bluuebunny/crossref_metadata_2025_split huggingface dataset:
Studies on Stereoselective [2+2] Cycloadditions between N,N‐Dialkylhydrazones and Ketenes
Authors: Martín‐Zamora Eloísa , Ferrete Ana , Llera José M. , Muñoz Jesús M. , Pappalardo Rafael R. , Fernández Rosario , Lassaletta José M. 
Published: November 2004

AbstractStaudinger‐like cycloadditions between chiral, non‐racemic N,N‐dialkylhydrazones 1 and functionalized ketenes constitute an efficient methodology for the stereoselective construction of the β‐lactam ring. The potential for fine tuning of the dialkylamino auxiliary structure, the availability of a high‐yielding deprotection method for the release of the free azetidinones, and the high thermal and chemical stability of hydrazones as N‐dialkylamino imines are highlighted as the key elements for the success of the strategy. This last aspect is of particular importance concerning generality: even hydrazones from easily enolizable aldehydes or from formaldehyde reacted to afford the corresponding cycloadducts with high chemical and stereochemical yields. The syntheses of the β‐amino‐α‐hydroxyacids (2R,3S)‐phenylisoserine (42) and (2R,3S)‐norstatin (45) were accomplished as illustrative examples of the synthetic utility of this procedure. A model system for the cycloaddition of g series auxiliaries was studied by ab initio computational methods. The collected results support a two‐step mechanism through zwitterionic intermediates, and explain the observed absolute and relative stereochemistry in terms of the preferred outward cycloaddition to the Re face of the hydrazone.
Palladium‐Catalyzed Intramolecular Hydroalkylation of Alkenyl‐ β‐Keto Esters, α‐Aryl Ketones, and Alkyl Ketones in the Presence of Me3SiCl or HCl
Authors: Han Xiaoqing , Wang Xiang , Pei Tao , Widenhoefer Ross A. 
Published: November 2004

AbstractReaction of 3‐butenyl β‐keto esters or 3‐butenyl α‐aryl ketones with a catalytic amount of [PdCl2(CH3CN)2] (2) and a stoichiometric amount of Me3SiCl or Me3SiCl/CuCl2 in dioxane at 25–70 °C formed 2‐substituted cyclohexanones in good yield with high regioselectivity. This protocol tolerated a number of ester and aryl groups and tolerated substitution at the allylic, enolic, and cis and trans terminal olefinic positions. In situ NMR experiments indicated that the chlorosilane was not directly involved in palladium‐catalyzed hydroalkylation, but rather served as a source of HCl, which presumably catalyzes enolization of the ketone. Identification of HCl as the active promoter of palladium‐catalyzed hydroalkylation led to the development of an effective protocol for the hydroalkylation of alkyl 3‐butenyl ketones that employed sub‐stoichiometric amounts of 2, HCl, and CuCl2 in a sealed tube at 70 °C.
The Mechanism of Magnetic Interactions in the Bulk Ferromagnet para‐(Methylthio)Phenyl Nitronyl Nitroxide (YUJNEW): A First Principles, Bottom‐Up, Theoretical Study
Authors: Deumal Mercè , Bearpark Michael J. , Robb Michael A. , Pontillon Yves , Novoa Juan J. 
Published: November 2004

AbstractThe mechanism of magnetic interactions in the bulk ferromagnet para‐(methylthio)phenyl nitronyl nitroxide crystal (YUJNEW) has been theoretically reinvestigated, using only data from ab initio calculations and avoiding any a priori assumptions. We first calculate the microscopic magnetic interactions (JAB exchange couplings) between all unique radical pairs in the crystal, and then generate the macroscopic magnetic properties from the energy levels of the corresponding Heisenberg Hamiltonian. We thus propose a first principles, bottom‐up (i.e. micro‐to‐macro) approach that brings theory and experiment together. We have applied this strategy to study the magnetism of YUJNEW using data from the previously reported 298 and 114 K crystal structures, and also data from a 10 K neutron diffraction structure fully reported in this work. The magnetic topology at 298 K is two‐dimensional: noninteracting planes, with three different in‐plane JAB pair interactions (+0.24, +0.09, and −0.11 cm−1) and one numerically negligible (+0.02 cm−1) inter‐plane JAB interaction. In contrast, the magnetic topology at 114 and 10 K is three‐dimensional, with two non‐negligible in‐plane JAB constants (+0.11 and +0.07 cm−1 at 114 K; +0.22 and +0.07 cm−1 at 10 K) and one inter‐plane pair interaction (+0.07 cm−1 at 114 K; +0.08 cm−1 at 10 K). Although this three‐dimensional magnetic topology is consistent with YUJNEW being a bulk ferromagnet, there is only a qualitative agreement between computed and experimental magnetic susceptibility χT(T) data at 114 K. However, the experimental χT(T) curve is quantitatively reproduced at 10 K. The heat capacity curve presents a peak at around 0.12 K, close to the estimated experimental peak (0.20 K).
Role of the Special Pair in the Charge‐Separating Event in Photosynthesis
Authors: Ozeki Hidekane , Nomoto Akihiro , Ogawa Kazuya , Kobuke Yoshiaki , Murakami Masataka , Hosoda Kou , Ohtani Masana , Nakashima Satoru , Miyasaka Hiroshi , Okada Tadashi 
Published: November 2004

AbstractWe synthesized special‐pair/electron‐acceptor systems consisting of a complementary slipped cofacial dimer of imidazolyl‐substituted zinc porphyrin, bearing pyromellitdiimide as the electron acceptor. In the case of the dimer, the first and second oxidation potentials were split into a total of four peaks in the differential pulse voltammetry measurement. Furthermore, the shift values of the first oxidation potentials obtained by changing the solvent polarity for the dimer were almost half of those observed for the monomer. These results indicate that the radical cation is delocalized over the whole π system of the dimer. Time‐resolved transient absorption measurements revealed that, relative to the corresponding monomer, the dimer accelerated the charge separation rate, but decelerated the charge recombination rate. The smaller reorganization energy of the slipped cofacial dimer relative to that of the monomeric system demonstrates the significance of the special‐pair arrangement for efficient charge separation in photosynthesis.
Spatial‐spectral holographic MR interpretation
Authors: Kiruluta Andrew J.M. 
Published: November 2004

AbstractThe fundamental MR imaging equation can be derived from a spatial‐spectral holographic wavefront reconstruction formulation similar to that in quantum optics. This spatial‐spectral holographic interpretation arises naturally in MR from the inhomogeneous linewidth broadening (1/πT) due to either an imposed set of linear orthogonal gradients fields or from the intrinsic chemical shift/molecular environment of the spin system. In this work, it is shown experimentally that an inhomogeneously broadened NMR absorber can accomplish key holographic characteristics such as storage, recall, time‐reversal, and matched filtering of gradient weighted RF pulses in a three‐pulse stimulated echo experiment. This interpretation has implications on selective RF pulse design, holographic‐based high‐resolution microscopy applications, and the use of conjugate imaging for field inhomogeneity corrections using the time‐reversed component of the readout. © 2004 Wiley Periodicals, Inc. Concepts Magn Reson 23A: 76–88, 2004
Variation of mitochondrial size during the cell cycle: A multiparameter flow cytometric and microscopic study
Authors: Kennady P. Kavin , Ormerod M. G. , Singh Shashi , Pande Gopal 
Published: November 2004

AbstractBackgroundChanges in mitochondrial structure and size are observed in response to alterations in cell physiology. Flow cytometry provides a useful tool to study these changes in intact cells. We have used flow cytometry and digital fluorescence microscopy to analyze the variations in mitochondrial size in relation to specific phases of the cell cycle.MethodsSupravital staining of rat fibroblasts was done with Hoechst 33342 and rhodamine 123, and cells were analyzed in a dual‐laser flow cytometer. Synchronized cells at various stages of the cell cycle were analyzed for changes in mitochondrial size. These cells were also examined by electron microscopy, digital fluorescence microscopy and computerized image analysis to compare the lengths of the mitochondria.ResultsBy using fluorescence pulse width analysis, we observed two populations of mitochondria in intact cells. The percentage of cells with small and large mitochondria at specific stages of the cell cycle indicated that mitochondrial size increases during the cell cycle; early G1 phase cells had the smallest mitochondria and the mitotic phase cells had the largest mitochondria. These results were confirmed by microscopic analysis of cells.ConclusionsFlow cytometry can distinguish the relative mitochondrial size in intact cells, and in combination with digital microscopy it can be used to study mitochondrial variation during the cell cycle. © 2004 Wiley‐Liss, Inc.
Der Weg in die Vergangenheit
Authors: Hallmann Heinz W. , Forner Jörg‐Ulrich 
Published: November 2004

AbstractWege prägen das Gesicht von Gärten und Parks. Das wussten schon die Pioniere der Landschaftsgärtnerei. Wenn heute historische Wege rekonstruiert werden, ist dies nicht nur für die Denkmalpflege aufschlussreich
Das Klima auf der Luftdruckschaukel
Authors: Brümmer Burghard 
Published: November 2004

AbstractDas Wetter in unseren Breiten lässt sich gut für einige Tage vorhersagen. Wie es aber um die langfristigen Trends im Klimasystem des Nordatlantiks steht, ist weitgehend unbekannt. Meteorologen erforschen die Grundlagen
An efficient molecular docking using conformational space annealing
Authors: Lee Kyoungrim , Czaplewski Cezary , Kim Seung‐Yeon , Lee Jooyoung 
Published: November 2004

AbstractMolecular docking falls into the general category of global optimization problems because its main purpose is to find the most stable complex consisting of a receptor and its ligand. Conformational space annealing (CSA), a powerful global optimization method, is incorporated with the Tinker molecular modeling package to perform molecular docking simulations of six receptor–ligand complexes (3PTB, 1ULB, 2CPP, 1STP, 3CPA, and 1PPH) from the Protein Data Bank. In parallel, Monte Carlo with the minimization (MCM) method is also incorporated into the Tinker package for comparison. The energy function, consisting of electrostatic interactions, van der Waals interactions, and torsional energy terms, is calculated using the AMBER94 all‐atom empirical force field. Rigid docking simulations for all six complexes and flexible docking simulations for three complexes (1STP, 3CPA, and 1PPH) are carried out using the CSA and the MCM methods. The simulation results show that the docking procedures using the CSA method generally find the most stable complexes as well as the native‐like complexes more efficiently and accurately than those using the MCM, demonstrating that CSA is a promising search method for molecular docking problems. © 2004 Wiley Periodicals, Inc. J Comput Chem 26: 78–87, 2005
Chromatographic separation of nucleosides using a cross‐linked xylose isomerase crystal stationary phase
Authors: Jokela Jouni , Leisola Matti 
Published: November 2004

AbstractCross‐linked xylose isomerase (EC 5.3.1.5., from Streptomyces rubiginosus) crystals (CLXIC) packed into a 7.8×300 mm steel column showed specific affinity towards uridine (Urd), cytidine (Cyd), adenosine (Ado), guanosine (Guo), and thymidine. These nucleosides eluted out of the CLXIC column in the same order as the corresponding nucleoside bases, indicating that the retention depends mainly on the base component of the molecule. The interaction of nucleosides with the CLXIC material was not based merely on ion exchange or hydrophobic interactions but also on the unique properties of the CLXIC column. Decrease in temperature increased the retention but not the resolution factors of the adjacent nucleosides. The CLXIC column maintained its separation capacity even when 100 mg of ribonucleosides in equimass amounts were injected into the column in a volume of 1 mL corresponding to 10% of the total column volume. Analysis of sugar beet molasses, a side stream from sucrose production, showed it to contain 1–2.5 mg mL–1 of Urd, Cyd, Ado, and Guo. The CLXIC column was able to separate and enrich these nucleosides also from highly viscous sugar beet molasses. The CLXIC column was especially efficient in the purification of guanosine. Other commercially interesting sugar beet molasses components such as the acidic compounds betaine, γ‐amino butyric acid, and D‐ and L‐pyroglutamic acids or neutral sucrose did not interact with the CLXIC material.
Capillary columns in liquid chromatography: between conventional columns and microchips
Authors: Saito Yoshihiro , Jinno Kiyokatsu , Greibrokk Tyge 
Published: November 2004

AbstractLiquid chromatography on columns with small internal diameters has been reviewed as the intermediate technique between conventional liquid chromatography and microchip separations. The development of micro column separations in the early years has been described, starting with the papers of Horváth and co‐workers and Ishii and co‐workers, continuing into the first part of the eighties, then making a leap in time to recent innovations with small‐bore columns. Based on internal diameters a classification of the different analytical HPLC columns has been suggested. The advantages of small‐bore columns have been discussed, with particular emphasis on the advantage of coupling to concentration sensitive detectors when the sample amount is limited. Open tubular columns are treated as a part of the historic background. The recent developments include a brief look into the current status of monolithic columns, the use of packed nano columns and micro columns with electrospray mass spectrometry, and the potential of two‐dimensional comprehensive liquid chromatography. Finally, the coupling of sample preparation to analytical columns and the future applications of the novel technological improvements to the microchip separation methods have been discussed.
Phosphoproteomics by mass spectrometry and classical protein chemistry approaches
Authors: Salih Erdjan 
Published: November 2004

AbstractThe general fields of biological sciences have seen phenomenal transformations in the past two decades at the level of data acquisition, understanding biological processes, and technological developments. Those advances have been made partly because of the advent of molecular biology techniques (which led to genomics) coupled to the advances made in mass spectrometry (MS) to provide the current capabilities and developments in proteomics. However, our current knowledge that ∼30,000 human genes may code for up to 1 million or more proteins disengage the interface between the genome sequence database algorithms and MS to generate a major interest in independent de novo MS/MS sequence determination. Significant progress has been made in this area through procedures to covalently modify peptide N‐ and C‐terminal amino‐acids by sulfonation and guanidination to permit rapid de novo sequence determination by MS/MS analysis. A number of strategies that have been developed to perform qualitative and quantitative proteomics range from 2D‐gel electrophoresis, affinity tag reagents, and stable‐isotope labeling. Those procedures, combined with MS/MS peptide sequence analysis at the subpicomole level, permit the rapid and effective identification and quantification of a large number of proteins within a given biological sample. The identification of proteins per se, however, is not always sufficient to interpret biological function because many of the naturally occurring proteins are post‐translationally modified. One such modification is protein phosphorylation, which regulates a large array of cellular biochemical pathways of the biological system. Traditionally, the study of phosphoprotein structure–function relationships involved classical protein chemistry approaches that required protein purification, peptide mapping, and the identification of the phosphorylated peptide regions and sites by N‐terminal sequence analysis. Recent advances made in mass spectrometry have clearly revolutionized the studies of phosphoprotein biochemistry, and include the development of specific strategies to preferentially enrich phosphoproteins by covalent‐modifications that incorporate affinity tags that use the physicochemical properties of phosphoaminoacids. The phosphoserine/phosphothreonine‐containing proteins/peptides are derivatized under base‐catalyzed conditions by thiol agents; mono‐ and di‐thiol reagents both have been used in such studies. The thiol agent may have: (i) an affinity tag for protein enrichment; (ii) stable‐isotopic variants for relative quantitation; or (iii) a combination of the moieties in (i) and (ii). These strategies and techniques, together with others, are reviewed, including their practical application to the study of phosphoprotein biochemistry and structure–function. The consensus of how classical protein chemistry and current MS technology overlap into special case of proteomics, namely “phosphoproteomics,” will be discussed. © 2004 Wiley Periodicals, Inc., Mass Spec Rev 24:828–846, 2005
Myocytes from congenital myotonic dystrophy display abnormal Na+ channel activities
Authors: Bernareggi Annalisa , Furling Denis , Mouly Vincent , Ruzzier Fabio , Sciancalepore Marina 
Published: November 2004

AbstractNa+ currents were measured in myocytes from a fetus with congenital myotonic dystrophy type 1 (DM1) using the patch‐clamp whole‐cell technique. Steady‐state activation and inactivation properties of Na+ channels were not substantially different between these cells and age‐matched control cells. However, a decrease in Na+ channel density and a faster rate of recovery from inactivation were found in myocytes from congenital DM1 suggesting that changes in functional Na+ channels may affect cell excitability of muscle cells of patients with this disorder. Muscle Nerve, 2005
Towards a Fundamental Understanding of the Mechanics of Crystal Agglomeration: A Microscopic and Molecular Approach
Authors: Simons Stefaan J. R. , Pratola Federica , Jones Alan G. , Brunsteiner Michael , Price Sally L. 
Published: November 2004

AbstractA novel experimental apparatus has been developed which enables the measurement of adhesion forces between two crystals suspended in a supersaturated solution and allowed to agglomerate over a fixed time period. The geometry of the crystal surfaces at the contact points and the dynamic development of the bond are captured on video and characterised using an image analysis technique. The experimental apparatus has been designed to allow control of supersaturation, orientation of crystal faces, distance between crystals, relative movement of crystals and contact time. The experimental results show that the agglomerate bond strength, expressed as the agglomerate adhesion force per unit contact area, increases with increasing supersaturation and is higher for faster growing faces than for slower growing faces. In addition, a qualitative comparison has been made between the measured force and a theoretical estimation of the interaction force between crystal faces, determined through molecular modelling. It is shown that the speed of approach of two opposing crystal faces is a key parameter in the nature of the subsequent bond, as is their atomic structure.
Predicting the Performance of Granulation Binders Through Micro‐Mechanistic Observations
Authors: Rossetti Damiano , Simons Stefaan J. R. , Pagliai Paolo , Ward Rob , Fitzpatrick Shaun 
Published: November 2004

AbstractThe selection of an appropriate polymeric binder to be used to agglomerate drug with excipients is a critical issue for the development of high shear wet granulation processes for pharmaceutical tablet systems. The aim of the study reported here is to determine the potential for successful granulation through measurement of the interactions of two polymer binder solutions, hydroxypropyl methylcellulose (HPMC) and polyvinyl‐pyrrolidone (PVP), with individual paracetamol drug crystals. A novel micro‐force balance (MFB) has been used to measure different parameters of the crystal‐to‐binder interaction, including the forces exerted by axially strained liquid bridges formed between either two paracetamol crystals or between a reservoir of binder solution and a single paracetamol crystal, the paracetamol‐to‐binder wettability, the post rupture volume distribution and the residue deposited on each crystal. Video images of the separation sequences were obtained simultaneously for analysis of bridge geometry, contact angles, volume distribution and binder residues. It was found that the formation of liquid bridges and their ability to bond particles together depends on the amount of binder left on a crystal after contacting a reservoir of binder (for example, large binder drop). Crystals in contact with HPMC were able to retain more liquid from a binder reservoir than those contacted with PVP solutions. This behaviour is seen to be more important to the final granule strength than the liquid binding force holding particles together in the wet agglomerate.
Improvements in Silo Design for Moist and Cohesive Bulk Solids by Using a Silo Centrifuge
Authors: Großstück Marco , Schwedes Jörg 
Published: November 2004

AbstractThe Jenike‐method is state of the art in silo design for trouble‐free flow, even for cohesive bulk solids. However, for some bulk solids, especially very cohesive and moist bulk solids, even the correct application of the Jenike‐method can lead to an over‐design of the silo outlet. If a reliable estimation of the critical outlet dimension is possible the dimension as well as the machinery costs can be reduced. Model testing can help to reduce the over‐design but reasonable test equipment and flexibility are only possible with silo centrifuge testing. Results, regarding the state of stress and the critical outlet dimensions, from experiments using a silo centrifuge with cohesive and moist bulk solids are presented. The influence of creeping effects on silo design is investigated using the silo centrifuge with moist gypsum.
5α‐dihydrotestosterone inhibits 1α,25‐dihydroxyvitamin D3‐induced expression of CYP24 in human prostate cancer cells
Authors: Lou Yan‐Ru , Nazarova Nadja , Talonpoika Riikka , Tuohimaa Pentti 
Published: November 2004

AbstractBACKGROUNDA cross‐talk between 1α,25‐dihydroxyvitamin D3 [1α,25‐(OH)2D3] and 5α‐dihydrotestosterone (DHT) in the growth inhibition has been demonstrated, but the mechanism is unknown.METHODSThe expression of 25‐hydroxyvitamin D3 24‐hydroxylase (24‐hydroxylase) was measured using a real‐time quantitative RT‐PCR assay and the catabolism of 1α,25‐(OH)2D3 was measured using a radioreceptor assay.RESULTSReal‐time RT‐PCR showed that DHT at 1–100 nM significantly inhibited 1α,25‐(OH)2D3‐induced expression of 24‐hydroxylase in LNCaP cells. Furthermore, the catabolism of 1α,25‐(OH)2D3 was decreased by 10 nM DHT. An androgen receptor (AR) antagonist, Casodex antagonized the DHT effect, whereas an AR agonist (due to the mutant AR in LNCaP cells) hydroxyflutamide did not.CONCLUSIONSWe demonstrated, for the first time, that DHT reduces the ability of 1α,25‐(OH)2D3 to induce 24‐hydroxylase expression. Our results not only support the earlier finding of a cross‐talk between androgen and vitamin D in human prostate cancer cells but also provide a possible mechanism how androgen and vitamin D signaling pathways may interact. © 2004 Wiley‐Liss, Inc.
Cubature grids
Authors: Rees D. , Hall G. G. 
Published: November 2004

AbstractThis article applies group theory to the problem of calculating accurate cubature grids for three‐dimensional (3D) integrals that have an exponential weighting factor. The nodes of a cubature are divided into structures, each with the full symmetry of the octahedral group. The sequence of structures is derived from a basis set of polynomials forming a Sturmian basis for the function space. Several cubatures, of up to eighth degree accuracy, are reported and their features discussed. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005