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71.
Unusually Strong Long‐Distance Metal–Metal Coupling in Bis(ferrocene)‐Containing BOPHY: An Introduction to Organometallic BOPHYs 下载免费PDF全文
Hannah M. Rhoda Kullapa Chanawanno Alexander J. King Yuriy V. Zatsikha Prof. Christopher J. Ziegler Prof. Victor N. Nemykin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(50):18043-18046
The first organometallic BOPHY (BOPHY=bis(difluoroboron)‐1,2‐bis{(pyrrol‐2‐yl)methylene}hydrazine) containing two ferrocene substituents was prepared through a Knoevenagel condensation between tetramethyl substituted BOPHY and ferrocene carboxaldehyde. An unprecedentedly strong long‐range (≈17.2 Å) metal–metal coupling in this new complex was investigated using electrochemical, spectroelectrochemical, and chemical oxidation methods. Electrochemical data is indicative of a 200 mV separation between the first and the second ferrocene‐centered oxidation processes. Formation of the mixed‐valence states and appearance and disappearance of two NIR bands were observed during stepwise oxidation of the first organometallic BOPHY. The electronic structure and the nature of the excited states in this new chromophore were studied by DFT and TDDFT calculations. 相似文献
72.
Ammonia Activation by a Nickel NCN‐Pincer Complex featuring a Non‐Innocent N‐Heterocyclic Carbene: Ammine and Amido Complexes in Equilibrium 下载免费PDF全文
Rudy M. Brown Dr. Javier Borau Garcia Juuso Valjus Christopher J. Roberts Dr. Heikki M. Tuononen Dr. Masood Parvez Prof. Roland Roesler 《Angewandte Chemie (International ed. in English)》2015,54(21):6274-6277
A Ni0‐NCN pincer complex featuring a six‐membered N‐heterocyclic carbene (NHC) central platform and amidine pendant arms was synthesized by deprotonation of its NiII precursor. It retained chloride in the square‐planar coordination sphere of nickel and was expected to be highly susceptible to oxidative addition reactions. The Ni0 complex rapidly activated ammonia at room temperature, in a ligand‐assisted process where the carbene carbon atom played the unprecedented role of proton acceptor. For the first time, the coordinated (ammine) and activated (amido) species were observed together in solution, in a solvent‐dependent equilibrium. A structural analysis of the Ni complexes provided insight into the highly unusual, non‐innocent behavior of the NHC ligand. 相似文献
73.
Polymersomes Prepared from Thermoresponsive Fluorescent Protein–Polymer Bioconjugates: Capture of and Report on Drug and Protein Payloads 下载免费PDF全文
Chin Ken Wong Alistair J. Laos Dr. Alexander H. Soeriyadi Prof. Jörg Wiedenmann Prof. Paul M. G. Curmi Prof. J. Justin Gooding Dr. Christopher P. Marquis Prof. Martina H. Stenzel Assoc. Prof. Pall Thordarson 《Angewandte Chemie (International ed. in English)》2015,54(18):5317-5322
Polymersomes provide a good platform for targeted drug delivery and the creation of complex (bio)catalytically active systems for research in synthetic biology. To realize these applications requires both spatial control over the encapsulation components in these polymersomes and a means to report where the components are in the polymersomes. To address these twin challenges, we synthesized the protein–polymer bioconjugate PNIPAM‐b‐amilFP497 composed of thermoresponsive poly(N‐isopropylacrylamide) (PNIPAM) and a green‐fluorescent protein variant (amilFP497). Above 37 °C, this bioconjugate forms polymersomes that can (co‐)encapsulate the fluorescent drug doxorubicin and the fluorescent light‐harvesting protein phycoerythrin 545 (PE545). Using fluorescence lifetime imaging microscopy and Förster resonance energy transfer (FLIM‐FRET), we can distinguish the co‐encapsulated PE545 protein inside the polymersome membrane while doxorubicin is found both in the polymersome core and membrane. 相似文献
74.
Synthesis and Intracellular Redox Cycling of Natural Quinones and Their Analogues and Identification of Indoleamine‐2,3‐dioxygenase (IDO) as Potential Target for Anticancer Activity 下载免费PDF全文
Christopher E. Blunt Dr. Canan Torcuk Dr. Yang Liu Dr. William Lewis Dr. David Siegel Prof. Dr. David Ross Prof. Dr. Christopher J. Moody 《Angewandte Chemie (International ed. in English)》2015,54(30):8740-8745
Natural quinones, often linked with cellular oxidation processes, exhibit pronounced biological activity. In particular, the structurally unique isothiazolonaphthoquinone aulosirazole, isolated from blue‐green alga, possesses selective antitumor cytotoxicity, although its mechanism of action is unknown. The first synthesis of aulosirazole uses a route centered upon a late‐stage regioselective Diels–Alder reaction. The structurally related natural product pronqodine A, an inhibitor of prostaglandin release, and analogues thereof, were also prepared for comparison. Biological evaluation of the compounds identified one potential target as the immunoregulatory enzyme indoleamine‐2,3‐dioxygenase (IDO). The isothiazoloquinones are also efficient substrates for the human quinone reductase NQO1, and undergo intracellular NQO1‐dependent redox cycling resulting in the generation of reactive oxygen species, and at lower doses have the potential to alter the ratio of intracellular oxidized to reduced pyridine nucleotides. 相似文献
75.
Self‐Assembly of a Giant Tetrahedral 3 d–4 f Single‐Molecule Magnet within a Polyoxometalate System 下载免费PDF全文
Dr. Masooma Ibrahim Dr. Valeriu Mereacre Dr. Nicolas Leblanc Prof. Wolfgang Wernsdorfer Dr. Christopher E. Anson Prof. Annie K. Powell 《Angewandte Chemie (International ed. in English)》2015,54(51):15574-15578
A giant tetrahedral heterometallic polyoxometalate (POM) [Dy30Co8Ge12W108O408(OH)42(OH2)30]56?, which shows single‐molecule magnet (SMM) behavior, is described. This hybrid contains the largest number of 4f ions of any polyoxometalate (POM) reported to date and is the first to incorporate two different 3d–4f and 4f coordination cluster assemblies within same POM framework. 相似文献
76.
Structural Insights into the Incorporation of the Mo Cofactor into Sulfite Oxidase from Site‐Directed Spin Labeling 下载免费PDF全文
Dr. Aaron Hahn Christopher Engelhard Dr. Stefan Reschke Dr. Christian Teutloff Prof. Dr. Robert Bittl Prof. Dr. Silke Leimkühler Prof. Dr. Thomas Risse 《Angewandte Chemie (International ed. in English)》2015,54(40):11865-11869
Mononuclear molybdoenzymes catalyze a broad range of redox reactions and are highly conserved in all kingdoms of life. This study addresses the question of how the Mo cofactor (Moco) is incorporated into the apo form of human sulfite oxidase (hSO) by using site‐directed spin labeling to determine intramolecular distances in the nanometer range. Comparative measurements of the holo and apo forms of hSO enabled the localization of the corresponding structural changes, which are localized to a short loop (residues 263–273) of the Moco‐containing domain. A flap‐like movement of the loop provides access to the Moco binding‐pocket in the apo form of the protein and explains the earlier studies on the in vitro reconstitution of apo‐hSO with Moco. Remarkably, the loop motif can be found in a variety of structurally similar molybdoenzymes among various organisms, thus suggesting a common mechanism of Moco incorporation. 相似文献
77.
Locating Gases in Porous Materials: Cryogenic Loading of Fuel‐Related Gases Into a Sc‐based Metal–Organic Framework under Extreme Pressures 下载免费PDF全文
Jorge Sotelo Dr. Christopher H. Woodall Dr. Dave R. Allan Eugene Gregoryanz Dr. Ross T. Howie Konstantin V. Kamenev Dr. Michael R. Probert Prof. Paul A. Wright Dr. Stephen A. Moggach 《Angewandte Chemie (International ed. in English)》2015,54(45):13332-13336
An alternative approach to loading metal organic frameworks with gas molecules at high (kbar) pressures is reported. The technique, which uses liquefied gases as pressure transmitting media within a diamond anvil cell along with a single‐crystal of a porous metal–organic framework, is demonstrated to have considerable advantages over other gas‐loading methods when investigating host–guest interactions. Specifically, loading the metal–organic framework Sc2BDC3 with liquefied CO2 at 2 kbar reveals the presence of three adsorption sites, one previously unreported, and resolves previous inconsistencies between structural data and adsorption isotherms. A further study with supercritical CH4 at 3–25 kbar demonstrates hyperfilling of the Sc2BDC3 and two high‐pressure displacive and reversible phase transitions are induced as the filled MOF adapts to reduce the volume of the system. 相似文献
78.
Wei-Chang Tseng Keng-Chang Hsu Christopher Stephen Shiea Yeou-Lih Huang 《Analytica chimica acta》2015
Trace element speciation in biomedical and environmental science has gained increasing attention over the past decade as researchers have begun to realize its importance in toxicological studies. Several nanomaterials, including titanium dioxide nanoparticles (nano-TiO2), carbon nanotubes (CNTs), and magnetic nanoparticles (MNPs), have been used as sorbents to separate and preconcentrate trace element species prior to detection through mass spectrometry or optical spectroscopy. Recently, these nanomaterial-based speciation techniques have been integrated with microfluidics to minimize sample and reagent consumption and simplify analyses. This review provides a critical look into the present state and recent applications of nanomaterial-based microanalytical systems in the speciation of trace elements. The adsorption and preconcentration efficiencies, sample volume requirements, and detection limits of these nanomaterial-based speciation techniques are detailed, and their applications in environmental and biological analyses are discussed. Current perspectives and future trends into the increasing use of nanomaterial-based microfluidic techniques for trace element speciation are highlighted. 相似文献
79.
Dr. Christopher J. Heard Prof. Roy L. Johnston Prof. Dr. J. Christian Schön 《Chemphyschem》2015,16(7):1461-1469
The energy landscapes of sub‐nanometre bimetallic coinage metal clusters are explored with the Threshold Algorithm coupled with the Birmingham Cluster Genetic Algorithm. Global and energetically low‐lying minima along with their permutational isomers are located for the Cu${_4 }$ Ag${_4 }$ cluster with the Gupta potential and density functional theory (DFT). Statistical tools are employed to map the connectivity of the energy landscape and the growth of structural basins, while the thermodynamics of interconversion are probed, based on probability flows between minima. Asymmetric statistical weights are found for pathways across dividing states between stable geometries, while basin volumes are observed to grow independently of the depth of the minimum. The DFT landscape is found to exhibit significantly more frustration than that of the Gupta potential, including several open, pseudo‐planar geometries which are energetically competitive with the global minimum. The differences in local minima and their transition barriers between the two levels of theory indicate the importance of explicit electronic structure for even simple, closed shell clusters. 相似文献
80.
Chromatographic enantioseparations on the order of a few seconds can be achieved by supercritical fluid chromatography using short columns packed with chiral stationary phases. The evolution of ‘world record’ speeds for the chromatographic separation of enantiomers has steadily dropped from an industry standard of 20–40 min just two decades ago, to a current ability to perform many enantioseparations in well under a minute. Improvements in instrument and column technologies enabled this revolution, but the ability to predict optimal separation time from an initial method development screening assay using the tmin cc predictor greatly simplifies the development and optimization of high‐speed chiral chromatographic separations. In this study, we illustrate how the use of this simple tool in combination with the workhorse technique of supercritical fluid chromatography on customized short chiral columns (1–2 cm length) allows us to achieve ultrafast enantioseparations of pharmaceutically relevant compounds on the 5–20 s scale, bringing the technique of high‐throughput enantiopurity analysis out of the specialist realm and into the laboratories of most researchers. 相似文献