共查询到20条相似文献,搜索用时 15 毫秒
1.
Summary. Upon irradiation of 3,4-di-O-benzyl-hypericin and proton sponge (bis-1,8-N,N-dimethylamino-naphthalene) in benzene solution, a stable radical ion pair formed which exhibited an intense absorption
band around 800 nm. This was advanced by UV/Vis, NMR, and ESR spectroscopy. In presence of oxygen, irradiation of this photoproduct
led to an activated oxygen species which then attacked the proton sponge.
Received July 17, 2000. Accepted July 20, 2000 相似文献
2.
Paul F. van Hutten Georges Hadziioannou 《Monatshefte für Chemie / Chemical Monthly》2001,132(1):129-139
Summary. Organic opto-electronic devices comprise one or more organic layers and the electrodes. The interfaces between these very
different components play a crucial role to the performance of the devices. In donor–acceptor composites for photovoltaics,
the electronic processes occurring at the interface will benefit from a particular interface morphology on the 10–100 nanometer
level; this is demonstrated for composites of oligophenylenevinylene and C60. Phase separation on such a scale may be achieved naturally in diblock copolymers. The synthesis of an OPV–C60 diblock copolymer is described.
Received June 23, 2000. Accepted (revised) July 18, 2000 相似文献
3.
To explore the interactions between ubiquinones and oxygen in living organisms, the thermodynamics of a series of electron
and hydrogen transfer reactions between semiquinone radicals, as well as their corresponding protonated forms, and oxygen,
singlet or triplet, were studied using the hybrid Hartree–Fock–density functional theory method Becke's three parameter hybrid
method with the Lee, Yang, and Parr correlation functional. Effects of the solvent and of the isoprenyl tail on the electron
and hydrogen transfer reactions were also investigated. It is found that semiquinone radicals (semiquinone anion radicals
or protonated semiquinone radicals) cannot react with triplet oxygen to form the superoxide anion radical O2
−. In contrast, neutral quinones can scavenge O2
− efficiently. In the gas phase, only protonated semiquinone radicals can react spontaneously with singlet oxygen to produce
peroxyl radical (HO2). However, both semiquinone anion radicals and protonated semiquinone radicals can react with singlet oxygen to produce harmful
oxygen radicals (O2
−
a
l
l
b
u
l
l
and HO2, respectively) in aqueous and protein environments. The free-energy changes of the corresponding reactions obtained for different
ubiquinone systems are very similar. It clearly shows that the isoprenyl tail does not influence the electron and hydrogen
transfer reactions between semiquinone radicals and oxygen significantly. Results of electron affinities, vertical ionization
potentials, and proton affinities also show that the isoprenyl tail has no substantial effect on the electronic properties
of ubiquinones.
Received: 3 July 2000 / Accepted: 6 September 2000 / Published online: 21 December 2000 相似文献
4.
Christian Amatore Anny Jutand Jacques Périchon Yolande Rollin 《Monatshefte für Chemie / Chemical Monthly》2000,131(12):1293-1304
Summary. The mechanism of the nickel-catalyzed electrosynthesis of ketones by heterocoupling of phenacyl chloride and benzyl bromide
has been investigated by fast scan rate cyclic voltammetry with [Ni(bpy)2+
3](BF4
−)2 as the catalytic precursor (bpy = 2,2{−}{ bipyridine}). The key step is an oxidative addition of Ni0(bpy) (electrogenerated by reduction of the Ni(II) precursor) to PhCH2Br whose rate constant is found to be 10 times higher than that of PhCH2COCl. The complex PhCH2NiIIBr(bpy) formed in the oxidative addition is reduced at the potential of the NiII/Ni0 reduction by a two-electron process which affords an anionic complex PhCH2Ni0(bpy)− able to react with PhCH2COCl to generate eventually the homocoupling product PhCH2COCH2Ph. The formation of the homocoupling product PhCH2COCOCH2Ph is prevented because of the too slow oxidative addition of Ni0(bpy) to PhCH2COCl compared to PhCH2Br. The formation of the homocoupling product PhCH2CH2Ph is also prevented because PhCH2Ni0(bpy)− does not react with PhCH2Br. This explains why the electrosynthesis of the ketone can be performed selectively in a one-pot procedure, starting from
an equal mixture of PhCH2COCl and PhCH2Br and a nickel catalyst ligated by the bpy ligand.
Received June 27, 2000. Accepted July 11, 2000 相似文献
5.
Hybrid quantum mechanical/molecular mechanical electronic structure calculations reveal the transition state for C–H bond
cleavage in [(LCu)2 (μ-O)2]2+ (L=1,4,7-tribenzyl-1,4,7-triazacyclononane) to be consistent with a hydrogen-atom-transfer mechanism from carbon to oxygen.
At the MPW1K/double-zeta effective core potential(+)|univeral force field level, 0 K activation enthalpies for the parent,
p-CF3, and p-OH substituted benzyl systems are predicted to be 8.8, 9.5, and 7.8 kcal/mol. Using a one-dimensional Eckart potential to
estimate quantum effects on the reaction coordinate, reaction in the unsubstituted system is predicted to proceed with a primary
kinetic isotope effect of 22 at 233 K. Structural parameters associated with the hydrogen-atom transfer are consistent with
the Hammond postulate.
Received: 10 October 2000 / Accepted: 3 November 2000 / Published online: 3 April 2001 相似文献
6.
Xiao-Song Li Lei Liu Ting-Wei Mu Qing-Xiang Guo 《Monatshefte für Chemie / Chemical Monthly》2000,131(8):849-855
Summary. AM1 and PM3 modeling of β-hydroxyethyl ether and α-(1→4)-glucobiose indicated that PM3 is advantageous to AM1 in cyclodextrin
(CD) chemistry. The conclusion was supported by direct structure optimization of α- and β-CD with AM1 and PM3, in which AM1 gave badly distorted geometries due to unreasonable hydrogen bonding, whereas PM3 reproduced
the crystalline structures rather well. Ab initio calculation was for the first time performed on CD, demonstrating the feasibility of this method for future studies concerning CD chemistry. The results also provided valuable insights into the driving forces in CD molecular recognition.
Received January 7, 2000. Accepted (revised) March 22, 2000 相似文献
7.
Rhony Aufdenblatten Simon Diezi Antonio Togni 《Monatshefte für Chemie / Chemical Monthly》2000,131(12):1345-1350
Summary. Starting from the dinuclear chloro-bridged Ir(I) complexes [IrCl(PP)]2 (PP = (R)-(6,6′-dimethylbiphenyl-2,2′-diyl)-1,1′-bis-(diphenylphosphine), (R)-(6,6′-dimethoxy-biphenyl-2,2′-diyl)-1,1′-bis-(diphenylphosphine), and (R)-1-((S)-2-(diphenylphosphino-ferrocenyl))-ethyldicyclohexylphosphine), a new class of cyclopentadienyl Ir(I) complexes containing
a chiral bisphosphine ([IrCp(PP)]) was prepared and characterized. These new complexes are suited precatalysts for the direct hydroarylation of norbornene
with benzamide. 2-(exo-Norbornyl)-benzamide is formed with an enantiomeric excess of up to 94% by the use of 1 mol% iridium, albeit in low yield.
Received July 10, 2000. Accepted August 27, 2000 相似文献
8.
Emilio Bustelo Isaac de los Ríos Manuel J. Tenorio M. Carmen Puerta Pedro Valerga 《Monatshefte für Chemie / Chemical Monthly》2000,131(12):1311-1320
Summary. The solid-state tautomerization of the hydrido-alkynyl derivatives [Cp
*RuH(C&*CR)-(dippe)][BPh4] (Cp* = C5Me5; R = SiMe3, Ph, H; dippe = 1,2-bis-(diisopropylphosphino)-ethane) to their vinylidene isomers [Cp
*Ru*C*CHR(dippe)][BPh4] was studied by IR spectroscopy. Characteristic isothermic αvs. t curves for each individual rearrangement process were recorded. Their shape, and hence the isomerization mechanism, depends
strongly on the nature of the substituent R. The kinetic analysis of the above curves using the Avrami-Erofeev provided some mechanistic information about the isomerization process in the solid.
Received July 7, 2000. Accepted August 29, 2000 相似文献
9.
Nabila M. Guindy Zeinab M. Abou-Gamra Michel F. Abdel-Messih 《Monatshefte für Chemie / Chemical Monthly》2000,131(8):857-866
Summary. The kinetics of the formation of the 1:3 complex of chromium(III) with L-glutamic acid and DL-lysine were studied spectrophotometrically at and 550 nm. The reaction was found to be first order in both reactants. Increasing the hydrogen ion concentration from 3.2×10−5 to 1.0×10−3 molċdm−3 retarded the reaction rate which is of the form . Values of 28.8 and 63.6 kJċmol−1 were obtained for the energy of activation and −184 and −116 Jċ K−1ċmol−1 for the entropy of activation for L-glutamic acid and DL-lysine. The logarithms of the formation constants of the two complexes were found to be 5.9 and 5.1.
Received January 7, 2000. Accepted (revised) March 8, 2000 相似文献
10.
Zorica Bugarcěić Slobodan Novokmet Zěeljko Senić Zěivadin Bugarcěić 《Monatshefte für Chemie / Chemical Monthly》2000,131(7):799-802
Summary. Carbonyl compounds of the type XPhCOR (R = H, Me, Ph; X = H, Me, Cl, Br) are prepared in high yields by reaction of the corresponding benzylic alcohols XPhCHOHR with KNa4 [Ag(HIO6)2]×12H2O in alkaline solution. This method allows the selective oxidation of benzylic alcohols in compounds containing other types
of alcoholic functional groups.
Received January 18, 2000. Accepted (revised) February 23, 2000 相似文献
11.
Juozas Kulys Heinz-Josef Deussen Kastis Krikstopaitis Palle Schneider Arturas Ziemys 《Monatshefte für Chemie / Chemical Monthly》2001,132(2):295-304
Summary. N-Aryl-N-hydroxy urethanes (AHUs), which are promising N*OH mediators for oxidoreductase catalysis, are electrochemically active redox compounds with a redox
potential of 0.35–0.40 V vs. SCE (0.59–0.64 V vs. NHE). Alkyl substituents in the carbamic acid residue have, as expected, only little influence on the redox potential. The
highest potential was noticed for N-hydroxy-N-(4-cyanophenyl)-carbamic acid methyl ester. Recombinant Coprinus cinereus peroxidase (rCiP) catalyzes oxidation of the AHUs with apparent bimolecular constants k
ox of 2.5ċ104–7.5ċ104 M
−1s−1 at pH = 8.5 and 25°C.
Structure-function connectivities of the substrates were analysed within the framework of the Marcus cross relationship and by using ab initio quantum chemical calculations. An excellent correlation of the redox potentials and the HOMO energies could be found. However,
no correlation of log(k
ox) with redox potential and HOMO energy was indicated as predicted by theory. This was explained by specific docking of the
substrates in the active center of rCiP.
Received June 26, 2000. Accepted (revised) August 9, 2000 相似文献
12.
Ahmad S. Shawali Rifaat H. Hilal Said El-Sheikh 《Monatshefte für Chemie / Chemical Monthly》2001,132(6):715-720
Summary. Bis-hydrazonoyl chlorides react regioselectively with pyrimidine-2-thiones, which contain a masked thiourea residue, to give
the hitherto unknown annelated 2,3-bis-arylhydrazono-thiazoles and 3,3′-bis-1,2,4-triazoles. Reaction of bis-hydrazonoyl chlorides with 2-methylthio derivatives gave only 3,3′-bis-1,2,4-triazoles.
Received October 4, 2000. Accepted (revised) December 20, 2000 相似文献
13.
Urška L. Štangar Boris Orel Neva Grošelj Patrick Judeinstein Franco Decker Panagiotis Lianos 《Monatshefte für Chemie / Chemical Monthly》2001,132(1):103-112
Summary. A hybrid silicon precursor (ICS-PPG) obtained by reaction of 3-isocyanatopropyltriethoxy silane with poly-(propyleneglycol)-bis-(2-aminopropyl ether) was recognized as a potential host for various salts and molecular species. It has been used for electrochromic,
gasochromic, photovoltaic, and fuel cell applications. This focuses on proton conducting gels (PWA/ICS-PPG, SiWA/ICS-PPG, and W-PTA/ICS-PPG) obtained after the incorporation of polyoxometalates in the ICS-PPG host. IR spectroscopic measurements are used to reveal the entrapment, the aggregation, and the interactions of W-PTA, PWA, or SiWA with the sol-gel derived network. The proton conductivity of the composites, measured using impedance spectroscopy, increases
with increasing concentration of the polyoxometalates from 10−6 to 10−3 S/cm.
Received June 23, 2000. Accepted (revised) September 18, 2000 相似文献
14.
Juraj Černák Janusz Lipkowski Ivan Potočňák Alexander Hudák 《Monatshefte für Chemie / Chemical Monthly》2001,132(2):193-202
Summary. [Cu(tn)2Ni(CN)4]2ċ4H2O and Cu(tn)2Ni(CN)4 (tn = 1,3-diaminopropane) were prepared and characterized. The hydrate is unstable on air and readily dehydrates to Cu(tn)2Ni(CN)4. Crystal structure analysis of the hydrate at 150 K revealed a novel tetranuclear molecular structure of the tetracyanonickellate.
The building elements are two [Cu(tn)2]2+ cations (coordination numbers of Cu: 5 and 6, respectively), two [Ni(CN)4)2− anions, and crystal water. The two cations are linked by one tetracyanonickellate anion via bridging cyano groups placed in cis positions. The second anion is bound weakly (Cu-N = 2.82 ?) via one μ2-bridging cyano ligand. The tetranuclear molecules and pairs of solvate water molecules are linked by strong hydrogen bonds,
thus forming infinite planes which are linked in the third dimension by considerably weaker hydrogen bonds.
Received May 9, 2000. Accepted (revised) August 21, 2000 相似文献
15.
Summary. A crystal structure determination of the 9-acyl-dipyrrinone 9-butanoyl-2,3,7,8-tetramethyl-(10H)-dipyrrin-1-one indicates the presence of intermolecularly hydrogen-bonded dimers; however, in CHCl3 solution the pigment is monomeric as determined by vapor pressure osmometry measurements. Lacking an alkyl group at C(8),
the 9-acyl-dipyrrinone exhibits only a weak tendency to form dimers in CHCl3 (K
A ∼ 60 M
−1) as determined by analysis of variable temperature 1H NMR data. In contrast, when the 9-acyl group is replaced by formyl or when the acyl group is fixed in a syn orientation to the pyrrole NH, the dipyrrinone is strongly prone to dimerization in CHCl3.
Received August 22, 2000. Accepted September 5, 2000 相似文献
16.
Erik Henke Sascha Schuster Hong Yang Uwe T. Bornscheuer 《Monatshefte für Chemie / Chemical Monthly》2000,131(6):633-638
Summary. The resolution of ibuprofen by transesterification of its corresponding vinylester using lipase B from Candida antarctica is described. Compared to transesterification or hydrolysis of the ibuprofen ethyl ester (E < 2, 28–48 h), the reaction with vinylesters occurred significantly faster (1.5–5 h) and with considerably higher enantioselectivity
(E = 8–39).
Received December 20, 1999. Accepted January 12, 2000 相似文献
17.
Thomas Kavc Wolfgang Kern Christian Zenz Guünther Leising Gerald Kranzelbinder Eric Toussaere 《Monatshefte für Chemie / Chemical Monthly》2001,132(4):531-540
Summary. Poly-(4-vinylbenzyl-thiocyanate) (PVBT) was investigated as a photoreactive polymer which changes its refractive index upon UV irradiation as is required for the
production of phase gratings. After UV irradiation, the refractive index of PVBT films increased from nD
20 = 1.629 to nD
20 = 1.660 (Δn = +0.031). The change in the refractive index resulted mainly from the photoinduced isomerization of thiocyanate
(SCN) to isothiocyanate (NCS) groups. It was possible to modify irradiated PVBT with 1-naphthylmethyl amine which lead to a further increase of the refractive index. Both the isomerization and the modification
were followed with FTIR spectroscopy. This modification of the irradiated zones also yields an advantageous stabilization
of phase gratings enscribed in PVBT. The investigations were carried out in the realm of novel organic distributed feedback (DFB) lasers.
Received August 22, 2000. Accepted September 22, 2000 相似文献
18.
Martin Studer Christina Wedemeyer-Exl Felix Spindler Hans-Ulrich Blaser 《Monatshefte für Chemie / Chemical Monthly》2000,131(12):1335-1343
Summary. The first case of an enantioselective hydrogenation of monosubstituted pyridines and furans with homogeneous rhodium diphosphine
catalysts with low but significant enantioselectivities and catalyst activities is reported. Best enantioselectivities (ees of 24–27%) were obtained for the hydrogenation of 2- and 3-pyridine carboxylic acid ethyl ester and 2-furan carboxylic acid
with catalysts prepared in
situ from [Rh(nbd)2]BF4 and the chiral ligands diop, binap, or ferrocenyl diphosphines of the josiphos type. Turnover numbers (ton) were in the order of 10–20, turnover frequencies (tof) usually 1–2 h−1. Diphosphines giving 6- or 7-ring chelates led to higher ees than 1,2-diphosphines; otherwise, no clear correlation between ligand properties and catalytic performance was found. In
some experiments black precipitates were observed at the end of the reaction, indicating the decomposition of the homogeneous
catalysts for certain ligand/metal/substrate combinations.
Received April 5, 2000. Accepted (revised) May 2, 2000 相似文献
19.
Summary. Starting from 2-anilino-2-ethoxy-3-oxothiobutyric acid anilides and (R, R)-or (S, S)-trans-1,2-diaminocyclohexane, chiral C2-disubstituted perhydrobenzimidazole and trans-4a,5,6,7,8,8a-hexahydroquinoxaline derivatives were obtained depending on the polarity of the solvent.
Received April 10, 2000. Accepted May 2, 2000 相似文献
20.
Summary. The reaction of NiCl2 · 6H2O, Na2MoO4 ċ 2H2O, and sulfur in a mixture of diethylenetriamine and 0.2 M ammonia solution (1:4) under solvothermal conditions leads to the formation of orange-red crystals of the oxothiomolybdate
Ni(dien)2[Mo2O2S6] (dien = diethylenetriamine) in nearly 100% yield. The structure consists of [Ni(dien)2]2+ cations and discrete dimeric [Mo2O2S6]2− anions. The compound crystallizes in the monoclinic space group P21/c (a = 8.726(2), b = 18.111(4), c = 14.419(3) ?, β = 101.686(3)°). Upon heating the compound decomposes in a single step starting at about 250°C. The final
decomposition product was identified by X-ray powder diffractometry as MoS2 and Ni3S2. Spectroscopic data as well as detailed synthetic procedures for Ni(dien)2[Mo2O2S6] are reported.
Received November 6, 2000. Accepted November 17, 2000 相似文献