bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ferricytochrome c encapsulated in silica nanoparticles: Structural stability and functional properties
Authors: Fiandaca Gianluca , Vitrano Eugenio , Cupane Antonio 
Published: April 2004

AbstractUsing a modified sol–gel technique, we have succeeded in encapsulating ferric cytochrome c in silica nanoparticles obtained from hydrolysis and polycondensation of tetramethylorthosilicate. Particles dimensions have been determined with dynamic light scattering; this technique yields an hydrodynamic radius of about 100 nm, each nanoparticle containing about 102–103 proteins. If stored in the cold at low ionic strength, nanoparticles are stable for more than one week, even if a slow radius increase with time is observed. CD measurements show that encapsulated proteins exhibit substantially increased stability against guanidinium hydrochloride induced denaturation. Reduction kinetics of encapsulated ferric cytochrome c by sodium dithionite, measured with standard stopped flow techniques, are slower by a factor of ten with respect to those measured in solution. Analogous experiments with myoglobin suggest that this slowing down is due to the diffusion time of dithionite within the silica matrix. Indeed, if a smaller ligand like CO is used, the intrinsic kinetic properties of encapsulated proteins are found to be unaltered even in the millisecond time range. The reported data show that our nanoparticles are extremely useful both for basic research, to study the stability and functions of encapsulated proteins, and for their potential biotechnological applications. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004
Fourier transform infrared spectroscopic study on the conformational reorganization in Escherichia coli complex I due to redox‐driven proton translocation
Authors: Hellwig Petra , Stolpe Stefan , Friedrich Thorsten 
Published: April 2004

AbstractThe proton‐pumping NADH:ubiquinone oxidoreductase (complex I) couples the transfer of electrons from NADH to ubiquinone with the translocation of protons across the membrane. Electron transfer is accomplished by flavin mononucleotide (FMN) and a series of iron–sulfur (Fe/S) clusters. A novel mechanism has been proposed wherein the electron transfer reaction induces conformational changes that subsequently lead to the translocation of protons. Redox‐induced Fourier transform infrared difference spectra have been obtained, showing strong conformational changes in the amide I region. The amplitude of the signal is pH dependent, as expected for an energy coupling step in the enzymes reaction. Furthermore, pH‐dependent protonation events and quinone binding were detected. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004
Resonance Raman spectroscopy of xanthophylls in pigment mutant thylakoid membranes of pea
Authors: Andreeva Atanaska , Stoitchkova Katerina , Busheva Mira , Apostolova Emilia , Várkonyi Zsuzsanna , Garab Gyözö 
Published: April 2004

AbstractLow‐temperature resonance Raman spectroscopy was used to study the changes in the molecular structure and configuration of the major xanthophylls in thylakoid membranes isolated from mutants of pea with modified pigment content and altered structural organization of their pigment–protein complexes. The Raman spectra contained four known groups of bands, ν1–ν4, which could be assigned to originate mainly from the long wavelength absorbing lutein and neoxanthin upon 514.5 nm and at 488 nm excitations, respectively. The overall configuration of these bound xanthophyll molecules in the mutants appeared to be similar to the wild type, and the configuration in the wild type was almost identical with that in the isolated main chlorophyll a/b light harvesting protein complex of photosystem II (LHCII). Significant differences were found mainly in the region of ν4 (around 960 cm−1), which suggest that the macroorganization of PS II–LHCII supercomplexes and/or of the LHCII‐only domains are modified in the mutants compared to the wild type. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004
Delayed fluorescence from the photosynthetic reaction center measured by electronic gating of the photomultiplier
Authors: Filus Z. , Laczkó G. , Wraight C. A. , Maróti P. 
Published: April 2004

AbstractThe decay of the delayed fluorescence (920 nm) of reaction centers from the photosynthetic bacterium Rhodobacter sphaeroides R26 in the P+QA‐ charge‐separated state (P and QA are the primary donor and quinone, respectively) has been monitored in a wide (100 ns to 100 ms) time range. The photomultiplier (Hamamatsu R3310–03) was protected from the intense prompt fluorescence by application of gating potential pulses (‐280 V) to the first, third, and fifth dynodes during the laser pulse. The gain of the photomultiplier dropped transiently by a factor of 1 × 106. The delayed fluorescence showed a smooth but nonexponential decay from 100 ns to 1 ms that was explained by the relaxation of the average free energy between P* and P+QA‐ changing from ‐580 to ‐910 meV. This relaxation is due to the slow protein response to charge separation and can be described by a Kohlrausch relaxation function with time constant of 65 μs and a stretching exponent of α = 0.45. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004
In situ Raman investigation of single lipid droplets in the water‐conducting xylem of four woody plant species
Authors: Rösch P. , Schneider H. , Zimmermann U. , Kiefer W. , Popp J. 
Published: April 2004

AbstractA micro‐Raman spectroscopy approach was used for the direct in situ characterization of lipid bodies in the water‐conducting branch xylem of an African resurrection plant and three deciduous European tree species. Because of average diameters of at least 1 μm, the lipid bodies of all investigated species proved to be easily accessible by this technique. All vesicle‐forming xylem lipids were identified as fatty acid esters, which may correspond to phospholipids. Whereas in the resurrection plant saturated lipids were dominant, the lipid bodies of the European trees consisted of highly unsaturated fatty acids. A comparison of the spectra of lipid droplets of lime obtained in situ and from isloated xylem sap revealed slightly different signatures. This finding suggests that micro‐Raman spectroscopy may be used to detect modifications of the chemical composition of biological substances as a result of the extraction mode. © 2004 Wiley Periodicals, Inc. Biopolymers 74: 00–000, 2004
Effects of hydraulic retention time and sulfide toxicity on ethanol and acetate oxidation in sulfate‐reducing metal‐precipitating fluidized‐bed reactor
Authors: Kaksonen Anna H. , Franzmann Peter D. , Puhakka Jaakko A. 
Published: April 2004

AbstractThe effects of hydraulic retention time (HRT) and sulfide toxicity on ethanol and acetate utilization were studied in a sulfate‐reducing fluidized‐bed reactor (FBR) treating acidic metal‐containing wastewater. The effects of HRT were determined with continuous flow FBR experiments. The percentage of ethanol oxidation was 99.9% even at a HRT of 6.5 h (loading of 2.6 g ethanol L−1 d−1), while acetate accumulated in the FBR with HRTs below 12 h (loading of 1.4 g ethanol L−1 d−1). Partial acetate utilization was accompanied by decreased concentrations of dissolved sulfide (DS) and alkalinity in the effluent, and eventually resulted in process failure when HRT was decreased to 6.1 h (loading of 2.7 g ethanol L−1 d−1). Zinc and iron precipitation rates increased to over 600 mg L−1 d−1 and 300 mg L−1 d−1, respectively, with decreasing HRT. At HRT of 6.5 h, percent metal precipitation was over 99.9%, and effluent metal concentrations remained below 0.08 mg L−1. Under these conditions, the alkalinity produced by substrate utilization increased the wastewater pH from 3 to 7.9–8.0. The percentage of electron flow from ethanol to sulfate reduction averaged 76 ± 10% and was not affected by the HRT. The lowest HRT did not result in significant biomass washout from the FBR. The effect of sulfide toxicity on the sulfate‐reducing culture was studied with batch kinetic experiments in the FBR. Noncompetitive inhibition model described well the sulfide inhibition of the sulfate‐reducing culture. (DS) inhibition constants (Ki) for ethanol and acetate oxidation were 248 mg S L−1 and 356 mg S L−1, respectively, and the corresponding Ki values for H2S were 84 mg S L−1 and 124 mg S L−1. In conclusion, ethanol oxidation was more inhibited by sulfide toxicity than the acetate oxidation. © 2004 Wiley Periodicals, Inc.
Solanaceae — a model for linking genomics with biodiversity
Authors: Knapp Sandra , Bohs Lynn , Nee Michael , Spooner David M. 
Published: April 2004

AbstractRecent progress in understanding the phylogeny of the economically important plant family Solanaceae makes this an ideal time to develop models for linking the new data on plant genomics with the huge diversity of naturally occurring species in the family. Phylogenetics provides the framework with which to investigate these linkages but, critically, good species‐level descriptive resources for the Solanaceae community are currently missing. Phylogeny in the family as a whole is briefly reviewed, and the new NSF Planetary Biodiversity Inventories project ‘PBI: Solanum—a worldwide treatment’ is described. The aims of this project are to provide species‐level information across the global scope of the genus Solanum and to make this available over the Internet. The project is in its infancy, but will make available nomenclatural information, descriptions, keys and illustrative material for all of the approximately 1500 species of Solanum. With this project, the opportunity of linking valid, up‐to‐date taxonomic information about wild species of Solanum with the genomic information being generated about the economically important species of the genus (potato, tomato and eggplant) can be realized. The phylogenetic framework in which the PBI project is set is also of enormous potential benefit to other workers on Solanum. The community of biologists working with Solanaceae has a unique opportunity to effectively link genomics and taxonomy for better understanding of this important family, taking plant biology to a new level for the next century. Copyright © 2004 John Wiley & Sons, Ltd.
On the tetraploid origin of the maize genome
Authors: Swigonova Zuzana , Lai Jinsheng , Ma Jianxin , Ramakrishna Wusirika , Llaca Victor , Bennetzen Jeffrey L. , Messing Joachim 
Published: April 2004

AbstractData from cytological and genetic mapping studies suggest that maize arose as a tetraploid. Two previous studies investigating the most likely mode of maize origin arrived at different conclusions. Gaut and Doebley proposed a segmental allotetraploid origin of the maize genome and estimated that the two maize progenitors diverged at 20.5 million years ago (mya). In a similar study, using larger data set, Brendel and colleagues (quoted in) suggested a single genome duplication at 16 mya. One of the key components of such analyses is to examine sequence divergence among strictly orthologous genes. In order to identify such genes, Lai and colleagues sequenced five duplicated chromosomal regions from the maize genome and the orthologous counterparts from the sorghum genome. They also identified the orthologous regions in rice. Using positional information of genetic components, they identified 11 orthologous genes across the two duplicated regions of maize, and the sorghum and rice regions. Swigonova et al. analyzed the 11 orthologues, and showed that all five maize chromosomal regions duplicated at the same time, supporting a tetraploid origin of maize, and that the two maize progenitors diverged from each other at about the same time as each of them diverged from sorghum, about 11.9 mya. Copyright © 2004 John Wiley & Sons, Ltd.
MAGIC Database and interfaces: an integrated package for gene discovery and expression
Authors: Cordonnier‐Pratt Marie‐Michèle , Liang Chun , Wang Haiming , Kolychev Dmitri S. , Sun Feng , Freeman Robert , Sullivan Robert , Pratt Lee H. 
Published: April 2004

AbstractThe rapidly increasing rate at which biological data is being produced requires a corresponding growth in relational databases and associated tools that can help laboratories contend with that data. With this need in mind, we describe here a Modular Approach to a Genomic, Integrated and Comprehensive (MAGIC) Database. This Oracle 9i database derives from an initial focus in our laboratory on gene discovery via production and analysis of expressed sequence tags (ESTs), and subsequently on gene expression as assessed by both EST clustering and microarrays. The MAGIC Gene Discovery portion of the database focuses on information derived from DNA sequences and on its biological relevance. In addition to MAGIC SEQ‐LIMS, which is designed to support activities in the laboratory, it contains several additional subschemas. The latter include MAGIC Admin for database administration, MAGIC Sequence for sequence processing as well as sequence and clone attributes, MAGIC Cluster for the results of EST clustering, MAGIC Polymorphism in support of microsatellite and single‐nucleotide‐polymorphism discovery, and MAGIC Annotation for electronic annotation by BLAST and BLAT. The MAGIC Microarray portion is a MIAME‐compliant database with two components at present. These are MAGIC Array‐LIMS, which makes possible remote entry of all information into the database, and MAGIC Array Analysis, which provides data mining and visualization. Because all aspects of interaction with the MAGIC Database are via a web browser, it is ideally suited not only for individual research laboratories but also for core facilities that serve clients at any distance. Copyright © 2004 John Wiley & Sons, Ltd.
Photosensitized Degradation of Dyes in Polyoxometalate Solutions Versus TiO2 Dispersions under Visible‐Light Irradiation: Mechanistic Implications
Authors: Chen Chuncheng , Zhao Wei , Lei Pengxiang , Zhao Jincai , Serpone Nick 
Published: April 2004

AbstractThis article examines the photoxidation of a dye (rhodamine‐B, RhB) by visible‐light irradiation in the presence of a polyoxometalate (12‐tungstosilicic acid, H4SiW12O40), and compares it with the analogous process in the presence of TiO2. The photoreaction processes were examined by UV‐visible spectroscopy, fluorescence spectroscopy, high‐performance liquid chromatography (HPLC), liquid chromatography/mass spectral techniques (LC‐MS), and total organic carbon (TOC) assays in order to identify the intermediates produced. Formation of oxygen species, such as H2O2 and O2.−, was also investigated to clarify the details of the reaction pathway. With the use of SiW12O404− ions as the photocatalyst, the photoreaction leads mainly to N‐dealkylation of the chromophore skeleton. In contrast, cleavage of the whole conjugated chromophore structure predominates in the presence of TiO2. Strong O2.−/HO2.− ESR signals were detected in the TiO2 dispersions, whereas only weak ESR signals for the O2.− radical ion were seen in the SiW12O404− solutions during the irradiation period. Experimental results imply that reduction of O2 occurs by different pathways in the two photocatalytic systems.
Towards Surface‐Supported Supramolecular Architectures: Tailored Coordination Assembly of 1,4‐Benzenedicarboxylate and Fe on Cu(100)
Authors: Lingenfelder Magalí A. , Spillmann Hannes , Dmitriev Alexandre , Stepanow Sebastian , Lin Nian , Barth Johannes V. , Kern Klaus 
Published: April 2004

AbstractWe present a comprehensive investigation of the modular assembly of surface‐supported metal–organic coordination systems with specific topologies and high structural stability formed by vapor deposition of 1,4‐benzenedicarboxylic acid molecules and iron atoms on a Cu(100) surface under ultra‐high vacuum conditions. By making use of the two carboxylate moieties available for lateral linkage to Fe atoms, we succeeded in the fabrication of distinct Fe–carboxylate coordination architectures at the surface by carefully adjusting the ligand and metal concentration ratio and the temperature of the post‐deposition annealing treatment. The mononuclear, 1D‐polymeric and fully 2D‐reticulated metallosupramolecular arrangements obtained were characterized in situ at the single‐molecule level by scanning tunneling microscopy.
Synthesis, Nuclear, and Magnetic Structures and Magnetic Properties of [Mn3(OH)2(SO4)2(H2O)2]
Authors: Ben Salah Mohsen , Vilminot Serge , André Gilles , Richard‐Plouet Mireille , Bourée‐Vigneron Françoise , Mhiri Tahar , Kurmoo Mohamedally 
Published: April 2004

Abstract[Mn3(OH)2(SO4)2(H2O)2] and its deuterated anlaogue were synthesized by a hydrothermal technique and characterized by differential thermal analysis, thermogravimetric analysis, and IR spectroscopy. Its nuclear structure, determined by single‐crystal X‐ray analysis and Rietveld analysis of neutron powder‐diffraction data, consists of a 3D network of chains of edge‐sharing Mn(1)O6, running along the c axis, connected by the apices of Mn(2)O6 and SO4 units. It is isostructural to the nickel analogue. Determination of the magnetic structure and measurements of magnetization and heat capacity indicate the coexistence of both magnetic long‐range ordering (LRO) and short‐range ordering (SRO) below a Néel temperature of 26 K, while the SRO is retained at higher temperatures. The moments of the two independent Mn atoms lie in the bc plane, and that of Mn(1) rotates continuously by 54° towards the c axis on decreasing the temperature from 25 to 1.4 K. While the SRO may be associated with frustration of the moments within a Mn3 trimer, the LRO is achieved by antiparallel alignment of the four symmetry‐related trimers within the magnetic unit cell. A spin‐flop field, measured by dc and ac magnetization on a SQUID, is observed at 15 kOe.
The Direct Catalytic Asymmetric Cross‐Mannich Reaction: A Highly Enantioselective Route to 3‐Amino Alcohols and α‐Amino Acid Derivatives
Authors: Córdova Armando 
Published: April 2004

AbstractThe first proline‐catalyzed direct catalytic asymmetric one‐pot, three‐component cross‐Mannich reaction has been developed. The highly chemoselective reactions between two different unmodified aldehydes and one aromatic amine are new routes to 3‐amino aldehydes with dr>19:1 and up to >99 % ee. The asymmetric cross‐Mannich reactions are highly syn‐selective and in several cases the two new carbon centers are formed with absolute stereocontrol. The reaction does not display nonlinear effects and therefore only one proline molecule is involved in the transition state. The reaction was also catalyzed with good selectivity by other proline derivatives. The Mannich products were converted into 3‐amino alcohols and 2‐aminobutane‐1,4‐diols with up to >99 % ee. The first one‐pot, three‐component, direct catalytic asymmetric cross‐Mannich reactions between unmodified aldehydes, p‐anisidine, and ethyl glyoxylate have been developed. The novel cross‐Mannich reaction furnishes either enantiomer of unnatural α‐amino acid derivatives in high yield and up to >99 % ee. The one‐pot, three‐component, direct catalytic asymmetric reactions were readily scaled up, operationally simple, and conductible in environmentally benign and wet solvents. The mechanism and stereochemistry of the proline‐catalyzed, one‐pot, three‐component, asymmetric cross‐Mannich reaction are also discussed.
Structural Motifs in Secondary Ammonium Halides: Ring‐Stacking and Ring‐Laddering in the Organic Solid State
Authors: Bond Andrew D. 
Published: April 2004

AbstractThe ring‐stacking and ring‐laddering concepts of structural inorganic chemistry may be applied to rationalize motifs observed for secondary ammonium halides R2NH2X (X = Cl, Br) in the organic solid state. General examination of the directional preferences of N+⋅⋅⋅X− contacts in 166 crystal structures confirms that the shortest contacts (3.0–3.2 and 3.2–3.4 Å, X = Cl, Br) are N+H⋅⋅⋅X− hydrogen bonds lying approximately along the directions of the N+H bond vectors. The next shortest N+⋅⋅⋅X− contacts display two preferred directions of approach: i) contacts in the distance range 3.2–3.5 (X = Cl) and 3.2–3.9 Å (X = Br) lie close to the HN+H plane, along the direction of the bisector of the HN+H angle; ii) contacts in the distance range 4.0–4.2 (X = Cl) and 4.0–4.4 Å (X = Br) lie close to the HN+H plane, along the direction of an axis extending to the rear of one of the N+H bonds. Both directions of approach lead frequently to association of R2NH2+X− ion pairs into laddered motifs. Stacking association is also observed, giving rise in one case to discrete cubanes and in several other cases to extended stacked‐cube arrangements. In each case, the distribution of N+⋅⋅⋅X− contacts reflects a balance between the directional properties of the N+H⋅⋅⋅X− hydrogen bonds and (primarily steric) interactions between the R groups of the organic moieties. The ladder and stack motifs of the organic ammonium halides are in many cases directly comparable to those in alkali metal amides, [R2NM]n, and information derived from the extensive organic sample provides insight into the motifs adopted by the inorganic complexes.
A Neutral Organometallic Fluoro Complex Can Be a Good Ligand
Authors: Coue Laurent , Cuesta Luciano , Morales Dolores , Halfen Jason A. , Pérez Julio , Riera Lucía , Riera Víctor , Miguel Daniel , Connelly Neil G. , Boonyuen Supakorn 
Published: April 2004

AbstractThe reaction of the complex [Mo(OTf)(η3‐C3H4‐Me‐2)(CO)2(phen)] (1) (OTf = trifluoromethylsulfonate; phen = 1,10‐phenanthroline) with tetrabutylammonium fluoride trihydrate afforded the fluoride complex [MoF(η3‐C3H4‐Me‐2)(CO)2(phen)] (2). The IR spectrum and the oxidation potential of 2 reflect the fact that its metal center is more electron‐rich than that of the chloro analogue [MoCl(η3‐C3H4‐Me‐2)(CO)2(phen)]. Compound 2 reacted with 1 affording the homobinuclear complex [{Mo(η3‐C3H4‐Me‐2)(CO)2(phen)}2(μ‐F)][OTf] (3), with a fluoride bridge. Compound 2 also reacts with the species generated in situ by triflate abstraction from [M(OTf)(CO)3(′NN′)] (M = Mn, Re; ′NN′ = 2,2′‐bipyridine (bipy), phen) using NaBAr′4 (Ar′ = 3,5‐bis(trifluoromethyl)phenyl), affording the heterobinuclear complexes [{Mo(η3‐C3H4‐Me‐2)(CO)2(phen)}(μ‐F){M(CO)3(′NN′)}][BAr′4] (M = Mn, ′NN′ = bipy (4); M = Re, ′NN′ = phen (5)). All new compounds have been characterized by spectroscopic methods (IR and NMR) and, in the case of 1, 2, 3, and 4, also by means of X‐ray diffraction analysis.
Stable Optically Pure Phosphino(silyl)carbenes: Reagents for Highly Enantioselective Cyclopropanation Reactions
Authors: Krysiak Jerzy , Lyon Céline , Baceiredo Antoine , Gornitzka Heinz , Mikolajczyk Marian , Bertrand Guy 
Published: April 2004

AbstractThe stability of phosphino(trimethylsilyl)carbenes bearing cyclic diamino substituents on phosphorus is strongly dependent on the steric hindrance of the nitrogen substituents. Phosphinocarbenes 3 and 7, derived from the trans‐N,N′‐diisopropylcyclohexane‐1,2‐diamine and N,N′‐diisopropyl‐1,2‐ethanediamine, are not observed; instead the 1,3‐diphosphete 4 and a novel six‐membered heterocycle 8, which results from the dimerization of 3 and the reaction of 7 with its diazo precursor 6, respectively, have been isolated. In contrast, the phosphino(silyl)carbene 14 derived from N,N′‐di‐tert‐butyl‐1,2‐ethanediamine has been isolated in high yield. By using the enantiomerically pure (S,S)‐, and (R,R)‐N,N′‐di‐tert‐butyl‐1,2‐diphenyl‐1,2‐ethanediamines, the first optically pure phosphino(sily)carbenes (S,S)‐17 and (R,R)‐17 have been prepared. They react with methyl acrylate to give the corresponding cyclopropanes (S,S,R,R)‐19 and (R,R,S,S)‐19 with a total syn diastereoselectivity and an excellent enantioselectivity (de>98 %).