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211.
The reaction between BH4? and CH2O has been investigated in the gas phase using ion cyclotron resonance spectroscopy. No hydride transfer from BH4? to the carbonyl group is observed, however a novel reaction between enolate ions and diborane has been observed. 相似文献
212.
213.
The production of highly excited hydrogen atoms by passing a proton beam though a thin carbon foil has been investigated within the energy range 5–30 keV. The population of atoms in states with principal quantum number, n, between 14 and 25 have been determined using the field ionization technique and found to scale as n?4.35±0.2. 相似文献
214.
Adam W. McMahon Swapan K. Chowdhury Ale X. G. Harrison 《Journal of mass spectrometry : JMS》1989,24(8):620-624
There are four neutralization-reionization processes which can be studied. In the first two, gaseous cations are collisionally reduced and the resulting fast neutrals are either oxidized by collisional electron removal (NR) or reduced further by collisional electron attachment (NR?). In the third and fourth processes, gaseous anions are collisionally oxidized and the resulting fast neutrals are either oxidized further by collisional electron removal (?NR) or reduced by collisional electron attachment (?NR?). These four processes are illustrated briefly using the interrelated species [SF5]+ and [SF5]?. Negative-ion-negative-ion neutralization-reionization (?NR?) processes are illustrated for [CH3O]?, [C2H5O]?, [CO3]? and [HCO3]? and compared with ?NR processes. In addition, collisional electron attachment ionization of fast neutrals formed in unimolecular fragmentation of cations is illustrated. The ?NR? studies of [CO3]? and [HCO3]? show that both CO3 and HCO3 are stable neutral species with lifetimes greater than 0.7 μs. 相似文献
215.
McMahon LM Luo S Hayes M Tse FL 《Rapid communications in mass spectrometry : RCM》2000,14(21):1965-1971
A semi-automated solid-phase extraction (SPE) liquid chromatography/mass spectrometry (LC/MS) procedure was validated for the simultaneous determination of everolimus (RAD001) and cyclosporin A (CsA) in human blood. Whole blood samples (350microL) were pretreated with acetonitrile/zinc sulfate mixture to precipitate the sample proteins. The samples were centrifuged and the resulting supernatants were manually transferred to a 96-well plate format. All subsequent sample transfer and solid phase extraction was automated using a Tomtec Quadra 96 workstation. Samples were analyzed by LC/MS using an atmospheric pressure chemical ionization (APcI) interface. In order to enhance sensitivity, the MS method used negative ion mode for RAD001 ([M]-) and its internal standard and positive ion mode for CsA ([M + H]+) and its internal standard. The lower limit of quantitation was 0.375 ng.ml(-1) for RAD001 and 6.95 ng.ml(-1) for CsA. The reproducibility of the method was evaluated by analyzing six replicates at five or more quality control (QC) levels over the nominal concentration range 0.375 to 253 ng.ml(-1) for RAD001 and 6.95 to 1,530 ng.ml(-1) for CsA. The inter- and intra-day accuracy was found to range from 89.7 to 114% with precision (% CV) of less than 12% for both compounds. The sensitivity, small sample volume needed and high sample throughput of this method make it an attractive option for pharmacokinetic studies in pediatric patients. 相似文献
216.
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218.
Herman Gershon Donald D. Clarke John J. McMahon 《Monatshefte für Chemie / Chemical Monthly》2003,134(8):1099-1104
Summary. Polyhalo-8-quinolinols with chlorine or bromine in position 4 were not stable in DMSO or DMF. The degradation product from 4,5-dichloro-8-quinolinol was 5-chloro-4,8-quinolindiol and the major product from 4,5-dibromo-8-quinolinol was 3,5-dibromo-4,8-quinolindiol. 4,5,7-Trichloro- and 4,5,7-tribromo-8-quinolinols yielded similar hydrolytic products, and for the bromo compound, a rebrominated product in DMSO. In DMF rebromination did not occur. In pyridine-d5 these reactions did not take place, indicating a special ability of DMSO and DMF to cause such hydrolysis at position 4 of 4-halo-8-quinolinols.Received December 13, 2002; accepted January 7, 2003
Published online June 23, 2003 相似文献
219.
Milanowski DJ Gustafson KR Rashid MA Pannell LK McMahon JB Boyd MR 《The Journal of organic chemistry》2004,69(9):3036-3042
A cytotoxic aqueous extract from the marine hydroid Gymnangium regae provided a novel linear pentapeptide, designated gymnangiamide (1). The planar structure of 1 was elucidated by interpretation of spectral data as well as chemical degradation and derivatization studies. In addition to the amino acids isoleucine and phenylserine, this peptide contained N-desmethyldolaisoleuine, O-desmethyldolaproine, and alpha-guanidino serine, three residues that have not previously been reported in a natural product. The absolute configurations of the constituent amino/guanidino acids were determined by chemical degradation and derivatization, followed by HPLC and LC-MS comparison with authentic standards. Gymnangiamide (1) was moderately cytotoxic against a number of human tumor cell lines in vitro. 相似文献