bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photocatalytic Hydrogen Generation from Water with Iron Carbonyl Phosphine Complexes: Improved Water Reduction Catalysts and Mechanistic Insights
Authors: Gärtner Felix , Boddien Albert , Barsch Enrico , Fumino Koichi , Losse Sebastian , Junge Henrik , Hollmann Dirk , Brückner Angelika , Ludwig Ralf , Beller Matthias 
Published: April 2011

AbstractAn extended study of a novel visible‐light‐driven water reduction system containing an iridium photosensitizer, an in situ iron(0) phosphine water reduction catalyst (WRC), and triethylamine as sacrificial reductant is described. The influences of solvent composition, ligand, ligand‐to‐metal ratio, and pH were studied. The use of monodentate phosphine ligands led to improved activity of the WRC. By applying a WRC generated in situ from Fe3(CO)12 and tris[3,5‐bis(trifluoromethyl)phenyl]phosphine (P[C6H3(CF3)2]3, Fe3(CO)12/PR3=1:1.5), a catalyst turnover number of more than 1500 was obtained, which constitutes the highest activity reported for any Fe WRC. The maximum incident photon to hydrogen efficiency obtained was 13.4 % (440 nm). It is demonstrated that the evolved H2 flow (0.23 mmol H2 h−1 mg−1 Fe3(CO)12) is sufficient to be used in polymer electrolyte membrane fuel cells, which generate electricity directly from water with visible light. Mechanistic studies by NMR spectroscopy, in situ IR spectroscopy, and DFT calculations allow for an improved understanding of the mechanism. With respect to the Fe WRC, the complex [HNEt3]+[HFe3(CO)11]− was identified as the key intermediate during the catalytic cycle, which led to light‐driven hydrogen generation from water.
Synthesis and Characterization of a Symmetric Bis(7‐hydroxyflavylium) Containing a Methyl Viologen Bridge
Authors: Diniz Ana M. , Pinheiro Carlos , Petrov Vesselin , Parola A. Jorge , Pina Fernando 
Published: April 2011

AbstractA symmetric bis(flavylium) constituted by two 7‐hydroxyflavylium moieties linked by a methylviologen bridge was synthesized. The thermodynamic and kinetics of the network of chemical reactions involving bis(flavylium) and the model compound 7‐hydroxy‐4′‐methylflavylium was completely characterized by means of direct and reverse pH jumps (stopped flow) and flash photolysis. Both compounds follow the usual pH‐dependent network of chemical reactions of flavylium derivatives. The equilibrium species of the model compound are the flavylium cation (acidic species) and the trans‐chalcone (basic species) with an apparent pK′a=2.85. In the case of the bis(flavylium) it was possible to characterize by 1H NMR spectroscopy three species with different degrees of isomerization: all flavylium, flavylium‐trans‐chalcone, and all trans‐chalcone. Representation of the time‐dependent mole fraction distribution of these three forms after a pH jump from equilibrated solutions of all‐flavylium cation (lower pH values) to higher pH values, shows that formation of trans‐chalcone is not completely stochastic (two independent isomerizations), the isomerization of one flavylium showing a small influence on the isomerization of the other. The radical of the methyl viologen bridge is formed upon reduction of the bis(trans‐chalcone) with dithionite. The system is reversible after addition of an oxidant in spite of the occurrence of some decomposition.
Absolute configurations and stability of cyclic guanosine mono‐adducts with glyoxal and methylglyoxal
Authors: Lai Congfang , Lin Guangxin , Wang Wenyue , Luo Hai 
Published: April 2011

AbstractGlyoxal and methylglyoxal are two endogenous and mutagenic 1,2‐dicarbonyl compounds, which can readily form adducts with guanosine. The molecular structures of cyclic guanosine‐glyoxal (G‐g) and guanosine‐methylglyoxal (G‐mg) mono‐adducts have been extensively studied before. However, diastereoisomers of these adducts have not yet been studied in detail. In this work, one pair of G‐g and two pairs of G‐mg diastereoisomers were baseline separated by reverse phase HPLC, whose structures were identified as the previously reported cyclic forms, and their absolute configurations were determined by circular dichroism, the octant rule, and molecular modeling. According to the HPLC elution order, configurations of two G‐g (as well as trans G‐mg) were (6R,7R) and (6S,7S), respectively. Meanwhile, the stability of each isomer in neutral solution was also investigated, which revealed the stability order G‐g > cis G‐mg > trans G‐mg and also indicated distinct transformation processes for different G‐mg configurations. Trans G‐mg only racemized between each other, while cis G‐mg transformed to both cis and trans forms. Different intermediates in the racemization processes were proposed to explain the observations. These results may shed light on further understanding the roles of these two small molecules in mutagenesis. Chirality, 2011. © 2011 Wiley‐Liss, Inc.
Enantiomeric separation of triazole fungicides with 3‐μm and 5‐μml particle chiral columns by reverse‐phase high‐performance liquid chromatography
Authors: Qiu Jing , Dai Shouhui , Zheng Chuangmu , Yang Shuming , Chai Tingting , Bie Mei 
Published: April 2011

AbstractThis study used chiral columns packed with 3‐μm and 5‐μm particles to comparatively separate enantiomers of 9 triazole fungicides, and Lux Cellulose‐1 columns with chiral stationary phase of cellulose‐tris‐(3,5‐dimethylphenylcarbamate) were used on reverse‐phase high‐performance liquid chromatography with flow rates of 0.3 and 1.0 mL min−1 for 3‐μm and 5‐μm columns, respectively. The (+)‐enantiomers of hexaconazole (1), tetraconazole (4), myclobutanil (7), fenbuconazole (8) and the (−)‐enantiomers of flutriafol (2) diniconazole (3), epoxiconazole (5), penconazole (6), triadimefon (9) were firstly eluted from both columns, the elution orders identified with an optical rotation detector didn't change with variety of column particles and mobile phases (acetronitrile/water and methanol/water). The plots of natural logarithms of the selectivity factors (ln α) for all fungicides except penconazole (6) versus the inverse of temperature (1/T) were linear in range of 5–40°C. The thermodynamic parameters (ΔH°, ΔS°, ΔΔH° and ΔΔS°) were calculated using Van't Hoff equations to understand the thermosynamic driving forces for enantioseparation. This work will be very helpful to obtain good enantiomeric separation and establish more efficient analytical method for triazole fungicides. Chirality, 2011. © 2011 Wiley‐Liss, Inc.
Chiral gas chromatography as a tool for investigations into illicitly manufactured methylamphetamine
Authors: Morrison Calum , J Smith Frank , Tomaszewski Tomasz , Stawiarska Karolina , Biziuk Marek 
Published: April 2011

AbstractThe aim of this study was to develop a chiral gas chromatographic method for the separation of compounds likely to be found in the EMDE synthesis of methylamphetamine, a heavily abused stimulant drug. Here we describe the separation of the enantiomers of ephedrine, pseudoephedrine, chlorinated intermediates and methylamphetamine using fluorinated acid anhydrides as chemical derivatization reagents prior to gas chromatographic analysis on a 2,3‐di‐O‐methyl‐6‐t‐butyl silyl‐β‐cyclodextrin stationary phase (CHIRALDEX™ B‐DM). Separation of the enantiomers of pseudoephedrine, methylamphetamine and chloro‐intermediates was achieved using PFPA derivatization, and enantiomers of ephedrine using TFAA derivatization, in run times of less than 40 minutes. The use of HFBA as a derivatization reagent for this set of analytes is also discussed. Chirality, 2011. © 2011 Wiley‐Liss, Inc.
Application of Magnetic Filters in Bioprocess Engineering. Part 3 – New Measuring Method for Quantification of Magnetic Beads in Flowing Suspensions
Authors: Kampeis Percy , Lieblang Michael , Krause Hans‐Joachim 
Published: April 2011

AbstractDie Hochgradienten‐Magnetseparation (HGMS) erlaubt eine Fest/Fest/Flüssig‐Trennung in einem Schritt und eignet sich daher als erster Capture‐Schritt in Aufbereitungsverfahren für biotechnologische Produkte. Während der Magnetfiltration bilden sich Magnetbead‐Anlagerungsbereiche aus. Es besteht die Möglichkeit, dass die durchströmende Biomasse einen Teil der Magnetbeads und damit auch sorbiertes Produkt mitreißt. Für den sicheren Prozessbetrieb des HGMS‐Filters muss die Magnetbead‐Konzentration in der den Filter verlassenden Suspension auch in Gegenwart von Biomasse bestimmt werden. Hierzu wurde ein Messverfahren mit einem Durchfluss‐Magnetsensor zur Quantifizierung der Magnetbeads in strömenden Suspensionen entwickelt.
Ring‐size effect in the reaction of α,ω‐dibromoalkanes with ethyl acetoacetate and its application to the synthesis of some disubstituted oxa‐ and aza‐heterocycles
Authors: Yong‐Yue Lin , Xiao‐Guang (Hiu‐Kuang Leung) Liang , Yuk‐Yee Chan 
Published: April 2011

AbstractUnder basic condition, β‐ketoester has two sites at which alkylation can occur. In the reaction of ethyl acetoacetate with α, ω‐dibromoalkanes (n = 2, 3, 4), the alkylation is dependent on the ring size of the possible cyclic product formed. When n = 2 or 4, cyclopropane 3 or cyclopentane 10 was formed, respectively, as a result of two successive C‐alkylations. However, when n = 3, dihydropyran 7 was formed, arising from a C‐alkylation followed by an alkylation. For the last case, the formation of the six‐member ring is the driving force of the whole process. Cyclopropane 3, when treated with an aromatic amine, was transformed to dihydropyrrole 15 via the possible intermediate of cyclopropyl Shiff's base 14. However, similar reaction was not observed for cyclopentane 10. We attribute this phenomenon to the ring‐size effect again, as in the former case, the steric strain of the cyclopropane ring is released during the rearrangement of the Schiff's base to the final product.
Investigation on preparation and structure of YSr2‐x Cax V3O9‐y
Authors: Jian Meng , Yu‐Fang Ren , Ping He 
Published: April 2011

AbstractNew rare earth vanadates YSr2‐xCaxCaxV3O9‐y (x—0.0, 0.67, 1.0, 1.33 and 2.0) have been synthesized by a new simple method. X‐ray powder diffraction results show that they are mono‐phase. They belong to orthorhombic structure and their lattice constants are calculated. The results of weight gains in TG curves show that the lower valent vanadium is oxidized to higher valent state at higher temperature. The oxygen contents of new compounds are calculated from the weight gains. Both V3+ and V4+ coexist in YSr2‐xCaxV3O9‐y. These compounds exhibit low electric resistivity at room temperature.
Studies on sulfinatodehalogenation: XVII. The sulfinatodehalogenation of primary perfluoroalkyl iodides and bromides by Rongalite
Authors: Bing‐Nan Huang , Jin‐Tao Liu 
Published: April 2011

AbstractUsing acetonitrile or DMF as cosolvent, both perfluoroalkyl iodides such as Cl(CF2)nI (n = 4,6,8, la—lc), CF3 (CF2)n I (n = 5,6,7, ld—lf), I (CF2)n O (CF2) SO3 Na(n = 2,4,6, lg—li) and perfluoroalkyl bromides such as Cl (CF2)n Br (n = 4,6, 3a—3b) and C7F15 Br (3e) reacted with Rongalite in aqueous solution to give the corresponding sulfinates Cl (CF2)n SO2 Na (n = 4,6,8, 2a—2c), CF3‐(CF2)nSO2Na (n = 5,6,7, 2d—2f) and NaO2S(CF2)nO(CF2)2SO3Na (n = 2,4,6, 2g—2i) in moderate yields. 1 H‐perfluoroalkanes were formed as the main products when other solvents such as ethanol. iso‐propanol, 1,4‐dioxane and morpholine were used.
The reaction of perfluoroalkanesulfinates: IV. Perfluoroalkyl radical addition to olefins initiated by single electron oxidation of perfluoroalkanesulfinate
Authors: Wei‐Yuan Huang , Yuan Xie 
Published: April 2011

AbstractSodium perfluoroalkanesulfinates [Cl (CF2)n SO2 Na (1), a, n = 4; b, n = 6; c, n = 8] with the reduction potentials about 0.95—1.00V could be oxidized readily with various oxidizing agents such as Mn (OAc)3 2H2O, Ce (SO4)2, HgSO4 and Co2O3 to generate perfluoroalkyl radicals which added to the olefins RCH  CHR' to give two kinds of adducts, namely RCH (Rf) CHXR' (3, X  H; 4, X  OAc), with good yields depending upon the solvent system used. Different oxidizing agents showed slight variation on the yields of the adducts. The reaction time could be greatly shortened at higher temperature. Thus, this reaction provides a new way for introducing a perfluoroalkyl group into olefinic compounds.
A study on the sulfenylchlorination of cembrene and the related cembranoids
Authors: Zhu‐Jin Liu , Yun‐Long Li , Qing‐Zhi Chen , Wei‐Qi Wang 
Published: April 2011

Abstractp‐Tolylsulfenyl chloride adds regioselectively at the C(11)  C(12) bond of cembrene 1 to give 11‐(R)‐p‐tolylthio‐1‐(S)‐cembra‐2E, 4Z, 7E, 12(20)‐tetraene 2 following a rapid HCl elimination. Two new cembranoids, 1‐(S)‐cembra‐2E, 4Z, 7E, 12(20)‐tetraene 3 and 1‐(S)‐cembra‐2E, 4Z, 7E, 11Z‐tetraen‐20‐ol 4 are prepared from 2.
AC impedance study on semiconducting properties of anodic plumbous oxide film
Authors: Cong Pu , Zhuo‐Li He , Hou‐Tian Liu , Xia‐Lin Chen , Wei‐Fang Zhou 
Published: April 2011

AbstractThe semiconducting properties of anodic film formed on Pb in 4.5mol·dm−3H2SO4 solution (30°C) at 0.9 V (vs. Hg/Hg2SO4) for 2 h were studied using AC impedance method. The phase composition of the film is PbSO4 and PbO·PbSO4. The semiconducting properties are due to the latter. The Mott‐Schottky plots show that the said film is an n‐type semiconductor with flat‐band potential of −0.9 V (vs. Hg/Hg2SO4) and donor density of 1×1016 cm−3. The surface density measured at 410–2500 Hz is (2–5)×1012 cm−2 eV−1.
A DNMR study on the ring inversion of oxazolidines
Authors: Li Yang , Kun Gao , Su‐Ling Kong , Yao‐Zu Chen 
Published: April 2011

AbstractRing inversion of eight substituted 2‐phenyl‐4, 4‐dimethyloxazolidines in o‐dichlorobenzene‐d4 was studied by 1H DNMR. Very high inversion barriers (ΔGo≠ = 86.7–93.4 kJ·mol−1) were found for these oxazolidine rings. The magnitude of the inversion barrier is dependent on the polarity of the substituent on the phenyl group. A linear correlation is present between the ΔGo≠ of the inversion and the substituent constant, σ+, of the substituent.
A novel 2‐C reactivity studies of 1‐aroyl‐1,2‐dihydro‐3H‐naphtho[2,1‐b]pyran‐3‐ones
Authors: El‐Kasaby  , Hassan  , Shiba  , Abou‐El‐Regal  
Published: April 2011

AbstractThe 2‐C, methylene group of 1‐aroyl‐1,2‐dihydro‐3H‐naphtho[2,1‐b]pyran‐3‐ones (2) have been showed to possess a superior reactivity towards many of organic reagents. The naphthopyrones (2) condensed with aromatic aldehydes to give the 2‐arylidine derivatives (3). Bromination of 2 gave 1,2‐dibromo (4) or 5‐bromo (5) derivatives depending on the reaction conditions. The base catalyzed addition or cycloaddition of naphthopyrones (2) to 4‐methoxy benzalacetophenone gave the expected Michael adduct (6) or the cyclic adducts (7–9) depending on the type of catalytic base and reaction conditions. Structures of the products have been established by elemental analyses, IR and 1H NMR spectroscopic methods.
Studies on the alcohol exchange reactions of methoxide ditungsten [W(IV)] compound W2Cl4(OCH3)4 (CH3OH)2, prepared from (n‐Bu4N)3W2Cl9
Authors: Hong Bo , Jin Song‐Lin , Yih‐Tong (Gu, Yi‐Dong) Ku , Chen Ming‐Qin 
Published: April 2011

Abstract(n‐Bu4N)3W2Cl9, prepared from K3W2Cl9, can be readily converted to a series of [W(IV)] cluster compounds, W2Cl4 (μ‐OR)2 (OR')2 (R'OH)2, including seven known compounds and two new compounds with R=Me, R'=i‐Pr and sec‐Bu. The crystallographic data of 7 and 8 are hereby presented.
Influence of Negative Ions on Drift Waves in a Low‐Density Ar/O2‐Plasma
Authors: Knist S. , Greiner F. , Biss F. , Piel A. 
Published: April 2011

AbstractThe effect of negative ions on the drift wave instability has been studied in detail in a linear device by means of Langmuir probes and cross‐correlation analysis. Drift waves are excited in low‐density (5 × 1014 m–3) and strongly magnetized (0.5 T) pure argon plasmas and in the presence of an oxygen admixture. The radial density profile of negative ions is hollow. For increasing concentration of negative ions the wave frequency decreases by about 25%. Despite of an axial density gradient, a global wave frequency is established for the entire column length. While for the noble gas case the drift wave frequency is given by the equilibrium plasma parameters in the mid‐plane, there is no such relationship for the argon plasma with oxygen admixture. This different finding is attributed to the inhomogeneous distribution of the negative ions (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dust Self‐Organized Structures II. Solutions of Master Equations for Small Diffusion
Authors: Tsytovich V. , Morfill G. 
Published: April 2011

AbstractMaster equations for spherical dust structures are solved numerically using the asymptotic solutions at the center of the structures for the case of absence of external ionization and small diffusions. The structures are determined by a single parameter, the external plasma flux at the surface of the structure. The equilibrium states that are possible in a limited range of this parameter are investigated numerically. It is demonstrated that in the range of existence of equilibria the structures are changing their shapes and type of distributions inside the structures. For large external fluxes the ion and dust distributions can have peaks inside the structures while for low external fluxes the dust distribution has a single maximum at the structure center. The lower is the external flux supporting the structure the larger is its size. An increase of the external flux decreases the accumulation of dust and ions at the center. The total number of dust confined by the structure is larger for larger size structures. Estimates of dust crystallization inside structures are given. The role of diffusion is calculated by perturbations and is shown to be small in all structure regions except the structure edges. In the perturbation theory we use the exact expressions of the diffusion coefficients calculated previously numerically. The regions with dust density peaks inside the structures have been calculated with two order of magnitude larger precision that allows to resolve the structure parameter dependencies inside the peaks. It is shown that although in peaks the gradients of all parameters are increased the diffusion flux is still small and that the continuity and hydrodynamic approach are applicable within an accuracy about several %‐s (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Dust Self‐Organized Structures III. Solutions of Master Equations in Presence of Volume Ionization
Authors: Tsytovich V. , Morfill G. 
Published: April 2011

AbstractThe shapes of dust self‐organized structures in presence of volume ionization is investigated. Master Equations for small diffusions and presence of an external ionization describing spherical dust structures are solved numerically using asymptotic solutions at the center of the structures. The structures are determined by two parameters, the external plasma flux at the surface of the structures and the power of volume ionizations. It is shown that the range of possible equilibrium states is reduced with an increase of the ionization power. This reduction is due mainly to an increase of the minimum possible value of ion density at the center of the structure for which the equilibrium is possible (an increase of minimum possible external flux). It is found that for certain large ionization power the equilibrium structure without void at the center cannot exist. The critical value of ionization power is found numerically. In the range of ionization power where the equilibria is possible the distribution of the parameters inside the structures are investigated by solving the Master Equations in the limits of small and large ionization power (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Heparan sulfate proteoglycan specificity during axon pathway formation in the Drosophila embryo
Authors: Smart Ashley D. , Course Meredith M. , Rawson Joel , Selleck Scott , Van Vactor David , Johnson Karl G. 
Published: April 2011

AbstractAxon guidance is influenced by the presence of heparan sulfate (HS) proteoglycans (HSPGs) on the surface of axons and growth cones (Hu, [2001]: Nat Neurosci 4:695–701; Irie et al. [2002]: Development 129:61–70; Inatani et al. [2003]: Science 302:1044–1046; Johnson et al. [2004]: Curr Biol 14:499–504; Steigemann et al. [2004]: Curr Biol 14:225–230). Multiple HSPGs, including Syndecans, Glypicans and Perlecans, carry the same carbohydrate polymer backbones, raising the question of how these molecules display functional specificity during nervous system development. Here we use the Drosophila central nervous system (CNS) as a model to compare the impact of eliminating Syndecan (Sdc) and/or the Glypican Dally‐like (Dlp). We show that Dlp and Sdc share a role in promoting accurate patterns of axon fasciculation in the lateral longitudinal neuropil; however, unlike mutations in sdc, which disrupt the ability of the secreted repellent Slit to prevent inappropriate passage of axons across the midline, mutations in dlp show neither midline defects nor genetic interactions with Slit and its Roundabout (Robo) receptors at the midline. Dlp mutants do show genetic interactions with Slit and Robo in lateral fascicle formation. In addition, simultaneous loss of Dlp and Sdc demonstrates an important role for Dlp in midline repulsion, reminiscent of the functional overlap between Robo receptors. A comparison of HSPG distribution reveals a pattern that leaves midline proximal axons with relatively little Dlp. Finally, the loss of Dlp alters Slit distribution distal but not proximal to the midline, suggesting that distinct yet overlapping pattern of HSPG expression provides a spatial system that regulates axon guidance decisions. © 2010 Wiley Periodicals, Inc. Develop Neurobiol 71: 608–618, 2011
Bergman Cyclization of Fluorinated Benzo‐Fused Enediynes to Naphthalene Derivatives: Syntheses and Structures
Authors: Kane Christopher M. , Meyers Tiffany B. , Yu Xin , Gerken Michael , Etzkorn Markus 
Published: April 2011

AbstractFluorinated naphthalene derivatives were prepared by Bergman cyclization of fluorinated benzo‐fused enediynes. This route provides access to the aromatic target compounds in a two‐step procedure from commercially available precursors, via a Sonogashira cross‐coupling and a subsequent, thermally initiated Bergman cyclization. Crystal structures of six fluorinated benzo‐enediynes and three fluorinated naphthalene derivatives display significant diversity in their molecular structures and in the crystal packing arrangements. The rather subtle structural change from di‐ to tetrafluorobenzo‐enediynes, as well as the variation in the terminal acetylene subunit led to different non‐covalent interactions in the solid state that ultimately govern their crystal structures.
N‐Arylcarbonylpseudoprolines as Tunable Chiral Derivatizing Agents for the Determination of the Absolute Configuration of Secondary Alcohols
Authors: Han So‐Yeong , Choi Kihang 
Published: April 2011

AbstractNew chiral derivatizing agents, 3‐arylcarbonyl‐2,2‐dimethyloxazolidine‐4‐carboxylic acids (N‐arylcarbonylpseudoprolines), were prepared through a simple, short‐step synthesis. The absolute configuration of secondary alcohols can be assigned on the basis of the NMR spectroscopic chemical shift difference between diastereomeric pseudoproline esters. Preparation of more efficient agents was achieved simply by using aromatic groups with stronger anisotropic effect.