Mass spectrometry protonated

The alkaloidal fraction was then further separated using preparative silica gel thin layer chromatography (TLC). The material was separated on Silica Gel 60 (0.25 mm, Merck) using cyclohexane chloroform diethylamine (5 4 1), and six discrete fractions were identified. The major alkaloid had an Rf of 0.43, and this fraction was by far the most active in the nicotinic receptor assay. This active fraction was then further characterized by mass spectrometry, proton and C13 NMR spectroscopy, and was identified as methylly-caconitine (MLA,Fig.l). It was found to have a Kinh value for displacing 3Hot-BGTX of less than 0.5 nM (Fig.2). 

Using mass spectrometry, proton nuclear magnetic resonance ( H NMR), COSY H NMR analysis, and calculation on the relative thermodynamic stability, Tan et al. (1998) identified a novel melatonin metabolite as cyclic 3-hydroxymelatonin. This is the product of reaction of melatonin with HO generated in two different cell-free in vitro systems. Cyclic 3-hydroxymelatonin also existed in urine of both human and rat. When rats were challenged with ionising radiation (800 cGy = LD50 for a one month period), as expected, urinary cyclic 3-hydroxymelatonin was doubled over that of the controls (P = 0.002). 

Chemical methods As with many areas of natural product chemistry, new impetus in the chemistry of lichen substances is provided by the more rapid and improved methods for detecting, isolating and purifying these compounds and in determining their structure. The techniques of preparative TLC, radial chromatography and preparative HPLC provide rapid and efficient methods for the purification of lichen substances and developments in mass spectrometry, proton and carbon-13 nuclear magnetic resonance (NMR) spectroscopy and X-ray analysis greatly aid structural smdies. 

Shimamura, M., T. Endo, Y. Inoue, and S. Inoue A Novel Neutral Oligosaccharide Chain Found in Polysialoglycoproteins Isolated from Pacific Salmon Eggs. Structural Studies by Secondary Ion Mass Spectrometry, Proton Nuclear Magnetic Resonance Spectroscopy, and Chemical Methods. Biochemistry 22, 959 (1983). 

See also Fragmentation in Mass Spectrometry Ion Energetics in Mass Spectrometry Ion Molecule Reactions in Mass Spectrometry Metastable Ions Neutralization-Reionization in Mass Spectrometry Photoelectron-Photoion Coincidence Methods in Mass Spectrometry (PEPICO) Photoionization and Photodissociation Methods in Mass Spectrometry Proton Affinities. 

See also Fast Atom Bombardment Ionization in Mass Spectrometry Proton Microprobe (Method and Background) Time of Flight Mass Spectrometers. 

Norman, M. D., Griffin,W. L., Pearson, N. J., and Garcia, M. O. (1998). Quantitative analysis of trace element abundances in glasses and minerals a comparison of laser ablation inductively coupled plasma mass spectrometry, solution inductively coupled plasma mass spectrometry, proton microprobe and electron microprobe data. J. Anal. At. Spectrom. 13(5), 477. 

The spectroscopic methods, NMR and mass spectrometry for predicting cetane numbers have been established from correlations of a large number of samples. The NMR of carbon 13 or proton (see Chapter 3) can be employed. In terms of ease of operation, analysis time (15 minutes), accuracy of prediction (1.4 points average deviation from the measured number), it is... 

Some of the target molecules gain so much excess internal energy in a short space of time that they lose an electron and become ions. These are the molecular cation-radicals found in mass spectrometry by the direct absorption of radiation. However, these initial ions may react with accompanying neutral molecules, as in chemical ionization, to produce protonated molecules. 

Laser-desorption mass spectrometry (LDMS) or matrix-assisted laser desorption ionization (MALDI) coupled to a time-of-flight analyzer produces protonated or deprotonated molecular ion clusters for peptides and proteins up to masses of several thousand. 

Mass Spectrometry. Field desorption mass spectrometry has been used to analy2e PPO (179). Average molecular weight parameters (M and could be determined using either protonated (MH + ) or cation attachment (MNa + ) ions. Good agreement was found between fdms and data supphed by the manufacturer, usually less than 5% difference in all cases up to about 3000 amu. Laser desorption Fourier transform mass spectrometry was used to measure PPG ion and it was claimed that ions up to m/2 9700 (PEG) can be analy2ed by this method (180). 

Mass spectral analysis of quaternary ammonium compounds can be achieved by fast-atom bombardment (fab) ms (189,190). This technique rehes on bombarding a solution of the molecule, usually in glycerol [56-81-5] or y -nitroben2yl alcohol [619-25-0], with argon and detecting the parent cation plus a proton (MH ). A more recent technique has been reported (191), in which information on the stmcture of the quaternary compounds is obtained indirectly through cluster-ion formation detected via Hquid secondary ion mass spectrometry (Isims) experiments. 

Isoindole, 2,5-dimethyl-1,3-diphenyl-protonation, 4, 47 Isoindole, 1,3-diphenyl-mass spectrometry, 4, 187... 

This technique provides quantitative information about tautomeric equilibria in the gas phase. The results are often complementary to those obtained by mass spectrometry (Section VII,E). In principle, gas-phase proton affinities, as determined by ICR, should provide quantitative data on tautomeric equilibria. The problem is the need to correct the measured values for the model compounds, generally methyl derivatives, by the so-called N-, 0-, or S-methylation effect. Since the difference in stability between tautomers is generally not too large (otherwise determination of the most stable tautomer is trivial) and since the methylation effects are difficult to calculate, the result is that proton affinity measurements allow only semi-quantitative estimates of individual tautomer stabilities. This is a problem similar to but more severe than that encountered in the method using solution basicities (76AHCS1, p. 20). 

The information derived from 13C NMR spectroscopy is extraordinarily useful foT structure determination. Not only can we count the number of nonequivalent carbon atoms in a molecule, we can also get information about the electronic environment of each carbon and can even find how many protons each is attached to. As a result, we can answer many structural questions that go unanswered by TR spectroscopy or mass spectrometry. 

The total number of protons and neutrons in a nucleus is called the mass number, A, of the atom. A nucleus of mass number A is about A times as heavy as a hydrogen atom, which has a nucleus that consists of a single proton. Therefore, if we know that an atom is a certain number of times as heavy as a hydrogen atom, then we can infer the mass number of the atom. For example, because mass spectrometry shows that the three varieties of neon atoms are 20, 21, and 22 times as heavy as a hydrogen atom, we know that the mass numbers of the three types of neon atoms are 20, 21, and 22. Because for each of them Z = 10, these neon atoms must contain 10, 11, and 12 neutrons, respectively (Fig. B.7). 

High Pressure Mass Spectrometry with a m.e.v. Proton Beam... 

Electrospray is the softest mass spectrometry ionization technique and electrospray spectra therefore usually consist solely of molecular ions. Electrospray is unique, however, in that if the analyte contains more than one site at which protonation (in the positive-ion mode) or deprotonation (in the negative-ion mode) may occur, a number of molecular ions with a range of charge states is usually observed. For low-molecular-weight materials (< 1000 Da), the number of sites... 

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