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81.
Nicole M. Else-Quest Janet S. Hyde Ahalya Hejmadi 《Mathematical Thinking and Learning》2013,15(1):5-35
Mathematics is often thought of as a purely intellectual and unemotional activity. Recently, researchers have begun to question the validity of this approach, arguing that emotions and cognition are intertwined. The emotions expressed during mathematics work may be linked to mathematics achievement. We used behavioral measures to identify the emotions expressed by U.S. mothers and their 11-year-old children while solving pre-algebra tasks in the home. The most notable positive emotions displayed by mothers and children included positive interest, affection, joy, and pride, whereas the most notable negative emotions expressed included tension, frustration, and distress. Reflecting the social aspects of doing homework together, mothers' and children's emotions were highly correlated. Independent of pre-existing differences in knowledge, children's emotions were associated with their performance on a mathematics post-test: tension was linked to poorer performance while positive interest, humor, and pride were linked to better performance. We found no evidence of gender differences in the emotions while working the tasks, although boys responded with more tension following an incorrect solution than did girls. 相似文献
82.
Solid microparticles of several different insoluble organic compounds were mechanically immobilized on the surface of graphite
electrodes and immersed into a liquid electrolyte in order to study their electrochemical reactions. Cyclic staircase voltammetry
and square-wave voltammetry were used. Quinhydrone was found to be a stable intermediate in the reversible redox reaction
of solid quinone and hydroquinone on the electrode surface. The reaction occurs on the surface of the solid particle which
is in contact with water. Indigo can be reduced to leucoindigo and oxidized to dehydroindigo in two separate reversible redox
reactions. In strongly basic medium indigo dissolves in water upon electroreduction. A hydroacridine radical was detected
as a stable intermediate in the electrochemically irreversible redox reaction of acridine and dihydroacridine. Famotidine
can be electrooxidized and the product of this reaction can be electroreduced in two separate chemically irreversible reactions.
Probucol is oxidized to a semiquinone radical which can be re-reduced in an electrochemically irreversible redox reaction.
Propyl- thiouracil can be also oxidized to an unknown product which can be re-reduced in a chemically reversible, but slow
solid state surface redox reaction. Reductions of solid thionicotinoylanilide and nicotinoylanilide are totally irreversible.
Received September 22, 1998. Revision March 19, 1999. 相似文献
83.
Dzyadevych SV Soldatkin AP El'skaya AV Martelet C Jaffrezic-Renault N 《Analytica chimica acta》2006,568(1-2):248-258
The key theoretical principles of the work on ion-selective field-effect transistor connected with their application in bioanalytical practice, some specifics of modern microtechnologies for their creation, and measurement schemes with set-ups are discussed. The achievements in the creation of enzyme biosensors based on ion-selective field-effect transistors and prospects for their application are described in detail. 相似文献
84.
me3Si? CCl2?Sime2Cl (me ? CH3) läßt sich mit n-buLi (bu ? C4H9) bei–100°C (Lösungsmittel THF/Äther) in me3Si? CCl(Li)? Sime2Cl a überführen. das mit meJ me3Si? CClme? Sime2Cl bildet. Wird a in Abwesenheit eines Abfangreagenzes langsam erwärmt, so bildet sich unter Abspaltung von LiCl (Cl aus der SiCl-Gruppe) über eine reaktive Zwischenstufe des Bicyclobutans b . Die Struktur von b ist durch NMR-Untersuchung, Röntgenstrukturanalyse und Abbaureaktionen gesichert. Mit HBr bzw. CH3OH werden die Si? C-Bindungen der Dreiringe in b gespalten, so daß sich me3Si? CH2? C(Sime2X)2Sime3 (X ? Br, OCH3) bildet. Formation of Organosilicon Compounds. 85. Formation, Reactions, and Structure of 1,1,3,3-Tetramethyl-2,4-bis(trimethylsilyl)-1,3-disilabicyclo[1, 1, 0]butane me3Si? CCl2? Sime2Cl (me ? CH3) with n-buLi (bu ? C4H9) at –100°C (solvent: THF/ether) yields me3Si? CCl(Li)? Sime2Cl a , which forms me3Si? CClme? Sime2Cl with meI. By warming a slowly in absence of any trapping reagent the bicyclobutane b is obtained via a reactive intermediate under elimination of LiCl (Cl from the SiCl group). The structure of b is established by nmr investigations, X-ray structure determination and chemical derivatisation. 相似文献
85.
Distribution coefficients and capacities have been determined for many different organic compounds on a new molecular sieve called silicalite, which does not adsorb water but does adsorb small organic molecules with diameters up to 6 A, from both liquid and gaseous streams. The characteristics of silicalite have been examined closely and new applications for it are briefly described. 相似文献
86.
Biesemans M Martins JC Jurkschat K Pieper N Seemeyer S Willem R 《Magnetic resonance in chemistry : MRC》2004,42(9):776-780
It is demonstrated that long-range nJ(1H,117Sn) coupling constants down to 0.3 Hz, can be accurately quantified from non-linear fitting of the sine modulation of the associated 1H-117Sn correlation cross-peak intensities sampled as a function of the heteronuclear antiphase coherence preparation time in the 1H-117Sn J-HMQC pulse sequence. The contribution of additional, undesired modulations is illustrated and assessed using the product operator formalism, and is traced back to contributions that arise from miss-setting of the wandering 180 degrees pulse angle in the constant time period. The power of the method and its use in the characterization of weak intramolecular donor-acceptor interactions are illustrated by the determination of long-range nJ(1H,117Sn) coupling constants of bis[3-(dimethylamino)propyl]tin derivatives, [Me2N(CH2)3]2SnR2 (', R = Me; 3, R = Ph; 4, R = t-Bu). By comparing these with the values found for the corresponding bis(4-methylpentyl)tin derivatives, [Me2CH(CH2)3]2SnR2 (2', R = Me; 3', R = Ph), which lack such interactions, the use of long-range coupling constants to detect intramolecular donor-acceptor interactions is evaluated. It is concluded that nJ(1H,117Sn) couplings up to six bonds through an organic carbon chain can be quantified, whether donor-acceptor interactions are present or not. Furthermore, evidence is presented that, when two scalar coupling pathways co-exist, the pathway involving an intramolecular donor-acceptor interaction can have opposite sign, thus decreasing the overall coupling constant to a value smaller than that actually measured in the absence of a donor-acceptor interaction, where only one coupling pathway is active. There is nevertheless clear numerical value discrimination in the series of compounds investigated between long-range couplings in derivatives without weak intramolecular donor-acceptor interactions and those where such interactions can exist. 相似文献
87.
T. A. Furstch L. T. Taylor T. W. Fritz G. Fortner E. Khor 《Journal of polymer science. Part A, Polymer chemistry》1982,20(5):1287-1298
Five polyimide films prepared from 3,3′,4,4′-benzophenone tetracarboxylic acid'dianhydride (BTDA) and diamines, 4,4′-oxydianiline (ODA), 3,3′-diaminobenzophenone (DABP), or 3,3′-diaminodiphenylcarbinol (DADPC) and doped with Li2PdCl4 (LTP) or Pd[(CH3)2S]2Cl2 (PDS) were selected for a detailed x-ray photoelectron spectroscopic (XPS) study to determine the oxidation state of palladium and the relative distribution of this and other elements in these films, especially as they relate to electrical resistivity. XPS shows that Pd in the films is present as a mixture of zero and +2 valence states. Films that contain lithium as part of the dopant all show that metal is present as Li+ and Li2O, a fact that may have a bearing on film electrical properties. An Auger electron spectroscopic (AES) or XPS profiling was performed on two of the electrically conductive films. A film doped with PDS reveals a majority of palladium at the surface as Pd(0) and much smaller amounts in film bulk as a mixture of Pd(0) and Pd(II). Film behavior is similar to a metal-vapor deposited film. An LTP doped film, by contrast, exhibits a homogeneous composition with a mixture of Pd(0) and Pd(II). These studies support others that use chemical etching on the film surfaces. Scanning electron microscopy (SEM) has been used to provide surface evaluations. 相似文献
88.
Schmitt-Jansen M Bartels P Adler N Altenburger R 《Analytical and bioanalytical chemistry》2007,387(4):1389-1396
The occurrence of pharmaceuticals in the environment is an emerging issue. Several studies observed that the non-steroidal
anti-inflammatory drug diclofenac is ubiquitously present in most of the surveyed surface waters, worldwide. Phototransformation
of diclofenac was reported from laboratory assays as well as in natural water systems, raising the question of possible adverse
effects of the phototransformation products of diclofenac to aquatic organisms. In this study the phytotoxicity of diclofenac
exposed to natural sunlight was evaluated using synchronized cultures of the unicellular chlorophyte Scenedesmus vacuolatus. Diclofenac dissolved in ultra-pure water at 50 mg L−1 was exposed to natural midsummer sunlight for a maximum of 145 h. Twice a day subsamples were taken for chromatography and
parallel phytotoxicity assessment. Inhibition of algal reproduction of the initial diclofenac solution was in the mg L−1 range indicating no specific toxicity of diclofenac towards S. vacuolatus. Fast degradation of diclofenac was observed with half lives between 3.3 and 6.4 h during the first and the third day of
exposure, respectively. Phytotoxicity increased after 3.5 h of exposure of diclofenac to sunlight and showed a maximum of
sixfold enhanced toxicity after 53 h of exposure to sunlight. Several phototransformation products were found during the experiment.
The time courses of the relative concentration of three transformation products significantly correlated with enhanced phytotoxicity
during the experiment. This indicates a high toxicity potential of phototransformation products of diclofenac at concentration
levels that may come close to environmental concentrations of residual diclofenac after degradation. We conclude that toxicity
assessment of phototransformation products should be included in the risk assessment of pharmaceuticals in the environment. 相似文献
89.
Nicole Harmgarth Phil Liebing Liane Hilfert Volker Lorenz Felix Engelhardt Sabine Busse Frank T. Edelmann 《无机化学与普通化学杂志》2019,645(17):1101-1109
New homoleptic complexes of selected rare‐earth elements containing the unsymmetrically substituted amidinate ligand [MeC(NEt)(NtBu)]– [= (L)–] were synthesized and fully characterized. Treatment of in situ‐prepared Li(L) ( 1 ) with anhydrous lanthanide(III) chlorides, LnCl3 (Ln = Sc, La, Ce, Ho), afforded three different types of amidinate complexes depending on the ionic radius of the central metal atom. The large La3+ formed the octa‐coordinate DME solvate La(L)3(DME) ( 2 ). Using Ce3+, the octa‐coordinate “ate” complex Li(THF)[Ce(L)4] ( 3 ) was formed. Depending on the crystallization conditions, compound 3 could be crystallized in two modifications differing in the coordination environment around Li. In the case of the smaller Sc3+ and Ho3+ ions, six‐coordinate homoleptic Sc(L)3 ( 4 ) and Ho(L)3 ( 5 ) were isolated. The title compounds were fully characterized by spectroscopic and analytical methods as well as single‐crystal X‐ray diffraction. With Ln = La and Ce, several by‐products incorporating lithium, chlorine and/or oxygen were also isolated and structurally characterized. 相似文献
90.
Corden VA Duhme-Klair AK Hostachy S Perutz RN Reddig N Becker HC Hammarström L 《Inorganic chemistry》2011,50(3):1105-1115
A heteroditopic ligand H(2)-L consisting of a dihydroxybenzene (catechol)-unit linked via an amide bond to a pyridyl-unit and its methyl-protected precursor Me(2)-L were synthesized, characterized, and their photophysical properties investigated. The three accessible protonation states of the ligand, H(3)-L(+), H(2)-L, and H-L(-), showed distinct (1)H NMR, absorption and emission spectroscopic characteristics that allow pH-sensing. The spectroscopic signatures obtained act as a guide to understand the signaling mechanism of the luminescent pH and molybdate sensor [Re(bpy)(CO)(3)(H(2)-L)](+). It was found that upon deprotonation of the 2-hydroxy group of H(2)-L, a ligand-based absorption band emerges that overlaps with the Re(dπ)→bpy metal-to-ligand charge transfer (MLCT) band of the sensor, reducing the quantum yield for emission on excitation in the 370 nm region. In addition, deprotonation of the catechol-unit leads to quenching of the emission from the Re(dπ)→bpy (3)MLCT state, consistent with photoinduced electron transfer from the electron-rich, deprotonated catecholate to the Re-based luminophore. Finally, reaction of 2 equiv of [Re(bpy)(CO)(3)(H(2)-L)](+) with molybdate was shown to give the zwitterionic Mo(VI) complex [MoO(2){Re(CO)(3)(bpy)(L)}(2)], as confirmed by electrospray ionization (ESI) mass spectrometry and X-ray crystallography. The crystal structure determination revealed that two fully deprotonated sensor molecules are bound via their oxygen-donors to a cis-dioxo-MoO(2) center. 相似文献