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排序方式: 共有1326条查询结果,搜索用时 31 毫秒
31.
Wiest O Harrison CB Saettel NJ Cibulka R Sax M König B 《The Journal of organic chemistry》2004,69(24):8183-8185
Two new artificial photolyase models that recognize pyrimidine dimers in protic and aprotic organic solvents as well as in water through a combination of charge and hydrogen-bonding interactions and use a mimic of the flavine to achieve repair through reductive photoinduced electron transfer are presented. Fluorescence and NMR titration studies show that it forms a 1:1 complex with pyrimidine dimers with binding constants of approximately 10(3) M(-1) in acetonitrile or methanol, while binding constants in water at pH 7.2 are slightly lower. Excitation of the complex with visible light leads to clean and rapid cycloreversion of the pyrimidine dimer through photoinduced electron transfer catalysis. The reaction in water is significantly faster than in organic solvents. The reaction slows down at higher conversions due to product inhibition. 相似文献
32.
33.
Serge Schubert Philippe Renaud Pierre-Alain Carrupt Kurt Schenk 《Helvetica chimica acta》1993,76(7):2473-2489
Radical addition to enamines using Bu3SnH as reducing agent are reported (Schemes 2 and 4). The diastereoselectivity of these reactions was examined in different systems (Tables 1 and 2). Enamines derived from cyclic ketones such as cyclohexanone were alkylated with high diastereoselectivity with preferential formation of the cis-disubstituted cycloalkanes. In acyclic systems such as enamines derived from propiophenone and diethyl ketone, moderate to high stereoselectivities were observed in the H-abstraction step. A model based principally on minimization of allylic 1,3-strain (A1,3 strain) was deduced from the experimental results and semi-empirical (AM1) calculations. 相似文献
34.
Mahbod Morshedi Soraia Meghdadi Kurt J. Schenk 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(3):m87-m89
The quinquedentate ligand 2,2′‐[1,1′‐(4‐azaheptane‐1,7‐diyldinitrilo)diethylidyne]diphenol in the title compound, [Cu(C22H27N3O2)], furnishes an N3O2 donor set, which results in a distorted square‐pyramidal coordination; the two O and two imine N atoms lie in the basal plane, while the secondary amine N atom of the ligand occupies the axial position. The axial Cu—N bond is 0.33 Å longer than the average of the equatorial bonds, and the O atoms are trans. The symmetry of the molecule is lowered by the twist–boat and chair conformations adopted by the two CuNN chelate rings. The complex contains two intramolecular C—H⋯O interactions, and two molecules of the complex are linked into a dimer by means of moderate N—H⋯O hydrogen bonds. Spectroscopic evidence supports the presence of hydrogen bonds. 相似文献
35.
Paloma Sevillano Sven Koenig Daniel Himmel Olaf Fuhr Dieter Fenske 《无机化学与普通化学杂志》2005,631(11):2236-2240
The reactions of [Co2(CO)8] with E(SiMe3)2 (E = Se, Te) in CH2Cl2 result in the formation of the compounds [Co4Se2(CO)10]> ( 1 ) and [Co4Te2(CO)11] ( 2 ), respectively. Both cluster complexes have similar molecular structures in which the cobalt atoms form four‐membered rings with μ4‐bridging chalcogen atoms (Se and Te) above and below the plane of the metal atoms and the carbonyl ligands as either terminal or μ2‐bridging ligands. DFT‐calculations for both compounds have been carried out in order to obtain some more information about their electronic distribution. In the presence of the phosphine Ph2PC≡CPPh2 (dppa), the reaction of [Co2(CO)8] with Se(SiMe3)2 leads to the formation of [Co8Se4(CO)16(μ‐dppa)2] ( 3 ). During the reaction two molecules of [Co2(CO)8] have been added to the acetylene groups of the dppa ligands, whilst the remaining cobalt atoms coordinate to the phosphorus atoms of the phosphine. In this compounds the selenium atoms act as μ3‐ligands, bridging the metal atoms bonded to the phosphorus with those bonded to the acetylene groups. 相似文献
36.
Karim Fahmy Olaf Weidlich Martin Engelhard Jörg Tittor Dieter Oesterhelt Friedrich Siebert † 《Photochemistry and photobiology》1992,56(6):1073-1083
Abstract— In order to assign the proton acceptor for Schiff base deprotonation in bacteriorhodopsin to a specific Asp residue, the photoreaction of the Asp85 → Glu mutant, as expressed in Halobacterium sp . GRB, was investigated by static low-temperature and time-resolved infrared difference spec-troscopy. Measurements were also performed on the mutant protein labeled with [4-13 C]Asp which allowed discrimination between Asp and Glu residues. 14,15-di13 C-retinal was incorporated to distinguish amide-II absorbance changes from changes of the ethylenic mode of the chromophore. In agreement with earlier UV-VIS measurements, our data show that from both the 540 and 610 nm species present in a pH-dependent equilibrium, intermediates similar to K and L can be formed. The 14 ms time-resolved spectrum of the 540 nm species shows that a glutamic acid becomes protonated in the M-like intermediate, whereas the comparable difference spectrum of the 610 nm species demonstrates that in the initial state a glutamic acid is already protonated. In conjunction with earlier observations of protonation of an Asp residue in wild-type M, the data provide direct evidence that the proton acceptor in the deprotonation reaction of the Schiff base is Asp85. 相似文献
37.
Wolfdieter A. Schenk Michael Stubbe Michael Hagel 《Journal of organometallic chemistry》1998,560(1-2):257-263
The P–Ph cleavage of phenyldibenzophosphole (1) with lithium in THF gives lithium dibenzophospholide (2). Reaction of 2 with ethyleneglycol ditosylate produces the known chelate ligand 1,2-bis(dibenzophospholyl)ethane (3) in good yield. Similarly, 2 and (2R,3R)-butanediol ditosylate give the new chiral chelate ligand (2S,3S)-bis(dibenzophospholyl)butane (4). Ligand exchange of [CpRu(PPh3)2Cl] with 3 or 4 yields the halfsandwich complexes [CpRu(C12H8PC2H4PC12H8)Cl] (5) and [CpRu((S,S)-C12H8PCHMeCHMePC12H8)Cl] (6). Complex 6 was characterized crystallographically (monoclinic, space group P21 (no. 4), a=820.6(4), b=1501.0(3), c=1172.8(6) pm, β=108.87(2)°, V=1.367(1)×109 pm3, Z=2). The most conspicuous feature of the structure of 6 is the perfect coplanarity of the two dibenzophosphole moieties imposed by their steric interaction with the Cp ligand. Complex 6 and the thiophene complex [CpRu((S,S)-C12H8PCHMeCHMePC12H8)(SC4H4)]BF4 (7) derived therefrom are remarkably unreactive with regard to ligand substitutions. A possible explanation is the lack of intramolecular –C stabilization en route to the transition state of ligand substitution. The enantiomeric purity of 6 and 7 could nevertheless be demonstrated by conversion to diastereomerically pure [CpRu((S,S)-C12H8PCHMeCHMePC12H8)((S)-CNCHMePh)]BF4 (8). 相似文献
38.
The title compound (1) was prepared by the reaction of 3,5-bis(CF3)C6H3P(i-C3H7)2 (L1) and Co2(CO)8. Its solubility in supercritical carbon dioxide was measured at varying temperatures and pressures using a modified analytical extraction device. Solubility data were determined in the temperature and pressure ranges between 40 and 70 °C and between 100 and 300 bar, respectively. The solubility of 1 is lower compared to (p-CF3C6H4)3P, but much higher than for transition metal complexes bearing phosphines without fluorinated substituents. 相似文献
39.
40.
Dr. Thies Olaf Petersen Dustin Simone Prof. Dr. Ingo Krossing 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(44):15847-15855
Attempts to prepare previously unknown simple and very Lewis acidic [RZn]+[Al(ORF)4]? salts from ZnR2, AlR3, and HO?RF delivered the ion‐like RZn(Al(ORF)4) (R=Me, Et; RF=C(CF3)3) with a coordinated counterion, but never the ionic compound. Increasing the steric bulk in RZn+ to R=CH2CMe3, CH2SiMe3, or Cp*, thus attempting to induce ionization, failed and led only to reaction mixtures including anion decomposition. However, ionization of the ion‐like EtZn(Al(ORF)4) compound with arenes yielded the [EtZn(arene)2]+[Al(ORF)4]? salts with arene=toluene, mesitylene, or o‐difluorobenzene (o‐DFB)/toluene. In contrast to the ion‐like EtZn(η3‐C6H6)(CHB11Cl11), which co‐crystallizes with one benzene molecule, the less coordinating nature of the [Al(ORF)4]? anion allowed the ionization and preparation of the purely organometallic [EtZn(arene)2]+ cation. These stable materials have further applications as, for example, initiators of isobutene polymerization. DFT calculations to compare the Lewis acidities of the zinc cations to those of a large number of organometallic cations were performed on the basis of fluoride ion affinity. The complexation energetics of EtZn+ with arenes and THF was assessed and related to the experiments. 相似文献