Humboldt-Spektrum 2-3/2003
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Das Institut für Chemie in Adlershof Das Jahr der Chemie
Erhard Kemnitz
Heft 2-3/2003, S. 8-10.
www.chemie.hu-berlin.de/kemnitz/index.html
abstract
Die Chemie steht wohl wie kaum eine andere Wissenschaft im Spannungsfeld sehr unterschiedlicher Bewertung: Sie hat - für viele unbewusst - mit ihren Produkten derart breiten Einzug in unser Leben vollzogen, dass eine funktionierende Gesellschaft ohne direkte oder indirekte chemische Produkte überhaupt nicht mehr vorstellbar wäre. Andererseits wird die Chemie aber auch wie keine andere Wissenschaft - häufig ungerechtfertigt - mit Umweltproblemen und daraus resultierenden Gefahren in Zusammenhang gebracht. Bezüglich dieser beiden Antipoden stellt sich bei genauerer Analyse heraus, dass die wirklichen Zusammenhänge vom »Nichtfachmann« häufig gar nicht oder nur ungenügend verstanden sind. Die häufig anzutreffende, eher reservierte Haltung gegenüber der Chemie resultiert aus nicht ausreichender und sogar häufig unrichtiger Darstellung in den allgemeinen Publikationsorganen. Andererseits muss auch kritisch konstatiert werden, dass die Chemische Wissenschaft und vor allem die Chemische Industrie das notwendige, publizistische Engagement in den zurückliegenden Jahrzehnten nicht beachtet haben. Diese Erkenntnis hat sich inzwischen durchgesetzt, weshalb nunmehr deutlich größere Anstrengungen unternommen werden. Das »Jahr der Chemie« mit all seinen Aktivitäten in diesem Jahr ist dabei nur ein - wenn auch sehr wichtiger - Mosaikstein. (mehr... )
Chemie im 21. Jahrhundert
Hans-Werner Abraham
Heft 2-3/2003, S. 12-13.
www.chemie.hu-berlin.de/abraham/index.html
abstract
Chemische Forschung enthält nicht nur einen guten Teil an Handwerk und Methodik, sondern ist, nimmt man Kreativität und Schaffung von neuen Strukturen, durchaus mit der Kunst vergleichbar. Wohin sind also Kunst und Handwerk der Chemie heute und zukünftig gerichtet? (mehr... )
Beruf des Chemikers als Wissenschaftler. Studienziele und charakteristische Wege an der Humboldt-Universität
Nikolaus Ernsting
Heft 2-3/2003, S. 14-15.
abstract
Es kann sehr spannend sein, ein chemisches Problem zu erkennen und kreativ zu lösen. Dazu braucht man möglichst tiefe Einsicht in Materialien und Moleküle, Bindung und Reaktivität, Struktur und Dynamik und gleichzeitig viel praktische Erfahrung im Labor. Im Beruf des Chemikers sind Theorie und Praxis meistens gleich stark betont. Die Erfindung von Funktionsstoffen, das Auffinden von Wirkstoffen, die Aufklärung von Strukturen und Mechanismen sind lohnende Ziele, wirtschaftlich wie persönlich, und erfordern die ganze Person und den vollen Einsatz. Chemiker für Forschung und Entwicklung werden immer gesucht - zwar nicht beliebig viele, aber immer sehr gute. (mehr... )
Chemie für Schüler. Informationsveranstaltungen für Schüler der gymnasialen Oberstufen zum Chemiestudium
Dr. Horst Hennig / Dr. Hartmut Vogt
Heft 2-3/2003, S. 16-17.
abstract
Es gibt eine Vielzahl von Aktivitäten des Instituts für Chemie, die über das Chemiestudium und die zukünftigen Berufsaussichten informieren. Ziel ist es, mathematisch-naturwissenschaftlich interessierte Schüler schrittweise an die chemische Denk- und Arbeitsweise heranzuführen, ihr naturwissenschaftliches Interesse zu entwickeln und weiter zu festigen. (mehr... )
Supramolecular Chemistry. Molecular Recognition and Molecular Machines
Hans-Werner Abraham
Heft 2-3/2003, S. 18-22.
www.chemie.hu-berlin.de/abraham/index.html
abstract
Two topics of supramolecular chemistry are studied in the Supramolecular Photochemistry group: host-guest complexes based on calixarenes and photoswitchable rotaxanes. - Newly designed calix[4]arenes, substituted with a different number of cycloheptatrienyl or tropylium functions at the upper rim can engender an improvement in the inclusion capability for organic cations, due to an enlargement of the p-basic wall of the host cavity. - Rotaxanes are considered to be prototype molecular machines the »fuel« of which would be light energy at best. Therefore photoactive elements have to be incorporated into such rotaxanes. In order to develop the photo-driven rotaxanes we have chosen as photoreaction the generation of ionic species from neutral precursors. - Actual the first principle investigated is the photoinitiated formation of substituted tropylium salts from arylcycloheptatrienes bearing a leaving group such as the methoxy group. (mehr...)
Tailoring the Chemical Reactivity and Optical Properties of Nanoclusters by Size, Structures and Lasers
Vlasta Bonacic-Koutecký
Heft 2-3/2003, S. 24-27.
www.chemie.hu-berlin.de/vbk/index.html
abstract
The reduction of dimensionality of solid materials imposes extraordinary novel features. Discovery and understanding of the chemical and physical properties of nanostructures (-10-9 m) and other low-dimensional systems have led to numerous technological applications. Prominent examples are new light sources, lasers, information storage and information processing technologies, etc. Agglomerates of atoms - clusters in the size regime in which the structure and the number of atoms control their properties, that means each atom counts, belong to such nanoscale materials. Our research on pure and doped metal clusters focuses on fundamentals as well as on novel applications in the following areas: I. Chemical reaction control or laser selective chemistry of nanoclusters with tailored light fields (ultrashort laser pulse shaping); II. Structure-reactivity relationships of metal oxide clusters as foundations for the development and design of nanoscale catalytic materials and III. Photophysical and photochemical size selective properties of metallic clusters and their potential for optical storage elements and for emitters in optical devices. We bridge the nano with bio science by investigating the metal binding site in the octarepeat domain of the prion protein (PrP) which might induce transition from the native to the pathological form of PrP being responsible for mad cow disease and Creutzfeld-Jacob disease (CJD) in humans. Investigation of above topics requires development of theoretical concepts and methods combining ab initio quantum chemistry with molecular dynamics as well as close cooperation with experimentalists. (mehr... )
Collision-Induced Reactions of Molecular Clusters
Wolfgang Christen
Heft 2-3/2003, S. 28-30.
http://wolfgang-christen.net/home.php
abstract
Due to their importance for heterogeneous catalysis and materials science the interaction of gas-phase particles with solid surfaces has attracted enormous interest. Most investigations however deal with thermal energies and isolated particles, while very little is known about the chemical reactivity at large energy- and particle densities. An exciting, cross-disciplinary approach for the experimental elucidation of chemical and physical processes under such unusual conditions involves the use of molecular reactants embedded in a cluster that is impacted on a solid surface at hypersonic velocities, providing a perfectly defined system on a nanometre scale. These investigations reveal a variety of relevant fundamental mechanisms, including energy transfer, charge transfer, and chemical reactions under (momentarily) extreme conditions of pressure and temperature. (mehr... )
Optical Broadband Spectroscopy with Femtosecond Time Resolution
Nikolaus Ernsting
Heft 2-3/2003, S. 32-35.
www.chemie.hu-berlin.de/ernsting/index.html
abstract
When a dye molecule absorbs a photon from the visible or UV spectral region, then its structure and properties are changed almost instantaneously. The microscopic surrounding (for instance a biopolymer) is thus perturbed and relaxes towards a new equilibrium. The relaxation, which takes about 10-12 s for the systems studied, causes a shift of the fluorescence spectrum over time. By monitoring the fluorescence shift, we measure the ultrafast motion of the surrounding and thereby hope to gain insight into the functioning of the biopolymer. (mehr... )
Metallorganische Chemie des Chroms in ungewöhnlichen Oxidationsstufen und Koordinationsgeometrien.
Modellverbindungen für Heterogenkatalysatoren der Olefin-Polymerisation
Alexander C. Filippou / Sven Schneider
Heft 2-€“3/2003, S. 36-€“40.
abstract
Organometallverbindungen bestehen aus Molekülen mit Metall-Kohlenstoff-Bindungen und bilden die Schnittstelle zwischen Anorganischer und Organischer Chemie. Für die Stabilisierung solcher Verbindungen sind in der Regel Liganden notwendig, welche um das Metallzentrum in wohl definierter räumlicher Anordnung eine Ligandenhülle, (Ligandensphäre) aufbauen. Durch geeignete Wahl des Metalls und der Liganden kann die Reaktivität von Organometallverbindungen gezielt auf vielfältige Weise beeinflusst werden. Diese Vielfalt und die Strukturvariabilität bilden die Grundlage für die vielseitigen Anwendungen von Organometallverbindungen in der organischen Synthese, der Katalyse und den Materialwissenschaften. Unsere Arbeitsgruppe beschäftigt sich mit der Synthese, der analytischen und spektroskopischen Charakterisierung und den Reaktionen von metallorganischen Verbindungen. Im Mittelpunkt stehen dabei die Darstellung neuer Verbindungsklassen, die Bestimmung von Struktur/Wirkungsbeziehungen und deren Verständnis mit Hilfe bindungstheoretischer Ansätze der Quantenchemie. Diese Untersuchungen zielen auf die Entdeckung neuer Reaktionen und die Erschließung neuer Anwendungsgebiete für Organometallverbindungen.(mehr... )
Nanoscience with Atomic Precision
Bernhard Kaiser / Bert Stegemann
Heft 2-3/2003, S. 42-€“45.
abstract
At length scales of several nanometers material properties differ completely from the well-known bulk behavior, i.e. effects due to the reduced size of the system become dominant. Nanotechnology will make use of the emerging new chemical and physical properties of these nanomaterials. The research in the group focuses on how these properties depend on the size of the system in order to design new materials with well-defined functionality.(mehr... )
Properties of »Perfect« and »Imperfect« Solid State Materials
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Erhard Kemnitz
Heft 2-3/2003, S. 46-€“49.
www.chemie.hu-berlin.de/kemnitz/index.html
abstract
Inorganic solid state chemistry has been an innovative field of research for quite some time. The development, modification, and characterization of inorganic solids are, more and more, providing new materials for diverse areas of applications. Solid state chemistry covers an infinite number of aspects, not only the goal of obtaining new crystalline solids with a perfect structure, but also solids with highly distorted structures that are very reactive. In the case of very ordered solids, interest lies in structure motifs determined by single crystal analysis and the corresponding physical properties of this solid. The reactivity of these ordered solids is low, however »imperfect« solids, which have a degree of disorder, are often used in chemical reactions as reactive components, for example for applications in the field of heterogeneous catalysis.(mehr... )
Stereoselective Synthesis
Jürgen Liebscher
Heft 2-€“3/2003, S. 50-52.
www.chemie.hu-berlin.de/liebscher/index.html
abstract
The research interest of the group is directed to the development of new synthetic methods and new products, in particular biologically important compounds. Stereoselective synthesis using amino acids, terpenes or sugar derivatives as chiral agents plays a key function in the synthetic activities. Synthetic targets are analogues of natural products, natural products and activity directed heterocyclic products. Several pharmacological activities, specific enzyme inhibition, molecular recognition and formation of supramolecular assemblies are targeted. At present the group is active in the following projects.(mehr... )
Oxygenations with Metaloxo Compounds. Reactive Intermediates, Mechanisms, and Models
Christian Limberg
Heft 2-€“3/2003, S. 54-€“58.
http://www.chemie.hu-berlin.de/aglimberg/
abstract
Oxygen (lat.: oxygenium) being abundantly present in the air (as dioxygen) would in principal possess enough chemical power to spontaneously »oxidise« all organic matter (including the organisms living on earth), i.e. to convert it into an oxygen-richer form. The fact, that it refrains from doing so, has its origin in a naturally established barrier allowing reactions with most organic compounds only after significant supply of energy (ignition); the resulting process of combustion, however, only leads to useless products like carbon dioxide. Nevertheless, the high oxidative power of dioxygen can be used at room temperature for the synthesis of fine chemicals when metals are utilised, i.e. when for the oxidation of hydrocarbons metaloxo compounds are employed (obtainable form dioxygen via detours) and reactions of that type are of vital importance not only in nature but also in academic and industrial laboratories. With such metaloxo compounds, oxygenation systems and processes we are dealing in our research, and emphasis lies on the clarification of the mostly very complex mechanisms as well as on the synthesis of novel oxygenation reagents and catalysts.(mehr... )
Interactions between Biosphere and Environment. Analysis of Chemically Modified DNA
Michael Linscheid
Heft 2-€“3/2003, S. 60-€“64.
www.chemie.hu-berlin.de/linscheid/index.html
abstract
The food we eat, the air we breathe, the things that surround us, and the drugs we take to overcome our illnesses they all contain natural or man-made compounds which can interact with our cells' building blocks. Most of these reactions are essential to life and follow the paths nature worked out and optimized over the centuries in order to guarantee our survival. This is valid, too, for traditional and modern drugs as well as artificially developed compounds, with the difference that nature enabled our body to identify new and unknown structures, and to deal with them. In case the compounds are useless or even dangerous, certain processes will try to remove them as soon as possible. The compounds will be changed by chemical reactions and made water-soluble, so that they can be eliminated. If this process fails or is too complicated, intermediate compounds can form which react with formerly not attacked parts of the cells, for example the DNA.(mehr... )
INORGANIC MATERIALS / CATALYSIS
The Reactivity of Molecules and Solids. Examples from the Chemistry of Phosphorus
Manfred Meisel
Heft 2-€“3/2003, S. 66-€“69.
abstract
When Henning Brand, a german alchemist, discovered the element phosphorus (greek for bearing light) in 1669, he opened up one of the most fascinating areas in chemistry: the realm of phosphorus compounds. Phosphorus engages in a lot of binding modes, forming a multitude of different compounds. This versatility makes phosphorus one of the ›jack of all trades‹ in inorganic, organic as well as biological chemistry. There are literally thousands of industrial applications of phosphorus compounds, ranging from highly specialized bioresorbable polymers for surgical applications to bulk chemicals like detergents or even fertilizers, which are produced on a scale of millions of tons per year. Other applications include flame proofing agents, food additives, materials for non-linear optics and ferroelectrics.(mehr... )
Chemical Semiconductor Sensors
Werner Moritz
Heft 2-3/2003, S. 70-€“72.
www.chemie.hu-berlin.de/wmoritz/index.html
abstract
Chemical sensors based of the field effect in the semiconductor were developed both for the detection of gases and ions in liquids. A laterally resolved concentration measurement as well as an impedance analysis are likewise possible under use of the photoelectric effect in the semiconductor. The resolution of the method was improved by us down to the submicrometer range.(mehr... )
Molecular Structures, Dynamics and Interactions
Clemens Mügge
Heft 2-€“3/2003, S. 74-€“77.
www.chemie.hu-berlin.de/nmr
abstract
High resolution NMR spectroscopy is one of the most important methods for molecular structure elucidation on atomic level. By means of different measurement techniques NMR can provide information about the molecular structure as well as dynamics and intra- and intermolecular interactions. The applications of NMR spectroscopy embrace the whole range of molecules starting from low weight and inorganic compounds up to high molecular biopolymers (900 kDa proteins).(mehr... )
STRUCTURE AND REACTIVITY OF CLUSTERS
Friction on the Nanometer-Scale. Controlled Manipulation of Nano-Particles by Means of a Homebuilt Scanning Force Microscope
Klaus Rademann / Claudia Ritter
Heft 2-3/2003, S. 78-€“82.
www.chemie.hu-berlin.de/agrad/index.html
abstract
The technique of Dynamic Surface Modification (DSM) by using a homebuilt Scanning Force Microscope (SFM) allows us to perform precise nano-manipulation experiments with adsorbed particles on surfaces and on the substrate itself. We have successfully patterned Polymethylmethacrylate (PMMA) films, Polystyrene (PS) films and manipulated miscellaneous nanoparticles on surfaces, e.g. antimony islands, gold islands, small latex spheres as well as cells. By choosing appropriate values for the energy input into the sample surface, the presented technique allows to easily switch between the different SFM modes: imaging, »writing« on a substrate, translation or in-plane rotation of nanoparticles, marking single nanoparticles, cutting and splitting of nanoparticles and »healing« of these fragments. A direct comparison of the corresponding energy values gives evidence about motion and tribological properties of the adsorbate-substrate system. These experiments give the possibility to obtain insight into basic phenomena of motion and friction. Due to this flexibility, this manipulation technique was found to be suitable to study adhesion, cohesion, and friction of nanoparticles adsorbed on surfaces..(mehr... )
Highlighting Excited Molecules. From Photochemical Mechanisms to Application as Fluorescent Probes
Wolfgang Rettig / Wilfried Weigel
Heft 2-€“3/2003, S. 84-€“89.
www.chemie.hu-berlin.de/wr/index.html
abstract
The field of photochemistry covers all processes which involve chemical changes brought about by absorption of visible or ultraviolet radiation. The major difference between thermal and photochemical reactions originates from the difference in electron distribution in ground and photoexcited states of a molecule. This can lead to a complete alteration of the chemical behavior. The dissipation of the excess energy of an excited species mainly occurs via radiative and nonradiative transitions. Fluorescence and phosphorescence are the two types of radiative transitions where an excited species passes from the excited state to the ground state with the emission of a photon. The photoexcited states that are involved in fluorescence decays usually have very short lifetimes (< 10-6 s). Nonradiative transitions can be viewed as chemical reactions combining reaction paths on ground- and excited state surfaces. Advanced steady-state and time-resolved spectroscopic methods in combination with systematic variations of properties of the surrounding medium, such as the polarity of the solvent or the temperature, can be applied as important tools to elucidate details of the mechanism of the relaxation of photoexcited states.(mehr... )
Structure, Dynamics and Reactivity of Molecules, Clusters, and Solids
Joachim Sauer / Veronica Ganduglia-Pirovano / Jens Döbler / Alexander Hofmann
Heft 2-€“3/2003, S. 90-€“95.
www.chemie.hu-berlin.de/ag_sauer
abstract
Catalysts speed up chemical reactions and direct them to desired products. The production of almost all the materials of our modern life such as polymers and synthetic fibres rely on catalysts. The fuel we burn in the engines of our cars is the product of catalytic processes and the exhaust gas is converted by a catalyst into environmentally less harmful gases. The food we eat is grown with the help of fertilisers with ammonia as a key component. Since 1914 the famous Haber-Bosch process catalytically synthesises ammonia from nitrogen and hydrogen. Enzymes which regulate chemical processes in living organisms are nothing else then highly active and highly selective catalysts.(mehr... )
Biopolymers. Molecular Diagnostics Chemical Biology of Nucleic Acids
Oliver Seitz
Heft 2-€“3/2003, S. 96-€“100.
http://www.chemie.hu-berlin.de/seitz/index.html
abstract
Biopolymers are the key players of life. While nucleic acids are regarded as the molecule of life the majority of life functions are mediated by another class of biopolymers, the proteins. Carbohydrates are yet another class, which constitutes a large portion of biomass. It is our aim to develop new strategies for the synthesis and modification of biopolymers in order to improve upon the existing repertoire of biomolecular tools for biological and medical research. The chapters are intended to summarize our efforts in the field of nucleic acid chemistry and illustrate how chemistry can help in constructing tailor-made probes for the study of biological problems.(mehr... )
Spin resonance as a Bridge between Material- and Bioscience
Reinhard Stösser / Gudrun Scholz / Jeannette Klein / Andrea Zehl / Werner Herrmann
Heft 2-€“3/2003, S. 102-€“109.
abstract
The method of electron paramagnetic resonance (EPR) is based analogously to the nuclear magnetic resonance (NMR) on the interaction of electromagnetic radiation with magnetic moments, i.e. with electronic spin moments and electronic orbital moments interacting among each other, with nuclear moments and with external fields. Unpaired electrons yield in most cases a non-zero spin angular momentum, which can be used as a spectroscopic probe. Corresponding molecular systems are for instance free radicals, biradicals, triplet states, ions of transition metals and lanthanides. Beside the latter, point defects like trapped electrons and holes can be additionally observed in solids. Moreover, special structural and energetic situations allow the stabilization of atomic species such as H, N or free radicals as already mentioned.(mehr... )
Preparative Organic Photochemistry
Pablo Wessig
Heft 2-€“3/2003, S. 110.
http://pro122lin.chemie.hu-berlin.de/wessig/index.html
abstract
Our research group is working on several areas of Preparative Organic Photochemistry. The photochemical preparation of organic compounds differs from other methods in that the energy is supplied by irradiation instead of heating. By this way a reaction course can be achieved, which often differs substantially from that of thermal reactions. Furthermore, owing to the high energies supplied to a molecule by photochemical excitation, highly strained and reactive products can be obtained.(mehr... )
INSTITUT FÜR ANGEWANDTE CHEMIE / ACA
Heterogene Katalyse. Eine ständige Herausforderung an die anwendungsorientierte Forschung
Manfred Baerns / Angelika Brückner / Evgenii Kondratenko / David Linke / Andreas Martin / Uwe Rodemerck
Heft 2-€“3/2003, S. 112-115.
www.aca-berlin.de/german/index.html
abstract
Das Verständnis der Katalyse und die Entwicklung heterogener Katalysatoren für chemische Produktionsprozesse ist während der letzten 100 Jahre eine ständige Herausforderung an Wissenschaft und Technik gewesen, ohne dass ein Erkenntnisstand erreicht ist, der es in der Regel erlaubte, a priori Voraussagen über die katalytische Wirkungsweise eines Feststoffmaterials für ein industrielles Verfahren zu treffen. Aktuelle Beispiele aus der Arbeit des Instituts für Angewandte Chemie Berlin-Adlershof e.V. (ACA), das dem Institut für Chemie der Humboldt-Universität zu Berlin eng verbunden ist, dienen der Erläuterung der erforderlichen anwendungsorientierten Forschung auf diesem Gebiet. Es werden katalytische Reaktionen und die dabei auftretenden Wechselwirkungen zwischen Reaktanten und Katalysator sowie methodische Vorgehensweisen bei der Entwicklung neuer Katalysatoren, denen eine aus der Biologie bekannte Evolutionsstrategie zugrunde liegt, sowie der Einsatz von mikrostrukturierten Reaktoren als Entwicklungs- und Produktionswerkzeug erläutert.(mehr... )
Peptide Chemistry
Michael Bienert
Heft 2-3/2003, S. 118-€“119.
www.fmb-berlin.de
abstract
Peptides and proteins are the most abundant biological macromolecules, ranging in size from relatively small peptides to huge polymers. They are constructed from a set of 20 amino acids, covalently linked in characteristic sequences, exhibiting strikingly different biological properties. Even the smallest peptide can exert biological effects at very low concentrations.(mehr... )
GDCh Memorandum Analytics. German Chemical Society (GDCh)
Georg-Alexander Hoyer
Heft 2-€“3/2003, S. 122-€“123.
http://www.gdch.de/
abstract
Analytics is an interdisciplinary science that embraces various branches of learning; if materials are the main focus it is also known as »Analytical Chemistry«. The end results of Analytics can be expressed in terms of quantity and quality. Material-analytical problems are indeed ubiquitous and by no means related solely to disciplines of the natural science. On the contrary, Analytics increasingly represents a dominating force in industry's added value chain. Ever increasing numbers of quality characteristics are attributed to products and processes, which illustrates the spreading dominance of Analytics in all areas of life.(mehr... )
Juniorprofessuren / Neuerscheinungen
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