bluuebunny/crossref_metadata_2025_split huggingface dataset:
Carbon Dioxide Fixation by Lithium Amides: DFT Studies on the Reaction Mechanism of the Formation of Lithium Carbamates
Authors: Lill Sten O. Nilsson , Köhn Uwe , Anders Ernst 
Published: June 2004

AbstractA realistic picture of the complete insertion reaction for a representative example of the formation of carbamates from lithium amides is given by combining experimental information with detailed DFT investigations. The chiral lithium (S)‐2‐(pyrrolidin‐1‐ylmethyl)pyrrolidide (2) reacts with CO2 to form its corresponding carbamate. In this reaction the second pyrrolidine ring functions as an intramolecular ligand, and therefore, “symmetrical” as well as “unsymmetrical” dimers of 2 have to be taken into account. On the energetically preferred reaction pathway this amide exists predominantly as a (solvated) dimer 4. Attack by CO2 occurs in an “end‐on” manner to give several heterodimers 5 which are composed of a lithium amide and a lithium carbamate. This exergonic step is rate determining, and the activation barrier was estimated to be about 10 kcal mol−1. A second lithium‐mediated CO2 insertion into a nitrogen−lithium bond yields the encounter complex 5d−(CO2), which then goes on to form several almost isoenergetic homodimeric carbamates 6. This strongly exergonic insertion reaction has a barrier of 9.7 kcal mol−1. We also report on novel lithium‐mediated CO2 insertion reactions into oxygen−lithium bonds in lithium carbamates. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Preparation of α,β‐Unsaturated γ‐Keto Aldehydes and New Tetronic Acid and Pyridazine Derivatives by Oxidative Transformations of Alkoxyallene‐Based Dihydrofurans
Authors: Flögel Oliver , Reißig Hans‐Ulrich 
Published: June 2004

AbstractOxidation of 3‐alkoxy‐substituted dihydrofuran derivatives 6 and 11 with DDQ unexpectedly provided α,β‐unsaturated γ‐keto aldehydes 10 and 12. A mechanism for this new oxidative ring‐cleavage is presented. Since α,β‐unsaturated γ‐keto aldehydes are versatile intermediates, other 3‐methoxy‐substituted dihydrofuran derivatives 24, 26, and 28 were prepared from lithiated methoxyallene and the corresponding aldehydes. Oxidation of dihydrofuran derivatives with DDQ and subsequent treatment with sodium chlorite furnished hydroxy‐substituted tetronic acid derivatives, such as 30 and 31. Condensation of 30 with hydrazine provided the unsaturated pyridazinone derivative 32. A second route to pyridazine derivatives involves DDQ‐mediated oxidation of dihydrofurans and reaction of the products with hydrazine hydrate. This leads to 4‐methoxypyridazines 33, 34, 35, and 36 in good overall yields. The oxidative transformations of dihydrofuran derivatives reported here demonstrate new examples of reactivity umpolung; the lithiated alkoxyallenes are equivalents of the unusual synthons B and C, which represent anions of malondialdehyde or malonaldehydic acid. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Cover Picture: The High‐Intrinsic Diels−Alder Reactivity of (−)‐Galiellalactone; Generating Four Quaternary Carbon Centers under Mild Conditions (Eur. J. Org. Chem. 13/2004)
Authors: von Nussbaum Franz , Hanke Roman , Fahrig Thomas , Benet‐Buchholz Jordi 
Published: June 2004

AbstractThe cover picture shows a further chapter in the excitingDiels−Alder story around the natural product (−)‐galiellalactone. This story started with Steglich′s proposal on the Diels−Alder biosynthesis of galiellalactone, that was then experimentally confirmed by T. Anke, H. Anke, and Sterner. The producer of galiellalactone, the ascomycete Galiella rufa, is shown in the background (photo by Pamela Kaminski). Now a surprising intrinsic Diels−Alder reactivity of galiellalactone has been found. Remarkable Diels−Alder transformations are triggered by acylation of the natural product. In the presented case four quaternary carbon centers are generated under mild conditions, yielding a dimer of unprecedented architecture. Details are discussed in the article by F. von Nussbaum et al. on page 2783 ff.
Numerical methods for large‐eddy simulation in general co‐ordinates
Authors: Tang Gefeng , Yang Zhiyin , McGuirk James J. 
Published: June 2004

AbstractLarge scale unsteady motions in many practical engineering flows play a very important role and it is very unlikely that these unsteady flow features can be captured within the framework of Reynolds averaged Navier–Stokes approach. Large‐eddy simulation (LES) has become, arguably, the only practical numerical tool for predicting those flows more accurately since it is still not realistic to apply DNS to practical engineering flows with the current and near future available computing power.Numerical methods for the LES of turbulent flows in complex geometry have been developed and applied to predict practical engineering flows successfully. The method is based on body‐fitted curvilinear co‐ordinates with the contravariant velocity components of the general Navier–Stokes equations discretized on a staggered orthogonal mesh. For incompressible flow simulations the main source of computational expense is due to the solution of a Poisson equation for pressure. This is especially true for flows in complex geometry. A multigrid 3D pressure solver is developed to speed up the solution. In addition, the Poisson equation for pressure takes a simpler form with no cross‐derivatives when orthogonal mesh is used and hence resulting in increased convergence rate and producing more accurate solutions. Copyright © 2004 John Wiley & Sons, Ltd.
Robust handling of non‐linear constraints for GA optimization of aerodynamic shapes
Authors: Peigin S. , Epstein B. 
Published: June 2004

AbstractA new approach to the robust handling of non‐linear constraints for GAs (genetic algorithms) optimization is proposed. A specific feature of the approach consists of the change in the conventional search strategy by employing search paths which pass through both feasible and infeasible points (contrary to the traditional approach where only feasible points may be included in a path). The method (driven by full Navier–Stokes computations) was applied to the problem of multiobjective optimization of aerodynamic shapes subject to various geometrical and aerodynamic constraints. The results demonstrated that the method retains high robustness of conventional GAs while keeping CFD computational volume to an acceptable level, which allowed the algorithm to be used in a demanding engineering environment. Copyright © 2004 John Wiley & Sons, Ltd.
Novel method for studying myelination in vivo reveals that EDTA is a potent inhibitor of myelin protein and mRNA expression during development of the rat sciatic nerve
Authors: Meintanis Stathis , Thomaidou Dimitra , Jessen Kristjan R. , Mirsky Rhona , Matsas Rebecca 
Published: June 2004

AbstractTo probe the effects of possible inhibitors or enhancers of in vivo myelination, we have modified a technique widely used in studies of the developing neuromuscular system that involves incorporation of test compounds into a silicon rubber solution, which solidifies on contact with air. U‐shaped rubber implants are inserted around the sciatic nerve of 1‐day‐old rats and left in place for 24–48 h. Sections from the region of the nerve lying within the implant, with or without the test compound, are then immunolabeled, examined with in situ hybridization or electron microscopy. Application of EDTA (440 μg/implant) in this way strongly suppressed the levels of the myelin‐associated molecules protein P0, myelin basic protein (MBP), and galactocerebroside (Galc). mRNA levels for P0 and the myelin‐related transcription factor Krox‐20 were also reduced, further supporting association of the EDTA‐induced effect with the myelinating Schwann cells. In contrast, no obvious differences were observed in either neurofilament (NF) protein or glial fibrillary acidic protein (GFAP) expression, suggesting absence of influence on axons or nonmyelinating Schwann cells. Despite the severely altered molecular composition of myelin in the presence of EDTA, examination in the electron microscope did not reveal any apparent ultrastructural changes in the myelin sheaths or nerve development. This work introduces a novel method for studying nerve development and shows that EDTA, which chelates divalent cations such as Ca2+ and Mg2+, strongly and selectively reduces levels of molecules, which, on postnatal days 1–4, are expressed in myelinating cells at much higher levels than in cells not engaged in myelination. © 2004 Wiley‐Liss, Inc.
K+channel blockade impairs remyelination in the cuprizone model
Authors: Bacia Andrzej , Wollmann Robert , Soliven Betty 
Published: June 2004

AbstractThe adult CNS has the capacity to remyelinate following metabolic, toxic and autoimmune demyelinating insults. In cuprizone‐induced demyelination, spontaneous remyelination occurs after the cessation of cuprizone diet. We used the cuprizone model to investigate the role of glial K+channels in oligodendroglial (OLG) regeneration and remyelination in vivo. We found that treatment with 4‐aminopyridine (4‐AP), a broad‐spectrum K+channel antagonist, results in: (1) decreased number of oligodendroglial progenitors (OP) and OLGs; (2) diminished astrogliosis; and (3) decreased remyelination in the corpus callosum based on the immunoreactivity to myelin basic protein (MBP), Rip monoclonal antibody, and by electron microscopy. Our findings support the concept that glial K+channels play an important role during OLG regeneration and remyelination, a crucial factor to be considered during the development of therapeutic strategies to facilitate recovery in demyelinating diseases and spinal cord injury. © 2004 Wiley‐Liss, Inc.
Effects of diabetes mellitus on astrocyte GFAP and glutamate transporters in the CNS
Authors: Coleman Elaine , Judd Robert , Hoe Lori , Dennis John , Posner Philip 
Published: June 2004

AbstractDiabetes mellitus increases the risk of central nervous system (CNS) disorders such as stroke, seizures, dementia, and cognitive impairment. The cellular mechanisms responsible for the increased risk of these disorders are incompletely understood. Astrocytes are proving critical for normal CNS function, and alterations in their activity could contribute to diabetes‐related disturbances in the brain. We examined the effects of streptozotocin (STZ)‐induced diabetes in rats on the level of the astrocyte intermediate filament protein, glial fibrillary acidic protein (GFAP), number of astrocytes, and levels of the astrocyte glutamate transporters, glutamate transporter‐1 (GLT‐1) and glutamate/aspartate transporter (GLAST), in the cerebral cortex, hippocampus, and cerebellum by Western blotting (WB) and immunohistochemistry (IH). Studies were carried out at 4 and 8 weeks of diabetes duration. Diabetes resulted in a significant decrease in GFAP protein levels (WB) in the hippocampus and cerebellum at 4 weeks and in the cerebral cortex, hippocampus and cerebellum by 8 weeks. Attenuated GFAP immunoreactivity (IH) was evident in the hippocampus, cerebellum and white matter regions such as the corpus callosum and external capsule at both 4 and 8 weeks of diabetes. Astrocyte cell counts of adjacent sections immunoreactive for S‐100B were not different between control and diabetic animals. No significant differences were noted in astrocyte glutamate transporter levels in the cerebral cortex, hippocampus, or cerebellum at either time period (WB, IH). With the expanding list of astrocyte functions in the CNS, the role of astrocytes in diabetes‐induced CNS disorders clearly warrants further investigation. © 2004 Wiley‐Liss, Inc.
Gap junction channels coordinate the propagation of intercellular Ca2+ signals generated by P2Y receptor activation
Authors: Suadicani S.O. , Flores C.E. , Urban‐Maldonado M. , Beelitz M. , Scemes E. 
Published: June 2004

AbstractAstrocytes express gap junction proteins and multiple types of P2Y receptors (P2YRs) that contribute to the propagation of intercellular Ca2+ waves (ICW). To gain access to the role played by gap junctional communication in ICW propagation generated by P2YR activation, we selectively expressed P2Y1,2,4R subtypes and Cx43 in the human 1321N1 astrocytoma cell line, which lacks endogenous P2 receptors. Fluorescence recovery after photobleaching revealed that 1321N1 cells are poorly dye‐coupled and do not propagate ICW. Forced expression of Cx43 in 1321N1 cells (which did not show functional hemichannels) increased dye coupling and allowed short‐range ICW transmission that was mainly mediated by intercellular diffusion of Ca2+ generated in the stimulated cells. Astrocytoma clones expressing each of the P2YR subtypes were also able to propagate ICWs that were likely dependent on IP3 generation. These waves exhibited properties particular to each P2YR subtype. Co‐expression of eGFP‐hCx43 and P2Y1R modified the properties of P2Y1R‐generated ICW to those characteristics of P2Y2R. Increased coupling in P2Y4R clones induced by expression of eGFP‐hCx43 abolished the ICWs observed in uncoupled P2Y4R clones. No changes in the behavior of ICWs generated in P2Y2R clones were observed after forced expression of Cx43. These data indicate that in 1321N1 cells gap junctional communication provides intercellular integration of Ca2+ signals generated by P2YR activation, thus coordinating the propagation of intercellular calcium waves. © 2004 Wiley‐Liss, Inc.
Estimation of multiscale neurophysiologic parameters by electroencephalographic means
Authors: Robinson P.A. , Rennie C.J. , Rowe D.L. , O'Connor S.C. 
Published: June 2004

AbstractIt is shown that new model‐based electroencephalographic (EEG) methods can quantify neurophysiologic parameters that underlie EEG generation in ways that are complementary to and consistent with standard physiologic techniques. This is done by isolating parameter ranges that give good matches between model predictions and a variety of experimental EEG‐related phenomena simultaneously. Resulting constraints range from the submicrometer synaptic level to length scales of tens of centimeters, and from timescales of around 1 ms to 1 s or more, and are found to be consistent with independent physiologic and anatomic measures. In the process, a new method of obtaining model parameters from the data is developed, including a Monte Carlo implementation for use when not all input data are available. Overall, the approaches used are complementary to other methods, constraining allowable parameter ranges in different ways and leading to much tighter constraints overall. EEG methods often provide the most restrictive individual constraints. This approach opens a new, noninvasive window on quantitative brain analysis, with the ability to monitor temporal changes, and the potential to map spatial variations. Unlike traditional phenomenologic quantitative EEG measures, the methods proposed here are based explicitly on physiology and anatomy. Hum. Brain Mapping 23:53–72, 2004. © 2004 Wiley‐Liss, Inc.
Monocular visual activation patterns in albinism as revealed by functional magnetic resonance imaging
Authors: Schmitz Bernd , Käsmann‐Kellner Barbara , Schäfer Torsten , Krick Christoph M. , Grön Georg , Backens Martin , Reith Wolfgang 
Published: June 2004

AbstractHuman albinism is characterized by a disturbance of the chiasmatic projection system leading to predominant representation of just one eye in the contralateral hemisphere. Patients show congenital nystagmus without perceiving oscillopsia. The purpose of the present study was to demonstrate the consequences of atypical chiasmatic crossing with monocular visual stimulation using functional magnetic resonance imaging (fMRI). Sixteen patients with albinism and fifteen normally pigmented controls were stimulated with a monocular visual activation paradigm using flickering checkerboards. In patients, we observed contralaterally dominated activation of visual cortices correlating to clinical albinism parameters. This confirms albinism as a continuous range of hypopigmentation disorders. Additionally, albinos showed activation of the superior colliculus and of visual motion areas although the stimulus was stationary. Activation of visual motion areas is due probably to congenital nystagmus without a conscious correlate like oscillopsia. Hum. Brain Mapping 23:40–52, 2004. © 2004 Wiley‐Liss, Inc.
Nonlinear analysis of EEG during NREM sleep reveals changes in functional connectivity due to natural aging
Authors: Terry John R. , Anderson Clare , Horne James A. 
Published: June 2004

AbstractThe spatial organization of nonlinear interactions between different brain regions during the first NREM sleep stage is investigated. This is achieved via consideration of four bipolar electrode derivations, Fp1F3, Fp2F4, O1P3, O2P4, which are used to compare anterior and posterior interhemispheric interactions and left and right intrahemispheric interactions. Nonlinear interdependence is detected via application of a previously written algorithm, along with appropriately generated surrogate data sets. It is now well understood that the output of neural systems does not scale linearly with inputs received and, thus, the study of nonlinear interactions in EEG is crucial. This approach also offers significant advantages over standard linear techniques, in that the strength, direction, and topography of the interdependencies can all be calculated and considered. Previous research has linked delta activity during the first NREM sleep stage to performance on frontally activating tasks during waking hours. We demonstrate that nonlinear mechanisms are the driving force behind this delta activity. Furthermore, evidence is presented to suggest that the aging brain calls upon the right parietal region to assist the pre‐frontal cortex. This is highlighted by statistically significant differences in the rates of interdependencies between the left pre‐frontal cortex and the right parietal region when comparing younger subjects (<23 years) with older subjects (>60 years). This assistance has been observed in brain‐imaging studies of sleep‐deprived young adults, suggesting that similar mechanisms may play a role in the event of healthy aging. Additionally, the contribution to the delta rhythm via nonlinear mechanisms is observed to be greater in older subjects. Hum. Brain Mapping 23:73–84, 2004. © 2004 Wiley‐Liss, Inc.
Alcohol continues to affect sleepiness related driving impairment, when breath alcohol levels have fallen to near‐zero
Authors: Barrett P. R. , Horne J. A. , Reyner L. A. 
Published: June 2004

AbstractEpidemiological findings point to very low blood alcohol levels heightening the risk of sleep‐related fatal road crashes. This was further assessed using a full sized interactive car simulator. Twenty, sleep restricted, healthy young men underwent a 2 h simulated afternoon monotonous drive, having previously consumed nil alcohol or 3 units >90 min previously, and having near‐zero breath alcohol (BrACs) at the start of the drive. In a repeated measures, double‐blind, balanced design, driving performance, subjective sleepiness and EEG were monitored throughout. Compared with nil alcohol, the alcohol condition initially increased sleepiness‐related driving impairment. However, this was not mirrored by subjective sleepiness or EEG. An unexpected reversal (i.e. improvement) in driving impairment occurred with the alcohol group, in the second hour of the drive. This was supported by a trend for improved subjective alertness. Alcohol continued to interact with sleepiness‐related driving impairment after BrACs had reached zero. However, a lack of subjective perception of increased sleepiness, at this time, further points to the dangerous combination of even modest alcohol intake and sleepiness, and confirms the road crash findings. BrACs are a poor guide to driver impairment. Copyright © 2004 John Wiley & Sons, Ltd.
Proliferation and differentiation of osteoblasts on Biocement D modified with collagen type I and citric acid
Authors: Hempel U. , Reinstorf A. , Poppe M. , Fischer U. , Gelinsky M. , Pompe W. , Wenzel K. W. 
Published: June 2004

AbstractIn this study, the proliferation and differentiation of rat calvarial osteoblasts cultured on either (1) calcium‐phosphate bone cement Biocement D, (2) Biocement D with 2.5% (w/w) mineralized collagen type I, or (3) Biocement D with 2.5% (w/w) mineralized collagen type I and 3% (w/w) citric acid were investigated. Incubation of the composites in cell‐culture medium resulted in a fast decrease of pH and calcium concentration as well as in an increase of phosphate concentration. Although these effects occurred with all investigated materials, the lowest extent could be observed for the citric‐acid‐containing composites. As shown by scanning‐electron microscopy, osteoblasts adhered to the composite surfaces. Proliferation and differentiation of the cells grown on the composites were found to be reduced compared to cells grown on tissue‐culture polystyrene. Cells cultured in the vicinity of the composites but without direct contact also exhibited a reduced rate of proliferation, reduced alkaline phosphatase activity, and reduced mineralization. Simulating the changes in calcium and phosphate concentration occasioned by the composites through exposing cells to EGTA and phosphate gives rise to the same effects of reducing proliferation, ALP activity, and mineralization. No indication for apoptosis in cells exposed to low calcium and high phosphate concentrations was found. The number of necrotic cells, however, increased after incubation with EGTA and phosphate. For assessment of cell‐composite interactions and the success of the composites in vivo, as well as for more effective material development, it seems to be important to know how changes in microenvironmental pH and ion composition of the material affect cellular proliferation and differentiation. © 2004 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 71B: 130–143, 2004
Expression and function of periostin‐isoforms in bone
Authors: Litvin Judith , Selim Abdul‐Hafez , Montgomery Michael O. , Lehmann Kiyoko , Rico Mario C. , Devlin Hugh , Bednarik Daniel P. , Safadi Fayez F. 
Published: June 2004

AbstractPeriostin was originally identified in MC3T3‐E1 osteoblast‐like cells. We have identified an isoform of periostin referred to as periostin‐like‐factor (PLF). It is homologous to other proteins such as fasciclin I (fas I), MPB70, βIG‐H3, and Algal‐CAMs. All of these proteins are implicated in regulating cell adhesion. PLF and the other isoforms of periostin differ in their C‐terminal sequences. PLF and periostin differ in two specific regions, between 673 and 699 amino acids (aa) and 785–812 aa. Periostin isoforms are expressed in vivo and in vitro during the stages of osteoblast differentiation and maturation. Their mRNAs are present in pre‐osteoblast cells as detected by in situ hybridization, and the proteins are between 86 and 93 kD in size as determined by Western blot analysis. Antisense oligonucleotides and antibodies directed against the isoforms of periostin were used to block the activity of these proteins. In both cases, the levels of osteoblast‐specific‐differentiation markers were markedly reduced suggesting a role for these proteins in osteoblast differentiation. © 2004 Wiley‐Liss, Inc.