bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of the Solvent on the Conformation of Isolated MEH‐PPV Chains Intercalated Into SnS2
Authors: Aharon Eyal , Breuer Steffen , Jaiser Frank , Köhler Anna , Frey Gitti L. 
Published: June 2008

AbstractPhotophysical processes in conjugated polymers are influenced by two competing effects: the extent of excited state delocalization along a chain, and the electronic interaction between chains. Experimentally, it is often difficult to separate the two because both are controlled by chain conformation. Here we demonstrate that it is possible to modify intra‐chain delocalization without inducing inter‐chain interactions by intercalating polymer monolayers between the sheets of an inorganic layered matrix. The red‐emitting conjugated polymer, MEH‐PPV, is confined to the interlayer space of layered SnS2. The formation of isolated polymer monolayers between the SnS2 sheets is confirmed by X‐ray diffraction measurements. Photoluminescence excitation (PLE) and photoluminescence (PL) spectra of the incorporated MEH‐PPV chains reveal that the morphology of the incorporated chains can be varied through the choice of solvent used for chain intercalation. Incorporation from chloroform results in more extended conformations compared to intercalation from xylene. Even highly twisted conformations can be achieved when the incorporation occurs from a methanol:chloroform mixture. The PL spectra of the MEH‐PPV incorporated SnS2 nanocomposites using the different solvents are in good agreement with the PL spectra of the same solutions, indicating that the conformation of the polymer chains in the solutions is retained upon intercalation into the inorganic host. Therefore, intercalation of conjugated polymer chains into layered hosts enables the study of intra‐chain photophysical processes as a function of chain conformation.
Comparison of the Electrochemical and Luminescence Properties of Two Carbazole‐Based Phosphine Oxide EuIII Complexes: Effect of Different Bipolar Ligand Structures
Authors: Xu Hui , Yin Kun , Huang Wei 
Published: June 2008

AbstractThe photoluminescence (PL), electrochemical, and electroluminescence (EL) properties of EuIII complexes, [Eu(cppo)2(tta)3] (1) and [Eu(cpo)2(tta)3] (2; TTA=2‐thenoyltrifluoroacetonate) with two carbazole‐based phosphine oxide ligands, 9‐[4‐(diphenylphosphinoyl)phenyl]‐9H‐carbazole (CPPO) and 9‐(diphenylphosphoryl)‐9H‐carbazole (CPO), which have different bipolar structures, donor–π‐spacer–acceptor (D–π–A) or donor–acceptor (D–A) systems respectively, are investigated. The CPPO with D–π–A architecture has improved PL properties, such as higher PL efficiency and more efficient intramolecular energy transfer, than CPO with the D–A architecture. Gaussian simulation proved the bipolar structures and the double‐carrier injection ability of the ligands. The carrier injection abilities of triphenylphosphine oxide, CPO, and CPPO are gradually improved. Notably, the Gaussian and electrochemical investigations indicate that before and after coordination, the carrier injection ability of the ligands show remarkable changes because of the particularity of the D‐π–A and D–A systems. The electrochemical studies demonstrate that coordination induces the electron cloud to migrate from electron‐rich carbazole to electron‐poor diphenylphosphine oxide, and consequently increases the electron‐cloud density on diphenylphosphine oxide, which weakens its ability for electron affinity and induces the elevation of LUMO energy levels of the complexes. Significantly, the π‐spacer in the D–π–A system exhibits a distinct buffer effect on the variation of the electron‐cloud density distribution of the ligand, which is absent in the D–A system. It is demonstrated that the adaptability of the D–π–A systems, especially for coordination, is stronger than that of D–A systems, which facilitates the modification of the complexes by designing multifunctional ligands purposefully. 1 seems favorable as the most efficient electroluminescent EuIII complex with greater brightness, higher efficiencies, and more stable EL spectra than 2. These investigations demonstrate that the phosphine oxide ligands with D–π–A architecture are more appropriate than those with D–A architecture to achieve multifunctional electroluminescent EuIII complexes.
First and Second Proton Affinities of Carbon Bases
Authors: Tonner Ralf , Heydenrych Greta , Frenking Gernot 
Published: June 2008

AbstractQuantum chemical calculations at the MP2/TZVPP//BP86/SVP level are reported for the first and second proton affinities (PAs) of divalent carbon‐donor molecules. The molecules investigated are imidazol‐2‐ylidenes (“normal” NHCs) and the tautomeric imidazol‐4/5‐ylidenes (“abnormal” NHCs). PAs are also calculated for acyclic and cyclic carbodiphosphoranes, carbophosphoranesulfide, unsaturated and saturated carbodicarbenes, tetraaminoallenes and carbon suboxide. The results are discussed in terms of divalent carbon(II) compounds (carbenes) CR2, which have one lone electron pair at carbon, and carbon(0) compounds CL2, which have two lone pairs at carbon and two C←L donor–acceptor bonds. Divalent C(0) compounds (carbones) not only have very high first PAs, but the second PA is also large and strong enough to isolate doubly protonated C(0) species as salts in a condensed phase. The first PA of divalent carbon(II) compounds (carbenes) are also large. However, they have much smaller second PAs than the divalent carbon(0) compounds. The divalent C(0) character of a compound is not always obvious when the bonding situation in the equilibrium geometry is considered. This is the case, for example, for tetraaminoallenes (TAAs). Protonation of TAAs changes the bonding situation of the central moiety from doubly bonded (R2N)2CCC(NR2)2 to a donor–acceptor description (R2N)2C→C(H+)n←C(NR2) [n=1, 2]. The atomic partial charge at the carbon donor atom does not correlate with the PA and the trend of the second PA may be quite different from the trend of the first. The trends of the first and second PA correlates quite well with the eigenvalues of the highest‐lying carbon lone‐pair orbitals.
Chemical Engineering Challenges and Investment Opportunities in Sustainable Energy
Authors: Heller Adam 
Published: June 2008

AbstractThe chemical and energy industries are transforming as they adjust to the new era of high‐priced petroleum and severe global warming. As a result of the transformation, engineering challenges and investment opportunities abound. Rapid evolution and fast growth are expected in cathode and anode materials as well as polymeric electrolytes for vehicular batteries and in high‐performance polymer–ceramic composites for wind turbines, fuel‐efficient aircraft, and lighter and safer cars. Unique process‐engineering opportunities exist in sand‐oil, coal, and possibly also shale liquefaction to produce transportation fuel; and also in genetic engineering of photosynthesizing plants and other organisms for their processing into high‐performance biodegradable polymers and high‐value‐added environmentally friendly chemicals. Also, research on the feasibility of mitigation of global warming through enhancement of CO2 uptake by the southern oceans by fertilization with trace amounts of iron is progressing. Because chemical engineers are uniquely well trained in mathematical modeling of mass transport, flow, and mixing, and also in cost analysis, they are likely to join the oceanographers and marine biologists in this important endeavor.
Toward an autonomous platform for spatio‐temporal EEG‐signal analysis based on cellular nonlinear networks
Authors: Gollas Frank , Niederhöfer Christian , Tetzlaff Ronald 
Published: June 2008

AbstractAlthough in the field of epileptic seizure prediction many spatio‐temporal approaches have been carried out, the precursor detection problem remains unsolved up to now. It can be observed that an increasing number of algorithms are developed based on cellular nonlinear networks (CNNs). They are dealing with the extraction of signal features using intracranial EEG recordings in order to detect possible preseizure states. In general, reliable precursor detections cannot be obtained for all treated cases. The performance of these algorithms can be enhanced by adapting them to specific patients. Combining different features in a feature vector in a future seizure anticipation platform may lead to a reliably working seizure prediction system.In this contribution we focus on two different CNN‐based algorithms—a nonlinear identification approach and a prediction algorithm. They will be discussed in detail and recently obtained results will be given. Copyright © 2008 John Wiley & Sons, Ltd.
Performance evaluation of CSMA/ID MAC protocol for IP over WDM ring networks
Authors: Ho Jih‐Hsin , Chen Wen‐Ping , Hwang Wen‐Shyang , Shieh Ce‐Kuen 
Published: June 2008

AbstractIn this paper, a packet pre‐classification media access control protocol based on a carrier sense multiple access with idle detection (CSMA/ID) scheme is investigated for supporting IP packets over all‐optical WDM ring networks. The purpose of the protocol is to increase throughput and to decrease the packet transmission delay of IP packets over optical networks in a metropolitan area network. This protocol avoids both packet collision and packet fragmentation. In order to improve the utilization of the network, the packets transmitted from a local area network are first pre‐classified into various class queues of an access point (AP) according to their length. After checking the available space based on the wavelength received by the receivers of the AP, the packets in the queues are transmitted. An analytical model is developed to evaluate the performance of the protocol, with simulation results showing good network efficiency. The proposed network has short‐term variations that introduce unfairness conditions. This problem could be overcome by assigning a quota on individual queues to allow all queues fair access. Copyright © 2008 John Wiley & Sons, Ltd.
Low complexity bit allocation algorithm for OFDM systems
Authors: Lee Changwook , Jeon Gi J. 
Published: June 2008

AbstractA bit allocation algorithm is presented for orthogonal frequency division multiplexing (OFDM) systems. The proposed algorithm is derived from the geometric progression of the additional transmission power required by the subcarriers and the arithmetic–geometric means inequality. Consequently, this algorithm has a simple procedure and low computational complexity. Copyright © 2008 John Wiley & Sons, Ltd.
Apoptotic cell death, long‐term persistence, and neuronal differentiation of aneuploid cells generated in the adult brain of teleost fish
Authors: Rajendran R. Samuel , Wellbrock Ursula M. , Zupanc Günther K.H. 
Published: June 2008

AbstractAneuploidy, caused by segregation defects during mitosis, has previously been identified in adult‐born cells of mammals and teleosts. In the present study, we have examined the fate of these cells in the brain of the teleost fish Apteronotus leptorhynchus. By immunostaining against active caspase‐3, we have shown that both cells with normal nuclear morphology and cells with mitotic segregation defects undergo apoptosis, but the relative number of apoptotic cells is higher among cells of the latter category. Long‐term survival of cells with mitotic segregation defects could be demonstrated by incorporation of 5‐bromo‐2′‐deoxyuridine into newly synthesized DNA during the S‐phase of mitosis, and by employment of postadministration survival times of up to 860 days. Moreover, by combining 5‐bromo‐2′‐deoxyuridine immunolabeling with immunostaining against the neuron‐specific marker protein Hu, we have shown that among the long‐term persistent cells with mitotic segregation defects a similar portion develops into neurons as does among the long‐term persistent cells without such defects. It is possible that aneuploid cells play a role in the regulation of gene expression by somatic genomic alterations during postnatal development. © 2008 Wiley Periodicals, Inc. Develop Neurobiol, 2008.
A subset of signal transduction pathways is required for hippocampal growth cone collapse induced by ephrin‐A5
Authors: Yue Xin , Dreyfus Cheryl , Kong Tony Ah‐Ng , Zhou Renping 
Published: June 2008

AbstractThe Eph family tyrosine kinase receptors and their ligands, ephrins, play key roles in a wide variety of physiological and pathological processes including tissue patterning, angiogenesis, bone development, carcinogenesis, axon guidance, and neural plasticity. However, the signaling mechanisms underlying these diverse functions of Eph receptors have not been well understood. In this study, effects of Eph receptor activation on several important signal transduction pathways are examined. In addition, the roles of these pathways in ephrin‐A5‐induced growth cone collapse were assessed with a combination of biochemical analyses, pharmacological inhibition, and overexpression of dominant‐negative and constitutively active mutants. These analyses showed that ephrin‐A5 inhibits Erk activity but activates c‐Jun N‐terminal kinase. However, regulation of these two pathways is not required for ephrin‐A5‐induced growth cone collapse in hippocampal neurons. Artificial Erk activation by expression of constitutively active Mek1 and B‐Raf failed to block ephrin‐A5 effects on growth cones, and inhibitors of the Erk pathway also failed to inhibit collapse by ephrin‐A5. Inhibition of JNK had no effects on ephrin‐A5‐induced growth cone collapse either. In addition, inhibitors to PKA and PI3‐K showed no effects on ephrin‐A5‐induced growth cone collapse. However, pharmacological blockade of phosphotyrosine phosphatase activity, the Src family kinases, cGMP‐dependent protein kinase, and myosin light chain kinase significantly inhibited ephrin‐A5‐induced growth cone collapse. These observations indicate that only a subset of signal transduction pathways is required for ephrin‐A5‐induced growth cone collapse. © 2008 Wiley Periodicals, Inc. Develop Neurobiol, 2008.
The role of cell death in sexually dimorphic muscle development: Male‐specific muscles are retained in female bax/bak knockout mice
Authors: Jacob Dena A. , Ray Theresa , Bengston C. Lynn , Lindsten Tullia , Wu Junmin , Thompson Craig B. , Forger Nancy G. 
Published: June 2008

AbstractThe bulbocavernosus (BC) and levator ani (LA) muscles are present in males but absent or severely reduced in females, and the fate of these muscles controls the survival of motoneurons in the sexually dimorphic spinal nucleus of the bulbocavernosus. However, the mechanism underlying the sex difference in BC and LA development has been controversial. We examined the role of cell death in sexual differentiation of the bulbocavernosus BC/LA muscles in mice. Muscle development was mapped from embryonic day 16 (E16) to postnatal day 5 (P5). A sex difference (male > female) first arose on E17 (BC) or E18 (LA), and increased in magnitude postnatally. TUNEL labeling revealed dying cells in the BC and LA muscles of both sexes perinatally. However, females had a significantly higher density of TUNEL‐positive cells than did males. A role for the proapoptotic factors, Bax and Bak, in BC/LA development was tested by examining mice lacking one or both of these proteins. In females lacking either Bax or Bak, the BC was absent and the LA rudimentary. Deletion of both bax and bak genes, however, rescued the BC, increased LA size ∼20‐fold relative to controls, and virtually eliminated TUNEL‐positive cells in both muscles. We conclude that cell death plays an essential role in sexual differentiation of the BC/LA muscles. The presence of either Bax or Bak is sufficient for cell death in the BC/LA, whereas the absence of both prevents sexually dimorphic muscle cell death. © 2008 Wiley Periodicals, Inc. Develop Neurobiol, 2008.
Organometallic Access to Intermetallic θ‐CuE2 (E = Al, Ga) and Cu1–xAlx Phases
Authors: Cokoja Mirza , Jagirdar Balaji R. , Parala Harish , Birkner Alexander , Fischer Roland A. 
Published: June 2008

AbstractIn this work, we compare different precursor approaches for the mild decomposition to copper–aluminum and –gallium powder materials in nonaqueous solution. Referring to previous work on the preparation of Cu–Al alloy materials from [(AlCp*)4] and [CpCu(PMe3)], the amine‐stabilized metal trihydrides [(Me3N)AlH3] and [(quinuclidine)GaH3] were used as alternative sources for Al and Ga. In a comparative study, [(Me3N)AlH3] and [(AlCp*)4] were treated with the Cu precursors [CpCu(PMe3)] and [{Cu(mesityl)}5] in mesitylene solution in various molar ratios at 150 °C and 3 bar H2 to give metallic precipitates of the composition Cu1–xAlx (x = 0.67, 0.50, 0.31). Whereas the combination [(AlCp*)4] with [{Cu(mesityl)}5] did not yield an intermetallic phase, all other Cu/Al precursor combinations led to alloyed Cu–Al materials. For x = 0.67, the θ‐CuAl2 phase formed, as shown by X‐ray powder diffraction (XRD) and solid‐state magic‐angle‐spinning (MAS)NMR spectroscopic studies. Similarly, the reaction of [{Cu(mesityl)}5] with [(quinuclidine)GaH3] immediately led to the precipitation of a gray powder, without the addition of hydrogen. The powder was identified by means of XRD as θ‐CuGa2. At x = 0.50 and below, the reactions were less phase selective depending on the precursor combination. [CpCu(PMe3)] combined with both Al precursors afforded a mixture of several Cu–Al phases, whereas [{Cu(mesityl)}5] was treated with [(Me3N)AlH3] to yield a material whose X‐ray signature was assigned to the monoclinic Cu0.51Al0.49 phase. The γ‐Cu9Al4 phase could not be obtained from [CpCu(PMe3)]; instead, solid solutions of α‐Cu were obtained. The treatment of [{Cu(mesityl)}5] with [(Me3N)AlH3] in the Cu/Al molar ratio of 9:4 (x = 0.31) gave a gray powder, which could be identified by XRD as γ‐Cu9Al4.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Anion‐Directed Template Synthesis and Hydrolysis of Mono‐Condensed Schiff Base of 1,3‐Pentanediamine and o‐Hydroxyacetophenone in NiII and CuII Complexes
Authors: Mukherjee Pampa , Drew Michael G. B. , Ghosh Ashutosh 
Published: June 2008

AbstractBis(o‐hydroxyacetophenone)nickel(II) dihydrate, on reaction with 1,3‐pentanediamine, yields a bis‐chelate complex [NiL2]·2H2O (1) of mono‐condensed tridentate Schiff baseligand HL {2‐[1‐(3‐aminopentylimino)ethyl]phenol}. The Schiff base has been freed from the complex by precipitating the NiII as a dimethylglyoximato complex. HL reacts smoothly with Ni(SCN)2·4H2O furnishing the complex [NiL(NCS)] (2) and with CuCl2·2H2O in the presence of NaN3 or NH4SCN producing [CuL(N3)]2 (3) or [CuL(NCS)] (4). On the other hand, upon reaction with Cu(ClO4)2·6H2O and Cu(NO3)2·3H2O, the Schiff base undergoes hydrolysis to yield ternary complexes [Cu(hap)(pn)(H2O)]ClO4 (5) and [Cu(hap)(pn)(H2O)]NO3 (6), respectively (Hhap = o‐hydroxyacetophenone and pn = 1,3‐pentanediamine). The ligand HL undergoes hydrolysis also on reaction with Ni(ClO4)2·6H2O or Ni(NO3)2·6H2O to yield [Ni(hap)2] (7). The structures of the complexes 2, 3, 5, 6, and 7 have been confirmed by single‐crystal X‐ray analysis. In complex 2, NiII possesses square‐planar geometry, being coordinated by the tridentate mono‐negative Schiff base, L and the isothiocyanate group. The coordination environment around CuII in complex 3 is very similar to that in complex 2 but here two units are joined together by end‐on, axial‐equatorial azide bridges to result in a dimer in which the geometry around CuII is square pyramidal. In both 5 and 6, the CuII atoms display the square‐pyramidal environment; the equatorial sites being coordinated by the two amine groups of 1,3‐pentanediamine and two oxygen atoms of o‐hydroxyacetophenone. The axial site is coordinated by a water molecule. Complex 7 is a square‐planar complex with the Ni atom bonded to four oxygen atoms from two hap moieties. The mononuclear units of 2 and dinuclear units of 3 are linked by strong hydrogen bonds to form a one‐dimensional network. The mononuclear units of 5 and 6 are joined together to form a dimer by very strong hydrogen bonds through the coordinated water molecule. These dimers are further involved in hydrogen bonding with the respective counteranions to form 2‐D net‐like open frameworks. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Lanthanide Complexes and Quantum Dots: A Bright Wedding for Resonance Energy Transfer
Authors: Charbonnière Loïc J. , Hildebrandt Niko 
Published: June 2008

AbstractIn this microreview we describe the principle of Förster resonance energy transfer (FRET) occurring between closely spaced energy‐donor and ‐acceptor molecules. The theoretical treatment is depicted in relation with the data extractable from spectroscopic measurements. We present the specific case of semiconductor nanocrystals (or quantum dots – QDs) as energy donors in FRET experiments and a particular emphasis is put on the specific advantages of these fluorophores with regard to both their exceptional photophysical properties and their nanoscopic morphology. In a following section, the special attributes of luminescent lanthanide complexes (LLCs) are outlined with illustrations of properties such as their characteristic emission spectra, long‐lived luminescence, and large “Stokes shift”. Finally, the successful combination of LLCs and QDs in FRET experiments is demonstrated, showing the unrivaled benefits of this singular marriage, opening doors for energy transfer at very large distances and excellent sensitivity of detection within the frame of time‐resolved fluoroimmunoassays.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
The Synthesis of Ruthenium and Rhodium Complexes with Functionalized N‐Heterocyclic Carbenes and Their Use in Solid Phase Peptide Synthesis
Authors: Lemke Jessica , Metzler‐Nolte Nils 
Published: June 2008

AbstractWhile N‐heterocyclic carbenes (NHCs) are ubiquitous ligands in catalysts for organic or industrial synthesis, their potential to form stable transition metal complexes has hardly been exploited in metal bioconjugates. In this work, we describe a straightforward synthesis of carboxylato‐functionalized imidazolium salts for covalent binding to peptides. Carbene complexes of Ru and Rh were prepared from these imidazolium salts using Ag2O, followed by transmetallation. The neuropeptide [Leu5]‐enkephalin (Tyr‐Gly‐Gly‐Phe‐Leu) was chosen as a model peptide. Exploratory NMR experiments identified the Ru(p‐cymene)Cl2 complex of the asymmetrically substituted imidazol‐2‐ylidene 3b as the most suitable metal carbene precursor for solid phase peptide synthesis (SPPS). After optimization of the conditions for SPPS, a ruthenium‐NHC pseudoenkephalin (dichloro(η6‐p‐cymene)[1‐methyl‐3‐(methyl‐p‐benzoyl‐Gly‐Gly‐Phe‐Leu‐OH)imidazol‐2‐ylidene]ruthenium(II), 12) was synthesized from 3b on solid phase using the 2‐Cl‐Trt resin and cleavage by 2 % TFA to yield the free carboxylic acid. Peptide 12 was fully characterized by HPLC, 1H and 13C NMR and ESI‐MS. Characteristic NMR signals, as well as the isotope pattern of Ru in the ESI‐MS, unequivocally confirm the formation of this metal‐carbene peptide bioconjugate.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)