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111.
Rivera M Caignan GA Astashkin AV Raitsimring AM Shokhireva TKh Walker FA 《Journal of the American Chemical Society》2002,124(21):6077-6089
The (13)C pulsed ENDOR and NMR study of [meso-(13)C-TPPFe(OCH(3))(OO(t)Bu)](-) performed in this work shows that although the unpaired electron in low-spin ferrihemes containing a ROO(-) ligand resides in a d(pi) orbital at 8 K, the d(xy) electron configuration is favored at physiological temperatures. The variable temperature NMR spectra indicate a dynamic situation in which a heme with a d(pi) electron configuration and planar porphyrinate ring is in equilibrium with a d(xy) electron configuration that has a ruffled porphyrin ring. Because of the similarity in the EPR spectra of the hydroperoxide complexes of heme oxygenase, cytochrome P450, and the model heme complex reported herein, it is possible that these two electron configurations and ring conformations may also exist in equilibrium in the enzymatic systems. The ruffled porphyrinate ring would aid the attack of the terminal oxygen of the hydroperoxide intermediate of heme oxygenase (HO) on the meso-carbon, and the large spin density at the meso-carbons of a d(xy) electron configuration heme suggests the possibility of a radical mechanism for HO. The dynamic equilibrium between the ruffled (d(xy)) and planar (d(pi)) conformers observed in the model complexes also suggests that a flexible heme binding cavity may be an important structural motif for heme oxygenase activity. 相似文献
112.
Knippenberg S Nixon KL Mackenzie-Ross H Brunger MJ Wang F Deleuze MS François JP Winkler DA 《The journal of physical chemistry. A》2005,109(41):9324-9340
Results of a study of the valence electronic structure of norbornene (C(7)H(10)), up to binding energies of 30 eV, are reported. Experimental electron momentum spectroscopy (EMS) and theoretical Green's function and density functional theory approaches were utilized in this investigation. A stringent comparison between the electron momentum spectroscopy and theoretical orbital momentum distributions found that, among the tested models, the combination of the Becke-Perdew functional and a polarized valence basis set of triple-zeta quality provides the best representation of the electron momentum distributions for all 19 valence orbitals of norbornene. This experimentally validated model was then used to extract other molecular properties of norbornene (geometry, infrared spectrum). When these calculated properties are compared to corresponding results from independent measurements, reasonable agreement is typically found. Due to the improved energy resolution, EMS is now at a stage to very finely image the effective topology of molecular orbitals at varying distances from the molecular center, and the way the individual atomic components interact with each other, often in excellent agreement with theory. This will be demonstrated here. Green's Function calculations employing the third-order algebraic diagrammatic construction scheme indicate that the orbital picture of ionization breaks down at binding energies larger than about 22 eV. Despite this complication, they enable insights within 0.2 eV accuracy into the available ultraviolet emission and newly presented (e,2e) ionization spectra. Finally, limitations inherent to calculations of momentum distributions based on Kohn-Sham orbitals and employing the vertical depiction of ionization processes are emphasized, in a formal discussion of EMS cross sections employing Dyson orbitals. 相似文献
113.
Mario Bossa Elena Cervone Carmine Garzillo Andrea Peluso 《Journal of Molecular Structure》1997,390(1-3):101-107
The electronic absorption spectra of Ni, Zn and Mg hemiporphyrazine derivatives are presented and discussed together with theoretical results obtained by INDO/S computations. The absorption spectra of all the metal derivatives show marked red shifts of the lowest energy absorption bands with respect to those of the metal free hemiporphyrazine. The possible explanation that in metal derivatives low lying excited states with a fully conjugated π electron system are present is supported by theoretical computations. 相似文献
114.
Alberto Bargagna Pietro Schenone Francesco Bondavalli Mario Longobardi 《Journal of heterocyclic chemistry》1980,17(1):33-37
Cycloaddition of sulfene to N,N-disubstituted 4-amino-3-methyl-3-buten-2-ones (III) occurred in fair to good yield only in the case of aliphatic N-substitution to give 4-dialkylamino-3,4-dihydro-5,6-dimethyl-1,2-oxathiin 2,2-dioxides, whereas N,N-disubstituted 1-amino-1-penten-3-ones (II) did not react at all. Cycloaddition of dichloroketene to II, III and N,N-disubstituted 4-amino-3-buten-2-ones occurred only in the case of the methylphenylamino derivative, giving in good to moderate yield 6,(5)(di)alkyl-3,3-dichloro-3,4-dihydro-4-methylphenylamino-2-Hpyran-2-ones, which were dehydrochlorinated with DBN to 6,(5)(di)alkyl-3-chloro-4-methylphenylamino-2H-pyran-2-ones. 相似文献
115.
Paolo Domiano Amos Musatti Mario Nardelli Corrado Pelizzi Giovanni Predieri 《Transition Metal Chemistry》1979,4(6):351-354
Summary The x-ray crystal structure of the title complex is described Crystals are monoclinic, space groupP21/n, with unit-cell dimensions:a=18.070(2),b=13.471(2),c=6.788(2) Å,=94.70(1),Z=4. The structure was solved from diffractometer data by Patterson and Fourier methods and refined by least-squares techniques toR=5.0% for 2451 independent reflections. It consists of complex molecules, in which the copper atom square planar coordination comprises the chlorine atom, Cu-Cl=2.240(3) Å, and the organic ligand which acts as terdentate through the oxygen atom [Cu-O=1.948(3) Å] and a nitrogen atom, [Cu-N=1.933(5) Å] from the hydrazidic chain and the oxygen atom, [Cu-O = 1.894(4) Å] from the pyridoxal group. 相似文献
116.
Raimund Winkler 《Fresenius' Journal of Analytical Chemistry》1973,267(4):261-266
Zusammenfassung Eisen-55 wurde in Neuherberg bei München seit März 1970 in monatlich gesammelten Luftstaubproben und seit Januar 1971 in Monatsniederschlagsproben bestimmt. Nach dem Veraschen der Proben wurde Eisen durch Extraktion' mit Di-iso-propyläther abgetrennt. Zur weiteren Entfernung störender Radionuklide des Fallouts wurde eine Ionenaustauschertrennung angeschlossen. Nach der elektrolytischen Abscheidung des Eisens auf Kupferplättchen wurden die Röntgenspektren mit einem Proportionalzähler sowie einem Si(Li)-Detektor aufgenommen.Die mittlere spezifische Luftaktivität betrug in Neuherberg 1,0 fCi/m3 im Jahr 1970 (ab März), 1,2 fCi/m3 im Jahr 1971 und 0,36 fCi/m3 im Jahr 1972. Die dem Boden durch den Niederschlag zugeführte Aktivität wurde zu 697 pCi/m2 · Jahr für 1971 und 178 pCi/m2 · Jahr für 1972 bestimmt.Vortrag anläßlich der Tagung Spurenanalyse, 2. bis 5. April 1973 in Erlangen. 相似文献
117.
The reaction between arachno-4-CB(8)H(14) and PCl(3) in the presence of PS (PS = proton sponge = 1,8-dimethylamino naphthalene) (dichloromethane, rt, 24 h) produced the neutral phosphacarborane closo-2,1-PCB(8)H(9) (35% yield), while a similar reaction of nido-1-CB(8)H(12) gave the isomeric compound closo-6,1-PCB(8)H(9) (27% yield). The structures of both compounds were derived on the basis of the combined ab initio/GIAO/NMR ((1)H, (11)B, (13)C) approach. The optimized structures at a correlated level of theory (MP2) with 6-31G* basis set were used as a basis for calculations of the (11)B and (13)C chemical shifts at GIAO-SCF/II and GIAO-MP2/II, the latter showing excellent agreement with experimental data. 相似文献
118.
To explore tertiary contact formation in alpha-synuclein, a natively unfolded protein implicated in Parkinson's disease, we have measured the rates of reaction between a powerful electron donor, the tryptophan (W) triplet excited state, and an acceptor, 3-nitro-tyrosine (Y(NO2)) in six different variants, probing loop sizes between 15 and 132 residues. Electron transfer rates decrease with loop size with the fastest contact time of 140 ns for the N-terminal pair and the slowest of 1.2 mus for the N- to C-terminal pair. Diffusion coefficients ranging from approximately 2 x 10-6 to approximately 10-5 cm2 s-1 were extracted from simultaneous fits of the W to Y(NO2) electron (triplet excited state) and energy transfer (singlet excited state) kinetics. 相似文献
119.
Gianni Zotti Giuseppe Pilloni Mario Bressan Mario Martelli 《Journal of Electroanalytical Chemistry》1977,75(2):607-612
The electrochemical reduction of chlorodi-(1,3-bisdiphenylphosphinopropane)ruthenium(II)hexafluorophosphate, [RuCl(DPP)2](PF6), has been studied on the mercury electrode in 1,2-dimethoxyethane +0.1 M TBAP. The polarogram shows two reversible one-electron waves corresponding to the formation of [RuCl(DPP)2] and [RuCl(DPP)2]. Both products are unstable and decay through a disproportionation pathway and a fast internal metalation via Cl? elimination with formation of HRu(C6H4PPh·CH2CH2 CH2·PPh2)(DPP), respectively. The hypothesis is put forward that the geometry of a metal-complex can be one of the factors which allow us to obtain d7 monomeric complexes by electrochemical methods. 相似文献
120.
Giorgio Roma Aldo Ermili Alessandro Balbi Elda Massa Mario Di Braccio 《Journal of heterocyclic chemistry》1981,18(8):1619-1623
The reaction of 3-(dimethylamino)-1-oxo-1H-naphtho[2,1-b]pyran-2-carbaldehyde (Ia) with o-phenylenediamines or N-monosubstituted o-phenylenediamines in refluxing glacial acetic acid afforded the corresponding naphtho[1′,2′:5,6]pyrano[2,3-b][1,5]benzodiazepin-15-(8H)ones V in very good yields. A similar result was achieved when the reaction was carried out in refluxing pyridine, using N-monosubstituted o-phenylenediamine hydrochlorides. The isolation of a significant intermediate as well as the synthesis through a different univocal pathway confirmed the structure of the compounds V. Moreover the reaction of Ia with N-monosubstituted o-phenylenediamines in refluxing pyridine generally afforded only low yields of compounds V, sometimes together with naphtho[1′,2′:5,6]pyrano[2,3-b][1,5]benzodiazepin-15-(13H)ones VII, isomers of V. 相似文献