bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies on the synthesis and thermal properties of copoly(L‐lactic acid/glycolic acid) by direct melt polycondensation
Authors: Lan Ping , Zhang Yaopeng , Gao Qinwei , Shao Huili , Hu Xuechao
Published: March 2004

A two‐step direct copolymerization process of L‐lactic acid (L‐LA)/glycolic acid (GA) was developed. The first step was to produce an oligomer of L‐LA/GA and then the oligomer was polymerized with binary catalyst tin chloride dihydrate/p‐toluenesulfonic acid. In this way, the copoly(L‐LA/GA) (PLGA), without any organic solvent, was synthesized directly. The thermal properties and solubility in chloroform of PLGA were studied by DSC and NMR. The results showed that the melting point of PLGA decreases with increasing mole fraction of GA units in copolymer. In addition, the melting point of polymer also decreased with increasing degree of racemization of polymer. The solubility of PLGA in chloroform decreased with the increase of the average lengths of the glycolic acid units. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2163–2168, 2004
Effect of some service conditions on the electrical resistivity of conductive styrene–butadiene rubber–carbon black composites
Authors: Mohanraj G. T. , Chaki T. K. , Chakraborty A. , Khastgir D.
Published: March 2004

Conductive polymer composites were prepared using vulcanized styrene–butadiene rubber as a matrix and conductive carbon black as a filler. The filler loading was varied from 10 to 60 phr. The volume resistivity was measured against the loading of the carbon black to verify the percolation limit. The electrical conductivity of filled polymer composites is attributed to the formation of some continuous conductive networks in the polymer matrix. These conductive networks involve specific arrangements of conductive elements (carbon black aggregates) so that the electrical paths are formed for free movement of electrons. The effects of temperature and pressure on the volume resistivity of the composites were studied. The volume resistivity of all the composites increased with increase in temperature, and the rate of increase in the resistivity against temperature depended on the loading of carbon black. The change in volume resistivity during the heating and cooling cycle did not follow the same route, leading to the phenomena of electrical hysteresis and electrical set. It was found that the composites with 40 and 60 phr carbon black become more conductive after undergoing the heat treatment. Generally, all the composites showed a positive temperature coefficient of resistivity. The volume resistivity of all the composites decreased with increase in pressure. The relaxation characteristic of the volume resistivity of the composites was studied with respect to time under a constant load. It was found that the volume resistivity of the compressed specimen of the composites decreased exponentially with time. It was observed that initially a faster relaxation process and later a slower relaxation process occurred in these composites. Some mechanical properties of these composites were also measured to confirm the efficacy of these composites for practical applications. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2179–2188, 2004
Atom‐transfer radical polymerization of methyl methacrylate with α,α′‐dichloroxylene/CuCl/N,N,N′,N″,N″‐pentamethyldiethylenetriamine initiation system under microwave irradiation
Authors: Li Xu , Zhu Xiulin , Cheng Zhenping , Xu Wenjian , Chen Gaojian
Published: March 2004

The atom‐transfer radical polymerization (ATRP) of methyl methacrylate (MMA), using α,α′‐dichloroxylene as initiator and CuCl/N,N,N′,N″,N″‐pentamethyldiethylenetriamine as catalyst was successfully carried out under microwave irradiation (MI). The polymerization of MMA under MI showed linear first‐order rate plots, a linear increase of the number‐average molecular weight with conversion, and low polydispersities, which indicated that the ATRP of MMA was controlled. Using the same experimental conditions, the apparent rate constant (k) under MI (k = 7.6 × 10−4 s−1) was higher than that under conventional heating (k = 5.3 × 10−5 s−1). © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2189–2195, 2004
Spectroscopic study of the modification of cellulose with polyethylenimines
Authors: De La Orden M. U. , Matías M. C. , Martínez Urreaga J.
Published: March 2004

The reaction of cellulose with polyethylenimines (PEIs) was studied using diffuse reflectance ultraviolet–visible (UV–vis) spectroscopy, diffuse reflectance FTIR spectroscopy, and standard colorimetry. PEIs were applied from aqueous solutions at the natural pH (pH ∼ 11) and at pH = 6. The obtained materials were exposed to different thermal treatments in air. Celluloses treated at pH = 11 suffer the reversible formation of amine bicarbonate salts. This reaction was not observed in celluloses treated at pH = 6 because of the protonation of the amine groups. In all treated celluloses, the PEI amine groups reacted with cellulose carbonyl groups at moderate temperatures to form Schiff bases, which were responsible for the yellowing of the material. At higher temperatures other oxidation products were detected in the UV–vis and infrared spectra. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2196–2202, 2004
Three‐dimensional architecture and distribution of collagen components in the goat hypophysis
Authors: Nishimura Shotaro , Tabata Shoji , Nakamura Yoshi‐Nori , Okano Kaoru , Iwamoto Hisao
Published: March 2004

The three‐dimensional architecture of collagen fibrils in the connective tissue framework and the distribution of collagen types in the goat hypophysis were studied by the cell maceration method in combination with scanning electron microscopy (SEM) and immunohistochemistry. The pars distalis of the adenohypophysis consisted of many cell clusters. SEM revealed that the wall of cell clusters appeared as various‐sized flat bundles of collagen fibrils woven in a basket‐like configuration. In the pars tuberalis, the aggregates of collagen fibrils were denser and bundles thicker compared to the pars distalis. The density of collagen fibrils changed from the pars tuberalis to pars distalis without a distinct border. The collagen framework in the pars intermedia was mainly divided into three parts, the dorsal region with large hollows, the middle region, and the ventral sheet facing the cavum hypophysis. In the lobus nervosus of the neurohypophysis, the collagen network exhibited a sponge‐like appearance at low magnification. Collagen fibrils of various sizes consisted of loose wavy bundles distributed around the cavities. Immunohistochemistry revealed types I, III, IV, V, and VI collagen throughout the hypophysis. It is concluded that to maintain structural and functional integration, the components of collagen are in different configurations throughout the regions of the goat hypophysis. Anat Rec Part A 277A:275–286, 2004. © 2004 Wiley‐Liss, Inc.
Identification of cDNA clones that encode hLAMP‐1, a component of the particulate matrix associated with cardiac mesenchyme formation
Authors: Sinning Allan R. , McKay Kimberly J.
Published: March 2004

The heart extracellular matrix protein hLAMP‐1 (lectin‐associated matrix protein in the heart) is a component of the particulate matrix that activates the AV endothelium prior to its transformation into mesenchyme within the atrioventricular canal and proximal outflow tract of the heart. The role of hLAMP‐1 in this process has yet to be determined, in part because of the limited amount of material available for analysis. To overcome this liability, a monoclonal antibody to hLAMP‐1 has been used to recognize proteins expressed by cDNA clones. The isolated cDNAs encode an mRNA consistent with previously published immunohistochemical results (Sinning and Hewitt, Acta Anat. 1996;155:219–230; Sinning, J. Cell Biochem. 1997;66:112–122). Expression profiles of these clones by in situ hybridization revealed staining in areas of the heart that expressed hLAMP‐1 by immunocytochemistry. Taken together, these results suggest that these clones, which represent an expressed sequence tag for hLAMP‐1, should provide the basis for isolating a full‐length cDNA of hLAMP‐1, a prerequisite for determining the functional role of this protein in heart development. Anat Rec Part A 277A:307–311, 2004. © 2004 Wiley‐Liss, Inc.
Accessibility and use of information sources among computer scientists and software engineers in Israel: Academy versus industry
Authors: Yitzhaki Moshe , Hammershlag Gloria
Published: March 2004

Hypothesizing that workplace significantly affects information‐seeking patterns, this study compared accessibility and use of information sources among 233 Israeli computer scientists and software engineers, employed in industry and academy, using a mail questionnaire, which yielded a usable reply rate of 33%. The two groups were found to differ significantly in age, education, seniority, and type of research they performed (basic vs. applied). Printed textbooks, professional journals, and oral discussions with colleagues or experts in the organization were common to both groups, topping almost all lists of accessibility and use. For most information sources, however, the two groups differed significantly and consistently. Printed professional journals as well as printed and electronic conference or meeting papers were consistently more accessible and more often used by the academy group, while the industry group reported greater access to and more frequent use of electronic textbooks and trade or promotional literature. In regard to handbooks and standards, in‐house technical reports (printed), government technical reports (Internet), librarians and technical specialists (Internet), and oral discussions with supervisors, no significant differences in accessibility were found, but their use by the industry group was much higher. In both groups, accessibility was only partly related to use, and more so among the academy than the industry group.
The relationships between half‐life (t1/2) and mean residence time (MRT) in the two‐compartment open body model
Authors: Sobol Eyal , Bialer Meir
Published: March 2004

Rationale. In the one‐compartment model following i.v. administration the mean residence time (MRT) of a drug is always greater than its half‐life (t1/2). However, following i.v. administration, drug plasma concentration (C) versus time (t) is best described by a two‐compartment model or a two exponential equation:

C=Ae−αt+Be–βt, where A and B are concentration unit‐coefficients and α and β are exponential coefficients. The relationships between t1/2 and MRT in the two‐compartment model have not been explored and it is not clear whether in this model too MRT is always greater than t1/2.

Methods. In the current paper new equations have been developed that describe the relationships between the terminal t1/2 (or t1/2β) and MRT in the two‐compartment model following administration of i.v. bolus, i.v. infusion (zero order input) and oral administration (first order input).

Results. A critical value (CV) equals to the quotient of (1−ln2) and (1−β/α) (CV=(1−ln2)/(1−β/α)=0.307/(1−β/α)) has been derived and was compared with the fraction (f1) of drug elimination or AUC (AUC‐area under C vs t curve) associated with the first exponential term of the two‐compartment equation (f1=A/α/AUC). Following i.v. bolus, CV ranges between a minimal value of 0.307 (1−ln2) and infinity. As long as f1t1/2 and vice versa, and when f1=CV, then MRT=t1/2. Following i.v. infusion and oral administration the denominator of the CV equation does not change but its numerator increases to (0.307+βT/2) (T‐infusion duration) and (0.307+β/ka) (ka‐absorption rate constant), respectively. Examples of various drugs are provided.

Conclusions. For every drug that after i.v. bolus shows two‐compartment disposition kinetics the following conclusions can be drawn (a) When f1<0.307, then f1t1/2. (b) When β/α>ln2, then CV>1>f1 and thus, MRT>t1/2. (c) When ln2>β/α>(ln4−1), then 1>CV>0.5 and thus, in order for t1/2>MRT, f1 has to be greater than its complementary fraction f2 (f1>f2). (d) When β/α<(ln4−1), it is possible that t1/2>MRT even when f2>f1, as long as f1>CV. (e) As β gets closer to α, CV approaches its maximal value (infinity) and therefore, the chances of MRT>t1/2 are growing. (f) As β becomes smaller compared with α, β/α approaches zero, the denominator approaches unity and consequently, CV gets its minimal value and thus, the chances of t1/2>MRT are growing. (g) Following zero and first order input MRT increases compared with i.v. bolus and so does CV and thus, the chances of MRT>t1/2 are growing. Copyright © 2004 John Wiley & Sons, Ltd.
Fine tuning of growth factor signals depends on fibrillin microfibril networks
Authors: Charbonneau Noe L. , Ono Robert N. , Corson Glen M. , Keene Douglas R. , Sakai Lynn Y.
Published: March 2004

Growth factors, potent regulators of cell differentiation, tissue morphogenesis, tissue homeostasis, and cellular response to injury, reside in the extracellular matrix. Genetic evidence in humans and mice as well as biochemical data implicate fibrillins and LTBPs in the extracellular control of TGFβ and BMP signaling. Fibrillins and LTBPs form tissue‐specific and temporally regulated microfibril networks. In the developing embryo, three fibrillins and four LTBPs contribute molecular heterogeneity to microfibril networks, and provide different templates upon which TGFβ‐related growth factors can be positioned. By accommodating this molecular heterogeneity, microfibril architecture can orchestrate a variety of different signals in very specific tissue locations. Human fibrillinopathies display a broad phenotypic spectrum from tall to short stature, from hypermobile joints to joint contractures and stiffness, and from severe to mild or no cardiovascular manifestations. A spectrum of growth factor dysregulation may be caused by differential effects of mutations in fibrillins on microfibril architecture, thus altering appropriate targeting or positioning of growth factors within microfibril networks. Growth factor dysregulation may help to explain the broad phenotypic spectrum of the fibrillinopathies. Birth Defects Research (Part C) 72:37–50, 2004. © 2004 Wiley‐Liss, Inc.
The role of ECM molecules in activity‐dependent synaptic development and plasticity
Authors: Pavlov Ivan , Lauri Sari , Taira Tomi , Rauvala Heikki
Published: March 2004

Growth and guidance of neurites (axons and dendrites) during development is the prerequisite for the establishment of functional neural networks in the adult organism. In the adult, mechanisms similar to those used during development may regulate plastic changes that underlie important nervous system functions, such as memory and learning. There is now ever‐increasing evidence that extracellular matrix (ECM)‐associated factors are critically involved in the formation of neuronal connections during development, and their plastic changes in the adult. Here, we review the current literature on the role of ECM components in activity‐dependent synaptic development and plasticity, with the major focus on the thrombospondin type I repeat (TSR) domain‐containing proteins. We propose that ECM components may modulate neuronal development and plasticity by: 1) regulating cellular motility and morphology, thus contributing to structural alterations that are associated with the expression of synaptic plasticity, 2) coordinating transsynaptic signaling during plasticity via their cell surface receptors, and 3) defining the physical parameters of the extracellular space, thereby regulating diffusion of soluble signaling molecules in the extracellular space (ECS). Birth Defects Research (Part C) 72:12–24, 2004. © 2004 Wiley‐Liss, Inc.
Matrix loading: Assembly of extracellular matrix collagen fibrils during embryogenesis
Authors: Kadler Karl
Published: March 2004

Nothing in biology stimulates the imagination like the development of a single fertilized egg into a newborn child. Consequently, a major focus of biomedical research is aimed at understanding cell differentiation, proliferation, and specialization during child health and human development. However, the fact that the increase in size and shape of the growing embryo has as much to do with the extracellular matrix (ECM) as with the cells themselves, is largely overlooked. Cells in developing tissues are surrounded by a fiber‐composite ECM that transmits mechanical stimuli, maintains the shape of developing tissues, and functions as a scaffold for cell migration and attachment. The major structural element of the ECM is the collagen fibril. The fibrils, which are indeterminate in length, are arranged in different tissues in exquisite supramolecular architectures, including parallel bundles, orthogonal lamellae, and concentric weaves. This article reviews our current understanding of the synthesis and assembly of collagen fibrils, and discusses challenging questions about how cells assemble an organized ECM during embryogenesis. Birth Defects Research (Part C) 72:1–11, 2004. © 2004 Wiley‐Liss, Inc.
Fibulins in development and heritable disease
Authors: Chu Mon‐Li , Tsuda Takeshi
Published: March 2004

Fibulins are a family of five extracellular glycoproteins found in a variety of tissues in association with diverse supramolecular structures, including elastic fibers, basement membrane networks, fibronectin microfibrils, and proteoglycan aggregates. Studies of the developmental expression patterns have indicated that several fibulins are prominently expressed at sites of epithelial‐mesenchymal transformations during embryogenesis; among these sites, the cardiovascular system has been analyzed in more detail. Gene targeting of fibulins in mice has provided important insights into their biological roles, and has led to the identification of gene mutations in a congenital disorder of humans, cutis laxa. Genetic linkage and molecular studies have also associated several fibulin genes with various human heritable disorders that affect a wide range of organs, including limb, eye, blood, and arteries. In this review, we discuss the role of fibulins in development, with an emphasis on the cardiovascular system, and their involvement in human genetic disease. Birth Defects Research (Part C) 72:25–36, 2004. © 2004 Wiley‐Liss, Inc.
Peptide design using α,β‐dehydro amino acids: From β‐turns to helical hairpins
Authors: Mathur Puniti , Ramakumar S. , Chauhan V. S.
Published: March 2004

Incorporation of α,β‐dehydrophenylalanine (ΔPhe) residue in peptides induces folded conformations: β‐turns in short peptides and 310‐helices in larger ones. A few exceptions—namely, α‐helix or flat β‐bend ribbon structures—have also been reported in a few cases. The most favorable conformation of ΔPhe residues are (ϕ,ψ) ∼ (−60°, −30°), (−60°, 150°), (80°, 0°) or their enantiomers. ΔPhe is an achiral and planar residue. These features have been exploited in designing ΔPhe zippers and helix–turn–helix motifs. ΔPhe can be incorporated in both right and left‐handed helices. In fact, consecutive occurrence of three or more ΔPhe amino acids induce left‐handed screw sense in peptides containing L‐amino acids. Weak interactions involving the ΔPhe residue play an important role in molecular association. The CH···OC hydrogen bond between the ΔPhe side‐chain and backbone carboxyl moiety, π–π stacking interactions between ΔPhe side chains belonging to enantiomeric helices have shown to stabilize folding. The unusual capability of a ΔPhe ring to form the hub of multicentered interactions namely, a donor in aromatic CH···π and CH···OC and an acceptor in a CH3···π interaction suggests its exploitation in introducing long‐range interactions in the folding of supersecondary structures. © 2004 Wiley Periodicals, Inc. Biopolymers (Pept Sci), 2004
Insights into stabilizing weak interactions in designed peptide β‐hairpins
Authors: Searle Mark S.
Published: March 2004

β‐Hairpin peptides (two anti‐parallel strands linked by a reverse β‐turn) have emerged as the simplest systems for probing weak interactions in β‐sheet folding. We describe a model 16‐residue hairpin system (peptide β1: KKYTVSINGKKITVSI) designed around the anti‐parallel β‐sheet DNA binding motif of the Met repressor dimer in which two β‐strand sequences are linked through an Asn‐Gly type I′ β‐turn. The peptide is significantly folded in aqueous solution and has a well‐defined conformation as evident from an abundance of NOE data. We review a number of analogues of β1 designed to estimate the energetic contribution of electrostatic (ion pairing) interactions to hairpin stability, to examine effects of cooperativity and preorganization in determining the energetics of weak interactions, and examine the effects on stability and conformation of incorporation of a three‐histidine motif on one face of the hairpin capable of zinc complexation. © 2004 Wiley Periodicals, Inc. Biopolymers (Pept Sci), 2004
Amphipathic peptides and drug delivery
Authors: Fernández‐Carneado Jimena , Kogan Marcelo J. , Pujals Silvia , Giralt Ernest
Published: March 2004

The discovery of cell‐penetrating peptides as gene delivery systems and the interest in the mechanism by which these vectors cross the cell membrane have generated a large number of studies. Among the parameters involved in the translocation process, controversy has arisen about the role of the amphipathicity of the carriers in the interaction and reorganization of the cell membrane. In this review we have summarized the vectors with primary or secondary amphipathicity related to secondary structure. Some of the insights into the relationship between the aggregation state of the peptide at the concentrations used for internalization studies and its interaction with the cell membrane result from our contribution to the field with a new family of amphipathic proline‐rich peptides. © 2004 Wiley Periodicals, Inc. Biopolymers (Pept Sci), 2004
Preparation of mammalian cell‐enclosing subsieve‐sized capsules (<100 μm) in a coflowing stream
Authors: Sakai Shinji , Kawabata Kenji , Ono Tsutomu , Ijima Hiroyuki , Kawakami Koei
Published: March 2004

The droplet breakup technique with an immiscible liquid coflowing stream was investigated for the preparation of mammalian cell‐enclosing subsieve‐sized capsules of less than 100 μm in diameter. The major parts of the droplet generation device were a needle of several hundred micrometers in diameter for extruding the cell‐suspending sodium alginate zzueous solution and a tubule of 2.5 mm in diameter through which the extruded alginate solution flowed into ambient immiscible liquid paraffin. The needle was positioned upstream in the vicinity of the coaxial tubule. The droplet diameter of the viscous sodium alginate aqueous solution could be controlled from several dozen to several hundred micrometers by changing the velocities of the inner and ambient fluids and the diameter of the needle. By utilizing a 300‐μm diameter needle, CHO‐K1 cell‐enclosing droplets of 48 ± 8 μm in diameter were obtained by extruding a cell‐suspending sodium alginate solution at a velocity of 1.2 cm/sec into the ambient liquid paraffin flowing at a velocity of 23.5 cm/sec. The breakup process did not influence the viability of the enclosed cells, since more than 95% of the CHO‐K1 cells remained alive after the enclosing process. © 2004 Wiley Periodicals, Inc.
Luftpiraten an der Küste: Papageitaucher und Nahrungsschmarotzer
Authors: Rüppell Georg
Published: March 2004

Papageitaucher sind erfolgreiche Fischjäger des Nordatlantiks. Ihre Eigenart, viele Fische im Schnabel zur Bruthöhle zu tragen, lädt zum Nahrungsschmarotzen ein. Die verschiedenen Möwenarten sind dabei mit ihren speziellen Verhaltensweisen unterschiedlich erfolgreich. Besonders auf den Farne‐Inseln in Nordost‐England nehmen die Papageitaucher und damit auch das Nahrungsschmarotzen zu. Ein Bericht über verhaltensbiologische und ökologische Zusammenhänge.
10 Karriere‐Tipps für angehende Biowissenschaftler
Authors: Debus‐Spangenberg Isolde
Published: March 2004

Je früher Biowissenschaftler ihre Karriere planen, um so größere Chancen bieten sich ihnen auf dem weiterhin recht angespannten Arbeitsmarkt. Mit der Medienwissenschaftlerin und Karriereberaterin Isolde Debus‐Spangenberg startet BIUZ deshalb in dieser Ausgabe ein Bewerbungstraining für Studenten. Den Anfang machen zehn Karriere‐Tipps, in der nächsten Ausgabe folgen konkrete Ratschläge für eine erfolgreiche Bewerbung.
Selektionsfaktor Jagd
Authors: Kronberg Inge
Published: March 2004

Werden aus einer Population gezielt bestimmte Merkmalsträger entfernt und von der Reproduktion ausgeschlossen, werden die Genotyp‐Häufigkeiten verändert: Es findet Evolution statt. Vögel fressen beispielsweise vor allem diejenigen Birkenspanner, die schlecht an den Untergrund angepasst sind. Auch Menschen erlegen bei der Jagd Wildtiere, die sie nach bestimmten Gesichtspunkten auswählen. Handelt es sich dabei um erbliche Merkmale, kann sich die Wildpopulation evolutiv verändern.
„Missing Link”︁ als echter Eukaryot enttarnt
Authors: Brennicke Axel
Published: March 2004

Am Zellkern scheiden sich die Lebewesen auf unserem Planeten: Wer einen besitzt, heißt Eukaryot, wer keinen hat, heißt Prokaryot und gehört zu den Archaea oder den Bakterien. Die Eukaryoten haben für spezielle chemische Reaktionen abgeteilte Kammern wie beispielsweise die Mitochondrien, die aus integrierten Prokaryoten entstanden sind. Für die Zwischenstufe dieser Entwicklung (Zellkern — aber noch keine Mitochondrien) gab es unter den heutigen Organismen mehrere Kandidaten. Jetzt wurden auch in dem letzten Zwischenwesen Giardia intestinalis Mitochondrien nachgewiesen. Damit stellt sich die Frage, ob es solche Intermediate überhaupt geben kann, oder ob die Aufnahme der endosymbiotischen Mitochondrien gleichzeitig mit der Ausbildung des Zellkerns erfolgte und diesen vielleicht erst ermöglichte.
Wespenspinnen — Selbstmord für mehr Nachwuchs
Authors: Irsch Wilhelm
Published: March 2004

Zebra‐ oder Wespenspinne (Argyope bruennichi) ist eine wärmeliebende Art. Seit einigen Jahren breitet sie sich von Süden weiter nach Norden aus und gilt daher als Vorbote einer langsamen klimatischen Veränderung. Doch nicht nur ihr Auftauchen in neuen Lebensräumen macht die Radnetzspinne und damit Verwandte unserer Kreuzspinne für den Biologen interessant. Wespenspinnen verfügen auch über ein recht aufregend wirkendes Sexualleben, dessen Kenntnis durch jüngste Forschungen um ein spannendes Kapitel erweitert werden konnte.
Your health, SIR!
Authors: Kronberg Inge
Published: March 2004

Von Jungbrunnen bis Anti‐Aging: Jede Generation hat ihren eigenen Ausdruck gefunden für den übereinstimmenden Wunsch nach ewiger Jugend. Seit langem weiß man, dass eine kalorienreduzierte Diät das Altern verlangsamen kann. Dem Menschen erscheint dieses Verfahren aber oft zu entbehrungsreich und mühsam. Die Suche nach einem pharmazeutisch nutzbaren Stoff mit vergleichbarer Wirkung läuft daher auf Hochtouren.
Analysis of the aconitine alkaloids in traditional Chinese medicines by nonaqueous capillary electrophoresis using a new recording mode
Authors: Zhao Shengguo , Pan Zhongwei , Chen Xingguo , Hu Zhide
Published: March 2004

The determination of three aconitine alkaloids (hypaconitine, aconitine, mesaconitine) in ﬁve traditional Chinese medicines including two Tibetan medicines, Chuanwu, Caowu, Fuzi, Aconitum Tanguticum Maxim and Aconitum Gymnandrum Maxim by non‐aqueous capillary electrophoresis using a new recording mode is described. The dissociation constants of aconitine, mesaconitine and hypaconitine have also been determined by CZE and were 7.71, 6.60 and 6.25, respectively. The separation was achieved by optimizing the applied voltage, the pH and the concentration of the buffer. The electrophoretic medium was 20 mm borax–70% (v/v) methanol (pH 8.5) and an uncoated capillary (50 cm × 75 µm i.d.) was used. Detection was carried out with a UV monitor at 214 nm. The total time for separation and determination was under 13 min. Copyright © 2004 John Wiley & Sons, Ltd.
Generic personality and emotion simulation for conversational agents
Authors: Egges Arjan , Kshirsagar Sumedha , Magnenat‐Thalmann Nadia
Published: March 2004

This paper describes a generic model for personality, mood and emotion simulation for conversational virtual humans. We present a generic model for updating the parameters related to emotional behaviour, as well as a linear implementation of the generic update mechanisms. We explore how existing theories for appraisal can be integrated into the framework. Then we describe a prototype system that uses the described models in combination with a dialogue system and a talking head with synchronized speech and facial expressions. Copyright © 2004 John Wiley & Sons, Ltd.
Analysis of co‐articulation regions for performance‐driven facial animation
Authors: Fidaleo Douglas , Neumann Ulrich
Published: March 2004

A facial gesture analysis procedure is presented for the control of animated faces. Facial images are partitioned into a set of local, independently actuated regions of appearance change termed co‐articulation regions (CRs). Each CR is parameterized by the activation level of a set of face gestures that affect the region. The activation of a CR is analyzed using independent component analysis (ICA) on a set of training images acquired from an actor. Gesture intensity classification is performed in ICA space by correlation to training samples. Correlation in ICA space proves to be an efficient and stable method for gesture intensity classification with limited training data. A discrete sample‐based synthesis method is also presented. An artist creates an actor‐independent reconstruction sample database that is indexed with CR state information analyzed in real time from video. Copyright © 2004 John Wiley & Sons, Ltd.
The Chemodiversity of Purine as a Constituent of Natural Products
Authors: Rosemeyer Helmut
Published: March 2004

In this review, I describe various natural manifestations of purine systems, i.e., methylated, higher‐alkylated, and glycosylated forms. These comprise the purine alkaloids, cytokinines, as well as the purine nucleoside antibiotics. In part, the compounds described herein were isolated from natural sources already long ago. However, some have been reported only during the last few years. The biological activities of most of the purine derivatives are briefly described, and, in some cases, syntheses are formulated. In particular, this article introduces the main synthetic principles for the generation of the purine ring system. The last chapter describes modern preparative routes for C‐alkylation and C‐arylation of purines.
Novel Lipid‐Peroxidation‐ and Cyclooxygenase‐Inhibitory Tannins from Picrorhiza kurroa Seeds
Authors: Zhang Yanjun , DeWitt David L. , Murugesan Sorimuthu , Nair Muraleedharan G.
Published: March 2004

From the AcOEt extract of the seeds of Picrorhiza kurroa were isolated picrorhiza acid (1), picrorhizoside A (2), picrorhizoside B (3), picrorhizoside C (4), (−)‐shikimic acid (5), gallic acid (6), ellagic acid (7), isocorilagin (8), 1‐O‐galloyl‐β‐D‐glucose (9), 1‐O,3‐O,6‐O‐trigalloyl‐β‐D‐glucose (10), and 1‐O,2‐O,3‐O,4‐O,6‐O‐pentagalloyl‐β‐D‐glucose (11), and their structures were established by extensive NMR and chemical studies. Constituents 1–4 are novel compounds, and the known compounds 5–11 have been isolated for the first time from the seeds of P. kurroa. Compounds 2 and 3 were hydrolyzed and yielded 12, isochebulic acid. Compounds 1–12 showed 89.6, 77.3, 56.1, 50.5, 11.0, 86.4, 50.5, 29.2, 70.9, 50.5, 56.5, and 86.1% inhibition of lipid peroxidation at 5 μg/ml, respectively. The commercial antioxidants BHA (1.8 μg/ml), BHT (2.2 μ/ml), and TBHQ (1.66 μg/ml) inhibited lipid peroxidation at 85.6, 87.1, and 81.1%, respectively. The inhibition of cyclooxygenase‐1 (COX‐1) by 2–5, 7, 8, and 10–12 at 100 μg/ml was 41.9, 28.4, 32.9, 9.3, 70.7, 34.7, 16.0, 89.6, and 53.4%, respectively. Similarly, compounds 1–8 and 11 and 12, at 100 μg/ml, inhibited COX‐2 by 12.6, 15.3, 25.1, 5.3, 13.2, 21.7, 2.0, 42.4, 43.4, and 36.9%, respectively.
Modelling of the Complex between a 15‐Residue Peptide from mSos2 and the N‐Terminal SH3 Domain of Grb2 by Molecular‐Dynamics Simulation
Authors: Calero Sofía , Lago Santiago , van Gunsteren Wilfred F. , Daura Xavier
Published: March 2004

Under specific conditions, the complex formed by the adaptor protein Grb2 and the guanine‐nucleotide exchange factor Sos2 is responsible for the activation of Ras, a low‐molecular‐weight GTPase involved in the control of cell proliferation and differentiation. The interaction between the N‐terminal SH3 domain of the mouse Grb2 and one of its potential target sequences in the mouse, Sos2, a 15‐residue peptide corresponding to residues 1264–1278, had been studied by NMR. However, the resulting data provided very limited information on the structure of the peptide and its interaction with the protein. Here, we present results from a molecular‐dynamics simulation aimed at producing a realistic, atomic model for the interaction between the N‐terminal SH3 domain of Grb2 and the SPLLPKLPPKTYKRE peptide from Sos2. In the simulation, the peptide adopts an extended conformation over the protein's binding surface. The proposed polyproline‐type‐II helicity appears only locally, and the peptide displays substantial flexibility. It is found that the peptide residues Lys10 to Tyr12 could be responsible for most of the specificity of the interaction.
Pentacoordinate Nickel(II) Complexes Double Bridged by Phosphate Ester or Phosphinate Ligands: Spectroscopic, Structural, Kinetic, and Magnetic Studies
Authors: Santana M. Dolores , García Gabriel , Lozano A. Abel , López Gregorio , Tudela José , Pérez José , García Luis , Lezama Luis , Rojo Teófilo
Published: March 2004

The bis(phosphatediester)‐bridged complexes [{Ni([12]aneN3)(μ‐O2P(OR)2)}2](PF6)2 {[12]aneN3=Me3[12]aneN3, 2,4,4‐trimethyl‐1,5,9‐triazacyclododec‐1‐ene; R=Me (1), Bu (2), Ph (3), Ph‐4‐NO2 (4); [12]aneN3=Me4[12]aneN3, 2,4,4,9‐tetramethyl‐1,5,9‐triazacyclododec‐1‐ene; R=Me (5), Bu (6), Ph (7), Ph‐4‐NO2 (8)} were prepared by hydrolysis of the phosphate triester with the hydroxo complex [{Ni([12]aneN3)(μ‐OH)}2](PF6)2 or by acid–base reaction of the dialkyl or diaryl phosphoric acid and the above hydroxo complex. The acid–base reaction was also used to synthesise the phosphinate‐bridged complexes [{Ni([12]aneN3)(μ‐O2PR2)}2](PF6)2 {[12]aneN3=Me3[12]aneN3, R=Me (9), Ph (10); [12]aneN3=Me4[12]aneN3, R=Me (11), Ph (12)}. The molecular structures of complexes 2, 3 and 12 were established by single crystal X‐ray diffraction studies. The eight‐membered rings defined by the nickel atoms and the bridging ligands show distorted twist‐boat, chair and boat–boat conformations in 2, 3 and 12, respectively. The experimental susceptibility data for compounds 2, 3 and 12 were fitted by least‐squares methods to the analytical expression given by Ginsberg. The best fit was obtained with values of J=−0.11 cm−1, D=−9.5 cm−1 and g=2.20 for 2; J=−0.97 cm−1, D=−9.3 cm−1 and g=2.21 for 3; and J=−0.14 cm−1, D=−11.9 cm−1 and g=2.195 for 12. The magnetic‐exchange pathways must involve the phosphate/phosphinate bridges, because these favour antiferromagnetic interactions. The observation of a higher exchange parameter for compound 3 is a consequence of a favourable disposition of the OPO bridges. The kinetics for the hydrolysis of TNP (tris(4‐nitrophenyl)phosphate) with the dinuclear nickel(II) hydroxo complex [{Ni(Me3[12]aneN3)(μ‐OH)}2](PF6)2 was studied by UV‐visible spectroscopy. The proposed mechanism for TNP‐promoted hydrolysis can be described as one‐substrate/two‐product, and can be fitted to a Michaelis–Menten equation.
Low‐Temperature Destruction of Carbon Tetrachloride over Lanthanide Oxide‐Based Catalysts: From Destructive Adsorption to a Catalytic Reaction Cycle
Authors: Van der Avert Pieter , Podkolzin Simon G. , Manoilova Olga , de Winne Hendrik , Weckhuysen Bert M.
Published: March 2004

The catalytic destruction of carbon tetrachloride in the presence of steam, CCl4 + 2 H2O→4 HCl + CO2, was investigated at 200–350 °C over a series of lanthanide (La, Ce, Pr and Nd) and alkaline‐earth metal (Mg, Ca, Sr and Ba) oxide‐based catalysts with kinetic experiments, Raman spectroscopy, X‐ray photoelectron spectroscopy, IR spectroscopy, X‐ray diffraction, and DFT calculations. This new catalytic reaction was achieved by combining destructive adsorption of CCl4 on a basic oxide surface and concurrent dechlorination of the resulting partially chlorinated solid by steam. The combination of the two noncatalytic reactions into a catalytic cycle provided a rare opportunity in heterogeneous catalysis for studying the nature and extent of surface participation in the overall reaction chemistry. The reaction is proposed to proceed over a terminal lattice oxygen site with stepwise donation of chlorine atoms from the hydrocarbon to the surface and formation of the gas‐phase intermediate COCl2, which is readily readsorbed at the catalyst surface to form CO2. In a second step, the active catalyst surface is regenerated by steam with formation of gas‐phase HCl. Depending on the reaction conditions, the catalytic material was found to transform dynamically from the metal oxide state to the metal oxide chloride or metal chloride state due to the bulk diffusion of oxygen and chlorine atoms. A catalyst obtained from a 10 wt % La2O3/Al2O3 precursor exhibited the highest destruction rate: 0.289 g CCl4 h−1 g−1 catalyst at 350 °C, which is higher than that of any other reported catalyst system.
A Systematic Investigation into the Mechanism of the Reaction Between CF3 Radicals and CO/O2
Authors: Burgos Paci Maximiliano A. , Argüello Gustavo A.
Published: March 2004

A complete study of the reaction of CF3 radicals in the presence of CO and O2 was carried out by using isotopically labeled reagents to form, selectively, all the possible isotopomers of the intermediate trioxide, CF3OC(O)OOOC(O)OCF3, and of the stable peroxide, CF3OC(O)OOC(O)OCF3. Analyses were carried out by means of FTIR spectroscopy in combination with ab initio calculations. At temperatures close to 0 °C, the acyloxy radicals formed were shown to exist long enough to yield a statistical mixture of isotopomers. In previous reports their lifetime was considered to be too short.
Control of Hydrogen Bond Strengths through Push–Pull Effects Triggered by a Remote Reaction Center: A Theoretical Study
Authors: Hwang Tsong‐Song , Juan Ning , Chen Hsing‐Yin , Chen Cheng‐Chung , Lo Shih‐Jung , Chao Ito
Published: March 2004

In an effort to manipulate the bond strengths of hydrogen bonds, we have studied a three‐component chemical system consisting of a reaction center, a conjugated bridge, and a hydrogen‐bonding site. Protonation of the reaction center triggers intramolecular charge transfer from the hydrogen‐bonding site, altering its affinity to bind to an acceptor. Previously, we had found that this communication (signal transduction) between the reaction center and the hydrogen‐bonding site does not necessarily die out with increasing length of the conjugated bridge. In certain cases, this signal transduction is maintained—and even amplified—over long distances (I. Chao, T.‐S. Hwang, Angew. Chem. 2001, 113, 2775–2777; Angew. Chem. Int. Ed. 2001, 40, 2703–2705). In this study we report the results of an extensive theoretical investigation of this problem to provide insights into this intriguing phenomenon. In the systems we investigated it was found that the push–pull process between the hydrogen‐bonding site and the protonatable reaction center was mediated with the greatest facility by conjugated bridges with low‐lying π and π* orbitals.
Dynamic Combinatorial Carbohydrate Libraries: Probing the Binding Site of the Concanavalin A Lectin
Authors: Ramström Olof , Lohmann Sophie , Bunyapaiboonsri Taridaporn , Lehn Jean‐Marie
Published: March 2004

Dynamic combinatorial chemistry (DCC) has emerged as an efficient approach to receptor/ligand identification based on the generation of combinatorial libraries by reversible interconversion of the library constituents. In this study, the implementation of such libraries on carbohydrate–lectin interactions was examined with the plant lectin Concanavalin A as a target species. Dynamic carbohydrate libraries were generated from a pool of carbohydrate aldehydes and hydrazide linker/scaffold components through reversible acylhydrazone exchange, resulting in libraries containing up to 474 constituents. Dynamic deconvolution allowed the efficient identification of the structural features required for binding to Concanavalin A and the selection of a strong binder, a tritopic mannoside, showing an IC50‐value of 22 μM.
Homogeneous Catalysts Supported on Soluble Polymers: Biphasic Suzuki–Miyaura Coupling of Aryl Chlorides Using Phase‐Tagged Palladium–Phosphine Catalysts
Authors: an der Heiden Markus , Plenio Herbert
Published: March 2004

The Suzuki–Miyaura coupling of aryl chlorides and PhB(OH)2 under biphasic conditions (DMSO/heptane) can be performed in almost quantitative yields over several cycles by means of polymeric Pd catalysts with soluble polyethylene glycol phase tags. Three sterically demanding and electron‐rich phosphines 1‐CH2Br,4‐CH2P(1‐Ad)2‐C6H4, and 2‐PCy2,2′‐OH‐biphenyl, and 2‐PtBu2,2′‐OH‐biphenyl were covalently bonded to 2000 Dalton MeOPEG‐OH. The catalysts, which were formed in situ from Na2[PdCl4], the respective polymeric phosphine, KF/K3PO4, and PhB(OH)2, efficiently couple aryl chlorides at 80 °C at 0.5 mol % loading, resulting in a >90 % yield of the respective biphenyl derivatives. The use of polar phase tags allows the efficient recovery of palladium–phosphine catalysts by simple phase separation of the catalyst‐containing DMSO solution and the product‐containing n‐heptane phase. The high activity (TOF) of the catalyst remains almost constant over more than five reaction cycles, which involve the catalytic reaction, separation of the product phase from the catalyst phase, and addition of new reactants to initiate the next cycle. The Buchwald type biphenyl phosphines form the most active Pd catalysts, which are 1.3–2.8 times more active than catalysts derived from diadamantyl–benzylphosphine, but appear to be less robust in the recycling experiments. There is no apparent leaching of the catalyst into the heptane solution (<0.05 %), as evidenced by spectrophotometric measurements, and contamination of the product with Pd is avoided.
Design, Synthesis and Structural Investigations of a β‐Peptide Forming a 314‐Helix Stabilized by Electrostatic Interactions
Authors: Rueping Magnus , Mahajan Yogesh R. , Jaun Bernhard , Seebach Dieter
Published: March 2004

Two different strategies have been employed for the synthesis of Fmoc‐protected β3‐homoarginine; the Arndt–Eistert homologation of α‐arginine and the guanidinylation of β3‐homoornithine. Solid‐phase β‐peptide synthesis was used for the preparation of β‐heptapeptide 1, which was designed to form a helix stabilized by electrostatic interactions through positively (β3hArg) and negatively charged (β3hGlu) amino acid residues. CD measurements and corresponding NMR investigations in MeOH and aqueous solutions do indeed show that the β‐peptidic 314‐helix can be stabilized by salt‐bridge formation.
Reaction of Alkenes with Hydrogen Peroxide and Sodium Iodide: A Nonenzymatic Biogenic‐Like Approach to Iodohydrins
Authors: Barluenga José , Marco‐Arias María , González‐Bobes Francisco , Ballesteros Alfredo , González José M.
Published: March 2004

An efficient protocol to synthesize iodohydrins from alkenes is presented. Reactions were conducted in aqueous media using safe and readily available sodium iodide (the most abundant form of the element), and a highly convenient oxidant such as hydrogen peroxide. Addition of a protic acid triggers a faster and efficient process, a role formally related to that played by haloperoxidase enzymes in naturally occurring transformations. The successful application of these conditions to multigram scale preparations and over natural products derivatives is also discussed.
Titanocene‐Catalyzed Cascade Cyclization of Epoxypolyprenes: Straightforward Synthesis of Terpenoids by Free‐Radical Chemistry
Authors: Justicia José , Rosales Antonio , Buñuel Elena , Oller‐López Juan L. , Valdivia Mónica , Haïdour Ali , Oltra J. Enrique , Barrero Alejandro F. , Cárdenas Diego J. , Cuerva Juan M.
Published: March 2004

The titanocene‐catalyzed cascade cyclization of epoxypolyenes, which are easily prepared from commercially available polyprenoids, has proven to be a useful procedure for the synthesis of C10, C15, C20, and C30 terpenoids, including monocyclic, bicyclic, and tricyclic natural products. Both theoretical and experimental evidence suggests that this cyclization takes place in a nonconcerted fashion via discrete carbon‐centered radicals. Nevertheless, the termination step of the process seems to be subjected to a kind of water‐dependent control, which is unusual in free‐radical chemistry. The catalytic cycle is based on the use of the novel combination Me3SiCl/2,4,6‐collidine to regenerate the titanocene catalyst. In practice this procedure has several advantages: it takes place at room temperature under mild conditions compatible with different functional groups, uses inexpensive reagents, and its end step can easily be controlled to give exocyclic double bonds by simply excluding water from the medium.
Realization of Unusual Ligand Binding Motifs in Metalated Container Molecules: Synthesis, Structures, and Magnetic Properties of the Complexes [(LMe)Ni2(μ‐L′)]n+ with L′=NO3−, NO2−, N3−, N2H4, Pyridazine, Phthalazine, Pyrazolate, and Benzoate
Authors: Hausmann Julia , Klingele Marco H. , Lozan Vasile , Steinfeld Gunther , Siebert Dieter , Journaux Yves , Girerd Jean Jacques , Kersting Berthold
Published: March 2004

A series of dinickel(II) complexes with the 24‐membered macrocyclic hexaazadithiophenol ligand H2LMe was prepared and examined. The doubly deprotonated form (LMe)2− forms complexes of the type [(LMe)Ni${{{\rm II}\hfill \atop 2\hfill}}$(μ‐L′)]n+ with a bioctahedral N3NiII(μ‐SR)2(μ‐L′)NiIIN3 core and an overall calixarene‐like structure. The bridging coordination site L′ is accessible for a wide range of exogenous coligands. In this study L′=NO3−, NO2−, N3−, N2H4, pyrazolate (pz), pyridazine (pydz), phthalazine (phtz), and benzoate (OBz). Crystallographic studies reveal that each substrate binds in a distinct fashion to the [(LMe)Ni2]2+ portion: NO2−, N2H4, pz, pydz, and phtz form μ1,2‐bridges, whereas NO3−, N3−, and OBz− are μ1,3‐bridging. These distinctive binding motifs and the fact that some of the coligands adopt unusual conformations is discussed in terms of complementary host–guest interactions and the size and form of the binding pocket of the [(LMe)Ni2]2+ fragment. UV/Vis and electrochemical studies reveal that the solid‐state structures are retained in the solution state. The relative stabilities of the complexes indicate that the [(LMe)Ni2]2+ fragment binds anionic coligands preferentially over neutral ones and strong‐field ligands over weak‐field ligands. Secondary van der Waals interactions also contribute to the stability of the complexes. Intramolecular ferromagnetic exchange interactions are present in the nitrito‐, pyridazine‐, and the benzoato‐bridged complexes where J=+6.7, +3.5, and +5.8 cm−1 (H=−2 JS1S2, S1=S2=1) as indicated by magnetic susceptibility data taken from 300 to 2 K. In contrast, the azido bridge in [(LMe)Ni2(μ1,3‐N3)]+ results in an antiferromagnetic exchange interaction J=−46.7 cm−1. An explanation for this difference is qualitatively discussed in terms of bonding differences.
Synthesis, Crystallographic Studies, and Characterization of K2Bi8Se13‐xSx Solid Solutions.
Authors: Kyratsi Theodora , Kanatzidis Mercouri G.
Published: March 2004

For Abstract see ChemInform Abstract in Full Text.
X‐Ray Single‐Crystal Investigation of Rare Earth Osmium Silicides.
Authors: Rizzoli C. , Salamakha P. S. , Sologub O. L. , Belletti D. , Goncalves A. P. , Almeida M.
Published: March 2004

For Abstract see ChemInform Abstract in Full Text.
Superplastic Behavior of a High‐Cr TiAl Alloy in Its Cast State.
Authors: Wang Yong , Wang J. N. , Yang Jie
Published: March 2004

For Abstract see ChemInform Abstract in Full Text.
Effect of Nb2O5 Content on Hydrogen Reaction Kinetics of Mg.
Authors: Barkhordarian Gagik , Klassen Thomas , Bormann Ruediger
Published: March 2004

For Abstract see ChemInform Abstract in Full Text.