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101.
Krishnamurthy D Kasper GD Namuswe F Kerber WD Narducci Sarjeant AA Moënne-Loccoz P Goldberg DP 《Journal of the American Chemical Society》2006,128(44):14222-14223
The synthesis of a mononuclear, five-coordinate ferrous complex [([15]aneN4)FeII(SPh)](BF4) (1) is reported. This complex is a new model of the reduced active site of the enzyme superoxide reductase (SOR), which is comprised of a [(NHis)4(Scys)FeII] center. Complex 1 reacts with alkylhydroperoxides (tBuOOH, cumenylOOH) at low temperature to give a metastable, dark red intermediate (2a: R = tBu; 2b: R = cumenyl) that has been characterized by UV-vis, EPR, and resonance Raman spectroscopy. The UV-vis spectrum (-80 degrees C) reveals a 526 nm absorbance (epsilon = 2150 M-1 cm-1) for 2a and a 527 nm absorbance (epsilon = 1650 M-1 cm-1) for 2b, indicative of alkylperoxo-to-iron(III) LMCT transitions, and the EPR data (77 K) show that both intermediates are low-spin iron(III) complexes (g = 2.20 and 1.97). Definitive identification of the Fe(III)-OOR species comes from RR spectra, which give nu(Fe-O) = 612 (2a) and 615 (2b) cm-1, and nu(O-O) = 803 (2a) and 795 (2b) cm-1. The assignments for 2a were confirmed by 18O substitution (tBu18O18OH), resulting in a 28 cm-1 downshift for nu(Fe-18O), and a 46 cm-1 downshift for nu(18O-18O). These data show that 2a and 2b are low-spin FeIII-OOR species with weak Fe-O bonds and suggest that a low-spin intermediate may occur in SOR, as opposed to previous proposals invoking high-spin intermediates. 相似文献
102.
Frabetti PL Cheung HW Cumalat JP Dallapiccola C Ginkel JF Greene SV Johns WE Nehring MS Butler JN Cihangir S Gaines I Garbincius PH Garren L Gourlay SA Harding DJ Kasper P Kreymer A Lebrun P Shukla S Vittone M Bianco S Fabbri FL Sarwar S Zallo A Culbertson R Gardner RW Greene R Wiss J Alimonti G Bellini G Caccianiga B Cinquini L Corato MD Giammarchi M Inzani P Leveraro F Malvezzi S Menasce D Meroni E Moroni L Pedrini D Perasso L Sala A Sala S Torretta D Buchholz D Claes D Gobbi B O'Reilly B 《Physical review D: Particles and fields》1994,50(5):R2953-R2956
103.
Frabetti PL Cheung HW Cumalat JP Dallapiccola C Ginkel JF Greene SV Johns WE Nehring MS Butler JN Cihangir S Gaines I Garbincius PH Garren L Gourlay SA Harding DJ Kasper P Kreymer A Lebrun P Shukla S Bianco S Fabbri FL Sarwar S Zallo A Culbertson R Gardner RW Greene R Wiss J Alimonti G Bellini G Caccianiga B Cinquini L Di Corato M Giammarchi M Inzani P Leveraro F Malvezzi S Menasce D Meroni E Moroni L Pedrini D Perasso L Sala A Sala S Torretta D Vittone M Buchholz D Claes D Gobbi B O'Reilly B 《Physical review letters》1994,72(7):961-964
104.
Kalesse M Chary KP Quitschalle M Burzlaff A Kasper C Scheper T 《Chemistry (Weinheim an der Bergstrasse, Germany)》2003,9(5):1129-1136
Callystatin A is a prominent member of a class of natural products which display promising growth inhibition of cancer cells in their biological profile. The challenging structure and the interesting biological activity of (-)-callystatin A fueled our interest in the synthesis of this marine natural product. We achieved the total synthesis using a highly convergent approach joining four subunits together with a Wittig olefination, a selective Heck reaction and an aldol reaction as the pivotal steps. The aldol reaction as one of the final transformations during the synthesis opens fast access to a variety of structural analogues and circumvents tedious protecting group manipulations. Here we report an improved synthesis utilizing a modified vinyl iodide which shortens the synthesis by two steps. Additionally, first biological results will be reported. 相似文献
105.
The structure and transformation behavior of β-Ag2HgI4 have been investigated by X-ray diffraction methods using single crystals. It has been verified that a single crystal of the β-form, stable at room temperature, transforms to a single crystal of the α-phase, stable above 50°C. The reverse transformation, α → β, on the other hand, is found to result in a multidomain arrangement of the β-phase and not to yield a new cubic modification. The β-structure is tetragonal: a = 6.322 (2) Å, c = 12.605 (15) Å, with space group and Z = 2. The chalcopyrite type of cation ordering, proposed by Hahn et al. (7), is confirmed. The iodine arrangement is considerably distorted from ideal cubic close packing with preservation of normal cation-iodine distances. No significant amount of disorder or occupancy of vacant sites has been found. 相似文献
106.
Yerin Park Alice L. Baumann Hyejin Moon Stephen Byrne Marc-Andr Kasper Songhwan Hwang Han Sun Mu-Hyun Baik Christian P. R. Hackenberger 《Chemical science》2021,12(23):8141
Vinyl- and ethynyl phosphorus(v) electrophiles are a versatile class of thiol-reactive reagents suitable for cysteine-selective peptide and protein modifications, especially for the generation of antibody conjugates. Herein we investigated the reactivity of various P(v) reagents towards thiol addition. Complementing previous studies, we observed that the heteroatoms X (X = S, O, NH) as well as the vinyl- vs. ethynyl-substituent bound to phosphorus greatly influence the overall reactivity. These experimentally observed trends, as well as the high Z-selectivity for thiol additions to ethynyl derivatives, were further elucidated using DFT calculations. Hyperconjugation was a key means of stabilizing the intermediate generated upon the thiol addition, thus determining both the reactivity and stereoselectivity of unsaturated P(v) electrophiles. Specifically, the energetically low-lying σ antibonding orbital of the P–S bond more readily stabilizes the electron density from the lone pair (LP) of the generated carbanion, rendering the phosphonothiolates more reactive compared to the derivatives bearing oxygen and nitrogen. Our studies provide a detailed mechanistic picture for designing P(v)-based electrophiles with fine-tuned reactivity profiles.Computational analysis of different unsaturated phosphorus(v) electrophiles revealed a mechanistic picture to rationalize their selectivity and reactivity in cysteine-selective peptide and protein modifications. 相似文献
107.
Morten Gotthold Vinum Laura Voigt Steen H. Hansen Colby Bell Kensha Marie Clark Ren Wugt Larsen Kasper S. Pedersen 《Chemical science》2020,11(31):8267
The quest for simple ligands that enable multi-electron metal–ligand redox chemistry is driven by a desire to replace noble metals in catalysis and to discover novel chemical reactivity. The vast majority of simple ligand systems display electrochemical potentials impractical for catalytic cycles, illustrating the importance of creating new strategies towards energetically aligned ligand frontier and transition metal d orbitals. We herein demonstrate the ability to chemically control the redox-activity of the ubiquitous acetylacetonate (acac) ligand. By employing the ligand field of high-spin Cr(ii) as a switch, we were able to chemically tailor the occurrence of metal–ligand redox events via simple coordination or decoordination of the labile auxiliary ligands. The mechanism of ligand field actuation can be viewed as a destabilization of the dz2 orbital relative to the π* LUMO of acac, which proffers a generalizable strategy to synthetically engineer redox-activity with seemingly redox-inactive ligands.Tailoring the chemical surroundings of chromium(ii) allows reversible electron-transfer to the ubiquitous, purportedly redox-inactive acetylacetonate. 相似文献
108.
Nickel hydroxide is widely used as an active material in Ni-Cd and Ni-MeH batteries. The electrochemical properties such as
charge acceptance, electronic conductivity etc. can be dramatically influenced by doping β-Ni(OH)2 with small amounts of Co, Cd or Zn. Stabilizing of α-Ni(OH)2 offers the possibility to obtain nickel electrodes with enhanced capacity. The stabilizing of α-Ni(OH)2 is achieved by replacing at least 20% of the nickel by a trivalent metal ion.
The structural features of the undoped and doped nickel hydroxides and the resulting electrochemical properties are discussd
and reviewed.
Paper presented at the 3rd Euroconference on Solid State Ionics, Teulada, Sardinia, Italy, Sept. 15–22, 1996 相似文献
109.
110.
The effectiveness of utility-maximization techniques for portfolio management relies on our ability to estimate correctly the parameters of the dynamics of the underlying financial assets. In the setting of complete or incomplete financial markets, we investigate whether small perturbations of the market coefficient processes lead to small changes in the agent’s optimal behavior, as derived from the solution of the related utility-maximization problems. Specifically, we identify the topologies on the parameter process space and the solution space under which utility-maximization is a continuous operation, and we provide a counterexample showing that our results are best possible, in a certain sense. A novel result about the structure of the solution of the utility-maximization problem, where prices are modeled by continuous semimartingales, is established as an offshoot of the proof of our central theorem. 相似文献