bluuebunny/crossref_metadata_2025_split huggingface dataset:
Could Redox‐Switched Binding of a Redox‐Active Ligand to a Copper(II) Centre Drive a Conformational Proton Pump Gate? A Synthetic Model Study
Authors: He Zhicong , Colbran Stephen B. , Craig Donald C. 
Published: December 2002

AbstractA proposal for a redox‐linked conformational gate to proton translocation—a proton pump gate—based upon a transition‐metal redox‐switchable hemilabile ligand (RHL) system is made. Consideration of the requirements for such a system reveals copper(II) to be the ideal metal centre. To test the proposal and, thereby, to provide an artificial proton pump gate, the copper coordination chemistry of three tris(pyridylmethyl)amine (tpa) ligands with one “leg” (PY*) substituted at the 6‐position of the pyridine ring by a dimethoxyphenyl (L1), a hydroquinone (H2L2) or a quinone (L3) substituent has been investigated. Crystal structures of sp‐[Cu(κ4N‐L1)Cl]Cl⋅3 H2O (sp=square pyramidal), sp‐[Cu(κ3N‐H2L2)Cl2] and tbp‐[Cu(κ4N,κO‐HL2)][PF6] (tbp=trigonal bipyramidal) have been determined. The CuI complexes [Cu(L)(MeCN)n]+ (L=L1, H2L2) display physicochemical properties consistent with a “dangling” PY* leg; from the NMR spectra, the barriers to inversion of the ligand amine donor for the CuI complexes are estimated to be within the range of about 30–45 kJ mol−1. In the CuII complexes, coordination of the PY* leg is finely balanced and critically depends on the nature of the PY* substituent and the availability of potential co‐ligand(s). For example, tbp‐[Cu(κ4N‐L1)Cl]+ reacts cleanly with Cl− ions to afford sp‐[Cu(κ3N‐L1)Cl2]; Vis/NIR spectrophotometric titrations suggest the affinity of tbp‐[Cu(κ4N‐L1)Cl]+ for Cl− ion in dichloromethane is 9.7×102 and is at least 104‐fold greater than that of tbp‐[Cu(κ4N‐L3)Cl]+. The complex sp‐[Cu(κ3N‐H2L2)Cl2] has a “dangling” PY* leg, in which an intramolecular OH(hydroquinone)⋅⋅⋅N(pyridine) hydrogen bond “ties‐up” the pyridyl nitrogen atom, and reacts with Brønsted bases to give tbp‐[Cu(κ4N,κO‐HL2)]+. Two‐electron oxidation of sp‐[Cu(κ3N‐H2L2)Cl2] is linked to loss of two protons and a conformational change, and affords tbp‐[Cu(κ4N‐L3)Cl]+. The [Cu(κ3N‐H2L2)Cl2]–[Cu(κ4N‐L3)Cl]+ system provides a first demonstration of the critical step in the proposed proton pumping cycle, namely a redox‐driven and proton‐linked conformational change. The possible biological relevance of this work to proton pumping in cytochrome c oxidase is mentioned.
How To Turn the Catalytic Asymmetric Hydroboration Reaction of Vinylarenes into a Recyclable Process
Authors: Segarra Anna M. , Guerrero Ramon , Claver Carmen , Fernández Elena 
Published: December 2002

AbstractOptically pure rhodium(I) complexes [Rh(cod)(LL)]X (cod=cyclooctadiene; LL= (R)‐2,2′‐bis(diphenylphosphino)1‐1′‐binaphthyl ((R)‐BINAP), (S,S)‐2,4‐bis(diphenylphosphino)pentane ((S,S)‐BDPP), 2‐diphenylphosphino‐1‐(1′‐isoquinolyl)naphthalene ((S)‐QUINAP); X=BF4, PF6, SO3CF3, BPh4) were immobilised onto smectite clays such as montmorillonite K‐10 (MK‐10) and bentonite (Na+‐M). 19F, 31P and 11B NMR experiments recorded in CDCl3 during the impregnation process provided evidence that montmorillonite K‐10 may immobilise ionic metal complexes throughout the cationic and anionic counterparts. However, when bentonite was used as the solid, only the cationic metal complex was immobilised through cationic exchange while the counteranion remained in solution. When we used these preformed catalytic systems in the hydroboration of prochiral vinylarenes, we obtained high activities and enantiomeric excess with (S)‐1‐(2‐diphenylphosphino‐1‐naphthyl)isoquinoline‐modified rhodium complexes. These activities and selectivities are competitive with the homogeneous counterparts. The significant features of this method are the simple separation and good retention of the active metal in the solid, which allows efficient recycling even on exposure to air.
High Thermodynamic Stability and Extraordinary Kinetic Inertness of Copper(II) Complexes with 1,4,8,11‐Tetraazacyclotetradecane‐1,8‐bis(methylphosphonic acid): Example of a Rare Isomerism between Kinetically Inert Penta‐ and Hexacoordinated Copper(II) Complexes
Authors: Kotek Jan , Lubal Přemysl , Hermann Petr , Císařová Ivana , Lukeš Ivan , Godula Tomáš , Svobodová Ivona , Táborský Petr , Havel Josef 
Published: December 2002

AbstractIn an aqueous solution at room temperature, 1,4,8,11‐tetraazacyclotetradecane‐1,8‐bis(methylphosphonic acid) (H4L1) and CuII form a pentacoordinated (pc) complex, pc‐[Cu(L1)]2−, exhibiting conformation I of the cyclam ring. At high temperature, the complex isomerises to a hexacoordinated isomer, trans‐O,O‐[Cu(L1)]2−, with a trans‐III conformation of the cyclam ring. In pc‐[Cu(L1)]2−, four ring nitrogen atoms and one phosphonate oxygen atom are arranged around CuII in a structure that is half‐way between a trigonal bipyramid and a tetragonal pyramid, with one phosphonic acid group uncoordinated. In the trans‐O,O‐[Cu(L1)]2− isomer, the nitrogen atoms form a plane and the phosphonic acid groups are in a mutually trans configuration. A structurally very similar ligand, 4‐methyl‐1,4,8,11‐tetraazacyclotetradecane‐1,8‐bis(methylphosphonic acid) (H4L2), forms an analogous pentacoordinated complex, pc‐[Cu(L2)]2−, at room temperature. However, the complex does not isomerise to the octahedral complex analogous to trans‐O,O‐[Cu(L1)]2−. Because of the high thermodynamic stability of pc‐[Cu(L1)]2−, (log β=25.40(4), 25 °C, I=0.1 mol dm−3 KNO3) and the formation of protonated species, CuII is fully complexed in acidic solution (−log [H+]≈3). Acid‐assisted decomplexation of both of the isomers of [Cu(H2L1)] takes place only after protonation of both uncoordinated oxygen atoms of each phosphonate moiety and at least one nitrogen atom of the cycle. The exceptional kinetic inertness of both isomers is illustrated by their half‐lives τ1/2=19.7 min for pc‐[Cu(H2L1)] and τ1/2 about seven months for trans‐O,O‐[Cu(H2L1)] for decomplexation in 5 M HClO4 at 25 °C. The mechanism of formation of pc‐[Cu(L1)]2− is similar to those observed for other macrocyclic complexes.For classification of the cyclam ring conformation in complexes, see B. Bosnich, K. Poon, M. Tobe, Inorg. Chem. 1965, 4, 1102.
Amination of Benzylic CH Bonds by Arylazides Catalyzed by CoII–Porphyrin Complexes: A Synthetic and Mechanistic Study
Authors: Ragaini Fabio , Penoni Andrea , Gallo Emma , Tollari Stefano , Li Gotti Claudia , Lapadula Marta , Mangioni Enrica , Cenini Sergio 
Published: December 2002

AbstractCoII–porphyrin complexes catalyze the reaction of aromatic azides (ArN3) with hydrocarbons that contain a benzylic group (ArR1R2CH) to give the corresponding amines (ArR1R2CNHAr). When at least one of the R substituents is hydrogen, the catalytic reaction proceeds further to give the imine ArRCNAr in good yields. The reaction mechanism has been investigated. The reaction proceeds through a reversible coordination of the arylazide to the CoII–porphyrin complex. This unstable adduct can either react with the hydrocarbon in the rate‐determining step or decompose by a unimolecular mechanism to afford a putative “nitrene” complex, which reacts with more azide, but not with the hydrocarbon, to afford the byproduct diaryldiazene. The kinetics of the catalytic reaction have been investigated for a range of azides and substituted toluenes. Arylazides with electron‐withdrawing substituents react at a faster rate and a good correlation is found between the log(k) and the Taft parameters. On the other hand, an excellent correlation between the logarithm of the rate for substituted toluenes relative to that of toluene and a radical parameter (σ$\rm{_{JJ}^{{\bf \cdot }}}$) alone was found, with no significant contribution by polar parameters. An explanation has been proposed for this anomalous effect and for the very high isotopic effect (kH/kD=14) found.
Monte Carlo Simulation of the Assembly of bis‐Biotinylated DNA and Streptavidin
Authors: Richter Jan , Adler Michael , Niemeyer Christof M. 
Published: December 2002

AbstractWe present Monte Carlo simulations of the self‐assembly of bivalent bis‐biotinylated DNA molecules with the tetravalent biotin‐binding protein streptavidin (STV). By fitting the STV binding probabilities for the four possible valencies, the modelling correctly reproduces the dependencies of various network parameters experimentally observed in an earlier study. The combined results from the experimental and theoretical studies suggest that the binding probability for divalent STV formation is about 50 times larger than for the formation of trivalent and about 200 times larger than for tetravalent STV. In accordance with the experimental results, the modelling also indicates that the mixture of an equimolar ratio of DNA and STV leads to a maximum in size of the oligomeric DNA–STV clusters formed. Furthermore, we found a percolation transition in which the DNA cluster size increases rapidly with increasing DNA concentration resulting in the formation of a single supercluster at elevated concentrations. This behaviour coincides with the occurrence of an immobile band previously observed in electrophoretic experiments, indicating the formation of extremely large DNA–STV aggregate networks.
Syntheses of Purines Bearing Carbon Substituents in Positions 2, 6 or 8 by Metal‐ or Organometal‐Mediated C−C Bond‐Forming Reactions
Authors: Hocek Michal 
Published: December 2002

AbstractApproaches to the synthesis of purine derivatives bearing carbon substituents in positions 2, 6, or 8, mediated and/or catalysed by organometallic compounds and metals, are reviewed. Both the generation and the reactions of purinylorganometallic compounds are covered, as well as cross‐coupling and cycloaddition reactions between purines and organometallic compounds. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
The Unexpected Conversion of 1,5,8,12‐Tetraazadodecane‐Glyoxal Bisaminal into Its Amidinium Salt in an Acidic Medium
Authors: Bernard Hélène , Del Rio Garcia Eugenia , Ferec Sonia , Kervarec Nelly , Handel Henri 
Published: December 2002

AbstractWhen refluxed in aqueous hydrochloric acid solution, 1,5,8,12‐tetraazadodecane‐glyoxal bisaminal is quantitatively converted into its amidinium salt, which is a lactam precursor. The mechanism of this unexpected reaction is discussed. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Cover Picture: Eur. J. Org. Chem. 2/2003
Authors: Tomasini Claudia , Trigari Valerio , Lucarini Simone , Bernardi Fernando , Garavelli Marco , Peggion Cristina , Formaggio Fernando , Toniolo Claudio 
Published: December 2002

AbstractThe cover picture shows the side views of the DFT‐optimized Boc‐(L‐Oxd)n‐OBn (n = 2−5) foldameric structures (in the circle) and the front view of Boc‐(L‐Oxd)5‐OBn (in the centre). Details are discussed in the article by M. Garavelli, C. Toniolo et al. on p. 259 ff.
Two morphological types of pineal window in catfish in relation to photophase and scotophase activity: a morphological and experimental study
Authors: Srivastava S. 
Published: December 2002

AbstractThe pineal window is a transparent/translucent pineal covering on the dorsal surface of the cranium of certain fishes and is associated with light reactions of fish. In the present study, catfish species Clarias batrachus, Heteropneustes fossilis, Mystus vittatus, M. seenghala, and M. cavassius were examined for the type of pineal window present. Two morphologically different types of pineal window were found: an opaque‐looking pineal window in C. batrachus and H. fossilis and a translucent type of pineal window in M. vittatus, M. seenghala, and M. cavassius. The distributional pattern of pigments in the melanophores at the pineal window were studied in terms of Melanophore Index (MI). In all of the species studied, a pineal foramen, a subepidermal lens‐like tissue, and pineal end vesicle were present.Experiments were carried out on catfish having the opaque pineal window, as it is uncommon in catfish. Catfish with normal and shielded pineal window were exposed to conditions of artificial constant illumination (LL) and darkness (DD) to evaluate the effects of altered photoperiods on the state of pigmentation of melanophores at the pineal window. Recordings of diel activity patterns, which are light dependent in catfish, were carried out under both natural and artificial photoperiods in fish with a normal or shielded window in order to assess its functional nature. The existence of two morphologically and functionally different types of pineal window in a relatively closely related group of catfish has been demonstrated in this study. The nature of the opaque type of pineal window has been reconsidered based on new experimental evidence. J. Exp. Zool. 295A:17–28, 2003. © 2003 Wiley‐Liss, Inc.
Simulation and Evaluation of Compounding Processes
Authors: Potente Helmut , Kretschmer Karsten 
Published: December 2002

AbstractCo‐rotating twin‐screw extruders are the most important types of machine for the compounding of plastics from the economic point of view. The term ‘compounding’ is basically used to describe all processes that are needed to produce a plastic with a desired property profile from the raw polymer. In most processes found today, multi‐component material systems are used. These may consist of polymer/filler combinations (compounds) or polymer/polymer combinations (blends). After presenting mathematical models to describe the behavior of binary systems, a description is given of the melting profile of polymer/filler compounds. After this, models are presented that enable the degree of dispersion of compounding processes to be calculated. These models have been implemented in a software program for simulating the process characteristics of co‐rotating twin‐screw extruders. With the aid of this software, it is possible to conduct a comprehensive analysis of the process behavior of co‐rotating twin‐screw extruders. The processing unit can then be optimized on the basis of this analysis.
Screw configuration for examining the dispersion.magnified imageScrew configuration for examining the dispersion.
Improved Design of Shearing Sections with New Calculation Models Based on 3D Finite‐Element Simulations
Authors: Potente Helmut , Többen Wilhelm H. 
Published: December 2002

AbstractNew models for the Maddock and spiral shearing sections have been developed, employing three‐dimensional finite element analysis (3D FEA). These models describe the pressure‐throughput and power consumption behavior of the shearing sections for both the extrusion and the injection molding process and have been implemented in the REX 6.0 and PSI 4.0 simulation software. As a consequence it is now possible to describe the process behavior of these shearing sections within just a few seconds with the accuracy of FEA calculations.
Actual Maddock shearing section (left) and actual spiral shearing section (right).magnified imageActual Maddock shearing section (left) and actual spiral shearing section (right).
Global Concept for Describing and Investigation of Wall Slip Effects in the Extrusion Process
Authors: Potente Helmut , Ridder Helmut , Cunha Renata Viegas 
Published: December 2002

AbstractWhen it comes to the design of extrusion line components such as single‐screw extruders or extrusion dies, no one has yet succeeded in developing a well‐functioning concept for wall‐slipping materials. This article examines the fundamental influences of the wall slippage effect on flow behavior in the extrusion die and plastification unit. New and extended methods of calculation for describing this flow phenomenon are presented for both these extrusion line components, and the general possibilities for linking the two approaches are discussed.
Diagram of the flow curve (τ = shear stress, $\dot \gamma$ = shear rate) of wall‐slipping plastics for constant pressure.magnified imageDiagram of the flow curve (τ = shear stress, $\dot \gamma$ = shear rate) of wall‐slipping plastics for constant pressure.
Sperm surface hyaluronan binding protein (HABP1) interacts with zona pellucida of water buffalo (Bubalus bubalis) through its clustered mannose residues
Authors: Ghosh Ilora , Datta Kasturi 
Published: December 2002

AbstractSperm–oocyte interaction during fertilization is multiphasic, with multicomponent events, taking place between zona pellucida (ZP) glycoproteins and sperm surface receptor. d‐mannosylated glycoproteins, the major constituents of ZP are considered to serve as ligands for sperm binding. The presence of hyaluronan binding protein 1 (HABP1) on sperm surface of different mammals including cattle and its possible involvement in sperm function is already reported. Recently, we have demonstrated the specificity of clustered mannose as another ligand for HABP1 (Kumar et al., 2001: J Biosci 26:325–332). Here, we report that only N‐linked mannosylated zona‐glycoproteins bind to sperm surface HABP1. Labeled HABP1 interacts with ZP of intact oocyte of Bubalus bubalis, which can be competed with unlabeled HABP1 or excess d‐mannosylated albumin (DMA). This data suggests the specific interaction of HABP1 with ZP, through clustered mannose residues. In order to examine the physiological significance of such an interaction, the capacity of sperm binding to oocytes under in vitro fertilization plates was examined either in presence of DMA alone or in combination with HABP1. The number of sperms, bound to oocytes was observed to reduce significantly in presence of DMA, which could be reversed by the addition of purified recombinant HABP1 (rHABP1) in the same plate. This suggests that sperm surface HABP1 may act as mannose binding sites for zona recognition. Mol. Reprod. Dev. 64: 235–244, 2003. © 2003 Wiley‐Liss, Inc.
Optimization of superovulation induction by human menopausal gonadotropin in guinea pigs based on follicular waves and FSH‐receptor homologies
Authors: Suzuki Osamu , Koura Minako , Noguchi Yoko , Takano Kaoru , Yamamoto Yoshie , Matsuda Junichiro 
Published: December 2002

AbstractThe guinea pig represents an excellent animal model for the study of reproduction in humans and most domestic animals because unlike the mouse and rat, it undergoes a complete estrous cycle. In this study, we investigated the availability of ovarian oocytes during the estrous cycle, and the follicle stimulating hormone (FSH) receptor (FSH‐R) homologies between guinea pigs and other species, in order to identify an effective gonadotropin and optimal time‐of‐application for the induction of superovulation in the guinea pig. The number of collectable ovarian oocytes showed biphasic changes with peaks at the midluteal and pre‐ovulatory stages. On the other hand, the number of oocytes that matured in vitro remained constant (∼10 oocytes) until day 14 post‐ovulation and increased thereafter. The deduced amino acid sequence of the guinea pig FSH‐R showed greater similarity to the primate FSH‐R than to the rodent FSH‐R, which suggests that commercially available human menopausal gonadotropin (hMG) may be a better inducer of superovulation in guinea pigs. Indeed, significantly more oocytes (5.4 ± 1.6, range 0–17, n = 10) were obtained from hMG‐treated guinea pigs at the pre‐ovulatory stage than during spontaneous ovulation (3.6 ± 0.1, n = 96; P < 0.05), whereas guinea pigs that received hMG at the midluteal stage (n = 3) did not ovulate. These results indicate that hMG is an effective, albeit stage‐dependent, inducer of superovulation in the guinea pig, and that FSH‐R homologies should be taken into account when choosing hormones for superovulation. Mol. Reprod. Dev. 64: 219–225, 2003. © 2003 Wiley‐Liss, Inc.
Mean Particle Diameters. Part III: An Empirical Evaluation of Integration and Summation Methods for Estimating Mean Particle Diameters from Histogram Data
Authors: Alderliesten Maarten 
Published: December 2002

AbstractMean particle diameters of histograms of size distributions were estimated by integration and by summation over the histogram intervals using several, partly model, size distributions. The Summation method, used in the Moment‐Ratio (M‐R) method, tends to be more accurate than the Integration method and is less sensitive to low values of the lower limit of size distributions. The mathematical equations for the Integration method appear to be difficult to apply in daily practice and their complexity may easily hide the physical background of a mean particle diameter. The Integration approach leads to peculiar saw‐tooth shaped histograms, which makes the calculation of (histograms of) density distributions of other particle quantities irreversible and the calculation of mean diameters ambiguous. The Summation method equations are straightforward and generally applicable. Owing to the use of midpoints of particle size classes, the method is both unambiguous and reversible. The order of a mean diameter appears to be a useful quantity for the visualization of properties of methods to estimate mean particle diameters. The Summation method is therefore proposed as the method of choice for standardization.
Simultaneous Measurement of Particle Size and Particle Velocity by the Spatial Filtering Technique
Authors: Petrak Dieter 
Published: December 2002

AbstractThe objective of this study was to compare the measuring results of a fiber‐optical probe based on a modified spatial filtering technique with given size distributions of different test powders and also with particle velocity values of laser Doppler measurements. Fiber‐optical spatial filtering velocimetry was modified by fiber‐optical spot scanning in order to determine simultaneously the size and the velocity of particles. The fiber‐optical probe system can be used as an in‐line measuring device for sizing of particles in different technical applications. Spherical test particles were narrow‐sized glass beads in the range 30–100 μm and irregularly shaped test particles were limestone particles in the range 10–600 μm. Particles were dispersed by a brush disperser and the measurements were carried out at a fixed position in a free particle‐laden air stream. Owing to the measurement of chord lengths and to the influence of diffraction and divergent angle, the probe results show differences from the given test particle sizes. Owing to the particle‐probe collisions, the mean velocity determined by the probe is smaller than the laser Doppler mean velocity.
Raman Spectroscopy of Laser‐Shocked Nitrobenzene
Authors: Kozu Naoshi , Kadono Toshihiko , Hiyoshi Reiko I. , Nakamura Jun , Arai Mitsuru , Tamura Masamitsu , Yoshida Masatake 
Published: December 2002

AbstractA technique for in situ Raman spectroscopy of laser‐shocked nitrobenzene was developed. Raman spectra of shocked nitrobenzene are obtained up to ∼3.5 GPa, and peak shifts at particular frequencies are observed. The shifts are plotted as a function of density and compared with the data under isothermal compression. Both data provide the same results. This indicates that the numbers of peak shifts of nitrobenzene depend solely on material density.
Effect of incident probe on HAADF STEM images
Authors: Watanabe K. , Nakanishi N. , Yamazaki T. , Kawasaki M. , Hashimoto I. , Shiojiri M. 
Published: December 2002

AbstractAtomic‐resolution incoherent high‐angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) images of [011]‐oriented Si have been recorded using different incident beam probes, and analysed by means of dynamical image calculation based on the Bloch wave description. It is shown how atomic‐resolution images are influenced by the semiangle of the probe and the spherical aberration and defocus of the probe‐forming lens. The resolution of an incoherent HAADF STEM image can be simply perceived by the contrast transfer function of incoherent imaging which is the Fourier transform of the incident probe intensity.