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21.
Alan M Bond Enrico Mocellin Cherrie B Pascual Panit Wedkanjana Grard Jaouen Siden Top 《应用有机金属化学》1990,4(5):557-568
Electrochemical oxidation of α- and β-diastereomers of a range of steroid hormone receptor marker chromium tricarbonyl complexes, (steroid)Cr(CO)3, have been examined at platinum electrodes in dichloromethane. Data confirm the general nature of previously published conclusions on the oxidation of (arene)Cr(CO)3 complexes (arene = benzene or steroid). That is, with 0.1 M Bu4NPF6 as the electrolyte, and in the absence of nucleophiles, a reversible oneelectron process, (steroid)Cr(CO)3 ? [(steroid)Cr(CO)3]+ + e?, is observed, followed by an irreversible one-electron process at considerably more positive potentials. The reversible half-wave potentials (approximately E°-values) calculated for the [(steroid)Cr(CO)3]+/(steroid)Cr(CO)3 redox couple are shown to be dependent on whether the α- or β-diastereomer is oxidized. Similarly the rate of nucleophilic attack on the 17-electron cation [(steroid)Cr(CO)3]+ by nucleophiles such as ClO, PPh3 and bis(diphenylphosphine)methane confirms a previous observation that the stereochemistry of this class of compound is important with respect to redox, kinetic and hormone receptor properties. The nature of the electrochemical data obtained on the (arene)Cr(CO)3 complexes in the presence of nucleophiles suggests that reactions associated with the nucleophilic attack on the 17-electron cations are complex and that a range of reaction pathways occur simultaneously. Electrochemical studies on the oxidation of (benzene)Cr(CO)2PPh3 and (oestradiol)Cr(CO)2PPh3 confirm some aspects of the proposed mechanisms, although it is clear that a great deal still has to be learned concerning mechanistic aspects of nucleophilic attack on these 17-electron complexes. 相似文献
22.
Fabio Ponticelli Enrico Marinello Roberto Pagani Lucia Terzuoli 《Journal of heterocyclic chemistry》1991,28(5):1225-1227
The reaction of B6 vitamins 1–3 with cyanate, in the presence of equivalent amounts of hydrochloric acid, yields different adducts according to the structure of the starting material. Regiospecific attack on the amino group or the phenolic hydroxy group was found for 2a,b and 3a,b , respectively. From the aldehydes 1a,b , the 2H-pyrido[3,4-e]-1,3-oxazin-2-ones 7a,b were obtained through an attack on both the phenolic and aldehyde group. 相似文献
23.
Andreoli R Manini P Poli D Bergamaschi E Mutti A Niessen WM 《Analytical and bioanalytical chemistry》2004,378(4):987-994
A new and simple method for the determination of fat-soluble vitamins (retinol, alpha-tocopherol, and beta-carotene) in human serum was developed and validated by using liquid chromatography-tandem mass spectrometry with atmospheric pressure chemical ionization (LC-APCI-MS-MS). Different solvent mixtures were tested to obtain deproteinization and extraction of the analytes from the matrix. As a result, a volume of 240 microL of a 1:1 (v/v) ethanol/ethyl acetate mixture added to 60 microL of serum was found to be suitable for both protein precipitation and antioxidants solubilization, giving the best recovery for all three analytes. Deproteinized samples (20 microL) were injected after dilution, without the need for concentration or evaporation to dryness and reconstruction of the sample. Vitamins were separated on a C-8 column using a 95:5 (v/v) methanol/dichloromethane mixture and ionized in the positive-ion mode; detection was performed in the selected-reaction monitoring mode. Linearity of the LC-APCI-MS-MS method was established over 5 orders of magnitude for retinol and alpha-tocopherol, whereas in the case of beta-carotene it was limited to 4 orders. Lower limits of quantitation were 1.7, 2.3, and 4.1 nM for retinol, alpha-tocopherol, and beta-carotene, respectively. Serum concentrations of retinol, alpha-tocopherol, and alpha+beta-carotene determined in a group of healthy volunteers were 2.48, 38.07, and 0.50 microM, respectively, in samples collected in winter ( n=122) and 2.69, 45.88, and 0.90 microM during summer ( n=66). 相似文献
24.
Enrico Borgarello Jean Desilvestro Michael Grtzel Ezio Pelizzetti 《Helvetica chimica acta》1983,66(6):1827-1834
Conduction band electrons produced by band gap excitation of TiO2-particles reduce efficiently thiosulfate to sulfide and sulfite. \documentclass{article}\pagestyle{empty}\begin{document}$ {\rm 2e}_{{\rm cb}}^ - ({\rm TiO}_{\rm 2}) + {\rm S}_{\rm 2} {\rm O}_3^{2 - } \longrightarrow {\rm S}^{2 - } + {\rm SO}_3^{2 - } $\end{document} This reaction is confirmed by electrochemical investigations with polycrystalline TiO2-electrodes. The valence band process in alkaline TiO2-dispersions involves oxidation of S2O to tetrathionate which quantitatively dismutates into sulfite and thiosulfate, the net reaction being: \documentclass{article}\pagestyle{empty}\begin{document}$ 2{\rm h}^{\rm + } ({\rm TiO}_{\rm 2}) + 0.5{\rm S}_{\rm 2} {\rm O}_{\rm 3}^{{\rm 2} - } + 1.5{\rm H}_{\rm 2} {\rm O} \longrightarrow {\rm SO}_3^{2 - } + 3{\rm H}^{\rm + } $\end{document} This photodriven disproportionation of thiosulfate into sulfide and sulfite: \documentclass{article}\pagestyle{empty}\begin{document}$ 1.5{\rm H}_{\rm 2} {\rm O } + 1.5{\rm S}_{\rm 2} {\rm O}_{\rm 3}^{{\rm 2} - } \mathop \to \limits^{h\nu} 2{\rm SO}_3^{2 - } + {\rm S}^{{\rm 2} - } + 3{\rm H}^{\rm + } $\end{document} should be of great interest for systems that photochemically split hydrogen sulfide into hydrogen and sulfur. 相似文献
25.
Menozzi E Busi M Ramingo R Campagnolo M Geremia S Dalcanale E 《Chemistry (Weinheim an der Bergstrasse, Germany)》2005,11(10):3136-3148
The self-assembly of open ditopic and tetratopic cavitand complexes has been investigated by using monofunctionalized cavitand ligands and suitable metal precursors. In the case of ditopic complexes, self-assembly protocols, leading exclusively to the formation of both thermodynamically stable cis-Pt square-planar complexes 8 and 9 and the kinetically inert fac-Re octahedral complex 14, have been elaborated. The use of cis-[Pt(CH3)CN)2Cl2] as metal precursor led to the formation of monotopic trans-10 and ditopic trans-11 cavitand complexes, while cis-[Pt(dmso)2Cl2] afforded both cis-13 and trans-11 isomers. The self-assembly of tetratopic cavitand complexes has been achieved by using mononuclear [Pd(CH3CN)4(BF4)2] and dinuclear [M2(tppb)(OTf)4] (19: M = Pt; 20: M = Pd) metal precursors. Only the tetratopic dinuclear complexes 21 and 22 were stable. The ligand configuration with two phosphorus and two cavitand ligands at the metal centers is the most appropriate to build tetratopic cavitand complexes with sufficient kinetic stability. 相似文献
26.
Gaetano Dattolo Girolamo Cirrincione Anna Maria Almerico Enrico Aiello Isabella D'Asdia 《Journal of heterocyclic chemistry》1986,23(5):1371-1373
Pyrrolo[1,2-f]phenanthridines were prepared in good yields by the diazotization in acetic acid of the amines la,b and subsequent treatment with hypophosphorous acid. The necessity for hypophosphorous acid in the reaction was demonstrated. 相似文献
27.
Casella L Monzani E Fantucci P Gullotti M De Gioia L Strini A Chillemi F 《Inorganic chemistry》1996,35(2):439-444
The effect of strain in the axial coordination of imidazole to the heme has been studied in the chelate complexes deuterohemin-histidine (DH-His) and deuterohemin-alanylhistidine (DH-AlaHis). Molecular mechanics calculations indicate that three types of distortion of the axial ligand occur in DH-His, due to the relatively short length of the arm carrying the donor group: tilting off-axis, tipping, and inclination of the imidazole plane with respect to the axial Fe-N bond. The effects of tilting (Deltagamma approximately 10 degrees ) and inclination of the imidazole ring (Deltadelta approximately 17 degrees ) are dominant, while tipping is small and is probably of little importance here. By contrast, the axial imidazole coordination is normal in DH-AlaHis and other computed deuterohemin-dipeptide or -tripeptide complexes where histidine is the terminal residue, the only exception being DH-ProHis, where the rigidity of the proline ring reduces the flexibility of the chelating arm. The distortion in the axial iron-imidazole bond in DH-His has profound and negative influence on the binding and catalytic properties of this complex compared to DH-AlaHis. The former complex binds more weakly carbon monoxide, in its reduced form, and imidazole, in its oxidized form, than the latter. The catalytic efficiency in peroxidative oxidations is also reduced in DH-His with respect to DH-AlaHis. The activity of the latter complex is similar to that of microperoxidase-11, the peptide fragment incorporating the heme that results from hydrolytic cleavage of cytochrome c. 相似文献
28.
DFT calculations have been carried out for 2-, 3- and 4-methoxybenzyl alcohol radical cations (1+, 3+ and 4+, respectively) and the α-methyl derivatives 2+ and 5+ using the UB3LYP/6-31G(d) method. The theoretical results have been compared with the experimental rate constants for deprotonation of 1+-5+ under acidic and basic conditions. In acidic solution, the decay of 1+-5+ proceeds by cleavage of the C-H bond, while in the presence of −OH all the radical cations undergo deprotonation from the α-OH group. This pH-dependent change in mechanism has been interpreted qualitatively in terms of simple frontier molecular orbital theory. The −OH induced α-O-H deprotonation is consistent with a charge controlled reaction, whereas the C-H deprotonation, observed when the base is H2O, appears to be affected by frontier orbital interactions. 相似文献
29.
Bonomo RP Cucinotta V Giuffrida A Impellizzeri G Magri A Pappalardo G Rizzarelli E Santoro AM Tabbi G Vagliasindi LI 《Dalton transactions (Cambridge, England : 2003)》2005,(1):150-158
An aqueous solution spectroscopic (Vis and EPR) study of the copper(II) complexes with the Ac-HGGG-NH2 and Ac-PHGGGWGQ-NH2 polypeptides (generically designated as L) suggests square base pyramids ascribable to [Cu(L)H(-2)] complex species, which contain three nitrogen donor atoms, arising from imidazole and peptide groups, in the equatorial plane and for a pseudo-octahedral geometry in the case of [CuLH-3]- and [Cu(L)H-4]2- which have four nitrogen donor atoms in their equatorial plane. The coordination sphere of the copper complex in the [Cu(L)H(-2)] species, which is present at neutral pH values, is completed by two oxygen donor atoms. ESI-MS spectra ascertained that water molecules are not present in the coordination equatorial plane of this latter species, in comparison with other copper(II) complexes with ligands bearing nitrogen and oxygen donor atoms and surely having equatorial water molecules. This indicates the coordination of a carbonyl oxygen atom in the equatorial plane has to be invoked. However, no direct proof about the involvement of a carbonyl group oxygen donor atom apically linked to copper was obtained, due to the flexibility of these structures at room temperature. Additionally, the low A(ll) value leads one to consider another oxygen atom of a carbonyl group being involved in the apical bond to copper in a fast exchange fashion. This apical interaction, which may also involve a water molecule, is more pronounced in the Cu-Ac-HGGG-NH2 than in the analogous Cu-Ac-PHGGGWGQ-NH2 system, probably because of the presence of tryptophan and proline in the polypeptide sequence. 相似文献
30.
Di Natale G Grasso G Impellizzeri G La Mendola D Micera G Mihala N Nagy Z Osz K Pappalardo G Rigó V Rizzarelli E Sanna D Sóvágó I 《Inorganic chemistry》2005,44(20):7214-7225
Copper(II) complexes of the neurotoxic peptide fragments of human and chicken prion proteins were studied by potentiometric, UV-vis, CD, and EPR spectroscopic and ESI-MS methods. The peptides included the terminally blocked native and scrambled sequences of HuPrP106-126 (HuPrPAc106-126NH2 and ScrHuPrPAc106-126NH2) and also the nona- and tetrapeptide fragments of both the human and chicken prion proteins (HuPrPAc106-114NH2, ChPrPAc119-127NH2, HuPrPAc109-112NH2, and ChPrPAc122-125NH2). The histidyl imidazole-N donor atoms were found to be the major copper(II) binding sites of all peptides; 3N and 4N complexes containing additional 2 and 3 deprotonated amide-N donors, respectively, are the major species in the physiological pH range. The complex formation processes for nona- and tetrapeptides are very similar, supporting the fact that successive deprotonation and metal ion coordination of amide functions go toward the N-termini in the form of joined six- and five-membered chelates. As a consequence, the peptide sequences investigated here, related to the neurotoxic region of the human PrP106-126 sequence, show a higher metal-binding affinity than the octarepeat fragments. In the case of the HuPrP peptide sequences, a weak pH-dependent binding of the Met109 residue was also detected in the 3N-coordinated complexes. 相似文献