bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stable P‐Heterocyclic Carbenes: Scope and Limitations
Authors: Masuda Jason D. , Martin David , Lyon‐Saunier Celine , Baceiredo Antoine , Gornitzka Heinz , Donnadieu Bruno , Bertrand Guy 
Published: November 2006

AbstractThe conjugate acids (PHCH+s) of P‐heterocyclic carbenes (PHCs) are prepared by formal [3+2] cycloaddition of a 1,3‐diphosphaallyl or 1,3‐phosphinophosphenium cation with various nitriles. The effect of the phosphorus substituent on the fate of the cyclization and on that of the counteranion and base in the subsequent deprotonation reaction are reported. Two PHCs that are indefinitely stable in the solid state are described. In solution, one of them, made from acetonitrile, undergoes a facile [3+2] cycloreversion, whereas the other, based on dimethyl cyanamide, is stable, presumably owing to its zwitterionic structure, which involves a tricoordinate pentavalent phosphorus atom. The reactivity of PHCs is strongly driven by the high electrophilicity of the phosphorus centers, as demonstrated by their reactivity with water and benzaldehyde. Although both PHCs reported in this paper are direct analogues of the least‐basic NHCs, their basicity is comparable to those of the more strongly basic NHCs (as determined by comparison of the carbonyl stretching frequencies of their corresponding cis‐[RhCl‐(CO)2(L)] complexes).
Dehalogenation of 1,3‐Diiodotricyclo[3.3.0.03,7]octane: Generation of 1,3‐Dehydrotricyclo[3.3.0.03,7]octane, a 2,5‐Methano‐Bridged [2.2.1]Propellane
Authors: Ayats Carles , Camps Pelayo , Fernández José A. , Vázquez Santiago 
Published: November 2006

AbstractCompounds isolated from the reaction of (±)‐1,3‐diiodotricyclo[3.3.0.03,7]octane with molten sodium or tBuLi suggest the intermediate formation of (±)‐1,3‐dehydrotricyclo[3.3.0.03,7]octane. Worthy of note is the formation of stereoisomeric bi(5‐methylenebicyclo[2.2.1]hept‐2‐ylidene) derivatives, probably by coupling of two units of (±)‐1,3‐dehydrotricyclo[3.3.0.03,7]octane of the same or different absolute configuration followed by fragmentation, processes that have been studied by theoretical calculations.
Michael Additions of Methylene Active Compounds to Chalcone in Ionic Liquids without any Catalyst: The Peculiar Properties of Ionic Liquids
Authors: Mečiarová Mária , Toma Štefan 
Published: November 2006

AbstractMichael additions of malonodinitrile as well as several other reagents to chalcone have been found to proceed well in pure ionic liquids, without the addition of any catalyst. The catalytic effect of the residual acidity caused by hydrolysis of ionic liquids anions was excluded because HCl in dichloromethane did not catalyse the Michael addition of malonodinitrile. Piperidine was tested as the catalyst and was found to be a much better catalyst in ionic liquids than in dichloromethane. Therefore, the following question arose: what is the effect of ionic liquids on the dissociation constants of CH acids?
Experimental and DFT Study of the Tautomeric Behavior of Cobalt‐Containing Secondary Phosphine Oxides
Authors: Wei Chu‐Hung , Wu Cheng‐En , Huang Yi‐Luen , Kultyshev Roman G. , Hong Fung‐E. 
Published: November 2006

AbstractNew cobalt‐containing secondary phosphine oxides [(μ‐PPh2CH2PPh2)Co2(CO)4{μ,η‐PhCCP(O)(H)(R)}] (8 a: R=tBu; 8 b: R=Ph) were prepared by reaction of secondary phosphine oxides PhCCP‐ (O)(H)(R) (6 a: R=tBu; 6 b: R=Ph) with dppm‐bridged dicobalt complex [(μ‐PPh2CH2PPh2)Co2(CO)6] (2). The molecular structures of 8 a and 8 b were determined by single‐crystal X‐ray diffraction. Although palladium‐catalyzed Heck reactions employing 8 b as ligand gave satisfying results, 8 a performed poorly in the same reaction. Judging from these results, a tautomeric equilibrium between 8 b and its isomeric form [(μ‐PPh2CH2PPh2)Co2(CO)4{μ,η‐PhCCP(OH)(Ph)}] 8 b′ indeed takes place, but it is unlikely between 8 a and [(μ‐PPh2CH2PPh2)Co2(CO)4{μ,η‐PhCCP(OH)(tBu)}] (8 a′). The DFT studies demonstrated that reasonable activation energies for the tautomeric conversions can be achieved only via a bimolecular pathway. Since a tBu group is much larger than a Ph group, the conversion is presumably only feasible in the case of 8 b⇌8 b′, but not in the case of 8 a⇌8 a′. Another cobalt‐containing phosphine, namely, [(μ‐PPh2CH2PPh2)Co2(CO)4{μ,η‐PhCCP(NEt2)(tBu)}] (7 a), and its oxidation product [(μ‐PPh2CH2PPh2)Co2(CO)4{μ,η‐PhCCP(O)(NEt2)(tBu)}] 7 a′ were prepared from the reaction of PhCCP(NEt2)(tBu) (5 a) with 2. The molecular structures of 7 a and 7 a′ were determined by single‐crystal X‐ray diffraction. The phosphorus atom is surrounded by substituents in a tetrahedral environment. A PN single bond (1.676(3) Å) is observed in the molecular structure of 7 a. Heck reactions employing 7 a/Pd(OAc)2 as catalyst system exhibited efficiency comparable to that of 8 a/Pd(OAc)2.
Total Syntheses of the Actin‐Binding Macrolides Latrunculin A, B, C, M, S and 16‐epi‐Latrunculin B
Authors: Fürstner Alois , De Souza Dominic , Turet Laurent , Fenster Michaël D. B. , Parra‐Rapado Liliana , Wirtz Conny , Mynott Richard , Lehmann Christian W. 
Published: November 2006

AbstractThe latrunculins are highly selective actin‐binding marine natural products and as such play an important role as probe molecules for chemical biology. A short, concise and largely catalysis‐based approach to this family of bioactive macrolides is presented. Specifically, the macrocyclic skeletons of the targets were forged by ring‐closing alkyne metathesis (RCAM) or enyne–yne metathesis of suitable diyne or enyne–yne precursors, respectively. This transformation was best achieved with the aid of [(tBu)(Me2C6H3)N]3Mo (37) as precatalyst activated in situ with CH2Cl2, as previously described. This catalyst system is strictly chemoselective for the triple bond and does not affect the olefinic sites of the substrates. Moreover, the molybdenum‐based catalyst turned out to be broader in scope than the Schrock alkylidyne complex [(tBuO)3WCCMe3] (38), which afforded cycloalkyne 35 in good yield but failed in closely related cases. The required metathesis precursors were assembled in a highly convergent fashion from three building blocks derived from acetoacetate, cysteine, and (+)‐citronellene. The key fragment coupling can either be performed via a titanium aldol reaction or, preferentially, by a sequence involving a Horner–Wadsworth–Emmons olefination followed by a protonation/cyclization/diastereoselective hydration cascade. Iron‐catalyzed CC‐bond formations were used to prepare the basic building blocks in an efficient manner. This synthesis blueprint gave access to latrunculin B (2), its naturally occurring 16‐epimer 3, as well as the even more potent actin binder latrunculin A (1) in excellent overall yields. Because of the sensitivity of the 1,3‐diene motif of the latter, however, the judicious choice of protecting groups and the proper phasing of their cleavage was decisive for the success of the total synthesis. Since latrunculin A and B had previously been converted into latrunculin S, C and M, respectively, formal total syntheses of these congeners have also been achieved. Finally, a previously unknown acid‐catalyzed degradation pathway of these bioactive natural products is described. The cysteine‐derived ketone 18, the tetrahydropyranyl segment 31 serving as the common synthesis platform for the preparation of all naturally occurring latrunculins, as well as the somewhat strained cycloalkyne 35 formed by the RCAM reaction en route to 2 were characterized by X‐ray crystallography.
Stereochemical identification of (R)‐ and (S)‐ibuprofen using residual dipolar couplings, NMR, and modeling
Authors: Marathias Vasilios M. , Tawa Gregory J. , Goljer Igor , Bach Alvin C. 
Published: November 2006

AbstractIn this work, we describe an NMR‐based method that utilizes an orientation media composed of the chiral polypeptide liquid crystal poly‐γ‐benzyl‐L‐glutamate (PBLG) dissolved in CDCl3, to measure the 1H‐1H, 1H‐13C and 13C‐13C residual dipolar couplings (RDCs) of (R) and (S)‐ibuprofen. Calculated RDCs, obtained from the lowest energy conformers, are then compared with the experimentally measured RDCs to predict the stereochemistry of each enantiomer. Excellent agreement between calculated and experimental RDCs was found when the lowest energy structure of each enantiomer, obtained in a simulated PBLG/CDCl3 environment, was used to back‐calculate the RDCs. This method is generally useful for small molecular weight molecules that possess either one or two chiral centers, are soluble in low viscosity organic solvents, and will not crystallize (Clegg, Crystal Structure Analysis. Principles and Practice. New York: Oxford University Press; 2002) or cannot be derivatized with a Mosher's reagent (Dale and Mosher, J Am Chem Soc 1973;95:512–519). Chirality, 2006. © 2006 Wiley‐Liss, Inc.
Growth and properties of an organometallic nonlinear optical crystal: bis(isothiocyanato)‐bis(4‐methylpyridine)zinc(II) (Zn(SCN)2(C6H7N)2)
Authors: Zhu L. Y. , Xu D. , Wang X. Q. , Liu X. J. , Zhang G. H. , Sun J. 
Published: November 2006

AbstractBis(isothiocyanato)‐bis(4‐methylpyridine)zinc(II)(Zn(SCN)2(C6H7N)2), (abbreviated as ZBNC) single crystals of optical quality have been grown from acetone solution by the slow temperature‐lowering method. Its solubilities at different temperatures in acetone were measured. The X‐ray powder diffraction (XRPD) spectroscopy of ZBNC crystal was performed at room temperature. The second harmonic generation (SHG) efficiency was determined by powder technique of Kurtz and Perry using Nd:YAG laser, which is equivalent to KDP crystal. The thermal decomposition process was characterized by thermal gravity and differential thermal analysis (TG\DTA). The specific heat of the crystal is 1440.67 J/mol·K at 325 K. The IR spectrum was recorded in the 500∼3500 cm–1 region, using KBr pellets on a Nicolet 170sx FT‐IR spectrometer. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Optimal allocation of distributed generation and reactive sources considering tap positions of voltage regulators as control variables
Authors: Golshan Mohamad Esmail Hamedani , Ali Arefifar Seyed 
Published: November 2006

AbstractIn this paper, by defining and solving an optimization problem, amount of distributed generators (DGs) and reactive power sources (RSs) in selected buses of a distribution system are computed to make up a given total of distributed generation for minimizing losses, line loadings, and total required reactive power capacity. The formulated problem is a combinatorial problem, therefore Tabu search algorithm is applied for solving the optimization problem. Results of solving the optimization problem for a radial 33‐bus distribution system and a meshed 6‐bus system are presented. When using less amount of reactive capacity, regarding tap positions of voltage regulators as control variables has considerable role in loss reduction and improvement of voltage profile. In the case of meshed systems, including line loadings in the cost function can significantly change results of solving the optimization problem such as amount of the required reactive capacity and how to assign DGs and RSs to the selected buses. Copyright © 2006 John Wiley & Sons, Ltd.
Monte Carlo simulation techniques for optimisation of phase shifter settings
Authors: Verboomen J. , Van Hertem D. , Schavemaker P. H. , Spaan F. J. C. M. , Delince J‐M. , Belmans R. , Kling W. L. 
Published: November 2006

AbstractThe Netherlands has installed two phase shifting transformers (PSTs) in order to more evenly distribute the load on the interconnectors with Germany. Belgium is planning to install four devices to tackle the problem of transit flows between France and Germany and to control the flow on the parallel paths between Belgium and France. One phase shifter on the border of the Netherlands and Germany was already installed for a long time. The coordination of all the phase shifters is very important in order to take full advantage of these devices, but also to guarantee a safe situation and not to mutually counteract control actions. In this paper, a new Monte Carlo based approach is proposed to find the optimal settings of different phase shifters. The goal is to maximise the import capacity for both the Netherlands and Belgium. Copyright © 2006 John Wiley & Sons, Ltd.
A new reduction method for reliability assessment of bulk electric power systems
Authors: Gharaghozloo H. , Haghifam M.‐R. , Haubrich H.‐J. , Firozabad M. Fotuhi 
Published: November 2006

AbstractData requirements and large computation times are still major difficulties in bulk electric systems (BES). When small area of BES is noticed as area of interest (AI) in reliability studies, the other parts of the network can be considered as interconnected area (IA). A reduction method based on generations and loads importance of IA is presented in this paper to equivalent the IA. Generation Reliability Importance Factor (GRIF) of generation units and Load Reliability Importance Factor (LRIF) of loads with respect to power system reliability are defined for the generation and load points associated with the IA. Application of graph theory concept is used for obtaining the equivalent network. With some rules based on graph networks, an equivalent network will be obtained for this network and some nodes are remained in final network such as main nodes based on GRIF and LRIF indices. The applicability of the proposed approach is examined using the 3‐area IEEE‐RTS network and the results are presented and compared for various case studies. Copyright © 2006 John Wiley & Sons, Ltd.
Cortical brain responses during passive nonpainful median nerve stimulation at low frequencies (0.5–4 Hz): An fMRI study
Authors: Ferretti Antonio , Babiloni Claudio , Arienzo Donatello , Del Gratta Cosimo , Rossini Paolo Maria , Tartaro Armando , Romani Gian Luca 
Published: November 2006

AbstractPrevious findings have shown that the human somatosensory cortical systems that are activated by passive nonpainful electrical stimulation include the contralateral primary somatosensory area (SI), bilateral secondary somatosensory area (SII), and bilateral insula. The present study tested the hypothesis that these areas have different sensitivities to stimulation frequency in the condition of passive stimulation. Functional MRI (fMRI) was recorded in 24 normal volunteers during nonpainful electrical median nerve stimulations at 0.5, 1, 2, and 4 Hz repetition rates in separate recording blocks in pseudorandom order. Results of the blood oxygen level‐dependent (BOLD) effect showed that the contralateral SI, the bilateral SII, and the bilateral insula were active during these stimulations. As a major finding, only the contralateral SI increased its activation with the increase of the stimulus frequency at the mentioned range. The fact that nonpainful median‐nerve electrical stimuli at 4 Hz induces a larger BOLD response is of interest both for basic research and clinical applications in subjects unable to perform cognitive tasks in the fMRI scanner. Hum Brain Mapp 2006. © 2006 Wiley‐Liss, Inc.
Caffeine attenuates practice effects in word stem completion as measured by fMRI BOLD signal
Authors: Bendlin Barbara B. , Trouard Theodore P. , Ryan Lee 
Published: November 2006

AbstractCaffeine ingestion results in increased brain cell metabolism (Nehlig et al. [1992] Brain Res Brain Res Rev 17:139–170) and decreased cerebral blood flow (Field et al. [2003] Radiology 227:129–135; Mulderink et al. [2002] Neuroimage 15:37–44). The current study investigated the effect of caffeine in a word stem completion task using only novel word stems (no repeated stimuli). Resting perfusion was measured with arterial spin labeled perfusion MRI, along with blood oxygenation level‐dependent (BOLD) signal before and after ingestion of regular coffee, decaffeinated coffee, and water. Based on previous research (Laurienti et al. [2002] Neuroimage 17:751–757; Mulderink et al. [2002] Neuroimage 15:37–44), we hypothesized that caffeine would result in increased BOLD signal intensity and extent of BOLD activation. As expected, caffeine resulted in a significant decrease in cerebral perfusion. However, both the control and caffeine groups showed an increase in BOLD signal amplitude across two sets of novel word stems. Additionally, the control group showed a 50% reduction in the extent of BOLD activation, while the caffeine group showed no change in activation extent. Neither group showed changes in BOLD baseline signal over time, which had been suggested to mediate caffeine‐related BOLD signal changes. The results suggest that caffeine may attenuate general task practice effects that have been described in recent functional MRI studies of word stem completion (Buckner et al. [2000] Brain 123:620–640). Hum Brain Mapp 2006. © 2006 Wiley‐Liss, Inc.
Polyribosomes are increased in spines of CA1 dendrites 2 h after the induction of LTP in mature rat hippocampal slices
Authors: Bourne Jennifer N. , Sorra Karin E. , Hurlburt Jamie , Harris Kristen M. 
Published: November 2006

AbstractEnduring long‐term potentiation (LTP) requires immediate protein synthesis, hence we assessed whether more polyribosomes are present in dendritic spines of mature hippocampal dendrites after the induction of LTP. Reconstructions from serial section transmission electron microscopy (sSTEM) revealed more dendritic polyribosomes 2 h posttetanus, relative to low‐frequency stimulation (LFS). Polyribosomes were present in spines of all shapes with larger postsynaptic densities after 2 h, suggesting a coordinated local protein synthesis among many synapses to replenish proteins utilized during an earlier phase of LTP. © 2006 Wiley‐Liss, Inc.
Intranuclear paracrystals observed in striated muscle specific LIM protein‐deficient mouse cardiomyocytes
Authors: Muto M. , Sargeant A. , Tangkawattana P. , Takeyasu K. , Nishijima Y. , Bonagura J. , Hoshijima M. , Nakade T. , Hosaka Y. , Faulkner G. , Tomono K. , Yamaguchi M. 
Published: November 2006

AbstractA paracrystalline structure was observed within left ventricular cardiomyocyte nuclei of MLP−/− mice. The paracrystal possessed cross lines, ∼8.0 μm long and 0.3 μm wide, with a slender spindle shape and a periodicity of 13 nm. Paracrystals were best observed along the longitudinal orientation of myofibrils and were detected in less than 10% of the nuclei observed. One dimension of the protein unit forming the paracrystal was 8.5 nm long. The electron density of the paracrystal appeared to be slightly higher than that of heterochromatin, suggesting that RNA‐associated proteins are constituents of the paracrystal. This is the first report of intranuclear paracrystals in cardiomyocytes, which appear to be unique to MLP−/− mice. Microsc. Res. Tech. 2007. © 2006 Wiley‐Liss, Inc.
Mechanisms controlling venom expulsion in the western diamondback rattlesnake, Crotalus atrox
Authors: Young Bruce A. , Kardong Kenneth V. 
Published: November 2006

AbstractAlthough many studies have documented variation in the amount of venom expended during bites of venomous snakes, the mechanistic source of this variation remains uncertain. This study used experimental techniques to examine how two different features of the venom delivery system, the muscle surrounding the venom gland (the Compressor Glandulae in the rattlesnake) and the fang sheath, could influence venom flow in the western diamondback rattlesnake, Crotalus atrox. Differential contraction of the Compressor Glandulae explained only approximately 30% of the variation in venom flow. Lifting (compression) of the fang sheath as occurs during a normal strike produced marked increases in venom flow; these changes were closely correlated and exceed in magnitude by almost 10 × those recorded from the Compressor Glandulae alone. These results suggest that variation in these two aspects of the venom delivery system—both in terms of magnitude and temporal patterning—explain most of the observed variation in venom injection. The lack of functional or mechanical links between the Compressor Glandulae and the fang sheath, and the lack of skeletal or smooth muscle within the fang sheath, make it unlikely that variation in venom flow is under direct neural control. Instead, differential venom injection results from differences in the pressurization by the Compressor Glandulae, the gate keeping effects of the fang sheath and enclosed soft‐tissue chambers, and by differences in the pressure returned by peripheral resistance of the target tissue. J. Exp. Zool. 305A:18–27, 2007. © 2006 Wiley‐Liss, Inc.
Uteroglobin induces the development and cellular proliferation of the mouse early embryo
Authors: Riffo Marta , González Keybell Díaz , Nieto Antonio 
Published: November 2006

AbstractTwo‐cell mouse embryos cultured in vitro in the presence of either purified rabbit uteroglobin (UG) or recombinant human UG developed and proliferated faster than controls cultured in the absence of this protein. Both the percentage of embryos developing to the blastocyst stage and the number of cells per embryo were increased. Treatment with UG for 3 hr was enough to trigger this response. The effect of UG was blocked by genistein, an inhibitor of tyrosine protein kinases, suggesting the involvement of these kinases in the stimulation of the embryo by UG. To further support this suggestion, embryos were metabolically labeled in vitro with [32P] and the phosphorylated proteins were immunoprecipitated with anti‐phosphotyrosine. Analysis of the immunoprecipitates by SDS‐PAGE showed that UG induced the phosphorylation of several proteins of Mr between 200 and 37 kDa. This induction was observed after 1 hr of stimulation with UG and further increased after 3 hr of treatment. Since UG is synthesized and secreted in the uterus and the oviduct, these results suggest a physiological role of this protein in the correct development of the embryo in vivo. J. Exp. Zool. 305A:28–34, 2007. © 2006 Wiley‐Liss, Inc.