bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear ac responses of electro-magnetorheological fluids
Authors: Huang J. P. , Yu K. W.
Published: October 2004

We apply a Langevin model to investigate the nonlinear ac responses of electro-magnetorheological (ERMR) fluids under the application of two crossed dc magnetic (z axis) and electric (x axis) fields and a probing ac sinusoidal magnetic field. We focus on the influence of the magnetic fields which can yield nonlinear behaviors inside the system due to the particles with a permanent magnetic dipole moment. Based on a perturbation approach, we extract the harmonics of the magnetic field and orientational magnetization analytically. To this end, we find that the harmonics are sensitive to the degree of anisotropy of the structure as well as the field frequency. Thus, it is possible to real-time-monitor the structure transformation of ERMR fluids by detecting the nonlinear ac responses.
Flow animation by unsteady temperature fields
Authors: Yariv Ehud , Brenner Howard
Published: October 2004

Simple mass conservation principles show that unsteady temperature fields in thermally expandable fluids are always accompanied by flow, even in the absence of gravity. This mechanism is demonstrated using several model problems, which exhibit its peculiar features. The thermally induced flows become substantial in small-scale systems, suggesting possibilities for microfluidic applications.
On asymmetry between superheating and supercooling in solid-liquid transitions: Landau models
Authors: Luo Sheng-Nian , Swift Damian C.
Published: October 2004

We investigated the asymmetry between superheating and supercooling in solid-liquid transitions using two Landau-type models for the first-order phase transitions, the Landau–Devonshire and Landau–de Gennes models. The Landau models reproduced the asymmetric behavior described by the classical nucleation theory.
Chemical-reaction-zone lengths in condensed-phase explosives
Authors: Engelke Ray , Sheffield Stephen A. , Stacy Howard L.
Published: October 2004

Numerous workers have suggested that the “A” parameter in the relation D(R)=D(∞)[1−A/R] is a measure of the steady-state one-dimensional chemical-reaction-zone length of a detonating explosive. This equation relates the steady-state detonation speed in an explosive material to the lateral dimension of the (usually cylindrical) charge [e.g., the cylinder’s radius (R)]. D(∞) is the detonation speed at infinite lateral charge size. The argument for A being the chemical-reaction-zone length is purely a dimensional one. We show that this supposed relation between A and an explosive’s steady one-dimensional chemical-reaction-zone length is untrue—because the A value is different for the same explosive fired in two types of confinement. However, we give experimental evidence that the ratio of the A values for closely related pairs of explosives, fired in the same confinement material, is a measure of the two explosive’s relative chemical-reaction-zone length. This is done by firing two closely related nitromethane-based explosives in two different types of confinement. We apply this positive result to examining the relative chemical-reaction-zone lengths of other closely related explosive pairs. In all cases, the A ratios agreed with intuition based on experimental results.
Rovibrational-state-selected pulsed field ionization-photoelectron study of methyl iodide using two-color infrared-vacuum ultraviolet lasers
Authors: Wang P. , Xing X. , Lau K.-C. , Woo H. K. , Ng C. Y.
Published: October 2004

The preparation of methyl iodide (CH3I) in selected rovibrational states [ν7=1 (C-H stretch); J] by infrared (IR) excitation prior to vacuum ultraviolet (VUV) photoionization has greatly simplified the observed pulsed field ionization-photoelectron (PFI-PE) spectra, allowing the direct determination of the rotational constants B+(C+)=0.254±0.003 cm−1 for CH3I+(X̃ 2E3/2;ν7+) and the ionization energy (76 896.9±0.2 cm−1) for CH3I+(X̃ 2E3/2;ν7+=1,J+=3/2)←CH3I(X̃ 1A1;ν7=1,J=0). The IR-VUV-PFI-PE and IR-VUV-photoion measurements also provide relative state-to-state (ν7+=1, J+←ν7=1, J) cross sections for the photoionization process.
Darwinian adaptation of proteorhodopsin to different light intensities in the marine environment
Authors: Bielawski Joseph P. , Dunn Katherine A. , Sabehi Gazalah , Béjà Oded
Published: October 2004

Proteorhodopsin, a retinal-binding protein, represents a potentially significant source of light-driven energy production in the world's oceans. The distribution of photochemically divergent proteorhodopsins is stratified according to depth. Here, we present evidence that such photochemical diversity was tuned by Darwinian selection. By using a Bayesian method, we identified sites targeted by Darwinian selection and mapped them to three-dimensional models of proteorhodopsins. We suggest that spectral fine-tuning results from the combined effect of amino acids that directly interact with retinal and those that influence the confirmation of the retinal-binding pocket.
Genomic analysis of
Bacteroides fragilis
reveals extensive DNA inversions regulating cell surface adaptation
Authors: Kuwahara Tomomi , Yamashita Atsushi , Hirakawa Hideki , Nakayama Haruyuki , Toh Hidehiro , Okada Natsumi , Kuhara Satoru , Hattori Masahira , Hayashi Tetsuya , Ohnishi Yoshinari
Published: October 2004

Bacteroides
are predominant human colonic commensals, but the principal pathogenic species,
Bacteroides fragilis
(BF), lives closely associated with the mucosal surface, whereas a second major species,
Bacteroides thetaiotaomicron
(BT), concentrates within the colon. We find corresponding differences in their genomes, based on determination of the genome sequence of BF and comparative analysis with BT. Both species have acquired two mechanisms that contribute to their dominance among the colonic microbiota: an exceptional capability to use a wide range of dietary polysaccharides by gene amplification and the capacity to create variable surface antigenicities by multiple DNA inversion systems. However, the gene amplification for polysaccharide assimilation is more developed in BT, in keeping with its internal localization. In contrast, external antigenic structures can be changed more systematically in BF. Thereby, at the mucosal surface, where microbes encounter continuous attack by host defenses, BF evasion of the immune system is favored, and its colonization and infectious potential are increased.
Robust
in vivo
gene transfer into adult mammalian neural stem cells by lentiviral vectors
Authors: Consiglio Antonella , Gritti Angela , Dolcetta Diego , Follenzi Antonia , Bordignon Claudio , Gage Fred H. , Vescovi Angelo Luigi , Naldini Luigi
Published: October 2004

Stable genetic modification of adult stem cells is fundamental for both developmental studies and therapeutic purposes. Using
in vivo
marking studies, we showed that injection of lentiviral vectors (LVs) into the subventricular zone of the adult mouse brain enables efficient gene transfer into long-term self-renewing neural precursors and steady, robust vector expression in their neuronal progeny throughout the subventricular zone and its rostral extension, up to the olfactory bulb. By clonal and population analysis in culture, we proved that
in vivo
-marked neural precursors display self-renewal and multipotency, two essential characteristics of neural stem cells (NSCs). Thus, LVs efficiently target long-term repopulating adult NSCs, and the effect of the initial transduction is amplified by the continuous generation of NSC-derived, transduced progeny. LVs may thus allow novel studies on NSCs' physiology
in vivo
, and introduction of therapeutic genes into NSCs may allow the development of novel approaches for untreatable CNS diseases.
Broadband relaxation-optimized polarization transfer in magnetic resonance
Authors: Khaneja Navin , Li Jr-Shin , Kehlet Cindie , Luy Burkhard , Glaser Steffen J.
Published: October 2004

Many applications of magnetic resonance are limited by rapid loss of spin coherence caused by large transverse relaxation rates. In NMR of large proteins, increased relaxation losses lead to poor sensitivity of experiments and increased measurement time. In this article, we develop broadband relaxation-optimized pulse sequences that approach fundamental limits of coherence transfer efficiency in the presence of very general relaxation mechanisms that include cross-correlated relaxation. These broadband transfer schemes use techniques of chemical shift refocusing (specific trajectory adapted refocusing echoes) that are tailored to specific trajectories of coupled spin evolution. We present simulations and experimental data indicating significant enhancement in the sensitivity of multidimensional NMR experiments of large molecules through these methods.
Specific antigen vaccination to treat autoimmune disease
Authors: McDevitt Hugh
Published: October 2004

Specific antigen vaccination by administration of the target antigen in aqueous solution has resulted in significant decreases of disease severity in animal models of experimental allergic encephalomyelitis, type I diabetes, and several forms of antigen-induced arthritis, even if administered after the initiation of symptoms. However, in experimental autoimmune encephalomyelitis (EAE) and type I diabetes in nonobese diabetic (NOD) mice, repeated administration of peptide fragments of target antigens in incomplete Freund's adjuvant has resulted in severe anaphylactic reactions. Although these methods of administration are known to potentiate CD4 T helper 2 (Th2) responses, which is the goal of specific antigen vaccination, the risk of anaphylaxis raises a red flag concerning use of this therapy for diseases such as type I diabetes, where the survival time after onset is quite long. It is clear that specific antigen vaccination is effective in preventing several animal models of autoimmune disease, and in treating these diseases once the symptoms are overt. However, the risks of this therapy require serious consideration of alternative methods for down-regulation of the autoimmune process.
Synaptic homeostasis and input selectivity follow from a calcium-dependent plasticity model
Authors: Yeung Luk Chong , Shouval Harel Z. , Blais Brian S. , Cooper Leon N.
Published: October 2004

Modifications in the strengths of synapses are thought to underlie memory, learning, and development of cortical circuits. Many cellular mechanisms of synaptic plasticity have been investigated in which differential elevations of postsynaptic calcium concentrations play a key role in determining the direction and magnitude of synaptic changes. We have previously described a model of plasticity that uses calcium currents mediated by
N
-methyl-
d
-aspartate receptors as the associative signal for Hebbian learning. However, this model is not completely stable. Here, we propose a mechanism of stabilization through homeostatic regulation of intracellular calcium levels. With this model, synapses are stable and exhibit properties such as those observed in metaplasticity and synaptic scaling. In addition, the model displays synaptic competition, allowing structures to emerge in the synaptic space that reflect the statistical properties of the inputs. Therefore, the combination of a fast calcium-dependent learning and a slow stabilization mechanism can account for both the formation of selective receptive fields and the maintenance of neural circuits in a state of equilibrium.
Distinct endothelial phenotypes evoked by arterial waveforms derived from atherosclerosis-susceptible and -resistant regions of human vasculature
Authors: Dai Guohao , Kaazempur-Mofrad Mohammad R. , Natarajan Sripriya , Zhang Yuzhi , Vaughn Saran , Blackman Brett R. , Kamm Roger D. , García-Cardeña Guillermo , Gimbrone Michael A.
Published: October 2004

Atherosclerotic lesion localization to regions of disturbed flow within certain arterial geometries, in humans and experimental animals, suggests an important role for local hemodynamic forces in atherogenesis. To explore how endothelial cells (EC) acquire functional/dysfunctional phenotypes in response to vascular region-specific flow patterns, we have used anin vitrodynamic flow system to accurately reproduce arterial shear stress waveforms on cultured human EC and have examined the effects on EC gene expression by using a high-throughput transcriptional profiling approach. The flow patterns in the carotid artery bifurcations of several normal human subjects were characterized by using 3D flow analysis based on actual vascular geometries and blood flow profiles. Two prototypic arterial waveforms, “athero-prone” and “athero-protective,” were defined as representative of the wall shear stresses in two distinct regions of the carotid artery (carotid sinus and distal internal carotid artery) that are typically “susceptible” or “resistant,” respectively, to atherosclerotic lesion development. These two waveforms were applied to cultured EC, and cDNA microarrays were used to analyze the differential patterns of EC gene expression. In addition, the differential effects of athero-prone vs. athero-protective waveforms were further characterized on several parameters of EC structure and function, including actin cytoskeletal organization, expression and localization of junctional proteins, activation of the NF-κB transcriptional pathway, and expression of proinflammatory cytokines and adhesion molecules. These global gene expression patterns and functional data reveal a distinct phenotypic modulation in response to the wall shear stresses present in atherosclerosis-susceptible vs. atherosclerosis-resistant human arterial geometries.
A comparative analysis of transcribed genes in the mouse hypothalamus and neocortex reveals chromosomal clustering
Authors: Boon Wee-Ming , Beissbarth Tim , Hyde Lavinia , Smyth Gordon , Gunnersen Jenny , Denton Derek A. , Scott Hamish , Tan Seong-Seng
Published: October 2004

The hypothalamus and neocortex are subdivisions of the mammalian forebrain, and yet, they have vastly different evolutionary histories, cytoarchitecture, and biological functions. In an attempt to define these attributes in terms of their genetic activity, we have compared their genetic repertoires by using the Serial Analysis of Gene Expression database. From a comparison of 78,784 hypothalamus tags with 125,296 neocortical tags, we demonstrate that each structure possesses a different transcriptional profile in terms of gene ontological characteristics and expression levels. Despite its more recent evolutionary history, the neocortex has a more complex pattern of gene activity. Gene identities and levels of gene expression were mapped to their chromosomal positions by usingin silicodefinition of GC-rich and GC-poor genome bands. This analysis shows contrasting views of gene activity on a genome scale that is unique to each brain substructure. We show that genes that are more highly expressed in one tissue tend to be clustered together on a chromosomal scale, further defining the genetic identity of either the hypothalamus or neocortex. We propose that physical proximity of coregulated genes may facilitate transcriptional access to the genetic substrates of evolutionary selection that ultimately shape the functional subdivisions of the mammalian brain.
Small interfering RNA targeting
Fas
protects mice against renal ischemia-reperfusion injury
Authors: Hamar Péter , Song Erwei , Kökény Gabor , Chen Allen , Ouyang Nengtai , Lieberman Judy
Published: October 2004

Fas-mediated apoptosis has been suggested to contribute to tubular cell death after renal ischemia-reperfusion injury. Here we investigate whether small interfering RNA (siRNA) duplexes targeting
Fas
protect mice from acute renal failure after clamping of the renal artery. Renal ischemia-reperfusion injury was induced by clamping the renal vein and artery for 15 or 35 min. Mice were treated before or after ischemia with siRNA targeting
Fas
or a control gene, administered by hydrodynamic injection, low-volume renal vein injection, or both. Treated mice were evaluated for renal Fas protein and mRNA expression, tissue histopathology, and apoptosis by terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling (TUNEL) staining. Blood urea nitrogen and survival were monitored in mice in which the contralateral kidney had been removed. A single hydrodynamic injection of
Fas
siRNA reduced
Fas
mRNA and protein expression in the kidney 4-fold. Kidneys from mice that received
Fas
siRNA two days earlier had substantially less renal tubular apoptosis by TUNEL staining and less tubular atrophy and hyaline damage. Whereas 90% of mice pretreated with saline or
GFP
siRNA died, only 20% of
Fas
-siRNA-pretreated animals died. The same survival advantage was provided by a single low-volume
Fas
siRNA injection into the renal vein. Moreover, postischemic injection through the renal vein protected 38% of mice from death. This study confirms the importance of Fas-mediated apoptosis in renal ischemia-reperfusion injury. Silencing
Fas
by systemic or local catheterization holds therapeutic promise to limit ischemia-reperfusion injury.
Sphingosine-dependent apoptosis: A unified concept based on multiple mechanisms operating in concert
Authors: Suzuki Erika , Handa Kazuko , Toledo Marcos S. , Hakomori Senitiroh
Published: October 2004

Exposure of 3T3/A31 cells to serum-free medium, one type of apoptotic stimulus, causes a rapid increase in the sphingosine (Sph) level, which initiates a series of processes: (
i
) activation of caspase 3 through an enhanced “cascade” of caspases, (
ii
) release of the C-terminal-half kinase domain of PKCδ (PKCδ KD) by caspase 3, and (
iii
) activation of Sph-dependent kinase 1 (SDK1), which was previously identified as PKCδ KD. The activation of caspase 3 and release of PKCδ KD are inhibited strongly by the incubation of cells with the ceramidase inhibitor
d
-erythro-2-tetradecanoylamino-1-phenyl-1-propanol and, to a much lesser extent, by
l
-cycloserine, an inhibitor of
de novo
ceramide synthesis. Exogenous addition of Sph or
N
,
N
-dimethyl-Sph to U937 cells causes caspase 3 activation and release of PKCδ KD (SDK1), leading to apoptosis. The Sph-induced apoptotic process associated with activation of caspase 3 and release of PKCδ KD (SDK1) may promote the proapoptotic effect of BAD or BAX through an increase of phosphorylated 14-3-3. In addition, Sph induces apoptosis through a separate process: the blocking of “survival signal” through the Akt kinase pathway induced by α3β1-mediated cell adhesion to laminin 10/11 in extracellular matrix. We hereby propose a unified concept of Sph-dependent apoptosis based on these multiple mechanisms operating in concert.
Domesticating Urban Theory? US Concepts, British Cities and the Limits of Cross-national Applications
Authors: Wood Andrew M.
Published: October 2004

The efficacy of the urban regime and growth machine concepts beyond the US remains a matter of considerable debate. Some argue that these frameworks retain considerable value so long as they are 'properly' applied and that recent concerns about the limits to these frameworks result from no more than their 'misapplication'. I critically examine this argument through a review of recent work on the mobilisation of business interests in British cities. The central claim is that, even when focused on the 'right' issues and questions, US frameworks quickly exhaust their explanatory capacity. In the context of a widening diversity of alternative approaches, I suggest that it is time to move squarely beyond growth coalition and regime accounts. The paper makes a number of suggestions for ways in which this new phase of theory building might proceed.
Network Accessibility and the Spatial Distribution of Economic Activity in Eastern Asia
Authors: Paez Antonio
Published: October 2004

The continued integration of international economies is an unfolding process that has accelerated in recent years and that is believed to have the potential to impact on the structure of the spatial economy. The process is of interest from the viewpoint of the transport scholar, because a relevant question is whether, and if so to what extent, the economic changes implied by integration can be guided and influenced by transport infrastructure and services. A number of studies have been conducted, in particular in a European setting, that examine the potential links between accessibility and economic activity. The objective of this paper is to analyse the relationship between intermodal network accessibility and the spatial distribution of economic activities in an east Asian setting. To this end, a multivariate framework based on the use of spatial statistical models is proposed that furthers the methodological possibilities of accessibility analysis. The empirical findings suggest that, once contextual factors are considered, the influence of accessibility as an explanatory factor of the spatial distribution of economic activity in the region becomes very much diminished.
Migration and Urbanisation in Francophone West Africa: An Overview of the Recent Empirical Evidence
Authors: Beauchemin Cris , Bocquier Philippe
Published: October 2004

How does migration contribute to the urbanisation process in Africa? Migrants have traditionally been viewed as responsible for excessive urban growth, for the uncontrolled expansion of urban areas and for urban surplus labour. In light of recent research, this article proposes to re-examine these views in Francophone west Africa. The first part of the article presents the context of urbanisation in this region, the theoretical framework and the recent surveys on which most of the analyses are based. Next, adopting a demographic perspective, the paper shows that migration in fact contributes moderately to urban growth and that new trends in urban to rural migration flows are emerging. The focus then shifts to examine how migrants influence the shape of cities. The final section of this article re-examines the role of migrants in the urban economy.
IFDR: An Efficient Iterative Optimization Algorithm for Standard Cell Placement
Authors: Cheng Feng , Mao Junfa
Published: October 2004

In the automatic placement of integrated circuits, the force directed relaxation (FDR) method [Goto, S. (1981). An efficient algorithm for the two‐dimensional placement problem in electrical circuit layout. IEEE Trans. on Circuits and Systems,
CAS‐28(1), 12‐18] is a good iterative optimization algorithm. In this article, an improved force
directed relaxation (IFDR) method for standard cell placement is presented, which provides a more flexible and efficient cell location adjustment scheme and a more extensive searching scale for better iterative placement optimization than the FDR method. A new heuristic algorithm based on local optimization is combined with the IFDR method to improve the placement. Experiments on the Microelectronics Center of North Carolina (MCNC) standard cell benchmarks [http://www.cbl.ncsu.edu/pub/Benchmark_ dirs/Layout Synth92/] have been
done, and the results show that total wire length is reduced up to 25% and by an average of 16% in comparison with that from the placement algorithm of TimberWolf7.0.
The E and Z isomers of 3-(benzoxazol-2-yl)prop-2-enoic acid
Authors: Trujillo-Ferrara Jose G. , Padilla-Martínez Itzia I. , Martínez-Martínez Francisco J. , Höpfl Herbert , Farfan-García Norberto , García-Báez Efrén V.
Published: October 2004

The carboxylic acid group and the double bond are coplanar in (E)-3-(benzoxazol-2-yl)prop-2-enoic acid, C10H7NO3, whereas in isomeric (Z)-3-(benzoxazol-2-yl)prop-2-enoic acid, also C10H7NO3, they are almost orthogonal. In both isomers, a strong O—H...N hydrogen bond, with the carboxylic acid group as a donor and the pyridine-like N atom as an acceptor, and weak C—H...O interactions contribute to the observed supramolecular structures, which are completed by π–π stacking interactions between oxazole and benzenoid rings.
3,3-Bis(2-methoxyphenyl)-3H-benzo[f]chromene
Authors: Huang Hua-Ming , Ding Ying , Chen Pei-Li , Meng Ji-Ben
Published: October 2004

The substituent methoxy group at the phenyl ortho position in the title compound, C27H22O3, has an insignificant effect on the length of the Csp
3—O bond and on the non-planarity of the pyran ring. The cause of the changes in the photochemical properties is discussed.
The one-dimensional structure of Cu(dmen)2Pd(CN)4 (dmen is N,N-dimethylethylenediamine)
Authors: Kuchár Juraj , Černák Juraj , Abboud Khalil A.
Published: October 2004

The title compound, catena-poly[[μ-cyano-1:2κ2
C:N-dicyano-1κ2
C-bis(N,N-dimethylethylenediamine-2κ2
N,N′)palladium(II)copper(II)]-μ-cyano-1:2′κ2
C:N], [CuPd(CN)4(C4H12N2)2]
n
, consists of infinite quasi-linear chains with all metal positions on centers of symmetry. The paramagnetic [Cu(dmen)2]2+ cations are linked by diamagnetic [Pd(CN)4]2− anions via bridging cyano groups, which occupy trans positions in both cation and anion, giving rise to 2,2-TT-type chains. The coordination polyhedron of the paramagnetic Cu atom is an octahedron exhibiting typical elongation due to the Jahn–Teller effect, with two longer Cu—N([triple-bond]C) bonds in the axial positions [2.5528 (13) Å] and four shorter Cu—Ndmen bonds (dmen is N,N-dimethylethylenediamine) in the equatorial plane [1.9926 (11) and 2.1149 (12) Å]. The Cu—N[triple-bond]C angle is 138.03 (12)°. Neighboring chains form weak N—H...NC hydrogen bonds.
Methyl 4-(2-chloro-5-nitrophenyl)-2,7,7-trimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carboxylate
Authors: Linden Anthony , Şafak Cihat , Aydın Fırat
Published: October 2004

The title compound, C20H21ClN2O5, has potential calcium modulatory properties. The 1,4-dihydropyridine ring has the usual shallow boat conformation. The 2-chloro-5-nitrophenyl ring is oriented such that the chloro substituent is in a synperiplanar orientation with respect to the 1,4-dihydropyridine ring plane, while the nitro substituent sits over the 1,4-dihydropyridine ring. The cyclohexenone ring has a conformation that is approximately half-way between that of an envelope and that of a half-chair. The molecules are linked into chains by intermolecular N—H...O hydrogen bonds.
Comparative study of two chemically isostructural polymers: [Cu2(VO2)(HPO4)2(NO3)(bpy)2]·2H2O/H3PO4 (bpy is 2,2′-bipyridine)
Authors: Moreno Yanko , Vega Andrés , Spodine Evgenia , Ushak Esvetlana , Baggio Ricardo
Published: October 2004

The title compounds, poly[bis(2,2′-bipyridine)bis(μ3-hydrogen phosphato)nitratodi-μ2-oxo-dicopper(II)vanadium dihydrate], [Cu2(VO2)(HPO4)2(NO3)(C10H8N2)2]·2H2O, (I), and poly[bis(2,2′-bipyridine)bis(μ3-hydrogen phosphato)nitratodi-μ2-oxo-dicopper(II)vanadium phosphoric acid solvate], [Cu2(VO2)(HPO4)2(NO3)(C10H8N2)2]·H3PO4, (II), were obtained by similar hydrothermal methods but under different crystallization conditions. The trinuclear entity which serves as the basic unit in both structures presents two independent CuII ions immersed in similar square-pyramidal N2O3 environments plus an octahedral VO6 core and is organized into a one-dimensional polymer, which is essentially identical in the two structures. The compounds are stabilized by different solvates, viz. two crystallization water molecules in (I) and a phosphoric acid molecule in (II), which provide the main structural differences through the diversity of interchain interactions in which they serve as bridges.
The twinned crystal structure of rac-(R,R)-N,N′-oxalyldivalinol
Authors: Štefanić Zoran , Meden Anton , Lutz Martin , Schreurs Antoine M. M. , Kojić-Prodić Biserka
Published: October 2004

The title compound, rac-(R,R)-N,N′-bis(1-hydroxy-3-methyl-2-butyl)oxalamide, C12H24N2O4, crystallizes as a non-merohedral twin in the triclinic space group P\overline1. The twin is generated by a twofold rotation about c*. The terminal hydroxy groups of molecules related by an inversion center form hydrogen-bonded dimers. This hydrogen-bonding pattern is further extended into a one-dimensional chain by N—H...O hydrogen bonds.
Poly[diaqua-μ4-oxalato-di-μ6-phosphato-tetrazinc]
Authors: Zhong You-Ju , Sun Yan-Qiong , Yang Guo-Yu
Published: October 2004

The structure of the title compound, [Zn4(C2O4)(PO4)2(H2O)2]
n
, which was synthesized under hydrothermal conditions, consists of zinc phosphate layers joined by bridging oxalate ligands to generate a three-dimensional framework. An extended zinc phosphate layer lies parallel to the ab plane and within this layer there are helical chains, composed of ZnO6 octahedra and ZnO5 square pyramids, that run parallel to the b axis and coincide with the 21 screw element. The oxalate groups sit on crystallographic inversion centers.
Polarized molecular–electronic structures and supramolecular aggregation in 1-(6-amino-1,3-benzodioxol-5-yl)-3-arylprop-2-en-1-ones
Authors: Low John N. , Cobo Justo , Nogueras Manuel , Cuervo Paola , Abonia Rodrigo , Glidewell Christopher
Published: October 2004

Molecules of 1-(6-amino-1,3-benzodioxol-5-yl)-3-(4-methylphenyl)prop-2-en-1-one, C17H15NO3, (I), 1-(6-amino-1,3-benzodioxol-5-yl)-3-(4-methoxyphenyl)prop-2-en-1-one, C17H15NO4, (II), and 1-(6-amino-1,3-benzodioxol-5-yl)-3-[4-(trifluoromethyl)phenyl]prop-2-en-1-one, C17H12F3NO3, (III), all contain an intramolecular N—H...O hydrogen bond and all exhibit polarized molecular–electronic structures. The molecules of (I) are linked into simple sheets, generated by translation, by means of one N—H...O and one C—H...π(arene) hydrogen bond. Compound (II) crystallizes as two concomitant polymorphs, viz. (IIa), with Z′ = 1 in P21/c, and (IIb), with Z′ = 2 in P\overline 1. In (IIa), intra- and intermolecular N—H...O hydrogen bonds generate a helical chain of rings, and these chains are linked into sheets by simple helical chains built from a C—H...π(arene) hydrogen bond, while in (IIb), the molecules are linked into simple chains by a C—H...O hydrogen bond. In (III), where Z′ = 2, each type of molecule forms a simple N—H...O hydrogen-bonded chain generated by translation and the two types of chain are linked by a single π–π stacking interaction.
Bis(1,10-phenanthroline-κ2
N,N′)(squarato-κO)copper(II) trihydrate
Authors: Bulut Ahmet , Uçar İbrahim , Yeşilel Okan Zafer , İçbudak Hasan , Ölmez Halis , Büyükgüngör Orhan
Published: October 2004

The title mononuclear [Cu(sq)(phen)2]·3H2O complex [sq is squarate (C4O4) and phen is 1,10-phenanthroline (C12H8N2)] has been synthesized and the structure consists of a neutral mononuclear [Cu(sq)(phen)2] unit and three solvate water molecules. The CuII ion has distorted square-pyramidal coordination geometry, comprised of one carboxylate O atom from a monodentate squarate ligand and four N atoms from two chelating phen ligands. An extensive three-dimensional network of OW—H...O/OW hydrogen bonds, face-to-face π–π interactions between the 1,10-phenanthroline aromatic rings and a weak π–ring interaction are responsible for crystal stabilization.
catena-Poly[[bis(quinoxaline-κN)cobalt(II)]-di-μ-dicyanamido-κ2
N
1:N
5] and catena-poly[[bis(quinoxaline-κN)copper(II)]-di-μ-dicyanamido-κ2
N
1:N
5]
Authors: Luo Jun , Liu Bao-Shu , Zhou Xi-Geng , Weng Lin-Hong , Li Yan-Rong , Wu Hui-Xia
Published: October 2004

Two new complexes, [Co(C2N3)2(C8H6N2)2], (I), and [Cu(C2N3)2(C8H6N2)2], (II), are reported. They are essentially isomorphous. Complex (I) displays distorted octahedral geometry, with the Co atom coordinated by four dicyanamide nitrile N atoms [Co—N = 2.098 (3) and 2.104 (3) Å] in the basal plane, along with two monodentate quinoxaline N atoms [Co—N = 2.257 (2) Å] in the apical positions. In complex (II), the Cu atom is surrounded by four dicyanamide nitrile N atoms [Cu—N = 2.003 (3) and 2.005 (3) Å] in the equatorial plane and two monodentate quinoxaline N atoms [Cu—N = 2.479 (3) Å] in the axial sites, to form a distorted tetragonal–bipyramidal geometry. The metal atoms reside on twofold axes of rotation. Neighbouring metal atoms are connected via double dicyanamide bridges to form one-dimensional infinite chains. Adjacent chains are then linked by π–π stacking interactions of the quinoxaline molecules, resulting in the formation of a three-dimensional structure.
catena-Poly[[silver(I)-μ-ethane-1,2-diamine-κ2
N:N′] trifluoromethanesulfonate]
Authors: You Zhong-Lu , Zhu Hai-Liang
Published: October 2004

The title complex, {[Ag(C2H8N2)](CF3SO3)}
n
, is a mononuclear silver(I) compound. The AgI atom lies on a mirror plane and is bicoordinated in a linear configuration by two N atoms from two ethane-1,2-diamine ligands, giving zigzag polymeric chains with an [—Ag—N—C—C—N—]
n
backbone running along the b axis. These chains are interconnected by N—H...O hydrogen bonds involving the trifluoromethanesulfonate anions (which also lie on mirror planes), forming a three-dimensional network.
Hydrogen-bonding patterns in cis-4-ammoniocyclohexanecarboxylate hemihydrate
Authors: Ávila Edward E. , Mora Asiloé J. , Delgado Gerzon E. , Ramírez Belkis M. , Bahsas Alí , Koteich Sonia
Published: October 2004

In the title compound, C7H13NO2·0.5H2O, cis-4-aminocyclohexanecarboxylic acid exists as a zwitterion and co-crystallizes with water molecules in a 2:1 amino acid–water ratio. The cyclohexane ring adopts a chair conformation, with the carboxylate and ammonium groups in axial and equatorial positions, respectively. The basic motif in the crystal structure is a sandwich structure, formed by two amino acid units linked by head-to-tail hydrogen bonds. Hydrogen bonds of the type N+—H...O—C—O− link these motifs, forming helicoidally extended chains running along the c axis. The water molecule lies on a twofold axis and interacts with the chains by means of O—H...O hydrogen bonds.
Poly[[diaquacobalt(II)]-di-μ-4-cyanobenzoato-κ4
O:O′]
Authors: He Hong-Yin , Chen Jie , Wang Xiao-Hua , Zhu Long-Guan
Published: October 2004

The title compound, [Co(C8H4NO2)2(H2O)2]
n
, which was obtained by the reaction of CoCl2·6H2O with 4-cyanobenzoic acid, is the first two-dimensional 4-cyanobenzoate cobalt(II) polymer. The Co atom lies on a centre of symmetry and its coordination polyhedron is a slightly distorted octahedron, defined by two water and four carboxylate O atoms. The 4-cyanobenzoate (cba) anion is bridging in a syn-skew coordination mode, which ensures a two-dimensional architecture with the building block Co4(cba)4.
Metabolism of Desipramine in Japanese Psychiatric Patients: The Impact of CYP2D6 Genotype on the Hydroxylation of Desipramine
Authors: Shimoda Kazutaka , Morita Sachiyo , Hirokane Genta , Yokono Aya , Someya Toshiyuki , Takahashi Saburo
Published: October 2004

We investigated the impact of the genotype of CYP2D6 on the hydroxylation of desipramine in eighteen patients who were administered desipramine hydrochloride per os. Significantly higher plasma concentration of desipramine/daily dose of desipramine/body weight was observed in the subjects with two mutated alleles than in the subjects with either no mutated alleles or one mutated allele (two mutated alleles versus no mutated alleles=530.4±215.2 versus 118.1±63.9 ng/ml/mg/kg, t=5.68, P<0.001; two mutated alleles versus one mutated allele=530.4±215.2 versus 176.2±62.3 ng/ml/mg/kg, P<0.001; One‐way analysis of variance followed by Bonferroni's multiple comparison test, respectively). Significantly higher ratio of desipramine/2‐hydroxy‐desipramine was observed in the subjects with two mutated alleles compared to subjects with no mutated alleles or the subjects with one mutated allele (two mutated alleles versus one mutated allele=4.39±0.36 versus 2.00±0.64, t=5.12, P<0.001; two mutated alleles versus no mutated alleles=4.39±0.36 versus 2.02±0.59, t=4.42, P<0.01). The genotyping of CYP2D6 only grossly predicts the steady state concentration of desipramine, mainly predicts the risk of getting very high plasma levels. Within each genotype there is marked interindividual variability.
Inhibitory Effects of Silibinin on Cytochrome P‐450 Enzymes in Human Liver Microsomes
Authors: Beckmann‐Knopp Svane , Rietbrock Stephan , Weyhenmeyer Roland , Böcker Ronald H. , Beckurts K. Tobias , Lang Werner , Hunz Miriam , Fuhr Uwe
Published: October 2004

Silibinin, the main constituent of silymarin, a flavonoid drug from silybum marianum used in liver disease, was tested for inhibition of human cytochrome P‐450 enzymes. Metabolic activities were determined in liver microsomes from two donors using selective substrates. With each substrate, incubations were carried out with and without silibinin (concentrations 3.7–300 μM) at 37° in 0.1 M KH2PO4 buffer containing up to 3% DMSO. Metabolite concentrations were determined by HPLC or direct spectroscopy. First, silibinin IC50 values were determined for each substrate at respective KM concentrations. Silibinin had little effect (IC50>200 μM) on the metabolism of erythromycin (CYP3A4), chlorzoxazone (CYP2E1), S(+)‐mephenytoin (CYP2C19), caffeine (CYP1A2) or coumarin (CYP2A6). A moderate effect was observed for high affinity dextromethorphan metabolism (CYP2D6) in one of the microsomes samples tested only (IC50=173 μM). Clear inhibition was found for denitronifedipine oxidation (CYP3A4; IC50=29 μM and 46 μM) and S(−)‐warfarin 7‐hydroxylation (CYP2C9; IC50=43 μM and 45 μM). When additional substrate concentrations were tested to assess enzyme kinetics, silibinin was a potent competitive inhibitor of dextromethorphan metabolism at the low affinity site, which is not CYP2D6 (Ki,c=2.3 μM and 2.4 μM). Inhibition was competitive for S(−)‐warfarin 7‐hydroxylation (Ki,c=18 μM and 19 μM) and mainly non‐competitive for denitronifedipine oxidation (Ki,n=9 μM and 12 μM). With therapeutic silibinin peak plasma concentrations of 0.6 μM and biliary concentrations up to 200 μM, metabolic interactions with xenobiotics metabolised by CYP3A4 or CYP2C9 cannot be excluded.
DNA Adduct Levels and Intestinal Lesions in Congenic Rapid and Slow Acetylator Syrian Hamsters Administered the Food Mutagens 2‐Amino‐1‐methyl‐6‐phenylimidazo[4,5‐b]pyridine (PhIP) or 2‐Amino‐3‐methylimidazo[4,5‐f]quinoline (IQ
Authors: Steffensen Inger‐Lise , Fretland Adrian J. , Paulsen Jan Erik , Feng Yi , Eide Tor Jacob , Devanaboyina Udaya‐Sankar , Hein David W. , Alexander Jan
Published: October 2004

Epidemiological studies indicate that rapid acetylators with a high intake of well‐done red meat have an increased risk of colorectal cancer. Arylamine N‐acetyltransferase enzymes (E.C. 2.3.1.5) activate carcinogenic heterocyclic amines found in the crust of fried meat via O‐acetylation of their N‐hydroxylamines to reactive intermediates that bind covalently to DNA and produce mutations. Syrian hamsters as well as humans express two N‐acetyltransferase isozymes (NAT1 and NAT2) which differ in substrate specificity and genetic control. Nucleic acid substitutions in the NAT2 gene segregate individuals into rapid, intermediate and slow acetylator phenotypes. In the present paper, we examined the role of the polymorphic NAT2 acetylator genotype in carcinogenesis induced by the food mutagens 2‐amino‐1‐methyl‐6‐phenylimidazo[4,5‐b]pyridine (PhIP) or 2‐amino‐3‐methylimidazo[4,5‐f]quinoline (IQ) by comparing Syrian hamster lines congenic at the NAT2 locus. No differences were found between rapid and slow acetylator congenic hamsters in levels of intestinal PhIP‐DNA adducts. In contrast to previous studies in rats, no carcinogen‐related induction of the preneoplastic lesions aberrant crypt foci or tumors was found in the intestines of rapid and slow acetylator congenic Syrian hamsters administered PhIP or IQ.
Human Isolated Coronary Artery Contraction to Sumatriptan Characterised by the Selective 5‐HT1B/1D Receptor Antagonist GR55562
Authors: MaassenVanDenBrink Antoinette , Reekers Marije , Bax Willem A. , Saxena Pramod R.
Published: October 2004

The antimigraine drug, sumatriptan, contracts the human coronary artery both in vivo and in vitro. Because sumatriptan has been associated with cardiac side effects, it is important to characterise the receptor involved in sumatriptan‐induced coronary artery contraction. Using the agonists sumatriptan and 5‐carboxamidotryptamine and the selective 5‐HT1B/1D receptor antagonist GR55562, we have investigated the involvement of 5‐HT1B/1D receptors in the contraction of the human isolated coronary artery. Contractions to sumatriptan (pEC50: 6.1±0.2, maximal effect: 21±4% of 100 mM K+‐induced contraction) were competitively antagonised by GR55562. The pA2 of GR55562 (7.40±0.16) was in accord with its reported affinity at the human 5‐HT1B receptor. Since the contractions to 5‐carboxamidotryptamine did not reach a maximum with the highest concentration used (10 μM), pEC50 values could not be calculated for Schild analysis. However, using the pEC10%K+ values (negative logarithm of the concentration needed to induce 10% of the contraction to 100 mM K+), GR55562 proved a less potent antagonist against 5‐carboxamidotryptamine than against sumatriptan. These results show that sumatriptan contracts the human isolated coronary artery via 5‐HT1B/1D receptors, most probably the 5‐HT1B subtype. 5‐Carboxamidotryptamine may contract the human isolated coronary artery, at least partly, via a novel yet to be characterised, receptor.
Preserved granulocyte formation and function, as well as bone marrow innervation, in subjects with complete spinal cord injury
Authors: Iversen Per Ole , Nicolaysen Anne , Hjeltnes Nils , Njå Arild , Benestad Haakon B.
Published: October 2004

Patients with a spinal cord injury are at risk of infections and is partly attributed to immobilization. Their lymphocyte‐mediated immunity is impaired and the growth of blood progenitor cells is reduced. An adequate immune response depends on granulocytes being mobilized rapidly and activated properly, at the inflammatory site. Possibly this requires a coordinated interaction between the autonomous nervous system and cells within the haematopoietic bone marrow. Granulocyte function in the spinal cord injured has not been evaluated. Although there is evidence that the bone marrow in rodents is innervated, it is uncertain whether human bone marrow is similarly affected. Microscopy and immunolabelling followed by flow cytometry, showed that blood and bone marrow counts of leucocyte subsets were similar in paraplegic, tetraplegic and control subjects (P > 0·05). Neutrophilic migration and oxygen consumption, as well as eosinophil activation, assayed as release of eosinophilic cationic protein or CD69 expression, were not altered after spinal cord injury (P > 0·05). Cryostat sections of human bone marrow biopsies stained positive with glyoxylic acid, indicating the presence of catecholamine‐containing nerves in both the patients and the controls. We conclude that terminal differentiation and formation of granulocytes, as well as their functional capacity, do not depend appreciably on supraspinal nervous regulation.
A global relationship between the heterotrophic and autotrophic components of soil respiration?
Authors: Bond‐Lamberty Ben , Wang Chuankuan , Gower Stith T.
Published: October 2004

Soil surface CO2 flux (RS) is overwhelmingly the product of respiration by roots (autotrophic respiration, RA) and soil organisms (heterotrophic respiration, RH). Many studies have attempted to partition RS into these two components, with highly variable results. This study analyzes published data encompassing 54 forest sites and shows that RA and RH are each strongly (R2>0.8) correlated to annual RS across a wide range of forest ecosystems. Monte Carlo simulation showed that these correlations were significantly stronger than any correlation introduced as an artefact of measurement method. Biome type, measurement method, mean annual temperature, soil drainage, and leaf habit were not significant. For sites with available data, there was a significant (R2=0.56) correlation between total detritus input and RH, while RA was unrelated to net primary production. We discuss why RA and RH might be related to each other on large scales, as both ultimately depend on forest carbon balance and photosynthate supply. Limited data suggest that these or similar relationships have broad applicability in other ecosystem types. Site‐specific measurements are always more desirable than the application of inferred broad relationships, but belowground measurements are difficult and expensive, while measuring RS is straightforward and commonly done. Thus the relationships presented here provide a useful method that can help constrain estimates of terrestrial carbon budgets.
Recent climate warming forces contrasting growth responses of white spruce at treeline in Alaska through temperature thresholds
Authors: Wilmking Martin , Juday Glenn P. , Barber Valerie A. , Zald Harold S. J.
Published: October 2004

Northern and high‐latitude alpine treelines are generally thought to be limited by available warmth. Most studies of tree‐growth–climate interaction at treeline as well as climate reconstructions using dendrochronology report positive growth response of treeline trees to warmer temperatures. However, population‐wide responses of treeline trees to climate remain largely unexamined. We systematically sampled 1558 white spruce at 13 treeline sites in the Brooks Range and Alaska Range. Our findings of both positive and negative growth responses to climate warming at treeline challenge the widespread assumption that arctic treeline trees grow better with warming climate. High mean temperatures in July decreased the growth of 40% of white spruce at treeline areas in Alaska, whereas warm springs enhance growth of additional 36% of trees and 24% show no significant correlation with climate. Even though these opposing growth responses are present in all sampled sites, their relative proportion varies between sites and there is no overall clear relationship between growth response and landscape position within a site. Growth increases and decreases appear in our sample above specific temperature index values (temperature thresholds), which occurred more frequently in the late 20th century. Contrary to previous findings, temperature explained more variability in radial growth after 1950. Without accounting for these opposite responses and temperature thresholds, climate reconstructions based on ring width will miscalibrate past climate, and biogeochemical and dynamic vegetation models will overestimate carbon uptake and treeline advance under future warming scenarios.
Habitat loss, resource specialization, and extinction on coral reefs
Authors: Munday Philip L.
Published: October 2004

Coral reefs worldwide are being degraded because of global warming (coral bleaching) and coastal development (sedimentation and eutrophication). Predicting the risk of species extinctions from this type of habitat degradation is one of the most challenging and urgent tasks facing ecologists. Habitat specialists are thought to be more prone to extinction than generalists; however, specialists may be more susceptible to extinction because (1) they are specialistsper se, (2) they are less abundant than generalists, or (3) both. Here, I show that declines in coral abundance lead to corresponding declines in the abundance of coral‐dwelling fishes, but with proportionally greater losses to specialists than generalists. In addition, specialists have smaller initial population sizes than generalists. Consequently, specialists face a dual risk of extinction because their already small populations decline more rapidly than those of generalists. Corresponding with this increased extinction risk, I describe the local extinction of one specialist species and the near‐global extinction of another species. I conclude that habitat specialists will be the first species lost from coral reefs because their small populations suffer the most from human‐induced disturbances.