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Asymmetric and Selective Biocatalysis

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ISBN: 9783038978466 9783038978473 Year: Pages: 154 DOI: 10.3390/books978-3-03897-847-3 Language: eng
Publisher: MDPI - Multidisciplinary Digital Publishing Institute
Subject: Science (General) --- Chemistry (General)
Added to DOAB on : 2019-06-26 09:16:44
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This Issue contains one communication, six articles, and two reviews. The communication from Paola Vitale et al. represents a work where whole cells were used as biocatalysts for the reduction of optically active chloroalkyl arylketones followed by a chemical cyclization to give the desired heterocycles. Among the various whole cells screened (baker’s yeast, Kluyveromyces marxianus CBS 6556, Saccharomyces cerevisiae CBS 7336, Lactobacillus reuteri DSM 20016), baker’s yeast provided the best yields and the highest enantiomeric ratios (95:5) in the bioreduction of the above ketones. In this respect, valuable chiral non-racemic functionalized oxygen-containing heterocycles (e.g., (S)-styrene oxide, (S)-2-phenyloxetane, (S)-2-phenyltetrahydrofuran), amenable to be further elaborated on, can be smoothly and successfully generated from their prochiral precursors. Studies about pure biocatalysts with mechanistical studies, application in different reactions, and new immobilization methods for improving their stability were reported in five different articles. The article by Su-Yan Wang et al. describes the cloning, expression, purification, and characterization of an N-acetylglucosamine 2-epimerase from Pedobacter heparinus (PhGn2E). For this, several N-acylated glucosamine derivatives were chemically synthesized and used to test the substrate specificity of the enzyme. The mechanism of the enzyme was studied by hydrogen/deuterium NMR. The study at the anomeric hydroxyl group and C-2 position of the substrate in the reaction mixture confirmed the epimerization reaction via ring-opening/enolate formation. Site-directed mutagenesis was also used to confirm the proposed mechanism of this interesting enzyme. The article by Forest H. Andrews et al. studies two enzymes, benzoylformate decarboxylase (BFDC) and pyruvate decarboxylase (PDC), which catalyze the non-oxidative decarboxylation of 2-keto acids with different specificity. BFDC from Pseudomonas putida exhibited very limited activity with pyruvate, whereas the PDCs from S. cerevisiae or from Zymomonas mobilis showed virtually no activity with benzoylformate (phenylglyoxylate). After studies using saturation mutagenesis, the BFDC T377L/A460Y variant was obtained, with 10,000-fold increase in pyruvate/benzoylformate. The change was attributed to an improvement in the Km value for pyruvate and a decrease in the kcat value for benzoylformate. The characterization of the new catalyst was performed, providing context for the observed changes in the specificity. The article by Xin Wang et al. compares two types of biocatalysts to produce D-lysine L-lysine in a cascade process catalyzed by two enzymes: racemase from microorganisms that racemize L-lysine to give D,L-lysine and decarboxylase that can be in cells, permeabilized cells, and the isolated enzyme. The comparison between the different forms demonstrated that the isolated enzyme showed the higher decarboxylase activity. Under optimal conditions, 750.7 mmol/L D-lysine was finally obtained from 1710 mmol/L L-lysine after 1 h of racemization reaction and 0.5 h of decarboxylation reaction. D-lysine yield could reach 48.8% with enantiomeric excess (ee) of 99%. In the article by Rivero and Palomo, lipase from Candida rugosa (CRL) was highly stabilized at alkaline pH in the presence of PEG, which permitted its immobilization for the first time by multipoint covalent attachment on different aldehyde-activated matrices. Different covalent immobilized preparation of the enzyme was successfully obtained. The thermal and solvent stability was highly increased by this treatment, and the novel catalysts showed high regioselectivity in the deprotection of per-O-acetylated nucleosides. The article by Robson Carlos Alnoch et al. describes the protocol and use of a new generation of tailor-made bifunctional supports activated with alkyl groups that allow the immobilization of proteins through the most hydrophobic region of the protein surface and aldehyde groups that allows the covalent immobilization of the previously adsorbed proteins. These supports were especially used in the case of lipase immobilization. The immobilization of a new metagenomic lipase (LipC12) yielded a biocatalyst 3.5-fold more active and 5000-fold more stable than the soluble enzyme. The PEGylated immobilized lipase showed high regioselectivity, producing high yields of the C-3 monodeacetylated product at pH 5.0 and 4 °C. Hybrid catalysts composed of an enzyme and metallic complex are also treated in this Special Issue. The article by Christian Herrero et al. describes the development of the Mn(TpCPP)-Xln10A artificial metalloenzyme, obtained by non-covalent insertion of Mn(III)-meso-tetrakis(p-carboxyphenyl)porphyrin [Mn(TpCPP), 1-Mn] into xylanase 10A from Streptomyces lividans (Xln10A). The complex was found able to catalyze the selective photo-induced oxidation of organic substrates in the presence of [RuII(bpy)3]2+ as a photosensitizer and [CoIII(NH3)5Cl]2+ as a sacrificial electron acceptor, using water as oxygen atom source. The two published reviews describe different subjects with interest in the fields of biocatalysis and mix metallic-biocatalysis, respectively. The review by Anika Scholtissek et al. describes the state-of-the-art regarding ene-reductases from the old yellow enzyme family (OYEs) to catalyze the asymmetric hydrogenation of activated alkenes to produce chiral products with industrial interest. The dependence of OYEs on pyridine nucleotide coenzyme can be avoided by using nicotinamide coenzyme mimetics. In the review, three main classes of OYEs are described and characterized. The review by Yajie Wang and Huimin Zhao highlights some of the recent examples in the past three years that combine transition metal catalysis with enzymatic catalysis. With recent advances in protein engineering, catalyst synthesis, artificial metalloenzymes, and supramolecular assembly, there is great potential to develop more sophisticated tandem chemoenzymatic processes for the synthesis of structurally complex chemicals. In conclusion, these nine publications give an overview of the possibilities of different catalysts, both traditional biocatalysts and hybrids with metals or organometallic complexes to be used in different processes—particularly in synthetic reactions—under very mild reaction conditions.

Siloxane-Based Polymers

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ISBN: 9783038971252 / 9783038971269 Year: Pages: 188 DOI: 10.3390/books978-3-03897-126-9 Language: eng
Publisher: MDPI - Multidisciplinary Digital Publishing Institute
Subject: Technology (General) --- Chemical Engineering
Added to DOAB on : 2019-08-28 11:21:27
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This book, a collection of 12 original contributions and 4 reviews, provides a selection of the most recent advances in the preparation, characterization, and applications of polymeric nanocomposites comprising nanoparticles. The concept of nanoparticle-reinforced polymers came about three decades ago, following the outstanding discovery of fullerenes and carbon nanotubes. One of the main ideas behind this approach is to improve the matrix mechanical performance. The nanoparticles exhibit higher specific surface area, surface energy, and density compared to microparticles and, hence, lower nanofiller concentrations are needed to attain properties comparable to, or even better than, those obtained by conventional microfiller loadings, which facilitates processing and minimizes the increase in composite weight. The addition of nanoparticles into different polymer matrices opens up an important research area in the field of composite materials. Moreover, many different types of inorganic nanoparticles, such as quantum dots, metal oxides, and ceramic and metallic nanoparticles, have been incorporated into polymers for their application in a wide range of fields, ranging from medicine to photovoltaics, packaging, and structural applications.

Keywords

fabrication --- multielectrode array (MEA) --- PDMS --- PDMS etching --- plateau-shaped electrode --- recessed electrode --- spinal cord signal recording --- underexposure --- organosilane --- quartz microcrystal --- encapsulant --- refractive index --- thermal conductivity --- poly(dimethylsiloxanes) --- surface modification --- nanosilica --- diethyl carbonate --- carbon content --- morphology --- coatings --- fillers --- hybrid hydrogel --- MAPOSS --- mechanical properties --- swelling --- drug release --- dental resin --- methacryl POSS --- shrinkage --- hardness --- scratch resistance --- ceramizable silicone rubber --- borate --- halloysite --- composite --- ceramizable mechanism --- polysiloxanes --- mortar --- basalt fibre --- roughness --- surface free energy --- poly(ethylene glycol) (PEG) --- hydrophilic --- non-releasable --- polydimethylsiloxane --- coatings --- cross-linking --- surface --- amphiphilic --- anti-bioadhesion --- hyperbranched poly(methylhydrosiloxanes) --- hydrolytic polycondensation --- 29Si-NMR --- topology of polysiloxane chains --- polyhedral oligomeric silsesquioxanes --- high molecular weight --- nanoparticles --- PDMS --- sugar templating process --- 3D porous network --- thermal stability --- TG-FTIR --- X-ray (Micro-CT) microtomography --- sol-gel --- hybrids --- chlorogenic acid --- bioactivity --- FTIR --- TG --- polysiloxanes --- theranostics --- drug delivery --- nanomedicine --- PDMS --- silicon --- ultraviolet (UV) curable coatings --- low surface energy materials --- fluorinated siloxane resin

Carotenoids

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ISBN: 9783039218646 / 9783039218653 Year: Pages: 168 DOI: 10.3390/books978-3-03921-865-3 Language: eng
Publisher: MDPI - Multidisciplinary Digital Publishing Institute
Subject: Science (General) --- Biology
Added to DOAB on : 2020-01-07 09:08:26
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Carotenoids are a group of natural pigments, consisting of more than 750 compounds. They are mostly yellow, orange, or red in color, due to the system of conjugated double bonds. This structural element is also responsible for the good antioxidant properties of many carotenoids. Carotenoids have shown numerous biological activities (not only as provitamin A), e.g., preventive properties of fruits and vegetables. As lipophilic compounds, their uptake and storage in the body are dependent on various conditions. In vitro and in vivo data showed stimulating and inhibitory effects of matrix compounds on bioaccessibility and bioavailability of carotenoids.

Keywords

?-carotene --- lycopene --- antioxidants --- free radicals --- ageing --- fruit --- vegetables --- ?-carotene --- HIV --- nelfinavir --- interaction --- pharmacokinetics --- carotenoids --- astaxanthin --- oxidative stress --- antioxidant --- chelating compound --- metal ions --- antireductant --- antiradical --- cationic lipid --- carotenoid --- antisense oligonucleotide --- exon skipping --- Duchenne muscular dystrophy --- ?-carotene --- lutein --- chlorophyll --- spent coffee grounds --- soil amendment --- lettuce --- accelerated solvent extraction --- pressurized fluid extraction --- ethanol --- carrots --- ?-carotene --- antioxidants --- marine carotenoids --- inflammation --- oxidative stress --- cardiovascular disease --- flavonoids --- carotenoids --- antioxidant synergism --- antioxidant antagonism --- free radical kinetics --- dye-sensitized solar cells --- carotenoid and chlorophyll derivatives --- singlet-triplet annihilation --- carotenoids --- xanthophylls --- fluorocarotenoids --- chlorocarotenoids --- bromocarotenoids --- iodocarotenoids --- silicon carotenoids --- nitrogen carotenoids --- sulfur carotenoids --- selenium carotenoids --- iron carotenoids --- carotenoids --- xanthophylls --- cancer chemoprevention --- mechanisms --- B16F10 --- ?-carotene --- PC-3 --- SK-Hep-1 --- VEGF --- oxidative stress --- ROS --- RNS --- antioxidants --- carotenoids --- cardiovascular disease --- carotenoids --- hydrophilic --- esterification --- PEG conjugates --- cycloaddition --- carotenoid --- stability --- feed processing --- storage --- carotenoids --- extraction --- solubility --- injection solvent --- liquid chromatography

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