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Electronic Characteristics (electronic + characteristic)

Distribution by Scientific Domains

Chemistry	87%

Selected Abstracts

Synthesis and Characterization of Radical Cations Derived from Mono- and Biferrocenyl-Substituted 2-Aza-1,3-butadienes: A Study of the Influence of an Asymmetric and Oxidizable Bridge on Intramolecular Electron Transfer

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2005
Vega Lloveras
Abstract The synthesis and study of structural and electronic properties of mono-ferrocenyl ,-conjugated complexes 5a,d, whose electronic characteristics have been systematically varied by introducing an electron-donating or electron-withdrawing substituent either at the 1-position or at the 4-position of the 2-aza-1,3-butadiene moiety linked to the ferrocenyl unit, are presented. The structural and electronic properties of the homobimetallic complex 5f, with two ferrocene units linked through the asymmetric and oxidizable 2-aza-1,3-butadiene bridge, is also reported. The crystal structures of complexes 5b, 5d, and 5f show a large degree of conjugation in this family of compounds. Complexes 5 show a rich electrochemical behavior due both to the oxidation of ferrocenyl units and the 2-aza-1,3-butadiene bridge, as revealed by cyclic voltammetry. Radical cations 5+· were prepared from 5 by coulometric oxidations following their generation by absorption spectroscopy. The electronic properties of all reported neutral and oxidized ,-conjugated complexes have been investigated by means of UV/Vis,near-IR, EPR and 57Fe Mössbauer spectroscopy. The detailed study of mono-oxidized species 5a+·,5f+· has permitted the determination of the influence of an asymmetric bridge with an electroactive character on the intramolecular electron transfer (IET) phenomenon, thus demonstrating that the 2-aza-1,3-butadiene bridge promotes the IET between the two metallic units of 5f+· through two different pathways. The experimental data and conclusions are supported by DFT computations (B3LYP/3-21G*) and time-dependent DFT methods. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Structure and bonding in some S -methylsulfonium halides

HETEROATOM CHEMISTRY, Issue 4 2005
D. B. Chesnut
Density functional theory (DFT) calculations have been carried out at the B3LYP 6-311+G(d,p) level to characterize the geometric and electronic characteristics of a series of S-methylsulfonium halides that possess unusual molecular structures. Atoms-in-molecules (AIM), electron localization function (ELF), and NMR data support the idea that the binding in these gas phase species is predominately ionic with some small degree of covalent bonding. © 2005 Wiley Periodicals, Inc. 16:263,270, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20087 [source]

Computational modeling of tetrahydroimidazo-[4,5,1-jk][1,4]-benzodiazepinone derivatives: An atomistic drug design approach using Kier-Hall electrotopological state (E-state) indices

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 11 2008
Nitin S. Sapre
Abstract Quantitative structure-activity relationships (QSAR), based on E-state indices have been developed for a series of tetrahydroimidazo-[4,5,1-jk]-benzodiazepinone derivatives against HIV-1 reverse transcriptase (HIV-1 RT). Statistical modeling using multiple linear regression technique in predicting the anti-HIV activity yielded a good correlation for the training set (R2 = 0.913, R = 0.897, Q2 = 0.849, MSE = 0.190, F -ratio = 59.97, PRESS = 18.05, SSE = 0.926, and p value = 0.00). Leave-one-out cross-validation also reaffirmed the predictions (R2 = 0.850, R = 0.824, Q2 = 0.849, MSE = 0.328, and PRESS = 18.05). The predictive ability of the training set was also cross-validated by a test set (R2 = 0.812, R = 0.799, Q2 = 0.765, MSE = 0.347, F -ratio = 64.69, PRESS = 7.37, SSE = 0.975, and p value = 0.00), which ascertained a satisfactory quality of fit. The results reflect the substitution pattern and suggest that the presence of a bulky and electropositive group in the five-member ring and electron withdrawing groups in the seven-member ring will have a positive impact on the antiviral activity of the derivatives. Bulky groups in the six-member ring do not show an activity-enhancing impact. Outlier analysis too reconfirms our findings. The E-state descriptors indicate their importance in quantifying the electronic characteristics of a molecule and thus can be used in chemical interpretation of electronic and steric factors affecting the biological activity of compounds. © 2008 Wiley Periodicals, Inc. J Comput Chem, 2008 [source]

Bound electronic states on a dislocation kink in semiconductors

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2007
Robert A. Vardanyan
Abstract We discuss electron localization on dislocation kinks, that is essential for multiphonon capture of carriers by the dislocation, in view of the problem of recombination-enhanced defect glide in wide-band semiconductors. In the case of a smooth kink (when the continuum model is applicable) the formation of bound electronic states is analyzed analytically. The eigenstates and corresponding wave functions are found, depending both on kink parameters and electronic characteristics of the semiconductor. A possible application of the obtained results for the analysis of electron localization on an abrupt kink is considered. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Cluster approach to the Ti2Ni structure type

ACTA CRYSTALLOGRAPHICA SECTION B, Issue 1 2006
D. Rodi
It has been established that the 16(c) first coordination clusters in the Ti2Ni structure type (space group Fd3m) follow icosahedral-face orientational ordering along regular tetrahedron edge directions. The actual crystal structure appears due to the prevalence of the face-centred cubic translational ordering over the cluster assembling. This way, the competition of the `regular' crystal phase and its icosahedral analogue is reconstructed at the atomic level. The model accounts for the markedly different electronic characteristics at the different crystallographic positions obtained by hyperfine interaction measurements, and other curious experimental facts help to create an exact physical definition of the first coordination in the solid state and to distinguish between various structure types on fundamental principles. [source]

Modular Solid-Phase Synthetic Approach To Optimize Structural and Electronic Properties of Oligoboronic Acid Receptors and Sensors for the Aqueous Recognition of Oligosaccharides

CHEMISTRY - A EUROPEAN JOURNAL, Issue 1 2004
Duane Stones Dr.
Abstract This article describes the design and optimization of the first entirely modular, parallel solid-phase synthetic approach for the generation of well-defined polyamine oligoboronic acid receptors and fluorescence sensors for complex oligosaccharides. The synthetic approach allows an effective building of the receptor polyamine backbone, followed by the controlled diversification of the amine benzylic side chains. This approach enabled the testing, in a modular fashion, of the effect of different arylboronic acid units substituted with unencumbering para electron-withdrawing or electron-donating groups. The feasibility of this approach toward automated synthesis was also investigated with the assembly of a sublibrary of receptors by means of the Irori MiniKan technology. Several sublibraries of anthracene-capped sensors containing two or three arylboronic acids were synthesized, and their binding to a series of model disaccharides was examined in neutral aqueous media. The calculation of association constants by fluorescence titrations confirmed that subtle changes in the structures of the interamine spacers in the polyamine backbone can have a significant effect on the stability of the resulting complexes. Most importantly, this study led to the determination of the preferred electronic characteristics for the arylboronate units, and suggests that a new generation of receptors containing very electron-poor arylboronic acids could lead to a significant improvement of binding affinities. [source]

Discovery of Potent Vascular Endothelial Growth Factor Receptor-2 Inhibitors

CHEMMEDCHEM, Issue 1 2010
Athanasios Papakyriakou Dr.
Abstract Substantial evidence over the last decades has implicated uncontrolled angiogenesis with various pathological states, including cancer. Vascular endothelial growth factor (VEGF) plays a critical role in its regulation. Because the tyrosine kinase VEGF receptor-2 (VEGFR-2) is the major mediator of the mitogenic, angiogenic, and permeability-enhancing effects of VEGF, it has become one of the most profound anti-angiogenesis targets. Inspired by the anthranilamide class of VEGFR-2 inhibitors, we performed a computational analysis of some potent representative members, using docking and molecular dynamics calculations. Based on the observations drawn from introducing the effect of the receptor's flexibility in implicit aqueous environment, we designed, synthesized, and characterized several new analogues of related scaffolds with modifications in their steric and electronic characteristics. In,vitro evaluation of these compounds revealed several novel VEGFR-2 inhibitors that are less cytotoxic and more potent than the parent compounds. [source]

Environmentally friendly coloured materials: cellulose/titanium dioxide/inorganic pigment composite spherical microbeads prepared by viscose phase-separation method

COLORATION TECHNOLOGY, Issue 6 2007
Shoji Nagaoka
In order to develop environmentally friendly coloured materials, cellulose composite spherical microbeads hybridised with titanium dioxide (TiO2) particles and inorganic pigment were prepared by a phase-separation method using viscose and an aqueous solution containing sodium polyacrylate. Findings regarding the relationships between cellulose xanthate and the electronic characteristics of TiO2 particles used in the cellulose/inorganic material composite sphering process are also reported. These findings suggest that the location of TiO2 particles in cellulose microbeads is related to electrical repulsion between the xanthate (CSS,) group and TiO2. The use of TiO2 powder as colour pigment is limited, as its colour is white. The cellulose composite spherical microbeads covered with TiO2 and Fe2O3 particles were developed by addition of iron oxide (Fe2O3). Their surfaces were viewed by laser microscope and using SEM images. These composite microbeads retained the photocatalytic property of TiO2. Cellulose/TiO2/Fe2O3 composite spherical microbeads with both colour function and photocatalytic properties were successfully prepared. [source]