bluuebunny/crossref_metadata_2025 huggingface dataset:
Recent Developments in the Field of β‐Lactam Antibiotics
Authors: Dürckheimer Walter , Blumbach Jürgen , Lattrell Rudolf , Scheunemann Karl Heinz
Published: December 2003

The era of β‐lactam antibiotics, which represent the most important class of drugs against infectious diseases caused by bacteria, began more than fifty years ago with the discovery of penicillin G. Further improvements by isolation and structure elucidation of new natural compounds, and systematic chemical modification of these, is a striking example of to what extent chemistry can contribute to the progress of drug therapy. The complex relationship between structure and activity requires, even today, a largely empirical approach. The minimum structural unit for antibiotic activity had to be revised several times over decades. Both the activated β‐lactam ring with an acidic group and the nature and spatial arrangement of the other substituents and rings decisively affect the potency, antibacterial spectrum, pharmacokinetics, and toxicity. Totally synthetic mono‐ and bicyclic compounds from the series of monobactams, penems, carbapenems, 1‐oxacephems, and 1‐carbacephems are increasingly joining the classic groups obtained by semisynthesis from 6‐amino‐penicillanic acid and 7‐aminophalosporanic acid.
Organocobalt Compounds in the Synthesis of Pyridines–An Example of Structure‐Effectivity Relationships in Homogeneous Catalýsis
Authors: Bönnemann Helmut
Published: December 2003

The cocyclization of alkynes with cyano compounds using organocobalt catalysts of the type [YCoL] has evolved into a versatile and technically useful method for synthesizing pyridine and its derivatives. An important advance came with the realization that the organo group Y remains attached to the cobalt throughout the catalytic cycle. This opened up the possibility of optimizing the catalyst by varying the controlling ligand Y.
Catalytic Synthesis of Organolithium and Organomagnesium Compounds and of Lithium and Magnesium Hydrides—Applications in Organic Synthesis and Hydrogen Storage
Authors: Bogdanović Borislav
Published: December 2003

A recent development in homogeneous catalysis is the discovery of catalysts that are active for the lithiation of 1‐alkenes to alkenyllithium compounds and lithium hydride as well as for the hydrogenation of lithium and magnesium under mild conditions. The catalytically prepared magnesium hydride is highly reactive and adds to 1‐alkenes to give diorganomagnesium compounds and can also be used in the preparation of, for example, silane and “active” magnesium. The use of metal hydrides in hydrogen storage is discussed: hydrogenation/dehydrogenation experiments show that the catalytically prepared magnesium hydride (which can be doped with a second metal) can be used as a high‐temperature hydrogen storage material.
Radwaste Immobilization by Structural Modification—the Crystallochemical Properties of SYNROC, a Titanate Ceramic
Authors: White Timothy J. , Segall Robert L. , Turner Peter S.
Published: December 2003

New studies utilizing electron microscopic techniques have revealed the immobilization of radionuclides in crystalline ceramic waste forms to be not merely a question of substituting waste elements into the appropriate crystallographic sites of a host matrix. Rather than entering the ceramic as a “continuous” solid solution it has been found that the incorporation of highly radioactive waste elements is commonly accompanied by structural modification. This may take the form of cation ordering, crystallographic shear, or twinning on a unit cell scale. Such mechanisms considerably enhance the capacity of a ceramic to immobilize (simulated) radwaste and impart to it the flexibility to respond to inevitable variations in wastestream composition.
Complexes of 1,5‐Di(p‐tolyl)‐1,4‐pentaazadien‐3‐ide, Crystal Structures of [Cu(tolylNNNNNtolyl)]3 and [Ni(tolylNNNNNtolyl)2]2
Authors: Beck Johannes , Strähle Joachim
Published: December 2003

Three linearly arranged Cu⊕ ions, coordinated by three parallel N5 zig‐zag chains in such a way that each metal ion is surrounded by a trigonal planar array of N atoms, are present in the pentaazadienide complex 1. The red crystals of 1 exhibit weak paramagnetism; the CuCu distances in the chains are the shortest observed so far in copper(I) complexes.
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Photosignal II as an Indicator for Damage to Forests ‐ EPR Spectroscopic Investigation of Spruce Needles
Authors: Stegmann Hartmut B. , Ruff Hans J. , Scheffler Klaus
Published: December 2003

Following the exposure of spruce needles to SO2 and NOx, it is possible to detect changes in the electron transport chain of the photosynthetic apparatus by EPR spectroscopy and to clearly distinguish between the needles of healthy and of damaged trees.
Nitrogen Monoxide as a Source for Oxo Ligands—Acetylene‐Oxo Complexes of Tungsten
Authors: Alt Helmut G. , Hayen Heidi I.
Published: December 2003

The fragmentation of an alkenyl ketone ligand into an alkyne‐and methyl‐or acetylligand is surprisingly achieved in the reaction of CpW(CO)2CHCHCOCH3 with nitrogen monoxide. NO provides its oxygen for the formation of an oxoligand.
NaGe—High‐Pressure Formation of the NaPb‐Type Structure
Authors: Evers Jürgen , Oehlinger Gilbert , Sextl Gerhard , Weiss Armin
Published: December 2003

An increase in coordination numbers from 6:6 to 7:7 accompanies the conversion of the normal‐pressure modification of NaGe, the only compound of the NaGe type, into a NaPb‐type modification under pressure. This increase is in turn accompanied by an increase in density of ca. 5%. The Ge substructure, consisting of isolated tetrahedra, remains unaltered. Large changes in electrical properties are to be expected in a modification with 8:8 coordination, which could be obtained at still higher pressures.
Chiral Compounds Synthesized by Biocatalytic Reductions [New Synthetic Methods (51)]
Authors: Simon Helmut , Bader Johann , Günther Helmut , Neumann Stefan , Thanos Jordanes
Published: December 2003

It has been known for many decades that chiral compounds can be obtained by stereospecific biocatalytic reduction. Further significant methodological developments in this field have, however, only been made during the past ten years; they include the application of previously unused microorganisms and electron donors, the discovery of additional substrates for the known reductases, the development of methods for regenerating reduced pyridine nucleotides, and the discovery of new reductases which were sought for specific preparative purposes. Many chiral compounds can now be synthesized by microbial hydrogenation using H2 and hydrogenase‐containing microorganisms as well as by electromicrobial or electroenzymatic reduction. In the two latter methods, anaerobic or aerobic organisms are supplied with electrons from electrochemically reduced, artificial mediators, e.g., methyl viologen. Reductases that do not require pyridine nucleotides and can accept electrons directly from reduced viologens are especially useful. Two examples of this type of enzyme are described which are of preparative interest. Many cells contain methyl viologen‐dependent NAD(P) reductases, a large number of which have still not been characterized. A productivity number is proposed which allows different methods of bioconversion with microorganisms to be compared. The productivity numbers of compounds synthesized by the methods described in this review are often 10‐ to 100‐fold higher than those of substances obtained by conventional techniques.
Phase Behavior of Ternary Systems of the Type H2OOilNonionic Amphiphile (Microemulsions)
Authors: Kahlweit Manfred , Strey Reinhard
Published: December 2003

Liquid multicomponent systems of the type H2O‐oil‐amphiphile‐electrolyte are of growing interest, both in industry and in research. In applications technology, there are two problems to solve: 1. To prepare stable homogeneous solutions of H2O and nonpolar liquids with as little amphiphile as possible which can be diluted with H2O in all proportions without phase separation; e.g., concentrated solutions of drugs, herbicides, or insecticides. 2. To prepare stable mixtures of an aqueous, an amphiphile, and an oil phase with as little amphiphile as possible which are employed in tertiary oil recovery and in the pharmaceutical industry. Furthermore, such systems may be used for performing chemical reactions in heterogeneous liquid mixtures with continuously variable properties. In research, such systems are of interest for both experimental and theoretical studies of critical phenomena, especially near so‐called tricritical points. Last but not least, their properties may stimulate further research in the field of associated solutions. In this paper we summarize the results of our studies on the phase behavior of ternary systems with nonionic amphiphiles, in particular with respect to the evolution of liquid three‐phase bodies. The results suggest that the tricritical points in such systems should be regarded as kinds of pivot points from which the phase behavior evolves. If this were an approach to reality, the phase behavior would be governed in more or less good approximation by universal scaling laws, irrespective of the particular microstructure of the solutions. Finally, we discuss the effect of electrolytes on the phase behavior both in a quaternary phase tetrahedron and a pseudoternary phase prism representation. Although in practice most systems consist of mixtures of oils, amphiphiles, and electrolytes, an understanding of the phase behavior of truly ternary and quaternary systems with chemically well‐defined components permits at least qualitative predictions with respect to the phase behavior of the multicomponent mixtures encountered in practice.
Calculation of the Charge Distribution in Conjugated Systems by a Quantification of the Resonance Concept
Authors: Gasteiger Johann , Saller Heinz
Published: December 2003

The assignment of weights to the resonance structures of organic compounds and the determination of the resulting charge distribution can be rapidly accomplished using a new calculation procedure. The method takes into consideration, among other things the π‐orbital electronegativities and changes in the bonding structure.
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Transition Metal Polysulfides: Coordination Compounds with Purely Inorganic Chelate Ligands
Authors: Draganjac Mark , Rauchfuss Thomas B.
Published: December 2003

It has been long known that certain transition metal sulfides dissolve in aqueous ammonium polysulfide. Although it was assumed that they thereby formed metal polysulfides, attention was first paid to such compounds only a few years ago. In recent years a host of new complexes with polysulfido chelate ligands have been isolated and characterized. The complexes are of interest not only regarding their structure and reactivity but also in view of their potential uses; they can be used for the directed preparation of sulfur rings of a given size, and there are indications that they will find applications in catalysis.
The Generative Grammar of the Immune System (Nobel Lecture)
Authors: Jerne Niels K.
Published: December 2003

The basic concepts of immunology and their development as part of biology during the last 100 years is the starting point of Niels K. Jerne's lecture, which he presented on the occasion of accepting the 1984 Nobel Prize for Physiology and Medicine. Each half of an antibody molecule consists of a light polypeptide chain containing about 214 amino acid residues and a heavy polypeptide chain containing a little more than 400 amino acid residues.
Skeletal Isomerization of the [Pt3(μ‐PPh2)3Ph(PPh3)2] Cluster by Recrystallization in Various Solvents
Authors: Bender Robert , Braunstein Pierre , Tiripicchio Antonio , Camellini Marisa Tiripicchio
Published: December 2003

The solvent used for crystallization determines which of the two structural isomers of [Pt3(μ‐PPh2)3Ph(PPh3)2] 1 is formed. The isomer 1a is obtained in crystalline form from toulene/pentane, the isomer 1b · 2CH2Cl2 from CH2Cl2/pentane. The two isomers differ in their PtPt distances and PtPPh2Pt angles.
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Arene Complexes of Univalent Gallium, Indium, and Thallium
Authors: Schmidbaur Hubert
Published: December 2003

Arene complexes of main‐group metals were, until recently, rare species—in contrast to the now classical, analogous complexes of transition metals. In systematic investigations, it has been possible to prepare and structurally characterize arene complexes of the univalent elements gallium, indium, and thallium, which directly follow the d‐block elements in the periodic table. This new type of compound is characterized by centric (η6) coordination of the metal to the arene; both mono‐ and bis(arene) complexes are known. The interaction can be explained by the perfect agreement between the HOMO/LUMO symmetry of the arene and of the low‐valent metal. The electronic states of the nd10(n + 1)s2 configuration, which are partially modified by relativistic effects, play a particularly important role. The relationship to the few known complexes of the neighboring elements (SnII, PbII) becomes plausible via the isoelectronic principle. The arene/GaI, InI, TlI systems are of potential significance as homogeneous reducing agents and as agents for the activation of aromatic compounds, the purification of metals, and the separation of metals from nonaqueous media.
Phosphorus, Arsenic, Antimony, and Bismuth Multiply Bonded Systems with Low Coordination Number — Their Role as Complex Ligands
Authors: Scherer Otto J.
Published: December 2003

Multiply bonded systems with low coordination number (one to three) involving phosphorus and its homologues, whether isolable or generatedin situat a metal complex, are versatile ligands that can function as two‐, four‐, six‐ or eight‐electron donors to transition metal fragments and that may be coordinated in η1(terminal), η2(side‐on), edge‐ or face‐bridging modes. The (p‐p)π bonding system of the ligand is thereby rendered capable of addition and intra‐ or intermolecular cycloaddition reactions. Some of the polycyclic species thus generated represent novel, polydentate ligands.
The Revised Structure and Absolute Configuration of Chaksine
Authors: Voelter Wolfgang , Winter Werner , Ahmad Viquar Uddin , Usmanghani Mohammad
Published: December 2003

Chaksine, a constituent of the seeds of Cassia abuss (var. Chaksa), is an alkaloid containing a 16‐membered bislactone ring. In 1958, Wiesner et al. proposed a structure with an eight‐membered lactone ring for the alkaloid. Although elemental analyses and NMR data are concordant with both structures, the field desorption mass spectrum suggests a dimeric species, proof for which has finally been provided by an X‐ray structre analysis.
A Dithioester as Allylic‐Type 4e Ligand
Authors: Schenk Wolfdieter A. , Rüb Doris , Burschka Christian
Published: December 2003

Novel complexes with methyl dithioacetate as η3‐ligand have been synthesized from nitrile complexes and characterized, inter alia, by X‐ray structure analysis of 1. The SCS group of the ligand is exactly planar and is bound in an allyl‐like fashion to the metal. Electrophilic attack at the “thione” sulfur leads to dinuclear complexes or η2‐dithiocarbenium derivatives.
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The σ2π4 Triple Bond between Molybdenum and Tungsten Atoms: Developing the Chemistry of an Inorganic Functional Group
Authors: Chisholm Malcolm H.
Published: December 2003

Numerous analogies between organic and inorganic chemistry have emerged in recent years. The most prominent example is the isolobal relationship. Many reactions have shown that metal‐metal double and triple bonds exhibit a pattern of reactivity similar to that of alkenes and alkynes. In compounds containing a σ2π4 triple bond between molybdenum and tungsten atoms, the MM bond order can be increased from three to four by reductive elimination or decreased from three to two or one by oxidative addition. Complexes with MM bonds can be used to prepare clusters or can serve as catalysts. In this review relationships between structure (electronic and stereochemical) and reactivity that are characteristic for modern inorganic chemistry are discussed.
The Chemistry of the Noncrystalline State
Authors: Elliott Stephen R. , Rao C. N. R. , Thomas John M.
Published: December 2003

This article sets out to describe and account for the chemical and physical consequences of the presence of gross disorder in solids. Knowledge of the structure of such disordered materials is an obvious prerequisite to a further understanding of other properties and behavior, and our current knowledge of the structure of various noncrystalline systems is discussed together with the experimental techniques which need to be employed in order to obtain such information. The so‐called glass transition, which takes place as a liquid is supercooled below the crystallization temperature, is discussed in terms of the various models which have been proposed to account for this phenomenon. The effect of noncrystallinity on electronic properties is also discussed, and we highlight new developments in the understanding of electron localization and transport processes. Finally, two applications of amorphous solids are considered in some detail: optical fibers for use in communication networks and “superionic” glasses for possible use in solid‐state batteries.
Multiple Bonds between Transition Metals and “Bare” Main Group Elements: Links between Inorganic Solid State Chemistry and Organometallic Chemistry
Authors: Herrmann Wolfgang A.
Published: December 2003

The last two decades have seen a dramatic development in the study of metal‐metal multiple bonds, particular successes being recorded in the field of organometallic chemistry. Syntheses designed to produce novel transition metal complexes with single, double, triple and quadruple metal‐metal bonds occupy a most important place in such research, as also do reactivity studies. A striving to establish general principles has provided much of the motivation for such work, but one less obvious goal—the commercial application of the catalytic properties of metal‐metal multiple bonding systems, in the medium and long term—should not be overlooked. All aspects of the investigations of metal‐metal multiple bonds also apply to a particular class of compound that has, however, enjoyed little lime‐light and thus deserves the present review: complexes with multiple bonds between transition metals and substituent‐free (“bare”) main group elements. Although based mostly on accidental discoveries, the few noteworthy examples are now beginning to unfold general concepts of synthesis that are capable of being extended and thus are deserving of exploitation in preparative chemistry. The availability of further structural patterns exhibiting multiple bonds between transition metals and ligand‐free main group elements might enable preparative organometallic chemistry to expand in a completely new direction (for instance by the stabilizing or activation of small molecules at the metal complex). This essay discusses the chemistry of complexes of bare carbon, nitrogen, and oxygen ligands (carbido‐, nitrido‐, and oxo‐complexes) and their relationships to higher homologues from both a synthetic and a structural point of view.
Ag3O4, the First Silver(II,III) Oxide
Authors: Standke Burkhard , Jansen Martin
Published: December 2003

The silver oxide Ag3O4 contains crystallographically differentiable di‐ and trivalent silver ions, each in square‐planar oxygen environment. From the bond lengths it is concluded that extensive charge equalization takes place between Ag2+ and Ag3+, Ag3O4 is obtained by anodic oxidation of silver salt solutions.
Metathesis of Alkyl Radicals and Alkenes–a Novel Elementary Reaction of Alkyl Radicals
Authors: Metzger Jürgen O.
Published: December 2003

The experimental detection of the transfer of a β‐H atom from an alkyl radical to an alkene closes a gap in the system of elementary reactions of alkyl radicals. It is very unlikely that the chain transfer in polymerizations takes place via this reaction.
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Trithiometaphosphate PS—an Anion with Phosphorus of Coordination Number 3
Authors: Roesky Herbert W. , Ahlrichs Reinhart , Brode Stefan
Published: December 2003

Monomeric metaphosphate PO and its analogues have long attracted the interest of inorganic chemists and biochemists, yet PO itself could hitherto not be detected in the solid state. There is now evidence in support of this having been accomplished in the case of the homologous PS ion; this ion is formed in the reaction of P4S10 with KCN and H2S and can be isolated as the Ph4As salt. Calculations support the proposed planar structure with D3h symmetry for the anion in the gas phase. A monomeric, pyramidal structure could also be present in the solid.
3‐Chloropropyltrialkoxysilanes—Key Intermediates for the Commercial Production of Organofunctionalized Silanes and Polysiloxanes
Authors: Deschler Ulrich , Kleinschmit Peter , Panster Peter
Published: December 2003

Silicon and carbon may be looked upon as the two fundamental antipodes with respect to the naturally occurring forms of matter and life on earth: Silicon plays the key role in the “petrification” of inanimate matter, while carbon is the representative element for the “incarnation” of living organisms. If a scientist were to search for a highly efficient method of uniting inorganic and organic matter, he would, at a very early stage of attempting to solve this problem, combine these two natural principles of matter and think of “bireactive” molecules containing a silicon functionality for bonding to inorganic material on the one hand and a carbon functionality for anchoring to an organic counterpart on the other. The title compounds and their derivatives epitomize such molecules: they are wanderers between both (chemical) worlds. Owing to their bifunctionality they are capable of binding to inorganic (especially siliceous) systems as well as to organic polymers. Whether their commercial application concerns the strengthening of polyester resins with glass fibers for use in boatbuilding or the incorporation of silica as a filler in rubber mixtures for the manufacture of wear‐resistant tires or even the immobilization of enzymes on glass spheres for carrying out reactions in enzyme reactors—in all cases organofunctionalized silanes guarantee a reliable and permanent union between two otherwise “incompatible” material systems.
Valence Tautomerism of the Heptaheteronortricycles [P7 − xAsx]3−
Authors: Hönle Wolfgang , von Schnering Hans‐Georg
Published: December 2003

Solutions of the mixed crystals Rb3[P7−xAsx] in ethylenediamine contain almost the entire series of the heptaheteronortricycle anions P7−xAsx, as has been demonstrated by 31P‐NMR spectroscopy; only [PAs6]3‐ could not be detected with certainty. [P6As]3− and [P5As2]3− are preferentially formed, but not [P4As3]3− as would be expected on the basis of the concept of topological charge stabilization. Very suprisingly, exchange reactions do not take place.
15N‐NMR Spectroscopy—New Methods and Applications [New Analytical Methods (28)]
Authors: von Philipsborn Wolfgang , Müller Raffaello
Published: December 2003

The nitrogen nucleus is the third most important probe (after 1H and 13C) for structural investigations of organic and bioorganic molecules by NMR spectroscopy. For a long time, however, the insufficient sensitivity and low natural abundance of the 15N isotope hampered detection of the 15N nucleus, and the quadrupolar 14N nucleus proved unsuitable for the study of larger molecules with several nonequivalent nitrogen atoms. The advent of new techniques, such as pulse sequences and polarization transfer, in conjunction with the use of high‐field magnets and large‐sample probe heads largely solved the detection problem. As a result, the last few years have seen a dramatic development of 15N‐NMR spectroscopy as a versatile method for studying molecular structure, both in isotropic (liquid) and anisotropic (solid) phases. The scope of chemical applications extends from inorganic, organometallic, and organic chemistry to biochemistry and molecular biology, and includes the study of reactive intermediates, biopolymers, enzyme‐inhibitor complexes, and nitrogen metabolism. Two‐dimensional NMR techniques offer additional possibilities for detailed studies of biological systems.
Superactive Alkali Metal Hydride Metalation Reagents: LiH, NaH, and KH
Authors: Klusener Peter A. A. , Brandsma Lambert , Verkruijsse Hermann D. , von Ragué Schleyer Paul , Friedl Thomas , Pi Rafael
Published: December 2003

Alkali metal hydrides would be ideally suitable for the synthesis of carbanions, since only H2 would be formed as second product; unfortunately, however, they are normally not very reactive. A synthesis of LiH, NaH and KH by hydrogenation of BuM (M = Li, Na, K) in hexane is now described here which leads to highly reactive metal hydrides. In addition, they deprotonate more selectively than other metalation reagents.
Epoxidation of Olefins with Elemental Fluorine in Water/Acetonitrile Mixtures
Authors: Rozen Shlomo , Brand Michael
Published: December 2003

Not fluorinated compounds but rather epoxides are formed in good yields from alkenes with the reagent F2/MeCN/H2O. Both alkenes with a terminal double bond, which are especially sensitive to oxidation, and enones react smoothly.
[MoR(η3‐C3H5)3], R = Alkyl: Alkylmolybdenum Complexes with Agostic CH ⇀ Mo Bond
Authors: Benn Reinhard , Holle Sigrid , Jolly Peter W. , Mynott Richard , Romão Carlos C.
Published: December 2003

A dramatic high‐field shift of an 1H‐NMR signal characterizes the agostic Mo↼HC interaction in the isopropylmolybdenum complex 2. The bright yellow compound is accessible in 65% yield by reaction of the binuclear molybdenum complex 1 with isopropylmagnesium chloride at −78°C in ether.
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Recovering Phase Information from Intensity Data (Nobel Lecture)
Authors: Karle Jerome
Published: December 2003

Todays triumphant advance of X‐ray structure analysis is due in large part to the development of the “direct methods” by Herbert Hauptman and Jerome Karle. Previously, it was generally assumed to be impossible to determine a structure directly from the diffraction pattern of a crystal, for a normal diffraction experiment afforded only amplitudes, but no phases of the diffraction maxima. This phase problem was overcome in a series of steps that involved recognition that the required phase information was contained in the measured intensities, the derivation of a foundation mathematics that displayed relationships between phases and magnitudes and even among phases alone and, finally, the development of practical methods for structure determination, strategies that brought together in a more or less optimal fashion the mathematical relationships with suitably adjusted and refined experimental data.
[U3(μ3‐Cl)2(μ2‐Cl)3(μ1,η2‐AlCl4)3(η6‐C6Me6)3][AlCl4]—A Trinuclear Arene Complex of UIII
Authors: Cotton F. Albert , Schwotzer Willi , Simpson Charles Q.
Published: December 2003

Donor‐acceptor complexes of f‐block elements with neutral π‐ligands are few in number. It has now been possible to synthesize the trinuclear UIII‐title complex from UCl4, AlCl3, C6Me6 and aluminum by a modified Friedel‐Crafts reaction. Each U atom is coordinated in a pentagonal bipyramidal fashion by six Cl atoms and C6Me6.
An Isocyanide Radical as Complex Ligand
Authors: Seitz Friedrich , Fischer Helmut , Riede Jürgen , Schöttle Thomas , Kaim Wolfgang
Published: December 2003

The stable, neutral complexes 1 and 2, containing the dimesitylmethyl(isocyano) radical, are formed via a SET (single electron transfer) mechanism from the corresponding 2‐azaallenylidene complexes. The structure of 1 (violet crystals) was established by X‐ray structure analysis (R = mesityl).
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Bilayer‐Immobilized Films Containing Mesogenic Azobenzene Amphiphiles—Electrically Controllable Permeability
Authors: Okahata Yoshio , Fujita Shinsuke , Iizuka Noami
Published: December 2003

A model system for the study of transport phenomena in membranes consists of bilayer films of the cations 1 or 2 and polystyrenesulfonate anions. These bilayer films are immobilized, in turn, on a polyester grid. Application of an electric field increases the permeability of these artificial membranes with respect to a water‐soluble, neutral dye molecule. Surprisingly, however, only a field parallel to the membrane is effective in the case of 1 and only a field perpendicular to the membrane in that of 2.
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Microbial Degradation of Halogenated Hydrocarbons: A Biological Solution to Pollution Problems?
Authors: Müller Rudolf , Lingens Franz
Published: December 2003

Chlorinated hydrocarbons are widely used because of their chemical and thermal stability as well as their fungicidal, herbicidal, and insecticidal properties. Unfortunately, it is just this stability that makes the compounds persistent in nature; half‐lives of more than 15 years are not uncommon. In many countries the use of some chlorinated compounds has been prohibited, even though many such compounds (e.g., DDT) exhibit exactly the desired spectrum of effects. Surprisingly, microbiol systems that can degrade most chlorinated hydrocarbons have been found in nature. Indeed, it is possible, in many cases, to isolate pure cultures of bacteria that can utilize these compounds as the sole source of carbon and energy. Even polychlorinated compounds, such as the wood preservative and herbicide pentachlorophenol, can be utilized as a source of carbon by some bacteria. The study of the biodegradation of halogenated hydrocarbons has led to the discovery of novel catabolic pathways in which unusual and previously undescribed enzymatic activities have been detected. Bacterial enzymes have even been isolated that can replace halogen substituents in aliphatic and aromatic compounds with hydroxyl groups or hydrogen atoms. Improved understanding of the biodegradation of halogenated hydrocarbons, as described in this article, will almost certainly result in new biotechnological applications, especially in the area of waste‐water treatment.
Computer Graphics in the Study of Metal Cluster Compounds
Authors: Henrick Kim , McPartlin Mary , Morris Jill
Published: December 2003

Polynuclear carbonylmetal compounds provide convenient molecular analogues for the reactions occurring at metal surfaces during catalytic processes. Many properties of these cluster compounds are determined by the type and distribution of the ligands covering the metal polyhedral surface. Computer simulated space‐filling models of these complicated molecules provide readily assimilated information about the arrangement of surface ligands, and in many cases lead to conclusions not readily deduced from other approaches.
Selective Synthesis by Use of Lewis Acids in the Presence of Organocopper and Related Reagents. New Synthetic Methods (61)
Authors: Yamamoto Yoshinori
Published: December 2003

Organometallic compounds with pronounced nucleophilicity such as organocopper and organolithium compounds, and powerful electrophiles, such as BF3 and AlCl3, are generally thought to be incompatible under normal, homogeneous reaction conditions. As a matter of course, it is anticipated that the two species cannot coexist and undergo transmetalation reactions. To our surprise, however, RCu and BF3 are compatible at low temperature. RCu·BF3 and related organocopper‐Lewis acid reagents exhibit new and unique reactivities and selectivities: in conjugate additions, e.g., not only activation but also high regio‐, stereo‐, and chemo‐selectivity as well as very high asymmetric induction is observed; allylic derivatives are alkylated regioselectively, and reaction towards carbonyl groups, imines, epoxides, aziridines, ethers, acetals, orthoformates, and pyridinium salts is in each case found to be selective. RLi·BF3 and related organolithium‐Lewis acid reagents also exhibit noteworthy selectivities and reactivities. These complex reagents are utilized in the key steps of the total synthesis of many important natural products, such as certain terpenes, steroids, and alkaloids.
Hydroxide Ion Initiated Reactions Under Phase Transfer Catalysis Conditions: Mechanism and Implications. New Synthetic Methods (62)
Authors: Rabinovitz Mordecai , Cohen Yoram , Halpern Marc
Published: December 2003

The development of Phase Transfer Catalysis (PTC) represents a major step forward in the employment of many organic reactions and renders them very convenient and useful processes. These reactions involve the application of nucleophiles in general, anions and bases in particular, in reactions carried out in a water‐organic solvent system. They can be performed both in the laboratory and on an industrial scale. The ease of application of PTC processes is the main reason for their increasing utilization in industry. An outstanding achievement of this technique is the employment of aqueous bases in reactions which traditionally would otherwise require a strong base in a nonaqueous medium. The classical procedures that require severe anhydrous conditions, expensive solvents and dangerous bases such as metal hydrides and organometallic reagents are now replaced by aqueous solutions of, e.g., sodium or potassium hydroxides (PTC/OH processes). In contrast to the extensive synthetic applications of PTC/OH systems, the detailed mechanisms of these processes have been the subject of a great deal of controversy and various mechanisms have been suggested. However, it would seem that our knowledge concerning the mechanistic aspects of such reactions has now reached the stage where it can be used to advantage in synthesis planning. A better understanding of the various factors which influence the reaction would undoubtedly help to optimize PTC/OH processes such as to enable higher yields in shorter reaction times at lower temperatures. The importance of, inter alia, the catalyst will be pointed out and it is highly recommended that such catalysts be always available in the laboratory, for the range of organic reactions that they can efficiently, conveniently and safely catalyze is vast indeed.
Crystal Structure of Cl2O6
Authors: Tobias Klaus M. , Jansen Martin
Published: December 2003

Cl2O6 is present as ionic chloryl perchlorate, ClOClO, in the crystalline state. This is not surprising in view of the chemical behavior of Cl2O6–it is used as perchlorate “supplier” for the synthesis of anhydrous perchlorates–but was not to be expected according to the results of earlier structural investigations. The Cl–O distance in the ClO ion (ca. 141 pm) is much shorter than in the neutral ClO2 in the gas phase. Each cation is coupled with two anions (and conversely) to give polymeric groups.
1‐Phospha‐1,2,3‐butatriene
Authors: Märkl Gottfried , Sejpka Hans , Dietl Stefan , Nuber Bernd , Ziegler Manfred L.
Published: December 2003

The first phosphacumulenes of type 1 have been synthesized from dichloro(2,4,6‐tri‐tert‐butylphenyl)phosphane and lithioallenes. According to an X‐ray structure analysis, the unit in 1a, R′ = R″ = Ph, is linear. In the case of 1b, with Me and SiMe3 as substituents (R′, R″), the expected E/Z isomer could be isolated.
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Preorganization—From Solvents to Spherands
Authors: Cram Donald J.
Published: December 2003

This article assesses the importance of molecular preorganization to the rapidly developing field of complexation involving designed synthetic organic compounds. Since its birth as a science, organic chemistry has drawn heavily on biological chemistry as a vast storehouse of evolutionary structures, reactions, and control mechanisms that serve as inspiration for designed organic‐compounds mimics. Biological systems, through highly structured complexation, accomplish complicated tasks. The receptor sites of enzymes, the genes, the antibodies, and ionophores possess high degree of preorganization. In other words, their functional groups act cooperatively as binding or catalytic sites which are largely collected and oriented prior to complexation.—The strength of the organic chemist derives from his ability to design organic compounds, organic reactions, synthetic sequences, and test systems to evaluate hypotheses. The design of highly structured complexs and the discovery of the rules that govern their behavior are described here. Research in this field is particularly rewarding because scientific and aesthetic content merge and become visible in the structures of many of the complexes.
Stereoselective Aldol Reactions with α‐Unsubstituted Chiral Enolates
Authors: Braun Manfred
Published: December 2003

The aldol reaction is among the most important methods of forming carbon‐carbon bonds. The addition of an enolate to an aldehyde leads to the formation of at least one chiral center. In the case of α‐substituted enolates it has to a large extent been possible to control the product stereochemistry, while the aldol reaction of α‐unsubstituted chiral enolates was for many years a “problem child” for synthetic chemists because of its insufficient stereoselectivity. Progress in this area has only been made in the last few years using either new chiral auxiliaries or alternatives to the aldol reaction.
[CH3C6H5BiCl2][AlCl4] and [(CH3)6C6BiCl2] [AlCl4]–Compounds containing η6‐Arene‐Complexed BiCl Units
Authors: Frank Walter , Weber Jürgen , Fuchs Elisabeth
Published: December 2003

The ability of AlCl3 to abstract chloride ions from BiCl3 makes it possible to synthesize the title compounds in the presence of toluene and hexamethyl benzene, respectively. 1, the hexamethylbenzene complex, is an arene‐stabilized, dimeric dichlorobismuth(III) tetrachloroaluminate. The coordination of bismuth can be described as strongly distorted octahedral; five Cl ligands (two shorter, three longer Bi–Cl distances), one arene ligand.
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Difficulties in the Emergence of the Polymer Concept—an Essay
Authors: Morawetz Herbert
Published: December 2003

The emergence of polymer science as a discipline in itself followed a long and tortuous road, pitted with misconceptions. Indeed, in view of the importance today of plastics and man‐made fibers, it is hard to imagine these early difficulties. The essay begins with the first true polymer experiments at the beginning of the last century and ends with the establishment of the polymer concept approximately fifty years ago.
Nuclear Quadrupole Interaction and Time‐Resolved Perturbed γ‐γ‐Angular Correlation Spectroscopy: Applications in Chemistry, Materials Science, and Biophysical Chemistry. New Analytical Methods (31)
Authors: Lerf Anton , Butz Tilman
Published: December 2003

The study of nuclear quadrupole interactions, i.e. of the strength, symmetry, and orientation of the electric field gradient tensor, yields valuable information on charge density distributions on an atomic scale. Apart from the nowadays “conventional” methods of NMR and Mössbauer spectroscopy there is yet another technique: time‐resolved perturbed γ‐γ‐angular correlation spectroscopy. This technique is very well suited for applications in chemistry (e.g. comparative studies of bond conditions of inorganic complexes in the solid and in solution or in the melt), in molecular biology (e.g. intramolecular dynamics in biomolecules), and in materials science (e.g. investigation of catalyst surfaces) because of, inter alia, the extremely small sample requirements and the temperature independence of the sensitivity. The variation of the electric field gradient tensor (strength, symmetry, possibly orientation) is observed as a function of external parameters or, in the case of reactions, as a function of the degree of reaction. The interpretation of results requires the assignment of observed signals to known species or configurations. In this progress report we review modern areas of application of perturbed angular correlation spectroscopy.
Sulfur Pentafluoride Cyanate, F5SOCN
Authors: Schmuck Arno , Seppelt Konrad
Published: December 2003

A new member has been added to the scries of pcntafluorochalcogen cyanates and isocyanates. The title compound 1 was prepared from F5SOCI and CI2CNCI via the adduct F5SOCCl2NCl2, which could be stepwise deculorinated. Heating of compound 1 at high temperatures affords only traces of F5SNCO.
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The Crystal Structure of Mn2O7
Authors: Simon Arndt , Dronskowski Richard , Krebs Bernt , Hettich Bernhard
Published: December 2003

Mn2O7—a long‐known compound, whose crystal structure has finally been elucidated: the Mn atoms are surrounded tetrahedrally by O atoms; the bridging and the terminal Mn–O bonds are, as expected, of different lengths. The Mn2O7 molecules are packed in such a way that an only slightly distorted fcc arrangement results for the O atoms.
Chromatographic Separation of Higher Polythionates SnO (n = 3…22) and Their Detection in Cultures of Thiobacillus ferroxidans; Molecular Composition of Bacterial Sulfur Secretions
Authors: Steudel Ralf , Holdt Gabriele , Göbel Thomas , Hazeu Willem
Published: December 2003

Polythionate ions containing up to 22 sulfur atoms have been separated by ion‐pair chromatography. The ions are formed in mixtures of thiosulfate and chlorosulfanes and upon oxidation of tetra‐ or pentathionate with Thiobacillus ferrooxidans. The sulfur globules formed as intermediates were also investigated. Their core consists mainly of S8 with polythionate ions on the hydrophilic surface. The eluent consisted of a mixture of acetonitrile and water with a linearly decreasing concentration of (NBu4)H2PO4 and Na2CO3.
Isolation and Photoisomerization of Simply Substituted Nitrile Oxides
Authors: Maier Günther , Teles Joaquim Henrique
Published: December 2003

Simple derivatives of fulminic acid, such as 1a–c, can be isolated in an argon matrix, identified spectroscopically, and transformed photochemically into the isocyanates 2a–c. The educts 1 are formed by gas‐phase pyrolysis of the corresponding hydroxmoyl halides X(Hal)CNOH.
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Transcription in Eukaryotes—The Role of Transcription Complexes and Their Components
Authors: Wingender Edgar , Seifart Klaus H.
Published: December 2003

The fact that DNA is transcribed into RNA has long been known and has become part of the “central dogma” of molecular genetics. The mechanisms responsible for controlling this process at the individual genes of higher cells (eukaryotes), however, are still not completely understood. RNA polymerases apparently require a number of auxiliary factors (transcription factors) for gene recognition. These factors combine with the enzyme at the gene to form a transcription complex. The structures of these complexes are starting to become clearer; most is known about the control of RNA polymerase III, the enzyme responsible for the synthesis of certain small RNA molecules. The model character of the results obtained with this system is clearly underlined by a series of recent publications. TF III A is an especially intensively studied protein, which is a positive regulator for the expression of ribosomal 5S RNA and possesses structural properties that were previously unknown in DNA‐binding proteins. It is becoming increasingly evident that the “architecture” of TF III A is not an exotic curiosity but probably exemplifies a general structural plan.
A New Photosynthesis‐like System for the Light‐induced Reduction of Water to Molecular Hydrogen
Authors: Schuhmann Wolfgang , Josel Hans‐Peter , Parlar Harun
Published: December 2003

Two zinc porphyrinate‐modified Pt electrodes form the essential part of a very promising solar energy conversion system in which ultimately water is reduced to hydrogen. The Na2 salt of ethylenediaminetetraacetic acid (H4 EDTA) is employed as sacrificial electron donor; methyl viologen (MV2⊕) functions as electron transfer agent and platinized TiO2 as reduction catalyst. Decisive is that the anode is coated with an n‐semiconducting porphyrinate (zinc 5‐(4‐pyridyl)‐10,15,20‐tritolylporphyrinate) and the cathode with a p‐semiconducting porphyrinate (zinc 5,10,15,20‐tetra(4‐pyridyl)porphyrinate). Currently, the yields of H2 still lie in the μmol range.
Two Different Intercalate Structures in the Intercalation Compounds of Graphite with Perfluorobutanesulfonic Acid
Authors: Ruisinger Bernd , Boehm Hanns‐Peter
Published: December 2003

Two types of layers which differ in the arrangement of the acid anions and acid molecules and which also have different thicknesses were found on electro–chemical intercalation of perfluorobutanesulfonic acid in graphite. Such a phenomenon, which occurs in the first and second stage of the graphite salt, has never been observed in other graphite compounds. It is of interest, inter alia, in connection with the packing of alkyl chains in crystalline polymers, especially poly (tetrafluoroethylene), and with respect to the investigation of phase transformations in quasi two‐dimensional molecular assemblages.
Dinuclear Complexes of Gold(I) Containing Bridging Cyclometalated Arylphosphane or Arylarsane Ligands
Authors: Bennett Martin A. , Bhargava Suresh K. , Griffiths K. David , Robertson Glen B. , Wickramasinghe Wasantha A. , Willis Anthony C.
Published: December 2003

For corrigendum see DOI:10.1002/anie.198805891
Structure of Triphenylarsane Diiodide, [Ph3As · I2], a Compound Formed in the Thermal Decomposition of [Mn(OAsPh3 )3I2 (SO2)2]
Authors: McAuliffe Charles A. , Beagley Brian , Gott George A. , Mackie Anthony G. , MacRory Philomena P. , Pritchard Robin G.
Published: December 2003

For corrigendum see DOI:10.1002/anie.198703702
Sequential Configuration Analysis of Peptides
Authors: Bolte Thomas , Yu Dahai , Stüwe Hans‐Thomas , König Wilfried A.
Published: December 2003

The determination of the degree of racemization of the amino acids at each position of a peptide is possible by means of a new procedure. The peptide is first treated with tert‐butyl isocyanate; the N‐terminal amino acid of the resulting N‐tert‐butylcarbamoylpeptide is then cleaved off as the ester 1 with iPrOH/HCl. This step is repeated until the peptide has been fully degraded. The degree of racemization of 1 can be determined by enantioselective gas chromatography (or HPLC).
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First ENDOR Investigations of Biologically Relevant Organic Radicals in Reversed Micelles
Authors: Bretz Norbert , Mastalsky Ingrid , Elsner Martin , Kurreck Harry
Published: December 2003

Reversed micelles as problem solvers: They stabilize enzymes with respect to hydrophobic interactions, suppress possibly undesired properties of modified cofactors such as aggregate formation, and now make possible, among other things, EPR and ENDOR spectroscopy of the radical anions of riboflavin, flavin mononucleotide (FMN), and flavin adenine dinucleotide (FAD) in aqueous media, without water being the actual solvent. In this way, problems arising from high microwave dielectric loss can be avoided.
Azoalkane‐Nitrene Cleavage on an Fe3‐Cluster
Authors: Wucherer Edward J. , Vahrenkamp Heinrich
Published: December 2003

The transformation of the μ3 ligand EtNNEt into two μ3 ligands :NEt occurs upon heating the Fe3 complex 1 to 120°C. In addition to ca. 5% of decomposition products, ca. 75% of 2 and ca. 20% of 1 are obtained. The reaction 1→ 2 is the simplest example so far of a cluster‐induced fragmentation of a ligand. The overall composition of the complex does not change as a result of the NN cleavage.
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IR Spectroscopic Determination of the Enzyme Content of Carrier‐fixed Enzymes
Authors: Herzog Willi , Keller Reinhold , Neukum Erhart , Wullbrandt Dieter
Published: December 2003

In order to find optimal conditions for the immobilization of enzymes it is necessary to determine the enzyme content as well as the activity and to calculate the specific activity. In this way one obtains activities referred to the amount of enzyme used, thus enabling a comparison of the catalysts. A catalyst prepared from aminated silica gel, glutaraldehyde and α‐chymotrypsin serves as example. The enzyme content can be determined IR spectroscopically. The decrease in activity during use of the catalyst can be attributed to a loss of enzyme.