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  • 1
    Language: English
    In: Journal of the American Chemical Society, 02 May 2012, Vol.134(17), pp.7333-6
    Description: We present the first example of a surface-initiated group transfer polymerization (SI-GTP) mediated by rare earth metal catalysts for polymer brush synthesis. The experimentally facile method allows rapid grafting of polymer brushes with a thickness of 〉150 nm in 〈5 min at room temperature. We show the preparation of common poly(methacrylate) brushes and demonstrate that SI-GTP is a versatile route for the preparation of novel polymer brushes. The method gives access to both thermoresponsive and proton-conducting brush layers.
    Keywords: Chemistry;
    ISSN: 00027863
    E-ISSN: 1520-5126
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  • 2
    Language: English
    In: Vision Research, 01 June 2011, Vol.51(11), pp.1223-1231
    Description: ► Participants grasped cylindrical objects while attending to a RSVP stimulus. ► Perceptual performance strongly deteriorated due to the grasping task. ► Movement times and maximum grip aperture were unaffected by the perceptual task. ► However, the perceptual task led to a delayed adaptation of the grip to object size. ► We conclude that attention is required for the effective control of grasp kinematics. We investigated the effects of visuo-spatial attention on the kinematics of grasping movements by employing a dual-task paradigm. Participants had to grasp cylindrical objects of different sizes (motor task) while simultaneously identifying a target digit presented at a different spatial location within a rapid serial visual presentation (perceptual task). The grasping kinematics in this dual-task situation were compared with the those measured in a single-task condition. Likewise, the identification performance was also measured in a single-task condition. Additionally, we kept the visual input constant across conditions by asking participants to fixate. Without instructions about the priority of tasks (Experiment 1) participants showed a considerable drop of identification performance in the dual-task condition. Regarding grasping kinematics, the concurrent perceptual task resulted in a less accurate adaptation of the grip to object size in the early phase of the movement, while movement times and maximum grip aperture were unaffected. When participants were instructed to focus on the perceptual task (Experiment 2), the identification performance stayed at about the same level in the dual-task and the single-task conditions. The perceptual improvement was however associated with a further decrease in the accuracy of the early grip adjustment. We conclude that visual attention is needed for the effective control of the grasp kinematics, especially for a precise adjustment of the hand to object size when approaching the object.
    Keywords: Grasping ; Visual Attention ; Motor Control ; Dual-Task ; Medicine ; Anatomy & Physiology
    ISSN: 0042-6989
    E-ISSN: 1878-5646
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  • 3
    Language: English
    In: Psychological Science, March 2011, Vol.22(3), pp.339-347
    Description: When reaching for objects, people frequently look where they reach. This raises the question of whether the targets for the eye and hand in concurrent eye and hand movements are selected by a unitary attentional system or by independent mechanisms. We used the deployment of visual attention as an index of the selection of movement targets and asked observers to reach and look to either the same location or separate locations. Results show that during the preparation of coordinated movements, attention is allocated in parallel to the targets of a saccade and a reaching movement. Attentional allocations for the two movements interact synergistically when both are directed to a common goal. Delaying the eye movement delays the attentional shift to the saccade target while leaving attentional deployment to the reach target unaffected. Our findings demonstrate that attentional resources are allocated independently to the targets of eye and hand movements and suggest that the goals for these effectors are selected by separate attentional mechanisms.
    Keywords: Attention ; Saccades ; Reaching ; Hand Movements ; Psychology
    ISSN: 0956-7976
    E-ISSN: 1467-9280
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  • 4
    In: Nature Neuroscience, 2010, Vol.14(2), p.252
    Description: Many cells in retinotopic brain areas increase their activity when saccades (rapid eye movements) are about to bring stimuli into their receptive fields. Although previous work has attempted to look at the functional correlates of such predictive remapping, no study has explicitly tested for better attentional performance at the future retinal locations of attended targets. We found that, briefly before the eyes start moving, attention drawn to the targets of upcoming saccades also shifted to those retinal locations that the targets would cover once the eyes had moved, facilitating future movements. This suggests that presaccadic visual attention shifts serve to both improve presaccadic perceptual processing at the target locations and speed subsequent eye movements to their new postsaccadic locations. Predictive remapping of attention provides a sparse, efficient mechanism for keeping track of relevant parts of the scene when frequent rapid eye movements provoke retinal smear and temporal masking.
    Keywords: Saccadic Eye Movements ; Nervous System ; Retina ; Receptive Field ; Visual Perception ; Brain ; Attention ; Biochemical & Neurophysiological Correlates, Lesions and Stimuli ; Developmental Neuroscience;
    ISSN: 1097-6256
    E-ISSN: 15461726
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  • 5
    Language: English
    In: Vision Research, Oct 15, 2012, Vol.71, p.37(7)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.visres.2012.08.014 Byline: Constanze Hesse (a)(b), Thomas Schenk (c), Heiner Deubel (d) Keywords: Visual attention; Motor control; Dual-task; Grasping; Dorsal; Ventral Abstract: a* Grasping kinematics change when a concurrent perceptual task is performed. a* Dual-task interferences are observed in movement planning and movement control. a* Ventral and dorsal stream are not controlled by separate attentional mechanisms. a* Efficient grasping requires attentional resources. Author Affiliation: (a) Cognitive Neuroscience Research Unit, Wolfson Research Institute, Durham University, UK (b) Department of Psychology, University of Aberdeen, UK (c) Neurology, University of Erlangen-Nurnberg, Germany (d) Allgemeine und Experimentelle Psychologie, Ludwig-Maximilians-Universitat, Munchen, Germany Article History: Received 13 April 2012; Revised 7 August 2012
    Keywords: Neurosciences
    ISSN: 0042-6989
    Source: Cengage Learning, Inc.
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  • 6
    Language: English
    In: PLoS ONE, 2011, Vol.6(9), p.e24744
    Description: Japanese encephalitis virus (JEV) is a mosquito-borne flavivirus that causes public health problems in Asian countries. Only a limited number of JEV-infected individuals show symptoms and develop severe encephalitis, indicating host-dependent susceptibilities. ; C3H/HeN and DBA/2 mice, which exhibit different mortalities when infected by intraperitoneal inoculation with JEV, were used as experimental models to compare viral pathogenesis and host responses. One hundred infectious virus particles killed 95% of C3H/HeN mice whereas only 40% of DBA/2 mice died. JEV RNA was detected with similar low levels in peripheral lymphoid organs and in the sera of both mouse strains. High levels of viral and cytokine RNA were observed simultaneously in the brains of C3H/HeN and DBA/2 mice starting on days 6 and 9 post-infection, respectively. The kinetics of the cytokines in sera correlated with the viral replication in the brain. Significantly earlier and higher titers of neutralizing antibodies were detected in the DBA/2 strain. Primary embryonic fibroblasts, bone marrow-derived dendritic cells and macrophages from the two mouse strains were cultured. Fibroblasts displayed similar JEV replication abilities, whereas DBA/2-derived myeloid antigen-presenting cells had lower viral infectivity and production compared to the C3H/HeN–derived cells. ; Mice with different susceptibilities to JEV neuroinvasion did not show changes in viral tropism and host innate immune responses prior to viral entry into the central nervous system. However, early and high neutralizing antibody responses may be crucial for preventing viral neuroinvasion and host fatality. In addition, low permissiveness of myeloid dendritic cells and macrophages to JEV infection may be elements associated with late and decreased mouse neuroinvasion.
    Keywords: Research Article ; Biology ; Medicine ; Immunology ; Virology ; Infectious Diseases ; Physiology ; Neuroscience ; Pathology
    E-ISSN: 1932-6203
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  • 7
    Language: English
    In: Acta Psychologica, 2011, Vol.138(2), pp.302-310
    Description: Reaching with the hand is characterized by a decrease in sensitivity to tactile stimuli presented to the moving hand. Here, we investigated whether tactile suppression can be canceled by attentional orienting. In a first experiment, participants performed a dual-task involving a goal-directed movement paired with the speeded detection of a tactile pulse. The pulse was either delivered to the moving or stationary hand, during movement preparation, execution, or the post-movement phase. Furthermore, stimulation was delivered with equal probability to either hand, or with a higher probability to either the moving or resting hand. The results highlighted faster RTs under conditions of higher probability of stimulation delivery to both moving and resting hands, thus indicating an attentional effect. For the motor preparation period, RTs were faster only at the resting hand under conditions where tactile stimulation was more likely to be delivered there. In a second experiment, a non-speeded perceptual task was used as a secondary task and tactile discrimination thresholds were recorded. Tactile stimulation was delivered concomitantly at both index fingers either in the movement preparation period (both before and after the selection of the movement effector had taken place), in the motor execution period, or, in a control condition, in the time-window of motor execution, but the movement of the hand was restrained. In the preparation period, tactile thresholds were comparable for the two timings of stimulation delivery; i.e., before and after the selection of the movement effector had taken place. These results therefore suggest that shortly prior to, and during, the execution of goal-directed movements, a combined facilitatory and inhibitory influence acts on tactile perception. ► We investigated if tactile suppression can be cancelled by attentional orienting. ► Tactile stimulation was delivered to either the moving or resting hand. ► Faster tactile RTs for higher probabilities of stimulation: an attentional effect. ► Comparable thresholds before and after selecting the effector: a suppression effect. ► Facilitation and inhibition act on tactile perception during movement.
    Keywords: Tactile Suppression ; Attention ; Motor Preparation ; Endogenous ; Dual-Tasking ; Psychology
    ISSN: 0001-6918
    E-ISSN: 1873-6297
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  • 8
    Language: English
    In: Journal of the American Chemical Society, 08 February 2006, Vol.128(5), pp.1654-63
    Description: The mechanism of the formation of dinuclear platinum(II) mu-hydroxo complexes from cisplatin hydrolysis products, their interconversion, decomposition, and reactions with biomolecules has been explored using a combined DFT/CDM approach. All activation barriers for the formation of [cis-{Pt(NH(3))(2)(X)}-(mu-OH)-cis-{Pt(NH(3))(2)(Y)}](n)()(+) (X, Y = Cl, OH(2), OH) via nucleophilic attack of a hydroxo complex on an aqua complex are lower than the activation barriers for cisplatin hydrolysis. Considering therapeutic Pt(II) concentrations in tumors, however, only the reaction between two molecules of cis-[Pt(NH(3))(2)(OH(2))(OH)](+) (E) yielding [cis-{Pt(NH(3))(2)(OH(2))}-(mu-OH)-cis-{Pt(NH(3))(2)(OH)}](2+) (5) remains kinetically superior to cisplatin hydrolysis. 5 is strongly stabilized by intramolecular hydrogen bonding between the terminal aqua and hydroxo ligands, resulting in an unusually high pK(a) of 5 and a low pK(a) of its conjugate acid. Unimolecular cyclization of 5 yields the dimers [cis-{Pt(NH(3))(2)}(mu-OH)](2)(2+) (7a with antiperiplanar OH groups and 7b with synperiplanar OH groups). The electronic structure of several diplatinum(II) complexes has been analyzed to clarify whether there are metal-metal interactions. The overall reactivity to guanine (Gua) and dimethyl sulfide (Met, representing the thioether functional group of methionine) increases in the order 5 〈 7a approximately 7b 〈 mononuclear complexes, whereas the kinetic selectivity to Gua relative to Met increases in the order 7a approximately 5 〈 7b approximately monocationic mononuclear complexes 〈 dicationic mononuclear complex. The results of this work (i) help assess whether dinuclear metabolites play a role in cisplatin chemotherapy, (ii) elucidate the toxicity and pharmacological inactivity of [cis-{Pt(NH(3))(2)}(mu-OH)](2)(2+), and (iii) suggest future investigations of dinuclear anticancer complexes that contain one mu-hydroxo ligand.
    Keywords: Cisplatin -- Analogs & Derivatives
    ISSN: 0002-7863
    E-ISSN: 15205126
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  • 9
    Language: English
    In: Journal of the American Chemical Society, 04 February 2004, Vol.126(4), pp.996-7
    Description: Thermodynamic electron-transfer potentials from biology textbooks elucidate the sequence of electron-transfer events in the respiratory chain in mitochondria. In this study, thermodynamic and kinetic oxygen-transfer potentials have been defined and predicted for oxidants and substrates using density functional theory, aiming to rationalize multiple oxygen-transfer events in chemical catalysis, particularly in current developments of the Sharpless dihydroxylation. Key transition states for competing mechanisms in a recent dihydroxylation method containing the olefin, osmium tetraoxide, methyltrioxorhenium(VII), a chiral tertiary amine, and the green terminal oxidant hydrogen peroxide have been investigated rigorously. The calculations show the amine to function as an oxygen-transfer mediator between rhenium peroxides and osma-2,5-dioxolanes, in addition to its role as a carrier of chiral information. Unique mechanistic and stereoelectronic patterns in this oxygen-transfer cascade explain the unexpected failure of reactivity predictions using simpler models such as Marcus theory.
    Keywords: Biomimetic Materials -- Chemistry ; Oxygen -- Chemistry
    ISSN: 0002-7863
    E-ISSN: 15205126
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  • 10
    Language: English
    In: Journal of the American Chemical Society, 19 May 2004, Vol.126(19), pp.5999-6004
    Description: The kinetic competition of sulfur and nitrogen nucleophiles L in the substitution reactions of cisplatin derivatives, cis-[Pt(II)(NH(3))(2)(X)(OH(2))](n)(+) + L --〉 cis-[Pt(II)(NH(3))(2)(X)(L)](m)(+) + H(2)O (X = Cl(-), H(2)O), has been studied using density functional theory and continuum dielectric calculations. The calculations reveal an intrinsic kinetic preference of platinum(II) for nitrogen over sulfur ligands. However, biologically relevant substituents can mask this preference for nitrogen nucleophiles. Investigation of the activation free energies of the substitution reactions in dependence of the dielectric constant epsilon demonstrates the microenvironment to be crucial in the binding of cisplatin to its intracellular targets. The fused aromatic heterocycle of guanine stabilizes the transition state for platination at a smaller epsilon more efficiently than do the functional groups of amino acid residues. The results of this work suggest a relatively facile platination of guanine-N7 sites of DNA in regions of low epsilon, particularly in the proximity of histone cores.
    Keywords: Antineoplastic Agents -- Metabolism ; Cisplatin -- Metabolism ; Nitrogen Compounds -- Chemistry ; Sulfur Compounds -- Chemistry
    ISSN: 0002-7863
    E-ISSN: 15205126
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