New challenges for artificial metalloenzymes based on the Biotin-(Strept)avidin technology

Artificial metalloenzymes are designed to gather advantages of both homogeneous catalysts and enzymes. The biotin-(strept)avidin technology insures the incorporation of an active catalyst in a proteinic scaffold which provides a chiral environment. The combination of these two parts provides efficient artificial metalloenzymes applied in various asymmetric reactions such as hydrogenation, transfer hydrogenation, allylic alkylation, etc… In this work, the properties of (strept)avidin were used to explore new challenges for artificial metalloenzymes. Artificial hydrogenases were used as model reaction to demonstrate that artificial metalloenzymes can be more than a concept. With this goal in mind, the loading of the artificial hydogenase was reduced to 0.1% and the concentration of substrate increased to 60 mM with very small erosion of activity and selectivity. The scale of the reaction was increased 15 times without any impact on conversion and ee. Recycling of the artificial hydrogenase was investigated by immobilizing streptavidin using biotin sepharose. The resulting artificial metalloenzymes could be used twice without any loss of activity. Lyophilisation of the artificial hydrogenase allows a convenient storage of the artificial hydrogenase. The versatibilty of the biotin-streptavidin technology was exploited to create and optimize artificial allylic alkylases. The thermostability of streptavidin and its high tolerance towards organic solvents resulted good conversions and ee values up to 97%. The thermostability of streptavidin was further investigated as a potential rapid purification strategy towards screening heat-treated cell-free extracts. With the aim of selective modification of tyrosine-residues, the potential of the artificial allylic alkylases was extended towards the use of phenol as nucleophile. The reaction was optimized to operate under physiological conditions. Detailed investigations of the reaction suggested self-alyllation of the tyrosine residues of the artificial metalloenzyme. Artificial ligases were developed by incorporation of a biotinylated Hoveyda-Grubbs 2nd generation catalyst in (strept)avidin. The optimization of the artificial metalloenzyme gave good conversions for ring closing metathesis of diallyltosylamine under acidic pH and high salt concentration

Analysis of the determinants of fertilizer use decision by farmers in Senegal using a logit model

In Sub Saharan Africa, agriculture plays a central role against hunger and in poverty alleviation. However, it has been noted that agricultural productivity in this area is one of the lowest in the world. One of the reasons of this fact is a decrease of soils fertility due to a lack of nutrients in the soils. To reverse this trend, a solution would be using improved agricultural technologies, like fertilizer. This article aims at determining factors influencing farmers to use fertilizer in Senegal. Data have been collected in five agro ecological zones namely Peanut Basin, Casamance, Niayes, Eastern Senegal and Senegal River Valley. The study sampled 734 household heads for the analysis. For this purpose, a logit model has been estimated through the Maximum Likelihood procedure. Results revealed that household size, gender, relation with extension and research services, farmer organization membership, perception of the cultural practices impact on the land regeneration, connection with Agri-inputs suppliers, cropping cereals and vegetables were statistically significant. The policy implications for a better use of fertilizer are: (i) strengthening extension services capacities in terms of logistics and human resources; (ii) sensitizing farmers to join farmers’ organizations; (iii) strengthening farmers’ capacities in specific themes like good agricultural practices; (iv) putting in place proximity selling points to facilitate fertilizer access to farmers living in isolated areas

Les déterminants de la décision d’utilisation de l’engrais par les producteurs au Sénégal

In Sub Saharan Africa, agriculture plays a central role against hunger and in poverty alleviation. However, it has been noted that agricultural productivity in this area is one of the lowest in the world. One of the reasons of this fact is a decrease of soils fertility due to a lack of nutrients in the soils. To reverse this trend, a solution would be using improved agricultural technologies, like fertilizer. This article aims at determining factors influencing farmers to use fertilizer in Senegal. Data have been collected in five agro ecological zones namely Peanut Basin, Casamance, Niayes, Eastern Senegal and Senegal River Valley. The study sampled 734 household heads for the analysis. For this purpose, a logit model has been estimated through the Maximum Likelihood procedure. Results revealed that household size, gender, relation with extension and research services, farmer organization membership, perception of the cultural practices impact on the land regeneration, connection with Agri-inputs suppliers, cropping cereals and vegetables were statistically significant. The policy implications for a better use of fertilizer are: (i) strengthening extension services capacities in terms of logistics and human resources; (ii) sensitizing farmers to join farmers’ organizations; (iii) strengthening farmers’ capacities in specific themes like good agricultural practices; (iv) putting in place proximity selling points to facilitate fertilizer access to farmers living in isolated areas.En Afrique Sub Saharienne, l’agriculture joue un rôle essentiel dans la lutte contre la faim et dans l’éradication de la pauvreté. Toutefois, dans cette partie du monde, la productivité agricole y est très faible par rapport aux autres régions. Une des raisons avancées constitue la baisse de la fertilité des sols à cause d’un manque de nutriments dans le sol. Pour pallier ce fléau, une solution pourrait être le recours à des technologies agricoles améliorées, notamment les engrais. L’objectif de cet article est d’étudier les déterminants de l’utilisation de l’engrais par les producteurs au Sénégal. Les données ont été collectées dans cinq zones agro écologiques à savoir le Bassin Arachidier, la Casamance, les Niayes, le Sénégal Oriental et la Vallée du fleuve Sénégal. L’étude a impliqué 734 chefs de ménage. A cet effet, un modèle logit a été estimé par la méthode du maximum de vraisemblance. Les résultats ont montré que la taille du ménage, le sexe, la relation avec les services de recherche et de vulgarisation, l’appartenance à une organisation de producteurs, la perception des producteurs de l’impact des pratiques culturales sur la régénération des terres, la connaissance d’un réseau de fournisseurs d’intrants agricoles et la culture de céréales et de légumes se sont révélés statistiquement significatifs. Ainsi, les recommandations formulées sont les suivantes : (i) renforcer les capacités des services de vulgarisation en termes de logistique et ressources humaines ; (ii) inciter les producteurs à être membres d’organisations de producteurs ; (iii) renforcer les capacités des producteurs sur des thématiques spécifiques telles que les bonnes pratiques culturales ; (iv) mettre en place des points de vente de proximité pour faciliter l’accès de l’engrais aux producteurs vivant dans des zones éloignées