Oxygen reduction reaction (ORR) in alkaline solution catalysed by an atomically precise catalyst based on a Pd(II) complex supported on multi-walled carbon nanotubes (MWCNTs). Electrochemical and structural considerations.

A new atomically precise, single-ion catalyst (MWCNT-LPd) for ORR (oxygen reduction reaction), consisting of a Pd(II) complex of a tetraazacycloalkane anchored on multiwalled carbon nanotubes, has been prepared through a supramolecular approach ensuring a uniform distribution of catalytic centres on the support surface. A tetraazacycloalkane was chosen to saturate the four coordination sites of the typical square planar coordination geometry of Pd(II) with the aim of ascertaining whether the metal ion must have free coordination sites to function effectively in the ORR or whether, as predicted by quantum mechanical calculations, the catalytic effect can be originated from an interaction of O2 in the fifth coordinative position. The results clearly demonstrated that tetracoordination of Pd(II) does not influence its catalytic capacity in the ORR. Electrodes based on this catalyst show ORR performance very close to that of commercial Pt electrodes, despite the low Pd(II) content (1.72% by weight) in the catalyst. The onset potential (Eon) value and the half-wave potential (E1/2) of the catalyst are, respectively, only 53 mV and 24 mV less positive than those observed for the Pt electrode and direct conversion of O2 to H2O reaches 85.0%, compared to 89% of the Pt electrode. Furthermore, a preliminary galvanostatic test (simulating a working fuel cell at a fixed potential) showed that the catalyst maintains its efficiency continuing to produce water throughout the process (the average number of electrons exchanged over time per O2 molecule remains close to 4).

Control over attentional capture within 170 ms by long-term memory control settings: Evidence from the N2pc.

Observers adopt attentional control settings (ACSs) based on their goals that guide the capture of attention: Searched-for stimuli capture attention, and stimuli that are not searched for do not. While previous behavioural research indicates that observers can adopt long-term memory (LTM) ACSs (Giammarco et al. Visual Cognition, 24, 78-101, 2016), it seems surprising that representations in LTM could guide attention quickly enough to control attentional capture. To assess the claim that LTM ACSs exert control over early attentional orienting, we recorded electroencephalography while participants studied and searched for 30 target objects in an attention cueing task. Participants reported the studied target and ignored the preceding cues. To control for perceptual evoked responses, on each trial we presented two cue objects (one studied and one nonstudied). Even though participants were instructed to ignore the cues, studied cues produced the N2pc event-related potential, indicating early attentional orienting that was preferentially directed towards the studied cue versus the nonstudied cue. Critically, the N2pc was detectable within 170 ms, confirming that LTM ACSs rapidly control early capture. We propose an update to contemporary models of attentional capture to account for rapid attentional guidance by LTM ACSs.

Pyrene-Containing Polyamines as Fluorescent Receptors for Recognition of PFOA in Aqueous Media.

The globally widespread perfluorooctanoic acid (PFOA) is a concerning environmental contaminant, with a possible toxic long-term effects on the environment and human health The development of sensible, rapid, and low-cost detection systems is a current change in modern environmental chemistry. In this context, two triamine-based chemosensors, L1 and L2, containing a fluorescent pyrene unit, and their Zn(II) complexes are proposed as fluorescent probes for the detection of PFOA in aqueous media. Binding studies carried out by means of fluorescence and NMR titrations highlight that protonated forms of the receptors can interact with the carboxylate group of PFOA, thanks to salt bridge formation with the ammonium groups of the aliphatic chain. This interaction induces a decrease in the fluorescence emission of pyrene at neutral and slightly acidic pH values. Similarly, emission quenching has also been observed upon coordination of PFOA by the Zn(II) complexes of the receptors. These results evidence that simple polyamine-based molecular receptors can be employed for the optical recognition of harmful pollutant molecules, such as PFOA, in aqueous media.

Evaluation of coumarin-tagged deferoxamine as a Zr(IV)-based PET/fluorescence dual imaging probe.

Desferoxamine (DFO) is currently the golden standard chelator for 89Zr4+, a promising nuclide for positron emission tomography imaging (PET). The natural siderophore DFO had previously been conjugated with fluorophores to obtain Fe(III) sensing molecules. In this study, a fluorescent coumarin derivative of DFO (DFOC) has been prepared and characterized (potentiometry, UV-Vis spectroscopy) for what concerns its protonation and metal coordination properties towards PET-relevant ions (Cu(II), Zr(IV)), evidencing strong similarity with pristine DFO. Retention of DFOC fluorescence emission upon metal binding has been checked (fluorescence spectrophotometry), as it would - and does - allow for optical (fluorescent) imaging, thus unlocking bimodal (PET/fluorescence) imaging for 89Zr(IV) tracers. Crystal violet and MTT assays on NIH-3 T3 fibroblasts and MDA-MB 231 mammary adenocarcinoma cell lines demonstrated, respectively, no cytotoxicity nor metabolic impairment at usual radiodiagnostic concentrations of ZrDFOC. Clonogenic colony-forming assay performed on X-irradiated MDA-MB 231 cells showed no interference of ZrDFOC with radiosensitivity. Morphological biodistribution (confocal fluorescence, transmission electron microscopy) assays on the same cells suggested internalization of the complex through endocytosis. Overall, these results support fluorophore-tagged DFO as a suitable option to achieve dual imaging (PET/fluorescence) probes based on 89Zr.

Polyamine receptors containing anthracene as fluorescent probes for ketoprofen in H2O/EtOH solution.

Triamine receptors containing anthracene units are able to bind and sense ketoprofen via fluorescence enhancement in a H2O/EtOH 50 : 50 (Vol : Vol) mixture exploiting their protonation features, which are tuned by the interaction with the analyte.

Glyphosate sensing in aqueous solutions by fluorescent zinc(II) complexes of [9]aneN3-based receptors.

Herein we describe the binding abilities of Zn(II) complexes of [12]aneN4- (L1) and [9]aneN3-based receptors (L2, L3) towards the herbicides N-(phosphonomethyl)glycine (glyphosate, H3PMG) and 2-amino-4-[hydroxy(methyl)phosphoryl]butanoic acid (glufosinate, H2GLU), and also aminomethylphosphonic acid (H2AMPA), the main metabolite of H3PMG, and phosphate. All ligands form stable Zn(II) complexes, whose coordination geometries allow a possible interaction of the metal center with exogenous anionic substrates. Potentiometric studies evidenced the marked coordination ability of the L2/Zn(II) system for the analytes considered, with a preferential binding affinity for H3PMG over the other substrates, in a wide range of pH values. 1H and 31P NMR experiments supported the effective coordination of such substrates by the Zn(II) complex of L2, while fluorescence titrations and a test strip experiment were performed to evaluate whether the H3PMG recognition processes could be detected by fluorescence signaling.

Exploring the Ability of Luminescent Metal Assemblies to Bind and Sense Anionic or Ionizable Analytes A Ru(phen)2bipy-Based Dizinc Complex for Bisphenol A (BPA) Recognition.

The synthesis of a new RuII complex, in which the metal is coordinated by two 1,10-phenanthroline ligands and a 2,2'-bipyridyl unit linked, via methylene bridges in its 4 and 4' positions, to two 1,4,7,10-tetraazacyclododecane (cyclen) macrocycles ([Ru(phen)2 L]2+) is reported. Protonation and ZnII binding by [Ru(phen)2 L]2+ have been analyzed by potentiometric titration, evidencing the formation of mixed hetero-binuclear and hetero-trinuclear ZnII/RuII complexes. These complexes were tested as bis-phenol A (BPA) binders. Only the dizinc complex with [Ru(phen)2 L]2+ is able to bind BPA in aqueous solution, affording a remarkably stable {Zn2[Ru(phen)2 L]BPA(H-2)}4+ adduct at neutral pH, in which BPA is bound in its doubly deprotonated form to the two ZnII ions. BPA binding was found to quench the luminescence emission of the RuII(phen)2bipy core. Although the quenching effect is modest, this study demonstrates that appropriately designed dizinc complexes can be used for binding and optical sensing of BPA in water.

Getting it right from the start: Attentional control settings without a history of target selection.

Observers can adopt attentional control settings that regulate how their attention is drawn to salient stimuli in the environment. Do observers choose their attentional control settings voluntarily, or are they primed in a bottom-up manner based on the stimuli that the observer has recently attended and responded to (i.e., target-selection history)? In the present experiment, we tested these two accounts using a long-term memory attentional control settings paradigm, in which participants memorized images of 18 common visual objects, and then searched for those objects in a spatial blink task. Unbeknownst to participants, we manipulated priming by dividing the set of target objects into two subsets: nine objects appeared frequently as targets in the spatial blink task (frequently primed objects), and nine infrequently (infrequently primed objects). We assessed attentional capture by presenting these objects as distractors in the spatial blink task and measuring their effect on task accuracy. We found that both subsets of objects captured attention more than non-studied objects, and frequently primed objects did not capture attention more than infrequently primed objects. Moreover, a follow-up analysis revealed that all studied objects captured attention, even before those objects had appeared as targets in the spatial blink task. These findings suggest that priming through target-selection history plays little-to-no role in long-term memory attentional control settings. Rather, these findings align with a growing body of evidence that attentional control settings are primarily implemented through voluntary control.

No role for activated long-term memory in attentional control settings.

Visual spatial attentional capture is contingent on an observer's goals, or attentional control settings. Recent research has demonstrated that observers can adopt attentional control settings based on numerous visual objects represented in episodic long-term memory (LTM). But why do LTM representations that comprise an attentional control set bias attentional capture, when other LTM representations do not? In the present study, we tested the activated LTM account-that LTM representations form an attentional control set if, and only if, they are represented in activated LTM-by mixing a working memory task to test for representation in activated LTM, with a spatial blink task to test for the state of participants' attentional control settings. In Experiments 1 and 2, inducing participants to represent complex visual objects in activated LTM did not result in those objects forming an attentional control set. In Experiment 3, we found a dissociation between activated LTM and attentional control settings; objects that were represented in activated LTM produced greater intrusion effects (indicating representation in activated LTM) than objects that were part of an attentional control set, yet smaller capture effects. These results do not support the activated LTM account. We conclude that representation in activated LTM is not the factor that determines which LTM representations comprise an attentional control set, and discuss the implications of these findings for research on attentional templates and hybrid visual and memory search. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Dual-task backward compatibility effects are episodically mediated.

In dual-task performance, the backward compatibility effect (BCE; faster Task 1 reaction time when Task 1 and Task 2 responses are compatible) is thought to represent automatic activation of Task 2 response information in parallel with attended Task 1 performance. Work by Hommel and Eglau (Psychological Research, 66, 260-273, 2002) has suggested the BCE relies on stimulus-response learning in long-term memory. Subsequent work by Ellenbogen and Meiran (Memory and Cognition, 36, 968-978, 2008), however, proposed that the BCE is mediated by Task 2 rules held in working memory (WM) during Task 1 performance. The present study aimed to dissociate these two theoretical claims. In Experiment 1, we assessed the effects of prior single-task practice with Task 1 or Task 2 of a subsequent dual-task paradigm. Where the WM-mediated model predicts both BCE and overall reaction time improvement relative to prior task practice, an episodic learning model makes divergent predictions for BCE based on the context specificity of prior Task 2 learning. Results showed a close fit with episodic predictions and contradicted WM model predictions. Experiment 2 examined the finer grained timecourse of BCE over initial development, subsequent interference of this initial learning on BCE development with new conflicting Task 2 response mappings, and finally reestablishment of BCE in the original dual task. Data again showed close agreement with long-term learning predictions. We argue in favor of an episodic account of the BCE, and consider implications of WM and episodic mechanisms of automatic response activation on other aspects of dual-task performance.

Context-specific control and the Stroop negative priming effect.

The present study highlights the utility of context-specific learning for different probe types in accounting for the commonly observed dependence of negative priming on probe selection. Using a Stroop priming procedure, Experiments 1a and 1b offered a demonstration that Stroop priming effects can differ qualitatively for selection and no-selection probes when probe selection is manipulated between subjects, but not when it is manipulated randomly from trial to trial within subject (see also Moore, 1994). In Experiments 2 and 3, selection and no-selection probes served as two contexts that varied randomly from trial to trial, but for which proportion repeated was manipulated separately. A context-specific proportion repeated effect was observed in Experiment 2, characterized by modest quantitative shifts in the repetition effects as a function of the context-specific proportion repeated manipulation. However, with a longer intertrial interval in Experiment 3, a context-specific proportion repeated manipulation that focused on the no-selection probes changed the repetition effect qualitatively, from negative priming when the proportion repeated was .25 to positive priming when the proportion repeated was .75. The results are discussed with reference to the role of rapid, context-specific learning processes in the integration of prior experiences with current perception and action.