bluuebunny/crossref_metadata_2025_split huggingface dataset:
Organometallic and Classical Coordination Sites in Highly Preorganized Pyrazolate‐Based Hybrid Systems: The Mn/Ni Case
Authors: Zhang Huaxin , Dechert Sebastian , Linseis Michael , Winter Rainer F. , Meyer Franc 
Published: August 2007

AbstractA series of unsymmetric heterodinuclear Mn/Ni complexes is reported in which an organometallic CpMn(CO)2 fragment and a classical Werner‐type nickel(II) subunit are arranged in close proximity by means of a bridging pyrazolate. The two metalloligand scaffolds (1 and 2) employed differ in the chelate size of the tripodal tetradentate {N4} binding site for nickel. Molecular structures have been determined for (1‐H)Ni(NO3) (3), (2‐H)Ni(NO3) (4), and (2‐H)Ni(OAc) (5). Comparison with the molecular structures of the related Mn/Mn, Mn/Co, and Mn/Zn systems confirms that structural flexibility is greater for the complexes based on ligand 2 due to the longer chelate arms. According to IR and UV/Vis spectroelectrochemistry, oxidation of the heterobimetallic systems is highly localized at the organometallic manganese site. Structural and spectroscopic features as well as trends for the redox potentials of the MnI/MnII couple suggest that ligand variations at the nickel(II) Werner‐type subunit exert only a small influence on the properties of the organometallic part. In contrast, reduction occurs at the nickel site and is strongly dependent on the anion present. The effects at the organometallic CpMn(CO)2 subunit upon reduction of the proximate nickel ion are most pronounced for 5. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Methylation of a Terdentate Schiff Base Ligand NNO‐Coordinated to Palladium with Nitromethane
Authors: Arnaiz Ana M. , Carbayo Arancha , Cuevas José V. , Diez Virginia , García‐Herbosa Gabriel , González Roberto , Martínez Abigail , Muñoz Asunción 
Published: August 2007

AbstractThe reaction of the complex [Pd(κ3‐NN′O)CH3] [NN′O = 2‐Py‐CH=N‐(o‐C6H4)O–] (1a) with nitromethane affords a mixture of 2a and 2b. In this reaction methylation of the ligand takes place. These complexes display exchange equilibrium in solution. The methylation reaction is proposed to occur through nucleophilic attack of the nitronate anion on the iminic carbon atom. DFT calculations are presented in order to support a part of the mechanism and these calculations show that the participation of water in the migration of a proton is important. The crystal structure of the derivative productafter spontaneous release of methane (3) is presented as well. Attempts to extend the reaction to other nitroalkanes resulted in a mixture of complexes that was not easy to characterize. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Phospha‐ and Arsaalkenes RE=C(NMe2)2 (E = P, As) as Novel Phosphinidene‐ and Arsinidene‐Transfer Reagents
Authors: Weber Lothar 
Published: August 2007

AbstractPhosphinidenes (phosphanylidenes) (RP) are electronically and coordinatively unsaturated phosphorus compounds, which, as six‐electron species, are formally analogous to the more familiar carbenes and nitrenes. In contrast to carbenes (CR2), the extremely reactive phosphinidenes cannot be isolated without decomposition. Thus, our knowledge on phosphinidenes is mainly limited to trapping reactions and quantum‐chemical calculations. There are a number of synthetic methods for phosphinidenes available, for example photolysis or thermolysis of cyclic phosphanes and oligophosphanes, dehalogenation of organodihalophosphanes, liberation of dinitrogen from organodiazidophosphanes, or decomposition of phosphoranylidene‐σ4‐phosphoranes (arylP=PMe3). A plethora of information is available on the generation of highly reactive terminal phosphinidene complexes [RPW(CO)5] and their chemistry. Many of these methods suffer from comparatively harsh conditions (strong base, heat, etc.) which limit their preparative use. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Straightforward Synthesis of Donor‐Stabilised Phosphenium Adducts from Imidazolium‐2‐carboxylate and Their Electronic Properties
Authors: Azouri Michèle , Andrieu Jacques , Picquet Michel , Richard Philippe , Hanquet Bernard , Tkatchenko Igor 
Published: August 2007

AbstractCationic imidazolium‐2‐phosphanes were obtained by the addition of a chlorophosphane (R2PCl, R = Ph, iPr or Cy) to 1,3‐dimethylimidazolium‐2‐carboxylate without the need for a purification step. An additional anion exchange reaction with KPF6 led to the corresponding halide‐free ligands in excellent yields. The molecular structure of one of them was examined both in the solid state and in solution. The lone pair of electrons on the phosphorus atom is not delocalised to the imidazolium fragment and thus remains available for further metal coordination. As such compounds can be described as phosphenium cations stabilised by a N‐heterocarbene donor base, the electronic properties of the Lewis acceptor phosphorus centre was evaluated upon nickel tricarbonyl coordination, and the properties are surprisingly similar to those found for phosphites. The stronger π‐acceptor character of these imidazolium‐2‐phosphanes relative to that of neutral tertiary phosphanes can thus explain the higher catalytic activities observed with the corresponding rhodium complexes in styrene hydroformylation reactions. Additionally, a preliminary study of platinum coordination chemistry indicated that the steric demand of 1,3‐dimethylimidazolium‐2‐phosphanes is comparable to mixed arylalkylphosphanes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Evidence for Ligand‐Centered Reactivity of a 17e Radical Cationic 2H‐Azaphosphirene Complex
Authors: Helten Holger , Neumann Christoph , Espinosa Arturo , Jones Peter G. , Nieger Martin , Streubel Rainer 
Published: August 2007

AbstractReactions of 2H‐azaphosphirene complex1with electron‐rich nitrile derivatives2a–ein the presence of substoichiometric amounts of ferrocenium hexafluorophosphate yielded regioselectively 2H‐1,4,2‐diazaphosphole complexes3a–eunder mild conditions. The dependence of the reaction on the amount of ferrocenium hexafluorophosphate is discussed. In the reactions of1with electron‐poor nitrile derivatives HCN (2f), EtOC(O)CN (2g), and C6F5CN (2h), byproducts possessing a P–F bond are formed, which indicates that the hexafluorophosphate anion is involved in the reaction course. Apart from NMR spectroscopic (3a–f) and X‐ray data (3b,3d–e), a detailed DFT study is included that provides first insight into the reaction pathway.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Calorimetry of edible oils: Isothermal freezing curve for assessing extra‐virgin olive oil storage history
Authors: Angiuli Marco , Ferrari Carlo , Righetti Maria Cristina , Tombari Elpidio , Salvetti Giuseppe 
Published: August 2007

AbstractThe calorimetric method described here investigates the solid‐liquid phase transitions in a Tuscan extra‐virgin olive oil in order to evaluate the changes induced by light exposition. The parameters of the freezing and the melting curves show high sensitivity to oil quality degradation, in agreement with the data from routine tests at disposal. Possible applications of the method are discussed.
Oxidative Nucleophilic Substitution (SNOx) of the Benzylic Position as a Tunable Synthesis of Tetrahydroisoquinoline Natural Alkaloid Analogues
Authors: Aubry Sylvain , Pellet‐Rostaing Stéphane , Lemaire Marc 
Published: August 2007

AbstractSynthetic investigations of 1,3‐dichloro‐5,6‐dicyanobenzoquinone‐mediated benzylic oxidation is reported for the synthesis of natural alkaloid analogues. Extensive explorations of the oxidative nucleophilic substitution of the benzylic position of β‐phenylethylamine derivatives and the synthesis of functionalized tetrahydroisoquinolines of ecteinascidin 743 precursors have been carried out. Starting from L‐DOPA, a tunable oxazolidinone group was installed under oxidative benzylic conditions. This derivative 13 was submitted to benzylic oxidation reactions using a wide range of carboxylic acids and subsequent chemical transformations of these compounds were attempted. Moreover, an efficient synthesis of an aromatic ketone derivative 20 was achieved and gave rise to tetrahydroisoquinoline 24 through a direct Pictet–Spengler cyclisation reaction. Subsequently, 24 was transformed into functionalized α‐amino alcohols 31a and 31b, precursors of ecteinascidin 743 analogues. In addition, in order to assess the viability of our synthetic strategy, the reaction of 24 with methyl thioglycolate was performed and the stereoselectivity confirmed by X‐ray analysis of 33a. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Oreacerebrosides: Bioactive Cerebrosides with a Triunsaturated Sphingoid Base from the Sea Star Oreaster reticulatus
Authors: Costantino Valeria , de Rosa Caterina , Fattorusso Ernesto , Imperatore Concetta , Mangoni Alfonso , Irace Carlo , Maffettone Carmen , Capasso Domenica , Malorni Livia , Palumbo Rosanna , Pedone Carlo 
Published: August 2007

AbstractThe sea star Oreaster reticulatus contains, along with the known ophidiacerebrosides C–E, nine new glycosphingolipids named oreacerebrosides A–I. Their structures were elucidated by a combination of spectroscopic methods and chemical degradation. All compounds contain a 4,8,10‐triunsaturated sphingoid base. Oreacerebrosides A–C have a β‐glucopyranoside as the sugar residue, as found in ophidiacerebrosides C–E and in all known compounds of this type; in contrast, oreacerebrosides D–I are the first examples of β‐galactosylceramides containing this unusual sphingoid base. Four representative glycosphingolipids were tested for cytotoxic activity on rat glioma C6 cells and were shown to be mildly cytotoxic; the glucosylceramides were more active than the galactosylceramides. In addition, oreacerebroside I, but not ophidiacerebroside E, was shown to exert proangiogenic activity and was able to increase VEGF‐induced human endothelial cell proliferation.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Highly Selective Synthesis of Enantiopure (S,E)‐α,β‐Unsaturated γ‐Amino Esters Through a Sequential Reaction of Ethyl Dibromoacetate with α‐Amino Aldehydes Promoted by Chromium Dichloride
Authors: Concellón José M. , Méjica Carmen 
Published: August 2007

AbstractA sequential reaction of ethyl dibromoacetate with various enantiopure N,N‐dibenzyl‐ or N‐Boc‐α‐amino aldehydes (derived from natural α‐amino acids), promoted by chromium dichloride, afforded optically active (S,E)‐α,β‐unsaturated γ‐amino esters. The C=C double bond was generated with total or very high E‐selectivity and the (S,E)‐α,β‐unsaturated γ‐amino esters were obtained with complete enantiomeric purity, except from N‐Boc‐phenylalaninal (as determined by chiral HPLC). A mechanism is proposed to explain this transformation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Synthesis of Pinguisane‐Type Sesquiterpenoids Acutifolone A, Pinguisenol, and Bisacutifolones by a Diels–Alder Dimerization Reaction
Authors: Shiina Junichi , Oikawa Masataka , Nakamura Kensuke , Obata Rika , Nishiyama Shigeru 
Published: August 2007

AbstractThe total synthesis of pinguisane‐type sesquiterpenoids, acutifolone A (1) and pinguisenol (2), has been achieved by using the Mukaiyama aldol reaction as the key step. The intermolecular Diels–Alder reaction of these monomeric natural products successfully led to stereoselective dimerization, leading to bisacutifolones A (3) and B (4). Theoretical calculations revealed that the dimerization reaction proceeded through the most stable transition state. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Novel Approach to Stabilize Unstable Molecular Wires by Simultaneous Rotaxane Formation – Synthesis of Inclusion Complexes of Oligocarbynes with Cyclic Host Molecules
Authors: Sugiyama Jiro , Tomita Ikuyoshi 
Published: August 2007

AbstractAn effective method to stabilize oligocarbynes as a modelfor polycarbyne by the simultaneous complexation withα‐cyclodextrin (α‐CD) is described. 1,12‐Bis(9‐phenanthryl)‐1,3,5,7,9,11‐dodecahexayne possessing one or two α‐CD molecules was prepared by the oxidative coupling reaction of the corresponding triyne in the presence of α‐CD. The resulting rotaxanes proved to be stable enough in comparison with the corresponding free oligoynes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Highly Efficient Direct Alkylation of Activated Methylene by Cycloalkanes
Authors: Zhang Yuhua , Li Chao‐Jun 
Published: August 2007

AbstractA simple FeCl2‐catalyzed C–C bond formation by direct alkylation of activated methylene by using simple cycloalkanes was developed. Several kinds of alkanes were found to react with phenyl β‐ketone ester and diketone compounds to afford alkylated 1,3‐dicarbonyl compounds in 10–88 % yields. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Direct Electrochemistry of Hemoglobin Immobilized on Carbon‐Coated Iron Nanoparticles for Amperometric Detection of Hydrogen Peroxide
Authors: Zhang Hai‐Li , Zou Xiao‐Zhi , Lai Guo‐Song , Han De‐Yan , Wang Fang 
Published: August 2007

AbstractA novel method for preparation of hydrogen peroxide biosensor was presented based on immobilization of hemoglobin (Hb) on carbon‐coated iron nanoparticles (CIN). CIN was firstly dispersed in a chitosan solution and cast onto a glassy carbon electrode to form a CIN/chitosan composite film modified electrode. Hb was then immobilized onto the composite film with the cross‐linking of glutaraldehyde. The immobilized Hb displayed a pair of stable and quasireversible redox peaks and excellent electrocatalytic reduction of hydrogen peroxide (H2O2), which leading to an unmediated biosensor for H2O2. The electrocatalytic response exhibited a linear dependence on H2O2 concentration in a wide range from 3.1 μM to 4.0 mM with a detection limit of 1.2 μM (S/N=3). The designed biosensor exhibited acceptable stability, long‐term life and good reproducibility.
Multistrip Western blotting to increase quantitative data output
Authors: Aksamitiene Edita , Hoek Jan B. , Kholodenko Boris , Kiyatkin Anatoly 
Published: August 2007

AbstractThe qualitative and quantitative measurements of protein abundance and protein modification states are essential in understanding their role in diverse cellular processes. Traditional Western blotting technique, though sensitive, is prone to produce substantial errors and is not readily adapted to high‐throughput technologies. We propose a modified immunoblotting procedure, which is based on simultaneous transfer of proteins from multiple gel‐strips onto the same membrane, and is compatible with any conventional gel electrophoresis system. As a result, the data output per single blotting cycle can readily be increased up to ten‐fold. In contrast to the traditional “one protein detection per electrophoresis cycle”, this procedure allows simultaneous monitoring of up to nine different proteins. In addition to maintaining the ability to detect picogram quantities of protein, the modified system substantially improves data accuracy by reducing signal errors by two‐fold. Multistrip Western blotting procedure allows making statistically reliable side‐by‐side comparisons of different or repeated sets of data. Compared to the traditional methods, this approach provides a more economical, reproducible, and effective procedure, facilitating the generation of large amounts of high‐quality quantifiable data.
An optimized procedure for solubilization, reduction, and transfer of human breast cancer membrane‐enriched fraction by 2‐DE
Authors: Ruan Yusong , Wan Mingxi 
Published: August 2007

AbstractThe separation of integral and peripheral membrane proteins is still a challenge, although many achievements have been made in the 2‐DE‐based membrane proteomics. Using a human breast cancer cell line, MCF‐7, we investigated the influences of Tris, reducing reagents, cup loading, and SDS on membrane protein solubilization and separation by 2‐DE. The addition of Tris to the sample solution improved the solubilization of the membrane‐enriched fraction, and the best‐quality gel patterns were obtained at 20 mM Tris. Tributylphosphine (TBP), a reducing agent, was not optimum in the 2‐DE process because it not only decreased the solubilization of hydrophobic proteins but also caused some proteins, such as hsp60, prohibitin, and actin, to be resolved to a string of spots. However, when combined with DTT, TBP could improve the resolution of 2‐DE patterns. Cup loading significantly facilitated the entrance of membrane proteins into IPG strips and over 1000 protein spots with high resolution were visualized. Adopting this strategy, an ATP synthase α chain was resolved into two adjacent spots for the first time in 2‐DE gel patterns through the adding DTT in the middle of the IEF. A high SDS concentration in the equilibration buffer enhanced the transfer and increased the staining intensity of ˜50% of the protein spots in the gels, but also resulted in losses of some spots.
Microscale immunoaffinity SPE and MEKC in fast determination of testosterone in male urine
Authors: Amundsen Lotta K. , Nevanen Tarja K. , Takkinen Kristiina , Rovio Stella , Sirén Heli 
Published: August 2007

AbstractConventional methods for the determination of testosterone in body fluids typically suffer from poor recovery, lack of specificity, complex sample pretreatment, or the need for derivatization. Here, a simple, specific, and fast analysis method for testosterone was developed, with a methodology based on testosterone‐specific immunoaffinity SPE (IA‐SPE) and subsequent analysis by partial filling MEKC (PF‐MEKC). An immunosorbent consisting of a recombinant antitestosterone Fab fragment covalently attached to activated Sepharose was prepared. IA‐SPE and PF‐MEKC were set up in hyphenated and off‐line constructions, and the applicability of the two constructions in analysis of testosterone in male urine was investigated. The results obtained with the hyphenated construction proved to be only indicative of the presence of testosterone. The off‐line IA‐SPE and PF–MEKC construction, however, was successfully used in the determination of free testosterone in male urine samples after enzymatic hydrolysis of the glucuronide conjugates. Except for the hydrolysis reaction, no sample pretreatment was required. After hydrolysis, the overall analysis time per sample was only 14 min. The off‐line IA‐SPE and PF‐MEKC method proved to be robust, sensitive (LOQ 35 μg/L), and specific, enabling separation of testosterone from four related steroids. Thus, it provides attractive features when compared to traditional methods for determination of testosterone in male urine.
Protein‐bound glutathione measurement in cultured cells by CZE with LIF detection
Authors: Zinellu Angelo , Sotgia Salvatore , Posadino Anna Maria , Pasciu Valeria , Zinellu Elisabetta , Usai Maria Franca , Scanu Bastianina , Chessa Roberto , Gaspa Leonardo , Tadolini Bruna , Deiana Luca , Carru Ciriaco 
Published: August 2007

AbstractProtein modification due to S‐glutathio(ny)lation, usually a reversible process in intact cells, arises interest as a possible mode of regulatory events that may potentially modify a large number of cellular processes. However, since less than 1% of the total protein is S‐thiolated in resting cells, high sensitivity methods are required for its evaluation. We set up a new method by CE with LIF detection that allows to measure all forms of intracellular GSH involved in the process. For total and reduced glutathione, cell lysates were rapidly derivatized by 5‐iodoacetoamidofluorescein (5‐IAF), a selective reagent which traps thiol groups, thus minimizing auto‐oxidation. Derivatized samples were separated in a 47 cm×75 μm id capillary by using 7 mmol/L sodium phosphate at pH 11.6. For the evaluation of S‐glutathio(ny)lation, intracellular proteins from cell lysates were precipitated and washed to eliminate free GSH. After protein resuspension with NaOH and reduction treatment with tri‐n‐butylphosphine (TBP), the freed GSH was dried in a vacuum concentrator and directly dissolved in the derivatization mixture. GSH–IAF adduct was detected in a 6 mmol/L sodium phosphate, 3 mmol/L boric acid, and 75 mmol/L N‐methylglucamine run buffer in less than 5 min. The high sensitivity ensured by 5‐IAF use and sample concentration, allowed to quantify GSH at levels as low as 5 nmol/L, value suitable for the evaluation of protein S‐glutathio(ny)lation. The method suitability was checked both in HUVEC and ECV304 cultured cells.
Dynamic modification of poly(methyl methacrylate) chips using poly(vinyl alcohol) for glycosaminoglycan disaccharide isomer separation
Authors: Zhang Yong , Ping Guichen , Kaji Noritada , Tokeshi Manabu , Baba Yoshinobu 
Published: August 2007

AbstractWe describe a microchip electrophoresis (MCE) method for the assay of unsaturated disaccharides of chondroitin sulfates, dermatan sulfates, and hyaluronic acid (HA). Poly(vinyl alcohol) (PVA) could be irreversibly adsorbed onto poly(methyl methacrylate) (PMMA) substrates and this approach was applicable for dynamic coating. The characteristics of the PMMA surface with PVA coating were evaluated in terms of the wettability, EOF, and adsorption of 2‐aminoacridone (AMAC)‐labeled disaccharide. The water contact angle decreased from ˜73° on a pristine PMMA surface to ˜37.5° on a PVA‐coated surface, indicating that the PVA coating increased hydrophilicity. EOF was reduced approximately twofold and was relatively stable. Scanning electron microscopy and fluorescence microscopy images showed that adsorption of AMAC‐labeled disaccharides was dramatically suppressed. Using the PVA coating, baseline separation of two pairs of glycosaminoglycan (GAG) disaccharide isomers, ΔDi‐diSB/ΔDi‐diSD and ΔDi‐0S/ΔDi‐HA, was achieved in Tris‐borate buffer within 130 s by MCE.
Base excision repair pathway is involved in the repair of lesions generated by flavonoid‐enriched fractions of pepper tree (Schinus terebinthifolius, Raddi) stem bark
Authors: Varela‐Barca Francisco Napoleão Túlio , Agnez‐Lima Lucymara Fassarella , de Medeiros Sílvia Regina Batistuzzo 
Published: August 2007

AbstractCell‐free and bacterial assays indicate that flavonoid‐enriched fractions and the flavonoids of pepper tree stem bark from Schinus terebinthifolius Raddi have genotoxic rather than antigenotoxic properties. In the present report, we have examined the ability of flavonoid‐enriched fractions to damage plasmid DNA and the repair pathways involved in the recognition of these DNA lesions. High concentrations of two flavonoid‐enriched fractions were able to break phosphodiester bonds in DNA. In addition, studies using bacterial strains deficient in nucleotide excision repair and base excision repair (BER) enzymes indicated that the flavonoid‐enriched fractions generated lesions that were substrates for enzymes belonging to the BER pathway. In addition, in vitro studies indicated that the DNA damage produced by the flavonoid‐enriched fractions was also a substrate for exonuclease III and that the phosphodiester breakage was amplified by copper ions. These results indicate that flavonoids from the pepper tree (Schinus terebinthifolius, Raddi) generate lesions on DNA that are potential targets of FPG and MutY glycosylase from the BER pathway. Chromatographic and spectral analyses helped to support the hypothesis that the flavonoids of the Brazilian pepper tree bark are the main factors involved in the fraction's damage potential. The isolated flavonoids from Fraction II were also tested in vitro and support the oxidative damage potential of these flavonoids. Environ. Mol. Mutagen., 2007. © 2007 Wiley‐Liss, Inc.