applications in nanobiotechnology. Our main focus is to study how protein amyloid formation could be used for the controlled assembly of hybrid protein-polymer supramolecular nanostructures via non-covalent interactions. Experimental studies (Betancourt) and simulations (Hall) will investigate how site-selective modification of amyloidogenic peptides with hydrophilic synthetic polymers can modulate the self assembly of hybrid amyloids into nanostructures of specific sizes and configurations. Initial studies will be carried out with the amyloidogenic peptide sequence of the Alzheimer’s disease related amyloid Aβ protein (KLVFFAE). Self-assembled nanostructures will be characterized via dynamic light scattering, chemical staining, electron microscopy, X-ray diffraction, atomic force microscopy, and circular dichroism spectroscopy.
Polyimide Membranes with Enhanced Flexibility, Permeability, and Selectivity
Dr. Chad Booth (Texas State) & MRSEC partner Dr. Joseph Tracy (NCSU).
The work proposed was to build on our existing technology of nano-composite polyimide
membranes. The series of polyimide membranes studied composed of a series of aliphatic diamines with 6-FDA (figure 1). The original work utilized TIO2 as an additive. It was shown that the introduction of the TiO2 allowed for the development of a “selective surface flow”; thereby increasing both permeation and selectivity. Our largest limitation to date has been that of limited percent incorporation of the TiO2 (at of less than 5 weight %).
During the PREM we propose to explore the use of magnetically oriented nano-composites (Figure 2). The will use the Fe3O4 magnetic nano-particles developed by Professor Joe Tracy at NCSU and coat them with TiO2 using a solgel process. From there we plan on introducing the TiO2 coated magnetic nano-composites into a previously synthesized poly(amic acid) solution of appropriate composition, figure 1. The use of untrasonification will afford a homogeneous dispersion of the particles. We will then cast a film of the poly(amic acid) and use magnetic field orientation to align the magnetic nano-particles within the polymer film. The film with be then thermally cured and thus “lock in” the aligned nature of the magnetic nano-particles.
We are currently attempting to coat the magnetic nano-particle with the TiO2. We are using a solgel method, previously used in our group, to carry this out. We have, to date, synthesized TiO2 nano-particles in the presence of the magnetic nano-particles but the resulting particles are not magnetic. We are investigating this.
In addition, we wish to examine the potential use of this technology as a way to develop catalytic nano-particle films. This would allow for the investigation of membranes that allow catalytic reactions to occur by simply passing a gas through the membrane. This will, originally, be something like Pd or Pt in an attempt to simply catalyze an alkene reduction.
Transparent Conductive Substrates for Conducting Polymer Growth and Testing
Dr. Jennifer Irvin (Texas State) & Dr. Ben Wiley (Duke). Conducting polymers are commonly deposited onto conductive substrates via electrochemically-controlled oxidative polymerization. While those conductive substrates are often precious metals such as gold or platinum, less expensive substrates are desirable. Additionally, transparent conductive substrates are needed for applications such as electrochromics or light emission, where changes in the polymer (color and/or light emission) must be visible from outside the electrochemical cell. While indium tin oxide coatings are often used as transparent conductive coatings, the films are brittle, expensive, and not suitable for some conducting polymers. New transparent conductive coatings are therefore needed that are less expensive, more robust, and suitable for other conducting polymers. The Wiley group has developed copper nanowire-based transparent conductive coatings as well as copper-nickel core-shell nanoparticle-based transparent conductive coatings. The utility of these two types of coatings for conducting polymer deposition will be investigated in a joint effort between the Irvin and Wiley groups to study the deposition of conducting polymers on the Wiley substrates. The electrochemical windows of these substrates will be determined, and attempts will be made to deposit conducting polymers on the substrates. If polymer coatings can be formed on these substrates, polymer electrochemistry (oxidation/reduction potentials and electrochemical activity/stability) on these novel substrates will be compared with that on traditional substrates. Spectroelectrochemistry experiments will be conducted to examine the utility of these substrates for investigating the UV-Vis-nIR spectra of conducting polymers as a function of applied potential. To date, joint preliminary experiments have been conducted when Dr. Irvin traveled to Duke and worked with members of the Wiley group, and follow-on experiments have been designed.
Colloidal Templating of Conducting Polymers for Energy Storage
Dr. Jennifer Irvin (Texas State) & Dr. Olin Velev (NCSU). The redox processes of conducting polymers (ICPs) allow the polymers to be used as electrodes in electrochemical capacitors (ECs). While in inorganic ECs only the surface of the inorganic oxide is capable of storing charge, the entire accessible volume of ICP-based ECs is available to store charge. Low porosity in conducting polymer films may limit accessibility, so that redox processes only occur at the surface of film, resulting in low capacities. To maximize capacity, therefore, it is necessary to maximize surface area in polymer films, which requires highly porous films. While porous films are commonly achieved in electrochemically-prepared polymers, solution-cast polymers often suffer from low porosity. Porosity can be improved through the use of templates. Soluble, neutral ICPs will be deposited around organic and inorganic templates prepared with guidance from O. Velev. Additonally, solutions of monomers will be used to potentiostatically deposit insoluble ICPs in the interstices of the template. After drying, the templating materials will be removed, leaving ICPs with inverse opal nanoarchitectures. Porosities of the resultant films will be investigated using scanning electron microscopy. Oxidation and reduction potentials, capacities, and electrochemical stabilities will be determined for the ICPs and compared to ICP films prepared using traditional methods. The ICP nanoarchitectures will be tested as working electrodes in two electrode electrochemical capacitors. The proposed work plan includes training of Irvin group members by Velev group members in colloidal assembly techniques.
Self-Assembly Studies of Layered Chalcogenides
Dr. Ben Martin (Texas State), Dr. Olin Velev (NCSU), Dr. Joe Tracy (NCSU) & Dr. Ben Wiley (Duke).
Edge decorated layered chalcogenides will be synthesized using thiol linkage chemistry. Wet chemical techniques will be initially employed to selectively derivatize the edges of metal sulfides with metal ions, and specificity will be confirmed using EDS analysis. The self-assembly of functionalized derivatized colloidal particles will be initially evaluated based on their interactions with superhydrophobic surfaces (Orlin), convective assembly (Orlin), interactions in electric fields (Wiley), and interactions with nanoparticles, including magnetic particles (Tracy). The structure and properties of biosynthesized metal chalcogenides will be explored in collaboration with Stefan Zauscher. The core/shell structure of magnetic nanoparticles will be evaluated by scanning electron microscopy in collaboration with Joseph Tracy.
Convective Assembly of 2-D Nanosheets
Dr. Luyi Sun (Texas State), Dr. Gary Beall (Texas State) & Dr. Orlin Velev, NCSU). Convective assembly is arguably one of the simplest methods for the creation of ordered structures. It has been used with success to make two-dimensional and three-dimensional monodisperse and binary colloidal structures, and even to make hetero-structures. In the convective assembly scheme, a colloidal crystal is formed through the evaporation of suspension solvent. The evaporation process causes suspended particles to flow through the liquid to the drying edge, where they assemble. Convective assembly of nanoparticles has been well investigated, but much less work on the convective assembly of 2-D nanosheets has been explored. Considering the vast majority work on convective assembly is to form 2-D structure, using nanosheets would bring advantage in terms to formation process and the property of the formed structure. I plan to work with Dr. Orlin Velev to conduct convective assembly of 2-D nanosheets, including α-zirconium phosphate, layered double hydroxides, montmorillonite. The focus will be on the correlation among the nanosheet structure and surface functionality, assembly process, and the property of the formed 2-D structure.
Dispersion and Assembly of 2-D Nanosheets and 1-D Nanowires
Dr. Luyi Sun & Dr. Ben Wiley (Duke). My group has been working on the 2-D nanosheets assisted dispersion of 0-D nanoparticles. We have found that charged 2-D nanosheets can effectively facilitate the dispersion of 0-D nanoparticles, which in turn helps the assembly of 0-D nanoparticles at the later step. Dr. Ben Wiley has been working on the assembly of 1-D nanowires to fabricate various devices. How to disperse and align such 1-D nanowires has been a challenge. I plan to work with him to use our charged 2-D nanosheets to facilitate the 1-D nanowire dispersion and assembly on both even and uneven surface. It is hoped that the charged 2-D sheets can be better manipulated under external force, and their presence may bring additional advantage for certain applications where 1-D nanowires should be separated.
Mechanistic Basis for Ligand-Regulated Control of Protein Self-Assembly Into Fibril Nanostructures
Dr. Steve Whitten (Texas State) & Dr. Yara Yingling (NCSU). (Whitten-TxState, Yingling-NCSU). Self-assembly of the prion protein into ordered nanofibrils can be trigger by interactions with small cyclic peptides that have the sequence cyclo-CGGKFAKFGGC. A similar peptide with the sequence of cyclo-CGKFAKFGC, however, has been observed to block fibril conversion of monomeric prion protein. To better understand these opposite results, for almost identical peptides, molecular dynamic simulations will be performed to investigate the structural origins to ligand-regulated control of the self-assembly process. Initial simulations will focus on the solution character of cyclo-CGGKFAKFGGC and cyclo-CGKFAKFGC in the absence of binding interaction with the prion protein. Subsequent studies will focus on simulations of binding between the prion protein and both peptides. The proposed simulations will be carried out at both the Texas State PREM and the MRSEC partner NCSU.