Ideas in Chemistry and Molecular Sciences: Where Chemistry Meets Life
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Surface science applied to materials—particularly to organic materials—is of growing importance and will expand significantly with the development of new materials for biotechnology, medicine, information technology, and nanotechnology. To achieve these goals will require, among many other things, a dramatic increase in the interactions among chemists, engineers, biologists, and physicists. Since early civilization humans have been interested in the properties of the various minerals found in the earth.
The discovery that materials we now recognize as iron oxides could be heated with charcoal to produce iron led to wonderful new tools in the Iron Age, while similar transformation of other minerals led to copper, tin, and other metals. Although we think of them as common, few metals are naturally occurring; they are produced by chemical reactions of their naturally occurring compounds. One of the earliest synthetic materials is glass, produced over 5, years ago by heating various natural minerals together.
Clearly, the discovery, refinement, and creation of materials has arisen from the chemical sciences and processing technology and sometimes vice versa. The story of polymers is one that shows enormous effects on human life. Though polymer science revolutionized 20th century life and is now a well-developed academic field, polymer synthesis is still progressing rapidly. Synthetic polymers have often consisted of long chains of identical subunits.
Sometimes the synthetic polymer chains have cross-links between the chains in proteins, cross-links within a chain help determine a specific folded geometry. For many years, copolymers have also been produced to gain the beneficial properties from more than one monomer. Glassy polymers can be blended with rubbery ones to generate desirable mechanical properties.
Block copolymers—produced with long runs of one or the other monomer—phase separate on a nanoscopic scale typically 10 to 50 nm that is determined by the block molecular weight. These microphase-separated polymers often have remarkably better properties than blends of the two components, and are an early example of using self-assembly to produce new materials. The architecture of macromolecules is another important synthetic variable. New materials with controlled branching sequences or stereoregularity provide tremendous opportunity for development.
New polymerization catalysts and initiators for controlled free-radical polymerization are driving many new materials design, synthesis, and production capabilities. Combined with state-of-the-art characterization by probe microscopy, radiation scattering, and spectroscopy, the field of polymer science is poised for explosive development of novel and important materials. New classes of nonlinear structured polymeric materials have been invented, such as dendrimers. These structures have regularly spaced branch points beginning from a central point—like branches from a tree trunk. New struc-.
High-molecular-weight polymers can be useful as solid materials and in solution, and lower molecular weight polymers can make liquids that are unusual in character. Synthetic adhesives illustrate liquid-phase materials that cross-link or polymerize when they set. Water-based paints are another example, liquids with suspended solid polymer particles that form uniform solid films during drying.
So-called liquid crystals illustrate another exciting example of complex fluid materials; these are liquid-phase materials made up of anisotropic, usually fairly rigid, molecules of high aspect ratio that have strong electric dipole moments. Such molecules are prone to adopt preferred orientations, especially under the influence of surfaces, electric fields, and flow processes. Control over preferred orientations gives high anisotropic strength of materials and switchable optical properties, making them useful in displays such as those on digital watches and laptop computers.
Multicomponent systems having molecules of macromolecular size and heterogeneous composition can be exquisitely sensitive to the delicate balance of intermolecular forces. The fine interplay among a suite of noncovalent interactions e. Molecular organization and interaction cause collective and cooperative behavior to dictate macroscopic properties. Often the balance of forces is such that self-assembly occurs to generate aggregates, arrays, or other supramolecular structures. Large molecular size enables amplification of a small segmental effect into a large intermolecular effect.
Self-assembly can amplify the small forces between small objects to produce large-scale structures useful for macroscopic creations for patterning, sieving, sorting, detecting, or growing materials, biological molecules, or chemicals. Learning to understand and harness intermolecular interactions in multicomponent polymer and composite systems offers huge challenges, as well as opportunities to mimic nature, which has learned to do this in many instances. Self-assembled monolayers SAMs are ordered, two-dimensional crystals or quasi-crystals formed by adsorption and ordering of organic molecules or metal complexes on planar substrates.
Development of these monolayers is based on early studies in which chemists learned to attach chemicals to surfaces—for purposes ranging from adhesion to chromatography to electrochemistry—but often without strong ordering in the monolayers. The ordered structures have made it possible to develop a rational surface science of organic materials. They provide the best current example of the power of self-assembly to make possible the design of the properties of materials.
They have made routine the control of wetting, adhesion, and corrosion in certain systems, and—through soft lithography—they have provided a new approach to microfabrication that is uniquely chemical in its versatility. They have also greatly advanced the field of biomaterials by making it possible to control the interface between cells and synthetic materials at the molecular level.
Building ever smaller devices has been a dominant trend in microelectronics technology for 50 years. The technology used for this type of fabrication is photolithography. This astonishingly sophisticated technology is a kind of photography: The pattern that is to be a part of the circuit is formed by shining ultraviolet light through a mask a pattern of chromium on silica , through a reducing lens, onto a thin film of photosensitive polymer a photoresist covering the surface of a silicon wafer. After exposure, the exposed polymer differs in its solubility from unexposed material, and a suitable solvent allows the selective dissolution of either exposed or unexposed regions.
The exposed regions are then treated by deposition of metal, etching, or implantation of ions to make a part of the final device. Photolithography is the basis of one of the technologies that has genuinely changed the world—it has made possible the computing and information revolution. But it is not suited for making every possible type of small structure.
An alternative to photolithography has been developed that is—for many applications in chemistry and biology—more versatile and much less expensive. The element in these methods is a stamp or mold that is fabricated in a transparent, chemically inert elastomer, poly dimethyl siloxane PDMS. Because the stamp can deform, it is called soft; the organic materials that are printed and molded are also called soft matter by physicists—hence the name soft lithography.
If the stamp is sealed to another surface, the patterns become microchannels for analysis of nucleic acids, proteins, or cells. Soft Lithography. Figures a-c illustrate a soft-lithographic technique called microcontact printing. A PDMS stamp with features in bas-relief is coated with an ethanolic solution of octadecanethiol, and placed in contact with the surface of a thin metallic film nm of gold, silver, or palladium.
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A self-assembled monolayer SAM of octadecanethiolate forms on the surface of the metal in the regions where it contacts the PDMS stamp. The stamp is removed and the regions of the metallic film without a SAM are dissolved by wet-chemical etching. Figure d is a schematic diagram of a long, serpentine, palladium wire 2 m with contact pads that are connected to the wire at every 0.
Figure e is a SEM image of a section of the pattern. Drawings a-c courtesy of George M. Whitesides; d-e reprinted with permission from D. Wolfe et al. Soft lithography is very simple, and it does not require expensive instrumentation or access to clean rooms.
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It does not give the lateral accuracy of photolithography, but it is much less expensive. The size of the features it can make is not limited by optical diffraction, but rather by van der Waals contacts and by deformations in the polymer used. It has become a tool that is widely used in chemistry to make micro- and nanostructures. Micelles, liposomes, shell-linked particles, and vesicles are all results of the spontaneous self-assembly of amphiphilic molecules to form enclosed or aggregate structures that contain solvophobic regions surrounded by solvent-loving moieties.
In all of these structures, opportunities abound to exploit them for chemical separations, controlled release, directed transport, and synthesis. Fundamental studies of these organized systems have increased in the recent decade. The pursuit is often biologically inspired, but in creating mimics we still fall short of the natural systems. Combining this activity with concerted synthetic chemistry and biochemistry provides great potential for the future.
The properties of modern electronic, optoelectronic, photonic, and magnetic devices provide another story of great science that has affected most of humankind. Electronic devices require special materials: materials that emit light when struck by a beam of electrons for use in television screens and computer monitors, materials to make the semiconductors that are the heart of electronic and microelectronic circuits, and materials that are used in magnetic memory storage devices for computers.
Classical electronic circuits and communication lines are made of metal to conduct electricity. Now we have the prospect of massively communicating by optical signals. The great progress in the use of optical fibers to permit light to travel in and between devices results from major achievements in materials processing. Special surface coatings on the fibers reduce signal degradation; optical switches allow connections with devices communicating through optical fibers. The optical fiber revolution provides very high speed plus the ability to pack much more information into a given transmission.
There is considerable interest in developing new types of magnetic materials, with a particular hope that ferroelectric solids and polymers can be constructed— materials having spontaneous electric polarization that can be reversed by an electric field. Such materials could lead to new low-cost memory devices for computers. The fine control of dispersed magnetic nanostructures will take the storage and tunability of magnetic media to new levels, and novel tunneling microscopy approaches allow measurement of microscopic hysteresis effects in iron nanowires.
One of the most exciting properties of some materials is superconductivity. Some complex metal oxides have the ability to conduct electricity free of any resistance, and thus free of power loss. Many materials are superconducting at very low temperatures close to absolute zero , but recent work has moved the so-called transition temperature where superconducting properties appear to higher and higher values. There are still no superconductors that can operate at room temperature, but this goal is actively pursued. As more current is passed through.
The development of a full, predictive theory of high-temperature superconductivity would be a major asset to the realization of practical materials in this area. The materials studied to date are also difficult to process—they are easily corroded or brittle—thus motivating further study of novel processing or assembly techniques. If practical superconductors can be made that will conduct appreciable currents at reasonable temperatures—perhaps even from organic materials—it may become possible to transfer electric power over long distances with high efficiency, and to exploit magnetic levitation for transportation systems.
The first demonstration of continuous electrical tunability of spin coherence the state and degree of alignment of electronic spins in semiconductor nanostructures has recently been made. This opens possibilities for the field of quantum computation by permitting properties other than electronic charge—and particularly the quantum property of spin—to be manipulated for computing purposes. Spin, often described by analogy with rotation of the earth, is a quantum property of electrons and some atomic nuclei that must have one of two possible values analogous to clockwise or counter-clockwise rotation of a rotating body.
While magnetic fields are conventionally used to manipulate spins in familiar magnetic devices like hard-disk drives, this demonstration of electrical control of aligned spins represents a significant step toward making new spin-based technologies. One future technology is quantum computing, where many schemes make use of electron spin states as bits of information analogous to the 0 and 1 of binary computing.
Unlike ordinary bits, quantum bits can be any combination of both 0 and 1 simultaneously, corresponding to a continuous range of possible directions. By classical mechanics, magnetic fields can modify the behavior of spins by inducing precession, which is an additional rotation of the spin axis with respect to the magnetic field. While the speed of electron spin precession in a magnetic field is generally fixed by the particular materials used, recent research has shown that both the speed and direction of precession can be continuously adjusted by applying electric fields in specially engineered quantum structures.
Salis, Y. Kato, K. Ensslin, D. Driscoll, A. Gossard, D. Awschalom, Nature , , , Such spin gates are an example of the rapidly developing field of spintronics, which studies electronic devices that are based on electron spin. Spintronics uses magnetic fields to manipulate the distribution of spin coherence, whereas electronics uses electric fields to manipulate charge distribution.
This raises the question, What might spintronics do that electronics cannot? In addition to the longer-term goal of quantum computing, spintronics offers the near-term possibility of revolutionizing the way we think about piecing together different technologies. The creation of nanoscale sandwiches of compound semiconductor heterostructures, with gradients of chemical composition that are precisely sculpted, could produce quantum wells with appropriate properties.
One can eventually think of a combined device that incorporates logic, storage, and communication for computing—based on a combination of electronic, spintronic, photonic, and optical technologies. Precise production and integrated use of many different materials will be a hallmark of future advanced device technology. The opportunities to develop new structures for computing, quantum computation, and spintronics—together with other areas in molecular electronics—raise important issues about the role of computation in the chemical sciences Chapter 6.
In order for chemical scientists to play a major role in converting clever new ideas for computational devices into full-fledged computers, they will have to become increasingly competent in the architectures, algorithms, and protocols that are necessary for reliable computation. Inorganic substances are the components of ceramics, such as those in dinner plates. Ceramics have important industrial uses as well; a typical example is the ceramic insulating materials that are used to suspend power lines.
Ceramics are typically poor conductors of heat and electricity, and they perform well at high temperatures. Consequently, they find applications that take advantage of these properties. Some use of ceramics in automobile engines is being developed to achieve improved fuel efficiency at higher-temperature operation. The fragility of current ceramics and the difficulty in machining them relative to machining. One approach to ceramics with better properties is to overcome their fragility by incorporating them into composites. As chemistry moves from pure materials to organized systems of different materials, composites are leading the way.
A challenge for the future is to invent improved structural materials, probably composites based on resins or on ceramics, that are stable at high temperatures and easily machined. Carbon atoms in pure form can be obtained as materials having two classic types of molecular structure: diamond and graphite. In diamond each carbon atom is linked by equivalent single bonds to four neighboring carbons. The result is a clear very hard material that is used for cutting, in saws with tiny diamonds imbedded in the blades, as tough coatings for metals, and in other industrial uses as well as in jewelry.
By contrast, each carbon atom in graphite is linked to only three neighboring carbons, in a sheet, and some of the electrons are in delocalized pi orbitals that permit them to move easily along the sheets. The extensive aromaticity of carbon sheets leads to electronic transitions with energies in the visible light region, so that graphite absorbs throughout the visible region and is a black material.
In addition, the mobility of the pi electrons in graphite makes it an electrical conductor, in stark contrast to the insulating properties of diamond. A new type of structure has recently been discovered in which the sheets of graphite-like carbons are curved. The first example, called fullerene after the geodesic domes of Buckminster Fuller , has 60 carbons in a sphere. It resembles a soccer ball with its five- and six-sided polygons in contrast to graphite, which resembles a floor tile pattern, with hexagons only. A Nobel prize was awarded in to Robert F. Curl, Jr. Kroto, and Richard E.
Smalley for their discovery of fullerenes. Instead of curling into a sphere, the sheets of carbon with hexagons can also curve into tubes with diameters on the order of 1 nm often called nanotubes , tiny whiskers that are sometimes quite long. Because of the electrical conductivity of pi electrons, these tubes are also electrically conducting, somewhat like graphite. While they are already used in research instruments to probe microscopic structures, one of the challenges is to use these new structures in miniature devices, or as building blocks for organized chemical structures.
The importance of crystal form often is underappreciated. In many applications—from drugs in which bioavailability may be determined by crystal form to explosives where crystals may differ in stability and optical devices where the nonlinear optical properties required for the device are based on a particular crystalline architecture —the correct crystalline form is essential to obtaining the desired chemical and physical properties of a material. Crystallization has long been an art rather than a science; sometimes the same substances will exhibit polymorphism and adopt different crystalline forms depending on the crystallization conditions.
Crystal engineering—the prediction and control of molecular crystal structures based on the constituent molecular structures—is on the verge of becoming a science. The current generation of computers is finally powerful. As computer capability increases, and as the sophistication of the programs used increases, it seems very probable that it will soon be possible to predict the structures of crystals. Learning to template or guide desired organization of molecules will have great utility. The scale of components in complex condensed matter often results in structures having a high surface-area-to-volume ratio.
In these systems, interfacial effects can be very important. The interfaces between vapor and condensed phases and between two condensed phases have been well studied over the past four decades. These studies have contributed to technologies from electronic materials and devices, to corrosion passivation, to heterogeneous catalysis. In recent years, the focus has broadened to include the interfaces between vapors, liquids, or solids and self-assembled structures of organic, biological, and polymeric nature.
In a simple material, its surface properties are dictated by the properties of the bulk, which are not necessarily desirable. For example, we may need a bulk material for its strength but want to make a medical device—such as an artificial heart—where the surface must not cause a reaction leading to rejection or blood clotting.
This leads to the challenge of learning how to add biocompatible surface layers to materials.
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This challenge is not yet fully met, but interesting approaches to creating biomimetic functionality on surfaces are rapidly emerging. This field is an example of the transition of chemistry from pure materials to organized systems and materials, in this case the organization being the modification of the surface with a different material for a biofunctional purpose. The ability to modify surfaces by attaching chemicals to them has for years encouraged scientists to attempt to design surface adhesive and wetting properties.
The advent of self-assembled monolayers, including mixtures of molecules in a monolayer, has led to more detailed control and understanding of surface adhesion and wetting. This capability has been extended with the use of novel monolayers to alter liquid-crystalline anchoring processes, surface friction, and biocompatibility. Important applications of this approach have arisen in microfluidics and liquid crystalline displays.
Work pioneered by Nuzzo and Allara at Bell Laboratories in the early s with thiol self-assembled monolayers on gold has led to a great deal of research, much of which has been revolutionary. Thus the study of surfaces has emerged as an important focus in the chemical sciences, and the relationship between surfaces of small systems and their performance has emerged as a major technological issue. Flow in microfluidic systems—for example, in micromechanical systems with potential problems of stiction sticking and adhesion and for chemistry on gene chips—depends on the properties of system surfaces.
Complex heterogeneous phases with high surface areas—suspensions of colloids and liquid crystals—have developed substantial. In certain size ranges, we have seen new and scientifically engaging phenomena, such as electron tunneling through nanometer-thick insulators and diffraction of light in photonic band-gap crystals.
New tools and systems—from scanning tunneling microscope and atomic force microscope STM and AFM to self-assembled monolayers and carbon nanotubes—have fundamentally changed our ability to characterize and prepare these complex systems. Finally, microelectronics—complex systems of small functional components fabricated in silicon and silicon dioxide, and other materials—have become so important that we must develop the science and technology relevant to future systems of small components, whether based on microelectronics or other technologies.
The microelectronics industry is entirely based on chemical processing, using such techniques as chemical vapor deposition CVD , plasma processing, etching, and electroless deposition. As the analytical, synthetic, and physical characterization techniques of the chemical sciences have advanced, the scale of material control moves to smaller sizes.
Nanoscience is the examination of objects—particles, liquid droplets, crystals, fibers—with sizes that are larger than molecules but smaller than structures commonly prepared by photolithographic microfabrication. The definition of nanomaterials is neither sharp nor easy, nor need it be. Single molecules can be considered components of nanosystems and are considered as such in fields such as molecular electronics and molecular motors. We will define somewhat arbitrarily nanoscience as the study of the preparation, characterization, and use of substances having dimensions in the range of 1 to nm.
Many types of chemical systems, such as self-assembled monolayers with only one dimension small or carbon nanotubes buckytubes with two dimensions small , are considered nanosystems. Whether there is currently a nanotechnology is a question of definition. There is, however, a range of important technologies—especially involving colloids, emulsions, polymers, ceramic and semiconductor particles, and metallic alloys—that currently exist.
But there is no question that the field of nanoscience already exists. As new tools have become available for the preparation and characterization of systems with these dimensions, the opportunities in the chemical sciences have grown enormously. The attention. There is great interest in the electrical and optical properties of materials confined within small particles known as nanoparticles. These are materials made up of clusters of atoms or molecules that are small enough to have material properties very different from the bulk.
These are key players in what is hoped to be the nanoscience revolution. There is still very active work to learn how to make nanoscale particles of defined size and composition, to measure their properties, and to understand how their special properties depend on particle size. One vision of this revolution includes the possibility of making tiny machines that can imitate many of the processes we see in single-cell organisms, that possess much of the information content of biological systems, and that have the ability to form tiny computer components and enable the design of much faster computers.
However, like truisms of the past, nanoparticles are such an unknown area of chemical materials that predictions of their possible uses will evolve and expand rapidly in the future. Several techniques are now available for the fabrication of nanostructures. These techniques arise from four approaches, and their simultaneous applicability to a common set of targets is one of the reasons for the excitement in the field. The first set includes the classical techniques developed from microfabrication:.
The characterization of simple nanostructures is now possible with remarkable detail, but is highly dependent on access to the tools of measurement science and to scanning probe microscopies.
These methods have made available a set of nanostructured systems that have begun to reveal the characteristics of nanoscale matter. The long list of discoveries in the last decade includes:. Two important conclusions have emerged in this field. First, the methods employed for microelectronics—photolithography using UV wavelengths—are unlikely to provide inexpensive access to nanostructures. In particular, chemical affinities should make it possible for tiny structures and devices to self-assemble spontaneously, an appealing idea for large-scale manufacturing.
Many of the challenges of the formation and processing of new materials will be met with advances in the chemical sciences. There are some revolutionary things happening in materials: organic electronics and spintronics, attempting to replace classical silicon electronics, the exploration of single-molecule electronics to achieve the ultimate in size reduction, sophisticated biocompatible materials for tissue engineering, implants, man-machine hybrids, ferromagnetic organic materials, materials with negative index of refraction, nanoelectronics, and functional colloids.
Self-assembly and nanotechnology are advancing rapidly, but the challenge still remains to develop a means of fabrication and manufacturing. The rapid developments in synthetic chemistry produce myriad new polymeric and composite materials. These advances are enhanced by progress in optical, micromechanical, and spectroscopic probes. The miniaturization and diversification of synthesis through biological or combinatorial approaches provide unprecedented. The approach to the future should be a holistic one, with synthetic advances moving in concert with assembly and microstructural control.
Summarized below are a few of the leaps that can be viewed as important aspirations for the chemical science community. The development of templated syntheses—of metallic, ceramic or semiconductor particles, wires using novel synthetic and self-assembling structures such as dendrimers, micelles, and nanotubes—is in its infancy. This is a prime example where synthetic advances in the creation of new lipids, surfactants, and amphiphilic polymers work together with probes of structure and function of infinitesimal wires or particles.
New techniques such as scanning microscopy must be developed to follow the electronic and magnetic processes occurring in the small systems. Spectroscopists, microscopists, engineers, and chemists must work together at the frontiers involving techniques developed by those from disparate fields of electronics and biology. The ability to program synthetic polymers with the correct information to self-assemble, recognize analytes, or provide biological function seems fairly futuristic.
However, the close interplay between chemical composition and physical interactions makes this a possibility; new synthetic approaches involving controlled living polymerizations and biological synthetic pathways allow control of molecular composition.
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Additional research on the balance of physical forces driving self-assembly, recognition, field responsive behavior, and biological compatibility should be closely tied to the synthetic efforts. New approaches in synthetic chemistry and biochemistry pave the way for tremendous advances in self-assembly. Highly controlled living polymerizations will allow the creation of ever more complex macromolecules having prescribed architectures branching, stereoregularity and chemical specificity.
Many welcome the possibilities in industry to enter management positions, while others continue their research as senior scientists. You can find graduates from our program in many places, not restricted to the academia or industry. There are people working for the government, writing articles for scientific papers, making policies in all sorts of fields, working for consultancy bureaus, etcetera. A professional academic career usually starts with a PhD followed by a post-doc.
If you are a domestic student, most often you do your PhD in The Netherlands and your post-doc somewhere else, typically in Europe, North America or Oceania. After that you acquire a position at a university or research institute, often in the form of a tenure or habilitation track depending on the country. The highest rank that you can reach is that of full professor. There are professors in microbiology, physical chemistry, cell biology, organic chemistry, biotechnology, etcetera, who did our MSc program in Molecular Life Sciences.
After following some courses in education and an education internship it is possible to become a full registered teacher in Chemistry 'eerstegraadsbevoegdheid Scheikunde'. After this you follow the education master's of the university of Utrecht or Radboud University Nijmegen. Usuallly half year of education courses followed during the MSc Molecular Life Sciences count as a part this eduction master's.
The other year will be extra after your graduation in Wageningen. The Dutch government provides some extra financial support for students following the education master's for chemistry. For orientation on education please visit the site of the education minor and the site of Education and Competence studies of Wageningen University. Go directly to: Content Search box Breadcrumb. Careers There are probably no two individuals with the same career.