bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lithium Diisopropylamide: Solution Kinetics and Implications for Organic Synthesis
Authors: Collum David B. , McNeil Anne J. , Ramirez Antonio 
Published: March 2007

AbstractLithium diisopropylamide (LDA) is a prominent reagent used in organic synthesis. In this Review, rate studies of LDA‐mediated reactions are placed in the broader context of organic synthesis in three distinct segments. The first section provides a tutorial on solution kinetics, emphasizing the characteristic rate behavior caused by dominant solvation and aggregation effects. The second section summarizes substrate‐ and solvent‐dependent mechanisms that reveal basic principles of solvation and aggregation. The final section suggests how an understanding of mechanism might be combined with empirical methods to optimize yields, rates, and selectivities of organolithium reactions and applied to organic synthesis.
Chemiluminescent picture of diphenyleneiodonium‐inhibited NADPH oxidase: a bimodal process and its logistic–exponential model‐based description
Authors: Kochel Bonawentura , Vocks Andreas , Arnhold Jürgen 
Published: March 2007

AbstractA chemiluminescence (CL) study of diphenyleneiodonium‐inhibited NADPH oxidase was performed on a cellular system containing neutrophils stimulated by phorbol myristate acetate, indicating a complex bimodal structure of CL processes corresponding to different stages of the inhibition. The complex structure of these processes was described by a superposition of two logistic–exponential (LE) models, characterizing these processes as bimodal ones. To determine the mechanistic foundation of the LE model‐described processes, a generalized form of the second‐order dynamic system of CL reactions, the solution to which corresponds to the LE model, was constructed. The diphenyleneiodonium effects on neutrophil NADPH oxidase were separated from the total bimodal CL of the whole measurement system by the use of difference CL processes. These difference processes were also found to be bimodal; thus, inhibitor‐induced reduction of CL could be described by a second‐order dynamic system. The rate constants and initial concentrations in this dynamic system were determined by the least squares method applied to numerical solutions approximating the difference processes. Using interrelations between the parameters of the dynamic system, cooperative effects in the inhibitor reactions with NADPH oxidase were found and described quantitatively. Other evidences of cooperativity were obtained from integral characteristics of the CL reduction process, i.e. dose–response and progress curves, determined by numerical integration of the LE models constituting the superposition. On this basis, it was also possible to detect a specific binding of the inhibitor to the enzyme. Finally, putative reaction mechanisms suggested by the model obtained were considered and compared with those known at present. Copyright © 2007 John Wiley & Sons, Ltd.
Modification of β‐lactoglobulin by microbial transglutaminase under high hydrostatic pressure: Localization of reactive glutamine residues
Authors: Partschefeld Claudia , Richter Sandy , Schwarzenbolz Uwe , Henle Thomas 
Published: March 2007

AbstractMicrobial transglutaminase (mTG) mediated modification of bovine β‐lactoglobulin (bLG) at ambient and high hydrostatic pressure was investigated in order to characterize preferred sites of the crosslinking reaction by identifying reactive glutamine residues. bLG was labeled with triglycine (GGG) by incubation with mTG at ambient pressure or at 400 MPa, respectively, and was subjected to an enzymatic digestion with trypsin. The resulting peptides were separated and those containing glutamine residues modified with GGG were unambiguously identified using RP‐HPLC with ESI‐TOF‐MS. For bLG treated with mTG at ambient pressure for 1 h at 40°C, no labeling was observed, thus confirming that the native protein is no substrate for mTG. After incubation of the protein with mTG at 400 MPa for 1 h at 40°C, four out of nine glutamine residues, namely at positions 5, 13, 35, and 59 were identified as accessible for the mTG catalyzed reaction, indicating partial unfolding of bLG under pressure and exposure of previously unaccesible glutamine residues. Thus, only a limited number of glutamine residues were substrates for mTG, which points to a pronounced substrate specificity of mTG toward individual glutamine residues within a protein.
Mapping of the epitope of monoclonal antibody 2B4 to the proline‐rich region of human Huntingtin, a region critical for aggregation and toxicity
Authors: Dehay Benjamin , Weber Chantal , Trottier Yvon , Bertolotti Anne 
Published: March 2007

AbstractHuntington's disease is a neurodegenerative disease caused by a polyglutamine (polyQ) expansion in Huntingtin, which provokes aggregation of a proteolytic amino‐terminal fragment of the affected protein encompassing the polyQ expansion. Accumulation of mutant Huntingtin somehow triggers cellular dysfunction and leads to a progressive degeneration of striatal neurons. Despite considerable efforts, the function of Huntingtin as well as the precise molecular mechanisms by which the expanded polyQ elicits cellular dysfunction remain unclear. In addition, no treatment is available to prevent, cure, or even slow down the progression of this devastating disorder. Antibodies are valuable tools to understand protein function and disease mechanisms. Here, we have identified the epitope recognized by the mAb 2B4, a broadly used antibody generated against the amino‐terminal region of Huntingtin, which detects both aggregated and soluble Huntingtin. The 2B4 antibody specifically recognizes amino acids 50–64 of human Huntingtin but not the murine homologous region. Furthermore, the 2B4 epitope resides within the proline‐rich region of Huntingtin, which is critical for polyQ aggregation and toxicity. These properties suggest that the 2B4 antibody might be useful in antibody‐based therapeutic strategies.
Unique side chain conformation of a leu residue in a triple‐helical structure
Authors: Okuyama Kenji , Narita Hirotaka , Kawaguchi Tatsuya , Noguchi Keiichi , Tanaka Yuji , Nishino Norikazu 
Published: March 2007

AbstractSingle crystal structures of host‐guest peptides, (Pro‐Hyp‐Gly)4‐Leu‐Hyp‐Gly‐(Pro‐Hyp‐Gly)5 (LOG1) and (Pro‐Hyp‐Gly)4‐ (Leu‐Hyp‐Gly)2‐(Pro‐Hyp‐Gly)4 (LOG2), have been determined at 1.6 Å and 1.4 Å resolution, respectively. In these crystals, the side chain conformations of the Leu residues were (+)gauche‐trans. This conformational preference for the Leu side chain in the Leu‐Hyp‐Gly sequence was explained by stereochemical considerations together with statistical analysis of Protein Data Bank data. In the (+)gauche‐trans conformation, the Leu side chain can protrude along the radial direction of the rod‐like triple‐helical molecule. One strong hydrophobic interaction of the Leu residue was observed between adjacent molecules in the LOG2 crystal. Because the Leu‐Hyp‐Gly sequence is one of the most frequently occurring triplets in Type I collagen, this strong hydrophobic interaction can be expected in a fibrillar structure of native collagen. All the Leu residues in the asymmetric unit of the LOG1 and LOG2 crystals had water molecules hydrogen bonded to their NH. These water molecules made three additional hydrogen bonds with the Hyp OH, the Gly OC, and a water molecule in the second hydration shell, forming a tetrahedral coordination of hydrogen bonds, which allows a smaller mean‐square displacement factor of this water oxygen atom than those of other water molecules. These hydrogen bonds stabilize the molecular and packing structures by forming one OC(Gly)‐‐‐W‐‐‐OH(Hyp) intra‐molecular linkage and two NH(Leu)‐‐‐W‐‐‐OC(Gly) and NH(Leu)‐‐‐W‐‐‐OH(Hyp) inter‐molecular linkages. © 2007 Wiley Periodicals, Inc. Biopolymers 86: 212–221, 2007.This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
Bis(phosphinimino)methanide Rare Earth Amides: Synthesis, Structure, and Catalysis of Hydroamination/Cyclization, Hydrosilylation, and Sequential Hydroamination/Hydrosilylation
Authors: Rastätter Marcus , Zulys Agustino , Roesky Peter W. 
Published: March 2007

AbstractA series of yttrium and lanthanide amido complexes [Ln{N(SiHMe2)2}2{CH(PPh2NSiMe3)2}] (Ln=Y, La, Sm, Ho, Lu) were synthesized by three different pathways. The title compounds can be obtained either from [Ln{N(SiHMe2)2}3(thf)2] and [CH2(PPh2NSiMe3)2] or from KN(SiHMe2)2 and [Ln{CH(PPh2NSiMe3)2}Cl2]2, while in a third approach the lanthanum compound was synthesized in a one‐pot reaction starting from K{CH(PPh2NSiMe3)2}, LaCl3, and KN(SiHMe2)2. All the complexes have been characterized by single‐crystal X‐ray diffraction. The new complexes, [Ln{N(SiHMe2)2}2{CH(PPh2NSiMe3)2}], were used as catalysts for hydroamination/cyclization and hydrosilylation reactions. A clear dependence of the reaction rate on the ionic radius of the center metal was observed, showing the lanthanum compound to be the most active one in both reactions. Furthermore, a combination of both reactions—a sequential hydroamination/hydrosilylation reaction—was also investigated.
Three‐Dimensional Lanthanide(III)–Copper(II) Compounds Based on an Unsymmetrical 2‐Pyridylphosphonate Ligand: An Experimental and Theoretical Study
Authors: Ma Yun‐Sheng , Li Hui , Wang Jun‐Jie , Bao Song‐Song , Cao Rong , Li Yi‐Zhi , Ma Jing , Zheng Li‐Min 
Published: March 2007

AbstractBased on an unsymmetrical 2‐pyridylphosphonate ligand, two types of LnIII–CuII compounds with three‐dimensional structures were obtained under hydrothermal conditions, namely, Ln2Cu3(C5H4NPO3)6⋅4 H2O (1⋅Ln; Ln=La, Ce, Pr, Nd) and Ln2Cu3(C5H4NPO3)6 (2⋅Ln; Ln=Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho). Compounds 1⋅Ln are isostructural and crystallize in chiral cubic space group I213. In these structures, each Ln ion is nine‐coordinate and has a tricapped triprismatic geometry, while each Cu center is six‐coordinate with an octahedral environment. The {LnO9} polyhedra and {CuN2O4} octahedra are connected by edge sharing to form an inorganic open framework structure with a 3‐connected 10‐gon (10,3) topology in which the Ln and Cu atoms are alternately linked by the phosphonate oxygen atoms. Compounds 2⋅Ln are isostructural and crystallize in trigonal space group R$\bar 3$. In these structures, the {LnO6} octahedra are triply bridged by the {CPO3} tetrahedra by corner sharing to form an infinite chain along the c axis. Each chain is connected to its six equivalents through corner sharing of {CPO3} tetrahedra and {CuN2O2} planes to form a three‐dimensional framework structure in which the Ln and Cu atoms are linked purely by O‐P‐O units. The formation of these two types of structures is rationalized by quantum chemical calculations, which showed that both the lanthanide contraction and the electron configuration of CuII play important roles. When CuII was replaced by ZnII, only the first type of compounds resulted. The magnetic properties of complexes 1⋅Ln and 2⋅Ln were investigated. The nature of LnIII–CuII (Ln=Ce, Pr, Nd) interactions is illustrated by comparison with their LnIII–ZnII analogues.
Left bundle‐branch block—pathophysiology, prognosis, and clinical management
Authors: Francia Pietro , Balla Cristina , Paneni Francesco , Volpe Massimo 
Published: March 2007

AbstractGiven its broad use as a screening tool, the electrocardiogram (ECG) has largely become one of the most common diagnostic tests performed in routine clinical practice. As a result, the finding of left bundle‐branch block (LBBB) in the absence of a well‐defined clinical setting has become relatively frequent and raises questions and often concerns. While in the absence of clinically detectable heart disease LBBB does not necessarily imply poor outcomes, physicians should be aware of the role of LBBB in stratifying risk of cardiovascular events and death in subjects with both ischemic and nonischemic heart disease. This paper reviews historical landmarks, pathophysiologic features, prognostic implications, and clinical management of LBBB in apparently healthy subjects and those with heart disease. Copyright © 2007 Wiley Periodicals, Inc.
Fibroblast growth factor–hedgehog interdependence during retina regeneration
Authors: Spence Jason R. , Aycinena Juan‐Carlos , Del Rio‐Tsonis Katia 
Published: March 2007

AbstractThe embryonic chick is able to regenerate the retina after it has been removed. We have previously shown that proliferating stem/progenitor cells present in the ciliary body/ciliary marginal zone (CB/CMZ) of the chick eye are responsible for regeneration, which can be induced by ectopic fibroblast growth factor‐2 (FGF2) or Sonic hedgehog (Shh). Here, we reveal the mechanisms showing how FGF2 and Shh signaling are interdependent during retina regeneration. If the FGF pathway is inhibited, regeneration stimulated by Shh is inhibited. Likewise, if the Hedgehog pathway is inhibited, regeneration stimulated by FGF2 is inhibited. We examined early signaling events in the CB/CMZ and found that FGF2 or Shh induced a robust Erk phosphorylation during the early stages of retina regeneration. Shh also up‐regulated the expression of several members of the FGF signaling pathway. We show that ectopic FGF2 or Shh overexpression increased the number of phosphohistone 3 (PH3)‐positive cells in the CB/CMZ and inhibition of either pathway decreased the number of PH3‐positive cells. Additionally, both FGF and Hh signaling are required for cell survival in the CB/CMZ, whereas Hh and not FGF signaling plays a role in maintaining the identity of the retinal progenitor population in this region. Combined, our results support a model where the FGF and Hedgehog pathways work together to stimulate retina regeneration. Developmental Dynamics 236:1161–1174, 2007. © 2007 Wiley‐Liss, Inc.
ICER/CREM‐mediated transcriptional attenuation of IL‐2 and its role in suppression by regulatory T cells
Authors: Bodor Josef , Fehervari Zoltan , Diamond Betty , Sakaguchi Shimon 
Published: March 2007

AbstractHere, we report that inducible cAMP early repressor/cAMP response element modulator (ICER/CREM) is induced early in CD25+CD4+ regulatory T cell (TR) assays mainly in activated Foxp3– effector T cells and this induction correlates with sharp decrease in number of IL‐2‐expressing T cells. Importantly, RNAi targeting of ICER/CREM in responder CD25–CD4+ T cells antagonizes TR‐mediated suppression. Moreover, forced expression of Foxp3 in naive CD25– T cells induces constitutive expression of ICER/CREM in T cells with a regulatory phenotype. Foxp3 facilitates expression of ICER/CREM both in Foxp3 transductants as well as CD25– responder T cells suggesting that induction of TR function in suppression assays may utilize contact‐dependent interaction. Indeed, CTLA‐4 blockade or use of B7‐deficient CD25– responder T cells prevents ICER/CREM accumulation and leads to the rescue of IL‐2 expression. Therefore, we propose that CTLA‐4 binding to B7 ligands expressed on activated ligand‐bearing Foxp3– effector T cells results in ICER/CREM‐mediated transcriptional attenuation of IL‐2. Collectively, these data suggest that Foxp3 expression in TR cells imposes suppression in contact‐dependent fashion by induction of constitutive ICER/CREM expression in activated CD25+ Foxp3– T cell effectors thus preventing them from producing IL‐2.
Mast cells play a key role in the developmentof late airway hyperresponsiveness through TNF‐αin a murine model of asthma
Authors: Kim Young‐Suk , Ko Hyun‐Mi , Kang Nam‐In , Song Chang‐Ho , Zhang Xin , Chung Woo‐Chan , Kim Jae‐Hong , Choi In‐Hak , Park Young‐Min , Kim Gi‐Young , Im Shun‐Young , Lee Hern‐Ku 
Published: March 2007

AbstractWe have investigated the role of TNF‐α in mast cell‐mediated late airway hyperresponsiveness (AHR) using mast cell‐deficient WBB6F1‐W/Wv (W/Wv) mice in a murine model of asthma, which exhibits a biphasic increase in AHR. TNF‐α levels in the airway and magnitude of late AHR in response to airway allergen challenge were severely impaired in W/Wv mice compared to their littermates. In addition to TNF‐α, cytosolic phospholipase A2 (cPLA2) phosphorylation and enzymatic activity in the lungs were also impaired in W/Wv mice. Either anti‐TNF‐α antibody or an inhibitor of cPLA2 abolished late AHR in congeneic +/+ mice. Intratracheal administration of TNF‐α resulted in increases in late AHR, cPLA2 phosphorylation, cPLA2 activity, and phosphorylation of mitogen‐activated protein kinases. Mast cell replacement restored airway TNF‐α level, cPLA2 phosphorylation and enzymatic activity in the lungs as well as late AHR in W/Wv mice. These data indicate that mast cells play a key role in the development of late AHR through liberation of TNF‐α.
Functional and phenotypic characterizationof tetanus toxoid‐specific human CD4+ T cellsfollowing re‐immunization
Authors: Cellerai Cristina , Harari Alexandre , Vallelian Florence , Boyman Onur , Pantaleo Giuseppe 
Published: March 2007

AbstractThe formation of immunological memory is a hallmark of adaptive immunity and the goal of vaccination. For CD8+ T cells, successful generation of memory cells has been linked to IL‐7 receptor alpha (IL‐7Rα) expression, suggesting a role for IL‐7 signaling, which in turn is important for preventing T cell apoptosis. We thus investigated the kinetics and changes of IL‐7Rα and anti‐apoptotic protein Bcl‐2 expression levels in tetanus toxoid (TT)‐specific CD4+ T cells at different time points prior and after TT re‐immunization of TT‐immune individuals. Prior to re‐immunization, most TT‐specific CD4+ T cells were high IL‐2 producers, CD45RA–CCR7+, IL‐7RαhighBcl‐2high cells, resembling typical long‐lived central memory cells. Already 5 days, and more importantly at the peak of the response, after TT re‐immunization, a substantial fraction of these cells secreted also IFN‐γ, down‐regulated CCR7, IL‐7Rα and Bcl‐2 and became Ki67 positive, resembling effector memory cells. In contrast, TT‐specific CD4+ T cells found 60 days or later after re‐immunization were again as baseline. Interestingly, a significant fraction of IL‐7RαhighBcl‐2high TT‐specific CD4+ T cells, i.e. the proposed memory cell precursors, remained stable at any time point upon re‐immunization. Together, these results suggest that IL‐7Rα expression levels might be a useful marker for identifying long‐lived Ag‐specific CD4+ T cells in memory T cells.
Synthesis, Crystal Structures, and Photoluminescence of a Series of Coordination Polymers with Two Homologous Functional Flexible Ligands
Authors: Zhou Hong‐Ping , Wang Peng , Hu Zhang‐Jun , Li Lin , Chen Jing‐Jin , Cui Yang , Tian Yu‐Peng , Wu Jie‐Ying , Yang Jia‐Xiang , Tao Xu‐Tang , Jiang Min‐Hua 
Published: March 2007

AbstractTwo functional, flexible ligands, namely 3,6‐dipyrazolyl‐9‐ethylcarbazole (L1) and 3,6‐diimidazolyl‐9‐ethylcarbazole (L2) have been synthesized and characterized and their coordination to various AgI, CdII, and CoII salts investigated. Six new complexes, 1–6, have been obtained and fully characterized by IR spectroscopy, elemental analysis, and single‐crystal X‐ray diffraction. The 2D double helix framework of the complex [CdL1I2]n (1) is formed by C–H···I hydrogen bonds, whereas the same 2D double helix framework of compound [{AgL1SO3PhCH3}2(CH3OH)(H2O)]n (2) is formed by S–O···H and C–H···O hydrogen bonds and weak π–π interactions. The coordination modes of CdII and CoII in [CdL22(NCS)2]n (3), [CoL22(NCS)2(CHCl3)2]n (4), [CdL22(NO3)2(CH3OH)2]n (5), and [CoL22(NO3)2(CH3OH)2]n (6) are the same, but in the packing diagram interlayers form a 3D network through C–H···S interactions and π–π interactions in 3, interlayers form a 3D network through S···S interactions and π–π interactions in 4, novel 3D structures are formed by interchain O···H–C hydrogen bonding and interlayer O···H–C hydrogen‐bonding and π–π interactions in 5 and 6. The structural differences between these complexes show the influence of the orientation of the coordinating group of the ligand. These results also show that the metal ion, anion, and nonbonding and π–π interactions are significant factors in controlling the structural topology of these metal‐organic supramolecular architectures. In addition, the luminescence properties of L1, 1, L2, and 3 are investigated in the solid state at room temperature. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Receptor versus Counterion: Capability of N,N′‐Bis(2‐aminobenzyl)‐diazacrowns for Giving Endo‐ and/or Exocyclic Coordination of ZnII
Authors: Vaiana Lea , Platas‐Iglesias Carlos , Esteban‐Gómez David , Avecilla Fernando , de Blas Andrés , Rodríguez‐Blas Teresa 
Published: March 2007

AbstractThe structure of ZnII complexes with receptors L1 and L2[L1 = N,N′‐bis(2‐aminobenzyl)‐1,10‐diaza‐15‐crown‐5 and L2 = N,N′‐bis(2‐aminobenzyl)‐4,13‐diaza‐18‐crown‐6] was studied both in the solid state and in acetonitrile solution. Both receptors form mononuclear ZnII complexes in this solvent, while no evidence for the formation of dinuclear complexes was obtained. This is in contrast with previous investigations that demonstrated the formation of dinuclear complexes of L2 with first‐row transition metals such as NiII, CoII and CuII. Compounds of formula [Zn(L1)](ClO4)2 (1), [Zn(L1)](NO3)2·2CH3CN (2), [Zn(L2)](ClO4)2 (3) and [Zn(L2)(NO3)2] (4) were isolated and structurally characterised by X‐ray diffraction analyses. L1 forms seven‐coordinate ZnII complexes in the presence of both nitrate and perchlorate anions, as a consequence of the good fit between the macrocyclic cavity and the ionic radius of the metal ion. The ZnII ion is deeply buried into the receptor cavity and the anions are forced to remain out of the metal coordination sphere. The cation [Zn(L1)]2+ present in 1 and 2 is one of the very few examples of seven‐coordinate Zn complexes. Receptor L2 provides a very rare example of a macrocyclic receptor allowing endocyclic and exocyclic coordination on the same guest cation, depending on the nature of the anion present. Thus, in 3 the ZnII ion is endocyclically coordinated, placed inside the crown hole coordinated to four donor atoms of the ligand in a distorted tetrahedral environment, whereas in 4, the presence of a strongly coordinating anion such as nitrate results in an exocyclic coordination of ZnII, which is directly bound only to the two primarily amine groups of L2 and two nitrate ligands. Spectrophotometric titrations of [Zn(L2)]2+ with tetrabutylammonium nitrate in acetonitrile solution demonstrate the stepwise formation of 1:1 and 1:2 adducts with this anion in acetonitrile solution. The [Zn(L1)]2+, [Zn(L2)]2+ and [Zn(L2)(NO3)2] systems were characterised by means of DFT calculations (B3LYP model). The calculated geometries show an excellent agreement with the experimental structures obtained from X‐ray diffraction analyses. Calculated binding energies of the macrocyclic ligands to ZnII are also consistent with the experimental data.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)
Cover Picture: Active Site Protonation of 1‐Azafagomine in Glucosidases Studied by Solid‐State NMR Spectroscopy (Eur. J. Org. Chem. 11/2007)
Authors: Sivertsen Astrid C. , Gasior Magdalena , Bjerring Morten , Hansen Steen U. , Lopez Lopez Oscar , Nielsen Niels C. , Bols Mikael 
Published: March 2007

AbstractThe cover picture shows the glycosidase inhibitor 1‐azafagomine binding to the enzyme β‐glucosidase in the magnetic field of a solid‐state NMR spectrometer. Details are discussed in the article by N. C. Nielsen, M. Bols et al. on p. 1735 ff.