Virgil Percec - US grants

This research deals with the synthesis and properties of a new class of polymers, i.e., polyethers that exhibit liquid- crystalline behavior. The polyether functionality will be placed in the so-called main chain of the polymers. Recent work by the principal investigator has shown that such polymers are both thermotropic and lyotropic. The major effort of this research will be directed toward the synthesis of a variety of polyethers of this type. An effort will be made to derive a better understanding of structure-property relationships in liquid- crystalline polymers containing flexible "spacers," such as aliphatic or oligooxyethylenic groups. Exploratory experiments are also planned on the synthesis of ring-shaped and biaxial nematic liquid-crystalline polymers.

This award is for the renewal of the Materials Research Group at Case Western Reserve University (Grant of structure, dynamics, and transitions of liquid crystalline polymers. The primary goal of the research by the group is to understand the physical and chemical requirements for generation of crystalline structures containing fully extended chains from neumatic columnar hexagonal phases and copolymers containing these phases. The research emphasis is on synthesis of polymers, having controlled molecular structure, which are predicted to have neumatic of columnar phases, with focus on main chain polyesters and polyethers in which asymmetric mesogens are linked by flexible spacers. The work also includes synthesis of supramolecular self- assembling polymers designed to have cylindrical conformations, preparation and characterization of micro-phase-separated supramolecular assemblies, based on block co-polymers that contain different mesomorphic and glassy segments. The structure and dynamics of these polymers is being determined by x-ray and neutron scattering, static and dynamic light scattering, fluorescence energy transfer spectroscopy, and nuclear magnetic resonance spectroscopy. The electronic, magnetic, optical, and dielectric properties are also being determined. Theoretical analyses of the molecular assembly, dynamics, phase transitions, rheology and other physical properties of the mesophases is also being done in parallel with the experimental effort.

For the past 150 years, organic chemists were concerned with the understanding of the covalent bond. Recently, research on molecular recognition (generated by weak, non-covalent interactions) has been recognized worldwide as an important intellectual and technological frontier. Endo- (generated by convergent cavities) and exo (generated by larger bodies of similar size and shapes, or surfaces) molecular recognition, preorganization and self-organization provide the basis of spontaneous generation of functional supramolecular architectures via self-assembly from their components. It is now accepted that molecular recognition directed synthesis and self-assembly are responsible for the generation and properties of biological systems. This research aims to use molecular recognition both to self-assemble synthetic supramolecular liquid crystalline polymers and to direct their phase behavior. Two novel classes of polymers will be investigated: functional supramolecular polymers which self-assemble by using principles that resemble those of tobacco mosaic virus, and both cyclic main-chain polymers, as well as polymers containing liquid crystalline cyclophane (i.e., cyclic derivatives of main-chain liquid-crystalline oligomers) receptors as structural units. The second class of liquid-crystalline polymers will display molecular recognition directed phase transitions. It is expected that this research will produce molecular devices such as self-assembled supramolecular synthetic ion channels and various other systems which, by analogy with natural biological systems, will combine selective recognition with external regulation. Most important, this research will enable a step ahead in understanding some of the processes that nature uses and about which we know so little, and transplant them to the field of synthetic su pramolecular polymers.

This award supports the participation of 13 U.S. scientists in a U.S.-Japan Seminar on Macromolecular Design for Advanced Materials, to be held in Napa Valley, California November 6 to 12, 1993. The co-organizers are Professor Virgil Percec of Case Western Reserve University and Professor Yukio Imanishi of Kyoto University. The focus of the meeting will be on the most recent advances in the elaboration of novel polymerization methods and their use in the design of new and well-defined complex macromolecular architectures capable of generating advanced materials with controlled optical, electronic, ionic, biomedical, high-strength and other special properties. This meeting is the sixth in a series of U.S.-Japan seminars in this field held over a period of 18 years. The seminar is timely because advanced materials underlie current and projected developments in the electronics, communications, aerospace, automotive, and health care industries. Important contributions are being made in each of these areas in the United States and Japan, and increased exchange of ideas and information should lead to further collaborative research between scientists in the two countries.

This award is in response to the Nanoscience and Engineering (NSE) solicitation(NSF-00-119) and involves a nanoscience Interdisciplinary Research Team (NIRT) at the University of Pennsylvania with broad-ranging national and international collaborations. It is being co-supported by the Polymers Program of the Division of Materials Research (DMR), the Special Programs of the Division of Chemistry (CHE), and the Interfacial, Transport and Thermodynamic Processes Program of the Division of Chemical & Transport Systems (CTS).
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The ability to transition nanoscience and engineering (NSE) research to nanotechnology will depend on the development of efficient new synthetic methods to produce monodisperse nanoscale objects. To this end, the primary goal of this Nanoscale Interdisciplinary research team (NIRT) is to enable a rational approach to the design and synthesis of libraries of complex functional monodisperse objects of well-defined shapes, dimensions up to the wavelength of light, surface, and internal compartmentalized architecture. To accomplish this goal, the NIRT combines synthetic methodologies from Materials and the Life Sciences. The NIRT has assembled expertise in organic, macromolecular, supramolecular, and peptide synthesis, along with theory and modeling, and structural analysis by x-rays, TEM, and SFM. The team effort is amplified by exploiting established links with partners in industry and in Europe. Success will reveal the principles required for the construction of libraries of monodisperse self-assembling dendritic building blocks, to enable the hierarchical design of monodisperse single molecule functional nanostructures (SMN) with shape, chirality, internal and external structure, and function controlled at the level of precision currently available only in biological systems. The NIRT will investigate the structure and properties of these nanoscale objects at the level of the single molecule and in 2-D and 3-D assemblies. Novel applications of SMNs are elaborated that have potential to yield nanoscale devices for electronic, optical, chemical and medical technologies.

TECHNICAL SUMMARY: This proposal will elaborate strategies for the synthesis of programmed synthetic macromolecules that are instructed to self-assemble and self-organize into complex functional nanoarchitectures with chemical organization on all levels. This concept is currently available only in biological systems. A programmed synthetic macromolecule is a macromolecule with precise primary structure, that includes monodisperse molecular weight distribution, composition, sequence distribution and stereochemistry, that is instructed to self-assemble into the 3-dimensional (3-D) nanoarchitecture required to provide a specific function. This architecture must be controlled at its seconday, tertiary and quaternary levels and is called complex functional architecture. Currently available polymerization methods cannot be used to design programmed macromolecules. Therefore, an accelerated design strategy via retrostructural analysis will be used to develop libraries of programmed macromolecules via combinations of divergent and convergent iterative synthetic methods. Simultaneously, a self-interrupted polymerization method will be elaborated. This method is expected to apply to all chain and step polymerizations known and generate the first polymerization method that will produce monodisperse synthetic macromolecules. Libraries of programmed macromolecules that self-assemble into various biological mimics such us porous proteins, hollow globular protein, supramolecular capsules, chiral supramolecular nanostructures from achiral building blocks, and supramolecular nanospheres that exhibit intramolecular chirality will be developed. These nanoarchitectures will facilitate access to extremely efficient biological functions such as transmembrane channels, antimicrobials, reversible encapsulation and delivery, enzymatic-like catalysis, electronic materials, stochastic sensing, new sources of energy, separation processes, memory effects and also amplify already known material properties.
NON-TECHNICAL SUMMARY: Current approaches to materials with specific properties are cost and time inefficient and generate only minimal improvements. This proposal intends to apply biological nanostructural principles to the design of synthetic nanomaterials with specific functions. An accelerated design strategy that involves expertise from chemistry, physics and biology with collaboration between universities in US and abroad, governmental laboratories and industry will develop the principles required to amplify materials properties by up to several orders of magnitude. Extremely efficient separation processes, enzymatic-like catalysis, sensing, new sources of energy and new approaches to medicine are expected to emerge from this research. This research will change our way to design materials properties at the most fundamental level and affect accordingly the education of a new generation of graduate, undergraduate and high school students.

The grand challenge in efficiently harvesting and converting solar radiation into electricity lies in engineering materials on multiple length scales with architectures that direct the flow of energy and the transfer and transport of charge, as in naturally occurring light harvesting systems. Organic-inorganic hybrids, prepared from functional, electro-active organic and nanostructured inorganic materials, combine desirable and tunable chemical and physical properties of the constituent organic and inorganic building blocks in a single composite, making them promising systems for solar technologies. Hybrid materials incorporate the low-cost, large-area processing and high absorbance and quantum efficiencies of organic materials with the adjustable optical properties, high carrier conductivities, and good photostability of inorganic nanostructures. Solar photovoltaic and luminescent solar concentrator technologies will be dramatically advanced if the organic and inorganic building blocks of hybrid structures can be positioned and oriented on the nanometer scale to regulate the competitive processes of charge transfer and transport, emission, and energy transfer.

Hybrid organic-inorganic materials promise one of the best architectures for ultra-low-cost photovoltaic devices. Currently, the efficiency of hybrid photovoltaic devices is limited by the availability of red-absorbing, high-mobility organic and inorganic components (to match the solar spectrum and efficiently collect charge) and of composites with structures that achieve high surface area junctions, yet form well-connected organic and inorganic pathways. This project aims to produce significantly improved hybrid structures for photovoltaics. Improved hybrid materials may also enable creation of high-efficiency luminescent solar concentrators, which currently are limited in performance by materials challenges; organic and inorganic materials alone have not been found to satisfy the broad-spectrum collection, near-unity photoluminescence efficiency, low re-absorption, and good photostability required.

This project brings together advances in chemical synthesis, mathematical modeling, and self-organization to control the position and orientation of organic and inorganic building blocks, exploiting advances at the frontier of chemistry, materials science, and mathematics. We will combine precisely controlled 1) molecular and supramolecular dendrimeric systems tailored to assemble with different structural motifs and 2) nanocrystals of tunable size, shape, and composition that self-assemble into single and multi-component superlattices. Structural, optical, and electrical probes will be combined with mathematical modeling of the effects of interface geometry to optimize charge transfer and transport, emission, and energy transfer. The results will enable engineering of organic-inorganic materials that will be integrated in photovoltaic devices and luminescent solar concentrators.

More broadly, the research program will develop new synthetic methods and mathematical formalisms for the self-assembly of hybrid materials with tailored architectures that is important to provide materials with superior structural, electronic, and optical properties. These materials have applications in imaging, therapeutics, and information technology, in addition to energy harvesting. The project's emphasis on mathematical techniques for engineered self-assembling systems offers the potential for impact in robotics and biological systems. The project will also electronically and optically probe and establish mathematical models of the behavior of organic-inorganic heterojunctions key to their application in a range of electronic and optical devices.

Technical Summary

A complex system is a system with a large number of elements, building blocks, or agents, capable of exchanging stimuli with one another and with the environment. They can be identified by what they do, display organization without a central organizing authority-emergence, and also by how they may or may not be analyzed. In contrast to complicated systems, complex systems cannot be understood by simply analyzing their individual parts in isolation and can therefore not be strictly designed and engineered. This research project aims to use biology and structural-biology principles guiding the emergence of complex biological systems so as to elaborate fundamental principles required for the design and synthesis of programmed macromolecules (monodisperse, with precise and instructed primary structure) that will ultimately emerge into predictable complex molecular systems. Self-assembling dendrons and dendrimers will be employed as building blocks in these investigations. These building blocks will be used to (1) elaborate generational and deconstruction-design strategies for the discovery of new libraries of primary structures and supramolecular assemblies; (2) elaborate strategies to predict the primary structure that mediates the generation of a specific complex functional system; and (3) elucidate the principles and mechanisms for the emergence of complex molecular systems and generate their design principles.


Non-Technical Summary

Complex systems are characterized by adaptation, self-control, self-organization, memory -- they are emergent and evolving but cannot be designed and engineered. Examples of complex systems include highways, the internet, life, social and political organizations, financial and economic systems, most of the biological systems, some molecular chemical systems and selected chemical reactions. This research will transplant biological principles to synthetic molecular systems, elucidate their mechanism of assembly, and lead to design and engineering strategies for complex molecular systems. The lessons learned from complex molecular systems are expected to apply to other complex systems. Immediate applications should generate efficient strategies to solar energy conversion and other technological issues of broad and daily concern. This program will provide mechanisms to educate undergraduate, graduate, and postdoctoral students at the frontiers and interfaces of molecular, biological, and physical sciences with other complex systems and societal concerns. This research also includes a number of broadly based collaborations.

PART 1: NON-TECHNICAL SUMMARY

This research program will draw inspiration from a combination of fundamental principles derived from the metallurgy of metal alloy phases and some of the most fundamental principles of biology such as homochirality, and apply them to the design and synthesis of individual macromolecules with simple and complex architectures that may include memory effects, which will allow to discover new concepts in complex polymeric materials. These concepts are anticipated to be competitive with the most efficient methodologies currently available in biology. The outcome of this work is expected to facilitate control of supramolecular electronic properties of interest for applications such as solar cells, new tools for medical devices including drug delivery, environmental aspects of polymer materials, and other uses. This research involves an interdisciplinary program at the interface between organic, macromolecular and supramolecular chemistry, physics, biology, synthetic biology, and materials science; it also includes collaborations with scientists from around the world. This program will also enable the education of undergraduate and graduate students, high-school students, and postdoctoral scientists.


PART 2: TECHNICAL SUMMARY

The Frank-Kasper phases were first discovered and employed in metal alloys. In soft matter they were discovered in a related NSF program and recently also in block-copolymers, surfactants and other assemblies. They are expected to evolve soon into new technological applications. However, many supramolecular spherical assemblies are helical and therefore chiral and the molecular mechanism as well as the role of homochirality in these phases remains to be understood. The structures and properties generated by memory effects in these materials are accessible only by chiral supramolecular dendrimers and by other monodisperse assemblies. Therefore, this project will elucidate the role of chirality in Frank-Kasper soft phases and will be fundamental for the development of new material properties from polymers and any other organic materials.

Even though most polymeric and organic materials exhibit helical structures and are therefore chiral, they are considered to be racemic when assembled from achiral or racemic building blocks and display low-ordered structures and properties. This supramolecular trend is similar to that of isotactic (homochiral), syndiotactic (heterochiral), and atactic (racemic) polymers. A new mechanism of crystallization, the cogwheel mechanism that disregards chirality, has recently been discovered and shown to be potentially able to eliminate the difference regarding the perfection of helical structures generated from chiral versus racemic building blocks. The generality of this mechanism to combinations of racemic and achiral building blocks to generate the same material properties as the homochiral ones will be studied. The outcome of this research will have broad scientific impact across many types of materials, including electronic, medical, and other applications.

Another aspect of this project involves monodisperse polymers. Monodisperse polymers containing single-dimension species are produced only by biology. This research will include continued development of self-interrupted living polymerization, which will enable study of similarities and differences between the structure and properties of truly monodisperse polymers versus those of narrow dispersity produced by standard living polymerizations. These will also impact broad areas involving the design of polymeric materials with numerous potential applications.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

PART 1: NON-TECHNICAL SUMMARY

Biological macromolecules such as proteins, nucleic acids, carbohydrates and their conjugates to lipids are the most common building blocks produced by nature. Their properties are determined by a perfect arrangement of their atoms in their structure and in their complex assemblies. Even though they are pervasively used in our daily lives and in many health, defense and other technological applications, synthetic polymers are not able to match the properties of metals and biological macromolecules. This research program aims to use biological principles in the construction of polymers and their complex assemblies to increase the level of structural precision of synthetic polymers to that of metals and natural macromolecules and expand their applications in daily life to the precision and sophistication encountered in biological systems. The project involves design, synthesis, and characterization of macromolecules to a variety of complex assemblies, followed by study of their structure and properties. This project will provide interdisciplinary education for high school, undergraduate, graduate students and postdocs, including minorities, at the interface of disciplines including organic, polymer, supramolecular synthesis, catalysis, physics, biology, synthetic biology, nanoscience, nanomedicine, and supercomputing. Group members will work in the laboratories of the PI and colleagues at Penn, collaborated with scientists in the US and abroad, and interact with industry. The principles and lessons learned from this project will be applicable to scientific, industrial and societal complex systems.


PART 2: TECHNICAL SUMMARY

Complex assemblies generated from metal atoms and from large biological macromolecules are strikingly dissimilar as concepts but identical in their extraordinary level of structural perfection and functions. Synthetic covalent and supramolecular polymers have statistical chain length distribution, chirality, composition and sequence. Therefore, they cannot provide the level of structural perfection and properties of inorganic and biological assemblies. This project will use monodisperse, homochiral and sequence-defined components to elucidate principles required to produce noncovalent-supramolecular and covalent polymers that will self-organize into complex assemblies exhibiting the precision of inorganic and biological assemblies. The following topics will be investigated: (1) The principles of self-organization of Frank-Kasper phases will be elucidated; these are seen in metals, metal alloys, some gases, lipids and even in some viruses and recently also in narrow molecular-weight-distribution polymers, monodisperse polymer components, and supramolecular polymers. Together with their supramolecular orientational memory Frank-Kasper phases will provide a first access to biological precision. (2) The generality of the cogwheel double-helix, hat-shape deracemizing and “rigid” solid-angle tobacco mosaic virus-like supramolecular helical polymerizations accompanied by deracemization will be investigated and elucidated. They will provide homochiral assemblies, of biological precision and even higher, containing sequence-defined and monodisperse components obtained by deracemization. (3) The scope and limitations of self-interrupted living polymerization for the synthesis of monodisperse biological-like polymers by non-iterative methods will be investigated and elucidated. Alternative methodologies for the synthesis of monodisperse polymers will also be explored.
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This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.