Mass spectrometric studies on gibberellins

Based on the element maps of twenty-two gibberellin methyl esters fragmentations are discussed, which are characteristic of the common structural features as well as structural modification in gibberellin homologues.     

Mass spectrometric studies of 2-nitrosophenols

The mass spectra of 2-nitrosophenols are independent of the insertion temperature, suggesting that the compounds either do not exhibit tautomerism in the vapour phase or that the enthalpy of isomerization is low. However, their fragmentation patterns suggest tautomerism in the molecular ion.     

Mass spectrometric studies of phenoxarsine derivatives

Nine phenoxarsine derivatives with arsenic in the trivalent state and the pentavalent state are synthesized and studied by mass spectrometry. Their characteristic fragmentation modes and the fragment ions with common structures are discussed. Phenoxarsinic acids are found to be unstable in the gaseous phase at the temperatures studied and tend to form their corresponding anhydrides.     

Mass spectrometric studies on azidomorphine derivatives

The mass spectrometric behaviour of nine azidomorphine derivatives have been studied. These compounds proved to have surprisingly specific and selective fragmentation under electron-impact. For 6-deoxy-6-azido-dihydro-isomorphine derivatives (I to V) the main decomposition pathway involves the loss of an N₂ molecule followed by a very rapid and selective fragmentation process. On the other hand, the molecular ions of 6-deoxy-8-azido-pseudomorphine derivatives (VI to VIII) and 6-deoxy-6-azido-14-hydroxy-isocodein (IX) primarily decompose by loss of the N₃ radical. This is due to the allylic effect of the double bond in ring C, corresponding to the chemical behaviour of these compounds.     

Mass spectrometric studies of anomeric glycopyranosyl azides

We studied the mass spectrometric behaviour of peracetylated and underivatized anomeric hexopyranosyl azides and 5-thioglucopyranosyl azides by means of different mass spectrometric techniques. The unstable molecular ions fragment predominantly by losing either N3 radical or N2 molecule. Loss of N2 molecule and the protonation of the derived nitrene were characteristic of the studied compounds. The presence of BF3.Et2O in the ion source is favorable for producing the protonated nitrene form. The protonated nitrene shows a new type of ring expansion rearrangement. The abundances of the [M + H - N2]+ ion makes it possible to identify the anomeric configuration of the azido group.     

Mass spectrometric studies of some novel sulfonamides

A recent paper described the overall 5-endo cyclisation of homoallylic sulfonamides to give pyrrolidines. This reaction was also used to prepare polycyclic systems. Mass spectrometric analysis using classical electron ionisation spectra and accurate mass measurement played a vital role in confirming the proposed structures for the products. These materials were not amenable to newer mass spectrometric methods and this study shows the continuing importance of older techniques.     

Mass spectrometric studies of dithiophosphinato metal complexes

Electron impact induced fragmentation reactions of planar, tetrahedral, octahedral and oligomeric metal dithiophosphinates Me(II)L₂ (L=Et₂PS₂^?; Me(II)=Zn, Cd, Hg, Pb, Co, Mn, Ni, Pd, Pt), Me(III)L₃ (Me(III) = Sb, Bi, In, Rh, Ir) and (Me(I)I)_n (Me(I)/n=Tl/1, Au/2, Cu/4) have been studied. Fragmentation patterns, which are in accordance with metastable peak determinations by linked scans, are reported. In the case of the transition metals the spectra of the complexes show abundant [M]^+· predominantly metal containing ions and, the former being weak and the intensities of the latter being considerably reduced in the case of metal complexes with filled d shells. With planar or tetrahedral transition metal complexes no dependence of fragmentation on the coordination geometry can be observed. The dependence of fragmentation on d configuration, ionization energy of the metal and metal ligand π bonding is discussed. In the case of the oligomeric complexes strong metal-metal interaction is observed even under electron impact.     

Mass spectrometric studies of the pterocarpan skeleton

The mass spectrometric characteristics of the pterocarpan skeleton have been studied with the aid of metastable decomposition (CAD-MIKES), high resolution mass measurements and specific deuterium labeling. New structural rotations have been postulated for the [M - H](+) ions which can explain the fragmentation routes for the pterocarpan skeleton.     

Mass spectrometric studies of cisplatin-induced changes of hemoglobin

This study reports on structural changes of hemoglobin (Hb) that were induced by cisplatin binding. Two techniques, nanoelectrospray quadrupole time-of-flight mass spectrometry (nanoES-MS) and high-performance liquid chromatography with inductively coupled plasma mass spectrometry (HPLC/ICPMS), were developed to facilitate this study. Nanospray MS analyses of cisplatin and Hb reaction mixtures demonstrated that the ion at m/z 616.5, the heme group, increased with an increase of cisplatin concentration, indicating the loss of heme groups from the intact protein. This conclusion was also supported by the increase of cisplatin-alpha or -beta complex formation. The change of the Hb-bound Fe was further investigated by monitoring Fe signals using size-exclusion HPLC/ICPMS. After incubation with cisplatin at clinically relevant concentrations, under physiological conditions, the amount of Fe bound to Hb was reduced while formation of cisplatin-Hb complexes increased. Flow-injection ICPMS analysis of the Fe contents in the low molecular weight fraction (<3000 Da) of the reaction mixtures after size fractionation further demonstrated a corresponding increase of Fe with the increase of cisplatin concentrations. HPLC/ICPMS detected three Hb-cisplatin complexes, one of which eluted at the same retention time as Hb while the other two complexes eluted later than Hb. With clinically relevant concentrations of cisplatin (0.05-1.0 microM) and 10 microM of Hb, the concentrations of the Hb-cisplatin complexes were determined in the range 0.1-64 nM. These results, obtained from nanoES-MS, HPLC/ICPMS, and FIA-ICPMS, demonstrate that cisplatin binding to Hb resulted in the dissociation of the heme group from the intact protein.     

Mass spectrometric and pyrolytic studies of diphenylarsine derivatives

The trivalent diphenylarsine derivatives studied gave molecular ions and diagnostic common fragment ions at m/e 229, 227, 154, 153, 152, 151, 77 and 51. The diphenylarsine odd electron ion, m/e 229, undergoes the “ortho coupling” reaction before splitting off the arsenic atom. The correlation between the ion fragmentation and the pyrolytic decompositions is discussed.     

Mass spectrometric studies of 4-oxo-4,5,6,7-tetrahydrobenzofurans

The mass spectra of alkyl and aryl 4-oxo-4,5,6,7-tetrahydrobenzofurans have been determined and the fragmentation patterns are established unambiguously by deuterium labelling in the 5,5,7,7-d₄ position.     

Mass spectrometric studies of lithium-containing oxides at high temperature

The sublimation and vaporization of various lithium containing oxides have been studied by high temperature mass spectrometry. The installed Knudsen cell apparatus gave some useful information about the vapor species, appearance potentials, partial pressures and heats of reactions involved. The investigated oxides are Li₂O, Li₂O-Al₂O₃, Li₂O-MoO₂ and Li₂O-SiO₂ systems. This paper mainly presents the most recent data for the Li₂O-SiO₂ system. A relationship for the decomposition reaction of ortho-Li₄SiO₄ was deduced. The heat of the reaction was determined by the third law method.The activity of the Li₂O component in the double oxides was estimated from the partial pressures of the vapor species. γ-LiAlO₂ and meta-Li₂SiO₃ showed fairly low activities in comparison with Li₂O oxide. The activity coefficients decreased with the Li₂O mole fraction in the lithium compounds.The heats of formation and atomization of LiO and Li₂O gaseous species were determined.     

Mass spectrometric studies of trimethylsilylpantothenic acid and related substances

The characteristic fragment of trimethylsilylated pantothenic acid (TMS-PA) at m/z 291 upon electron ionization was shown to originate from the molecular ion by a McLafferty rearrangement instead of by ejection of 1,1,3,3-tetramethyl-1,3-disilacyclobutane. The verification consisted of labelling experiments and high-resolution mass spectrometry of the fragment and studies on its isotopic distribution. The remaining fragmentation pathways of TMS-PA were clarified by B/E-linked scans and collision-induced dissociation.     

Mass spectrometric studies of 2-aryl-5-acetylthiazole derivatives

Electron ionisation mass spectrometry was usefully used to characterize structurally 2-aryl-5-acetylthiazole derivatives in the gas phase. The compounds show characteristic fragmentation pathways depending on the chemical nature of the substituent at position 2, consisting mainly in the cleavage of both the 1,2- and 3,4-bonds of the thiazole ring. Liquid secondary ion mass spectrometry was applied to study the effects of protonation on the gas-phase unimolecular reactions of this class of compound. Tandem mass spectrometric experiments, carried out on molecular and protonated molecular ions, and also on fragment ions produced in the source, allowed the elucidation of gas-phase decompositions of low-internal energy ions.     

Mass spectrometric studies of alkyl-, phenyl- and chloropyrimidines

The mass spectra of alkyl- and chloropyrimidines are recorded. A generalised fragmentation mechanism for the derivatives of pyrimidine is proposed. The principle of α-cleavage for heterocyclic compounds as proposed in the previous paper is shown to be valid for pyrimidine derivatives. Electronic structures of some molecular and intermediate ions are calculated by the openshell CNDO/2 and INDO methods.     

Mass spectrometric studies on platinum (II) complexes

Several platinum(I1) complexes were subjected to mass spectrometric investigation. The major fragmentation pathways for dichloro-bis(phosphine) platinum(II) were elucidated to be: (i) successive loss of hydrogen chloride or chlorine depending on the structure of the phosphine, (ii) cleavage of P–R bond with the loss of R group, (iii) the presence of [R¹R²R³P—Cl]+ in the mass spectra and (iv) fragmentation of the free phosphine.