bluuebunny/crossref_metadata_2025 huggingface dataset:
Reaction Dynamics of Aligned Molecules
Authors: Comes Franz Josef
Published: December 2003

Photofragmentation—also termed ‘half collision’—is a method to comprehend the complicated process of a chemical reaction (the ‘full collision’) better. The use of polarized light enabled the study of the spectroscopy of aligned molecules, yielding information about the photochemically produced intermediate state—the transition state. Even though stable reaction products were studied, the forces responsible for the motions of the fragments can be visualized. In this way a model can be constructed that represents the part of the potential hypersurface responsible for the observed motions. The application of this spectroscopic method to hydrogen peroxide H2O2 has become a classic example. The complex decomposition of hydrazoic acid, HN3, represented a challenge, and its successful solution proves the general applicability of this method.
Perlithiated and Hyperlithiated Methane
Authors: Maercker Adalbert
Published: December 2003

Of both theoretical and preparative interest are hyper‐ and perlithiated hydrocarbons. Recently the research group of H. Kudo in Japan succeeded in detecting CLi6 in the mass spectrometer. Thus ab initio calculations from 1983 that predicted a considerable stability for this molecule containing hexavalent carbon were corroborated. CLi4 is accessible on a preparative scale, but its synthesis is by no means trivial. It is much easier to exchange all hydrogen atoms for lithium atoms in certain alkynes and to use the products as versatile perlithiated building blocks.
The Epidemic Spread of Fullerene Research
Authors: Braun Tibor
Published: December 2003

For corrigendum see DOI:10.1002/anie.199215401
OH Bond Activation in the Gas Phase: The Reactions of Water and Methanol with [FeCH3]+
Authors: Blum Ofer , Stöckigt Detlef , Schröder Detlef , Schwarz Helmut
Published: December 2003

That even cationic fragments of late transition metals can activate OH bonds in the gas phase is shown by studies of reaction (a) (RH, CH3), in which a large deuterium isotope effect can be observed (kH//kD > 15). An oxidative addition mechanism is proposed for this transformation; the first step is the coordination of the dipolar H2O or CH3OH molecule to the [FeCH3]+ fragment, while the rate‐determining step is the transfer of the H atom of the ROH group to the Fe atom.
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Solid‐State NMR Spectroscopic and X‐Ray Diffraction Studies of the Low‐Temperature Structural Transformation of Hydrated Porous Aluminophosphate VPI‐5
Authors: Rocha João , Kolodziejski Waclaw , Gameson Ian , Klinowski Jacek
Published: December 2003

Only from NMR spectra can the reversible structural transformation at low temperatures in the hydrated aluminophosphate molecular sieve VPI‐5 be detected. Although powder diffraction experiments reveal a continuous shortening of the c axis of the unit cell, magic‐angle‐spinning solid‐state NMR spectroscopy shows completely reversible changes between 190 K and 220 K, which are possibly attributable to the freezing of the motion of encapsulated water molecules. In these studies, variable temperature 27Al quadrupole nutation NMR with magic‐angle‐spinning was used for the first time.
Addition of Benzyl Radicals to Alkenes: The Role of Radical Deformation in the Transition State
Authors: Héberger Károly , Walbiner Manfred , Fischer Hanns
Published: December 2003

Nonplanar radical centers in the transition state are responsible for the slow rate of addition of benzyl and para‐substituted benzyl radicals to monosubstituted and 1,1‐disubstituted alkenes. This was shown by ESR spectroscopy, since the para‐substituents do not significantly affect the rate of the addition. The conclusion is in agreement with the calculated transition‐state structures for the addition of simple alkyl radicals to alkenes.
Proof of the Catalytic Activity of a Naked Metal Cluster in the Gas Phase
Authors: Schnabel Patrick , Weil Konrad G. , Irion Manfred P.
Published: December 2003

An experiment with five steps within a mass spectrometer (labeled MSn) showed that in the gas phase the naked Fe ion forms the molecule C6H6, probably benzene, from ethene via [Fe4(C2H2)m]+ complexes (m = 1–4), and thus acts as a catalytic center. The MS1–MS5 steps of the complex experiment are sketched below. CID = collision‐induced deactivation, a = isolation, m = 1–3.
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Selenonium Hexafluoroantimonate, H3Se+SbF
Authors: Minkwitz Rolf , Kornath Andreas , Sawodny Wolfgang
Published: December 2003

In the super acid HF/SbF5 at −78°C, hydrogen selenide can be protonated to form the cation of the selenonium salt 1 [Eq. (a)]. It is only stable in the solid state below −60°C. H3Se+ is the last preparatively accessible onium ion in the series H3O+, H3S+, H3Se+. H2Te decomposes spontaneously into the elements in HF/SbF5 at −78°C.
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A Novel Polyoxotungstate Containing a triangulo Ni Cluster with Ferromagnetic Exchange Interactions and an S = 3 Ground State
Authors: Gómez‐García Carlos J. , Coronado Eugenio , Ouahab Lahcéne
Published: December 2003

Flanked by [PW9O34] and [WO6] units, the Ni cluster in the salt 1 is magnetically isolated. Within this triangulo Ni cluster, however, ferromagnetic exchange interactions take place. According to magnetic measurements μeff increases with decreasing temperature to a value of 8.1 μB mol−1 at 5 K, supporting a spin ground state of S = 3.
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Transition Structures of Hydrocarbon Pericyclic Reactions
Authors: Houk Kendall N. , Li Yi , Evanseck Jeffrey D.
Published: December 2003

Twenty‐five years after the discovery of a vast class of organic reactions named “pericyclic reactions” by Woodward and Hoffmann, ab initio quantum mechanics provides a detailed analysis of the geometries, energies, and electronic characteristics of the transition structures of these reactions. Common features are found in all these reactions, and generalizations permit prediction of other transition‐structure geometries and energies. At the same time, great diversity is observed—from strongly bonded, rigid, closed‐shell entities to weakly interacting, flexible diradical structures.
Selective Binding of Sugar to β‐Cyclodextrin: A Prototype for Sugar–Sugar Interactions in Water
Authors: Aoyama Yasuhiro , Nagai Yoshiro , Otsuki Jun‐ichi , Kobayashi Kenji , Toi Hiroo
Published: December 2003

Not only the hydrophobicity of the sugar to be complexed determines the strength of its bond to β‐cyclodextrin. Steric factors also play a large role. In water, aldopentoses are bound better as their hydrophobicity increases, but aldohexoses do not form complexes with β‐cyclodextrin even though some are clearly more hydrophobic than all the pentoses studied. This is the first example of a selective oligosugar–sugar interaction in water.
“Kinetically Enhanced Metalation”— How Substituents Direct ortho Lithiation
Authors: van Eikema Hommes Nicolaas J. R. , von Ragué Schleyer Paul
Published: December 2003

Not the complexation of the ground state but rather of the transition state explains the directing and activating effect of electronegative ortho substituents in the lithiation of aromatic compounds. Ab initio calculations show that the ground state of a C6H5FLiH complex for para metalation (complexation by the benzene ring) is energetically more favorable than that for ortho metalation (complexation by F), by −12.8 vs. −12.4 kcalmol−1. In the transition state, however, the tables are turned; the respective activation barriers are +17.9 and + 6.5 kcalmol−1. This is in accord with the experimental findings that only orhto‐fluorolithiobenzene is formed.
Retro‐Inverso Amide Bonds between Trifunctional Amino Acids
Authors: Dürr Hansjörg , Goodman Murray , Jung Günther
Published: December 2003

In a highly functionalized nonapeptide the amide linkage CONH between glutamine and arginine was inverted to NHCO. As an example of this difficult modification to the peptide backbone, a retro‐inverso killer‐cell epitope was synthesized for the first time with a combination of solution and solid‐phase peptide synthesis techniques. The synthetic methods used are of importance for the rational design of drugs based on peptides.
Nuclear Magnetic Resonance Fourier Transform Spectroscopy (Nobel Lecture)
Authors: Ernst Richard R.
Published: December 2003

The development of NMR spectroscopy into a multifaceted tool for chemists, biochemists, and medical doctors is certainly due in part to the research of Richard R. Ernst, who received the Nobel Prize in Chemistry last year. In his Nobel lecture he describes the evolution of the field from the first Fourier transform NMR spectra to two‐, three‐, and four‐dimensional experiments. With spectra of the cyclopeptide antamanide he illustrates how information on constitution, configuration, and conformation may be obtained with various NMR techniques.
Photoselective Processes in Cyclooctasulfur Layers: Desorption versus Polymerization
Authors: Geyer Jens , Stülpnagel Heinrich , Rademann Klaus
Published: December 2003

Since the desorption rate depends on the light intensity, a purely thermal desorption mechanism for a thin sulfur film at λ = 225 nm can be rejected. Nonthermal desorption of adsorbed cyclooctasulfur was hitherto unknown. By contrast, at λ = 328 and 382 nm only a small amount of light‐induced desorption was detected. Instead, polymerization of sulfur was observed at these wavelengths to significantly larger extent than at λ = 255 nm.
Molecular Modeling of the Class I Human Histocompatibility Molecule HLA‐A2 Presenting an Allele‐Specific Nonapeptide from Influenza Matrix Protein
Authors: Zimmermann Norbert , Rötzschke Olaf , Falk Kirsten , Rognan Didier , Folkers Gerd , Rammensee Hans‐Georg , Jung Günther
Published: December 2003

The conformation is not α‐helical, but extended when the antigenic peptide binds in the pocket of the human major histocompatibility complex (MHC) protein HLA‐A2 of class I. This was established by molecular modeling studies and molecular dynamics simulations on a complex of HLA‐A2 and one nonapeptide from the influenza matrix protein. The investigations are based on the structure of HLA‐A2 determined by X‐ray crystallography and the recently determined HLA‐A2‐specific peptide binding motif. The described model supports the present ideas about MHC‐limited antigenic binding.
Synthesis, Structure, and Bonding of [CpCoW2(OCH2tBu)6], and Comments on the Combining Properties of CO and CpCo
Authors: Chisholm Malcom H. , Johnston Victor J. , Eisenstein Odile , Streib William E.
Published: December 2003

A triangle comprising one cobalt and two tungsten atoms is the central unit of the title compound 1, which is accessible from [CpCo(C2H4)2] and [W(OCH2tBu)6(py)] (py = pyridine). The structure of 1 shows a striking resemblance to the structure of the CO complex 2, which can be traced to the isolobal analogy between CO and CpCo. Compounds of the type [W2(OR)6] should also be suitable for the synthesis of further heterometallic clusters.
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Synthetic Chain‐Substituted Phospholipids: Ion Transport Across Their Bilayer Membranes
Authors: Menger Fredric M. , Aikens Patricia
Published: December 2003

The passage of ions through phospholipid vesicles is facilitated by building alkyl substituents into the lipid chains. The effect of the size, position, and number of substituents on the ion flux can be studied by monitoring the decrease in fluorescence of a pH‐sensitive dye within the vesicles on lowering the pH of the surrounding water. Substituents in the middle of the chains were most efficient in altering the flux. Such studies are of interest for the development of systems for controlled drug release.
The Pyrolysis of Tetranitromethane in the Gas Phase
Authors: Bock Hans , Zanathy László
Published: December 2003

C(NO2)4, one of the methane derivatives with the largest oxygen content (>65 wt.%) and therefore not exactly hazard‐free, decomposes in the gas phase at 10−5 mbar and 610 K exclusively into the gaseous products •NO2, •NO, CO2, and CO. Together with the known kinetics for a radical dissociation as the first step, the temperature‐dependent photoelectronic spectra and comprehensive quantum chemical calculations enable a mechanism to be proposed that explains all experimental findings. Conversions on silver wool and charcoal, and the cothermolysis of dimethylamine and dimethylnitramine suggest possibilities for further investigations.
Preparation and Properties, Reactions, and Applications of Radialenes
Authors: Hopf Henning , Maas Gerhard
Published: December 2003

Radialenes are alicyclic compounds in which every ring atom is sp2‐hybridized and carries an exocyclic CC double bond. Because of their unusual topology and electronic structures these hydrocarbons have aroused the interest of both preparative chemists and theoreticians. Although considerable progress has been achieved recently, directed and efficient syntheses of these molecules remain a challenge. The study of their chemical behavior offers vast opportunities. Very recently materials scientists have become interested in these unusual compounds in their search for organic conductors and ferromagnets.
In Vitro Selection of Specific Ligand‐binding Nucleic Acids
Authors: Famulok Michael , Szostak Jack W.
Published: December 2003

In vitro selection is a method that allows the simultaneous screening of very large numbers of nucleic acid molecules for a wide range of properties from binding characteristics to catalytic properties; moreover, the isolation of the very rare functional molecules becomes possible. Binding sites between proteins and nucleic acids, for example, have been evaluated by this methodology in order to gain information about protein/nucleic acid interactions. Structure and function of catalytic RNA (“ribozymes”) has been studied by in vitro selection and has led to new ribozymes with improved catalytic function. Substrate specificity of catalytic RNA has been changed and has led to a ribozyme that cleaves DNA. Other applications include the isolation of nucleic acids that bind specifically to small organic molecules and of RNA molecules that form triple helices with double‐stranded DNA. In this article we discuss the background, design, and results of in vitro genetic experiments, which bridge biochemical/molecular biological and organic chemical approaches to molecular recognition.
Peptide Nucleic Acids(PNAs)—Unusual Properties of Nonionic Oligonucleotide Analogues
Authors: Meier Chris , Engels Joachim W.
Published: December 2003

The phosphate–sugar backbone of oligonucleotides was replaced with peptides in recent work by P. E. Nielsen et al. Specially designed by molecular modeling, these oligonucleotides offer several advantages over chemically modified natural oligonucleotides: they are available on a large scale by the Merrifield synthesis, relatively inert to nucleases because of the nonionic peptide section, and have very good hybridization properties as PNA–DNA binding studies testify. These new DNA mimics are thus exceptionally interesting subjects for study since they may be employed as antisense agents.
Kinetics of Hydride Transfers from CH, SiH, GeH, and SnH Groups to Carbenium Ions
Authors: Mayr Herbert , Basso Nils
Published: December 2003

As a hydride donor, tributylstannane is five orders of magnitude more reactive than triphenylsilane as shown in kinetic studies on the hydride‐transfer reactions of hydrides of the type HER3 (E = C, Si, Ge, Sn) with diarylcarbenium ions [Eq. (a)]. The reactivity relationship is independent of the electrophilicity of the hydride abstractors and can thus be used as a guide in planning syntheses.
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Synthesis of Cubane‐like and Double Cubane‐like Tungsten‐Copper‐Sulfur Clusters from the “Butterfly” Cluster [Cu2S3W(O)(PPh3)3]
Authors: Du Shaowu , Zhu Nianyong , Chen Pengcheng , Wu Xintao
Published: December 2003

The denticity of the thiolato ligand decides whether the cubane‐like cluster 1 or the bicubane‐like cluster 2 is obtained in the reaction of copper thiolates with the “butterfly” cluster [Cu2S3W(O)(PPh3)3]. This could also be confirmed by further cluster syntheses. Tungsten–copper–sulfur clusters such as 1 and 2 are of interest, inter alia, as models for the active centers of some enzymes.
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Synthetic Approaches toward Molecular and Polymeric Carbon Allotropes
Authors: Diederich François , Rubin Yves
Published: December 2003

Life on earth is based on compounds that have carbon frames and backbones. Today, chemists have added to the world of biomolecules and biopolymers approximately 107 different synthetic molecules and polymers, the structures of which also depend on the formation of strong, stable carbon–carbon bonds. Although the stability of carbon–carbon bonds has been recognized for more than a century, the two natural modifications graphite and diamond were, until recently, the only allotropic forms of carbon on earth that were available in macroscopic quantities and were structurally well characterized. With the synthesis of macroscopic quantities of buckminsterfullerene (C60) and the higher fullerenes (C70, C76, C78, etc.) and the exploration of the fascinating properties of these all‐carbon spheres, this situation has completely changed. In the coming decades, the design, preparation, and study of novel molecular and polymeric allotropic forms of carbon will be a central topic in chemistry. Research in this area will dramatically advance the fundamental knowledge on carbon‐based matter and, as already illustrated by the ongoing work on C60, generate unprecedented technological perspectives. This review surveys synthetic organic‐chemical approaches toward the preparation and study of all‐carbon molecules and polymers that differ from the familiar networks of graphite and diamond as well as from the fullerenes. We will also discuss the ongoing research on fullerenes with a particular focus on the synthetic approaches to these all‐carbon spheres and their transition metal complexes.
Flexible Molecules with Defined Shape—Conformational Design
Authors: Hoffmann Reinhard W.
Published: December 2003

Chemists have for a long time considered molecules simply in terms of their constitution. The importance of molecular shape was recognized perhaps for the first time by the semio‐chemists, who were interested in the interactions of fragrant substances with a receptor. Apart from the case of rigid molecules, our ideas and concepts of molecular shape simply reflect an instantaneous situation, because flexible molecules take advantage of the whole range of conformation that is available to them. Nature frequently utilizes flexible molecules whose conformational space is restricted, in other words, molecules that can adopt only a few preferred conformations. This review discusses some of the principles that nature employs in order to impart a defined shape to flexible molecules. The purposeful application of these principles then allows the conformational design of molecular skeletons.

For corrigendum see DOI:10.1002/anie.199215401

For corrigendum see DOI:10.1002/anie.199216571
The Organosulfur Chemistry of the Genus Allium – Implications for the Organic Chemistry of Sulfur
Authors: Block Eric
Published: December 2003

A Cook's tour is presented of the organosulfur chemistry of the genus Allium, as represented, inter alia, by garlic (Allium sativum L.) and onion (Allium cepa L.). We report on the biosynthesis of the S‐alk(en)yl‐L‐cysteine S‐oxides (aroma and flavor precursors) in intact plants and on how upon cutting or crushing the plants these precursors are cleaved by allinase enzymes, giving sulfenic acids—highly reactive organosulfur intermediates. In garlic, 2‐propenesulfenic acid gives allicin, a thiosulfinate with antibiotic properties, while in onion 1‐propenesulfenic acid rearranges to the sulfine (Z)‐propanethial S‐oxide, the lachrymatory factor (LF) of onion. Highlights of onion chemistry include the assignment of stereochemistry to the LF and determination of the mechanism of its dimerization; the isolation, characterization, and synthesis of thiosulfinates which most closely duplicate the taste and aroma of the freshly cut bulb, and additional unusual compounds such as zwiebelanes (dithiabicyclo[2.1.1]hexanes), a bis‐sulfine (a 1,4‐butanedithial S,S′‐dioxide), antithrombotic and antiasthmatic cepaenes (α‐sulfinyl disulfides), and vic‐disulfoxides. Especially noteworthy in the chemistry of garlic are the discovery of ajoene, a potent antithrombotic agent from garlic, and the elucidation of the unique sequence of reactions that occur when diallyl disulfide, which is present in steam‐distilled garlic oil, is heated. Reaction mechanisms under discussion include [3, 3]‐ and [2, 3]‐sigma‐tropic rearrangements involving sulfur (e.g. sulfoxide‐accelerated thio‐ and dithio‐Claisen rearrangements) and cycloadditions involving thiocarbonyl systems. In view of the culinary importance of alliaceous plants as well as the unique history of their use in folk medicine, this survey concludes with a discussion of the physiological activity of the components of these plants: cancer prevention, antimicrobial activity, insect and animal attractive/repulsive activity, olfactory–gustatory–lachrymatory properties, effect on lipid metabolism, platelet aggregation inhibitory activity and properties associated with ajoene. And naturally, comments about onion and garlic induced bad breath and heartburn may not be overlooked.
New Impetus for Inorganic Host‐Guest Chemistry
Authors: Reuter Hans
Published: December 2003

Already in 1826 Berzelius described (NH4)3[(PO4)Mo12O36]. Its anion consists of a shell of twelve MoO6 octahedrons surrounding a P atom, but can also be described as a central phosphate ion whose O atoms form part of the shell. Related to this ancient chemistry are more recent findings in inorganic supramolecular chemistry, which include results as diverse as the characterization of Cd(CN)2 · neopentane, in which the host Cd(CN)2 forms a network structure trapping neopentane within its cavities in an ordered fashion, and the binding of a NH4Cl dimer in a giant anionic cage, described by A. Müller et al. in this issue (see p. 1192).
Selective Oxidation of Methane to CO and H2 over Ni/MgO at Low Temperatures
Authors: Choudhary Vasant R. , Mammon Ajit S. , Sansare Subhash D.
Published: December 2003

Very active, selective, and efficient—a Ni/MgO catalyst converts methane at relatively low temperatures (300–700 °C) to H2 and CO in the molar ratio 2:1. The high activity of the catalyst makes it possible to operate at high space velocities (low contact times) and therefore in the region of kinetic control for the selectivity.
The Thermal Conversion of Poly[(silylene)‐diacetylene] Metal Oxide Composites: A New Approach to β‐SiCMC Ceramics
Authors: Corriu Robert , Gerbier Philippe , Guérin Christian , Henner Bernard
Published: December 2003

Cross‐linking of 1, formation of a SiC network, and reduction of the encapsulated TiO2 particles are the three steps in the reaction of poly[(dimethylsilylene)diacetylene] (1) and TiO2 which produces SiCTiC ceramics [Eq. (a)]. The reduction of the metal oxide in this case is possible at much lower temperatures than with carbon alone. This method can be applied to a number of metal oxides, and also B2O3. The ceramic's composition can be modulated by variation of the polymer.
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August Wilhelm Hofmann—“Reigning Chemist‐in‐Chief”
Authors: Meinel Christoph
Published: December 2003

One hundred and twenty‐five years ago, on November 11th, 1867, the German Chemical Society of Berlin held its inaugural meeting. The main purpose of the Society was to unite pure and applied chemistry and to foster cooperation between academic research and the chemical industry. And, indeed, it soon became the major forum of German and even European chemistry. Its program clearly bears the hallmark of a single individual: August Wilhelm Hofmann, the Society's first president, who died 100 years ago. For his contemporaries, Hofmann represented a new type of chemistry professor. At no time since have professional chemists felt as abundantly endowed with potential for the future and with public esteem. Hofmann's portrait was monumental even then, and still today it would belong in any gallery devoted to our distinguished forebears.

Anniversaries provide an opportunity to direct our attention toward the past—and thus to ourselves as well. We are, after all, heirs to that period from which the modern world derives its profile. Questions from our own time lead us to reacquaint ourselves with one of the founders of modern chemistry, but we may also benefit from a fresh look at an epoch which, beneath the surface of prosperity and progress, was as contradictory as our own, an epoch struggling to understand the role of science in the new industrial era.
The Chemistry of GALLEX—Measurement of Solar Neutrinos with a Radiochemical Gallium Detector
Authors: Henrich Edmund , Ebert Klaus H.
Published: December 2003

In the GALLium Experiment, GALLEX, low‐energy solar neutrinos produced in the main hydrogen fusion reaction inside the Sun are being counted for the first time in a radiochemical gallium detector. In this way, the theories about stellar structure may be verified and the question of the existence of a neutrino rest mass be brought closer to a solution. The experiment is being carried out with international collaboration at the Gran Sasso underground laboratory (LNGS) in the Abruzzi mountains in Italy. In this paper we survey the planning, construction and initial experimental operation of the gallium detector, paying special attention to the chemical aspects of the experiment. The chemical problem to be solved is the separation of very few 71Ge atoms from 100 metric tons of a highly concentrated GaCl3 solution acidified with hydrochloric acid. In addition, these Ge atoms must be isolated and converted into germane, GeH4, for low‐level counting of 71Ge in a gas proportional counter. After extensive preparatory work to meet the extreme requirements of the experiment, the first results have now become available.
“[Cp*CoCoCp*]” is a Hydride
Authors: Kersten Jörg L. , Rheingold Arnold L. , Theopold Klaus H. , Casey Charles P. , Widenhoefer Ross A. , Hop Cornelis E. C. A.
Published: December 2003

The supposed synthesis of the cobalt complex [Cp*CoCoCp*] was in the spotlight at the end of last year (Angew. Chem. Int. Ed. Engl. 1991, 30, 1124). But the compound described at that time is actually the mixed‐valent cobalt hydride 2. The reaction of the dinuclear complex 1 with LiAlH4 yields two paramagnetic cobalt complexes (2 and 3), which have been fully characterized by X‐ray crystallography and spectroscopic methods, as well as by protonation and carbonylation. See also the Corrigendum on p. 1392.
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Structure of a Product of Double Addition to C70: [C70{Ir(CO)Cl(PPhMe2)2}2]·3C6H6
Authors: Balch Alan L. , Lee Joong W. , Olmstead Marilyn M.
Published: December 2003

The addition occurs at opposite poles of C70 when two Ir complexes each coordinate in a dihapto fashion to a 6‐6 ring junction to form the title compound. Although the splitting of the 31P NMR signals of this complex at low temperatures implies that an isomeric mixture is present, X‐ray studies on the products of different batches reveal only one isomer in the solid state.
Cationic Metallocene Polymerization Catalysts. Synthesis and Properities of the First Base‐Free Zirconocene Hydride
Authors: Yang Xinmim , Stern Charlotte L. , Marks Tobin J.
Published: December 2003

High electrophilicity and polymerization activityas well as ion‐pairing effects not based on the bridging hydrogen atoms are the most notable characteristics of the cation in2, a model compound for Ziegler‐Natta catalysts. This hydrido complex is accessible by hydrogenolysis of1or by hydride abstraction from3.equation image
Proteins from the D‐Chiral World
Authors: Jung Günther
Published: December 2003

The chiroptical properties and substrate specificity of the D‐enantiomer of the naturally occurring HIV protease synthesized by Kent et al. demonstrate that the three‐dimensional structures of D‐ and L‐enzymes really are mirror images of one another—that is, identical amino acid sequences actually fold in the same way in the tertiary structure. Interest in D‐proteins goes beyond basic research, as the enzymatic stability may allow important medical applications; additional areas of application include protein crystallography.
Solving the Structure of a Metal‐Substituted Aluminum Phosphate Catalyst by Electron Microscopy, Computer Simulation, and X‐ray Powder Diffraction
Authors: Wright Paul A. , Natarajan Srinivasan , Thomas John Meurig , Bell Robert G. , Gai‐Boyes Pratibha L. , Jones Richard H. , Chen Jiesheng
Published: December 2003

A new method for the solution of solid‐state structures—especially if the compounds can only be obtained as powders—is reported. A combination of electron microscopy, electron diffraction, and computer simulation of the lowest energy structure allowed the determination of the structure of the Mg‐ and Zn‐substituted forms of the catalytically active aluminophosphate MeALPO‐36. This novel structure has kinships with those of the aluminophosphate ALPO‐5 and the zeolite cancrinite Na6[Al6Si6O24]CaCO3 · 2H2O.
Se3N2Cl2, a Novel Selenium–Nitrogen Chloride: Reinvestigation of “Se4N2”
Authors: Siivari Jari , Chivers Tristram , Laitinen Risto
Published: December 2003

Not the binary compound tetraselenium dinitride, as previously reported, but rather Se3N2Cl2 (1) is the product of the reaction of trimethylsilyl azide and selenium monochloride in dichloromethane [Eq. (a)]. Compound 1 can also be obtained quantitatively in a pure form from selenide 2 and selenium tetrachloride/selenium monochloride [Eq. (b)], and is of interest as a synthetic building block in the little developed SeN chemistry.
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Formate‐Driven, Non‐Enzymatic NAD(P)H Regeneration for the Alcohol Dehydrogenase Catalyzed Stereoselective Reduction of 4‐Phenyl‐2‐butanone
Authors: Westerhausen Von Dorothée , Herrmann Sabine , Hummel Werner , Steckhan Eberhard
Published: December 2003

(2,2′‐Bipyridyl)(pentamethylcyclopentadienyl)rhodium complexes are homogeneous catalysts for the formate‐driven, in situ regeneration of the cofactors NADH and NADPH in enantioselective, enzymatic reductions of carbonyl compounds. A non‐enzymatic cofactor regeneration scheme in combination with four NAD(P)H‐dependent alcohol dehydrogenases was tested with the reduction of 4‐phenyl‐2‐butanone. High turnovers and high enantioselectivities were achieved for the formation of the (R) and (S) alcohols.
Emil Fischer's Proof of the Configuration of Sugars: A Centennial Tribute
Authors: Lichtenthaler Frieder W.
Published: December 2003

Today's textbooks convey the deceptive impression that chemistry developed in a rational and orderly process with discoveries following one upon another in a vertical progression—an impression that tends to classify Fischer's achievement as a matter‐of‐fact historical development. This misconception does not consider the instances of serendipity invariably involved, and entirely fails to appreciate the human endeavor, the intellectual struggle of the dedicated researcher, and the forging force of his personality that eventually led to this key insight. The hundredth anniversary of Fischer's classical piece of work provides a welcome opportunity not only to highlight its paramount importance for the development of carbohydrate chemistry, and of organic chemistry in general, but to trace the creative processes underlying this fundamental discovery, the thought patterns at a conceptual level, and the constructive reasoning that eventually led to it. Their understanding and appreciation is essential for emulating Fischer's achievement in a modern context.

Die Geschichte einer Wissenschaft ist diese Wissenschaft selbst, J. W. von Goethe
Synchrotron X‐ray and Neutron Diffraction Studies in Solid‐State Chemistry
Authors: Cheetham Anthony Kevin , Wilkinson Angus Paul
Published: December 2003

Neutron diffraction studies, especially with powders, play an important role in structural solid‐state chemistry, making possible the precise determination of the location of light atoms, particularly hydrogen, and enabling a distinction to be made between certain neighboring elements in the periodic table that are difficult to distinguish in experiments with X‐rays. Neutron diffraction investigations also make a unique contribution in the area of magnetic structure determination. The availability of intense synchrotron X‐rays sources, however, is opening up new opportunities to the structural chemist, many of them complementary to the “traditional” strengths of neutron methods. The key features of synchrotron radiation in relation to structural studies are the wavelength tunability, which facilitates the use of resonant diffraction methods, and the high brightness and excellent vertical collimation of the source, which make possible the construction of diffractometers with unparalleled angular and spatial resolution. The following types of experiments are now possible with synchrotron X‐ray diffraction: (1) The ab initio determination of structures from powder diffraction data. (2) The differentiation between different oxidation states of an element (valence contrast experiments) based upon the sensitivity of an absorption edge to the valence of the element in question. (3) The differentiation of elements adjacent to each other in the periodic table, which is now feasible with synchrotron X‐rays for all elements beyond chromium. (4) Site‐selective X‐ray absorption spectroscopy. (5) The study of cation occupancies in materials where more than one element occupies a site that is, or may be, partially occupied. (Such problems are important in zeolite chemistry and high‐temperature superconductors.) (6) The determination of crystal structures from microcrystals. (7) In situ and rapid, time‐resolved diffraction studies. This review examines the roles played by X‐ray and neutron diffraction studies in modern solid‐state chemistry, and describes some recent examples in which the use of neutron radiation or synchrotron X‐rays has been advantageous.
A Milestone in Genome Sequencing: The Complete DNA Sequence of the Yeast Chromosome III
Authors: Winnacker Ernst‐L.
Published: December 2003

315357 Base pairs in length, chromosome III of baker's yeast was sequenced by 147 scientists from 35 European laboratories at a cost of approximately DM 10 per base pair. The sequence contains 182 open reading frames coding for proteins more than 100 amino acids long. Until now, the classical genetic map of this chromosome had listed only 34 genes, that is, only 20% of the actual number of genes. If one extrapolates this result to the human genome, the estimated number of our genes must be revised dramatically upwards, to 500 000 or more.
Mutual Catalysis of Neutral and Anionic Cobalt Carbonyls in Their CO Scrambling Reactions
Authors: Fachinetti Giuseppe , Funaioli Tiziana
Published: December 2003

Redox‐condensation equilibria, probably with the participation of [Co3(CO)10]− as intermediate, and not ion pairing as previously postulated, explain the acceleration of the CO scrambling in [Co(CO)4]− by alkali metal counterions. The studies described here show that neutral carbonyl complexes catalyze the CO scrambling for anionic metal carbonyls and vice versa, and that the catalysis is less effective in the presence of free CO. The latter is in agreement with [Co3(CO)10]− as the intermediate. These results are important mainly because neutral and anionic metal carbonyls frequently exist together as a result of side reactions.
Determination of the HN–Hα Coupling Constant in Large Isotopically Enriched Proteins
Authors: Seip Stephan , Balbach Jochen , Kessler Horst
Published: December 2003

The 3J coupling constants of very large proteins can be determined independent of the width of the signal in the NMR experiments described here. Both pulse sequences correlating 15N with 13Cα and HN were used to determine 3J in the P13 domain of mannose permease. This coupling constant provides information on the range of values for the angle φ, which is important in molecular dynamics calculations.
Rate Constants for the Attack of Carbenium Ions at Arenes—A Link between the Chemistry of Aliphatic and Aromatic π Systems
Authors: Mayr Herbert , Bartl Jörg , Hagen Gisela
Published: December 2003

The mechanism of the Friedel‐Crafts reaction is one of the most thoroughly studied, yet the absolute rate constants for the key step—the attack of the carbenium ion at arene—have only now been determined for the arylcarbenium ion. Since rate constants for reactions of these carbenium ions with alkenes and complexes of main group elements with the allyl group are already known, a direct comparison between the nucleophilicity or aromatic and aliphatic π systems is now possible.
Salting Out Selective Extraction—A Novel Method for the Optical Resolution of Chiral Sulfinylcarboxylic Acids and Its Application for the Convenient Determination of Optical Purity
Authors: Rábai József
Published: December 2003

When fractional recrystallization fails to separate diastereomeric salts, the enantiomers may still be resolved by the selective extraction of the diastereomeric salts. Racemic sulfinylcarboxylic acids were treated with cinchona bark alkaloids and NaOH (or KHCO3). Repeated extractions led to high enantiomeric excesses.
Marine Metabolites and Metal Ion Chelation: The Facts and the Fantasies
Authors: Michael Joseph P. , Pattenden Gerald
Published: December 2003

The marine environment is a seemingly inexhaustible treasury of organisms whose secondary metabolites bear witness to the lavishness and inventiveness with which nature is able to manipulate molecular architecture. But to what purpose are these diverse and often grotesque compounds produced? This review is founded on the premise that some of them may be involved in the uptake and transport of metal ions present in the aquatic milieu. Many metabolites produced by terrestrial organisms are known to act as ionophores, but the case for similar behavior by their marine counterparts is far hazier. Notwithstanding the relative abundance of certain metal ions in the oceans, and of metabolite structures possessing features that should facilitate the chelation of metal ions, few attempts to establish a connection between these two phenomena have been reported. We have whittled down the voluminous literature of natural products derived from marine sources to expose a core of observations and speculations germane to our premise. These facts and fantasies are evaluated in this review. A mere handful of metal‐containing complexes has actually been isolated; furthermore, attempts to prepare such complexes in vitro are rare, and spectroscopic evidence for metal–metabolite interactions, whether in vivo or in vitro, is not common. Only with the vanadium‐sequestering tunichromes does a logical (but by no means complete) picture begin to emerge. In several other cases, the plausibility of metal chelation, though mooted by authors, remains unsupported by experimental evidence. However, continuing efforts to obtain structural, and particularly conformational, information on the metabolites by means of X‐ray crystallography, nuclear magnetic resonance spectroscopy, and molecular mechanics calculations would seem to provide the key to a rational approach to this neglected topic. On the basis of recent studies dealing with such structural aspects, we present a selection of candidate compounds, some of which are the targets of our own synthetic attentions, whose potential for binding to metal cations merits further research.
Bonding in Endohedral Metal–Fullerene Complexes: f‐Orbital Covalency in Ce@C28
Authors: Rösch Notker , Häberlen Oliver D. , Dunlap Brett I.
Published: December 2003

Three conditions must be met if an endohedral metal–fullerene complex is to be stable : 1. Metal valence orbitals and fullerene frontier orbitals must have complementary symmetry. 2. The metal atomic orbitals must fit inside the fullerene cavity. 3. The resulting complex must have a closed‐shell configuration. According to scalar‐relativistic calculations these conditions are met in Ce@C28. The binding energy is calculated to be 13.7 eV, and the Ce f orbitals contribute significantly to the covalent bond.
Extending the Metal Cluster–Metal Surface Analogy
Authors: Gates Bruce C.
Published: December 2003

Reactivity and catalytic properties–are there analogies between metal clusters and metal surfaces here too? In the 1980s the conclusion had been reached that such analogies could only be formulated about structure and bonding. But new work from Yates et al. and Chisholm et al. has given rise to new hope. They studied CO dissociation on sparsely covered Mo surfaces and in tetranuclear tungsten clusters, respectively. These reactions proceed in a similar fashion; however, their rate‐determining steps and reaction rates differ.
The Application of Au55 Clusters as Quantum Dots
Authors: Simon Ulrich , Schön Günter , Schmid Günter
Published: December 2003

The beginning–or the end—of the metallic state is attained in ligand‐stabilized Au55 clusters. As quantum dots with two last “switchable” electrons they are the nonpareils of electronic miniaturization and can be used as microelectronic quantum devices.
Superconductivity and Phase Separation in NaxNbO2 (x < 1)
Authors: Rzeznik Maria A. , Geselbracht Margret J. , Thompson Mark S. , Stacy Angelica M.
Published: December 2003

Below 4.2 K is the onset of superconductivity in sodium niobates NaxNbO2 for values of x between 0.65 and 0.9. The samples studied all contain two phases, a sodium‐rich phase, which is isostructural with NaNbO2, and a sodium‐poor phase with a related layered structure. The latter phase exhibits superconductivity.
S‐Glycosylated Cyclic Peptides
Authors: Gerz Manfred , Matter Hans , Kessler Horst
Published: December 2003

The high chemical and enzymatic stability of thioglycosides stimulated the synthesis of S‐glycosylated cyclopeptides. The structural properties of this new class of compounds were established by conformational analysis with 2D NMR methods and molecular dynamics calculations. These substances are of interest for the development of site‐specific drugs.
Two New High‐Pressure Modifications of NaOH
Authors: Beck Horst P. , Lederer Gunda
Published: December 2003

Only stable under pressure, two new high‐pressure modifications of NaOH were structurally characterized for the first time by refined X‐ray diffraction methods. Both structures proved to be interesting variants of common types and result from the nonspherical symmetry of the OH groups.
Iodine Azide
Authors: Buzek Peter , Klapötke Thomas M. , von Ragué Schleyer Paul , Tornieporth‐Oetting Inis C. , White Peter S.
Published: December 2003

Very pure and crystalline, iodine azide IN3 (1) can be obtained by reaction of silver azide and iodine in CFCl3 and subsequent sublimation. According to the results of the X‐ray structure analysis in the solid state IN3 consists of layers of chains, which contain twofold coordinated iodine atoms. The structural parameters of the IN3 unit are in good agreement with the results of an ab initio calculation for IN3.
Propionyl‐Aza(dethia)coenzyme A as Pseudosubstrate of the Biotin‐Containing Transcarboxylase
Authors: Martini Harald , Rétey János
Published: December 2003

How is the carboxyl group of 1′‐N‐carboxybiotin transferred to the substrate? To resolve the controversy surrounding the mechanism the title compound was used as substrate for propionyl‐CoA‐oxaloacetate transcarboxylase. It was not carboxylated in the reaction, but induced the decarboxylation of oxaloacetate. This communication gives a plausible explanation for this observation.
A Hemerythrin Model Complex with Catalase Activity
Authors: Mauerer Bert , Crane Jonathan , Schuler Jürgen , Wieghardt Karl , Nuber Bernhard
Published: December 2003

The catalytic disproportionation of H2O2 to O2 and H2O is achieved with the asymmetric hemerythrin model complex 1, which has a reactive coordination site. The catalytic cycle proceeds via the oxyhemerythrin form with a coordinated hydrogenperoxo ligand. L  1,4,7‐trimethyl‐1,4,7‐triazacyclononane, bpy  2,2′‐bipyridine.
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Defect Chemistry: Composition, Transport, and Reactions in the Solid State; Part I: Thermodynamics
Authors: Maier Joachim
Published: December 2003

Within the last few decades—though its foundations were laid over 60 years ago—a direction of research has developed almost unnoticed by the classical chemical disciplines, such that one can now recognize a chemistry within the solid state that is analogous to the long‐familiar chemistry in the liquid state. It arises from those departures from the ideal structure that are thermodynamically unavoidable, the point defects, and is referred to as defect chemistry. It includes the description of ionic and electronic effects, and it considers diffusion as a special step of the overall reaction. This area of chemistry enables one to describe and treat in a unified way many widely different phenomena such as ionic conduction in crystals, doping effects and p–n junctions in semiconductors, color centers in alkali metal halides, image development in photography, passivation and corrosion of metals, the kinetics of synthesis and sintering of solid materials, problems of rock formation during the earth's evolution, the mechanisms of gas sensors and high temperature fuel cells, the performance of photosensitive electrodes, variations of the electron balance in high‐temperature superconductors, elementary processes of heterogeneous catalysis, nonequilibrium transitions and oscillations in semiconductors in electric fields, and many more. In such phenomena the equilibrium concentration of defects has an important double role: it not only determines the disorder and the departure from the Dalton composition in the equilibrium state, but also, together with the mobility as the kinetic parameter, is the key parameter concerning the rates of physicochemical processes. Accordingly, in this first part of the review the emphasis will be on the equilibrium thermodynamics of point defects, whereas the second part will be specifically concerned with the kinetic aspects. Both parts will emphasize the fact that the defect chemistry of solids, as well as being the counterpart of solution chemistry in the liquid state, also provides a unifying approach in which electronic and ionic charge carriers are treated by analogous methods, both in the bulk and in boundary layers, and allows diffusion to be incorporated naturally into the overall kinetics of reactions as an elementary chemical process.