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31.
Fabio Cameli Prof. Dr. Joop H. ter Horst Dr. René R. E. Steendam Dr. Ir. Christos Xiouras Prof. Dr. Georgios D. Stefanidis 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(6):1344-1354
Herein, the pivotal role of secondary nucleation in a crystallization-enhanced deracemization process is reported. During this process, complete and rapid deracemization of chiral conglomerate crystals of an isoindolinone is attained through fast microwave-assisted temperature cycling. A parametric study of the main factors that affect the occurrence of secondary nucleation in this process, namely agitation rate, suspension density, and solute supersaturation, confirms that an enhanced stereoselective secondary nucleation rate maximizes the deracemization rate. Analysis of the system during a single temperature cycle showed that, although stereoselective particle production during the crystallization stage leads to enantiomeric enrichment, undesired kinetic dissolution of smaller particles of the preferred enantiomer occurs during the dissolution step. Therefore, secondary nucleation is crucial for the enhancement of deracemization through temperature cycles and as such should be considered in further design and optimization of this process, as well as in other temperature cycling processes commonly applied in particle engineering. 相似文献
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Dr. Damien Hudry Dr. Christos Apostolidis Dr. Olaf Walter Dr. Thomas Gouder Dr. Eglantine Courtois Dr. Christian Kübel Dr. Daniel Meyer 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(17):5297-5305
Very little is known about the size and shape effects on the properties of actinide compounds. As a consequence, the controlled synthesis of well‐defined actinide‐based nanocrystals constitutes a fundamental step before studying their corresponding properties. In this paper, we report on the non‐aqueous surfactant‐assisted synthesis of thorium and uranium oxide nanocrystals. The final characteristics of thorium and uranium oxide nanocrystals can be easily tuned by controlling a few experimental parameters such as the nature of the actinide precursor and the composition of the organic system (e.g., the chemical nature of the surfactants and their relative concentrations). Additionally, the influence of these parameters on the outcome of the synthesis is highly dependent on the nature of the actinide element (thorium versus uranium). By using optimised experimental conditions, monodisperse isotropic uranium oxide nanocrystals with different sizes (4.5 and 10.7 nm) as well as branched nanocrystals (overall size ca. 5 nm), nanodots (ca. 4 nm) and nanorods (with ultra‐small diameters of 1 nm) of thorium oxide were synthesised. 相似文献
35.
Christos Liolios Christos Sachpekidis Antonios Kolocouris Antonia Dimitrakopoulou-Strauss Penelope Bouziotis 《Molecules (Basel, Switzerland)》2021,26(6)
Multimeric ligands consisting of multiple pharmacophores connected to a single backbone have been widely investigated for diagnostic and therapeutic applications. In this review, we summarize recent developments regarding multimeric radioligands targeting integrin αvβ3 receptors on cancer cells for molecular imaging and diagnostic applications using positron emission tomography (PET). Integrin αvβ3 receptors are glycoproteins expressed on the cell surface, which have a significant role in tumor angiogenesis. They act as receptors for several extracellular matrix proteins exposing the tripeptide sequence arginine-glycine-aspartic (RGD). Cyclic RDG peptidic ligands c(RGD) have been developed for integrin αvβ3 tumor-targeting positron emission tomography (PET) diagnosis. Several c(RGD) pharmacophores, connected with the linker and conjugated to a chelator or precursor for radiolabeling with different PET radionuclides (18F, 64Cu, and 68Ga), have resulted in multimeric ligands superior to c(RGD) monomers. The binding avidity, pharmacodynamic, and PET imaging properties of these multimeric c(RGD) radioligands, in relation to their structural characteristics are analyzed and discussed. Furthermore, specific examples from preclinical studies and clinical investigations are included. 相似文献
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Meissner U Gatsogiannis C Moeller A Depoix F Harris JR Markl J 《Micron (Oxford, England : 1993)》2007,38(7):754-765
Hemocyanins are giant extracellular proteins that transport oxygen in the hemolymph of many molluscs. Molluscan hemocyanins are cylindrical decamers or didecamers of a 350-400 kDa subunit that contains seven or eight different covalently linked globular functional units (FUs), arranged in a linear manner. Each FU carries a single copper active site and reversibly binds one dioxygen molecule. As a consequence, the decamer can carry up to 70 or 80 O(2) molecules. Although complete sequence information is now available from several molluscan hemocyanins, many details of the quaternary structure are still unclear, including the topology of the 10 subunits within the decamer. Here we show 3D reconstructions from cryo-electron micrographs of the hemocyanin decamer of Nautilus pompilius (Cephalopoda) and Haliotis tuberculata (Gastropoda) at a resolution of 11A (FSC(1/2-bit) criterion). The wall structure of both hemocyanins is very similar and shows, as in previous reconstructions, three tiers with 20 functional units each that encircle the cylinder wall, and the 10 oblique minor and major wall grooves. However, the six types of wall FUs of the polypeptide subunit, termed a-b-c-d-e-f, are now for the first time individually discernable by their specific orientation, shape, and connections. Also, the internal collar complex of the decamers shows superior resolution which, in this case, reveals striking differences between the two hemocyanins. The five arcs (FU-g pairs) of the central collar (in both hemocyanins) and the five slabs (FU-h pairs) of the peripheral collar (only present in Haliotis hemocyanin), as well as their connections to the wall and to each other are now more clearly defined. The arc is attached to the wall through a feature termed the anchor, a previously undescribed structural element of the hemocyanin wall. 相似文献
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Ariadni Zianna Maja Šumar Ristović Antonis Hatzidimitriou Christos D. Papadopoulos Maria Lalia-Kantouri 《Journal of Thermal Analysis and Calorimetry》2014,118(3):1431-1440
In this study, three novel tetranuclear nickel(II) cubane-type clusters with the general formula [Ni4(L)4(μ3-CH3O)4(CH3OH)4] [L: the anion of 5-methyl-2-hydroxybenzaldehyde (1), 2-hydroxypropiophenone (2), and 2-hydroxybenzophenone (3)] were synthesized and characterized by single-crystal X-ray diffraction analysis. The crystal structure of each compound contains a tetranuclear cubane core [Ni4O4] based on an approximately cubic array of altering nickel and oxygen atoms with intracluster metal–metal separations of 3.04–3.14 Å. Each Ni(II) atom is surrounded by two oxygen atoms from the ligand (L) and by the μ3-CH3O oxygen atom that bridges three Ni atoms of the cubane core. The coordination sphere of Ni is completed with one methanol molecule and making six-coordinate with a distorted octahedral geometry. These complexes were characterized also by spectroscopy (IR and UV–Vis). Simultaneous TG/DTG–DTA techniques were used to analyze their thermal behavior under inert atmosphere, with particular attention to determine their thermal degradation pathways, which was found to be a multi-step decomposition accompanied by the release of the ligand molecules. Finally, the kinetic analysis of the decomposition processes was performed for the first step of complex (3), since only this verifies the requirement of applying an isoconversional method like Kissinger–Akahira–Sunose (KAS). For this step, we found the average value E a = 107.8 ± 4.5 kJ mol?1. 相似文献
39.
Maximilian Joost Dr. Pauline Gualco Dr. Yannick Coppel Dr. Karinne Miqueu Dr. Christos E. Kefalidis Dr. Laurent Maron Dr. Abderrahmane Amgoune Dr. Didier Bourissou 《Angewandte Chemie (International ed. in English)》2014,53(3):747-751
Oxidative addition plays a major role in transition‐metal catalysis, but this elementary step remains very elusive in gold chemistry. It is now revealed that in the presence of GaCl3, phosphine gold chlorides promote the oxidative addition of disilanes at low temperature. The ensuing bis(silyl) gold(III) complexes were characterized by quantitative 31P and 29Si NMR spectroscopy. Their structures (distorted Y shape) and the reaction profile of σ(Si? Si) bond activation were analyzed by DFT calculations. These results provide evidence for the intermolecular oxidative addition of σ(Si? Si) bonds to gold and open promising perspectives for the development of new gold‐catalyzed redox transformations. 相似文献
40.
Air‐Stable Solid Aryl and Heteroaryl Organozinc Pivalates: Syntheses and Applications in Organic Synthesis 下载免费PDF全文
Sophia M. Manolikakes Mario Ellwart Dr. Christos I. Stathakis Prof. Dr. Paul Knochel 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(38):12289-12297
A wide range of air‐stable, solid, polyfunctional aryl and heteroarylzinc pivalates were efficiently prepared by either magnesium insertion or Hal/Mg exchange followed by transmetalation with Zn(OPiv)2 (OPiv=pivalate). By reducing the amount of LiCl the air stability could be significantly enhanced compared with previously prepared reagents. An alternative route is directed magnesiation using TMPMgCl ? LiCl (TMP=2,2,6,6‐tetramethylpiperidyl) followed by transmetalation with Zn(OPiv)2 or, for very sensitive substrates, direct zincation by using TMPZnOPiv. These zinc reagents not only show excellent stability towards air, but they also undergo a broad range of C?C bond‐formation reactions, such as allylation and carbocupration reactions, as well as addition to aldehydes and 1,4‐addition reactions. Acylation reactions can be performed by using an excess of TMSCl to overcome side reactions of the omnipresent pivalate anion. 相似文献