Amyloid fibrils are self‐assembled protein structures with important roles in biology (either pathogenic or physiological), and are attracting increasing interest in nanotechnology. However, because of their high aspect ratio and the presence of some polymorphism, that is, the possibility to adopt various structures, their characterization is challenging and basic information such as their mass is unknown. Here we show that charge‐detection mass spectrometry, recently developed for large self‐assembled systems such as viruses, provides such information in a straightforward manner. 相似文献
The application of the direct electrospray ionization mass spectrometry (ESI-MS) assay to quantify interactions between bovine
β-lactoglobulin (Lg) and a series of fatty acids (FA), CH3(CH2)xCOOH, where x = 6 (caprylic acid, CpA), 8 (capric acid, CA), 10 (lauric acid, LA), 12 (myristic acid, MA), 14 (palmitic acid,
PA) and 16 (stearic acid, SA), is described. Control ESI-MS binding measurements performed on the Lg-PA interaction revealed
that both the protonated and deprotonated gas phase ions of the (Lg + PA) complex are prone to dissociate in the ion source,
which leads to artificially small association constants (Ka). The addition of imidazole, a stabilizing solution additive, at high concentration (10 mM) increased the relative abundance
of (Lg + PA) complex measured by ESI-MS in both positive and negative ion modes. The Ka value measured in negative ion mode and using sampling conditions that minimize in-source dissociation is in good agreement
with a value determined using a competitive fluorescence assay. The Ka values measured by ESI-MS for the Lg interactions with MA and SA are also consistent with values expected based on the fluorescence
measurements. However, the Ka values measured using optimal sampling conditions in positive ion mode are significantly lower than those measured in negative
ion mode for all of the FAs investigated. It is concluded that the protonated gaseous ions of the (Lg + FA) complexes are
kinetically less stable than the deprotonated ions. In-source dissociation was significant for the complexes of Lg with the
shorter FAs (CpA, CA, and LA) in both modes and, in the case of CpA, no binding could be detected by ESI-MS. The affinities
of Lg for CpA, CA, and LA determined using the reference ligand ESI-MS assay, a method for quantifying labile protein–ligand
complexes that are prone to in-source dissociation, were found to be in good agreement with reported values. 相似文献
Xenografts are commonly used to test the effect of new drugs on human cancer. However, because of their heterogeneity, analysis of the results is often controversial. Part of the problem originates in the existence of tumor cells at different metabolic stages: from metastatic to necrotic cells, as it happens in real tumors. Imaging mass spectrometry is an excellent solution for the analysis of the results as it yields detailed information not only on the composition of the tissue but also on the distribution of the biomolecules within the tissue. Here, we use imaging mass spectrometry to determine the distribution of phosphatidylcholine (PC), phosphatidylethanolamine (PE), and their plasmanyl- and plasmenylether derivatives (PC-P/O and PE-P/O) in xenografts of five different tumor cell lines: A-549, NCI-H1975, BX-PC3, HT29, and U-87 MG. The results demonstrate that the necrotic areas showed a higher abundance of Na+ adducts and of PC-P/O species, whereas a large abundance of PE-P/O species was found in all the xenografts. Thus, the PC/PC-ether and Na+/K+ ratios may highlight the necrotic areas while an increase on the number of PE-ether species may be pointing to the existence of viable tumor tissues. Furthermore, the existence of important changes in the concentration of Na+ and K+ adducts between different tissues has to be taken into account while interpreting the imaging mass spectrometry results.
The goal of this work was to assess differences in the composition of red wine produced in Poland, Hungary, Moldova, and Bulgaria, related to their geographical origin. Inductively coupled plasma–mass spectrometry results obtained for 23 elements were submitted to principal component analysis, indicating the association of Li, Co, Se, Cu, Sr with Moldovan products; Hungarian and Moldovan wines were characterized by V, As, Al, Fe variables, whereas Be was distinctive for Hungarian products. Polish wines were grouped with Cd and Pb and Bulgarian with Tl, Ba, Rb, and Mo; U and Mn were found as characteristic variables for wines from Bulgaria and Moldova. According with current legislation, the investigated wines were not contaminated with heavy metals and might be even considered a good source of essential elements (Cu, Mn, Fe, Zn, Cr, and Co). Gas chromatography–high-resolution time-of-flight mass spectrometry was used as a complementary analytical tool, targeting nonvolatile organic compounds amenable for silylation. Statistical data analysis revealed that geographical factors strongly affected the metabolic profiles. Specifically, 15 compounds presenting higher abundances in Bulgarian as compared to Polish wines were found, including monosaccharides, polyols, organic acids, sugar acids, and the amino acid proline. The highest fold change was obtained for ribose (37.9), followed by proline (12.2) and inositol (5.68), suggesting that these compounds might be especially useful for discrimination purposes. The obtained results encourage for further studies aimed at the discrimination of wine produced over the entire Central-East European region based on metal/metalloid profiling and on the evaluation of specific metabolites. 相似文献
Surface modification of polymers by low-pressure plasmas has gained scientific and industrial importance for controlling adhesion of coatings, wettability, printability, bio-compatibility and other surface-related properties. However, more is to be learned about the complex interactions at the plasma-polymer interface. The present study is designed to investigate these plasma-polymer surface interactions by means of mass spectrometry. Various polymer specimens (polyethylene, polypropylene, polyethylene terephthalate, and polyimide) were placed directly on an electrode which contains the sampling aperture into a quadrupole mass spectrometer. We have identified various molecular fragments from these polymers, which were liberated by chain scissions provoked by various energetic plasma constituents, in particular, bombarding ions and vacuum ultraviolet (VUV) photons. 相似文献
Journal of Analytical Chemistry - A method is proposed for the determination of some ketosteroids in human urine, including enzymatic hydrolysis using β-glucuronidase from E. coli followed by... 相似文献
Intermolecular interactions modulate the electro-optical properties of molecular materials and the nature of low-lying exciton states. Molecular materials composed by oligoacenes are extensively investigated for their semiconducting and optoelectronic properties. Here, we analyze the exciton states derived from time-dependent density functional theory (TDDFT) calculations for two oligoacene model aggregates: naphthalene and anthracene dimers. To unravel the role of inter-molecular interactions, a set of diabatic states is selected, chosen to coincide with local (LE) and charge-transfer (CT) excitations within a restricted orbital space including two occupied and two unoccupied orbitals for each molecular monomer. We study energy profiles and disentangle inter-state couplings to disclose the (CT) character of singlet and triplet exciton states and assess the influence of inter-molecular orientation by displacing one molecule with respect to the other along the longitudinal translation coordinate. The analysis shows that (CT) contributions are relevant, although comparably less effective for triplet excitons, and induce a non-negligible mixed character to the low-lying exciton states for eclipsed monomers and for small translational displacements. Such (CT) contributions govern the La/Lb state inversion occurring for the low-lying singlet exciton states of naphthalene dimer and contribute to the switch from H- to J-aggregate type of the strongly allowed Bb transition of both oligoacene aggregates. 相似文献
In a successful fortification program, the stability of micronutrients added to the food is one of the most important factors. The added vitamin D3 is known to sometimes decline during storage of fortified milks, and oxidation through fatty acid lipoxidation could be suspected as the likely cause. Identification of vitamin D3 oxidation products (VDOPs) in natural foods is a challenge due to the low amount of their contents and their possible transformation to other compounds during analysis. The main objective of this study was to find a method to extract VDOPs in simulated whole milk powder and to identify these products using LTQ-ion trap, Q-Exactive Orbitrap and triple quadrupole mass spectrometry. The multistage mass spectrometry (MSn) spectra can help to propose plausible schemes for unknown compounds and their fragmentations. With the growth of combinatorial libraries, mass spectrometry (MS) has become an important analytical technique because of its speed of analysis, sensitivity, and accuracy. This study was focused on identifying the fragmentation rules for some VDOPs by incorporating MS data with in silico calculated MS fragmentation pathways. Diels–Alder derivatization was used to enhance the sensitivity and selectivity for the VDOPs’ identification. Finally, the confirmed PTAD-derivatized target compounds were separated and analyzed using ESI(+)-UHPLC-MS/MS in multiple reaction monitoring (MRM) mode.
Laser electrospray mass spectrometry (LEMS) measurement of the dissociation constant (Kd) for hen egg white lysozyme (HEWL) and N,N′,N″-triacetylchitotriose (NAG3) revealed an apparent Kd value of 313.2?±?25.9 μM for the ligand titration method. Similar measurements for N,N′,N″,N″’-tetraacetylchitotetraose (NAG4) revealed an apparent Kd of 249.3?±?13.6 μM. An electrospray ionization mass spectrometry (ESI-MS) experiment determined a Kd value of 9.8?±?0.6 μM. In a second LEMS approach, a calibrated measurement was used to determine a Kd value of 6.8?±?1.5 μM for NAG3. The capture efficiency of LEMS was measured to be 3.6?±?1.8% and is defined as the fraction of LEMS sample detected after merging with the ESI plume. When the dilution is factored into the ligand titration measurement, the adjusted Kd value was 11.3 μM for NAG3 and 9.0 μM for NAG4. The calibration method for measuring Kd developed in this study can be applied to solutions containing unknown analyte concentrations.
