bluuebunny/crossref_metadata_2025 huggingface dataset:
Complexity of the phase transition in La1–

x
Sr
x
CoO3
Authors: Louca Despina
Published: April 2004

The complex nature of modern materials is strongly dependent on their intrinsic microstructure. Their collective behaviour at the nanoscale strongly correlates to their macroscopic functionalities. Thus it has become necessary to understand the true nature of atomic disorder in order to understand its effects on the mechanical, elastic, magnetic and electronic transitions. Carefully calibrated and environment-controlled atomistic measurements can significantly further our understanding of the mechanisms responsible for macroscopic properties. To demonstrate these effects, La1–

x
Sr
x
CoO3 is used as an example as it serves as a prototype for demonstrating lattice distortions through phase transitions.
Structural aspects of the M1 and M2 phases in MoVNbTeO propane ammoxidation catalysts
Authors: DeSanto Peter , Buttrey Douglas J. , Grasselli Robert K. , Lugmair Claus G. , Volpe Anthony F. , Toby Brian H. , Vogt Thomas
Published: April 2004

The structures of M1 and M2 in MoVNbTeO propane ammoxidation catalysts have been solved using a combination of TEM, neutron powder diffraction, and synchrotron X-ray powder diffraction. The unit cell of M1 is Pba2 (No. 32) with a = 21.134(2) Å, b = 26.658(2) Å, c = 4.0146(3) Å and Z = 4. The formula unit is Mo7.8V1.2NbTe0.937O28.9. The unit cell of M2 is Pmm2 (No. 25) with a = 12.6294(6) Å, b = 7.29156(30) Å, c = 4.02010(7) Å and Z = 4. The formula unit is Mo4.31V1.36Te1.81Nb0.33O19.81. Tellurium sites in hexagonal channels of both phases are displaced toward vanadium-occupied framework sites, whereas Te in the heptagonal channel of M1 is near the channel center. The chemical topology resulting from oxidation states and Madelung site potentials presents active moieties for the ammoxidation of propane in M1 and propene in M2. EPR confirmed the presence of V4+ and possibly Mo5+ in M1 and V4+ in M2.
High pressure study of a Zr-based bulk metallic glass and its composite
Authors: Halevy Itzhak , Üstündag Ersan , Salhov S. , Yue Alan F. , Broide A. , Hu Jingzhú
Published: April 2004

Energy dispersive X-ray diffraction was used to study the structural evolution of a bulk metallic glass (BMG) alloy and its composite with W particles under hydrostatic pressure. The diffraction data, especially the pair distribution function (PDF) of the BMG allowed the direct measurement of its elastic strain. The results suggest that PDF patterns of BMGs can be used to deducetheir strain evolution in composites as well as in monolithic form. Although the PDF method of strain measurement in amorphous alloys offers lower resolution compared to the analysis of Bragg reflections from crystalline materials, the PDF techique yields valuable information about the deformation of BMGs.
Nanoporous thin films and porous inorganic substrates for lipid bilayer support materials
Authors: Baker Shenda M. , Kolthammer W. Stephen , Tan Johannes B. , Smith Gregory S.
Published: April 2004

Synthetic lipid bilayers are excellent mimics of cell membranes. In order to experimentally access these thin layers and oriented proteins in membranes, suitable supports which allow for membrane fluidity while assuring membrane stability need to be developed. Nanoporous polymer templates created from the natural phase segregation of immiscible diblock copolymers are uniform arrays with pore sizes naturally on the scale of macromolecules, tens of nanometers, and grain sizes currently on the order of microns. We study the suitability of such templates, appropriately treated to present a hydrophilic surface, as substrates for lipid bilayers with scanning force microscopy and neutron reflectometry. In the process, we use tip deflection curves to establish simple criteria for determining the presence of a lipid layer on the substrates. Gold coated porous polymers and silicon oxide templates in silicon both appear to be suitable support materials.
Using the information seeker to elicit construct models for search engine evaluation
Authors: Crudge Sarah E. , Johnson Frances C.
Published: April 2004

With the rise of interactive search engines, direct access to information is available to the end user. Evaluation of these systems is clearly important for their comparison and development. From the perspective of the user engaged with the system in some information‐seeking task, the range of relevant evaluation factors could be considerable. This article presents an investigation into the suitability of repertory grid technique eliciting a mental model of search engines in the user. Such a model comprises constructs held important to the user, which can be used to evaluate the system. The design of the repertory grid application is described and the data analyzed in two stages. The important issues in determining the suitability of the method are identified and the constructs are analyzed to determine their association, discriminatory ability, and clustering around a central overall rating. From this, it is concluded that repertory grid technique is appropriate for user‐centered determination of evaluative constructs. Further analysis of the characteristics of the resulting construct set is undertaken towards establishing an underlying user model of the search engines, and further research is identified for its use in system evaluation.
Manipulating the covalent link between distal side tryptophan, tyrosine, and methionine in catalase‐peroxidases: An electronic absorption and resonance Raman study
Authors: Santoni Elisa , Jakopitsch Christa , Obinger Christian , Smulevich Giulietta
Published: April 2004

Electronic absorption and resonance Raman spectroscopies have been applied to study the ferric and ferrous forms, and fluoride complexes of the Tyr249Phe and Met275Ile variants of the recombinant catalase‐peroxidase (KatG) from the cyanobacterium Synechocystis PCC 6803. Both crystal structures and mass spectrometric analysis demonstrated that Tyr249 and Met275 are part of a novel KatG‐specific covalent adduct including in addition a conserved tryptophan. Its role is not well established, but it has been shown to be essential for the catalase activity. In the present work we investigate the effect of mutation on the protein stability and ligand binding. The results clearly show that mutation weakens the heme binding to the protein, giving rise to a partial conversion from the 5‐coordinate high spin of the wild‐type protein to 6‐coordinate low‐spin heme. An internal ligand binds the heme iron on the distal side as a consequence of protein destabilization and partially prevents the binding of external ligand such as fluoride. The results are compared with those previously reported for the Trp122Ala and Trp122Phe variants. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004
Spectroscopic study on the enzymatic degradation of a biodegradable composite periodontal membrane
Authors: Reggiani Matteo , Taddei Paola , Tinti Anna , Fagnano Concezio
Published: April 2004

The enzymatic in vitro degradation of a commercial biodegradable hydroxyapatite (HA)‐polymer (poly(ε‐caprolactone)‐poly(oxyethylene)(POE)‐poly(ε‐caprolactone) block copolymer) composite membrane was investigated by Raman and IR spectroscopies in two enzymatic solutions at 37°C: esterase and α‐chymotrypsin in saline phosphate buffer (SPB, pH 7.4). The degradation was found to be faster in the enzymatic medium than in SPB and alkaline solutions. The fastest degradation rate was observed in esterase solution. The trend of properly chosen Raman and IR intensity ratios was evaluated to go deeper inside the degradation mechanism: both polymeric and apatitic components were found to be involved in degradation. The former underwent preferential degradation of POE blocks, while HA is removed by the degradation medium faster than the polymer. Vibrational spectroscopy proved a valid tool for investigating the degradation of the membrane. © 2004 Wiley Periodicals, Inc. Biopolymers, 2004
Using metabolic flux data to further constrain the metabolic solution space and predict internal flux patterns: the Escherichia coli spectrum
Authors: Wiback Sharon J. , Mahadevan Radhakrishnan , Palsson Bernhard Ø.
Published: April 2004

Constraint‐based metabolic modeling has been used to capture the genome‐scale, systems properties of an organism's metabolism. The first generation of these models has been built on annotated gene sequence. To further this field, we now need to develop methods to incorporate additional “omic” data types including transcriptomics, metabolomics, and fluxomics to further facilitate the construction, validation, and predictive capabilities of these models. The work herein combines metabolic flux data with an in silico model of central metabolism of Escherichia coli for model centric integration of the flux data. The extreme pathways for this network, which define the allowable solution space for all possible flux distributions, are analyzed using the α‐spectrum. The α‐spectrum determines which extreme pathways can and cannot contribute to the metabolic flux distribution for a given condition and gives the allowable range of weightings on each extreme pathway that can contribute. Since many extreme pathways cannot be used under certain conditions, the result is a “condition‐specific” solution space that is a subset of the original solution space. The α‐spectrum results are used to create a “condition‐specific” extreme pathway matrix that can be analyzed using singular value decomposition (SVD). The first mode of the SVD analysis characterizes the solution space for a given condition. We show that SVD analysis of the α‐spectrum extreme pathway matrix that incorporates measured uptake and byproduct secretion rates, can predict internal flux trends for different experimental conditions. These predicted internal flux trends are, in general, consistent with the flux trends measured using experimental metabolic flux analysis techniques. © 2004 Wiley Periodicals, Inc.
Quantitative genome‐wide analysis of yeast deletion strain sensitivities to oxidative and chemical stress
Authors: Tucker Chandra L. , Fields Stanley
Published: April 2004

Understanding the actions of drugs and toxins in a cell is of critical importance to medicine, yet many of the molecular events involved in chemical resistance are relatively uncharacterized. In order to identify the cellular processes and pathways targeted by chemicals, we took advantage of the haploid Saccharomyces cerevisiae deletion strains (Winzeler et al., ). Although ∼4800 of the strains are viable, the loss of a gene in a pathway affected by a drug can lead to a synthetic lethal effect in which the combination of a deletion and a normally sublethal dose of a chemical results in loss of viability. We carried out genome‐wide screens to determine quantitative sensitivities of the deletion set to four chemicals: hydrogen peroxide, menadione, ibuprofen and mefloquine. Hydrogen peroxide and menadione induce oxidative stress in the cell, whereas ibuprofen and mefloquine are toxic to yeast by unknown mechanisms. Here we report the sensitivities of 659 deletion strains that are sensitive to one or more of these four compounds, including 163 multichemical‐sensitive strains, 394 strains specific to hydrogen peroxide and/or menadione, 47 specific to ibuprofen and 55 specific to mefloquine. We correlate these results with data from other large‐scale studies to yield novel insights into cellular function. Copyright © 2004 John Wiley & Sons, Ltd.
Shotgun cloning of transposon insertions in the genome of Caenorhabditis elegans
Authors: van der Linden Alexander M. , Plasterk Ronald H. A.
Published: April 2004

We present a strategy to identify and map large numbers of transposon insertions in the genome of Caenorhabditis elegans. Our approach makes use of the mutator strain mut‐7, which has germline‐transposition activity of the Tc1/mariner family of transposons, a display protocol to detect new transposon insertions, and the availability of the genomic sequence of C. elegans. From a pilot insertional mutagenesis screen, we have obtained 351 new Tc1 transposons inserted in or near 219 predicted C. elegans genes. The strategy presented provides an approach to isolate insertions of natural transposable elements in many C. elegans genes and to create a large‐scale collection of C. elegans mutants. Copyright © 2004 John Wiley & Sons, Ltd.
New computational tools for Brassica genome research
Authors: Love Christopher G. , Batley Jacqueline , Lim Geraldine , Robinson Andrew J. , Savage David , Singh Daniel , Spangenberg German C. , Edwards David
Published: April 2004

With the increasing quantities of Brassica genomic data being entered into the public domain and in preparation for the complete Brassica genome sequencing effort, there is a growing requirement for the structuring and detailed bioinformatic analysis of Brassica genomic information within a user‐friendly database. At the Plant Biotechnology Centre, Melbourne, Australia, we have developed a series of tools and computational pipelines to assist in the processing and structuring of genomic data, to aid its application to agricultural biotechnology research. These tools include a sequence database, ASTRA, a sequence processing pipeline incorporating annotation against GenBank, SwissProt and Arabidopsis Gene Ontology (GO) data and tools for molecular marker discovery and comparative genome analysis. All sequences are mined for simple sequence repeat (SSR) molecular markers using ‘SSR primer’ and mapped onto the complete Arabidopsis thaliana genome by sequence comparison. The database may be queried using a text‐based search of sequence annotation or GO terms, BLAST comparison against resident sequences, or by the position of candidate orthologues within the Arabidopsis genome. Tools have also been developed and applied to the discovery of single nucleotide polymorphism (SNP) molecular markers and the in silico mapping of Brassica BAC end sequences onto the Arabidopsis genome. Planned extensions to this resource include the integration of gene expression data and the development of an EnsEMBL‐based genome viewer. Copyright © 2004 John Wiley & Sons, Ltd.
RNAi for plant functional genomics
Authors: Matthew Louisa
Published: April 2004

A major challenge in the post‐genome era of plant biology is to determine the functions of all the genes in the plant genome. A straightforward approach to this problem is to reduce or knock out expression of a gene with the hope of seeing a phenotype that is suggestive of its function. Insertional mutagenesis is a useful tool for this type of study, but it is limited by gene redundancy, lethal knock‐outs, non‐tagged mutants and the inability to target the inserted element to a specific gene. RNA interference (RNAi) of plant genes, using constructs encoding self‐complementary ‘hairpin’ RNA, largely overcomes these problems. RNAi has been used very effectively in Caenorhabditis elegans functional genomics, and resources are currently being developed for the application of RNAi to high‐throughput plant functional genomics. Copyright © 2004 John Wiley & Sons, Ltd.
A comparison of global gene expression measurement technologies in Arabidopsis thaliana
Authors: Coughlan Sean J. , Agrawal Vikas , Meyers Blake
Published: April 2004

Microarrays and tag‐based transcriptional profiling technologies represent diverse but complementary data types. We are currently conducting a comparison of high‐density in situ synthesized microarrays and massively‐parallel signature sequencing (MPSS) data in the model plant, Arabidopsis thaliana. The MPSS data (available at http://mpss.udel.edu/at) and the microarray data have been compiled using the same RNA source material. In this review, we outline the experimental strategy that we are using, and present preliminary data and interpretations from the transcriptional profiles of Arabidopsis leaves and roots. The preliminary data indicate that the log ratio differences of transcripts between leaves and roots measured by microarray data are in better agreement with the MPSS data than the absolute intensities measured for individual microarrays hybridized to only one of the cRNA populations. The correlation was substantially improved by focusing on a subset of genes excluding those with very low expression levels; this selection may have removed noisy data. Future reports will incorporate more than 10 tissues that have been sampled by MPSS. Copyright © 2004 John Wiley & Sons, Ltd.
Antarctic genomics
Authors: Clark Melody S. , Clarke Andrew , Cockell Charles S. , Convey Peter , Detrich H. William , Fraser Keiron P. P. , Johnston Ian A. , Methe Barbara A. , Murray Alison E. , Peck Lloyd S. , Römisch Karin , Rogers Alex D.
Published: April 2004

With the development of genomic science and its battery of technologies, polar biology stands on the threshold of a revolution, one that will enable the investigation of important questions of unprecedented scope and with extraordinary depth and precision. The exotic organisms of polar ecosystems are ideal candidates for genomic analysis. Through such analyses, it will be possible to learn not only the novel features that enable polar organisms to survive, and indeed thrive, in their extreme environments, but also fundamental biological principles that are common to most, if not all, organisms. This article aims to review recent developments in Antarctic genomics and to demonstrate the global context of such studies. Copyright © 2004 John Wiley & Sons, Ltd.
Functional genomics in chickens: development of integrated‐systems microarrays for transcriptional profiling and discovery of regulatory pathways
Authors: Cogburn L. A. , Wang X. , Carre W. , Rejto L. , Aggrey S. E. , Duclos M. J. , Simon J. , Porter T. E.
Published: April 2004

The genetic networks that govern the differentiation and growth of major tissues of economic importance in the chicken are largely unknown. Under a functional genomics project, our consortium has generated 30 609 expressed sequence tags (ESTs) and developed several chicken DNA microarrays, which represent the Chicken Metabolic/Somatic (10 K) and Neuroendocrine/Reproductive (8 K) Systems (http://udgenome.ags.udel.edu/cogburn/). One of the major challenges facing functional genomics is the development of mathematical models to reconstruct functional gene networks and regulatory pathways from vast volumes of microarray data. In initial studies with liver‐specific microarrays (3.1 K), we have examined gene expression profiles in liver during the peri‐hatch transition and during a strong metabolic perturbation — fasting and re‐feeding — in divergently selected broiler chickens (fast vs. slow‐growth lines). The expression of many genes controlling metabolic pathways is dramatically altered by these perturbations. Our analysis has revealed a large number of clusters of functionally related genes (mainly metabolic enzymes and transcription factors) that control major metabolic pathways. Currently, we are conducting transcriptional profiling studies of multiple tissues during development of two sets of divergently selected broiler chickens (fast vs. slow growing and fat vs. lean lines). Transcriptional profiling across multiple tissues should permit construction of a detailed genetic blueprint that illustrates the developmental events and hierarchy of genes that govern growth and development of chickens. This review will briefly describe the recent acquisition of chicken genomic resources (ESTs and microarrays) and our consortium's efforts to help launch the new era of functional genomics in the chicken. Copyright © 2004 John Wiley & Sons, Ltd.
Residual Topological Isomerism of Intertwined Molecules
Authors: Lukin Oleg , Godt Adelheid , Vögtle Fritz
Published: April 2004

The growing number of molecular assemblies with unusual geometry and topology requires from time to time a revision of certain aspects of stereochemistry. The present paper analyzes several representatives of intertwined molecules that have bridges connecting their loops. In spite of the experimentally proven chirality, these species lack elements of both classical and topological chirality. Due to the relationship of these types of molecules to the well‐recognized topologically nontrivial compounds, such as catenanes and knots, we propose the term “residual topology” illustrated by a simple scheme of excessive or missing bridges that could be excluded or included, respectively, in molecular graphs of these species to render them topologically nontrivial. This concept paper represents, therefore, an update on the currently applied nomenclature.
Mechanism of Homogeneously and Heterogeneously Catalysed Meerwein–Ponndorf–Verley–Oppenauer Reactions for the Racemisation of Secondary Alcohols
Authors: Klomp Dirk , Maschmeyer Thomas , Hanefeld Ulf , Peters Joop A.
Published: April 2004

The mechanism of hydrogen transfer from alcohols to ketones, catalysed by lanthanide(III) isopropoxides or zeolite Beta has been studied. For the lanthanide catalysed reactions, (S)‐1‐phenyl‐(1‐2H1)ethanol and acetophenone were used as case studies to determine the reaction pathway for the hydrogen transfer. Upon complete racemisation all deuterium was present at the 1‐position, indicating that the reaction exclusively takes place via a carbon‐to‐carbon hydrogen transfer. Zeolite Beta with different Si/Al ratios was applied in the racemisation of (S)‐1‐phenylethanol. In this case the racemisation does not proceed via an oxidation/reduction pathway but via elimination of the hydroxy group and its re‐addition. This mechanism, however, is not characteristic for all racemisation reactions with zeolite Beta. When 4‐tert‐butyl cyclohexanone is reduced with this catalyst, a classical MPV reaction takes place exclusively. This demonstrates that zeolite Beta has a substrate dependent reaction pathway.
Multiple Recognition of Barbiturate Guests by “Hamilton‐Receptor”‐Functionalized Dendrimers
Authors: Dirksen Anouk , Hahn Uwe , Schwanke Frank , Nieger Martin , Reek Joost N. H. , Vögtle Fritz , De Cola Luisa
Published: April 2004

The well‐known unsubstituted “Hamilton receptor” was monofunctionalized with an amino group and attached at the periphery of poly(propyleneamine) dendrimers through the use of an activated ester. Four generations of Hamilton‐receptor‐functionalized dendrimers (HR‐dendrimers) were synthesized and characterized by 1H and 13C NMR spectroscopy and MALDI‐TOF mass spectrometry. The photophysical properties of the HR‐dendrimers were investigated by UV/Vis as well as with steady‐state and time‐resolved fluorescence spectroscopy. The dendrimers were used as multivalent hosts for the barbiturate guests Barbital (7) and [Re(Br)(CO)3(barbi‐bpy)] (8; barbi‐bpy=5‐[4‐(4′‐methyl)‐2,2′‐bipyridyl]methyl‐2,4,6‐(1 H,3 H,5 H)‐pyrimidinetrione). The stable adducts formed between the dendritic architectures (the hosts) and the barbiturate guests 7 and 8 were investigated by 1H NMR spectroscopy and photophysical methods. The binding constants of the barbiturate guests for binding to reference compound 2 (with a single receptor unit) in chloroform were found to be 1.4×103 M−1 and 1.5×105 M−1 for 7 and 8, respectively. Binding of 7 to the dendrimers enhances the weak emission of the Hamilton receptor. This increase in emission is also generation dependent; it was found to be most pronounced in the case of 2 and the least in the case of the fourth‐generation dendrimer 6. The unexpected increase in the quantum yield of emission from the HR‐dendrimers with increasing generation could be caused by the rather rigid conformation of the Hamilton receptors in later‐generation compounds, which is a result of intramolecular aggregation and steric hindrance at the periphery of the dendrimer. The photoinduced energy transfer from the excited state of the HR‐dendrimers to the lower‐lying excited state of the guest 8 was used to probe the formation of host–guest complexes. The rate of energy transfer was calculated to be 3.6×1010 s−1. Energy transfer in 2⊂8 only occurred in the presence of a strong base, which shows that the basic amine core in the HR‐dendrimers is crucial for this photoinduced process. The binding of 8 to the dendrimers is completely reversible: 8 can be exchanged with a competitive guest such as 7 and the emission of the HR‐dendrimer is restored.
Electrochemically Induced Sol–Gel Deposition of Zirconia Thin Films
Authors: Shacham Ronen , Mandler Daniel , Avnir David
Published: April 2004

A novel electrochemical method for deposition of ZrO2 thin films is described. The films, 50–600 nm thick, were obtained by applying moderate positive or negative potentials (+2.5 V to −1.5 V versus SHE) on conducting surfaces immersed in a 2‐propanol solution of zirconium tetra‐n‐propoxide [Zr(OPr)4] in the presence of minute quantities of water (water/monomer molar ratios in the range of 10−5 to 10−1), which was the limiting reagent. Oxidative electrochemical formation of solvated H+ and reductive formation of OH− catalyze the hydrolysis and condensation of the metal alkoxide precursor. The magnitude of the applied potential and its duration provide a convenient way of controlling the film thickness. The films consist of an amorphous phase, as revealed by XRD measurements. The effects of different parameters, such as the applied potential and its duration, the amount of added water and the current–time characteristics, were studied. A mechanism for the electrodeposition of the zirconia films which is in accordance with our findings is proposed.
Structure‐Switching Signaling Aptamers: Transducing Molecular Recognition into Fluorescence Signaling
Authors: Nutiu Razvan , Li Yingfu
Published: April 2004

The development of aptamer technology considerably broadens the utility of nucleic acids as molecular recognition elements, because it allows the creation of DNA or RNA molecules for binding a wide variety of analytes (targets) with high affinity and specificity. Several recent studies have focused on developing rational design strategies for transducing aptamer–target recognition events into easily detectable signals, so that aptamers can be widely exploited for detection directed applications. We have devised a generalizable strategy for designing nonfluorescent aptamers that can be turned into fluorescence‐signaling reporters. The resultant signaling probes are denoted “structure‐switching signaling aptamers” as they report target binding by switching structures from DNA/DNA duplex to DNA/target complex. The duplex is formed between a fluorophore‐labeled DNA aptamer and an antisense DNA oligonucleotide modified with a quencher (denoted QDNA). In the absence of the target, the aptamer hybridizes with QDNA, bringing the fluorophore into close proximity of the quencher for efficient fluorescence quenching. When this system is exposed to the target, the aptamer switches its binding partner from QDNA to the target. This structure‐switching event is coupled to the generation of a fluorescent signal through the departure of QDNA, permitting the real‐time monitoring of the aptamer–target recognition. In this article, we discuss the conceptual framework of the structure‐switching approach, the essential features of structure‐switching signaling aptamers as well as remaining challenges and possible solutions associated with this new methodology.
Synthesis, Structure, and Characterisation of a New Phenolato‐Bridged Manganese Complex [Mn2(mL)2]2+: Chemical and Electrochemical Access to a New Mono‐μ‐Oxo Dimanganese Core Unit
Authors: Hureau Christelle , Sabater Laurent , Anxolabéhère‐Mallart Elodie , Nierlich Martine , Charlot Marie‐France , Gonnet Florence , Rivière Eric , Blondin Geneviève
Published: April 2004

The dinuclear phenolato‐bridged complex [(mL)MnIIMnII(mL)](ClO4)2 (1(ClO4)2) has been obtained with the new [N4O] pentadentate ligand mL− (mLH=N,N′‐bis‐(2‐pyridylmethyl)‐N‐(2‐hydroxybenzyl)‐N′‐methyl‐ethane‐1,2‐diamine) and has been characterised by X‐ray crystallography. X‐ and Q‐band EPR spectra were recorded and their variation with temperature was examined. All spectra exhibit features extending over 0–800 mT at the X band and over 100–1450 mT at the Q band, features that are usually observed for dinuclear MnII complexes. Cyclic voltammetry of 1 exhibits two irreversible oxidation waves at E${{{\rm p}\hfill \atop 1\hfill}}$=0.89 V and E${{{\rm p}\hfill \atop 2\hfill}}$=1.02 V, accompanied on the reverse scan by an ill‐defined cathodic wave at E${{{\rm p}\hfill \atop 1^{\prime}\hfill}}$=0.56 V (all measured versus the saturated calomel electrode (SCE)). Upon chemical oxidation with tBuOOH (10 equiv) at 20 °C, 1 is transformed into the mono‐μ‐oxo species [(mL)MnIII‐(μ‐O)‐MnIII(mL)]2+ (2), which eventually partially evolves into the di‐μ‐oxo species [(mL)MnIII‐(μ‐O)2‐MnIV(mL)]n+ (3) in which one of the aromatic rings of the ligand is decoordinated. The UV/Vis spectrum of 2 displays a large absorption band at 507 nm, which is attributed to a phenolate→MnIII charge‐transfer transition. The cyclovoltammogram of 2 exhibits two reversible oxidation waves, at 0.65 and 1.16 V versus the SCE, corresponding to the MnIIIMnIII/MnIIIMnIV and MnIIIMnIV/MnIVMnIV oxidation processes, respectively. The one‐electron electrochemical oxidation of 2 leads to the mono‐μ‐oxo mixed‐valent species [(mL)MnIII‐(μ‐O)‐MnIV(mL)]3+ (2 ox). The UV/Vis spectrum of 2 ox exhibits one large band at 643 nm, which is attributed to the phenolate→MnIV charge‐transfer transition. 2 ox can also be obtained by the direct electrochemical oxidation of 1 in the presence of an external base. The 2 ox and 3 species exhibit a 16‐line EPR signal with first peak to last trough widths of 125 and 111 mT, respectively. Both spectra have been simulated by using colinear rhombic Mn‐hyperfine tensors. Mechanisms for the chemical formation of 2 and the electrochemical oxidation of 1 into 2 ox are proposed.
Competition between π and Non‐π Cation‐Binding Sites in Aromatic Amino Acids: A Theoretical Study of Alkali Metal Cation (Li+, Na+, K+)–Phenylalanine Complexes
Authors: Siu Fung Ming , Ma Ngai Ling , Tsang Chun Wai
Published: April 2004

To understand the cation–π interaction in aromatic amino acids and peptides, the binding of M+ (where M+ = Li+, Na+, and K+) to phenylalanine (Phe) is studied at the best level of density functional theory reported so far. The different modes of M+ binding show the same order of binding affinity (Li+>Na+>K+), in the approximate ratio of 2.2:1.5:1.0. The most stable binding mode is one in which the M+ is stabilized by a tridentate interaction between the cation and the carbonyl oxygen (OC), amino nitrogen (NH2), and aromatic π ring; the absolute Li+, Na+, and K+ affinities are estimated theoretically to be 275, 201, and 141 kJ mol−1, respectively. Factors affecting the relative stabilities of various M+–Phe binding modes and conformers have been identified, with ion–dipole interaction playing an important role. We found that the trend of π and non‐π cation bonding distances (Na+–π>Na+–N>Na+–O and K+–π>K+–N>K+–O) in our theoretical Na+/K+–Phe structures are in agreement with the reported X‐ray crystal structures of model synthetic receptors (sodium and potassium bound lariat ether complexes), even though the average alkali metal cation–π distance found in the crystal structures is longer. This difference between the solid and the gas‐phase structures can be reconciled by taking the higher coordination number of the cations in the lariat ether complexes into account.
Highly Conjugated p‐Quinonoid π‐Extended Tetrathiafulvalene Derivatives: A Class of Highly Distorted Electron Donors
Authors: Díaz Marta C. , Illescas Beatriz M. , Martín Nazario , Viruela Rafael , Viruela Pedro M. , Ortí Enrique , Brede Ortwin , Zilbermann Israel , Guldi Dirk M.
Published: April 2004

A new class of π‐extended TTF‐type electron donors (11 a–c) has been synthesized by Wittig–Horner olefination of bianthrone (9) with 1,3‐dithiole phosphonate esters (10 a–c). In cyclic voltammetry experiments, donors 11 a–c reveal a single, electrochemically irreversible oxidation—yielding the corresponding dicationic products—at relatively low oxidation potentials (∼0.7–0.8 V). Theoretical calculations, performed at the DFT level (B3 P86/6‐31 G*), predict a highly‐folded C2h structure for 11 a. In the ground state, the molecule adopts a double saddle‐like conformation to compensate the steric hindrance. The calculations suggest that the intramolecular charge transfer associated with the HOMO→LUMO transition is responsible for an absorption band observed above 400 nm. While the radical cation 11 a.+ retains the folded C2h structure predicted for the neutral molecule as the most stable conformation, the dication 11 a2+ has a fully aromatic D2 structure, formed by an orthogonal 9,9′‐bianthryl central unit to which two singly‐charged dithiole rings are attached. The drastic conformational changes that compounds 11 undergo upon oxidation account for their electrochemical properties. By means of pulse radiolysis measurements, radical‐induced one‐electron oxidation of 11 a–c was shown to lead to the radical cation species (11 a–c.+), which were found to disproportionate with generation of the respective dication species (11 a–c2+) and the neutral molecules (11 a–c).
Effects of Chain Length and Au Spin‐Orbit Coupling on 3(ππ*) Emission from Bridging Cn2− Units: Theoretical Characterization of Spin‐Forbidden Radiative Transitions in Metal‐Capped One‐Dimensional Carbon Chains [H3PAu(CC)nAuPH3]
Authors: Cao Zexing , Zhang Qianer
Published: April 2004

Density functional theory and CASSCF calculations have been used to optimize the geometries of binuclear gold(I) complexes [H3PAu(CC)nAuPH3] (n=1–6) in their ground states and selected lowest energy 3(ππ*) excited states. Vertical excitation energies obtained by time‐dependent density functional calculations for the spin‐forbidden singlet–triplet transitions have exponential‐decay size dependence. The predicted singlet–triplet splitting limit of [H3PAu(CC)∝AuPH3] is about 8317 cm−1. Calculated singlet–triplet transition energies are in reasonable agreement with available experimental observations. The effect of the heavy atom Au spin‐orbit coupling on the 3(ππ*) emission of these metal‐capped one‐dimensional carbon allotropes has been investigated by MRCI calculations. The contribution of the spin‐ and dipole‐allowed singlet excited state to the spin‐orbit‐coupling wave function of the 3(ππ*) excited state makes the low‐lying acetylenic triplet excited states become sufficiently allowed so as to appear in both electronic absorption and emission.
Photochemical and Electronic Properties of Conjugated Bis(azo) Compounds: An Experimental and Computational Study
Authors: Cisnetti Federico , Ballardini Roberto , Credi Alberto , Gandolfi Maria Teresa , Masiero Stefano , Negri Fabrizia , Pieraccini Silvia , Spada Gian Piero
Published: April 2004

We have investigated the photophysical, photochemical and electrochemical properties of two bis(azo) derivatives, (E,E)‐m‐1 and (E,E)‐p‐1. The two compounds, which can be viewed as being composed of a pair of azobenzene units sharing one of their phenyl rings, differ only for the relative position of the two azo groups on the central phenyl ring—meta and para for m‐1 and p‐1, respectively. The UV‐visible absorption spectra and photoisomerisation properties are noticeably different for the two structural isomers; (E,E)‐m‐1 behaves similarly to (E)‐azobenzene, while (E,E)‐p‐1 exhibits a substantial red shift in the absorption bands and a decreased photoreactivity. The three geometric isomers of m‐1, namely the E,E, E,Z and Z,Z isomers, cannot be resolved in a mixture by absorption spectroscopy, while the presence of three distinct species can be revealed by analysis of the absorption changes observed upon photoisomerisation of (E,E)‐p‐1. Quantum chemical ZINDO/1 calculations of vertical excitation energies nicely reproduce the observed absorption changes and support the idea that, while the absorption spectra of the geometrical isomers of m‐1 are approximately given by the sum of the spectra of the constituting azobenzene units in their relevant isomeric form, this is not the case for p‐1. From a detailed study on the E→Z photoisomerisation reaction it was observed that the photoreactivity of an azo unit in m‐1 is influenced by the isomeric state of the other one. Such observations indicate a different degree of electronic coupling and communication between the two azo units in m‐1 and p‐1, as confirmed by electrochemical experiments and quantum chemical calculations. The decreased photoisomerisation efficiency of (E,E)‐p‐1 compared to (E,E)‐m‐1 is rationalised by modelling the geometry relaxation of the lowest π–π* state. These results are expected to be important for the design of novel oligomers and polymers, based on the azobenzene unit, with predetermined photoreactivity.
Supramolecular Recognition: Protonmotive‐Driven Switches or Motors?
Authors: Crowley James D. , Goshe Andrew J. , Steele Ian M. , Bosnich Brice
Published: April 2004

A dicationic molecular receptor bearing two cofacially disposed terpyridyl‐Pd‐Cl units forms stable 1:1 host–guest complexes with planar, neutral platinum(II) complexes. When the guest is modified to incorporate a pyridine group, the now basic guest is protonated by trifluoroacetic acid in acetonitrile solutions. The basic yellow guest forms a stable, deep red 1:1 host–guest complex with the yellow palladium receptor. Addition of trifluoroacetic acid to this host–guest complex leads to the displacement of the guest from the receptor. It is proposed that the dissociation of the guest is caused by electrostatic repulsion between the dicationic receptor and the positively charged protonated guest. Addition of base restores the host–guest complex. This protonmotive translocation of the guest from the host to the solution is discussed in terms of the mechanisms that drive molecular motors, the power stroke and the Brownian ratchet. It is concluded that the system is best described as a molecular switch that operates by the same mechanism as one stroke of a molecular motor
Ferrocene‐Modified Purines as Potential Electrochemical Markers: Synthesis, Crystal Structures, Electrochemistry and Cytostatic Activity of (Ferrocenylethynyl)‐ and (Ferrocenylethyl)purines
Authors: Hocek Michal , Štěpnička Petr , Ludvík Jiří , Císařová Ivana , Votruba Ivan , Řeha David , Hobza Pavel
Published: April 2004

Palladium‐catalyzed Sonogashira cross‐coupling reactions of halopurines 9‐benzyl‐6‐chloropurine (2 a), 9‐benzyl‐8‐bromoadenine (2 b), and 9‐benzyl‐2‐chloroadenine (2 c) with ethynylferrocene (1) gave the corresponding (ferrocenylethynyl)purines 3 a–c in moderate to good yields. Catalytic hydrogenation of these alkynes over Pd/C afforded the respective saturated [2‐(ferrocenyl)ethyl]purines 4 a–c. The crystal structures 3 a, 3 b, 4 a and 4 b as determined by X‐ray diffraction show interesting solid‐state interactions, markedly different for purines 3 a and 4 a on one hand and adenines 3 b and 4 b that possess a free amino group on the other. Electrochemistry of electrochemically labelled purines 3 and 4 has been studied by voltammetry and cyclic voltammetry on platinum disc electrode and the experimental oxidation potentials were confirmed and explained by ionization potentials from theoretical DFT calculations. Several compounds of this series exhibited a considerable cytostatic effect.
The Structure of Metallomicelles
Authors: Griffiths P. C. , Fallis I. A. , Willock D. J. , Paul A. , Barrie C. L. , Griffiths P. M. , Williams G. M. , King S. M. , Heenan R. K. , Görgl Richard
Published: April 2004

The morphology of micelles formed by two novel metallosurfactants has been studied by small‐angle neutron scattering (SANS) and small‐angle‐X‐ray scattering (SAXS). The two surfactants both contain a dodecyl chain as the hydrophobic moiety, but differ in the structure of the head group. The surfactants are CuII complexes of monopendant alcohol derivatives of a) the face‐capping macrocycle 1,4,7‐triazacyclanonane (tacn), and b) an analogue based upon the tetraazamacrocycle 1,4,7,10‐tetraazacyclododecane. Here, neutron scattering has been used to study the overall size and shape of the surfactant micelles, in conjunction with X‐ray scattering to locate the metal ions. For the 1,4,7,10‐tetraazacyclododecane‐based surfactant, oblate micelles are observed, which are smaller to the prolate micelles formed by the 1,4,7‐triazacyclononane analogue. The X‐ray scattering analysis shows that the metal ions are distributed throughout the polar head‐group region, rather than at a well‐defined radius; this is in good agreement with the SANS‐derived dimensions of the micelle. Indeed, the same model for micelle morphology can be used to fit both the SANS and SAXS data.
A Mechanically Interlocked Bundle
Authors: Badjić Jovica D. , Balzani Vincenzo , Credi Alberto , Lowe James N. , Silvi Serena , Stoddart J. Fraser
Published: April 2004

The prototype of an artificial molecular machine consisting of a trisammonium tricationic component interlocked with a tris(crown ether) component to form a molecular bundle with averaged C3v symmetry has been designed and synthesized. The system is based on noncovalent interactions, which include 1) N+H⋅⋅⋅O hydrogen bonds; 2) CH⋅⋅⋅O interactions between the CH2NH2+CH2 protons on three dibenzylammonium‐ion‐containing arms, which are attached symmetrically to a benzenoid core, and three dibenzo[24]crown‐8 macrorings fused onto a triphenylene core; and 3) π⋅⋅⋅π stacking interactions between the aromatic cores. The template‐directed synthesis of the mechanically interlocked, triply threaded bundle involves post‐ assembly covalent modification, that is, the efficient conversion of three azide functions at the ends of the arms of the bound and threaded trication into bulky triazole stoppers, after 1,3‐dipolar cycloaddition with di‐tert‐butylacetylenedicarboxylate to the extremely strong 1:1 adduct that is formed in dichloromethane/acetonitrile (3:2), on account of a cluster effect associated with the paucivalent adduct. Evidence for the averaged C3v symmetry of the molecular bundle comes from absorption and luminescence data, as well as from electrochemical experiments, 1H NMR spectroscopy, and mass spectrometry. The photophysical properties of the mechanically interlocked bundle are very similar to those of the superbundle that precedes the formation of the bundle in the process of supramolecular assistance to covalent synthesis. Although weak non‐nucleophilic bases (e.g., nBu3N and iPr2NEt) fail to deprotonate the bundle, the strong tBuOK does, as indicated by both luminescence and 1H NMR spectroscopy. While deprotonation undoubtedly loosens up the interlocked structure of the molecular bundle by replacing relatively strong N+H⋅⋅⋅O hydrogen bonds by much weaker NH⋅⋅⋅O ones, the π⋅⋅⋅π stacking interactions ensure that any structural changes are inconsequential, particularly when the temperature of the solution of the neutral molecular bundle in dichloromethane is cooled down to considerably below room temperature.
Two Metalloid Ga22 Clusters Containing a Novel Ga22 Core with an Icosahedral Ga12 Center
Authors: Schnepf Andreas , Köppe Ralf , Weckert Edgar , Schnöckel Hansgeorg
Published: April 2004

In addition to the two so far known types of metalloid Ga22 clusters a new type is presented in two compounds containing the anions [Ga22Br{N(SiMe3)2}10Br10]3− (1) and [Ga22Br2{N(SiMe3)2}10Br10]2− (2). In both anions 10 Ga atoms of the icosahedral Ga12 core are directly connected to further Ga atoms. The two remaining Ga atoms (top and bottom) of the Ga12 icosahedron are bonded to one (1) and two Br atoms (2), respectively. The formation and structure of both compounds containing a slightly different average oxidation number of the Ga atoms is discussed and compared especially with regard to the Ga84 cluster compound and similar metalloid Aln clusters. Finally, the consequences arising from the presence of two very similar but not identical Ga22 cluster compounds are discussed and special consideration is given to the so far not understood physical properties (metallic conductivity and superconductivity) of the Ga84 cluster compound.
Synthesis, Structure, and Dynamics of Six‐Membered Metallacoronands and Metallodendrimers of Iron and Indium
Authors: Saalfrank Rolf W. , Deutscher Christian , Maid Harald , Ako Ayuk M. , Sperner Stefan , Nakajima Takayuki , Bauer Walter , Hampel Frank , Heß Bernd A. , van Eikema Hommes Nico J. R. , Puchta Ralph , Heinemann Frank W.
Published: April 2004

In the reaction of the N‐substituted diethanolamines (H2L1–3) (1–3) with calcium hydride followed by addition of iron(III) or indium(III) chloride, the iron wheels [Fe6Cl6(L1)6] (4) and [Fe6Cl6(L2)6] (6) or indium wheels [In6Cl6(L1)6] (5), [In6Cl6(L2)6] (8) and [In6Cl6(L3)6] (9) were formed in excellent yields. Exchange of the chloride ions of 6 by thiocyanate ions afforded [Fe6(SCN)6(L2)6] (7). Whereas the structures of 4, 5 and 7 were determined unequivocally by single‐crystal X‐ray analyses, complexes 8 and 9 were characterised by NMR spectroscopy. Contrary to what is normally presumed, the scaffolds of six‐membered metallic wheels are not generally rigid, but rather undergo nondissociative topomerisation processes. This was shown by variable temperature (VT) 1H NMR spectroscopy for the indium wheel [In6Cl6(L1)6] (5) and is highlighted for the enantiotopomerisation of one indium centre {${{ 1/6 }}$[S6‐5] ⇄ ${{ 1/6 }}$[S6‐5′]}. The self‐assembly of metallic wheels, starting from diethanolamine dendrons, is an efficient strategy for the convergent synthesis of metallodendrimers.
Cover Picture: Synthesis, Structure, and Dynamics of Six‐Membered Metallacoronands and Metallodendrimers of Iron and Indium (Chem. Eur. J. 8/2004)
Authors: Saalfrank Rolf W. , Deutscher Christian , Maid Harald , Ako Ayuk M. , Sperner Stefan , Nakajima Takayuki , Bauer Walter , Hampel Frank , Heß Bernd A. , van Eikema Hommes Nico J. R. , Puchta Ralph , Heinemann Frank W.
Published: April 2004

The cover picture shows the X‐ray structure of a six‐membered iron wheel. In order to support its existence in solution and to gain deeper insights into the possible flexibility of its scaffold, we prepared an indium analogue. Temperature‐dependent 1H NMR solution spectra of the indium wheel (depicted in the middle) revealed intramolecular dynamics as exemplarily monitored for the diastereotopic benzylic methylene protons. Evidently the iron wheels are not only frozen beauties, but are also bubbly lively species. More details are given in the communication by R. W. Saalfrank et al. on p. 1899 ff.
Ab initio High Pressure Investigations of InI
Authors: Becker Daniel , Beck Horst P.
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.
Nonplanarity at Tri‐Coordinated Aluminum and Gallium: Cyclic Structures for X3Hnm (X: B, Al, Ga)
Authors: Srinivas Gantasala N. , Anoop Anakuthil , Jemmis Eluvathingal D. , Hamilton Tracy P. , Lammertsma Koop , Leszczynski Jerzy , Schaefer Henry F. III
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.
A Ferroelectric Barium Titanate, BaTi2O5.
Authors: Kimura Teiichi , Goto Takashi , Yamane Hisanori , Iwata Hiroaki , Kajiwara Takashi , Akashi Takaya
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.
Lanthanum Indium Oxide from X‐Ray Powder Diffraction.
Authors: Park Hyun Min , Lee Hwack Joo , Park Sang Hyun , Yoo Han Ill
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.
Vanadate Garnet, Ca2NaMg2V3O12.
Authors: Nakatsuka Akihiko , Ikuta Yasuaki , Yoshiasa Akira , Iishi Kazuake
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.
Magnesium Diiodide, MgI2.
Authors: Brogan Michael A. , Blake Alexander J. , Wilson Claire , Gregory Duncan H.
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.
Structure and Magnetism of the Tetra‐Copper(II)‐Substituted Heteropolyanion [Cu4K2(H2O)8 (α‐AsW9O33)2]8‐.
Authors: Kortz Ulrich , Nellutla Saritha , Stowe Ashley C. , Dalal Naresh S. , van Tol Johan , Bassil Bassem S.
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.
Synthesis and Crystal Structure of CsCu3O2, Containing a New Type of Oxocuprate(I) Polyanion.
Authors: Sofin M. , Peters E. M. , Jansen M.
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.
Anhydrous Mercurous Chlorate, Hg2(ClO3)2.
Authors: Goebbels Dirk , Meyer Gerd
Published: April 2004

For Abstract see ChemInform Abstract in Full Text.