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The hydride and methyl compounds [Tism^PriBenz]MgH and [Tism^PriBenz]MgMe undergo insertion of the carbonyl moieties of non-enolizable aldehydes and ketones such as PhCHO and Ph₂CO into the Mg–H and Mg–Me bonds to form alkoxide compounds, namely [Tism^PriBenz]MgOCH₂Ph, [Tism^PriBenz]MgOCHPh₂, [Tism^PriBenz]MgMOCH(Me)Ph and [Tism^PriBenz]MgOCMePh₂. In contrast to the insertion of the carbonyl moiety, the reactions of the enolizable ketones Me₂CO and PhC(O)Me with [Tism^PriBenz]MgMe afford the enolate complexes, [Tism^PriBenz]MgOC(Me)=CH₂ and [Tism^PriBenz]MgOC(Ph)=CH₂. The formation of [Tism^PriBenz]MgOC(Me)=CH₂ is of note because methyl Grignard reagents preferentially react with acetone to form t-butoxide derivatives. The hydride compound, [Tism^PriBenz]MgH, also reacts with acetone to yield the enolate compound, [Tism^PriBenz]MgOC(Me)=CH₂,more » but while the overall transformation is similar to that of the methyl derivative, [Tism^PriBenz]MgMe, the enolate compound is not the initially formed product. Specifically, acetone undergoes preferential insertion into the Mg–H bond to generate the corresponding alkoxide, [Tism^PriBenz]MgOPrⁱ, which subsequently converts to the respective enolate in the presence of excess acetone. Furthermore, the relative ability of the hydride and methyl compounds to undergo insertion of carbonyl compounds into the Mg–H and Mg–Me bonds has been addressed computationally, which indicates that the barrier for insertion of the carbonyl group into the Mg–H bond is lower than that for insertion into the Mg–Me bond. The molecular structures of [Tism^PriBenz]MgOCH₂Ph, [Tism^PriBenz]MgOCHPh₂, [Tism^PriBenz]MgOCMePh₂, [Tism^PriBenz]MgOC(Me)=CH₂ and [Tism^PriBenz]MgOC(Ph)=CH₂ have been determined by X-ray diffraction.« less

Deconstruction of polyethylene terephthalate (PET) plastic waste generates opportunities for valorization to alternative products. We recently designed an enzymatic cascade that could produce terephthalaldehyde (TPAL) from terephthalic acid. Here, we showed that the addition of TPAL to growing cultures of Escherichia coli wild-type strain MG1655 and an engineered strain for reduced aromatic aldehyde reduction (RARE) strain resulted in substantial reduction. We then investigated if we could mitigate this reduction using multiplex automatable genome engineering (MAGE) to create an E. coli strain with 10 additional knockouts in RARE. Encouragingly, we found this newly engineered strain enabled a 2.5-fold higher retention ofmore » TPAL over RARE after 24 h. We applied this new strain for the production of para-xylylenediamine (pXYL) and observed a 6.8-fold increase in pXYL titer compared with RARE. Altogether, our study demonstrates the potential of TPAL as a versatile intermediate in microbial biosynthesis of chemicals that derived from waste PET.« less

Aldehydes are attractive chemical targets both as end products in the flavors and fragrances industry and as synthetic intermediates due to their propensity for C–C bond formation. Here, in this study, we identify and address unexpected oxidation of a model collection of aromatic aldehydes, including many that originate from biomass degradation. When diverse aldehydes are supplemented to E. coli cells grown under aerobic conditions, as expected they are either reduced by the wild-type MG1655 strain or stabilized by a strain engineered for reduced aromatic aldehyde reduction (the E. coli RARE strain). Surprisingly, when these same aldehydes are supplemented to restingmore » cell preparations of either E. coli strain, under many conditions we observe substantial oxidation. By performing combinatorial inactivation of six candidate aldehyde dehydrogenase genes in the E. coli genome using multiplexed automatable genome engineering (MAGE), we demonstrate that this oxidation can be substantially slowed, with greater than 50% retention of 6 out of 8 aldehydes when assayed 4 h after their addition. Given that our newly engineered strain exhibits reduced oxidation and reduction of aromatic aldehydes, we dubbed it the E. coli ROAR strain. We applied the new strain to resting cell biocatalysis for two kinds of reactions – the reduction of 2-furoic acid to furfural and the condensation of 3-hydroxybenzaldehyde and glycine to form a non-standard β-hydroxy-α-amino acid. In each case, we observed substantial improvements in product titer 20 h after reaction initiation (9-fold and 10-fold, respectively). Moving forward, the use of this strain to generate resting cells should allow aldehyde product isolation, further enzymatic conversion, or chemical reactivity under cellular contexts that better accommodate aldehyde toxicity.« less

Here, the compatibility of biodiesel blends with five common elastomers (acrylonitrile rubber or NBR, fluorocarbon, neoprene, ethylene propylene diene monomer or EPDM, and silicone) was assessed using Hansen solubility parameters. A solubility analysis was performed over the full diesel blend range and the model used methyl hydroperoxide, acetaldehyde, and formic acid to represent the decomposition products of biodiesel. An empirical study was also conducted to determine the efficacy of the approach to predict the volume swell of elastomers. This study included the influence of biodiesel with acetaldehyde and formic acid. The solubility model showed good agreement with measured volumes formore » fluorocarbon, neoprene, EPDM, and silicone. However, solubility curves for NBR did not reflect the measured volume changes, and therefore the solubility parameters used for NBR in this study are not considered reliable. The results showed that formic acid caused higher swelling in NBR, fluorocarbon, neoprene, and silicone than did acetaldehyde. For EPDM, the measured volume decreased with both biodiesel concentration and the addition of formic acid.« less