High Stability (high + stability)

Distribution by Scientific Domains
Distribution within Chemistry

Selected Abstracts

Targeted Synthesis of a Porous Aromatic Framework with High Stability and Exceptionally High Surface Area,

Teng Ben
Diamantenfieber: Ein Diamantgerüst, in dem C-C-Bindungen gegen Benzolringe ausgetauscht sind (siehe Bild), ist einerseits stabil und hat andererseits eine große innere Oberfläche. Das poröse aromatische Gerüst PAF-1 (Oberfläche 7100,m2,g,1) kann große Mengen an Wasserstoff und Kohlendioxid, Benzol- und Toluoldampf aufnehmen. [source]

Spherical Double Electric Layer Structure and Unprecedented High Stability of the P20O20 Cage and Its Anionic Endohedral Complex Na - @P20O20

CHEMINFORM, Issue 26 2004
Yanjin Wang
Abstract For Abstract see ChemInform Abstract in Full Text. [source]

High Stability of the Polyproline,II Helix in Polypeptide Bottlebrushes

Afang Zhang Prof.
Abstract Polymer bottlebrushes with monodisperse oligoproline side chains were efficiently synthesized, and the conformation of the peptide side chains in different solvents was investigated. Polymers with number-average degrees of polymerization (DPn) of 89 and 366 were obtained by polymerization of the macromonomer in iPrOH/MeCN (1:1) and hexafluoroisopropanol, respectively. Circular dichroism (CD) spectra of the bottlebrush polymers in the neutral and charged states reveal that the oligoproline side chains attain stable polyproline,II (PPII) helical conformations not only in aqueous solution, but also in aliphatic alcohol solutions. Dense attachment of oligopeptides onto a linear polymer chain did not lead to an increase in helix content. The possible effects of the main-chain length on the conformational stability were examined. The switching between the polyproline,I (PPI) and PPII helical conformations for the oligoproline side chains in aliphatic alcohol solutions is believed to be inhibited by the overcrowded structure in the polymer bottlebrushes. [source]

High stability of CdZnSSe active layers in ZnSe-based laser diodes by introducing strain-compensating barrier layers

Arne Gust
Abstract A series of four similar laser structures with an emission wavelength of 520 nm was grown by molecular beam epitaxy. The difference was the alternating implementation of an additional 5 nm thick ZnSSe layer with a high sulfur composition of 25% neighboring the quantum well on the n-, p- or n-& p-side. A high stability of the CdZnSSe active layer was observed by introducing such a kind of strain compensating barrier layers. In lifetime measurements a large improvement was noticed by the p- and n- & p-side barrier layers. With respect to the strain compensating effect of only one barrier layer, the p-side layer is more effective than the n-side one. It is assumed that the p-side barrier layer acts not only as strain-compensating layer, but also as blocking layer against the Cd diffusion into the p-doped layers. A lifetime extension of one order of magnitude could be achieved. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

First Propargyl Azides Bearing Strong Acceptor Substituents and Their Effective Conversion into Allenyl Azides: Influence of the Electronic Effects of Substituents on the Reactivity of Propargyl Azides,,

Joseph Rodolph Fotsing
Abstract We have succeeded in the synthesis of propargyl azides containing 1- or 3-phenylthio functionalities. The selective oxidation of their sulfur atoms to sulfoxides and sulfones allows access to the first propargyl azides bearing acceptor substituents. Interestingly, the prototropic rearrangement of the latter propargyl azides leads to the formation of allenyl azides with relatively high stabilities and with moderate to good yields. Propargyl azides containing phenylthio functionalities react in the presence of nucleophiles to afford the expected N -unsubstituted 1,2,3-triazoles via short-lived allenyl azides. These results are entirely different from those of the corresponding sulfoxides and sulfones, which react under the analogous conditions either to produce the corresponding bis(triazolo)pyrazine derivatives or to yield newly substituted vinyl azides. The latter compounds can successfully be used as starting material providing access to azirines. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

How to determine free Gd and free ligand in solution of Gd chelates.

A technical note
Abstract Gd(III) chelates are often used as reporting probes in magnetic resonance imaging applications. Their use relies on the assumption that their high stability ensures against the release of free ligand and free Gd3+ ions, which are both highly toxic to living systems. The presence of free Gd3+ ions may have a profound effect on the contrast in the MR image as they may form highly hydrated, macromolecular complexes endowed with very high relaxivity thus providing erroneous information on the extent of the contrast effect induced by the given reporting probe. Although the stability of a given complex may be high enough, the complexation step could not have been completed. Therefore any Gd complex preparation has to be carefully checked for the content of free ligand and free metal ions. Herein the currently used procedures that allow an assessment of the amounts of free metal ions and free ligand in a solution of a given Gd complex are described in detail. Copyright © 2006 John Wiley & Sons Ltd. [source]

The Influence of the Cathodic Pretreatment on the Electrochemical Detection of Dopamine by Poly(1-aminoanthracene) Modified Electrode

Estela de Pieri Troiani
Abstract In this study we demonstrated the influence of the cathodic pretreatment of poly(1-aminoanthracene) (PAA) electropolymerized on a platinum electrode for determination of dopamine (DA). The DA electrochemical response was obtained after a cathodic pretreatment of the PAA electrode which consisted of applying a potential of ,0.7,V (vs. Ag/AgCl) for 3,s before each measurement. The pretreatment of the electrode changed the PAA electrocatalytic properties so that the electrode began to present electrochemical response to DA without interference of ascorbic acid (AA). The anodic peak currents determined by differential pulse voltammetry using pretreated PAA showed a linear dependence on the DA concentration from 0.56 to 100,µM with a detection limit of 0.13,µM and a correlation coefficient of 0.9986. The electrode exhibits a relative standard deviation of 1.2,% for ten successive measurements of a 0.5,mM DA solution. The analysis by scanning electron microscopy and atomic force microscopy show a homogeneous and nanostructured film with globular structures with diameter of about 20,nm. The analytical results obtained for DA determination at a pretreated PAA electrode in pharmaceutical formulation sample were in good agreement with those obtained by a comparative procedure at a 95,% confidence level. PAA electrode after the pretreatment showed electrochemical responses to DA with excellent selectivity, sensitivity, and high stability without interference of AA. [source]

Electroanalysis of Norepinephrine at Bare Gold Electrode Pure and Modified with Gold Nanoparticles and S-Functionalized Self-Assembled Layers in Aqueous Solution

Teresa, uczak
Abstract Gold nanoparticles (Au-NPs), cystamine (CA) and 3,3,-dithiodipropionic acid (DTDPA) modified gold bare electrodes were applied in voltammetric sensors for simultaneous detection of norepinephrine (NEP), ascorbic (AA) and uric (UA) acids. A linear relationship between norepinephrine concentration and current response was obtained in the range of 0.1,,M to 600,,M M with the detection limit ,0.091,,M for the electrodes modified at 2D template and in the range of 0.1,,M to 700,,M M with the detection limit ,0.087,,M for the electrodes modified at 3D template The results have shown that using modified electrodes it is possible to perform electrochemical analysis of norepinephrine without interference of ascorbic and uric acids, whose presence is the major limitation in norepinephrine determination at a bare gold electrode. The modified SAMs electrodes show good selectivity, sensitivity, reproducibility and high stability. [source]

Polyaniline Film Based Amperometric pH Sensor Using A Novel Electrochemical Measurement System

Wei Gao
Abstract A polyaniline based amperometric pH sensor has been developed using a novel electrochemical measurement system. A polyaniline film (PANI) coated pencil graphite electrode (PGE) is connected in series between the working and counter electrodes of a potentiostat, and immersed in the solution together with a reference electrode. When an external potential is applied, the resulting current varies with the solution pH, which provides the basis for the amperoemtric pH sensor. Equations describing the measurement principle are presented. Based on pH dependent emeraldine salt,emeraldine base transition of PANI film, the pH sensor exhibits high stability, accuracy, selectivity, sensitivity and a short time. [source]

The Electrochemical Properties of Co(TPP), Tetraphenylborate Modified Glassy Carbon Electrode: Application to Dopamine and Uric Acid Analysis

Yunlong Zeng
Abstract We report the combination of the charge repelling property of tetraphenyl-borate (TPB) anion and the electrooxidation catalytic effect of cobalt(II) tetrakisphenylporphyrin (CoTPP) embedded in a sol gel ceramic film to develop a modified glassy carbon electrode (CoTPP-TPB-SGGCE) for the simultaneous determination of dopamine (DA) and uric acid (UA). The optimized CoTPP-TPB-SGGCE shows excellent sensitivity and selectivity for the DA and UA analysis. As high as 2000 fold acceptable tolerance of ascorbic acid (AA) for the determination of trace DA and UA is reached. In the presence of 0.10,mM AA, the linear concentration range for DA is from 6.0×10,8 to 2.5×10,5,M, and the detection limit is 2.0×10,8,M. For UA, the linear concentration range is from 1.0×10,7 to 3.5×10,5,M, and the detection limit is 7.0×10,8,M. Our study has also demonstrated that the novel CoTPP-TPB-SGGCE shows high stability and reliability. For 6.00,,M DA and UA, a total of 12,measurements were taken in one week, and the relative standard deviation is 2.05% and 2.68% respectively. No obvious shift of peak current and peak potential is observed over a three-month lifetime test. The response of the sensor is very quick and response time is approximately 1,s. Satisfactory results are also achieved when the CoTPP-TPB-SGGCEs being used to detect the DA and UA in human urine samples. [source]

CE coupled to MALDI with novel covalently coated capillaries

Stefan Bachmann
Abstract CE offers the advantage of flexibility and method development options. It excels in the area of separation of ions, chiral, polar and biological compounds (especially proteins and peptides). Masking the active sites on the inner surface of a bare fused silica capillary wall is often necessary for CE separations of basic compounds, proteins and peptides. The use of capillary surface coating is one of the approaches to prevent the adsorption phenomena and improve the repeatability of migration times and peak areas of these analytes. In this study, new capillary coatings consisting of (i) derivatized polystyrene nanoparticles and (ii) derivatized fullerenes were investigated for the analysis of peptides and protein digest by CE. The coated capillaries showed excellent run-to-run and batch-to-batch reproducibility (RSD of migration time ,0.5% for run-to-run and ,9.5% for batch-to-batch experiments). Furthermore, the capillaries offer high stability from pH 2.0 to 10.0. The actual potential of the coated capillaries was tested by combining CE with MALDI-MS for analysing complex samples, such as peptides, whereas the overall performance of the CE-MALDI-MS system was investigated by analysing a five-protein digest mixture. Subsequently, the peak list (peptide mass fingerprint) generated from the mass spectra of each fraction was entered into the Swiss-Prot database in order to search for matching tryptic fragments using the MASCOT software. The sequence coverage of analysed proteins was between 36 and 68%. The established technology benefits from the synergism of high separation efficiency and the structure selective identification via MS. [source]

Cationic Iridium Complexes with Chiral Dithioether Ligands: Synthesis, Characterisation and Reactivity under Hydrogenation Conditions

Leticia Flores-Santos
Abstract A series of cationic IrI complexes containing chiral dithioether ligands have been prepared in order to study the influence of the sulfur substituents and the metallacycle size on the acetamidoacrylate hydrogenation reaction. In the case of complexes 6, 7 and 10, a mixture of diastereomers is observed in solution due to the sulfur inversion processes. In contrast, this fluxional behaviour is efficiently controlled by using bicyclic ligands which inhibit the S-inversion in complexes 8 and 9. The solid-state structure of complex 10b shows only one diastereomer with the sulfur substituents in a relative anti disposition and in an overall configuration of SCSCSSSS at the coordinated dithioether ligand. Iridium complexes containing seven- and six-membered metallacycles (6b,d, 7b,c, 10a,b) react with the substrate through S-ligand substitution, and the rate of this substitution is related to the position of the fluorine atom on the aromatic ring. On the contrary, complexes containing a bismetallacycle (8 and 9) are not displaced by the substrate. The catalytic hydrogenation activity of complexes 8 and 9 is analysed in terms of the high stability of the corresponding dihydride complexes (13 and 14). In both cases, only two of the four possible diastereomeric dihydride species are formed in solution. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Thermostability of genetically modified sunflower oils differing in fatty acid and tocopherol compositions

Susana Marmesat
Abstract The objective of the study was to investigate the performance at frying temperature of a new sunflower oil with high content of oleic and palmitic acid (HOHPSO) and containing ,-tocopherol as the most abundant natural antioxidant. HOHPSO either containing ,- or ,-tocopherol (HOHPSO-, and HOHPSO-,, respectively) were obtained from genetically modified sunflower seeds and refined under identical conditions. The oil stability against oxidation, as measured by Rancimat at 120,°C, was much higher for the oil containing ,-tocopherol, suggesting the higher effectiveness of ,-tocopherol as compared to ,-tocopherol to delay oxidation. Experiments at high temperature (180,°C) simulating the conditions applied in the frying process clearly demonstrated that, for the same periods of heating, the oil degradation and the loss of natural tocopherol were significantly lower for the oil containing ,-tocopherol. Comparison of different genetically modified sunflower oils with different fatty acid compositions confirmed that oil degradation depended on the fatty acid composition, being higher at a higher degree of unsaturation. However, the loss of tocopherol for a similar level of oil degradation was higher as the degree of unsaturation decreased. Overall, the results showed that HOHPSO-, had a very high stability at frying temperatures and that mixtures of HOHPSO-, and HOHPSO-, would be an excellent alternative to fulfill the frying performance required by the processors and the vitamin,E content claimed by the consumers. [source]

Quantitative Removal of Mercury(II) from Water Through Bulk Liquid Membranes by Lipophilic Polyamines

Nicoletta Spreti
Abstract Transport of mercury(II) and copper(II) ions through bulk liquid membranes has been studied, the former because of its toxicity and wide distribution in the environment, the latter for comparative purposes. The abilities of two carriers, the known N,N, -bis[2-(hexadecylamino)ethyl]- N,N, -bis(hydroxyethyl)ethylenediamine (bis-HE16ED) and the new N,N,-bis(p -octyloxybenzyl)-3,6-dioxaoctane-1,8-diamine (bis- pODODA), to complex and transport the selected metal ions are reported. Bis-HE16ED is a good carrier for Cu2+ ions, but the high stability of the carrier/Hg2+ ion complex in the membrane results in a lack of its transport. On the other hand, the new carrier displays a very high efficiency in Hg2+ ion transport, effecting quantitative transfer of the metal ion into the receiving phase within 24 h, despite its chelating region being only slightly different from that in bis-HE16ED. The ability of bis- pODODA to transport 100,% of Hg2+ efficiently in consecutive cycles is also reported. This result provides a basis for future development of a decontamination process based on a carrier-mediated transport system. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]

Carrier-Mediated Transport of Toxic Heavy Metal Ions in Bulk Liquid Membranes

Lucia Brinchi
Abstract Transport through a dichloromethane liquid membrane has been studied to investigate the ability of 1,1,7,7-tetraethyl-4-tetradecyldiethylenetriamine (TE14DT), previously tested for the transport of copper, to act as a carrier for toxic heavy metal ions such as Cd2+, Pb2+ and Hg2+. The carrier displayed a remarkable capability to extract all the metal ions from the source to the organic phases but only cadmium was efficiently transported across the membrane. The experimental conditions optimised for the transport of copper are inadequate for lead and mercury. In fact, the inefficacy of their transport could be due, as regards lead, to the slow diffusion of the complex through the membrane, while mercury remained in the organic phase because of the high stability of the mercury-carrier complex. Selectivity tests using binary mixtures of the metal ions showed TE14DT's capability to transport copper or cadmium also in the presence of lead in the source phase. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

Transactional development of parent personality and child temperament

Niina Komsi
Abstract Stability and change in parental extraversion and neuroticism were studied in transaction with their views of their child's temperament from the age of six months to the age of five-and-a-half years in 109 mother,father,child triads (parent,daughter: n,=,61, parent,son: n,=,48). While parental traits showed high stability, infants' higher positive affectivity predicted an increase in parental extraversion over 5 years, and infant's higher activity predicted a decrease in parental neuroticism. Parent-rated temperament showed expected heterotypic continuity. Initially higher parental extraversion predicted an increase in the child's effortful control, and higher parental neuroticism predicted an increase in the child's negative affectivity. The results indicate that parental personality and child temperament develop in transaction promoting change in each other. Copyright © 2008 John Wiley & Sons, Ltd. [source]

A Transparent, Flexible, Low-Temperature, and Solution-Processible Graphene Composite Electrode

Haixin Chang
Abstract The synthesis and preparation of a new type of graphene composite material suitable for spin-coating into conductive, transparent, and flexible thin film electrodes in ambient conditions is reported here for the first time. Solution-processible graphene with diameter up to 50 ,m is synthesized by surfactant-assisted exfoliation of graphite oxide and in situ chemical reduction in a large quantity. Spin-coating the mixing solution of surfactant-functionalized graphene and PEDOT:PSS yields the graphene composite electrode (GCE) without the need for high temperature annealing, chemical vapor deposition, or any additional transfer-printing process. The conductivity and transparency of GCE are at the same level as those of an indium tin oxide (ITO) electrode. Importantly, it exhibits high stability (both mechanical and electrical) in bending tests of at least 1000 cycles. The performance of organic light-emitting diodes based on a GCE anode is comparable, if not superior, to that of OLEDs made with an ITO anode. [source]

High thermal and chemical stability of Thermus thermophilus seven-iron ferredoxin

FEBS JOURNAL, Issue 23 2003
Linear clusters form at high pH on polypeptide unfolding
To probe the stability of the seven-iron ferredoxin from Thermus thermophilus (FdTt), we investigated its chemical and thermal denaturation processes in solution. As predicted from the crystal structure, FdTt is extremely resistant to perturbation. The guanidine hydrochloride-induced unfolding transition shows a midpoint at 6.5 m (pH 7, 20 °C), and the thermal midpoint is above boiling, at 114 °C. The stability of FdTt is much lower at acidic pH, suggesting that electrostatic interactions are important for the high stability at higher pH. On FdTt unfolding at alkaline pH, new absorption bands at 520 nm and 610 nm appear transiently, resulting from rearrangement of the cubic clusters into linear three-iron species. A range of iron,sulfur proteins has been found to accommodate these novel clusters in vitro, although no biological function has yet been assigned. [source]

The RadA protein from a hyperthermophilic archaeon Pyrobaculum islandicum is a DNA-dependent ATPase that exhibits two disparate catalytic modes, with a transition temperature at 75 °C

FEBS JOURNAL, Issue 4 2000
Maria Spies
The radA gene is an archaeal homolog of bacterial recA and eukaryotic RAD51 genes, which are critical components in homologous recombination and recombinational DNA repair. We cloned the radA gene from a hyperthermophilic archaeon, Pyrobaculum islandicum, overproduced the radA gene product in Escherichia coli and purified it to homogeneity. The purified P. islandicum RadA protein maintained its secondary structure and activities in vitro at high temperatures, up to 87 °C. It also showed high stability of 18.3 kcal·mol,1 (76.5 kJ·mol,1) at 25 °C and neutral pH. P. islandicum RadA exhibited activities typical of the family of RecA-like proteins, such as the ability to bind ssDNA, to hydrolyze ATP in a DNA-dependent manner and to catalyze DNA strand exchange. At 75 °C, all DNAs tested stimulated ATPase activity of the RadA. The protein exhibited a break in the Arrhenius plot of ATP hydrolysis at 75 °C. The cooperativity of ATP hydrolysis and ssDNA-binding ability of the protein above 75 °C were higher than at lower temperatures, and the activation energy of ATP hydrolysis was lower above this break point temperature. These results suggest that the ssDNA-dependent ATPase activity of P. islandicum RadA displays a temperature-dependent capacity to exist in two different catalytic modes, with 75 °C being the critical threshold temperature. [source]

Highly Emissive and Electrochemically Stable Thienylene Vinylene Oligomers and Copolymers: An Unusual Effect of Alkylsulfanyl Substituents

Shehzad Jeeva
Abstract The synthesis, unexpected efficient photoluminescence, and reversible electrochemical p- and n-doping of new conjugated thienylene vinylene materials functionalized with alkylsulfanyl substituents poly(trithienylene vinylene) (PTTV) and poly(dithienylvinyl- co -benzothiadiazole) (PDTVB) along with dithienylvinylene-based oligomers is reported. The materials are studied by thermal and X-ray diffraction analysis, optical spectroscopy, cyclic voltammetry, and spectroelectrochemistry. Organic field-effect transistors (OFETs) are fabricated with PTTV and PDTVB. The polymers, prepared by Stille polycondensation, exhibit good thermal stability and a photoluminescent quantum yield in the range 34%,68%. Low bandgaps (1.5,1.8,eV), estimated by optical and electrochemical measurements along with high stability of both redox states, suggest that these structures are promising materials for photovoltaic applications. OFETs fabricated with PDTVB reveal a hole mobility of 7,×,10,3,cm2 V,1 s,1 with on/off ratio 105, which are comparatively high values for completely amorphous polymer semiconductors. [source]

Efficient and Long-Living Light-Emitting Electrochemical Cells

Rubén D. Costa
Abstract Three new heteroleptic iridium complexes that combine two approaches, one leading to a high stability and the other yielding a high luminescence efficiency, are presented. All complexes contain a phenyl group at the 6-position of the neutral bpy ligand, which holds an additional, increasingly bulky substituent on the 4-position. The phenyl group allows for intramolecular ,,, stacking, which renders the complex more stable and yields long-living light-emitting electrochemical cells (LECs). The additional substituent increases the intersite distance between the cations in the film, reducing the quenching of the excitons, and should improve the efficiency of the LECs. Density functional theory calculations indicate that the three complexes have the desired ,,, intramolecular interactions between the pendant phenyl ring of the bpy ligand and the phenyl ring of one of the ppy ligands in the ground and the excited states. The photoluminescence quantum efficiency of concentrated films of the complexes improves with the increasing size of the bulky groups indicating that the adopted strategy for improving the efficiency is successful. Indeed, LEC devices employing these complexes as the primary active component show shorter turn-on times, higher efficiencies and luminances, and, surprisingly, also demonstrate longer device stabilities. [source]

Functionalized Self-Assembled InAs/GaAs Quantum-Dot Structures Hybridized with Organic Molecules

Miaoxiang Chen
Abstract Low-dimensional III,V semiconductors have many advantages over other semiconductors; however, they are not particularly stable under physiological conditions. Hybridizing biocompatible organic molecules with advanced optical and electronic semiconductor devices based on quantum dots (QDs) and quantum wires could provide an efficient solution to realize stress-free and nontoxic interfaces to attach larger functional biomolecules. Monitoring the modifications of the optical properties of the hybrid molecule,QD systems by grafting various types of air-stable diazonium salts onto the QD structures surfaces provides a direct approach to prove the above concepts. The InAs/GaAs QD structures used in this work consist of a layer of surface InAs QDs and a layer of buried InAs QDs embedded in a wider-bandgap GaAs matrix. An enhancement in photoluminescence intensity by a factor of 3.3 from the buried QDs is achieved owing to the efficient elimination of the dangling bonds on the surface of the structures and to the decrease in non-radiative recombination caused by their surface states. Furthermore, a narrow photoluminescence band peaking at 1620,nm with a linewidth of 49 meV corresponding to the eigenstates interband transition of the surface InAs QDs is for the first time clearly observed at room temperature, which is something that has rarely been achieved without the use of such engineered surfaces. The experimental results demonstrate that the hybrid molecule,QD systems possess a high stability, and both the surface and buried QDs are very sensitive to changes in their surficial conditions, indicating that they are excellent candidates as basic sensing elements for novel biosensor applications. [source]

High-Density Periodically Ordered Magnetic Cobalt Ferrite Nanodot Arrays by Template-Assisted Pulsed Laser Deposition

Xingsen Gao
Abstract A novel nanopatterning method using pulsed laser deposition through an ultrathin anodic aluminium oxide (AAO) membrane mask is proposed to synthesize well-ordered nanodot arrays of magnetic CoFe2O4 that feature a wide range of applications like sensors, drug delivery, and data storage. This technique allows the adjustment of the array dimension from ,35 to ,300,nm in diameter and ,65 to ,500,nm in inter-dot distance. The dot density can be as high as 0.21 Terabit in.,2. The microstructure of the nanodots is characterized by SEM, TEM, and XRD and their magnetic properties are confirmed by well-defined magnetic force microscopy contrasts and by hysteresis loops recorded by a superconducting quantum interference device. Moreover, the high stability of the AAO mask enables the epitaxial growth of nanodots at a temperature as high as 550,°C. The epitaxial dots demonstrate unique complex magnetic domains such as bubble and stripe domains, which are switchable by external magnetic fields. This patterning method creates opportunities for studying novel physics in oxide nanomagnets and may find applications in spintronic devices. [source]

Cover Picture: Highly Fluorescent Poly(dimethylsiloxane) for On-Chip Temperature Measurements (Adv. Funct.

Highly fluorescent poly(dimethylsiloxane) (PDMS) doped with ZnO quantum dots (QDs) is conveniently generated and used directly for whole-chip temperature measurements, as described by Hongkai Wu and co-workers on page 324. A model is also given to elucidate the temperature sensitivity and extremely high stability of this material by studying the bonding between the QDs and the PDMS. [source]

Highly Fluorescent Poly(dimethylsiloxane) for On-Chip Temperature Measurements

Jianhua Zhou
Abstract This work describes a convenient method to generate a poly(dimethylsiloxane) (PDMS) composite containing ZnO quantum dots (QDs) for whole-chip temperature measurements. This composite is highly fluorescent and very sensitive to temperature changes (0.4,nm,°C,1, compared to 0.1,nm,°C,1 in commonly used CdSe QDs). It also shows extremely high fluorescent stability under various conditions over long time without phase separation or fluorescent changes. Both merits make this composite an ideal material for sensing temperature changes on microfluidic chips. The bonding between the QDs and PDMS is studied by comparing PDMS composites with ZnO QDs of different sizes, and a model is given to elucidate the high stability of this composite. [source]

Water Stability and Luminescence of Lanthanide Complexes of Tripodal Ligands Derived from 1,4,7-Triazacyclononane: Pyridinecarboxamide versus Pyridinecarboxylate Donors

Grégory Nocton
Abstract A series of europium(III) and terbium(III) complexes of three 1,4,7-triazacyclononane-based pyridine containing ligands were synthesized. The three ligands differ from each other in the substitution of the pyridine pendant arm, namely they have a carboxylic acid, an ethylamide, or an ethyl ester substituent, i.e., these ligands are 6,6,,6,-[1,4,7-triazacyclononane-1,4,7-triyltris(methylene)]tris[pyridine-2-carboxylic acid] (H3tpatcn), -tris[pyridine-2-carboxamide] (tpatcnam), and -tris[pyridine-2-carboxylic acid] triethyl ester (tpatcnes) respectively. The quantum yields of both the europium(III) and terbium(III) emission, upon ligand excitation, were highly dependent upon ligand substitution, with a ca. 50-fold decrease for the carboxamide derivative in comparison to the picolinic acid (=pyridine-2-carboxylic acid) based ligand. Detailed analysis of the radiative rate constants and the energy of the triplet states for the three ligand systems revealed a less efficient energy transfer for the carboxamide-based systems. The stability of the three ligand systems in H2O was investigated. Although hydrolysis of the ethyl ester occurred in H2O for the [Ln(tpatcnes)](OTf)3 complexes, the tripositive [Ln(tpatcnam)](OTf)3 complexes and the neutral [Ln(tpatcn)] complexes showed high stability in H2O which makes them suitable for application in biological media. The [Tb(tpatcn)] complex formed easily in H2O and was thermodynamically stable at physiological pH (pTb 14.9), whereas the [Ln(tpatcnam)](OTf)3 complexes showed a very high kinetic stability in H2O, and once prepared in organic solvents, remained undissociated in H2O. [source]

Generation, Spectroscopic Characterization by EPR, and Decay of a Pyranine-Derived Radical

Carolina Aliaga
Abstract The pyraninoxyl radical is readily formed from the MnO2 -promoted oxidation of pyranine. The free radical can be formed in high concentrations (mM), and presents a characteristic EPR spectrum that indicates a high spin-density delocalization. It is relatively stable under nitrogen (half-life ca. 50,min) but readily decays in presence of O2. In spite of its high stability, the radical readily reacts with antioxidants (phenols and ascorbic acid) with a partial recovery of the parent pyranine. High concentrations of the pyraninoxyl radical (ca. 9,,M) are present when pyranine is exposed to a free radical source (10,mM 2,2,-azobis[2-amidinopropane], 37°). The fact that these radicals readily react with antioxidants (ascorbic acid and caffeic acid) supports the proposal that protection by antioxidants of peroxyl radical-promoted pyranine bleaching is mainly due to the occurrence of a repair mechanism. [source]

Organic Single Crystal Field-effect Transistors Based on 6H -pyrrolo[3,2,b:4,5,b´]bis[1,4]benzothiazine and its Derivatives

Zhongming Wei
Single crystal effect-field transistors (SCFETs) are fabricated based on single crystal micro-ribbons of 6H -pyrrolo[3,2,b:4,5,b´]bis[1,4]benzothiazine and its 6-substituted derivatives (PBBTZ 1,3). High mobility (3.6,cm2 V,1,s,1) and high stability (no significant decrease in one year) are obtained from the devices. The quantum chemically calculated results on the crystals 1,3 (see figure) agrees well with the experimental data. [source]

A convenient synthesis of N - t -butyl- N,-aminocarbonyl- N -(substituted)benzoyl-hydrazine containing , -aminoalkylphosphonate groups in a one-pot procedure

Qingmin Wang
A variety of novel N-t-butyl-N,-aminocarbonyl-N-(substituted)benzoylhydrazines containing ,-aminoalkylphosphonate groups were synthesized. Treatment of ,-aminoalkylphosphonates with triphosgene yielded ,-isocyanatoalkylphosphonates, and subsequent addition with N-t-butyl-N-substituted benzoylhydrazines provided the title compounds in a one-pot procedure with good yields. The triphosgene-mediated reaction for the synthesis of ,-isocyanatoalkylphosphonates enjoys a number of advantages: the reaction is carried out under mild condition in good yield, triphosgene is relatively safe to handle because of its low vapor pressure and high stability, and the experimental procedure is simple. This method can be applicable to the synthesis of other ,-isocyanatoalkyl-phosphonates and urylenediphosphonates. The structures of all of the products and by-products were confirmed by 1H NMR, 31P NMR, IR and mass spectroscopy, and elemental analysis. We also found that some of the compounds possess potential antitobacco mosaic virus (TMV) activities and anticancer activities. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:68,72, 2001 [source]

Highly Surface-roughened "Flower-like" Silver Nanoparticles for Extremely Sensitive Substrates of Surface-enhanced Raman Scattering

Hongyan Liang
Abstract Surface-enhanced Raman scattering (SERS) is a new optical spectroscopic analysis technique with potential for highly sensitive detection of molecules. Recently, many efforts have been made to find SERS substrates with high sensitivity and reproducibility. In this Research News article, we provide a focused review on the synthesis of monodispersed silver particles with a novel, highly roughened, "flower-like" morphology by reducing silver nitrate with ascorbic acid in aqueous solutions. The nanometer-scale surface roughness of the particles can provide several hot spots on a single particle, which significantly increases SERS enhancement. The incident polarization-dependent SERS of individual particles is also studied. Although the different "hot spots" on a single particle can have a strong polarization dependency, the total Raman signals from an individual particle usually have no obvious polarization dependency. Moreover, these flower-like silver particles can be measured by SERS with high enhancement several times, which indicates the high stability of the hot spots. Hence, the flower-like silver particles here can serve as highly sensitive and reproducible SERS substrates. [source]