Biocatalytic Synthesis of Nitriles through Dehydration of Aldoximes: The Substrate Scope of Aldoxime Dehydratases

Nitriles, which are mostly needed and produced by the chemical industry, play a major role in various industry segments, ranging from high‐volume, low‐price sectors, such as polymers, to low‐volume, high‐price sectors, such as chiral pharma drugs. A common industrial technology for nitrile production is ammoxidation as a gas‐phase reaction at high temperature. Further popular approaches are substitution or addition reactions with hydrogen cyanide or derivatives thereof. A major drawback, however, is the very high toxicity of cyanide. Recently, as a synthetic alternative, a novel enzymatic approach towards nitriles has been developed with aldoxime dehydratases, which are capable of converting an aldoxime in one step through dehydration into nitriles. Because the aldoxime substrates are easily accessible, this route is of high interest for synthetic purposes. However, whenever a novel method is developed for organic synthesis, it raises the question of substrate scope as one of the key criteria for application as a “synthetic platform technology”. Thus, the scope of this review is to give an overview of the current state of the substrate scope of this enzymatic method for synthesizing nitriles with aldoxime dehydratases. As a recently emerging enzyme class, a range of substrates has already been studied so far, comprising nonchiral and chiral aldoximes. This enzyme class of aldoxime dehydratases shows a broad substrate tolerance and accepts aliphatic and aromatic aldoximes, as well as arylaliphatic aldoximes. Furthermore, aldoximes with a stereogenic center are also recognized and high enantioselectivities are found for 2‐arylpropylaldoximes, in particular. It is further noteworthy that the enantiopreference depends on the E and Z isomers. Thus, opposite enantiomers are accessible from the same racemic aldehyde and the same enzyme.     

A Peroxygenase from Chaetomium globosum Catalyzes the Selective Oxygenation of Testosterone

Unspecific peroxygenases (UPO, EC 1.11.2.1) secreted by fungi open an efficient way to selectively oxyfunctionalize diverse organic substrates, including less‐activated hydrocarbons, by transferring peroxide‐borne oxygen. We investigated a cell‐free approach to incorporate epoxy and hydroxyl functionalities directly into the bulky molecule testosterone by a novel unspecific peroxygenase (UPO) that is produced by the ascomycetous fungus Chaetomium globosum in a complex medium rich in carbon and nitrogen. Purification by fast protein liquid chromatography revealed two enzyme fractions with the same molecular mass (36 kDa) and with specific activity of 4.4 to 12 U mg^?1. Although the well‐known UPOs of Agrocybe aegerita (AaeUPO) and Marasmius rotula (MroUPO) failed to convert testosterone in a comparative study, the UPO of C. globosum (CglUPO) accepted testosterone as substrate and converted it with total turnover number (TTN) of up to 7000 into two oxygenated products: the 4,5‐epoxide of testosterone in β‐configuration and 16α‐hydroxytestosterone. The reaction performed on a 100 mg scale resulted in the formation of about 90 % of the epoxide and 10 % of the hydroxylation product, both of which could be isolated with purities above 96 %. Thus, CglUPO is a promising biocatalyst for the oxyfunctionalization of bulky steroids and it will be a useful tool for the synthesis of pharmaceutically relevant steroidal molecules.     

Method for Characterization of Solvents for Physical Absorption Processes

A method for solvent screening and searching for additives in the field of physical absorption processes is presented. A model based on the concept of virtual components and on the concept of a simplified abstract flow sheet is created. An estimation procedure for thermodynamically consistent property sets for the virtual component is developed. The model is implemented into MATLAB®. Its application is demonstrated in two studies including a study for a solvent additive. Potential candidates can be characterized and ranges for properties of the solvent or additive are found by means of the model. Conclusions obtained from the model support the screening process by a reduction of the number of further investigated components.     

Field intercomparison of the gas/particle partitioning of oxygenated organics during the Southern Oxidant and Aerosol Study (SOAS) in 2013

We present results of the first intercomparison of real-time instruments for gas/particle partitioning of organic species. Four recently-developed instruments that directly measure gas/particle partitioning in near-real time were deployed in Centreville, Alabama during the Southern Oxidant Aerosol Study (SOAS) in 2013. Two instruments were filter inlet for gases and aerosols high-resolution chemical ionization mass spectrometers (FIGAERO-HRToF-CIMS) with acetate (A-CIMS) and iodide (I-CIMS) ionization sources, respectively; the third was a semi-volatile thermal desorption aerosol GC-MS (SV-TAG); and the fourth was a high-resolution thermal desorption proton-transfer reaction mass spectrometer (HR-TD-PTRMS). Signals from these instruments corresponding to several organic acids were chosen for comparison. The campaign average partitioning fractions show good correlation. A similar level of agreement with partitioning theory is observed. Thus the intercomparison exercise shows promise for these new measurements, as well as some confidence on the measurement of low versus high particle-phase fractions. However, detailed comparison show several systematic differences that lie beyond estimated measurement errors. These differences may be due to at least eight different effects: (1) underestimation of uncertainties under low signal-to-noise; (2) inlet and/or instrument adsorption/desorption of gases; (3) differences in particle size ranges sampled; (4) differences in the methods used to quantify instrument backgrounds; (5) errors in high-resolution fitting of overlapping ion groups; (6) differences in the species included in each measurement due to different instrument sensitivities; and differences in (7) negative or (8) positive thermal decomposition (or ion fragmentation) artifacts. The available data are insufficient to conclusively identify the reasons, but evidence from these instruments and available data from an ion mobility spectrometer shows the particular importance of effects 6–8 in several cases. This comparison highlights the difficulty of this measurement and its interpretation in a complex ambient environment, and the need for further improvements in measurement methodologies, including isomer separation, and detailed study of the possible factors leading to the observed differences. Further intercomparisons under controlled laboratory and field conditions are strongly recommended.

Copyright © 2017 American Association for Aerosol Research     

Capillary electrophoresis-mass spectrometry as a powerful tool in clinical diagnosis and biomarker discovery

Proteome analysis is now emerging as key technology for deciphering biological processes and the discovery of biomarkers for diseases from tissues and body fluids. The complexity and wide dynamic range of protein expression poses a formidable challenge to both peptide separation technologies and mass spectrometry (MS). Here we review the efforts that have been undertaken to date, focussing on capillary electrophoresis coupled to mass spectrometry (CE-MS). We discuss CE-MS from an application point of view evaluating its merits and vices in regard to biomarker discovery and clinical applications. As examples, we present the use of CE-MS for the determination of protein patterns in urine, serum, and other body fluids. Finally, the benefits and limitations of CE-MS for the analysis of proteins in clinical samples are discussed against the background of alternative technologies.     

Hot corrosion of TBC-coated components upon combustion of low-sulfur fuels

Gas turbine reliability is a crucial requirement for passenger safety in aviation and a secure energy supply. Hence, corrosive degradation of combustor parts, vanes, and blades in gas turbines must be prevented. One of the most severe forms of corrosion is alkali-sulfate-induced hot corrosion, which is associated with internal sulfidation of components and is usually anticipated to fade in importance in the absence of sulfur. However, the literature suggests that hot corrosion might still occur in low-sulfur combustion gases. In this study, established thermodynamic modeling methods are used to analyze the low-sulfur hot corrosion regime. Liquid sodium chromate is found to be stable in these conditions. A comparison of calculation results and engine findings suggests that high alkali levels can negatively impact thermal barrier coating life even if sulfur is absent in the fuel. Laboratory tests are carried out to validate the chromate formation on MCrAlY-coated specimens. It is shown that molten sodium chromate can alter the oxidation behavior of MCrAlY, promoting the formation of voluminous spinel. This represents a new and different form of hot corrosion compared to type I hot corrosion.     

Inhibition of HIV-1 by a peptide ligand of the genomic RNA packaging signal Psi

The interaction of the nucleocapsid NCp7 of the human immunodeficiency virus type 1 (HIV-1) Gag polyprotein with the RNA packaging signal Psi ensures specific encapsidation of the dimeric full length viral genome into nascent virus particles. Being an essential step in the HIV-1 replication cycle, specific genome encapsidation represents a promising target for therapeutic intervention. We previously selected peptides binding to HIV-1 Psi-RNA or stem loops (SL) thereof by phage display. Herein, we describe synthesis of peptide variants of the consensus HWWPWW motif on membrane supports to optimize Psi-RNA binding. The optimized peptide, psi-pepB, was characterized in detail with respect to its conformation and binding properties for the SL3 of the Psi packaging signal by NMR and tryptophan fluorescence quenching. Functional analysis revealed that psi-pepB caused a strong reduction of virus release by infected cells as monitored by reduced transduction efficiencies, capsid p24 antigen levels, and electron microscopy. Thus, this peptide shows antiviral activity and could serve as a lead compound to develop new drugs targeting HIV-1.     

Amino Acid Transporter LAT1 (SLC7A5) Mediates MeHg-Induced Oxidative Stress Defense in the Human Placental Cell Line HTR-8/SVneo

The placental barrier can protect the fetus from contact with harmful substances. The potent neurotoxin methylmercury (MeHg), however, is very efficiently transported across the placenta. Our previous data suggested that L-type amino acid transporter (LAT)1 is involved in placental MeHg uptake, accepting MeHg-L-cysteine conjugates as substrate due to structural similarity to methionine. The aim of the present study was to investigate the antioxidant defense of placental cells to MeHg exposure and the role of LAT1 in this response. When trophoblast-derived HTR-8/SVneo cells were LAT1 depleted by siRNA-mediated knockdown, they accumulated less MeHg. However, they were more susceptible to MeHg-induced toxicity. This was evidenced in decreased cell viability at a usually noncytotoxic concentration of 0.03 µM MeHg (~6 µg/L). Treatment with ≥0.3 µM MeHg increased cytotoxicity, apoptosis rate, and oxidative stress of HTR-8/SVneo cells. These effects were enhanced under LAT1 knockdown. Reduced cell number was seen when MeHg-exposed cells were cultured in medium low in cysteine, a constituent of the tripeptide glutathione (GSH). Because LAT1-deficient HTR-8/SVneo cells have lower GSH levels than control cells (independent of MeHg treatment), we conclude that LAT1 is essential for de novo synthesis of GSH, required to counteract oxidative stress. Genetic predisposition to decreased LAT1 function combined with MeHg exposure could increase the risk of placental damage.     

Highly reflective coatings for interior and exterior steel cladding and the energy efficiency of buildings

The effect of surface heat-radiation properties of coil-coated steel cladding material on the energy efficiency of buildings in Nordic climate is addressed by parallel temperature and energy usage measurements in a series of test cabins with different exterior solar reflectivity and interior thermal reflectivity. During one year, a number of one- or two-week experiments with air conditioner cooling and electrical floor heating were made while logging air-, radiation- and surface temperatures, energy consumption and weather conditions. Measurements show significant energy savings in the test cabins by the use of high thermal reflectivity interior surfaces both during heating and cooling and a strongly reduced cooling demand by the use of high solar reflectivity exterior surfaces. Results are interpreted within the context of a steady-state energy flux model, to illuminate the importance of surface resistance properties (radiation and convective heat dissipation).     

Excessive cross-linking of caseins by microbial transglutaminase and its impact on physical properties of acidified milk gels

By varying cross-linking intensity, the effect of microbial transglutaminase on acid gels made from casein solution and raw milk was studied. To avoid any impact of heating, N-ethylmaleimide was used for enzyme inactivation after appropriately checking its efficiency. Up to a specific degree of oligomerisation gel stiffness and firmness increased and tan δ, time at gelation onset and syneresis decreased. Above approximately 70% and 25% of cross-linked protein in casein solution and raw milk, respectively, these parameters showed an opposite behaviour, and weak gels with high syneresis were obtained. Substrate differences, such as preferred cross-linking of adjoining κ-caseins on the surface of the micelle enhanced the effect of steric hindrance in raw milk and impaired proper rearrangements upon acidification at a much lower level of oligomerised protein. It is mainly dimeric and trimeric casein that successfully contributed to the enhanced properties of milk protein gels.