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    Selected Abstracts

    N -(Aryl)picolinamide Complexes of Ruthenium: Usual Coordination and Strategic Cyclometalation

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2007
    Sumon Nag
    Abstract Reaction of five N -(4- R -phenyl)picolinamides (R = OCH3, CH3, H, Cl, and NO2) with [Ru(PPh3)2(CO)2Cl2] in refluxing 2-methoxyethanol in the presence of a base (NEt3) affords two geometrical isomers of a group of complexes (1-R and 2-R), each of which contains an amide ligand coordinated to the metal center as a monoanionic bidentate N,N donor along with two triphenylphosphanes, a carbonyl, and a hydride. Similar reaction of N -(naphthyl)picolinamide with [Ru(PPh3)2(CO)2Cl2] affords an organometallic complex, 3, in which the amide ligand is coordinated to the metal center, by C,H activation of the naphthyl ring at the 8-position, as a dianionic tridentate N,N,C donor along with two triphenylphosphanes and one carbonyl. Structures of the 1-OCH3, 2-CH3, and 3 complexes have been determined by X-ray crystallography. In all the complexes the two triphenylphosphanes are trans. In the 1-R complexes the hydride is trans to the pyridine nitrogen and in the 2-R complexes it is trans to the amide-nitrogen. All the complexes are diamagnetic, and show characteristic 1H NMR signals and intense MLCT transitions in the visible region. Cyclic voltammetry on all the complexes shows a RuII,RuIII oxidation within 0.71,0.93 V versus SCE. An oxidation and a reduction of the coordinated amide ligand are also observed within 1.29,1.69 V versus SCE and ,1.02 to ,1.21 V versus SCE respectively.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    Synthesis, Structures, and Magnetic Properties of N -Trialkylsilyl-8-amidoquinoline Complexes of Chromium, Manganese, Iron, and Cobalt as well as of Wheel-Like Hexanuclear Iron(II) and Manganese(II) Bis(8-amidoquinoline)

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2010
    Astrid Malassa
    Abstract The transamination of 8-(tert -butyldimethylsilylamino)quinoline with (thf)2Cr[N(SiMe3)2]2 yields monomeric bis[8-(tert -butyldimethylsilylamido)quinoline]chromium(II) (1). Similar reactions of M[N(SiMe3)2]2 (M = Mn, Fe, Co) with 8-(trialkylsilylamino)quinoline lead to the formation of monomeric bis[8-(trialkylsilylamido)quinoline]metal(II) [M = Mn, SiR3 = SiMe2tBu (2a), SiiPr3 (2b); M = Fe, SiR3 = SiMe2tBu (3a),SiiPr3 (3b); M = Co, SiR3 = SiMe2tBu (4a), SiiPr3 (4b)]. The transamination of 8-aminoquinoline with M[N(SiMe3)2]2 (M = Mn, Fe, Co) allows the isolation of the heteroleptic 1:1 and homoleptic 2:1 products. The 1:1 complexes bis[8-amidoquinoline metal(II)bis(trimethylsilyl)amide] [M = Mn (5), Fe (6), Co (7)] are dimeric with bridging 8-amidoquinoline moieties. The 2:1 complexes of Mn and Fe, bis(8-amidoquinoline)manganese(II) (8) and bis(8-amidoquinoline)iron(II) (9), form hexamers with wheel-like molecular structures consisting of metal-centered nitrogen octahedra interconnected by common N···N edges. The cobalt complex, bis(8-amidoquinoline)cobalt(II) (10), precipitates as a microcrystalline powder. Investigations of the magnetic properties by DFT corroborate the experimental data for the Mn derivative 8, where an antiferomagnetic coupling is observed. By contrast, calculations on the Fe6 -wheel 9 yield very close-lying ferromagnetically and antiferromagnetically coupled states. [source]

    Reactions of [Hg(Tab)2](PF6)2 [Tab = 4-(trimethylammonio)benzenethiolate] with NaX (X = Cl, NO2, NO3): Isolation and Structural Characterization of a Series of Mono- and Binuclear Hg/Tab/X Compounds

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2008
    Xiao-Yan Tang
    Abstract The complex [Hg(Tab)2](PF6)2 [Tab = 4-(trimethylammonio)benzenethiolate] (1) reacts with one or two equivalents of NaCl to afford the mononuclear complex [Hg(Tab)2Cl](PF6) (2) and the dinuclear complex [{Hg(,-Tab)(Tab)Cl}2]Cl2·H2O (3·H2O), respectively. Similar reactions of 1 with NaCl and NaX (molar ratio = 1:1) produce the dinuclear species [{Hg(,-Tab)(Tab)Cl}2]X2 [X = NO2 (4), NO3 (5)], while those with NaNO2 or NaNO3 give rise to [{Hg(,-Tab)(Tab)X}2]X2 [X = NO2 (6), NO3 (7)]. Complexes 2,7 have been characterised by elemental analysis, IR, UV/Vis, and 1H NMR spectroscopy, and X-ray crystallography. The Hg atom of the [Hg(Tab)2Cl]+ cation in 2 adopts a T-shaped coordination geometry. Two [Hg(Tab)2Cl]+ cations in 3·H2O, 4, and 5 are linked by a pair of weak Hg,S bonds to form a dimeric [Hg(,-Tab)(Tab)Cl]22+ dication, and the centrosymmetric [Hg(,-Tab)(Tab)X]22+ dication in 6 and 7 consists of two [Hg(Tab)2X]+ cations linked by a couple of weak Hg,S bonds. The hydrogen-bonding interactions in 2,7 lead to the formation of interesting 2D (5, 7) or 3D (2,4, 6) hydrogen-bonded networks.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source]

    Synthesis and Glycosidase Inhibitory Activities of Pyrrolidines and Piperidines with N -(Polyhydroxyalkyl) Side Chains

    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 18 2007
    Sabrina Boutefnouchet
    Abstract Amidification of L -proline (3) with (+)-(R,R)- 6 and (,)-(S,S)-tartaric anhydride diacetate (7) gave N -substituted L -proline derivatives 8a,b, respectively. Acids 8a,b were transformed into diesters 9a,b with MeOH/HCl. Similar reactions with methyl (2S,4R)- 4 and (2R,4S)-4-acetoxypipecolate (5) led to bicyclic lactams 14a,b and 15a. Compounds 8a,b were converted into N -(trihydroxybutyl)pyrrolidine derivatives 8c,d, 10a,b and 11a,b. Methyl (2S,4R)- 20a and (2R,4S)-4-acetoxy- N -[(2S,3S)-1,2,3-trihydroxybutyl]pipecolate (20b) were obtained by displacement of (,)-(2S,2S)-2- O -benzyl-3,4- O -isopropylidene-1-deoxy-1-iodothreitol (19) by 4 and 5. Compounds 20a,b were converted into (2S,4R,2,S,2,S)- 21a and(2R,4S,2,S,3,S)-4-hydroxy-2-hydromethyl- N -(2-benzyloxy-3,4-isopropylidenedioxy)piperidine (21b) and finally into unprotected pentols 22a,b. Nonprotected (2S,2,S,3,S)- 11a and (2S,2,R,3,R)- N -(1,2,3-trihydroxybutyl)prolinol (11b), as well as 22a,b, did not inhibit any of the 13 glycosidases assayed. However, a triacetoxy derivative, (2S,3S)-2,3-diacetoxy-4-[(2R,4S)-4-acetoxy-2-(methoxycarbonyl)piperidin-1-yl]-4-oxobutanoic acid (13b) is an inhibitor (IC50 = 157 ,M) of ,- L -fucosidase from bovine kidney.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    Chemo-Enzymatic Synthesis of All Isomers of 2-Methylbutane-1,2,3,4-tetraol , Important Contributors to Atmospheric Aerosols

    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 8 2007
    Anders Riise Moen
    Abstract By a combination of stereospecific osmium catalyzed oxidation of dimethyl citraconate and lipase catalysed enantioselective resolution of the formed dimethyl (2R*,3S*)-2,3-dihydroxy-2-methylbutanedioate, followed by reduction, (2R,3S)- and (2S,3R)-2-methylbutane-1,2,3,4-tetraol were isolated. Similar reactions starting with dimethyl mesaconate gave the isomers, (2R,3R)- and (2S,3S)-2-methylbutane-1,2,3,4-tetraol. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    Synthesis of C-14-labeled novel IKK inhibitor: 2-[14C]- N -(6-chloro-9H-pyrido [3,4-b]indol-8-yl)-3-pyridinecarboxamide

    JOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 5 2005
    Yuexian Li
    Abstract 2-[14C]- N -(6-Chloro-9H-pyrido [3,4-b]indol-8-yl)-3-pyridinecarboxamide (9A, also referred to as [14C]-PS-1145) was synthesized from [14C]-paraformaldehyde in five steps in an overall radiochemical yield of 15%. The key intermediate 1-[14C]-6-chloro-1,2,3,4-tetrahydro- , -carboline was obtained by Pictet,Spengler cyclization of chlorotryptamine with [14C]-paraformaldehyde. Similar reactions were conducted with tryptamine to address the generality of the methodology. Copyright © 2005 John Wiley & Sons, Ltd. [source]

    Dissolution and Enzymatic Degradation Studies Before and After Artificial Ageing of Silk- or Linen-Reinforced Gelatin Laminates, 1

    MACROMOLECULAR MATERIALS & ENGINEERING, Issue 5 2003
    M. Boyanova
    Abstract In an attempt to overcome the poor mechanical properties of native, i.e., untreated gelatin, laminates based on gelatin and gelatin/starch blend reinforced with fabrics (linen or silk) were prepared by melt pressing. The mechanical properties of fresh and artificially aged samples were reported previously. In the present series of two consecutive papers we present data concerning the dissolution and biodegradation of these laminates. A two-step procedure for treatment of the laminates was used. The first step is treatment with an aqueous buffer solution, the second with a buffered solution of the enzyme subtilisin. The time-course of the absorbance at 280 nm of the "washing" solutions was followed. A number of kinetic characteristics was determined and discussed with respect to laminate composition and their treatments. In the present Part 1 about the environmental behavior of these new biodegradable materials, the non-enzymatic solubilization in water and buffer solution (i.e., simple dissolution) of fresh and artificially aged samples is described. The dissolution process was followed spectrophotometrically as well as by the weight losses. It was found that gelatin-based silk- or linen-reinforced laminates were subject to dissolution, similarly to the gelatin and gelatin-based materials studied in previous works. In addition, it was established that the thermal treatment of the laminates during their melt pressing leads to postcondensation reactions and crosslinking of the gelatin macromolecules. Similar reactions occur between the matrix and the reinforcing element silk, thus improving their mutual adhesion. Decreased gelatin dissolution ability was observed after the thermal treatment, in the presence of reinforced fabrics and upon "additional" crosslinking with methylenedi(p -phenyl) diisocyanate. The untreated gelatin is the only one that dissolves completely in water. The artificially aged samples tend to dissolve better than the respective fresh samples due to degradation processes during aging. [source]

    Ligand Reprogramming in Dinuclear Helicate Complexes: A Consequence of Allosteric or Electrostatic Effects?

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 18 2007

    Abstract The ditopic ligand 6,6,-bis(4-methylthiazol-2-yl)-3,3,-([18]crown-6)-2,2,-bipyridine (L1) contains both a potentially tetradentate pyridyl-thiazole (py-tz) N - donor chain and an additional "external" crown ether binding site which spans the central 2,2,-bipyridine unit. In polar solvents (MeCN, MeNO2) this ligand forms complexes with ZnII, CdII, HgII and CuI ions via coordination of the N donors to the metal ion. Reaction with both HgII and CuI ions results in the self-assembly of dinuclear double-stranded helicate complexes. The ligands are partitioned by rotation about the central pypy bond, such that each can coordinate to both metals as a bis-bidentate donor ligand. With ZnII ions a single-stranded mononuclear species is formed in which one ligand coordinates the metal ion in a planar tetradentate fashion. Reaction with CdII ions gives rise to an equilibrium between both the dinuclear double-stranded helicate and the mononuclear species. These complexes can further coordinate s-block metal cations via the remote crown ether O - donor domains; a consequence of which are some remarkable changes in the binding modes of the N-donor domains. Reaction of the HgII - or CdII -containing helicate with either Ba2+ or Sr2+ ions effectively reprogrammes the ligand to form only the single-stranded heterobinuclear complexes [MM,(L1)]4+ (M=HgII, CdII; M,=Ba2+, Sr2+), where the transition and s-block cations reside in the N- and O-donor sites, respectively. In contrast, the same ions have only a minor structural impact on the ZnII species, which already exists as a single-stranded mononuclear complex. Similar reactions with the CdII system result in a shift in equilibrium towards the single-stranded species, the extent of which depends on the size and charge of the s-block cation in question. Reaction of the dicopper(I) double-stranded helicate with Ba2+ shows that the dinuclear structure still remains intact but the pitch length is significantly increased. [source]

    Enhanced reactivity in the ammonolysis of phenyl thiolacetates in aqueous medium

    INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 1 2002
    D. Rajarathnam
    The ammonolysis of several substituted phenyl thiolacetates is kinetically studied in aqueous medium, 18°C, ionic strength 0.1 M (KCl). By following the leaving groups spectrophotometrically (,max = 260,410 nm), under excess free ammonia, pseudo-first-order rate coefficients (kobs) are obtained. The plots of (kobs , kH) against free ammonia concentration are linear at constant pH. The macroscopic nucleophilic substitution rate coefficients (kN) are obtained as the slopes of these plots and found to be pH-independent for all the thiolesters. The Brönsted-type plot (log kN against pKa of leaving groups) and the Hammett plot (log kN against , values of substituents) obtained for the title reactions of thiolesters are linear with slope values of ,lg = ,0.34 and , = 0.74 respectively. From the magnitude of these values, experimental data, the kinetic law, and the analysis of products, it is deduced that the ammonolysis of thiolesters proceeds through a simple bimolecular nucleophilic substitution pathway with a zwitterionic tetrahedral addition intermediate (T±), whereby its formation is rate-determining (k1 step). Comparison of this reaction of thiolesters with a similar reaction of analogue oxyesters shows a mechanistic difference. Further, for thiolesters there is a rate enhancement with larger kN values. The change in mechanism and enhanced reactivity observed by substitution of the oxygen atom by sulphur atom on the phenyl moiety are discussed in detail. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 18,26, 2002 [source]

    Structure, Morphology and Properties of a Novel Molecular Composite by In-Situ Blending of Anionic Polyamide 6 with a Polyamide Copolymer Containing Rigid Segments

    MACROMOLECULAR MATERIALS & ENGINEERING, Issue 2 2007
    Xiaochun Wang
    Abstract Molten caprolactam, in which a polyamide copolymer (HPN) containing rigid segments was dissolved, was polymerized by means of anionic ROP to in produce polyamide (PA, nylon) 6 blends with HPN in situ. A novel molecular composite was achieved in which toughness and strength were simultaneously improved, as well as modulus, compared to virgin PA6. In view of the interchange reaction between PA6 and PA1212 (and PA66) in blends fabricated in the same way, it was deduced that a similar reaction between PA6 and HPN took place during the blending and led to copolymerization between the two components. The formation of copolymers was verified by their single glass transition and single melting peak, measured through DMA and DSC, respectively. DSC analysis also showed that the occurrence of the interchange reaction inhibited the crystallization and suppressed the melting point of PA6. Analysis by FT-IR spectroscopy indicated that the difference in the distance between the amide groups for PA6 and HPN induced a decrease in the amount and strength of hydrogen bonding. Moreover, characterization by POM and XRD revealed that the spherulite size of the PA6 crystals decreased dramatically and the amount of , crystal increased slightly with the majority of crystallites being , crystals. Furthermore, it was found through the observation of the morphology by SEM that no phase separation existed in the composites. On the basis of detailed analysis and a comparison between the in situ PA6/PA66 and PA6/HPN blends, it is believed that the combination of markedly decreasing spherulite size and similar segmental mobility resulted in the simultaneous improvement of mechanical properties for the in situ PA6/HPN blends. [source]

    A highly efficient synthesis of (Z)-1-aryl-2-silyl-1- stannylethenes and their conversion to (E)-2- arylethenyl-, (Z)-2-(2-pyridyl)ethenyl- and allenyl-silanes

    APPLIED ORGANOMETALLIC CHEMISTRY, Issue 3 2007
    Takanori Endo
    Abstract A Pd(dba)2,P(OEt)3 combination allowed the silastannation of arylacetylenes, 1-hexyne or propargyl alcohols with tributyl(trimethylsilyl)stannane to take place at room temperature, producing (Z)-2-silyl-1-stannyl-1-substituted ethenes in high yields. Novel silyl(stannyl)ethenes were fully characterized by 1H-, 13C-, 29Si- and 119Sn-NMR as well as infrared and mass analyses. Treatment of a series of (Z)-1-aryl-2-silyl-1-stannylethenes and (Z)-1-(3-pyridyl)-2-silyl-1-stannylethene with hydrochloric acid or hydroiodic acid in the presence of tetraethylammonium chloride (TEACl) or tetrabutylammonium iodide (TBAI) led to the exclusive formation of (E)-trimethyl(2-arylethenyl)silanes with high stereoselectivity. A similar reaction of (Z)-1-(2-anisyl)-2-silyl-1-stannylethene also produced E -type trimethyl[2-(2-anisyl)ethenyl]silane, while (Z)-trimethyl [2-(2-pyridyl)ethenyl]silane was produced exclusively from (Z)-1-(2-pyridyl)-2-silyl-1-stannylethene. Protodestannylation of (Z)-1-[hydroxy(phenyl)methyl]-2-silyl-1-stannylethene with trifluoroacetic acid took place via the ,-elimination of hydroxystannane, providing trimethyl(3-phenylpropa-1,2-dienyl)silane quite easily. The destannylation products were also fully characterized. Copyright © 2007 John Wiley & Sons, Ltd. [source]

    The structure of l -rhamnulose-1-phosphate aldolase (class II) solved by low-resolution SIR phasing and 20-fold NCS averaging

    ACTA CRYSTALLOGRAPHICA SECTION D, Issue 5 2002
    Markus Kroemer
    The enzyme l -rhamnulose-1-phosphate aldolase catalyzes the reversible cleavage of l -rhamnulose-1-phosphate to dihydroxyacetone phosphate and l -­lactaldehyde. It is a homotetramer with an Mr of 30,000 per subunit and crystallized in space group P3221. The enzyme shows a low sequence identity of 18% with the structurally known l -fuculose-1-­phosphate aldolase that splits a stereoisomer in a similar reaction. Structure analysis was initiated with a single heavy-atom derivative measured to 6,Å resolution. The resulting poor electron density, a self-rotation function and the working hypothesis that both enzymes are C4 symmetric with envelopes that resemble one another allowed the location of the 20 protomers of the asymmetric unit. The crystal-packing unit was a D4 -symmetric propeller consisting of five D4 -­symmetric octamers around an internal crystallographic twofold axis. Presumably, the propellers associate laterally in layers, which in turn pile up along the 32 axis to form the crystal. The non-crystallographic symmetry was used to extend the phases to the 2.7,Å resolution limit and to establish a refined atomic model of the enzyme. The structure showed that the two enzymes are indeed homologous and that they possess chemically similar active centres. [source]

    Chemoselective synthesis of peptides containing major advanced glycation end-products of lysine and arginine

    CHEMICAL BIOLOGY & DRUG DESIGN, Issue 3 2005
    P. Gruber
    Abstract:, Useful methodologies have been developed, enabling the straightforward synthesis of peptides containing N, -(carboxymethyl)- l -lysine (CML) and N, -(carboxyethyl)- l -lysine (CEL), the major glycation end-products of lysine. These lysine derivatives were successfully incorporated into growing peptide chains via standard Fmoc/Ot -Bu peptide synthesis procedures. For the synthesis of peptides containing major glycation end-products of arginine, synthetic routes have been developed enabling the transformation of ornithine residues in peptides into the well-known arginine-derived advanced glycation end-products (AGEs) Glarg, carboxymethyl- l -arginine (CMA), MG-H1, MG-H2, MG-H3, and carboxyethyl- l -arginine (CEA), respectively, by means of special modifying agents. Furthermore, it was shown that Glarg-containing peptides become quantitatively hydrolyzed into CMA-peptides under physiologic conditions. A similar reaction was observed in case of a MG-H3-peptide, which turned into a CEA-peptide under these conditions. [source]

    Novel Hypervalent Complexes of Main-Group Metals by Intramolecular Ligand,Metal Electron Transfer*

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 23 2004
    Matthias Driess Prof. Dr.
    Abstract New fascinating electronic features of the simple diketoamine chelate ligand HN[CH2C(tBu)O]2 (1) are described. Unexpectedly, the corresponding trianionic amido-dienolate form of 1 is capable of reducing main-group metal atoms M after initial coordination and intramolecular L,M two-electron transfer and of stabilizing main-group elements in unusual low oxidation states. This is impressively shown by the synthesis and structural characterization of the novel Ge and Sn complexes 4,6 by redox reactions of lithiated 1 with the corresponding metal halides GeCl4 and MCl2 (M=Ge, Sn). Surprisingly, conversion of tris-lithiated 1 with GeCl4 readily consumes two molar equivalents of GeCl4 and results in the formation of the neutral GeCl3 complex 4 and GeCl2. The former represents the second example of a structurally characterized neutral octahedrally coordinated germanium compound. Reaction of dilithiated 1 with GeCl2 does not lead to the expected ClGe(+2) complex but affords the novel dimeric germylene 5, whereas similar reaction using SnCl2 furnishes the monomeric stannylene (ClSn(+2) complex) 2 and elemental tin due to the higher oxidation potential of Sn(+2). Unexpectedly, a similar redox reaction of dilithiated 1 with PbCl2 furnishes the first air- and water-stable lithium 1,2-diketoimine,enolate 7 and elemental lead. Compound 7 is tetrameric in the solid state and consists of a strongly distorted Li4O4 cubic core with trigonal-bipyramidal coordinated Li+ ions. [source]

    Synthesis and Structure of [nPr3N(CH2)6NnPr3][CuFe3Br3(SePh)6], [Cu5Fe(SePh)7(PPh3)4] and [Cu4Fe3(SePh)10(PPh3)4],

    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 1 2007
    Andreas Eichhöfer
    Abstract CuBr and Fe(OOCCH3)2 react with PhSeSiMe3 in acetonitrile in the presence of the diammonium salt [nPr3N(CH2)6NnPr3]Br2 to yield ionic [nPr3N(CH2)6NnPr3][CuFe3Br3(SePh)6]. The neutral complexes [Cu5Fe(SePh)7(PPh3)4] and [Cu4Fe3(SePh)10(PPh3)4] were obtained by similar reactions of different stoichiometric mixtures of CuOOCCH3 and FeCl2 with PPh3 and PhSeSiMe3. The crystal structures of the compounds were determined by single-crystal X-ray analysis to give new structural types of molecular cluster compounds formed by copper, iron and selenium. Thermal treatment of [Cu5Fe(SePh)7(PPh3)4] and [Cu4Fe3(SePh)10(PPh3)4] resultsin the formation of mixtures of binary Cu2Se and ternaryCuFeSe2.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

    Social Presence and Children: Praise, Intrinsic Motivation, and Learning With Computers

    JOURNAL OF COMMUNICATION, Issue 1 2004
    Cheryl Campanella Bracken
    The computers are social actors (CASA) paradigm asserts that human computer users interact socially with computers, and the paradigm has provided extensive evidence that this is the case for adults. This experiment examined whether or not children have similar reactions to computers by comparing children's predictable responses to praise from a teacher to their responses to praise from a computer. Eight- to 10-year-old participants (N= 42) received either praise or neutral feedback from a computer. Independent variables were the feedback (praise or neutral), and participants' age and gender. Dependent variables measured via a paper-and-pencil questionnaire were learning (recall and recognition memory), perceived ability, and intrinsic motivation. Results provide evidence that children do have social responses to computers and that such social responses can lead to increases in learning (recall and recognition) in young children. [source]

    Conformational Structure and Energetics of 2-Methylphenyl(2,-methoxyphenyl)iodonium Chloride: Evidence for Solution Clusters

    CHEMISTRY - A EUROPEAN JOURNAL, Issue 34 2010
    Dr. Yong-Sok Lee
    Abstract Diaryliodonium salts allow the efficient incorporation of cyclotron-produced [18F]fluoride ions into electron-rich and electron-deficient arenes to provide potential radiotracers for molecular imaging in vivo with positron emission tomography (PET). This process (ArI+Ar,+18F,,Ar18F+Ar,I) is still not well understood mechanistically. To better understand this and similar reactions, it would be valuable to understand the structures of diaryliodonium salts in organic media, where the reactions are typically conducted. In this endeavor, the X-ray structure of a representative iodonium salt, 2-methylphenyl(2,-methoxyphenyl)iodonium chloride (1), was determined. Our X-ray structure analysis showed 1 to have the conformational M,P dimer as the unit cell with hypervalent iodine as a stereogenic center in each conformer. With the ab initio replica path method we constructed the inversion path between the two enantiomers of 1, thereby revealing two additional pairs of enantiomers that are likely to undergo fast interconversion in solution. Also LC,MS of 1 showed the presence of dimeric and tetrameric anion-bridged clusters in weak organic solution. This observation is consistent with the energetics of 1, both as monomeric and dimeric forms in MeCN, calculated at the B3LYP/DGDZVP level. These evidences of the existence of dimeric and higher order clusters of 1 in solution are relevant to achieve a deeper general understanding of the mechanism and outcome of reactions of diaryliodonium salts in organic media with nucleophiles, such as the [18F]fluoride ion. [source]