bluuebunny/crossref_metadata_2025_split huggingface dataset:
Strong Binding of Alkylguanidinium Ions by Molecular Tweezers: An Artificial Selective Arginine Receptor Molecule with a Biomimetic Recognition Pattern
Authors: Schrader Thomas 
Published: July 2007

AbstractBisphosphonates 2 and 3 represent the first artificial receptor molecules for alkylguanidinium ions. They bind to the guanidinium moiety by forming a 1:1 chelate complex, stabilized by a planar network of electrostatic interactions and hydrogen bonds. This hydrogen bonding configuration is identical to the „arginine fork”︁ postulated by Frankel as a key element in RNA–protein recognition of the AIDS virus. Our guanidinium–bisphosphonate complexes thus constitute the first synthetic model for this important biological interaction and demonstrate that the high binding energy can be a driving force for a conformational change in the receptor (induced fit, e.g., in the RNA). Although binding of monosubstituted alkylguanidines is generally strong (Ka ≈ 10 000 in DMSO), molecular tweezer 3 recognizes N‐ and C‐amide‐protected arginine derivatives especially well (Ka ≈ 300 000 in DMSO), because an additional hydrogen bond is formed between the amide and the phosphonate. Since 3 does not bind amines effectively, it is highly selective for arginine, even in the presence of lysine or other amino acids. For di‐, tri‐, and tetrasubstituted guanidines the association constant remains low (Ka⩽1000 in DMSO) reflecting the increase in the steric bulk of the guest.
The Nature of the Metal—Silicon Bond in [M(SiR3)H3(PPh3)3] (M = Ru, Os) And the Crystal Structure of [Os{Si(N‐pyrrolyl)3}H3(PPh3)3]
Authors: Hübler Klaus , Hübler Ute , Roper Warren R. , Schwerdtfeger Peter , James Wright L. 
Published: July 2007

AbstractThe compounds [M(SiR3)H3(PPh3)3] (1: M = Ru, R = 1 ‐ NC4H4 = pyr; 2a‐c: M = Os, R = pyr, Et, Ph) are prepared through reaction of either [RuH2(PPh3)4] or [OsH4(PPh3)3] with the appropriate silane HSiR3 (3a‐c: R = pyr, Et, Ph). The X‐ray structure analysis of compound 2 a and ab initio calculations on the model compounds [Os(SiR3)H3(PH3)3] (4a‐c: R = H, NH2, pyr) reveal a trigonal distortion along the Os‐Si axis from an idealised tetrahedral geometry for the central OsSiP3 heavy‐atom skeleton. The structure can be described as two face‐shared octahedra, one based on osmium (OsH3P3) and the other based on silicon (SiH3N3). Studies of the bonding situation in 2 a reveal that the N‐pyrrolyl substituents have a marked shortening effect on the osmium‐silicon distance (229.3(3) pm) and that each of the three hydride ligands participates in partial three‐centre bonding involving osmium, silicon and hydrogen. 1H, 13C, 29Si and 31P NMR spectra were used to determine the solution structures of complexes 1 and 2 a.
Carbohydrate‐Modified Metal Carbenes: Synthesis And First Applications
Authors: Heinz Dötz Karl , Ehlenz Richard 
Published: July 2007

AbstractCarbohydrate‐modified carbene complexes can be synthesised by combining a sugar electrophile with a metalate nucleophile or vice versa. Acyclic sugar skeletons adopt conformations that are controlled by the minimisation of 1,3‐interactions and are not significantly affected by the incorporation of a metal fragment. Thus, the latter can be used exclusively for reactivity tuning. Sugar carbene complexes undergo regio‐ and stereoselective ligand‐ and metal‐centred reactions such as C2‐homologisation and benzannulation.
Intermediates in the Catalytic Dehydrogenative Coupling of Arylgermanes
Authors: Bender John E. , Litz Kyle E. , Giarikos Dimitrios , Wells Norman J. , Banaszak Holl Mark M. , Kampf Jeff W. 
Published: July 2007

AbstractThe use of a new electron‐withdrawing germane, H2Ge[3,5‐(CF3)2C6H3]2 (3), has facilitated the isolation and characterization of three new complexes implicated in the dehydrogenative coupling of bisarylgermanes by Pt0‐phos‐phane complexes. The intermediates include a digermyl species, trans‐[(Et3P)2Pt{GeH(Ar)2}2] (7), a bound digermane showing the first stage of Ge‐Ge catenation, cis‐[(Et3P)2Pt(H){Ge(Ar)2‐GeH(Ar)2}] (8), and the Ge‐H activated form of this product, [(Et3P)2HPtGe(Ar)2‐Ge(Ar)2PtH(PEt3)2] (6). Complexes such as 6 and 8 have not previously been isolated as intermediates in dehydrogenative coupling reactions. An X‐ray crystal structure was determined for complex 6, confirming the cis geometry of the hydrogen and germanium ligands; this provides yet another example of the stability of germyl hydrides towards reductive elimination. A similar cis geometry was observed for complex 8. Performing the dehydrogenative coupling reaction under a CO2 atmosphere failed to yield any products containing trapped germylene species.
Biomimetic Crystallization of Calcium Carbonate Polymorphs by Means of Collagenous Matrices
Authors: Falini Giuseppe , Fermani Simona , Gazzano Massimo , Ripamonti Alberto 
Published: July 2007

AbstractCrosslinked gelatin films with entrapped poly‐L‐aspartate were used to induce the crystallization of calcite and aragonite polymorphs. Calcite with high degrees of isomorphous substitution (up to 12mol% magnesium) has been obtained. The morphology and layered organization of magnesium calcite crystals grown inside the crosslinked gelatin films with entrapped poly‐L‐aspartate resemble some structural features of radial calcitic ooids. The concentration of entrapped poly‐L‐aspartate and the uniaxial deformation of the films control the growth of aragonite aggregates inside the films. Such aggregates grown inside uniaxially deformed films consist of parallel rods with an architectural assembly similar to that found in some marine organisms. The crystals' aggregation and the control of calcium carbonate polymorphism are related to the modelling of the nucleation sites by poly‐L‐aspartate structure and concentration, local supersaturation and microenvironment shape. The results indicate that the collagenous matrices with entrapped polyelectrolytes are versatile systems which can contribute to the elucidation of strategies for biomimetic materials chemistry.
A Quintupled Superstructure of the KHg2 Type Realized for the New Stannide EuAuSn
Authors: Pöttgen Rainer , Hoffmann Rolf‐Dieter , Müllmann Ralf , Mosel Bernd D. , Kotzyba Gunter 
Published: July 2007

AbstractThe title compound was prepared from the elements by reaction in a sealed tantalum tube at 1320 K followed by slow cooling to 970 K. EuAuSn crystallizes with a pronounced subcell of space group Imma (KHg2 type). Additional very weak reflections required a quintupled b axis. The superstructure was refined from single‐crystal four‐circle diffractometer data (Imm 2, a = 479.1(1) pm, b = 3833.6(5) pm, c = 820.1(1) pm, Z = 20, wR2 = 0.0834, 3675 F2 values and 94 variables). Six crystallographically different europium sites occur in the superstructure. Each europium site has an ordered near‐neighbour environment of six gold and six tin atoms in the form of two tilted hexagons. Magnetic susceptibility measurements show Curie‐Weiss behaviour above 50 K with an experimental magnetic moment of 7.6(1) μB/Eu, indicating divalent europium. EuAuSn orders antiferromagnetically at about 12 K and undergoes a metamagnetic transition at a critical field of 2.0(2) T. Electrical conductivity measurements show metallic behaviour with a room temperature value of 260 μΩcm. 151Eu and 119Sn Mössbauer spectroscopic experiments are compatible with divalent europium and show complex magnetic hyperfine field splitting at low temperature.
2,3,7,8,12,13,17,18‐Octafluoro‐5,10,15,20‐Tetraphenylporphyrin: First Synthesis and X‐Ray Crystal Structure of the ZnII Complex
Authors: Leroy Jacques , Bondon Arnaud , Toupet Loïc , Rolando Christian 
Published: July 2007

Abstract2,3,7,8,12,13,17,18‐Octafluoro‐5,10,15,20‐tetraphenylporphyrin has been prepared from 3,4‐difluoropyrrole and benzaldehyde under Lindsey conditions. An X‐ray crystal structure study of its ZnII complex has shown that the macrocycle core is nonplanar, a result in apparent contradiction with a blue‐shifted UV/Vis spectrum. The results reported here demonstrate that a wide range of β‐octafluoro‐meso‐arylated porphyrins, a new class of highly electron‐deficient ligands, are potentially accessible from 3,4‐difluoropyrrole, thus opening the door to, inter alia, efficient and robust oxidation catalysts.
Total Synthesis of Oxazole‐ and Cyclopropane‐Containing Epothilone A Analogues by the Olefin Metathesis Approach
Authors: Nicolaou K. C. , Vallberg Hans , King N. Paul , Roschangar Frank , He Yun , Vourloumis Dionisios , Nicolaou Christopher G. 
Published: July 2007

AbstractFor structure‐activity relationship studies, two series of epothilone A (1) analogues have been designed and synthesized, one containing an oxazole moiety instead of the thiazole heterocycle and the other containing a spirocyclopropane moiety in place of the gem‐dimethyl group at position C‐4 (4,4‐ethano‐epothilones). The olefin metathesis strategy in solution was utilized for the chemical synthesis of these compounds starting with key building blocks 7–9 for the oxazole series (compounds 2, 14–18, 21–26) and building blocks 8, 30, and 31 for the 4,4‐ethano series (compounds 3,39–43, 46–51). The convergent strategy towards the designed epothilone A series involved a) an aldol condensation reaction, b) an esterification reaction, c) an olefin metathesis reaction catalyzed by [RuCl2(=CHPh)‐(PCy3)2], and d) epoxidation of the macrocycle double bond.
Total Synthesis of Oxazole‐ and Cyclopropane‐Containing Epothilone B Analogues by the Macrolactonization Approach
Authors: Nicolaou K. C. , Sarabia Francisco , Finlay M. Ray V. , Ninkovic Sacha , King N. Paul , Vourloumis Dionisios , He Yun 
Published: July 2007

AbstractIn order to probe structure‐activity relationships in the epothilone area, two series of epothilone B analogues have been designed and synthesized. The first series containing an oxazole moiety in place of a thiazole on the side chain was constructed by utilizing key intermediates 7–9 or 10, 12, and 13 (Scheme 1), whereas the second series containing an ethano group instead of the gem‐dimethyl group at position 4 was synthesized from fragments 42 and 43. A Yamaguchi‐type macrolactonization reaction was used to construct the macrocycle from a secoacid, which was assembled, in both cases, by means of a) an aldol reaction, b) an Enders alkylation, and c) a Wittig‐type reaction. This convergent strategy provided access to oxazole analogues 2,4,29–32 and 4,4‐ethano derivatives 3,40,60–63 for biological studies.
Enantioselective Cathodic Reduction of 4‐Methylcoumarin: Dependence of Selectivity on Reaction Conditions and Investigation of the Mechanism
Authors: Nielsen Merete Folmer , Batanero Belen , Löhl Thorsten , Schäfer Hans J. , Würthwein Ernst‐Ulrich , Fröhlich Roland 
Published: July 2007

AbstractThe cathodic reduction of 4‐methylcoumarin (1) in acidic methanol/water in the presence of yohimbine leads to formation of a mixture of the hydrogenation product 4‐methyl‐3,4‐dihydrocoumarin (2), with an enantiomeric excess (ee) of (R)‐2of 0–67%, and the hydrodimer3. The relative yields of2and3and theeeof2depend on a number of experimental parameters such as pH, supporting electrolyte, working potential, and the concentrations of substrate and yohimbine, as demonstrated by a series of preparative‐scale experiments. In addition, a series of voltammetric and kinetic measurements were carried out to investigate the influence of the individual experimental parameters. Three mechanistic possibilities have been examined, and by combination of the analytical data with the results of the preparative experiments, a single model is put forward which is in accord with the available results. The main features of the mechanistic model can be summarized as follows: 1) under acidic conditions (pH 2–3) the electroactive species is a complex between1and H3O+, the reduction of which leads to an enolic radical; 2) this radical is not reduced at the working potential but tautomerizes into the more easily reduced keto radical or dimerizes; 3) the keto radical is reduced and further protonated; 4) the function of the yohimbineH+is to catalyze the tautomerization and enantioselectively protonate the final carbanion. Additionally, we conclude that the concentration of yohimbine in the immediate vicinity of the electrode is considerably higher than its stoichiometric concentration. Quantum chemical calculations demonstrate thatsiprotonation of the intermediate anion by yohimbineH+to give (R)‐2is energetically favored.
Rapid Coupling of Methyl Iodide with Aryltributylstannanes Mediated by Palladium(0) Complexes: A General Protocol for the Synthesis of 11CH3‐Labeled PET Tracers
Authors: Suzuki Masaaki , Doi Hisashi , Björkman Margareta , Andersson Yvonne , Långström Bengt , Watanabe Yasuyoshi , Noyori Ryoji 
Published: July 2007

AbstractThe reaction of methyl iodide and (excess) aryltributylstannane to give a methylarene has been studied with the focus on the realization of rapid coupling for incorporation of short‐lived radionuclides into bioactive organic compounds. The coupling of methyl iodide with tributylphenylstannane (40 equiv) is accomplished in >90% yield within 5 min at 60°C with a tri‐o‐tolylphosphine‐bound, coordinatively unsaturated Pd0 complex together with a CuI salt and K2CO3 in DMF. This protocol is applicable to a variety of homo‐ and heteroaromatic tin compounds, to give the corresponding methylated derivatives. The effects of the tri‐o‐tolylphosphine ligand, a Cu(I) salt, and DMF are discussed. This new protocol provides a firm chemical basis for the synthesis of 11CH3‐incorporated PET tracers.
Topologic Equivalents of Coronands, Cryptands and Their Inclusion Complexes: Synthesis, Structure and Properties of {2}‐Metallacryptands and {2}‐Metallacryptates
Authors: Saalfrank Rolf W. , Dresel Andreas , Seitz Verena , Trummer Stefan , Hampel Frank , Teichert Markus , Stalke Dietmar , Stadler Christian , Daub Jörg , Schünemann Volker , Trautwein Alfred X. 
Published: July 2007

AbstractThe synthesis and structural characterisation of two dinuclear iron(III) complexes are reported. The compounds of general structure [Fe2L] [8; L1 = dianion of 2,2′‐dicyano‐2,2′‐isophthaloyldi(isopropyldicarboxylate)] and [K ⊂ Fe2L]+ (PF6)‐ [10; L2 = dianion of 1,1′‐(2,6‐pyridylene)bis‐1,3‐(4‐dimethyl)‐pentanedione] are formed by the deprotonation of ligands 7 and 9 with triethylamine and potassium hydride respectively, followed by addition of iron(III) chloride and work up with water or aqueous potassium hexafluorophosphate. X‐ray crystallographic studies reveal that 8 is a racemic mixture composed of triple helicates with (Δ,Δ)‐fac and (Δ,Δ)‐fac configuration at the two iron bridgeheads. In contrast to racemic 8, the two iron centres in the meso‐10 [(Δ,Δ)‐fac] have opposite configuration. Investigations of the redox‐active iron centres in {2}‐metallacryptand 8 and {2}‐metallacryptate 10 by cyclic voltammetry show slightly different behaviour. The peaks for the two consecutive reductions of the two iron centres of 8 can hardly be resolved, whereas 10 shows two well‐separated peaks. Mössbauer measurements were performed on 8 and 10 between 4.2 and 300 K, with and without a field applied perpendicular or parallel to the γ‐beam. All zero‐field and 20 mT spectra exhibit a broad and unresolved absorption pattern. Application of 5.3 T at 4.2 K results in well‐resolved magnetic hyperfine patterns which are practically the same for 8 and 10.
Differential, age‐dependent MEK‐ERK and PI3K‐Akt activation by insulin acting as a survival factor during embryonic retinal development
Authors: Chavarría Teresa , Valenciano Ana I. , Mayordomo Raquel , Egea Joaquim , Comella Joan X. , Hallböök Finn , de Pablo Flora , de la Rosa Enrique J. 
Published: July 2007

AbstractProgrammed cell death is a genuine developmental process of the nervous system, affecting not only projecting neurons but also proliferative neuroepithelial cells and young neuroblasts. The embryonic chick retina has been employed to correlate in vivo and in vitro studies on cell death regulation. We characterize here the role of two major signaling pathways, PI3K‐Akt and MEK‐ERK, in controlled retinal organotypic cultures from embryonic day 5 (E5) and E9, when cell death preferentially affects proliferating neuroepithelial cells and ganglion cell neurons, respectively. The relative density of programmed cell death in vivo was much higher in the proliferative and early neurogenic stages of retinal development (E3–E5) than during neuronal maturation and synaptogenesis (E8–E19). In organotypic cultures from E5 and E9 retinas, insulin, as the only growth factor added, was able to completely prevent cell death induced by growth factor deprivation. Insulin activated both the PI3K‐Akt and the MEK‐ERK pathways. Insulin survival effect, however, was differentially blocked at the two stages. At E5, the effect was blocked by MEK inhibitors, whereas at E9 it was blocked by PI3K inhibitors. The cells which were found to be dependent on insulin activation of the MEK‐ERK pathway at E5 were mostly proliferative neuroepithelial cells. These observations support a remarkable specificity in the regulation of early neural cell death. © 2007 Wiley Periodicals, Inc. Develop Neurobiol 67:1777–1788, 2007
Summary of ‘School‐based secondary prevention programmes for preventing violence’
Authors: Milne Andrea 
Published: July 2007

AbstractThis is a summary of a Cochrane review, published in this issue of EBCH, first published as: Mytton J, DiGuiseppi C, Gough D, Taylor R, Logan S. School‐based secondary prevention programmes for preventing violence. Cochrane Database of Systematic Reviews 2006, Issue 3. Art. No.: CD004606. DOI: 10.1002/14651858.CD004606.pub2.Further information for this Cochrane review is available in this issue of EBCH in the accompanying Commentary and Characteristics and Key Findings Tables articles. Copyright © 2007 John Wiley & Sons, Ltd.
Summary of ‘Nitric oxide for respiratory failure in infants born at or near term’
Authors: Milne Andrea 
Published: July 2007

AbstractThis is a summary of a Cochrane review, published in this issue of EBCH, first published as: Finer NN, Barrington KJ. Nitric oxide for respiratory failure in infants born at or near term. Cochrane Database of Systematic Reviews 2006, Issue 4. Art. No.: CD000399. DOI: 10.1002/14651858.CD000399.pub2.Further information for this Cochrane review is available in this issue of EBCH in the accompanying Commentary and Characteristics and Key Findings Tables articles. Copyright © 2007 John Wiley & Sons, Ltd.
Summary of ‘Systemic antibiotics versus topical treatments for chronically discharging ears with underlying eardrum perforations’
Authors: Milne Andrea 
Published: July 2007

AbstractThis is a summary of a Cochrane review, published in this issue of EBCH, first published as: Macfadyen CA, Acuin JM, Gamble C. Systemic antibiotics versus topical treatments for chronically discharging ears with underlying eardrum perforations. Cochrane Database of Systematic Reviews 2006, Issue 1. Art. No.: CD005608. DOI: 10.1002/14651858.CD005608.Further information for this Cochrane review is available in this issue of EBCH in the accompanying Commentary and Characteristics and Key Findings Tables articles. Copyright © 2007 John Wiley & Sons, Ltd.
Commentary on ‘School‐based secondary prevention programmes for preventing violence’
Authors: LeBlanc John , Cameron Paula 
Published: July 2007

AbstractThis is a commentary on a Cochrane review, published in this issue of EBCH, first published as: Mytton J, DiGuiseppi C, Gough D, Taylor R, Logan S. School‐based secondary prevention programmes for preventing violence. Cochrane Database of Systematic Reviews 2006, Issue 3. Art. No.: CD004606. DOI: 10.1002/14651858.CD004606.pub2.Further information for this Cochrane review is available in this issue of EBCH in the accompanying EBCH Summary and Characteristics and Key Findings Tables articles. Copyright © 2007 John Wiley & Sons, Ltd.
Tips and tricks for understanding and using SR results. No. 6: development of a search strategy
Authors: Lundh Andreas , Kremer Leontien C. M. , Leclercq Edith 
Published: July 2007

AbstractThis sixth article in the series ‘Tips and tricks for understanding and using SR results’ is, like the previous ones, aimed at helping the readers to understand the results of systematic reviews and to use these results in clinical practice. Earlier articles in the Tips and Tricks section of this journal have addressed the sources of evidence, i.e. the bibliographic databases where primary studies for a Cochrane systematic review may be identified. This article will focus on how reviewers actually search an electronic bibliographic database for studies to go into Cochrane systematic reviews. The information summarized in this article is based on earlier papers, the Cochrane Handbook and the authors' experience in evidence‐based medicine and searching medical databases (1–9). Copyright © 2007 John Wiley & Sons, Ltd.
Characteristics and key findings for ‘School‐based secondary prevention programmes for preventing violence’
Authors: van Dalen Elvira , Offringa Martin , Kremer Leontien 
Published: July 2007

AbstractThese are the characteristics and key findings for a Cochrane review, published in this issue of EBCH, first published as: Mytton J, DiGuiseppi C, Gough D, Taylor R, Logan S. School‐based secondary prevention programmes for preventing violence. Cochrane Database of Systematic Reviews 2006, Issue 3. Art. No.: CD004606. DOI: 10.1002/14 651 858.CD004606.pub2.Further information for this Cochrane review is available in this issue of EBCH in the accompanying EBCH Summary and Commentary articles. Copyright © 2007 John Wiley & Sons, Ltd.
Characteristics and key findings for ‘Antibiotics for the prevention of acute and chronic suppurative otitis media in children’
Authors: van Dalen Elvira , Offringa Martin , Kremer Leontien 
Published: July 2007

AbstractThese are the characteristics and key findings for a Cochrane review, published in this issue of EBCH, first published as: Leach AJ, Morris PS. Antibiotics for the prevention of acute and chronic suppurative otitis media in children. Cochrane Database of Systematic Reviews 2006, Issue 4. Art. No.: CD004401. DOI: 10.1002/14 651 858.CD004401.pub2.Further information for this Cochrane review is available in this issue of EBCH in the accompanying EBCH Summary and Commentary articles. Copyright © 2007 John Wiley & Sons, Ltd.
Characteristics and key findings for ‘Nitric oxide for respiratory failure in infants born at or near term’
Authors: van Dalen Elvira , Offringa Martin , Kremer Leontien 
Published: July 2007

AbstractThese are the characteristics and key findings for a Cochrane review, published in this issue of EBCH, first published as: Finer NN, Barrington KJ. Nitric oxide for respiratory failure in infants born at or near term. Cochrane Database of Systematic Reviews 2006, Issue 4. Art. No.: CD000399. DOI: 10.1002/14 651 858.CD000399.pub2.Further information for this Cochrane review is available in this issue of EBCH in the accompanying EBCH Summary and Commentary articles. Copyright © 2007 John Wiley & Sons, Ltd.