bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractDescribed 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

AbstractWe 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

AbstractThe 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

AbstractThe 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

AbstractComplex 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

AbstractThe 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

AbstractThe 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

AbstractSperm 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

AbstractThe 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

AbstractNielsen 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

AbstractLinkage 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

AbstractWell 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

AbstractCalcium 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

AbstractThe 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

AbstractSome 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

AbstractSingle 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

AbstractIndexing 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

AbstractChemokines 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.