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Artículos de revistas sobre el tema "Chimical reactivity"

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Autor: Grafiati
Publicado: 4 de mayo de 2024

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1

Verrier, Charlie, Sébastien Carret y Jean-François Poisson. "Ynol Ethers: Synthesis and Reactivity". CHIMIA International Journal for Chemistry 70, n.º 1 (24 de febrero de 2016): 93–96. http://dx.doi.org/10.2533/chimia.2016.93.

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2

Grimmel, Stephanie A. y Markus Reiher. "On the Predictive Power of Chemical Concepts". CHIMIA International Journal for Chemistry 75, n.º 4 (28 de abril de 2021): 311–18. http://dx.doi.org/10.2533/chimia.2021.311.

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Many chemical concepts can be well defined in the context of quantum chemical theories. Examples are the electronegativity scale of Mulliken and Jaffé and the hard and soft acids and bases concept of Pearson. The sound theoretical basis allows for a systematic definition of such concepts. However, while they are often used to describe and compare chemical processes in terms of reactivity, their predictive power remains unclear. In this work, we elaborate on the predictive potential of chemical reactivity concepts, which can be crucial for autonomous reaction exploration protocols to guide them by first-principles heuristics that exploit these concepts.
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3

Togni, Antonio. "70 Years Ferrocene!" CHIMIA International Journal for Chemistry 75, n.º 9 (15 de septiembre de 2021): 805–6. http://dx.doi.org/10.2533/chimia.2021.805.

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Some of the most important features of ferrocene chemistry – structure, reactivity, redox properties, and applications – are presented. Their value in the context of conveying many fundamental aspects of molecular chemistry is considered.
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4

Monkcom, Emily C., Pradip Ghosh, Emma Folkertsma, Hidde A. Negenman, Martin Lutz y Robertus J. M. Klein Gebbink. "Bioinspired Non-Heme Iron Complexes: The Evolution of Facial N, N, O Ligand Design". CHIMIA International Journal for Chemistry 74, n.º 6 (24 de junio de 2020): 450–66. http://dx.doi.org/10.2533/chimia.2020.450.

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Iron-containing metalloenzymes that contain the 2-His-1-Carboxylate facial triad at their active site are well known for their ability to activate molecular oxygen and catalyse a broad range of oxidative transformations. Many of these reactions are synthetically challenging, and developing small molecular iron-based catalysts that can achieve similar reactivity and selectivity remains a long-standing goal in homogeneous catalysis. This review focuses on the development of bioinspired facial N,N,O ligands that model the 2-His-1-Carboxylate facial triad to a greater degree of structural accuracy than many of the polydentate N-donor ligands commonly used in this field. By developing robust, well-defined N,N,O facial ligands, an increased understanding could be gained of the factors governing enzymatic reactivity and selectivity.
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5

Catalán, Silvia, Sócrates B. Munoz y Santos Fustero. "Unique Reactivity of Fluorinated Molecules with Transition Metals". CHIMIA International Journal for Chemistry 68, n.º 6 (26 de junio de 2014): 382–409. http://dx.doi.org/10.2533/chimia.2014.382.

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6

Shetaya, Waleed H. y Jen-How Huang. "Reactivity of Soil Mercury by Stable Isotope Dilution". CHIMIA International Journal for Chemistry 74, n.º 1 (26 de febrero de 2020): 58. http://dx.doi.org/10.2533/chimia.2020.58.

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7

Nóvoa, Luis, Laura Trulli, Alejandro Parra y Mariola Tortosa. "Copper, Boron and Vinyl Epoxides: from 1,4-Diols to Cyclopropylboronates". CHIMIA International Journal for Chemistry 74, n.º 11 (25 de noviembre de 2020): 852–56. http://dx.doi.org/10.2533/chimia.2020.852.

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Herein we describe the reactivity found between vinyl epoxides and catalytically generated copper-boryl complexes. By tuning the substituents of the alkene and/or the reaction conditions, 1,4-diols, allylic alcohols or cyclopropylboronates can be prepared. The stereochemical information of the vinyl epoxide is transferred to the products with high levels of stereocontrol.
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8

Jorner, Kjell. "Putting Chemical Knowledge to Work in Machine Learning for Reactivity". CHIMIA 77, n.º 1/2 (22 de febrero de 2023): 22. http://dx.doi.org/10.2533/chimia.2023.22.

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Machine learning has been used to study chemical reactivity for a long time in fields such as physical organic chemistry, chemometrics and cheminformatics. Recent advances in computer science have resulted in deep neural networks that can learn directly from the molecular structure. Neural networks are a good choice when large amounts of data are available. However, many datasets in chemistry are small, and models utilizing chemical knowledge are required for good performance. Adding chemical knowledge can be achieved either by adding more information about the molecules or by adjusting the model architecture itself. The current method of choice for adding more information is descriptors based on computed quantum-chemical properties. Exciting new research directions show that it is possible to augment deep learning with such descriptors for better performance in the low-data regime. To modify the models, differentiable programming enables seamless merging of neural networks with mathematical models from chemistry and physics. The resulting methods are also more data-efficient and make better predictions for molecules that are different from the initial dataset on which they were trained. Application of these chemistry-informed machine learning methods promise to accelerate research in fields such as drug design, materials design, catalysis and reactivity.
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9

Meyet, Jordan, Mark A. Newton, Jeroen A. van Bokhoven y Christophe Copéret. "Molecular Approach to Generate Cu(II) Sites on Silica for the Selective Partial Oxidation of Methane". CHIMIA International Journal for Chemistry 74, n.º 4 (29 de abril de 2020): 237–40. http://dx.doi.org/10.2533/chimia.2020.237.

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The selective partial oxidation of methane to methanol remains a great challenge in the field of catalysis. Cu-exchanged zeolites are promising materials, directly and selectively converting methane to methanol with high yield under cyclic conditions. However, the economic viability of these aluminosilicate materials for potential industrial applications remains a challenge. Exploring copper supported on non-microporous oxide supports and rationalising the structure/reactivity relationships extends the scope of material investigation and opens new possibilities. Recently, copper on alumina was demonstrated to be active and selective for the partial oxidation of methane. This work aims to explore the formation of well-defined Cu(II) oxo species on silica via surface organometallic chemistry and examines their reactivity for the selective transformation of methane to methanol. Isolated Cu(II) sites were generated via grafting of a tailored molecular precursor. Activation under oxidative conditions and subsequent removal of organic moieties from the grafted copper centres led to the formation of small copper (II) oxide clusters, which are active in the partial oxidation of methane under mild conditions, albeit significantly less efficient than the corresponding isolated Cu(II) sites on alumina.
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10

Robert, Emma G. L. y Jérôme Waser. "Silylium-Catalyzed Activation of Donor- Acceptor Strained Rings and Annulation with Indoles". CHIMIA 78, n.º 4 (24 de abril de 2024): 234–37. http://dx.doi.org/10.2533/chimia.2024.234.

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Leveraging the unique reactivity profile of donor-acceptor aminocyclopropanes and cyclobutanes allows the preparation of complex nitrogen-substituted molecules. While most reports focus on donor-acceptor strained rings with two geminal carbonyl groups as acceptors, mono carbonyl acceptor systems, despite their synthetic relevance, have been considerably less studied. Herein we describe catalytic annulation reactions ofaminocyclopropane and aminocyclobutane monoesters employing silylium catalysis to activate these less reactive donor-acceptor systems.
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11

Tortoreto, Cecilia, Thierry Achard, Martina Austeri, Walid Zeghida y Jérôme Lacour. "Original Reactivity of α-Diazo-β- ketoesters Catalyzed by CpRu Complexes". CHIMIA International Journal for Chemistry 68, n.º 4 (30 de abril de 2014): 243–47. http://dx.doi.org/10.2533/chimia.2014.243.

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12

Borsari, Chiara, Alexandra Ioana Corfu y Paola Conti. "Understanding Intrinsic Warhead Reactivity and Cysteine Druggability in Covalent Drug Discovery". CHIMIA 77, n.º 5 (31 de mayo de 2023): 349. http://dx.doi.org/10.2533/chimia.2023.349.

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13

Housecroft, Catherine E., Cornelia G. Palivan, Karl Gademann, Wolfgang Meier, Michel Calame, Viktoria Mikhalevich, Xiaoyan Zhang et al. "'Active Surfaces' as Possible Functional Systems in Detection and Chemical (Bio) Reactivity". CHIMIA International Journal for Chemistry 70, n.º 6 (29 de junio de 2016): 402–12. http://dx.doi.org/10.2533/chimia.2016.402.

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14

Griesbeck, Axel y Seyma Bozkus. "Spin Photochemistry: Electron Spin Multiplicity as a Tool for Reactivity and Selectivity Control". CHIMIA 75, n.º 10 (11 de octubre de 2021): 868. http://dx.doi.org/10.2533/chimia.2021.868.

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Spin chemistry involving small organic molecules without heavy atoms is highly sensitive to spin-orbit-coupling (SOC) modulating biradical conformation as well as hyperfine coupling (HFC) modulating magnetic isotope interactions. Several easily available reaction properties such as chemo-, regio-, and diastereoselectivity as well as quantum yields serve as analytical tools to follow intersystem crossing dynamics and allows titrating spin selectivities.
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15

Chang Chien, Tzu-Chin y Murielle F. Delley. "Interfacial Chemistry and Catalysis of Inorganic Materials". CHIMIA 78, n.º 1/2 (28 de febrero de 2024): 7–12. http://dx.doi.org/10.2533/chimia.2024.7.

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Heterogeneous catalysis is essential to most industrial chemical processes. To achieve a better sustainability of these processes we need highly efficient and highly selective catalysts that are based on earth-abundant materials rather than the more conventional noble metals. Here, we discuss the potential of inorganic materials as catalysts for chemical transformations focusing in particular on the promising transition metal phosphides and sulfides. We describe our recent and current efforts to understand the interfacial chemistry of these materials that governs catalysis, and to tune catalytic reactivity by controlled chemical modification of the material surfaces and by use of interfacial electric fields.
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16

Di Battista, Veronica, Agnieszka Gajewicz-Skrętna, Kai Werle, Lars Michael Skjolding, Nina Jeliazkova, Anders Baun y Wendel Wohlleben. "24 Safe-by-Design Guidance for Multicomponent Nanostructured Materials (MCNM): Heavy Metals Containing Perovskites". Annals of Work Exposures and Health 67, Supplement_1 (1 de mayo de 2023): i46. http://dx.doi.org/10.1093/annweh/wxac087.111.

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Abstract Industry develops increasingly complex and advanced materials while incorporating the Safe-by-Design (SbD) concept into the R&D goals. Within HARMLESS (EU H2020), we use concepts of similarity for the risk screening during the SbD iterations. We rely predominantly on Novel Approach Methodologies (NAMs) due to ethical reasons, speed and parallel testing of several SbD versions. In general, aerosolization of nanostructured materials leading to inhalation of respirable fraction is considered one of the most important routes of exposure. Depending on the physicochemical properties of the materials, MCNM may either dissolve or persist within the lung. We selected in chimico NAMs (i.e., biodissolution in lung simulant fluids and surface reactivity assay) to understand how the properties of six different perovskites, intended to be used in the automotive catalysis sector, are connected to inhalation hazard endpoints. They all share a common concern: Co and Ni (heavy metals) in the structure. We found that the composition and surface properties play an important role in determining the particles fate upon inhalation, influencing metals bioavailability and the induced oxidative damage. At pH 7.5 and 4.5 simulant fluids, both relevant for pulmonary clearance, dissolution depended minimally on the noble metal doping but rather on the %weight of heavy metal in the structure. Furthermore, high surface reactivity was observed for all perovskites. Interestingly, the induced oxidative damage was correlating with the Ni %weight, surface thickness and Ni oxidation state. The results allowed us to rank different SbD versions against benchmarks, providing Safe-by-Design guidance on multicomponent, heavy metals-containing perovskites.
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17

Logallo, Alessandra y Eva Hevia. "Tuning NaCo(II) Bimetallic Cooperativity to Perform Co–H Exchange / C–F Bond Activation Processes in Polyfluoroarenes". CHIMIA 78, n.º 4 (24 de abril de 2024): 238–42. http://dx.doi.org/10.2533/chimia.2024.238.

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Recent advances in cooperative chemistry have shown the potential of heterobimetallic complexes combining an alkali-metal with an earth abundant divalent transition metal for the functionalisation of synthetically relevant aromatic molecules via deprotonative metalation. Pairing sodium with cobalt (II), here we provide an overview of the reactivity of bimetallic [NaCo(HMDS)3] [HMDS = N(SiMe3)2] towards C-H and C-F functionalisation of a wide range of perfluorinated molecules. These studies also uncover the enormous potential of this heterobimetallic base to perform Co-H exchanges with excellent selectivity and exceptional stoichiometric control as well as shedding light on the key role played by the alkali-metal.
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18

Ranocchiari, Marco y Jeroen Anton van Bokhoven. "Synthesis and Reactivity of Zn–Biphenyl Metal–Organic Frameworks, Introducing a Diphenylphosphino Functional Group". CHIMIA International Journal for Chemistry 67, n.º 6 (26 de mayo de 2013): 397–402. http://dx.doi.org/10.2533/chimia.2013.397.

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19

Toscano, Jutta. "Rotational-state-selected Carbon Astrochemistry". CHIMIA 78, n.º 1/2 (28 de febrero de 2024): 40–44. http://dx.doi.org/10.2533/chimia.2024.40.

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The addition of individual quanta of rotational excitation to a molecule has been shown to markedly change its reactivity by significantly modifying the intermolecular interactions. So far, it has only been possible to observe these rotational effects in a very limited number of systems due to lack of rotational selectivity in chemical reaction experiments. The recent development of rotationally controlled molecular beams now makes such investigations possible for a wide range of systems. This is particularly crucial in order to understand the chemistry occurring in the interstellar medium, such as exploring the formation of carbon-based astrochemical molecules and the emergence of molecular complexity in interstellar space from the reaction of small atomic and molecular fragments.
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20

Bradbury, Christopher R., Christa Bünzli, Jianjun Zhao, Michel Carrara, Gabriela P. Kissling, Evren Aslan-Guerel y David J. Fermín. "Modulating the Reactivity of Electrode Surfaces by Electrostatic Assembly of Metal Nanoparticles and Quantum Dots". CHIMIA International Journal for Chemistry 62, n.º 10 (29 de octubre de 2008): 841–46. http://dx.doi.org/10.2533/chimia.2008.841.

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21

Pais, Joana M., Bruna Pereira, Filipe A. Almeida Paz, Susana M. Cardoso y Susana S. Braga. "Solid γ-Cyclodextrin Inclusion Compound with Gingerols, a Multi-Component Guest: Preparation, Properties and Application in Yogurt". Biomolecules 10, n.º 2 (22 de febrero de 2020): 344. http://dx.doi.org/10.3390/biom10020344.

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Gingerols from the rhizome of fresh ginger (Zingiber officinale) were obtained by a simple extraction, followed by purification. The gingerols extract was composed of 6-gingerol (54%), 8-gingerol (20%), and 10-gingerol (26%). It was included into γ-cyclodextrin by classic co-dissolution procedures. Solid-state characterisation of γ-cyclodextrin·gingerols shows that this inclusion compound features 1:1 host-to-guest stoichiometry and that it is a microcrystalline powder with a crystalline cell that belongs to the tetragonal space group 4212, having the host molecules stacked in infinite channels where the gingerols are accommodated. In chimico studies with ABTS•+ scavenging, NO• scavenging, β-carotene peroxidation, and 5-LOX inhibition show that γ-cyclodextrin is a suitable carrier for gingerols, because it does not alter their reactivity towards these substances. Yogurt was tested as a matrix for the incorporation of gingerols and γ-cyclodextrin·gingerols into foodstuff. The colour of the fortified yogurt suffered little alterations. In the case of yogurt with the inclusion compound, γ-cyclodextrin·gingerols, as fortificant, these alterations were not perceptible to the naked eye. Moreover, yogurt with γ-cyclodextrin·gingerols showed a good antioxidant activity, thus being suitable for use in nutraceutical applications.
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22

Weymuth, Thomas y Markus Reiher. "Immersive Interactive Quantum Mechanics for Teaching and Learning Chemistry". CHIMIA International Journal for Chemistry 75, n.º 1 (28 de febrero de 2021): 45–49. http://dx.doi.org/10.2533/chimia.2021.45.

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The impossibility of experiencing the molecular world with our senses hampers teaching and understanding chemistry because very abstract concepts (such as atoms, chemical bonds, molecular structure, reactivity) are required for this process. Virtual reality, especially when based on explicit physical modeling (potentially in real time), offers a solution to this dilemma. Chemistry teaching can make use of advanced technologies such as virtual-reality frameworks and haptic devices. We show how an immersive learning setting could be applied to help students understand the core concepts of typical chemical reactions by offering a much more intuitive approach than traditional learning settings. Our setting relies on an interactive exploration and manipulation of a chemical system; this system is simulated in real-time with quantum chemical methods, and therefore, behaves in a physically meaningful way.
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23

Vallapurackal, Jaicy. "Towards the Directed Evolution of Artificial Metalloenzymes". CHIMIA International Journal for Chemistry 75, n.º 4 (28 de abril de 2021): 257–60. http://dx.doi.org/10.2533/chimia.2021.257.

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Artificial metalloenzymes (ArMs) are a class of enzymes holding great promise. In contrast to natural enzymes, the core of ArMs is a synthetic metallocofactor, with potential for bio-orthogonal reactivity, incorporated within a host protein. Next to chemical optimization of the metallocofactor, genetic optimization of the protein allows the further improvement of the ArM. Genetic optimization through directed evolution requires extensive screening of a large sequence-scape to enable the optimization of a desired phenotype. The process is however mostly limited by the throughput of the tools and methods available for screening. In recent years, versatile methods based on droplet microfluidics have been developed to address the need for higher throughput. This article aims to give an introduction into ArMs and the recent technological developments allowing high-throughput directed evolution of enzymes.
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24

Zhang, Jiayu y Mónica H. Pérez-Temprano. "Intramolecular C(sp3)–H Bond Amination Strategies for the Synthesis of Saturated N-containing Heterocycles". CHIMIA International Journal for Chemistry 74, n.º 11 (25 de noviembre de 2020): 895–903. http://dx.doi.org/10.2533/chimia.2020.895.

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The selective functionalization of C(sp3)–H bonds via intramolecular amination reactions represents a very attractive strategy for the construction of saturated N-containing heterocycles (SNHets). Over the past de- cades, the chemical community has devoted its efforts towards expanding the synthetic toolbox with the aim of facilitating access to these key fragments in a controllable, reproducible and efficient manner. This review covers selected examples of the most recent advances in intramolecular C(sp3)–N bond-forming reactions by three main approaches: (1) the Hofmann-Löffler-Freytag (HLF) reaction; (2) transition-metal-catalyzed nitrene C(sp3)–H inser- tion; and (3) transition-metal-catalyzed ligand-assisted C(sp3)–N bond-forming reactions via a reductive elimination step. We will discuss reactivity, selectivity and the major mechanistic insights into these transformations.
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25

Patra, Subrata, Vasiliki Valsamidou y Dmitry Katayev. "Simplifying Nitration Chemistry with Bench-stable Organic Nitrating Reagents". CHIMIA 78, n.º 1/2 (28 de febrero de 2024): 32–39. http://dx.doi.org/10.2533/chimia.2024.32.

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Nitro compounds play a crucial role in academia and industries, serving as building blocks for the synthesis of drugs, agrochemicals, and materials. Nitration, a fundamental process in organic synthesis, has undergone significant evolution since the 19th century. While electrophilic nitration dominates historically, recent decades have seen a focus on new reagents and their reactivity modes for achieving mild and robust synthesis of nitro compounds. Our group has a longstanding interest in developing cost-effective, readily available, recyclable nitrating reagents derived from organic scaffolds. These reagents serve as a controllable source of nitryl radical and nitronium ion species, enabling mild and practical nitration of hydrocarbons with exceptional functional group tolerance. This account details the development of nitrating reagents and their diverse applications in catalytic nitration across various classes of organic molecules.
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26

Tortajada, Andreu y Eva Hevia. "Uncovering the Untapped Potential of the Use of Sodium Amides for Regioselective Arene Functionalisation". CHIMIA 77, n.º 4 (26 de abril de 2023): 225. http://dx.doi.org/10.2533/chimia.2023.225.

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Alkali-metal amides have become key reagents in synthetic chemistry, with special focus in deprotonation reactions. Despite the higher reactivity found in the heavier sodium and potassium amides, their insolubility and low stability has favoured the use of the more soluble lithium analogues, converting them into the most used non-nucleophilic bases. Studying the coordination effects of Lewis donor molecules such as tridentate amine PMDETA (N,N,N’,N’’,N’’-pentamethyldiethylenetriamine) in combination with the sodium amide NaTMP (TMP = 2,2’,6,6’-tetramethylpiperidide), we have been able to unlock the use of these reagents for the functionalisation of arenes, i.e. the deuterium incorporation by hydrogen isotope exchange and the deprotonative borylation of unactivated arenes. These findings show how sodium amides are not just a simple more sustainable replacement of their lithium counterparts, but also that they can display significantly enhanced reactivities allowing for the development of new transformations.
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27

Masferrer-Rius, Eduard, Raoul M. Hopman, Jishai van der Kleij, Martin Lutz y Robertus J. M. Klein Gebbink. "On the Ability of Nickel Complexes Derived from Tripodal Aminopyridine Ligands to Catalyze Arene Hydroxylations". CHIMIA International Journal for Chemistry 74, n.º 6 (24 de junio de 2020): 489–94. http://dx.doi.org/10.2533/chimia.2020.489.

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The development of catalysts for the selective hydroxylation of aromatic C–H bonds is an essential challenge in current chemical research. The accomplishment of this goal requires the discovery of powerful metal-based oxidizing species capable of hydroxylating inert aromatic bonds in a selective manner, avoiding the generation of non-selective oxygen-centered radicals. Herein we show an investigation on the ability of nickel(ii) complexes supported by tripodal tetradentate aminopyridine ligands to catalyze the direct hydroxylation of benzene to phenol with H2O2 as oxidant. We have found that modifications on the ligand structure of the nickel complex do not translate into different reactivity, which differs from previous findings for nickel-based arene hydroxylations. Besides, several nickel(ii) salts have been found to be effective in the oxidation of aromatic C–H bonds. The use of fluorinated alcohols as solvent has been found to result in an increase in phenol yield; however, showing no more than two turn-overs per nickel. These findings raise questions on the nature of the oxidizing species responsible for the arene hydroxylation reaction.
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28

Dhankhar, Jyoti y Ilija Čorić. "Direct C–H Arylation". CHIMIA 76, n.º 9 (21 de septiembre de 2022): 777. http://dx.doi.org/10.2533/chimia.2022.777.

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Bonds between hydrogen and carbon atoms are the most frequent type of bonds in organic molecules. The ability to replace hydrogen atoms by making other types of bonds to carbon atoms can enable simpler access to complex organic molecules by substituting multistep synthetic sequences. The use of transition metal catalysts to activate C–H bonds is particularly attractive as it offers control over the reactivity and selectivity through catalyst design. However, such functionalization includes the difficult breaking of strong C–H bonds that are not activated by the presence of other groups. Additionally, the common presence of a number of C–H bonds in a molecule raises the issue of site-selectivity because differentiation of C–H bonds that are in sterically and electronically similar environments is a challenge. We discuss selected recent developments that are a part of the long-term research interest in mild and selective C–H activation reactions with a focus on the replacement of C–H bonds with C–aryl groups and an emphasis on the work of our group.
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29

Koichi, Shungo y Hans P. Lüthi. "Exploring Machine Learning Tools for the Prediction of the Stability of New Togni-type Reagents". CHIMIA International Journal for Chemistry 73, n.º 12 (18 de diciembre de 2019): 990–96. http://dx.doi.org/10.2533/chimia.2019.990.

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In the context of the prediction of the (in-)stability of chemical compounds using machine learning tools, we are often confronted with a basic issue: Whereas much information is available on stable (existing) compounds, little is known about compounds that might well exist, but that have not yet been successfully synthesized, or compounds that are inherently unstable (kinetically and thermodynamically). In the search for Togni-type reagents, many of them kinetically instable, the stability of the prospects can be assessed based on the transition state for the conversion to their non-hypervalent inactive isomer. In earlier work, we determined the barriers of conversion for over one-hundred reagents, still not enough information to train a tool such as a vector support machine. Here, instead, we focus on the early intermediate structures expressed along the isomerization pathway, i.e. transition state searches are replaced by finding (local) minima. Based on an array of 382 Togni-type reagents whose behaviour was known in advance, we show that it is possible to have the machine predict the intermediate form expressed. The approach introduced here can be used to make predictions on the stability and possibly also the reactivity of Togni-type reagents in general.
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30

Hevia, Eva. "Towards a Paradigm Shift in Polar Organometallic Chemistry". CHIMIA International Journal for Chemistry 74, n.º 9 (30 de septiembre de 2020): 681–88. http://dx.doi.org/10.2533/chimia.2020.681.

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Core tools of synthetic chemistry, polar organometallic reagents (typified by organolithium and Grignard reagents) are used worldwide for constructing compounds, especially aromatic compounds, which are ubiquitous in organic chemistry and thus in numerous commodities essential to everyday life. By isolation and characterisation of key organometallic intermediates, research in our group has led to the design of polar mixed-metal reagents imbued with synergistic effects that display chemical properties and reactivity profiles far exceeding the limits of traditional single-metal reagents. These studies have improved existing, or established new fundamentally important, synthetic methodologies based on either stoichiometric or catalytic reactions. Bimetallic cooperative effects have been demonstrated in an impressive array of important bond forming reactions including deprotonative metallation, transition metal-free C–C bond formation and metal–halogen exchange to name just a few. Towards greener, more sustainable, safer chemical transformations, our group has also pioneered the use of polar organometallic reagents under air and/or with water present using biorenewable solvents such as Deep Eutectic Solvents (DES) and 2-methyl THF. Herein we summarize some of our recent efforts in this intriguing area, which we believe can make inroads towards a step change in the practice and future scope of polar organometallic chemistry.
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31

Matile, Stefan. "Organic Chemistry for First Year Medical Students: Addressing the 'Grand Public'". CHIMIA International Journal for Chemistry 75, n.º 1 (28 de febrero de 2021): 27–32. http://dx.doi.org/10.2533/chimia.2021.27.

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Experiences from 20 years of teaching organic chemistry at the Medical School of the University of Geneva are recollected. Emphasis is on the question how to address a large audience without particular passion for chemistry. The key lesson learned is to offer a substantial justification for every topic right at the beginning, before the basics are covered. For instance, the course opens with vancomycin resistance, achieved by changing one functional group, even one atom into another, and introductory topics are then developed literally on the structure of a beautifully complex natural product (relation of molecules, functional groups and atoms, introduction of functional groups, the octet rule, hybridization, later on also peptide chemistry, stereochemistry, etc.). Tamiflu is launched right afterwards as a possible justification why medical students should learn reaction mechanisms, long before the concerned reaction, the transformation of an acetal into a hemiacetal, is discussed. Not all classical teaching topics are compatible with such ' relevance-triggered teaching ' (nomenclature certainly not, nor halogenoalkanes, aromatic substitutions, alkynes, most of alkenes, spectroscopy, etc.). Other topics deserve more attention, like the more complex cyclic structures of sugars and steroids in the structural part and carbonyl chemistry, including catalysis, as the center of the reactivity part of the course. Difficult to measure, such ' relevance-triggered ' course restructuring, inconceivable from a classical educational point of view, has been overall surprisingly well received, although definitely not by all students.
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32

Yeasmin, Sanjida, Bo Wu, Ahasan Ullah, Xueqiao Zhang y Li-Jing Cheng. "Enzyme-Free Glucose Monitoring Patch". ECS Meeting Abstracts MA2022-01, n.º 54 (7 de julio de 2022): 2489. http://dx.doi.org/10.1149/ma2022-01542489mtgabs.

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Monitoring of glucose levels in non-invasive biofluids, such as saliva and sweat, can advance personal health tracking. However, the approach remains challenging due to the low glucose concentration in saliva and sweat, about 100 times lower than in the blood. Commercial glucose sensors rely on glucose oxidase to measure blood glucose levels with enzyme reactions. The enzyme activity varies with pH, oxygen level, and temperature (more than 40ºC). Also, the method often suffers from cross-reactivity with other sugar molecules, such as maltose and xylose [1]. Thus, it is crucial to develop highly sensitive and stable non-enzymatic sensors for detecting glucose in non-invasive biological fluids. In this work, we present an enzyme-free, reagent-free electrochemical glucose monitoring patch based on a glucose imprinted polymer nanocomposite. The nanocomposite comprises redox-active chitosan-ferrocene (Cs-Fc) wrapped multi-walled carbon nanotubes (MWCNTs). The Cs-Fc is a polymer with covalently secured redox-active ferrocene, effectively preventing the out leakage of redox substances [2]. The incorporation of MWCNTs increases the surface area, conductivity, and electron transfer rate. The glucose imprinted layer was grown on the surface of the nanocomposite by electropolymerization of functional monomers o-phenylenediamine (o-PD) and 3-aminophenylboronic acid (APBA) in the presence of glucose templates. The successful removal of template molecules created glucose specific recognition sites in the polymer matrices. The sensor directly detected the presence of glucose upon their binding into these cavities. The electrochemical property of the modified sensor was characterized by cyclic voltammetry (CV) in a potential range of 0-0.5 V at a scan rate of 100 mVs-1 in 1x PBS (pH 7.4) solution. For glucose sensing, the sensor was immersed in a sample solution containing different glucose concentrations for 30 min. We have optimized the composition ratio and assay conditions for sensitive glucose detection. Preliminary results indicated a change in redox peak current of ~2.7 times relative to the control upon adding 1 mM glucose, as shown in Figure 1. The proposed glucose patch is label-free, reagentless, cost-effective, easy fabrication, and expected to be utilized for sensitive and selective glucose detection from sweat. References [1] Hwang, D.W., Lee, S., Seo, M. and Chung, T.D., 2018. Recent advances in electrochemical non-enzymatic glucose sensors–a review. Analytica chimica acta, 1033, pp.1-34. [2] Wu, B., Yeasmin, S., Liu, Y., and Cheng, L.J., 2022. Sensitive and selective electrochemical sensor for serotonin detection based on ferrocene-gold nanoparticles decorated multiwall carbon nanotubes. Sensors and Actuators B: Chemical, 354, p.131216. Figure 1
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33

"Thermochemical Reactivity of Metal Carbonates". CHIMIA 45, n.º 9 (25 de septiembre de 1991): 262. http://dx.doi.org/10.2533/chimia.1991.262.

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The thermochemical reactivity of alkaline earth metal and transition-metal carbonates is discussed. Emphasis is given to the dependence of degradation mechanisms and the concomitant formation of solid and volatile products on temperature range, gas atmosphere, and type of energy impact. The experimental findings comprise informative aspects, how immobilized inorganic carbon, i.e. as metal carbonate, can be converted by heterogeneous solid-state decompositions and/or in situ catalysis into inorganic solid products and into volatile organic carbon compounds.
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34

"Facing Glycoscience". CHIMIA 55, n.º 10 (31 de octubre de 2001): 839. http://dx.doi.org/10.2533/chimia.2001.839.

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This essay describes an approach facing some of the challenges of glycoscience, concentrating on the relation between structure and reactivity. This has resulted in new methods, precursors of carbohydrate-derived reactive intermediates, analysis of their reactivity, and application mostly in synthesis. It has also led to the design, synthesis, and use of enzyme inhibitors, and to novel carbohydrate mimics and nucleotide analogues.
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35

"Reactivity and Function of Macrocyclic Metal Complexes". CHIMIA 54, n.º 10 (25 de octubre de 2000): 574. http://dx.doi.org/10.2533/chimia.2000.574.

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The introduction of side chains into tetraazamacrocycles allows the preparation of metal complexes with functional properties. On the one hand donor groups at the end of the side chain can be used to control the coordination geometry of the metal ion. On the other hand reactive groups can be incorporated into the side chain and their reactivity can be enhanced by the fact that the group comes close to the metal ion (metal ion induced reaction). Finally the side chain can be used to covalently attach macrocyclic metal complexes to antibodies for diagnostic and therapeutic applications in nuclear medicine.
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36

"Reactivity of Allenes towards Iron Carbonyl Complexes". CHIMIA 48, n.º 9 (28 de septiembre de 1994): 362. http://dx.doi.org/10.2533/chimia.1994.362.

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A series of monosubstituted allenes was reacted with Fe2(CO)9 to give dinuclear iron-carbonyl complexes containing organic ligands derived either from monomeric or dimerized allene. A mechanism of formation is proposed based on isolated intermediates. These intermediates point to an allene dimerization via addition of a reactive allene iron complex to free allene. Unusual chemical shifts were observed for many resonances in the 1H- and 13C-NMR spectra of the new compounds.
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37

"Organic Chemistry at Chemically Resistant Polymer Surfaces: Modification of Surface Reactivity and Surface Properties". CHIMIA 44, n.º 10 (31 de octubre de 1990): 316. http://dx.doi.org/10.2533/chimia.1990.316.

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This contribution will describe strategies for carrying out surface-selective modification reactions of fluoropolymers at the solution-polymer surface interface. The effects of solvent, temperature, and reagent structure on reactivity and surface selectivity will be discussed. The objective of these modification reactions is to introduce versatile organic functional groups to the surfaces of chemically resistant polymer surfaces; chemical transformations of the functional groups can then be carried out without affecting the structure of the inert 'support' film. Surface properties of these film samples can, thus, be correlated with surface-chemical structure. The chemical reactivity of the surface functional groups, particularly the OH group, will be discussed in some detail. The thermal stability and thermal reconstruction path of one modified surface will be described; the correlation of coefficient of friction with surface structure will be discussed. The synthesis of a surface that was designed to spontaneously adhere to metal oxides will also be presented.
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38

"Snapshots". CHIMIA 55, n.º 10 (31 de octubre de 2001): 767. http://dx.doi.org/10.2533/chimia.2001.767.

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Reactive intermediates – their generation, characterization, and manipulation – is the central theme running through the research program in the Chen group. The range of chemical systems studied spans organic, organometallic, and physical chemistry. The inherently multidisciplinary work leads to new insights in chemical reactivity, as well as applications in fields as diverse as drug discovery, homogeneous catalysis, and combustion chemistry.
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39

Gatti, Carlo Edoardo. "TAVOLA PERIODICA SOTTO PRESSIONE: UNA PERIODICITA' DIVERSA ED UNA CHIMICA ESOTICA". Istituto Lombardo - Accademia di Scienze e Lettere - Incontri di Studio, 10 de octubre de 2019. http://dx.doi.org/10.4081/incontri.2019.552.

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Our general and operative notion of chemistry, that enabling us to describe and interpret the structural, bonding and reactivity properties of the various compounds, is essentially rooted in the periodicity of properties of their constituting elements. Periodicity drove the path towards the proposition of the periodic table of elements and its rationalization thanks to the gradually acquired knowledge on the atomic electronic structure. Atomic radii periodicity mirrors the periodicity of the electronic configurations of the atoms’ outermost shell. The changes in atomic radii differentiate the chemical properties, hence the structures and properties of the elemental solids and of their compounds. Yet, under an external pressure, such a fully rationalized scenario may drastically change. When an atom is compressed, its average electron density increases and its outermost electronic shell is the easiest one to compress. At 100 Giga Pascal (GPa), that is at 106 atmospheres, the change of the atomic radius along a period of the Periodic Table becomes much less evident and at 1000 GPa our classical notion of periodicity is completely lost. Under pressure, the energy due to the compression work made on a system adds up to its internal energy. With such an energy gain the system may reach regions of the potential energy surface which would not be otherwise accessible. The chemical bond nature may change, even radically, and new structures and bonding patterns, characterized by totally unexpected properties, become energetically stable and possible. For instance, sodium, which is a silvery-white, highly reactive metal, becomes a fully transparent insulator, while boron is turned into a partially ionic solid elemental phase because charge transfer takes place between differently clustered groups of boron atoms. The incredible chemical inertness of helium finally falls as it forms a stable compound with sodium, Na2He. Under a suitable pressure, compounds with unusual stoichiometry (Na3Cl2, Na2Cl, Na3Cl, NaCl3, NaCl7) may be observed, despite their formula would be immediately rejected if proposed by a student at any high-school or university exam, or new carbon allotropes may appear or the aromatic character of benzene may vanish. This new chemistry is usually predicted through ab-initio quantum mechanical methods and interpreted and rationalized with the most modern chemical bonding approaches. However, compounds anticipated in silico have then be reproduced experimentally in many cases, by using diamond anvil cells to synthesize them and a variety of in situ instrumental techniques to characterize them properly.
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40

"Zeolite Microcrystals as Hosts for Supramolecular Organization of Dye Molecules". CHIMIA 52, n.º 10 (28 de octubre de 1998): 525. http://dx.doi.org/10.2533/chimia.1998.525.

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Zeolite microcrystals can act as host for supramolecular organization of molecules, complexes, clusters, and quantum-size particles. They allow the design of precise and reversible functionalities. Techniques for arranging zeolite microcrystals of good quality and narrow size distribution as dense monograin layers on different substrates can be used to realize specific properties. The chemical reactivity between the intercalated molecules offers possibilities for in situ synthesis of molecular chains, clusters, and quantum-size particles, which might not be accessible otherwise. In some cases, guest-host reactivity must be considered. The reactivity of intercalated compounds with (small) molecules penetrating from the outside is an option for changing the composition of a material, i.e., molecules intercalated as monomers in a first step can be linked to form chains. New electronic structures are accessible either by specific geometrical arrangements made possible by the structure of the host and/or by explicitly involving its electronic properties. Some systems meet the conditions necessary for the occurrence of intrazeolite charge transport (ionic and electronic), realized by the guests in their ground state and in electronically excited states under high-vacuum conditions or in the presence of a solvent, depending on the composition and the structure of the material. In this article, we focus on organic dye molecules in the one-dimensional channels of zeolites with a hexagonal framework. This system consists of supramolecularly organized dye molecules. It is shown to provide fascinating possibilities for building an artificial antenna device which consists of highly concentrated monomeric dye molecules of up to 0.4M with a large Förster energy-transfer radius and a high luminescence quantum yield in an ideal geometrical arrangement of optimal size. Extremely fast electronic excitation-energy transport has been demonstrated by us in oxonine- and pyronine-dye-loaded zeolite L microcrystals. Many other highly organized dye-zeolite materials can be prepared, and they are expected to show a wide variety of challenging properties. We report on methods to distinguish between dye molecules which are inside of a microcrystal and those adsorbed on its outer surface, and we explain a demonstration experiment illustrating the intercalation of thionine into zeolite L and the thus resulting improved chemical stability of this dye.
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41

"About Bases and Superbases". CHIMIA 50, n.º 12 (18 de diciembre de 1996): 650. http://dx.doi.org/10.2533/chimia.1996.650.

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Butyllithium requires activation in order to become capable of abstracting a proton from weakly acidic hydrocarbons like cyclopropanes, simple olefins, or arenes. The addition of a stoichiometric amount of potassium tert-butoxide is a most effective means of enhancing the rate of a hydrogen/metal exchange process. The superbasic alkyllithium/potassium alcoholate mixtures are endowed not only with an unsurpassed reactivity but also with a surprisingly high selectivity as evidenced by a series of optionally site-selective arene metalations.
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42

"Increasing the Sustainability of Biocatalytic Processes". CHIMIA 76, n.º 7-8 (24 de agosto de 2022): 669. http://dx.doi.org/10.2533/chimia.2022.669.

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The number of industrial processes which include one or more enzyme-mediated step is growing rapidly, together with our understanding of how biocatalysts can be adapted to efficiently perform chemical reactions, often only remotely related to their natural reactivity. While enzymes as naturally biodegradable molecules are the most sustainable approach to catalysis, a more global vision of the overall sustainability of enzymatic process must be considered. Here an insight of how sustainability can be further improved when enzymes are immobilized on solid supports is discussed.
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43

"Reaktionstechnische Vorteile in Konkurrenz zum Gefahrenpotential". CHIMIA 52, n.º 12 (23 de diciembre de 1998): 691. http://dx.doi.org/10.2533/chimia.1998.691.

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In most industrial syntheses, one or more reactive groups must be introduced in a raw material before any synthesis becomes possible at all. Since natural raw materials are mostly not reactive by themselves, they are forced to reaction by the use of highly reactive materials. This high reactivity may appear to be an advantage in that a high reaction rate, meaning high productivity, is achieved. But the drawback is that the high reaction rate is often coupled to a poor selectivity. Thus, the use of highly reactive materials is submitted to the art of chemists and chemical engineers, in order to obtain the desired result.Additionally, the high reactivity is also the cause of the hazards linked to the handling of these materials. If released, they are able to react in an undesired way with the environment or with living bodies. Thus, most of them are toxic for humans or for the environment. Consequently, they can only be used if specific safety measures are taken, which presents a technical challenge and is also a cost factor. The fact that products whose objective is to improve the quality of life can only be manufactured by using highly reactive materials is either unknown or, if known, not accepted by the public. Some examples stemming from the industrial practice will illustrate the way how highly reactive materials can be used in a safe and economic way despite of the restraining conditions implied by the hazards. The technical development allowed great improvements, but there is also space for even more improvements in the future.
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44

"From Synthetic Methods to γ-Peptides – From Chemistry to Biology". CHIMIA 55, n.º 10 (31 de octubre de 2001): 831. http://dx.doi.org/10.2533/chimia.2001.831.

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The research activities of our group are demonstrated by examples in the following fields: (i) TADDOL auxiliary system (combinatorial synthesis, a chiral hydroperoxide, immobilization on controlled-pore glass silica gel); (ii) a geminally diphenyl-substituted 4-isopropyl-1,3-oxazolidinone as a superior Evans-type auxiliary (for enantioselective enolate alkylation, aldol addition, Michael addition, and Diels-Alder reactions); (iii) enantioselective reactivity umpolung (with a lithiated methylthiomethyl derivative of an oxazolidinone), and (iv) chemical and biological investigations of γ-peptides (folding to helices and turns, stability against peptidases). The impact of biology on the projects of a synthetic organic group is discussed.
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45

"Sorption Phenomena at Environmental Solid Surfaces". CHIMIA 51, n.º 12 (17 de diciembre de 1997): 893. http://dx.doi.org/10.2533/chimia.1997.893.

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Sorption phenomena from the aqueous and from the gaseous phase to solid surfaces play an important role for the fate of inorganic and organic compounds and of bacteria in the environment. Case studies illustrating the role of different sorption mechanisms for various classes of compounds and for bacteria are presented. They show that sorption at solid surfaces ranges from weak unspecific interactions to very specific and strong complexation. Strong surface complexation in particular affects the surface reactivity. Studies of model systems provide a conceptual framework to understand and predict the behavior of substances and of bacteria in complex environmental systems, such as aquifers and sediments.
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46

"Alkali Metal Metal(ates) Containing Divalent Earth Abundant Transition Metals". CHIMIA 76, n.º 4 (27 de abril de 2022): 336. http://dx.doi.org/10.2533/chimia.2022.336.

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Recent advances in cooperative chemistry have shown the enormous potential of main group heterobimetallic complexes for the functionalisation of aromatic molecules. Going beyond main group metal chemistry, here we provide an overview on the synthesis, structure and reactivity of bimetallic complexes which combine an alkali-metal (AM= Li, Na) with a divalent earth-abundant transition metal (M= Mn, Fe, Co, Ni), containing the utility silyl amide HMDS (HMDS = N(SiMe3)2). Advancing the understanding on how cooperative effects operate in these bimetallic (ate) systems, selected examples of their applications in deprotonative metalation are also discussed with special emphasis on the constitution of the metalated intermediates.
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47

"Reactivity and Redox Potential of Heme-Thiolate Proteins – Results from Enzymes and Enzyme Models". CHIMIA 55, n.º 4 (25 de abril de 2001): 366. http://dx.doi.org/10.2533/chimia.2001.366.

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The redox potential is a characteristic parameter of various intermediates of the catalytic cycle of heme-thiolate proteins (cytochromes P450, NO-synthase, chloroperoxidase) which significantly influences catalytic turnover. E0 values of these proteins are surprisingly positive compared to synthetic active site analogues that have an arylthiolate or an alkylthiolate coordinating to the iron. This report examines factors underlying this phenomenon and describes the design of enzyme mimics having redox potentials close to those of heme-thiolate proteins.
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48

"6-Unsubstituierte 2H-Pyran-2-one Synthese und Reaktivität". CHIMIA 46, n.º 12 (23 de diciembre de 1992): 457. http://dx.doi.org/10.2533/chimia.1992.457.

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Although the 2H-pyran-2-ones have been known for more than 100 years, their importance as versatile intermediates was not widely recognized before the sixties of this century. Until then, the C(6)-unsubstituted derivatives represented only a small minority due to their difficult accessibility. This review is dealing in the first part with the syntheses as well as, in the second part, with the reactivities of most of the C(6)-unsubstituted 2H-pyran-2-ones known so far. Of all reactions of the 2H-pyran-2-ones, the Diels-Alder cycloaddition is the most studied. Depending on conditions, the 2H-pyran-2-one ring can react as dienophile or as enophile. Furthermore, the subsequent elimination of CO2 from the formed bicyclolactone can frequently be influenced. This opens the opportunity of stereoselective syntheses. Recently, there were also reports on [4+3] and [3+2] cycloadditions. The photochemistry of the 2H-pyran-2-ones was studied intensely in the seventies of this century. Again, the enormous versatility of this ring system was demonstrated. Depending on conditions and substituent patterns, some ring contraction, ring opening, or dimerization by [4+4], [2+2], or [4+2] cycloaddition occurs. However, the highest variability in the reactivity of the C(6)-unsubstituted 2H-pyran-2-ones is demonstrated in their reactions with nucleophiles. These reactions, mostly accompanied by ring opening, give different, often otherwise difficultly accessible products depending on the conditions. The reactions with N-nucleophiles were the most productive so far, but also H-, O-, and C-nucleophiles gave interesting products. In recent years, much more became known about the synthesis and reactivity of C(6)-unsubstituted 2H-pyran-2-ones. This opened further possibilities of their applications in all fields of modern organic synthesis.
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49

"Der ideale Polymethinzustand". CHIMIA 45, n.º 10 (30 de octubre de 1991): 288. http://dx.doi.org/10.2533/chimia.1991.288.

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The theory of the ideal polymethine state equally existing between the aromatic state and the polyene state (triad theory) provides a comprehensive understanding of the chemistry and physics of conjugated organic compounds. This is shown by modelling new colorants, by investigating of the light-induced charge transfer (CT) and charge resonance (CR), by examination colour and constitution relationships, by the interpretation of reactivity, by elucidating the origin and limitations of linear free energy relationships, and by designing organic metals and organic materials with nonlinear optical properties.The present state of the art challenges writers of textbooks in organic chemistry to adapt the theory of the ideal polymethine state as an intrinsic part of the chemistry of conjugated organic compounds.
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50

"Electronic Configuration and Reactivity: First Semi-Quantitative Assessment of Relative Reactivities for the 3d Transition Metal Vapors Toward p-Bromotoluene in a Methylcyclohexane Solution". CHIMIA 44, n.º 3 (28 de marzo de 1990): 59. http://dx.doi.org/10.2533/chimia.1990.59.

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A specifically designed metal vapor synthesis apparatus makes possible the semi-quantitative assessment of the reactivities for the elements of the first transition series toward p-bromotoluene kept in a ?118°C solution of methylcyclohexane. In all cases, the two main processes are coupling and reduction of the substrate. The intrinsic reactivity of the substrate displays a behavior highly dependent upon the metal electronic configuration, suggesting a direct importance of the 18e rule in ruling these phenomena. Zn and Mn are the less reactive of the studied metals. In a way reminiscent of Rieke coupling of haloaromatics by metal powders, Ni vapor displays the highest ability in mediating the coupling of the substrate.
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