bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of thin film structure based on MgF2, CeO2 and Al2O3 layers for optical applications
Authors: Asghar M. H. , Shoaib M. , Naseem S. , Placido F.
Published: March 2008

Thin film multilayer structures based on MgF2, CeO2 and Al2O3 layers were prepared on a BK7 glass substrate with resistive heating evaporation as an antireflection coating in the 450–750 nm spectral range. Prior to deposition of the multilayer structure, individual layers of the materials used were characterized. A three-layer structure of MgF2/CeO2/Al2O3/BK7 was then prepared using the same deposition conditions as for individual layers. Reasonably low reflection was observed for the as-deposited sample with R < 0.8% from 500–750 nm and R
ave < 1% over the desired spectrum. Further, low surface roughness and small particle size were seen for the as-deposited sample. Only a few low intensity peaks for the materials were observed with X-ray diffraction. Optical and structural properties were studied as a function of annealing temperature in the range 250°C–450°C. A slight shift of reflection spectra was observed with annealing, however, an increase in particle size (35 nm–70 nm) along with surface roughness was also observed.
Effect of Cr and V on phase equilibria in Co–WC based hardmetals
Authors: Frisk Karin , Markström Andreas
Published: March 2008

New measurements of the influence of Cr and V on the melting temperature of the binder phase in Co-based hardmetals are presented. It was shown that both Cr and V affect the melting temperature significantly. Cr decreases the melting temperature by over 100°C, and V by approximately 40°C. This is due to the high solubility of Cr and V in liquid Co, and this solubility was determined by experiments and calculations. The solubility of Cr in solid fcc-Co is also discussed, as well as the composition of the MC, M7C3 and the M6C carbides in alloys with Cr and V. The new experimental information is used to obtain a reliable thermodynamic description of the binder phase (Co-rich) in C – Co – Cr – W and C – Co – V – W alloys. Calculated equilibria are compared with experiments.
Influence of previous ageing treatments on the strength of an Al-4.3 wt.% Mg-1.2 wt.% Cu alloy processed by ECAE
Authors: Zhang Zheng-Rong , Van Houtte Paul , Verlinden Bert
Published: March 2008

The interaction of equal channel angular extrusion (ECAE) with precipitation hardening during warm ECAE at 180°C in a Al-4.3 wt.% Mg-1.2 wt.% Cu alloy, annealed at various stages of ageing, was studied by room temperature compression tests and transmission electron microscopy. It was observed that peak aged samples lose much of their strength during ECAE due to fragmentation of precipitates. The highest strength after four ECAE passes (route Bc) at 180°C is obtained with samples in the under-aged condition although in this case dissolution of precipitates into the matrix occurs. After four ECAE passes fine equiaxed grains with an average size of approximately 200 nm with some traces of remnant elongated grains were obtained.
Initial stage of bi-modal microstructure in TiO2-doped α-Al2O3 ceramics induced by SiO2 impurity
Authors: Qian Pengxiang , Gu Hui , Aldinger Fritz
Published: March 2008

Uni-modal and bi-modal microstructures were concurrently observed in a TiO2-doped -Al2O3 ceramic material with some SiO2 impurity. The segregation of Ti and Si to grain boundaries was systematically evaluated to reveal their role at the start of anisotropic grain growth. In general, in the bi-modal area grain boundaries exhibit higher Si excess than those in the uni-modal area. However, the basal plane of anisotropic grains was always found to contain more segregated Si while the non-basal planes were found to contain less Si. Such enrichment of SiO2 was also found at the basal planes of equiaxed grains in the uni-modal area, which occurred in the initial stage of anisotropic grain growth. Before and after this stage, the grain boundary composition was relatively uniform with the mole ratio of SiO2 to TiO2 as 2.3: 1 and 5.8: 1, respectively. The latter should be related to the composition of eutectic liquid formed during the sintering, which is responsible for the development of the bi-modal microstructure.
High‐Energy Electron Diffraction
Authors: Zuo Jian‐Min
Published: March 2008

High‐energy electrons have very short wavelengths associated with particle waves and electron diffraction is used to probe the atomic structure of both inorganic and organic materials. Electrons have a large scattering cross section and can be focused into small probes by magnetic lenses. This makes electron diffraction very useful for studying “small” crystals, surfaces, or material's microstructure. The principles and the modern aspects of electron diffraction are described here with the intention to provide an introduction that both the novice and the expert will find useful as a guide for electron diffraction. The chapter starts with an introduction to different electron diffraction techniques. This is followed by the background theories which are useful for the interpretation of diffraction patterns. Experimental procedures are described at the end of the technical background. The applications section has a large collection of examples from relatively straightforward tasks to more advanced ones that are under development for their promises. Experimental details are provided when it is appropriate to give some idea of what it takes to do electron diffraction.
High Resolution Electron Energy‐Loss Spectroscopy
Authors: Soriaga Manuel P. , Chen Xiaole , Li Ding , Stickney John L.
Published: March 2008

The determination of the identity and structure of molecular species present in no more than monolayer quantities at solid surfaces is one of the more difficult tasks in interfacial science. In this regard, vibrational spectroscopy is an invaluable technique; in the evaluation of the molecular integrity of surface‐bound compounds, it has few equals. Optical methods such as infrared spectroscopy, while rather uncomplicated for bulk materials, lack the high sensitivity needed for most surface species due to minuscule molecular amounts. A much more responsive alternative is based on the use of low‐energy electrons to interact with the molecular oscillators on the surface. If inelastic interactions occur, the energy of the backscattered electrons will be lower than that of the incident electrons, and the energy loss will correspond to a vibrational‐mode frequency. The present article briefly describes the fundamental principles of and instrumental considerations in high‐resolution electron energy‐loss spectroscopy (HREELS), and cites seminal applications in the study of the adsorption of organic and inorganic molecules at metal and semiconductor surfaces. A limited list of HREELS work published since the turn of the century is added in the last section.
Microwave Rotational Spectroscopy
Authors: Xu Yunjie , Jäger Wolfgang
Published: March 2008

Since its inception in 1934, microwave rotational spectroscopy has provided some of the most accurate data for numerous small to medium sized molecules, including structural parameters, force field parameters, and electronic charge distributions. We give a very brief review of the history of microwave spectroscopy, leading up to the most recent developments, that is, instruments that use Fourier transform techniques. Since these Fourier transform microwave spectrometers are not commercially available, a brief discussion about their general design is given. Analyses of the recorded rotational spectra can yield a number of spectroscopic parameters, depending on the molecular symmetry and the various angular momenta present, such as nuclear spins and electronic momenta. The physical significance of the more common spectroscopic parameters, such as rotational constants, centrifugal distortion constants, nuclear quadrupole coupling constants, etc. is given. We also indicate how these parameters can be used to characterize the molecule in terms of, for example, structural parameters, dynamical behavior, and bond character. The remainder of the article is devoted to case studies. These include the discovery of covalent bonds involving the noble gas atom argon, structural characterization of organometallic compounds, such as ferrocenes, bonding in diatomic transition metal‐containing compounds, a description of laboratory studies of molecules which are of atmospheric and astrophysical interest, and studies of weakly bound complexes with relevance to inorganic chemistry.
Nuclear Resonance Vibrational Spectroscopy (
NRVS
)
Authors: Zeng Weiqiao , Silvernail Nathan J. , Scheidt W. Robert , Sage J. Timothy
Published: March 2008

Nuclear Resonance Vibrational Spectroscopy (NRVS) utilizes the simultaneous excitation of the Mössbauer nucleus and vibrational quanta. Vibrational features appear as sidebands on the recoilless resonance. NRVS reveals the complete vibrational spectrum of the probe nucleus with the resolution almost equal to that of Raman or infrared. Major advantages include selectivity to vibrations of the Mössbauer isotope with quantitative information on vibrational amplitudes, as well as frequencies. Single crystal measurements are selective for motion along the exciting X‐ray beam. NRVS is equally applicable to all ligation and oxidation states. Questions that can be addressed include the strength of metal coordination, the energetic cost of probe displacement, discrimination of metal‐ligand vibrations from cofactor or peptide vibrations, and the local vs. global character of active site vibrations.
Photoelectron Spectroscopy
Authors: Gruhn Nadine E. , Lichtenberger Dennis L.
Published: March 2008

Photoelectron spectroscopy measures the energies for emission of electrons from molecules or materials through application of the photoelectric effect. For neutral molecules this is a direct measure of the ionization energies. The ionizations are explicitly defined in terms of transitions between the ground state of a molecule and accessible states of the molecular positive ion, but in a first order approximation, each ionization of a molecule can be described as removal of an electron from an individual orbital. The ionization energies can then be considered as measures of orbital energies, and shifts can be interpreted in terms of orbital stabilizations or destabilizations due to changes in electron distributions and bonding. The intensities and profiles of the ionization bands in the photoelectron spectra provide additional information on the characters and bonding natures of the orbitals. All orbitals can be probed, from valence orbitals such as lone pairs and bonds to orbitals in the cores of heavy atoms. Photoelectron spectroscopy is a large field of study that has many subfields and new techniques continue to be introduced. These different subfields all have different instrumental and sample constraints, but taken as a whole photoelectron spectroscopic experiments can be performed on almost any system of interest in inorganic chemistry. This article summarizes the basic physical principles of photoelectron emission caused by one or more photons, the relationship of photoelectron spectra to the electronic structure of neutral and anionic molecules, and the additional considerations for photoionization of bulk samples. Auger electron spectroscopy (AES) and Penning ionization electron spectroscopy (PIES), techniques which are closely related to photoelectron spectroscopy, are also discussed. Case studies are given for applications of photoelectron spectroscopy to study of bioinorganic model complexes, including iron‐sulfur and molybdenum‐sulfur bonding and covalency, electronic structure of porphyrins and metalloporphyrins, negative‐ion photoelectron spectroscopy of phthalocyanines, and the use of the technique to measure inner‐sphere reorganization energies.
Photoluminescence and Electroluminescence, Solid State
Authors: Deye Joel R. , Walters Keith A.
Published: March 2008

The measurement of photoluminescence or electroluminescence on solid samples can provide details on the electronic nature of the material in question. The majority of these measurements involve the examination of the electronic structure of semiconductors, especially those under consideration for use as light‐emitting diodes or photoelectric cells. The presence of defects in these materials (in the form of excitons and acceptor/donor centers) can dramatically alter the observed spectral properties. However, the technique is largely limited to electronic profiling, so significant structural information and sample morphology must be probed with complementary techniques. Basic instrumentation and techniques for recording these spectra are presented, along with special considerations for solid‐state samples. Numerous examples of recent literature reports utilizing this technique are also presented.
Electronic Spectroscopy
Authors: Hughes Joseph L. , Krausz Elmars
Published: March 2008

Developments in the ability of electronic spectroscopy to provide insights into the fundamental electronic structure, photophysical and/or photochemical processes in inorganic and bioinorganic systems are outlined. These are highlighted by a number of examples across a range of chemical and biochemical systems. Some fundamental constraints regarding the application of electronic spectroscopy to a wider range of chemical questions are identified, as well as both practical and intrinsic limitations associated with the processes of measurement. The ubiquitous phenomenon of spectral broadening in optical and UV spectroscopy is given particular attention and the important concept of homogeneous versus inhomogeneous broadening is highlighted. The overall focus is on absorption‐based spectroscopies of chromophores at variable and low temperatures in either glassy, crystalline, or protein environments. The utilization of some of the powerful emerging technologies such as tuneable laser sources or synchrotron sources, along with the very high efficiency charge coupled device (CCD) and semiconductor diode detectors that are now available, allows the rapid accumulation of high quality spectra of small samples as well as measurements in minimal actinic fluences.
Electron‐Nuclear Double Resonance (
ENDOR
) Spectroscopy
Authors: Telser Joshua
Published: March 2008

Electron‐nuclear double resonance (ENDOR) spectroscopy is a magnetic resonance technique that was invented in the mid 1950s by George Feher, then at Bell Telephone Laboratories. The first applications of ENDOR were to problems in solid state physics, but beginning in the 1970s, and particularly since the late 1980s, ENDOR has been widely applied to bioinorganic systems. ENDOR is fundamentally an electron paramagnetic resonance (EPR) technique, however, it also has aspects of nuclear magnetic resonance (NMR) spectroscopy. Essentially, ENDOR consists of the monitoring of an EPR signal, while effecting NMR transitions. The EPR signal can be either a continuous wave (CW) signal or a pulsed, electron spin echo (ESE) signal, in both cases caused by the application of microwave energy to a sample in an external magnetic field. As with EPR itself, ENDOR can thus be either a CW or pulsed (time‐domain) spectroscopic technique. The NMR transitions are caused by the application of radiofrequency (rf) energy, as with NMR itself. NMR transitions only of nuclei magnetically (hyperfine) coupled to the paramagnetic center (i.e., the center giving rise to the EPR signal) affect the intensity of this EPR signal, whether CW or pulsed, and provide characteristic ENDOR spectra. As a consequence of its double resonance nature, ENDOR has a great deal of flexibility in spectroscopic parameters. The parameters that affect EPR signals, e.g., microwave power, can also play a role in ENDOR spectral appearance. Additionally, there are parameters relevant to the NMR aspects of ENDOR that affect ENDOR spectra. In both CW and pulsed ENDOR there is experimental flexibility, which is described here. As a result, ENDOR spectroscopy can provide detailed information on multiple, magnetically active nuclei that comprise a paramagnetic center in a bioinorganic system. This information includes identification of such nuclei and metrical information on their relation to the paramagnetic center. This article uses a multifaceted case study to illustrate the application of ENDOR spectroscopy in bioinorganic chemistry. Specifically, the case study describes the application of multinuclear (
1, 2
H,
13
C,
57
Fe,
95
Mo) CW and pulsed ENDOR to enhance our understanding of the iron–molybdenum cofactor in nitrogenase. ENDOR allows identification of the constituent metal ions and their formal oxidation states, and identifies the nature of the substrate analog or inhibitor binding to the cluster. In combination with resting state structural information, and computational and model system studies, ENDOR can provide a structural picture of the intermediates in nitrogen fixation.
Freeze‐Quench Kinetics
Authors: de Vries Simon
Published: March 2008

Rapid‐mixing, rapid‐freezing techniques are employed for the study of enzyme or chemical catalytic mechanisms. The techniques aim to provide electronic and molecular structures of transient intermediates formed during the reaction by means of spectroscopic analyses of the rapidly frozen samples. Briefly, the mixing‐sampling procedure consists of the rapid mixing of two reactants, for example, enzyme and substrate, followed by rapid freezing of the mixture in a liquid cryo‐medium or on a cold plate to quench the reaction progress. The resulting frozen powder is subsequently sampled and made available for further low‐temperature spectroscopic analyses such as UV‐Vis spectroscopy, multifrequency Electron Paramagnetic Resonance (EPR) spectroscopy, Electron Nuclear Double Resonance (ENDOR) spectroscopy, Electron Spin Echo Envelope Modulation (ESEEM), Magnetic Circular Dichroïsm (MCD) spectroscopy, Mössbauer spectroscopy, resonance Raman spectroscopy, or X‐ray Absorption Spectroscopy. By preparing a series of samples freeze‐quenched after various times, a full kinetic profile of the catalytic cycle of an enzyme or any other chemical reaction is obtained. The structures of intermediates are assigned in conjunction with (a selection of) the spectroscopic techniques listed above.

This article details various aspects of continuous‐flow and stopped‐flow rapid‐mixing techniques, considering mixer design, freeze‐quenching methodology, and sampling. The scope and limitations to (bio)chemical research of the well‐established rapid freeze‐quench (RFQ) and the recently developed microsecond freeze‐hyperquenching (MHQ) technologies are specifically highlighted.
Perspective‐driven text comprehension
Authors: Kaakinen Johanna K. , Hyönä Jukka
Published: March 2008

The present article reports results of an eye‐tracking experiment, which examines whether the perspective‐driven text comprehension framework applies to comprehension of narrative text. Sixty‐four participants were instructed to adopt either a burglar's or an interior designer's perspective. A pilot test showed that readers have more overlapping prior knowledge with the burglar‐relevant than with the interior designer‐relevant information of the experimental text. Participants read either a transparent text version where the (ir)relevance of text segments to the perspective was made apparent, or an opaque text version where no direct mention of the perspective was made. After reading participants wrote a free recall of the text. The results showed that perspective‐related prior knowledge modulates the perspective effects observed in on‐line text processing and that signalling of (ir)relevance helps in encoding relevant information to memory. It is concluded that the proposed framework generalizes to the on‐line comprehension of narrative texts. Copyright © 2008 John Wiley & Sons, Ltd.
The acquisition of document search strategies in grade school students
Authors: Rouet Jean‐François , Coutelet Béatrice
Published: March 2008

Skilled comprehension includes the ability to search complex documents in order to retrieve and make use of information of interest. Two studies investigated the acquisition of document search skills by 9‐ to 13‐year‐old students. Experiment 1 explored third, fifth and seventh grade students' book search strategies as a function of question complexity. There was a sharp decrease across grades in time on task and need for experimenter assistance. Older students' search strategies evolved from mere flipping through the pages to top‐down search based on the use of structural organizers, for example the table of contents and index. Experiment 2 replicated the effects of grade on text search strategies using a more controlled setting. Older students were significantly faster at searching longer texts, and they used more top‐down strategies based on the use of text organizers. We discuss the contribution of metatextual knowledge and self‐regulation in expert text processing strategies. Copyright © 2008 John Wiley & Sons, Ltd.
Advances in text comprehension: model, process and development
Authors: Verhoeven Ludo , Perfetti Charles
Published: March 2008

To a very large extent, children learn in and out of school from written text. Information Communications Technologies (ICT) offers many possibilities to facilitate learning by confronting children with multimodal texts. In order to be able to implement learning environments that optimally facilitate children's learning, insight is needed into the cognitive processes underlying text comprehension. In this light, the aim of this special issue is to report on new advances in text comprehension research in perspective of educational implications. Starting from recent theoretical frameworks on the cognitive processes underlying text comprehension, the online processing of text will be discussed in adults and in school children. Copyright © 2008 John Wiley & Sons, Ltd.
Gd2O(CO3)2 · H2O Particles and the Corresponding Gd2O3: Synthesis and Applications of Magnetic Resonance Contrast Agents and Template Particles for Hollow Spheres and Hybrid Composites
Authors: Li I‐Fang , Su Chia‐Hao , Sheu Hwo‐Shuenn , Chiu Hui‐Chi , Lo Yi‐Wei , Lin Wei‐Ting , Chen Jyh‐Horng , Yeh Chen‐Sheng
Published: March 2008

The solution approach was employed to yield multifunctional amorphous Gd2O(CO3)2 · H2O colloidal spheres by reflux of an aqueous solution containing GdCl3 · 6H2O and urea. By elongating the reaction time, crystalline rhombus‐ shaped Gd2O(CO3)2 · H2O with at least 87% yield could be formed and were also accompanied by some rectangular particles. High‐resolution synchrotron powder X‐ray diffraction provides crystal structure information, such as cell dimensions, and indexes the exact crystal packing with hexagonal symmetry, which is absent from the Joint Committee on Powder Diffraction Standards file, for the crystalline rhombus sample. Particle formation was studied based on the reaction time and the concentration ratio of [urea]/[GdCl3 · 6H2O]. After a calcination process, the amorphous spheres and crystalline rhombus Gd2O(CO3)2 · H2O particles convert into crystalline Gd2O3 at temperatures above 600 °C. For in vitro magnetic resonance imaging (MRI), both Gd2O(CO3)2 · H2O and Gd2O3 species show the promising T1‐ and T2‐weighted effects and could potentially serve as bimodal T1‐positive and T2‐negative contrast agents. The amorphous Gd2O(CO3)2 · H2O contrast agent further demonstrates enhanced contrast of the liver and kidney using a dynamic contrast‐enhanced MR imaging (DCE‐MRI) technique for in vivo investigation. The multifunctional capability of the amorphous Gd2O(CO3)2 · H2O spheres was also evidenced by the formation of nanoshells using these amorphous spheres as the template. Surface engineering of the amorphous Gd2O(CO3)2 · H2O spheres could be performed by covalent bonding to form hollow silica nanoshells and hollow silica@Fe3O4 hybrid particles.
Incorporation of a Hydrophobic Antibacterial Peptide into Amphiphilic Polyelectrolyte Multilayers: A Bioinspired Approach to Prepare Biocidal Thin Coatings
Authors: Guyomard Aurélie , Dé Emmanuelle , Jouenne Thierry , Malandain Jean‐Jacques , Muller Guy , Glinel Karine
Published: March 2008

A non‐water‐soluble natural antibacterial peptide, gramicidin A, has been successfully incorporated into polyelectrolyte assemblies to elaborate biocidal thin films. For this, we used a double strategy, the first step of which consists of complexing the peptide by a non‐denaturing anionic amphiphilic polysaccharide, namely a hydrophobically modified carboxymethylpullulan. We demonstrate that the use of this amphiphilic anionic derivative allows to efficiently solubilize the peptide in aqueous solution, without denaturation. The amount of peptide solubilized by the amphiphilic polysaccharide was optimized by systematically varying the hydrophobicity and the molar mass of the CMP derivative. In a second step, the negatively charged complex was layer‐by‐layer assembled with cationic poly(L‐lysine) to form biofunctionalized thin films. The amount of peptide incorporated in the multilayers was controlled by changing the number of deposited complex layers, and was quantified by UV spectroscopy. The antibacterial activity of the resulting biofunctionalized films was evidenced against a gram‐positive bacterium, E. faecalis. We demonstrated that the biocidal activity resulted from a double mechanism: contact between bacteria and the film surface, and release of the peptide into the solution surrounding the film. We also showed that the peptide was not completely removed from the film after rinsing, which insured preservation of the biocidal activity of the film surface.
Tetraphenylimidazole‐Based Excited‐State Intramolecular Proton‐Transfer Molecules for Highly Efficient Blue Electroluminescence
Authors: Park Sanghyuk , Seo Jangwon , Kim Se Hun , Park Soo Young
Published: March 2008

Aiming for highly efficient blue electroluminescence, we have designed and synthesized a novel class of tetraphenylimidazole‐ based excited‐state intramolecular proton‐transfer (ESIPT) molecules with covalently linked charge‐transporting functional groups (carbazole‐ and oxadiazole‐functionalized hydroxyl‐substituted tetraphenylimidazole (HPI), i.e., HPI‐Cbz and HPI‐Oxd, respectively). High Tg (ca. 130 °C) amorphous films of HPI‐Cbz and HPI‐Oxd showed intense and ideal blue‐light emission (λmax = 462 and 468 nm, ΦPL = 0.44 and 0.38) with a large Stokes shift of over 160 nm and a narrow full width at half‐maximum of less than 65 nm. Organic light‐emitting devices using HPI‐Cbz and HPI‐Oxd as the emitting layer generated an efficient blue electroluminescence (EL) emission peaking at around 460 nm with excellent CIE coordinates of (x, y) = (0.15, 0.11). A maximum external quantum efficiency of 2.94%, and a maximum brightness of 1 229 cd m−2 at 100 mA cm−2, as well as a low turn‐on voltage of 4.8 V were achieved in this work.
Hydroxyapatite Modified with Carbon‐Nanotube‐Reinforced Poly(methyl methacrylate): A Nanocomposite Material for Biomedical Applications
Authors: Singh Manoj Kumar , Shokuhfar Tolou , Gracio José Joaquim de Almeida , de Sousa António Carlos Mendes , Fereira José Maria Da Fonte , Garmestani Hamid , Ahzi Said
Published: March 2008

The paper reports on a freeze‐granulation technique to prepare a novel nanocomposite of poly(methyl methacrylate) (PMMA)‐modified hydroxyapatite (HA) with multiwalled carbon nanotubes (MWCNTs) as reinforcement for a new generation biomedical bone cement and implant coatings. By using this technique it is possible to increase material homogeneity and also enhance the dispersion of MWCNTs in the composite matrix. The phase composition and the surface morphology of the nanocomposite material were studied using X‐ray diffraction, field‐emission scanning electron microscopy, and micro‐Raman spectroscopy. Additionally, nanomechanical properties of different concentrations of MWCNT‐reinforced nanocomposite were performed by a nanoindentation technique, which indicates that a concentration of 0.1 wt % MWCNTs in the PMMA/HA nanocomposite material gives the best mechanical properties.
Antimicrobial Gallium‐Doped Phosphate‐Based Glasses
Authors: Valappil Sabeel P. , Ready Derren , Neel Ensanya A. Abou , Pickup David M. , Chrzanowski Wojciech , O'Dell Luke A. , Newport Robert J. , Smith Mark E. , Wilson Michael , Knowles Jonathan C.
Published: March 2008

Novel quaternary gallium‐doped phosphate‐based glasses (1, 3, and 5 mol % Ga2O3) were synthesized using a conventional melt quenching technique. The bactericidal activities of the glasses were tested against both Gram‐negative (Escherichia coliandPseudomonas aeruginosa) and Gram‐positive (Staphylococcus aureus, methicillin‐resistantStaphylococcus aureus, andClostridium difficile) bacteria. Results of the solubility and ion release studies showed that these glass systems are unique for controlled delivery of Ga3+.71Ga NMR measurements showed that the gallium is mostly octahedrally coordinated by oxygen atoms, whilst FTIR spectroscopy provided evidence for the presence of a small proportion of tetrahedral gallium in the samples with the highest gallium content. FTIR and Raman spectra also afford an insight into the correlation between the structure and the observed dissolution behaviorviaan understanding of the atomic‐scale network bonding characteristics. The results confirmed that the net bactericidal effect was due to Ga3+, and a concentration as low as 1 mol % Ga2O3was sufficient to mount a potent antibacterial effect. The dearth of new antibiotics in development makes Ga3+a potentially promising new therapeutic agent for pathogenic bacteria includingMRSAandC. difficile.
Unusual Strain Accommodation and Conductivity Enhancement by Structure Modulation Variations in Sr4Fe6O12+δ Epitaxial Films
Authors: Solís Cecilia , Rossell Marta D. , Garcia Gemma , Van Tendeloo Gustaaf , Santiso José
Published: March 2008

Mixed ionic and electronic conducting (MIEC) films can be applied in solid state electrochemical devices such as oxygen separation membranes for producing pure oxygen, gas sensors or as cathode in solid oxide fuel cells. The current interest in layered perovskite‐related phases, like Sr4Fe6O13 (SFO), arises from their significant oxygen permeability as predicted from theoretical studies. Nevertheless, before any practical application further fundamental study on this fairly unknown oxide is required mainly to assess the mechanisms affecting the transport properties. Epitaxial Sr4Fe6O12+δ (SFO) films of b‐axis orientation with different thicknesses have been prepared by the pulsed laser deposition technique onto different perovskite substrates: SrTiO3, NdGaO3 and LaAlO3. The strain accommodation has been found to vary as a function of film thickness as well as the substrate material causing different type of defects in the film microstructure, as well as variations in the oxygen anion content and ordering. Correspondingly, the total electrical conductivity of the films has been also found to vary significantly as a function of thickness and substrate type showing an unexpected enhancement for strained thin films. The variations in the transport properties are discussed in terms of the different strain accommodation mechanisms and the variation of the modulated structure observed for this compound.
How an energy company takes a human rights approach
Authors: Sherman John
Published: March 2008

Two CPR Fall 2007 Meeting panelists re‐team to expand their focus on corporate social responsibility and its relationship to conflict resolution. First, John Sherman, of Westborough, Mass., describes why his employer, energy provider National Grid, focuses substantial business efforts on giving communities a voice in its efforts. Caroline Rees, of Cambridge, Mass., examines the need for grievance mechanisms to address inevitable local conflicts. Both authors provide practical advice based on adaptable existing models.
Ethylene polymerization by diphenyl ether bridged dinuclear titanocenes/MAO
Authors: Nie Yujing , Sun Junquan , Cheng Jin , Ren Hua , Schumann Herbert
Published: March 2008

Two diphenyl ether bridged dinuclear titanocenes, (C5H5TiCl2)2{[(RC5H3)CH2](p‐C6H4)O(C6H4‐p) [CH2(C5H3R)] [R = H(5), Me(6)] have been synthesized and characterized by 1H‐NMR spectroscopy and elemental analysis. In the presence of methylaluminoxane (MAO), 5 and 6 are efficient catalysts for ethylene polymerization. The influences of the polymerization conditions such as [MAO]/[Cat] molar ratio, catalyst concentration, polymerization temperature and time have been studied in detail. Compounds 5 and 6 produce 105 g polyethylene (PE)/(mol Ti h), which is in the same range as that produced by the binuclear titanocenes {(C5H5TiCl2)2[(C5H4CH2) (p‐C6 H4)(C6H4‐p)(CH2C5H4)]} (7) and (C5H5TiCl2)2(C5H4CH2 CH2OCH2 CH2C5H4) (8). However, the molecular weight of PE is somewhat higher than that of PE using 7 and 8. The high temperature gel permeation chromatography (GPC) results show that the molecular weight distributions of PE produced by 5 and 6 (MWD = 6.17 and 7.56) were obviously broader than those of PE produced by 7 (MWD = 4.28) and 8 (MWD = 5.90). The melting points of the PE produced by 5 and 6 are higher than 132°C, indicating ahighly linear and highly crystalline PE. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
pH‐sensitivity and air/water interfacial activity of poly(N‐isopropylacrylamide‐co‐methacrylic acid‐co‐octadecyl acrylate)
Authors: Choi Jae‐Hyung , Lee Hyeon Youg , Kim Jin‐Chul
Published: March 2008

The copolymers of N‐isopropylacrylamide and methacrylic acid (P(NIPAM‐co‐MAA)), and the copolymers of N‐isopropylacrylamide, methacrylic acid, and octadecyl acrylate (P(NIPAM‐co‐MAA‐co‐ODA)) were synthesized by a free radical reaction. MAA was copolymerized as a pH‐sensitive residue and ODA as a hydrophobic moiety. The transmittances of P(NIPAM‐co‐MAA) solutions were almost constant in the pH 2.0–8.5. On the other hand, the transmittances of P(NIPAM‐co‐MAA‐co‐ODA) solutions were reduced in the pH 2–5, whereas the values were almost invariable in the pH 5.0–8.5. In the low range of pH, most of carboxyl groups are in unionized forms. Therefore, the hydrophobic interactions among ODAs might be greater than the electrostatic repulsions. Self‐assemblies such as polymeric micelles could be formed, leading to the reduced transmittances. In the measurement of air/water interfacial tensions, the surface activities of both P(NIPAM‐co‐MAA) and P(NIPAM‐co‐MAA‐co‐ODA) were lower in alkali pHs than in acidic conditions. This is possibly because that the copolymers are more hydrophilic at higher pHs due to the ionization of the carboxyl groups. P(NIPAM‐co‐MAA‐co‐ODA) was more surface‐active than P(NIPAM‐co‐MAA) in the full range pH, pH 2.0–8.5, due to the hydrophobic effect of ODA. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008
Generalized Nonaqueous Sol–Gel Synthesis of Different Transition‐Metal Niobate Nanocrystals and Analysis of the Growth Mechanism
Authors: Zhang Lizhi , Garnweitner Georg , Djerdj Igor , Antonietti Markus , Niederberger Markus
Published: March 2008

A general nonaqueous route for the synthesis of phase‐pure transition‐metal niobate (InNbO4, MnNb2O6, and YNbO4) nanocrystals was developed based on the one‐pot solvothermal reaction of niobium chloride and the corresponding transition‐metal acetylacetonates in benzyl alcohol at 200 °C. All samples were carefully characterized by XRD, TEM, HRTEM, and energy‐dispersive X‐ray (EDX) analysis. The crystallization mechanism of these niobate nanocrystals points to a two‐step pathway. First, metal hydroxide crystals and amorphous niobium oxide are formed. Second, metal niobate nanocrystals are generated from the intermediates by a dissolution–recrystallization mechanism. The reaction mechanisms, that is, the processes responsible for the oxygen supply for oxide formation, were found to be rather complex and involve niobium‐mediated ether elimination as the main pathway, accompanied by solvolysis of the acetylacetonate ligands and benzylation reactions.
Eine Enzyklopädie für das Kaiserreich
Authors: Stöltzner Michael
Published: March 2008

An Encyclopedia for the Empire.In the preface to the universal encyclopediaDie Kultur der Gegenwart(The Culture of the Present), the editor‐in‐chief Paul Hinneberg places his project – not openly but nevertheless unequivocally – in the tradition of the FrenchEncyclopédiethat Diderot and d'Alembert had organized from 1751 until 1765. The attempt to accomplish anew such a large‐scale project and, in this way, to win the German Empire the kind of intellectual leadership which theEncyclopédie,in historical retrospect, had achieved for the epoch of Enlightenment, required to convince the leading scholars, scientists, and technicians of the nation to participate in the endeavor and to assemble their contributions under a common systematic agenda through which this universal encyclopedia would distinguish itself from all dictionaries and disciplinary encyclopedias. While theEncyclopédiefollowed to a large extent an empiricist philosophy, Hinneberg trusted in the integrative function of the concept of culture and the ability of his contributors to elucidate the history of their respective disciplines and to connect them with neighboring fields of culture. The present contributions argues that although, from a philosophical point of view, the historicist tack taken by Hinneberg makes the concept of culture quite blurry, it nevertheless provides enough cohesive structure such that the work, even though unfinished as a consequence of war and inflation, represents a faithful picture of its epoch that Hinneberg understands as an epoch of transition.
Delivery of peptides to the brain: Emphasis on therapeutic development
Authors: Banks William A.
Published: March 2008

Peptides and regulatory proteins hold great promise as therapeutic agents for the central nervous system (CNS). However, the blood–brain barrier (BBB) is a major obstacle to the delivery of these potential therapeutics to their site of action. We concentrate here on the vascular BBB, which is comprised of the capillary bed of the brain specially modified to prevent the production of a plasma ultrafiltrate. For many peptides and proteins, this physical barrier is reinforced by enzymatic activities at the BBB, CNS, and peripheral tissues, short half‐lives and large volumes of distribution in the blood, binding proteins in blood, and brain‐to‐blood efflux systems. Nevertheless, there are pathways through which substances can cross. Small, lipid soluble substances cross by the nonsaturable mechanism of transmembrane diffusion, but even water‐soluble peptides can cross to some degree. Many endogenous peptides and regulatory proteins cross the BBB by way of selective, saturable transport systems. For enzymatically resistant substances with long circulating half‐lives and small volumes of distribution, such as antibodies, erythropoietin, and enzymes, substances can enter the CNS in therapeutic amounts through the residual leak of the BBB, termed the extracellular pathways. Recent examples show that the BBB transporters for peptides and regulatory substances are modifiable. This provides both a therapeutic opportunity and the potential for disease to arise from BBB dysfunctions. In the last case, the BBB itself is a therapeutic target. © 2008 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 90: 589–594, 2008.

This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
Conformational constraint in protein ligand design and the inconsistency of binding entropy
Authors: Udugamasooriya D. Gomika , Spaller Mark R.
Published: March 2008

It is an accepted practice in ligand design to introduce conformational constraint with the expectation of improving affinity, justified by the theoretical possibility that an unfavorable change in binding entropy will be reduced. This rationale of minimizing the entropic penalty through imposing structural constraints upon a ligand, however, has been voiced more often than verified. Here we examine three modified cyclic peptides, along with multiple versions of their linear control analogs, and determine their thermodynamic parameters when binding the same host, the third PDZ domain (PDZ3) of the mammalian postsynaptic density‐95 (PSD‐95) protein. To begin a two‐stage investigation, the initial evaluation involved solution binding studies with isothermal titration calorimetry (ITC), which provided the changes in Gibbs free energy (ΔG), enthalpy (ΔH), and entropy (TΔS) upon formation of the protein‐ligand complex. In the second stage, a selected macrocycle along with two matched linear controls were subjected to more rigorous analysis by ITC, which included (1) change in heat of buffer ionization (ΔHion) titrations, to examine the role of proton transfer events; (2) change in heat capacity (ΔCp) determinations, to indirectly probe the nature of the binding surface; and (3) osmotic stress experiments, to evaluate desolvation effects and quantitate water release. Together, these demonstrate that the entropic relationship between a macrocyclic ligand and a linear counterpart can be a complex one that is difficult to rationalize. Further, the addition of constraint can, counterintuitively, lead to a less favorable change in binding entropy. This underscores the need to use matched linear control ligands to assure that comparisons are made in a meaningful manner. © 2008 Wiley Periodicals, Inc. Biopolymers 89: 653–667, 2008.

This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com
B12‐retro‐Riboswitches: Guanosyl‐Induced Constitutional Switching of B12 Coenzymes
Authors: Gschösser Sigrid , Kräutler Bernhard
Published: March 2008

Complete B12 derivatives are natural “molecular switches” as a result of the coordinative switch (“base on” or “base off”) of the natural nucleotide base. Certain predesigned B12–nucleotide conjugates were shown recently to behave as “retro riboswitches”, in which the nucleotide environment modified the equilibrium between these two isomeric B12 structures. In contrast, the “reverse” situation has been discovered in natural B12 riboswitches, in which the binding of coenzyme B12 induces a conformational switch in the RNA species. The first (predesigned) B12‐retro‐riboswitches were DNA conjugates of methylcobalamin. We describe herein two representative B12‐retro‐riboswitches, in which an appended (RNA) nucleotide is used to destabilize the base‐on form and induce the base‐on to base‐off switch. Through use of heterogeneous solid‐phase synthetic methods, Coβ–cyanocobalamin‐(3′′→2′)‐2′′‐methoxyguaninyl‐3′′‐ate was prepared first as the crucial covalent RNA conjugate of vitamin B12. This cyanocorrinoid opened the door to two organometallic B12–nucleotide conjugates, which were made by electrosynthetic means: the cyanocorrinoid was cleanly methylated or adenosylated at the cobalt center to furnish covalent RNA conjugates of the organometallic B12 cofactors methylcobalamin and coenzyme B12, respectively. At room temperature, aqueous solutions of both of these organometallic RNA–B12 conjugates exhibited properties indicative of significant weakening of the axial (CoN) bond (of their base‐on forms) and of an enhanced formation of the base‐off species. The base‐on to base‐off switch was studied by UV/Vis and NMR spectroscopic studies, which showed that the switch was very temperature‐dependent and was accentuated with increasing temperatures. Thermodynamic data of the two organometallic RNA–B12 conjugates revealed an important contribution of entropic effects to the observed base‐on to base‐off switch. The two organometallic RNA–B12 conjugates thus acted as B12‐retro‐riboswitches and allowed the observation of a temperature‐dependent reverse switch in the B12 cofactor moiety, induced by the appended nucleotide moiety. This behavior may be of interest in the “RNA‐world” hypothesis, in which (simple) B12 derivatives are thought to act as possible catalytic enhancers (“cofactors”) in RNA‐based “B12 ribozymes”.
Tin–Oxo Clusters Based on Aryl Arsonate Anions
Authors: Xie Yun‐Peng , Yang Jin , Ma Jian‐Fang , Zhang Lai‐Ping , Song Shu‐Yan , Su Zhong‐Min
Published: March 2008

Reactions of Ph3SnOH or Ph3SnCl with aryl arsonic acids RAsO3H2, where R=C6H5 (1), 2‐NH2C6H4 (2), 4‐NH2C6H4 (3), 2‐NO2C6H4 (4), 3‐NO2C6H4 (5), 4‐NO2C6H4 (6), 3‐NO2‐4‐OHC6H3 (7), 2‐ClC6H4 (8) and 2,4‐Cl2C6H3 (9), gave 18 Sn–O cluster compounds. These compounds can be classified into four types: type A: [{(PhSn)3(RAsO3)3(μ3‐O)(OH)(R′O)2}2Sn] (R=C6H5, 2‐NH2C6H4, 4‐NH2C6H4, 2‐NO2C6H4, 3‐NO2C6H4, 2‐ClC6H4, 2,4‐Cl2C6H3, and 3‐NO2‐4‐OHC6H3; R′=Me or Et); type B: [{(PhSn)3(RAsO3)2(RAsO3H)(μ3‐O)(R′O)2}2] (R=4‐NO2C6H4, R′=Me); type C: [{(PhSn)3(RAsO3)3(μ3‐O)(R′O)3}2Sn] (R=2,4‐Cl2C6H3, R′=Me); type D: [{Sn3Cl3(μ3‐O)(R′O)3}2(RAsO3)4] (R=2‐NO2C6H4 and 4‐NO2‐C6H4; R′=Me or Et). Structures of types A and B contain [Sn3(μ3‐O)(μ2‐OR′)2] building blocks, while in types C and D the stannoxane cores are built from two [Sn3(μ3‐O)(μ2‐OR′)3] building blocks. The reactions proceeded with partial or complete dearylation of the triphenyltin precursor. These various structural forms are realized by subtle changes in the nature of the organotin precursors and aryl arsonic acids. The syntheses, structures, and structural interrelationship of these organostannoxanes are discussed.
Nonpolar Dihydrogen Bonds—On a Gliding Scale from Weak Dihydrogen Interaction to Covalent HH in Symmetric Radical Cations [HnE‐H‐H‐EHn]+
Authors: Krapp Andreas , Frenking Gernot , Uggerud Einar
Published: March 2008

The electronic structures and bonding patterns for a new class of radical cations, [HnE‐H‐H‐EHn]+(EHn=element hydride, E=element of Groups 15–18), have been investigated by applying quantum‐chemical methods. All structures investigated give rise to symmetric potential energy minimum structures. We envisage clear periodic trends. The HH bond length is shorter for elements toward the bottom of the periodic table of elements, and a short HH bond corresponds to accumulation of electron density in the central HH region. All [HnE‐H‐H‐EHn]+of Groups 15–17 are thermodynamically unstable towards loss of either H2or H. The barriers for these dissociations are rather low. The Group 18 congeners, except E=Xe, appear to be global minima of the respective potential energy surfaces. The findings are discussed in terms of H2bond activation, and a general mechanistic scheme for the standard reduction process 2H++ 2e−→ H2is given. Finally, it is proposed that some of the symmetric radical cations are likely to be observed in mass spectrometric or matrix isolation experiments.
Controllable Synthesis of VSB‐5 Microspheres and Microrods: Growth Mechanism and Selective Hydrogenation Catalysis
Authors: Liu Shu‐Juan , Cheng Hai‐Yang , Zhao Feng‐Yu , Gong Jun‐Yan , Yu Shu‐Hong
Published: March 2008

Nanoporous VSB‐5 nickel phosphate molecular sieves with relatively well controllable sizes and morphology of microspheres assembled from nanorods were synthesized at 140 °C over a short time in the presence of hexamethylenetetramine (HMT) by a facile hydrothermal method. The pH value, reaction time, and ratio of HMT to NaHPO2⋅H2O crucially influence the morphology and quality of the final products. By adjusting the pH value of the initial reaction solution, the morphology changes from disperse rods to microspheres assembled from rods and finally to a large quantity of fibers, and the diameters of the VSB‐5 rods can be varied. The catalytic activity of VSB‐5 in selective hydrogenation of several unsaturated organic compounds was tested. Nickel(II) in VSB‐5 can selectively catalyze hydrogenation of CC in trans‐cinnamaldehyde and 3‐methylcrotonaldehyde. In addition, since nitrobenzene (NB) and 2‐chloronitrobenzene could be reduced to aniline (AN) and 2‐chloroaniline with high selectivity, VSB‐5 could have potential applications in synthesizing dyes, agrochemicals, and pharmaceuticals.