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151.
Tastet L Schaumlöffel D Bouyssiere B Lobinski R 《Analytical and bioanalytical chemistry》2006,385(5):948-953
A method based on ICP collision-cell MS detection in capillary HPLC was developed to gain an insight into the purity and identity of selenium-containing proteins separated by 1-D and 2-D electrophoresis. The bands and spots obtained after the separation of water-soluble proteins in selenized yeast were digested with trypsin prior to chromatography. Selenium could be detected down to the subpicogram level. The method, assisted by information obtained by MALDI TOF MS on the 5000 Da cut-off fraction, permitted the purity of bands and spots to be estimated and the efficiency of tryptic digestion and the quantity of selenium present in individual peptides to be evaluated. Owing to the high sensitivity and the lack of matrix suppression effects, the method provided chromatograms with signal-to-noise ratios of 10–1000 in conditions where the common ES Q–TOF MS detection failed.
相似文献
152.
Guldi DM Rahman GM Qin S Tchoul M Ford WT Marcaccio M Paolucci D Paolucci F Campidelli S Prato M 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(8):2152-2161
Dispersible single-walled carbon nanotubes grafted with poly(4-vinylpyridine), SWNT-PVP, were tested in coordination assays with zinc tetraphenylporphyrin (ZnP). Kinetic and spectroscopic evidence corroborates the successful formation of a SWNT-PVPZnP nanohybrid. Within this SWNT-PVPZnP nanohybrid, static electron-transfer quenching (2.0+/-0.1) x 10(9) s(-1) converts the photoexcited-ZnP chromophore into a radical-ion-pair state with a microsecond lifetime, namely one-electron oxidized-ZnP and reduced-SWNT. 相似文献
153.
Tetrakis(p‐tolyl)oxalamidinato‐bis[acetylacetonatopalladium(II)] ([Pd2(acac)2(oxam)]) reacted with Li–C≡C–C6H5 in THF with formation of [Pd(C≡C–C6H5)4Li2(thf)4] ( 1a ). Reaction of [Pd2(acac)2(oxam)] with a mixture of 6 equiv. Li–C≡C–C6H5 and 2 equiv. LiCH3 resulted in the formation of [Pd(CH3)(C≡C–C6H5)3Li2(thf)4] ( 2 ), and the dimeric complex [Pd2(CH3)4(C≡C–C6H5)4Li4(thf)6] ( 3 ) was isolated upon reaction of [Pd2(acac)2(oxam)] with a mixture of 4 equiv. Li–C≡C–C6H5 and 4 equiv. LiCH3. 1 – 3 are extremely reactive compounds, which were isolated as white needles in good yields (60–90%). They were fully characterized by IR, 1H‐, 13C‐, 7Li‐NMR spectroscopy, and by X‐ray crystallography of single crystals. In these compounds Li ions are bonded to the two carbon atoms of the alkinyl ligand. 1a reacted with Pd(PPh3)4 in the presence of oxygen to form the already known complexes trans‐[Pd(C≡C–C6H5)2(PPh3)2] and [Pd(η2‐O2)(PPh3)2]. In addition, 1a is an active catalyst for the Heck coupling reaction, but less active in the catalytic Sonogashira reaction. 相似文献
154.
Dibutylmagnesium (contaminated with Al(n-Bu)3; nMg:nAl ca. 1:0.2) was found to react with MeOCH2CH2OH followed by the addition of PhSCH(Me)Ph in the presence of 0.2 equiv n-butyllithium yielding [Mg7(μ3-OCH2CH2OMe)6(μ-OCH2CH2OMe)6][Al(n-Bu)4]2 (1) as the principal product (yield 40–45% referred to MeOCH2CH2OH). The single-crystal X-ray diffraction analysis revealed that the centrosymmetric cationic heptamagnesium complex is built up from seven edge-shared MgO6 octahedra. The [Al(n-Bu)4]− anions adopt approximately a tetrahedral AlC4 symmetry. 1H, 13C and 27Al NMR spectroscopic measurements showed that in THF solution the structures both of the heptamagnesium complex and the tetrabutylaluminate anion are preserved and that there are no cation–anion interactions reducing the symmetry. The 27Al resonance (151.6 ppm) was found to be very sharp (w1/2 = 5 Hz), the coupling constant 1J(27Al,13C) amounts to 72.3 Hz. 相似文献
155.
Rhenium Dicarbonyl‐Nitrosyl Complexes with Imidazole Different rhenium‐dicarbonyl‐nitrosyl complexes with imidazole (Im) as monodentate ligand have been synthesized and characterized, starting from [NEt4][ReCl3(CO)2(NO)] and [ReCl(μ?Cl)(CO)2(NO)]2. Whereas the complexes [ReCl2(Im)(CO)2(NO)] and [ReCl(Im)2(CO)2(NO)]+ were achieved in high yields, the complex [Re(Im)3(CO)2(NO)]2+ with three imidazole ligands could only be isolated after complete removal of all halide ions (with AgBF4) in low yield. The synthesis of a corresponding 99mTc‐dicarbonyl‐nitrosyl complex with imidazole opens a new perspective for such compounds as potential radiopharmaceuticals and alternatives to the already established 99mTc‐tricarbonyl complexes. 相似文献
156.
Miller AK Hughes CC Kennedy-Smith JJ Gradl SN Trauner D 《Journal of the American Chemical Society》2006,128(51):17057-17062
A concise, stereoselective, and convergent total synthesis of the unnatural enantiomer of the neodolastane diterpenoid heptemerone B has been completed. Saponification of (-)-heptemerone afforded (-)-guanacastepene E. The absolute stereochemistry of (-)-heptemerone B was thus established as 5-(S), the same as (-)-guanacastepene E. The longest linear sequence of the synthesis comprises 17 (18) steps from simple known starting materials. Our general synthetic approach integrates a diverse set of reactions, including an intramolecular Heck reaction to create one quaternary stereocenter and a cuprate conjugate addition for the establishment of the other. The central seven-membered ring was closed with an uncommon electrochemical oxidation, whereas the five-membered ring was formed through ring-closing metathesis. The absolute configuration of the two key building blocks was established through an asymmetric reduction and an asymmetric ene reaction. 相似文献
157.
Iacono ST Budy SM Ewald D Smith DW 《Chemical communications (Cambridge, England)》2006,(46):4844-4846
New fluorovinylene aromatic ether polymers, possessing dual reactivity, have been successfully prepared via the step-growth polymerization of commercial bis(trifluorovinyl) aromatic ethers and bisphenols. 相似文献
158.
Letzel M Kirchhoff D Grützmacher HF Stein D Grützmacher H 《Dalton transactions (Cambridge, England : 2003)》2006,(16):2008-2016
The unimolecular reactions of radical cations and cations derived from phenylarsane, C6H5AsH2 (1) and dideutero phenylarsane, C6H5AsD2 (1-d2), were investigated by methods of tandem mass spectrometry and theoretical calculations. The mass spectrometric experiments reveal that the molecular ion of phenylarsane, 1*+, exhibits different reactivity at low and high internal excess energy. Only at low internal energy the observed fragmentations are as expected, that is the molecular ion 1*+ decomposes almost exclusively by loss of an H atom. The deuterated derivative 1-d2 with an AsD2 group eliminates selectively a D atom under these conditions. The resulting phenylarsenium ion [C6H5AsH]+, 2+, decomposes rather easily by loss of the As atom to give the benzene radical cation [C6H6]*+ and is therefore of low abundance in the 70 eV EI mass spectrum. At high internal excess energy, the ion 1*+ decomposes very differently either by elimination of an H2 molecule, or by release of the As atom, or by loss of an AsH fragment. Final products of these reactions are either the benzoarsenium ion 4*+, or the benzonium ion [C6H7]+, or the benzene radical cation, [C6H6]*+. As key-steps, these fragmentations contain reductive eliminations from the central As atom under H-H or C-H bond formation. Labeling experiments show that H/D exchange reactions precede these fragmentations and, specifically, that complete positional exchange of the H atoms in 1*+ occurs. Computations at the UMP2/6-311+G(d)//UHF/6-311+G(d) level agree best with the experimental results and suggest: (i) 1*+ rearranges (activation enthalpy of 93 kJ mol(-1)) to a distinctly more stable (DeltaH(r)(298) = -64 kJ mol(-1)) isomer 1 sigma*+ with a structure best represented as a distonic radical cation sigma complex between AsH and benzene. (ii) The six H atoms of the benzene moiety of 1 sigma*+ become equivalent by a fast ring walk of the AsH group. (iii) A reversible isomerization 1+<==>1 sigma*+ scrambles eventually all H atoms over all positions in 1*+. The distonic radical cation 1*+ is predisposed for the elimination of an As atom or an AsH fragment. The calculations are in accordance with the experimentally preferred reactions when the As atom and the AsH fragment are generated in the quartet and triplet state, respectively. Alternatively, 1*(+) undergoes a reductive elimination of H2 from the AsH2 group via a remarkably stable complex of the phenylarsandiyl radical cation, [C6H5As]*+ and an H2 molecule. 相似文献
159.
160.
Pandey D Zemlyanov DY Bevan K Reifenberger RG Dirk SM Howell SW Wheeler DR 《Langmuir : the ACS journal of surfaces and colloids》2007,23(9):4700-4708
Molecular layers formed from 4-trifluoromethylbenzenediazonium tetrafluoroborate and 4-Methylbenzenediazonium tetrafluoroborate have been assembled on H-passivated Si(111) and studied by UHV STM and XPS. STM imaging shows well-developed Si(111) step edges and terraces both on Si(111):H and Si(111) substrates covered with a molecular layer. STM I(V) data acquired at different tip-substrate separations reveals a factor of approximately 10 enhancement in current for positive bias voltage when current flows through the 4-trifluoromethyl molecule when compared to the 4-methyl variant. The observed current enhancement in I(V) can be understood by comparing the projected density of states of the two molecule-Si systems calculated using a density functional theory local density approximation after geometry optimization was performed via the conjugate gradient method. XPS data independently confirm that H-passivated Si(111) remains oxygen free for short exposures to ambient conditions and provide evidence that the molecules chemically react with the silicon surface. 相似文献