bluuebunny/crossref_metadata_2025_split huggingface dataset:
Enantiomerically Pure Titanium Complexes Containing an [OSSO]‐Type Bis(phenolate) Ligand: Synthesis, Structure, and Formation of Optically Active Oligostyrenes
Authors: Meppelder Geert‐Jan M. , Beckerle Klaus , Manivannan Ramanujachary , Lian Bing , Raabe Gerhard , Spaniol Thomas P. , Okuda Jun 
Published: July 2008

AbstractChiral 1,2‐trans‐dithiocyclohexanediyl‐bridged bis(phenols) of the type [2,2′‐{HOC6H2‐6‐R1‐4‐R2}2S2C6H10] ([OSSO]H2, R1=tBu, iPr, H; R2=tBu, iPr, Me) could be conveniently and selectively synthesized in three steps, starting from cyclohexene oxide and arene thiolate. The racemic bis(phenols) could be resolved using an enantiopure (S)‐camphorsulfonic ester auxiliary or by (chiral) HPLC. Complexation of the racemic bis(phenols) to TiX4 (X=Cl, OiPr) proceeds in a diastereoselective fashion to give only the Λ,R,R and Δ,S,S enantiomers. Racemic [Ti{(OC6H2‐6‐tBu‐4‐Me)2S2C6H10}Cl2] reacts with benzyl magnesium bromide to afford the crystallographically characterized dibenzyl complex. The benzyl cation formed using B(C6F5)3 in C6D5Br slowly decomposes at temperatures above +10 °C. When treated with methylaluminoxane, the dichloro complexes [Ti{OSSO}Cl2] polymerize styrene with activities up to 146 kg (mol catalyst)−1 [styrene (mol L−1)]−1 h−1; diisopropoxy complexes [Ti{OSSO}(OiPr)2] show mere trace activity. With 1‐hexene as a chain‐transfer agent, activated enantiopure titanium complexes give low‐molecular‐weight homochiral isotactic oligostyrenes, terminated by one to five 1‐hexene units with Mn values as low as 750 g mol−1 for R=tBu and 1290 g mol−1 for R=Me. Below Mn≈5000 these oligostyrenes show optical activity.
Synthesis of Bifunctional Imido Alkylidene BisPyrrolide Complexes of Molybdenum and Their Conversion into Bifunctional Imido Alkylidene Diolate Complexes That Can Be Employed as ROMP Initiators
Authors: Gabert Andrea J. , Schrock Richard R. , Müller Peter 
Published: July 2008

AbstractAddition of four equivalents of lithium 2,5‐dimethylpyrrolide to a solution of [Mo(NAr)(ORF6)2(CHC5H4)]2Fe (ORF6=OCMe(CF3)2) in dichloromethane led to [Mo(NAr)(Me2Pyr)2(CHC5H4)]2Fe (2; Me2Pyr=2,5‐dimethylpyrrolide) and lithium hexafluoro‐tert‐butoxide, which crystallizes out upon cooling the reaction mixture to −35 °C. Attempts to prepare parent pyrrolide complexes analogous to 2 resulted in the formation of a mixture of two products. The one that could be isolated contains one equivalent of lithium pyrrolide per molybdenum, that is [Mo(NAr)(Pyr)3(CHC5H4)]2FeLi2 (3). The X‐ray structure obtained shows it to be a dimer of dimers in which each lithium atom is bound to three pyrrolides. Addition of four equivalents of lithium 2,5‐dimethylpyrrolide to [Mo(NAr)(ORF6)2]2(DME)2(CH‐1,4‐C6H4CH) (1 b) in cold DME produced [Mo(NAr)(Me2Pyr)2]2(CH‐1,4‐C6H4CH) (4) in good yield, in which the bridging alkylidene is derived from 1,4‐divinylbenzene. Three equivalents of (S)‐H2[Biphen] are required for a clean reaction with 3 to form [Mo(NAr)(Biphen)(CHC5H4)]2Fe (5) (H2[Biphen]=3,3′‐di‐tert‐butyl‐5,5′,6,6′‐tetramethyl‐1,1′‐biphenyl‐2,2′‐diol), Li2[Biphen], and two equivalents of pyrrole. Reactions involving 4 with the chiral diols are the best behaved. Brown [Mo(NAr)(Benz2Bitet)]2(CH‐1,4‐C6H4CH) (6) can be isolated upon addition of (R)‐H2[Benz2Bitet] (H2[Benz2Bitet]=(3,3′‐dibenzhydryl‐5,5′,6,6′,7,7′,8,8′‐octahydro‐1,1′‐binaphthyl‐2,2′‐diol) to 4, while addition of (R)‐H2[Mes2Bitet] (H2[Mes2Bitet]=3,3′‐dimesityl‐5,5′,6,6′,7,7′,8,8′‐octahydro‐1,1′‐binaphthyl‐2,2′‐diol) to 4 yields [Mo(NAr)(Mes2Bitet)]2(CH‐1,4‐C6H4CH) (7). Compounds 5, 6, and 7 were employed as initiators for the polymerization of 2,3‐dicarbomethoxynorbornadiene (DCMNBD) and 2,3‐bis(trifluoromethyl)norbornadiene (NBDF6).
Microflow System Controlled Carbocationic Polymerization of Vinyl Ethers
Authors: Nagaki Aiichiro , Iwasaki Takeshi , Kawamura Kohsuke , Yamada Daisuke , Suga Seiji , Ando Tuyoshi , Sawamoto Mitsuo , Yoshida Jun‐ichi 
Published: July 2008

AbstractA “cation pool” of an N‐ acyliminium ion was found to serve as an effective initiator of cationic polymerization of vinyl ethers in a microflow system consisting of two micromixers (IMM micromixer) and two microtube reactors. The cationic polymerization of n‐butyl vinyl ether in CH2Cl2 at −78 °C led to very narrow molecular weight distribution (Mw/Mn=1.14). The molecular weight (Mn) increased linearly with an increase in monomer/initiator ratio. The carbocationic polymer end was effectively trapped by allyltrimethylsilane. Additionally, the synthesis of block polymers was accomplished by the present microflow system controlled method. The polymerization was also conducted using commercially available trifluoromethanesulfonic acid (TfOH) as an initiator. A high level of molecular weight control was attained even at −25 °C. The TfOH‐initiated polymerization could be conducted using a microflow system based on T‐shaped micromixers, which serves as a practical tool for microflow system controlled carbocationic polymerization.
Fullerene‐like Mo(W)1−xRexS2 Nanoparticles
Authors: Deepak Francis Leonard , Popovitz‐Biro Ronit , Feldman Yishay , Cohen Hagai , Enyashin Andrey , Seifert Gotthard , Tenne Reshef 
Published: July 2008

AbstractInorganic fullerene‐like (IF) Mo1−xRexS2 and W1−xRexS2 nanoparticles have been synthesized by a gas‐phase reaction involving the respective metal halides with H2S. The IF‐Mo(W)1−xRexS2 nanoparticles, containing up to 5 % Re, were characterized by a variety of experimental techniques. Analyses of the X‐ray powder diffraction and different electron microscopy techniques show that the Re is doped in the MoS2 host lattice. Interestingly, Re‐doped MoS2 nanotubes are present as well, although in small quantities (∼5 %). XPS results confirm the nanoparticles to be more n‐type arising from the effect of Re doping. Additionally, density‐functional tight‐binding (DFTB) calculations support the observed n‐type behavior.
Silicon‐Bridge Effects on Photophysical Properties of Silafluorenes
Authors: Shimizu Masaki , Tatsumi Hironori , Mochida Kenji , Oda Katsunari , Hiyama Tamejiro 
Published: July 2008

AbstractThe preparation of 4,5‐dimethylsilylene‐ or 4,5‐tetramethyldisilylene‐bridged 9‐silafluorenes was achieved by lithiation of 2,2′,6,6′‐tetrabromobiphenyls followed by silylation with dichlorodimethylsilane or 1,2‐dichloro‐1,1,2,2‐tetramethyldisilane, respectively. X‐ray analysis of the silylene‐bridged silafluorene revealed that the molecular framework was perfectly planar and four SiC(methyl) σ bonds were completely orthogonal to the plane. Both the silicon atoms and the benzene rings were significantly deformed from the normal tetrahedral and hexagon shapes, respectively. The silicon bridge at the 4,5‐positions was found to induce a red shift of the absorption and fluorescence spectra measured in cyclohexane, compared with 9‐silafluorenes. It is remarkable that the disilylene‐bridged silafluorene emitted blue light (λem=450 nm) with a large Stokes shift. The emission maxima of the silicon‐bridged silafluorenes in thin films were similar to those measured in cyclohexane solution. DFT calculations suggested that introduction of the silicon bridge led to increases in both the HOMO and LUMO levels compared with 9‐silafluorene.
Conjugated Polyelectrolytes for Protein Assays and for the Manipulation of the Catalytic Activity of Enzymes
Authors: An Lingling , Wang Shu , Zhu Daoben 
Published: July 2008

AbstractA new method has been developed to discriminate between proteins with different isoelectric points by using fluorescent conjugated polyelectrolytes. Charged water‐soluble polyfluorenes that contain 2,1,3‐benzothiadiazole (BT) units demonstrate intramolecular energy transfer from the fluorene units to the BT sites when oppositely charged proteins are added to the mixture. This results in a shift in emission color from blue to green and a change in the emission intensity of conjugated polyelectrolytes, which makes it possible to assay proteins. The formation of conjugated polyelectrolyte/enzyme complexes by electrostatic interactions can be utilized to manipulate the activity of enzymes by means of local alteration of enzyme charge density. The oppositely charged substrate binds to conjugated polyelectrolyte and reduces the distance between the enzyme and the substrate, leading to an increase in the cleavage reaction rate. The new method has three important features: 1) it offers a convenient “mix‐and‐detect” continuous approach for protein assays and rapid detection of enzyme activity; 2) the use of water‐soluble conjugated polyelectrolytes imparts the sensor with a high sensitivity; 3) this method does not require fluorescent labels on the targets, which should significantly reduce the cost.
Synthesis of Bulky Arylphosphanes by Rhodium‐Catalyzed Formal [2+2+2] Cycloaddition Reaction and Their Use as Ligands
Authors: Kobatake Takayuki , Kondoh Azusa , Yoshida Suguru , Yorimitsu Hideki , Oshima Koichiro 
Published: July 2008

AbstractTreatment of 1‐alkynylphosphane sulfides with 1,6‐ or 1,7‐diynes in the presence of a cationic rhodium catalyst results in a formal [2+2+2] cycloaddition reaction to afford the corresponding aromatic phosphane sulfides. The aromatic rings formed in the cycloaddition naturally bear one or two substituents at the ortho positions to the phosphorus atom, which creates a sterically hindered environment around the phosphorus atom. The following desulfidation of the products is facile under radical conditions or with the aid of tris(dimethylamino)phosphane, providing the corresponding bulky phosphanes. Dicyclohexyl(2,6‐diphenylaryl)phosphane, which is available through this sequence, proves to serve as an efficient ligand in palladium‐catalyzed cross‐coupling amination reactions.
Chiral Schiff Bases as Highly Active and Enantioselective Catalysts in Catalytic Addition of Dialkylzinc to Aldehydes
Authors: Tanaka Takanori , Sano Yuki , Hayashi Masahiko 
Published: July 2008

AbstractWe have developed chiral Schiff base catalysts based on the ONO‐tridentate ligand for the catalytic enantioselective addition of dialkylzinc to aldehydes. Various aldehydes were smoothly converted into corresponding optically active secondary alcohols with high enantioselectivity (up to 98 % ee) in high yield. Furthermore, we have succeeded in decreasing the catalyst loading minimum to 0.1 mol % in the chiral Schiff base‐catalyzed enantioselective alkylation of aldehydes.
Marked Deuterium Isotope Effects on the Enantioselectivity in Rhodium‐Catalyzed Asymmetric Hydrogenation of Enamides
Authors: Imamoto Tsuneo , Itoh Takuma , Yoshida Kazuhiro , Gridnev Ilya D. 
Published: July 2008

AbstractDeuterium isotope effects on the enantioselectivity in the rhodium‐catalyzed asymmetric hydrogenation of enamides and related substrates have been studied. Distinct deuterium isotope effects were observed in the hydrogenation of aryl‐substituted enamides having an ortho substituent that is capable of forming a hydrogen bond. The observed isotope effects are interpreted in terms of the competitive reactions of two dihydride intermediates and dideuteride intermediates that exist in equilibrium in the catalytic cycle.
A General Preparation of Polyfunctional Benzylic Zinc Organometallic Compounds
Authors: Metzger Albrecht , Schade Matthias A. , Manolikakes Georg , Knochel Paul 
Published: July 2008

AbstractA new method for the preparation of highly functionalized benzylic zinc chlorides by the direct insertion of zinc dust into the corresponding benzylic chlorides in the presence of LiCl is described without the formation of homocoupling products (<5 %). Various reactions of these benzylic zinc reagents with a broad range of electrophiles, which lead to polyfunctionalized products, are reported. In particular, the cross‐coupling reactions of the benzylic zinc chlorides with aromatic chlorides, bromides, and tosylates in the presence of [Ni(acac)2] (acac=acetylacetonate) and PPh3 proceeded in good to excellent yields to give the corresponding diaryl and heterodiaryl methanes.
Catalytic Stereoselective Glycosidation with Glycosyl Diphenyl Phosphates: Rapid Construction of 1,2‐cis‐α‐Glycosidic Linkages
Authors: Koshiba Miyuki , Suzuki Noritoshi , Arihara Ryoichi , Tsuda Toshifumi , Nambu Hisanori , Nakamura Seiichi , Hashimoto Shunichi 
Published: July 2008

AbstractA commercially available 0.1 M solution of HClO4 in dioxane has been shown to catalyze the glycosidation of glycosyl diphenyl phosphates. The per‐O‐benzyl‐protected glucosyl and galactosyl donors and the 3,4,6‐tri‐O‐acetyl‐2‐azido‐2‐deoxygalactosyl donor each react with a range of acceptor alcohols in the presence of 0.05–0.2 equiv of HClO4 in dioxane/Et2O (1:1) to afford glycosides in good yields with good to excellent α selectivities. The synthetic utility of this glycosidation method was demonstrated by a stereoselective synthesis of the α‐galactosylceramide KRN7000, an activator of natural killer (NK) T cells through CD1d molecules.
Synthesis and Application of Easily Recyclable Thiomorpholines for Use in Sulfur Ylide Mediated Asymmetric Epoxidation of Aldehydes
Authors: Hansch Markus , Illa Ona , McGarrigle Eoghan M. , Aggarwal Varinder K. 
Published: July 2008

AbstractChiral nonracemic thiomorpholines have been synthesized in four to six steps from limonene or achiral alkenes using α‐methylbenzylamine to control absolute stereochemistry. These aminosulfides have been used to generate sulfur ylides, which have been applied in the asymmetric epoxidation of aldehydes as easily recoverable catalysts. Excellent yields (up to 98 %), enantioselectivities (up to 97:3 e.r.), and diastereoselectivities (≥98:2 trans/cis) were achieved in these epoxidations and the sulfides were easily recovered in high yield (up to 97 %) by simple acid/base extraction.
The effect of consequential thinking on trust game behavior
Authors: Kugler Tamar , Connolly Terry , Kausel Edgar E. 
Published: July 2008

AbstractContrary to rational Expected Monetary Value (EMV) predictions that no money will be transferred in Trust Games, in experiments players make positive transfers. Theorists have proposed modifying the Sender's utility function while retaining utility‐maximization assumptions to account for this behavior. Such accounts assume that Senders can grasp the possible outcomes of their choices, their probabilities, and utilities. In reality, however, Senders' choices are unexpectedly complex, and the assumption that they approximate expected utility maximization is highly implausible. Instead, we suggest that Senders are guided by general propensities to trust others. Two experiments examine the effect of inducing consequential thought on Sender behavior. One induced consequential thought directly; the other did so indirectly. The amount sent was significantly reduced following either manipulation. This suggests that models of Sender behavior in Complex Trust Games should not assume that participants routinely engage in consequential thinking (CT) of the depth that would be required for utility maximization. Copyright © 2008 John Wiley & Sons, Ltd.
Enhanced Complexity and Catalytic Efficiency in the Hydrolysis of Phosphate Diesters by Rationally Designed Helix‐Loop‐Helix Motifs
Authors: Razkin Jesus , Lindgren Johan , Nilsson Helena , Baltzer Lars 
Published: July 2008

AbstractHJ1, a 42‐residue peptide that folds into a helix‐loop‐helix motif and dimerizes to form a four‐helix bundle, successfully catalyzes the cleavage of “early stage” DNA model substrates in an aqueous solution at pH 7.0, with a rate enhancement in the hydrolysis of heptyl 4‐nitrophenyl phosphate of over three orders of magnitude over that of the imidazole‐catalyzed reaction, k2(HJ1)/k2(Im)=3135. The second‐order rate constant, k2(HJ1) was determined to be 1.58×10−4 M−1 s−1. The catalyst successfully assembles residues that in a single elementary reaction step are capable of general‐acid and general‐base catalysis as well as transition state stabilization and proximity effects. The reactivity achieved with the HJ1 polypeptide, rationally designed to catalyze the hydrolysis of phosphodiesters, is based on two histidine residues flanked by four arginines and two adjacent tyrosine residues, all located on the surface of a helix‐loop‐helix motif. The introduction of Tyr residues close to the catalytic site improves efficiency, in the cleavage of activated aryl alkyl phosphates as well as less activated dialkyl phosphates. HJ1 is also effective in the cleavage of an RNA‐mimic substrate, uridine‐3′‐2,2,2‐trichloroethyl phosphate (leaving group pKa=12.3) with a second‐order rate constant of 8.23×10−4 M−1 s−1 in aqueous solution at pH 7.0, some 500 times faster than the reaction catalyzed by imidazole, k2(HJ1)/k2(Im)=496.
Modular Assembly Using Sequential Palladium Coupling Gives Easy Access to the SMoC Class of Cellular Transporters
Authors: Rebstock Anne‐Sophie , Visintin Cristina , Leo Elisabetta , Garcia Posada Cristina , Kingsbury Sarah R. , Williams Gareth H. , Stoeber Kai , Selwood David L. 
Published: July 2008

AbstractThe transducing ability of the third helix of transcription factor homeodomains is effectively mimicked by a biphenyl system displaying guanidine groups. The biphenyl class of small molecule carriers (SMoCs) can carry biomolecules into a wide variety of cell types. A “combinatorial” approach to the synthesis of SMoCs is described using sequential Pd0 coupling chemistry to assemble the molecules from highly functionalized building blocks. SMoCs coupled to the DNA licensing repressor protein geminin can inhibit DNA replication in vitro. We conducted a structure–activity investigation utilizing a range of SMoC–geminin conjugates and demonstrate that both electrostatic and structural features are important for efficient uptake and functional activity. The best analogue was more efficient than either (Arg)4 or (Arg)8 linked to geminin. Effective inhibition of DNA synthesis was achieved in fibroblasts and osteosarcoma cell lines.
Blue‐Light Induced Interaction of LOV Domains from Chlamydomonas reinhardtii
Authors: Kutta Roger J. , Hofinger Edith S. A. , Preuss Hendrik , Bernhardt Günther , Dick Bernhard 
Published: July 2008

AbstractThe phototropin from Chlamydomonas reinhardtii is a 120 kDa blue light receptor that plays a key role in gametogenesis of this green alga. It comprises two light‐sensing domains termed LOV1 and LOV2 (light oxygen and voltage) and a serine/threonine kinase domain. The post‐translationally incorporated chromophore is flavin mononucleotide (FMN). Upon absorption of blue light, LOV domains undergo a photocycle that activates a Ser/Thr kinase. The mechanism of this activation is still unknown. We studied the oligomerization of the recombinant LOV1 domain (amino acids 16–133) of C. reinhardtii by means of UV/Vis spectroscopy, size‐exclusion chromatography (SEC), and chemical cross‐linking with glutardialdehyde. The thermal back‐reaction of LOV1 from the signaling state to the dark state as monitored by UV/Vis spectroscopy after an intensive blue light pulse could not be explained by a monoexponential model, although the spectra did not indicate the presence of an additional species. Therefore, we investigated the quaternary structure of the LOV1 domain by size‐exclusion chromatography in the dark. This revealed an equilibrium between dimers and higher oligomers (MW>200 kDa) under native conditions. No monomers were detected by SEC. However, by analysis of the equilibrium by cross‐linking of the protein with glutardialdehyde and subsequent SDS‐PAGE, monomers and dimers were identified. Exposure of LOV1 to blue light resulted in a decrease in the monomer/dimer ratio, followed by re‐equilibration in the dark. Calculation of the solvent‐accessible surface area and the Conolly surfaces of the LOV1 dimers present in the crystal structure support the experimental observation that no mononomers are detected in the native state. A model is presented that accounts for a blue‐light‐driven change in the quaternary structure of the LOV1 domain and gives hints to the molecular basis of light activation and regulation in LOV‐containing proteins.
Dynamic Combinatorial Self‐Assembly of Cyclophilin hCyp‐18 Ligands through Oxorhenium Coordination
Authors: Clavaud Cécile , Le Gal Julien , Thai Robert , Moutiez Mireille , Dugave Christophe 
Published: July 2008

AbstractThe dynamic combinatorial assembly of independent modules A and B through oxorhenium(V) coordination by a NS2+S motif in the presence of cyclophilin hCyp‐18—an important peptidyl‐prolyl isomerase—was investigated. Increasing glutathione (GSH) concentrations were used to dissociate [A⋅ReVO⋅B] complexes that displayed low affinity for hCyp‐18. Conversely, coordinates that displayed submicromolar affinities for hCyp‐18 were protected against thiol exchange and could be detected by LC‐MS. Determination of the GSH concentration that decreased the extracted ionic current of the complex by 50 % (CC50) enabled the selection of three oxorhenium coordinates that were shown to bind to the active site of hCyp‐18 and to inhibit its peptidyl–prolyl isomerase activity in the micromolar to submicromolar range.
Multivalent Carbohydrate Recognition on a Glycodendrimer‐Functionalized Flow‐Through Chip
Authors: Branderhorst Hilbert M. , Ruijtenbeek Rob , Liskamp Rob M. J. , Pieters Roland J. 
Published: July 2008

AbstractDendrimers were fitted out with up to eight mannose moieties by “click” chemistry. They were subsequently attached to aluminum oxide chips via a spacer that was linked to the dendrimer core; this resulted in a microarray of glycodendrimers. Binding of the glycodendrimers to the fluorescent lectins ConA and GNA was observable in real time. In a single experiment it was possible to observe the multivalency enhancement or cluster effect in the binding event. This effect was small for ConA, in agreement with its widely spaced binding sites, whereas it was large for GNA, with its twelve much more closely spaced binding sites. The dendrimer‐fitted chip represents a valuable screening tool for multivalency effects. Furthermore kinetic and thermodynamic data on binding events can be deduced. Inhibition experiments are also possible with the system as was shown for ConA with α‐methyl mannose as the inhibitor.
A Gold(I)‐Catalyzed Intramolecular Reaction of Propargylic/Homopropargylic Alcohols with Oxirane
Authors: Dai Lun‐Zhi , Shi Min 
Published: July 2008

AbstractThe gold(I)‐catalyzed cycloisomerization of epoxy alkynes in the presence of a nucleophile is an efficient protocol to provide ketal skeletons with high stereoselectivity. An intramolecular reaction of propargylic/homopropargylic alcohols with oxirane to produce ketal/spiroketals in moderate yields under mild conditions has been reported. Moreover, the mechanism of this kind of reaction has been discussed on the basis of a series of control and 18O tracer experiments.