Bioinspired membrane design, synthesis, and characterization to control microstructure and enable efficient molecular separations

Natural resources are limited, and the failure to capture, store, and re-supply such resources can cause global economic, political, and humanitarian crises such as water scarcity. To mitigate these global risks, membrane separations have been an attractive technology due to their energy efficient and environment-friendly nature compared to other separation technologies such as distillation or chromatography. However, the development of new membranes with good separation properties and processability have been an ongoing challenge. One example is biomimetic membranes. Due to the unexpectedly fast transport and selective separation performances observed in nature, biological membrane components have been attempted for integration into scalable membranes. But maintaining the coherence of their nanoscale transport property at practice-relevant scales have been critically challenging. Bioinspired synthetic membranes have emerged as a good alternative to help resolve these roadblocks faced by biomimetic membranes. Molecular designs of synthetic membranes components enable precise control of microstructures and improve the nanoscale homogeneity of the membranes, both of which are critical for improving membrane separation properties, while increasing reproducibility, cost-efficiency, and processability of the membranes. This dissertation research aims to provide scientific details needed for the developments of bioinspired membranes, spanning the broad considerations from nano- to macroscopic perspectives. First, a new type of artificial water channels (AWCs) is presented as a transport element of bioinspired membranes. A new water permeation mechanism, water-wire networks formed by these AWCs, was shown to achieve fast and selective water transport that exceeds current polymer membranes’ permeability-selectivity limit. Next, a strategy of integrating such bioinspired membrane components, AWCs and amphiphilic block copolymers as transport and barrier elements respectively, into scalable membranes are studied. A series of analyses on transport experiments and computer simulations indicated a strong coherence between nanoscale and membrane scale transport properties, demonstrating successful channel integration for molecular separations. Lastly, further insights on transforming the AWC structures to viable membranes for large-scale applications are presented, specifically targeting gas separations. Leveraging these studies, this dissertation intends to provide guidance to researchers on development of new bioinspired membranes.Chemical Engineerin

Les déterminants des performances scolaires des élèves marocains

Le Maroc fait partie des pays en développement dont le niveau des acquis des élèves reste relativement faible. En dépit des efforts engagés en vue d’améliorer en partie la qualité des apprentissages, les résultats des enquêtes internationales et nationales révèlent de faibles niveaux des acquis. Dès lors, l’objectif de cet article est de revenir sur les facteurs qui influencent les performances scolaires des élèves. Nous nous intéressons plus spécifiquement aux déterminants microéconomiques de la qualité de l’éducation à travers les performances des élèves. Les études sur les déterminants des performances scolaires sont riches d’enseignement. Les premières contributions se sont focalisées sur le rôle de l’environnement familial dans l’explication de la réussite des élèves (Coleman, 1966, par exemple). D’autres, plus récemment, ont abordé les facteurs liés à l’établissement scolaire. Pour autant, les contributions récentes mettent en avant l’importance à la fois de l’environnement familial et de l’école (Hanushek, 2003). Des travaux plus récents oulignent également l’influence des pairs sur les performances scolaires. Le présent travail s’inscrit dans cette logique. Son originalité se situe à un double niveau. La première réside dans la mise en évidence de l’ensemble des facteurs explicatifs des performances des élèves et des inégalités scolaires. Malgré l’existence d’une littérature abondante sur le sujet, cette question n’a pas été abordée, à notre connaissance, dans le cas marocain. La seconde cherche à corriger les problèmes d’endogénéité dans les modèles multiniveaux. Enfin, La technique d’imputation adoptée permet de traiter de façon pertinente les valeurs manquantes dans les bases de données. Cet article est structuré en trois parties. La première aborde la littérature empirique sur les déterminants de la réussite scolaire des élèves. La deuxième partie examine le modèle utilisé et décrit la base de données du Programme national d’évaluation des acquis (PNEA). Elle examine l’approche et la méthodologie utilisée. Enfin, la troisième partie traite des résultats obtenus et nous permet de formuler les principaux enseignements pouvant être tirés de nos résultats en matière de politiques publiques

Enzyme engineering of bovine trypsin

Bovine trypsin is a biocatalyst widely used to cleave recombinant proteins during the downstream processing of therapeutic proteins, and is used particularly for insulin bioprocessing. Evolution has produced a wealth of natural biocatalysts over billions of years, which are generally not optimised for specific industrial applications. Bovine trypsin has a relatively broad specificity towards cleavage at the C-terminal end of arginine or lysine residues. Consequently it has a tendency to cleave alternative sites in the insulin process leading to loss of yield and more complex downstream processing. This project describes efforts to alter the primary specificity of bovine trypsin. Trypsin variants were generated using two traditional random mutagenesis methods tailored to improve the chance of producing a useful mutant. These were focussed error prone PCR (fepPCR) and multiple-site saturation mutagenesis (MSSM). In order to select residues useful for MSSM, a study of the correlation between (1) mutations enhancing specificity or activity and (2) sequence entropy and distance of mutations from the active site was carried out based on past examples of directed and rational evolution. This analysis along with biochemical information for trypsin aided the selection of two specificity "hotspots" for random mutagenesis, each comprising four residues. These hotspots were regions in the trypsin gene close to or directly involved in substrate binding. Depending on the mutagenesis method used, the size of the mutant libraries differed considerably. For example, fepPCR of a 522 bp region of the trypsin gene required approximately 3,000 mutants to encompass all possibilities whereas the library size for MSSM was 160,000 for each of the selected four-residue regions. Two alternative library screening approaches, with different throughput capabilities, were tested to isolate mutants of interest. Automated colony screening was considered suitable for the smaller fepPCR library and consisted of the following steps: (1) transformation of a plasmid library into E. coli BL21-Gold(DE3) cells (2) fermentation of individual colonies in 384 square-well microplates (3) lysis of the cultures and (4) spectrophotometric activity measurement on a variety of substrates. The best mutant had a 2.54-fold improvement in arginine specificity. For the larger MSSM libraries, a nutritional selection method was developed using E. coli arg-auxotrophic strains. An alternative approach to generating trypsin variants was also explored based on the known ability of bovine trypsin to autolyse into "pseudo-trypsins". Since these pseudo-trypsins are variants of the native form of the enzyme, it was anticipated that they would have specificities different to that of the native enzyme. Efforts were made to separate the variants via novel chromatographic techniques and to characterise them with respect to molecular weight and specificity. Finally, the activity profile of bovine trypsin was comprehensively carried out on a range of novel substrates, and a comparison made between commercially available bovine trypsin and Eli Lilly's recombinant trypsin. Similar reaction profiles were returned by both enzymes on all substrates with the previously unreported finding that there was a preference for cleavage at the C-terminal end of two positively charged basic residues (i.e. KR or RR rather than GR)

Modelling human choices: MADeM and decision‑making

Research supported by FAPESP 2015/50122-0 and DFG-GRTK 1740/2. RP and AR are also part of the Research, Innovation and Dissemination Center for Neuromathematics FAPESP grant (2013/07699-0). RP is supported by a FAPESP scholarship (2013/25667-8). ACR is partially supported by a CNPq fellowship (grant 306251/2014-0)

25th annual computational neuroscience meeting: CNS-2016

The same neuron may play different functional roles in the neural circuits to which it belongs. For example, neurons in the Tritonia pedal ganglia may participate in variable phases of the swim motor rhythms [1]. While such neuronal functional variability is likely to play a major role the delivery of the functionality of neural systems, it is difficult to study it in most nervous systems. We work on the pyloric rhythm network of the crustacean stomatogastric ganglion (STG) [2]. Typically network models of the STG treat neurons of the same functional type as a single model neuron (e.g. PD neurons), assuming the same conductance parameters for these neurons and implying their synchronous firing [3, 4]. However, simultaneous recording of PD neurons shows differences between the timings of spikes of these neurons. This may indicate functional variability of these neurons. Here we modelled separately the two PD neurons of the STG in a multi-neuron model of the pyloric network. Our neuron models comply with known correlations between conductance parameters of ionic currents. Our results reproduce the experimental finding of increasing spike time distance between spikes originating from the two model PD neurons during their synchronised burst phase. The PD neuron with the larger calcium conductance generates its spikes before the other PD neuron. Larger potassium conductance values in the follower neuron imply longer delays between spikes, see Fig. 17.Neuromodulators change the conductance parameters of neurons and maintain the ratios of these parameters [5]. Our results show that such changes may shift the individual contribution of two PD neurons to the PD-phase of the pyloric rhythm altering their functionality within this rhythm. Our work paves the way towards an accessible experimental and computational framework for the analysis of the mechanisms and impact of functional variability of neurons within the neural circuits to which they belong

Unique selectivity trends of highly permeable PAP[5] water channel membranes

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Beyond Aquaporins: Recent Developments in Artificial Water Channels

A molecular scale understanding of the fast and selective water transport in biological water channels, aquaporins (AQPs), has inspired attempts to mimic its performance in synthetic structures. These synthetic structures, referred to as artificial water channels (AWCs), present several advantages over AQPs in applications. After over a decade of efforts, the unique transport properties of AQPs have been reproduced in AWCs. Further, recent developments have shown that the performance of benchmark AQP channels can be exceeded by new AWC designs using novel features not seen in biology. In this Perspective, we provide a brief overview of recent AWC developments, and share our perspective on forward-looking AWC research.11Nsciescopu

Artificial water channels: toward and beyond desalination

Artificial water channels (AWCs) are synthetic mimics of biological water channel proteins, aquaporins. They combine the characteristic features of aquaporins, including a transmembrane orientation in biomimetic membrane matrices and the possibility of combining high water permeability with high water/solute selectivity, with higher processability and stability compared to protein channels. AWCs have thus emerged as a platform for biomimetic membrane development. During the last few years, remarkable progress has been made in AWC synthesis and characterization but bridging these advances to practical membrane development still remains a significant challenge. In this article, we review some recent concepts regarding permeability in water channels and its relevance to AWCs, common misconceptions and need for better clarity in permeability and selectivity characterization of AWCs, and prospective applications of channel-based membranes beyond desalination. © 201911Nsciescopu

Water-wire networks: new avenue for engineering polymer membranes using bioinspired artificial water channels

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