Secondary-ion mass spectra of pennogenin glycosides

LSIMS mass spectra of pennogenin glycosides have been studied; the most characteristic ions are (M+H–H₂O)⁺ (with glycerol as the liquid matrix) and (M+Na)⁺ (with glycerol +NaCl as matrix). In both cases the peaks of ions formed as the result of the successive elimination of the carbohydrate units, the breakdown of the bonds of the terminal pyranoses, the cleavage of the bonds of the rings D and E, and the peaks of the ions Agl⁺ and (Agl–H₂O)⁺ were observed.Institute of Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. All-Union Scientific-Research Institute for Agricultural Biotechnology, All-Union Academy of Agricultural Sciences, Moscow. Pacific Institute of Bioorganic Chemistry, Far Eastern Branch, Academy of Sciences of the USSR, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 523–525, July–August, 1991.     

Fragmentation of sesquiterpene lactones related to leucomisin

The mass spectra of seven sesquiterpene lactones — leucomisin, austricin, parishin B, parishin C, matricarin, artelin, and artelin diacetate — have been studied. It has been shown that the presence of the conjugated bonds C(1)=C(10), C(2)=0, and C(3)=C(4), and also C(5)=C(6), stabilizes M⁺, and the main fragmentation process is that of the splitting out of the lactone ring. The presence of hydroxy substituents at C(3) and C(8) of the guaiane system does not change the stability of M⁺ under electron impact. The directions of fragmentation have been confirmed by an analysis of spectra obtained by the metastable defocussing of daughter ions and by measuring the accurate masses of the main peaks of the fragmentary ions.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 96–101, January–February, 1987.     

Secondary-ion mass spectra of pennogenin glycosides

LSIMS mass spectra of pennogenin glycosides have been studied; the most characteristic ions are (M+H−H₂O)⁺ (with glycerol as the liquid matrix) and (M+Na)⁺ (with glycerol +NaCl as matrix). In both cases the peaks of ions formed as the result of the successive elimination of the carbohydrate units, the breakdown of the bonds of the terminal pyranoses, the cleavage of the bonds of the rings D and E, and the peaks of the ions Agl⁺ and (Agl−H₂O)⁺ were observed. Institute of Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. All-Union Scientific-Research Institute for Agricultural Biotechnology, All-Union Academy of Agricultural Sciences, Moscow. Pacific Institute of Bioorganic Chemistry, Far Eastern Branch, Academy of Sciences of the USSR, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 523–525, July–August, 1991.     

Features of the mass spectra of C18-diterpene alkaloids

Fragmentation under electron impact of eleven C₁₈-diterpene alkaloids with an oxygen function at C-4 has been investigated. The contributions of various modes of forming the (M - CH₃)⁺ ions have been determined. The mechanism of the appearance of the fragments (M - CH₃)⁺ and (M - OCH₃)⁺ at the expense of the methoxy groups at C-14 and C-16 has been considered. The characteristic nature of the parameters of the metastable peaks in the transitions to these daughter ions has been shown. Minor directions of the fragmentation of 3,4-epoxy- and 4-hydroxy bases have been characterized.Institute of the Chemistry of Plant Substances, Uzbek SSR Academy of Sciences, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 95–106, January–February, 1989.     

Metastable transitions in the mass spectra of ketals and ketones. Competition between loss of small and large radicals

An investigation of competing metastable transitions in the mass spectra of ethylene ketals R_SR_LC(OCH₂)₂ (where R_L is a larger n-alkyl group than R_S) has established that in most cases R_S is lost with a lower activation energy than R_L. This technique has also been applied to ketones R_SR_LC?O, to show again that R_S is usually lost with the lower activation energy (thus supporting earlier data based on relative daughter ion abundances at the threshold). In the classes of compounds so far investigated, although [M⁺ ? R_S] ions are formed with lower activation energies than [M⁺ ? R_L] ions, the ion yield of [M⁺ ? R_S] ions is anomalously low from ions of high internal energy. Factors which may influence the [M⁺ ? R_S]/[M⁺ ? R_L] ratio of daughter ion intensities are examined. It is suggested that at the threshold [M⁺ ? R_S] and [M⁺ ? R_L] ions may be formed with rearrangement, or from an electronic state that cannot be effectively populated from molecular ions of high internal energies.     

Mass spectra of permethylates of spirostanol tetraosides

The design of the new MKh 1310 mass spectrometer with double focusing permits the recording of the spectra of sparingly volatile natural compounds with molecular weights of up to 1700 and, in particular, the permethylates and peracetates of spirostanol and furostanol saponins. The results are given of an investigation of the mass spectra of five spirostanol tetraosides in the form of their permethylates. The spectra contain the peaks of the molecular ions and of the products of their decomposition at the glycosidic bonds. The most important feature of the spectra is the fragmentation of the skeletons of the terminal saccharide residues starting directly from M⁺ in directions close to the directions of decomposition of the nonreducing unit of permethylates of oligosaccharides. The origin of the ions (M -191)⁺, (M - 175)⁺, (M - 162)⁺, (M - 147)⁺, (M - 131)⁺, (M - 118)⁺, and (M - 102)⁺ arising this way have been confirmed by measurements of their elementary compositions.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 661–666, September–October, 1979.     

Mass spectrometry of pennogenin glycosides

The electron-impact mass spectra of five unesterified pennogenin glycosides, which contain the M⁺ or (M - H₂O)⁺ peaks, have been obtained. The characteristic features of the fragmentation of these compounds have been studied. In addition to ions characterizing the successive elimination of carbohydrate units, fragments have been detected which show the breakdown of the terminal pyranose ring. Five new directions of the fragmentation of the spirostanol skeleton due to the presence of an OH group at C-17 have been found.Institute of the Chemistry of Plant Substance, Academy of Sciences of the Uzbek SSR, Tashkent. Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Science Center of the Academy of Sciences of the USSR, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 337–341, May–June, 1986.     

Spectra of the metastable ions on steroid sapogenins and their dihydro derivatives

Characteristic distinguishing features of the mass spectra of steroid sapogenins of the spirostan series and their dihydroderivatives are considered. The MD and B/E = const spectra of all the key ions have been studied. It has been established that the relative intensities of the metastable peaks obtained by the two methods have close values. The orders of these magnitudes are the same for monotypical fragmentation processes. The correlation between the parameters of the spectra is disturbed if a daughter of one has a number of alternative formation pathways. On the whole, the linked-scanning spectra are characteristic to the extent that they contain metastable peaks of analogous transitions possessing close parameters.Institute of Chemistry of the Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Special Design Bureau of Analytical Instrument Construction, Scientific and Technical Branch, Academy of Sciences of the USSR, Leningrad. Translated from Khimiya Priorodnykh Soedinenii, No. 4, pp. 489–497, July–August, 1990.     

Dadi spectra of gossypol hexamethyl ethers and mixtures of them

The DADI spectra of the M⁺ ions of hexamethyl ethers of three tautomeric forms of gossypol and of mixtures of them have been studied. A specific fragmentation pathway of M⁺ for each form has been shown. On the basis of the results obtained, the amounts of the hexamethyl ethers of each tautomeric form produced in the methylation of gossypol have been found.Institute of Bioorganic Chemistry, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 38–42, January–February, 1980.     

Mass spectra and structures of isomeric phenylaminopyrazoles

The processes involved in the dissociative ionization of isomeric phenylaminopyrazoles under the influence of electron impact were studied. The pathways of fragmentation of the molecular ion (M⁺) were proved rigorously by means of the spectra of the metastable ions. The empirical compositions of the fragment ions were confirmed by the high-resolution mass spectra. It was established on the basis of the mass spectra of the amino-group-deuterated analogs that M⁺ exists exclusively in the amide from. A rearrangement leading to the formation of benzodiazepine cation radicals precedes fragmentation of M⁺. The elimination of an HCN particle in the first step of the fragmentation of M⁺ does not involve the amino group. The pK_a values are presented for all of the investigated phenylaminopyrazoles.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1381–1388, October, 1978.     

Fragmentation of the unsubstituted carbohydrate units of cardenolide monosides

In the mass spectra of unsubstituted monosides of cardenolide nature are observed the M⁺ peaks, and also, in each case, three characteristic processes of the fragmentation of the carbohydrate unit. The formation of the ions AglOCH=OH⁺ is the most universal property of these compounds. The stability of ions of the type under consideration depends on the nature and position of attachment of the sugar residue and on the number of polar groups in the aglycone. The laws of the fragmentation of the carbohydrate unit are extended to the spectra of glycosides of other classes.Deceased.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodynykh Soedinenii, No. 3, pp. 345–354, 1983.     

Formation and fragmentation of gas-phase ion-molecule complexes of transition-metal ions with organic molecules containing two functional groups

A mass spectrometer fast atom bombardment source has been used to synthesize, in the gas phase, the ion-molecule complexes of transition-metal ions (Ni⁺, CO⁺, Fe⁺, and Mn⁺) with α- or β-unsaturated alkenenitriles, RCH=CHCN (R=H, CH₃, and C₂H₅) and CH₃CH=CHCH₂CN, and 2-methyl glutaronitrile. The metastable ion fragmentations of the complexes are monitored in the first held-free region by B/E linked scans. Surprisingly, an intense HCN loss via an intermediate (C _n H_2n ?2)?M⁺?(HCN) is observed for the complexes of the alkenenitriles. The metal ions significantly affect the fragmentation processes. The coexistence of both end-on and side-on coordination modes is suggested to explain the fragmentations.     

A mass spectrometric investigation on some 4,7-dioxo-4,5,6,7-tetrahydroindole derivatives

The mass spectrometric behaviour of a series of 2-aryl substituted 4,7-dioxo-4,5,6,7-tetrahydroindoles has been studied in different ionization conditions (Electron Ionization and Fast Atom Bombardment), with the aid of the metastable ion studies. In electron ionization conditions all the compounds exhibit a highly favoured, primary H₂ loss giving rise to the corresponding indole-4,7-diones; in the usual spectra no evidence for the molecular ions in the enolic form was found, while the OH* loss observed in the MIKE (mass analyzed ion kinetic energy) spectra of molecular ions suggests that species at low internal energy content isomerize to the corresponding tautomeric enolic form. FAB mass spectra show easy formation of an unusual [M + 2H]⁺ species, together with abundant [M + H]⁺ and M⁺ cations.     

Translational energy release and stereochemistry of steroids. VIII-The mechanism of the elimination of water from metastable ions in epimeric 3-hydroxy steroids of the 5α-series

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.     

Secondary-ion mass spectrometry of lycotetraosides of the spirostan and furostan series

The secondary-ion mass spectra of seven steroid lycotetraosides have been obtained by the SIMS method. On the use of a glycerol matrix, all the compounds of the spirostan series, including those with an additional carbohydrate substituent a C-24, formed the (M+H)⁺ ions, while a lycotetraoside of the furostan series formed the (M–H₂O+H)⁺ ion. They subsequently decomposed by the alternative successive elimination of the terminal carbohydrate units of the lycotetraose. Substituents at C-25 and C-26 were ejected in the form of glucose molecules. Fragments of the aglycon and of the lycotetraoside moieties of the molecules were recorded. When NaCl was added to the same matrix, all the compounds gave preferentially the (M+Na)⁺ and (M+2Na–H)⁺ ions.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. All-Union Scientific-Research Institute of Agricultural Biotechnology, Lenin All-Union Academy of Agricultural Sciences, Moscow. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 53–58, January–February, 1991.     

Formation of M+ ions and electronic excitation under fast-atom bombardment conditions by using a liquid matrix

Japan The mechanism for the formation of molecular ions M^+· under fast-atom bombardment (FAB) conditions with a liquid matrix is discussed on the basis of the mass spectra of pyrene, coronene, and fullerene C₆₀ obtained by using electron impact, gas-phase fast-atom bombardment, and gas-phase fast-molecule bombardment techniques. The obtained results suggest that formation of the M^+· ions under FAB conditions is not due to direct collisions between analytes M and fast atoms A, but is due to collision interactions between M and recoiling matrix molecules B or matrix ions. It has been confirmed, furthermore, that the FAB conditions with a liquid matrix are sufficient in energy for formation of singly charged ions M^+· and insufficient for the formation of multiply charged ions M ^z+ (z=2, 3) of pyrene, coronene, and C₆₀.     

Consecutive reactions in the vitamin D series. A New insight into the mechanism of vitamin D and provitamin D isomerizations in the mass spectrometer

The individual steps of the consecutive reactions arising from metastable molecular ions, derived from vitamin D₃, vitamin D₂ and their respective provitamins (7-dehydrocholesterol, ergosterol), were examined in different field-free regions of a triple-sector mass spectrometer of B/E/E geometry. The comparison of the translational energy release (T) and the metastable peak shapes corresponding to these reactions, as well as unimolecular and collision-induced dissociation mass-analysed ion kinetic energy spectra, showed that there are probably two structures of the [M – H₂O]⁺˙ and [M – CH₃˙]⁺ ions depending upon whether the respective ions are formed in the ion source through high-energy reactions, or from the fragmentation of metastable molecular ions through slow, low-energy processes which occur in the first field-free region.     

Metastabile Übergänge des Ions C2H3O+ im Massenspektrometer

The metastable transitions of C₂H₃O⁺ ions generated from ten different compounds have been investigated. The intensity ratios of the metastable peaks have been found to be independent of the structure of the initial compound. They are dependent however on the internal energy of the ions. The variation of the intensity ratios with the molecular size is in agreement with the degrees-of-freedom-effect. C₂H₃O⁺ ions decompose from the same structure (mixture of structures) in all cases.

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On the structures and fragmentation of [Me2S∵SMe2]+ and [Et2S∵SEt2]+: Tandem mass spectrometry metastable and collision-induced dissociation results

An experimental study of the metastable and collision-induced dissociation (CID) spectra of [Me₂S∵SMe₂]⁺ and [Et₂S∵SEt₂]⁺ has been carried out. These ions are examples of species that contain two-center-three-electron (2c–3e) sulfur-sulfur bonds. The metastable and CID spectra provide experimental evidence of the atomic connectivity and of the 2c–3e bonds. The metastable cleavage of the S∵S 2c–3e bonds appears to occur with no reverse activation barriers and to result in small average kinetic energy releases. Fragmentation of the same bonds by CID results in the most intense product for both ions. Comparisons with the metastable and CID spectra of [MeSSMe]⁺, an ion with a two-center-two-electron (2c–2e) sulfur-sulfur bond, are made and strongly support the difference in the sulfur-sulfur bonding.     

Mass spectrometry of aryl substituted di- and trisiloxanes

The mass spectra of arylpentamethyldisiloxanes, sym-diaryltetramethyldisiloxanes and 1,5-diaryl-1,1,3,3,5,5-hexamethyltrisiloxanes were examined. Isotopic labeling and peak matching were used to substantiate the proposed fragmentation mechanisms. Siliconium ions dominate the spectra. Loss of neutral fragments from the [M-15]⁺ ions is important. Phenylpentamethyldisiloxane, sym-tetramethyldiphenyldisiloxane and 1,1,3,3,5,5-hexamethyl-1,5-diphenyltrisiloxane are representative examples of the three classes of compounds discussed. The [M-15]⁺ ion of phenylpentamethyldisiloxane loses methane, dimethylsilanone [(CH₃)₂Si?O] and phenylmethylsilanone [PhCH₃Si?O] to yield daughter siliconium ions. The [M-15]⁺ ion of sym-tetramethyldiphenyldisiloxane loses benzene, methane, dimethylsilanone and phenylmethylsilanone to yield daughter siliconium ions. The [M-15]⁺ ion of 1,1,3,3,5,5-hexamethyl-1,5-diphenyltrisiloxane loses benzene, tetramethylcyclodisiloxane and phenyltrimethylcyclodisiloxane to yield daughter siliconium ions. Finally, doubly charged ions are important in the mass spectra of the three series of aryl substituted di- and trisiloxanes discussed.