Home About us Contact
|
Home About us Contact | ||
|
|
||
Ion Fragmentations (ion + fragmentation)
Selected AbstractsInfrared multiple photon dissociation spectroscopy of ions in Penning trapsMASS SPECTROMETRY REVIEWS, Issue 3 2009John R. Eyler Abstract The ability of Paul and Penning traps to contain ions for time periods ranging from milliseconds to minutes allows the trapped ions to be subjected to laser irradiation for extended lengths of time. In this way, relatively low-powered tunable infrared lasers can be used to induce ion fragmentation when a sufficient number of infrared photons are absorbed, a process known as infrared multiple photon dissociation (IRMPD). If ion fragmentation is monitored as a function of laser wavelength, a photodissociation action spectrum can be obtained. The development of widely tunable infrared laser sources, in particular free electron lasers (FELs) and optical parametric oscillators/amplifiers (OPO/As), now allows spectra of trapped ions to be obtained for the entire "chemically relevant" infrared spectral region. This review describes experiments in which tunable infrared lasers have been used to irradiate ions in Penning traps. Early studies which utilized tunable carbon dioxide lasers with a limited output range are first reviewed. More recent studies with either FEL or OPO/A irradiation sources are then covered. The ionic systems examined have ranged from small hydrocarbons to multiply charged proteins, and they are discussed in approximate order of increasing complexity. © 2009 Wiley Periodicals, Inc., Mass Spec Rev 28:448,467, 2009 [source] Microsynthesis and mass spectral study of Chemical Weapons Convention related 2-alkyl-1,3,6,2-dioxathiaphosphocane-2-oxidesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 12 2008Meehir Palit Chemical Weapons Convention (CWC)-related compounds where the phosphorus atom is part of a ring have very limited representation in mass spectral libraries and the open literature. Here we report electron ionization (EI), chemical ionization (CI) and electrospray ionization tandem mass spectrometry (ESI-MSn) spectra and retention indices for 2-alkyl-1,3,6,2-dioxathiaphosphocane-2-oxides (alkyl C1 to C3) which are new cyclic chemicals covered under the CWC. The EI mass spectra show a pattern of ion fragmentation that is similar to that of other cyclic phosphonates in that loss of the alkylphosphonic acid as a neutral loss is more important than the presence of the protonated alkylphosphonic acid. In contrast to other cyclic phosphonates, the 2-alkyl-1,3,6,2-dioxathiaphosphocane-2-oxides show almost no protonated alkylphosphonic acid and as a result the spectra do not carry the same distinctive signature of the phosphorus,carbon bond that is required for the chemical to be covered under the CWC. Copyright © 2008 John Wiley & Sons, Ltd. [source] Negative ion fragmentations of deprotonated peptides.RAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 13 2009The unusual case of isoAsp: a joint experimental, theoretical study. The following peptides have been examined in this study: GLDFG(OH), caeridin 1.1 [GLLDGLLGLGGL(NH2)], 11 Ala citropin 1.1 [GLFDVIKKVAAVIGGL(NH2)], Crinia angiotensin [APGDRIYVHPF(OH)] and their isoAsp isomers. It is not possible to differentiate between Asp- and isoAsp-containing peptides (used in this study) using negative ion electrospray mass spectrometry. This is because the isoAsp residue cleaves to give the same fragment anions as those formed by , and , backbone cleavage of Asp. The isoAsp fragmentations are as follows: RNHCH(CO2H),CHCONHR,,,,[RNH,(HO2CCHCHCONHR,)],,,RNH,+HO2CCHCHCONHR, and RNHCH(CO2H),CHCONHR,,,,[RNH,(HO2CCHCHCONHR,],,,,O2CCHCHCONHR,+RNH2. Calculations at the HF/6-31+G(d)//AM1 level of theory indicate that the first of these isoAsp cleavage processes is endothermic (by +115,kJ mol,1), while the second is exothermic (,85,kJ mol,1). The barrier to the highest transition state is 42,kJ mol,1. No diagnostic cleavage cations were observed in the electrospray mass spectra of the MH+ ion of the Asp- and isoAsp-containing peptides (used in this study) to allow differentiation between these two amino acid residues. Copyright © 2009 John Wiley & Sons, Ltd. [source] A liquid chromatography/tandem mass spectrometry method for detecting UGT-mediated bioactivation of drugs as their N -acetylcysteine adducts in human liver microsomesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 5 2009Hiroshi Harada The detection of the reactive metabolites of drugs has recently been gaining increasing importance. In vitro trapping studies using trapping agents such as glutathione are usually conducted for the detection of reactive metabolites, especially those of cytochrome P450-mediated metabolism. In order to detect the UDP-glucuronosyltransferase (UGT)-mediated bioactivation of drugs, an invitro trapping method using N -acetylcysteine (NAC) as a trapping agent followed by liquid chromatography/tandem mass spectrometry (LC/MS/MS) was developed in this study. After the test compounds (diclofenac and ketoprofen) had been incubated in human liver microsomes with uridine diphosphoglucuronic acid (UDPGA) and NAC, the NAC adducts formed through their acyl glucuronides were analyzed using LC/MS/MS with electrospray ionization (ESI). The NAC adduct showed a mass shift of 145 units as compared to its parent, and the characteristic ion fragmentations reflected the parent. This is a concise and high-throughput method for evaluating reactive metabolites by UGT-mediated bioactivation. Copyright © 2009 John Wiley & Sons, Ltd. [source] A study of the electrospray ionisation and ion-trap fragmentation of [M,,,H], ions of new 3,5-disubstituted tetrahydro-2H -1,3,5-thiadiazin-2-thionesRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 10 2001Roberto Martínez-Alvarez The electrospray ionisation (ESI) in negative mode of the pharmacologically significant 3,5-disubstituted tetrahydro-2H -1,3,5-thiadiazin-2-thiones, and their subsequent fragmentations using an ion-trap mass spectrometer, have been investigated. Experiments on sequential product ion fragmentations (MSn) were performed in order to elucidate the degradation pathways for these compounds. The data presented show that the fragmentation of the even-electron [M,,,H], ions could proceed through an internal nucleophilic substitution displacement. Decarboxylation and extrusion of carbon disulfide are other fragmentations observed. Copyright © 2001 John Wiley & Sons, Ltd. [source] | ||||||||||