Stefan Diez Max-Planck-Institute of Molecular Cell Biology and Genetics
Banahalli R. Ratna Naval Research Laboratory
J. Fraser Stoddart University of California-Los Angeles
Linda Turner Rowland Institute at Harvard
Air Force Office of Scientific Research
AA1: Polymeric Actuators
Wednesday PM, April 19, 2006
Room 3016 (Moscone West)
2:30 PM - **AA1.1
Photoresponsive Smectic LC-polymers and -elastomers.
Rudolf Zentel 1 , Patrick Beyer 1 , Ralf Stannarius 2 Show Abstract
1 Chemistry, University Mainz, Mainz Germany, 2 Physics, Univ. of Magdeburg, Magdeburg Germany
LC-elastomers combine LC-phases and the resulting anisotropic properties with the mechanical properties of a soft rubbery solid. They are presently finding an increasing interest as actuators. Generally size changes are found at phase transition temperatures, especially at the transition from the LC to the isotropic phase. To improve these properties two aspects have to be optimized: 1.The anisotropy of the radius of gyration of the polymer chains in the LC-phase, which is the precondition for the size change at the phase transition, should be as large as possible. In this respect smectic phases are attractive, because they usually possess a larger anisotropy of the polymer chains compared to nematic phases. 2.An isothermal shift of the phase transition temperature by an external stimulus is more desirable than a temperature variation. In this respect photochromic dyes, which destabilize the LC-phase during isomerization are attractive.We work on synthetic concepts to prepare smectic LC-polymers and -elastomers of different main chain topology, i.e. on smectic side-chain polymers (polysiloxanes) and on combined polymers (polyesters), which possess mesogens both in the main chain and as side groups.Concerning side chain LC-elastomers  we succeeded in the synthesis of azo containing polysiloxanes with broad smectic C* and A phases. In these polymers the spontaneous polarization can be altered reversibly by irradiation with UV (cis) or VIS (trans) light. Depending on the amount of azo-dye a shift of the phase transition temperatures by up to 17°C could be detected. It is possible to photo-crosslink these films into an LC-elastomer without disturbing its monodomain structure. To measure the mechanical properties we work with thin elastomer films in the form of bubbles  and free standing films . Temperature dependent measurements on elastomer bubbles (LC-elastomer balloons ) allow a sensitive measurement of the elasticity. Stretching of free standing films allows it to investigate the deformation. In this way it was possible to show that the thickness in the direction parallel to the smectic layer normal of the smectic elastomer films get thinner during stretching. This is different from the behavior claimed by Finkelmann for similar, but not identical systems . X-ray measurements show that the mechanical stress during stretching is strong enough to change the smectic layer thickness. It gets thinner in proportionality with the macroscopic thickness.Reference: P. Beyer, R. Zentel, Macromol. Rapid Commun. 26, 874 – 879 (2005) H. Schüring, R. Stannarius, C. Tolksdorf, R. Zentel, Macromolecules 34, 3962 -3972 (2001);R. Stannarius, H. Schüring, C. Tolksdorf, R. Zentel, Mol. Cryst. Liq. Cryst. 364, 305 - 312 (2001) Y. Aksenov, J. Bläsing, R. Stannarius, M. Rössle, R. Zentel, Liq. Cryst. 32, 805 -813 (2005)
3:00 PM - **AA1.2
Breaking the Nanometer Barrier in Single-Molecule Studies
Steven Block 1 2 Show Abstract
1 Biological Sciences, Stanford University, Stanford, California, United States, 2 Applied Physics, Stanford, Stanford, California, United States
3:30 PM - AA1.3
Thermo-Mechanical Modeling of Shape Memory Polymers
Hang Qi 1 , Chris Yakacki 1 , Robin Shandas 1 , Ken Gall 2 Show Abstract
1 Department of Mechanical Engineering, University of Colorado, Boulder, Colorado, United States, 2 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Shape memory polymers (SMP) are a group of polymers that are capable of recovering a predetermined shape after significant mechanical deformations. Typically, a SMP can be pre-deformed from an initial shape to a deformed shape by applying an external mechanical load at temperature Td. A subsequently lowering down the temperature to Ts will maintain this deformed shape after the external mechanical load is removed. The shape memory effect is then activated by increasing the temperature to Tr, where the initial shape is recovered. In general, Td and Tr are in the vicinity of the glassy transition temperature Tg, whilst Ts is below Tg. Recent advances in material science make it possible to vary the Tg by controlling chemistry or structure of SMP for a variety of applications, such as SMP based medical devices and microsystem actuation components. In these applications, it is highly desirable that the deformation history of SMP can be predicted and the recovery properties can be optimized. This, in turn, requires finite deformation constitutive models that capture the thermo-mechanical response of SMP polymers based on the fundamental understanding of structure-function relationships. In this paper, a three-dimensional constitutive model that describes the thermo-mechanical response of shape memory polymers is proposed. The model is based on the finite deformation theory and fundamental understanding of the structure-function relationship of SMP. Previous studies on SMP have revealed the shape memory mechanism of being due to the transition of portions of a polymer from a state dominated by entropic energy to a state dominated by internal energy as temperature decreases. In the proposed model, such a transition is described based on the finite deformation theory and is captured through an internal variable which evolves with the history of temperature variations. Numerical simulations of a series of thermo-mechanical tests verify the efficiency of the model. This model will serve as a modeling tool to consider more complicated SMP based devices.
3:45 PM - AA1.4
Electric Field Actuation of a Liquid Sulfonate Polymer
Holly Ricks-Laskoski 1 , Arthur Snow 1 Show Abstract
1 Chemistry Division, Naval Research Laboratory, Washington, District of Columbia, United States
Continual exploration into new ionic polymers is very important in the development of electro-active materials for use in space systems, biomedical applications, and robotics. After reviewing previous reports and outlining drawbacks of known electro-active ionic polymers such as hydrogel systems, we have synthesized and fully characterized a non-aqueous AMPS (2-Acrylamido-2-methyl-1-propanesulfonic acid)-derivatized homopolymer. This new liquefied ammonium salt polymer consists of two components desired for their ionic nature, low volatility, Tg depression, and ease of polymerization. Using the crystalline AMPS monomer as the ionic component and oxyethylene substituted amine as the mobile ion, a liquid AMPS monomer salt was produced. This monomer salt maybe bulk polymerized yielding stable electric field actuated material. In this presentation we describe the synthesis, characterization, and actuation of a new liquefied polymer salt.
4:00 PM - AA1: PolAct
4:30 PM - AA1.5
Storm in a Raindrop: Creating Micro-tornadoes in a Sol-gel Synthesis.
C. Prendergast 1 , A. McMahon 1 , A. Doyle 1 Show Abstract
1 Advanced Materials Group, Dalton Research Institute, Manchester Metropolitan University, Chester St., Manchester, M1 5GD United Kingdom
In the search for materials systems where molecular recognition is controllable, an exciting new phenomenon has been recorded on film under a cross-polarised optical microscope for the very first time. The synthesis of mesoporous silica by sol-gel mineralization of cellulose nanorod nematic suspensions has been studied in the past (E. Dujardin 2003), but the reaction under a magnetic field has never been investigated. The presence of a thermal gradient in a fluid mixture induces a relative matter flow of the components and is known as the Ludwig-Soret effect. (R. Piazza 2002) Cellulose microcrystals are helical in nature and align under a magnetic field (J. F. Revol 1994). By applying a magnetic field in the region of 50 mT to the cellulose suspension, a novel spectacle is observed. The effect displayed is confined within a microdrop and is similar to a Tornado vortice as it rotates at high speeds moving erratically around the drop. Like a contained storm system, a combination of factors governs the resultant rotations. The helicity of the ionic cellulose, together with the reacting of the pre-hydrolysed silanol solution evolving gases is not enough to explain the high speed rotation, neither is the presence of a thermal gradient in the fluid. The aim of this paper is to report the phenomenon and to propose hypotheses as to what is actually occurring and harness this new discovery. With further research and development, this micro-tornado could be developed into a new generation of chemical motor.E. Dujardin, M. B., S. Mann (2003). "The synthesis of mesoporous silica by sol-gel mineralization of cellulose nanorod nematic suspensions." J. Mater. Chem 13: 696-699.J. F. Revol, X. M. D., D.G. Gray, H. Chanzy, G. Maret (1994). "Chiral nematic suspensions of cellulose crystallites; Phase separation and magnetic field." Liquid Crystal 16: 127.R. Piazza, A. G. (2002). "Soret effect in interacting micellar solutions." Physical Review Letters 88: 208302.
4:45 PM - **AA1.6
Biomimetic Design of Modular Multi-domain Polymers as Advanced Biomaterials
Zhibin Guan 1 , Jason Roland 1 , Dora Guzman 1 , Aaron Kushner 1 Show Abstract
1 Department of Chemistry, University of California, Irvine, Irvine, California, United States
Nature had evolved well-defined materials with exceptional properties by using elegant molecular mechanisms not observed in man-made materials. The giant muscle protein titin attracts a lot attention recently because of their unique modular structure which affords a combination of mechanical strength, toughness, and elasticity. Single molecule nanomechanical studies on titin suggest that these exceptional properties arise from a modular elongation mechanism. The sequential unfolding allows modular biopolymers to sustain a large force over the whole extension of the chain, which makes the polymer strong, along with a large area under the force-extension curve, making it tough as well. In addition, when the external force is removed, the unfolded domains of modular proteins will refold automatically, making them elastic. Inspired by nature, one research effort in my group is aimed at designing synthetic macromolecules that form high order structures by programming non-covalent interactions into polymer chain. The goal is to achieve synthetic biomaterials with combined strength, toughness and elasticity. Three classes of well-defined modular polymers have been synthesized in our laboratory: (1) using quadruple hydrogen-bonding motif 2-ureidon-4-pyrimidone (Upy) to direct the formation loops along a polymer chain (J. Am. Chem. Soc. 2004, 126, 2058); (2) using a peptidomimetic beta-sheet based double-closed loop (DCL) as module (J. Am. Chem. Soc. 2004, 126, 14328); and (3) an engineered protein G domain III as module. Single molecule force-extension experiments revealed the sequential unfolding of the loops or domains as these modular polymers are stretched, resulting in sawtooth-patterned curves similar to those seen in titin and other biopolymers. In this talk, we will discuss our designs, syntheses and single-molecule studies of polymers having modular domain structures.
5:15 PM - AA1.7
Constitutive Modeling of Large Deformation Behavior of Thermo-Responsive Hydrogels
Kristofer Westbrook 1 , Hang Qi 1 Show Abstract
1 Department of Mechanical Engineering, University of Colorado, Boulder, Colorado, United States
Hydrogels are a group of crosslinking polymers that are hydrophilic and highly water-swollen while maintaining their structure especially under finite deformations. In a hydrogel, a three-dimensional network is formed by crosslinking macromolecular chains through covalent bonds, hydrogen bonds, van der Waals interactions, or simply physical entanglements. Under the change of certain environmental conditions, some of which are found in the body, such as temperature, pH value, and electric signals, hydrogels can experience an abrupt volume change and hence hold or release a large amount of water. Because of their unique capability to achieve a large yet reversible volume change without any external mechanical interactions, hydrogels have been widely used in biomedical applications, such as hydrogel sensors, novel drug delivery systems, and novel scaffolding materials. In order to precisely control volume change and deformation behaviors of hydrogels under physiological conditions in biomedical applications, it is highly desirable to develop a large deformation constitutive model that can accurately describe the thermo-mechanical response of hydrogels during the variation of environmental conditions, such as temperature.In this paper, a physics-based large deformation constitutive model that determines responses of thermo-responsive hydrogels upon environmental temperature changes is proposed. The hybrid model of Arruda-Boyce 8-chain model for hyperelasticity and Flory-Erman constraint model is used as a starting point to capture the large deformation stress-strain behavior of hydrogels under equilibrium swelling ratio. The equilibrium swelling ratio is then employed as an internal variable which depends on the temperature and is determined through evolution equations. Two examples of prevailing drug delivery design and scaffolding system are studied to illustrate the predictability and efficacy of the model.
5:30 PM - **AA1.8
Solvent Vapor Induced Shape Changes in Liquid Crystal Elastomers
Peter Palffy-Muhoray 1 , Tibor Toth-Katona 1 , Michael Shelley 2 Show Abstract
1 Liquid Crystal Institute, Kent State University, Kent, Ohio, United States, 2 Courant Institute , New York University, New York, New York, United States
Liquid crystal elastomers (LCEs) are exceptionally responsive materials due to the coupling between orientational order and mechanical strain. Mechanical deformations change the orientational order, and hence alter the optical and dielectric properties of these materials. Perhaps more interestingly, changes in orientational order can give rise to mechanical deformations. Orientational order can be changed by a wide variety of excitations, such as heat and light, as well as electric, magnetic and chemical concentration fields. We have studied the dynamics of shape changes in LCE samples due to exposure to organic solvent vapors. Unlike isotropic elastomers, which simply swell, LCEs show dramatic anisotropic shape changes when exposed to solvent vapors due to resulting changes in orientational order. We present results for the excitation and relaxation dynamics of shape changes for a variety of isotropic elastomers and LCEs in the presence of different solvent vapors. Experiments suggest that the absorption of solvent vapor can cause a nematic-paranematic phase transition. We consider potential applications, such as chemical sensors, switches and motors. We conclude by outlining one approach to modelling binary LCE-solvent systems.
Stefan Diez Max-Planck-Institute of Molecular Cell Biology and Genetics
Banahalli R. Ratna Naval Research Laboratory
J. Fraser Stoddart University of California-Los Angeles
Linda Turner Rowland Institute at Harvard
AA2: From Single Molecules to Bio-Hybrid Systems
Thursday AM, April 20, 2006
Room 2007 (Moscone West)
10:00 AM - AA2.1
Materials Development by Hierarchical Self-assembly of Tobacco Mosaic Viruses.
Zhongwei Niu 1 , Su Long 1 , Venkata Kotakadi 1 , Michael Bruckman 1 , Jinbo He 2 , Lin Yang 3 , Pappannan Thiyagarajan 4 , Yue Zhao 5 , Jiyu Fang 5 , Thomas Russell 2 , Qian Wang 1 Show Abstract
1 Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina, United States, 2 Polymer Science, University of Massachusetts, Amherst, Massachusetts, United States, 3 , Brookhaven National Laboratory, Upton, New York, United States, 4 , Argonne National Laboratory, Argonne, Illinois, United States, 5 Mechanical, Materials and Aerospace Engineering, University of Central Florida, Orlando, Florida, United States
The generation of nano materials with hierarchical ordered structure is the basis for the development of novel optical, electronic, acoustic and magnetic materials. Plant viruses can be considered as nature nanoparticles that can be tailored chemically and genetically. Compared with the inorganic nanoparticles, the uniform shape and size of viruses provide highly promising possibilities in self-assembly study for the construction of nanoscale materials with hierarchical ordering. Herein, we report the controlled 1D, 2D and 3D self-assemblies of rod-like tobacco mosaic virus (TMV). In addition, TMV templated nanocomposites with silica and other polymers can be prepared based on the virus self-assembly along with polymerization or sol-gel process. For example, functional nanofibers were synthesized by the one-dimensional assembly of TMV and sequential polymerization. Two-dimensional ordered films were produced using interfacial assembly of TMV. Finally, three-dimensional ordered composite materials were prepared by combination of sol-gel process and in situ TMV.
10:15 AM - AA2.2
Micro-hydraulic Actuation using Biological Ion Transporters Reconstituted on Artificial BLM.
Vishnu Baba Sundaresan 1 , Donald Leo 1 Show Abstract
1 Mechanical Engineering Department, Virginia Tech, Blacksburg, Virginia, United States
Plants and animals have the natural ability to exhibit force through controlled pressurization of cellular compartments. The mechanism through which force is generated is powered by biological fuels. The process involves pushing ions against an established concentration gradient expending free energy from bio-fuels like Adenosine-tri-phosphate (ATP), kinesin etc., Materials inspired from the mechanism used by plants do mechanical work are called Nastic materials. This abstract details our efforts in developing a micro-hydraulic actuator inspired by plants. Energetics analysis done by Leo et. al (Proceedings of IMECE-2004, Anaheim, CA) showed that it is possible to develop actuators with energy density of 100 kJ/m^3 using biological fuels. This analysis used a three dimensional arrangement of capsules on a substrate to form an Organized Microcapsule Array. A proof of concept micro-hydraulic actuator uses the same concept for actuation on a planar bilayer lipid membrane. The ion transporters are reconstituted on the planer lipid membrane and pump ions into an enclosed cavity. A thermodynamic constitutive model was developed for the chemo-mechanical actuation of the actuator for a pH4.0/pH7.0 gradient. Parametric analysis demonstrated the ability to generate 5% strain by Sundaresan et. al (SPIE Smart structures conference, San Diego, 2005). Controlled fluid transport through AtSUT4 reconstituted on a 1-Palmitoyl-2-Oleoyl-sn-Glycero-3- [Phospho-L-Serine] (Sodium Salt) (POPS), 1-Palmitoyl-2-Oleoyl-sn-Glycero- 3-Phosphoethanolamine (POPE) BLM on lead silicate glass plate having an array of 50 um holes driven by proton gradient was demonstrated by Sundaresan et al (Proceedings of IMECE-2005). AtSUT4 (H+-sucrose co-transporter from Arabidopsis thaliana) proteins were made available suspended in pH7.0 medium (16.6 mg/ml) for our experiments from our collaborator in the Medical School at University of Cincinnati. Bulk fluid flux of 1.2 μl/min was observed for each μl of SUT4 transporter protein mix reconstituted on the BLM for a pH4.0 - pH7.0 gradient. We have fabricated a prototype device made of photo curable polypropylene glycol with two chambers kept separated by a polycarbonate membrane. The porous polycarbonate serves as a substrate to house the bilayer lipid membrane with the ion transporters. The chambers measure 5 mm in diameter and is 4 mm deep. The bottom chamber is fed by a reservoir. The top chamber is covered with a 2.5 micron thick Mylar membrane that deforms due to influx of ions from the bottom chamber through the reconstituted ion transporter. The deformation on Mylar due to the applied pH gradient is measured using a Polytec laser vibrometer. We will be presenting our experimental result to demonstrate strain in the current actuator configuration and compare the result with the constitutive model that estimates the deformation for the applied chemical energy.
10:30 AM - AA2.3
Assemble GaN Nanocrystals with M13 bacteriophages
Jifa Qi 1 , Soo-Kwan Lee 1 , Jennifer Hsieh 1 , Louise Giam 1 , Angela Belcher 1 Show Abstract
1 DMSE, MIT, Cambridge, Massachusetts, United States
GaN and the related III–V nitride compound semiconductors have attracted intense attention due to their successes in commercial production of blue/green light emitting diodes, lasers, and other optoelectronic devices. We recently reported a solution phase synthesis approach to the colloidal GaN nanocrystals. The GaN nanocrystals that can be suspended in water and organic solvent enable manipulation and assembling the nanocrystals through self-assemble process in the solution. It is known that many applications of the bottom-up nano-systems largely depend on controlling the placement of nano-building blocks into order array or other nano-architectures. Biological systems often possess highly specific recognition capabilities and can exert rational control over inorganic material nucleation, phase stabilization, assembly, and pattern formation. In previous works, we have demonstrated that engineered viruses can recognize specific semiconductor surfaces through the method of selection by combinatorial phage display. These specific recognition properties of the virus provide a way for self-assembling the nanocrystal materials, semiconductor, metal or insulator, into a three-dimensional ordered film structures, or the templates to nucleate or bind desired materials on surfaces to form phage-inorganic nanowires and single crystalline nanowires. In this work, we extended this technology to the GaN nanomaterials to forming the new bio-inorganic hybrid functional materials that does not exist naturally. We have isolated both the pIII and pVIII type binding motifs capable of specific recognition and binding of GaN material through a general biopanning technique by interaction pIII and pVIII type engineered M13 bacteriophage library with GaN. The type III and VIII engineered M13 bacteriophage served as the vehicles to bind GaN nanocrystal self-assembling them into three-dimensional ordered structures of self-support film, or templates of assembling GaN into one-dimensional nanowires. These novel bio-inorganic hybrid materials exhibit bright photoluminescence in ultraviolet-blue wavelength region which may find potential applications in light emitting device, biosensors and other optoelectronic devices.
10:45 AM - AA2.4
Can Photosnythesis Help In The Design On Dye-Sensitised Solar Cells: Concepts From Bacterial Photosynthesis?
Richard Cogdell 1 Show Abstract
1 Biochem. and Mole. Biol., Univ. of Glasgow, Glasgow United Kingdom
11:00 AM - AA2: BioMolSys
11:30 AM - AA2.5
Toward Bio-inspired Photovoltaic Devices.
Hongjun Liang 1 , Chi Nguyen 1 , Gregg Whited 2 , Galen Stucky 1 Show Abstract
1 , UCSB, Santa Barbara, California, United States, 2 , Genencor International, Palo Alto, California, United States
11:45 AM - AA2.6
Reflex-arc on a Chip: An In Silico Cell Culture Analogue.
Kerry Wilson 1 , Peter Molnar 1 , Mainak Das 1 , James Hickman 1 Show Abstract
1 Nanoscience Technology Center, University of Central Florida, Orlando, Florida, United States
12:00 PM - AA2.7
Mechanically Coupled Carbon Nanotubes as Integrated NEMS Devices.
Moneesh Upmanyu 1 , Haiyi Liang 1 Show Abstract
1 Engineering Division, Materials Science Program, Colorado School of Mines, Golden, Colorado, United States
The structural integrity of carbon nanotubes (CNTs) combined with attendant electro-/thermo-/optico-mechanical couplings have driven the development of novel classes of nanelectromechanical systems (NEMS) such as switches, actuators, resonance oscillators, springs and nanomotors. In almost all cases, device operation entails electrostatic actuation of appropriately patterned CNTs. Here, we show that chirality and curvature induced intrinsic mechanico-mechanical couplings, specifically between axial and torsional strains in single-walled carbon nanotubes, can be quite substantial. Electro-/thermo-/optico-mechanical actuation of axial strain induced torsion (a-SIT) and associated transitions in their electromagnetic properties can completely eliminate the need for electrostatic actuation, a significant step forward towards fabrication of novel class of integrated, robust, tunable and high quality NT- and nanowire-based nanosystems and devices.
12:15 PM - AA2.8
Ferroelectric-specific Peptides as Building Blocks for Bio-inorganic Devices.
Brian Reiss 1 2 , Guo-Ren Bai 1 , Orlando Auciello 1 , Leonidas Ocola 2 , Millicent Firestone 1 2 Show Abstract
1 Materials Science, Argonne National Laboratory, Argonne, Illinois, United States, 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Combinatorial phage display methods have been used to identify a circularly constrained heptapeptide sequence, ISLLHST, that strongly associates with a perovskite ferroelectric, lead zirconium titanate, Pb(ZrxTi1-x)O3 (PZT). The affinity and selectively of binding to polycrystalline MOCVD deposited PZT thin films supported on Si/SiO2/Pt substrates were determined by titering and immunofluorescence microscopy, and the peptide was shown to selectively bind PZT in the presence of Pt, Si, Au, and several different photoresists. Ferroelectric properties were determined by measurement of the P-E hysteresis loop on unmodified and phage bound PZT thin films, and no change in the coercive field, Ec, or the saturation polarization, Ps was observed after contacting the PZT with aqueous buffer or phage binding. This work represents an important first step towards rendering perovskite ferroelectrics compatible with biological molecules. Work is currently underway to study how conformational and positional control of tethered biomolecules can be controlled by the surface charge and/or polarization state of PZT as well as integration into several proto-type device architectures.
AA3: Biological Motors in Engineered Systems
Linda Turner Stern
Thursday PM, April 20, 2006
Room 2007 (Moscone West)
2:30 PM - **AA3.1
From Molecular Robotics to Active Self-assembly: Biomolecular Motors do the Job.
Henry Hess 1 Show Abstract
1 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States
Biomolecular motors, such as the motor protein kinesin, convert the chemical energy stored in adenosine triphosphate with high efficiency into mechanical work. Their nanoscale dimensions and independence from external connections enables them to act as independent agents in a liquid environment, capable of performing a variety of tasks in nanotechnology, such as directed transport or active assembly and disassembly. The integration of such nanoengines into nanodevices and multifunctional materials raises a host of intriguing engineering questions, some related to the biological origin of the motors and others of general relevance to the field of molecular motors. One example is the balance between external control and self-organization in these multi-agent systems. Other questions are related to the achievable gains in required energy, the limits of power density, or the prediction of device and material characteristics. Finally, fundamental research has to be complemented by directed work towards applications. Our increasing experience with the integration of biomolecular motors into synthetic devices and the expanding knowledge about the biological functions of motor proteins sharpen the focus on the uniqueness and feasibility of application ideas related to, for example, biosensors and advanced materials.
3:00 PM - **AA3.2
Actuators and Polymers: Understanding Active and Dynamic Assembly Processes.
George Bachand 1 , Marlene Bachand 1 , Amanda Carroll-Portillo 1 , Amanda Trent 1 , Erik Spoerke 2 , Matthew Farrow 1 , Bruce Bunker 1 Show Abstract
1 Biomolecular Interfaces & Systems, Sandia National Laboratories, Albuquerque, New Mexico, United States, 2 Electronic & Nanostructured Materials, Sandia National Laboratories, Albuquerque, New Mexico, United States
3:30 PM - AA3.3
Biotemplated Generation of Motor Protein Nanotracks for the Directed Motion of Microtubule Transporters.
Cordula Reuther 1 , Robert Tucker 2 , Stefan Diez 1 Show Abstract
1 , Max Planck Institute of Molecular Cell Biology and Genetics, Dresden Germany, 2 , University of Florida, Gainsville, Florida, United States
Biological machines have recently found an increasing number of applications in hybrid bionanodevices, where they fulfill tasks of biomolecular transport and manipulation in engineered environments. For example, microtubule-based gliding motility assays have been used to transport micro- and nanometer-sized objects, such as small beads, quantum dots and DNA molecules. Spatial control of motility is a crucial criterion for the successful implementation of these nanoscale transport systems. So far, a combination of topographic channels with selective surface chemistry has proven to yield the most efficient guiding. However, the fabrication of such structures is labour-intensive and costly. Moreover, if the channels are narrower than the cargo diameter that approach might pose a problem for cargo transport. Recent attempts to achieve reliable guiding with chemical surface modifications only (structural width in the range of microns) have been unsuccessful due to the walk-off of microtubules when reaching the boundaries with large approach angles. Here, we present a method to deposit submicrometer-wide tracks of motor proteins (nanotracks) on unstructured surfaces. Specifically, we use microtubules themselves as biological templates for the stamping and alignment of motor proteins. Compared to other soft lithography techniques like microcontact printing our approach circumvents protein denaturation due to drying and conformational changes caused by mechanical stress. Given the large persistence length of microtubules their encounters with the boundaries of our nanotracks are limited to shallow approach angles. This way, the generated structures prove very efficient for the guiding of microtubules without topographical barriers. Furthermore, our assay comprises a novel means to study biologically relevant mechanical functions (such as microtubule-microtubule sliding) in vitro.
3:45 PM - AA3.4
Micromechanical Measurements on Mechano-chemical Proteins.
Stefan Schwan 1 , Andreas Heilmann 1 , Uwe Spohn 1 Show Abstract
1 Biological Materials, Interfaces, Fraunhofer Institut Werkstoffmechanik, Halle (Saale) Germany
Mechanochemical protein aggregates in plants, e.g. the P-protein bodies in phloem cells of legumes (Forisomes ), transform chemical free enthalpy of their reaction with Ca (or Sr, Ba) ions into mechanical work. The thermodynamic cycle process is nearly closed by the extraction of these calcium ions with ethylenediaminetetraacetic acid (EDTA) or nitrilotriacetic acid (NTA). Due to the reaction with Ca(II), the protein aggregates contract by 10 to 40% of its original length and increase their cross sectional area. The switching level of the free Ca(II) ion concentration was approximately 70 µM in air saturated aqueous Tris buffer solutions at pH 7.3. In the absence of oxygen the switching point is shifted to lower concentrations. The switching in oxygen free water is almost reversible. To determine the force generated by the switching Forisom in aqueous solutions the bending of thin glass fibres was measured. The Forisome is bound by chemisorption at the tips of a stator and the bending fibre. In a novel designed laser optical measuring system the bending fibre is used as a light guide. The displacement of the laser beam coming out of the fibre was be detected by a position sensitive detector (PSD). Taking into consideration the elastic modulus of the fibre and the fibre geometry the displacement of the fibre tip can be correlated with the measured static force. The bending fibre is fixed at a micropressor controlled 2D piezoelectric actuator to put the forisom back to its initial length. This technique opens up a way to measure the maximum forces generated by the forisom in liquids in dependence on the Ca(II) ion concentration and the pH value. This set-up allows measurements of static and dynamical forces between 0.1 and 1000 nN along precisely determined geometric vectors. The dependencies of the measured forces on the Ca(II) concentration and the pH value were investigated. By reacting with 10 mM of Ca(II) various Forisomes generate forces between 20 and 150 nN. The maximum mechanical work related to the protein mass is approximately ten times higher than that of the main muscle of a bird wing. The relatively strong forces opens up a new way to construct bioactuators for microfluidic systems. M. Knoblauch, G.N. Noll, T. Mueller, D. Pruefer, I. Schneider-Huether, D. Scharner, A.J.E. van Bel, W. S. Peters; Nature Materials 2 (2003), 600
4:00 PM - AA3: BioMotEng
4:30 PM - **AA3.5
Single Molecule Mechanics and the Myosin Family of Molecular Motors.
James Spudich 1 , David Altman 1 Show Abstract
1 Biochemistry, Stanford University School of Medicine, Stanford, California, United States
5:00 PM - **AA3.6
Engineered, Self-Organizing Living Muscle Actuators
Robert Dennis 1 , Ellen Arruda 2 Show Abstract
1 Biomedical Engineering, UNC - Chapel Hill, Chapel Hill, North Carolina, United States, 2 Mechanical Engineering, University of Michigan, Ann Arbor, Michigan, United States
The use of molecular motors to provide mechanical power for nano- and micro-machines is a concept that is rapidly gaining popularity. There are many interesting and challenging problems related to the use of molecular motors in practical mechanisms of any size. Many of these challenges have been addressed during evolution by living cells and tissues, in particular, issues related to the volumetric efficiency, control, functional adaptation and power transduction between molecular motors and the outside environment. Our research focuses on the development of living muscle tissues as practical mechanical actuators. The size scale for our intended applications is in general in the range of mm to cm, so this would include bio-hybrid micro robotics and hybrid prosthetic devices. We address the fundamental problems of developing and maintaining viable, functional musculoskeletal tissues in an ex vivo culture environment. This leads directly to the two fundamental technical problems in musculoskeletal tissue engineering: (1) the development of functional musculoskeletal tissue interfaces, and (2) the development of integrated bioreactor systems to allow the guided phenotypic development of functional muscle tissue systems ex vivo. We will present our current work on integrated bioreactor system development, and our recent advances in self-organizing musculoskeletal tissues and tissue interfaces.
5:30 PM - **AA3.7
Cytoskeletal Polymerization Motors in Engineered Systems
Marileen Dogterom 1 Show Abstract
1 , FOM Institute for Atomic and Molecular Physics, Amsterdam Netherlands
Dynamic cytoskeletal polymers such as microtubules and actin filaments provide forces for various types of cellular and intracellular motility. To understand how these polymerization motors work we use optical tweezers-based techniques and microfabricated barriers that allow us to study both actin and microtubule force generation at a single polymer level. We can measure force-velocity relations and monitor how the polymer assembly dynamics responds to force, both in the absence and presence of relevant microtubule and actin binding proteins. In addition, we use microfabricated devices to mimic the physical confinement of living cells and study, for example, the role of microtubule-based force generation in the positioning of microtubule organizing centers. In cells, this positioning results from a complex interplay between dynamic, force-generating microtubules, the cell cortex, the cell geometry, and regulatory proteins. In microfabricated chambers, we have previously shown that in simple cases the pushing of the growing microtubules on the chamber walls is enough to center the organizing center. We have now refined this type of experiment by adding specific biochemical activity to the chamber walls. This allows us to study the effect of localized motor proteins and cortical regulatory proteins on microtubule organization and the positioning of microtubule organizing centers.
AA4: Poster Session: Molecular Motors, Nanomachines and Engineered Bio-Hybrid Systems
Friday AM, April 21, 2006
Salons 8-15 (Marriott)
9:00 PM - AA4.1
Computer Simulation of Kinesin-Powered Molecular Shuttle Movements in Microfabricated Patterns.
Takahiro Nitta 1 , Akihito Tanahashi 1 , Motohisa Hirano 1 , Henry Hess 2 Show Abstract
1 Engineering, Gifu University, Gifu Japan, 2 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States
Kinesin-powered molecular shuttles are a biology-inspired transportation system for Lab-on-a-chip devices. Molecular shuttles have been developed from a combination of the kinesin/microtubule gliding in-vitro motility assay and advanced microfabrication techniques. The integrated molecular motors remove the need for pumps or electrodes and enable transport in channels of sub-micrometer width. These features are expected to advance nanofluidics. In pursuit of this transition from microfluidics to nanofluidics, various components of the envisioned Lab-on-a-chip devices, such as cross junctions, T-junctions, concentrators, and rectifiers, have already been constructed and investigated. However, the performance of the devices and components cannot be predicted during the design phase. Computer simulations of molecular shuttle movements in such components will enable us to predict the performance. Here, we present a computer simulation of molecular shuttle movements in such components, based on our previous experimental study (Nitta and Hess, Nano Letters, 2005), and validate the simulation by quantitative comparisons with published experimental results. We proceed to predict the computer simulated motions of molecular shuttles in simple networks of the components. This study will provide a method to predict the performance of Lab-on-a-chip devices integrating active transport by kinesin-powered molecular shuttles and enable their computer-aided design.
9:00 PM - AA4.10
Single Molecule Mechanics for Probing Metal-Mediated Adhesion and Catalyzed Covalent Bond Formation in Mussel Adhesive Proteins
Haeshin Lee 1 , Phillip Messersmith 1 2 Show Abstract
1 Biomedical Engineering, Northwestern University, Evanston, Illinois, United States, 2 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
3,4-L-dihydroxyphenylalanine (DOPA) is an amino acid found at high concentration in the adhesive secretions of certain marine invertebrates such as mussels (Mytilus edulis). This amino acid possesses an enediol side chain, is post-translationally modified from tyrosine, and is believed to confer adhesive characteristics on mussel adhesive proteins (MAPs). Complexes between diols and transition metals have been well established in organometallic chemistry, and it has been speculated that the formation of coordination complexes by mussel adhesive proteins results in crosslinking of DOPA through a process called quinone-tanning, which hardens and insolubilizes the secreted protein glue. Electron paramagnetic resonance (EPR) studies suggest that iron catalyzed DOPA oxidation produces radicals in the phenyl side chains, also contributing to quinone-tanning. However, these iron-mediated quinone-tanning processes have been understudied even though they have important implications for designing new inorganic-organic hybrid materials. Furthermore, the potential role of metal-DOPA complexes in mediating interfacial adhesion remains unexplored. In this study, we probed the effects of iron on the molecular mechanics of mussel adhesion at a single molecule level using atomic force microscopy (AFM). In the absence of Fe, single molecule force-distance curves of DOPA adhesion on a titanium oxide substrate yielded pull-off forces of ca. 800 pN. Similar measurements of DOPA interacting with Fe3O4 revealed a lower binding force of ca. 400 pN. DOPA interacting with an iron chelated DOPA-coated substrate also showed a binding strength of ca. 380 pN, although this feature was undetected in the presence of EDTA. Finally, covalent bond formation between DOPA and organic surfaces was observed under conditions favoring quinine tanning, and reflected by pull-off forces of several nNs. Our single molecule study further elucidated the effects of metal complexation on the mechanics of DOPA adhesion, and confirmed the mechanism of quinone-tanning in mussel adhesives.
9:00 PM - AA4.2
Induction of Muscle Cell Alignment Using Hybrid Copolymer-Collagen Type I Biofilms.
Dean Ho 1 2 , Yong Chen 1 Show Abstract
1 Electrical Engineering, California Institute of Technology, Pasadena, California, United States, 2 Mechanical and Aerospace Engineering, University of California at Los Angeles, Los Angeles, California, United States
Functionalizing block copolymer thin films with collagen utilizes a synthetic biological approach to integrate a biologically-relevant capacity (collagen) into an otherwise abiotic structure (copolymer). This approach takes advantage of the increased durability and ability to tailor block copolymer function for specific applications to serve as a supporting matrix for thin-film deposition of collagen. The merger of these two materials results in the formation of an extremely robust hybrid film that is envisioned to enable cell culture on any surface that is capable of supporting a Langmuir-Blodgett film. With the advent of a new generation of devices in medicine, nanorobotics, and energy based upon biotic-abiotic collaboration, the ability to effectively manipulate this interaction will play an increasingly important role. It has previously been shown that collagen can be tethered to a Langmuir air/water interface using block copolymers as interfacial amphiphilic substrates. Optimal deposition parameters (25ul collagen) resulted in the observation of high collapse pressures (> 50mN/m). This, in turn, enabled the deposition of these hybrid films on solid surfaces such as MEMS devices, silicon, glass, etc. In addition, double immunofluorescence imaging revealed the presence of collagen-based domains within the hybrid films. These collagen-copolymer blends have been observed to produce nanoscale film thicknesses which are ideal for the future development of cellular-artificial interfaced systems. C2C12 mouse myoblasts were subsequently cultured using copolymer-collagen Type I composite substrates to observe the abilities of these composites to facilitate cell adhesion and growth. Samples grown on glass substrates resulted in a high degree of random growth and dense cell presence. Cells cultured on the composite films resulted in the presence of cellular aggregate structures with a high degree of linearity (<250um in length). The presence of collagen-based domains, along with Langmuir isotherms indicative of collagen interfacial intercalation between the copolymer molecules indicated that the possible presence of stiffness gradients along the film. However, it was believed that collagen may have possessed a chief role of promoting cell adhesion given the lack of observed random and dense growth seen with cell culture on glass. In addition, previous work has shown that certain cellular mechanosensing elements (e.g. N-RAP) may be responsible for such phenomena as myofibrillogenesis. Further work will explore variation of cellular linearization that is dependent on collagen concentration, as well as examinations into the mechanisms that drive formation of these aggregations while situated on the composite membranes. Materials based upon biotic-abiotic integration may possess important implications towards the interrogation and studies of biological systems and as devices for biomimetic coatings.
9:00 PM - AA4.3
Nano Scale Non Invasive Patch Clamp For Neural Analysis
Ravikiran Kondama Reddy 1 , Sudhaprasanna Padigi 1 , Shalini Prasad 1 Show Abstract
1 ECE, Portland State University,OR, Portland, Oregon, United States
9:00 PM - AA4.4
Fabrication of Complex Bio-structures and, Controlled 3-D Porous Resorbable Bioceramic Scaffolds via the Fused Deposition Modeling
Vadim Litoshik 1 , Vikas Somani 1 , Samar Kalita 1 Show Abstract
1 MMAE, University of Central Florida, Orlando, Florida, United States
In our research, we have created three-dimensional anatomical models and controlled porosity resorbable ceramic scaffolds as bone grafts using the direct and the indirect fused deposition modeling (FDM) process. The fused deposition (FD) process, commercialized by Stratasys as Fused Deposition Modeling (FDM) is a RP technique where three-dimensional (3-D) objects are built layer by layer from a computer-aided design (CAD) file on a computer-controlled fixtureless platform. In recent years, rapid prototyping (RP) or solid freeform fabrication (SFF) techniques have been explored to fabricate controlled porosity ceramic structures for different applications. We have constructed models of human pelvis, skull, and jaw to see how accurately the FDM technology could construct these complex structures in order to fabricate resorbable ceramic bone-grafts with intricate internal and external geometry. We have developed porous bioceramic structures to mimic the inner structure of bone. In this process, porous polymeric molds with the negative geometry of the desired structure were first fabricated via fused deposition using polymeric filaments. The molds were then infiltrated with ceramic slurry made of metal ion doped β-tricalcium phosphate (β-TCP) that has shown to control the resorption rate of b-TCP in our previous research. Green molds were heat-treated in a muffle furnace for binder removal and sintering to produce porous ceramic scaffolds of desired structures. Porous resorbable scaffolds were characterized for physical and mechanical properties using the XRD technique, SEM, immersion technique, compression strength and flexural strength. This poster will present our work and results obtained in this project.
9:00 PM - AA4.5
Biologically-Directed Nanoscale Materials Assembly
Erik Spoerke 1 , George Bachand 1 , Bruce Bunker 1 , Jun Liu 1 , Christina Warrender 1 , Ann Bouchard 1 , Gordon Osbourn 1 Show Abstract
1 , Sandia National Laboratories, Albuquerque, New Mexico, United States
9:00 PM - AA4.6
Fabrication and Characterisation of Purple Membrane – Bioinorganic Nanocomposite Films.
Keith Bromley 1 , Avinash Patil 1 , Annela Seddon 2 , Stephen Mann 1 Show Abstract
1 Department of Chemistry, University of Bristol, UK, Bristol United Kingdom, 2 Department of Biochemistry, University of Bristol, UK, Bristol United Kingdom
Bacteriorhodospin (BR) is an integral membrane protein from the archae Halobacterium salinarum that exists in 2D arrays in lipid bilayers known as purple membrane (PM) fragments. The PM fragments harvest light to create a proton gradient in low oxygen environments for the production of ATP. Oriented PM multilayers created by electrophoretic deposition have potential in applications such as chip-to-chip or short distance optical communication and biophotoreceivers. In this study, PM bionanocomposite films were prepared by facile procedures. The films were insoluble in water and showed resistance to denaturing in ethanol. Structural studies on the intact films were undertaken using PXRD and cross-sections of samples prepared by Focused Ion Beam (FIB) were investigated by TEM. Energy Dispersive X-ray (EDX) analysis and SEM were also used to characterise the bionanocomposite films. The results suggest that properties associated with hybrid materials based on self-assembled PM fragments could significantly extend the range of potential applications for BR-based devices in bionanotechnology and optical communication.
9:00 PM - AA4.7
Motor Driven Self-Assembly at the Nanoscale.
Isaac Luria 1 , Michelle Kinahan 1 , Henry Hess 1 Show Abstract
1 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States
Self-assembly, a key bottom-up fabrication technique, relies on the motion of the building blocks to establish predetermined connections. To achieve this motion, we can rely on diffusion, which is most effective for molecular scale building blocks, or agitation and stirring, which aids the assembly of macroscopic structures. However, for nanoscale to mesoscale building blocks diffusive transport becomes slow and fluidic mixing is not yet effective due to the laminar flow conditions. Active transport driven by molecular motors, employed in biological systems to bridge diffusion and pressure-driven fluid flow regimes, can accelerate the transport of nano- and mesoscale building blocks. Moreover, the strong and directed forces exerted by the motors lead to surprising self-organization phenomena in the assembly process. For example, correct matching of building blocks can result in a vanishing force on the connection, while mismatched parts experience a strong pull from motors acting in opposite directions. Importantly, a new degree of control over the assembly process can be exerted by controlling motor density, distribution, and activation, which is dependent on the source of energy (ATP in our case). We have studied the self-assembly of individual components propelled by molecular motors in a biomimetic system. Specifically, we used kinesin motor proteins bound to a surface to propel biotinylated microtubules; adding streptavidin allowed the microtubules to stick to each other. This left us with a surface covered in motor-propelled, “sticky” components capable of forming nanoscale structures. On a planar surface, these “sticky” building blocks will self-assemble into long “wires” which subsequently form rotating “spool” structures of varying radius. By using patterned surfaces we attempted to exert control over this self-assembling process, and successfully prevented the formation of “spools”, forcing a preference for the “wire” conformation with predictable probability depending on the surface. Thus, the motor-driven, constrained motion of the building blocks and intermediate assemblies guided the formation of the structures, despite the non-specific nature of the binding. We envision that the ability to restrict and define the transport of building blocks will complement the design of specific connections between building blocks in self-assembled systems.
9:00 PM - AA4.8
Biosensors: Optimized Protocol Based on Senstivity and Selectivity.
Dileep Goyal 1 , Anu Subramanian 1 , Dan Thompson 2 , John Woollam 2 Show Abstract
1 Chemical Engineering, University of Nebraska Lincoln, Lincoln, Nebraska, United States, 2 Electrical Engineeting, University of Nebraska Lincoln, Lincoln, Nebraska, United States
Biosensor is an analytical device which converts a biological response into detectable and measurable signal. The sensitivity and selectivity of these biosensors are still point of discussion among researchers. The objective of this paper is to maximize selectivity and sensitivity of sensing devices which converts biological response to detectable optical signal. In this paper dense, homogeneous and complete self-assembled monolayers with epoxy surface groups were fabricated from silane compounds to serve as a template for covalent attachment of proteins or peptides on the surfaces. We formed epoxysilane layers on hydroxylated surfaces of silicon wafers by using three different silane compounds (3-glycidoxypropyl)trimethoxysilane, 3-aminopropyltriethoxysilane (APTES) and mixed silane layer. The mixed silane layer contained two kinds of compounds, APTES and methyl triethoxy silane (MTES). The silicon surfaces modified with APTES and mixed silane layer was then reacted with diepoxy compound or gluteraldehyde to yield epoxy and aldehyde group on the surface respectively. All the above samples were then used to attach peptide, ligand and antibody against target protein of interest on surface. Dynamic ellipsometric study of target protein attachment over mixture of proteins on these surfaces leads us to comment on the selectivity of these surfaces. The quantitative estimation and coverage of specifically binded target protein was done by use of dynamic ellipsometry, ELISA and fluorescent technique. All the surfaces were also characterized by using Ellipsometry, FTIR, Atomic Force Microscopy and contact angle measurements to study their thickness, morphology and surface properties. The optimal protocol based on the sensitivity and selectivity of target protein will then be used as standard protocol for synthesis of Biosensors.
9:00 PM - AA4.9
The Design and Implementation of Drug Encapsulated Nanoparticles Embedded in Chitosan Hydrogels for the Controlled Release of Drug Delivery to Brain Tumor Sites.
Kristina Dearborn 1 , Ryan Toomey 1 , Michael VanAuker 1 , Norma Alcantar 1 Show Abstract
1 Chemical Engineering, University of South Florida, Tampa, Florida, United States
The emerging field of nanoparticle material science has become increasingly important in the biomedical and bioengineering fields owing to the ability to incorporate nanostructured materials in the design of life-saving technologies. The treatment of malignant cancer cells after major brain surgery is one such area that could benefit from the application of nanostructured materials. Traditional cancer treatments, such as chemotherapy, are not practical options in this situation due to the sensitivity and care that must be taken when dealing with matters of the brain. The goal of this research is to design a technique of drug delivery to brain tumor cells, which is efficient and effective by controlling the release rate of the drug. The smart-packaging technique that this research proposes incorporates a double control mechanism that would allow for the maximum determination of the release rate. Fluorescent carboxyfluoroscein (CF) dye is encapsulated in a non-ionic surfactant vesicle, or niosome, and embedded in a biodegradable chitosan polymer hydrogel. Carboxyfluoroscein dye is used as a tracer dye and indicates the release of the drug from the system. Chitosan is a temperature and –pH sensitive polymer that will begin to gel and form the hydrogel network at physiological conditions (T=37°C; pH=6.2). This feature allows for the direct formation of the smart-packaging system at the point of contact within the brain cavity, which eliminates the risk of contamination or interference from other secondary sources. A unique property of the chitosan polymer is its ability to be molded into any shape desired. This allows for the cavity-specific shape of the system to be made, thus eliminating the risk of unevenly distributing the drug. The release rate of the CF dye was determined for the system at various volumes for various time intervals. The concentration of the CF dye was determined using fluorescence spectrometry. CF dye has an excitation/emission range of 492 nm/514nm. It was determined that the release rate was able to be controlled using the niosome/hydrogel system and that the smart-packing method is a potential technique that could be used in treatment of cancer cells in brain tumor cavities. It will be shown that the CF dye release rate from the niosome could be determined as well as the release rate from the chitosan hydrogel as the polymer decomposed. This information is important because CF dyes have similar molecular weights to chemotherapy drugs and it shows that there can be advanced control for the release rate of drugs using nanoparticle materials. This knowledge, along with the future development and optimization of the design of the smart-packaging system for the brain, has the potential to decrease the toxicity of medication to other parts of the body, increase direct utilization of the drug, increase the survival time of the patients, and improve their quality of life.
Stefan Diez Max-Planck-Institute of Molecular Cell Biology and Genetics
Banahalli R. Ratna Naval Research Laboratory
J. Fraser Stoddart University of California-Los Angeles
Linda Turner Rowland Institute at Harvard
AA5: Synthetic Molecular Machines
Friday AM, April 21, 2006
Room 2007 (Moscone West)
9:30 AM - **AA5.1
First Principles Approaches to the Design and Characterization of Molecular Machines.
William Goddard 1 , Weiqiao Deng 1 Show Abstract
1 Chemistry (134-74), California Institute of Technology, Pasadena , California, United States
We will use concepts of oxidatively driven motions pioneered by the Stoddart group at UCLA to design and fabricate in silico a molecular machine and to characterize its performance.
10:00 AM - **AA5.2
Artificial Molecular Machines.
Amar Flood 1 Show Abstract
1 Chemistry Department, Indiana University , Bloomington, Indiana, United States
A bistable and palindromically-constituted rotaxane incorporating two mechanically-mobile rings interlocked around a linear dumbbell component, has been designed to operate like the sarcomeres of skeletal muscle. Contraction and extension occurs when the inter-ring distance of the two rings switch, ideally, between 4.2 and 1.4 nm upon redox stimulation either chemically or electrochemically in the solution phase. When the mobile rings of these artificial molecular muscles are bound onto the tops of gold-coated, micron-scale cantilever beams, their controllable nanometer motions have a chance to be amplified along the long axis of each cantilever. It turns out that ~6 billion of the self-assembled rotaxanes can bend the cantilevers in a bistable manner concomitant with the cycled addition of redox agents. The extent of bending is commensurate with 10's of pN of force per rotaxane. Recent studies on a set of “single-shot” control rotaxanes have provided additional evidence for the origins of the force generation as it arises from a molecule-based electrostatic repulsion energy of about 10 kcal/mol at 300 K. These findings will be presented in terms of the underlying thermodynamics and kinetics that have been utilized extensively to direct the design and synthesis of artificial molecular machines and which may also serve as a guide for the rational design of unidirectional molecular motors.
10:30 AM - AA5.3
Molecular Rotors in the Crystals of Molecular Magnetic and Conducting Materials.
Takayoshsi Nakamura 1 , Tomoyuki Akutagawa 1 Show Abstract
1 , Research Institute for Electronic Science, Hokkaido University, Sapporo Japan
The [Ni(dmit)2] monovalent anion has an open-shell electronic structure with S=1/2 spin, which is easily oxidized to the mixed valence state. Molecular solids of [Ni(dmit)2], therefore, show a variety of electrical and magnetic properties according to the configuration and oxidation state of the molecule in the crystal. We have been introducing supramolecular structure as the counter cation of [Ni(dmit)2], which form interesting functional units such as ion channel structures. In this paper, we describe supramolecular rotor structures introduced in [Ni(dmit)2] crystals. In the crystal of (PhNH3+)(crown-6)[Ni(dmit)2] (1), the phenyl-ring of anilinium rotate (flip) at around 106 Hz. The [Ni(dmit)2] part formed a spin-ladder, which was confirmed by magnetic susceptibility, 1H-NMR and μSR measurements. No interaction was, however, observed between magnetism and molecular rotation.On the other hand, strong correlation between magnetism ans molecular rotaion was observed for the crystal of Cs2(crown-6)3[Ni(dmit)2]2 (2). In the crystal crown-6 was rotating due to the thermal fluctuation, which was examined by X-ray analysis and NMR measurements. The rotation stopped at around 220 K by lowering the temperature. The molecular rotation of crown-6 affected largely the magnetic behavior arising form [Ni(dmit)2]- dimers. Over the temperature range from 4 to 160 K, the χmol - T behavior of salt 2 was fitted using the singlet - triplet (S - T) thermal excitation model with a variable J = -218 K. As expected from the dimeric structure of [Ni(dmit)2]-, the χmol - T behavior at lower temperatures showed good agreement to the S - T model. Above 160 K, however, significant deviation from the S - T model was observed, with a broad maximum of χmol at around 200 K, which was due to the rotation of crown-6. In addition, the molecular rotation was stopped by applying hydrostatic pressure, which is one of the necessary conditions for unidirectional rotation through Brownian ratchet mechanism. The introduction of molecular rotors in [Ni(dmit)2] conducting salts as well as attempts on utilizing polyoxometalates as a counter anion of supuramolecular rotors will be discussed.Molecular rotors coupled with electrical and magnetic properties may be utilized to develop novel energy conversion systems, which can extract electromagnetic energy from the kinetic energy of unidirectional molecular rotation.References1. T. Nakamura et al., Nature, 394, 159 (1998)2. T. Akutagawa et al., Chem. Eur. J., 7, 4902 (2001) 3. S. Nishihara et al., Chem. Commun., 408 (2002)4. T. Akutagawa, et al., J. Am. Chem. Soc., 127, 4397 (2005).
10:45 AM - AA5.4
Unidirectional Aryl-Aryl Bond Rotation in Biaryl Lactone Prototypical Synthetic Molecular Motors.
Bart Dahl 1 2 3 , Ying Lin 1 2 3 , Bruce Branchaud 1 2 3 Show Abstract
1 Chemistry Department, University of Oregon, Eugene, Oregon, United States, 2 , Oregon Nanoscience and Microtechnologies Institute, Eugene, Oregon, United States, 3 Materials Science Institute, University of Oregon, Eugene, Oregon, United States
Several biaryl lactone systems have been synthesized and are capable of directed bond rotation about the aryl-aryl bond axis. One class of biaryl lactones are achiral and use chiral nucelophilic "fuels" to break the lactone ring diastereoselectively to afford non-racemizing biaryls resulting in a 90 degree directed bond rotation. Subsequent re-lactonization using an acyl-activating "fuel" exploits the orthogonal reactivity of the two reactive ortho substituents on the ring, resulting in 180 degree directed bond rotation. This process can be repeated, resulting in iterative net unidirectional bond rotation. Another class of biaryl lactones are chiral and use achiral nucleophilic "fuels" to break the lactone ring diastereoselectively to afford non-racemizing biaryls resulting in a 90 degree directed bond rotation. Acyl activation causes a selective re-lactonization that results in 180 directed bond rotation. These reactions can be repeated, resulting in iterative net unidirectional bond rotation. A primary advantage of this system is that only 2 synthetic steps are required to achieve 180 degree directed bond rotation in high yields. Another advantage is that numerous nucleophilic "fuels" are capable of driving the lactone ring-opening and numerous methods of acyl activation (e.g. acid, oxidation, photchemical, electrochemical) are capable of driving the re-lactonization. We will present the synthesis and characterizaton of each prototypical molecular motor system.
11:00 AM - AA5: SynMolMach
11:30 AM - AA5.5
The Design and Control of Catalytic Motors: Manipulating Colloids and Fluids with Self-Generated Forces.
Timothy Kline 1 , Walter Paxton 1 , Darrell Velegol 2 , Thomas Mallouk 1 , Ayusman Sen 1 Show Abstract
1 Department of Chemistry, Center for Nanoscale Science, Pennsylvania State University, University Park, Pennsylvania, United States, 2 Department of Chemical Engineering, Pennsylvania State University, University Park, Pennsylvania, United States
The principle of converting chemical energy to mechanical energy at the nano-microscale using heterogeneous catalytic reactions may significantly impact the field of nanotechnology. We have selected the platinum and silver catalyzed decomposition of hydrogen peroxide to water and oxygen as a means to demonstrate a method to convert chemical energy to mechanical motion through an interfacial tension gradient. In one case we engineered ferromagnetic segments into a platinum-gold nanorod and observed the first catalytically driven yet remotely steered nanorod. Now we have control over these nanorods presenting a possible use as roving remote controlled sensors. We have also created the first catalytic micropump by immobilizing our catalyst onto a surface with conventional microfabrication techniques. The microscale silver patterned gold surface produced convective motion of positively charged microspheres (one type of tracer) and rods suspended in dilute solutions of hydrogen peroxide. Negatively, charge microspheres exhibited a patterning effect. We have found that a self-generated electric field can account for our observations rather than an interfacial tension gradient. The fluid moved through electroosmosis and the tracers through electrophoresis. Our innovation in microfluidic pumps presents a low power, cost-effective and mechanically efficient alternative in microfluidics. Now that we are able to move fluids on the microscale region, we are interested in controlling fluid and particle motions. One of our tracers, gold nanorods, can be covalently modified with self-assembled monolayers (SAMs) to impart different surface charges. In electrokinetics, the zeta potential (surface charge) of the particle dictates the direction of movement for the electrophoretic component of the observed velocity and electroosmosis comprises the remaining part of the particle velocity. Gold nanorods were modified with charged and neutral SAMs to vary the zeta potential of the gold rod, successfully dictating the movement of the gold rod. We tuned the behavior of the gold rod from convection, to pattern formation, to Brownian motion by using no SAM, a negatively terminated SAM, and a neutral SAM respectively. Our work shows that the electrophoretic component of electrokinetics is the dominate force moving the nanorods. Another way of controlling the fluid/particle motion is with a photochemical switch, similar to the magnetic switch we employed with the moving rods. For fluid motion, we used UV light to increase the oxygen evolution in our system without having gold present (i.e. no electrochemistry can occur) and demonstrated a switchable fluid flow with a direction independent of the charge on the tracer used (e.g. not electrophoresis). The incorporation of a switch into the pump creates an attractive method to externally actuate the fluid motion.
11:45 AM - AA5.6
Catalytically Induced Autonomous Motion of Colloidal Particles.
Walter Paxton 1 , Ayusman Sen 1 , Thomas Mallouk 1 Show Abstract
1 Chemistry, Penn State, University Park, Pennsylvania, United States
We recently reported the catalytically induced autonomous motion of metallic colloidal particles. Asymmetric metallic nanorods (diameter=370 nm), with platinum and gold segments of 1 micron long each, moved at speeds up to 30 microns per second when placed in aqueous solutions of hydrogen peroxide. The magnitude of the nanorod velocities was closely related to the rate of catalytic decomposition of hydrogen peroxide. Understanding the mechanisms of motion operative at low Reynold’s number is required for rational design of useful nanomachinery. Such machines could be engineered to, among other things, interact with individual biological cells. Using interdigitated array electrodes, we investigated the contribution of electrokinetics in converting chemical energy into directed mechanical forces in the platinum/gold/hydrogen peroxide system. Specifically, we explored the role of both metals in the catalytic decomposition of H2O2 via an electrochemical pathway, where hydrogen peroxide is oxidized on the platinum and reduced on the gold surface. The catalytically generated electric field between interdigitated platinum and gold electrodes in the presence of hydrogen peroxide was related to the electroosmotic pumping of fluid between the two electrodes. The results of these experiments were then connected back to the motion of platinum/gold nanorods in hydrogen peroxide solutions.
12:00 PM - **AA5.7
Artificial Molecular Mmotors and Machines Powered by Light.
Alberto Credi 1 , Vincenzo Balzani 1 , Margherita Venturi 1 Show Abstract
1 Dipartimento di Chimica "G. Ciamician", University of Bologna, Bologna Italy
During the past few years the miniaturization race has encouraged scientists to investigate the possibility of designing and constructing motors and machines on the nanometer scale, i.e., at the molecular level. Such a daring goal finds its scientific origin in the existence of natural molecular machines. These are extremely complex systems, and any attempt to construct machines of such a complexity using the bottom-up molecular approach would be challenging. What can be done, at present, is to construct simple prototypes, consisting of a few molecular components capable of moving in a controllable way, and to investigate the challenging problems posed by interfacing them with the macroscopic world, particularly as far as energy supply is concerned.Nature shows that, in green plants, the energy needed to sustain the machinery of life is ultimately provided by sunlight via a charge separation reaction. Energy inputs in the form of photons or electrons/holes can indeed cause the occurrence of endergonic chemical reactions that can make a machine work, without formation of waste products. A further advantage offered by the use of photochemical techniques is that photons, besides supplying the energy needed to make a machine work, can also be useful to "read" the state of the system and thus to control and monitor the operation of the machine.Here we will describe the photophysical, photochemical and electrochemical properties of supramolecular species recently studied in our laboratories, with particular reference to their operation as molecular motors and machines. More specifically, we will show that in a two-state rotaxane, a shuttling movement of the ring component between two stations located on the axle component can be obtained in solution at room temperature by visible light energy inputs. Such a rotaxane performs indeed as an autonomous artificial nanomotor powered by photons. Limitations and perspectives of this kind of systems will also be discussed.References:V. Balzani, A. Credi, F. M. Raymo, J. F. Stoddart, Angew. Chem. Int. Ed. 2000, 39, 3348.V. Balzani, A. Credi, M. Venturi, Molecular Devices and Machines – A Journey into the Nano World, Wiley-VCH, Weinheim, 2003.J. D. Badjic, V. Balzani, A. Credi, S. Silvi, J. F. Stoddart, Science 2004, 303, 1845V. Balzani, A. Credi, B. Ferrer, S. Silvi, M. Venturi, Top. Curr. Chem., in press.