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Rafael Kandiyoti - One of the best experts on this subject based on the ideXlab platform.
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characterization of asphaltenes from hydrotreated products by sec ldms maldi nmr and xrd
Energy & Fuels, 2007Co-Authors: Fernando Trejo, Alan A. Herod, Jorge Ancheyta, Trevor J Morgan, Rafael KandiyotiAbstract:Maya crude was hydrotreated at different reaction conditions in a pilot plant. Asphaltenes were precipitated from hydrotreated products with n-heptane as a solvent in a pressurized system with heating and stirring. Structural characterization studies have been carried out on asphaltenes from Maya crude. Molecular-weight distributions were obtained by size-exclusion chromatography (SEC) using tetrahydrofuran (THF) and 1-methyl-2-pyrrolidinone (NMP) as solvents. Nonfragmenting techniques, such as laser Desorption Mass Spectrometry (LDMS) and matrix-assisted laser Desorption/ionization Mass Spectrometry (MALDI−MS), were also used for determining molecular-weight distributions. Crystallite parameters of asphaltenes were studied by X-ray diffraction (XRD) after they were precipitated. Average structural parameters were calculated from nuclear magnetic resonance (NMR) spectra. The influence of reaction conditions are studied in terms of structural changes in asphaltenes.
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fractionation of a wood tar pitch by planar chromatography for the characterisation of large molecular Mass materials
Journal of Chromatography A, 1999Co-Authors: María J. Lázaro, M. Domin, Alan A. Herod, Rafael KandiyotiAbstract:Abstract A commercial tar pitch derived from pine wood – Massen Pine (Pinus Massonia) and sold as Stockholm tar has been fractionated by planar chromatography with examination of the fractions by size exclusion chromatography in NMP eluent, by UV-fluorescence and by matrix assisted laser Desorption Mass Spectrometry. The relatively small molecules, mobile in planar chromatography, are shown to be non-polar. Large molecules were found in each fraction, corresponding in SEC elution times up to polystyrenes of molecular Mass of at least 1.8 million. Size exclusion chromatography profiles by UV light absorbance showed differences in relative absorbance of different wavelengths for large and small molecules, implying differences in structures. MALDI Mass spectra indicated molecules of Mass of several thousand Mass units with the upper limit of Mass not defined. Planar chromatography provides a fast, cheap method of isolating large molecular Mass fractions of this bioMass tar.
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large molecular Mass materials in coal derived liquids by 252cf plasma and matrix assisted laser Desorption Mass Spectrometry
Energy & Fuels, 1998Co-Authors: M. Domin, María J. Lázaro, Alan A. Herod, John W. Larsen, Shang Li, Rafael KandiyotiAbstract:The paper compares responses of 252Cf-plasma Desorption MS (PD-MS) and matrix-assisted laser Desorption (MALDI) MS to identical samples. The two pairs of samples selected for the comparison were known from previous work to differ significantly in their high Mass contents. MALDI-MS showed large differences in MM distributions within both pairs of samples. The PD-MS data showed a degree of similarity between one pair of samples (pyridine soluble/insoluble fractions of a coal tar pitch); for the second pair (a coal extract and its hydrocracked product), trends from the two MS techniques agreed closely. The MM range observed by PD-MS was somewhat narrower, extending to between 3000 and 5000 u. Significant differences within pairs of samples were observed by SEC and by UV-fluorescence spectroscopy, providing somewhat closer agreement with the MALDI spectra. The two MS instruments differ in two important respects: the ionization system (i.e., plasma vs laser Desorption) and the maximum available ion extraction...
Brian T. Chait - One of the best experts on this subject based on the ideXlab platform.
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Recombinant Hemoglobin a Produced in Transgenic Swine: Structural Equivalence with Human Hemoglobin A
Artificial Cells Blood Substitutes and Biotechnology, 1994Co-Authors: M. J. Rao, Klaus Schneider, Brian T. Chait, T. L. Chao, H. Keller, S. Anderson, B. N. Manjula, Ramesh Kumar, A. S. AcharyaAbstract:Recombinant human hemoglobin A produced by coexpressing human α and β globin genes in swine, and purified from the lysate of transgenic swine has been subjected to detailed protein chemical analysis. These structural studies involving laser Desorption Mass Spectrometry, separation of globin chains by RPHPLC, amino terminal sequence analysis of the isolated globin chains, the tryptic peptide mapping of the purified globin chains and the amino acid composition analysis of the purified tryptic peptides of globin chains have established the primary structural equivalence of the globin chains of the transgenic swine derived hemoglobin A with that of human hemoglobin A. These results demonstrate that the transgenic swine system correctly translates the human α and β globin m-RNA; carries out the correct cotranslational processing of globin chains, and does not introduce any unwanted post translational modifications into the mature chains. Thus, the transgenic swine expression system is an excellent approach for...
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Matrix-Assisted Laser Desorption Mass Spectrometry of Biotransformation Products of Dynorphin A in Vitro
Journal of the American Society for Mass Spectrometry, 1994Co-Authors: James Z. Chou, Mary Jeanne Kreek, Brian T. ChaitAbstract:The utility of matrix-assisted laser Desorption Mass Spectrometry for characterizing products of in vitro processing of synthetic dynorphin A (Dyn A) peptides in biologic matrices is described. A series of laser Desorption matrices were tested for their response to Dyn A (1–6), Dyn A (1–7), Dyn A (1–8), Dyn A (1–9), Dyn A (1–l0), Dyn A (1–13), Dyn A (2-17), and Dyn A (1–17). α-Cyano-4-hydroxycinnamic acid was chosen as a suitable matrix for subsequent studies. Mass spectra of dynorphin peptides indicated a good signal-to-noise response down to (1) 10 fmole of Dyn A (1–10) amide standard in aqueous acidic solution and (2) a concentration of 10^-7 M for seven dynorphin peptides spiked into human plasma. Two examples of the Mass spectrometric analysis of the products of in vitro processing are presented: Dyn A (1–13) and Dyn A (1–17) in human blood. The presence and identity of processed peptides can be simply inferred from the molecular Masses provided by the Mass spectrometric measurement without extensive sample purification. A comparison of matrixassisted laser Desorption Mass Spectrometry is made with high-performance liquid chromatography.
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protein ladder sequencing
Science, 1993Co-Authors: Brian T. Chait, Rong Wang, Ronald C Beavis, Stephen B. H. KentAbstract:A new approach to protein sequencing is described. It consists of two steps: (i) ladder-generating chemistry, the controlled generation from a polypeptide chain by wet chemistry of a family of sequence-defining peptide fragments, each differing from the next by one amino acid; and (ii) data readout, a one-step readout of the resulting protein sequencing ladder by matrix-assisted laser-Desorption Mass Spectrometry. Each amino acid was identified from the Mass difference between successive peaks, and the position in the data set defined the sequence of the original peptide chain. This method was used to directly locate a phosphoserine residue in a phosphopeptide. The protein ladder sequencing method lends itself to very high sample throughput at very low per cycle cost.
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californium 252 plasma Desorption Mass Spectrometry of oligosaccharides and glycoconjugates control of ionization and fragmentation
Analytical Chemistry, 1991Co-Authors: Subhodaya Aduru, Brian T. ChaitAbstract:The fragmentation of underivatized and peracetylated maltooligosaccharides, ranging in length from four to seven glucose residues, has been investigated by 252Cf plasma Desorption Mass Spectrometry (PDMS). Investigations are made of the effects on the Mass spectra of (1) peracetylation, (2) sample preparation by electrospray deposition onto metallic substrates versus adsorption onto nitrocellulose films, and (3) sodium addition to or elimination from the sample. Peracetylation enhances the Mass spectrometric response of the oligosaccharides and also enables the efficient removal from the sample of water-soluble components such as sodium salts. A rapid and simple method has been developed for controlling the amount and type of fragmentation of peracetylated maltooligosaccharides. The method involves control of the amount of sodium in the sample introduced into the Mass spectrometer. When a large molar excess of sodium is added to the sample, in the form of sodium chloride, the positive-ion Mass spectrum is dominated by a peak corresponding to the sodium-cationized molecule. On the other hand, when the sample is completely depleted of sodium, the spectrum shows no quasimolecular ions [(M + Na)+ or (M + H)+] whatsoever and is instead totally dominated by fragment ion species. Thus, it proves feasible to alternate between a spectrum dominated by the (M + Na)+ ion peak and one dominated by fragment ions. This method has also been found to be useful in controlling the fragmentation of permethylated gangliosides.
John W. Larsen - One of the best experts on this subject based on the ideXlab platform.
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large molecular Mass materials in coal derived liquids by 252cf plasma and matrix assisted laser Desorption Mass Spectrometry
Energy & Fuels, 1998Co-Authors: M. Domin, María J. Lázaro, Alan A. Herod, John W. Larsen, Shang Li, Rafael KandiyotiAbstract:The paper compares responses of 252Cf-plasma Desorption MS (PD-MS) and matrix-assisted laser Desorption (MALDI) MS to identical samples. The two pairs of samples selected for the comparison were known from previous work to differ significantly in their high Mass contents. MALDI-MS showed large differences in MM distributions within both pairs of samples. The PD-MS data showed a degree of similarity between one pair of samples (pyridine soluble/insoluble fractions of a coal tar pitch); for the second pair (a coal extract and its hydrocracked product), trends from the two MS techniques agreed closely. The MM range observed by PD-MS was somewhat narrower, extending to between 3000 and 5000 u. Significant differences within pairs of samples were observed by SEC and by UV-fluorescence spectroscopy, providing somewhat closer agreement with the MALDI spectra. The two MS instruments differ in two important respects: the ionization system (i.e., plasma vs laser Desorption) and the maximum available ion extraction...
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characterization of coal liquefaction heavy products using californium 252 plasma Desorption Mass Spectrometry
Energy & Fuels, 1994Co-Authors: John W. Larsen, Andrzej R Lapucha, Patrick C Wernett, William R AndersonAbstract:Californium plasma Desorption Mass Spectrometry (PDMS) has been used to analyze heavy distillation residues obtained from direct coal liquefaction processes. The characteristics of the 252 Cf PDMS technique for the analysis of these nonpolar materials were determined, especially the efficiency with which molecules of different chemical type are ionized and detected. The molecular weight distributions of several THF-soluble portions of nondistillable residual materials (850 °F + «resids») obtained from the Wilsonville pilot plant were determined. These data are compared to results obtained by field ionization Mass Spectrometry (FIMS) and gel permeation chromatography (GPC). In general, number-average molecular weights for all three techniques agreed well
Alan A. Herod - One of the best experts on this subject based on the ideXlab platform.
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characterization of asphaltenes from hydrotreated products by sec ldms maldi nmr and xrd
Energy & Fuels, 2007Co-Authors: Fernando Trejo, Alan A. Herod, Jorge Ancheyta, Trevor J Morgan, Rafael KandiyotiAbstract:Maya crude was hydrotreated at different reaction conditions in a pilot plant. Asphaltenes were precipitated from hydrotreated products with n-heptane as a solvent in a pressurized system with heating and stirring. Structural characterization studies have been carried out on asphaltenes from Maya crude. Molecular-weight distributions were obtained by size-exclusion chromatography (SEC) using tetrahydrofuran (THF) and 1-methyl-2-pyrrolidinone (NMP) as solvents. Nonfragmenting techniques, such as laser Desorption Mass Spectrometry (LDMS) and matrix-assisted laser Desorption/ionization Mass Spectrometry (MALDI−MS), were also used for determining molecular-weight distributions. Crystallite parameters of asphaltenes were studied by X-ray diffraction (XRD) after they were precipitated. Average structural parameters were calculated from nuclear magnetic resonance (NMR) spectra. The influence of reaction conditions are studied in terms of structural changes in asphaltenes.
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fractionation of a wood tar pitch by planar chromatography for the characterisation of large molecular Mass materials
Journal of Chromatography A, 1999Co-Authors: María J. Lázaro, M. Domin, Alan A. Herod, Rafael KandiyotiAbstract:Abstract A commercial tar pitch derived from pine wood – Massen Pine (Pinus Massonia) and sold as Stockholm tar has been fractionated by planar chromatography with examination of the fractions by size exclusion chromatography in NMP eluent, by UV-fluorescence and by matrix assisted laser Desorption Mass Spectrometry. The relatively small molecules, mobile in planar chromatography, are shown to be non-polar. Large molecules were found in each fraction, corresponding in SEC elution times up to polystyrenes of molecular Mass of at least 1.8 million. Size exclusion chromatography profiles by UV light absorbance showed differences in relative absorbance of different wavelengths for large and small molecules, implying differences in structures. MALDI Mass spectra indicated molecules of Mass of several thousand Mass units with the upper limit of Mass not defined. Planar chromatography provides a fast, cheap method of isolating large molecular Mass fractions of this bioMass tar.
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large molecular Mass materials in coal derived liquids by 252cf plasma and matrix assisted laser Desorption Mass Spectrometry
Energy & Fuels, 1998Co-Authors: M. Domin, María J. Lázaro, Alan A. Herod, John W. Larsen, Shang Li, Rafael KandiyotiAbstract:The paper compares responses of 252Cf-plasma Desorption MS (PD-MS) and matrix-assisted laser Desorption (MALDI) MS to identical samples. The two pairs of samples selected for the comparison were known from previous work to differ significantly in their high Mass contents. MALDI-MS showed large differences in MM distributions within both pairs of samples. The PD-MS data showed a degree of similarity between one pair of samples (pyridine soluble/insoluble fractions of a coal tar pitch); for the second pair (a coal extract and its hydrocracked product), trends from the two MS techniques agreed closely. The MM range observed by PD-MS was somewhat narrower, extending to between 3000 and 5000 u. Significant differences within pairs of samples were observed by SEC and by UV-fluorescence spectroscopy, providing somewhat closer agreement with the MALDI spectra. The two MS instruments differ in two important respects: the ionization system (i.e., plasma vs laser Desorption) and the maximum available ion extraction...
M. Domin - One of the best experts on this subject based on the ideXlab platform.
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fractionation of a wood tar pitch by planar chromatography for the characterisation of large molecular Mass materials
Journal of Chromatography A, 1999Co-Authors: María J. Lázaro, M. Domin, Alan A. Herod, Rafael KandiyotiAbstract:Abstract A commercial tar pitch derived from pine wood – Massen Pine (Pinus Massonia) and sold as Stockholm tar has been fractionated by planar chromatography with examination of the fractions by size exclusion chromatography in NMP eluent, by UV-fluorescence and by matrix assisted laser Desorption Mass Spectrometry. The relatively small molecules, mobile in planar chromatography, are shown to be non-polar. Large molecules were found in each fraction, corresponding in SEC elution times up to polystyrenes of molecular Mass of at least 1.8 million. Size exclusion chromatography profiles by UV light absorbance showed differences in relative absorbance of different wavelengths for large and small molecules, implying differences in structures. MALDI Mass spectra indicated molecules of Mass of several thousand Mass units with the upper limit of Mass not defined. Planar chromatography provides a fast, cheap method of isolating large molecular Mass fractions of this bioMass tar.
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large molecular Mass materials in coal derived liquids by 252cf plasma and matrix assisted laser Desorption Mass Spectrometry
Energy & Fuels, 1998Co-Authors: M. Domin, María J. Lázaro, Alan A. Herod, John W. Larsen, Shang Li, Rafael KandiyotiAbstract:The paper compares responses of 252Cf-plasma Desorption MS (PD-MS) and matrix-assisted laser Desorption (MALDI) MS to identical samples. The two pairs of samples selected for the comparison were known from previous work to differ significantly in their high Mass contents. MALDI-MS showed large differences in MM distributions within both pairs of samples. The PD-MS data showed a degree of similarity between one pair of samples (pyridine soluble/insoluble fractions of a coal tar pitch); for the second pair (a coal extract and its hydrocracked product), trends from the two MS techniques agreed closely. The MM range observed by PD-MS was somewhat narrower, extending to between 3000 and 5000 u. Significant differences within pairs of samples were observed by SEC and by UV-fluorescence spectroscopy, providing somewhat closer agreement with the MALDI spectra. The two MS instruments differ in two important respects: the ionization system (i.e., plasma vs laser Desorption) and the maximum available ion extraction...