bluuebunny/crossref_metadata_2025 huggingface dataset:
Scanning Tunneling Microscopy Investigations of Self‐Organized Poly(3‐hexylthiophene) Two‐Dimensional Polycrystals
Authors: Grévin B. , Rannou P. , Payerne R. , Pron A. , Travers J.‐P.
Published: June 2003

Scanning tunneling microscopy images of thin films of polythiophene cast on highly oriented pyrolytic graphite gives structural insight on both local (chain‐packing and conformational) and mesoscopic (polycrystal structure) scales. It is revealed that 2D polycrystals form mono‐domains (20 nm parallel and perpendicular to the polymer backbone) (see Figure), partially interconnected by folded chains.
Highly Anisotropic Opto‐electronic Properties of Aligned Films of Self‐Assembled Platinum Molecular Wires
Authors: Debije M.G. , de Haas M.P. , Savenije T.J. , Warman J.M. , Fontana M. , Stutzmann N. , Caseri W.R. , Smith P.
Published: June 2003

Self‐assembled columns of alternating tetrachloro‐ and tetraalkylaminoplatinum moieties form stable, highly oriented, optically anisotropic films on a friction‐deposited polytetrafluoroethylene surface (see Figure). Charge transport in the films is rapid (mobility ≥ ca. 10–2 cm2 V–1 s–1) and highly one‐dimensional along the axis of the columns (anisotropy ≥ 20), further substantiating the potential application of these materials in molecular opto‐electronic devices.
Cell‐Responsive Synthetic Hydrogels
Authors: Lutolf M.P. , Raeber G.P. , Zisch A.H. , Tirelli N. , Hubbell J.A.
Published: June 2003

Synthetic biomaterial matrices have been formed in the presence of cells by a Michael‐type addition reaction between a difunctional protease substrate peptide, a monofunctional cell adhesion peptide, and a tetrafunctional poly(ethylene glycol). These materials locally degrade in response to cell‐surface proteases, allowing cells to create paths for 3D cell migration (see Figure).
Fabrication of the MgCxCo3 Ternary Phase Encapsulated in Carbon Nanoflasks
Authors: Rana R.K. , Xu X.N. , Yeshurun Y. , Gedanken A.
Published: June 2003

Carbon nanoflasks encapsulating the MgCxCo3 ternary phase have been synthesized. Structural and compositional analyses of the encapsulated particles (see Figure) revealed that the MgCxCo3 particles are crystalline and well protected by the covering graphene layers. The encapsulated particles exhibit mixed superparamagnetic and ferromagnetic behavior.
Stimulated Emission from a Needle‐like Single Crystal of an End‐Capped Fluorene/Phenylene Co‐oligomer
Authors: Zhu X. , Gindre D. , Mercier N. , Frère P. , Nunzi J.‐M.
Published: June 2003

Owing to light confinement, naturally shaped needle‐like organic semiconductor single crystals of an end‐capped fluorene/phenylene co‐oligomer provide low‐threshold unidimensional stimulated emission. The Figure shows a photograph of the ∼1.5 mm long crystals, and gain‐narrowed normalized emission spectra from a polycrystal (dotted line) and a single crystal at 700 μJ cm–2 (unbroken line).
Chemical Neuroimmunology: Health in a Nutshell Bidirectional Communication between Immune and Stress (Limbic‐Hypothalamic‐Pituitary‐Adrenal) Systems
Authors: Lozovaya Natalya , Miller Andrew D.
Published: June 2003

Stress is a ubiquitous and pervasive part of modern life that is frequently blamed for causing a plethora of diseases and other discomforting medical conditions. All higher organisms, including humans, experience stress in the form of a wide variety of stressors that range from environmental pollutants and drugs to traumatic events or self‐induced trauma. Stressors registered by the central nervous system (CNS) generate physiological stress responses in the body (periphery) by means of the limbic‐hypothalamic‐pituitary‐adrenal (LHPA) axis. This LHPA axis operates through the use of chemical messengers such as the stress hormones corticotropin‐releasing hormone (CRH) and glucocorticoids (GCs). Under conditions of frequent exposure to acute stress and/or chronic, long‐term exposure to stress, the LHPA axis becomes dysfunctional and in the process frequently overproduces both CRH and GCs, which results in many mild to severely toxic side effects. Bidirectional communication between the LHPA axis and immune/inflammatory systems can dramatically potentiate these side effects and create environments in the CNS and periphery ripe for the triggering and/or promotion of tissue degeneration and disease. This review aims to present as far as possible a molecular view of the processes involved so as to provide a bridge from the diffuse range of studies on molecular structure and receptor interactions to the burgeoning biological and medical literature that describes the empirical interplay between stress and disease. We hope that our review of this fast‐growing field, which we christen chemical neuroimmunology, will give a clear indication of the striking range and depth of current molecular, cellular and medical evidence linking stress hormones to degeneration and disease. In so doing, we hope to provide encouragement for others to become interested in this critical and far‐reaching field of research, which is very much at the heart of many important disease processes and very much a critical part of the crucial interface between chemistry and biology.
A Molecular Mechanism of Enantiorecognition of Tertiary Alcohols by Carboxylesterases
Authors: Henke Erik , Bornscheuer Uwe T. , Schmid Rolf D. , Pleiss Jürgen
Published: June 2003

Carboxylesterases containing the sequence motif GGGX catalyze the hydrolysis of esters of chiral tertiary alcohols, albeit with only low to moderate enantioselectivity, for three model substrates (linalyl acetate, methyl‐1‐pentin‐1‐yl acetate, 2phenyl‐3‐butin‐2‐yl acetate). In order to understand the molecular mechanism of enantiorecognition and to improve enantioselectivity for this interesting substrate class, the interaction of both enantiomers with the substrate binding sites of acetylcholinesterases and p‐nitrobenzyl esterase from Bacillus subtilis was modeled and correlated to experimental enantioselectivity. For all substrate–enzyme pairs, enantiopreference and ranking by enantioselectivity could be predicted by the model. In p‐nitrobenzyl esterase, one of the key residues in determining enantioselectivity was G105: exchange of this amino acid for an alanine residue led to a sixfold increase of enantioselectivity (E=19) towards 2phenyl‐3‐butin‐2‐yl acetate. However, the effect of this mutation is specific: the same mutant had the opposite enantiopreference towards the substrate linalyl acetate. Thus, depending on the substrate structure, the same mutant has either increased enantioselectivity or opposite enantiopreference compared to the wild‐type enzyme.
Mollusk Shell Acidic Proteins: In Search of Individual Functions
Authors: Gotliv Bat‐Ami , Addadi Lia , Weiner Steve
Published: June 2003

Acidic proteins play a major role in the biomineralization process. These proteins are generally thought to control mineral formation and growth. Thus, characterization of individual acidic proteins is important as a first step toward linking function to individual proteins, which is our ultimate goal. In order to characterize the protein(s) responsible for the assemblage of biominerals, a new gel electrophoresis fixing and staining protocol was developed and many, if not all of the acidic proteins were visualized on the gel for the first time. In an in vitro assay we show that proteins extracted from an aragonitic shell layer induce the formation of amorphous calcium carbonate prior to its transformation into the aragonitic crystalline form. This study removes some major obstacles in the characterization of acidic proteins and sheds more light on the functions of these proteins in the biomineralization process.
One‐Pot TiO2‐Catalyzed Synthesis of Nucleic Bases and Acyclonucleosides from Formamide: Implications for the Origin of Life
Authors: Saladino Raffaele , Ciambecchini Umberto , Crestini Claudia , Costanzo Giovanna , Negri Rodolfo , Di Mauro Ernesto
Published: June 2003

A novel one‐pot TiO2‐catalyzed synthesis of nucleobases and acyclonucleosides from formamide is reported. Since formamide can be formed under prebiotic conditions, these reactions have implications for the origin of life. While a number of purine derivatives have been found as products of non‐TiO2‐catalyzed reactions, important compounds that would not otherwise occur (namely, thymine, 5hydroxymethyluracil, and acyclonucleosides) are formed in acceptable yields by TiO2‐catalyzed reactions. Moreover, TiO2 selectively affects the rates of degradation of nucleobases, as single units and when embedded in polynucleotides.
Cover Picture: Selective Protein Degradation by Ligand‐Targeted Enzymes: Towards the Creation of Catalytic Antagonists (ChemBioChem 6/2003)
Authors: Davis Benjamin G. , Sala Rafael F. , Hodgson David R. W. , Ullman Astrid , Khumtaveeporn Kanjai , Estell David A. , Sanford Karl , Bott Richard R. , Jones J. Bryan
Published: June 2003

The cover picture shows a ligand‐targeted proteinase enzyme or “catalytic antagonist” acting as a molecular angler fish: By precisely positioning different binding ligands (L) around the active site “mouth” of a degradative proteinase enzyme, target proteins (TP) can be plucked from solution, locked in position adjacent to the catalytic triad “jaws”, and in this way readily and specifically degraded. The hunting strategy of the deep sea angler fish, which uses a lure above its mouth, illustrates this principle. Further details can be found in the article by B. Davis, R. R. Bott, J. B. Jones et. al. on pp. 533–537.
Synthesis and Properties of [CoCp*(2,5‐PC4tBu2H2)]: The First Monophosphacobaltocene
Authors: Burney Claire , Carmichael Duncan , Forissier Kareen , Green Jennifer C. , Mathey François , Ricard Louis
Published: June 2003

The reduction of the phosphacobaltocenium salt [CoCp*(2,5‐PC4tBu2H2)]+[BPh4]− (3; Cp*=pentamethylcyclopentadienyl) by magnesium in tetrahydrofuran (THF) furnishes the stable air‐sensitive phosphacobaltocene [CoCp*(2,5‐PC4tBu2H2)] (4) in yields of up to 80 %. The crystal structure of 4 shows long CoCα and short CαCβbonds in the phospholyl ligand, consistent with a semi‐occupied molecular orbital (SOMO) having a″ symmetry. A combined Amsterdam density functional (ADF)/photoelectron spectroscopic study, which confirms this assignment, gives ionisation energies (IE) of 5.02 eV from the SOMO and 8.89 eV from the phosphorus “lone pair”. A comparison of cyclovoltammograms for 3 and the corresponding cyclopentadienyl complex [CoCp*(1,3‐C5tBu2H3)]+ [BPh4]− (5) shows that replacing a CH group by an sp2 phosphorus atom results in an anodic first reduction potential shift of 0.29 V.
Interplay between Solvent and Counteranion Stabilization of Highly Unsaturated Rhodium(III) Complexes: Facile Unsaturation‐Induced Dearomatization
Authors: Gandelman Mark , Konstantinovski Leonid , Rozenberg Haim , Milstein David
Published: June 2003

Abstraction of the chloride ligand from the PCN‐based chloromethylrhodium complex 2 by AgX (X=BF4−, CF3SO3−) or a direct C–C cleavage reaction of the PCN ligand 1 with [(coe)2Rh(solv)n]+X− (coe=cyclooctene) lead to the formation of the coordinatively unsaturated rhodium(III) complexes 3. Compound 3 a (X=BF4−) exhibits a unique medium effect; the metal center is stabilized by reversible coordination of the bulky counteranion or solvent as a function of temperature. Reaction of [(PCN)Rh(CH3)(Cl)] with AgBArf in diethyl ether leads to an apparent rhodium(III) 14‐electron complex 4, which is stabilized by reversible, weak coordination of a solvent molecule. This complex coordinates donors as weak as diethyl ether and dichloromethane. Upon substitution of the BF4− ion in [(PCN)Rh(CH3)]BF4 by the noncoordinating BArf− ion in a noncoordinating medium, the resulting highly unsaturated intermediate undergoes a 1,2‐metal‐to‐carbon methyl shift, followed by β‐hydrogen elimination, leading to the Rh‐stabilized methylene arenium complex 5. This process represents a unique mild, dearomatization of the aromatic system induced by unsaturation.
Photoinduced Electron Transfer between the Interlocked Components of Porphyrin Catenanes: Effect of the Presence of Nonequivalent Reduction Sites on the Charge Recombination Rate
Authors: Flamigni Lucia , Talarico Anna Maria , Serroni Scolastica , Puntoriero Fausto , Gunter Maxwell J. , Johnston Martin R. , Jeynes Tyrone P.
Published: June 2003

[2]Catenanes made up of several polyether‐strapped porphyrin macrocycles interlinked with the cyclic electron acceptor cyclobis(paraquat‐p‐phenylene) were spectroscopically, photophysically, and electrochemically characterized. The catenanes exhibit very rich redox behavior due to the presence of several different and interacting electro‐active subunits. The redox patterns represent useful “fingerprints” that provide detailed information on the electronic interactions and the chemical environments that the electroactive subunits experience in the supramolecular arrays. A photoinduced electron transfer from the porphyrin excited state (charge separation CS) occurs with τ=20 ps in the catenanes with a larger strap and faster than 20 ps (instrumental resolution) in the catenanes with a shorter strap. The resulting charge‐separated state recombines to the ground state (charge recombination CR) with lifetimes similar in all cases, 41±4 ps. Comparison of the electron transfer rates CS and CR in the host–guest complexes of the same porphyrins with the noncyclic electron acceptor paraquat, indicate slower reactions in the [2]catenanes. This behavior is assigned to the different separation between reacting partners determined by the type of bond (weak interaction or mechanical) and to a two‐step consecutive electron transfer to different sites of the macrocyclic electron acceptor in the catenanes which retards charge recombination.
The 1Δg Dioxygen Ene Reaction with Propene: A Density Functional and Multireference Perturbation Theory Mechanistic Study
Authors: Maranzana Andrea , Ghigo Giovanni , Tonachini Glauco
Published: June 2003

This study aims to determine whether a balance between concerted and non‐concerted pathways exists, and in particular to ascertain the possible role of diradical/zwitterion or peroxirane intermediates. Three non‐concerted pathways, via 1) diradical or 2) peroxirane intermediates, and 3) by means of hydrogen‐abstraction/radical recoupling, plus one concerted pathway (4), are explored. The intermediates and transition structures (TS) are optimized at the DFT(MPW1K), DFT(B3LYP) and CASSCF levels of theory. The latter optimizations are followed by multireference perturbative CASPT2 energy calculations. 1) The polar diradical forms from the separate reactants by surmounting a barrier (ΔE${^{\ne }_{{\rm MPW}1{\rm K}}}$=12, ΔE${^{\ne }_{{\rm B}3{\rm LYP}}}$=14, and ΔE${^{\ne }_{{\rm CASPT}2}}$=16 kcal mol−1 and can back‐dissociate through the same TS, with barriers of 11 (MPW1K) and 8 kcal mol−1 (B3LYP and CASPT2). The diradical to hydroperoxide transformation is easy at all levels (ΔE${^{\ne }_{{\rm MPW}1{\rm K}}}$<4, ΔE${^{\ne }_{{\rm B}3{\rm LYP}}}$=1 and ΔE${^{\ne }_{{\rm CASPT}2}}$=1 kcal mol−1). 2) Peroxirane is attainable only by passing through the diradical intermediate, and not directly, due to the nature of the critical points involved. It is located higher in energy than the diradical by 12 kcal mol−1, at all theory levels. The energy barrier for the diradical to cis‐peroxirane transformation (ΔE≠=14–16 kcal mol−1) is much higher than that for the diradical transformation to the hydroperoxide. In addition, peroxirane can very easily back‐transform to the diradical (ΔE≠<3 kcal mol−1). Not only the energetics, but also the qualitative features of the energy hypersurface, prevent a pathway connecting the peroxirane to the hydroperoxide at all levels of theory. 3) The last two‐step pathway (hydrogen‐abstraction by 1O2, followed by HOO‐allyl radical coupling) is not competitive with the diradical mechanism. 4) A concerted pathway is carefully investigated, and deemed an artifact of restricted DFT calculations. Finally, the possible ene/[π2+π2] competition is discussed.
Palladium(0)‐Catalyzed Intramolecular [2+2+2] Alkyne Cyclotrimerizations with Electron‐Deficient Diynes and Triynes
Authors: Yamamoto Yoshihiko , Nagata Asako , Nagata Hitomi , Ando Yoji , Arikawa Yasuhiro , Tatsumi Kazuyuki , Itoh Kenji
Published: June 2003

In the presence of 2.5 mol % of [Pd2(dba)3] (dba=dibenzylideneacetone) and 5 mol % of PPh3, nearly equimolar amounts of dimethyl nona‐2,7‐diyne‐1,9‐dioate derivatives (diyne diesters) and dialkyl acetylenedicarboxylates were allowed to react in toluene at 110 °C to afford [2+2+2] cycloadducts in moderate‐to‐good yields. Similarly, dimethyl trideca‐2,7,12‐triyne‐1,13‐dioate derivatives (triyne diesters) were catalytically transformed into phthalic acid ester analogues in excellent yields. To gain insight into the mechanism of these intramolecular alkyne cyclotrimerizations, stoichiometric reactions of [Pd2(dba)3] with a diyne diester and a triyne diester bearing ether tethers were conducted in acetone at room temperature to furnish an oligomeric bicyclopalladacyclopentadiene and a Pd0 triyne complex, respectively. The structures of these novel complexes were unequivocally determined by Xray structure analysis. The isolated triyne complex was heated at 50 °C or treated with PPh3 in acetone at room temperature to afford the arene product. Furthermore, the same complex catalyzed the triyne cyclization with or without PPh3.
Columnar Mesomorphism from Hemi‐Disklike Metallomesogens Derived from 2,6‐Bis[3′,4′,5′‐tri(alkoxy)phenyliminomethyl]pyridines (L): Crystal and Molecular Structures of [M(L)Cl2] (M=Mn, Ni, Zn)
Authors: Morale Francesca , Date Richard W. , Guillon Daniel , Bruce Duncan W. , Finn Rachel L. , Wilson Claire , Blake Alexander J. , Schröder Martin , Donnio Bertrand
Published: June 2003

Four new series of non‐disklike complexes of general formula [MCl2(Ln)] based upon substituted 2,6‐bis(3′,4′,5′‐trialkoxyphenyliminomethyl)pyridine ligands (Ln) and with M=ZnII, CoII, MnII, and NiII have been prepared and examined for liquid crystallinity. A complete analysis of the thermal behavior by polarized‐light optical microscopy, differential scanning calorimetry, and small‐angle Xray scattering revealed a rich and varied mesomorphism. Moreover, the high thermal stability of the compounds leads to rather extended mesomorphic ranges. The nature and thermal stability of each mesophase depend on both the length of the six terminal alkoxy chains, n (n=8, 10, 12, 14, 16), and on the metal ions. As demonstrated by small‐angle Xray diffraction experiments, the mesomorphism of these complexes is solely of the columnar type. One compound shows an oblique columnar phase, while most of them show a hexagonal columnar phase, Colh, and several types of rectangular columnar phase, Colr. Xray single‐crystal structures obtained for three methoxy derivatives confirm the 1:1 metal–ligand stoichiometry of the complexes, in which the metal is pentacoordinate with a distorted, trigonal bipyramidal geometry. The crystalline structures also reveal the existence of some columnar organization in the solid state, the columns resulting from an alternated stacking of the complexes in one direction. By combining these results with those obtained from dilatometry experiments, a model for the molecular organization within the mesophases is proposed in which an antiparallel arrangement of the metallomesogens is retained in the mesophase.
Electronic Coupling in a Highly Preorganized Bimetallic Complex Comprising Pyrazolate‐Bridged CpMn(CO)2 Moieties
Authors: Röder Jens C. , Meyer Franc , Hyla‐Kryspin Isabella , Winter Rainer F. , Kaifer Elisabeth
Published: June 2003

By means of a multistep synthetic procedure a dimanganese complex has been prepared, in which a N,N′‐bridging pyrazolate ligand spans two CpMn(CO)2 subunits in a highly preorganized chelate arrangement. The Xray crystallographic analyses of the MnIMnI complex K+1− and of its non‐chelate precursor complex elucidate details of the molecular structure, in particular an unusual pyrazolate binding mode in the solid state and intertwining of the CO ligands in the crowded bimetallic array 1−. The MnIMnI compound (1−), the mixed‐valent MnIMnII (1), and the oxidized MnIIMnII form (1+) have been characterized by various analytical and spectrosopic methods, such as electrochemistry, variable‐temperature EPR spectroscopy, IR spectroelectrochemistry, and UV/Vis/NIR spectroelectrochemistry as well as by DFT and TD‐DFT calculations. Strong electronic coupling in the mixed‐valent complex is observed, but time‐ (and temperature‐) dependent valence detrapping occurs, thus placing 1 in class II according to the Robin and Day assignment, close to the class II/III transition. From variable‐temperature EPR spectroscopy a rough estimate of the activation energy and rate for thermal electron transfer can be deduced, with Eth≠=13.6 kJ mol−1 and kth=2.6×1010 s−1 at 298 K. Unexpectedly, no intervalence CT transition for 1 is detected in solution, but one appears in the optical spectrum of solid 1. The conclusions drawn from experiments are fully supported by DFT calculations that were carried out for all three forms of the dimanganese complex. A broken symmetry treatment for mixed‐valent 1 reveals almost perfect localization of both spin and charge on one Mn center. According to TD‐DFT the first excited states of 1 give rise to the IT processes in the NIR‐energy region, as observed in the solid‐state spectrum. The HOMOs are located at the Mn ions and are favorably arranged for π interactions with the bridging pyrazolate.
Rhodium(I) and Rhodium(III) Complexes Formed by Coordination and CH Activation of Bulky Functionalized Phosphanes
Authors: Canepa Giuseppe , Brandt Carsten D. , Ilg Kerstin , Wolf Justin , Werner Helmut
Published: June 2003

The reaction of [{RhCl(C8H14)2}2] (2) with iPr2PCH2CH2C6H5 (L1) led, via the isolated dimer [{RhCl(C8H14)(L1)}2] (3), to a mixture of three products 4 a–c, of which the dinuclear complex [{RhCl(L1)2}2] (4 a) was characterized by Xray crystallography. The mixture of 4a–c reacts with CO, ethene, and phenylacetylene to give the square‐planar compounds trans‐[RhCl(L)(L1)2] (L=CO (5), C2H4 (6), CCHPh (9)). The corresponding allenylidene(chloro) complex trans‐[RhCl(CCCPh2)(L1)2] (11), obtained from 4 a–c and HCCC(OH)Ph2 via trans‐[RhCl{CCHC(OH)Ph2}(L1)2] (10), could be converted stepwise to the related hydroxo, cationic aqua, and cationic acetone derivatives 12—14, respectively. Treatment of 2 and [{RhCl(C2H4)2}2] (7) with two equivalents of tBu2PCH2CH2C6H5 (L2) gave the dimers [{RhCl(C8H14)(L2)}2] (15) and [{RhCl(C2H4)(L2)}2] (16), which both react with L2 in the molar ratio of 1:2 to afford the five‐coordinate aryl(hydrido)rhodium(III) complex [RhHCl(C6H4CH2CH2PtBu2‐κ2C,P)(L2)] (17) by CH activation. The course of the reactions of 17 with CO, H2, PhCCH, HCl, and AgPF6, leading to the compounds 19–21, 24, and 25 a, respectively, indicate that the coordinatively unsaturated isomer of 17 with the supposed composition [RhCl(L2)2] is the reactive species. Labeling experiments using D2, DCl, and PhCCD support this proposal. With either [Rh(C8H14)(η6‐L2‐κP]PF6 or [Rh(C2H4)(η6‐Ln‐κP]PF6 (n=1 and 2) as the starting materials, the corresponding halfsandwich‐type complexes 27, 28, and 32 were obtained. The nonchelating counterpart of the dihydrido compound 32 with the composition [RhH2(PiPr3)(η6‐C6H6)]PF6 (35) was prepared stepwise from [Rh(C2H4)(PiPr3)(η6‐C6H6)]PF6 and H2 in acetone via the tris(solvato) species [RhH2(PiPr3)(acetone)3]PF6 (34) as intermediate. The synthesis of the bis(chelate) complex [Rh(η4‐C8H12)(C6H5OCH2CH2PtBu2‐κ2O,P)]BF4 (39) is also described. Besides 4 a, the compounds 17, 25 a, and 39 have been characterized by Xray crystal structure analysis.
Reaction of Enol Ethers with Alkynes Catalyzed by Transition Metals: 5exo‐digversus 6endo‐digCyclizations via Cyclopropyl Platinum or Gold Carbene Complexes
Authors: Nevado Cristina , Cárdenas Diego J. , Echavarren Antonio M.
Published: June 2003

The intramolecular reaction of enol ethers with alkynes in methanol is catalyzed by electrophilic PtII, PdII, and AuIIIchlorides and by a CuIcomplex to give five‐ or six‐membered rings bearing dimethyl acetals. The reaction takes place by anantiaddition of the enol ether and the metal to the alkyne. The possible involvement of vinylidene complexes in this reaction is excluded. In addition to the usual 5exo‐dig(or 6exo‐dig) pathways, a 6endo‐digpathway has also been found to take place with certain enynes. One case of 5endo‐digcyclization has also been found. A general scheme for the alkoxycyclization of enynes catalyzed by transition metals based on DFT calculation of PtCl2and AuCl3complexes that includesexoandendocyclizations is presented.
Pd0‐Catalyzed Coupling Cyclization Reaction of Aryl or 1Alkenyl Halides with 1,2‐Allenyl Ketones: Scope and Mechanism. An Efficient Assembly of 2,3,4‐, 2,3,5‐Tri‐ and 2,3,4,5‐Tetrasubstituted Furans
Authors: Ma Shengming , Zhang Junliang , Lu Lianghua
Published: June 2003

Described herein is the Pd0‐catalyzed coupling cyclization reaction of 1,2‐allenyl ketones with organic halides leading efficiently and conveniently to not only 2,3,4‐ and 2,3,5‐trisubstituted furans but also 2,3,4,5‐tetrasubstituted furans. Furthermore, this method showed high substituent‐loading capability and tolerance of various substituents. The reactions of 1,2‐allenyl ketones 1 e, 1 p, 1 q, and deuterated [D]1 c were performed for a mechanistic study, which demonstrated that instead of an enolization pathway, the reaction may proceed via the intermediacy of dienolate palladium and intramolecular nucleophilic attack on the π‐allyl palladium intermediate by the carbonyl oxygen.
A Molecular Approach to Self‐Assembly of Trimethylsilylacetylene Derivatives on Gold
Authors: Katsonis Nathalie , Marchenko Alexandr , Taillemite Sébastien , Fichou Denis , Chouraqui Gaëlle , Aubert Corinne , Malacria Max
Published: June 2003

We recently discovered that a linear multifunctional trimethylsilylacetylene (TMSA) compound forms long‐range and highly stable self‐assembled monolayers (SAMs) on reconstructed Au(111). To better understand the interactions governing self‐assembly in this new system, we synthesized a series of homologue organosilanes and performed scanning tunneling microscopy (STM) measurements at the Au(111)/n‐tetradecane interface. The four TMSA‐terminated linear silanes that we synthesized self‐assemble in similar ways on gold, with the molecules standing upright on the surface. In contrast, compounds with a slightly modified terminal group but the same polyunsaturated linear chain above the TMSA head do not self‐assemble. In particular, substituting a methyl group of TMSA with a more bulky one prevents self‐assembly. Removing the CC triple bond of TMSA or substituting the Si atom by a C atom also hinders self‐assembly. Finally, substituting one methyl group of TMSA by a hydrogen atom induces self‐assembly but in a different geometry, with the molecules lying flat on the gold surface in a quasi‐epitaxy mode. Our molecular approach demonstrates the key role played by the TMSA head in self‐assembly, its origin being twofold: 1) the TMSA layers are commensurate to the Au(111) adlattice along the 〈112〉 direction, and 2) the CC triple bond of TMSA activates the Si atom and induces the creation of a surface SiAu chemical bond. The highly stable TMSA‐based SAMs appear then as promising materials for applications in surface modification.
Structural Study of 2,6‐Bis[(dimethylaminomethyl)phenyl]butyl Stannanes: Nonconventional Behaviour of Triorganotin(IV) Halides
Authors: Růžička Aleš , Jambor Roman , Císařová Ivana , Holeček Jaroslav
Published: June 2003

The four organotin (IV) compounds ([2,6‐bis(dimethylaminomethyl)phenyl](n‐butyl)R1R2stannane, with R1=R2=nBu (1), R1=nBu, R2=Cl (2), R1=nBu, R2=Br (3) and R1=R2=Br (4)), have been prepared and their structures have been investigated in various solvents and at various temperatures (NMR). The structures of these compounds in solution are solvent‐ and temperature‐dependent. The solid state structures of 2 and 3 were studied using CP/MAS NMR spectroscopy and Xray diffraction techniques. The tetraorganotin compound 1 exhibits tetrahedral geometry with very weak SnN coordination. The dynamic process of SnN bond(s) association/dissociation was observed using low‐temperature NMR measurements. The tin central atom in 2 and 3 is [4+2]‐coordinated in toluene solutions and the NMR low‐temperature measurements reveal the same dynamic behavior as for 1 in this solution, with retention of the covalent halogentin bond. However, this bond is dissociated in methanol solutions, yielding ionic species, where the tin atom is only [3+2]‐coordinated, and the halogen atom lies outside of the primary coordination sphere of the tin atom. In addition, while the same ionic structure as in methanol was found in the whole measured temperature range in the chloroform solution of 3, the structure of 2 varies in this solvent. In this compound, the covalent SnCl bond (similar structure as in toluene solution), which is retained at room temperature in chloroform solution, is continuously dissociated with a decrease in temperature, leading to ionic bonding (a similar structure as in methanol solution). All the above‐mentioned processes are reversible in all the solvents and at all temperatures. In the solid state, the covalent SnCl bond is observed for 2, while an ionic bond was found in 3.
Preparation, Structure, and Unique Thermal [2+2], [4+2], and [3+2] Cycloaddition Reactions of 4Vinylideneoxazolidin‐2‐one
Authors: Horino Yoshikazu , Kimura Masanari , Tanaka Shuji , Okajima Toshiya , Tamaru Yoshinao
Published: June 2003

The terminal allene CαCβ bonds of 4vinylidene‐2‐oxazolidinone (2) readily undergo [2+2] cycloaddition with a wide variety of terminal alkynes, alkenes, and 1,3‐dienes irrespective of their electronic nature under strictly thermal activation conditions (70–100 °C) and provide 3substituted (Z)‐methylenecyclobutenes 6, 3substituted methylenecyclobutanes 7 and 8, and 3vinylmethylenecyclobutanes 9, respectively, in good to excellent yields. Alkenes react with 2 with complete retention of configuration. The [2+2] cycloaddition is concluded to proceed via a concerted [(π2s+π2s)allene + π2s] Hückel transition state on the basis of experimental evidences and quantum mechanical methods. Some highly polarized enones and nitrile oxide, on the other hand, react with 2 selectively at the internal C4Cα double bonds and give spiro compounds 10 and 11, respectively. The bent allene bonds (173–176°) and the unique reactivity associated with 2 are attributed to a low‐lying LUMO (CαCβ) that is substantiated by a through‐space σ*(N‐SO2)–π*(CαCβ) orbital interaction.
Synthesis of Complex Oligosaccharides by Using a Mutated (1,3)‐β‐D‐Glucan Endohydrolase from Barley
Authors: Fairweather Jon K. , Hrmova Maria , Rutten Simon J. , Fincher Geoffrey B. , Driguez Hugues
Published: June 2003

Complex oligosaccharides with newly formed (1,3)‐β‐glycosidic linkages were obtained in good to excellent yields when substituted or unsubstituted α‐laminaribiosyl fluorides, acting as donors, were condensed onto mono‐ and disaccharide β‐D‐hexopyranoside acceptors by using a (1,3)‐β‐D‐glycosynthase. These linear and branched (1,3)‐β‐linked oligosaccharides could prove to be important in a range of medical, pharmaceutical, and agricultural applications. Furthermore, the observation that the (1,3)‐β‐D‐glucan glycosynthase accommodates (1,3)‐, (1,4), ‐ and (1,6)‐β‐oligosaccharides in its acceptor subsites suggests novel, yet unexpected physiological roles for the wild type (1,3)‐β‐D‐glucan endohydrolase from higher plants.
Synthesis, Molecular Structure, and CC Coupling Reactions of Carbeneruthenium(II) Complexes with C5H5Ru(CRR′) and C5Me5Ru(CRR′) as Molecular Units
Authors: Braun Thomas , Münch Gerhard , Windmüller Bettina , Gevert Olaf , Laubender Matthias , Werner Helmut
Published: June 2003

The ethene derivatives [(η5‐C5R5)RuX(C2H4)(PPh3)] with R=H and Me, which have been prepared from the η3‐allylic compounds [(η5‐C5R5)Ru(η3‐2‐MeC3H4)(PPh3)] (1, 2) and acids HX under an ethene atmosphere, are excellent starting materials for the synthesis of a series of new halfsandwich‐type ruthenium(II) complexes. The olefinic ligand is replaced not only by CO and pyridine, but also by internal and terminal alkynes to give (for X=Cl) alkyne, vinylidene, and allene compounds of the general composition [(η5‐C5R5)RuCl(L)(PPh3)] with L=C2(CO2Me)2, Me3SiC2CO2Et, CCHCO2R, and C3H4. The allenylidene complex [(η5‐C5H5)RuCl(CCCPh2)(PPh3)] is directly accessible from 1 (R=H) in two steps with the propargylic alcohol HCCC(OH)Ph2 as the precursor. The reactions of the ethene derivatives [(η5‐C5H5)RuX(C2H4)(PPh3)] (X=Cl, CF3CO2) with diazo compounds RR′CN2 yield the corresponding carbene complexes [(η5‐C5R5)RuX(CRR′)(PPh3)], while with ethyl diazoacetate (for X=Cl) the diethyl maleate compound [(η5‐C5H5)RuCl{η2‐Z‐C2H2(CO2Et)2}(PPh3)] is obtained. Halfsandwich‐type ruthenium(II) complexes [(η5‐C5R5)RuCl(CHR′)(PPh3)] with secondary carbenes as ligands, as well as cationic species [(η5‐C5H5)Ru(CPh2)(L)(PPh3)]X with L=CO and CNtBu and X=AlCl4 and PF6, have also been prepared. The neutral compounds [(η5‐C5H5)RuCl(CRR′)(PPh3)] react with phenyllithium, methyllithium, and the vinyl Grignard reagent CH2CHMgBr by displacement of the chloride and subsequent CC coupling to generate halfsandwich‐type ruthenium(II) complexes with η3‐benzyl, η3‐allyl, and substituted olefins as ligands. Protolytic cleavage of the metal–allylic bond in [(η5‐C5H5)Ru(η3‐CH2CHCR2)(PPh3)] with acetic acid affords the corresponding olefins R2CCHCH3. The by‐product of this process is the acetato derivative [(η5‐C5H5)Ru(κ2‐O2CCH3)(PPh3)], which can be reconverted to the carbene complexes [(η5‐C5H5)RuCl(CR2)(PPh3)] in a one‐pot reaction with R2CN2 and Et3NHCl.
Cover Picture: A Molecular Approach to Self‐Assembly of Trimethylsilylacetylene Derivatives on Gold (Chem. Eur. J. 11/2003)
Authors: Katsonis Nathalie , Marchenko Alexandr , Taillemite Sébastien , Fichou Denis , Chouraqui Gaëlle , Aubert Corinne , Malacria Max
Published: June 2003

The cover picture shows a 3D STM image (40×40 Å2) of a self‐assembled monolayer formed by a linear polyunsaturated trimethylsilyl‐acetylene (TMSA) derivative on a reconstructed gold (111) surface. Molecular resolution reveals that the TMSA molecules stand upright with the TMSA heads in contact with gold (each white‐topped bump of the STM image corresponds to a single TMSA molecule). Our molecular approach demonstrates the key role played by the TMSA head in self‐assembly, its origin being twofold: 1) the TMSA overlayers are commensurate to the Au (111) adlattice along the 〈112〉 direction, and 2) the CC triple bond of the TMSA moiety activates the Si atom and induces the creation of a surface complex through a SiAu chemical bond. Long‐range and highly stable TMSA self‐assemblies constitute an alternative to well‐known alkanethiols and appear to be promising materials for applications in surface modifications. More details are given by Fichou et al. on pp. 2574 ff.
Control of flatfish sperm motility by CO2 and carbonic anhydrase
Authors: Inaba Kazuo , Dréanno Catherine , Cosson Jacky
Published: June 2003

Sperm motility in flatfishes shows unique characteristics. The flagellar movement either in vivo or in permeabilized models is arrested by the presence of 25–100 mM HCO3−, or by gentle perfusion with CO2 gas. To understand the molecular basis of this property, sperm Triton‐soluble proteins and flagellar proteins from several species were analyzed by sodium dodecyl sulfate polyacrylamide gel electrophoresis. An abundant 29‐kDa protein was observed only in flatfish species. Partial amino acid sequences identified this protein as a carbonic anhydrase, an enzyme involved in the interconversion of CO2 and HCO3−. 6‐ethoxyzolamide, a specific inhibitor of carbonic anhydrase inhibits sperm motility, especially at low pH. In the case of HCO3−‐arrested sperm, the motility is restored by addition of 6‐ethoxyzolamide. Taken together, these results suggest that a novel pH/ HCO3−‐dependent regulatory mechanism mediated by carbonic anhydrase is involved in the motility control in flatfish sperm. Cell Motil. Cytoskeleton 55:174–187, 2003. © 2003 Wiley‐Liss, Inc.
Reconstruction of the projection periodicity and surface architecture of the flagellar central pair complex
Authors: Mitchell David R.
Published: June 2003

The substructure of central pair microtubule‐associated components has been analyzed by comparing thin section and freeze‐etch images of Chlamydomonas flagellar axonemes. The longitudinal periodicity of central pair projections that were previously described from cross‐sectional image averages was determined from thin sections of axonemes isolated from either wild type or central pair assembly‐defective strains. All projections directed toward one quadrant of the central pair repeat at 32 nm, while those in the other three quadrants all show 16‐nm spacing. The surface architecture of these projections as seen in rapid‐freeze deep‐etch images of central pair complexes includes elements that form circumferentially oriented fibers around most of the central pair. This appearance changes dramatically along the lateral edge of the C1 microtubule where material is arranged in rows of separate particles that may play a unique role in spoke‐mediated regulation of flagellar dynein activity. Cell Motil. Cytoskeleton 55:188–199, 2003. © 2003 Wiley‐Liss, Inc.
Requirement for the βI and βIV tubulin isotypes in mammalian cilia
Authors: Jensen‐Smith Heather C. , Ludueña Richard F. , Hallworth Richard
Published: June 2003

Nielsen et al., [2001: Curr Biol 11:529–533], based on studies in Drosophila, have proposed that β tubulin in axonemal microtubules must contain a specific acidic seven amino acid sequence in its carboxyl terminus. In mammals, the two βIV isotypes (βIVa and βIVb) contain that sequence. In order to test the application of this hypothesis to mammals, we have examined the expression of β tubulin isotypes in four different ciliated tissues (trachea, ependyma, uterine tube, and testis) using isotype‐specific antibodies and indirect immunofluorescence. We find that βIV tubulin is present in all ciliated cell types examined, but so is βI tubulin. Taken together with recent studies that show that βI and βIV tubulin are both present in the cilia of vestibular hair cells, olfactory neurons, and nasal respiratory epithelial cells, we propose that both βI tubulin and βIV tubulin may be required for axonemal structures in mammals. Cell Motil. Cytoskeleton 55:213–220, 2003. © 2003 Wiley‐Liss, Inc.
Genomic organization, alternative splicing, and expression of human and mouse N‐RAP, a nebulin‐related LIM protein of striated muscle
Authors: Mohiddin Saidi A. , Lu Shajia , Cardoso John‐Paul , Carroll Stefanie , Jha Sanjaya , Horowits Robert , Fananapazir Lameh
Published: June 2003

Linkage analysis identifies 10q24‐26 as a disease locus for dilated cardiomyopathy (DCM), a region including the N‐RAP gene. N‐RAP is a nebulin‐like LIM protein that may mediate force transmission and myofibril assembly in cardiomyocytes. We describe the sequence, genomic structure, and expression of human N‐RAP, as well as an initial screen to determine whether N‐RAP mutations cause cardiomyopathy. Human expressed sequence tag databases were searched with the published 3,528‐bp mouse N‐RAP open reading frame (ORF). Putative cDNA sequences were interrogated by direct sequencing from cardiac and skeletal muscle RNA. We identified two human N‐RAP isoforms with ORFs of 5,085 bp (isoform C) and 5,190 bp (isoform S), encoding products of 193–197 kDa. Genomic database searches localize N‐RAP to human chromosome 10q25.3 and match isoforms C and S to 41 and 42 exons. Only isoform C is detected in human cardiac RNA; in skeletal muscle, approximately 10% is isoform C and approximately 90% is isoform S. We investigated apparent differences between human N‐RAP cDNA and mouse sequences. Two mouse N‐RAP isoforms with ORFs of 5,079 and 5,184 bp were identified with ∼85% similarity to human isoforms; published mouse sequences include cloning artifacts truncating the ORF. Murine and human isoforms have similar gene structure, tissue specificity, and size. N‐RAP is especially conserved within its nebulin‐like and LIM domains. We expressed both N‐RAP isoforms and the previously described truncated N‐RAP in embryonic chick cardiomyocytes. All constructs targeted to myofibril precursors and the cell periphery, and inhibited myofibril assembly. Several human N‐RAP polymorphisms were detected, but none were unique to cardiomyopathy patients. N‐RAP is highly conserved and exclusively expressed in cardiac and skeletal muscle. Genetic abnormalities remain excellent candidate causes for cardiac and skeletal myopathies. Cell Motil. Cytoskeleton 55:200–212, 2003. © 2003 Wiley‐Liss, Inc.
Asymmetric twinning crystals of Zinc oxide formed in a hydrothermal process
Authors: Xu HaiYan , Wang Hao , Zhang YongCai , Wang Shu , Zhu ManKang , Yan Hui
Published: June 2003

Well crystallized ZnO powders with various morphologies such as hour glass‐shaped, shortened prismatic, flake‐like and prismatic form have been synthesized by adopting the system of Zn(Ac)2‐KOH‐H2O via a hydrothermal process at 200 °C for 2 h. It was found that the as‐synthesized hour glass‐shaped ZnO crystallites are asymmetric both in shape and stoichiometry: while the atomic ratio of O/(Zn+O) at the bigger end ranges from about 60% to 40% along the polar axis of the hour glass‐shaped ZnO crystallites, the atomic ratio of O/(Zn+O) at the smaller end remains almost constant at approximately 50%.
Optical characterization and crystal structure of the novel bronzetype CaxBa1‐xNb2O6 (x = 0.28; CBN‐28)
Authors: Eßer M. , Burianek M. , Held P. , Stade J. , Bulut S. , Wickleder C. , Mühlberg M.
Published: June 2003

Calcium barium niobate (CBN), also like strontium barium niobate (SBN), belongs to the materials family of partially filled tetragonal tungsten bronzes, which show relaxor‐type ferroelectric phase transitions and large electro‐optic effects. For the first time, it was possible to grow large single crystals of Ca0.25Ba0.75Nb2O6 (CBN‐25) and CBN‐28 by using different growing techniques. The successful single crystal growth allowed to investigate several physical properties of the novel phase. Herein, we report on measurements of differential thermal analysis (DTA), wavelength dispersion of the refractive indices, temperature dependence of the birefringence and light absorption. Additionally, results of the single crystal X‐ray structure analysis are presented.
Electrical and dielectric behavior of the system Gd1‐xBaxCoO3 (x = 0.00, 0.10, 0.20) synthesized by chemical route
Authors: Mandal K. D. , Behera L. , Prasad R. L. , Behera R. C.
Published: June 2003

The samples in the system Gd1‐xBaxCoO3 (x = 0.00, 0.10, 0.20) were prepared by chemical route. These samples form single‐phase materials, which were confirmed by XRD and TGA studies. The presence of interfacial polarization is responsible for high value of dielectric constant in these materials. The conductivity observed in Gd1‐xBaxCoO3 system may be due to mobile holes created by excitation of an electron from the π* band to an acceptor level.
Some physical and magnetic properties of Mg‐Zn ferrite
Authors: Mazen S. A. , Mansour S. F. , Zaki H. M.
Published: June 2003

Some physical properties (such as lattice parameter, density and porosity) and magnetic properties of the system Mg1‐xZnxFe2O4; where x=0,0.1,0.2,0.3,0.4,0.5and 0.6 have been studied. It was found that the lattice parameter increases with increasing the zinc concentration. The composition dependence of the physical properties is divided into two regions. The first one is for x ≤ 0.3 and the second one is for x > 0.3. From the magnetization measurements, the basic composition (MgFe2O4) shows the lowest magnetization, while the composition of x=0.4 shows the highest one. The behaviour of magnetization M versus composition shows also two regions for x <>0.3. The behaviour of M versus x was discussed in the bases of cation distribution. From the B‐H loops, the remanence induction Br, saturation induction Bs and the coercive force Hc were determined and studied with x. The Curie temperature TC was determined from the measurements of the initial permeability μi versus temperature. It was found TC decreases with increasing Zn‐content. Also paramagnetic temperature TP was determined from the behaviour of MS vs. T. In general it was found TP > TC by about 7‐10 K.
X‐ray studies on quaternary system RbXK1‐XBrYCl1‐Y
Authors: Mohanlal S. K. , Pathinettam Padiyan D.
Published: June 2003

Single crystals of the quaternary crystalline solid solution system RbxK1‐xBryCl1‐y have been grown by melt technique for three different compositions y = 0.25, 0.50 and 0.75, keeping x = 0.5 and X‐ray diffraction studies have been carried out for each case independently, using spherically ground single crystals. The results indicate an enhancement of Debye‐Waller B(total) factors for the compositions y = 0.25 and 0.75 whereas for the intermediate composition, y = 0.5, the factor B(total) is close to the end member value. This experimental investigation show that for this composition, the crystalline solid solution behaves like an end member crystal.
Determination of the crystallographic parameters of a fcc metal by means of electron channelling patterns
Authors: Uguz A.
Published: June 2003

Indexing and mapping of selected area electron channelling patterns (SAECPs) of an Al‐Zn‐Mg alloy have been performed. Although, channelling patterns are similar for crystals having the same system, since the interplanar spacing and the angular band width depend on lattice parameter, the details of the map will differ for every material. Angles between the poles and the angular separations of channelling bands were measured on the micrographs and calculated with the well known equations and found to be well in agreement within the error limits. Also the channelling line widths were calculated with the help of extinction distances of the reflecting planes. Structure factors and atomic scattering factors for selected reflections were also calculated for the present alloy whose a = 4.054 Å.
Chemokines in islet allograft rejection
Authors: Abdi Reza , Means Terry K. , Luster Andrew D.
Published: June 2003

Chemokines have emerged as important regulators in the development, differentiation, and anatomic distribution of leukocytes. Studies of renal and cardiac allograft biopsies have revealed that the expression of many chemokine receptors and their ligands was associated with acute allograft rejection. However, the importance of these chemokine receptor systems varies in the host response to a particular allograft. In this regard, CXCR3 appears to play a more important role in cardiac allograft rejection than CCR2 and CCR5. We have found that CCR2, CCR5, and CXCR3 and their ligands, as well as Th1 cytokines are induced to high levels in rejecting islet allografts. Interestingly, targeting CCR5 resulted in a significant prolongation of islet allograft survival. This prolongation was associated with a Th2 response. Our data indicate that in the process of acute rejection, the temporal expression and the ultimate function of a given chemokine vary among different organs or tissues. Hence, each organ or tissue may require a unique set of chemokines to generate acute rejection. Targeting the appropriate chemokine receptors may provide a clinically useful strategy to prevent islet allograft rejection. Copyright © 2003 John Wiley & Sons, Ltd.