bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phase Behavior of Ternary Systems of the Type H2OOilNonionic Amphiphile (Microemulsions)
Authors: Kahlweit Manfred , Strey Reinhard 
Published: December 2003

AbstractLiquid 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.
Transition Metal Polysulfides: Coordination Compounds with Purely Inorganic Chelate Ligands
Authors: Draganjac Mark , Rauchfuss Thomas B. 
Published: December 2003

AbstractIt 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.
Arene Complexes of Univalent Gallium, Indium, and Thallium
Authors: Schmidbaur Hubert 
Published: December 2003

AbstractArene 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

AbstractMultiply 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 σ2π4 Triple Bond between Molybdenum and Tungsten Atoms: Developing the Chemistry of an Inorganic Functional Group
Authors: Chisholm Malcolm H. 
Published: December 2003

AbstractNumerous 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

AbstractThis 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

AbstractThe 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.
3‐Chloropropyltrialkoxysilanes—Key Intermediates for the Commercial Production of Organofunctionalized Silanes and Polysiloxanes
Authors: Deschler Ulrich , Kleinschmit Peter , Panster Peter 
Published: December 2003

AbstractSilicon 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.
15N‐NMR Spectroscopy—New Methods and Applications [New Analytical Methods (28)]
Authors: von Philipsborn Wolfgang , Müller Raffaello 
Published: December 2003

AbstractThe 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.
Microbial Degradation of Halogenated Hydrocarbons: A Biological Solution to Pollution Problems?
Authors: Müller Rudolf , Lingens Franz 
Published: December 2003

AbstractChlorinated 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

AbstractPolynuclear 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

AbstractOrganometallic 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

AbstractThe 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.
Preorganization—From Solvents to Spherands
Authors: Cram Donald J. 
Published: December 2003

AbstractThis 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

AbstractThe 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.
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

AbstractThe 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.
Transcription in Eukaryotes—The Role of Transcription Complexes and Their Components
Authors: Wingender Edgar , Seifart Klaus H. 
Published: December 2003

AbstractThe 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.
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

AbstractFor 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

AbstractFor corrigendum see DOI:10.1002/anie.198703702