Enzyme immobilization inside the porous wood structure: a natural scaffold for continuous-flow biocatalysis

Enzymes are often immobilized on solid supports to enable their recovery from reaction solutions, facilitate their reuse and hence increase cost-effectiveness in their application. Immobilized enzymes may even be used for flow-through applications in continuous processes. However, the synthesis of traditional immobilization scaffolds and immobilization techniques lack sustainability as they are often based on fuel-based materials and tedious synthesis- and immobilization approaches. Here, we present the natural material wood as a green alternative for enzyme immobilization. Its natural structure provides a mechanically stable porous scaffold with a high inner surface area that allows for directional flow-through of liquids. Enzymes were immobilized by nanoparticle-mediated adsorption, a simple, versatile and completely water-based process. The resulting wood–enzyme hybrids were intensely investigated for the model enzyme laccase. Reaction kinetics, as well as catalytic activities at various pH-values, temperatures, and ionic strengths were determined. The wood–enzyme hybrids could quickly and completely be removed from the reaction solution. Hence, they allow for multifold reusability. We show a series of 25 consecutive reaction cycles with a remaining activity in the last cycle of 90% of the maximal activity. Moreover, the anisotropic porosity of wood enabled the application of the hybrid material as a biocatalytic flow-through reactor. Flow-rate dependent productivity of a single-enzyme reaction was determined. Moreover, we show a two-step reaction cascade in continuous flow by the immobilization of the enzymes glucose oxidase and horseradish peroxidase. Therefore, the natural material wood proved to be a promising material for application in continuous-flow biocatalysis.

Green biocatalytic systems for continuous-flow cascade reactions are realized by enzyme immobilization inside the porous wood structure.     

Human hippocampal increases in low-frequency power during associative prediction violations

Environmental cues often trigger memories of past events (associative retrieval), and these memories are a form of prediction about imminent experience. Learning is driven by the detection of prediction violations, when the past and present diverge. Using intracranial electroencephalography (iEEG), we show that associative prediction violations elicit increased low-frequency power (in the slow-theta range) in human hippocampus, that this low-frequency power increase is modulated by whether conditions allow predictions to be generated, that the increase rapidly onsets after the moment of violation, and that changes in low-frequency power are not present in adjacent perirhinal cortex. These data suggest that associative mismatch is computed within hippocampus when cues trigger predictions that are violated by imminent experience.     

Brief Report: CANTAB Performance and Brain Structure in Pediatric Patients with Asperger Syndrome

By merging neuropsychological (CANTAB/Cambridge Neuropsychological Test Automated Battery) and structural brain imaging data (voxel-based-morphometry) the present study sought to identify the neurocognitive correlates of executive functions in individuals with Asperger syndrome (AS) compared to healthy controls. Results disclosed subtle group differences regarding response speed on only one CANTAB subtest that is thought to tap fronto-executive network functions (SWM/spatial working memory). Across all participants, SWM performance was significantly associated with two brain regions (precentral gyrus white matter, precuneus grey matter), thus suggesting a close link between fronto-executive functions (SWM) and circumscribed fronto-parietal brain structures. Finally, symptom severity (ADOS total score) was best predicted by response speed on a set-shifting task (IES) thought to tap fronto-striatal functions (corrected R² 56 %).