Photocurrents from photosystem II in a metal oxide hybrid system: electron transfer pathways

We have investigated the nature of the photocurrent generated by Photosystem II (PSII), the water oxidizing enzyme, isolated from Thermosynechococcus elongatus, when immobilized on nanostructured titanium dioxide on an indium tin oxide electrode (TiO2/ITO). We investigated the properties of the photocurrent from PSII when immobilized as a monolayer versus multilayers, in the presence and absence of an inhibitor that binds to the site of the exchangeable quinone (QB) and in the presence and absence of exogenous mobile electron carriers (mediators). The findings indicate that electron transfer occurs from the first quinone (QA) directly to the electrode surface but that the electron transfer through the nanostructured metal oxide is the rate-limiting step. Redox mediators enhance the photocurrent by taking electrons from the nanostructured semiconductor surface to the ITO electrode surface not from PSII. This is demonstrated by photocurrent enhancement using a mediator incapable of accepting electrons from PSII. This model for electron transfer also explains anomalies reported in the literature using similar and related systems. The slow rate of the electron transfer step in the TiO2 is due to the energy level of electron injection into the semiconducting material being below the conduction band. This limits the usefulness of the present hybrid electrode. Strategies to overcome this kinetic limitation are discussed

‘A storm of post-it notes’: Experiences of perceptual capacity in autism and ADHD

Lab-based tasks suggest autistic people have increased perceptual capacity (i.e. process more information at any one time) compared to non-autistic people. Here, we explored whether this increase is reflected in autistic people's day-to-day perceptual experiences and, when compared to those with ADHD/neurotypical people, whether commonalities/divergences in these experiences can illuminate differences between neurotypes. UK-based adults (108 autistic, 40 with ADHD, 79 autistic with ADHD, 85 neurotypical) completed an online survey about experiences of attention and distraction. Responses were analysed using thematic analysis. We found that participants of all neurotypes experienced periods of intense focus. Neurodivergent participants reported experiencing a barrage of information; autistic participants found this overwhelming, whereas those with ADHD referred to overload. This finding may reflect increased perceptual capacity for autistic people (adding ecological validity to previous findings regarding increased autistic perceptual capacity) vs. difficulties maintaining attentional priorities for those with ADHD. While differences between neurodivergent and neurotypical people were evident, discrepancies between experiences of neurodivergent groups were more subtle, suggesting that increased perceptual capacity may extend beyond autism. Consequently, perceptual capacity offers a useful framework to promote better understanding of one's own perceptual experiences, and to guide strategies to ameliorate any challenges encountered

‘A storm of post-it notes’:experiences of perceptual capacity in autism and ADHD

Lab-based tasks suggest autistic people have increased perceptual capacity (i.e., process more information at any one time) compared to non-autistic people. Here, we explored whether this increase is reflected in autistic people’s day-to-day perceptual experiences and, when compared to those with ADHD/neurotypical people, whether commonalities/divergences in these experiences can illuminate differences between neurotypes. UK-based adults (108 autistic, 40 with ADHD, 79 autistic with ADHD, 85 neurotypical) completed an online survey about experiences of attention and distraction. Responses were analysed using thematic analysis. We found that participants of all neurotypes experienced periods of intense focus. Neurodivergent participants reported experiencing a barrage of information; autistic participants found this overwhelming, whereas those with ADHD referred to overload. This finding may reflect increased perceptual capacity for autistic people (adding ecological validity to previous findings regarding increased autistic perceptual capacity) vs. difficulties maintaining attentional priorities for those with ADHD. While differences between neurodivergent and neurotypical people were evident, discrepancies between experiences of neurodivergent groups were more subtle, suggesting that increased perceptual capacity may extend beyond autism. Consequently, perceptual capacity offers a useful framework to promote better understanding of one’s own perceptual experiences, and to guide strategies to ameliorate any challenges encountered

Wiring of Photosystem II to Hydrogenase for Photoelectrochemical Water Splitting.

In natural photosynthesis, light is used for the production of chemical energy carriers to fuel biological activity. The re-engineering of natural photosynthetic pathways can provide inspiration for sustainable fuel production and insights for understanding the process itself. Here, we employ a semiartificial approach to study photobiological water splitting via a pathway unavailable to nature: the direct coupling of the water oxidation enzyme, photosystem II, to the H2 evolving enzyme, hydrogenase. Essential to this approach is the integration of the isolated enzymes into the artificial circuit of a photoelectrochemical cell. We therefore developed a tailor-made hierarchically structured indium-tin oxide electrode that gives rise to the excellent integration of both photosystem II and hydrogenase for performing the anodic and cathodic half-reactions, respectively. When connected together with the aid of an applied bias, the semiartificial cell demonstrated quantitative electron flow from photosystem II to the hydrogenase with the production of H2 and O2 being in the expected two-to-one ratio and a light-to-hydrogen conversion efficiency of 5.4% under low-intensity red-light irradiation. We thereby demonstrate efficient light-driven water splitting using a pathway inaccessible to biology and report on a widely applicable in vitro platform for the controlled coupling of enzymatic redox processes to meaningfully study photocatalytic reactions.This work was supported by the U.K. Engineering and Physical Sciences Research Council (EP/H00338X/2 to E.R. and EP/G037221/1, nanoDTC, to D.M.), the UK Biology and Biotechnological Sciences Research Council (BB/K002627/1 to A.W.R. and BB/K010220/1 to E.R.), a Marie Curie Intra-European Fellowship (PIEF-GA-2013-625034 to C.Y.L), a Marie Curie International Incoming Fellowship (PIIF-GA-2012-328085 RPSII to J.J.Z) and the CEA and the CNRS (to J.C.F.C.). A.W.R. holds a Wolfson Merit Award from the Royal Society.This is the final version of the article. It first appeared from ACS Publications via http://dx.doi.org/10.1021/jacs.5b0373