bluuebunny/crossref_metadata_2025 huggingface dataset:
Perspectives in Supramolecular Chemistry—From Molecular Recognition towards Molecular Information Processing and Self‐Organization
Authors: Lehn Jean‐Marie
Published: December 2003

The selective binding of a substrate by a molecular receptor to form a supramolecular species involves molecular recognition which rests on the molecular information stored in the interacting species. The functions of supermolecules cover recognition, as well as catalysis and transport. In combination with polymolecular organization, they open ways towards molecular and supramolecular devices for information processing and signal generation. The development of such devices requires the design of molecular components performing a given function (e.g., photoactive, electroactive, ionoactive, thermoactive, or chemoactive) and suitable for assembly into an organized array. Light‐conversion devices and charge‐separation centers have been realized with photoactive cryptates formed by receptors containing photosensitive groups. Eleclroactive and ionoactive devices are required for carrying information via electronic and ionic signals. Redox‐active polyolefinic chains, like the “caroviologens”, represent molecular wires for electron transfer through membranes. Push‐pull polyolefins possess marked nonlinear optical properties. Tubular mesophases, formed by organized stacking of suitable macro‐cyclic components, as well as “chundle”‐type structures, based on bundles of chains grafted onto a macrocyclic support, represent approaches to ion channels. Lipophilic macrocyclic units form Langmuir‐Blodgett films that may display molecular recognition at the air‐water interface. Supramolecular chemistry has relied on more or less preorganized molecular receptors for effecting molecular recognition, catalysis, and transport processes. A step beyond preorganization consists in the design of systems undergoing self‐organization, that is, systems capable of spontaneously generating a well‐defined supramolecular architecture by self‐assembling from their components under a given set of conditions. Several approaches to self‐assembling systems have been pursued: the formation of helical metal complexes, the double‐stranded helicates, which result from the spontaneous organization of two linear polybipyridine ligands into a double helix by binding of specific metal ions; the generation of mesophases and liquid crystalline polymers of supramolecular nature from complementary components, amounting to macroscopic expression of molecular recognition; the molecular‐recognition‐directed formation of ordered solid‐state structures. Endowing photo‐, electro‐, and ionoactive components with recognition elements opens perspectives towards the design of programmed molecular and supramolecular systems capable of self‐assembly into organized and functional supramolecular devices. Such systems may be able to perform highly selective operations of recognition, reaction, transfer, and structure generation for signal and information processing at the molecular and supramolecular levels.
Isotope Effects Associated with α‐Olefin Insertion in Zirconocene‐Based Polymerisation Catalysts: Evidence for an α‐Agostic Transition State
Authors: Krauledat Hehmuth , Brintzinger Hans‐Herbert
Published: December 2003

The hydrodimerization of trans‐ and of cis‐1‐deuterio‐l‐hexene to the threo‐ and erythro‐isomers of 6‐deuterio‐5‐deuteriomethylundecane with the chiral pre‐catalyst rac‐ethylenebis(tetrahydroindenyl)zirconium dichloride gave diastereomeric ratios of 2.4:1, which, depending on (E)‐ or (Z)‐configuration of the diene, reverse. The results confirm observations by Pino et al. that α‐olefins insert into Zr—H and Zr—alkyl bonds with opposite enantiofacial orientation.
Spontaneous Formation of Stable Phosphino(silyl)‐carbenes from Unstable Diazo Compounds
Authors: Gillette Gregory R. , Baceiredo Antoine , Bertrand Guy
Published: December 2003

The carbene‐like compounds 1, which are formed almost quantitatively from phosphanyldiazomethanes already at T ≤ 35°C if the tetramethylpiperidine(tmp)‐R residue is one of the substituents on the phosphorus, are stable for several weeks in solution. With the exception of 1a, the compounds 1 react with BuNC to give the ketenimines 2. a, R  NiPr2, R′  Me; b, R  NMe2, R′  Me; c, R  NMe2, R′  iPr; d, R  Ph, R′  Me.
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FeO⊕ Activates Methane
Authors: Schröder Detlef , Schwarz Helmut
Published: December 2003

—whereby predominantly FeOH⊕ + CH and Fe⊕ + CH3OH are formed. This reaction is, however, four times slower than that described in the previous communication; nevertheless, the chances for a catalytic activation are not bad, since the Fe⊕ regenerated from the intermediate 1 during the course of the reductive elimination by N2O can easily be reintroduced in the cycle for further reaction.
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Synthesis and Transmission Electron Microscopic Investigation of Bi(Pb)SrCaCuO Superconductors
Authors: Müller Jan‐Henrik , Schwarz Martin , Gruehn Reginald
Published: December 2003

High‐resolution transmission electron microscopic photographs have shown that the real structures of the (BiO)2Sr2Can−1CunO2n+2 superconductors are characteized by a high proportion of structural defects, e.g. by changing layer seences. The type and extent of defects can differ in individual cases so that the difficulty of obtaining reproducible sample properties is not surprising.
Molecular Systems with Perfect Metal Structure
Authors: Süss‐Fink Georg
Published: December 2003

The no‐man's‐land between typical homogeneous and heterogeneous catalysts is slowly being explored. Particularly important have been the multinuclear metal clusters synthesized and characterized in recent years. They not only serve as models for heterogeneous catalysts but also display unusual catalytic properties. The criteria governing the structures of these large clusters are revealed very clearly by the cluster dianion [Os20(CO)40]2⊖ obtained by B. F. G. Johnson and J. Lewis et al. (see also p. 107 ff.).
Dynamic HPLC: A Method for Determining Rate Constants, Energy Barriers, and Equilibrium Constants of Molecular Dynamic Processes
Authors: Veciana Jaume , Crespo Maria I.
Published: December 2003

For corrigendum see DOI:10.1002/anie.199102161
The Reduction of the NbX5/AlX3 System with Aluminum in the Presence of Aromatic Hydrocarbons: An Approach to Niobium(II), Niobium(I), and Niobium(0) Organometallics
Authors: Calderazzo Fausto , Pampaloni Guido , Rocchi Lucia , Strähle Joachim , Wurst Klaus
Published: December 2003

The niobium(0) compound [Nb(mes)2] (mes = 1,3,5‐trimethylbenzene) was prepared not only by metal atom–ligand cocondensation, but also according to Equation (a). The chemical behavior of this compound is similar to that of the analogous complex [V(mes)2]. For example, it reacts under carbon monoxide atmosphere to give the green salt [Nb(mes)2(CO)][Nb(CO)6]. This new, simple approach to niobium(0) compounds should facilitate their study (DME = dimethoxyethane).
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Towards the Chemical Synthesis of Proteins
Authors: Bayer Ernst
Published: December 2003

The chemical total synthesis of proteins using solid supports has made great progress. It is therefore becoming a reality whatE. Fischeralready predicted in 1902: “I foresee the time when physiological chemistry… is able to prepare synthetic enzymes.” The synthesis of peptides of up to 20 amino acids by the well‐established solid‐phase procedure on polymeric supports (SPPS) has made great progress through the development of newer supports. At the same time, methods have emerged which facilitate the separation and characterization of peptides, thus allowing optimization of the synthesis of pure materials. The new supports which enable one to synthesize peptides by a rapid continuous flow procedure are characterized by hydrophilicity, beads of approximately equal size, similar swelling properties in the solvents used for peptide synthesis, and stability at high pressure. With graft copolymers of weakly cross‐linked polystyrene and linear polyethylene glycol (PEG), the synthetic cycle for coupling of one amino acid can routinely be reduced to 10–20 min with a concomitant higher yield. With beads of monodispersed graft copolymer of 10 μm diameter, a synthetic cycle can, in principle, be shortened to 1–5 min. By utilizing this high‐speed solid‐phase procedure, larger peptides up to the size of proteins could also be prepared in a few hours. With newer mass spectroscopic methods such as ion‐spray mass spectrometry, peptides of up to a molecular mass of 100 kDa can be characterized, and with the advent of capillary electrophoresis, another very efficient separation tool, besides HPLC, is at our disposal.
The Bioinorganic Chemistry of Vanadium
Authors: Rehder Dieter
Published: December 2003

Vanadium is a trace element that plays an important, perhaps essential and general role in the regulation of enzymatic phosphorylations. Several forms of life, including the fly agaric toadstool (Amanita muscaria) and certain sea squirts (ascidians), are able to concentrate vanadium. In other organisms vanadium is part of the active site of some enzymes. Well‐studied examples are the nitrogen‐fixing bacterium Azotobacter and various seaweeds that use vanadate‐dependent peroxidases to synthesize halogenated organic compounds. Despite its importance as a “biometal” both in primitive, prokaryotic organisms (Azotobacter) and in the highly organized ascidians, which represent an early stage in the evolution of vertebrates, the bioinorganic chemistry of vanadium is still in its infancy. Just as young, but undergoing explosive development, is the chemistry of model compounds for vanadium‐containing biomolecules, a domain of the bioinorganic coordination chemist, who almost daily discovers compounds with new and surprising structural features. This article reviews this fascinating area of bioinorganic chemistry.
Synthesis of Nonstabilized Phosphaalkynes by Vacuum Gas‐Solid HCl Elimination
Authors: Guillemin J. C. , Janati T. , Denis J. M. , Guenot P. , Savignac P.
Published: December 2003

The choice of starting compound for the synthesis of the unstabilized phosphaalkynes 3 has proved to be the (dichloroalkyl)phosphanes 2. They were formed by the reduction of the phosphonates 1 with AlHCl2 and dehydrohalogenized over hot K2CO3 (230–350°C) in the gas phase. The simple phosphaalkynes 3 are stable in THF at room temperature also—who would have expected that! R = H, Me, Et, nBu, Me3Si.
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[InAs3]6⊖ and [AlSb3]6⊖, Trigonal Planar Anions in Cs6InAs3 and Cs6AlSb3
Authors: Blase Wolfgang , Cordier Gerhard , Peters Karl , Somer Mehmet , von Schnering Hans Georg
Published: December 2003

The anions of the complex salts Cs6InAs3 and Cs6AlSb3 are isosteric with borates. Both salts can be obtained as shiny metallic crystals directly from the elements. In the crystal the Cs atoms form a bundle of four chains of trigonal prisms which are centered by the atoms of the trigonal planar anions: {Cs12/2[MX3]}. The InAs and AlSb bond lengths (261.5 and 263.7 pm, respectively) fall in the range typical for single bonds.
Metallomesogens: Metal Complexes in Organized Fluid Phases
Authors: Giroud‐Godquin Anne‐Marie , Maitlis Peter M.
Published: December 2003

Metallomesogens, metal complexes of organic ligands which exhibit liquid crystalline (mesomorphic) character, combine the variety and range of metal‐based coordination chemistry with the extraordinary physical properties exhibited by liquid crystals. Thermotropic metallomesogens have been made incorporating many metals, including representatives of s‐, p‐, d‐and even f‐block elements. Both rodlike (calamitic) and disklike (discotic) thermotropic metallomesogens are known, and examples of all the main mesophase types are found. Many different varieties of ligand can be used: monodentate (4‐substituted pyridines), bidentate (β‐diketonates, dithiolenes, carboxylates, cyclometalated aromatic amines), or polydentate (phthalocyanines, porphyrins). As with organic mesogens, molecular shape and intermolecular forces play an important role, i.e. the ligands are important in determining mesophase character. The chief requirement for a metallomesogen is a rigid core, usually unsaturated and either rod‐ or disklike in shape, bearing several long hydrocarbon tails. The metal atom is usually at or near the center of gravity of the molecule. In some cases the ligands are themselves mesogenic, but this is not a requirement. The presence of one or more metals opens many exciting possibilities: new shapes, not easily generated by organic compounds, and hence new properties are then accessible. The incorporation of d‐block metals brings with it features such as color and paramagnetism. Profound effects arise from the large and polarizable concentration of electron density that every metal atom possesses, since the molecular polarizability is a key factor in determining whether a molecule will form liquid crystals. Enhanced physical properties (e.g. high birefringencies), as well as new and unexpected ones, will result. A major requirement for metallomesogens to find applications in new device technology is that the metal–ligand bonds are strong and inert and the complexes stable; this can be accomplished with, for example, chelating ligands and the 5d metals.
[{Re2Cl4(dppm)2}2 (μ‐TCNQ)], a Novel Charge Transfer Complex Derived from a Donor with a Metal‐Metal Multiple Bond
Authors: Bartley Stuart L. , Dunbar Kim R.
Published: December 2003

Black crystals of the title complex are obtained by slow diffusion of THF solutions of [Re2Cl4, (dppm)2] (ReRe) and tetracyanoquinodimethane (TCNQ). Although their conductivity is only ca. 10−5 S cm−1, the magnetic and structural features of this charge transfer complex are remarkable. The bridging of two metal complexes by a TCNQ unit is without precedent. The concept of using metal‐metal multiple‐bond systems as donors for inorganic/organic CT complexes appears viable.
Chemical Characterization of Aerosols: On‐Line and In Situ
Authors: Nießner Reinhard
Published: December 2003

Whereas aerosols were formerly considered to be important in meteorological processes but in little else, today they play a significant role not only in environmental protection but also in “new technologies” such as the formation of high performance ceramics, sinter metals, optical waveguides, and superconductors. Analytical procedures which are capable of a continuous qualitative and quantitative description of processes in which aerosols are formed are, however, still almost unknown. The present review will discuss initial developments (which will often appear exotic in nature) such as the use of the condensation properties of ultrafine particles or time‐resolved laser‐induced aerosol fluorescence spectroscopy. The progress of analytical chemistry in the last few years makes it clear that advances in miniaturization, data processing, and optronics will probably be capable of solving many problems which are presently regarded as unsolvable.
Chemical Sensors and Biosensors—Principles and Applications
Authors: Cammann Karl , Lemke Udo , Rohen Anja , Sander Jürgen , Wilken Hildegard , Winter Babette
Published: December 2003

Chemical and environmental engineering and biotechnology are among the fields now being transformed by continually increasing levels of automation. Whereas the objective in other sectors of industry is simply to increase efficiency, here considerations of system theory or safety demand a high level of automation. Either the processes are too complex and require multifunctional control with feedback, or an analysis of the safety requirements shows the necessity for a certain degree of redundancy in the safety measures, and for elimination of human error as a risk factor. With regard to quality control, cost‐benefit analyses lead to striking conclusions which again indicate the need for highly automated, and above all reliable, systems to eliminate rejects. The crux of any automated system is the measurement and control technology; of central importance is the rapid, reliable, and in some cases continuous, measurement and interpretation of key processes or control variables. For this purpose a wide variety of recording instruments and sensors are used to give as accurate a picture as possible of the state of the system. It is obvious from this that the performance of the control system is critically dependent on the sensors. Errors in the measured quantities can become amplified in the control variables or, in dynamic systems, can lead to undesirable operating conditions. Moreover, as a consequence of great advances in microelectronics, “intelligent sensors” which can calibrate and control themselves will be one of the key technologies of the nineties. Unless fast and immediate information on the true current status of a system is available, microprocessors as control devices react blindly and unpredictably to errors in input information. New discoveries in the fields of electronic, electrochemical, and optical transducers are now being applied in heterogeneous catalysis and surface physics, and in biochemistry (enzymology and immunology); in these fields new chemical sensor principles are being tested, which could revolutionize instrumental methods of molecular analysis in particular, owing to their very favorable cost‐performance relationship. This article aims to give an up‐to‐date overview of the current state of the art in these developments, with emphasis on their importance for analysis and their significance in relation to the chemist's interest in mechanisms for identifying substances.
Proof of Strong SHċS Bridges in [Ru(SH2)(PPh3)(′S4′)]. THF, the First H2S Complex Characterized by X‐Ray Crystallography
Authors: Sellman Dieter , Lechner Peter , Knoch Falk , Moll Matthias
Published: December 2003

What are the properties of H2S complexes of transition metals? These reactive compounds probably play an important role in many geochemical and biological processes, although they have not been completely characterized. An X‐ray structural analysis has now been carried out on the ruthenium complex 1. THF, (′S4′)2⊖ = 2,2′‐ (ethylenedithio)‐bis(thiophenolate). Surprisingly, the H2S lig‐and was found to be stabilized by strong SHċs bridges. On exposure to air, 1 is rapidly oxidized to the μ‐S2, complex 2 [Eq. (a)].
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Direct Observation of Streptavidin Specifically Adsorbed on Biotin‐Functionalized Self‐Assembled Monolayers with the Scanning Tunneling Microscope
Authors: Häussling Lukas , Michel Bruno , Ringsdorf Helmut , Rohrer Heinrich
Published: December 2003

Surface recognition of biotin‐functionalized, chemisorbed thiol monolayers by streptavadin results in the formation of protein‐covered surfaces with no longrange order. This is due to the low lateral and vertical mobility of the solidbound thiols. On the other hand, protein surfaces transferred from a water surface reveal a good crystal structure under the scanning electron microscope, but the adhesion of these applied layers to the solid is unsatisfactory.
Chemically Modified Oligonucleotides as Probes and Inhibitors
Authors: Englisch Uwe , Gauss Dieter H.
Published: December 2003

Oligonucleotides bind specifically to single‐stranded nucleic acids to form a double helix if there is a complementary antiparallel nucleotide sequence. In addition, certain oligonucleotides bind specifically to a variety of proteins. Therefore, biological processes involving these nucleic acids or proteins can be modulated (normally inhibited) by addition of the respective oligonucleotides. The effects of these oligonucleotides and the fields of potential application can be broadened by the introduction of chemically modified nucleotides. For instance, replacing oligonucleotide phosphate groups by methylphosphonates results in the loss of one negative charge per nucleotide and the oligonucleotide becomes more lipophilic. An oligonucleotide carrying a reactive group can modify its binding partner. An oligonucleotide covalently linked to a dye can be localized in a biological specimen. Oligonucleotides attached to an enzyme can be detected in very small amounts since the enzyme can catalyze the formation of large amounts of the substance assayed (e.g., a fluorescent product). An important biochemical application is the detection and localization of a messenger RNA or its gene. Medical applications include the detection of bacterial or viral sequences. There is also great interest in inhibiting the translation of messenger RNA and the transcription and replication of DNA. So‐called antisense oligonucleotides are currently being used for the inhibition of protein biosynthesis and of reverse transcription of retroviruses.
The Crystal Chemistry of Copper Oxometalates
Authors: Müller‐Buschbaum Hanskarl
Published: December 2003

Up to three or four years ago oxocuprates were a class of chemical compounds no more remarkable than countless others. Then, as a result of the euphoria surrounding the high‐temperature oxide superconductors and the discovery that copper plays an essential role in these materials, there was a world‐wide awakening of interest in copper‐containing oxide compounds. The number of scientists engaged in the synthesis and structure determination of copper oxometalates has grown from just a few to very many. As superconductivity is inseparably connected with the structure of the solid state, there has been a spontaneous awakening of interest in the role of copper in the crystal chemistry of solid materials, leading to new research projects on this aspect of oxocuprates. Most of the work published so far on the interesting chemistry of this group of compounds has related to individual compounds. New aids in describing complex solid state structures are now available through the development of methods that give three‐dimensional displays of crystal structures using computer graphics terminals, as this review illustrates for the example of the oxocuprates.
Complex Transition Metal Hydrides
Authors: Bronger Welf
Published: December 2003

Compounds having structural units formed by transition metals and hydrogen have only become known fairly recently. Only the synthesis and structural characterization of ternary metal hydrides AxMyHz in which A is an alkali or alkaline‐earth metal and M is a transition metal, led to the discovery of anionic complex groups of the form [MHz]. Although there are obvious structural similarities to the corresponding halides and oxides, the dynamic properties of the hydride ligand are somewhat unusual and are responsible for numerous phase transformations. Transitions throughout the range from saltlike to metallic behavior make us expect interesting physical properties and applications.
Light‐Directed Parallel Synthesis of Up to 250000 Different Oligopeptides and Oligonucleotides**
Authors: von Kiederowski Günter
Published: December 2003

250000 different controlled syntheses on one microscopy cover slide are achieved by a combination of solid‐phase synthesis and photolithography. Fodor et al. describe a procedure for the synthesis of oligopeptides and nucleotides in which photolabile protecting groups on fragments attached to the slide are removed selectively by irradiation through a mask to allow coupling at precisely defined sites. In this way different peptide or nucleotide sequences can be rapidly synthesized in close proximity.
Do Partial Charges Alone Govern the Relative Stability of the Isomeric Heptaheteronortricyclane Anions [P7−xASx]3⊖?
Authors: Burkhardt Armin , Hönle Wolfgang , Wedig Ulrich
Published: December 2003

The answer to the question in the title is “no” in the opinion of the authors. The decrease in the skeletal strain, rather than the slight differences in electronegativity between phosphorus and arsenic, seems to direct the As occupation of positions in the P framework. Ab initio calculations on [P7−xAsx]3⊖ systems with x = 0, 1, 2, 3, 7 show that the energy differences between the isomers contributes only ca. 10% of the activation energy for the valence tautomerism. Valence fluctuation therefore cannot favor any particular isomer.
Endohedral Cluster Compounds: Inclusion of Helium within C and C through Collision Experiments
Authors: Weiske Thomas , Böhme Diethard K. , Hrušák Jan , Krätschmer Wolfgang , Schwarz Helmut
Published: December 2003

Is host‐guest chemistry possible with fullerenes? Yes, but not as easily as once thought in the euphoric first weeks of preparative fullerene chemistry. Although the occurrence of metal‐ion inclusion is still controversial, indisputable evidence for inclusion of 3He and 4He within C and C radical ions has now been obtained. A reaction was initiated by collision of C and C ions with H2, D2, Ar, SF6, and He gases, but only He could be included, which agrees with the results of the initial calculations.
Chirality and Crop Protection
Authors: Tombo Gerardo M. Ramos , Belluš Daniel
Published: December 2003

The modern agrochemical industry is searching, more intensively than ever, for new substances to combat pests (weeds, deleterious insects, plant pathogens, etc.). In the complex and costly selection and optimization process, state‐of‐the‐art scientific methods are always needed. The aims of the interdisciplinary optimization are mainly the reduction of the rate of application of the new substance, an increase in the selectivity against the target organism, and the optimal ecological profile. If a promising crop protection compound is a racemate or a diastereoisomeric mixture, the chemist has a unique opportunity to contribute to this optimization process through the synthesis of enantiomerically pure isomers for testing purposes. If the single isomer proves to be biologically superior to the racemate, the development of an economical and ecologically sound process for the production of the single isomer presents an even greater challenge. The average price of a crop protection compound is much lower than that for a pharmaceutical product, and this fact imposes a severe limitation upon the flexibility of the chemist who is concerned with the synthesis and production of a stereochemically pure agrochemical. This forces the crop protection chemist to make full use of both his scientific and creative capabilities. Fortunately, parallel to the development of the above optimization aims of a modern and ecologically sound crop protection research, there has been a continuous and worldwide advance in the area of asymmetric synthesis. Due to the interplay of these two parallel efforts there has been a great accumulation of chemical, biological, and agronomical knowledge in recent years, which should have implications beyond merely the synthesis of enantiomerically pure agrochemicals.
The Elucidation of Peroxyl Radical Reactions in Aqueous Solution with the Help of Radiation‐Chemical Methods
Authors: von Sonntag Clemens , Schuchmann Heinz‐Peter
Published: December 2003

Whenever free radicals are formed, independent of whether this occurs thermally, is induced by UV or ionizing irradiation, or takes place in redox reactions, they are converted rapidly into the corresponding peroxyl radicals in the presence of oxygen. Peroxyl radical reactions in aqueous environments are observed not only in aquatic systems (e.g., rivers, lakes and oceans) but also in the living cell and to a considerable degree even in the atmosphere (in water droplets). The peroxyl radical chemistry occurring in this medium is often very different from that observed in the gas phase or in organic solvents. In spite of the great importance of these reactions in medicine (for example in anti‐cancer irradiation therapy and ischaemia) there have been comparatively few studies of peroxyl reactions in aqueous media. Radiation‐chemical techniques such as pulse radiolysis offer the best means for carrying out such studies, so that it is not surprising that the majority of the information available in this area has been obtained with the help of radiation‐chemical methods. The radiation chemistry of water can be con trolled in such a manner that the main products are ˙OH radicals (90 % yield), which react with substrate molecules to give substrate radicals and in the presence of oxygen to give substrate peroxyl radicals. The experimental conditions can also be varied in such a way that HO/O radicals can be formed in 100 % yield and caused to react with substrates. We therefore have a simple access to these intermediates, which are extremely important in biological systems. A detailed product analysis, supported by kinetic studies carried out with the help of pulse radiolysis, has been used to clarify the chemistry of a series of peroxyl radicals, so that sufficient material is now available to justify a review of the variety of the peroxyl radical reactions studied by means of radiation‐chemical methods. A more general survey of the physical properties of the peroxyl radicals and their unimolecular and bimolecular reactions will be followed by a discussion of selected examples of various classes of substance. Because of the great biological importance of radical‐induced DNA damage this area will also be treated briefly.
Single‐Crystal X‐Ray Diffraction Studies of Oligonucleotides and Oligonucleotide–Drug Complexes
Authors: Kennard Olga , Hunter William N.
Published: December 2003

Nucleic acids constitute the library of genetic information for all living organisms. They also play a regulatory role in many biological events concerned with the utilization of genetic information. The double‐helical model of DNA, proposed by Watson and Crick in 1953, suggested the structural basis for its biological role, but this insight into nucleic acid structures seems to have generated as many questions as it has provided answers. Experimental studies, in particular fiber diffraction work, yielded a wealth of information on the conformational flexibility of nucleic acids and on the importance of interactions with water and cations. Major advances in synthetic organic chemistry, with implications for molecular biology, propelled nucleic acid research forward in the late 1970s. The availability of milligram quantities of synthetic oligonucleotides of defined sequence and high purity paved the way for detailed and accurate structural analysis using single‐crystal X‐ray diffraction methods and, in more recent times, NMR spectroscopy. This article is a detailed survey of the structural results generated by crystallographic techniques as applied to DNA, RNA, and nucleic acid–drug complexes over the period 1979–1990. The appendix lists important definitions used in the characterization of oligonucleotide structures.
Medicinal Chemistry in the Golden Age of Biology: Lessons from Steroid and Peptide Research
Authors: Hirschmann Ralph
Published: December 2003

Collaboration between biologists and chemists has generated medicines of enormous benefit to society. The dynamics of this synergistic interaction combines two strengths: the rigor of chemistry and the ability of biologists to construct unifying concepts from diverse fields of investigation. The resulting contributions to the practice of medicine have reduced morbidity and mortality while increasing the quality of life. Building on the work of chemists such asRobinson,Prelog,Woodward, andPauling, medicinal chemists have advanced rational drug discovery, especially of enzyme inhibitors, to a degree unthinkable even twenty years ago. Some of the major contributions of medicinal chemistry to human and animal health stem directly from the creative application of structural and electronic reasoning, from advances in instrumentation, and from spectacular progress in biology. However, medicinal chemists have only begun to scratch the surface of the opportunities made possible by the impact of the “double‐helix revolution” of the 1950s.
Herbicide Resistance in Transgenic Plants through Degradation of the Phytotoxin to Urea
Authors: Maier‐Greiner Ursula H. , Klaus Christian B. A. , Estermaier Lydia M. , Hartmann Guido R.
Published: December 2003

The incorporation of the gene for cyanamide hydratase can make transgenic tobacco plants resistant to the herbicide cyanamide H2NCN. The herbicide is degraded by the expressed gene to the physiologically harmless urea H2NCONH2. In the presence of the ubiquitous plant enzyme urease, which degrades urea, the hydrolysis product NH can, in fact, serve as nitrogen source. The efficiency of this new approach is impressively demonstrated.
HETLOC, an Efficient Method for Determining Heteronuclear Long‐Range Couplings with Heteronuclei in Natural Abundance
Authors: Kurz Michael , Schmieder Peter , Kessler Horst
Published: December 2003

Exceptionally high accuracy and detection limits characterize the NMR experiment, a variant of TOSCY (TOSCY = Total Correlation Spectroscopy), described here for the determination of heteronuclear 3J couplings. No enrichment of the heteroatom is necessary. The process, which also yields coupling constants smaller than the signal width, is only applicable to proton‐bearing heteroatoms. In addition, the protons linked by TOSCY transfer should belong to the same spin system. Application in the determination of the angle ϕ in peptides demonstrates the performance of the process.
The Interaction of Tri‐tert‐butylgallium with White Phosphorus: Isolation of an Unusual Gallium Phosphorus Cluster
Authors: Power Michael B. , Barron Andrew R.
Published: December 2003

A Gap4 tricycle of type [1.1.1.0] is found in the structure of Ga2P4tBu6, which forms at room temperature already from elemental phosphorus (P4) and the Lewis acid GatBu3. This reaction, in which one side of the P4 tetrahedron is opened, provides a surprisingly simple access to potential precursors for semiconductor materials of the III/IV type.
Mechanisms of Molecular Recognition : Investigations of Organic Host–Guest Complexes
Authors: Schneider Hans‐Jörg
Published: December 2003

Noncovalent interactions constitute the basis for information transfer between molecules in living systems as well as in synthetic supramolecular structures. Despite ever more accurate descriptions of biological systems and a dramatically increasing diversity of synthetic host guest complexes, a systematic and general understanding of the underlying intermolecular forces is still in its infancy. Organic chemistry makes possible the targeted construction of infinitely variable host compounds with multiple centers interacting in complementary ways. This in turn opens the door to systematic experimental analyses based on binding increments, which can be shown to have a high degree of additivity. Even in the case of relatively simple ion pairs, several mechanisms are at work simultaneously, and either entropy or enthalpy contributions may prove to be decisive. Nevertheless, it is possible to identify individual interactions and then use them to practical advantage in ways analogous to the free‐energy relationships of physical organic chemistry. Contributions due to solvophobic effects, to interactions with permanent and induced dipoles, and to hydrogen bonds lend themselves to a high degree of empirical quantification on the basis of classical physical‐chemical principles. Water as a solvent plays a special role due to its low polarizability, apart from hydrophobic effects. Quantification of pairwise interactions and ultimate control over them through manipulation of the microenvironment should prove useful not only in the design of new synthetic host–guest complexes but also, for example, in the rational development of biologically active substances, molecular switches (e.g., for sensor technology), and catalysts that function analogously to enzymes. The results should also assist in the planning and analysis of biochemical experiments including techniques of genetic engineering.
Extension of Free Energy Correlations to Gas‐Phase Ionic Reactions. Competitive Alkylation of Substituted Benzonitriles by (CH3)2Cl+ Ions
Authors: Attinà Marina , Cacace Fulvio , Ricci Andreina
Published: December 2003

Hammett equations are now possible for ionic reactions in the gas phase. The combination of mass spectrometry and high pressure radiolysis techniques make it possible to set up a linear free energy relationship for reaction (a), which is analogous to the Hammett system. The value of the reaction constant ρ, ‐1.9, verifies that the C(CH3)2Cl+ ion is a typical though rather indiscriminant electrophile. Because investigations of ion–molecule reactions in the gas phase suffer no disruptive solvent effects, a direct correlation with theoretical findings is possible:
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Photolytic Cleavage of DNA by [Pt2(P2O5H2)4]4−
Authors: Kalsbeck William A. , Grover Neena , Thorp H. Holden
Published: December 2003

Only irradiation with visible light is needed for the isomerization of the complex of the tetraanionic [Pt(P2O5H2)4]4− (1) with the super helical form I of ϕX174‐DNA to the circular form II [Eq. (a) and (b)]. The reaction takes place without the direct binding of the reagent to the DNA and without the formation of high energy intermediates. Thus application in the imaging of other DNA structures is of interest.
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Volume Effect or Paddle‐Wheel Mechanism—Fast Alkali‐Metal Ionic Conduction in Solids with Rotationally Disordered Complex Anions
Authors: Jansen Martin
Published: December 2003

Transport phenomena in the solid state are of equal importance in basic research and practice. In the past two decades particular interest has been directed towards so‐called “fast” or “super” ionic conductors because of their attractive potential applications. We have synthesized highly conductive alkali‐metal ionic conductors based on ionic crystals in which, on the one hand, high concentrations of the charge carriers can be realized by doping (point defects in the cation substructure) and, on the other, the activation energy of the interchange of sites is decreased by translationally fixed but rotationally mobile complex anions. Mixed crystals with Na3PO4 or Na3AlF6 structures have proven especially suitable in this connection. With the object of establishing a broader experimental foundation for clarifying the controversially discussed question of whether the higher free transport volume or the rotational motion of the anions is responsible for the high cation mobility in these rotary phases we have systematically varied the type of anions and concentration of defects and monitored the resulting changes in conductivity. Although the macroscopical characteristics investigated are not suitable for explaining mechanisms in detail at the atomic level, the results afford clear support for the assumption of a “paddle wheel mechanism”; but also effects of the enlarged transport volume are not to be disputed. Both these effects enhancing the cationic conductivity are concomitantly operative in amounts varying from system to system; they cannot be totally separated from each other. Seen in this light, the alternative, “volume effect” or “paddle wheel mechanism,” is not as sharply defined as was previously discussed.
Chemistry and Crystal Growth
Authors: Hulliger Jürg
Published: December 2003

Single‐crystal materials, along with other forms of condensed matter (ceramics, polymers, liquid crystals, etc.) are fundamental to modern technology. The basic research and production of new materials with “tailored” solid‐state physical properties therefore necessitate not only chemical synthesis but also the production of single crystals of a particular morphology (either bulk or thin layer crystals) and well‐defined crystal defects (doping). In this review, an attempt is made to broaden the traditional synthetic concept of chemistry to the process of single‐crystal synthesis. The methods of the resulting approach, which takes into account the specific properties of solid materials, are discussed and illustrated by experimental set‐ups for the solution of a range of problems in chemical crystallization. Also included is recent work on the growing of single crystals of high‐temperature superconductors, organic non‐linear optical compounds, and proteins.
Spectroscopic and Reactivity Studies of a Copper‐Containing Metallacrown
Authors: Blake Alexander J. , Gould Robert O. , Grant Craig M. , Milne Paul E. Y. , Reed David , Winpenny Richard E. P.
Published: December 2003

Cu and Cu3Mg‐containing complexes form when the metallacrown 1 is treated with lead or magnesium nitrate, respectively. In the first reaction the sodium ion in the cavity formed by the six copper atoms of the macrocyclic host is replaced by a copper ion, which suggests the destruction of the structure of the macrocycle. In the replacement of the sodium ion by a magnesium ion in the second reaction the macrocycle is cut in half. According to the NMR spectrum of the metallacycle 1, its structure in the solid state is retained in solution. MeLH = 2‐hydroxy‐6‐methylpyridine.
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Difluoromethyl Compounds of Chalcogens: A NMR Study of the Reactions of Cd(CF3)2·2MeCN and ZnBr(CF3)·2MeCN with Dialkyl Chalcogenides and Boron Trifluoride
Authors: Naumann Dieter , Möckel Regina , Tyrra Wieland
Published: December 2003

CF2H derivatives of the chalcogens oxygen, sulfur, selenium, and tellurium form selectively in the carbenoid reactions of Cd(CF3)2 or Zn(CF3)Br with dimethyl or diethyl chalcogenides and boron trifluoride [Eq. (a) below is one example]. Onium ions such as [Et2SCF2H]+ were identified as intermediates by NMR spectroscopy.
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Enantioselective Reactions in a Static Magnetic Field
Authors: Zadel Guido , Eisenbraun Catia , Wolff Gerd‐Joachim , Breitmaier Eberhard
Published: December 2003

Shortly after publication, E. Breitmaier, C. Eisenbraun, and G. J. Wolff declared their disassociation from this article owing to apparent manipulation of results by G. Zadel.

Also see DOI: 10.1002/anie.199412011, 10.1002/anie.199414571, 10.1002/anie.199414581, 10.1002/anie.199414591.
Direct Metal–Metal Bonds Between High and Low Valent Complex Fragments: The Reaction of Metal Bases with the Metal Acids [Re(NR)3]+ and [Mo(NR)2]2+
Authors: Sundermeyer Jörg , Runge Diane , Field John S.
Published: December 2003

Shortened metal–metal bonds caused by electrostatic attraction within the dipolar (metalδ+ – metalδ−) structural unit were observed in the heterobi‐ and heterotrimetallic complexes of type 1 and 2. These complexes were synthesized from the imido complexes [(NtBu)3ReCl] or [(NtBu)2MoCl2] and the carbonyl metalates K[M]. [M] = CpMo(CO)3, CpW(CO)3, Mn(CO)5, CpFe(CO)2, Co(CO)4.
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A Clathrate Hydrate of Nitric Oxide
Authors: Hallbrucker Andreas
Published: December 2003

A somewhat surprising structural type was determined by X‐ray diffraction for the clathrate hydrate of NO: unlike CO, a molecule with very similar properties, NO forms a clathrate hydrate of structural type II, which hitherto had only been encountered for larger molecules (van der Waals radius > 5.8 Å) and nonpolar small molecules like N2 and O2. Thus, further study is required to establish the criteria that determine the structure type of clathrate hydrates.
Borophosphates—A Neglected Class of Compounds: Crystal Structures of MII[BPO5] (MII  Ca, Sr) and Ba3[BP3O12]
Authors: Kniep Rüdiger , Gözel Güller , Eisenmann Brigitte , Röhr Caroline , Asbrand Matthias , Kizilyalli Meral
Published: December 2003

Vertex‐sharing BO4 and PO4 tetrahedra form the framework of the title compounds. Ca[BPO5] and Sr[BPO5] crystallize in the stillwellite structural type and contain tetrahedral chain anions [BPO], which can be described as loop‐branched “dreier” single chains. In Ba3[BP3O12] the tetrahedral anions form “zweifach” open “vierer” single chains. Given these results and the known linking modes of tetrahedral units, it is expected that borophosphates with layered and framework structures, as well as microporous structures, can be found.
1,1‐Dimethyl‐1H‐silirene
Authors: Trommer Martin , Sander Wolfram , Marquard Claudia
Published: December 2003

In solution, in an organic glass, and in an argon matrix–the irradiation of the bisdiazo compound 1 always leads to the silirene 2 as the main product. The latter was characterized both directly by IR spectroscopy and by its products of trapping experiments. Compound 2 is the first silirene without substituents at the double bond.
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Synthesis and Properties of 2,4,6‐Trimethylphenylborane (Mesitylborane), a Stable Alternative to Thexylborane
Authors: Smith Keith , Pelter Andrew , Jin Zhao
Published: December 2003

Four advantageous properties characterize mesitylborane MesBH2 as a reagent: (1) It is readily accessible and quite stable. (2) It can be treated with two different 1‐alkenes in a stepwise fashion (→ MesBR1R2). (3) The regioselectivity of each individual step is > 99%. (4) The products MesBR1R2 can be readily transformed via MeOBR1R2 or directly to BR1R2R3. MesBR2 and BR1R2R3 are important precursors for the synthesis of ketones R1R2CO and tertiary alcohols R1R2R3COH, respectively, by the cyanoborate process.
A Mixed‐Valent, Unsymmetrical FeIIFeIII Complex with a Terminal Phenolato Ligand as a Model for the Active Site of Purple Acid Phosphatases
Authors: Bernard Elisabeth , Moneta William , Laugier Jean , Chardon‐Noblat Sylvie , Deronzier Alain , Tuchagues Jean‐Pierre , Latour Jean‐Marc
Published: December 2003

The structure and the magnetic and electrochemical properties of the active center of purple acid phosphatases are modeled by a complex that mimics the terminal coordination of the tyrosine residue and was prepared with a new heptadentate phenola‐to ligand system. The instability of the reduced FeIIFeII state of the enzyme may be attributed to the terminal ligand, since the phenolato ligand in the model is a destabilizing factor.
Reductive Disproportionation of NO Mediated by Copper Complexes: Modeling N2O Generation by Copper Proteins and Heterogeneous Catalysts
Authors: Ruggiero Christy E. , Carrier Susan M. , Tolman William B.
Published: December 2003

Nitrito‐O,O‐copper complexes and dinitrogen oxide are the products of the reaction of excess NO with the nitrosyl complexes [LCu(NO)] (L = substituted tris(pyrazolyl)hydroborate), a process that models environmentally important transformations carried out by copper ions in proteins and zeolites. According to the results of kinetic studies, the involvement of dimeric copper species in the rate‐determining step is ruled out, which suggests that NO coupling occurs at a single metal ion.
Evidence of Room‐Temperature Superconductivity in the BiSrCuO System
Authors: Burrows Richard S. , McDaniel Darl H.
Published: December 2003

A tetragonal phase SrCuO2 possibly causes the superconducting behavior of the samples with the nominal composition Bi2Sr2CuO6 prepared in the sol‐gel process. The results of the measurements indicate a critical temperature of 70 °C, and the superconductivity is attributed to a phase present in the sample in less than 0.1%. Eight samples show evidence of room‐temperature superconductivity, and an additional fourteen samples show superconductivity between 25 and 110 K.
Turning Points in Catalysis
Authors: Thomas John Meurig
Published: December 2003

This personal journey through the enlarging landscape of heterogeneous catalysis, pure and applied, starts with the discovery in 1823 of a dramatic example of the synthesis of water that was to serve as the basis of the first commercial exploitation of catalysis, Dobereiners lighter (tinder box). The quickening pace of successive industrial innovations and of academic insight during the intervening 170 years are summarized and the turning points, both major and minor, identified. Although new concepts and new ideas emerged in relative profusion, few exhibited the longevity predicted for them at birth by their proponents. Some concepts, like broken milestones on a vanished road, have ceased to retain their significance. Some have survived, even flourished. But in catalysis, as in most other branches of natural science, new tools and new techniques, rather than new concepts, tend to hold sway. And just as experimental advances in enzymology and immunology have led to the design of remarkable new biocatalysts so also, but not yet at the same level of delicate control, have the tools and techniques of solid‐state chemistry (including novel preparative and computational procedures), generated many powerful rationally designed inorganic catalysts.