bluuebunny/crossref_metadata_2025_split huggingface dataset:
Elucidating the Directing Effect of Lewis Acids on the Reaction Pathway in Formal [3+3] Cyclocondensation Reactions: A Comprehensive In Situ Spectroscopic Study
Authors: Knöpke Leif R. , Reimann Sebastian , Spannenberg Anke , Langer Peter , Brückner Angelika , Bentrup Ursula 
Published: July 2011

AbstractDifferent spectroscopic methods were applied in situ as well as ex situ to elucidate the mode of action of the Lewis acids TiCl4 and trimethylsilyl trifluoromethanesulfonate (TMSOTf) in the formal [3+3] cyclization reaction of a 1,3‐bis(silyloxy)‐1,3‐butadiene with fluorinated ketenacetales. Different products were formed depending on the type of Lewis acid employed, which can be explained by their completely different interaction with the ketenacetale. Results of attenuated total reflection infrared (ATR‐IR) and UV/vis spectroscopic studies revealed that TMSOTf interacts with only one site of the ketenacetale, forming an ionic species. In contrast, TiCl4 forms a bischelate complex, which was confirmed by using X‐ray crystal structure analysis. Both reaction pathways were studied by simultaneously applying in situ ATR‐IR/UV/vis spectroscopy in a specifically developed reaction cell. During cooling and subsequent heating of the reaction mixture, formation and structural changes of different intermediates were observed, in particular in the case of the TMSOTf catalyzed reaction. Although the TiCl4 mediated reaction proceeds in only one step, the TMSOTf route comprises two reaction steps. In situ spectroscopic results revealed that the applied workup procedure influences product formation and distribution as well.
Divergent Heparin Oligosaccharide Synthesis with Preinstalled Sulfate Esters
Authors: Tiruchinapally Gopinath , Yin Zhaojun , El‐Dakdouki Mohammad , Wang Zhen , Huang Xuefei 
Published: July 2011

AbstractTraditional chemical synthesis of heparin oligosaccharides first involves assembly of the full length oligosaccharide backbone followed by sulfation. Herein, we report an alternative strategy in which the O‐sulfate was introduced onto glycosyl building blocks as a trichloroethyl ester prior to assembly of the full length oligosaccharide. This allowed divergent preparation of both sulfated and non‐sulfated building blocks from common advanced intermediates. The O‐sulfate esters were found to be stable during glycosylation as well as typical synthetic manipulations encountered during heparin oligosaccharide synthesis. Furthermore, the presence of sulfate esters in both glycosyl donors and acceptors did not adversely affect the glycosylation yields, which enabled us to assemble multiple heparin oligosaccharides with preinstalled 6‐O‐sulfates.
Solid‐state circular dichroism and hydrogen bonding: Absolute configuration of massarigenin A from Microsphaeropsis sp
Authors: Hussain Hidayat , Ahmed Ishtiaq , Schulz Barbara , Draeger Siegfried , Flörke Ulrich , Pescitelli Gennaro , Krohn Karsten 
Published: July 2011

AbstractMassarigenin A (1) and papyracillic acids A (2) and B (3) were isolated from the endophytic fungus Microsphaeropsis sp. Their structures were elucidated by multidimensional nuclear magnetic resonance spectroscopy; the structure of massarigenin A (1) was also confirmed by X‐ray crystallography. The absolute configuration of massarigenin A (1) was established by means of circular dichroism (CD) spectroscopy and time‐dependent density functional theory (TDDFT) calculations. The impact of intermolecular hydrogen bonds detected in the crystal packing of 1 on CD spectra measured in the solid state was also investigated. Chirality, 2011. © 2011 Wiley‐Liss, Inc.
Chiral superstructures of insulin amyloid fibrils
Authors: Babenko Viktoria , Harada Takunori , Yagi Hisashi , Goto Yuji , Kuroda Reiko , Dzwolak Wojciech 
Published: July 2011

AbstractHydrodynamic forces are capable of inducing structural order in dispersed solid phases, and of causing symmetry‐breaking when chiral crystals precipitate from an achiral liquid phase. Until it was observed upon vortex‐assisted fibrillation of insulin, such behavior had been thought to be confined to few unbiological systems. In this paper we are discussing chiroptical properties of two chiral variants of insulin amyloid, termed +ICD and −ICD, which form during the process of chiral bifurcation in vortexed solutions of aggregating insulin. As conventional measurements of circular dichroism of solid, anisotropic substances are particularly vulnerable to overlapping influences of linear birefringence and linear dichroism, we have employed complementary tools including dedicated universal chiroptical spectrophotometer to rule out such artifacts. We propose that the strong chiroptical properties of +ICD and −ICD insulin fibrils are an aspect of genuine superstructural chirality of amyloid fibrils and of powerful excitonic couplings taking place within them. A comparison of thioflavin T complexes with fibrils formed by insulin and polyglutamic acid suggests that the extrinsic Cotton effect stemming from the level of single twisted dye molecules is weaker, although diagnostically useful, and cannot account for the overall magnitude of ICD of the dye bound to ±ICD insulin amyloid. Chirality, 2011. © 2011 Wiley‐Liss, Inc.
Cu(OTf)2 Catalyzed Synthesis of Bis(5‐methyl‐2‐furyl)methanes by Condensation of 2‐Methylfuran with Carbonyl Compounds under Solvent Free Conditions
Authors: Muthyala Manoj Kumar , Rao V. Kameswara , Kumar Anil 
Published: July 2011

AbstractA facile and efficient one‐pot three‐component synthesis of bis(5‐methyl‐2‐furyl)methanes has been achieved via the reaction of 2‐methylfuran with a series of aliphatic and aromatic aldehydes and aliphatic ketones in presence of copper(II) triflate under solvent free conditions. The bis(5‐methyl‐2‐furyl)methanes were obtained in 34% –72% yields and the catalyst was recycled up to four successive cycles without much loss in catalytic activity.
The effect of misspecification of random effects distributions in clustered data settings with outcome‐dependent sampling
Authors: Neuhaus John M. , McCulloch Charles E. 
Published: July 2011

AbstractGenetic epidemiologists often gather outcome‐dependent samples of family data to measure within‐family associations of genetic factors with disease outcomes. Generalized linear mixed models provide effective methods to estimate within‐family associations but typically require parametric specification of the random effects distribution. Although misspecification of the random effects distribution often leads to little bias in estimated regression coefficients in standard, prospective clustered data settings, some recent studies suggest that such misspecification will impact parameter estimates from outcome‐dependent cluster sampling designs. Using analytic results, simulation studies and fits to example data, this study examines the effect of misspecification of random effects distributions on parameter estimates in clustered data settings with outcome‐dependent sampling. We show that the effects are consistent with results from prospective cluster sampling settings. In particular, ascertainment corrected mixed model methods that assume normally distributed random intercepts and conditional likelihood approaches provide accurate estimates of within‐family covariate effects even under a misspecified random effects distribution. The Canadian Journal of Statistics 39: 488–497; 2011 © 2011 Statistical Society of Canada
Spin–Orbit Coupling in Phosphorescent Iridium(III) Complexes
Authors: Smith Arthur R. G. , Burn Paul L. , Powell Ben J. 
Published: July 2011

AbstractWe study the excited states of two iridium(III) complexes with potential applications in organic light‐emitting diodes: fac‐tris(2‐phenylpyridyl)iridium(III) [Ir(ppy)3] and fac‐tris(1‐methyl‐5‐phenyl‐3‐n‐propyl‐[1,2,4]triazolyl)iridium(III) [Ir(ptz)3]. Herein we report calculations of the excited states of these complexes from time‐dependent density functional theory (TDDFT) with the zeroth‐order regular approximation (ZORA). We show that results from the one‐component formulation of ZORA, with spin–orbit coupling included perturbatively, accurately reproduce both the results of the two‐component calculations and previously published experimental absorption spectra of the complexes. We are able to trace the effects of both scalar relativistic correction and spin–orbit coupling on the low‐energy excitations and radiative lifetimes of these complexes. In particular, we show that there is an indirect relativistic stabilisation of the metal‐to‐ligand charge transfer (MLCT) states. This is important because it means that indirect relativistic effects increase the degree to which SOC can hybridise singlet and triplet states and hence plays an important role in determining the optical properties of these complexes. We find that these two compounds are remarkably similar in these respects, despite Ir(ppy)3 and Ir(ptz)3 emitting green and blue light respectively. However, we predict that these two complexes will show marked differences in their magnetic circular dichroism (MCD) spectra.
Joule heating effects on electroosmotic flow in insulator‐based dielectrophoresis
Authors: Sridharan Sriram , Zhu Junjie , Hu Guoqing , Xuan Xiangchun 
Published: July 2011

AbstractInsulator‐based dielectrophoresis (iDEP) is an emerging technology that has been successfully used to manipulate a variety of particles in microfluidic devices. However, due to the locally amplified electric field around the in‐channel insulator, Joule heating often becomes an unavoidable issue that may disturb the electroosmotic flow and affect the particle motion. This work presents the first experimental study of Joule heating effects on electroosmotic flow in a typical iDEP device, e.g. a constriction microchannel, under DC‐biased AC voltages. A numerical model is also developed to simulate the observed flow pattern by solving the coupled electric, energy, and fluid equations in a simplified two‐dimensional geometry. It is observed that depending on the magnitude of the DC voltage, a pair of counter‐rotating fluid circulations can occur at either the downstream end alone or each end of the channel constriction. Moreover, the pair at the downstream end appears larger in size than that at the upstream end due to DC electroosmotic flow. These fluid circulations, which are reasonably simulated by the numerical model, form as a result of the action of the electric field on Joule heating‐induced fluid inhomogeneities in the constriction region.
Immunoglobulin G and bovine serum albumin streaming dielectrophoresis in a microfluidic device
Authors: Nakano Asuka , Chao Tzu‐Chiao , Camacho‐Alanis Fernanda , Ros Alexandra 
Published: July 2011

AbstractDielectrophoresis (DEP) has demonstrated to be a versatile tool to manipulate micro‐ and nanoparticles with applications for positioning, separation and fractionation. Recent developments of DEP have also shown that DEP can be used for the manipulation of biomolecules, such as DNA. Here, we focus on the manipulation of proteins using insulator‐based dielectrophoresis (iDEP). We designed suitable post arrays in a microfluidic channel and use numerical simulations to calculate the electric field distribution as well as concentration of proteins according to a convection–diffusion model for both negative and positive DEP. Experimentally, we find DEP trapping of mainly protein aggregates in phosphate buffer. However, when adding a charged zwitterionic detergent, we observed DEP streamlining of immunoglobulin G (IgG) and bovine serum albumin (BSA). Our experimental observations are in excellent agreement with numerical simulations and indicate positive DEP behavior of IgG and BSA under the employed experimental conditions. Our results demonstrate DEP streaming of proteins in an iDEP device for the first time and indicate the potential of protein DEP for separation and fractionation.
Capillary electrophoretic mobility shift assay for binding of DNA with NFAT3, a transcription factor from H9c2 cardiac myoblast cells
Authors: Park Soo Hyun , Ban Eunmi , Song Eun Joo , Lee Hyunjung , Chung Doo Soo , Yoo Young Sook 
Published: July 2011

AbstractNuclear factor of activated T‐cells (NFAT) is a transcription factor involved in the development of cardiac and skeletal muscle and the nervous system. NFAT is activated by calcium signal pathway and translocated into the nucleus. The quantification of binding between NFAT and NFAT‐specific DNA gives important information about cardiac hypertrophy. We investigated the binding of NFAT3 in nuclear extracts from H9c2 cells to its specific DNA by capillary electrophoretic mobility shift assay. The binding reaction time required for stable formation of the DNA–NFAT3 complex was 3 h and the separation of the complex and free DNA was achieved within 10 min by CE. The formation of NFAT3–DNA complex was confirmed by the competitive reaction. Comparison of the ratios of complex/free DNA peak area for 1 μM endothelin‐1 (ET‐1)‐treated cells and control cells showed the NFAT3 translocation into the nucleus promoted by ET‐1. The binding constant between NFAT3 and DNA was estimated to be 7.7×109 M−1 at 4°C.
Blue native/SDS‐PAGE combined with iTRAQ analysis reveals advanced glycation end‐product‐induced changes of synaptosome proteins in C57 BL/6 mice
Authors: Xie Chunliang , Liu Nvying , Long Jia , Tang Cheng , Li Jianglin , Huo Linju , Wang Xianchun , Chen Ping , Liang Songping 
Published: July 2011

AbstractEvidence shows that administration of high‐level D‐galactose induces the production of advanced glycation end‐products (AGEs) that have been implicated in the development of diabetic complications such as neuropathy. The deterioration of learning and memory during neuropathy might be associated with the altered expression of proteins in synapse. To evaluate AGE‐induced protein network alterations in synapse, blue native/SDS‐PAGE and iTRAQ proteomic methods were used to screen for differentially expressed synaptic proteins of cerebral cortex in D‐galactose‐induced C57 BL/6 mice. In total, the expression level of 84 proteins is changed during AGE accumulation. The significantly differentially expressed proteins mainly participate in neurotransmission, energy metabolism and signal transduction pathway, suggesting that energy metabolism is damaged and neurotransmission is attenuated in synapse. The results of in vivo activities of malondialdehyde and superoxide dismutase suggested that AGE accumulation in the brain leads to the generation of reactive oxygen species. Therefore, elucidating the differentially expressed proteins underlying the AGE accumulation will open a new window to the mechanism of learning and memory impairments in neuropathy.
Repetitive exposure to zinc oxide nanoparticles induces dna damage in human nasal mucosa mini organ cultures
Authors: Hackenberg Stephan , Zimmermann Franz‐Zeno , Scherzed Agmal , Friehs Gudrun , Froelich Katrin , Ginzkey Christian , Koehler Christian , Burghartz Marc , Hagen Rudolf , Kleinsasser Norbert 
Published: July 2011

AbstractData on the toxicological properties of zinc oxide nanoparticles (ZnO‐NPs) is incomplete. ZnO‐NPs may enter humans via inhalation or ingestion. The aim of the current study was to evaluate ZnO‐NP‐induced genotoxicity in three‐dimensional (3D) mini organ cultures (MOCs) of human nasal mucosa following repeated exposure to ZnO‐NP and regeneration. Nasal MOCs of 10 patients and ZnO‐NPs were cultivated for one week and then characterized by electron microscopy. Nasal MOCs were partially covered by ciliated epithelium after one week of cultivation. ZnO‐NPs were distributed to the cytoplasm and the nucleus. MOCs were exposed once, twice, or three times to 0.1 or 5 μg/ml of ZnO‐NPs for 1 hr per exposure and were then evaluated for cytotoxicity and genotoxicity. MOCs were cultivated for 24 hr after the triple ZnO‐NP exposure to allow for regeneration. ZnO‐NP exposure did not result in significant cytotoxicity or apoptosis, as determined by trypan blue exclusion and caspase‐3 activity, respectively. A significant increase in DNA damage was detected following repetitive exposure compared to single exposure to ZnO‐NPs at 5 μg/ml, but not 0.1 μg/ml ZnO‐NPs. At both concentrations of ZnO‐NP, DNA fragmentation increased after 24 hr of regeneration. In contrast, DNA damage which was induced by the positive control, methyl methanesulfonate, was significantly reduced after 24‐hr regeneration. Thus, our results suggest that repetitive exposure to low concentrations of ZnO‐NPs results in persistent or ongoing DNA damage. Environ. Mol. Mutagen. 2011. © 2011 Wiley‐Liss, Inc.
Equilibrium modeling: A pathway to understanding observed perfluorocarboxylic and perfluorosulfonic acid behavior
Authors: Webster Eva M , Ellis David A 
Published: July 2011

Abstract
Equilibrium distribution models of hydrophobic neutral partitioning of the perfluorinated carboxylic and sulfonic acids were shown, without the need for any physical chemical properties, to successfully predict the sediment–water distribution (DSW) directly from independently measured equilibrium tissue distributions known as the bioconcentration factor (BCF). The constant of proportionality required by the models successfully predicted the correlation between the biotic and abiotic distributions of both sets of chemicals, thus demonstrating the applicability of the assumptions inherent in the models, that is, hydrophobically driven partitioning of the neutral species, and thus the applicability of the models themselves. Colloquially speaking, the models are thus validated as applicable to these chemicals. Subsequent application of the standard equilibrium models showed order of magnitude agreement for 83% of measured BCF values and 88% of measured DSW for the perfluorinated carboxylic acids, confirming the physical chemical properties used. The applicability of the models to perfluorooctane sulfonic acid (PFOSA) was shown by the successful prediction of DSW from BCF. Therefore, the measured DSW and BCF could be used to calculate the octanol–water distribution, DOW, and hence the corresponding pKa:KOW solution set, thus providing independent experimentally based estimates of these properties. For both the perfluorinated carboxylic and sulfonic acids, the existing standard equilibrium models are shown to be applicable. Environ. Toxicol. Chem. 2011;30:2229–2236. © 2011 SETAC
Leukemia stem cells
Authors: Buss Eike C. , Ho Anthony D. 
Published: July 2011

AbstractLeukemia stem cells (LSCs) might originate from malignant transformation of normal hematopoietic stem cells (HSCs), or alternatively, of progenitors in which the acquired mutations have re‐installed a dysregulated self‐renewal program. LSCs are on top of a hierarchy and generate leukemia cells with more differentiated characteristics. While most leukemia cells are initially sensitive to chemo‐ and radiotherapy, LSCs are resistant and are considered to be the basis for disease relapse after initial response. Albeit important knowledge on LSC biology has been gained from xenogeneic transplantation models introducing human leukemia cells into immune deficient mouse models, the prospective identification and isolation of human LSC candidates has remained elusive and their prognostic and therapeutic significance controversial. This review focuses on the identification, enrichment and characterization of human LSC derived from patients with acute myeloid leukemia (AML). Experimental data demonstrating the clinical significance of estimating LSC burden and strategies to eliminate LSC will be summarized. For long‐term cure of AML, it is of importance to define LSC candidates and to understand their tumor biology compared to normal HSCs. Such comparative studies might provide novel markers for the identification of LSC and for the development of treatment strategies that might be able to eradicate them.
Synthesis of Conjugated Polymers in Chiral Nematic Liquid Crystal Fields
Authors: Matsushita Satoshi , Akagi Kazuo 
Published: July 2011

AbstractThis review presents the progress made on current research in the synthesis of π‐conjugated polymers in chiral nematic liquid crystal (N*‐LC) fields through either chemical or electrochemical polymerization. The following are noteworthy advances in the field of π‐conjugated polymers. (i) Helical aliphatic conjugated polymers of helical polyacetylene (H‐PA) were synthesized using asymmetric interfacial polymerization in N*‐LC fields. (ii) Helical aromatic conjugated polymers with electroactive properties, such as poly(3,4‐ethylenedioxythiophene) (PEDOT) and polybithiophene (PBT), were synthesized using asymmetric electrochemical polymerization in N*‐LC fields. (iii) Chiral aromatic conjugated copolymers, such as the poly(bithienylene‐phenylene) (PBTP) derivative, were synthesized using the asymmetric Stille polycondensation reaction in N*‐LC fields. Throughout the document, it has been emphasized that by using N*‐LC systems as asymmetric polymerization fields, helix formation is possible for aliphatic and aromatic π‐conjugated polymers without chiroptical substituents on the side chains.
Patients with sclerosteosis and disease carriers: Human models of the effect of sclerostin on bone turnover
Authors: van Lierop Antoon H , Hamdy Neveen AT , Hamersma Herman , van Bezooijen Rutger L , Power Jon , Loveridge Nigel , Papapoulos Socrates E 
Published: July 2011

Abstract
Sclerosteosis is a rare bone sclerosing dysplasia, caused by loss-of-function mutations in the SOST gene, encoding sclerostin, a negative regulator of bone formation. The purpose of this study was to determine how the lack of sclerostin affects bone turnover in patients with sclerosteosis and to assess whether sclerostin synthesis is decreased in carriers of the SOST mutation and, if so, to what extent this would affect their phenotype and bone formation. We measured sclerostin, procollagen type 1 amino-terminal propeptide (P1NP), and cross-linked C-telopeptide (CTX) in serum of 19 patients with sclerosteosis, 26 heterozygous carriers of the C69T SOST mutation, and 77 healthy controls. Chips of compact bone discarded during routine surgery were also examined from 6 patients and 4 controls. Sclerostin was undetectable in serum of patients but was measurable in all carriers (mean 15.5 pg/mL; 95% confidence interval [CI] 13.7 to 17.2 pg/mL), in whom it was significantly lower than in healthy controls (mean 40.0 pg/mL; 95% CI 36.9 to 42.7 pg/mL; p &lt; 0.001). P1NP levels were highest in patients (mean 153.7 ng/mL; 95% CI 100.5 to 206.9 ng/mL; p = 0.01 versus carriers, p = 0.002 versus controls), but carriers also had significantly higher P1NP levels (mean 58.3 ng/mL; 95% CI 47.0 to 69.6 ng/mL) than controls (mean 37.8 ng/mL; 95% CI 34.9 to 42.0 ng/mL; p = 0.006). In patients and carriers, P1NP levels declined with age, reaching a plateau after the age of 20 years. Serum sclerostin and P1NP were negatively correlated in carriers and age- and gender-matched controls (r = 0.40, p = 0.008). Mean CTX levels were well within the normal range and did not differ between patients and disease carriers after adjusting for age (p = 0.22). Our results provide in vivo evidence of increased bone formation caused by the absence or decreased synthesis of sclerostin in humans. They also suggest that inhibition of sclerostin can be titrated because the decreased sclerostin levels in disease carriers did not lead to any of the symptoms or complications of the disease but had a positive effect on bone mass. Further studies are needed to clarify the role of sclerostin on bone resorption. © 2011 American Society for Bone and Mineral Research