Soil organic carbon dynamics under perennial energy crops

The European renewable energy directive 2009/28/EC (E.C. 2009) provides a legislative framework for reducing GHG emissions by 20%, while achieving a 20% share of energy from renewable sources by 2020. Perennial energy crops could significantly contribute to limit GHG emissions through replacing equivalent fossil fuels and by sequestering a considerable amount of carbon into the soil through the large amounts of belowground biomass produced. The objective of this study is to evaluate the effects of land use change that perennial energy crops have on croplands (switchgrass) and marginal grasslands (miscanthus). For that purpose above and belowground biomass, SOC variation and Net Ecosystem Exchange were evaluated after five years of growth. At aboveground level both crops produced high biomass under cropland conditions as well as under marginal soils. At belowground level they also produced large amounts of biomass, but no significant influences on SOC in the upper layer (0-30 cm) were found. This is probably because of the "priming effect" that caused fast carbon substitution. In switchgrass only it was found a significant SOC increase in deeper layers (30-60 cm), while in the whole soil profile (0-60 cm) SOC increased from 42 to 51 ha-1. However, the short experimental periods (for both switchgrass and miscanthus), in which land use change was evaluated, do not permit to determine the real capacity of perennial energy crops to accumulate SOC. In conclusion the large amounts of belowground biomass enhanced the SOC dynamic through the priming effect resulting in increased SOC in cropland but not in marginal grassland.

The bright routes to five-membered heterocycles: a photoredox catalytic approach

Synthetic chemists constantly strive to develop new methodologies to access complex molecules more sustainably. The recently developed photocatalytic approach results in a valid and greener alternative to the classical synthetic methods. Here we present three protocols to furnish five-membered rings exploiting photoredox catalysis. We firstly obtained 4,5-dihydrofurans (4,5-DHFs) from readily available olefins and α-haloketones employing fac-Ir(ppy)3 as a photocatalyst under blue-light irradiation (Figure 1, top). This transformation resulted very broad in scope, thanks to its mild conditions and the avoidance of stoichiometric amounts of oxidants or reductants. Moreover, similar conditions could lead to β,γ-unsaturated ketones, or highly substituted tetrahydrofurans (THFs) by carefully differentiating the substitution pattern on the starting materials and properly adjusting the reaction parameters. We then turned our attention to the reactivity of allenamides employing analogous photocatalytic conditions to access 2-aminofurans (Figure 1, bottom). α-Haloketones again provided the radical generated by fac-Ir(ppy)3 under visible-light irradiation, which added to the π-system and furnished the cyclic molecule. The addition of a second molecule of the α-haloketone moiety led to the formation of the final highly functionalized furan, which might be further elaborated to afford more complex products. The two works were both supplied with mechanistic investigations supported by experimental and computational methods. As our last project, we developed a methodology to achieve cypentanonyl-fused N-methylpyrrolidines (Figure 2), exploiting N,N-dimethylamines and carboxylic acids as radical sources. In two separated photocatalytic steps, both functionalities are manipulated through the photoredox catalysis by 4CzIPN to add to an α,β-enone system, furnishing the bicyclic product.