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51.
Harvey DJ Martin RL Jackson KA Sutton CW 《Rapid communications in mass spectrometry : RCM》2004,18(24):2997-3007
N-Linked glycans were ionized from several matrices with a Shimadzu-Biotech AXIMA-QIT matrix-assisted laser desorption/ionization quadrupole ion trap time-of-flight mass spectrometer. [M+Na]+ ions were produced from all matrices and were accompanied by varying amounts of in-source fragmentation products. The least fragmentation was produced by 2,5-dihydroxybenzoic acid and the most by alpha-cyano-4-hydroxycinnamic acid and 6-aza-2-thiothymine. Sialic acid loss was extensive but could be prevented by formation of methyl esters. Fragmentation produced typical low-energy-type spectra dominated by ions formed by glycosidic cleavages. MS(n) spectra (n = 3 and 4) were used to probe the pathways leading to the major diagnostic ions. Thus, for example, an ion that was formed by loss of the core GlcNAc residues and the 3-antenna was confirmed as being formed by a B/Y rather than a C/Z mechanism. The proposed structures of several cross-ring cleavage ions were confirmed and it was shown that MS3 spectra could be obtained from as little as 10 fmol of glycan. 相似文献
52.
Gervais C Dupree R Pike KJ Bonhomme C Profeta M Pickard CJ Mauri F 《The journal of physical chemistry. A》2005,109(31):6960-6969
13C, 14N, 15N, 17O, and 35Cl NMR parameters, including chemical shift tensors and quadrupolar tensors for 14N, 17O, and 35Cl, are calculated for the crystalline forms of various amino acids under periodic boundary conditions and complemented by experiment where necessary. The 13C shift tensors and 14N electric field gradient (EFG) tensors are in excellent agreement with experiment. Similarly, static 17O NMR spectra could be precisely simulated using the calculation of the full chemical shift (CS) tensors and their relative orientation with the EFG tensors. This study allows correlations to be found between hydrogen bonding in the crystal structures and the 17O NMR shielding parameters and the 35Cl quadrupolar parameters, respectively. Calculations using the two experimental structures for L-alanine have shown that, while the calculated isotropic chemical shift values of 13C and 15N are relatively insensitive to small differences in the experimental structure, the 17O shift is markedly affected. 相似文献
53.
Kremser L Brückner A Heger A Grunert T Buchacher A Josic D Allmaier G Rizzi A 《Electrophoresis》2003,24(24):4282-4290
The isoforms distribution of the glycoprotein antithrombin III (ATIII) derived from human plasma was investigated by means of isoelectric focusing (IEF) in polyacrylamide gels with immobilized pH gradients (IPG) and two-dimensional gel electrophoresis (2-DE) as well as capillary electrophoretic methods. It turned out that the presence of high concentrations of chaotropics (urea, thiourea) and zwitterionic detergents (3-[(3-cholamidepropyl)dimethylammonio]-1-propanesulfonate (CHAPS)) was decisive for attaining good resolution of the protein isoforms. Resolution by IPG-IEF was obtained with excellent reproducibility and pI differences down to 0.01 pH units could be distinguished. ATIII-alpha and ATIII-beta-fractions preseparated by heparin affinity chromatography showed an analogous but shifted spot pattern consisting each of one major and three minor isoforms. The main isoforms of ATIII-alpha and ATIII-beta exhibit pI values of 5.18 and 5.32, respectively, both values determined in the presence of high concentrations of urea. The pI difference of 0.14 pH units correspond to the effect of two sialic acids absent in ATIII-beta. The formation and occurrence of ATIII dimers and trimers turned out to be dependent on the sample preparation. The results obtained by 2-DE were compared with those of capillary zone electrophoresis (CZE) and capillary IEF (CIEF). Quantitative analysis regarding the CZE separated isoforms of plasma derived ATIII yielded a content of about 70% ATIII-alpha main isoform and about 6.6% of ATIII-beta. The pI values of ATIII determined by CIEF with internal calibration were in fair agreement with the pI values of the main isoforms achieved with 2-DE. 相似文献
54.
Storr T Obata M Fisher CL Bayly SR Green DE Brudziñska I Mikata Y Patrick BO Adam MJ Yano S Orvig C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2004,11(1):195-203
Seven discrete sugar-pendant diamines were complexed to the {M(CO)(3)}(+) ((99m)Tc/Re) core: 1,3-diamino-2-propyl beta-D-glucopyranoside (L(1)), 1,3-diamino-2-propyl beta-D-xylopyranoside (L(2)), 1,3-diamino-2-propyl alpha-D-mannopyranoside (L(3)), 1,3-diamino-2-propyl alpha-D-galactopyranoside (L(4)), 1,3-diamino-2-propyl beta-D-galactopyranoside (L(5)), 1,3-diamino-2-propyl beta-(alpha-D-glucopyranosyl-(1,4)-D-glucopyranoside) (L(6)), and bis(aminomethyl)bis[(beta-D-glucopyranosyloxy)methyl]methane (L(7)). The Re complexes [Re(L(1)-L(7))(Br)(CO)(3)] were characterized by (1)H and (13)C 1D/2D NMR spectroscopy which confirmed the pendant nature of the carbohydrate moieties in solution. Additional characterization was provided by IR spectroscopy, elemental analysis, and mass spectrometry. Two analogues, [Re(L(2))(CO)(3)Br] and [Re(L(3))(CO)(3)Br], were characterized in the solid state by X-ray crystallography and represent the first reported structures of Re organometallic carbohydrate compounds. Conductivity measurements in H(2)O established that the complexes exist as [Re(L(1)-L(7))(H(2)O)(CO)(3)]Br in aqueous conditions. Radiolabelling of L(1)-L(7) with [(99m)Tc(H(2)O)(3)(CO)(3)](+) afforded in high yield compounds of identical character to the Re analogues. The radiolabelled compounds were determined to exhibit high in vitro stability towards ligand exchange in the presence of an excess of either cysteine or histidine over a 24 h period. 相似文献
55.
Chris McDonald 《Analytica chimica acta》2005,534(1):3-10
Studies of protein-protein and protein-ligand interactions are important for understanding biological functions of proteins. A new technique based on the partial proteolysis of proteins combined with quantitative mass spectrometry is developed as a means of tracking structural changes after the formation of a protein-ligand complex. In this technique, a protein of interest with and without the binding of a ligand is digested with an enzyme to generate a set of peptides, followed by separation of the peptides by liquid chromatography. Matrix-assisted laser desorption ionization (MALDI) mass spectrometry (MS) is used to identify chromatographically separated peptides, and locate their sequence alignments in the parent protein. Using an isotopically labeled protein as a sample against an unlabeled protein standard, quantitative information can be gathered. This overcomes the inherent lack of quantitative capability of MALDI MS. The utility of the technique to investigate protein-ligand interactions is demonstrated in a model system involving calcium binding to cardiac Troponin C (cTnC). Using this technique, the general location of the three calcium-binding sites of cTnC can be determined by using several different enzymes to generate overlapping peptide maps of cTnC. 相似文献
56.
57.
Varrot A Tarling CA Macdonald JM Stick RV Zechel DL Withers SG Davies GJ 《Journal of the American Chemical Society》2003,125(25):7496-7497
Glycosidases are some of the most ubiquitous enzyme in nature. Their biological significance, coupled to their enormous catalytic prowess derived from tight binding of the transition state, is reflected in their importance as therapeutic targets. Many glycosidase inhibitors are known. Imino sugars are often potent inhibitors, yet many facets of their mode of action, such as their degree, if any, of transition-state "mimicry" and their protonation state when bound to the target glycosidase remain unclear. Atomic resolution analysis of the endoglucanase, Cel5A, in complex with a cellobio-derived isofagomine in conjunction with the pH dependence of Ki and kcat/KM reveals that this compound binds as a protonated sugar. Surprisingly, both the enzymatic nucleophile and the acid/base are unprotonated in the complex. 相似文献
58.
59.
Asymmetric hydrogenation of ketone 1 using trans-RuCl(2)[(R)-xylbinap][(R)-daipen] (3) as a catalyst afforded secondary alcohol 2 quantitatively and in 99.4% ee. Further exploration of the effect of the thiazole ring substitution revealed that the catalyst was highly effective for the enantioselective hydrogenation of 5-benzoyl thiazoles, which afforded corresponding alcohols in 92-99% ee. The same protocol was applicable to a variety of aromatic-heteroaromatic ketones to generate secondary alcohols in excellent enantioselectivities. [reaction: see text] 相似文献
60.
G. Münninghoff W. Treutmann E. Hellner G. Heger D. Reinen 《Journal of solid state chemistry》1980,34(3):289-299
The structures of single crystals Rb2Cr1?xMnxCl4 (0 ? x ? 1) have been studied by neutron diffraction. A crystal of composition x = 0.01 shows a superstructure of the K2NiF4 type [space group Bbcm; a = b = 7.262Å, c = 15.733Å]. The structural refinement [R = 0.043] yields an antiferrodistortive order of tetragonally elongated octahedra (superimposed by a small orthorhombic component) with CrCl bond lengths of 2.43 Å (∥[001]) and 2.40 Å, 2.74 Å (⊥[001]). Structural results for x = 0.01/0.08/0.53/0.63/0.83/0.91/0.97 in space group [K2NiF4 type]—in particular the anomalous ms displacements of Cl(1) in the (001) plane—give evidence that the distortion of the (Mn, Cr)Cl6 octahedra decreases with increasing x. AOM calculations based on experimental ligand field energies indicate that the individual CrCl6 polyhedra are more strongly distorted than the (Jahn-Teller stable) MnCl6 octahedra in mixed crystals with larger x values. 相似文献