bluuebunny/crossref_metadata_2025 huggingface dataset:
Biosynthesis of Ribonucleic Acids
Authors: Richardson John P.
Published: December 2003

Biosynthesis of ribonucleic acids involves the polymerization of ribonucleotides on deoxyribonucleic acid templates and the conversion of these primary gene transcripts to mature RNA molecules. The present report reviews briefly our current understanding of these processes.
Asymmetric Membranes: Preparation and Applications
Authors: Saier H.‐D. , Strathmann H.
Published: December 2003

The separation of molecular mixtures by semipermeable membranes under the driving force of hydrostatic pressure has assumed major importance in recent years. Among other factors the development of membranes with asymmetric structure which, while having the same separating properties, afford a filtration output many times greater than that of the previously known symmetrical membranes, was decisive for this method. In the present progress report the structures of asymmetric membranes are discussed, as well as their preparation from various polymers and their application to the separation of molecular mixtures.
Formation, Detection, and Reactions of Phosphinidenes (Phosphanediyls)
Authors: Schmidt Ulrich
Published: December 2003

Formation and detection of phosphinidenes (RP̈:) in the decomposition of cyclophosphanes and in the reaction of dichlorophosphanes with metals are considered critically. Only in the thermolysis of pentaphenylcyclopentaphosphane can phenylphosphinidene be detected with certainty by pyrolysis‐mass spectroscopy. “Trapping reactions” such as “insertion” into SS or AsAs bonds, and addition reactions with 1,2‐diketones, 1,3‐dienes, or alkynes can also be interpreted without the assumption of free phosphinidenes. The pyrolysis products of cyclophosphanes add to 1,3‐dienes and alkynes, yielding five‐ and six‐membered heterocycles that contain one to three phosphorus atoms.
Painting of Ancient Ceramics
Authors: Noll Walter , Holm Reimer , Born Liborius
Published: December 2003

The painting of ancient ceramics has been investigated for its morphological characteristics and its elemental and phase composition with the aid of scanning electron microscopy, energy‐dispersive and in part wavelength‐dispersive X‐ray microanalysis, X‐ray diffraction, and electron spectroscopy. Some conclusions about the methods of production can be drawn from these results. It transpires that the painting of ancient ceramics constitutes an extremely important document for the history of chemical technology. The findings bring to light the wealth of experience acquired by the craftsmen and artists of the time and their knowledge of the mineral raw material and their possible utilization. The facts thus obtained are of great value for problems in archaeology and prehistory and at the same time open up new prospects for interdisciplinary collaboration.
Optical Properties of Pigments—Objective Methods for Testing and Evaluation
Authors: Völz Hans G.
Published: December 2003

Although man has used pigments to impart color to his surroundings since prehistoric times, it is only in the 20th century that methods for objective testing and evaluation of their optical properties have become available. Colorimetry and color‐order systems based on principles of color perception, in particular the Adams‐Nickerson system, which form the basis of these methods are described, and are followed by a discussion of the theories of light absorption and light scattering, in particular of the Kubelka‐Munk theory. Of the important optical pigment properties chromaticity and color difference, tinting strength and lightening power (of white pigments), and the hiding power of colored and uncolored coatings are discussed on the basis of the testing methods. Sweeping developments in computer technology during recent years have contributed significantly to the present advanced status of testing practice; further progress in testing methods may be expected in the future as our understanding of the visual process improves.
Reactions of Vinyl Azides
Authors: L'abbé Gerrit
Published: December 2003

This review is designed to demonstrate the versatility of vinyl azides in organic reactions. The reactive azide function is susceptible to thermolysis, photolysis, cycloadditions, and attack by nucleophiles and electrophiles. The neighboring double bond accentuates the reactivity of the azide function and provides additional intramolecular pathways for reaction. Last but not least, the presence of an appreciable electron density at the β‐vinyl carbon makes this class of compounds comparable with enamines in their reactions with electrophiles and 1,3‐dipoles.
Biomimetic Polyene Cyclizations
Authors: Johnson William S.
Published: December 2003

Certain polyenic substances having trans olefinic bonds in a 1,5 relationship can be induced to undergo stereospecific, non‐enzymic, cationic cyclization to give polycyclic products with all‐trans (“natural”) configuration. These transformations appear to mimic in principle the biogenetic conversion of squalene into polycyclic triterpenoids. Acetal and allylic alcohol functions are effective initiators for these cyclizations, and methylacetylenic end groups are particularly useful terminators since they lead to five‐membered rings. Thus a tetraenic acetal having no chiral centers has been converted in a single step into a tetracyclic product having seven such centers. The process is highly stereoselective, giving only two of 64 possible racemates. Systems have also been developed for effecting the total synthesis of the steroid nucleus in a single step starting from a substrate containing only one ring. The mechanism of these biomimetic cyclizations and also that of their enzymic counterparts is still unknown, but the balance of the evidence favors a synchronous process.
Bacteriorhodopsin as an Example of a Light‐Driven Proton Pump
Authors: Oesterhelt Dieter
Published: December 2003

Apart from the long known visual pigments, another retinal protein complex exists in nature, viz. bacteriorhodopsin from halobacteria. In contrast to the visual pigments such as the rhodopsins, which act as light sensors in the eye, bacteriorhodopsin actually transforms light energy. This energy conversion is connected with the asymmetric incorporation of bacteriorhodopsin in the lattice structure of the purple membrane which forms patches on the cell surface of halobacteria. Alongside the chlorophyll system, the purple membrane system represents the second light energy conversion principle to be discovered in living nature. Bacteriorhodopsin acts as a light‐driven proton pump or as the main component of such a pump system. Absorption of light triggers off a cycle of reactions coupled with the spatially oriented uptake and release of a proton. In the intact cell an electrochemical gradient is thus built up across the cell membrane of the bacterium in which part of the absorbed light energy is stored and which is not dependent upon redox processes as in the case of respiration or photosynthesis. This electrochemical gradient can supply the energy required for ATP synthesis in the cell; a reversible proton‐translocating ATPase serves as catalyst system.
Far‐Infrared Fourier Spectroscopy as a Method for Structure Determination in Chemistry
Authors: Knözinger Erich
Published: December 2003

Couched in the often confusing term “Fourier Spectroscopy” is the combined exploitation of a fundamental physical concept, a simple mathematical principle, and use of modern data technology. Introduction of this relatively young method into instrument technology has given great impetus to nuclear magnetic resonance and infrared spectroscopy. The infrared spectroscopic investigation of low frequency molecular vibrations has especially profited; in this connection one speaks of far infrared (FIR) Fourier Spectroscopy, which has opened up numerous interesting applications in organic, inorganic, and physical chemistry.
Biosynthesis of the Purple Membrane of Halobacteria
Authors: Sumper Manfred , Reitmeier Heribert , Oesterhelt Dieter
Published: December 2003

Halobacteria are extremely specialized organisms. They live exclusively in saturated solutions of common salt. The cell membrane of these bacteria exhibit insular regions which can be isolated by membrane fractionation. These regions consist of a lipid matrix containing bateriorhodopsin molecules in a hexagonal crystalline arrangement. Bacteriorhodopsin is a deep purple retinal‐protein complex (“purple membrane”). The purple membrane functions as a light energy converter.—How can such a differentiated membrane region arise? In vivo studies on the biosynthesis of the purple membrane showed another cell membrane fraction, the so‐called brown membrane, to be a biosynthetic precursor. Bacterioopsin (the retinal‐free protein) is initially incorporated into the brown membrane and can only form the purple membrane by crystallization in an energy‐dependent reaction after prior reaction with retinal. This reaction is reversible. Removal of the retinal by formation of retinal oxime causes the purple membrane regions to disappear. Reconstitution of the bacteriorhodopsin by addition of retinal regenerates the purple membrane.
Neuron Models
Authors: Hamprecht Bernd
Published: December 2003

The nervous system is made up of several kinds of cells which should ideally be examined separately in biochemical studies. Since we are not yet able to isolate the different kinds of cells, use is made of cell lines derived from a single cell which are isolated from tumors of the nervous system and which can be reproduced at will in the same way as bacteria. They include cell lines isolated from a mouse neuroblastoma which exhibit some of the properties of nerve cells. Hybrid cells obtained by fusion of mouse neuroblastoma cells with rat glioma cells display even more characteristics of nerve cells. This article considers properties which justify our regarding the hybrid cells as neuron models. Application of the cells to problems of the nervous system is then demonstrated: (1) processing of information arriving in the form of mutually opposing hormonal signals; (2) mode of action of morphine.
Chemical Ecology—A Chapter of Modern Natural Products Chemistry
Authors: Schildknecht Hermann
Published: December 2003

The chemical reaction of arthropods to their environment, i.e. their chemical ecology, can be studied particularly well with water beetles. Stenus comma, an aquatic beetle weighing only 2.5 mg, saves itself from drowning with the aid of an alkaloid, and the water beetle Ilybius fenestratus defends itself against small mammalian predators with a compound belonging to the same class. The water beetle Platambus maculatus employs a diterpene for precisely the same purpose and the whirligig beetle a norsesquiterpene, which also offers protection against troublesome microorganisms. As chemical artists, the ants can hardly be surpassed. In particular, the myrmecine ants guarantee their food supplies with plant growth substances. Since these compounds, depending upon concentration, can also act as inhibitors, we are confronted with an excellent example of an ecological equilibrium being established with the aid of organic chemicals. Even the little parasitic bombardier beetle Paussus favieri is tolerated, on account of its defensive chemistry, in the nest of the myrmecine ant Pheidole. In contrast, inorganic compounds are largely responsible for the stability of spiders' webs.
Nitrogen as Leaving Group: Aliphatic Diazonium Ions
Authors: Kirmse Wolfgang
Published: December 2003

Nitrogen is one of the best known leaving groups. Decomposition of aliphatic diazonium ions has rendered carbocations (carbon cations) accessible in cases where the solvolysis of halides or sulfonic esters follows different pathways. The limits of unassisted decomposition are seen in primary diazonium ions, where the participation of external nucleophiles and of neighboring groups in the elimination of nitrogen becomes noticeable. Cyclopropanediazonium ions occupy a position intermediate between aliphatic and aromatic diazonium ions. New versatile methods of generating aliphatic diazonium ions facilitate their preparative use.
Eutrophication and Wastewater Purification
Authors: Gleisberg Dietrich , Kandler Joachim , Ulrich Hansjörg , Hartz Peter
Published: December 2003

One of the nuisance conditions brought about by the impact of civilization on some regions is the accelerated eutrophication of receiving waters, especially of stagnant waters, owing to the increased supply of plant nutrients from industrial and municipal wastes. To counteract this situation it is recommended that effective measures be taken to reduce the supply of phosphorus and, in part, nitrogen to such waters. Insofar as the supply of these elements stems from communal wastewaters this objective can be achieved by extensive purification. While the most suitable method for removal of nitrogen is nitrification and denitrification, that which recommends itself for the removal of phosphorus is the method of phosphate precipitation, a well established, economic technique which can be employed in existing plant. The success of the measures taken, however, depends to a large extent on achieving wastewater having a very low phosphorus content.
Chemotherapy of Virus Diseases
Authors: Diana Guy D. , Pancic Francis
Published: December 2003

The purpose of this review is to provide an overview of current screening methodology and major advances in the area of viral chemotherapy. This presentation will be limited to those drugs which are currently in use and those which having shown activity against major human pathogenic viruses are now being evaluated in man.
Collisional Activation Mass Spectrometry—A New Probe for Determining the Structure of Ions in the Gas Phase
Authors: Levsen Karsten , Schwarz Helmut
Published: December 2003

Organic ions with high translational energy colliding inelastically with neutral atoms or molecules become excited electronically at the expense of their translational energy. The excitation energy enables a wide range of dissociation reactions to occur and the intensity relationships yield information about the structure of the ions concerned and also permit conclusions to be drawn about the mechanism of their formation.
Chemical Methods of Studying Ribosome Structure
Authors: Küchler Ernst
Published: December 2003

The use of chemical methods, and in particular affinity labeling, has greatly advanced our knowledge about the structure of the active sites of ribosomes. Experiments have shown that ribosomal proteins and ribosomal ribonucleic acids participate in the structure of the binding sites for messenger ribonucleic acid and transfer ribonucleic acid.
Detoxification of Automotive Exhaust Gases with Multifunctional Catalysts
Authors: Weigert Wolfgang M. , Koberstein Edgar
Published: December 2003

Carbon monoxide, hydrocarbons, and nitrogen oxides can be simultaneously transformed into inoffensive substances on multifunctional catalysts. Consisting of noble metals or base metal oxides deposited on an inert support, these catalysts can be used in monolithic form or as granular packings. Compared with other methods of automotive exhaust detoxification, multifunctional catalysts are distinguished by incurring fuel savings.
Catalyzed Addition of Aldehydes to Activated Double Bonds—A New Synthetic Approach
Authors: Stetter Hermann
Published: December 2003

In the presence of cyanide ions as catalyst, aromatic and heterocyclic aldehydes can be smoothly added to α,β‐unsaturated ketones, esters, and nitriles in aprotic solvents to form γ‐diketones, 4‐oxo carboxylic esters, and 4‐oxo nitriles. Thiazolium salts in the presence of bases are also suitable catalysts; they permit not only addition of aromatic and heterocyclic aldehydes but also the addition of aliphatic aldehydes.
Gaseous Chloride Complexes with Halogen Bridges—Homo‐Complexes and Hetero‐Complexes
Authors: Schäfer Harald
Published: December 2003

The chemistry of the gaseous halide complexes which have been observed in large numbers in recent years is discussed for the example of chlorides.Homo‐complexes—dimeric or polymeric chloride molecules containing chlorine‐bridge linkages [e.g.(NaCl)n,n= 2—4; (CuCl)n,n= 2—5; (BeCl2)n,n= 2—4; Pd6Cl12]—occur through broad areas of the Periodic Table. Comparison of the dissociation enthalpy of such molecules with the vaporization enthalpy of the liquid chlorides is particularly informative.Hetero‐complexesare formed from different chloride molecules by linkage through Cl bridges. Not only 1:1 complexes (e.g.NaAlCl4, TIPbCl3, KThCl5, CdPbCl4, AlUCl8) but also larger molecules (e.g.CoAl2Cl8, CrAl3Cl12, Cu2UCl6, In2UCl10) are known. Types of formulas, structures, and above all the formation enthalpies of such complexes are discussed critically. Hetero‐complexes are useful in chemical transport reactions, as aids in syntheses, and in gas‐chromatographic separations (lanthanoids, actinoids). They also play a part in many industrial processes (chlorination of ores) and in recently developed types of high‐pressure discharge tubes.
New Varieties of Sandwich Complexes
Authors: Werner Helmut
Published: December 2003

Metal sandwich complexes of the classical type M(CnHn)2 and related structural analogs are characterized by a sandwich‐like coordination of one central atom by its ligands. This structural principle has been extended in recent years now that di‐ and tri‐nuclear sandwich‐type complexes have become accessible. The best‐known representatives are the triple‐decker sandwich complexes. A survey of this topical field is presented in this report, which also underlines the utility of kinetic and mechanistic studies for the development of new synthetic pathways in organometallic chemistry.
Intramolecular [4+2] and [3+2] Cycloadditions in Organic Synthesis
Authors: Oppolzer Wolfgang
Published: December 2003

Numerous examples of intramolecular cycloaddition of 1,3‐dienes, nitrones, and azomethine imines attest the preparative value of this variant for regioselective and stereoselective synthesis of annelated and bridged ring systems. The common features, differences, and limitations of these types of reaction are systematically reviewed.
Serious Detonation during the Preparation of tert‐Butyl‐oxycarbonyl Azide (Boc‐Azide)
Authors: Feyen Peter
Published: December 2003

Caution with Boc azide! A serious explosion recently occurred during the preparation of tBuOCON3 (Boc azide) from the hydrazide (1) and HNO2 in ether. The reason is not known. It is urgently recommended that other reagents be employed for introducing the Boc protecting group.
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Isolation of Halohydroborates of Type [B10H10 − nXn]2−
Authors: Bührens Klaus‐Georg , Preetz Wilhelm
Published: December 2003

The hydrogen atoms of the hydrodecaborate ion (1) can be successively replaced by chlorine, bromine, or iodine. All halohydroborates of type (2) have now been detected by electrophoretic separation; many of them could be isolated pure as tetramethylammonium salts.
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Secondary and Tertiary Structure of Polysaccharides in Solutions and Gels
Authors: Rees David A. , Welsh E. Jane
Published: December 2003

Many polysaccharide chains can adopt ordered helical and ribbon‐like secondary structures. It seems however that these chains are often so stiff and extended that the cooperative interactions necessary for stability in the solvent environment can only be achieved when inter‐chain as well as intra‐chain interactions are favorable. Hence we commonly find two‐or more‐stranded associations of helices, of ribbons, or of helices with ribbons. These can be regarded as tertiary and higher levels of structure. The ordered secondary structure characteristically requires a regular repeating sequence of sugar residues, and the termination of this sequence by insertion of a residue of different type may also terminate the secondary structure and hence the association in which it is involved. This is the mechanism by which native polysaccharides may link up to form three dimensional networks, or gels, in which state they perform their natural roles in maintaining the hydration and integrity of biological tissues. For several polysaccharides there is evidence that the mechanism of biological control over the fine topology and properties of the gel network is mediated by enzymes which modify sugar residues at the polymer level to change the pattern of “interrupting” sugar residues.
N‐Acyl Isocyanides
Authors: Höfle Gerhard , Lange Bernd
Published: December 2003

The first acyl isocyanides have now become available. The pronounced carbonyl‐activation of benzoyl isocyanide (1) is manifested, e.g., in the acylation of ynamines; in contrast, (1) undergoes cycloaddition with acetylenedicarboxylates.
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[Zn2Cr(Oh)6]X·2H2O, New Layer Compounds Capable of Anion Exchange and Intracrystalline Swelling
Authors: Boehm Hanns‐Peter , Steinle Johann , Vieweger Carmen
Published: December 2003

Compounds with cationic layers and exchangeable anions are rare‐‐‐except for graphite salts. A new compound of this type is (1), which is formed from ZnO and aqueous solutions of chromium(III) salts.
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Efficiency and Evolution of Enzyme Catalysis
Authors: Albery W. John , Knowles Jeremy R.
Published: December 2003

A new function derived from kinetic data, the efficiency function, can be used to quantify the efficiency of a catalyst. For freely diffusing species the maximum efficiency is unity. The enzyme triose phosphate isomerase has an efficiency of 0.6 and is thus almost a perfect catalyst. The efficiency of the acetate ion as catalyst for the same reaction is 2.5 × 10−11. This increase in catalytic efficiency is discussed in terms of three types of evolutionary improvement: the uniform binding of the substrate to the enzyme, changes in the internal thermodynamics of the bound states, and more effective catalysis of elementary steps. These concepts are illustrated for triose phosphate isomerase.
The Pauli Principle and Chemical Bonding in Molecules and Solids
Authors: Jansen Laurens , Block Ruud
Published: December 2003

The starting point of this contribution is a discussion of the concept of exchange interactions and its relation to chemical bonding and valence. Then, a class of phenomena characterized by weak chemical bonding (≲1eV) in solids and molecules is analyzed in more detail, with “superexchange” in insulating solids with paramagnetic 3d‐cations serving as prototype. A model of “effective electrons” is developed for weak bonding on the basis of exchange perturbation theory, taking full account of the Pauli principle. The model is applied to: (i) magnetic interactions in solids (interaction energy 10−2 to 10−4 eV); (ii) stability of noble‐gas halides (binding energy ≈ 1eV); and (iii) rotational barriers in simple molecules (barrier heights of several 0.1 eV).
Flash Thermolysis of Organic Compounds
Authors: Seybold Günther
Published: December 2003

Flash thermolysis is a special form of gas‐phase thermolysis that is particularly suitable for the production and isolation of thermolabile reaction products. The theoretical basis and the instrumental requirements of the method are first given, and the preparative importance of flash thermolysis for the synthesis of thioketenes, allenes, arynes, highly strained ring systems, quinodimethanes, and other reactive compounds is then demonstrated with the aid of examples.
CC Linkage of Carboxylic Acids with Allyl Alcohols Using 2‐Phenylglycine as Vehicle
Authors: Engel Norbert , Kübel Börries , Steglich Wolfgang
Published: December 2003

A new method for the chain elongation of carboxylic acids leads to ketones under very mild conditions. Organometallic intermediates are avoided. The 2‐phenylglycine used as “vehicle” does not appear in the final product.
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Steric Interactions in Organic Chemistry: Spatial Requirements of Substituents
Authors: Förster Hans , Vögtle Fritz
Published: December 2003

From the very extensive factual material available on steric interactions in organic chemistry, the present paper reviews the investigations that provide information about the “size” (“spatial requirement”) of the substituents. After an introductory section on the results obtained with the aid of spectroscopic data and by analysis of chemical reactions, attention is turned to conformational processes, including hindered rotation in ethanes, in the biphenyl system, in butadienes, multiply substituted arenes, molecular propellers, and triptycenes. The main emphasis is placed on the explanation of sterically hindered ring inversions in bridged arenes, a class of compounds particularly suitable for the study of steric interactions. The results obtained by variation of the parameters in this system are also discussed with respect to the spatial requirements of organic substituents.
Entropy, Binding Energy, and Enzymic Catalysis
Authors: Page M. I.
Published: December 2003

Why are enzyme‐catalyzed reactions so much faster than uncatalyzed reactions, and why are enzymes so specific? What is the effect of mere approximation of enzyme and substrate, and what is the influence of the strain energy? Attempts to answer these questions have led to comparisons between entropy changes in intermolecular and intramolecular reactions, and to determinations of the intrinsic energy of the bond arising by non‐covalent interaction between enzyme and substrate.
Hexameric KN2Co [P(CH3)3]3—A Novel Potassium‐Dinitrogen Cluster
Authors: Hammer Reinhard , Klein Hans‐Friedrich , Friedrich Peter , Huttner Gottfried
Published: December 2003

A bimetallic dinitrogen complex (2) with a double cube skeleton made up of six K atoms and six N2 groups is surprisingly formed from ethereal solutions of (1) under 1 bar of N2. The complex crystallizes without ether or alkoxide donor ligands (olefin = propene, cyclopentene).
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“Organic Metals”—The Intermolecular Migration of Aromaticity
Authors: Perlstein Jerome H.
Published: December 2003

The electrical conductivity of a wide variety of organic materials is reviewed and a comparison made between those materials which transport charge efficiently and those that do not. This comparison reveals that the most efficient conductors contain molecules (a) whose radical ions form a new aromatic sextet upon one‐electron oxidation or reduction and (b) whose aromaticity can migrate by mixed‐valence interaction. The electrical data are presented in light of the chemistry of these materials and the importance of chemical bonding interactions in the electron transport process. Several new examples are discussed and directions for further research explored.
Catalyzed Rearrangement of Nitrile Oxides to Isocyanates
Authors: Trickes Georg , Meier Herbert
Published: December 2003

The simultaneous migration of two ligands makes the rearrangement of nitrile oxides (1) to isocyanates (2) one of the most interesting ones in organic chemistry. However, use of the thermal reaction (1) is severely limited by competing dimerization. The rearrangement proceeds in excellent yields with SO2 as catalyst.
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Macrolides. Recent Progress in Chemistry and Biochemistry
Authors: Masamune Satoru , Bates Gordon S. , Corcoran John W.
Published: December 2003

The progress of macrolide chemistry and biochemistry over the past several years has indeed been remarkable. This review attempts to cover the important contributions which have been made in the fields of structural and synthetic chemistry as well as in the biosynthesis and mode of antimicrobial activity of the “polyoxo” macrolide antibiotics. Emphasis has been placed on the recent synthetic achievements in this field.
The Electro‐Optical Kerr Effect in Conformational Analysis. New analytical methods (10)
Authors: Aroney Manuel James
Published: December 2003

Birefringence induced in a material by application of an electric field is known as the Kerr effect. The great sensitivity of this property to variations of molecular geometry and environment has made it the basis of a potent method for studying the conformations of molecules. It has, in addition, been effectively applied to investigations of the geometry of solvation and of solute aggregation. An outline is presented of the general technique of measurement of the Kerr effect, the extraction of directed effective polarizabilities of solute molecules and of structural groups, the calculation of theoretical Kerr constants for candidate structures of molecules, and the procedures used to determine solute conformations. The scope and limitations of the method are illustrated by specific conformational problems drawn from the literature. In the case of highly flexible molecules analysis of the measured Kerr constant is inhibited by uncertainties in conformational energy data. This paper is concerned mainly with the specification of detailed conformational energy data. This paper is concerned mainly with the specification of detailed conformational features of molecules. Reference is made, however, to the utilization of pulsed orienting fields to study shapes and dimensions of biological macromolecules.
Oxometallates with Planar Coordination
Authors: Müller‐Buschbaum Hanskarl
Published: December 2003

Oxo compounds whose coordination polyhedra have a planar structure are a rarity in solid state chemistry. The present state of this research area provides a wealth of interesting principles concerning one‐, two‐, and three‐dimensional linkage of square‐planar structural units. In certain cases the environment of these units in solids requires new conceptual models for the chemical bonding.
Phase‐Transfer Catalyzed Alkylation of diphenylphosphinic Amide—A New Versatile Synthesis of Primary and Secondary Amines
Authors: Zwierzak Andrzej , Podstawczyńska Iwona
Published: December 2003

A general synthesis of primary and secondary amines consists in the alkylation of diphenylphosphinic amide and N‐alkyldiphenylphosphinic amide under the conditions of phase‐transfer catalysis. Removal of the protecting group is accomplished with HCI gas in THF.
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Dicynophosphide
Authors: Schmidpeter Alfred , Zwaschka Franz
Published: December 2003

Pseudohalide properties are predicted for the dicyanophosphide ion by the “cyano displacement principle”. It has now been prepared for the first time in the form of the salt (1) and stabilized with [18]crown‐6.
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Isodiazomethane Complexes
Authors: Fehlhammer Wolf Peter , Buračas Peter , Bartel Klaus
Published: December 2003

Isodiazomethane (1), hitherto defying isolation in the pure state, has now been incorporated into complexes. Complex (2) experinces additional stabilization by ether molecules, while (3) is surprisingly stable.
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Oligo(difluorophosphoranes) by Direct Fluorination of Tertiary Phosphanes
Authors: Ruppert Ingo , Bastian Volker
Published: December 2003

The reaction of tertiary phosphanes (1) with fluorine leads to fluorinated phosphoranes (2) in good yield. No significant cleavage of PC and/or CH bonds was observed.
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Dependence of the Calcium Isotope Effect upon the Electrolyte Concentration in Ion‐Exchange Chromatography
Authors: Heumann Klaus G. , Ginder Ferdinand , Klöppel Helmut
Published: December 2003

Inversion of an isotope effect has now been accomplished—merely by a change in electrolyte concentration—in systems containing 48Ca2+, 44Ca2+, and 40Ca2+. This result is of interest in connection with pre‐enrichment of Ca isotopes.
ESR Spectroscopic Studies on the Radical Anion of [33S]‐2,2,4,4‐Tetramethylpentane‐3‐thione
Authors: Klages Claus‐Peter , Voss Jürgen
Published: December 2003

Hyperfine splitting by 33S nuclei has now been recorded for the first time in the ESR spectrum of a thioketyl. The 33S‐enriched radical anion (1) shows the expected satellite signals. Judging by the spin population, (1) resembles an alkyl radical more closely than a thiyl radical.
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Fluorinated Isocyanates and Their Derivatives as Intermediates for Biologically Active Compounds
Authors: Kühle Engelbert , Klauke Erich
Published: December 2003

Fluorinated aromatic isocyanates are valuable intermediates for the production of herbicides and insecticides. Unexpected rearrangements during the synthesis of 2‐(trifluoromethyl)phenyl isocyanates provide an entry to N‐trifluoromethylaminobenzoyl fluorides, a novel class of compounds having fungicidal properties. Carbamoyl fluorides, the products of HF addition to isocyanates, undergo ready sulfenylation. Use of these intermediates for the synthesis of N‐sulfenylcarbamate insecticides led to the discovery of the new principle of detoxification of carbamates by sulfenylation.
Titanium Tetrachloride in Organic Synthesis [New synthetic methods (21)]
Authors: Mukaiyama Teruaki
Published: December 2003

Titanium tetrachloride can accelerate numerous organic reactions. Valuable syntheses of, e.g., allyl sulfides, amides, enamines, and ketones are based upon transformations of functional groups with TiCl4. Particular mention should also be made of carbon‐carbon linkage with TiCl4 which permits the synthesis of hydroxy ketones and carbonyl compounds of the Michael adduct type. TiCl4 reduced in situ is suitable for the reduction of chloroarenes or the linkage of two aldehyde molecules to give an alkene.
A New Method for the Introduction of Trifluoromethyl Groups
Authors: Gölitz Peter , de Meijere Armin
Published: December 2003

The first general trifluoromethylation of alkanes has now been discovered. The CF3 substituent provides a means of making unstable molecules isolable; in addition, CF3 derivatives often exhibit enhanced pharmacological activity.
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Bombykal, a Second Pheromone Component of the Silkworm Moth Bombyx mori L
Authors: Kasang Gerhard , Kaissling Karl Ernst , Vostrowsky Otto , Bestmann Hans Jürgen
Published: December 2003

The chemical communication between the male and female silkworm moth is more complicated than hitherto assumed. The known attractant bombykol, an alcohol, acts on only one type of receptor cell in the male, whereas the female scent excites both kinds. Once it had been demonstrated that the corresponding synthetic aldehyde (bombykal) excites the other kind of receptor cells, this compound was sought and found in the abdominal glands of the female moth (ca. 15 ng per gland).
Solid‐State Photochemistry—A Method of Generating Unusual Valence States
Authors: Lehmann Gerhard
Published: December 2003

High‐energy radiation can give rise to pairs of complementary defects in nonmetallic solids by the transfer of electrons between various types of atoms. These “color centers” which are generally paramagnetic, can usually be described as unusual valence states of an element. They are destroyed by heating and in most cases regenerated by renewed irradiation. In a heteropolar solid the formation of color centers usually leads to cancellation of point charges due to foreign ions of other valence or to vacancies. This is shown by the examples of kunzite, brazilianite, smoky quartz, and citrine; the most important methods for the structural elucidation of color centers are also described. Application of the principle of charge balance opens up possibilities for the production of unusual valence states, e.g. Al2+, F2−, Fe4+, and O−. Moreover, the type of the color center often permits far‐reaching conclusions to be drawn about the defect structure of real crystals, which could hardly be clarified in other ways.
Interpenetrating Polymer Networks
Authors: Klempner Daniel
Published: December 2003

Besides mechanical blending and copolymerization there is a third possible way in which two polymers can be combined. Each polymer forms its own network, while both networks interpenetrate each other. There are no covalent bonds between the polymers. Such interpenetrating networks have been synthesized sequentially (from polymer A and monomer B) and simultaneously (from monomer A and monomer B). It is preferable that the polymers be of different chemical type; usually, an elastomer and a glass are combined, e.g. a polyurethane and a polyacrylate. Depending upon the ratio of component polymers either a strengthened elastomer or a glass having impact strength is formed. So far, there are no direct methods for establishing the degree of interpenetration.
Crystal Structure of Sb2O5
Authors: Jansen Martin
Published: December 2003

The nature of Sb2O5, a matter of dispute to the present day, has now been elucidated by crystal structure analysis. The principles of coordination and connection accord with those of BNb2O5. This is the first such relationship between the pentoxide of a main group element and that of a subgroup element.
Anodic NN Linkage by Oxidation of Anions of Primary and Secondary Amines
Authors: Bauer Reinhold , Wendt Hartmut
Published: December 2003

Electrochemical synthesis of hydrazines and azoalkanes can be accomplished by anodic oxidation of the amide anions of types (1) and (2). Direct anodic oxidation of NH3 or amines usually gives only very poor yields.
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17O‐NMR Spectroscopy as a Structural Probe
Authors: Klemperer Walter G.
Published: December 2003

17O‐NMR spectroscopy has found limited application as a structural probe due to the experimental problems associated with a quadrupolar nucleus having low natural abundance. A survey of data obtained from systematic studies of structurally related compounds shows, however, that large chemical shift differences are usually obtained for structurally nonequivalent nuclei, and that characteristic chemical shift values are observed for specific chemical environments. The present day availability of 17O enriched materials and Fourier transform NMR instrumentation should allow extensive application of the 17O‐NMR technique to structural problems in the immediate future.
Sodium‐23 Nuclear Magnetic Resonance Spectroscopy
Authors: Laszlo Pierre
Published: December 2003

With the availability of Fourier transform spectrometers,23Na‐NMR spectroscopy has become an important tool. It affords direct insight into solvation and ion pairing phenomena, both in organic and in bio‐inorganic systems. Monitoring the chemical shifts and linewidths of23Na signals gives access to binding constants, reorientational correlation times and the microdynamics of the sodium coordination shell. The binding of other cations can also be studied by23Na‐NMR spectroscopy, in competition experiments.
Aluminum Tris(dihydrogen Phosphate)
Authors: Kniep Rüdiger , Steffen Michael
Published: December 2003

The crystal structure of AI(H2PO4)3 is characterized by an almost centrosymmetric arrangement of the heavy atoms which is rendered significantly acentric merely by the orientation of the protons. Since a polar axis is also present, ferroelectricity should be possible.
Tris[(N,N,N′,N′‐tetramethylethylenediamine)‐lithium]hexamethylerbate(III) and ‐lutetate(III)
Authors: Schumann Herbert , Müller Jochen
Published: December 2003

The first peralkylated complexes of metals in the lanthanoid series have now been synthesized. The compounds are extremely sensitive to air and moisture but decompose only slowly at their melting points of 138–139°C (M  Er) and 141–142°C (M  Lu).
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Skeletal Rearrangements of Organoalkali Metal Compounds
Authors: Grovenstein Erling
Published: December 2003

Organometallic compounds of the alkali metals undergo concerted [1,n] sigmatropic migration of aryl, vinyl, carbonyl, alkoxycarbonyl, silyl, germyl, and related groups. Sigmatropic migration of alkyl, benzyl, and hydrogen occur only under special circumstances and then may occur by an alternate fragmentation‐recombination pathway. Allyl groups may migrate by the latter process or by a concerted [2,3] sigmatropic reaction. These molecular rearrangements are discussed from the viewpoint of simple molecular orbital theory. By suitable choice of the alkali metal, temperature, ligands of the alkali cation and/or the solvent, considerable control may be exercised over the rate of rearrangement, the relative migratory aptitude of groups, and the mechanistic pathway.
Mechanistic and Preparative Aspects of Vinyl Cation Chemistry
Authors: Hanack Michael
Published: December 2003

Compelling evidence for the intermediacy of vinyl cations has accumulated in recent years. Vinyl cations can be generated by electrophilic additions to alkynes and allenes, and on participation of such functions in solvolysis reactions. Heterolysis of vinyl compounds likewise affords vinyl cations. Syntheses of substituted indenes, cyclobutanones, and cyclopropyl ketones illustrate preparative applications.
Mouse Histocompatibility Antigens
Authors: Henning Roland
Published: December 2003

In this article experimental findings and new theories concerning the chemical structure and biological function of histocompatibility antigens in the immune surveillance of virus‐infected and malignant cells are discussed. Amongst these antigens, the H‐2 antigens of the mouse have been studied most extensively. They are membrane bound glycoproteins causing the rejection of transplants from foreign tissue. One future aim of this field of research is to utilize the immune surveillance system in the therapy of diseases which as yet cannot be treated.
Contamination of Amines with N‐Nitrosamines
Authors: Spiegelhalder Bertold , Eisenbrand Gerhard , Preussmann Rudolf
Published: December 2003

Caution is urgently recommended when handling amines! Commercial grade secondary and tertiary amines are contaminated with the extremely carcinogenic N‐nitrosamines. Nitrosamine contents of 0.03 to 53.0 mg/kg amine were found.
Tetrahedral Carbonylcobalt Clusters
Authors: Schmid Günter
Published: December 2003

A variety of general methods is available for the synthesis of tetrahedral heteronuclear cobalt clusters of type (CO)9Co3E(L)n (E=hetero element). The size of E has a limiting effect on the existence of such complexes. No compounds (CO)9Co3E(L)n have so far been prepared in which the covalent radius of E exceeds 1.30 Å;. Elements such as In, Sn, Pb, Sb, or Bi do not fit into the tetrahedral Co3E cluster unit and form open complexes E[Co(CO)4]n (n=3, 4). Structural variations among the heteronuclear clusters are encountered in the presence or absence of carbonyl bridges between the cobalt atoms: hetero atoms E bearing several ligands L favor bridging, whereas those bearing only one ligand or none at all permit terminal bonding of all the CO groups.
The First Oxostannate(II): K2Sn2O3
Authors: Braun Rolf Michael , Hoppe Rudolf
Published: December 2003

A new SnIIO compound, the first oxostannate(II) of defined structure, has been obtained as brownish‐yellow single crystals. X‐Ray structure analysis reveals a complicated perovskite variant (Sn1O3Sn2 double layers) in which half of the anions are missing in a regular manner.
Cobalt‐Catalyzed Pyridine Syntheses from Alkynes and Nitriles
Authors: Bönnemann Helmut
Published: December 2003

Soluble organocobalt catalysts permit selective formation of substituted pyridines under mild conditions in a single step: mono‐, di‐, and trisubstituted pyridines can be obtained at will in high conversions and high yields from nitriles and alkynes. Polynuclear derivatives such as bipyridines can also be prepared by this method.
Photochemical Reductive trans‐Elimination from trans‐Diazidotetracyanoplatinate(IV)
Authors: Vogler Arnd , Kern Alfred , Hüttermann Jürgen
Published: December 2003

The first light‐induced reductive trans elimination has been observed with the trans‐configurated PtIV complex (1). The primary photochemical step leads, via simultaneous two‐electron reduction avoiding a PtIII intermediate, to two N3 radicals which afford N2 and N atoms at low temperature.
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A Coordination Chemist's View of Surface Science
Authors: Muetterties E. L.
Published: December 2003

Structure, a necessary element for an understanding of chemistry, has not been precisely defined, in molecular detail, for the surface species formed at a solid‐gas interface. Dramatic advances in theory, instruments and experimental procedures have now provided the surface scientists with an impressive arsenal of structural and electronic probes. Chemistry in the form of the classic displacement reaction can also provide an insight to the structure of surface compounds. In fact, many of the experimental procedures and systematics of the coordination and organometallic chemist can be effectively utilized in a complementary fashion with surface physics techniques to gain a more definitive picture of chemisorption states and or reactions at a surface.
Preparation and Crystal Structure of Pd2Mo2(η5‐C5H5)2(μ3‐CO)2(μ2‐CO)4(PEt3)2. A Planar, Triangulated, Palladium‐Molybdenum‐Carbonyl Cluster
Authors: Bender Robert , Braunstein Pierre , Dusausoy Yves , Protas Jean
Published: December 2003

A Pd2Mo2 cluster—the very first heteropolymetallic Pd cluster to be obtained—has been synthesized in 75% yield from [Mo(η5‐C5H5)(CO)3]− and trans‐Pd(PEt3)2C12. As shown by X‐ray structure analysis, the Pd atoms of this compound have the unusual coordination number 8. Moreover, only one example of a planar triangulated cluster ([Re4(CO)16]2−) was formerly known.
cyclo‐Triarsenic as μ,η‐Ligand in Transition‐Metal Complexes
Authors: Di Vaira Massimo , Midollini Stefano , Sacconi Luigi , Zanobini Fabrizio
Published: December 2003

Complexes containing cyclo‐triarsene as a bridging ligand are obtained from As4, CoII or NiII‐aqua ions, and the tridentate ligand triphos. X‐Ray structure analysis shows the two cobalt atoms in [(triphos)Co‐μ(η‐As3)Co(triphos)]2+ to be six‐coordinated.
β‐Cyclodextrin Dodecahydrate: Crowding of Water Molecules within a Hydrophobic Cavity
Authors: Lindner Klaus , Saenger Wolfram
Published: December 2003

“Empty” cyclodextrins contain water in their annular cavities; the hydrate form of β‐cyclodextrin (cycloheptaamylose, β‐CD) has now been subjected to an X‐ray study. β‐CD·12H2O assumes an almost “round” shape. No far‐reaching changes of conformation take place on complex formation with guest molecules.
Physicochemical Principles of Extraction with Supercritical Gases
Authors: Schneider Gerhard M.
Published: December 2003

The present review considers some physicochemical properties of fluid mixtures that are of importance for fluid extraction and supercitical fluid chromatography (SFC). Firstly, the important types of phase diagrams are treated, the occurrence of solid phases also being considered in some simple cases. Specific examples are given of mixtures of a highly volatile component I (e.g.CO2, C2H6) with a relatively involatile component II (e.g.squalane) of very different molecular size, shape, structure, and/or polarity, and it is shown how the rather complicated types of phase diagrams can be calculated and correlated. The importance of fluid mixtures extends far beyond the fields of science and technology reviewed.
A Quick Method for the Microanalytical Evaluation of the Dissolving Power of Supercritical Gases
Authors: Stahl Egon , Schilz Winfried , Schütz Erwin , Willing Eberhard
Published: December 2003

A new method of microextraction with supercritical gases involving direct coupling with thin‐layer chromatography enables the solubility behavior of a large number of natural products to be investigated in pressure gradients of up to 400 bar. The results are summarized in general rules that enable the extractability to be predicted on the basis of the chemical structure. The substances that can be satisfactorily extracted in supercritical carbon dioxide and nitrous oxide are preferably lipophilic. The extracting capacity of the two gases was compared using alkaloids. In the case of polar compounds such as sugars and amino acids the solubility is so low even at pressures of 2500 bar (less than 10 μg/Nl) that application is not practicable. Quantitative tests of the solubility behavior of model substances in supercritical gases provide a basis for the technical application of the method.
Large‐Scale Industrial Plant for Extraction with Supercritical Gases
Authors: Eggers R.
Published: December 2003

Criteria for the design and construction of plant for obtaining carrier material or extracts are discussed for the example of the extraction of natural products with supercritical carbon dioxide. The parameters to be established and the course of the process in a large‐scale plant are indicated. Plant engineering and optimization must be attuned to specific process‐technological and construction problems.