Reducing Biomass Recalcitrance by Heterologous Expression of a Bacterial Peroxidase in Tobacco (\u3cem\u3eNicotiana benthamiana\u3c/em\u3e)

Commercial scale production of biofuels from lignocellulosic feed stocks has been hampered by the resistance of plant cell walls to enzymatic conversion, primarily owing to lignin. This study investigated whether DypB, the lignin-degrading peroxidase from Rodococcus jostii, depolymerizes lignin and reduces recalcitrance in transgenic tobacco (Nicotiana benthamiana). The protein was targeted to the cytosol or the ER using ER-targeting and retention signal peptides. For each construct, five independent transgenic lines were characterized phenotypically and genotypically. Our findings reveal that expression of DypB in the cytosol and ER does not affect plant development. ER-targeting increased protein accumulation, and extracts from transgenic leaves showed higher activity on classic peroxidase substrates than the control. Intriguingly, in situ DypB activation and subsequent saccharification released nearly 200% more fermentable sugars from transgenic lines than controls, which were not explained by variation in initial structural and non-structural carbohydrates and lignin content. Pyrolysis-GC-MS analysis showed more reduction in the level of lignin associated pyrolysates in the transgenic lines than the control primarily when the enzyme is activated prior to pyrolysis, consistent with increased lignin degradation and improved saccharification. The findings reveal for the first time that accumulation and in situ activation of a peroxidase improves biomass digestibility

Rational Design of a Second Generation Catalyst for Preparation of Allylsilanes Using the Silyl-Heck Reaction

Using rational ligand design, we have developed of a second-generation ligand, bis­(3,5-di-<i>tert</i>-butylphenyl)­(<i>tert</i>-butyl)­phosphine, for the preparation of allylsilanes using the palladium-catalyzed silyl-Heck reaction. This new ligand provides nearly complete suppression of starting material alkene isomerization that was observed with our first-generation catalyst, providing vastly improved yields of allylsilanes from simple alkene starting materials. The studies quantifying the electronic and steric properties of the new ligand are described. Finally, we report an X-ray crystal structure of a palladium complex resulting from the oxidative addition of Me₃SiI using an analogous ligand that provides significant insight into the nature of the catalytic system

Rational Design of a Second Generation Catalyst for Preparation of Allylsilanes Using the Silyl-Heck Reaction

Using rational ligand design, we have developed of a second-generation ligand, bis­(3,5-di-<i>tert</i>-butylphenyl)­(<i>tert</i>-butyl)­phosphine, for the preparation of allylsilanes using the palladium-catalyzed silyl-Heck reaction. This new ligand provides nearly complete suppression of starting material alkene isomerization that was observed with our first-generation catalyst, providing vastly improved yields of allylsilanes from simple alkene starting materials. The studies quantifying the electronic and steric properties of the new ligand are described. Finally, we report an X-ray crystal structure of a palladium complex resulting from the oxidative addition of Me₃SiI using an analogous ligand that provides significant insight into the nature of the catalytic system

Rational Design of a Second Generation Catalyst for Preparation of Allylsilanes Using the Silyl-Heck Reaction

Using rational ligand design, we have developed of a second-generation ligand, bis­(3,5-di-<i>tert</i>-butylphenyl)­(<i>tert</i>-butyl)­phosphine, for the preparation of allylsilanes using the palladium-catalyzed silyl-Heck reaction. This new ligand provides nearly complete suppression of starting material alkene isomerization that was observed with our first-generation catalyst, providing vastly improved yields of allylsilanes from simple alkene starting materials. The studies quantifying the electronic and steric properties of the new ligand are described. Finally, we report an X-ray crystal structure of a palladium complex resulting from the oxidative addition of Me₃SiI using an analogous ligand that provides significant insight into the nature of the catalytic system

Rational Design of a Second Generation Catalyst for Preparation of Allylsilanes Using the Silyl-Heck Reaction

Using rational ligand design, we have developed of a second-generation ligand, bis­(3,5-di-<i>tert</i>-butylphenyl)­(<i>tert</i>-butyl)­phosphine, for the preparation of allylsilanes using the palladium-catalyzed silyl-Heck reaction. This new ligand provides nearly complete suppression of starting material alkene isomerization that was observed with our first-generation catalyst, providing vastly improved yields of allylsilanes from simple alkene starting materials. The studies quantifying the electronic and steric properties of the new ligand are described. Finally, we report an X-ray crystal structure of a palladium complex resulting from the oxidative addition of Me₃SiI using an analogous ligand that provides significant insight into the nature of the catalytic system

A Bench-Stable, Single-Component Precatalyst for Silyl–Heck Reactions

Studies of the silyl-Heck reaction aimed at identifying active palladium complexes have revealed a new species that is formed in situ. This complex has been identified as the palladium iodide dimer, [(JessePhos)­PdI₂]₂, which has been found to be a competent single-component precatalyst for the silyl-Heck reaction. This complex is easily prepared and is temperature, moisture, and air stable. Additionally, this precatalyst provides higher activity and greater reproducibility compared to previous systems

Elucidation of Diels–Alder Reaction Network of 2,5-Dimethylfuran and Ethylene on HY Zeolite Catalyst

The reaction of 2,5-dimethylfuran and ethylene to produce <i>p</i>-xylene represents a potentially important route for the conversion of biomass to high-value organic chemicals. Current preparation methods suffer from low selectivity and produce a number of byproducts. Using modern separation and analytical techniques, the structures of many of the byproducts produced in this reaction when HY zeolite is employed as a catalyst have been identified. From these data, a detailed reaction network is proposed, demonstrating that hydrolysis and electrophilic alkylation reactions compete with the desired Diels–Alder/dehydration sequence. This information will allow the rational identification of more selective catalysts and more selective reaction conditions

A Bench-Stable, Single-Component Precatalyst for Silyl–Heck Reactions

Studies of the silyl-Heck reaction aimed at identifying active palladium complexes have revealed a new species that is formed in situ. This complex has been identified as the palladium iodide dimer, [(JessePhos)­PdI₂]₂, which has been found to be a competent single-component precatalyst for the silyl-Heck reaction. This complex is easily prepared and is temperature, moisture, and air stable. Additionally, this precatalyst provides higher activity and greater reproducibility compared to previous systems