Accumulation Of Side Products Research Articles

Production of indole by Corynebacterium glutamicum microbial cell factories for flavor and fragrance applications

BackgroundThe nitrogen containing aromatic compound indole is known for its floral odor typical of jasmine blossoms. Due to its characteristic scent, it is frequently used in dairy products, tea drinks and fine fragrances. The demand for natural indole by the flavor and fragrance industry is high, yet, its abundance in essential oils isolated from plants such as jasmine and narcissus is low. Thus, there is a strong demand for a sustainable method to produce food-grade indole.ResultsHere, we established the biotechnological production of indole upon l-tryptophan supplementation in the bacterial host Corynebacterium glutamicum. Heterologous expression of the tryptophanase gene from E. coli enabled the conversion of supplemented l-tryptophan to indole. Engineering of the substrate import by co-expression of the native aromatic amino acid permease gene aroP increased whole-cell biotransformation of l-tryptophan to indole by two-fold. Indole production to 0.2 g L−1 was achieved upon feeding of 1 g L−1l-tryptophan in a bioreactor cultivation, while neither accumulation of side-products nor loss of indole were observed. To establish an efficient and robust production process, new tryptophanases were recruited by mining of bacterial sequence databases. This search retrieved more than 400 candidates and, upon screening of tryptophanase activity, nine new enzymes were identified as most promising. The highest production of indole in vivo in C. glutamicum was achieved based on the tryptophanase from Providencia rettgeri. Evaluation of several biological aspects identified the product toxicity as major bottleneck of this conversion. In situ product recovery was applied to sequester indole in a food-grade organic phase during the fermentation to avoid inhibition due to product accumulation. This process enabled complete conversion of l-tryptophan and an indole product titer of 5.7 g L−1 was reached. Indole partitioned to the organic phase which contained 28 g L−1 indole while no other products were observed indicating high indole purity.ConclusionsThe bioconversion production process established in this study provides an attractive route for sustainable indole production from tryptophan in C. glutamicum. Industrially relevant indole titers were achieved within 24 h and indole was concentrated in the organic layer as a pure product after the fermentation.

Generation, Stability, and Utility of Lithium 4,4′-Di-tert-butylbiphenylide (LiDBB)

Several procedures were evaluated for the preparation of lithium 4,4'-di-tert-butylbiphenylide (LiDBB, Freeman's reagent) from lithium metal and 4,4'-di-tert-butylbiphenyl (DBB) in THF. Solutions with nominal concentration of 0.4 and 1.0 M were formed. The stability of LiDBB solutions was evaluated over time, and the gradual uptake of lithium metal was observed. At 0 °C the LiDBB solutions were stable for over a week in THF. At 20 °C the LiDBB solution underwent various decomposition pathways, which led to uptake of more lithium metal and the accumulation of side products. These decomposition pathways were studied, and the importance of ethene in the destruction of THF by LiDBB was observed. On a practical note, LiDBB solutions in THF were stable and effective for over a week at 0 °C or for more than 37 weeks when stored under argon at -25 °C. These observations will extend the utility of LiDBB as a reagent in organic synthesis.

Influence of Various Factors on the Monomethylacetamide Concentration in Regenerated N,N-Dimethylacetamide

The causes of N,N-dimethylacetamide degradation were studied. The influence of various destructive factors (temperature, light, contents of water and other impurities) on the formation and accumulation of side products in regenerated dimethylacetamide was studied. It was demonstrated that regenerated dimethylacetamide was less stable to the action of these factors than a commercial sample. The influence of each factor on the concentration increase of monomethylacetamide was established. The monomethylacetamide concentration was shown to be correlated with the intensity and duration of the factors.

Features of the kinetics of 4-nitroaniline and azoxybenzene hydrogenation in 2-propanol aqueous solutions

It is shown experimentally that the hydrogenation of 4-nitroaniline and azoxybenzene over a skeletal nickel catalyst in 2-propanol aqueous solutions proceeds selectively with the formation of the corresponding amines without the accumulation of side products in the bulk phase. It is concluded that during reduction, considerable participation of hydrogen bonded with active centers of a catalyst surface was observed. The competitive character of adsorption between the initial azoxybenzene and aniline formed as a result of reaction is established. It is ascertained that the character of changes in the rates of hydrogenation of nitro and azoxy groups is identical in the presence of additions of acid or base. It is demonstrated that a targeted change in the hydrogenation rates of these compounds is possible by introducing additions of acetic acid or sodium hydroxide into 2-propanol aqueous solution.

Alkene Epoxidations Catalyzed by Mo(VI) Supported on Imidazole-Containing Polymers: II. Recycling of Polybenzimidazole-Supported Mo(VI) in the Epoxidation of Cyclohexene

Mo(VI) has been supported on a polybenzimidazole resin and used as an epoxidation catalyst in the reaction of t-butylhydroperoxide (TBHP) with cyclohexene. A preliminary kinetic study has suggested that mass transfer of TBHP might be rate-limiting. The experimental activation energy is higher than that of an analogous homogeneous reaction catalysed by MoO 2acac 2. Nevertheless, the supported catalyst is highly active and has been recycled nine times with no detectable loss of Mo from the support, but with a decline in activity. Activation of the polymer catalyst by pretreatment with TBHP far periods up to 48 h does not influence the activity of the catalyst on first use; however, higher activity is retained on recycling. The imidazole ligand on the polymer appears to bind the Mo centres very effectively and Mo leaching is not responsible for the decay in activity on recycling. The most likely explanation for this is the blockage of access to catalytic sites in the polymer by accumulation of side-products (oligomer) from cyclohexene or its epoxide.