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221.
Palmblad M Tsybin YO Ramström M Bergquist J Håkansson P 《Rapid communications in mass spectrometry : RCM》2002,16(10):988-992
Liquid separation methods in combination with electrospray mass spectrometry as well as the recently introduced fragmentation method electron capture dissociation (ECD) have become powerful tools in proteomics research. This paper presents the results of the first successful attempts to combine liquid chromatography (LC) and Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS) with ECD in the analysis of a mixture of standard peptides and of a bovine serum albumin tryptic digest. A novel electron injection system provided conditions for ECD sufficient to yield extensive sequence information for the most abundant peptides in the mixtures on the time-scale of the chromatographic separation. The results suggest that LC/ECD-FTICRMS can be employed in the characterization of peptides in enzymatic digests of proteins or protein mixtures and identify and localize posttranslational modifications. 相似文献
222.
Bengtsson J Jansson B Hammarlund-Udenaes M 《Rapid communications in mass spectrometry : RCM》2005,19(15):2116-2122
A sensitive and reproducible method for the determination of morphine and the metabolites morphine-3-glucuronide (M3G) and morphine-6-glucuronide (M6G) was developed. The method was validated for perfusion fluid used in microdialysis as well as for sheep and human plasma. A C18 guard column was used to desalt the samples before analytical separation on a ZIC HILIC (hydrophilic interaction chromatography) column and detection with tandem mass spectrometry (MS/MS). The mobile phases were 0.05% trifluoroacetic acid (TFA) for desalting and acetonitrile/5 mM ammonium acetate (70:30) for separation. Microdialysis samples (5 microL) were directly injected onto the system. The lower limits of quantification (LLOQ) for morphine, M3G and M6G were 0.50, 0.22 and 0.55 ng/mL, respectively, and the method was linear from LLOQ to 200 ng/mL. For plasma, a volume of 100 microL was precipitated with acetonitrile containing internal standards (deuterated morphine and metabolites). The supernatant was evaporated and reconstituted in 0.05% TFA before the desalting process. The LLOQs for sheep plasma were 2.0 and 3.1 ng/mL and the ranges were 2.0-2000 and 3.1-3100 ng/mL for morphine and M3G, respectively. For human plasma, the LLOQs were 0.78, 1.49 and 0.53 ng/mL and the ranges were 0.78-500, 1.49-1000 and 0.53-500 ng/mL for morphine, M3G and M6G, respectively. 相似文献
223.
59Co- and 1H-NMR. spectra as well as preparative work have shown that oxygenation of solutions of triethylenetetramine cobalt(II) leads to a mixture of isomeric forms of [Co2(trien)2μ (O2, OH)]3+. Using a new preparative method, starting from mononuclear cobalt(III)-chelates, a binuclear μ-peroxo-cobalt(III) complex has been obtained in two different forms, where the chelate configuration is predominantly either α-cis or β-cis in both centres. The two configurations can be distinguished by IR. spectroscopy. 相似文献
224.
Alberto R Nef W Smith A Kaden TA Neuburger M Zehnder M Frey A Abram U Schubiger PA 《Inorganic chemistry》1996,35(11):3420-3427
The derivatized 19- and 20-membered macrocyclic thio crowns 3,6,9,12,15,18-hexathianonadecanol C(13)H(26)OS(6) (19-aneS6-OH) (1) and 3,6,9,13,16,19-hexathiacycloicosanol C(14)H(28)OS(6) (20-aneS6-OH) (2) have been synthesized by [1 + 1] cyclization in about 30% yield. The ligands 1 and 2 react readily at room temperature with different silver(I) salts in water and in organic solvents to form in quantitative yields the complexes [Ag(19-aneS6-OH)](+) (3) and [Ag(20-aneS6-OH)](+) (4) for which crystals of X-ray quality were grown by slow diffusion of diethylether into methanol. [Ag(19-aneS6-OH)][CF(3)SO(3)] crystallizes in the triclinic space group P&onemacr; with Z = 2, a = 10.760(1), b = 10.853(2) and c = 11.326(2)?, and alpha = 78.73(1), beta = 73.47(1), and gamma = 74.99(1) degrees. [Ag(20-aneS6-OH)][BF(4)] also crystallizes in the triclinic space group P&onemacr; with Z = 4. The unit cell constants were determined with a = 10.076(4), b = 10.525(3), and c = 22.135(8)?, alpha = 93.32(2), beta = 102.43(2), and gamma = 100.32(2) degrees. The complex cations [Ag(19-aneS6-OH)](+) and [Ag(20-aneS6-OH)](+) are coordinated through only four sulfur atoms; thus, a distorted tetrahedral coordination geometry is exhibited. In addition we found a highly asymmetric Ag-S bond lengths distribution throughout all complex cations. The stability constants of [Ag](+) with 1 and 2 and, for comparison with [18-aneS6] (5), have been determined in methanol by potentiometric [Ag](+) measurements. Log K values for the formation of 3, 4, and [Ag(18-aneS6](+) (6) are 12.04 +/- 0.19, 11.49 +/- 0.15, and 12.67 +/- 0.13 respectively. Owing to a comparable macrocyclic effect, the similar log K values are reasonable but, since 6 coordinates octahedrally, not expected. (1)H and (13)C NMR investigations at various temperatures give evidence for fluxional coordinative behavior between all six sulfur atoms in solution. Consequently [Ag(19-aneS6-OH)](+), [Ag(20-aneS6-OH)](+), and [Ag(18-aneS6](+) seem to exhibit principally the same solution structures although the solid structures are very different. 相似文献
225.
Marcus?LundbergEmail author Margareta R. A.?Blomberg Per E. M.?Siegbahn 《Theoretical chemistry accounts》2003,110(3):130-143
Water exchange on Mn centers in proteins has been modeled with density functional theory using the B3LYP functional. The reaction barrier for dissociative water exchange on [MnIV(H2O)2(OH)4] is only 9.6 kcal mol–1, corresponding to a rate of 6×105 s–1. It has also been investigated how modifications of the model complex change the exchange rate. Three cases of water exchange on Mn dimers have been modeled. The reaction barrier for dissociative exchange of a terminal water ligand on [(H2O)2(OH)2MnIV(-O)2MnIV(H2O)2(OH)2] is 8.6 kcal mol–1, while the bridging oxo group exchange with a ring-opening mechanism has a barrier of 19.2 kcal mol–1. These results are intended for interpretations of measurements of water exchange for the oxygen evolving complex of photosystem II. Finally, a tautomerization mechanism for exchange of a terminal oxyl radical has been modeled for the synthetic O2 catalyst [(terpy)(H2O)MnIV(-O)2MnIV(O)(terpy)]3+ (terpy=2,2:6,2-terpyridine). The calculated reaction barrier is 14.7 kcal mol–1.Contribution to the Björn Roos Honorary Issue 相似文献
226.
Reactions of oxygenated cobalt(II) complexes. XII. A binuclear μ-peroxodicobalt(III) complex with a macrocyclic bridging ring 1 XI: siehe [1]. Singly bridged [(tren) (NH3) CoO2(NH3) (tren)]4+ reacts with excess tren by replacement of NH3 in cis-position to the peroxo group and formation of a new type of doubly bridged μ-peroxo complex. An X-ray structure determination of [(tren)-Co(O2, tren)Co(tren)] (ClO4)4 · 2 H2O showed that the additional tren forms a macrocyclic bridging ring. The conformation of the CoOOCo group is transoid with a dihedral angle of 20°. The crystals are monoclinic with space group P21/c. The lattice constants are a = 9,798, b = 26,385, c = 16,385 Å, β = 110,2° with four formula units in the cell. The final R value is 0,124. ClO anions are disordered. The reactions of [(tren)Co(O2, tren)Co(tren)]4+ in aqueous solution are compared with those of [(tren) (NH3) CoO2Co (NH3tren)]4+. In acidic solution the new complex mainly decomposes to CoII and O2. In alcaline medium the bridging tren is replaced by an OH bridge, forming the well characterized doubly bridged [(tren)-Co(O2, OH)Co(tren)]3+. Differing from the singly bridged bis (ammino) complex, the reactions of which show no pH dependency at all, the decomposition of the tren bridged complex is H+-catalyzed. The kinetic data have been interpreted as (i) preceding fast protonation step which is followed by a conformational change of the bridging ring, (ii) acid hydrolysis of a Co-μ-tren bond and (iii) fast cleavage of the Co-OO bond which is labilized by coordinated H2O. 相似文献
227.
B.A. Jucker H. Harms S.J. Hug A.J.B. Zehnder 《Colloids and surfaces. B, Biointerfaces》1997,9(6):1205-343
Adhesion of bacterial cells to solid surfaces is often largely affected by bacterial surface polymers. In this study, we investigated the adsorption of three different O-antigens isolated from bacterial lipopolysaccharides on TiO2, Al2O3, and SiO2. The O-antigens of Escherichia coli 08 DSM 46243 and Citrobacter freundii PCM 1487 had high affinity for TiO2 and low affinity for Al2O3, whereas the O-antigens of Stenotrophomonas maltophilia 70401 had low affinities for both surfaces. Adsorption on SiO2 was low for all polysaccharides. The dependence of the adsorption on the molecular mass of polysaccharides was investigated with dextrans of various chain lengths. The affinity increased with the molecular mass. The affinity of the dextrans was reduced compared with the O-antigen of E. coli, which had similar chemical composition and molecular mass. The adsorption of the E. coli and C. freundii O-antigens on Al2O3 and TiO2 was irreversible, whereas for the S. maltophilia O-antigen it was partially reversible. The reversibility of dextran adsorption decreased with increasing molecular mass.
Infrared spectroscopy showed that all bacterial O-antigens and the dextrans formed hydrogen bonds with surface hydroxyl groups or interacted with surface-bound water of TiO2, Al2O3, and SiO2. A concentration-dependent mechanism of adsorption was observed with TiO2. At low polysaccharide concentrations, the surface water molecules ware replaced by the polysaccharides, and at increased concentration the surface hydroxyl groups were involved in the formation of hydrogen bonds. At higher surface coverages, the adsorbed polysaccharides formed loops between the few adsorbed units. 相似文献
228.
Tsybin YO Ramström M Witt M Baykut G Håkansson P 《Journal of mass spectrometry : JMS》2004,39(7):719-729
The analytical utility of the electron capture dissociation (ECD) technique, developed by McLafferty and co-workers, has substantially improved peptide and protein characterization using Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). The limitations of the first ECD implementations on commercial instruments were eliminated by the employment of low-energy electron-injection systems based on indirectly heated dispenser cathodes. In particular, the ECD rate and reliability were greatly increased, enabling the combination of ECD/FTICR-MS with on-line liquid separation techniques. Further technique development allowed the combination of two rapid fragmentation techniques, high-rate ECD and infrared multiphoton dissociation (IRMPD), in a single experimental configuration. Simultaneous and consecutive irradiations of trapped ions with electrons and photons extended the possibilities for ion activation/dissociation and led to improved peptide and protein characterization. The application of high-rate ECD/FTICR-MS has demonstrated its power and unique capabilities in top-down sequencing of peptides and proteins, including characterization of post-translational modifications, improved sequencing of peptides with multiple disulfide bridges and secondary fragmentation (w-ion formation). Analysis of peptide mixtures has been accomplished using high-rate ECD in bottom-up mass spectrometry based on mixture separation by liquid chromatography and capillary electrophoresis. This paper summarizes the current impact of high-rate ECD/FTICR-MS for top-down and bottom-up mass spectrometry of peptides and proteins. 相似文献
229.
Margareta Zehnder 《Helvetica chimica acta》1980,63(3):750-753
The crystal structure of 4-trimethyltin-quinuclidinium perchlorate has been determined by direct methods and refined by least squares techniques. Crystals of C10H22ClNO4Sn are monoclinic, space group I2/c with lattice parameters a = 29.445 (13), b = 18.400(8), c = 11.300(5) Å, β = 95.82(5)°, V = 6090.65Å3, and two independent molecules (Z = 16), Interatomic distances are compared with those of known structures of quinuclidinium chloride and 4-haloquinuclidinium chlorides and perchlorates. 相似文献
230.
Per E. M. Siegbahn Margareta R. A. Blomberg Robert H. Crabtree 《Theoretical chemistry accounts》1997,97(1-4):289-300
Quantum chemical model studies of hydrogen transfer between amino acids in the presence of radicals have been performed using
the density functional theory method B3LYP. These studies were made to investigate alternative mechanisms to the conventional
electron transfer-proton transfer mechanisms. The model reactions studied are such that the net result of the reaction is
a transfer of one neutral hydrogen atom. Simple models are used for the amino acids. Three different mechanisms for hydrogen
transfer were found. In the first of these, a transition state with a protonated intermediate residue is found, in the second,
the proton and electron take different paths and in the third, a neutral hydrogen atom can be identified along the reaction
pathway. A key feature of these mechanisms is that charge separation is always kept small in contrast to the previous electron
transfer-proton transfer mechanisms. It is therefore proposed that the processes normally considered as electron transfer
in the biochemical literature could in fact be better explained as hydrogen atom transfer, at least in cases where a suitable
hydrogen bonded chain pathway is present in the protein. The presence of such chains in principle allows the protein to define
the path of net hydrogen transfer. Another important conclusion is that standard quantum chemical methods can be used to treat
these mechanisms for hydrogen transfer, allowing for an accurate representation of the geometric changes during the reactions.
Received: 10 February 1997 / Accepted: 11 February 1997 相似文献