Vincent Mihálov

Low Temperature Thermolysis of Lignins - I. Reactions of ß—O—4 Model Compounds

Two pairs of model compounds of arylglyceroland arylglycol-j3-guaiacyl ether type, representing phenolic and non-phenolic variant of 0-O-4 structure, were heated in atmosphere of own decomposition products at rate 10 °C/min. up to 275 and 315 °C, for phenolic and non-phenolic derivatives, respectively. On the basis of qualitative and quantitative analysis of the thermolyzates by rneans of chromatography and mass spectrometry, the role of the following reactions is discussed: 1. cleavage of 0-ether linkage presumably via oxirane intermediate 2. a, 0-dehydration 3. cleavage of Cß-Cy bond presumably via oxetane intermediate 4. formation of -0Condensed Structures and 5. cleavage of C^-C^ bond. In the phenolic series, thermal transformations of hypothetical oxirane intermediate are the most representative reaction. In the non-phenolic series, thermal stability is considerably increased, and a, ßdehydration and Cß-Cy cleavage become the most characteristic feature of the thermolysis.

Structural analysis by mass spectrometry of oligosaccharides related to xylans

Abstract Fully methylated, xylan-type oligosaccharides, namely, positionally and inter-glycosidically isomeric O - D -xylopyranosyl-β- D -xylopyranoses (xylobioses, 2–7 ), a complete series of O -β- D -xylopyranosyl(l →4)- O -β- D -xylopyranosyl-β- D -xylopyranoses (xylotrioses, 8 , 9 , 11 , 12 , and 14 ), a branched β- D -xylotetraose ( 15 ), and α- D -xylopyranosyl β- D -xylopyranoside ( 1 ), have been studied by 70- and 12-eV mass spectrometry. By using high-resolution techniques metastable-transition measurements, ion species formed through hitherto unknown fragmentation-processes have been found for the (1→1)- and (1→3)-linked disaccharides 1 , 4 , and 5 . Based on the qualitative and quantitative differences in the fragmentations, criteria for unambiguous determination of the positional mode of linkage in xylobioses are proposed. Similarly, by studying the fragmentation of xylotriose ( 10 ) labelled in the side-chain with tri-deuteriomethyl groups, the fragmentation-pathways for xylotrioses have been clarified. A new fragmentation series has been discovered in the fission of trioses 13 and 14 having a D -xylopyranosyl group attached to O-3 of the nonreducing end of the basic (1→4)-linked skeleton. Within the series of di- and tri-saccharides studied, the criteria proposed permit reliable determination of any of the theoretically possible branching points. The basic possibilities for structural analysis by mass spectrometry of related pentose tetraoses are also shown.

Electron-impact mass spectrometry of methyl O-methylglucopyranosiduranamides

Abstract Mass-spectral fragmentation of the complete series of methyl O -methyl-α- d -glucopyranosiduronamides has been studied. Based on 70- and 12-eV spectra, deuteration (OD and ND 2 ) experiments, and metastable-transition and exact-mass measurements, new cleavage-reactions resulting from the simultaneous presence of hydroxyl and amido groups in the molecule have been found. The mass spectra provide information useful in the determination of number and locations of methyl groups in methyl O -methylhexopyranosiduronamides.

Mass spectrometry of the positionally isomeric, monobenzyl ethers of methyl glycopyranosides

Abstract The electron-impact, mass-spectrometric behavior of all theoretically possible, positionally isomeric monobenzyl ethers of methyl pento-, hexo-, and 6-deoxy-hexo-pyranosides is described, on the basis of 70- and 12-eV mass spectra. O-deuterium-labeling experiments, elemental composition, and metastable-transition measurements. The semiempirical MNDO quantum-chemical method was used for calculation of both the geometrical parameters (bond lengths, bond angles, and dihedral angles) and the distribution of net charges in the cyclic and acyclic forms of the abundant [C4H7O3]+ and [C5H9O4]+ ions. The results obtained show that the cyclic structures of both ions are the more stable. Differences in the fragmentation of the compounds studied have been applied for establishing criteria that permit simple and unambiguous localization of the benzyl group in monobenzyl ethers of methyl glycopyranosides.