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51.
Lu Deng Elena N. Kitova John S. Klassen 《Journal of the American Society for Mass Spectrometry》2013,24(1):49-56
Dissociation rate constants (k off ) for the model high affinity interaction between biotin (B) and the homotetramer of natural core streptavidin (S4) were measured at pH 7 and temperatures ranging from 15 to 45 °C using electrospray ionization mass spectrometry (ESI-MS). Two different approaches to data analysis were employed, one based on the initial rate of dissociation of the (S4? + ?4B) complex, the other involving nonlinear fitting of the time-dependent relative abundances of the (S4? + ?iB) species. The two methods were found to yield k off values that are in good agreement, within a factor of two. The Arrhenius parameters for the dissociation of the biotin–streptavidin interaction in solution were established from the k off values determined by ESI-MS and compared with values measured using a radiolabeled biotin assay. Importantly, the dissociation activation energies determined by ESI-MS agree, within 1 kcal?mol–1, with the reported value. In addition to providing a quantitative measure of k off , the results of the ESI-MS measurements revealed that the apparent cooperative distribution of (S4? + ?iB) species observed at short reaction times is of kinetic origin and that sequential binding of B to S4 occurs in a noncooperative fashion with the four ligand binding sites being kinetically and thermodynamically equivalent and independent. 相似文献
52.
Lan Liu Nobar Jalili Alyson Baergen Simon Ng Justin Bailey Ratmir Derda John S. Klassen 《Journal of the American Society for Mass Spectrometry》2014,25(5):751-757
This paper reports on the first experimental study of the energies of noncovalent fluorine bonding in a protein-ligand complex in the absence of solvent. Arrhenius parameters were measured for the dissociation of gaseous deprotonated ions of complexes of bovine β-lactoglobulin (Lg), a model lipid-binding protein, and four fluorinated analogs of stearic acid (SA), which contained (X =) 13, 15, 17, or 21 fluorine atoms. In all cases, the activation energies (Ea) measured for the loss of neutral XF-SA from the (Lg + XF-SA)7– ions are larger than for SA. From the kinetic data, the average contribution of each?>?CF2 group to Ea was found to be ~1.1 kcal mol–1, which is larger than the ~0.8 kcal mol–1 value reported for?>?CH2 groups. Based on these results, it is proposed that fluorocarbon–protein interactions are inherently stronger (enthalpically) than the corresponding hydrocarbon interactions. Figure
? 相似文献
53.
Fábio de Souza Dias Aline Klassen Marina Franco Maggi Tavares Jorge Maurício David 《Chromatographia》2013,76(9-10):559-563
Six phenolic compounds were separated and determined by capillary zone electrophoresis in red wine from Brazil’s region Vale do São Francisco with total analysis time of 12 min. The limit of detections varied from 1.59 to 2.24 mg L?1. The relative standard deviations (for n = 6) varied from 0.28 to 3.50 %. The red wine samples analyzed were bought in the local market and the phenolic compound recoveries were in the range of 98–101 %. The concentrations of gallic acid in the samples of wines varied from 16.0 to 42.0 mg L?1, caffeic acid (3.16–5.18 mg L?1), syringic acid (5.73–13.0 mg L?1), kaempferol (2.32–4.33 mg L?1), quercetin (1.68–4.03 mg L?1), myricetin (7.52–25.1 mg L?1). The concentrations found agree with data reported in the literature. 相似文献
54.
Stefan Büttner Alina Bunescu Sebastian Reimann T. H. Tam Dang Thomas Pundt Renske Klassen Andreas Schmidt Nazken K. Kelzhanova Zharylkasyn A. Abilov Tariel V. Ghochikyan Ashot S. Saghiyan Alexander Villinger Helmut Reinke Anke Spannenberg Peter Langer 《Helvetica chimica acta》2013,96(1):44-58
Functionalized 5‐alkyl‐3‐(trifluoromethyl)phenols were prepared by formal [3+3] cyclization of 1,3‐bis(silyloxy)buta‐1,3‐dienes with 1,1,1‐trifluoro‐4‐(silyloxy)alk‐3‐en‐2‐ones derived from 1,1,1‐trifluoroalkane‐2,4‐diones. The latter were prepared by condensation of the dianion of 1,1,1‐trifluoropentane‐2,4‐dione with alkyl halides. 相似文献
55.
O. Friedrichs C. López-Cartes T. Klassen A. Fernández 《Applied Surface Science》2006,252(6):2334-2345
Nanocrystalline Mg and MgH2 samples have been prepared by high-energy ball milling and gas phase condensation methods. Starting from these materials in their “as received” state without air exposure, a study of the oxygen and air passivation behaviour was carried out by “in situ” analysis of the samples by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The binding energy and photoemission Auger parameters have been determined for metallic magnesium as well as for magnesium hydride, oxide and hydroxide species. Values of the MgH2 material were reported for the first time. The study clearly shows the formation of an oxide passivation layer of ca. 3-4 nm in thickness for all the nanocrystalline magnesium samples handled under controlled inert gas atmospheres. A hydroxide like amorphous layer is formed at the topmost surface layers of the nanocrystalline Mg and MgH2 samples. The implication of these studies for H2 storage and transport applications of nanocrystalline magnesium is discussed. 相似文献
56.
57.
58.
Zhang P Razi N Eugenio L Fentabil M Kitova EN Klassen JS Bundle DR Ng KK Ling CC 《Chemical communications (Cambridge, England)》2011,47(45):12397-12399
The structure of the pentasaccharide S259-1 in the Consortium for Functional Glycomics was investigated using a variety of techniques. Surprisingly, the structure differs from the structure assumed from the previously established specificity of the human fucosyltransferase FUT-III used in the last step of chemoenzymatic synthesis. When presented with a tetrasaccharide substrate containing both type I and type II disaccharide moieties, the enzyme generates a pentasaccharide in which the type II moiety is preferentially fucosylated. The unexpected product generated by FUT-III in this case highlights the importance of performing detailed structural analysis on products generated by enzymes. 相似文献
59.
L Liu Y Bai N Sun L Xia TL Lowary JS Klassen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(38):12059-12067
The interactions between 3-O-methyl-mannose polysaccharides (MMPs), extracted from Mycobacterium smegmatis (consisting of a mixture of MMP-10, -11, -12 and -13) or obtained by chemical synthesis (MMP-5(s) , -8(s) , -11(s) and -14(s) ), and linear saturated and unsaturated fatty acids (FAs), and a commercial mixture of naphthenic acids (NAs) in aqueous solution at 25?°C and pH?8.5 were quantified by electrospray ionization mass spectrometry (ESI-MS). Association constants (K(a) ) for MMP binding to four FAs (myristic acid, palmitic acid, stearic acid and trans-parinaric acid) were measured by using an indirect ESI-MS assay, the "proxy protein" method. The K(a) values are in the 10(4) -10(5) M(-1) range and, based on results obtained for the binding of the synthetic MMPs with palmitic acid, increase with the size of the carbohydrate. Notably, the measured affinity of the extracted MMPs for trans-parinaric acid is two orders of magnitude smaller than the reported value, which was determined by using a fluorescence assay. Using a newly developed competitive binding assay, referred to as the "proxy protein/proxy ligand" ESI-MS method, it was shown that MMPs bind specifically to NAs in aqueous solution, with apparent affinities of approximately (5×10(4) )?M(-1) for the mixture of NAs tested. This represents the first demonstration that MMPs can bind to hydrophobic species more complex than those containing linear alkyl/alkenyl chains. Moreover, the approach developed here represents a novel method for probing carbohydrate-lipid interactions. 相似文献
60.
Ling Han Elena N. Kitova Ming Tan Xi Jiang John S. Klassen 《Journal of the American Society for Mass Spectrometry》2014,25(1):111-119
Noroviruses (NoVs), the major cause of epidemic acute gastroenteritis, recognize human histo-blood group antigens (HBGAs), which are present as free oligosaccharides in bodily fluid or glycolipids and glycoproteins on the surfaces of cells. The subviral P particle formed by the protruding (P) domain of the NoV capsid protein serves as a useful model for the study NoV–HBGA interactions. Here, we demonstrate the application of a catch-and-release electrospray ionization mass spectrometry (CaR-ESI-MS) assay for screening carbohydrate libraries against the P particle to rapidly identify NoV ligands and potential inhibitors. Carbohydrate libraries of 50 and 146 compounds, which included 18 and 24 analogs of HBGA receptors, respectively, were screened against the P particle of VA387, a member of the predominant GII.4 NoVs. Deprotonated ions corresponding to the P particle bound to carbohydrates were isolated and subjected to collision-induced dissociation to release the ligands in their deprotonated forms. The released ligands were identified by ion mobility separation followed by mass analysis. All 13 and 16 HBGA ligands with intrinsic affinities >500 M–1 were identified in the 50 and the 146 compound libraries, respectively. Furthermore, screening revealed interactions with a series of oligosaccharides with structures found in the cell wall of mycobacteria and human milk. The affinities of these newly discovered ligands are comparable to those of the HBGA receptors, as estimated from the relative abundance of released ligand ions. 相似文献