bluuebunny/crossref_metadata_2025_split huggingface dataset:
TiIV‐BINOLate‐Catalyzed Highly Enantioselective Additions of β‐Substituted Allylstannanes to Aldehydes
Authors: Weigand Stefan , Brückner Reinhard 
Published: September 2007

AbstractEnantiomerically pure homoallyl alcohols were prepared from aldehydes R1‐CHO (R1 = Ph, pentyl, Ph‐CHCH‐, iPr) and β‐substituted allyl‐stannanes H2CCR2‐CH2‐SnBu3 (R2 = pentyl, tBuPh2SiO‐CH2‐, tBuPh2SiO‐CH2‐CH2‐, PhS‐CH2‐CH2‐). These reactions were catalyzed by the same additives—Ti(OR)4 (10 mol%) and (R)‐BINOL (20 mol%)—that Keck et al. used in analogous reactions with methallyl‐and allyltributylstannane. To attain optimum ee values (96.4–99.2% in the reaction with hexanal) these additives had to be premixed for 2 h at room temperature. Ti(OEt)4 and Ti(OiPr)4 gave equally good results, while Ti(OMe)4, Ti(OCHEt2)4, and Ti(OtBu)4 were inferior. Our procedure works in the absence of molecular sieves [which were previously found to give rather unreliable results in reactions catalyzed by Ti(OiPr)4/(R)‐BINOL] and can be extended to enantioselective addition reactions with allyl‐ and methallyltributylstannane, too (+ hexanal: 97.4 and 97.0% ee, respectively).
Dendritic Models of Redox Proteins: X‐ray Photoelectron Spectroscopy and Cyclic Voltammetry Studies of Dendritic bis(Terpyridine) iron(II) Complexes
Authors: Chow Hak‐Fun , Chan Ida Y.‐K. , Chan Dominic T. W. , Kwok Raymund W. M. 
Published: September 2007

AbstractA series of iron‐containing metallodendrimers from the zeroth to the third generation was synthesized and characterized. The iron(II) ion of these metal complexes is encapsulated within a hydrophobic polyether dendritic envelope. X‐ray photoelectron spectroscopy analysis revealed that the bonding environment of the iron atom was essentially ronment of the iron atom was essentially the same in dendrimers of different generations. However, cyclic voltammetry studies indicated that the reversibility of the metal redox process decreased in the higher‐generation dendrimers. These observations were similar to those of a related electrochemical study conducted on the redox protein cytochrome C, in which the decrease in electron transfer reversibility was explained as a result of the increasing remoteness of the metal ion of the higher‐generation dendrimers from the electrode surface.
Catalytic Properties of Layered Gold–Palladium Colloids
Authors: Schmid Günter , West Heike , Malm Jan‐Olle , Bovin Jan‐Olv , Grenthe Carl 
Published: September 2007

AbstractLayered bimetallic gold‐palladium colloids in the size range of 20–56 nm have been synthesized by the seed=growth method: gold seeds were covered by palladium layers of various thickness and vice versa. The outer metal was coordinated by trisulfonated triphenylphosphine and sodium sulfanilate ligands to stabilize the bimetallic particles to such an extent that they could be isolated in the solid state. Owing to the hydrophilic ligand shell, redispersion in water was possible in any concentration. High‐resolution transmission electron microscopy and energy‐dispersive X‐ray analysis was used to characterized the colloids. Stabilized and nonstabilized gold‐palladium and palladium‐gold systems on a TiO2 support were used as heterogeneous catalysts for the hydrogenation of hex‐2‐yne to cis‐hex‐2‐ene. Both the palladium‐plated gold seeds and the gold‐plated palladium particles showed considerably increased activities compared with the pure metals. The ligand shell seems not to influence the catalytic behavior because protected and unprotected colloids behave very similarly.
Peptide Helices as Rigid Molecular Rulers: A Conformational Study of Isotactic Homopeptides from α‐Methyl‐α‐isopropylglycine, [L‐(αMe)Val]n
Authors: Polese Alessandra , Formaggio Fernando , Crisma Marco , Valle Giovanni , Toniolo Claudio , Bonora Gian Maria , Broxterman Quirinus B. , Kamphuis Johan 
Published: September 2007

AbstractTerminally blocked, isotactic homopeptides from the sterically demanding α‐methylvaline of general formula Y‐[L‐(αMe)Val]n‐OtBu (Y = Z, pBrBz, Ac; n = 2–8) have been prepared step‐by‐step in solution and fully characterized. The conformations preferred in solution (β‐turn and right‐handed 310‐helix) have been assessed by FT‐IR, 1H NMR and CD spectroscopy. The molecular and crystal structures of the Z‐protected trimer, hexamer, heptamer and octamer have been determined by X‐ray diffraction. In the crystal state, while the trimer is folded in a type III β‐turn conformation, the longest homopeptides form well‐developed, regular, right‐handed 310‐helices. The screw sense in the helix of the pBrBz‐blocked octamer has been confirmed to be right‐handed by solid‐state and solution CD spectroscopy. The possible exploitation of these peptide helices as rigid and precise molecular rulers is discussed.
A Convergent Synthesis of Carbohydrate‐Containing Dendrimers
Authors: Ashton Peter R. , Boyd Sue E. , Brown Christopher L. , Jayaraman Narayanaswamy , Nepogodiev Sergey A. , Stoddart J. Fraser 
Published: September 2007

AbstractThe synthesis of carbohydratecontaining dendrimers has been achieved by a convergent growth approach. The synthetic strategy involves: 1) the synthesis of the triglucosylated derivative of tris(hydroxymethyl)methylamine (TRIS), 2) the introduction of a glycine‐derived spacer and 3,3′‐iminodipropionic acid derived branching units on to the TRIS derivative by amide bond formation, 3) condensation of the above saccharidecontaining dendrons with a trifunctional 1,3,5‐benzenetricarbonyl derivative, used as the core, by formation of amide bonds, and 4) deprotection of the saccharide units. A 9‐mer and an 18‐mer, carrying nine and eighteen saccharide units at the periphery, respectively, have been synthesized, in high yields at each step, by this synthetic strategy. By a variety of chromatographic and spectroscopic techniques, the dendrimers were shown to be structurally homogeneous, monodisperse, and error‐free at all steps in their growth. These investigations were complemented by molecular modeling studies on the dendrimers. The presence of slightly distorted C3 symmetry was noted in both the 9‐mer and the 18‐mer.
Thermal and Light‐Induced Spin Transition in [Fe(bpen)X2] (bpen = 1,6‐Bis(2‐pyridyl)‐2,5‐diazahexane, X = NCS‐, NCSe‐)
Authors: Buchen T. , Gütlich P. , Toftlund H. 
Published: September 2007

AbstractThe thermal and light‐induced spin transitions in [Fe(bpen)(NCS)2] and [Fe(bpen)(NCSe)2] have been investigated by means of magnetic susceptibility and Mössbauer measurements. The HS → LS transition in [Fe(bpen)(NCS)2] is detected at temperatures below 120 K (T1/2 [when the fraction of high‐spin species γHS = 0.5] = 68 K) with a residual HS fraction of 8% at 20 K. The transition is fairly abrupt and no hysteresis is observed, in contrast to earlier studies (ref. [8]). The generation of metastable HS states in [Fe(bpen)(NCS)2] is achieved by rapid cooling of the sample and by irradiating the compound at low temperatures with light of appropriate wavelengths (LIESST). The HS → LS relaxation of the metastable spin states after rapid cooling is observed at temperatures between 35 and 42.5 K and shows strong deviations from single exponential behavior. The spin‐transition behavior changes drastically on substitution of the thiocyanate ions by NCSe‐. In [Fe(bpen)(NCSe)2] a gradual and complete spin transition between 140 and 250 K is observed (T1/2 = 181 K). Irradiation of the compound with green light at low temperatures does not result in formation of long‐lived metastable HS states. The spintransition curves derived from magnetic susceptibility and Mössbauer studies show good agreement for each compound, and no hints of significantly different Lamb–Mössbauer factors for the HS and LS states are observed.
High‐Spin → Low‐Spin Relaxation in [Fe(bpp)2](CF3SO3)2 H2O after LIESST and Thermal Spin‐State Trapping—Dynamics of Spin Transition Versus Dynamics of Phase Transition
Authors: Buchen T. , Gütlich P. , Sugiyarto K. H. , Goodwin H. A. 
Published: September 2007

AbstractThe iron(II) complex [Fe(bpp)2]‐(CF3SO3)2 H2O (bpp = 2,6‐bis(pyrazolyl‐3‐yl)pyridine) shows a thermal spin transition associated with a hysteresis of approximately 140 K width. The transition temperatures T1/2 (where the fraction of HS species γHS = 0.5) are 147 K and ≈︁285 K in the cooling and heating directions, respectively. The compound shows the LIESST and reverse‐LIESST effects at low temperatures. The relaxation of the metastable HS states generated by LIESST was observed quantitatively at temperatures between 77.5 and 85 K by Mössbauer spectroscopy. Metastable HS states can also be generated by rapid cooling of the sample. The relaxation of the metastable HS states formed by thermal spin‐state trapping was monitored at temperatures between 104 and 118 K by magnetic susceptibility measurements. The relaxation mechanisms of the HS states generated by LIESST and thermal spinstate trapping are completely different. We suggest that the HS → LS relaxation after thermal spin‐state trapping is triggered by an additional structural phase transition of the system.
9,10‐Dimetallatriptycenes of Group 14: A Novel Synthetic Approach from ortho‐Phenylenemagnesium
Authors: Dam Matheus A. , Akkerman Otto S. , De Kanter Franciscus J. J. , Bickelhaupt Friedrich , Veldman Nora , Spek Anthony L. 
Published: September 2007

Abstract9,10‐Dimetallatriptycenes of Group 14 are readily accessable by a novel synthetic approach: reaction of ortho‐phenylenemagnesium (1) with RMCl3 afforded 9,10‐dimethyl‐9,10‐dimetallatriptycenes (3; M = Si, Ge, Sn) or 9, 10‐dimethyl‐9‐germa‐10‐stannatriptycene (11). The reaction can even be tuned to afford unsymmetrically substituted triptycenes such as 9‐methyl‐10‐phenyl‐9,10‐digermatriptycene (8); in some of these reactions, strong indications were obtained for the intermediacy of tri‐Grignard reagents RM(2‐C6H4MgCl)3 (5, 10). The new triptycenes were characterised by their spectral data and in the case of 3c (M = Sn) by an X‐ray crystal structure determination.
The Unimolecular Chemistry of Protonated Glycinamide and the Proton Affinity of Glycinamide—Mass Spectrometric Experiments and Theoretical Model
Authors: Uggerud Einar , Hvistendahl Georg , Rasmussen Bård , Kinser Robin D. , Ridge Douglas P. 
Published: September 2007

AbstractThe potential energy hypersurface of protonated glycinamide (GAH+) has been investigated experimentally and theoretically. The calculated G2(MP2) value for the proton affinity of glycinamide, PAcalcd = 919 kJ mol‐1, is in good agreement with the measured value of 908PAexp<914kJ mol‐1. The fact that the amide group is a better hydrogenbond acceptor explains why glycinamide has a higher PA than glycine. Proton transfer experiments with glycinamide performed in a Fourier transform mass spectrometer and analysis of metastable GAH+ ions in a four‐sector mass spectrometer show that the lowest‐energy unimolecular reactions are two distinct processes: 1) loss of CO, which has a substantial barrier for the reverse reaction, and 2) loss of CO plus NH3, which has no barrier for the reverse reaction. Ab initio quantum chemical calculations give a reaction model that is consistent with the observed fragmentation pattern.
Molecular Structure of the Chloroiron(III) Derivative of the meso‐Unsubstituted 2,7,12,17‐Tetramethyl‐3,8,13,18‐tetramesitylporphyrin and Weak Ferromagnetic Exchange Interactions in the A1u Oxoiron(IV) Porphyrin π Radical Cation Complex
Authors: Ayougou Khadija , Mandon Dominique , Fischer Jean , Weiss Raymond , Müther Markus , Schünemann Volker , Trautwein Alfred X. , Bill Eckhard , Terner James , Jayaraj Karupiah , Gold A. , Austin Rachel N. 
Published: September 2007

AbstractThe molecular structure of the chloroiron(III) porphyrinate [FeIIICl‐ (tmtmp)] (1) is described. The doming off the bifacially encumbered tmtmp dianionic ligand present in 1 is characterized by a separation of 0.09 (1) Å between the mean plane of the four pyrrole nitrogens (4NP) and that of the porphyrin core. The coordination polyhedron of the five‐coordinate iron atom is a square pyramid of C4v symmetry. The metal is displaced by 0.44 (1) Å from the 4Np mean plane towards the axial chloro ligand. The Fe–Np and Fe‐Cl bond lengths are 2.057 (6) and 2.223(5) Å, respectively. Upon treatment of [FeIIITf(tmtmp)] (2) with m‐chloroperoxybenzoic acid, the green oxoferryl π radical cation complex [FeIV=O(tmtmp)]+ (3) is obtained. It has been studied by EPR, Mössbauer, and resonance Raman spectroscopy. It exhibits an EPR spectrum strikingly similar to those of compounds I of Micrococcus lysodeikticus catalase (APX‐I) and ascorbate peroxidase (APX‐I) The exchange interactions between the spins of the radical cation and the ferryl iron are of the ferromagnetic type and are the weakest ever found for a synthetic compound I model. The shift of + 22 cm‐1 in the radical marker band v2 in the resonance Raman spectra upon oxidation of 2 to 3 confirms that the electronic state of the porphyrin π radical cation is predominantly 2Alu in this tmtmp compound 1 model.
Homochiral and Heterochiral Dimers of the Methylzinc Alkoxide Formed from Dimethylzinc and Enantiomeric 3‐exo‐(Dimethylamino)isoborneol—Origin of the Distinct Differences in Solution‐Phase Behavior and Crystal Structures
Authors: Kitamura Masato , Yamakawa Masashi , Oka Hiromasa , Suga Seiji , Noyori Ryoji 
Published: September 2007

AbstractDimethylzinc reacts with (2S)‐or (2R)‐3‐exo‐(dimethylamino)isoborneol [(2S)‐ or (2R)‐DAIB] to eliminate methane and produce a tricoordinate methylzinc aminoalkoxide, which forms a dimeric structure. The homochiral dimerization of the enantiomeric compound leads to the chiral, (S,S) or (R,R) dinuclear Zn complex, while the heterochiral interaction forms the meso (S,R) dinuclear compound. In both solution and crystalline state, the heterochiral dimer is more stable than the homochiral dimer. This stability difference in solution is the origin of the chirality amplification observed in the amino alcohol promoted asymmetric addition of dimethylzinc to benzaldehyde. In toluene, the homochiral dimer dissociates more readily into the monomer than the heterchiral isomer and also undergoes dissociation of the N‐Zn dative bond making the two N‐methyl groups equivalent. The differences in solution behavior between the diastereomers can be understood by comparing their crystal structures. X‐ray analysis indicates that the labile Zn‐O and Zn‐N bonds in the (S,S) dimer are longer than those in the (S,R) isomer. Skeletal congestion caused by the polycyclic framework is the prime factor determining the properties of the dinuclear Zn complexes, with both steric and electronic factors governing their geometries. The distances between the C‐2 proton and N‐CH3 of the other DAIB moiety in the homochiral dimer are close to the sum of the van der Waals radii. A significant nuclear Overhauser effect is seen between these protons in the homochiral dimer. The tetrahedral Zn atoms in the dinuclear complexes are linked covalently to the methyl group, to two oxygen atoms through covalent/electrostatic hybrid bonds, and to the dimethylamino group through electrostatic interaction. The repulsive interaction of the 1, 3‐synoriented Zn‐CH3 bonds significantly contributes to the lower stability of the homochiral dimeric complex. The N‐Zn interaction in the homochiral dimer is labile, owing to the increase in the electrostatic interaction between the Zn atom and the neighboring oxygen atoms. This view is supported by the ab initio molecular orbital calculations of the model systems.
Predictive and prognostic value of FDG‐PET in nonsmall‐cell lung cancer
Authors: de Geus‐Oei Lioe‐Fee , van der Heijden Henricus F.M. , Corstens Frans H.M. , Oyen Wim J.G. 
Published: September 2007

AbstractFor several years, molecular imaging with 18F‐fluorodeoxyglucose positron emission tomography (FDG‐PET) has become part of the standard of care in presurgical staging of patients with nonsmall‐cell lung cancer (NSCLC), focusing on the detection of malignant lesions at early stages, early detection of recurrence, and metastatic spread. Currently, there is an increasing interest in the role of FDG‐PET beyond staging, such as the evaluation of biological characteristics of the tumor and prediction of prognosis in the context of treatment stratification and the early assessment of tumor response to therapy. In this systematic review, the literature on the value of the evolving applications of FDG‐PET as a marker for prediction (ie, therapy response monitoring) and prognosis in NSCLC is addressed, divided in sections on the predictive value of FDG‐PET in locally advanced and advanced disease, the prognostic value of FDG‐PET at diagnosis, after induction treatment, and in recurrent disease. Furthermore, the background and recommendations for the application of FDG‐PET for these indications will be discussed. Cancer 2007. © 2007 American Cancer Society.
Similarities and differences of human and experimental mouse lymphangiomas
Authors: Kasten Philipp , Schnöink Gerrit , Bergmann Astrid , Papoutsi Maria , Buttler Kerstin , Rössler Jochen , Weich Herbert A. , Wilting Jörg 
Published: September 2007

AbstractLymphangioma is a disfiguring malformation of early childhood. A mouse lymphangioma model has been established by injecting Freund's incomplete adjuvant (FIA) intraperitoneally, but has not been compared with the human disease. We show that, in accordance with studies from the 1960s, the mouse model represents an oil‐granuloma, made up of CD45‐positive leukocytes and invaded by blood and lymph vessels. Several markers of lymphatic endothelial cells are expressed in both mouse and human, like CD31, Prox1, podoplanin, and Lyve‐1. However, the human disease affects all parts of the lymphovascular tree. We observed convolutes of lymphatic capillaries, irregularly formed collectors with signs of disintegration, and large lymph cysts. We observed VEGFR‐2 and ‐3 expression in both blood vessels and lymphatics of the patients, whereas in mouse VEGFR‐2 was confined to activated blood vessels. The experimental mouse FIA model represents a vascularized oil‐granuloma rather than a lymphangioma and reflects the complexity of human lymphangioma only partially. Developmental Dynamics 236:2952–2961, 2007. © 2007 Wiley‐Liss, Inc.
Homeobox gene Sax2 deficiency causes an imbalance in energy homeostasis
Authors: Simon Ruth , Lufkin Thomas , Bergemann Andrew D. 
Published: September 2007

AbstractThe brain, in particular the hypothalamus and the brainstem, plays a critical role in the regulation of energy homeostasis by incorporating signals from the periphery and translating them into feeding behavior. Here we show that the homeobox gene Sax2, which is expressed predominantly in the brainstem, in the vicinity of serotonergic neurons, contributes to this physiological balance. Sax2 deficiency results in a decrease of fat and glycogen storage, reduced blood glucose levels, and raised serotonin levels in the hindbrain. Surprisingly, in the brainstem the expression levels of pro‐opiomelanocortin and neuropeptide Y were indicative of a fasting condition, opposed to the observed high serotonin levels implying satiation. Furthermore, Sax2‐directed lacZ expression reveals a dramatic change of the distribution of Sax2‐expressing cells in the null mutant occurring during perinatal development. These data strongly suggest that Sax2 is required for the coordinated crosstalk of factors involved in the maintenance of energy homeostasis. Developmental Dynamics 236:2792–2799, 2007. © 2007 Wiley‐Liss, Inc.
A flk‐1 promoter/enhancer reporter transgenic Xenopus laevis generated using the Sleeping Beauty transposon system: An in vivo model for vascular studies
Authors: Doherty Joanne R. , Johnson Hamlet Michelle R. , Kuliyev Emin , Mead Paul E. 
Published: September 2007

AbstractWe have used the Sleeping Beauty (SB) transposable element to generate transgenic Xenopus laevis with expression of green fluorescent protein (GFP) in vascular endothelial cells using the frog flk‐1 promoter. This is the first characterization of a SB‐generated transgenic Xenopus that has tissue‐restricted expression. We demonstrate that the transgene integrated into single genomic loci in two independent founder lines and is transmitted through the germline at the expected Mendelian frequencies. Transgene integration occurred through a noncanonical transposition process possibly reflecting Xenopus‐specific interactions with the SB system. The transgenic animals express GFP in the same spatial and temporal pattern as the endogenous flk‐1 gene throughout development and into adulthood. Overexpression of xVEGF122 in the transgenic animals disrupts vascular development that is visualized by fluorescent microscopy. These studies demonstrate the convenience of the SB system for generating transgenic animals and the utility of the xflk‐1:GFP transgenic line for in vivo studies of vascular development. Developmental Dynamics 236:2808–2817, 2007. © 2007 Wiley‐Liss, Inc.
Numerical characteristics of peer‐to‐peer (P2P) internet online hybrid test system and its application to seismic simulation of SRC structure
Authors: Wang Tao , Yoshitake Nobuya , Pan Peng , Lee Tae‐Hyung , Nakashima Masayoshi 
Published: September 2007

AbstractThe peer‐to‐peer (P2P) Internet online hybrid test system has been developed for the seismic simulation of a structure. In this study, the stability and accuracy of the system are investigated analytically by studying the spectral radius of the recursive matrix of the test scheme featuring a two‐round quasi‐Newton test scheme. The applicability of the system is further examined by exploring the seismic responses of a complex structure, a steel‐encased reinforced concrete (SRC) structure with a steel tower on the top. The structure is divided into two numerical substructures and one tested part for hybrid test. The numerical substructures are simulated by sophisticated finite element method (FEM) models with material nonlinearities to capture local plastifications. Two types of FEM programs, namely OpenSEES and ABAQUS, which are suitable for the SRC part and the steel tower, respectively, are employed. The results demonstrate that the P2P system is able to simulate complex structures with significant nonlinearities. As compared with the previous study in which two elastic numerical substructures were considered, increase in the number of iterations in this study is not significant, because the associated nonlinearities are limited due to the small time interval adopted in the test. Copyright © 2007 John Wiley & Sons, Ltd.