bluuebunny/crossref_metadata_2025 huggingface dataset:
A Paramagnetic, Mononuclear Organometallic Iridium(II) Complex: [Ir(C6Cl5)2(cod)]
Authors: García María P. , Jiménez M. Victoria , Oro Luis A. , Lahoz Fernando J. , Alonso Pablo J.
Published: December 2003

Unexpectedly stable, 2 is the first mononuclear IrII complex whose ligands are bound exclusively through C atoms. Complex 2, prepared by oxidation of 1 with I2 or Ag+, is close to square planar. The phenyl rings are almost perpendicular to the metal's coordination plane; the ortho Cl atoms are quite close to the Ir metal center, which could explain the remarkable stability of 2. cod = 1,5‐cyclooctadiene.
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Optimization of the Production and Separation of Fullerenes
Authors: Mittelbach Andreas , Hönle Wolfgang , von Schnering Hans Georg , Carlsen Jürgen , Janiak Rolf , Quast Helmut
Published: December 2003

Mixtures of C60 and C70 containing up to 50% C70 are obtained from the production of fullerenes with a DC furnace with high currents (400 A). In addition, two chromatographic methods using silica gel and reversed‐phase silica gel are introduced for the separations of 400 and 300 mg, respectively, of mixed fullerenes per hour. Larger amounts of fullerenes can thus be purified on standard chromatographic supports.
Mercury, a Structural Building Block and Source of Localized Reactivity in Extended Metal–Metal Bonded Systems
Authors: Gade Lutz H.
Published: December 2003

Transition metal–mercury complexes were among the first compounds of study for the concept of direct metal–metal bonding which was established more than three decades ago. Since then, a large number of such systems have been synthesized and studied. The fact that mercury is readily attached to a large variety of main group or transition metals has stimulated its use as a general building block in the systematic synthesis of mixed‐metal clusters. The past decade has witnessed a rapid expansion of bimetallic cluster chemistry in which species containing mercury have played a prominent role, and which has led to the discovery of many unprecedented cluster structures and reactions. In particular, the ability of mercury to form multicenter metal–metal bonds with polynuclear cluster fragments has substantially extended its coordination chemistry which was thus far dominated by simple linear structural arrangements. Although certain structural motifs are found to be common to many of the transition metal–mercury clusters investigated to date and thus enable a relatively systematic synthetic approach, the multitude of surprising discoveries has kept the interest in the chemistry of the element itself alive. The recent discovery of the redox and photochemical reactivity of some of these systems has opened up an exciting and promising area of cluster research. Its significance for the synthetic methodology lies in the fact that the increasing redox activity of molecular carbonyl clusters on going to higher nuclearities appears to set a limit on the size of metal frameworks attainable by the standard preparative methods. On the other hand, their potential use as photochromes or redox mediaters in coupled electron‐transfer reactions provides an additional stimulus for future studies in this field.
Transmembrane Signaling of T Lymphocytes by Ligand‐Induced Receptor Complex Assembly
Authors: Eichmann Klaus
Published: December 2003

T lymphocytes (T cells) are the central cell type initiating all immune responses. They are able to recognize other cells in the body that have been invaded by foreign living or nonliving matter. In such cells, foreign peptides generated by intracellular breakdown are complexed with molecules of the major histocompatibility complex (MHC) specially designed for peptide binding. Peptide‐loaded MHC molecules appear on the surface of these cells and alert the immune system. The molecular complex which T cells use for recognition of peptide‐loaded MHC molecules is among the most sophisticated and versatile receptor systems in biology. It consists of specific and nonspecific transmembrane components which assemble to a functional signal transduction unit as the result of ligand binding. Correct assembly leads to activation and relocation of enzymes including membrane‐associated, tyrosin‐specific protein kinases and phosphatases. Transmembrane signaling in T cells depends on the correct assembly and cooperation among multiple molecular components. This may be related to a multitude of different cellular responses of T cells at different stages of differentiation, all elicited through the T cell receptor complex.
[(Me3SnIV)2MoVIO4]: An Organometallic Quasi‐AB2 System with a Layered Structure
Authors: Behrens Ulrich , Brimah Abdul K. , Yünlü Kenan , Fischer R. Dieter
Published: December 2003

Are the tried‐and‐tested layered structures challenged as intercalators by organometallic systems? Because of packing, the polymeric title compound crystallizes with a layered structure, and not as the also feasible three‐dimensional network. The van der Waals interactions between the individual layers and the oxidation potential of the oxometalate(VI) units of each layer may “invite” potential guest molecules.
Sequential Transformations in Organic Chemistry: A Synthetic Strategy with a Future
Authors: Tietze Lutz F. , Beifuss Uwe
Published: December 2003

Organic‐chemical synthesis has always fascinated chemists and will not lose its importance in the future. It is a truism that all chemists—and others too—are dependent on the synthesis of those compounds with which they want to work. As a result, organic‐chemical synthesis today is more than ever before the cutting edge of organic chemistry, biology, biochemistry, medicine, physics, and material science. Synthesis is also the basis of the chemical industry. For the passionate synthetic chemist, however, synthesis is much more than just a method for obtaining compounds; it is the expression of his creativity, intelligence, ability, and also his perseverance.
Chemistry of and with Highly Reactive Metals
Authors: Fürstner Alois
Published: December 2003

Today, the synthetic chemist has a large repertoire of metal activation methods at his disposal. After a first breakthrough was made at the beginning of the seventies with the introduction of the Rieke metals, a series of further, in part more efficient methods were describes, based on which not only classical metal‐induced reactions could be substantially improved but also completely new reactions could be discovered. In this article the individual activation methods are discussed and compared as far as is possible using the currently available data. Especially noteworthy are the metal–graphite combinations because of their unsurpassed reactivity and concomitant easy preparation and manipulation. As shown by numerous applications of these reagents on polyfunctional substrates, particularly natural products, high reactivity of the metal and excellent selectivity are by no means precluded. Besides the purely preparative aspects also insights gained so far into the general principles and limits of metal activation are outlined, and attempts at determining the morphology of highly dispersed systems are reported.
An Evaluation of the Peer Review Process at Angewandte Chemie
Authors: Daniel Hans‐Dieter
Published: December 2003

Criticism on the referee system—and of course of the referees—also filters through all too often to the editorial office of Angewandte Chemie. So we were glad when in 1990 H.‐D. Daniel received permission from the Gesellschaft Deutscher Chemiker to examine our referee system under the auspices of the priority program “Research on Science” of the Deutsche Forschungsgemeinschaft. Of course, strict anonymity for authors and referees was observed. A concise selection of the results that will nevertheless provide much material for discussion in presented here. [The results will appear in full in summer in a book published by VCH.]
Ba[Si(OCH2CH2O)3], a Hexaalkoxysilicate Synthesized from SiO2
Authors: Hoppe Martin L. , Laine Richard M. , Kampf Jeffrey , Gordon Mark S. , Burggraf Larry W.
Published: December 2003

The reaction of BaO, SiO2, and an excess of ethylene glycol provides [Ba‐Si(OCH2CH2O)3] · 3.25 HO(CH2)2OH, the first amazingly stable hexaalkylsilicate, in 90% yield. This complex was characterized by X‐ray crystallography. The reactions with MgO and CaO give analogous compounds; with alkali metal oxides pentacoordinate silicates are formed.
Nitric Oxide, NO, an Intercellular Messenger
Authors: Galla Hans‐Joachim
Published: December 2003

Physiology, biochemistry, and analytical chemistry in the last few years have extensively studied NO, a colorless gas of relatively high stability, which, however, in physiological media has a lifetime of only a few seconds. According to new findings NO, which is formed, so to speak, from arginine in a short cut in the urea cycle, plays a very important role, for example, in the control of processes in the brain, of peristalsis in the intestine, and of erectile organs. Recently a specific sensor for the measurement of the NO content in blood vessels was described.
Structure of Diamagnetic [W(O‐4‐Me‐C6H4)2Cl2(PMePh2)2] and Comparison with Related Paramagnetic 2,6‐Diphenylphenoxido Complexes: A Steric Effect on π‐Bonding and Electronic Structure
Authors: Atagi Lauren M. , Mayer James M.
Published: December 2003

Steric differences alone explain why 1 has a diamagnetic and 2 a paramagnetic electronic ground state. In 1 the WO bonds are 0.12 Å shorter, which results in a stronger WO π bond and therefore a greater splitting of the t2g orbitals, which are degenerate for ideal octahedral symmetry. The bulky ligand in 2 precludes such short WO bonds. Comparisons with other control compounds show that electronic effects are not a factor.
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Structure and Symmetry of the Benzene Cation
Authors: Lindner Reiner , Sekiya Hiroshi , Beyl Bernhard , Müller‐Dethlefs Klaus
Published: December 2003

The benzene cation is planar with D6h symmetry in the ground state. This is the conclusion from its first photoelectron spectrum with fully resolved rotational lines (ZEKE photoelectron spectrum). The change in the ring structure on ionization deduced from the rotational parameters is less than predicted by ab initio calculations. The elongation of the ring bonds anticipated for the removal of an electron from a bonding orbital is only about 0.1% and thus approximately five times smaller than assumed from the calculations.
Reaction Tuning in Zeolites: An in situ MAS NMR Study of Acetaldehyde on HZSM‐5
Authors: Munson Eric J. , Haw James F.
Published: December 2003

Coadsorbants tune the reactivity of zeolite catalysts in organic reactions. 13C NMR studies showed that [1,2‐13C]acetaldehyde is converted on pure HZSM‐5 into a complex product mixture, on HZSM‐5 saturated with coadsorbed water into crotonaldehyde, and on HZSM‐5 saturated with a mixture of coadsorbed water and oxygen into acetic acid.
Sequence‐Specific Recognition and Modification of Double‐Helical DNA by Oligonucleotides
Authors: Thuong Nguyen T. , Hélène Claude
Published: December 2003

Nucleic acids can be selectively recognized by a large number of natural and synthetic ligands. Oligonucleotides provide the highest specificity of recognition. They can bind to a complementary single‐stranded sequence by forming Watson–Crick hydrogen bonds. They can also recognize the major groove of double‐helical DNA at specific sequences by forming Hoogsteen or reverse Hoogsteen hydrogen bonds with purine bases of the Watson‐Crick base pairs, resulting in a triple helix. Triple‐helix formation through oligonucleotide binding to DNA is a sequence–specific interaction involving primarily homopurine·homopyrimidine sequences in the double‐helical target. Extending the range of recognition sequences remains a challenge to chemists. Both thermodynamic and kinetic parameters for triplex formation have been determined. These parameters indicate, for example, that triple‐helix formation is a much slower process than duplex formation. Nuclease‐resistant oligonucleotides synthesized with the anomers of nucleosides (instead of the natural β‐anomers) also form triple helices with double–stranded DNA. Triple‐helix‐forming oligonucleotides can be modified, for example, by attaching DNA intercalating agents to enhance their binding affinity. They may also be modified with reagents that induce irreversible reactions in their target sequence upon chemical or photochemical activation. Thus, artificial nucleases can be developed with very high sequence specificity on megabase‐size DNA. Furthermore, triple‐helix‐forming oligonucleotides can be used to selectively control gene expression. When bound to the regulatory region(s) of specific genes they may prevent activation (or repression) of transcription. When binding occurs near or downstream from the transcription initiation site, elongation of the transcript may be inhibited. Therefore, the potential exists for developing new gene‐blocking agents with therapeutic applications in the treatment of gene disorders.
The Marcus Inverted Region from Theory to Experiment
Authors: Grampp Günter
Published: December 2003

Electron back‐transfer reactions are the reactions in which the occurrence of the inverted region predicted by the Marcus theory was detected for the first time in an intermolecular electron transfer. In this region, contrary to all intuition, a further increase in the exergonicity causes a decrease in the reaction rate. In each case the forward reactions showed the classical Rehm–Weller behavior the rate constant k approaches kdiff of the diffusion‐controlled reaction. This difference has not yet been explained satisfactorily.
Ion‐Spray Mass Spectrometry and High‐Performance Liquid Chromatography—Mass Spectrometry of Synthetic Peptide Libraries
Authors: Metzger Jörg W. , Wiesmüller Karl‐Heinz , Gnau Volker , Brünjes Jente , Jung Günther
Published: December 2003

Optimizing syntheses and characterizing complex mixtures of peptides (peptide libraries)—crucial to the search for new lead structures in drug development—is possible with ion‐spray mass spectrometry alone or combined with high‐performance liquid chromatography. This was shown in investigations of a small sublibrary made up of 48 octapeptides, which represents 1 % of the peptide pool exhibiting the murine major histocompatibility complex (MHC) class I H2‐Kb restricted sequence motif, and studies of a mixture of 24 576 peptides that bind to murine MHC class I Qa‐2a molecules.
Syntheses of Polycyclic Natural Products Employing the Intramolecular Double Michael Reaction
Authors: Ihara Masataka , Fukumoto Keiichiro
Published: December 2003

The one‐pot intramolecular double Michael reaction of compounds having two different α, β‐unsaturated carbonyl groups to form polycyclic compounds can be carried out by three different methods: in the first the substrate is treated with lithium hexamethyldisilazide, in the second with chlorotrimethylsilane, triethylamine, and zinc chloride at an elevated temperature, and in the third with tert‐butyldimethylsilyl trifluoromethanesulfonate and triethylamine. The reaction proceeds with complete regioselectivity and high stereoselectivity following a stepwise mechanism. Spiro‐fused bicyclo[2.2.2]octane derivatives can be constructed with high stereoselectivity by the intromolecular double Michael reaction by using the first method. Enantiomerically pure atisine and the enantiomer of atisirene were synthesized stereoselectively by application of this methodology. The syntheses of steroids and angular triquinane‐type sesquiterpenoids were possible with the second method. Heterocyclic compounds with a bridgehead nitrogen atom were obtained by the reaction of α, β‐unsaturated amides following the second and third methods. The asymmetric synthesis of tylophorine with diastereofacial control was achieved by the intramolecular reaction according to the third method. The sulfur‐mediated intramolecular double Michael reaction utilizing the third method produced trans‐hydroindane derivatives. Furthermore, the intramolecular Michael‐aldol reaction can be employed in synthesizing polycyclic systems with cyclobutane units by treatment with tert‐butyldimethylsilyl trifluoromethanesulfonate in the presence of triethylamine. The intermolecular double Michael reaction and related reactions will also be described.
Concerning “An Evaluation of the Peer Review Process at Angewandte Chemie”
Authors: Ross Paul F.
Published: December 2003

Is peer review working—that is, is it fair and does it identify significant papers? H. D. Daniel (Angew. Chem. Int. Ed. Engl. 1993, 32, 234) looked into this question in a study of the referee system of Angewandte Chemie that threw light on important aspects of this process. This further discussion between Ross and Daniel will therefore interest every reader.
Hexakis(benzotriazolato)tetrakis(2,4‐pentanedionato)pentacopper(II): A Model for Corrosion Inhibition
Authors: Handley Jane , Collison David , Garner C. David , Helliwell Madeleine , Docherty Robert , Lawson John R. , Tasker Peter A.
Published: December 2003

Each benzotriazolato (bta) ligand is bound to three copper(II) ions in the pentanuclear title complex. The known copper corrosion inhibitor, Hbta, might bind similarly to two metal atoms on the surface to be protected and one metal atom of the underlying layer. Results of molecular modeling studies suggest that the optimal interaction of bta− with the surfaces of Cu2O and CuO occurs for an orientation perpendicular to the (110) surface.
New Developments in the Chemistry of Catalytic Antibodies
Authors: Leumann Christian
Published: December 2003

In the deliberate stereoselective control of reactions and for application in therapy, the chemistry of the antibody catalysts have provided new impulses. Furthermore, recent developments in the field of immunology give rise to the hope that in the future semisynthetic, catalytically active antibodies can be directly prepared by molecular biology so that the classical immunological methods, which require testing on animals, can be replaced. For example, the antibodycatalyzed hydrolysis of cocaine is very promising.
The Battle of Calicheamicin γ
Authors: Nicolaou K. C.
Published: December 2003

The first total synthesis of calicheamicin γ was achieved approximately a year ago. In this article, the author presents a personal account of the events, in chronological order, that led to this success story in total synthesis.
The Coupled Activation of Molecular Oxygen and CH and CC Bonds in Gas‐Phase Reactions of [M(C2H4)]+ (M  ScZn) with O2
Authors: Schröder Detlef , Schwarz Helmut
Published: December 2003

Fe+ is the only cation that mediates the activation of molecular oxygen as well as that of the CH and CC bonds of the olefin when the complexes [M(C2H4)]+ of the transition metals (M  ScZn) are allowed to react with O2 under single‐collision conditions in the gas phase. This unique behavior parallels the role of iron complexes in important condensed‐phase processes in many chemical and biological systems.
Ba44Cu48(CO3)6O87.9: The Structure of “BaCuO2” from Simultaneous X‐ray and Neutron Powder Diffraction
Authors: Aranda Miguel A. G. , Attfield J. Paul
Published: December 2003

“BaCuO2” is not a simple ternary oxide but a complex oxocarbonate. It is a common component of superconducting oxocuprates. The complete elucidation of the structure by simultaneous X‐ray and neutron powder diffraction on samples of “BaCuO2” gave a statistically disordered carbonate group at the heart of the structure and resulted in the composition of this supposed oxide given in the title.
DNA Supercoiling Imaged in Three Dimensions by Scanning Force Microscopy
Authors: Samori Bruno , Nigro Carmelo , Armentano Valerio , Cimieri Salvatore , Zuccheri Giampaolo , Quagliariello Carla
Published: December 2003

Until now only planar projections of the molecular shape of supercoiled circular DNA molecules could be imaged with scanning force microscopy (SFM). In the three‐dimensional image of a supercoiled pBR322 DNA molecule in this report, the chirality and writhing number can be “read” directly. Local changes in the supercoiling in individual DNA molecules can be monitored, which should be important for our understanding of biological processes such as DNA transcription.
The Search for an Isolable Silyl Cation Must Continue
Authors: von Ragué Schleyer Paul , Buzek Peter , Müller Thomas , Apeloig Yitzhak , Siehl Hans‐Ullrich
Published: December 2003

Evidently a σ complex and not a free uncomplexed silyl cation is present in the crystals of 1· toluene. This follows from ab initio studies into the structure of the cationic complexes [Me3Sitoluene]+, [Me3Sibenzene]+, and [H3Sibenzene]+ as well as from IGLO calculations of the δ(29Si) values of these complexes. The differences between these and σ complexes with alkyl groups can be ascribed to the more effective CSi hyperconjugation. Compound 1. toluene was recently described as “the first free silyl cation”.
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Preparative Enantiomer Separation of the Anesthetic Enflurane by Gas Inclusion Chromatography
Authors: Schurig Volker , Grosenick Heiko , Green Bernard S.
Published: December 2003

Cyclodextrin derivatives dissolved in polysiloxanes could be used for the first time as the stationary phase in enantioselective preparative gas chromatography. The authors separated the racemates of the inhalation anesthetic enflurane which is still administered as a racemate.
Chemistry and Biology of Taxol
Authors: Nicolaou Kyriacos Costa , Dai Wei‐Min , Guy Rodney Kiplin
Published: December 2003

One can view plants as a reference library of compounds waiting to be searched by a chemist who is looking for a particular property. Taxol, a complex polyoxygenated diterpene isolated from the Pacific Yew, Taxus brevifolia, was discovered during extensive screening of plant materials for antineoplastic agents during the late 1960s. Over the last two decades, interest in and research related to taxol has slowly grown to the point that the popular press now seems poised to scoop each new development. What was once an obscure compound, of interest only to the most masochistic of synthetic chemists and an equally small number of cellular biologists, has become one of the few organic compounds, which, like benzene and aspirin, is recognizable by name to the average citizen. In parallel, the scientific study of taxol has blossomed. Physicians are currently studying its effects on nearly every known neoplasm. Biologists are using taxol to study the mechanisms of cell function by observing the effects of its interactions with the cellular skeletal systems. Synthetic chemists, absorbed by the molecule's unique and sensitive structure and functionality, are exploring seemingly every available pathway for its synthesis. Indeed, the demand for taxol has risen so in the last five years that alternative sources to the extraction of T. brevifolia are being vigorously pursued. Because of the rapidly expanding scope of research in the multifaceted study of taxol, those who are interested in the field may find acquisition of a reasonable base of knowledge an arduous task. For this reason, this account attempts to bring together, for the first time, in a cogent overview the chemistry and biology of this unique molecule.
Chemical Analysis of Inorganic and Organic Surfaces and Thin Films by Static Time‐of‐Flight Secondary Ion Mass Spectrometry (TOF‐SIMS)
Authors: Benninghoven Alfred
Published: December 2003

By using mass spectrometry to analyze the atomic and molecular secondary ions that are emitted from a solid surface when bombarded with ions, one obtains detailed information about the chemical composition of the surface. A time‐of‐flight mass spectrometer is especially suitable for the analysis of secondary ions because of its high transmission, high mass resolution, and ability to detect ions of different masses simultaneously. By using a finely focused primary ion beam it is also possible to analyze microareas and generate surface images with a lateral resolution of 0.1 μm or less. Static time‐of‐flight secondary ion mass spectrometry (TOF‐SIMS) allows monolayer imaging and local analysis of monolayers with high sensitivity, a wide mass range, high mass resolution, and high lateral resolution. Besides information on elements and isotopes, the technique yields direct information on the molecular level and can also be used to analyze surface species of high molecular mass that are thermally unstable and cannot be vaporized. The method can be applied to practically all types of materials and sample forms, including insulators in particular. In this article the basic principles of TOF‐SIMS are explained, and its analytical capabilities for both large area and imaging applications are illustrated by examples. These include silicon surfaces (both uniform and structured), thermally unstable organic molecules on surfaces, synthetic polymers, and synthetically prepared molecular surface films, particles, and fibers. Emitted neutral particles can also be analyzed by postionization with a laser, and the possibilities of this technique are discussed.
Polyynes–Fascinating Monomers for the Construction of Carbon Networks?**
Authors: Bunz Uwe H. F.
Published: December 2003

Carbon‐rich compounds are accessible from topologically unusual polyynes. Impressive advances have been made in this area recently by the research groups led by Moore, Tour, Diederich, and de Meijere. The novel monomers not only display fascinating chemistry of their own, they may also be suited for the synthesis of new carbon allotropes.
Combination of Superexchange and Spin‐Polarization Mechanisms Leads to a Novel Hydrocarbon Tetraradical with a High‐Spin Ground State
Authors: Jacobs S. Joshua , Dougherty Dennis A.
Published: December 2003

For corrigendum see DOI:10.1002/anie.199502401
Ozone Formation through Decomposition of CFCs in the Stratosphere
Authors: Argüello Gustavo A. , Jülicher Bernd , Willner Helge
Published: December 2003

Both in a matrix and in the gas phase, the electronically excited state of CF2 reacts with O2 to form F2CO and ozone. These are the results of photolysis experiments with difluorodiazirine as CF2 source. The significance of this reaction (which has not previously been taken into account) for the chemistry of the stratosphere is discussed.
A New Method for the Synthesis of Heterometallic Complexes: Syntheses and Structures of [(PhCH2CH2NLi)3Sb(thf)]2 and [Sb3(cyN)4(NMe2)2]Li
Authors: Edwards Andrew J. , Paver Michael A. , Raithby Paul R. , Rennie Moira‐Ann , Russell Christopher A. , Wright Dominic S.
Published: December 2003

Successive metalation of primary amines, first with nBuLi and then with Sb(NMe2)3, has enabled the preparation of the heterometallic complexes 1 and 2. Neutra [Ph(CH2)2N(H)Li]n and ionic Li[Sb(cyNH)4] occur as the intermediates in the formation of 1 and 2, respectively.
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[Cu96P30{P(SiMe3)2}6(PEt3)18], a New Phosphorus‐Bridged Copper Cluster
Authors: Fenske Dieter , Holstein Werner
Published: December 2003

One of the largest cluster complexes whose structure has been elucidated is the title compound, which is formed from CuCl, PEt3, and P(SiMe3)3, when the components are used in the ratio 1:0.5:0.6. The structure, which is difficult to describe, can be discussed as an intermediate in the formation of binary Cu3P.
Magnetic Properties of Aromatic Transition States: The Diels–Alder Reactions
Authors: Herges Rainer , Jiao Haijun , von Ragué Schleyer Paul
Published: December 2003

Changes in magnetic properties along the reaction coordinate of the Diels–Alder reactions of ethylene with butadiene and cyclopentadiene were computed ab initio with the IGLO method. Evidence for the aromaticity of the transition structures is provided by exalted magnetic susceptibilities and anisotropies, as well as chemical shift anomalies.
Conformational Requirements for Sweet‐Tasting Peptides and Peptidomimetics
Authors: Yamazaki Toshimasa , Benedetti Ettore , Kent Darin , Goodman Murray
Published: December 2003

The molecular basis o taste has been extensively studied over many years. The research carried out in our laboratories is focused on the elucidation of detailed structure–taste relationships of peptides and peptidomimetics using an “integrated” approach employing synthesis, analysis of NMR spectra, computer simulations, and X‐ray crystallography. Various peptidomimetic residues have been incorporated to introduce predictable structural constraints into taste ligands. These constraints eliminate some of the molecular flexibility and allow us to develop structure–activity relationships. We describe here the topochemical requirements of the sweet and bitter taste receptor(s) and develop detailed structure‐taste relationships with considerable predictive power for peptides and related molecules.
Bond‐Stretch Isomers and Spin‐State Isomers: A Comment on the Article “Bond‐Stretch Isomers: Fact not Fiction”
Authors: Parkin Gerard , Hoffmann Roald
Published: December 2003

What exactly is meant by bond‐stretch isomerism? Confusion seems to reign about the phenomenon, partly because the original papers did not explicitly define the term. However, if limited to its original meaning, no bond‐stretch isomers have yet been discovered, in spite of a recent claim to the contrary (see Correspondence by P. Giitlich, H. A. Goodwin, and D. N. Hendrickson in the second February issue of Angewandte Chemie).
A Highly Convergent Synthesis of the Lewisy Blood Group Determinant in Conjugatable Form
Authors: Behar Victor , Danishefsky Samuel J.
Published: December 2003

The versatility of glycals both as glycosyl donors and as glycosyl acceptors is used in the synthesis of the Lewisy determinant. This and the oligosaccharide described in the following communication consist of a determinant, a carbohydrate spacer, and a group suitable for the conjugation to a carrier protein. The spacer present in these new glycoproteins minimizes the likelihood that the protein carrier will distort the recognition property of the determinant.
Chlorine Trioxide: Spectroscopic Properties, Molecular Structure, and Photochemical Behavior
Authors: Grothe Hinrich , Willner Helge
Published: December 2003

Though postulated for years, now detected for the first time! The symmetric ClO3 radical was synthesized by vacuum flash pyrolysis of chlorine perchlorate and trapped by matrix isolation for UV and IR spectroscopic studies. The OClO bond angle is 113.5±2° and the ClO bond length 150.0±1 pm. The photolysis of ClO3 yields the unsymmetric isomer OClOO.
Hydrogenation of acrylonitrile–butadiene rubber latexes
Authors: Zhou Shuqin , Bai Huadong , Wang Jianguo
Published: December 2003

The hydrogenation of acrylonitrile–butadiene rubber (NBR) latex was carried out by a system consisting of hydrazine hydrate and hydrogen peroxide, with boric acid as catalyst. Highly saturated hydrogenated NBR (HNBR) latex was obtained through the optimization of the reaction conditions. The dried HNBR was found to be heavily gelled. The cause for the crosslink of dried hydrogenated NBR products was investigated. With the improvement of the hydrogenation system, that is, by adding gel inhibitor to the system, the crosslinking was controlled to a large extent, and dried HNBR with gel content of about 3% was prepared by the improved system. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2072–2078, 2004
Continuous tubular reactors for latex production: Conventional emulsion and miniemulsion polymerizations
Authors: Ouzineb Keltoum , Graillat Christian , McKenna Timothy
Published: December 2003

An investigation of the use of continuous tubular reactors for the production of polymeric latices is presented. In an initial step, it is demonstrated that tubular reactors can be used to produce latices by conventional emulsion polymerization at solids contents of up to 30% by volume. Under these conditions, the kinetics are identical to those found in batch reactors (as expected), and stable operating conditions are obtained, usually after one to two residence times. The use of a miniemulsion in a tubular reactor was also investigated, and it is demonstrated that in this case, solids contents of at least 60% can be obtained under stable operating conditions. It is therefore proposed that difficulties in operating tubular reactors with conventional emulsion polymerization arise essentially from the presence of monomer droplets in the early stages of the reaction. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2195–2207, 2004
Hot compaction of woven poly(ethylene terephthalate) multifilaments
Authors: Hine P. J. , Ward I. M.
Published: December 2003

Here we describe the development of a process, and the resulting mechanical properties, for hot‐compacted sheets of woven poly(ethylene terephthalate) (PET) multifilaments. Investigation of the various processing parameters showed that a key aspect was the time spent at the compaction temperature, termed the dwell time. Molecular weight measurements, using intrinsic viscosity, showed that hydrolytic degradation occurred rapidly at the temperatures required for successful compaction, leading to embrittlement of the resulting materials with increasing dwell time. A dwell time of 2 min was found to be optimum because this gave the required percentage of melted material to bind the structure together, while giving only a small decrease in molecular weight. A combination of techniques, including mechanical tests, differential scanning calorimetry, and scanning electron microscopy, was used to examine the mechanical properties and morphology of the optimum compacted sheets. These tests reinforced the view from previous studies on hot‐compacted polypropylene, of hot‐compacted sheets as self‐reinforced composites, whose behavior is a combination of the properties of the two components, that is, the original oriented multifilaments and the melted and recrystallized matrix. Other key findings from the research included a confirmation of the importance of obtaining high ductility in the melted and recrystallized phases, promoted by using a high molecular weight or by suppressing crystallinity during processing, and the proportionately high‐impact performance of hot‐compacted sheets, compared with that of other materials. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2223–2233, 2004
Swelling and drug‐release behavior of the poly(AA‐co‐N‐vinyl pyrrolidone)/chitosan interpenetrating polymer network hydrogels
Authors: Lee Wen‐Fu , Chiang Wen‐Hsuan
Published: December 2003

A series of novel hydrogels were prepared from acrylic acid (AA), N‐vinyl pyrrolidone (NVP), and chitosan by photopolymerization. The swelling behavior, gel strength, and drug release behavior of the poly(AA/NVP) copolymeric hydrogels and corresponding interpenetrating polymer network hydrogels were investigated. Results showed that the swelling ratios for the present hydrogels decreased with an increase of NVP content in the gel, but the gel strength increased with an increase of NVP content in the gel. Results also showed that the drug‐release behavior for the gels is related to the ionicity of drug and the swelling ratio of the gel. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2135–2142, 2004
Direct synthesis of poly(D,L‐lactic acid) by melt polycondensation and its application in drug delivery
Authors: Zhao Yaoming , Wang Zhaoyang , Wang Jun , Mai Hangzhen , Yan Bing , Yang Fan
Published: December 2003

Starting from D,L‐acid and SnCl2 as catalyst, poly(D,L‐lactic acid) (PDLLA) was directly synthesized by melt polycondensation. Under the appropriate conditions such as 0.5 wt % SnCl2, 170–180°C, 70 Pa, and 10 h, the viscosity‐average molecular weight (Mη) of PDLLA was 4100 Da. PDLLA produced by the most practical method was used as the drug‐delivery material for erythromycin and ciprofloxacin. The optimal conditions for the preparation of erythromycin–poly(D,L‐lactic acid)–microsphere (ERY–PDLLA–MS) for lung targeting was investigated, and further confirmed by good reappearance tests. DSC and SEM demonstrated that ERY–PDLLA–MS had good spherical shape. The release in vitro of ERY–PDLLA–MS was effective and the half‐time (T1/2) was 51.0 h. After 175 h, the accumulated release percentage was 80.0%. The test in vivo showed that ERY–PDLLA–MS was more easily distributed in rabbit lung tissue. When PDLLA was applied in an antibacterial ciprofloxacin drug‐delivery microsphere (CIP–PDLLA–MS), CIP–PDLLA–MS was also characterized with DSC and SEM, and the release T1/2 in vitro was 24.9 h. After 53.2 h, the accumulated release percentage reached 84.0%, which indicated that CIP–PDLLA–MS was advantageous to long‐term release. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2143–2150, 2004
Study on nanometer‐size styrene‐butadiene multiblock copolymer synthesized by reactive extrusion
Authors: Shishuang Gao , Ying Zhang , Anna Zheng , Xiao Huining
Published: December 2003

In this study, a novel styrene‐b‐butadiene block copolymer was synthesized by bulk anionic polymerization in a corotating closely intermeshing twin‐screw extruder. The structure of the S/B copolymer was determined by characterization methods including FTIR, NMR, dynamic mechanical analysis (DMA), and TEM. It is shown that the polymerized materials exhibit nanometer‐size styrene and butadiene (S/B) multiblock structure and ultrahigh elongation at break, which differs considerably from that of traditional solution polymerizing methods. In terms of the structure of the polymerized products, the mechanism of living anionic polymerization of S/B in a corotating intermeshing twin‐screw extruder is discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2265–2270, 2004
Effects of synthesis conditions on the pervaporation properties of poly[1‐(trimethylsilyl)‐1‐propyne] useful for membrane bioreactors
Authors: Volkov V. V. , Fadeev A. G. , Khotimsky V. S. , Litvinova E. G. , Selinskaya Y. A. , McMillan J. D. , Kelley S. S.
Published: December 2003

An integrated fermentation and membrane‐based recovery (pervaporation) process has certain economical advantages in continuous conversion of biomass into alcohols. This article presents new pervaporation data obtained for poly[1‐(trimethylsilyl)‐1‐propyne] (PTMSP) samples synthesized in various conditions. Three different catalytic systems, TaCl5/n‐BuLi, TaCl5/Al(i‐Bu)3, and NbCl5 were used for synthesis of the polymers. It was found that the catalytic system has a significant influence over the properties of membranes made from PTMSP. Although a combination of a high permeation rate and a high ethanol–water separation factor (not less than 15) was provided by all PTMSP samples, the PTMSP samples synthesized with TaCl5/n‐BuLi showed significant deterioration of membrane properties when acetic acid was present in the feed. In contrast, the PTMSP samples synthesized with TaCl5/Al(i‐Bu)3 or NbCl5 showed stable performance in the presence of acetic acid. When using a multicomponent mixture of organics and water, the copermeation of different organic components results in lower separation factor for both ethanol and butanol. These data are consistent with nanoporous morphology of PTMSP. It was demonstrated that pervaporative removal of ethanol improved the overall performance of the fermentation process. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2271–2277, 2004
Synthesis and characterization of new optically active poly(amide‐imide‐urethane) thermoplastic elastomers, derived from 4,4′‐(hexafluoroisopropylidene)‐N,N′‐bis(phthaloyl‐L‐leucine‐p‐aminobenzoic acid) and PEG‐MDI
Authors: Mallakpour Shadpour , Khoee Sepideh
Published: December 2003

A new class of optically active poly(amide‐imide‐urethane) was synthesized via two‐step reactions. In the first step, 4,4′‐methylene‐bis(4‐phenylisocyanate) (MDI) reacts with several poly(ethylene glycols) (PEGs) such as PEG‐400, PEG‐600, PEG‐2000, PEG‐4000, and PEG‐6000 to produce the soft segment parts. On the other hand, 4,4′‐(hexafluoroisopropylidene)‐N,N′‐bis(phthaloyl‐L‐leucine‐p‐amidobenzoic acid) (2) was prepared from the reaction of 4,4′‐(hexafluoroisopropylidene)‐N,N′‐bis(phthaloyl‐L‐leucine) diacid chloride with p‐aminobenzoic acid to produce hard segment part. The chain extension of the above soft segment with the amide‐imide 2 is the second step to give a homologue series of poly(amide‐imide‐urethanes). The resulting polymers with moderate inherent viscosity of 0.29–1.38 dL/g are optically active and thermally stable. All of the above polymers were fully characterized by IR spectroscopy, elemental analyses, and specific rotation. Some structural characterization and physical properties of this new optically active poly(amide‐imide‐urethanes) are reported. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2288–2294, 2004
Recycling of pharmaceutical waste gelatin for controlled‐release applications. I. A 2,4‐dicholorphenoxy acetic acid based system
Authors: Kandil Sherif , Kenawy El‐Refaie , El‐Maghraby Azza
Published: December 2003

Gelatin is a natural macromolecular protein. It contains a wide variety of amino acids in its polymer structure, and it is colorless to yellowish, water‐soluble, and tasteless. It is used as a dispersing agent, sizing medium, and coating for photographic films and in pharmaceutical formulations. In this study, biodegradable mulching, based on waste gelatin from pharmaceutical gelatin scraps (derived from pharmaceutical soft gelatin capsule production), was formulated via the casting of water solutions or suspensions into flexible and consistent films. Gelatin was blended with synthetic materials such as poly(vinyl alcohol) and other natural wastes such as sugar cane bagasse and sawdust. To all formulations, 2,4‐dichlorophenoxy acetic acid (2,4‐D) was added as a herbicide. The morphology and mechanical properties of the samples were investigated with scanning electron microscopy and tensile testing, respectively. The results showed that the produced films had controlled‐release properties. The effects of various additives and crosslinking on the films and the release of the herbicide 2,4‐D from the films were also investigated. The introduction of synthetic and natural additives reduced the release rate of 2,4‐D. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2313–2319, 2004
Effect of the reaction atmosphere on high‐density polyethylene functionalized by ultraviolet irradiation
Authors: Wu Shishan , Xu Xi
Published: December 2003

The structure and hydrophilicity of high‐density polyethylene (HDPE) functionalized by ultraviolet irradiation in air and O2 were studied with Fourier transform infrared, X‐ray photoelectron spectroscopy, differential scanning calorimetry, and contact‐angle measurements with water and liquid paraffin. The results showed that CO, C(O)O, and CO functional groups were introduced onto molecular chains of HDPE during irradiation in air and O2, and their contents increased with the irradiation time. The number of oxygen‐containing groups of HDPE irradiated in O2 was much higher than that in air. A higher functionalization efficiency for HDPE was achieved by irradiation in O2. After the irradiation, the contact angle of HDPE with water became smaller, the contact angle of HDPE with liquid paraffin became larger, and the surface tension increased; this showed that the hydrophilicity of irradiated HDPE was improved. HDPE irradiated in O2 exhibited better hydrophilicity than HDPE irradiated in air. Furthermore, with an increase in the irradiation time, the melting temperature of HDPE decreased, and the heat of fusion and the degree of crystallinity increased. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 00: 2326–2329, 2004
Preparation and characterization of CdS and CdS/polyacrylonitrile nanocomposites by γ‐irradiation and emulsion polymerization
Authors: Choi Seong‐Ho , Choi Min‐Seok , Lee Kwang‐Pill , Kang Hee‐Dong
Published: December 2003

CdS and CdS/polyacrylonitrile (PAN) nanocomposites were prepared by γ‐irradiation and emulsion polymerization. The CdS and CdS/PAN nanocomposites were characterized by powder X‐ray diffraction, infrared spectroscopy, Fourier transform Raman spectroscopy, transmission electron microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, and thermal analysis (thermogravimetric analysis/dynamic thermal analysis). In photoluminescence spectroscopy analysis, the maximum peak of CdS/PAN nanocomposites prepared by γ‐irradiation and emulsion polymerization was at about 485 nm, whereas the maximum peak of CdS nanocomposites was at about 460 nm. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2335–2342, 2004
Synthesis and characterization of a terpolymer of limonene, styrene, and methyl methacrylate via a free‐radical route
Authors: Sharma Saroj , Srivastava A. K.
Published: December 2003

The free‐radical terpolymerization of a monocyclic terpene, namely, limonene (Lim), with styrene (Sty) and methyl methacrylate (MMA) in xylene at 80 ± 0.1°C for 2 h, with benzoyl peroxide (BPO) as an initiator under an inert atmosphere of nitrogen was extensively studied. The kinetic expression was Rpα[BPO]0.5[Sty]1.0[MMA]1.0[Lim]−1.0, where Rp is the rate of polymerization. The overall energy of activation was calculated as 26 kJ/mol. Rp decreased as [Lim] increased. This was due to a penultimate unit effect. The Fourier transform infrared spectra of the terpolymer showed bands at 3025–3082, 1728, and 2851–2984 cm−1 due to CH stretching of phenyl (C6H5) protons of Sty, OCH3 of MMA, and trisubstituted olefinic protons of Lim, respectively. The 1H‐NMR spectra showed peaks at 7.3–8.1, 3.9–4.4, and 5.0–5.5 δ due to the phenyl, methoxy, and trisubstituted olefinic protons of Sty, MMA and Lim, respectively. The values of the reactivity ratios r1 (MMA; 0.33) and r2 (Sty + Lim; 0.06) were calculated with the Kelen–T̈udos method. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2343–2347, 2004
Properties of crosslinked blends of pellethene and multiblock polyurethane containing poly(ethylene oxide) for biomaterials
Authors: Yoo Hye‐Jin , Kim Han‐Do
Published: December 2003

A series of multiblock polyurethanes, containing various poly(ethylene oxide) (PEO; number‐average molecular weight = 400–3400) contents (0–80 wt %) and prepared from hexamethylene diisocyanate/PEO/poly(dimethylsiloxane) diol/polybutadiene diol/1,4‐butanediol, were used as modifying additives (30 wt %) to improve the properties of biomedical‐grade Pellethene. Different molecular weights of PEO were used to keep poly(ethylene glycol) at a fixed molar content, if possible, although the PEO content, related to the PEO block length in the multiblock polyurethanes, was varied from 0 to 80 wt %. The hydrophilic PEO component was introduced through the addition of PEO‐containing polyurethanes and dicumyl peroxide as a crosslinking agent in a Pellethene matrix. As the PEO content (PEO block length) increased, the hydrogen‐bonding fraction of the crosslinked Pellethene/multiblock polyurethane blends increased, and this indicated an increase in the phase separation with an increase in the PEO content in the crosslinked Pellethene/multiblock polyurethane blends. According to electron spectroscopy for chemical analysis, the ratio of ether carbon to alkyl carbon in the crosslinked Pellethene/multiblock polyurethane blends increased remarkably with increasing PEO content. The water contact angle of the crosslinked Pellethene/multiblock polyurethane blend film surfaces decreased with increasing PEO content. The water absorption and mechanical properties (tensile modulus, strength, and elongation at break) of the crosslinked Pellethene/multiblock polyurethane blend films increased with increasing PEO content. The platelet adhesion on the crosslinked Pellethene/multiblock polyurethane blend film surfaces decreased significantly with increasing PEO content. These results suggest that crosslinked Pellethene/multiblock polyurethane blends containing the hydrophilic component PEO may have potential for biomaterials that come into direct contact with blood. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2348–2357, 2004