Showing papers by "DECHEMA published in 2011"
TL;DR: In this contribution recent developments in the field of enzymatic reduction using whole cells and isolated enzymes are reviewed.
320 citations
TL;DR: The relevant topics that should be addressed to establish a (biotransformational) production process of pharmaceutically relevant triterpenes are covered in this review, which focuses on the production process using tissue engineering, the corresponding analytical techniques, and the biotransformation reaction required to obtain bioactive compounds from precursor molecules.
152 citations
TL;DR: In this article, it was shown that the dusting mechanism of austenitic materials like high alloy Cr-Ni steels and Ni base materials is one of graphite nucleation and growth within the near surface metal.
Abstract: Recent experimental investigations have widened the understanding of metal dusting significantly. Microscopic observations have been used to dissect dusting mechanisms. Iron dusts by growing a cementite surface scale, which catalyses graphite nucleation and growth. The resulting volume expansion leads to cementite disintegration. Cementite formation on iron can be suppressed by alloying with germanium. Nonetheless, dusting occurs via the direct growth of graphite into the metal, producing nanoparticles offerrite.This process is faster, because carbon diffusion is more rapid in α-Fe than in Fe 3 C. Austenitic materials cannot form cementite, and dust via formation of graphite at external surfaces and interior grain boundaries. The coke deposit consists of carbon nanotubes with austenite particles at their tips, or graphite particles encapsulating austenite. TEM studies demonstrate the inward growth of graphite within the metal interior. It is therefore concluded that the dusting mechanism of austenitic materials like high alloy Cr-Ni steels and Ni base materials is one of graphite nucleation and growth within the near surface metal. In all alloys examined, both ferritic and austenitic, the principal mass transfer process is inward diffusion of carbon. Alloying iron with nickel leads to a transformation from one mechanism with carbide formation to the other without. Copper alloying in nickel and high nickel content stainless steels strongly suppresses graphite nucleation, as does also an intermetallic Ni-Sn phase, thereby reducing greatly the overall dusting rate. A surface layer of intermetallic Ni-Sn Fe-base materials facilitates the formation of a Fe 3 SnC surface scale which also prevents coking and metal dusting. Current understanding of the roles of temperature, gas composition and surface oxides on dusting rates are summarised. Finally, protection against metal dusting by coatings is discussed in terms of their effects on catalysis of carbon deposition, and on protective oxide formation.
118 citations
TL;DR: With DSA and groundwater from a contaminated site, complete degradation of chloroethenes in groundwater was obtained for two months thus demonstrating the feasibility of the sequential bioelectro-approach for field application.
Abstract: This article for the first time demonstrates successful application of electrochemical processes to stimulate sequential reductive/oxidative microbial degradation of perchloroethene (PCE) in minera...
102 citations
TL;DR: Any application requiring immobilized biocatalysts on electrodes can make use of this immobilization approach, making future biosensors and biocAtalytic technologies more sensitive, simpler, reusable and less expensive while only requiring mild enzyme modifications.
82 citations
TL;DR: The versatile enzyme chloroperoxidase was used in a new reaction system, based on a gas diffusion electrode, for enzymatic chlorinations, sulfoxidations and oxidations, which is the first report on the combination of hydrogen peroxide production at a GDE with an enzyme reaction.
77 citations
Journal Article•
TL;DR: In this paper, a critical review of the information available on the substrate scope as well as the applications reported is presented, along with quantitative information such as productivity per catalyst, space-time yield (STY), cofactor utilisation, and stability.
Abstract: The alcohol dehydrogenase from Lactobacillus brevis (LbADH) is a versatile catalyst for enantioselective reduction of ketones. Its substrate scope is wide with high regioand enantioselectivity. In this critical review, we have gathered the information available on the substrate scope as well as the applications reported. Quantitative information such as productivity per catalyst, space-time yield (STY), cofactor utilisation, and stability are derived to allow comparison and assessment of practical value.
65 citations
31 Jan 2011
59 citations
TL;DR: The efficient coupling of redox cofactor oxidation and product formation, as determined in vitro, combined with the high in vivo activities make E. coli W3110 (pBT10) a promising biocatalyst for the preparative synthesis of terminally functionalized fatty acid methyl esters.
Abstract: The alkane monooxygenase AlkBGT from Pseudomonas putida GPo1 constitutes a versatile enzyme system for the ω-oxyfunctionalization of medium chain-length alkanes. In this study, recombinant Escherichia coli W3110 expressing alkBGT was investigated as whole-cell catalyst for the regioselective biooxidation of fatty acid methyl esters to terminal alcohols. The ω-functionalized products are of general economic interest, serving as building blocks for polymer synthesis. The whole-cell catalysts proved to functionalize fatty acid methyl esters with a medium length alkyl chain specifically at the ω-position. The highest specific hydroxylation activity of 104 U gCDW−1 was obtained with nonanoic acid methyl ester as substrate using resting cells of E. coli W3110 (pBT10). In an optimized set-up, maximal 9-hydroxynonanoic acid methyl ester yields of 95% were achieved. For this specific substrate, apparent whole-cell kinetic parameters were determined with a Vmax of 204±9 U gCDW−1, a substrate uptake constant (KS) of 142±17 μM, and a specificity constant Vmax/KS of 1.4 U gCDW−1 μM−1 for the formation of the terminal alcohol. The same E. coli strain carrying additional alk genes showed a different substrate selectivity. A comparison of biocatalysis with whole cells and enriched enzyme preparations showed that both substrate availability and enzyme specificity control the efficiency of the whole-cell bioconversion of the longer and more hydrophobic substrate dodecanoic acid methyl ester. The efficient coupling of redox cofactor oxidation and product formation, as determined in vitro, combined with the high in vivo activities make E. coli W3110 (pBT10) a promising biocatalyst for the preparative synthesis of terminally functionalized fatty acid methyl esters.
46 citations
TL;DR: In this paper, the authors present an industrial process of bacterial monoterpene oxidation in large volumes and in bioreactors, but no industrial process has been established up to date.
41 citations
TL;DR: Improved storage stabilities besides improved enzyme activities, as well as reduced substrate surplus and product inhibitions were found, while applying the most promising AMMOENG™ 101 in more detailed investigations.
Abstract: Ionic liquids represent a promising alternative to conventional cosolvents as biocompatible solubilisers for biocatalysis. This was shown using water miscible ionic liquids to facilitate the stereoselective reduction of hardly water soluble, aliphatic ketones catalysed by the alcohol dehydrogenase from Lactobacillus brevis . Ten ionic liquids were screened for activity and solubility. Improved storage stabilities besides improved enzyme activities, as well as reduced substrate surplus and product inhibitions were found, while applying the most promising AMMOENG™ 101 in more detailed investigations. Batch reactions with cofactor regeneration via a glucose dehydrogenase showed increased reaction rates; thus underlining the positive influence of AMMOENG™ 101. For ( R )-3-octanol, ( R )-2-nonanol, ( R )-2-decanol, and ( R )-2-octanol space time yields between 250 and 350 mmol L −1 d −1 were achieved.
TL;DR: In this article, the surface of hydrogen-permeable PdCu membranes acting as a catalyst for direct hydroxylation of benzene to phenol in the gas phase in a novel catalytic double-membrane reactor was modified by sputtering on it different catalytic layers with the aim to increase the formation rate and selectivity to phenoline.
Abstract: The surface of hydrogen-permeable PdCu membranes acting as a catalyst for direct hydroxylation of benzene to phenol in the gas phase in a novel catalytic double-membrane reactor was modified by sputtering on it different catalytic layers with the aim to increase the formation rate and selectivity to phenol. Three different systems are described: a 1 μm thick compact layer of Pd 90 Au 10 (10 wt.% Au), a 5 μm thick compact layer of PdGa (50 at.% Ga) and a thin film of Pd 90 Au 10 deposited on a discontinuous V 2 O 5 layer. The different systems were characterized by SEM, EDX, and mainly in terms of their catalytic properties for benzene hydroxylation. The formation rate and the selectivity to phenol could be increased substantially through the catalytic modification. With a maximum phenol selectivity of 67% at 150 °C and a maximum phenol formation rate of 1.67 × 10 −4 mol h −1 m −2 at 200 °C, PdAu reached the best performance in double-membrane operation mode. PdGa showed even more promising results compared to PdAu in kinetic experiments in co-feed operation mode, but suffers from the very low hydrogen permeability of PdGa which stands against its use as a continuous layer in the catalytic membrane reactor.
TL;DR: In this paper, a method for coating membranes with polypyrrole (PPy) has been developed, which can be applied as electrochemically switchable, functionalised membranes with controllabel and variable separation properties.
TL;DR: In this paper, a compact and versatile continuous reaction system for supercritical fluids as mobile phase was realized using commercially available components where possible, where the setup is completely automated by the help of computerized control and features a view cell for inline phase behavior observation.
TL;DR: In this article, a new approach to manufacture a complete thermal barrier coating system in a single step is studied in the frame of the European FP7 project PARTICOAT, where spherical Al particles are deposited on different substrate alloys.
Abstract: A new approach to manufacture a complete thermal barrier coating system in a single step is studied in the frame of the European FP7 project PARTICOAT. Spherical μm-Al particles are deposited on different substrate alloys. During the sintering process in air, the μm-Al particles are oxidized and converted into hollow alumina spheres forming a ceramic “foam” (top coat), and simultaneously an Al rich diffusion layer (bond coat) is formed in the subsurface zone of the substrate. The “green” coatings deposited by air brush on IN738, Rene80 and CM247 nickel based alloys were cured at 300 °C and then isothermally exposed at 800 and 1000 °C in air for up to 1000 h. The oxide formation and the microstructure of the coatings were studied by thermo gravimetrical analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM-EDX). The coatings were adherent for all the substrates and temperatures tested. Rene80 shows the lowest mass gain whereas IN738 and CM247 show higher mass gains at the temperatures studied. Additionally, the use of reactive element oxides in the coating was investigated, demonstrating the flexibility and viability of this low cost coating concept.
TL;DR: A biotechnological synthesis of fatty aldehydes based on Escherichia coli cells expressing an α-dioxygenase (αDOX) from Oryza sativa (rice) is presented and easy reuse of the cells was demonstrated by performing a second biotransformation without any loss of biocatalytic activity.
Abstract: Fatty aldehydes are an important group of fragrance and flavor compounds that are found in different fruits and flowers A biotechnological synthesis of fatty aldehydes based on Escherichia coli cells expressing an α-dioxygenase (αDOX) from Oryza sativa (rice) is presented α-Dioxygenases are the initial enzymes of α-oxidation in plants and oxidize long and medium-chain Cn fatty acids to 2-hydroperoxy fatty acids The latter are converted to Cn − 1 fatty aldehydes by spontaneous decarboxylation Successful expression of αDOX in E coli was proven by an in vitro luciferase assay Using resting cells of this recombinant E coli strain, conversion of different fatty acids to the respective fatty aldehydes shortened by one carbon atom was demonstrated The usage of Triton X 100 improves the conversion rate up to 1 g aldehyde per liter per hour Easy reuse of the cells was demonstrated by performing a second biotransformation without any loss of biocatalytic activity
TL;DR: In this article, a continuous biocatalytic synthesis of (R)-2-octanol carried out in an enzyme membrane reactor showed an excellent process stability, resulting in a turnover number of 15 million for the applied alcohol dehydrogenase.
TL;DR: For small-scale chemical production, batch processes are the predominant application as discussed by the authors and why this is the case and what factors dominate the decision, apart from technological reasons, socioeconomic, and human factors have to be accounted for.
Abstract: Continuous processes are highly attractive and their advantages are textbook knowledge. However, for small-scale chemical production (typically up to 100 t per year) batch processes are the predominant application. Why this is the case and what factors dominate the decision is analyzed. Apart from technological reasons, socioeconomic, as well as human factors have to be accounted for.
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TL;DR: The article as mentioned in this paper discusses the origin, classification, and industrial importance of Tars and Pitches and their industrial importance in the US economy, including the use of coal-tar pitch and coal-oil blends.
Abstract: The article contains sections titled:
1. Origin, Classification, and Industrial Importance of Tars and Pitches
1.1. Origin and Classification
1.2. History
1.3. Industrial Importance
2. Properties
3. Processing of Coke-Oven Coal Tar
3.1. Survey
3.2. Primary Distillation
3.3. Processing of Coal-Tar Pitch
3.3.1. Cooling
3.3.2. Production of Electrode Pitch
3.3.3. Production of Pitch Coke
3.3.4. Production of Special Pitches
3.3.5. Pitch–Oil Blends
3.4. Processing of Tar Distillates
3.4.1. Processing of Anthracene Oil
3.4.2. Processing of Wash Oil
3.4.3. Processing of Naphthalene Oil
3.4.4. Processing of Carbolic Oil
3.4.5. Processing of Light Oil
4. Processing of Low-Temperature Coal Tars
5. Processing of Other Tars and Tarlike Raw Materials
6. Uses of Tar Products and their Economic Importance
7. Toxicology and Ecotoxicology
7.1. Toxicology
7.2. Classification and Legislation
7.3. Ecotoxicology
TL;DR: In this paper, the ketone was used as a second organic phase to enable the straightforward synthesis of long chain aliphatic chiral alcohols, which has been shown to be useful for the alcohol dehydrogenase-catalysed conversion of longer chain alphatic substrates.
TL;DR: In this article, a new route for preparation of core-shell nanoparticles composed of an iron oxide core and a polypyrrole (PPy) shell is explored, and it is demonstrated that the magnetite cores can completely be dissolved by reaction with acid.
TL;DR: To increase its production, a CPO-expression cassette was integrated into the non-transcribed spacer regions of the rDNA in C. fumago to create one strain that had twice the CPO activity when grown in shake-flask and bioreactor compared to the wild-type.
Abstract: The filamentous fungus Caldariomyces fumago secretes a chloroperoxidase (CPO). To increase its production, we integrated a CPO-expression cassette into the non-transcribed spacer regions of the rDNA in C. fumago. One strain was obtained that had twice the CPO activity when grown in shake-flask and bioreactor compared to the wild-type. The highest CPO activity from the bioreactor cultivation was 3,236 U ml(-1). This is the highest value reported so far.
TL;DR: The chiral monoterpene alcohol citronellol was converted to the corresponding bromohydrin by the haem-thiolate enzyme chloroperoxidase (CPO) from Caldariomyces fumago in the presence of hydrogen peroxide and bromide ions and the reaction was shown to be non-stereospecific.
TL;DR: A facile reaction of 1-ethyl-3-methylimidazolium acetate with dichloromethane at room temperature was observed with esters among the products, and can be exploited for mild solvent-free esterification with a range of other carboxylate-based ionic liquids and alkyl halides.
TL;DR: Liposome based substrate delivery proved to be less suitable for the delivery of amphiphilic and non-symmetric substrate molecules than micelles due to substrate orientation within the liposome membrane and represents a starting point for a systematic design of liposomes based delivery of hydrophobic substrates in enzymatic conversions performed in aqueous media.
Abstract: Enzymatic conversions of strongly hydrophobic substrates can be conducted in non-denaturing aqueous reaction media if appropriate substrate delivery systems such as micelles or liposomes are applied. We investigated liposome based substrate delivery with regard to qualitative and kinetic effects of vesicle properties on the enzymatic reaction. The cleavage of highly hydrophobic carotenoid and xanthophyll substrates by Arabidopsis thaliana carotenoid cleavage dioxygenase 1 (AtCCD1) was used as model reaction for the investigation. Conversions of the partly polar xanthophylls and the fully non-polar carotenes showed different responses to variations in the phospholipid composition of the delivery vesicles. Furthermore, the cellular reaction environment of AtCCD1 was imitated by incorporation of the galactolipid monogalactosyl-diacylglycerol (MGDG) into the liposome membranes. This led to an increase of the specific AtCCD1 activity towards the fully non-polar β-carotene by approximately 70% at MGDG shares between 8 and 20 mol% while the specific activity towards the more hydrophilic zeaxanthin decreased with increasing MGDG content. Liposome based systems proved to be less suitable for the delivery of amphiphilic and non-symmetric substrate molecules than micelles due to substrate orientation within the liposome membrane. The results represent a starting point for a systematic design of liposome based delivery of hydrophobic substrates in enzymatic conversions performed in aqueous media.
TL;DR: In this paper, a new model concept for predicting mechanical oxide scale failure is applied to Al2O3, Cr2O2, Fe3O4 and NiO, and calculated critical strain values are plotted versus the physical defect size using a simplified version of the original h-w concept.
Abstract: A new model concept for predicting mechanical oxide scale failure is applied to Al2O3, Cr2O3, Fe3O4 and NiO. The calculated critical strain values are plotted versus the physical defect size using a simplified version of the original h-w-concept. A limited number of experimental data existing in the literature were entered into the plots and yield satisfactory agreement with the model data. Future efforts should focus on extending the experimental data basis and converting these data into h-values for the model.
TL;DR: In this article, the results of oxidation tests of α-Ti without any treatment, with Al-treatment and with a combination of Al- + F-treatment are presented, referring to the fluorine effect model for TiAl-alloys.
Abstract: Titanium is a widely used structural material because of its low specific weight, good mechanical properties and excellent corrosion resistance at ambient temperature. As a result of increased oxidation at elevated temperatures and environmental embrittlement the maximum operation temperature of standard Ti-alloys is only about 600 °C. The oxidation behaviour can be improved by different methods, e.g. coatings. This leads to an improvement which is, however, often limited. The combination of Al-enrichment in the sub surface zone, so that a TiAl-layer is formed, plus F-treatment gives impressively good results because a protective alumina scale is formed due to the fluorine effect. This alumina scale prevents oxygen inward diffusion which causes embrittlement and protects the material against environmental attack. The procedure is applied to alloys with a very low Al-content or even no Al at all. In the paper results of oxidation tests of α-Ti without any treatment, with Al-treatment and with a combination of Al- + F-treatment are presented. Aluminium was diffused into the samples by a powder pack process. Fluorine was applied by a liquid phase process. The formation of an alumina scale on treated samples was revealed by post experimental investigations. The results are discussed referring to the fluorine effect model for TiAl-alloys.
TL;DR: In this paper, a sputtering technique, electrochemical deposition and diffusion heat treatment were used to enrich a 9% chromium steels with manganese spinels, and uniform diffusion was obtained with all of the investigated processes.
Abstract: The oxidation resistance of ferritic-martensitic 9% chromium steels in water vapour containing atmospheres is not yet satisfactory. The chromia layer provides little protection because water vapour in the atmosphere is known to promote the formation of the volatile chromium species CrO2(OH)2. If a chromium manganese spinel is formed instead, the vapour pressure of the oxy-hydroxide is greatly reduced and evaporation can largely be avoided. Enrichment of the substrate with manganese was achieved using three different processes: using (i) a sputtering technique, (ii) electrochemical deposition both followed by a diffusion heat treatment, (iii) the pack cementation method. Uniform diffusion of manganese was obtained with all of the investigated processes. The improved oxidation behaviour of the coated samples in synthetic air with 10% water vapour at 650°C was demonstrated.
07 Apr 2011
TL;DR: In this article, it is assumed that most of the known so-called supergiant oil fi elds cross the oil peak, which comes along with a decrease in the discovery of novel oil springs.
Abstract: Processes in the chemical industry are historically based on fossil resources. During industrial revolution, energy sources like peat and such renewable biomasses as wood were substituted by coal and later on by natural gas and petroleum oil. The latter has been, until now, the main resource for raw materials and the energy supply for the private sector. Due to its very benefi cial properties in terms of chemical synthesis processes, only a minor proportion of approximately 10% of this plentiful resource is used for such purposes, whereas 90% is utilized for energy and transport. With regard to the increasing population and energy demand and oil consumption of developing countries, the limited availability of crude oil, and fi nancially motivated trading operations, the price of oil rises steadily and reached a peak of nearly 150 USD per barrel in 2008. It is assumed that most of the known so called supergiant oil fi elds cross the oil peak, which comes along with a decrease in the discovery of novel oil springs. Therefore, alternatives have to be introduced to reduce the dependency on these transient fossil fuels. But one has to keep in mind that alternative fuels and resources for chemical building blocks have to compete against classical fossil compounds. Currently, the prices of most bulk and specialty chemicals are too low for biotechnological routes to compete. It is estimated that competition begins at feedstock prices above $2 per kilogram. Nevertheless, the share of biotechnologically produced chemicals is expected to increase from approximately 5% to 20% in the year 2010. The greatest impact is expected in the segment of fi ne and specialty chemicals with up to 60% of the products based on biotechnological processes. Interfacing with green biotechnology for enhanced crop properties and increased plant breeding can be expected. More attention is paid to the lignocellulose feedstock, which is extensively discussed and examined to be used as a sustainable raw material for ethanol production. In addition, a few current trends focus on C1 carbonic compounds such as methanol and methane, fatty acids and glycerol from plant oil, and whey based substrates that can be used as input compounds for a chemical refi nery. If one has a closer look to current activities of oil companies, it is obvious that the time is changing. Several efforts to utilize sustainable biomass feedstocks for recovering fuel substitutes were carried out by these companies. But the