1,721,004 research outputs found
Gas-Phase Positive and Negative Ion Chemistry of Methyl Hydroperoxide.
No full textThe gas-phase ion chemistry of methyl hydroperoxide (1) was investigated by mass spectrometric and theoretical methods. The proton affinity of 1, 173.3 ± 2 kcal mol−1 measured by the FT-ICR bracketing technique and the kinetic method, is in excellent agreement with the value of 172.6 ± 2 kcal mol−1 from G2 ab initio calculations, which identify the α oxygen atom as the most basic site. Methylation of 1 by (CH3)2F+ gives a mixed population of ions methylated at both oxygen atoms. The experimental proton affinity of CH3OOCH3 is 176.2 ± 4 kcal mol−1, versus a theoretically computed value of 180.4 ± 2 kcal mol−1, the most nucleophilic site being again the α oxygen atom. Nitrosation of 1 yields a (CH3OOH·NO)+ adduct that behaves as both a nitrosating and a protonating agent. The results are discussed and compared with earlier pertinent studies
Gas-phase condensation of tert-butyl cations with Lewis bases
No full textt-Butyl cations, obtained in the dilute gas phase from the radiolysis of neopentane, react with H2O, MeOH, and EtOH giving high yields of the condensation products, t-butyl alcohol, t-butyl methyl ether, and t-butyl ethyl ether respectively; the relative rates of the condensations with H2O and MeOH, and of proton transfer to NH3, are very similar in gaseous neopentane at atmospheric pressure
5-Methylcytosine levels in nucleosome subpopulations differently involved in gene expression
No full textSucrose density gradient centrifugation in the presence or absence of Na-EDTA and at different ionic strengths allows one to obtain well-defined nucleosome subpopulations the DNA of which, examined by gas chromatography-mass spectrometry, is in all cases hypermethylated as compared to spacer regions, but to a different extent for the different subpopulations. The various nucleosomes differ also in their content of histones and of high-mobility-group proteins, as well as in the levels of RNA polymerase activity associated with them. Such data suggest that these nucleosome subpopulations originate from chromatin fractions differently involved in gene expression
A radiolytic study on the gas-phase protonation of pinacol. The first demonstration of pinacol rearrangement in the dilute gas state.
No full textProtonated nitric acid. Structure and relative stability of isomeric H2N03+ ions in the gas phase
No full textGaseous H2N03+ ions have been obtained from direct protonation of nitric acid by H3+, CH5+, and H30+ as well
as from the protonation of C2HSON02fo llowed by CzH4 loss. The proton affinity of nitric acid has been estimated to be
168 f 3 kcal mol-' from the results of bracketing experiments carried out by FT-ICR and CI mass spectrometry. Structural
analysis by MIKE and CID spectrometry of H2N03+ ions and of their 180-labeled isotopomers obtained from the exchange
with HZ1"0 provides strong evidence for the existence of two isomers, characterized by the (HO)zNO+ and the Hz0.NO2+
structure, and for the higher stability of the latter. The results are consistent with those of independent MO SCF calculations,
pointing to the higher stability of the H20.N02+ structure
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