bluuebunny/crossref_metadata_2025 huggingface dataset:
Oxidative Transformations of Organic Compounds Mediated by Redox Molecular Sieves
Authors: Arends Isabel W. C. E. , Sheldon Roger A. , Wallau Martin , Schuchardt Ulf
Published: January 2004

Zeolites are viewed by some as the “philosopher's stone” of modern chemistry.[1] They are more or less indispensable in oil refining and petrochemicals manufacture where they are widely applied as solid acid catalysts. More recently attention has been focused on their use in the manufacture of fine chemicals. The synthetic utility of zeolites and related molecular sieves (zeotypes) has been considerably extended by the incorporation of redox metals into their frameworks. The resulting redox molecular sieves catalyze a variety of selective oxidations under mild conditions in the liquid phase. Their structural diversity–including variation of the redox metal, incorporation of metal complexes, and the size and polarity of the micropores–provides the possibility of designing tailor‐made solid catalysts (“mineral enzymes”) for liquid‐phase oxidations with clean oxidants such as O2, H2O2, and RO2H. Hence, they have enormous potential in industrial organic synthesis as environmentally friendly alternatives to traditional oxidations employing inorganic oxidants in stoichiometric amounts. A primary aim of this review is to familiarize organic chemists with the synthetic potential of redox molecular sieves. An outline of their synthesis, structures, and chemical properties, highlighting their unique advantages, is followed by a discussion of general (mechanistic) features that influence the choice of a suitable catalyst for a particular type of oxidation. The main part of the review deals with the oxidation of various substrates of synthetic interest–such as alkanes, alkenes, (alkyl)arenes, alcohols, and amines–and emphasizes the advantages of redox molecular sieves (including selectivity and stability) over their homogeneous counterparts. New directions towards truly biomimetic solid catalysts, for example zeolite‐encapsulated chiral metal complexes as heterogeneous catalysts for asymmetric oxidations, are high‐lighted.
Alkenylidenes in Organic Synthesis
Authors: Kirmse Wolfgang
Published: January 2004

Alkenylidenes R2CC: (= alkylidene carbenes) undergo regio‐ and stereoselective intramolecular CH insertion reactions that are excellently suited for the synthesis of cyclopentenes. The 1, 2‐shifts occurring with RH and RAr are useful for the preparation of alkynes. Alkenylidenes are efficiently generated from carbonyl compounds by diazomethylation, from vinyl halides by α‐elimination, from alkynyliodonium salts by addition of nucleophiles, and from alkynes by retro‐1, 2‐shifts. Specific applications of the various methods, particularly in the synthesis of natural products, are discussed.
Electron Transfer Induced CS Bond Cleavage in Rhenium and Technetium Thioether Complexes: Structural and Chemical Evidence for π Back‐Donation to CS σ* Orbitals
Authors: Mullen Gregory E. D. , Went Michael J. , Wocadlo Sigrid , Powell Anne K. , Blower Philip J.
Published: January 2004

The trends in carbon‐sulfur bond length for complexes of 1,4,7‐trithiacyclononane (9S3) provide compelling evidence that CS σ* orbitals accept π‐electron density from the metal. As the metal d‐orbital energy and occupancy increase, this leads ultimately to cleavage of the CS bonds with concomitant release of ethene in the Re and Tc complexes [Eq. (a)].
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Tris(tri‐tert‐butylsilyl)digallanyl (tBu3Si)3Ga2: A New Type of Compound for a Heavy Group 13 Element
Authors: Wiberg Nils , Amelunxen Kerstin , Nöth Heinrich , Schwenk Holger , Kaim Wolfgang , Klein Axel , Scheiring Thomas
Published: January 2004

Blue‐black trisupersilyldigallanyl, a new metastable inorganic radical, forms in the reaction of GaCl3 with tBu3SiNa in pentane at room temperature according to Equation (a). The X‐ray structure analysis reveals that it contains a planar Si2GaIIGaI and a nearly linear GaIIGaISi framework; according to the ESR spectrum the unpaired electron resides in both Ga atoms. Surprisingly, the analogous reaction of AlCl3 and tBu3SiNa (Al instead of Ga in Equation (a)) does not lead to trisupersilyldialanyl, but to red tetrasupersilyldialane (tBu3Si)2Al–Al(SitBu3)2.
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Novel Reactions of Organomolybdenum and Organotungsten Compounds: Additive–Reductive Carbonyl Dimerization, Spontaneous Transformation of Methyl Ligands into μ‐Methylene Ligands, and Selective Carbonylmethylenation
Authors: Kauffmann Thomas
Published: January 2004

Hitherto there was no reaction known that permits transformations of R1R2‐CO → 0.5 R1R2R3C–CR1R2R3 in one step. This type of additive–reductive carbonyl dimerization is now possible using alkoxy(alkyl)tungsten(v) complexes with aromatic, heteroaromatic or α,β‐unsaturated aldehydes and ketones. When a corresponding phenyl complex was employed in a test experiment, it was revealed that an aliphatic ketone could be used as the substrate in this reaction. A second interesting type of reaction is the transformation of CH3 ligands into μ‐CH2 ligands, which occurs during the treatment of MeLi or Me3Al with molybdenum or tungsten chlorides (oxidation states VI and V, for Mo additionally IV) at low temperatures with liberation of CH4. Here, the question arises as to whether the intermediate involved has a terminal CH2 ligand (Schrock carbene complex) or a μ‐CH3 ligand (CH3 bound by a two‐electron three‐center bond to two metal atoms). Of all the μ‐CH2 complexes obtained, those which were synthesized by the action of MeLi on molybdenum chlorides can be recommended as reagents for carbonylmethylenation of aldehydes and ketones. They display high selectivity, very low basicity, a surprising resistance to protons, they are readily available, can be easily modified and, as regards their selective behavior, they have been investigated more thoroughly than other readily accessible carbonylmethylenation reagents of comparable selectivity. The results of NMR spectroscopic investigations on the structure of the μ‐CH2 complexes, and associated reaction mechanisms are discussed. A survey of carbonylmethylenation reagents, which have been reported in the literature, permits comparisons to be made with carbonylmethylenating molybdenum and tungsten complexes.
Combinatorial Chemistry for the Synthesis of Carbohydrate Libraries
Authors: Arya Prabhat , Ben Robert N.
Published: January 2004

The first step has been made. The research groups of Hindsgaul, Boons, and Kahne have successfully synthesized libraries of di‐ and trisaccharides with combinatorial methods. The synthesis of this important class of oligosaccharides is thus more feasible and will have a great impact on the understanding of cell‐surface interactions.
Stereoisomeric Peptide Libraries and Peptidomimetics for Designing Selective Inhibitors of the αvβ3 Integrin for a New Cancer Therapy
Authors: Haubner Roland , Finsinger Dirk , Kessler Horst
Published: January 2004

Cell–cell and cell–matrix interactions play a major role in biology. An important class of surface receptors are the integrins, which exist in a number of subtypes and are involved in many biological processes, for example embryonic development, blood coagulation, osteoporosis, cancer, and regulation of the balance between proliferation and death (apoptosis) of a cell. Therefore, selective inhibition of specific integrin subtypes is of great pharmaceutical interest. It is possible to develop highly selective and active inhibitors of integrins, especially the αvβ3 subtype, by the novel procedure of spatial screening. The resulting αvβ3 antagonists exhibit activity in the nanomolar range and suppress tumor‐induced angiogenesis (formation of new blood vessels). Tissues with intact blood vessels are not influenced. This opens a promising new way for cancer therapy.
Molecular Beam Studies on Semiconductor Clusters: Polarizabilities and Chemical Bonding
Authors: Becker Jörg August
Published: January 2004

This article discusses experiments that measure polarizabilities, permanent dipole moments, and absorption spectra of semiconductor clusters such as SiN, GaNAsM, and GeNTeM isolated in a molecular beam. The experiments show that the transition from the typical optoelectronic properties of macroscopic semiconductor crystals to the molecular properties of small polyhedral semiconductor molecules occurs in several steps. The bonding in nanometer‐sized semiconductor colloids with approximately 103–105 atoms is similar to that in the solid state. The bonding orbitals of the semiconductor crystals, which extend over a nanometer range, are, however, somewhat more strongly localized in these clusters and are therefore already slightly modified. Over the size range from 103 to 10 atoms, a gradual transition occurs from localized solid‐state‐like bonds to molecule‐like bonds. Interestingly, quantum size effects are found even in relatively small particles with about 102 atoms. These effects can be observed in the form of unusually small static polarizabilities of SiN clusters or in the absorption bands of GaNAsM clusters, which are strongly blue‐shifted relative to those of the solid state. For smaller clusters. These effects disappear over the size range 102−10 atoms, which is manifested by an increasing red‐shift of the absorption bands with decreasing cluster size.
Uncatalyzed Transfer Hydrogenation and Transfer Hydrogenolysis: Two Novel Types of Hydrogen‐Transfer Reactions
Authors: Rüchardt Christoph , Gerst Matthias , Ebenhoch Jochen
Published: January 2004

Uncatalyzed transfer hydrogenations are H2‐transfer reactions in which donors that contain weakly bound hydrogen atoms undergo an H‐atom transfer (retrodisproportionation) onto an acceptor containing unsaturated bonds such as CC, CO, CN, NN, NO. Transfer hydrogenolyses are reactions in which σ bonds are cleaved upon additon of H2. These hydrogenations are terminated by H, transfer; they do not follow a radical‐chain mechanism. The initial steps of both types of reactions, H‐atom transfer, complement the bimolecular formation of 1,4‐diradicals from alkenes or heteroalkenes within the scope of bimolecular radical formation (Molecule‐Induced Radical Formation, MIRF). The title reactions play an important role in coal liquefaction, aromatization reactions with nitroarenes or quinones, and possibly biochemical dehydrogenations. This review focuses on mechanistic studies, structure–reactivity relationships, and current applications of these reactions.
Harmony and Dissonance in the Concert of Proton Motions
Authors: Schowen Richard L.
Published: January 2004

Jencks's principle is fulfilled in these examples of double proton transfer reactions in a variety of media. The reactions proceed in a concerted manner when a high‐energy intermediate needs to be avoided and a stepwise manner when this is not neccessary. This is the result of detailed studies by the research groups of Ahlberg (mutarotation of tetramethylglucose), Limbach (tautomerization of porphyrins), Petrich (tautomerization of 7‐azaindole), and Zewail (tautomerization of 7‐azaindole dimers in the gas phase), which are discussed here.
Symmetry, Space, Stars, and C60 (Nobel Lecture)
Authors: Kroto Harold
Published: January 2004

Basic research must continue to be supported! This is one of the conclusions clearly evident from the story behind the discovery of the fullerenes. The questions to which answers were originally sought would not have been posed within the current confines of programs aimed increasingly at applied research. This and the fascination associated with C60 and other members of the fullerene family are the central messages in this Nobel lecture.
Discovering the Fullerenes (Nobel Lecture)
Authors: Smalley Richard E.
Published: January 2004

Bucky get the prize—eleven years after the discovery of C60 in 1985, the realization that carbon makes this truncated isosahedral molecule, and larger geodesic cages, all by itself is honored with the Nobel Prize. Only with the development of laser‐vaporization cluster beam methods did the particular signification of C60 become apparent. Indeed the discovery process with respect to fullerenes and the properties of carbon is far from being complete.
Designing a Solid Catalyst for the Selective Low‐Temperature Oxidation of Cyclohexane to Cyclohexanone
Authors: Maschmeyer Thomas , Oldroyd Richard D. , Sankar Gopinathan , Thomas John M. , Shannon Ian J. , Catlow C. Richard A. , Klepetko John A. , Masters Anthony F. , Beattie James K.
Published: January 2004

By immobilizing the cobalt complex 1 on the glycine‐functionalized inner walls of mesoporous silica (MCM‐41), and efficient heterogeneous catalyst for the selective oxidation of cyclohexane to cyclohexanone with tert‐butyl hydroperoxide is produced. The detailed atomic structure of the active site during catalysis was determined by in‐situ X‐ray absorption spectroscopy. The findings are important for the design of new efficient oxidation catalysts.
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Chemistry and Molecular Biology of Transmissible Spongiform Encephalopathies
Authors: Edenhofer Frank , Weiss Stefan , Winnacker Ernst‐Ludwig , Famulok Michael
Published: January 2004

Prion diseases are currently in the spotlight. Among them, the Creutzfeldt–Jakob disease in humans, scrapie in sheep, and bovine spongiform encephalopathy, or mad cow disease, are most commonly known. The term “spongiform” refers to the characteristic appearance of the lesions found in affected brains. It is likely that prion diseases originate from a causative agent that replicates independently of nucleic acids. Current research assumes that a structural isoform of prion protein, the scrapie form PrPSc, is the responsible pathogen. The three‐dimensional structure, but not the amino acid sequence of the isoform differs from that of the normal cellular isoform, PrPc. According to a widely accepted hypothesis, the normal isoform of the protein is converted by an autocatalytic process into the scrapie form upon contact with the latter. This hypothesis has not yet been proven. However, considerable progress has been made in the last few years, which might provide answers to many open questions about prion diseases, the subject of this review.
Electron‐Transfer Transition States: Bound or Unbound—That is the Question!
Authors: Zipse Hendrik
Published: January 2004

A third pathway other than the known outer‐sphere and inner‐sphere processes needs to be considered, according to quantum mechanical studies of electron‐transfer (ET) processes. This new outer‐sphere reaction type, which proceeds via “bound” transition states, shows clear stereochemical preferences as well as significant intermolecular orbital overlap in the transition state. In contrast to inner‐sphere ET processes, no bond formation occurs during the reaction.
Gas‐Phase Enantiodifferentiation of Chiral Molecules: Chiral Recognition of 1‐Phenyl‐1‐propanol/2‐Butanol Clusters by Resonance Enhanced Multiphoton Ionization Spectroscopy
Authors: Pierini Macro , Troiani Anna , Speranza Maurizio , Piccirillo Susanna , Bosman Cesare , Toja Daniela , Giardini‐Guidoni Anna
Published: January 2004

A combination of high‐resolution spectroscopy and time‐of‐flight mass spectrometry was used for the first time to study the fundamental properties of supersonically expanded van der Waals complexes between (R)‐(+)‐1‐phneyl‐1‐propanol (PR) and the enantiomers of 2‐butanol (BR or BS) at the microscopic level. Chiral discrimination is based on the different fragmentation patterns of PRBR and PRBS or on the different bathochromic shift of their electronic band origin relative to that of pure PR.
ELF: The Electron Localization Function
Authors: Savin Andreas , Nesper Reinhard , Wengert Steffen , Fässler Thomas F.
Published: January 2004

The chemical bond is always considered from different points of view, depending or on the chemical and physical aspects to be examined. In both cases, description of the chemical bond are chosen that are appropriate for the particular research or application. Therefore, there are significant differences in the understanding as what constitutes chemical bonding. This is acceptable in practice but proves to be a hindrance for true interdisciplinarity. The concept of the chemical bond offer a firm basis upon which to forge links not only within chemistry but also to all related sciences. The general desire and the growing necessity for interdisciplinary collaboration requires a careful treatment of these concepts and, if possible, a tightening and standardization to a level that is widely acceptable and beneficial. In the age of tremendously fast development of computers and computer science, we believe that the electron localization function (ELF) provides a new description of the chemical bond for almost all classes of compounds. Its graphical language earns it the ultimate qualification for enhanced interdisciplinarity.
Cell‐Mediated Immunity in Virus Infections (Nobel Lecture)
Authors: Doherty Peter C.
Published: January 2004

“Being isolated in those pre‐fax and pre‐e‐mail days in Australia was a great advantage, as it allowed time to discuss and to think things through. We had outspoken and informed local critics, the freedom and resources to pursue our own ideas, and were given full credit for our efforts. Those of us who have senior roles in science need to do everything possible to ensure that comparable opportunities and environments remain available to young scientists.” With this provocative exhortation P.C. Doherty ended his Nobel Lecture.
Cellular Immune Recognition and the Biological Role of Major Transplantation Antigens (Nobel Lecture)
Authors: Zinkernagel Rolf M.
Published: January 2004

In the complex balance between virus and host the T cells and the properties of the virus play an important role. The unexpected discovery of the MHC‐restricted T cell recognition (MHC = major histocompatibility complex) prompted many important investigations. Which have led to a detailed understanding on a molecular level of T cell recognition of virus‐infected target cells. As a result of these findings the immunological specificity as well as the immunological memory, and above all, pathogenesis of infectionus diseases and of autoimmunity can be better understood.
Difluorovinylidene, F2CC:
Authors: Breidung Jürgen , Bürger Hans , Kötting Carsten , Kopitzky Rodion , Sander Wolfram , Senzlober Michael , Thiel Walter , Willner Helge
Published: January 2004

An alkyne–vinylidene isomerization is also possible with the difluoro compounds 1 and 2! Irradiation of 2 (λ = 193 nm) in an Ar matrix yields 1 exclusively. The IR spectrum agrees with results of novel abinitio calculations, which also suggest that 1—in sharp contrast to the vinylidenes RHCC—is protected against isomerization into 2 by a kinetic barrier. Irradiation with light with λ > 230nm converts 1 back into 2. Already at 35–42 K 1 adds CO and N2 to yields F2CCCO and F2CCNN, respectively.
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Olefin Metathesis in Organic Chemistry
Authors: Schuster Matthias , Blechert Siegfried
Published: January 2004

Transition metal catalyzed CC bond formations belong to the most important reactions in organic synthesis. One particularly interesting reaction is olefin metathesis, a metal‐catalyzed exchange of alkylidene moieties between alkenes. Olefin metathesis can induce both cleavage and formation of CC double bonds. Special functional groups are not necessary. Although this reaction—which can be catalyzed by numerous transition metals—is used in industry, its potential in organic synthesis was not recognized for many years. The recent abrupt end to this Sleeping‐Beauty slumber has several reasons. Novel catalysts can effect the conversion of highly fictionalized and sterically demanding olefins under mild reaction conditions and in high yields. Improved understanding of substrate–catalyst interaction has greatly contributed to the recent establishment of olefin metathesis as a synthetic method. In addition to the preparation of polymers with fine‐tuned characteristics, the metathesis today also provides new routes to compounds of low molecular weight. The highly developed ring‐closing metathesis has been proven to be key step in the synthesis of a growing number of natural products. At the same time interesting applications can be envisioned for newly developed variants of bimolecular metathesis. Improvements in the selective cross‐metathesis of acyclic olefins as well as promising attempts to include alkynes as viable substrates provide for a vivid development of the metathesis chemistry.
Topological Bifurcation Analysis: Electronic Structure of CH
Authors: Marx Dominik , Savin Andreas
Published: January 2004

Chemical bonds in highly fluxional molecules—are such description useful? Results of fully quantum‐mechanical calculations together with a novel analysis of the electron localization functions (ELF) of the protonated methane molecule CHgive a positive answer to this question. The concept of three‐center, two‐electron bonding is impressively supported by this method.
Designed Epothilones: Combinatorial Synthesis, Tubulin Assembly Properties, abd Cytotoxic Action against Taxol‐Resistant Tumor Cells
Authors: Nicolaou K. C. , Vourloumis Dionisios , Li Tianhu , Pastor Joaquin , Winssinger Nicolas , He Yun , Ninkovic Sacha , Sarabia Francisco , Vallberg Hans , Roschangar Frank , King N. Paul , Finlay M. Ray V. , Giannakakou Pareskevi , Verdier‐Pinard Pascal , Hamel Ernest
Published: January 2004

A library of epothilone A and B analogues, which was constructed by solid‐phase combinatorial synthesis using SMART Microreactors and solution chemistry, was screened in two different tubulin binding assays. Selected compounds were subjected to cytotoxicity studies against a number of cell lines, including Taxol‐resistant cells. Important structure–activity relationship emerged from these studies, which sets the stage for further discoveries and developments in the anticancer field.
N‐Heterocyclic Carbenes
Authors: Herrmann Wolfgang A. , Köcher Christian
Published: January 2004

The chemistry of N‐heterocyclic carbenes has long been limited to metal coordination compounds derived from azolium precursors, a development that was started by Öfele and Wanzlick in 1968. Since free carbenes are now available through the work of Arduengo (1991), a renaissance in this little‐recognized area of chemistry has occurred. A leading motive is the advantages of N‐heterocyclic carbenes as ligands in organometallic catalysts, where they extend the scope of application reached by phosphanes (functionalized, chiral, water‐soluble, and immobilized derivatives). The present review summarizes the state of the art with regard to synthesis, structure, bonding theory, metal coordination chemistry, and catalysis. Chelating, functionalized, chiral, and immobilized ligands can be generated and attached to metal centers in straightforward procedures under mild conditions. A wealth of new chemistry is thus opened. It is also shown how carbenes derived from imidazoles and triazoles behave as ligands in catalysis. It is reasonable to assume that N‐heterocyclic carbenes surpass the ubiquitous phosphanes as ligands in a number of organometallic catalytic reactions.
Electron‐Density Relaxation and Oppositely Signed Reaction Constants in Dual Substituent Parameter Relationships in Dediazoniation Reactions
Authors: Glaser Rainer , Horan Christopher J. , Zollinger Heinrich
Published: January 2004

Why are there so few exceptions to the fact that ρR/ρF= λ is positive?A straightforward theoretical basis is provided for the interpretation of the dediazoniation of benzenediazonium ions, one of the most prominent examples of the few reactions for which the reaction constants ρRand ρF[Eq. (1)] have opposite signs. The results support the model that describes CN bonding as synergistic N → C σ dative and C → N π backdative bonding. The analysis furnishes details about the electronic structure that cannot be deduced from physical–organic studies alone.equation image
Chemistry in Microstructured Reactors
Authors: Jähnisch Klaus , Hessel Volker , Löwe Holger , Baerns Manfred
Published: January 2004

The application of microstructured reactors in the chemical process industry has gained significant importance in recent years. Companies that offer not only microstructured reactors, but also entire chemical process plants and services relating to them, are already in existence. In addition, many institutes and universities are active within this field, and process‐engineering‐oriented reviews and a specialized book are available. Microstructured systems can be applied with particular success in the investigation of highly exothermic and fast reactions. Often the presence of temperature‐induced side reactions can be significantly reduced through isothermal operations. Although microstructured reaction techniques have been shown to optimize many synthetic procedures, they have not yet received the attention they deserve in organic chemistry. For this reason, this Review aims to address this by providing an overview of the chemistry in microstructured reactors, grouped into liquid‐phase, gas‐phase, and gas–liquid reactions.
Cover Picture: Chemistry in Microstructured Reactors (Angew. Chem. Int. Ed. 4/2004)
Authors: Jähnisch Klaus , Hessel Volker , Löwe Holger , Baerns Manfred
Published: January 2004

Microstructured reactors such as the SuperFocus Interdigital micromixer offer an alternative to conventional large‐scale techniques. Flow patterns with reduced layer thicknesses lead to enlarged reactive surfaces that result in short mixing times, and thus high‐throughput reactions can be achieved. In their review on page 406 ff. K. Jähnisch, V. Hessel, et al. examine the potential of this new and powerful technology.
Importance of addressing National Electrical Code® violations that result in unusual exposure to 60 Hz magnetic fields
Authors: Adams Jack , Samuel Bitler J. , Riley Karl
Published: January 2004

We evaluated wiring in multifamily developments containing National Electrical Code® (NEC®) violations as a source of unusual exposure to 60 Hz magnetic fields. Two methods were used in this evaluation: measurement and modeling. We measured the building wiring as a source of magnetic fields in six multifamily developments in Michigan. In this small sample, building wiring proved to be an important source of exposure in four of the six cases. In all four cases with exposure from building wiring, one or more NEC violations were involved. To supplement our measurement efforts, we used computer modeling to compare magnetic field exposure due to building wiring with magnetic field exposure from external power lines. Our calculations showed that where the building wiring has a NEC violation leading to net current loops, the exposure due to wiring is likely to be more important than that from external power lines. Our results support the results obtained in a recent study of the exposure of Californian K‐12 students to magnetic fields, where building wiring with one or more NEC violation was found to be the single most important exposure source. If 60 Hz magnetic fields are important to avoid, then improved enforcement of the NEC, as required by law, is perhaps the single most important mitigation policy to adopt. Bioelectromagnetics 25:102–106, 2004. © 2004 Wiley‐Liss, Inc.
Teratological studies of prenatal exposure of mice to a 20 kHz sawtooth magnetic field
Authors: Kim Sung‐Ho , Song Ji‐Eun , Kim Se‐ra , Oh Heon , Gimm Youn‐Myoung , Yoo Done‐Sik , Pack Jeong‐Ki , Lee Yun‐Sil
Published: January 2004

In order to evaluate the importance of gestational age in possible effects due to exposure to a 20 kHz sawtooth magnetic field, pregnant ICR mice at gestational 2.5–15.5 days post‐coitus, which is the most sensitive stage for the induction of major congenital malformations, were exposed in a carrousel irradiator. The mice were exposed to a 20 kHz intermediate frequency (IF) sawtooth magnetic field had a 6.5 μT peak intensity for 8 h/day. The animals were sacrificed on the 18th day of gestation; and the fetuses were examined for mortality, growth retardation, changes in head size, and other morphological abnormalities. From the above conditions, it is concluded that the exposure to a 20 kHz sawtooth magnetic field with 6.5 μT peak intensity does not inflict any adverse effect on fetuses of pregnant mice. Bioelectromagnetics 25:114–117, 2004. © 2004 Wiley‐Liss, Inc.
Cellular phone use does not acutely affect blood pressure or heart rate of humans
Authors: Tahvanainen Kari , Niño Juanita , Halonen Pirjo , Kuusela Tom , Laitinen Tomi , Länsimies Esko , Hartikainen Juha , Hietanen Maila , Lindholm Harri
Published: January 2004

A recent study raised concern about increase of resting blood pressure after a 35 min exposure to the radiofrequency (RF) field emitted by a 900 MHz cellular phone. In this randomized, double blind, placebo controlled crossover trial, 32 healthy subjects were submitted to 900 MHz (2 W), 1800 MHz (1 W) cellular phone exposure, and to sham exposure in separate sessions. Arterial blood pressure (arm cuff method) and heart rate were measured during and after the 35 min RF and sham exposure sessions. We evaluated cardiovascular responses in terms of blood pressure and heart rate during controlled breathing, spontaneous breathing, head‐up tilt table test, Valsalva manoeuvre and deep breathing test. Arterial blood pressure and heart rate did not change significantly during or after the 35 min RF exposures at 900 MHz or 1800 MHz, compared to sham exposure. The results of this study indicate that exposure to a cellular phone, using 900 MHz or 1800 MHz with maximal allowed antenna powers, does not acutely change arterial blood pressure and heart rate. Bioelectromagnetics 25:73–83, 2004. © 2004 Wiley‐Liss, Inc.
Pulsed electromagnetic field stimulation of bone marrow cells derived from ovariectomized rats affects osteoclast formation and local factor production
Authors: Chang Kyle , Hong‐Shong Chang Walter , Yu Yen‐Hsin , Shih Chung
Published: January 2004

This study examined the effects of a specific pulsed electromagnetic field (PEMF) stimulation on osteoclast formation in bone marrow cells from ovariectomized rats and to determine if the signal modulates the production of cytokines associated with osteoclast formation. Adult female Wistar rats were subjected to bilateral or sham ovariectomy, and primary bone marrow cells were harvested at 4 days (Subgroup I) and 7 days (Subgroup II) after surgery. Primary bone marrow cells were subsequently placed in chamber slides and set inside solenoids powered by a pulse generator (300 μs, 7.5 Hz) for 1 h per day for 9 days (OVX + PEMF group). Others (INT, SHAM, and OVX groups) were cultured under identical conditions, but no signal was applied. Recruitment and authentication of osteoclast‐like cells were evaluated by determining multinuclear, tartrate‐resistant acid phosphatase (TRAP) positive cells on day 10 of culture and by pit formation assay, respectively. The PEMF signal caused significant reductions in osteoclast formation in both Subgroups I (−55%) and II (−43%). Tumor necrosis factor‐α (TNF‐α), interleukin 1β (IL‐1β), and interleukin 6 (IL‐6) in OVX + PEMF group of Subgroup I were significantly reduced at 5, 7, and 9 days as compared to OVX group. The results found in this study suggest that osteoclastogenesis can be inhibited by PEMF stimulation, putatively due to a concomitant decrease in local factor production. Bioelectromagnetics 25:134–141, 2004. © 2004 Wiley‐Liss, Inc.
Geomagnetic field effect on cardiovascular regulation
Authors: Gmitrov Juraj , Gmitrova Anna
Published: January 2004

The goal of the present research was try to explain the physiological mechanism for the influence of the geomagnetic field (GMF) disturbance, reflected by the indices of the geomagnetic activity (K, Kp, Ak, and Ap indices), on cardiovascular regulation. One hundred forty three experimental runs (one daily) comprising 50 min hemodynamic monitoring sequences were carried out in rabbits sedated by pentobarbital infusion (5 mg/kg/h). We examined the arterial baroreflex effects on the short term blood pressure and heart rate (HR) variabilities reflected by the standard deviation (SD) of the average values of the mean femoral arterial blood pressure (MAP) and the HR. Baroreflex sensitivity (BRS) was estimated from blood pressure/HR response to intravenous (i.v.) bolus injections of vasoconstrictor (phenylephrine) and vasodilator (nitroprusside) drugs. We found a significant negative correlation of increasing GMF disturbance (Kp) with BRS (P = 0.008), HR SD (P =0.022), and MAP SD (P = 0.002) signifying the involvement of the arterial baroreflex mechanism. The abrupt change in geomagnetic disturbance from low (K = 0) to high (K = 4–5) values was associated with a significant increase in MAP (83 ± 5 vs. 99 ± 5 mm Hg, P = 0.045) and myocardial oxygen consumption, measured by MAP and HR product (24100 ± 1800 vs. 31000 ± 2500 mm Hg · bpm, P = 0.034), comprising an additional cardiovascular risk. Most likely, GMF affects brainstem and higher neural cardiovascular regulatory centers modulating blood pressure and HR variabilities associated with the arterial baroreflex. Bioelectromagnetics 25:92–101, 2004. © 2004 Wiley‐Liss, Inc.
Mobile phones and children: Is precaution warranted?
Authors: van Rongen Eric , Roubos Eric W. , van Aernsbergen Lodewijk M. , Brussaard Gert , Havenaar Johan , Koops Frans B.J. , van Leeuwen Floor E. , Leonhard Helmut K. , van Rhoon Gerard C. , Swaen Gerard M.H. , van de Weerdt Rik H.J. , Zwamborn A. Peter M.
Published: January 2004

Are there health related arguments to recommend that children limit their use of mobile telephones? The International Expert Group on Mobile Phones from the UK concluded so, but did not come up with convincing scientific data to back this statement. The Health Council of the Netherlands approached the problem by considering whether developmental arguments might be found, i.e., asking if there reason to believe that the heads of children are more susceptible to the electromagnetic fields emitted by mobile telephones than those of adults. It concluded that no major changes in head development occur after the second year of life that might point at a difference in electromagnetic susceptibility between children and adults. The Health Council therefore sees no reason to recommend limiting the use of mobile phones by children. Bioelectromagnetics 25:142–144, 2004. © 2004 Wiley‐Liss, Inc.
High Oxidation State Organometallic Chemistry in Aqueous Media: New Opportunities for Catalysis and Electrocatalysis
Authors: Poli Rinaldo
Published: January 2004

Molybdenum has been used as a case study for the rational development of a new domain of organometallic chemistry, combining oxo‐stabilized high oxidation state metals and aqueous media. The pH‐dependent conversion of oxo, hydroxo, and aqua ligands allows the opening of free coordination sites, while the use of a redox active metal opens possible pathways for coupled proton and electron transfer to and from activated substrates. While our work has so far only concentrated on synthesis and analytical investigations, the development of catalytic and electrocatalytic processes in water or aqueous media is a promising application of this new research area.
Enthalpy of Solution of 1,4‐Naphthoquinone in CO2 + n‐Pentane in the Critical Region of the Binary Mixture: Mechanism of Solubility Enhancement
Authors: Mu Tiancheng , Zhang Xiaogang , Liu Zhimin , Han Buxing , Li Zhonghao , Jiang Tao , He Jun , Yang Guanying
Published: January 2004

The enthalpy of solution (ΔsolvHm) and solubility of 1,4‐naphthoquinone in CO2 + n‐pentane were measured at 308.15 K in the critical region of the binary fluid. In order to study the effect of phase behavior of the mixed solvent on ΔsolvHm, the experiments were carried out in the supercritical (SC) and subcritical region of the binary solvent. The density of the mixed solvent in different conditions was determined. The isothermal compressibility (KT) of the mixed solvent, and the partial molar volume (Vn‐pentane) of n‐pentane in the solution were calculated. It was demonstrated that the ΔsolvHm was negative in all conditions. ΔsolvHm is nearly independent of pressure or density in all the solvents in a high‐density region, in which compressibility of the solvent is very small; this indicates that the intermolecular interaction between the solvent and the solute is similar to that for liquid solutions. It is very interesting that ΔsolvHm in the mixed SC fluid differs from the ΔsolvHm in mixed subcritical fluids. The absolute value of ΔsolvHm in the mixed SC fluid is close to that in pure SC CO2 in the high‐density region, and is much lower than that in pure SC CO2 in the low‐density region. In the mixed subcritical fluids, the ΔsolvHm is also close to that in the pure CO2 in the high‐density region. However, at the same density, the absolute value of ΔsolvHm in the binary subcritical fluid is larger than that in pure CO2 in the high‐compressible region of the mixed solvent. The main reason for this is that the degree of clustering in the SC solutions is small at the density in which the degree of clustering is large in the subcritical solutions. It can be concluded that solubility enhancement by n‐pentane in the mixed SC fluid is entropy driven. In contrast, the solubility enhancement by n‐pentane in subcritical fluids is enthalpy driven. The intermolecular interaction in the SC solutions and subcritical solutions can be significantly different even if their densities are the same.
Sol–Gel Polycondensation of Tetraethyl Orthosilicate (TEOS) in Sugar‐Based Porphyrin Organogels: Inorganic Conversion of a Sugar‐Directed Porphyrinic Fiber Library through Sol–Gel Transcription Processes
Authors: Kawano Shin‐ichiro , Tamaru Shun‐ichi , Fujita Norifumi , Shinkai Seiji
Published: January 2004

Sugar‐appended porphyrins (1 a–e) with monosaccharide groups at their periphery have been rationally designed for a new class of gelating reagents. A few of these compounds have the tendancy to form one‐dimensional aggregates stable enough to show successful gelation ability for DMF–alcohol mixed solvents. The aggregation mode in the specific columnar super structures has been evaluated in detail by UV‐visible spectrometry (UV/Vis), circular dichroism (CD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). All UV‐visible spectra of sugar‐appended porphyrinic gels obtained from 1 a–c exhibit Soret band absorptions, which shift to lower wavelength and are significantly broadened. This phenomenon indicates that these porphyrin cores strongly interact with each other in an H‐aggregate fashion, which drives the generation of a one‐dimensional porphyrin‐stacking array. The CD spectra of the organogels from 1 a and 1 b, which are in anomers, exhibit an almost symmetric pattern, whereas the gel from 1 c gives a completely different pattern. This implies that the gel fibrils wind themselves in a right‐ or left‐handed fashion; this reflects chirality in the specific molecular structure of the gelators. The results from SEM for the gel fibrils are in good agreement with the CD patterns. The gel fibrils in 1 a possess left‐handed helicity, whereas those in 1 b wind themselves right‐handedly. Macroscopic helical morphology reflects the microscopic structure well at a molecular level, which gives structural variety of the gel fibrils, which can be defined by the sugar library. Inorganic conversion of the organic helical fibrils by a sol–gel transcription process successfully gives the helical‐silica structures, which finely inherit the organic morphology. A striking observation is that a unimolecular porphyrin‐stacking array is also transcribed into silica fibers when the optimized sol–gel reaction conditions are selected. A sugar‐based organic‐fiber library in porphyrinic gels thus provides a variety of inorganic materials through the sol–gel transcription process.
Chemical Tailoring of Porous Silica Xerogels: Local Structure by Vibrational Spectroscopy
Authors: Fidalgo Alexandra , Ilharco Laura M.
Published: January 2004

Monolithic porous silica xerogels were synthesized by the sol–gel process, and their local structure was analysed by vibrational spectroscopy. The silica alcogels were prepared by a two‐step hydrolytic polycondensation of tetraethoxysilane (TEOS) in isopropanol, with a water/TEOS molar ratio of 4. The hydrolysis step was catalysed by hydrochloric acid (HCl), with different HCl/TEOS molar ratios (ranging from 0.0005 to 0.009), and the condensation step was catalysed by ammonia (NH3), with different NH3/HCl molar ratios (ranging from 0.7 to 1.7). After appropriate ageing, the alcogels were washed with isopropanol and subcritically dried at atmospheric pressure. The diffuse reflectance infrared Fourier transform (DRIFT) spectra were analysed in terms of the main siloxane rings that form the silica particles, taking into account the splitting of the νasSiOSi mode into pairs of longitudinal and transverse optic components, by long‐range Coulomb interactions. It was proven that the proportion of residual silanol groups (which correlates with hydrophilicity), and the fraction of siloxane 6‐rings (which correlates with porosity) may be tailored by adequate catalytic conditions, mostly by the hydrolysis pH. This was explained in terms of the reactions' mechanisms taking place in the two‐step sol–gel process followed.
Stereocontrolled Synthesis of 8,11‐Dideoxytetrodotoxin, An Unnatural Analogue of Puffer Fish Toxin
Authors: Nishikawa Toshio , Urabe Daisuke , Yoshida Kazumasa , Iwabuchi Tomoko , Asai Masanori , Isobe Minoru
Published: January 2004

8,11‐Dideoxytetrodotoxin, an unnatural tetrodotoxin analogue, was synthesized in a highly stereoselective manner from a common intermediate from our synthetic studies on tetrodotoxin. The key features in the synthesis were as follows: neighboring group participation of a trichloroacetamide to allow regioselective and stereoselective hydroxylation, protection of a δ‐hydroxylactone as an ortho ester, and guanidine installation through the use of Boc‐protected isothiourea. Global deprotection of the fully protected intermediate under acidic conditions gave 8,11‐dideoxytetrodotoxin, which exhibited very weak biological activities.
Photohydroxylation of 1,4‐Benzoquinone in Aqueous Solution Revisited
Authors: von Sonntag Justus , Mvula Eino , Hildenbrand Knut , von Sonntag Clemens
Published: January 2004

In water, photolysis of 1,4‐benzoquinone,Qgives rise to equal amounts of 2‐hydroxy‐1,4‐benzoquinoneHOQand hydroquinoneQH2which are formed with a quantum yield ofΦ=0.42, independent of pH andQconcentration. By contrast, the rate of decay of the triplet (λmax=282 and ∼410 nm) which is the precursor of these products increases nonlinearly (k=(2→3.8)×106s−1) with increasingQconcentration ((0.2→10) mM). The free‐radical yield detected by laser flash photolysis after the decay of the triplet also increases with increasingQconcentration but follows a different functional form. These observations are explained by a rapid equilibrium of a monomeric tripletQ*and an exciplexQ2*(K=5500±1000 M−1). WhileQ*adds water and subsequent enolizes into 1,2,4‐trihydroxybenzenePh(OH)3,Q2*decays by electron transfer and water addition yielding benzosemiquinone.QHand.OH adduct radicals.QOH. The latter enolizes to the 2‐hydroxy‐1,4‐semiquinone radical.Q(OH)Hwithin the time scale of the triplet decay and is subsequently rapidly (microsecond time scale) oxidized byQtoHOQwith the concomitant formation of.QH. On the post‐millisecond time scale, that is, when.QHhas decayed,Ph(OH)3is oxidized byQyieldingHOQandQH2as followed by laser flash photolysis with diode array detection. The rate of this pH‐ andQconcentration‐dependent reaction was independently determined by stopped‐flow. This shows that there are two pathways to photohydroxylation; a free‐radical pathway at high and a non‐radical one at lowQconcentration. In agreement with this, the yield ofPh(OH)3is most pronounced at lowQconcentration. In the presence of phosphate buffer,Q*reacts with H2PO4−giving rise to an adduct which is subsequently oxidized byQto 2‐phosphato‐1,4‐benzoquinoneQP. The current view that.OH is an intermediate in the photohydroxylation ofQhas been overturned. This view had been based on the observation of the.OH adduct of DMPO whenQis photolyzed in the presence of this spin trap. It is now shown thatQ*/Q2*oxidizes DMPO (k≈1×108 M−1 s−1) to its radical cation which subsequently reacts with water.Q*/Q2*react with alcohols by H abstraction (rates in units ofM−1 s−1): methanol (4.2×107), ethanol (6.7×107), 2‐propanol (13×107) and tertiary butyl alcohol (∼0.2×107). DMSO (2.7×109) and O2(∼2×109) act as physical quenchers.
Synthesis of Scroll‐Type Composite Microtubes of Mo2C/MoCO by Controlled Pyrolysis of Mo(CO)6
Authors: Li Xiao‐Lin , Li Ya‐Dong
Published: January 2004

Composite microtubes of Mo2C/MoCO have been synthesized for the first time under well‐controlled conditions by thermal decomposition of Mo(CO)6 at about 600 °C. Here, thermal stability and phase transition of the products, as well as the influence of reaction temperature and argon flow rate, have been carefully investigated. All samples were characterized by X‐ray powder diffraction (XRD), scanning electron microscopy (SEM), and X‐ray photoelectron spectroscopy (XPS). The reaction model and rolling mechanism were proposed on the basis of the experimental facts.
Solid‐Phase Synthesis of 89 Polyamine‐Based Cationic Lipids for DNA Delivery to Mammalian Cells
Authors: Yingyongnarongkul Boon‐ek , Howarth Mark , Elliott Tim , Bradley Mark
Published: January 2004

The ability of non‐viral gene delivery systems to overcome extracellular and intracellular barriers is a critical issue for future clinical applications of gene therapy. In recent years much effort has been focused on the development of a variety of DNA carriers, and cationic liposomes have become the most common non‐viral gene delivery system. Solid‐phase synthesis was used to produce three libraries of polyamine‐based cationic lipids with diverse hydrophobic tails. These were characterised, and structure‐activity relationships were determined for DNA binding and transfection ability of these compounds when formulated as cationic liposomes. Two of the cationic lipids produced high‐efficiency transfection of human cells. Surprisingly, these two compounds were from the library with two headgroups and one aliphatic tail, a compound class regarded as detergent‐like and little investigated for transfection. These cationic lipids are promising reagents for gene delivery and illustrate the potential of solid‐phase synthesis methods for lipoplex discovery.