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Author: Jean Olivier Publisher: ISBN: Category : Languages : fr Pages :
Book Description
Les matériaux moléculaires se démarquent des autres types de matériaux par leur capacité à présenter plusieurs fonctions dans le domaine de l'optique, de la conductivité électronique ou du magnétisme. Avec l'utilisation de donneurs organiques dérivés de tétrathiafulvalène (TTF), nous avons voulu élaborer de nouveaux matériaux associant plusieurs de ces propriétés. Après la synthèse de ces molécules, deux axes de recherche ont été développés : d'une part, nous nous sommes attachés à oxyder ces dérivés par électrocristallisation afin d'induire des propriétés de conduction électronique dans les matériaux, et d'autre part ils ont été utilisés dans des complexes de métaux de transitions paramagnétiques. La diffraction par les rayons X a été déterminante dans l'étude de la structure et l'analyse des propriétés de nos composés. L'une de nos molécule en particulier a montré une faculté étonnante à s'organiser en chaînes et a permis la réalisation de polymères cristallins présentant en même temps des propriétés magnétiques et de conductivité électronique.
Author: Jean Olivier Publisher: ISBN: Category : Languages : fr Pages :
Book Description
Les matériaux moléculaires se démarquent des autres types de matériaux par leur capacité à présenter plusieurs fonctions dans le domaine de l'optique, de la conductivité électronique ou du magnétisme. Avec l'utilisation de donneurs organiques dérivés de tétrathiafulvalène (TTF), nous avons voulu élaborer de nouveaux matériaux associant plusieurs de ces propriétés. Après la synthèse de ces molécules, deux axes de recherche ont été développés : d'une part, nous nous sommes attachés à oxyder ces dérivés par électrocristallisation afin d'induire des propriétés de conduction électronique dans les matériaux, et d'autre part ils ont été utilisés dans des complexes de métaux de transitions paramagnétiques. La diffraction par les rayons X a été déterminante dans l'étude de la structure et l'analyse des propriétés de nos composés. L'une de nos molécule en particulier a montré une faculté étonnante à s'organiser en chaînes et a permis la réalisation de polymères cristallins présentant en même temps des propriétés magnétiques et de conductivité électronique.
Author: Jose M. Palomo Publisher: MDPI ISBN: 3038978469 Category : Science Languages : en Pages : 154
Book Description
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.
Author: O. Kahn Publisher: Springer Science & Business Media ISBN: 9780792341536 Category : Science Languages : en Pages : 678
Book Description
Molecular magnetism is a new field of research dealing with the synthesis and study of the physical properties of molecular assemblies involving open-shell units. It is essentially interdisciplinary, joining together organic, organometallic and inorganic chemists, as well as theoreticians, physicists and materials scientists. At the core of research into molecular magnetism lie design and synthesis of new molecular assemblies exhibiting bulk properties such as long-range magnetic ordering or bistability with an hysteresis effect, which confers a memory effect on the system. In such terms, magnetism may be considered a supramolecular function. The first eight contributions to this volume present the state of the art in organic supramolecular chemistry, emphasising interlocked systems and molecular trees. The following six articles are devoted to molecular materials constructed from organic radicals and transition metal units. Molecular bistability is then focused on, followed by metal-organic and coordination magnetic materials. A new approach to nano-sized particles closes the work.
Author: Wolfgang Linert Publisher: Springer Science & Business Media ISBN: 3709160189 Category : Science Languages : en Pages : 222
Book Description
The book deals with recent scientific highlights on molecular magnetism in Europe. Molecular magnetism is a new interdisciplinary discipline gathering together chemists and physicists, theoreticians and experimentalists. The book intends to provide the reader with documented answers to many current questions: How can chemists use soft conditions to transform molecules in light and transparent magnets. How does a molecular system can behave as a single molecule magnet. How to combine several functions in the same molecular system. How light can be used to switch molecular magnetic properties. How can molecules be used for ultimate high density information storage or in quantum computing. What kind of methods do physicists develop and use to explore these new properties of matter. What kind of concepts and calculations can be provided for theoreticians to design new objects and to better understand the field and to enlarge its exciting developments.
Author: Jean-Pierre Launay Publisher: Oxford University Press, USA ISBN: 0199297789 Category : Science Languages : en Pages : 511
Book Description
The purpose of this book is to provide the reader with essential keys to a unified understanding of the rapidly expanding field of molecular materials and devices: electronic structures and bonding, magnetic, electrical and photo-physical properties, and the mastering of electrons in molecular electronics. Chemists will discover how basic quantum concepts allow us to understand the relations between structures, electronic structures, and properties of molecular entities and assemblies, and to design new molecules and materials. Physicists and engineers will realize how the molecular world fits in with their need for systems flexible enough to check theories or provide original solutions to exciting new scientific and technological challenges. The non-specialist will find out how molecules behave in electronics at the most minute, sub-nanosize level. The comprehensive overview provided in this book is unique and will benefit undergraduate and graduate students in chemistry, materials science, and engineering, as well as researchers wanting a simple introduction to the world of molecular materials.
Author: Jean Olivier
Author: Jean Olivier
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Author: Jose M. Palomo
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Author: O. Kahn
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Author: Wolfgang Linert
Author: J. C. Maso
Author: Jean-Pierre Launay