bluuebunny/crossref_metadata_2025_split huggingface dataset:
Cell fate determination during tooth development and regeneration
Authors: Mitsiadis Thimios A. , Graf Daniel 
Published: September 2009

AbstractTeeth arise from sequential and reciprocal interactions between the oral epithelium and the underlying cranial neural crest‐derived mesenchyme. Their formation involves a precisely orchestrated series of molecular and morphogenetic events, and gives us the opportunity to discover and understand the nature of the signals that direct cell fates and patterning. For that reason, it is important to elucidate how signaling factors work together in a defined number of cells to generate the diverse and precise patterned structures of the mature functional teeth. Over the last decade, substantial research efforts have been directed toward elucidating the molecular mechanisms that control cell fate decisions during tooth development. These efforts have contributed toward the increased knowledge on dental stem cells, and observation of themolecular similarities that exist between tooth development andregeneration. Birth Defects Research (Part C) 87:199–211, 2009. © 2009 Wiley‐Liss, Inc.
Molecular regulation of vertebrate retina cell fate
Authors: Andreazzoli Massimiliano 
Published: September 2009

AbstractThe specification of retinal cell fate is a multistep process that begins during early development and results from the spatio‐temporal coordination of cell cycle, cell differentiation, and morphogenesis. This review focuses on recent advances in understanding the molecular mechanisms underlying the distinct steps of retinal specification. Emphasis is placed on key regulatory events that control the multipotency of retinal progenitors, the generation of cell diversity, and the establishment of the clock that determines the ordered generation of retinal cell types. These basic studies have paved the way to the latest progress on the isolation and in vitro generation of retinal stem cells, which is presented in the light of possible therapeutic applications. Birth Defects Research (Part C) 87:284–295, 2009. © 2009 Wiley‐Liss, Inc.
Syringolin A Selectively Labels the 20 S Proteasome in Murine EL4 and Wild‐Type and Bortezomib‐Adapted Leukaemic Cell Lines
Authors: Clerc Jérôme , Florea Bogdan I. , Kraus Marianne , Groll Michael , Huber Robert , Bachmann André S. , Dudler Robert , Driessen Christoph , Overkleeft Herman S. , Kaiser Markus 
Published: September 2009

AbstractThe natural product syringolin A (SylA) is a potent proteasome inhibitor with promising anticancer activities. To further investigate its potential as a lead structure, selectivity profiling with cell lysates was performed. At therapeutic concentrations, a rhodamine‐tagged SylA derivative selectively bound to the 20 S proteasome active sites without detectable off‐target labelling. Additional profiling with lysates of wild‐type and bortezomib‐adapted leukaemic cell lines demonstrated the retention of this proteasome target and subsite selectivity as well as potency even in clinically relevant cell lines. Our studies, therefore, propose that further development of SylA might indeed result in an improved small molecule for the treatment of leukaemia.
Study on the Synthesis of n‐Butyl Acetate by Catalytic Rectification
Authors: Du Y. , Guo J. 
Published: September 2009

AbstractWith Hβ zeolite as the catalyst and θ rings as the fillings, the technological process of synthesizing n‐butyl acetate with acetic acid and n‐butanol in a Φ 30 mm and 2 m tall catalytic rectifying column was studied. The influence of factors such as catalyst loading height, material feed site, reflux ratio and feed rate on the esterification reaction and the rectification effect was investigated. The study results suggested that the appropriate conditions of n‐butyl acetate synthesis by catalytic rectification include: The height ratio of the rectifying section, the reaction section and the stripping section is 1:1:1; acetic acid and n‐butanol are fed in upside and downside of the reaction section, respectively; the reflux ratio is 2.5; the liquid hourly space velocity of n‐butanol is 0.64 h–1. Under these conditions, the mass fraction of n‐butyl acetate in the column bottom is 98.64 %, and the total yield of n‐butyl acetate is 91.5 %.
Synthesis, Structure, and Highly Efficient Copper‐Catalyzed Aziridination with a Tetraaza‐Bispidine Ligand
Authors: Comba Peter , Haaf Christina , Lienke Achim , Muruganantham Amsaveni , Wadepohl Hubert 
Published: September 2009

AbstractThe distorted trigonal‐bipyramidal CuII complex [Cu(L1)(NCCH3)]2+ of the novel tetradentate bispidine‐derived ligand L1 with four tertiary amine donors (L1=1,5‐diphenyl‐3‐methyl‐7‐(1,4,6‐trimethyl‐1,4‐diazacycloheptane‐6‐yl)diazabicyclo[3.3.1]nonane‐9‐one) is a very efficient catalyst for the aziridination of olefins in the presence of a nitrene source. In agreement with the experimental data (in situ spectroscopy, product distribution, and its dependence on the geometry of the substrate and of the nitrene source), a theoretical analysis based on DFT calculations indicates that the active catalyst has the Cu center in its +II oxidation state, that electron transfer is not involved, and that the conversion of the olefin to an aziridine is a stepwise process involving a radical intermediate. The striking change of efficiency and reaction mechanism between classical copper–bispidine complexes and the novel L1‐based catalyst is primarily attributed to the structural variation, enforced by the ligand architecture.
Dinitrogen Activation by Fryzuk’s [Nb(P2N2)] Complex and Comparison with the Laplaza–Cummins [Mo{N(R)Ar}3] and Schrock [Mo(N3N)] Systems
Authors: Christian Gemma J. , Terrett Richard N. L. , Stranger Robert , Cavigliasso Germán , Yates Brian F. 
Published: September 2009

AbstractThe reaction profile of N2 with Fryzuk’s [Nb(P2N2)] (P2N2=PhP(CH2SiMe2NSiMe2CH2)2PPh) complex is explored by density functional calculations on the model [Nb(PH3)2(NH2)2] system. The effects of ligand constraints, coordination number, metal and ligand donor atom on the reaction energetics are examined and compared to the analogous reactions of N2 with the three‐coordinate Laplaza‐Cummins [Mo{N(R)Ar}3] and four‐coordinate Schrock [Mo(N3N)] (N3N=[(RNCH2CH2)3N]3−) systems. When the model system is constrained to reflect the geometry of the P2N2 macrocycle, the NN bond cleavage step, via a N2‐bridged dimer intermediate, is calculated to be endothermic by 345 kJ mol−1. In comparison, formation of the single‐N‐bridged species is calculated to be exothermic by 119 kJ mol−1, and consequently is the thermodynamically favoured product, in agreement with experiment. The orientation of the amide and phosphine ligands has a significant effect on the overall reaction enthalpy and also the NN bond cleavage step. When the ligand constraints are relaxed, the overall reaction enthalpy increases by 240 kJ mol−1, but the N2 cleavage step remains endothermic by 35 kJ mol−1. Changing the phosphine ligands to amine donors has a dramatic effect, increasing the overall reaction exothermicity by 190 kJ mol−1 and that of the NN bond cleavage step by 85 kJ mol−1, making it a favourable process. Replacing NbII with MoIII has the opposite effect, resulting in a reduction in the overall reaction exothermicity by over 160 kJ mol−1. The reaction profile for the model [Nb(P2N2)] system is compared to those calculated for the model Laplaza and Cummins [Mo{N(R)Ar}3] and Schrock [Mo(N3N)] systems. For both [Mo(N3N)] and [Nb(P2N2)], the intermediate dimer is calculated to lie lower in energy than the products, although the final NN cleavage step is much less endothermic for [Mo(N3N)]. In contrast, every step of the reaction is favourable and the overall exothermicity is greatest for [Mo{N(R)Ar}3], and therefore this system is predicted to be most suitable for dinitrogen cleavage.
Asymmetric Transfer Hydrogenation of Ketones Catalyzed by Amino Acid Derived Rhodium Complexes: On the Origin of Enantioselectivity and Enantioswitchability
Authors: Ahlford Katrin , Ekström Jesper , Zaitsev Alexey B. , Ryberg Per , Eriksson Lars , Adolfsson Hans 
Published: September 2009

AbstractAmino acid based thioamides, hydroxamic acids, and hydrazides have been evaluated as ligands in the rhodium‐catalyzed asymmetric transfer hydrogenation of ketones in 2‐propanol. Catalysts containing thioamide ligands derived from L‐valine were found to selectively generate the product with an R configuration (95 % ee), whereas the corresponding L‐valine‐based hydroxamic acids or hydrazides facilitated the formation of the (S)‐alcohols (97 and 91 % ee, respectively). The catalytic reduction was examined by performing a structure–activity correlation investigation with differently functionalized or substituted ligands and the results obtained indicate that the major difference between the thioamide and hydroxamic acid based catalysts is the coordination mode of the ligands. Kinetic experiments were performed and the rate constants for the reduction reactions were determined by using rhodium–arene catalysts derived from amino acid thioamide and hydroxamic acid ligands. The data obtained show that the thioamide‐based catalyst systems demonstrate a pseudo‐first‐order dependence on the substrate, whereas pseudo‐zero‐order dependence was observed for the hydroxamic acid containing catalysts. Furthermore, the kinetic experiments revealed that the rate‐limiting steps of the two catalytic systems differ. From the data obtained in the structure–activity correlation investigation and along with the kinetic investigation it was concluded that the enantioswitchable nature of the catalysts studied originates from different ligand coordination, which affects the rate‐limiting step of the catalytic reduction reaction.
Chiral Catalysts Dually Functionalized with Amino Acid and Zn2+ Complex Components for Enantioselective Direct Aldol Reactions Inspired by Natural Aldolases: Design, Synthesis, Complexation Properties, Catalytic Activities, and Mechanistic Study
Authors: Itoh Susumu , Kitamura Masanori , Yamada Yasuyuki , Aoki Shin 
Published: September 2009

AbstractAldolases are enzymes that catalyze stereospecific aldol reactions in a reversible manner. Naturally occurring aldolases include class I aldolases, which catalyze aldol reactions via enamine intermediates, and class II aldolases, in which Zn2+ enolates of substrates react with acceptor aldehydes. In this work, Zn2+ complexes of L‐prolyl‐pendant[15]aneN5 (ZnL3), L‐prolyl‐pendant[12]aneN4 (ZnL4), and L‐valyl‐pendant[12]aneN4 (ZnL5) were designed and synthesized for use as chiral catalysts for enantioselective aldol reactions. The complexation constants for L3 to L5 with Zn2+ [logKs(ZnL)] were determined to be 14.1 (for ZnL3), 7.6 (for ZnL4), and 9.6 (for ZnL5), indicating that ZnL3 is more stable than ZnL4 and ZnL5. The deprotonation constants of Zn2+‐bound water [pKa(ZnL) values] for ZnL3, ZnL4, and ZnL5 were calculated to be 9.2 (for ZnL3), 8.2 (for ZnL4), and 8.6 (for ZnL5), suggesting that the Zn2+ ions in ZnL3 is a less acidic Lewis acid than in ZnL4 and ZnL5. These values also indicated that the amino groups on the side chains weakly coordinate to Zn2+. We carried out aldol reactions between acetone and 2‐chlorobenzaldehyde and other aldehydes in the presence of catalytic amounts of the chiral Zn2+ complexes in acetone/H2O at 25 and 37 °C. Whereas ZnL3 yielded the aldol product in 43 % yield and 1 % ee (R), ZnL4 and ZnL5 afforded good chemical yields and high enantioselectivities of up to 89 % ee (R). UV titrations of proline and ZnL4 with acetylacetone (acac) in DMSO/H2O (1:2) indicate that ZnL4 facilitates the formation of the ZnL4⋅(acac)− complex (Kapp=2.1×102 M−1), whereas L‐proline forms a Schiff base with acac with a very small equilibrium constant. These results suggest that the amino acid components and the Zn2+ ions in ZnL4 and ZnL5 function in a cooperative manner to generate the Zn2+‐enolate of acetone, thus permitting efficient enantioselective CC bond formation with aldehydes.
Catalytic Activity Dependency on Catalyst Components in Aerobic Copper–TEMPO Oxidation
Authors: Kumpulainen Esa T. T. , Koskinen Ari M. P. 
Published: September 2009

AbstractThe influence of catalyst components in the copper–TEMPO (2,2,6,6‐tetramethylpiperidine N‐oxide) catalysed aerobic oxidation of alcohols was investigated. The type and amount of base greatly influences reactivity. The bipyridyl ligand concentration had no major influence on catalysis, but excessive amounts led to a decrease in activity for longer reaction times. The kinetic dependency for TEMPO was found to be 1.15, and for copper 2.25, which is an indication of a binuclear catalytic system. Optimised conditions with various allylic and aliphatic alcohols give good to excellent rapid oxidations.
Templated Synthesis of Copper(II) Azacyclam Complexes Using Urea as a Locking Fragment and Their Metal‐Enhanced Binding Tendencies towards Anions
Authors: Boiocchi Massimo , Fabbrizzi Luigi , Garolfi Mauro , Licchelli Maurizio , Mosca Lorenzo , Zanini Cristina 
Published: September 2009

AbstractCopper(II) azacyclam complexes 32+ and 42+ were obtained through a metal‐templated procedure involving the pertinent open‐chain tetramine, formaldehyde and a phenylurea derivative as a locking fragment. Both metal complexes can establish interactions with anions through the metal centre and the amide NH group. Equilibrium studies in DMSO by a spectrophotometric titration technique were carried out to assess the affinity of 32+ and 42+ towards anions. While the NH group of an amide model compound and the metal centre of the plain CuII(azacyclam)2+ complex do not interact at all with anions, 32+ and 42+ establish strong interactions with oxo anions, profiting from a pronounced cooperative effect. In particular, 1) they form stable 1:1 and 1:2 complexes with H2PO4− ions in a stepwise mode with both hydrogen‐bonding and metal–ligand interactions, and 2) in the presence of CH3COO−, they undergo deprotonation of the amido NH group and thus profit from axial coordination of the partially negatively charged carbonyl oxygen atom in a scorpionate binding mode.
Bifunctional Heterogeneous Catalysis of Silica–Alumina‐Supported Tertiary Amines with Controlled Acid–Base Interactions for Efficient 1,4‐Addition Reactions
Authors: Motokura Ken , Tanaka Satoka , Tada Mizuki , Iwasawa Yasuhiro 
Published: September 2009

AbstractWe report the first tunable bifunctional surface of silica–alumina‐supported tertiary amines (SA–NEt2) active for catalytic 1,4‐addition reactions of nitroalkanes and thiols to electron‐deficient alkenes. The 1,4‐addition reaction of nitroalkanes to electron‐deficient alkenes is one of the most useful carbon–carbon bond‐forming reactions and applicable toward a wide range of organic syntheses. The reaction between nitroethane and methyl vinyl ketone scarcely proceeded with either SA or homogeneous amines, and a mixture of SA and amines showed very low catalytic activity. In addition, undesirable side reactions occurred in the case of a strong base like sodium ethoxide employed as a catalytic reagent. Only the present SA‐supported amine (SA–NEt2) catalyst enabled selective formation of a double‐alkylated product without promotions of side reactions such as an intramolecular cyclization reaction. The heterogeneous SA–NEt2 catalyst was easily recovered from the reaction mixture by simple filtration and reusable with retention of its catalytic activity and selectivity. Furthermore, the SA–NEt2 catalyst system was applicable to the addition reaction of other nitroalkanes and thiols to various electron‐deficient alkenes. The solid‐state magic‐angle spinning (MAS) NMR spectroscopic analyses, including variable‐contact‐time 13C cross‐polarization (CP)/MAS NMR spectroscopy, revealed that acid–base interactions between surface acid sites and immobilized amines can be controlled by pretreatment of SA at different temperatures. The catalytic activities for these addition reactions were strongly affected by the surface acid–base interactions.
Anticancer Agents from the Australian Tropical Rainforest: Spiroacetals EBC‐23, 24, 25, 72, 73, 75 and 76
Authors: Dong Lin , Schill Heiko , Grange Rebecca L. , Porzelle Achim , Johns Jenny P. , Parsons Peter G. , Gordon Victoria A. , Reddell Paul W. , Williams Craig M. 
Published: September 2009

AbstractEBC‐23, 24, 25, 72, 73, 75 and 76 were isolated from the fruit of Cinnamomum laubatii (family Lauraceae) in the Australian tropical rainforests. EBC‐23 (1) was synthesized stereoselectively, in nine linear steps in 8 % overall yield, to confirm the reported relative stereochemistry and determine the absolute stereochemistry. Key to the total synthesis was a series of Tietze–Smith linchpin reactions. The novel spiroacetal structural motif, exemplified by EBC‐23 (1), was found to inhibit the growth of the androgen‐independent prostate tumor cell line DU145 in the mouse model, indicating potential for the treatment of refractory solid tumors in adults.
Gold‐Catalyzed Intermolecular Addition of Carbonyl Compounds to 1,6‐Enynes: Reactivity, Scope, and Mechanistic Aspects
Authors: Schelwies Mathias , Moser Ralph , Dempwolff Adrian L. , Rominger Frank , Helmchen Günter 
Published: September 2009

AbstractA full account of a recently discovered gold(I)‐catalyzed reaction, a cycloaddition of carbonyl compounds to enynes yielding 2‐oxabicyclo[3.1.0]hexanes with four stereogenic centers, is presented. The reaction proceeds with very high diastereoselectivity. The scope of the reaction has been investigated. In addition, experiments and DFT calculations concerning mechanistic aspects were carried out. The reaction course varies with the substitution pattern of the alkene moiety of the starting enyne. Branched olefins led to 2‐oxabicyclo[3.1.0]hexanes; terminally substituted olefins proceeded with the incorporation of two carbonyl components to give hexahydrocyclopenta[d][1,3]dioxines.
Stacking Structure of Confined 1‐Butanol in SBA‐15 Investigated by Solid‐State NMR Spectroscopy
Authors: Lin Yun‐Chih , Chou Hung‐Lung , Subramanyam Sarma Loka , Hwang Bing‐Joe 
Published: September 2009

AbstractUnderstanding the complex thermodynamic behavior of confined amphiphilic molecules in biological or mesoporous hosts requires detailed knowledge of the stacking structures. Here, we present detailed solid‐state NMR spectroscopic investigations on 1‐butanol molecules confined in the hydrophilic mesoporous SBA‐15 host. A range of NMR spectroscopic measurements comprising of 1H spin–lattice (T1), spin–spin (T2) relaxation, 13C cross‐polarization (CP), and 1H,1H two‐dimensional nuclear Overhauser enhancement spectroscopy (1H,1H 2D NOESY) with the magic angle spinning (MAS) technique as well as static wide‐line 2H NMR spectra have been used to investigate the dynamics and to observe the stacking structure of confined 1‐butanol in SBA‐15. The results suggest that not only the molecular reorientation but also the exchange motions of confined molecules of 1‐butanol are extremely restricted in the confined space of the SBA‐15 pores. The dynamics of the confined molecules of 1‐butanol imply that the 1H,1H 2D NOESY should be an appropriate technique to observe the stacking structure of confined amphiphilc molecules. This study is the first to observe that a significant part of confined 1‐butanol molecules are orientated as tilted bilayered structures on the surface of the host SBA‐15 pores in a time‐average state by solid‐state NMR spectroscopy with the 1H,1H 2D NOESY technique.
ScIII‐Doped Zeolites as New Heterogeneous Catalysts: Mukaiyama Aldol Reaction
Authors: Olmos Andrea , Alix Aurélien , Sommer Jean , Pale Patrick 
Published: September 2009

AbstractScIII‐doped solids based on zeolite materials have been investigated for the first time as catalysts in organic synthesis. ScIII–USY zeolite proved to be a novel and very efficient heterogeneous catalyst for the Mukaiyama aldol reaction. This easy‐to‐prepare catalyst exhibited wide scope and compatibility with functional groups and is very simple to use, easy to remove (by simple filtration), and is recyclable (up to three times without loss of activity).
The Influence of N‐Heterocyclic Carbenes (NHC) on the Reactivity of [Ru(NHC)4H]+ With H2, N2, CO and O2
Authors: Burling Suzanne , Häller L. Jonas L. , Mas‐Marzá Elena , Moreno Aitor , Macgregor Stuart A. , Mahon Mary F. , Pregosin Paul S. , Whittlesey Michael K. 
Published: September 2009

AbstractThe five‐coordinate ruthenium N‐heterocyclic carbene (NHC) hydrido complexes [Ru(IiPr2Me2)4H][BArF4] (1; IiPr2Me2=1,3‐diisopropyl‐4,5‐dimethylimidazol‐2‐ylidene; ArF=3,5‐(CF3)2C6H3), [Ru(IEt2Me2)4H][BArF4] (2; IEt2Me2=1,3‐diethyl‐4,5‐dimethylimidazol‐2‐ylidene) and [Ru(IMe4)4H][BArF4] (3; IMe4=1,3,4,5‐tetramethylimidazol‐2‐ylidene) have been synthesised following reaction of [Ru(PPh3)3HCl] with 4–8 equivalents of the free carbenes at ambient temperature. Complexes 1–3 have been structurally characterised and show square pyramidal geometries with apical hydride ligands. In both dichloromethane or pyridine solution, 1 and 2 display very low frequency hydride signals at about δ −41. The tetramethyl carbene complex 3 exhibits a similar chemical shift in toluene, but shows a higher frequency signal in acetonitrile arising from the solvent adduct [Ru(IMe4)4(MeCN)H][BArF4], 4. The reactivity of 1–3 towards H2 and N2 depends on the size of the N‐substituent of the NHC ligand. Thus, 1 is unreactive towards both gases, 2 reacts with both H2 and N2 only at low temperature and incompletely, while 3 affords [Ru(IMe4)4(η2‐H2)H][BArF4] (7) and [Ru(IMe4)4(N2)H][BArF4] (8) in quantitative yield at room temperature. CO shows no selectivity, reacting with 1–3 to give [Ru(NHC)4(CO)H][BArF4] (9–11). Addition of O2 to solutions of 2 and 3 leads to rapid oxidation, from which the RuIII species [Ru(NHC)4(OH)2][BArF4] and the RuIV oxo chlorido complex [Ru(IEt2Me2)4(O)Cl][BArF4] were isolated. DFT calculations reproduce the greater ability of 3 to bind small molecules and show relative binding strengths that follow the trend CO ≫ O2 > N2 > H2.
ChemInform Abstract: Relative Stability of closo‐closo, closo‐nido, and nido‐nido Macropolyhedral Boranes: The Role of Orbital Compatibility
Authors: Shameema Oottikkal , Jemmis Eluvathingal D. 
Published: September 2009

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Study of the Crystal Chemistry of the n = 2 Ruddlesden—Popper Phases Sr3FeMO6+δ (M: Fe, Co, and Ni) Using in situ High Temperature Neutron Powder Diffraction.
Authors: Mogni Liliana V. , Prado Fernando D. , Cuello Gabriel J. , Caneiro Alberto 
Published: September 2009

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Structural and Magnetic Properties of Pr18Li8Fe5‐xMxO39 (M: Ru, Mn, Co).
Authors: Dutton Sian E. , Battle Peter D. , Grandjean Fernande , Long Gary J. , Sougrati Moulay T. , van Daesdonk Peter A. , Winstone Emma 
Published: September 2009

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.