bluuebunny/crossref_metadata_2025_split huggingface dataset:
Influence of Copper Salts, Solvents, and Ligands on the Structures of Precatalytic Phosphoramidite Copper Complexes for Conjugate Addition Reactions
Authors: Zhang Hongxia , Gschwind Ruth M. 
Published: May 2007

AbstractFor copper‐catalyzed enantioselective conjugate addition reactions of organozinc reagents, the available knowledge about the mechanism and the structures involved is still insufficient to understand in detail the strong influences of solvent, salt, and ligand size, or to enable a rational control of this reaction. Screening with three phosphoramidite ligands and four copper(I) salts using NMR spectroscopy has revealed a binuclear copper complex with mixed trigonal/tetrahedral stereochemistry as the basic structural motif of the ground state of precatalysts with highly stereoselective ligands. Ligands with smaller amine moieties allow higher coordination numbers and higher aggregation levels, leading to reduced ee values. Since the ESI mass spectra of several precatalytic copper halide complexes show a striking correlation with the structures observed in solution, ESI‐MS may be used as a fast tool to determine the maximum number of phosphoramidite ligands attached to copper.
A Conceptual DFT Approach for the Evaluation and Interpretation of Redox Potentials
Authors: Moens Jan , Geerlings Paul , Roos Goedele 
Published: May 2007

AbstractConceptual DFT aims at describing the properties of molecules in interactions by using chemical reactivity descriptors. Herein, the redox behaviour of a given species, as quantified by the redox potential, is linked to DFT‐based descriptors. We made use of a hierarchical decomposition of the corresponding half‐reactions into one‐electron reduction, protonation, dissociation and water‐forming or dissociation reactions. Most of these reactions can be readily described through reactivity descriptors, such as the electrophilicity, nucleofugality and electrofugality, as defined in conceptual DFT. The final expression linking the corresponding free energy changes to the redox potential seems to give correct predictions for the redox potentials of bromo, chloro and nitro oxo acids in the gas phase, as in a polarised continuum model.
Ring‐Borylated 15‐Electron and 17‐Electron ansa‐Chromocene Complexes, their Physical Properties and Molecular Structures
Authors: Shapiro Pamela J. , Sinnema Piet‐Jan , Perrotin Philippe , Budzelaar Peter H. M. , Weihe Høgni , Twamley Brendan , Zehnder Ralph A. , Nairn Justin J. 
Published: May 2007

AbstractA detailed study of the thermal decomposition of the zwitterionic, ring‐borylated ansa‐chromocene hydrido carbonyl complex [Cr(CO)H{Me4C2(C5H4)[C5H3B(C6F5)3]}] (2) is described. This complex is formed in the reaction between [Cr(CO){Me4C2(C5H4)2}] (1) and B(C6F5)3 in toluene at −78 °C. Above −25 °C, 2 decomposes to a 50:50 mixture of the low‐spin, 17 e CrIII complexes [Cr(CO){Me4C2(C5H4)[C5H3B(C6F5)3]}] (3 b) and [Cr(CO){Me4C2(C5H4)2}][HB(C6F5)3] (4). Carbon monoxide elimination from 3 b generates high‐spin, 15 e [Cr{Me4C2(C5H4)[C5H3B(C6F5)3]}] (3 a), which coordinates two other electron‐donating ligands, such as xylyl isocyanide, PMe3, and PPh2Me to form the low‐spin, 17 e electron complexes 3 c, 3 d, and 3 e, respectively. High‐spin, 15 e [Cr{Me4C2(C5H4)2}][HB(C6F5)3] (5) is generated by heating 3 b in toluene at 100 °C and periodically removing the evolved CO. Efforts to isolate more than a few X‐ray quality crystals of 5 were thwarted by its tendency to form an insoluble precipitate (6) with the same molecular formula. Heating the solution of 5 at 120 °C results in its partial conversion (ca. 28 %) to 3 a, thereby allowing the formation of 3 a in yields as high as 74 % from the reaction between 1 and B(C6F5)3. The X‐ray crystal structures of 3 b–e and 5 are described. Cyclic voltammetry measurements on 3 a–e reveal a dramatic reduction in the redox potentials of the complexes relative to their non‐borylated analogues. DFT calculations show that this is due primarily to electrostatic stabilization of the oxidized species by the negatively charged borylate group. EPR and 19F NMR spectroscopy allow 3 a to be distinguished from its Lewis base adducts 3 b–e and reveal the relative affinities of different Lewis bases for the chromium.
Bridge Over Troubled Water: Resolving the Competing Photosystem II Crystal Structures
Authors: Petrie Simon , Stranger Rob , Gatt Phillip , Pace Ron J. 
Published: May 2007

AbstractDensity functional theory (DFT) calculations, at the Becke‐Perdew/TZP level of theory, were used to investigate a set of CaMn4‐containing clusters that model the active site of the water‐oxidizing complex (WOC) of photosystem II (PSII). Metal‐atom positions for three representative isomeric clusters of the formula [CaMn4C9N2O16H10]+⋅4 H2O are in good agreement with the disparate Mn4 geometries of the three most recent X‐ray crystal structures. Remarkably, interconversion between these three isomeric clusters is found to be facile, resulting from subtle changes in the coordination environment around the CaMn4 centre. This result provides a clear rationalisation of the marked differences in reported crystal structures. Recent concerns have been raised regarding the opportunity for X‐ray‐damage‐induced distortion of the metal‐containing active centre during crystallographic analysis. Our calculations suggest that an even greater problem may be presented by the apparent fluxionality of the CaMn4 skeleton within the active centre. Structural rearrangement may well precede crystallographic analysis, for example by the preferential “freezing‐out” of one of several near‐isoenergetic structures during the workup for crystallisation. This prospect, which our calculations cannot exclude, highlights the difficulties that will continue to be faced by experimentalists seeking unambiguous structural information on the WOC's active site.
Thuggacins, Macrolide Antibiotics Active againstMycobacterium tuberculosis: Isolation from Myxobacteria, Structure Elucidation, Conformation Analysis and Biosynthesis
Authors: Steinmetz Heinrich , Irschik Herbert , Kunze Brigitte , Reichenbach Hans , Höfle Gerhard , Jansen Rolf 
Published: May 2007

AbstractTwo novel antibiotics, thuggacin A (1) and B (2), were isolated from the myxobacteriumSorangium cellulosum.1and2are unique thiazole‐containing macrolides with side chains on both sides of the lactone group. Upon standing in solution, thuggacin A (1) rearranges by acyl migration of the lactone group to give a mixture with thuggacins B (2) and C (3). NOEs and vicinal coupling constants within the lactone ring provided distinct data for the generation of a structure model by PM3 calculations, which allowed an analysis of the conformation in solution and the relative configuration of six asymmetric centres. A minor sorangium metabolite was identified as 13‐methyl‐thuggacin A (4). Furthermore, two natural thuggacin variants,5and6, were found in another myxobacterium,Chondromyces crocatus. In these variants, one side chain is replaced by a methyl group and a hydroxy group is repositioned to give a primary alcohol at the former methyl site, in an α position with respect to the thiazole ring.1proved to be active against clinical isolates and reference strains ofMycobacterium tuberculosis.Preliminary studies on the mechanism of action indicate inhibition of the cellular electron‐transport chain.
Reaction Rates as a Function of Scale within Ionic Liquids: Microscale in Droplet Microreactors versus Macroscale Reactions in the Case of the Grieco Three‐Component Condensation Reaction
Authors: Dubois Philippe , Marchand Gilles , Gmouh Said , Vaultier Michel 
Published: May 2007

AbstractTask‐specific ionic liquids (TSILs) and more specifically binary task‐specific ionic liquids (BTSILs), a unique subclass, have been shown to be excellent supports for solution‐phase chemistry. The negligible volatility of ionic liquids enables their use as stable droplet microreactors in atmospheric environments without oil protection or confinement. These droplets can be moved, merged and mixed by electrowetting on a chip. Solution‐phase synthesis can be performed on these open digital microfluidic labs‐on‐a‐chip as illustrated by a study of the Grieco three‐component reaction in [tmba][NTf2]‐droplet (tmba=N‐trimethyl‐N‐butylammonium NTf2=bis(trifluoromethylsulfonyl)imide) microreactors. A detailed study of matrices and scale effects on conversion and kinetic rates of this three‐component condensation is presented in this paper. Reactions have been shown to be slower in droplets than in batches in the absence of additional mixing. Also, a significant influence of the ionic‐liquid matrix has been observed. Finally, an increase of droplet's temperature resulted in a kinetics enhancement so as to reach macroscale reaction rates, probably because of a much better mixing of reaction's components involving a Marangoni's effect.
Modelling unsaturated flow by using Mathematica
Authors: Mikhailov M. D. 
Published: May 2007

AbstractThe built‐in Mathematica function NDSolve is extended to solve nonlinear boundary‐value problems and a second‐order partial differential equation subjected to inconsistent boundary and initial conditions. This communication demonstrates the ability of the extended NDSolve to find steady‐state and transient solutions of unsaturated flow described by the one‐dimensional Richards equation. Only first kind boundary conditions are considered, but the extended NDSolve is applicable for first, second, and third kind boundary conditions. To verify the steady‐state numerical results, an original analytical solution is derived. The results given by numerical and analytical steady‐state solutions coincide. The residuum of transient solution is plotted to show that the numerical results satisfy the transient problem except in a singular point, where the boundary and initial conditions are inconsistent. The transient pressure head and soil moisture content are plotted for typical soil properties,
starting from different initial steady‐state distribution up to the time needed to reach the final steady‐state distribution. Copyright © 2007 John Wiley & Sons, Ltd.
Tree‐based characterization of low index circuit configurations without passivity restrictions
Authors: Encinas Alfonso J. , Riaza Ricardo 
Published: May 2007

AbstractThe present paper addresses index characterizations in differential‐algebraic models of electrical circuits without the need for passivity assumptions. Positive definiteness conditions on the conductance, capacitance and inductance matrices are replaced by certain algebraic assumptions on the so‐calledproper treesfor augmented node analysis andnormal treesfor modified node analysis. The current discussion is restricted to index‐0 and index‐1 systems; for the latter, the analysis is based upon certain matrix factorizations which split the topological information from the electrical features of the devices. Several examples illustrate the scope of our framework. Copyright © 2007 John Wiley & Sons, Ltd.
Targeting of the mouse Slc39a2 (Zip2) gene reveals highly cell‐specific patterns of expression, and unique functions in zinc, iron, and calcium homeostasis
Authors: Peters Jennifer L. , Dufner‐Beattie Jodi , Xu Wenhao , Geiser Jim , Lahner Brett , Salt David E. , Andrews Glen K. 
Published: May 2007

AbstractFourteen members of the Slc39a superfamily of metal ion uptake transporters have been identified in mice and humans, but the physiological functions of most remain obscure. Herein, we created mice with Zip2 (Slc39a2) genes in which the open reading frame was replaced with that of the enhanced green fluorescent protein (EGFP), to study temporal and spatial patterns of Zip2 gene expression and examine the physiological roles of this transporter. Expression of this gene was remarkably cell‐type specific and developmentally regulated in pericentral hepatocytes, developing keratinocytes, and a subset of immature dendritic cells in the immune system. In addition, the Zip2 gene was transiently expressed in giant trophoblast cells in the placenta. Although the Zip2 gene was not essential under conditions of normal dietary zinc, it played an important role in adapting to dietary zinc deficiency during pregnancy, and in the homeostasis of iron in the liver as well as iron and calcium in developing embryos. These studies suggest that active expression of the Zip2 gene in these few specific cell types, aforementioned, plays a particularly important role during zinc deficiency. These studies further reveal novel interactions between zinc transporter function and the homeostasis of other essential metals. genesis 45: 339–352, 2007. Published 2007 Wiley‐Liss, Inc.
The addition of a parent and clinician component to the eating disorder examination for children and adolescents
Authors: Couturier Jennifer , Lock James , Forsberg Sarah , Vanderheyden Debbie , Yen Huei Lee 
Published: May 2007

AbstractObjective:Our goal was to evaluate the addition of parent and clinician reports to the eating disorder examination (EDE) when used with children and adolescents.Method:The EDE was completed with 117 children and adolescents with eating disorders (mean age 14.95 ± 1.91 years). A slightly modified version of the EDE was completed with parents, and clinician summary scores were assigned. Repeated measures analysis was used to compare child, parent, and clinician scores.Results:In those 70 participants with anorexia nervosa (AN) or eating disorder not otherwise specified with a restrictive pattern (EDNOS‐R), child scores were significantly lower than parent scores and clinician scores on restraint and weight concerns. On eating concerns and shape concerns, child scores were lower than clinician scores. Participants with bulimia nervosa (BN) or eating disorder not otherwise specified with binge eating or purging (EDNOS‐BP), reported more restraint and shape concerns than parents (n = 47), but their scores did not differ from clinician ratings. No differences were seen in this group on weight concerns or eating concerns.Conclusion:Parent and clinician reports are particularly important when assessing children and adolescents with AN or EDNOS‐R, but may be less critical for those with BN or EDNOS‐BP. © 2007 by Wiley Periodicals, Inc. Int J Eat Disord 2007.
Season of birth and eating disorders: Patterns across diagnoses in a specialized eating disorders service
Authors: Button Eric , Aldridge Sarah 
Published: May 2007

AbstractObjective:In view of inconsistent findings from previous studies, the aim was to investigate possible seasonal variation in month of birth in patients with anorexia nervosa, bulimia nervosa, and eating disorder not otherwise specified.Method:We examined the month of birth in a cohort of 1,305 adult patients with a DSM‐IV eating disorder diagnosis at first presentation to a specialized eating disorders service.Results:When compared to general population data, we found no evidence of significant variation in month or season of birth in anorexia nervosa, bulimia nervosa, or eating disorder not otherwise specified.Conclusion:The authors question whether people who develop eating disorders differ from the general population in their season of birth. Caution is expressed about further speculation regarding the etiological significance of season of birth in eating disorders. © 2007 by Wiley Periodicals, Inc. Int J Eat Disord 2007.
Recirculating CD4 memory T cells mount rapid secondary responses without major contributions from follicular CD4 effectors and B cells
Authors: Luther Sanjiv A. , Serre Karine , Cunningham Adam F. , Khan Mahmood , Acha‐Orbea Hans , MacLennan Ian C. M. , Toellner Kai‐Michael 
Published: May 2007

AbstractFor weeks after primary immunization with thymus‐dependent antigens the responding lymph nodes contain effector CD4 T cells in T zones and germinal centers as well as recirculating memory T cells. Conversely, remote nodes, not exposed to antigen, only receive recirculating memory cells. We assessed whether lymph nodes with follicular effector CD4 T cells in addition to recirculating memory CD4 T cells mount a more rapid secondary response than nodes that only contain recirculating memory cells. Also, the extent to which T cell frequency governs accelerated CD4 T cell recall responses was tested. For this, secondary antibody responses to a superantigen, where the frequency of responding T cells is not increased at the time of challenge, were compared with those to conventional protein antigens. With both types of antigens similar accelerated responses were elicited in the node draining the site of primary immunization and in the contralateral node, not previously exposed to antigen. Thus recirculating memory cells are fully capable of mounting accelerated secondary responses, without the assistance of CD4 effector T cells, and accelerated memory responses are not solely dependent on higher T cell frequencies. Accelerated memory CD4 T cell responses were also seen in B cell‐deficient mice.
Elevated levels of endogenous apoptotic DNA and IFN‐α in complement C4‐deficient mice: Implications for induction of systemic lupus erythematosus
Authors: Finke Doreen , Randers Katharina , Hoerster Robert , Hennig Holger , Zawatzky Rainer , Marion Tony , Brockmann Christian , Klempt‐Giessing Katja , Jacobsen Kirsten , Kirchner Holger , Goerg Siegfried 
Published: May 2007

AbstractSystemic lupus erythematosus (SLE), an autoimmune disease characterized by chronic nephritis, arthritis and dermatitis, and the presence of antinuclear autoantibodies, is associated with complement factor deficiencies in the classical activation pathway. In addition, IFN‐α seems to be a key cytokine in SLE as an activated IFN‐α system is regularly observed in patients with SLE. Here, we demonstrate that in lupus‐susceptible, complement C4‐deficient mice the lack of complement results in elevated intravascular levels of apoptotic DNA. The apoptotic DNA is targeted to the splenic marginal zone where it accumulates and induces IFN‐α. As such, we present here a unifying hypothesis for the induction of SLE that incorporates the role of complement deficiency and elevated levels of IFN‐α.
Activities of erythropoietin on tumors: An immunological perspective
Authors: Ghezzi Pietro , Mengozzi Manuela 
Published: May 2007

AbstractThere is a growing interest in the non‐erythropoietic, tissue‐protective and restorative actions of erythropoietin (EPO). While studies in this field have indicated that EPO can ameliorate chemotherapy‐induced peripheral neuropathy and cardiotoxicity, the issue whether EPO can positively or negatively affect cancer patients is a hot one. In this debate, many activities of EPO are being considered, including tissue/neuroprotection, angiogenesis, anti‐inflammatory activity, growth promotion, and inhibition of apoptosis. However, few studies have explored the interactions of EPO with the immune system. A study in this issue of the European Journal of Immunology by Katz et al. adds one new piece to the puzzle by showing that EPO can stimulate B cell‐mediated immunity.See accompanying article: http://dx.doi.org/10.1002/eji.200637025
Magnetic and Infrared Properties of the Azide Complex of (2,7,12,17‐Tetrapropylporphycenato)iron(III): A Novel Admixing Mechanism of the S = 5/2 and S = 3/2 States
Authors: Neya Saburo , Takahashi Akihiro , Ode Hirotaka , Hoshino Tyuji , Hata Masayuki , Ikezaki Akira , Ohgo Yoshiki , Takahashi Masashi , Hiramatsu Hirotsugu , Kitagawa Teizo , Furutani Yuji , Kandori Hideki , Funasaki Noriaki , Nakamura Mikio 
Published: May 2007

AbstractThe five‐coordinate ferric azide complex of 2,7,12,17‐tetrapropylporphyrcene [Fe(TPrPc)N3] was characterized with proton NMR, electron paramagnetic resonance (EPR), Mössbauer, and IR techniques. The paramagnetic NMR showed the pyrrole‐H signal that exhibits anomalous anti‐Curie type of 1/T‐dependence over a 310–190 K range. The EPR of the solid sample resolved a signal with g = 5.42, 5.40, and 2.00 at 5 K. The quadrupole splitting parameter of the Mössbauer spectrum was 2.20 mm s–1 at 290 K, and the magnetic moment was 4.70 μB at 290 K for the microcrystalline sample. These results suggest that [Fe(TPrPc)N3] is not pure high‐spin (S = 5/2) but a spin mixture of the S = 5/2, 3/2 states. The azide in [Fe(TPrPc)N3] exhibited split IR bands ascribed to the two spin isomers at 2066 and 2049 cm–1. The 2049‐cm–1 band, assigned to the S = 3/2 species, was reversibly intensified with decreasing temperature. The IR results demonstrate that the S = 3/2, 5/2 states are not quantum‐mechanically admixed but in thermal equilibrium. The thermodynamic parameters associated with the spin equilibrium, ΔH = –3 990 cal mol–1 and ΔS = –16.5 cal mol–1 K–1, were obtained from the NMR shift analysis, and the population of the S = 3/2 isomer was calculated to be 0.19 at 293 K. A minimum lifetime of the two spin isomers was estimated to be 0.3 ps with IR. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Zirconium(IV) Tris(phosphinoamide) Complexes as a Tripodal‐Type Metalloligand: A Route to Zr–M (M = Cu, Mo, Pt) Heterodimetallic Complexes
Authors: Sue Takashi , Sunada Yusuke , Nagashima Hideo 
Published: May 2007

AbstractTreatment of ZrCl4 with 3 equiv. of Li(PPh2NR) (R = tBu, iPr) gives tris(phosphinoamide)zirconium complexes, (PPh2NR)3ZrCl [R = tBu (1a), iPr (1b)], in high yield. Crystal structures of 1a,b show that three phosphorus atoms are coordinated to the zirconium center in the solid state, whereas variable temperature NMR studies indicate a reversible coordination/dissociation process of three phosphorus atoms in the solution state. Reaction of 1a,b with CuCl give rise to the formation of Zr–Cu heterodimetallic complexes, ClCu(Ph2PNR)3ZrCl [R = tBu (2a), iPr (2b)]. The molecular structures of 2a,b show that the Cu atom adopts a pseudotetrahedral coordination geometry with tripodal phosphorus moieties and a chlorine atom, whereas the ligand arrangement around the Zr atom is trigonal bipyramidal with the linear Cl–Zr–Cu axis at the apical site. A Zr–Mo heterodimetallic complex, (CO)3Mo(Ph2PNiPr)3ZrCl (3), is synthesized from 1b and Mo(CO)3(CH3CN)3, in which the ligands around the Mo center are arranged octahedrally, and three phosphorus moieties are coordinated in the fac‐P3 fashion. The reaction of 1b with a square planar PtII precursor, such as (COD)PtCl2, is unique and gives (κ2‐Ph2PNiPr)Pt(Ph2PNiPr)2ZrCl3 (4), which is the first example of a Zr–Pt zwitterionic heterodimetallic complex. The reaction involves intramolecular migration of two chlorine atoms from Pt to Zr as well as that of a Ph2PNiPr moiety from Zr to Pt.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Low‐Valent Nickel and Palladium Complexes with 1,1′‐Bis(phosphanyl)ferrocenes: Syntheses and Structures of Acrylic Acid and Ethylene Complexes (Eur. J. Inorg. Chem. 16/2007)
Authors: Langer Jens , Fischer Reinald , Görls Helmar , Walther Dirk 
Published: May 2007

AbstractThe cover picture shows three types of nickel complexes that are stabilized by 1,1′‐bis(phosphanyl)ferrocene ligands, which can be considered as model complexes for the hypothetical metal‐mediated reaction between CO2 and ethylene to form acrylic acid. The (acrylic acid)nickel(0) complexes are of particular interest as they represent the first stable combination between Ni0 and this strong acid as a ligand. These complexes form hydrogen‐bonded dimers in the solid state and are surprisingly stable. Details of their synthesis and reactivity along with the description of the other complexes are discussed in the article by D. Walther et al. on p. 2257 ff. The artwork was created by Ulf Walther.