Dimer

Distribution by Scientific Domains
Distribution within Chemistry

Kinds of Dimer

  • acid dimer
  • centrosymmetric dimer
  • cyclic dimer
  • cyclobutane pyrimidine dimer
  • dichloride dimer
  • form dimer
  • heterochiral dimer
  • hydrogen-bonded dimer
  • inactive dimer
  • one dimer
  • other dimer
  • porphyrin dimer
  • protein dimer
  • pyrimidine dimer
  • ruthenium dichloride dimer
  • stable dimer
  • thymine dimer
  • tubulin dimer
  • water dimer

  • Terms modified by Dimer

  • dimer complex
  • dimer consisting
  • dimer equilibrium
  • dimer form
  • dimer formation
  • dimer interaction
  • dimer interface
  • dimer model
  • dimer structure
  • dimer unit

  • Selected Abstracts


    Synthesis, Crystal Structure, and Optical Properties of a New Molecular Complex of C60 with a Covalently Linked (FeIIITPP)2O Dimer

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2003
    Aleksey L. Litvinov
    Abstract A new molecular complex of C60 with covalently linked ,-oxo dimer (FeIIITPP)2O are (TPP = tetraphenylporphyrin) was obtained. The complex has a neutral ground state and is formed mainly by van der Waals forces. The X-ray analysis of the crystal structure of the complex showed it to have isolated packing of fullerenes in which each fullerene molecule is embraced in a pocket built by porphyrins. Optical properties and EPR behavior of the complex are described. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]


    Efficient Photosensitized Splitting of Thymine Dimer by a Covalently Linked Tryptophan in Solvents of High Polarity

    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 6 2005
    Qin-Hua Song
    Abstract Tryptophan-thymine dimer model compounds used to mimic the repair reaction of DNA photolyase have been synthesized. The photosensitized cleavage of the dimer by the covalently linked tryptophan is strongly solvent-dependent with the reaction rates increasing in increasingly polar solvents, for example, the quantum yield , = 0.004 in THF/hexane (5:95) and 0.093 in water. The fluorescence of the tryptophan residue is quenched by the dimer moiety by electron transfer from the excited tryptophan to the dimer. Fluorescence-quenching studies indicated that the electron transfer was efficient in polar solvents. The splitting efficiency of the dimer radical anion within the tryptophan·+,dimer·, species is also remarkably solvent-dependent and increases with the polarity of the solvents. The back-electron-transfer reaction in the charge-separated species, which competes with cleavage, was suppressed in polar solvents. These results are in contrast to those of earlier solvent-dependent studies of indole-dimer systems, but they can be rationalized in terms of the differences in the distances between the chromophore unit and the attached dimer. The pH-dependent measurements of the splitting reaction and the deuterium isotope effect showed that the tryptophan radical cation within the charge-separated species does not deprotonate prior to the cleavage of the dimer radical anion. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]


    Dimer-Based Three-Dimensional Photonic Crystals

    ADVANCED FUNCTIONAL MATERIALS, Issue 18 2010
    Ian D. Hosein
    Abstract The self-assembly of polystyrene dimer- and spherocylinder-shaped colloids is achieved via controlled drying on glass and silicon substrates. 3D monoclinic colloidal crystal structures are determined from scanning electron microscopy images of sections prepared using focused ion-beam (FIB) milling. Full photonic bandgaps between the eighth and ninth bands are found for a systematic range of colloidal dimer shapes explored with respect to the degree of constituent lobe fusion and radius ratio. The pseudogap between bands 2 and 3 for spherocylinder-based monoclinic crystals is also probed using normal incidence reflection spectroscopy. [source]


    Micrometer- and Nanometer-Sized, Single-Crystalline Ribbons of a Cyclic Triphenylamine Dimer and Their Application in Organic Transistors

    ADVANCED MATERIALS, Issue 16 2009
    Rongjin Li
    A cyclic triphenylamine dimer with high crystallinity is demonstrated. Micrometer- and nanometer-sized single-crystalline ribbons are easily produced by a physical vapor transport technique. Field-effect transistors of the ribbons exhibit mobilities up to 0.05,cm2 V,1 s,1. The mobility of the devices depends greatly on the size of the ribbons: the smaller the ribbons, the higher the mobility. [source]


    Quantitative Aggregation,Activity Relationship (QAAR): Supermolecular View, Dimer as the Simplest Aggregation State and Monomolecule

    MOLECULAR INFORMATICS, Issue 6 2007
    Feng Fan
    Abstract Aggregation state of bioactive compounds plays a key role in its bio-interactive procedure. In this paper, based on the structural information of dimers, the simplest model of aggregation state, classical QSAR, was used for the investigation of the relationship between aggregation state and bioactivity. Aided by the template of crystal structure of Teflubenzuron, two dimer descriptors of ,E and ,Rg which could describe parts of the aggregation state characters were used to establish the models. QSAR research implicates that the bioactivity may strongly depend on the molecular aggregation state. [source]


    1H-NMR Studies of Duplex DNA Decamer Containing a Uracil Cyclobutane Dimer: Implications Regarding the High UV Mutagenecity of CC Photolesions,

    PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2002
    Hyun Mee Lee
    ABSTRACT To determine the origin of the UV-specific CC to TT tandem mutation at the CC site, we made a duplex DNA decamer containing a uracil cis,syn cyclobutane dimer (CBD) as the deaminated model of a cytosine dimer. Two-dimensional 1H-NMR spectroscopy studies were performed on this sequence where two adenines (Ade) were opposite to the uracil dimer. Two imino protons of the uracil dimer were found to retain Watson,Crick hydrogen bonding with the opposite Ade, although the 5,-U(NH) of the dimer site showed unusual upfield shift like that of the 5,-T(NH) of the TT dimer, which seemed to be associated with deshielding by the flanking base rather than with reduced hydrogen bonding. (McAteer et al. 1998, J. Mol. Biol. 282:1013,1032). Hydrogen bondings at the dimer site were also supported by detecting typical strong nuclear Overhauser effects (NOE) between two imino protons and the opposite Ade H2 or NH2. But sequential NOE interactions of base protons with sugar protons were absent at the two flanking nucleotides of the 5, side of the uracil dimer and at the intradimer site, contrasting with its thymine analog where sequential NOE was absent only at the A4,T5 step. In addition, NOE cross peak for U5(NH) , A4(H2) was detected, although the NOE interactions of U6(NH) with A7(H2) and A17(H2) were not observed in contrast to the thymine dimer duplex. This different local structural alteration may be affected by the induced right-hand twisted puckering mode of cis,syn cyclobutane ring of the uracil dimer in the B-DNA duplex, even though the isolated uracil dimer had left-hand twisted puckering rigidly. In parallel, these observations may be correlated with observed differences in mutagenic properties between cis,syn UU dimer and cis,syn TT dimer. [source]


    Dimer,monomer equilibrium of human thymidylate synthase monitored by fluorescence resonance energy transfer

    PROTEIN SCIENCE, Issue 5 2010
    Filippo Genovese
    Abstract An ad hoc bioconjugation/fluorescence resonance energy transfer (FRET) assay has been designed to spectroscopically monitor the quaternary state of human thymidylate synthase dimeric protein. The approach enables the chemoselective engineering of allosteric residues while preserving the native protein functions through reversible masking of residues within the catalytic site, and is therefore suitable for activity/oligomerization dual assay screenings. It is applied to tag the two subunits of human thymidylate synthase at cysteines 43 and 43, with an excitation energy donor/acceptor pair. The dimer,monomer equilibrium of the enzyme is then characterized through steady-state fluorescence determination of the intersubunit resonance energy transfer efficiency. [source]


    Asymmetric Polymer Bridging Between Starch-Coated Colloidal Particles and Pulp Fibres by Cationic Polyacrylamide

    THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 5 2007
    Agatha Poraj-Kozminski
    Abstract Internal sizing agents are commonly used as additives in papermaking to impart hydrophobicity to paper. They are commonly added in the form of colloidal particles, stabilized by cationic starch. As an example we studied the deposition of micron-sized Alkyl Ketene Dimer (AKD) particles on pulp fibres by cationic polyacrylamide (cPAM), a common flocculent. It was found that cPAM did not adsorb on AKD particles stabilized by cationic starch. Despite this inability to adsorb, cPAM was found to drastically improve the deposition of AKD particles on pulp fibres. This deposition was ascribed to asymmetric polymer bridging, a phenomenon observed by us before, while studying clay deposition on fibres by polyethylene oxide. In asymmetric polymer bridging between two types of particles, the bridging polymer first adsorbs on one type of particle, since it is unable to adsorb on the second type. Asymmetric polymer bridging occurs when the enthalpy gain on both surfaces exceeds the entropy loss. The kinetics of AKD deposition on fibres was found to agree with the predictions of the asymmetric bridging theory. In addition, an increase in bond strength with time was found, due to starch and cPAM reconfiguration. The increase in AKD retention by cPAM is also observed in experiments on a laboratory twin-wire sheet former. Asymmetric polymer bridging by cPAM between starch-coated AKD particles and fibres is compared with classical polymer bridging by cPAM between fibres and AKD particles coated by carboxymethylcellulose. Des agents d'encollage internes sont communément utilisés comme additifs dans la fabrication du papier pour transmettre l'hydrophobicité au papier. Ils sont communément ajoutés sous la forme de particules colloïdales, stabilisées par l'amidon cationique. À titre d'exemple, on a étudié la déposition de particules microniques de dimère de cétène d'alkyle (AKD) sur des fibres de pâte par le polyacrylamide cationique (cPAM), un floculant commun. On a trouvé que le cPAM ne s'adsorbait pas sur les particules d'AKD stabilisées par l'amidon cationique. Malgré cette incapacité à s'adsorber, on a trouvé que le cPAM améliorait considérablement la déposition des particules d'AKD sur les fibres de pâte. Cette déposition est imputée au pontage de polymères asymétriques, un phénomène que nous avons observé précédemment, lors de l'étude de la déposition d'argile sur les fibres par l'oxyde de polyéthylène. Dans le pontage de polymères asymétriques entre deux types de particules, le polymère de pontage s'adsorbe d'abord sur un type de particules, vu qu'il est incapable de s'adsorber sur le second type de particules. Le pontage de polymères asymétriques survient lorsque le gain d'enthalpie sur les deux surfaces excède la perte d'entropie. On a trouvé que la déposition d'AKD sur les fibres concordait avec les prédictions de la théorie de pontage asymétrique. En outre, on a observé une augmentation de la force de liaison dans le temps, en raison de la reconfiguration de l'amidon et du cPAM. L'augmentation de la rétention de l'AKD par le cPAM est également observée dans les expériences sur un appareil de formage de feuilles à double toile de laboratoire. Le pontage de polymères asymétriques par le cPAM entre les particules d'AKD enduites d'amidon et les fibres est comparé au pontage de polymères classique par le cPAM entre les fibres et les particules d'AKD enduites de carboxyméthylcellulose. [source]


    Remarkable Site Difference of Vibrational Energy Relaxation in Benzene Dimer: Picosecond Time-Resolved IR,UV Pump,Probe Spectroscopy,

    ANGEWANDTE CHEMIE, Issue 39 2010
    Ryoji Kusaka
    Ganz entspannt: Die Schwingungsenergierelaxation (VER) von Isotopologen des Benzol-Dimers auf dem C-H-Streckschwingungsniveau wurde durch zeitaufgelöste Pikosekunden-IR-UV-Pump-Sonden-Spektroskopie untersucht (siehe Bild, h=C6H6, d=C6D6). Dabei ergab sich ein bemerkenswerter Unterschied in den Relaxationslebensdauern: Die Lebenszeit des ,stehenden" Benzolmoleküls (,Stem", 110,ps) ist 4.5mal kürzer als die des ,liegenden" (,Top", 500,ps). [source]


    ChemInform Abstract: New Families of Enantiopure Cyclohexenone cis-Diol, o-Quinol Dimer and Hydrate Metabolites from Dioxygenase-Catalyzed Dihydroxylation of Phenols.

    CHEMINFORM, Issue 42 2009
    Derek R. Boyd
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]


    ChemInform Abstract: Stoichiometry and Structure of Uranyl(VI) Hydroxo Dimer and Trimer Complexes in Aqueous Solution.

    CHEMINFORM, Issue 10 2008
    Satoru Tsushima
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]


    One-Step Synthesis of Lumazine and Xanthine: First Co-Crystal of Lumazine and Perchloric Acid with a Unique Monohydrated Hydronium Ion (H5O2+) Mediated Supramolecular Assembly of the Lumazine Dimer.

    CHEMINFORM, Issue 50 2007
    Shyamaprosad Goswami
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]


    Catalytic Conversion of Isocyanates to Carbodiimides by Cyclopentadienyl Manganese Tricarbonyl and Cyclopentadienyl Iron Dicarbonyl Dimer.

    CHEMINFORM, Issue 49 2007
    A. K. Fazlur Rahman
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]


    Computational Study of the Release of H2 from Ammonia Borane Dimer (BH3NH3)2 and Its Ion Pair Isomers.

    CHEMINFORM, Issue 48 2007
    Vinh Son Nguyen
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]


    Remarkable Dinitrogen Activation and Cleavage by the Gd Dimer: From Dinitrogen Complexes to Ring and Cage Nitrides.

    CHEMINFORM, Issue 26 2007
    Mingfei Zhou
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]


    Facile Synthesis of Pyrrolo[2,1-c][1,4]benzodiazepine-5,11-dione Dimer.

    CHEMINFORM, Issue 52 2006
    Naim H. Al-Said
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]


    Structure of the Boronic Acid Dimer and the Relative Stabilities of Its Conformers

    CHEMINFORM, Issue 48 2006
    Joseph D. Larkin
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]


    First Synthesis of Group-14 Polyanions by Extraction of a Binary Alloy with dmf and a Novel Conformation of the (Ge9,Ge9)6- Dimer: Crystal Structures of [K6(Ge9,Ge9)](dmf)12, [Rb6(Ge9,Ge9)](dmf)12 and [K2.5Cs3.5(Ge9,Ge9)] (dmf)12.

    CHEMINFORM, Issue 47 2006
    Anke Nienhaus
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]


    Reactivity of Titanium Dimer and Molecular Nitrogen in Rare Gas Matrices.

    CHEMINFORM, Issue 32 2006
    Electronic Spectra, Structure of Ti2N2., Vibrational
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]


    Novel One-Pot Synthesis of 5-Alkenyl-15-alkynylporphyrins and Their Derivatization to a Butadiyne-Linked Benzoporphyrin Dimer.

    CHEMINFORM, Issue 20 2006
    Hiroko Yamada
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source]


    New [4 + 4] Photodimerization of 5-Chloro-2-pyridone to the meso-cis-syn Dimer as an Inclusion Complex with 1,2,4,5-Benzenetetracarboxylic Acid.

    CHEMINFORM, Issue 22 2005
    Shinya Hirano
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]


    Synthesis and Evaluation of a Dimer of 2-(4-Pyridylmethyl)-1-indanone as a Novel Nonsteroidal Aromatase Inhibitor.

    CHEMINFORM, Issue 44 2004
    Ranju Gupta
    Abstract For Abstract see ChemInform Abstract in Full Text. [source]


    ChemInform Abstract: Solution and Solid-State Studies of 3,4-Dichloro-2,5-diamidopyrroles: Formation of an Unusual Anionic Narcissistic Dimer.

    CHEMINFORM, Issue 33 2002
    Salvatore Camiolo
    Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source]


    Autocatalytic Creation of Closed Dimer and Extended Helix Metallosupramolecular Architectures

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 39 2009
    Nobuto Yoshinari
    Hybrid architectures: Self-organization of the xylyl-linked dicobalt(III) complex with an L -cysteine residue into homochiral dimeric and helix supramolecular structures is reported (see figure). These two structures were randomly and exclusively formed in the absence of any external stimuli if [HgBr4]2, was incorporated as the counter ion, thanks to the conformational bistability of the xylyl linker. [source]


    The Heteropolytungstate Core {BW13O46}11, Derived as Monomer, Dimer, and Trimer

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 25 2007
    Nathalie Leclerc-Laronze Dr.
    Abstract A study of the borotungstate system has led to the characterization of new, original compounds based on the unconventional Keggin derivative [H3BW13O46]8, ion (denoted as 1). [H3BW14O48]6, (2) and the dimer [H6B2W26O90]12, (3) crystallize as mixed cesium/ammonium salts and have been characterized by single-crystal X-ray diffraction analysis. Anion 2 reveals an unusual arrangement, consisting of an outer {W3O9} core grafted onto the monovacant [BW11O39]9, Keggin moiety and exhibits an unprecedented distorted square-pyramidal arrangement for a cis -{WO2} core. Elemental analysis, supported by bond distance analysis, is consistent with the presence of three protons distributed over the terminal oxygens of the outer {W3O7} capping fragment. The [H6B2W26O90]12, ion (3) is formally derived from the direct condensation of two [H3BW13O46]8, subunits. The cisoid arrangement of the two [BW11O39]9, subunits, coupled with the antiparallel arrangement of the two quasi-linear OW,,,OWOH2 chains within the central {W4O12} connecting group, breaks any symmetry, thereby resulting in a chiral compound. Polarography and pH-metric titrations reveal the formation of the monomeric precursor [H3BW13O46]8, (anion 1) under stoichiometric conditions. 183W NMR analysis of 2 and 3 in solution gives complex spectra, consistent with the presence of equilibria between several species. In the frame of this study, we also report on a structural re-investigation of the [H6B3W39O132]15, ion (4) based on reliable results obtained in the solid state by means of single-crystal X-ray diffraction analysis, and in solution by means of 1D and 2D COSY 183W NMR. X-ray diffraction analysis revealed the presence of three attached aquo ligands on the central {W6O15} connecting core, generating three OW,,,OWOH2 quasi-linear chains, which are responsible for the chirality of the trimeric assembly. This structural arrangement accounts for the 39-line 183W solution spectrum. The 2D COSY spectrum permits reliable assignments of the six strongly shielded resonances (around ,250 and ,400,ppm) to the six central W atoms, as well as additional assignments. The origin of such strong shielding for these particular W atoms is discussed on the basis of previously published results. Infrared data for compounds 1, 3, and 4 are also presented. [source]


    Proton- and Redox-Controlled Switching of Photo- and Electrochemiluminescence in Thiophenyl-Substituted Boron,Dipyrromethene Dyes

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 3 2006
    Holger Röhr Dipl.-Phys.
    Abstract A luminescent molecular switch in which the active thiol/disulfide switching element is attached to a meso -phenyl-substituted boron,dipyrromethene (BDP) chromophore as the signalling unit is presented. The combination of these two functional units offers great versatility for multimodal switching of luminescence: 1) deprotonation/protonation of the thiol/thiolate moiety allows the highly fluorescent meso - p -thiophenol-BDP and its nonfluorescent thiolate analogue to be chemically and reversibly interconverted, 2) electrochemical oxidation of the monomeric dyes yields the fluorescent disulfide-bridged bichromophoric dimer, also in a fully reversible process, and 3) besides conventional photoexcitation, the well separated redox potentials of the BDP also allow the excited BDP state to be generated electrochemically (i.e., processes 1) and 2) can be employed to control both photo- and electrochemiluminescence (ECL) of the BDP). The paper introduces and characterizes the various states of the switch and discusses the underlying mechanisms. Investigation of the ortho analogue of the dimer provided insight into potential chromophore,chromophore interactions in such bichromophoric architectures in both the ground and the excited state. Comparison of the optical and redox properties of the two disulfide dimers further revealed structural requirements both for redox switches and for ECL-active molecular ensembles. By employing thiol/disulfide switching chemistry and BDP luminescence features, it was possible to create a prototype molecular ensemble that shows both fully reversible proton- and redox-gated electrochemiluminescence. In dieser Arbeit wird ein lumineszierender molekularer Schalter vorgestellt, bei dem das aktive Thiol/Disulfid-Schaltelement an einen meso-phenylsubstituierten Bordipyrromethen (BDP) Farbstoff als Signal gebende Komponente gekoppelt ist. Die Kombination dieser beiden funktionellen Einheiten offeriert eine hohe Vielseitigkeit für das multimodale Schalten der Lumineszenz: 1) die Deprotonierung/Protonierung der Thiol/Thiolat-Gruppe erlaubt es, das stark fluoreszierende meso-p-Thiophenol-BDP und das analoge, nicht fluoreszierende Thiolat chemisch reversibel ineinander zu überführen, 2) die elektrochemische Oxidation der monomeren Farbstoffe ergibt das fluoreszierende, disulfidverbrückte, bichromophore Dimer,dieser Prozess ist ebenfalls vollständig reversibel, und 3) neben der konventionellen Anregung mit Licht erlauben die deutlich getrennten Redoxpotenziale des BDPs ebenfalls eine elektrochemische Generierung des angeregten BDP-Zustandes, d.h., Prozesse 1) und 2) können dazu eingesetzt werden, sowohl die Photo- als auch die Elektrochemilumineszenz (ECL) des BDP zu steuern. Diese Arbeit stellt die Charakteristika der verschiedenen Zustände des Schalters vor und diskutiert die zu Grunde liegenden Mechanismen. Die Untersuchung des ortho-Analogen des Dimers vermittelte zudem Einsicht in mögliche Chromophor,Chromophor-Wechselwirkungen im Grund- wie im angeregten Zustand von solchen bichromophoren Architekturen. Der Vergleich der optischen und Redoxeigenschaften der beiden Disulfid-Dimere gab des Weiteren Aufschluss über strukturelle Voraussetzungen von Redoxschaltern sowie ECL-aktiven molekularen Ensembles. Unter Einsatz schaltbarer Thiol/Disulfid-Chemie und mit den Lumineszenzeigenschaften der BDPs war es möglich, ein erstes molekulares Ensemble zu entwickeln, das vollständig reversible protonen- als auch redoxgesteuerte Elektrochemilumineszenz zeigt. [source]


    Ionization-Induced Proton Transfer in Model DNA Base Pairs: A Theoretical Study of the Radical Ions of the 7-Azaindole Dimer

    CHEMPHYSCHEM, Issue 12 2004
    Hsing-Yin Chen Dr.
    Abstract Proton-transfer reactions of the radical anion and cation of the 7-Azaindole (7AI) dimer were investigated by means of density functional theory (DFT). The calculated results for the dimer anion and cation were very similar. Three equilibrium structures, which correspond to the non-proton-transferred (normal), the single-proton-transferred (SPT) and the double-proton-transferred (tautomeric) forms, were found. The transition states for proton-transfer reactions were also located. The calculations showed that the first proton-transfer reaction (normal,SPT) is exothermic and almost barrier-free; therefore, it should occur spontaneously in the period of a vibration. In contrast, the second proton-transfer reaction (SPT,tautomer) was found to be far less-probable in terms of reaction energy and barrier. Hence, it was concluded that both (7AI)2and (7AI)2exist in the SPT form. The conclusion was further confirmed by the calculated electron vertical detachment energy (VDE) of the SPT form of (7AI)2, 1.33 eV, which is very close to the experimental measurement of 1.35 eV. The calculated VDEs of the normal and tautomeric (7AI)2forms were too small compared to the experimental value. The proton transfer process was found to be multidimensional in nature involving not only proton motion but also intermolecular rocking motion. In addition, IR spectra were calculated and reported. The spectra of the three structures showed very different features and, therefore, can be considered as fingerprints for future experimental identifications. The implications of these results to biology and spectroscopy are also briefly discussed. [source]


    A New Hydroxo-bridged Chromium(III) Dimer [Cr(saltn)OH]2·4H2O: Synthesis, Crystal Structure and Magnetic Properties

    CHINESE JOURNAL OF CHEMISTRY, Issue 6 2005
    Ni Zhong-Hai
    Abstract A new hydroxo-bridged dimeric Cr(III) complex [Cr(saltn)OH]2·4H2O [H2saltn=N,N,-bis(salicylidene)trimethylenediamine] has been synthesized and its structural and magnetic properties have been investigated. The complex crystallizes in the triclinic space group P -1 with one dimeric formula unit in a cell of dimensions a=0.95828(19) nm, b=0.95926(19) nm, c=1.0437(2) nm, ,=86.77(3)°, ,=82.48(3)°, and ,=64.93(3)°. The geometry around each chromium(III) center is six-coordinate, distorted-octahedral. The bridging Cr2O2 unit is strictly planar, as required by the crystallographic symmetry. The CrOCr, bridging angle is 99.94(16)°, and the distance between Cr,Cr, is 0.3019 nm. The magnetic susceptibility of the complex has been examined in the range of 2-300 K. By using the spin-spin coupled model for an S1=S2=3/2 dimeric system , the magnetic data were fitted to give the parameters of g=2.01(1), J=-0.85(2) cm -1, and zJ' =0.18(3)cm -1, indicating the presence of a weak antiferromagnetic spin-exchange interaction between the Cr(III) ions in the binuclear complex. [source]


    Crystal structure of a ternary mononuclear copper (II) complex: 4-chloro-3-methyl-6[(N-2-picolyl)-1,-iminomethyl]phenolato copper(II)perchlorate

    CRYSTAL RESEARCH AND TECHNOLOGY, Issue 5 2006
    S. M. Malathy Sony
    Abstract The complex crystallizes in monoclinic space group P21/n with unit cell parameters a = 7.295(4), b = 19.627(5), c = 12.770(4) Å, , = 101.25(4)º, V = 1793.2(12) Å3, Z = 4, , = 1.684 Mg/m3 at T = 293(2)K. The structure was solved by Patterson method and refined by full-matrix least-squares procedures to final R = 0.0387 using 2906 observed reflections. The asymmetric unit of the complex contains a mononuclear tridentate ligand, a perchlorate group and a methanol molecule. The compound crystallizes as parallel layers of polymeric complex bridged through perchloarate groups. The molecular CuN2OO,O,,2 chromophore involves an elongated rhombic octahedral structure and the Cu-ligand bond shows greater disparity. The five-membered chelate ring and the pyridine ring lie in the same plane while the six membered chelate ring assumes sofa conformation. A strong O-H,O inter molecular interaction plays a key role in the formation of dimer along b-axis. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


    The ,II isotype of tubulin is present in the cell nuclei of a variety of cancers

    CYTOSKELETON, Issue 2 2004
    I-Tien Yeh
    Abstract Tubulin, the subunit protein of microtubules, has generally been thought to be exclusively a cytoplasmic protein in higher eukaryotes. We have previously shown that cultured rat kidney mesangial cells contain the ,II isotype of tubulin in their nuclei in the form of an ,,II dimer [Walss et al., 1999: Cell Motil. Cytoskeleton 42:274,284, 1999]. More recently, we examined a variety of cancerous and non-cancerous cell lines and found ,II in the nuclei of all of the former and only a few of the latter (Walss-Bass et al., 2002: Cell Tissue Res. 308:215,223]. In order to determine if ,II -tubulin occurs in the nuclei of actual cancers as well as in cancer cell lines, we used the immunoperoxidase method to look for nuclear ,II in a variety of tumors excised from 201 patients. We found that 75% of these tumors contain ,II in their nuclei. Distribution of nuclear ,II was highly dependent on the type of cancer, with 100% of the colon and prostate cancers, but only 19% of the skin tumors, having nuclear ,II. Nuclear ,II was particularly marked in tumors of epithelial origin, of which 83% showed nuclear ,II, in contrast to 54% in tumors of non-epithelial origin. In many cases, ,II staining occurred very strongly in the nuclei and not in the cytoplasm; in other cases, ,II was present in both. In many cases, particularly metastases, otherwise normal cells adjacent to the tumor also showed nuclear ,II, suggesting that cancer cells may influence nearby cells to synthesize ,II and localize it to their nuclei. Our results have implications for the diagnosis, biology, and chemotherapy of cancer. Cell Motil. Cytoskeleton 57:96,106, 2004. © 2004 Wiley-Liss, Inc. [source]