bluuebunny/crossref_metadata_2025 huggingface dataset:
Solid Ion Conductors in Heterogeneous Catalysis
Authors: Lintz Hans‐Günther , Vayenas Costas Georgios
Published: December 2003

The electrochemical measurement of oxygen activity using ion‐conducting solid electrolytes (λ‐sensors) has become widely known, at least since the application of three‐way catalysts in the postcombustion of exhaust gases from spark‐ignition engines. However, the use of solid ion conductors is not limited to control devices. There are various other potential applications and numerous problems which can be studied: the formation of oxides in the course of catalytic reactions on metal surfaces, the improvement of selectivity and yield of catalytic reactions, such as the epoxidation of ethylene on silver catalysts and, finally, the cogeneration of electrical energy during oxidation reactions, such as the partial oxidation of methanol to formaldehyde.
Probing Changes in the Structure and Performance of a Lithium Nickel Oxide Catalyst by in situ X‐Ray Diffraction During the High‐Temperature Oxidative Coupling of Methane
Authors: Pickering Ingrid J. , Maddox Peter J. , Thomas John M.
Published: December 2003

Communication: The advantages of in situ X‐ray diffraction in clarifying the onset and nature of the distinct kinds of catalytic action exhibited by a lithium nickel oxide for the oxidation of methane at elevated temperatures are demonstrated. Active solids may possess structural features quite unlike those deduced from measurements conducted at ambient temperatures and pressures emphasizing the need for the development of in situ methods.
Structure of Anodic Oxide Coatings on Aluminum
Authors: Kniep Rüdiger , Lamparter Peter , Steeb Siegfried
Published: December 2003

Communication: The structure of the remarkably uniform array of pores in surface coatings on aluminum has been investigated using X‐ray and neutron diffraction techniques. The almost hexagonally shaped cells make the films of interest for application in the field of synthetic membranes and as supports for active materials.
Calorimetric Studies of Biopolymers and Aggregates of Phospholipids
Authors: Ackermann Theodor
Published: December 2003

The structural transformations that biopolymers undergo in aqueous solution are complex processes, whose mechanisms can only be explained by the coupling of various partial processes. A spectroscopic analysis of the states of the system often requires considerable effort. In many cases, calorimetric studies have proven to be sufficient for a general characterization of the behavior of the system. These measurements provide information on the stability of the initial state and on the cooperativity of the total process. From the thermodynamic parameters of the system, knowledge on the structure‐determining influence of the various types of inter‐ and intramolecular interactions is obtained. This not only applies to solutions of biopolymers and analogous model substances, but also to solutions of biopolymer complexes with low‐molecular‐weight ligands and to aqueous suspensions of self‐aggregating phospholipids. Possibilities and limitations of the calorimetric methods of measurement are demonstrated for typical examples from the numerous polypeptide and polynucleotide systems and the phospholipid bilayer systems that have been studied. In addition, the special problems involved in carrying out measurements on dilute solutions are pointed out. Here, the latest advances made in measuring techniques are readily apparent.
Covalent versus Dative Bonds to Main Group Metals, a Useful Distinction
Authors: Haaland Arne
Published: December 2003

Textbooks of inorganic chemistry describe the formation of adducts by coordination of an electron donor to an electron acceptor, often using the amine‐boranes, X3N → BY3, as examples. In the Lewis (electron dot) formulas of the compounds, the dative bond in H3N → BH3 and the covalent bond in H3CCH3 are both represented by a shared electron pair. In the simple molecular orbital or valence bond models the wave functions of both electron pairs would be constructed in the same manner from the appropriate sp3 type atomic orbitals on the bonded atoms; the difference between the covalent and the dative bond becomes apparent only after the orbital coefficients have been analyzed. This may be the reason why many structural chemists seem reluctant to distinguish between the two types of bonds. The object of this article is to remind the reader that the physiocochemical properties of covalent and dative bonds may be – and often are – quite different, and to show that a distinction between the two provides a basis for understanding the structures of a wide range of main group metal compounds.
Visualization of Chromatographic Separations by NMR Imaging
Authors: Bayer Ernst , Müller Winfried , Ilg Martin , Albert Klaus
Published: December 2003

NMR imaging allows in‐situ observation of interactions between eluant and stationary phase in chromatographic columns. This method, referred to as magnetic resonance tomography in medicine, has been little used so far in chemistry. It provides information on the state of the column (e.g., packing quality and density, flow profile) and allows substances to be observed as they pass through the column.
Materials for the Next Millenium
Authors: Hondros Ernest D. , Bullock Edward
Published: December 2003

Review: The future of mankind will be influenced by our attitudes towards the overuse of today's materials and to the development and exploitation of new ones. Current supply and demand trends are analyzed and themes of future significance are examined, which include microstructure control and the design of functional materials.
Imaging Organic Molecules with the Scanning Tunneling Microscope
Authors: Rabe Jürgen P.
Published: December 2003

Research News: The lack of electrical conductivity and the constant molecular mobility of organic molecules have, in the past, restricted the successful imaging of these systems by STM. Recently, however, a number of new organic systems have been imaged. Jürgen Rabe reports on these new developments and in the future will write regularly for ADVANCED MATERIALS on surface analysis techniques especially scanning microscopy methods.
High Resolution Solid State NMR of Quadrupolar Nuclei
Authors: Blümich Bernhard
Published: December 2003

Research News: Dynamic Angle Spinning (DAS) and Double Rotation (DOR) solid state NMR are two new methods which have recently been applied to the study of elements with half integral quadrupolar spins. An increase in resolution is achieved over magic angle spinning (MAS) NMR by spinning the sample at two different angles, either sequentially (DAS), or simultaneously (DOR).
The Crystal Chemistry of High‐Temperature Oxide Superconductors and Materials with Related Structures
Authors: Müller‐Buschbaum Hanskarl
Published: December 2003

Never before in human history has a chemical substance been the object of collaborative research by so many scientists of different disciplines as in the case of the first high‐temperature (HTc) oxide superconductor La2−xSrxCuO4. If the importance of a class of materials is measured by the number of papers published in a given period, the new superconductors hold the all‐time record; moreover, this flood of publications also reflects the high expectations that are held worldwide for this class of substances. Every day seems to bring further surprises. From the two phases of HTc oxide superconductors that were recognized at the outset there have developed within a period of scarcely two years a series of new materials which all show superconductivity at temperatures above the boiling point of liquid nitrogen; this property is undoubtedly closely related to the crystal chemistry of the individual phases and compounds. This article will report and discuss the resemblances and differences between the HTc superconductors and materials with related structures.
Highly Conjugated, Substituted Polyacetylenes via the Ring‐Opening Metathesis Polymerization of Substituted Cyclooctatetraenes
Authors: Gorman Christopher B. , Ginsburg Eric J. , Marder Seth R. , Grubbs Robert H.
Published: December 2003

Communication: Soluble polyacetylenes with high conjugation length and high molecular weight are a goal of polymer scientists. The ring‐opening metathesis polymerization of substituted cyclooctatetraenes (COT) to form soluble substituted polyacetylenes which display iodine doped conductivities in the range 0.1 to 50 S/cm are reported. The solubility is imparted by the alkyl groups which occupy, on average, every eighth carbon atom of the polymer backbone.
The Nature of Materials Science Publishing
Authors: Gregory Peter
Published: December 2003

Editorial Essay: The best way to present results, opinion, news and information to the widest possible audience is the subject under discussion. As, in this issue, Advanced Materials and Angewandte Chemie appear together for the last time, it is appropriate to comment on the approaches taken by leading journals both in materials science and in other areas.
Polysilanes—A New Look at Some Old Materials
Authors: Miller Robert D.
Published: December 2003

In spite of the fact that the first polysilane derivatives were probably prepared in the mid 1920's, there was little scientific interest until recently. The synthesis of the first soluble homo and copolymers about 10 years ago has stimulated an explosive development of this class of materials. This brief review traces the historical development of the polysilanes and focuses on recent studies of polymer structure, electronic properties, photochemical reactions and mechanisms and finally on new applications.
Macromolecular Physics in Lodz
Authors: Byrne Hugh J.
Published: December 2003

Conference Reports: Rainhard Laag reports on the Powder Metallurgy '89 meeting, Hugh Byrne gives us a taste of macromolecular physics in Poland and Peter Bachmann describes a recent meeting on surface modification technology held in Switzerland.
Replication Experiments with Nucleotide Base Analogues
Authors: Tamm Christoph , Strazewski Peter
Published: December 2003

The principles governing the replication fidelity of genomes are not fully understood yet. Watson and Crick's base‐pairing principle for matched deoxyribonucleotide (DNA) bases can explain why the guanine–cytosine and adenine‐thymine base pairs are approximately one hundred times more stable thermodynamically than mismatched combinations. In vitro, DNA polymerases reduce the number of mismatched base pairs to about 10−6 per Watson–Crick base pair. Replication fidelity can further be enhanced to a mutation probability of 10−10or less in vivo if optimal conditions for DNA synthesis are provided by polymerase–assisting proteins and DNA‐repairing enzymes. The precise reasons for the formation of mismatched base pairs (mispairs), which are responsible for a substantial part of DNA mutations, are still in debate. Although it is agreed that a template‐directed “reading” of the hydrogen‐substitution pattern in the heterocyclic bases is crucial for proper base pairing during DNA synthesis, it is not clear which type of “misreading” leads to mispairs. Misreading may be due to a non‐Watson–Crick base pairing as well as to a change in the hydrogen‐substitution pattern, leading to Watson‐Crick‐like mispairs. The surprising discovery of the selective and quantitative DNA‐polymerase‐catalyzed formation of a pyridine‐pyrimidine base pair (involving a nucleotide base analogue) indicated that rare tautomeric forms in template DNA strands can lead to Watson‐Crick‐like mispairings that are hardly recognized by the polymerase's proofreading activity. This reveals new pathways for substitution mutations (replication‐dependent DNA point mutations) and suggests a new type of mutagen in vivo.
NMR Study of Nuclear Spin Polarization during Chemical Reactions with Ortho Hydrogen
Authors: Bargon Joachim , Kandels Jörg , Woelk Klaus
Published: December 2003

Polarization signals in NMR spectra do not necessarily point to reactions via radicals. This is confirmed by hydrogenations (a) with enriched ortho and para hydrogen, in which polarization signals were observed in each case, albeit with different intensity and reversed sequence of emission and absorption. The intensity ratio can be correlated with the ratio of the ortho and para hydrogen, and thus it is unequivocally confirmed that the nuclear spin states of the H2 molecules are responsible for the non‐equilibrium occupation of the product nuclear spin level.
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Structure–Magnetism Relationship in [TiIII‐OTiIII]4⊕ Complexes
Authors: Bodner Axel , Drueke Stefan , Wieghardt Karl , Nuber Bernhard , Weiss Johannes
Published: December 2003

The temperature‐independent magnetic moment in complex 1 corresponds almost exactly to the spin‐only value of one unpaired electron per TiIII center, whereas 2 is diamagnetic. This is attributed to the fact that the [TiOTi]4⊕ unit in 1 is very likely linear, while in 2 it is bent (122.7°). Other than in 2 the d orbitals in 1 cannot overlap, and a spin‐spin coupling is therefore ruled out here (L = N,N′,N′‐trimethyl‐1,4,7‐triazacyclononane).
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Boron‐Phosphorus Compounds and Multiple Bonding
Authors: Power Philip P.
Published: December 2003

Boron‐phosphorus compounds have not been as thoroughly studied as their boron‐nitrogen counterparts. Until recently many classes of B‐P compounds that had been well established in B‐N chemistry were either unknown or poorly characterized. This statement is particularly true for compounds involving possible multiple bonding between boron and phosphorus. For example, detailed structural information on simple monomeric phosphino‐boranes, R2BPR′2, did not become available until 1986 even though the isoelectronic SiC double bonded species, the silenes, had already been reported. However, new work has shown that it is possible to prepare and characterize several novel types of boron‐phosphorus compounds with varying degrees of multiple B—P bonding. These include not only monomeric phosphinoboranes but also phosphanediylborates (borylphosphides), three‐ and four‐membered rings (diphosphadi‐boretanes), boron phosphorus analogues of borazine, B‐P skeletal analogues of allyl cations and anions, butadiene and cage compounds. Structural, spectroscopic (mainly NMR) and theoretical studies reveal some important differences between B‐P and B‐N compounds which in many cases can be traced to the presence of a high inversion barrier at phosphorus that reduces the π interaction. This usually causes compounds such as R2BPR′2 to associate through σ bonding between B and P. Supporting evidence for this view comes from species that involve phosphorus and nitrogen in competitive π bonding with a boron p orbital in which the dative interaction between B and N is dominant and the phosphorus center remains pyramidal. Recently published work has shown that steric and electronic factors can be used to favor π bonding and give an approximately planar system. Furthermore, theoretical studies reveal that pp π overlap in a planar B‐P system is of similar efficiency to its B‐N analogue. Good examples are seen in the phosphanediyl borates, the boron‐phosphorus analogues of borazine and the π‐allyl cations, whose molecular configurations and B—P bond lengths support strong boron—phosphorus π bonding.
The Chemistry of Vitamin A and Vision
Authors: Rando Robert R.
Published: December 2003

Vision is initiated in the retina by the photochemical isomerization of an 11‐cis‐retinal Schiff base to its all‐transcounterpart in the photosensitive protein rhodopsin. All‐trans‐retinal is released, reduced to form all‐trans‐retinol (vitamin A), and finally esterified. In order for vision to proceed an 11‐cis‐retinoid must be regenerated in the eye.Kühneobserved in the 1870s that the pigment epithelium must be in place behind the retina in order for rhodopsin to form. And indeed it was in the pigment epithelium that an isomerase system was recently discovered that can produce 11‐cis‐retinol from added vitamin A.Paulingpredicted in the 1930s that certaincisdouble bonds in carotenoids and retinoids, including 11‐cis‐retinoids, should be quite unstable with respect to their all‐transcongeners. This prediction is borne out by experiment, but leaves open the crucial question as to where the energy comes from to drive the isomerization process in the eye. This question was answered by the demonstration that the energy is found in the membrane phospholipids. The fact that membranes may serve as an energy source reveals a previously unsuspected biological function of membranes. The chemistry of the novel energy‐linked isomerization process is explored in this review.
New Aspects of the Maillard Reaction in Foods and in the Human Body
Authors: Ledl Franz , Schleicher Erwin
Published: December 2003

The reactions that occur during the cooking, baking, and preservation of foods of all kinds are of great importance for the production of aroma, taste, and color. However, more recently it has been shown that these reactions may be accompanied by a reduction in nutritive value and the formation of toxic compounds. For these reasons, the very complex reactions between reducing sugars and the free amino groups of amino acids or proteins, known as non‐enzymatic browning or the Maillard reaction, have again caught the interest of chemists. The Maillard reaction came to be seen in a new light as it was realized that it actually occurred in the human body. As a general rule, the longer the half‐life of a protein, the larger the amount of its Maillard products found, i.e., important factors are the ‘age’ or persistence of the protein in the body and the glucose concentration, particularly in diabetics. Many of the symptoms developed by diabetics resemble those of premature aging, which leads to the possibility that glucose, because of its reactivity towards proteins, is fundamentally involved in the normally slow progress of aging.
The Coordination Chemistry and Organometallic Chemistry of Tridentate Oxygen Ligands with π‐Donor Properties
Authors: Kläui Wolfgang
Published: December 2003

Metal complexes are capable of accomplishing almost anything, provided they contain the proper metal/ligand combinations. A host of essential biochemical transformations—but also a great many industrially significant reactions—occur within the coordination spheres of metal ions. For instance, the particular arrangement of ligands in the zinc‐containing enzyme carboanhydrase is responsible for an acceleration in the hydration of CO2 by a factor of 109. It is the ligands that determine whether an iron atom will transfer molecular oxygen, as in the case of hemoglobin, or electrons, as with the cytochromes. By varying the ligands it is possible to establish in advance whether a metal ion in the presence of synthesis gas will cause an olefin to be hydrogenated or hydroformylated. Stated more generally, it is the ligands that stabilize the particular oxidation states of a metal and determine how substrate molecules will be coordinated and undergo reaction. The synthesis of new ligands that confer specific reactivity on metal ions is thus an important challenge for the coordination chemist. The following article describes organometallic compounds of the type [CpCo{P(O)R′R″}3]⊖, which have developed from an extremely unreactive laboratory curiosity into versatile oxygen‐containing ligands whose steric and electronic properties promise a series of interesting applications.
Solvent and Structure Effects in the Photobromination of Benzyltrimethylsilanes. A Mechanistic Changeover from Hydrogen‐Atom Transfer to Electron Transfer
Authors: Baciocchi Enrico , Crescenzi Manuela
Published: December 2003

The mechanistic dichotomy in the reaction of Br• with arenas could be demonstrated with the photobromination of aryltrimethylsilanes as example: depending on the solvent, benzyltrimethylsilane 1 reacts with Br• with hydrogen atom transfer [CC14 or AcOH; route (a)] or with electron transfer [AcOH/CF3CO2H; route (b)]. Electron donating substituents on the phenyl ring of 1 promote reaction according to route (b) in AcOH.
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Electromagnetic Traps for Charged and Neutral Particles (Nobel Lecture)
Authors: Paul Wolfgang
Published: December 2003

Individual atomic and subatomic particles may be observed over long periods by confining them in “traps without material walls”. The Nobel Prize in physics was awarded in 1989 to Hans Dehmelt and Wolfgang Paul (together with Nor‐man F. Ramsey) for first introducing this concept. Such traps are made possible by extending the principles of two‐dimensional focusing of particles to three dimensions. This led, in turn, to precision radiofrequency spectroscopy and quadrupole mass spectrometry. For example, side‐band cooling, in which electrons absorb photons with an energy just below the resonance energy and use their kinetic energy to supply the balance, allowed an electron to be held for ten months in the center of a magnetic trap. In this way, ½ g was determined to be 1.001159652188(4).
Syntheses, Conformations and X‐Ray Structure Analyses of the Saccharide Chains from the Core Regions of Glycoproteins
Authors: Paulsen Hans
Published: December 2003

The covalently bound carbohydrate moiety in glycoproteins can stabilize the protein molecule intramolecularly, or it may have an intermolecular function as receptor in biological recognition. The discovery of these biological phenomena has led to a renaissance of the chemistry and biochemistry of carbohydrates. Both N‐glycoproteins as well as O‐glycoproteins contain special, invariant oligosaccharide chains in the protein‐binding region, which occur again in all glycoproteins, and are described as the “core regions.” This review describes the various methods of oligosaccharide synthesis that may be used to arrive at the basic core structures by chemical means. Methods of oligosaccharide synthesis have improved so much that it is possible to synthesize complex lactosamine‐type structures, and “bisected”‐type structures up to nona‐ and undecasaccharides respectively. Oligosaccharide chains are considerably less flexible than peptide chains. Using modern methods of NMR spectroscopy, their preferred solution conformation can readily be determined. In the case of one branched octasaccharide, a comparison of the conformations in solution and in the crystal is possible. Oligosaccharides may be linked to the amide group of an asparagine, or to the hydroxyl groups of serine or threonine. By using suitable protecting groups, the glycosyl amino acids obtained can be extended with further amino acids at the N‐ or C‐terminus, thus arriving at the desired glycopeptide sequences. In the linkage region, glycopeptides prefer certain conformations. Future research into glycoprotein functions may involve the synthesis and biochemical study of modified glycoprotein segments.
The Myelin Membrane of the Central Nervous System—Essential Macromolecular Structure and Function
Authors: Stoffel Wilhelm
Published: December 2003

The neural sheaths that surround the nerve fibers (axons) are composed of myelin‐specific complex lipids and are assembled during the myelination phase either by the oligodendrocytes in the central nervous system (CNS) or by the Schwann cells in the peripheral nervous system. These multilayered myelin membranes insulate the axons and permit a rapid, saltatory conduction of excitation and a reduced axon diameter in comparison with noninsulated axons. Myelination was hence the decisive evolutionary event in miniaturization of the central nervous system (brain and spinal cord). The morphology of the myelin membrane has been studied in detail mainly by electron microscopy. Most of its biochemistry has been elucidated in recent years by molecular‐level analysis of both the lipid components (cholesterol, phospholipids and sphingolipids) and the constituent proteins. The multilamellar system is distinguished by a characteristic periodicity due to the 5‐nm‐thick bilayer formed by the myelin‐specific lipids. The bilayer interacts with the myelin basic protein (MBP) on the cytosolic side of the plasma membrane process, while the integral membrane protein proteolipid protein (PLP) has hydrophilic domains exposed on both the cytosolic and extracytosolic faces of the bilayer. Numerous protein‐chemical and ‐immunotopochemical findings have been summarized in a model of the myelin membrane. Through molecular biological studies, the genetic structure and chromosomal location of the myelin proteins have been determined. By employing techniques of molecular and cell biology together, it is now possible to analyze the process of myelinogenesis, the time‐ and location‐specific expression of myelin‐specific genes in the brain. Gene‐technological methods have been used to define the mutations in the models jimpy mouse and myelin‐deficient rat. These are animal models that correspond to genetically determined myelin defects (dysmyelinoses) in humans. Using them, it will be possible to study the cell death of oligodendrocytes on a molecular level; this process is the result of expression of mutant myelin proteins and is incompatible with life. Oligodendrocytes and the myelin structures they synthesize are the target structures of cytotoxic lymphocytes (Tc). In the course of the demyelination process in multiple sclerosis, these cause the breakdown of the myelin sheaths, in gradually appearing inflammations. Tc lymphocytes recognize myelin structures as epitopes and destroy them. The picture of the myelin membrane's molecular composition, which we are now perfecting, will also lead to a better understanding of demyelination on a molecular level, and hence to new therapeutic possibilities.
Direct Electron Transfer between Carbon Electrodes, Immobilized Mediator and an Immobilized Viologen‐accepting Pyridine Nucleotide Oxidoreductase
Authors: Günther Helmut , Paxinos Antonios S. , Schulz Michael , van Dijk Cees , Simon Helmut
Published: December 2003

The electron transfer between electrodes and the redox‐active prosthetic groups of oxidoreductases is usually too slow to be measurable, unless a mediator is used. Now, a mediator and the enzyme have been covalently immobilized on a functionalized carbon electrode. The electrons can thus flow from the cathode to the oxidoreductase via a “molecular wire”. The use of carbon felt having a larger inner surface area as electrode affords current densities at the lower end of the range used in industrial processes.
Isomerization of Benzoylalkylidene Sulfur Tetrafluorides C6H5–COCRSF4 to Dihydrooxathietes
Authors: Henkel Thomas , Krügerke Thomas , Seppelt Konrad
Published: December 2003

No Absract.
Catalytic Hydrosilylation or Hydrogenation at One Coordination Site of [Cp′Fe(CO)(X)] Fragments
Authors: Brunner Henri , Fisch Konrad
Published: December 2003

No Absract.
Phenyl‐Linked Quinone‐Substituted Porphyrin Trimers
Authors: Sessler Jonathan L. , Capuano Vincent L.
Published: December 2003

No Absract.
Synthesis and Structure of a Diphosphadigalletane: A Novel Base‐Stabilized Ga2P2 Ring System
Authors: Cowley Alan H. , Jones Richard A. , Mardones Miguel A. , Ruiz Jaime , Atwood Jerry L. , Bott Simon G.
Published: December 2003

No Absract.
Synthesis, Structure, and Catalase‐Type Activity of a Novel Oxo‐Bridged Tetranuclear Manganese Aggregate Exhibiting Short OċO Interactions
Authors: Stibrany Robert T. , Gorun Sergiu M.
Published: December 2003

No Absract.
The Tri‐μ‐amidobis[triamminecobalt(III)] Cation: The First Triply Amido‐bridged Complex
Authors: Frank Walter , Hoffmann Klaus , Heck Ludwig
Published: December 2003

No Absract.
Host‐Guest Complexes with Closed, Half‐open, and Stretched Receptors: Hydrophobic Cavity Effects and Induced Pole‐Dipole Interactions
Authors: Schneider Hans‐Jörg , Blatter Thomas , Zimmermann Patrick
Published: December 2003

No Absract.
Macrocyclically Fixed Diarylhexatrienes
Authors: Vögtle Fritz , Thilgen Carlo
Published: December 2003

No Absract.
Synthesis of D‐ and L‐2‐Amino‐2‐deoxyarabinose and 1,4‐Dideoxy‐1,4‐iminolyxitol by (C2 + C3)‐Nitroaldol Addition with 2‐O‐Benzylglyceraldehyde
Authors: Wehner Volkmar , Jäger Volker
Published: December 2003

No Absract.
Cyclization of N‐Protected l‐Amino‐4‐pentene‐2,3‐diols to lxyo‐Configurated Deoxyimino Sugars (cis‐Dihydroxypyrrolidines); Synthesis of Potential Glycosidase Inhibitors
Authors: Jäger Volker , Hümmer Walter
Published: December 2003

No Absract.
Book Review: Metal‐DNA Chemistry. (ACS Symp. Ser. 402). Edited by T. D. Tullius
Authors: Lippert Bernhard
Published: December 2003

No Absract.
What Will Chemistry Do in the Next Twenty Years?
Authors: Whitesides George
Published: December 2003

The path of chemistry in the future will be determined both by its participation in solving large‐scale societal problems and by its generation of new ideas through basic research. This article sketches four of the areas of societal “pull” in which chemistry will play a role in solving applied problems—national security, health care, the environment, and energy—and four areas in which basic research will be especially fruitful—materials chemistry, biological chemistry, computational chemistry, and chemistry exploring the limits of size and speed in chemical phenomena.
Molecular Thermodynamics for Chemical Process Design
Authors: Prausnitz John M.
Published: December 2003

Thermodynamic properties are essential for quantitative process design to produce chemical products. Caloric properties are required for heat balances, but these properties are usually available or estimated easily. More important—and often much more difficult to estimate—are the chemical potentials of components in mixtures; it is these potentials which determine phase equilibria, as required for separation operations, and chemical equilibria, as required for chemical reactors and for separation operations based on chemical reactions. Molecular thermodynamics is an engineering‐oriented science for calculating the desired chemical potentials from a minimum of experimental data. This applied science, based on classical and statistical thermodynamics, yields chemical potentials through models that are based on molecular physics and physical chemistry. Selected examples are cited to illustrate the applicability of molecular thermodynamics: group‐contribution methods for obtaining chemical potentials in highly nonideal mixtures as required for distillation‐column and process‐safety design; equation of state for precipitation of uniform‐sized crystals from supercritical fluids; molecular‐orbital calculations to guide process development for alternatives to environmentally dangerous chlorofluorohydrocarbons; molecular‐simulation calculations for separation of gas mixtures with porous adsorbents; equilibria in two‐phase aqueous systems for separation of protein mixtures; and, finally, extended polymer‐solution thermodynamics to guide synthesis of hydrogels suitable for protein recovery from soybeans and for novel drug‐delivery devices.
Perspectives in the Development of High‐Temperature Polymers
Authors: Hergenrother Paul M.
Published: December 2003

Research on high‐temperature organic polymers was initiated in the late 1950s primarily to meet the needs of the aerospace and electronics industry. Since then, many different heat‐resistant polymer systems have been reported, of which several are now commercially available. These polymers are used in many diverse applications such as circuitry in microelectronic components, coatings on cookware, binders in brake systems, sealants for fuel tanks in high‐speed aircraft, gears in copying machines, structural components in high‐speed aircraft, and space vehicles, films and wire coatings for electrical insulation. Worldwide use for high‐temperature polymers in 1988 was estimated at 90 million kilograms with a value of $ 2.3 billion. This market is expected to double by the end of this decade. The major polymer classes discussed in the present paper are polyimides and poly(aryl ethers).
Catalytic Antibodies: A New Class of Transition‐State Analogues Used to Elicit Hydrolytic Antibodies
Authors: Shokat Kevan M. , Ko Marcia K. , Scanlan Thomas S. , Kochersperger Lynn , Yonkovich Shirlee , Thaisrivongs Suvit , Schultz Peter G.
Published: December 2003

The design and generation of selective catalysts is an important aim of chemists and biologists. A number of successful strategies have emerged, including the synthesis and derivatization of synthetic hosts, the chemical modification and site‐directed mutagenesis of enzymes, and the attenuation of natural enzyme activities in organic solvents. Since 1986 several laboratories have exploited the immune system to generate selective catalysts capable of catalyzing a wide range of chemical transformations. These include acyl transfer, β‐elimination, carbon—carbon bond‐forming, carbon—carbon bond‐cleaving, porphyrin metalation, peroxidation, and redox reactions. The variety and number of transformations catalyzed by antibodies in this short period of time is testament to the versatility and power of the method in generating selective catalysts for applications in chemistry, biology, and medicine. Here we report the use of a new class of uncharged transition‐state analogues for generating antibodies capable of catalyzing ester and carbonate hydrolysis. These antibodies are compared to those raised against tetrahedral phosphate and phosphonate transition‐state analogues.
Structure and Molecular Stacking of Anthocyanins—Flower Color Variation
Authors: Goto Toshio , Kondo Tadao
Published: December 2003

In 1913 Willstätter made the striking observation that the same pigment can give rise to different colors. Thus, the same pigment, cyanin, is found in the blue cornflower and in the red rose. Willstätter attributed the variety of flower colors to different pH values in solution. Indeed, anthocyanin changes its color with pH; it appears red in acidic, violet in neutral, and blue in basic aqueous solution. Willstätter's pH‐theory for explaining flower color variation is still to be found in major text books of organic chemistry. Very recently, however, reinvestigation has disclosed that the color variation and stabilization of anthocyanins in aqueous solution could have other causes, namely self‐association, copigmentation and intramolecular sandwich‐type stacking. The stacking would be mainly brought about by intermolecular or intramolecular hydrophobic interaction between aromatic nuclei such as anthocyanidins, flavones and aromatic acids. In addition, hydrogen bonds and charge transfer interactions may also be involved. The most interesting molecular complexes of anthocyanins are the metalloanthocyanins such as commelinin and protocyanin (blue cornflower pigment). These seemingly pure blue complexes each consist of six anthocyanin and six flavone molecules and two metal ions; their molecular weight is nearly 10000. A structure is proposed for commelinin.
Highly‐Reduced Metal Carbonyls
Authors: Beck Wolfgang
Published: December 2003

Carbonyl metalates contain metals with formally negative oxidation numbers— that has been known since the days of Walter Hieber. Nevertheless, an ion like [Cr(CO)4]4⊖, which contains chromium(− IV), was considered inaccessible, although it obeys the 18‐electron rule. Through the activities of John E. Ellis and coworkers (see also p. 194 in this issue) the treasure‐chest of mononuclear metal carbonyls was enriched by many such jewels. Further gaps were systematically filled with [M(CO)6]2⊖, M  Ti, Zr, Hf and [M(CO)5]3⊖, M = V, Nb, Ta. The highly reduced metal carbonyls are not only interesting with regard to bonding theory, but are also useful as precursors in the synthesis of multinuclear complexes.
Spectroscopy of Fluid Phases—The Study of Chemical Reactions and Equilibria up to High Pressures
Authors: Buback Michael
Published: December 2003

The properties of fluid phases can be altered considerably by the external conditions. Phase equilibria and chemical equilibria can be greatly affected, and it is possible to carry out chemical reactions by exploiting the special properties of compressed fluid phases. The use of high pressure in chemical reactions is of considerable diagnostic and preparative value. Applied research is directed towards elucidating the details of existing technical high pressure processes and to the development of novel fluid phase reactions where the application of high pressure is able to induce selectivity. In order to pursue these lines of research, and to study structure and dynamics throughout the entire range from gaseous to liquidlike states, it is important to have spectroscopic methods for characterizing systems at high pressures and temperatures. This article is concerned with quantitative absorption spectroscopy in the infrared to the ultraviolet spectral region at pressures up to about 7 kbar and temperatures up to 900 K.
The Chemistry of Rose Pigments
Authors: Eugster Conrad Hans , Märki‐Fischer Edith
Published: December 2003

In this article we present a survey of the pigments found in the flowers and fruits of old and modern varieties of roses. The yellow colors are produced by carotenoids, the reds by anthocyanins, and the modern oranges by a mixture of the two. The great structural diversity of the carotenoids contrasts with a surprisingly small number of anthocyanins. For the carotenoids found in roses, a clear correspondence exists between the structure and the breeding partners used; the old yellow roses, which arose from crosses with Chinese varieties, mainly contain carotenoids from early stages in the biosynthesis, while in the modern yellow roses, which are descended from Central Asian foetida types, hydroxylations, epoxidations, and epoxide transformations readily occur. A recently elucidated carotenoid degradation sequence follows the scheme C40 → C13 + C27 → C13 + C14. The C13 compounds are odoriferous substances that contribute to the scent of roses. In the physiological pH region, copigmentation with flavonol glycosides is crucial for stabilization of the anthocyanin chromophores. Many roses, including the “apothecary's rose”, which was once used medicinally, contain large amounts of strongly astringent ellagitannins, monosaccharide esters of gallic acid.
Transition‐Metal Thiolates: From Molecular Fragments of Sulfidic Solids to Models for Active Centers in Biomolecules
Authors: Krebs Bernt , Henkel Gerald
Published: December 2003

Thiolates are presently a subject of great interest in the chemistry of complexes involving transition‐metal elements and soft ligands. The manifold electronic and steric capabilities offered by the monodentate ligands RS⊖ and the bidentate chelate ligands ⊖SRS⊖ have been used to stabilize a broad spectrum of mononuclear, oligomeric, and polymeric complexes with new and remarkable structures and properties. Impetus has especially been provided by the synthesis of polynuclear cagelike homo‐ and heteroleptic metal–sulfur frameworks, which can often be regarded as “molecular fragments” of the structures of inorganic sulfides. Thiolates and mixed sulfide‐thiolates of the late open‐ and closed‐shell 3d metals (Fe, Co, Ni, Cu, Zn) and some of their homologues (Au, Cd, Hg), as well as of Mo, are of particular importance as model complexes for biologically important metal centers coordinated by sulfur. They have played an important role in increasing our understanding of the structure, bonding, and function of the reactive centers in ferredoxins, rubredoxins, nitrogenases, blue copper proteins, metallothioneins, and antiarthritic drugs.
[Cu(η2‐H2)Cl], a Model Compound for H2 Complexes. Ab Initio Calculations and Identification by IR Spectroscopy
Authors: Plitt Harald S. , Bär Michael R. , Ahlrichs Reinhart , Schnöckel Hansgeorg
Published: December 2003

It cannot be simpler! This applies, however, to the structure of the title compound rather than to the experimental conditions under which it is prepared. This prototype for complexes with side‐on H2 bonding was formed by cocondensation of monomeric CuCl with H2 in an argon matrix and unambiguously characterized by IR spectroscopy. In such simple systems the ab initio calculations can almost take the place of experiment—they also clearly favor the side‐on coordination of the H2 ligand and predict the surprisingly high energy of formation (93 kJ mol−1).
Ag25Bi3O18, a Potentially Valence‐Unstable BiIII/BiV Compound
Authors: Bortz Manfred , Jansen Martin
Published: December 2003

An ideal model for the study of semiconductor/metal transitions is found in the new solid Ag25Bi3O18, which is characterized by a unique structural property: A Bi atom in an unambiguous + III valence state (as against + V) at ambient pressure is possibly converted reversibly into BV under pressure through delocalization of the lone pair. The study of this compound should also be relevant for the understanding of superconductivity in compounds with a bismuth oxide basis.
Protease‐Catalyzed Kinetically Controlled Peptide Synthesis
Authors: Schellenberger Volker , Jakubke Hans‐Dieter
Published: December 2003

In spite of the enormous progress in the synthesis of peptides and proteins using commercial peptide synthesizers and the immense technological possibilities of recombinant DNA technology, a CN ligase is an indispensable tool for the racemization‐free fragment condensation of peptides. Since activation of the C‐terminal α‐carboxyl group of a peptide segment could cause partial racemization, chemical condensations of peptide fragments are prone to racemization. For the synthesis of the huge number of peptides and proteins, however, nature has only developed the ribosomal peptidyltransferase, which exhibits its full catalytic function independent of the side‐chain functions of the amino acids being coupled. However, its function requires coordination with numerous other ribosomal factors. Besides the limited possibilities of using multienzyme complexes of bacterial peptide synthesis systems, the only alternatives to peptidyltransferase are proteases, which, based on their in vivo function as hydrolases, cannot act as ideal ligases. However, by exploiting the intrinsic reversibility of hydrolytic reactions and by adjusting appropriate physicochemical reaction parameters, the protease acitivity can be used in the direction of ligation. Undoubtedly, the course of kinetically controlled, serine and cysteine protease‐catalyzed reactions can be more efficiently influenced than the equilibrium‐controlled protease‐catalyzed synthesis. This article describes the influence of the enzyme specificity on the efficiency of kinetically controlled synthesis and points the way toward a broad exploitation of serine and cysteine proteases for the catalysis of CN bond formation.
Direct Observation of the Central Atom in [C{Au[C6H5)2(pC6H4Nme2)]}6](BF4)2 by 13C NMR Spectroscopy
Authors: Schmidbaur Hubert , Brachthäuser Benno , Steigelmann Oliver
Published: December 2003

The synthesis of the title compound in which the interstitial C atoms are mainly 13C isotopes makes the proof of these octahedral hypercoordinated atoms possible. The septet multiplicity and the coupling constants confirm the postulated surroundings and agree with the expectations regarding bonding. The chemical shift δ (13C) = 137.27 is more difficult to understand. Relativistic effects must be taken into account in the crucial theoretical calculations.
Solvated Electrons in the Synthesis of Ionic Clusters in Zeolites
Authors: Anderson Paul A. , Barr Donald , Edwards Peter P.
Published: December 2003

Larger metal aggregates do not form when the alkali‐metal ions in zeolites are reduced to low‐valent ion clusters by solvated electrons. Besides the ion cluster Na (n = 4–6) and K (n = 3,4) previously reported, the new cluster Na was obtained selectively and reproducibly. The solvated electron were prepared in situ from highly purified Li granules and propyl‐ or butylamine. One intriguing feature of these ion clusters is the unusual nature of the valence electrons‐not bound to one atom but also not completely delocalized as in a metal.
Organizing Principle of Complex Reactions and Theory of Coarctate Transition States
Authors: Herges Rainer
Published: December 2003

The majority of concerted reactions proceeds by a simultaneous breaking and making of only one bond at each atom involved in the reaction. If this process follows an alternating cyclic sequence, the reactions are called pericyclic. However, there is a hitherto never consistently characterized class of reactions that proceeds by breaking and making two bonds at one or more atoms at a time. The striking relationships that are purely descriptive and formal in the first instance are explained by a common physical principle. Theoretical insight not only permits predictions of mechanisms and stereochemistry; the qualitative theory is also used as an organizing principle for the known reactions and as a tool for predicting unprecedented reactions of this type.
Time‐Resolved Photoacoustic Calorimetry: From Carbenes to Proteins
Authors: Peters Kevin S.
Published: December 2003

Why have molecules only been seen but not heard? For over a century chemists have probed reactions with various spectroscopic methods to learn about structures, dynamics, and reactivities of their molecules. What they have not done is to listen to their molecules react. Although the photoacoustic phenomenon has been known since 1880, it is only in the last twenty years that technology has developed to the point where sound waves produced by reacting molecules can be time resolved and the information contained within the waves deciphered. The information content within the photoacoustic wave is indeed rich, for one can learn about the dynamics and the magnitude of enthalpy changes associated with the reaction as well as the changes in molecular volume. This review article chronicles the development of time‐resolved photoacoustic calorimetry and its application to a variety of reactions encountered in organic and organometallic chemistry and biochemistry.
Selective Measurement of the Time‐Dependence of Transient Overhauser Effects in Magnetic Resonance: Applications to Oligonucleotides
Authors: Vincent Sébastien J. F. , Zwahlen Catherine , Bodenhausen Geoffrey
Published: December 2003

The analysis of cross‐ and diagonal‐peak intensities is much faster with the one‐dimensional NMR experiments described here than with two‐dimensional NOESY. This accelerates the comparison of predictions from molecular dynamics calculations with experimental observations, as demonstrated by the example of cytosine‐9 in duplex d(CGCGAATTCGCG)2.
Fast Amide Cleavage under Mild Conditions: An Evolutionary Approach to Bioorganic Catalysis
Authors: Menger Fredric M. , Fei Zheng X.
Published: December 2003

The noncovalent aggregation of hexadecanoate in aqueous phosphate buffer with 3% acetonitrile gives rise to “catalytic clumps” that catalyze the hydrolysis of the amide group in 1. Amide cleavage is achieved with 108‐fold acceleration with catalyst concentrations of 10−5M at pH 7–8. These extremely simple catalysts, whose activity equals or exceeds that of catalytic antibodies, were found by rapid screening of hundreds of organic “clumps”.
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Making and Breaking of SiE (E = C, Si) Bonds by Oxidative Addition and Reductive Elimination Reactions
Authors: Schubert Ulrich
Published: December 2003

Important steps in metal‐mediated stoichiometric or catalytic reactions of organosilicon compounds are oxidative additions and reductive eliminations. Although the tools to tune the ability of a metal complex fragment to undergo such reactions are, in principle, known—for example, oxidative additions are facilitated by metals which are easily oxidized and by small ancillary ligands—the challenge for the chemist is to make these reactions, particularly for SiC and SiSi bonds, more predictable.
Conocurvone—Prototype of a New Class of Anti‐HIV Active Compounds?**
Authors: Laatsch Hartmut
Published: December 2003

For corrigendum see DOI:10.1002/anie.199416681
Selective Catalysis on Silicon Dioxide with Substrate‐Specific Cavities
Authors: Heilmann Jens , Maier Wilhelm F.
Published: December 2003

For corrigendum see DOI:10.1002/anie.199605541