 |
 |
J. Mass Spectrom. Soc. Jpn., 46(5), 429-432 (in Japanese), 1998
Achievement of the unit mass accuracy in the molecular mass determination of proteins has been stressed. Single mass change of proteins is caused by single amino acid substitutions including Glu/Lys, Asn/Leu, Asn/Ile, Asp/Asn and Glu/Gln, of which four mutations except for Asn/Leu are produced by single nucleotide changes. In the case of Hemoglobin Hoshida, a substitution of Asn for Asp was found in a peptide of 2056.9 Da with a decrease of single mass unit. In a structural study of the transferrin isoform which is characteristic of carbohydrate-deficient glycoprotein syndrome and missing asparagine-linked oligosaccharides, assignment of Asn but not Asp for the residue that should be glycosylated was necessary for delineating the molecular pathogenesis of this disorder. However, as demonstrated in beta2-microglobulin, proteins are often partially deamidated during sample preparation or in vivo. This may compromise the biological significance of the precise mass measurement of proteins.
J. Mass Spectrom. Soc. Jpn., 46(5), 433-436 (in Japanese), 1998
Mass spectra of doubly charged tellurium clusters were investigated by a secondary ion mass spectrometry. Cluster ions were produced by the Xe ions bombardment on the tellurium sheet and were mass-analyzed using a grand-scale sector type mass spectrometer. Te22+, Te32+, and Te52+ were observed.
J. Mass Spectrom Soc. Jpn., 46(5), 437-441, 1998
A new computer code 'TRIO-TOF' have been constructed. The code can calculate ion flight times in time-of-flight (TOF) mass spectrometers to a third-order approximation. Ion-optical characteristics and focusing properties of time-of-flight mass spectrometers, which consist of toroidal electrostatic condensers and electrostatic quadrupole lenses, can be estimated by this code. The influences of the fringing field on ion flight times have been taken into consideration. The precise calculation of ion flight times in the fringing-fields has been also described.
J. Mass Spectrom. Soc. Jpn., 46(5), 442-447, 1998
Gas-phase ion-molecule reactions have been investigated using a pulsed-electron beam mass spectrometer. The proton affinity(PA) of tetrahydrothiophene(THT), C4H8S, has been newly determined to be 205.4 kcal mol-1 by measuring the equilibria of the proton transfer reaction between 2-methyltetrahydrofuran and THT. The thermochemical data for the hydration reaction of protonated tetrahydrothiophene, C4H8SH+(H2O)n-1 + H2O = C4H8SH+(H2O)n, with n=1-3 were measured. The small and n-insensitive enthalpy changes (-delta Hon-1,n) , 11.5, 10.4 and 9.5 kcal mol-1 , with n=1, 2, and 3, respectively, have been obtained. The fall-off of -delta Hon-1,n vs n is small due to the positive charge dispersal in the protonated THT. The rate of proton transfer reaction from the proton-hydrates H3O+(H2O)n to THT was found to be roughly the collision rate in agreement with the findings due to Viggiano et al. Ab initio calculations have been carried out, and those energies(PA and deltaHon-1,n) have been reproduced satisfactorily.
J. Mass Spectrom. Soc. Jpn., 46(5), 448-453, 1998
The unimolecular decompositions of the metastable ions produced from 2,2,2-trifluoroethyl acetate, CH3COOCH2CF3, 1, (Mw:142), 2,2,2-trifluoroethyl trifluoroacetate, CF3COOCH2CF3, 2, (Mw:196), and S-ethyl trifluorothioacetate, CF3COSCH2CH3, 3, (Mw:158) upon electron ionization have been investigated by means of mass-analyzed ion kinetic energy (MIKE) spectrometry and D-labeling. The metastable ions 1+ decompose exclusively to give the ion at m/z 122 by losing HF via an 1,2-elimination. In the normal mass spectrum of 2, no molecular ion is observed, while the ion corresponding to the loss of CF3 gives rise to an intense peak at m/z 127 (about 90% of the base peak) and the ion corresponding to the loss of F gives the peak at m/z 177 with moderate intensity (about 20%). Both ions consist of two isomeric ions. Some interesting rearrangement processes, such as CF3 or OCH2CF3 migration followed by the loss of a CO molecule, occur during the metastable fragmentations of these ions. The molecular ion of 3, which is a base peak, decomposes into the ions at m/z 89 and 61 by losing CF3 and CF3CO, respectively, in the metastable time region. The relative abundance of ions in the MIKE spectrum are rationalized with the thermochemical data estimated by the PM 3 method.
J. Mass Spectrom Soc. Jpn., 46(5), 454-458, 1998
The effects of amines on the formation of molecular adduct ions of methyl hydroper-oxyoleates (OMH) in atmospheric pressure chemical ionization mass spectrometry were in-vestigated. The short-chain primary amines such as methylamine and ethylamine were more effective than ammonia on suppressing the thermal decomposition of OMH, and provided abundant [M+H+L]+ type ions (L: each amine molecule). The secondary and tertiary amines were unsuitable for the purpose in spite of their high basicity, probably due to the steric inter-ference. Aromatic and heterocyclic amines were also ineffective. The formation of amine ad-duct to OMH in liquid and/or condensed phases depends on both basicity and stereochemistry of each amine.
J. Mass Spectrom Soc. Jpn., 46(5), 459-470 (in Japanese), 1998
Recent progress on mass spectrometry of air pollutants is reviewed, including such studies as: Analysis of volatile organic compounds (VOCs) by GC/MS, analysis of pesticides by GC/MS and GC/MS/MS, analysis of polycyclic aromatic hydrocarbons (PAHs) by GC/MS, characterization of semi-volatile organic compounds (SVOCs) by GC/MS, analysis of non-volatile organic compounds (NVOCs) by LC/MS, and characterization of NVOCs by Liquid Ionization Mass Spectrometry. The newly-developed precise methods measuring pesticides by GC/CI-MS and GC/MS/MS are also demonstrated.
|
|