Search Results - (Author, Cooperation:J. M. Curtis)

0951-4198

Chemistry ; Analytical Chemistry and Spectroscopy

Wiley InterScience Backfile Collection 1832-2000

Physics

5 Ill.

Electronic Resource

2011-01-15

American Association for the Advancement of Science (AAAS)

0036-8075

1095-9203

Biology

Chemistry and Pharmacology

Computer Science

Medicine

Natural Sciences in General

Physics

*Animal Migration ; Animals ; Canada ; Female ; Fish Diseases/genetics/immunology/mortality ; *Gene Expression ; *Gene Expression Profiling ; Genome ; Gills ; Male ; Mortality ; Oligonucleotide Array Sequence Analysis ; Pacific Ocean ; Population Dynamics ; Principal Component Analysis ; Remote Sensing Technology ; *Reproduction ; Rivers ; Salmon/*genetics/*physiology ; Stress, Physiological ; Survival Analysis ; Virus Diseases/genetics/immunology/mortality/veterinary

0951-4198

Chemistry ; Analytical Chemistry and Spectroscopy

Wiley InterScience Backfile Collection 1832-2000

Physics

2 Ill.

Electronic Resource

0030-493X

Chemistry ; Analytical Chemistry and Spectroscopy

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

A mass spectrometric method of distinguishing between molecular ions of the three isomeric xylenes (dimethylbenzenes) was sought, in light of recent findigs that photoexcited ions could be distinguished via measurements of kinetic energy release accompanying expulsion of a methyl radical. Provided the molecular ions are formed with low internal energies, reproducible differences were found between relative intensities of collision induced reactions of higher critical energies, than for methyl expulsion. These differences exist both for collision energies in the kilovolt range (double focusing mass spectrometers) and in the range of a few tens of volts (triple quadrupole instrument). Though statistically significant, these differences were small. The mechanism of isomerization and fragmentation was investigated via isotopic labelling studies and measurements of kinetic energy release. Most of the present findings can be rationalized in terms of the most recent version of established mechanisms for reactions of ionized methylbenzenes.

7 Ill.

Electronic Resource

0030-493X

Chemistry ; Analytical Chemistry and Spectroscopy

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

The mechanism of water elimination from metastable molecular and [M - CH3·]+ ions, as well as from ions deprived of ring D, in epimeric 3-hydroxy steroids of the 5β-series has been elucidated by deuterium labelling, by the measurements of the translational energy released during loss of water, and by collision-induced decomposition mass-analysed ion kinetic energy spectrometry. It was found that the dehydration of the metastable molecular ion in 3α-hydroxy steroids of the 5β-series occurs mostly regiospecifically as an elimination of the 3α-hydroxyl together with the 9α-hydrogen atom. The ring A in the molecular ion has to flip to the boat conformation to make this reaction possible. In the metastable molecular ion of 3β-hydroxy steroids of the 5β-series a different dehydration mechanism operates, with very little participation of the 9α-hydrogen atom. The mechanisms of water loss from metastable [M - CH3·]+ ions and from ions deprived of ring D differ from that of the molecular ion.

10 Ill.

Electronic Resource

0030-493X

Chemistry ; Analytical Chemistry and Spectroscopy

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

The elimination of water from metastable molecular ions of epimeric hydroxy steroids of the Δ4-3-keto series containing a hydroxyl group in the conformationally rigid rings C and D has been studied. The measurement of translational energy released during the loss of water and collision-induced decomposition (CID) mass-analysed ion kinetic energy (MIKE) spectrometry were the techniques used. It was found that it is possible to determine the configuration of the hydroxy steroids of this series on the basis of the CID MIKE spectra of [M - H2O]+· ions formed by dehydration of metastable molecular ions in the first field-free region of a reversed geometry double-focusing mass spectrometer.

8 Ill.

Electronic Resource

0030-493X

Chemistry ; Analytical Chemistry and Spectroscopy

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

The mechanism of water elimination from metastable molecular, [M - CH3·]+ and [M - ring D]+· ions of epimeric 3-hydroxy steroids of the 5α-series has been elucidated. Deuterium labelling, the measurement of the translational energy released during the loss of water, and collision-induced decomposition mass-analysed kinetic energy spectrometry were the techniques used. It was found that the mechanisms of water loss from metastable M+· and [M - ring D]+· ions is different from that from [M - CH3·]+ ions.

9 Ill.

Electronic Resource

0030-493X

Chemistry ; Analytical Chemistry and Spectroscopy

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

The doubly charged isomeric ions [C6H7N]2+ formed from 2-, 3- and 4-methylpyridine and aniline were investigated via their unimolecular charge separation reactions and by electron capture induced decompositions (ECID). The ECID spectra were compared with the collision induced decomposition (CID) spectra of the singly charged ions in an attempt to investigate the structure of the doubly charged ions. The four isomers could be unambiguously identified by their unimolecular charge separations. These differences were greater than in the mass spectra, ECID spectra or CID spectra of singly charged ions.

5 Ill.

Electronic Resource

0030-493X

Chemistry ; Analytical Chemistry and Spectroscopy

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

Structure differentiation between [C5H8]+· ions, formed by electron ionization of various precursors, has been used as a test case for comparison of three experimental techniques involving collision-induced dissociation (CID). Low-energy CID in an rf-only quadrupole collision cell has been studied in the range 1-150 eV laboratory collision energy. These data have been compared with those obtained using mass-analyzed ion kinetic energy spectroscopy at 8 keV energy, and with results from dissociative charge-stripping (DCS) coupled with a second electron capture collision (EC) in order to remove intense interferences (DCS/EC). The greatest degree of structure differentiation was possible using the DCS/EC technique. The other two methods were comparable in this regard, although effects of pre-collision internal energy was apparent for collision energies much below 30 eV. Day-to-day reproducibility of spectra was most difficult to obtain for the low-energy CID technique. Of the [C5H8]+· ions thus tested, the isoprene molecular ion was clearly the best match to the fragment ion formed from limonene.

13 Ill.

Electronic Resource