bluuebunny/crossref_metadata_2025_split huggingface dataset:
New Insights into the Polymerization of Methyl Methacrylate Initiated by Rare‐Earth Borohydride Complexes: A Combined Experimental and Computational Approach
Authors: Barros Noémi , Schappacher Michèle , Dessuge Paul , Maron Laurent , Guillaume Sophie M. 
Published: December 2007

AbstractPolymerization of methyl methacrylate (MMA) initiated by the rare‐earth borohydride complexes [Ln(BH4)3(thf)3] (Ln=Nd, Sm) or [Sm(BH4)(Cp*)2(thf)] (Cp*=η‐C5Me5) proceeds at ambient temperature to give rather syndiotactic poly(methyl methacrylate) (PMMA) with molar masses M̄n higher than expected and quite broad molar mass distributions, which is consistent with a poor initiation efficiency. The polymerization of MMA was investigated by performing density functional theory (DFT) calculations on an η‐C5H5 model metallocene and showed that in the reaction of [Eu(BH4)(Cp)2] with MMA the borate [Eu(Cp)2{(OBH3)(OMe)CC(Me)2}] (e‐2) complex, which forms via the enolate [Eu(Cp)2{O(OMe)CC(Me)2}] (e), is calculated to be exergonic and is the most likely of all of the possible products. This product is favored because the reaction that leads to the formation of carboxylate [Eu(Cp)2{OOCC(Me)(CH2)}] (f) is thermodynamically favorable, but kinetically disfavored, and both of the potential products from a Markovnikov [Eu(Cp)2{O(OMe)CCH(Me)(CH2BH3)}] (g) or anti‐Markovnikov [Eu(Cp)2{O(OMe)CC(Me2)(BH3)}] (h) hydroboration reaction are also kinetically inaccessible. Similar computational results were obtained for the reaction of [Eu(BH4)3] and MMA with all of the products showing extra stabilization. The DFT calculations performed by using [Eu(Cp)2(H)] to model the mechanism previously reported for the polymerization of MMA initiated by [Sm(Cp*)2(H)]2 confirmed the favorable exergonic formation of the intermediate [Eu(Cp)2{O(OMe)CC(Me)2}] (e′′) as the kinetic product, this enolate species ultimately leads to the formation of PMMA as experimentally observed. Replacing H by BH4 thus prevents the 1,4‐addition of the [Eu(BH4)(Cp)2] borohydride ligand to the first incoming MMA molecule and instead favors the formation of the borate complex e‐2. This intermediate is the somewhat active species in the polymerization of MMA initiated by the borohydride precursors [Ln(BH4)3(thf)3] or [Sm(BH4)(Cp*)2(thf)].
Synthesis of a new C2‐symmetric chiral catalyst and its application in the catalytic asymmetric borane reduction of prochiral ketones
Authors: Zhou Yan , Wang Wen‐Hua , Dou Wei , Tang Xiao‐Liang , Liu Wei‐Sheng 
Published: December 2007

AbstractA new C2‐symmetric chiral catalyst 3,5‐bis[(2S)‐(hydroxy‐diphenylmethyl)‐ pyrrolidin‐1‐ylmethyl]‐1,3,4‐oxadiazole was successfully synthesized by the reaction of 2,5‐dichloromethyl‐1,3,4‐oxadiazole with (S)‐α,α‐diphenyl‐2‐pyrrolidinemethanol, and applied to the catalytic asymmetric reduction of prochiral ketones with borane. When the catalyst loading was 1 mol %, enantiomeric excesses of up to 86.8% and 94.5% were observed in reduction of aromatic and α‐halo ketones, respectively. Chirality, 2008. © 2007 Wiley‐Liss, Inc.
Candida rugosa lipase‐catalysed kinetic resolution of 2‐substituted‐aryloxyacetic esters with dimethylsulfoxide and isopropanol as additives
Authors: Ammazzalorso Alessandra , Amoroso Rosa , Bettoni Giancarlo , De Filippis Barbara , Fantacuzzi Marialuigia , Giampietro Letizia , Maccallini Cristina , Tricca Maria Luisa 
Published: December 2007

AbstractCandida rugosa lipase‐catalysed hydrolysis of three different 2‐substituted‐aryloxyacetic esters was performed in aqueous buffer containing dimethyl sulphoxide and isopropanol from 0 to 80% v/v as additives, in order to obtain an enhancement of the enantioselectivity. For 2‐(p‐chlorophenoxy)acetic acid and 2‐n‐butyl‐2‐(p‐chlorophenoxy)acetic acid ethyl esters, DMSO enhanced enzyme enantioselectivity more than IPA with an opposite enzymatic enantiopreference. The cosolvents moderately improved Candida rugosa lipase enantioselectivity for 2‐phenyl‐2‐(p‐chlorophenoxy)acetic acid ethyl ester. Chirality, 2008. © 2007 Wiley‐Liss, Inc.
Trends in childhood cancer incidence in the U.S. (1992–2004)
Authors: Linabery Amy M. , Ross Julie A. 
Published: December 2007

AbstractBACKGROUND.The etiology of most pediatric neoplasms remains elusive. Examination of population‐based incidence data provides insight regarding etiology among various demographic groups and may result in new hypotheses. The objective of the current study was to present updated information regarding childhood cancer incidence and trends in the U.S. overall and among demographic subgroups, including Asian/Pacific Islanders and Hispanics, for whom to the authors' knowledge trends have not been previously examined.METHODS.Data obtained by 13 registries of the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) program were evaluated to assess incidence and trends of common primary cancers diagnosed between 1992 and 2004 among children aged birth to 19 years. Frequencies, age‐adjusted incidence rates, and joinpoint regression results, including annual percent change (APC) in incidence rates (and 95% confidence intervals [95% CI]), were calculated.RESULTS.Between 1992 and 2004, a modest, nonsignificant increase in the average annual incidence rate (APC, 0.4%; 95% CI, −0.1%–0.8%) was observed for all pediatric cancer diagnoses combined. There was a suggestion of an increase in leukemia (APC, 0.7%; 95% CI, −0.1%–1.5%), and acute lymphoblastic leukemia in particular (APC, 0.8%; 95% CI, −0.4%–1.9%), whereas rates for central nervous system tumors overall were stable (APC, −0.1%; 95% CI, −1.1%–1.0%); 2 joinpoints were observed for astrocytoma. Rate increases were noted for hepatoblastoma (APC, 4.3%; 95% CI, 0.2%–8.7%) and melanoma (APC, 2.8%; 95% CI, 0.5%–5.1%). Differences by demographic group (sex, age, and race/ethnicity) are also described.CONCLUSIONS.The observed trends reinforce an ongoing need for population‐based surveillance and further etiologic studies. Cancer 2008. © 2007 American Cancer Society.
On the Energy Efficiency of Microwave‐Assisted Organic Reactions
Authors: Razzaq Tahseen , Kappe C. Oliver 
Published: December 2007

AbstractThe energy consumed for four different organic transformations carried out under microwave and conventional heating under otherwise identical reaction conditions was measured with the aid of a Wattmeter. In the case of open‐vessel reflux processing, microwave dielectric heating required significantly more energy than conventional techniques using oil baths or heating mantles. This is a consequence of the comparably low energy efficiency of the magnetron in converting electrical to microwave energy. Significant savings in energy were experienced by taking advantage of sealed‐vessel microwave processing at high temperatures. When comparing a conventionally heated reflux experiment with a microwave‐heated experiment using a superheated solvent in a sealed vessel, reaction times were reduced significantly from hours to minutes. The energy savings in these instances are, however, largely connected to the reduced reaction time and are not an inherent feature of microwave heating.
Regiodivergent Baeyer–Villiger Oxidation of Fused Ketones by Recombinant Whole‐Cell Biocatalysts
Authors: Mihovilovic Marko D. , Kapitán Peter , Kapitánová Petra 
Published: December 2007

AbstractRecombinantEscherichia colicells expressing monooxygenases of different bacterial origin were evaluated in microbial Baeyer–Villiger oxidations of racemic fused ketones. During the enzymatic oxidation process, both the “normal” lactone generated by migration of the more‐substituted carbon atom and/or the “abnormal” lactone resulting from migration of the less‐substituted carbon atom can be formed. Depending on the nature of the Baeyer–Villiger monooxygenase, either a regiodivergent biooxygenation to both lactones in high optical purities was observed or essentially racemic “normal” rearrangement product was formed. The complementary behavior of enzymes was found to correlate with our previous observation of clustering of cycloketone‐oxidizing proteins into two distinct clusters based on phylogenetic relationship and biocatalyst performance.
Regulation of the Drosophila lin‐41 homologue dappled by let‐7 reveals conservation of a regulatory mechanism within the LIN‐41 subclade
Authors: O'Farrell Fergal , Esfahani Shiva Seyedoleslami , Engström Ylva , Kylsten Per 
Published: December 2007

AbstractDrosophila Dappled (DPLD) is a member of the RBCC/TRIM superfamily, a protein family involved in numerous diverse processes such as developmental timing and asymmetric cell divisions. DPLD belongs to the LIN‐41 subclade, several members of which are micro RNA (miRNA) regulated. We re‐examined the LIN‐41 subclade members and their relation to other RBCC/TRIMs and dpld paralogs, and identified a new Drosophila muscle specific RBCC/TRIM: Another B‐Box Affiliate, ABBA. In silico predictions of candidate miRNA regulators of dpld identified let‐7 as the strongest candidate. Overexpression of dpld led to abnormal eye development, indicating that strict regulation of dpld mRNA levels is crucial for normal eye development. This phenotype was sensitive to let‐7 dosage, suggesting let‐7 regulation of dpld in the eye disc. A cell‐based assay verified let‐7 miRNA down‐regulation of dpld expression by means of its 3′‐untranslated region. Thus, dpld seems also to be miRNA regulated, suggesting that miRNAs represent an ancient mechanism of LIN‐41 regulation. Developmental Dynamics 237:196–208, 2008. © 2007 Wiley‐Liss, Inc.
HB‐EGF decelerates cell proliferation synergistically with TGFα in perinatal distal lung development
Authors: Minami Seigo , Iwamoto Ryo , Mekada Eisuke 
Published: December 2007

AbstractHeparin‐binding epidermal growth factor‐like growth factor (HB‐EGF) is a member of the EGF family of growth factors that is suggested to be involved in distal lung development. In HB‐EGF null (HBdel/del) newborns, a histopathologic analysis revealed abnormally thick saccular walls occurring from embryonic day 18.5 that reduced the terminal saccular space area. HB‐EGF gene deletion resulted in a significant increase in cell proliferation, indicating that HB‐EGF suppresses distal lung cell proliferation. Furthermore, an analysis of saccular morphology and proliferation in HB‐EGF and transforming growth factor‐α (TGFα) double‐mutant newborns revealed that HB‐EGF and TGFα function synergistically in this suppression. Finally, crosses between HBdel/del mice and waved 2 mice, a hypomorphic EGF receptor (EGFR) mutant strain, suggest that HB‐EGF and EGFR cooperate in this process. Thus, HB‐EGF has a novel suppressive function that contributes to decelerating distal lung cell proliferation synergistically with TGFα through EGFR in perinatal distal lung development. Developmental Dynamics 237:247–258, 2008. © 2007 Wiley‐Liss, Inc.
Ionic Liquid Based Approach to Luminescent LaPO4:Ce,Tb Nanocrystals: Synthesis, Characterization and Application
Authors: Zharkouskaya Aksana , Feldmann Claus , Trampert Klaus , Heering Wolfgang , Lemmer Uli 
Published: December 2007

AbstractLaPO4:Ce,Tb as a nanoscale phosphor is prepared via a microwave‐accelerated synthesis in ionic liquids. The underlying approach results in non‐agglomerated nanocrystals, 9–12 nm in size, and exhibiting quantum yields of 70 % (Tb‐related emission) and 90 % (Ce/Tb‐related emission). Based on the underlying concept of synthesis, application‐oriented aspects are focused. Driven by the addition of oleylamine, first, phase transfer from the polar phase of synthesis to non‐polar alkanes can be initiated. As a second aspect, dispersions of the title compound in ethanol are applied for ink‐jet printing of transparent luminescent layers on polymer substrates. Finally, ethanolic dispersions of LaPO4:Ce,Tb are used to realize a fully transparent dielectric barrier discharge (DBD) lamp as a prototype of a “luminescent window”. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Self‐Assembled Chiral Dimeric Capsules from Difunctionalized N,C‐Linked Peptidocalix[4]arenes: Scope and Limitations
Authors: Baldini Laura , Sansone Francesco , Faimani Giovanni , Massera Chiara , Casnati Alessandro , Ungaro Rocco 
Published: December 2007

AbstractIn this paper we report the synthesis of the first examples of upper (wide) rim calix[4]arene amino acids 5 and 27, together with the conformational, self‐assembly and molecular inclusion properties of the N,C‐linked peptidocalix[4]arenes obtained from them. Whereas the dipropyl derivative 5 readily undergoes peptide synthesis allowing a small library of calix[4]arene pseudopeptides 12–21 to be obtained, the tetrapropoxy compound 27 preferentially gives upper‐rim‐bridged derivatives (e.g., 28) which are formed through an intramolecular condensation reaction. The tetrapropoxycalix[4]arene pseudopeptide 33 shows conformational and self‐assembly properties quite different to those of the dipropoxy derivatives 12–21. The observed differences are explained on the basis of the different conformational flexibilities of the two calix[4]arene scaffolds. Calixarene 5 is more rigid than 27 thanks to the presence of two OH groups at the lower (narrow) rim that are involved in strong intramolecular hydrogen bonds. Only peptidocalix[4]arenes 12–21 but not 33 form hydrogen‐bonded dimeric capsules in which the two macrocycles approach each other face‐to‐face and rotated by 180° with respect to the other in order to allow hydrogen‐bonding complementarity between the interacting peptide chains, which, in some cases (17–19), form an antiparallel β sheet enhancing the stability of the capsule. The structures of the chiral dimeric capsules were established by molecular modelling calculations and NOESY NMR experiments, which give consistent results, whereas their stability in CDCl3 (69 ≤ Kdim ≤ 950 M–1) was determined by dilution NMR experiments. Compound 12 forms both 1:1 and 2:1 [K11 = (7.8±1.2) × 102 M–1, K21 = (1.8±0.2) × 105 M–2] host:guest complexes with the methylpyridinium (MePy+) cation in CD2Cl2/CDCl3 (10:1, v/v). There is no evidence for a guest template effect in stabilizing the supramolecular capsule.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Formation of Bicyclic Pyrroles and Furans Through an Enone Allene Photocycloaddition and Fragmentation Sequence
Authors: Lutteke Ginger , AlHussainy Rana , Wrigstedt Pauli J. , Hue B. T. B. , de Gelder René , van Maarseveen Jan H. , Hiemstra Henk 
Published: December 2007

AbstractThe [2+2] photocycloaddition of allenes 15–18, 23 and 26 was studied. Irradiation of a solution of these substrates in acetonitrile at 300 nm resulted in the clean conversion of the starting materials into a mixture of photoproducts. The major product in all cases was a bicyclic pyrrole or furan fused to an eight membered ring (43–70 % yield). The formation of these products is thought to be a result of a heteroatom‐induced fragmentation of the straight adduct (7). This is supported by irradiation of the carbon analogue 32 which allowed the isolation of straight adduct 45 after catalytic hydrogenation in 27 %. The minor crossed photoproducts were isolated in 10–20 % yield. The observed major/minor ratio of 4:1 was not affected by the variation of substituents on the cyclohexene ring. Introduction of a substituent on the allene had a more significant effect on the ratio which changed to 2:1.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Lignosulfonate‐Modified Electrode for Electrocatalytic Reduction of Acidic Nitrite
Authors: Milczarek Grzegorz 
Published: December 2007

AbstractSodium lignosulfonate (LS) undergoes oxidative electropolymerization on a glassy carbon (GC) electrode from sulfuric acid solution to form a chemically modified electrode exhibiting anionic character and redox activity. Cyclic voltammetry reveals the existence of two redox systems at E°′ values of +0.29 and +0.53 V, respectively. Peak currents are proportional to the scan rate as expected for surface confined systems. The GC|poly‐LS electrode shows electrocatalytic activity toward the reduction of acidic nitrite. When operating in a constant potential amperometric mode (at 0.0 V, vs. Ag/AgCl), a linear relationship between nitrite concentration and reduction current is observed over the range of 1 to 250 μM. The detection limit reaches 0.3 μM (S/N=3). The electrode may be practically applied for nitrite determination in human saliva.
Low‐Potential Detection of Glucose with a Biosensor Based on the Immobilization of Glucose Oxidase on Polymer/Manganese Oxide Layered Nanocomposite
Authors: Xu Jing‐Juan , Feng Jiu‐Ju , Zhong Xue , Chen Hong‐Yuan 
Published: December 2007

AbstractA nanocomposite with poly(diallyldimethylammonium), PDDA, intercalated between manganese oxide layers is constructed on a graphite electrode surface through one‐step electrodeposition and used to adsorb glucose oxidase (GOD). The immobilized GOD displays a pair of stable and quasireversible redox peaks with a formal potential of −468 mV in pH 7.0 buffer solutions and exhibits excellent electrocatalysis to the reduction of oxygen. In the presence of dissolved oxygen, the reduction peak current decreased gradually with the addition of glucose, indicating that the immobilized GOD kept its bioactivity. Thus a reagentless biosensor for glucose at a low detection potential was established. The linear concentration range is from 0.02 to 2.78 mM with a detection limit of 9.8 μM. The proposed glucose biosensor was insensitive to common interferences such as ascorbic and uric acids etc.
NQO1 and NFE2L2 polymorphisms, fruit and vegetable intake and smoking and the risk of colorectal adenomas in an endoscopy‐based population
Authors: Tijhuis Mariken J. , Visker Marleen H.P.W. , Aarts Jac M.M.J.G. , Laan Wijnand , de Boer Sybrand Y. , Kok Frans J. , Kampman Ellen 
Published: December 2007

AbstractBoth environment and genetics contribute to the pathogenesis and prevention of colorectal neoplasia. NAD(P)H:quinone oxidoreductase (NQO1) is a detoxification enzyme that is polymorphic and inducible. We investigated interactions between lifestyle factors and polymorphisms in NQO1 and its key regulatory transcription factor NFE2L2 in colorectal adenoma risk. The NQO1 c.609C>T and g.‐718A>G and NFE2L2 g.‐650C>A, g.‐684G>A and g.‐686A>G polymorphisms were determined among 740 Dutch adenoma cases and 698 endoscopy‐based controls. Dietary intake was assessed by food frequency questionnaire, other lifestyle information by questionnaire. The NQO1 609CT genotype was associated with a higher adenoma risk (OR 1.27, 95% CI 1.00–1.62) compared with the 609CC genotype, whereas the 609TT genotype was not (OR 1.03, 95% CI 0.56–1.88). The higher risk with the NQO1 609CT‐genotype was seen among smokers (OR 1.96, 95% CI 1.40–2.76), but not among nonsmokers (OR 0.91, 95% CI 0.62–1.35; interaction p = 0.030). Fruit and vegetable consumption did not protect smokers from adenomas and did not interact with the NQO1 609C>T polymorphism or the NFE2L2 polymorphisms. A higher adenoma risk seen with high fruit and vegetable consumption among NQO1 ‐718GG genotypes was absent among ‐718GA genotypes (interaction p = 0.071). Gene–gene interactions were observed between the NQO1 609C>T and NFE2L2 ‐686A>G polymorphisms (interaction p = 0.056) and between the NQO1 ‐718 G>A and NFE2L2 ‐650C>A polymorphisms (interaction p = 0.013). In conclusion: the NQO1 609CT genotype is associated with increased adenoma risk among smokers, which is not diminished by high fruit and vegetable consumption. The observed gene–gene interactions may point to a role for NFE2L2 polymorphisms in NQO1‐related adenoma formation. © 2007 Wiley‐Liss, Inc.
Type IV collagen α6 chain‐derived noncollagenous domain 1 (α6(IV)NC1) inhibits angiogenesis and tumor growth
Authors: Mundel Thomas M. , Yliniemi Anna‐Maija , Maeshima Yohei , Sugimoto Hikaru , Kieran Mark , Kalluri Raghu 
Published: December 2007

AbstractType IV collagen is a major component of vascular basement membranes. The noncollagenous (NC1) domains of several α‐chains of type IV collagen reveal a capacity to inhibit angiogenesis and tumor growth. Here, we demonstrate that the NC1 domain of the α6 chain of type IV collagen (α6NC1) is an endogenous inhibitor of angiogenesis and tumor growth. Recombinant α6NC1 inhibits human endothelial cell proliferation and neovascularization of Matrigel plugs in mice. The α6NC1 suppresses the growth of subcutaneously transplanted Lewis lung carcinoma and also spontaneous pancreatic insulomas that develop in the Rip1Tag2 mice. Inhibition of tumor growth is associated with significantly diminished microvascular density. Collectively, our results demonstrate that α6NC1 is an endogenous inhibitor of angiogenesis and tumor growth. © 2007 Wiley‐Liss, Inc.
Histone deacetylase inhibitor Helminthosporium carbonum (HC)‐toxin suppresses the malignant phenotype of neuroblastoma cells
Authors: Deubzer Hedwig E. , Ehemann Volker , Westermann Frank , Heinrich Ralf , Mechtersheimer Gunhild , Kulozik Andreas E. , Schwab Manfred , Witt Olaf 
Published: December 2007

AbstractThe survival rate of children with advanced neuroblastoma (NB) is dismal despite intensive multimodal therapy. The limited efficacy and the frequent and serious side effects of currently used therapeutic regimens necessitate the development of new, less toxic treatment strategies. This study shows that the histone deacetylase inhibitor Helminthosporium carbonum (HC)‐toxin suppresses the malignant phenotype of both established NB cell lines and primary NB cells with and without amplified MYCN at dosages lower than 20 nM. HC‐toxin induces cell cycle arrest and apoptosis as well as neuronal differentiation and diminishes both colony formation and invasive growth. These cellular changes are accompanied by the transcriptional repression of cell cycle regulators of the retinoblastoma (RB) tumor suppressor network found at high levels in NBs with poor prognosis, like E2F‐1 and its targets Skp2, N‐myc, Mad2 and survivin. The levels of the hypophosphorylated active form of RB, and of cyclin‐dependent kinase inhibitors including p15INK4b, p16INK4a, p21cip1/waf‐1 and p27kip1 are increased. In conclusion, nanomolar doses of the HDACI HC‐toxin cause a shift to a differentiated and benign phenotype of NB cells that is associated with an activation of the RB tumor suppressor network. © 2007 Wiley‐Liss, Inc.
Explicit ion, implicit water solvation for molecular dynamics of nucleic acids and highly charged molecules
Authors: Prabhu Ninad V. , Panda Manoranjan , Yang Qingyi , Sharp Kim A. 
Published: December 2007

AbstractAn explicit ion, implicit water solvent model for molecular dynamics was developed and tested with DNA and RNA simulations. The implicit water model uses the finite difference Poisson (FDP) model with the smooth permittivity method implemented in the OpenEye ZAP libraries. Explicit counter‐ions, co‐ions, and nucleic acid were treated with a Langevin dynamics molecular dynamics algorithm. Ion electrostatics is treated within the FDP model when close to the solute, and by the Coulombic model when far from the solute. The two zone model reduces computation time, but retains an accurate treatment of the ion atmosphere electrostatics near the solute. Ion compositions can be set to reproduce specific ionic strengths. The entire ion/water treatment is interfaced with the molecular dynamics package CHARMM. Using the CHARMM‐ZAPI software combination, the implicit solvent model was tested on A and B form duplex DNA, and tetraloop RNA, producing stable simulations with structures remaining close to experiment. The model also reproduced the A to B duplex DNA transition. The effect of ionic strength, and the structure of the counterion atmosphere around B form duplex DNA were also examined. © 2007 Wiley Periodicals, Inc. J Comput Chem, 2008