Presentation on theme: "* ǂ Self-assembly driven liquid crystals Collaborators Existing: Vicente, Zhang, Negulescu, Daly, Nesterov, F. Hung (ChE), Z. Liu (RNR), Q. Wu (RNR) Existing:"— Presentation transcript:
* ǂ Self-assembly driven liquid crystals Collaborators Existing: Vicente, Zhang, Negulescu, Daly, Nesterov, F. Hung (ChE), Z. Liu (RNR), Q. Wu (RNR) Existing: Vicente, Zhang, Negulescu, Daly, Nesterov, F. Hung (ChE), Z. Liu (RNR), Q. Wu (RNR)
Janus fuzzballs Janus was the Roman god of gates, doors, doorways, beginnings, endings and time. He had two faces, sometimes different, looking in both directions. The idea here is to make a submicron particle which has one side coated with polypeptide and the other side coated with something else, or uncoated at all. We think these particles will be good for applications like controlled surface chemistry (hydrophobic or hydrophilic, switchable) or capture/delivery of chiral molecules. For example, the polypeptide face could be oriented to capture a chiral molecule from solution and then spun around to deliver it into a different phase. The closest we have come to making a Janus fuzzball was the work of Erick Soto-Cantu, who managed to get one side of a silica particle coated with gold and the other coated with silica. Placement of an azide coupling agent on the silica side followed by click reaction with an alkyne-initiated polypeptide should produce the desired particle. Currently investigated by Cornelia Rosu of Romania ReturnReturn to Home Janus car!
Magnachain Some fuzzballs are equipped with a superparamagnetic* nougat. This enables them to exhibit magnetism but only in the presence of an applied field. So….when a magnetic field is applied, each particle develops a “north” and a “south” pole. These are attracted to each other, resulting in chains. Applications of this include viscosity modification (magnetorheological effect, found in shock absorbers in expensive luxury and sports cars) and optical polishing (long story). Our interest is trying to link the fuzzballs together once they are aligned. Then, taking advantage of the ability of polypeptides to expand and contract in response to temperature and pressure (and maybe one day light) we hope to expand and contract the chain, like muscle. Currently investigated by Cornelia Rosu of Romania ReturnReturn to Home
Saturn colloids The idea here is to make polypeptides that stick up in a ring around the middle of some colloid. Other groups achieve this behavior by placing polymer-coated colloids in liquid crystals. Our goal is to chain the colloids magnetically, then coat them with polypeptides. The surfaces where the colloids touch cannot get as much polypeptide as other surfaces. We also call this the “Friar Tuck” hairstyle, for obvious reasons: bald surrounded by tufts of “hair.” This project is related to Cowlick.Cowlick Currently investigated by Cornelia Rosu of Romania ReturnReturn to Home Friar Tuck
Cowlick It is a mathematical fact that hair on a sphere has to collect someplace. This leads to whorls (at right) but the most famous consequence is Alfalfa (above) from Little Rascals. Our goal is to chain the colloids magnetically, then coat them with polypeptides. The surfaces where the colloids touch cannot get as much polypeptide as other surfaces. We also call this the “Friar Tuck” hairstyle, for obvious reasons: bald surrounded by tufts of “hair.” This project is related to Saturn.Saturn Currently investigated by Cornelia Rosu of Romania ReturnReturn to Home Whorl 4theycallmemommy.blogspot.com
Polycolloid The idea here is to make polymers using colloidal-sized particles as monomers. These entities will be directly visible in an optical microscope, permitting dynamics experiments by particle tracking and maybe even manipulation into other superstructures. These might find utility in microfluidics devices— for example, as plugs or valves. Other groups around the world also make poly(colloids) as sensors of magnetic fields or originators of ciliary flow. Our approach is different, though: we hope to make particles of a highly precise length by taking advantage of photochemical linking in a patterned field. Currently investigated by Cornelia Rosu of Romania ReturnReturn to Home 4theycallmemommy.blogspot.com
Aerocrystals How light can an object be and still retain crystalline structure? We aim to find out by crosslinking aligned polymer liquid crystals, then removing the solvent without altering the structure. Such materials can serve as directed gas transport, artificial nose, and maybe hydrogen storage/delivery. Currently investigated by Wayne Huberty of Wisconsin ReturnReturn to Home 4theycallmemommy.blogspot.com
Polyelectrolyte dynamics Polymers that carry charge pose some of the most difficult questions in chemistry. For example, how can you even hold two charges very close together along a polymer chain? The energy of repulsion is quite large! Even more amazing, entire polymer chains with a net charge of, say, 1000 may actually attract each other in solution! Some people think this bears on origin of life issues. We are using dynamic light scattering, pattern fluorescence photobleaching and holographic grating photobleaching to investigate the lifetime of such transient aggregates. Currently investigated by Wayne Huberty of Wisconsin ReturnReturn to Home 4theycallmemommy.blogspot.com
Self-assembled Liquid Crystals Can small molecules trick large ones into forming a liquid crystal? The idea here is to assemble some molecules (see Stackers) into rods, raising the overall rod content of the system to beyond the lyotropic liquid crystalline transition point. Currently investigated by Wayne Huberty of Wisconsin ReturnReturn to Home 4theycallmemommy.blogspot.com
PEGL Rodlike polymers make very strong fibers, optical devices, and viscous solutions or gels. Rodlike polymers are often used in nature, too. From a fundamental point of view, rods pose very special problems. Most of them do not dissolve easily, and neither are they monodisperse (same size in a given sample). PEGL is a special polymer for our studies of rodlike polymer behavior. It has to be synthesized in the lab, and then a dye is placed on it. This will permit us to study transport, such as diffusion and viscosity in liquid crystalline phases. The information will be used to compute important questions for all rods, such as: How fast can they be made to dissolve? Can they be “tricked” into forming liquid crystalline phases by self- assembling small molecules? At right: PEGL synthetic scheme. PEGL Cholesteric liquid crystal and newly discovered microcrystals Currently investigated by Wayne Huberty of Wisconsin ReturnReturn to Home 4theycallmemommy.blogspot.com
Responsive Many groups around the world are making responsive colloids. Applications include such things as temperature or pH sensing, drug delivery, and laser hardening (optical changes in an intense field). The chemistry often is centered on N-isopropylacrylamide either as a microgel particle or this same polymer coated on some other colloid. Almost always, the transitions are observed in water. We endeavored to see if the sharp helix-to-coil transitions of polypeptides could exhibit transitions on a colloidal shell, especially in an organic solvent where the strong electrolyte effects available in water are absent. Currently investigated by Cornelia Rosu of Romania ReturnReturn to Home 4theycallmemommy.blogspot.com Pioneered by Sibel Turksen of Turkey (now at Horizon in Indianapolis).
Jamming Currently studied by Melissa Collins of Louisiana This is one of our most intricate and subtle projects. When particles bearing surface groups that can be extended rods but which can also be floppy random coils are jammed together by magnetic attraction, will the polymers choose the rodlike conformation in order to form “local liquid crystals” at the interfaces? If so, then we have coupled a magnetic field to a molecular (and optical) transformation. The very notion of a local liquid crystal was motivated by the observation of former student Jianhong Qiu that particles jammed together in good solvents for the shell polymers remained stuck to each other, while selecting a poor solvent for the shell resulted only in transient adhesion of the chained assembly of particles. The hypothesis that a local liquid crystal is involved is tested with small-and wide-angle X-ray scattering. The overall stability of the polypeptide-coated particles is being developed, too—for example, by dynamic light scattering measurements at modest concentrations. ReturnReturn to Home
Probe Diffusion/Microrheology Currently studied by Melissa Collins of Louisiana Did you ever wonder what it would be like to ride around on a molecule? How do particles see polymers in solution. We don’t know, but it’s really important because all sorts of particles from paints to proteins are dispersed with polymers. Suppose they are carrying drugs, trying to deliver them to the inside of a cell. How fast will they be able to go? Or, suppose you are trying to measure the viscosity of fluid inside a living cell, or the viscosity of supercritical CO 2 (considered a “green” solvent compared to some organic liqiuds, despite release of CO 2 to the atmosphere after evaporation). Well, you can just measure the speed of diffusion of some probe particle through the solution and back out the viscosity. Current research focuses on using polypeptide-coated spheres, whose surface can be altered. For example, can we have a particle diffuse around inside a living system, then undergo helix-to-coil transition to “latch onto” materials in the cell? We use dynamic light scattering and other methods to measure the probe speed. ReturnReturn to Home
Stackers Stackers are molecules that lay on top of each other to make a very long fiber. We study two basic kinds: porphyrins (with help from Prof. Vicente) and arborols. Both have a molecular weight of about 1000 g/mol—pretty small by our standards. The porphyrins are macrocycles, while the arborols assume the shape of a dumb-bell. The porphyrins can capture light. One of their main uses is photodynamic therapy—shine a light on them to release a drug. The arborols make great model systems for amyloid fibrils; we also hope to use them to force a solution containing rodlike polymers to switch into a liquid crystalline phase. This would let polymer liquid crystals perform certain sensing and possibly display applications. Multiple methods are used to understand Stackers. At right, results from small-angle X-ray scattering and cryo-transmission electron microscopy. Currently studied by Javoris Hollingsworth of Georgia ReturnReturn to Home and ChE undergrad Mohammed Abu Laban
The protein Cerato ulmin is one of nature’s most powerful surfactants. Produced by fungi, cerato ulmin and related proteins have been in the oceans for eons. Cerato ulmin rod-shaped bubbles. Elm afflicted with Dutch elm disease Tree: Oil-filled bubble can be moved using optical tweezers. Model of a comparable protein; note green hydrophobic and gray hydrophilic regimes. Mostly known for its toxicity to elm trees, yet safe to animals, cerato ulmin encapsulates air and oil in unusual cylindrical structures having remarkable stability. Very small quantities are required. Hydrophobins ReturnReturn to Home