Boosting Effect of Sterically Protected Glucosyl Substituents in Formic Acid Dehydrogenation by Iridium(III) 2-Pyridineamidate Catalysts.

[Cp*Ir(R-pica)Cl] (Cp*=pentamethylcyclopentadienyl anion, pica=2-picolineamidate) complexes bearing carbohydrate substituents on the amide nitrogen atom (R=methyl-ß-D-gluco-pyranosid-2-yl, 1; methyl-3,4,6-tri-O-acetyl-ß-D-glucopyranosid-2-yl, 2) were tested as catalysts for formic acid dehydrogenation in water. TOFMAX values over 12000 h-1 and 50000 h-1 were achieved at 333 K for 1 and 2, respectively, with TON values over 35000 for both catalysts. Comparison with the simpler cyclohexyl-substituted analogue (3) indicated that glucosyl-based complexes are much better performing under the same experimental conditions (TOFMAX=5144 h-1, TON=5000 at pH 2.5 for 3) owing to a lower tendency to isomerize to the less active k2-N,O isomer upon protonation. The 5-fold increase in TOFMAX observed for 2 with respect to 1 is reasonably due to an optimal steric protection by the acetyl substituent, which may prevent unproductive inner-sphere reactivity. These results showcase a powerful strategy for the inhibition of the common deactivation pathways of [Cp*Ir(R-pica)X] catalysts for FA dehydrogenation, paving the way for the development of better performing hydrogen storage systems.

Biosynthesis of silver nanoparticles using actinomycetes, phytotoxicity on rice seeds, and potential application in the biocontrol of phytopathogens.

To find effective silver nanoparticles (AgNPs) for control of phytopathogens, in this study, two strains of actinomycetes isolated from the soil of the Brazilian biome Caatinga (Caat5-35) and from mangrove sediment (Canv1-58) were utilized. The strains were identified by using the 16S rRNA gene sequencing as Streptomyces sp., related to Streptomyces mimosus species. The obtained AgNPs were coded as AgNPs 35 and AgNPs58 and characterized by size and morphology using dynamic light scattering, zeta potential, transmission electron microscopy, and Fourier transformed infrared (FTIR). The antifungal activity of the AgNPs35 and AgNPs58 was evaluated in vitro by the minimal inhibitory concentration (MIC) assay on the phytopathogens, Alternaria solani, Alternaria alternata, and Colletotrichum gloeosporioides. The phytotoxic effect was evaluated by the germination rate and seedling growth of rice (Oryza sativa). AgNPs35 and AgNPs58 showed surface plasmon resonance and average sizes of 30 and 60 nm, respectively. Both AgNPs presented spherical shape and the FTIR analysis confirmed the presence of functional groups such as free amines and hydroxyls of biomolecules bounded to the external layer of the nanoparticles. Both AgNPs inhibited the growth of the three phytopathogens tested, and A. alternate was the most sensible (MIC ≤ 4 µM). Moreover, the AgNPs35 and AgNPs58 did not induce phytotoxic effects on the germination and development of rice seedlings. In conclusion, these AgNPs are promising candidates to biocontrol of these phytopathogens without endangering rice plants.

Effects of mycogenic silver nanoparticles on organisms of different trophic levels.

Biogenic silver nanoparticles (AgNPs) are considered a promising alternative to their synthetic versions. However, the environmental impact of such nanomaterials is still scarcely understood. Thus, the present study aims at assessing the antimicrobial action and ecotoxicity of AgNPs biosynthesized by the fungus Aspergillus niger IBCLP20 towards three freshwater organisms: Chlorella vulgaris, Daphnia similis, and Danio rerio (zebrafish). AgNPs IBCLP20 showed antibacterial action against Klebsiella pneumoniae between 5 and 100 µg mL-1, and antifungal action against Trichophyton mentagrophytes in concentrations ranging from 20 to 100 µg mL-1. The cell density of the microalgae Chlorella vulgaris decreased 40% after 96 h of exposure to AgNPs IBCLP20, at the highest concentration analysed (100 µg L-1). The 48 h median lethal concentration for Daphnia similis was estimated as 4.06 µg L-1 (2.29-6.42 µg L-1). AgNPs IBCLP20 and silver nitrate (AgNO3) caused no acute toxicity on adult zebrafish, although they did induce several physiological changes. Mycosynthetized AgNPs caused a significant increase (p < 0.05) in oxygen consumption at the highest concentration studied (75 µg L-1) and an increase in the excretion of ammonia at the lower concentrations, followed by a reduction at the higher concentrations. Such findings are comparable with AgNO3, which increased the oxygen consumption on low exposure concentrations, followed by a decrease at the high tested concentrations, while impairing the excretion of ammonia in all tested concentrations. The present results show that AgNPs IBCLP20 have biocidal properties. Mycogenic AgNPs induce adverse effects on organisms of different trophic levels and understanding their impact is detrimental to developing countermeasures aimed at preventing any negative environmental effects of such novel materials.

Single-Site Iridium Picolinamide Catalyst Immobilized onto Silica for the Hydrogenation of CO2 and the Dehydrogenation of Formic Acid.

The development of an efficient heterogeneous catalyst for storing H2 into CO2 and releasing it from the produced formic acid, when needed, is a crucial target for overcoming some intrinsic criticalities of green hydrogen exploitation, such as high flammability, low density, and handling. Herein, we report an efficient heterogeneous catalyst for both reactions prepared by immobilizing a molecular iridium organometallic catalyst onto a high-surface mesoporous silica, through a sol-gel methodology. The presence of tailored single-metal catalytic sites, derived by a suitable choice of ligands with desired steric and electronic characteristics, in combination with optimized support features, makes the immobilized catalyst highly active. Furthermore, the information derived from multinuclear DNP-enhanced NMR spectroscopy, elemental analysis, and Ir L3-edge XAS indicates the formation of cationic iridium sites. It is quite remarkable to note that the immobilized catalyst shows essentially the same catalytic activity as its molecular analogue in the hydrogenation of CO2. In the reverse reaction of HCOOH dehydrogenation, it is approximately twice less active but has no induction period.

Biosynthesis of silver nanoparticles using actinomycetes, phytotoxicity on rice seeds, and potential application in the biocontrol of phytopathogens

To find effective silver nanoparticles (AgNPs) for control of phytopathogens, inthis study, two strains of actinomycetes isolated from the soil of the Brazilianbiome Caatinga (Caat5–35) and from mangrove sediment (Canv1–58) wereutilized. The strains were identified by using the 16S rRNA gene sequencing asStreptomycessp., related toStreptomyces mimosusspecies. The obtained AgNPswere coded as AgNPs35and AgNPs58and characterized by size andmorphology using dynamic light scattering, zeta potential, transmissionelectron microscopy, and Fourier transformed infrared (FTIR). The antifungalactivity of the AgNPs35and AgNPs58was evaluatedin vitroby the minimalinhibitory concentration (MIC) assay on the phytopathogens,Alternariasolani,Alternaria alternata, andColletotrichum gloeosporioides. The phytotoxiceffect was evaluated by the germination rate and seedling growth of rice(Oryza sativa). AgNPs35and AgNPs58showed surface plasmon resonance andaverage sizes of 30 and 60 nm, respectively. Both AgNPs presented sphericalshape and the FTIR analysis confirmed the presence of functional groups suchas free amines and hydroxyls of biomolecules bounded to the external layer ofthe nanoparticles. Both AgNPs inhibited the growth of the three phytopatho-gens tested, andA. alternatewas the most sensible (MIC≤4 μM). Moreover,the AgNPs35and AgNPs58did not induce phytotoxic effects on thegermination and development of rice seedlings. In conclusion, these AgNPsare promising candidates to biocontrol of these phytopathogens withoutendangering rice plants.