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Antioxidants (AO) inhibiting unspecific oxygen reactions are added to most susceptible industrial products, including liquid hydrocarbon-based aviation fuels. Regulatory approved jet fuel, whether synthetic or crude oil-based, requires the addition of performance antioxidants to inhibit radical-induced oxidation during storage and transport. While presently used antioxidants are petroleum-based, there have been no sustainable, less-toxic, bio-based equivalents reported so far. This study addresses the initial evaluation of carotenoid-based antioxidants as a substitution for current alkyl-phenolic antioxidants to kerosene. Inspired from natural products of Brevibacterium and Synechococcus genus synthesized analogues of candidate aromatic carotenoid cleavage products were evaluated for their effects on combustion characteristics of jet fuel, comparative radical scavenging, and endothelial cell-culture cytotoxicity. These bioinspired antioxidants show no adverse effect on jet fuel bulk properties and combustion chemistry. The radical scavenging properties of the evaluated phenolic compounds are superior to non-aromatic β-carotene cleavage products and in range with current alkyl-phenolic additives. Cytological assays demonstrated low toxicity towards human endothelial cells similar to butylated hydroxytoluene (BHT), one of the approved alkyl-phenol based additives to jet fuel, food, and cosmetics. The initial data set suggests, that the evaluated bioinspired compounds do not interfere with normal operations of jet engines and human fuel handling. Further developments towards the sustainable, biotechnological production and application of aromatic carotenoid cleavage products as antioxidants could contribute to reduced non-renewable consumption and possibly being an environmentally more compatible alternative due to their biosynthetic origin.

CotB2 catalyzes the first committed step in cyclooctatin biosynthesis of the soil bacterium Streptomyces melanosporofaciens. To date, CotB2 represents the best studied bacterial diterpene synthase. Its reaction mechanism has been addressed by isoptope labeling, targeted mutagenesis and theoretical computations in the gas phase, as well as full enzyme molecular dynamic simulations. By X-ray crystallography different snapshots of CotB2 from the open, inactive, to the closed, active conformation have been obtained in great detail, allowing us to draw detailed conclusions regarding the catalytic mechanism at the molecular level. Moreover, numerous alternative geranylgeranyl diphosphate cyclization products obtained by CotB2 mutagenesis have exciting applications for the sustainable production of high value bioactive substances.

A holistic bio-process based on the microbial upcycling of low-value feedstocks and leading to chemo-enzymatically derived, functionalized taxanoids was established. The upcycling of biotechnological by-product streams glycerol and corn steep liquor by an engineered Escherichia coli strain that constitutively expressed bottleneck enzymes within the MEP-pathway led to the formation of 364.4 ± 10.7 mg L−1 taxadiene within 44 h. In contrast to standard inducible systems, our constitutive microbial production system provided concomitant growth and taxadiene formation. This strategy is the basis for subsequent continuous taxadiene production processes, which is favorable under economic constraints. The growth dependent taxadiene production showed improved yields, reproducibility and transferability at any scale compared to inducible taxadiene production platforms examined in this study. Additionally, we developed new taxadiene isolation and purification strategies. To that end, these new downstream processing strategies display efficient alternatives to conventional biphasic, in situ extraction and purification procedures. Specifically, we developed a rapid and easy two-step extraction procedure followed by centrifugal partition chromatography purification. This process strategy provided 249.0 ± 11.1 mg L−1 taxadiene with 95% purity from E. coli high cell-density cultures at a liter scale. To functionalize taxadiene, a mild lipase mediated epoxidation reaction was devised. Optimization of this biology-oriented synthesis strategy led to a quantitative conversion of taxadiene to taxa-4(5),11(12)-bisepoxide with an enantiomeric excess of over 83%. The holistic process strategy afforded in excess of 215 mg taxa-4(5),11(12)-bisepoxide by upcycling the low-value feedstocks glycerol (300 g) and corn steep liquor (25 g).

With over 50.000 identified compounds terpenes are the largest and most structurally diverse group of natural products. They are ubiquitous in bacteria, plants, animals and fungi, conducting several biological functions such as cell wall components or defense mechanisms. Industrial applications entail among others pharmaceuticals, food additives, vitamins, fragrances, fuels and fuel additives. Central building blocks of all terpenes are the isoprenoid compounds isopentenyl diphosphate and dimethylallyl diphosphate. Bacteria like Escherichia coli harbor a native metabolic pathway for these isoprenoids that is quite amenable for genetic engineering. Together with recombinant terpene biosynthesis modules, they are very suitable hosts for heterologous production of high value terpenes. Yet, in contrast to the number of extracted and characterized terpenes, little is known about the specific biosynthetic enzymes that are involved especially in the formation of highly functionalized compounds. Novel approaches discussed in this review include metabolic engineering as well as site-directed mutagenesis to expand the natural terpene landscape. Focusing mainly on the validation of successful integration of engineered biosynthetic pathways into optimized terpene producing Escherichia coli, this review shall give an insight in recent progresses regarding manipulation of mostly diterpene synthases.

Leishmaniaspecies cause a spectrum of human diseases in tropical and subtropical regions of the world. We have sequenced the 36 chromosomes of the 32.8-megabase haploid genome ofLeishmania major(Friedlin strain) and predict 911 RNA genes, 39 pseudogenes, and 8272 protein-coding genes, of which 36% can be ascribed a putative function. These include genes involved in host-pathogen interactions, such as proteolytic enzymes, and extensive machinery for synthesis of complex surface glycoconjugates. The organization of protein-coding genes into long, strand-specific, polycistronic clusters and lack of general transcription factors in theL. major, Trypanosoma brucei, andTrypanosoma cruzi(Tritryp) genomes suggest that the mechanisms regulating RNA polymerase II–directed transcription are distinct from those operating in other eukaryotes, although the trypanosomatids appear capable of chromatin remodeling. Abundant RNA-binding proteins are encoded in the Tritryp genomes, consistent with active posttranscriptional regulation of gene expression.

The parallel density functional program PARAGAUSS has been extended by a tool for computing solvent effects based on the conductor-like screening model (COSMO). The molecular cavity in the solvent is constructed as a set of overlapping spheres according to the GEPOL algorithm. The cavity tessellation scheme and the resulting set of point charges on the cavity surface comply with the point group symmetry of the solute. Symmetry is exploited to reduce the computational effort of the solvent model. To allow an automatic geometry optimization including solvent effects, care has been taken to avoid discontinuities due to the discretization (weights of tesserae, number of spheres created by GEPOL). In this context, an alternative definition for the grid points representing the tesserae is introduced. In addition to the COSMO model, short-range solvent effects are taken into account via a force field. We apply the solvent module to all-electron scalar-relativistic density functional calculations on uranyl, UO22+, and its aquo complexes in aqueous solution. Solvent effects on the geometry are very small. Based on the model [UO2(H2O)5]2+, the solvation energy of uranyl is estimated to be about −400 kcal/mol, in agreement with the range of experimental data. The major part of the solvation energy, about −250 kcal/mol, is due to a donor–acceptor interaction associated with a coordination shell of five water ligands. One can interpret this large solvation energy also as a compounded effect of an effective reduction of the uranyl moiety plus a solvent polarization. The energetic effect of the structure relaxation in the solution is only about 8 kcal/mol. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001

A calculation of the optical conductivity and related optical properties of liquid silicon is presented. Starting from the results of a single superchain/effective medium approximation for the electronic properties, the frequency dependent conductivity is evaluated in terms of the Kubo-Greenwood formula. For a fast computation of the three and four centre terms therein the effective handling of the angular dependences of the Green's functions known from the sp³-fluid model is generalized to the current matrix elements. A good agreement of our results with experimental data for liquid silicon is found. At higher frequencies (>5 eV) and in the fitted Drude parameters, however, there are discrepancies due to the limitations of the sp³-model.

In order to combine the advantages of tight-binding integral equation methods with basis sets not restricted to the lowest two orbital quantum numbers we extend the molecular fluid approach for the sp3 model of Lomba et al to arbitrarily high orbital quantum numbers. As an example, we present a single-superchain/effective-medium calculation of the electronic density of states for liquid silicon within a tight-binding approximation that includes, besides the 3s and 3p orbitals, also the 3d orbitals. Comparison with results from the sp3 model and different molecular dynamics results shows that within this sp3 d5 model very good agreement with plane-wave calculations is found whereas the sp3 model leads to unsatisfactory results.

Oxocarbons and Related Compounds. 20. By Thiophenols Mediated Conversion of Semisquaric Hydrazides to Squaric-1,2-Diamides In the presence of thiophenols semisquaric hydrazides (4) are converted into squaric-1,2-diamides (6) upon heating in alcoholic solution. Proof is given that thiosquaric-S-ester-amides (8) are intermediates in this process.

The reaction of semisquaric hydrazides 5a-f, with thiols 6a-j, 12, 14 has been investigated. Depending upon the substitution pattern of the educts, the solvent, and the reaction temperature the S-alkyl and S-aryl thiosquarate amides 8a-m, 11a-g, 13, 15 were obtained