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991.
We describe a photochemical system for the generation of hydrogen by water reduction under visible light or sunlight irradiation of aqueous solutions containing the following components: a photosensitizer, the Ru (bipy) complex, for visible light absorption; a relay species, the Rh (bipy) complex, which mediates water reduction by intermediate storage of electrons via a reduced state; an electron donor, triethanolamine (TEOA) which provides the electrons for the reduction process and a redox catalyst, colloïdal platinum, which facilitates hydrogen formation. The conditions for efficient hydrogen production and the influence of the concentration of the components have been investigated; the metal complexes act as catalysts with high turnover numbers; excess bipyridine facilitates the reaction. The process contains two catalytic cycles: a ruthenium cycle and a rhodium cycle. The Ru cycle involves oxidative quenching of the *Ru(bipy) excited state by Rh(bipy) forming Ru(bipy) which is converted back to Ru(bipy) by oxidation of the electron donor TEOA, which is thus consumed. The Rh cycle comprises a complicated set of transformations of the initial Rh(bipy) complex. The reduced rhodium complex formed in the quenching process undergoes a series of transformations involving the Rh(bipy) complex and hydridorhodium-bipyridine species, from which hydrogen is generated by reaction with the protons of water. In view of the storage of two electrons in the reduced rhodium species, the process is formally a dielectronic water reduction. The properties and eventual participation of [Rh(III)(bipy)2LL′]n+(L,L′ = H2O, OH?) species are investigated. It is concluded that at neutral pH in presence of excess bipyridine, the cycle involving regeneration of the Rh(bipy) complex is predominant. A number of experiments have been performed with modified systems. Hydrogen evolution is observed with other photosensitizers (like proflavin), other relay species (like Rh(dimethylbipy) or Co(II)-bipyridine complexes), other donor species, or in absence of the platinum catalyst. It also occurs in absence of photosensitizer by sunlight of UV. irradiation of Rh(bipy) or by visible light irradiation of iridium (III)-bibyridine complexes. These systems deserve further investigations. The present photochemical hydrogen generating system represents the reductive component of a complete water splitting process. Its role in solar energy conversion and in photochemical fuel production is discussed. 相似文献
992.
Baranoff E Collin JP Furusho J Furusho Y Laemmel AC Sauvage JP 《Inorganic chemistry》2002,41(5):1215-1222
Complexes of the type Ru(phen)(2)L(2+), where L is a substituted bipyridine family member, have been prepared, and their photochemical substitution reactions have been investigated. In the presence of a bis-benzonitrile derivative, acting as a bidentate chelate, photoexpulsion of L is performed under the action of visible light, with quantitative formation of new complexes of the type Ru(phen)(2)L'(2+) (L' = bis-nitrile ligand). Several complexes have been characterized by X-ray crystallography. In particular, the bis-benzonitrile complexes could be crystallized, and the structure of these compounds, containing a 13-, 14-, or 15-membered metal incorporating ring, was obtained. By heating Ru(phen)(2)L'(2+) with a bipy derivative in refluxing ethylene glycol, quantitative formation of the starting complex [Ru(phen)(2)L(2+)] was carried out. The present series of compounds presents properties that could be profitably used in the design and construction of multicomponent systems acting as photochemically driven molecular machines. 相似文献
993.
Ikuta Y Ooidemizu M Yamahata Y Yamada M Osa S Matsumoto N Iijima S Sunatsuki Y Kojima M Dahan F Tuchagues JP 《Inorganic chemistry》2003,42(22):7001-7017
A new family of spin crossover complexes, [Fe(II)H(3)L(Me)](NO(3))(2).1.5H(2)O (1), [Fe(III)L(Me)].3.5H(2)O (2), [Fe(II)H(3)L(Me)][Fe(II)L(Me)]NO(3) (3), and [Fe(II)H(3)L(Me)][Fe(III)L(Me)](NO(3))(2) (4), has been synthesized and characterized, where H(3)L(Me) denotes a hexadentate N(6) tripod ligand containing three imidazole groups, tris[2-(((2-methylimidazol-4-yl)methylidene)amino)ethyl]amine. It was found that the spin and oxidation states of the iron complexes with this tripod ligand are tuned by the degree of deprotonation of the imidazole groups and by the 2-methyl imidazole substituent. Magnetic susceptibility and M?ssbauer studies revealed that 1 is an HS-Fe(II) complex, 2 exhibits a spin equilibrium between HS and LS-Fe(III), 3 exhibits a two-step spin transition, where the component [Fe(II)L(Me)](-) with the deprotonated ligand participates in the spin transition process in the higher temperature range and the component [Fe(II)H(3)L(Me)](2+) with the neutral ligand participates in the spin transition process in the lower temperature range, and 4 exhibits spin transition of both the Fe(II) and Fe(III) sites. The crystal structure of 3 consists of homochiral extended 2D puckered sheets, in which the capped tripodlike components [Fe(II)H(3)L(Me)](2+) and [Fe(II)L(Me)](-) are alternately arrayed in an up-and-down mode and are linked by the imidazole-imidazolate hydrogen bonds. Furthermore, the adjacent 2D homochiral sheets are stacked in the crystal lattice yielding a conglomerate as confirmed by the enantiomeric circular dichorism spectra. Compounds 3 and 4 showed the LIESST (light induced excited spin state trapping) and reverse-LIESST effects upon irradiation with green and red light, respectively. 相似文献
994.
Synthesis of N-Methyl- and N,N-Dimethylmerucathine and of N-Methyl- and N,N--Dimethylpseudomerucathine Starting from L -Alanine Starting form L -alanine, N-methylmerucathine (= (3R,4S)-4-(methylamino)1-phenyl-1-penten-3-ol; (3R,4S,)- 6 ), N,N-dimethylmerucathine (= (3R,4S)-4-(dimethylamino)-1-phenyl-1-penten-3-ol; (3R,4S)- 9 ), N-methylpseudomerucathine (= (3S,4S)-4-(methylamino)-1-phenyl-1-penten-3-01; (3S,4S)-6), and N,N-dimethylpseudomerucathine (= (3S,4S)-4-(dimethylamino)-1-phenyl-1-penten-3-ol; (3S,4S)- 9 ) were synthesized. The four compounds were analyzed by HPLC and compared with a natural khat extract. 相似文献
995.
Daniel Frhel Alain Badorc Jean-Marie Pereillo Jean-Pierre Maffrand 《Journal of heterocyclic chemistry》1985,22(4):1011-1016
This paper describes two new access routes to 5,6,7,8-tetrahydro-4H-thieno[2,3-d]azepine from 2-(2-thienyl)ethylamine or its N-(2-chlorobenzyl) derivative. One of these two syntheses involves a new ring expansion from a 6,7-dihydro[3,2-c]pyridinium derivative, chloromethylated in position 4. 相似文献
996.
The use of phenylsulfonylethylidene (PSE) acetal as a new 3′,5′-bridged protecting group in nucleoside chemistry is reported. The PSE acetal demonstrates to be compatible with Lewis acids used in standard glycosylation reactions. In addition, a selective 2′-O-deacylation from a 3′,5′-O-(phenylsulfonyl)-2′-O-acetyl nucleoside can be achieved, giving access to subsequent chemical modifications in 2′ position. However, the PSE acetal cleavage surprisingly appeared to be purine/pyrimidine base dependent. 相似文献
997.
Bardelang D Rockenbauer A Karoui H Finet JP Tordo P 《The journal of physical chemistry. B》2005,109(20):10521-10530
(1)H NMR and electron paramagnetic resonance (EPR) titrations were used to determine the association constants of the complexes of alpha-phenyl-N-tert-butylnitrone (PBN) analogues and their superoxide spin adducts, respectively, with methylated beta-cyclodextrins. A 1:1 stoichiometry for the nitrones with randomly methylated beta-cyclodextrin and 2,6-di-O-methyl-beta-cyclodextrin and 1:1 and 1:2 stoichiometries for the corresponding cyclodextrin-nitroxide complexes were observed. After the superoxide radical spin trapping reaction, EPR titrations afforded the association constants of the corresponding cyclodextrin-nitroxide complexes. Two-dimensional EPR simulations indicated a bimodal inclusion of the nitroxide free radical spin adducts into the cyclodextrins. For all the nitrone-cyclodextrin and nitroxide-cyclodextrin complexes, the association constants were always higher for the nitroxide complexes than for the nitrone complexes. A cooperative system concerning the complexation of the nitroxide spin adduct with a cyclodextrin was evidenced by EPR titrations. The efficiency of the cyclodextrin inclusion technique to trap superoxide and to resist bioreduction by sodium l-ascorbate was also investigated. 相似文献
998.
Jean-Pierre E. Grolier Jan J. Spitzer Robert H. Wood Ian R. Tasker 《Journal of solution chemistry》1985,14(6):393-405
Enthalpies of dilution, freezing temperatures, and densities of aqueous solutions of N,N-dimethylacetamide and N,N-dimethylpropionamide have been measured. Freezing temperatures of dilute aqueous solutions of formamide and N,N-dimethylformamide have also been measured. These data yield the pairwise molecular Gibbs energies and enthalpies of interaction: these have been treated according to a group additivity principle to give pairwise functional group Gibbs energies and enthalpies of interaction. The results indicate that substitution on the amide nitrogen may increase the Gibbs energy and enthalpy of interaction of the amide group with itself in an aqueous environment but the effect if present is small. 相似文献
999.
Stachowiak C Viguié JR Grolier JP Rogalski M 《Langmuir : the ACS journal of surfaces and colloids》2005,21(11):4824-4829
The interactions between asphaltenes and short- to medium-chain n-alkanes were studied using titration microcalorimetry and inverse chromatography. The exothermic heat effects observed upon mixing of asphaltenes and n-alkanes were interpreted in terms of assembling of the two types of compounds into mixed structures. We show that the energy of the interactions between n-alkanes and the asphaltene hydrocarbon chains is close to the energy of the interactions between the asphaltene chains. We propose that the latter interactions are responsible for the formation of the asphaltene aggregates and are the driving force of the aggregate assembly into higher structures. 相似文献
1000.
Donaire A Jiménez B Fernández CO Pierattelli R Niizeki T Moratal JM Hall JF Kohzuma T Hasnain SS Vila AJ 《Journal of the American Chemical Society》2002,124(46):13698-13708
The blue copper proteins (BCPs), pseudoazurin from Achromobacter cycloclastes and rusticyanin from Thiobacillus ferrooxidans, have been investigated by (1)H NMR at a magnetic field of 18.8 T. Hyperfine shifts of the protons belonging to the coordinated ligands have been identified by exchange spectroscopy, including the indirect detection for those resonances that cannot be directly observed (the beta-CH(2) of the Cys ligand, and the NH amide hydrogen bonded to the S(gamma)(Cys) atom). These data reveal that the Cu(II)-Cys interaction in pseudoazurin and rusticyanin is weakened compared to that in classic blue sites (plastocyanin and azurin). This weakening is not induced by a stronger interaction with the axial ligand, as found in stellacyanin, but might be determined by the protein folding around the metal site. The average chemical shift of the beta-CH(2) Cys ligand in all BCPs can be correlated to geometric factors of the metal site (the Cu-S(gamma)(Cys) distance and the angle between the CuN(His)N(His) plane and the Cu-S(gamma)(Cys) vector). It is concluded that the degree of tetragonal distortion is not necessarily related to the strength of the Cu(II)-S(gamma)(Cys) bond. The copper-His interaction is similar in all BCPs, even for the solvent-exposed His ligand. It is proposed that the copper xy magnetic axes in blue sites are determined by subtle geometrical differences, particularly the orientation of the His ligands. Finally, the observed chemical shifts for beta-CH(2) Cys and Ser NH protons in rusticyanin suggest that a less negative charge at the sulfur atom could contribute to the high redox potential (680 mV) of this protein. 相似文献