Positive Fast Atom Bombardment Research Articles

ISOLATION AND CHARACTERIZATION OF N-HEPTACOSANYL OLEATE FROM THE WHOLE AERIAL PARTS OF CENTELLA ASIATICA LINN.

ABSTRACTVarious studies have already been performed involving the whole aerial parts of Centella asiatica (L.) (Umbelliferae), commonly known as gotu kola orjalbrahmi, and thus, the present investigation has been carried out for the phytochemical study of an ethanolic extract of the aerial parts of C. asiatica.To perform this activity, the drug (1.5 kg) was exhaustively extracted in 95% ethanol using Soxhlet apparatus. The column chromatography wasperformed then for isolating the various phytoconstituents using the solvents of increasing polarity from petroleum ether to methanol. The isolatedcompounds were structurally elucidated using various spectral data analysis, i.e. infrared,1H nuclear magnetic resonance (NMR),13C NMR, and positiveion fast atom bombardment mass spectrometry. One of the isolated compounds was characterized as n-heptacosanyl oleate.Keywords: Whole aerial parts, Centella asiatica, Soxhlet, Column, Heptacosanyl oleate.

Synthesis, Characterization, and Crystal Structure of Pyridinium Tetrakis{1-trifluoromethyl-3-(1′-pyreno)-1,3-propanedionato}lanthanate(III) Complex

The reaction of 1-trifluoromethyl-3-(1′-pyreno)-1,3-propanedione with lanthanum(III) trichloride in the presence of pyridine leads to halide ligand exchange, yielding a novel pyridinium tetrakis{1-trifluoromethyl-3-(1′-pyreno)-1,3-propanedionato}lanthanate(III) complex with four polycyclic aromatic hydrocarbon moieties. This reaction easily proceeds under mild conditions (25°C, 24 h) producing the complex in a 90% isolated yield. The complex was characterized by infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and positive fast atom bombardment mass spectrometry, and its precise structure was determined by single crystal X-ray diffraction. Ultraviolet-visible spectroscopy, fluorescence spectroscopy, and X-ray analysis demonstrated that the four pyrene moieties were independently oriented.

Abietane, Labdane, and Pimarane Diterpenoids from the Pulp of Torreya nucifera

Torreya nucifera is an evergreen coniferous tree, widely distributed in Japan, Korea, and People's Republic of China. Its seeds exhibit significant insecticidal activity. The fruits of this evergreen are widely used in folk medicine for the treatment of tapeworm infestation in Korea and to induce abortion in Japan, but most chemical studies of T. nucifera have focused on its leaves and wood. A number of sesquiterpenoids, labdane and abietane diterpenoids, ligans, and flavonoids were identified as active secondary metabolites [1–8]. T. nucifera is a Taxaceae plant endemic to Korea, Japan, and China. In order to compare its constituents with those of Taxus spp. and to understand their taxonomic relationship, we investigated the chemical composition of Torreya nucifera. Five diterpenoids were isolated for the first time from the pulp of the title plant, including one labdane diterpenoid, two abietane diterpenoids, and two pimarane-type diterpenoids. Their structures were established on the basis of 1D and 2D NMR spectrascopic analysis. We report herein the isolation and structure characterization of these diterpenoids and detailed the 1H and 13C NMR data of compounds 1–5. Melting points were measured with an MRK micro-melting point apparatus and were uncorrected. Column chromatographic separations were carried out using silica gel (300–400 mesh, Qingdao Haiyang Chemical Group Corporation, Qingdao, P. R. China). Na2SO4 was the drying agent used in all workup procedures. Solvents and reagents of analytic grade (reagent grade used without further purification) were purchased from commercial sources. TLC was performed on precoated silica gel F254 glass-backed plates without activation. Fractions were monitored by TLC with visualization under UV light (254 and 365 nm) and by dipping the plates into a solution of 10% (v/v) H2SO4 in EtOH followed by heating on a hot plate for 5 min. Analytical HPLC was performed on a Waters 2695 separation module coupled to a 2996 photodiode array detector. Preparative HPLC was carried out on a Waters Delta Prep 3000 instrument coupled to a UV 2487 dual absorbance detector. Analytical HPLC was performed using two Whatman partisil 10 ODS-2 analytical columns (4.6 250 mm) in series. Preparative HPLC was performed using a partisil 10 ODS-2 MAG-20 preparative column (9.4 250 mm). The products were eluted with a 50 min linear gradient of acetonitrile (25 to 100%) in water at a flow rate of 3 mL/min (preparative HPLC). Positive ion fast atom bombardment mass spectra (FAB-MS) was obtained with a Vacuum Generators ZAB-HS instrument. All NMR spectra were recorded on a Varian Unity INOVA 600 or 500 NMR spectrometer equipped with a 5 mm probe at ambient temperature in CDCl3 solution. The 1H and 13C chemical shifts were referenced relative to TMS residue. Typical one-dimensional (1D) 1H and 13C spectra were acquired under standard condition on a Varian Unity INOVA 500/600 spectrometer operating at 499.861/599.913 and 125.690/150.848 MHz, respectively. 1H and 13C chemical shifts are expressed in the scale as parts per million (ppm).

Thioglycerol matrix interactions in the positive ion fast atom bombardment mass spectrometry of several Hantzsch and Biginelli ester derivatives of boronic acids

Fast atom bombardment (FAB) ionization is a valuable tool for analyzing non-volatile or thermally labile compounds when harder ionization methods (EI or CI) have been unsuccessful. Unexpected interactions between matrix and analyte may, however, occur in FAB ionization leading to the formation of artifacts whose structures have to be determined. We used esters synthesized by our research group following green chemistry protocols. Artifacts relating to the target molecules were produced in the solvent cage using positive ion FAB using thioglycerol as the matrix and analyzed by accurate mass measurement. Through interactions between thioglycerol and the boron atom, various adducts associated with boron-containing Hantzsch and Biginelli ester derivatives appeared in the FAB mass spectra. These interactions must arise in a solvent cage involving a Lewis acid-base bond. Accurate mass determinations of these adducts confirmed the presence of the target molecules. Interactions between the thioglycerol matrix and the eleven boron-containing Hantzsch and Biginelli ester derivatives in addition to the three reagents were seen in their FAB(+) spectra. These interactions, together with their accurate mass determinations, allowed us to determine the structures of the new molecules.

Oxidative damage to DNA constituents by iron-mediated Fenton reactions – the thymidine family

The degradative products formed from the exposure of derivatives of thymidine to iron-mediated Fenton reactions were identified by chromatographic resolution and analysis by UV absorption spectroscopy, radio-labeling, and positive and negative mode fast atom bombardment mass spectrometry. Fe2+/H2O2 and Fe3+/H2O2 were utilized to generate oxy-radicals and the effects of ethanol and N2-flushing were studied. Substrates included thymidine, 3′- and 5′-dTMP, TpT, oligo(dT), and oligo(dT)·poly(dA) and the results are compared to those reported for ionizing radiation. It is evident from the comparisons of the products that the damaging radical species and the product distribution are perturbed by interaction of the iron atom with the various phosphomono- and diester species that are present.

Photochromic Alkynes as Versatile Building Blocks for Metal Alkynyl Systems: Design, Synthesis, and Photochromic Studies of Diarylethene-Containing Platinum(II) Phosphine Alkynyl Complexes

The synthesis of newly designed photochromic dithienylethene-containing ethynylthiophene and ethynylthieno[3,2-b]thiophene has been described, and their incorporation as versatile ligands into the platinum(II) phosphine system was demonstrated. All platinum(II) complexes have been successfully characterized by (1)H and (31)P NMR spectroscopies, positive fast atom bombardment (FAB) mass spectrometry, as well as elemental analysis. One of the complexes has been characterized by X-ray crystallography. Their photophysical, photochromic, and electrochemical properties have been studied. Upon photoexcitation, all the photochromic diarylethene-containing alkynes and platinum(II) complexes exhibited reversible photochromism. The thermal bleaching kinetic of complex 6 was studied in toluene at 298 and 313 K. Complexes 1, 3, and 4, which contained the labile chloro- ligand, represent a new class of versatile building blocks for photoswitchable functional materials.

ChemInform Abstract: Mass Spectrometry of Prenylated Flavonoids

The fragmentation patterns originating from the degradation of prenyl group(s) in positive ion electron ionization (EI), fast-atom bombardment (FAB) and chemical ionization (CI) mass spectrometry (MS) of prenylated flavonoids were reviewed. The EI spectra showed the characteristic fragmentation patterns reflecting the location of prenyl group in the flavonoid compounds, whereas the FAB and CI spectra showed relatively monotonous patterns. It was described how the EI and FAB fragmentation patterns are useful for the identification of prenylated flavonoids

The relationship between the metabolism of sphingomyelin species and the hemolysis of sheep erythrocytes induced by Clostridium perfringens α-toxin

Clostridium perfringens alpha-toxin induces the hemolysis of sheep erythrocytes by activating the metabolism of sphingomyelin (SM) via a GTP binding protein in membranes. alpha-Toxin stimulated the formation of 15-N-nervonoyl sphingosine (C24:1-ceramide), which was identified by positive ion fast atom bombardment-MS and 1H-NMR spectroscopy. C24:1-ceramide stimulated the toxin-induced hemolysis of saponin-pretreated sheep erythrocytes and increased the production of sphingosine 1-phosphate (S1P) in the cells, but N-lignoceroyl sphingosine did not. These events elicited by the toxin in the presence of C24:1-ceramide were significantly attenuated by treatment with dihydrosphingosine, a sphingosine kinase inhibitor. TLC showed that the level of C24:1-ceramide was highest among the ceramides with an unsaturated bond in the fatty acyl chain in the detergent-resistant membranes (DRMs). The toxin specifically bound to DRMs rich in cholesterol, resulting in the hydrolysis of N-nervonoic sphingomyelin (C24:1-SM) in DRMs. Treatment of the cells with pertussis toxin (PT) inhibited the alpha-toxin-induced formation of C24:1-ceramide from C24:1-SM in DRMs and hemolysis, indicating that endogenous sphingomyelinase, which hydrolyzes C24:1-SM to C24:1-ceramide, is controlled by PT-sensitive GTP binding protein in membranes. These results show that the toxin-induced metabolism of C24:1-SM to S1P in DRMs plays an important role in the toxin-induced hemolysis of sheep erythrocytes.

Structural determination of monoacylglycerols extracted from marine sponge by fast atom bombardment tandem mass spectrometry

Five new monoacylglycerols (MAGs) were isolated from the marine sponge Stelletta sp. by reversed-phase high-performance liquid chromatography and analyzed by positive ion fast atom bombardment mass spectrometry (FAB-MS). FAB mass spectra of these compounds produced abundant sodium-adducted molecules [M+Na]+ from a mixture of 3-nitrobenzyl alcohol and sodium iodide. The structural elucidation of these sponge MAGs was carried out by FAB tandem mass spectrometry (MS/MS). To find diagnostic ions for the characterization of the MAGs, authentic MAGs were initially analyzed by collision-induced dissociation (CID) MS/MS. The CID MS/MS of [M+Na]+ precursor ions resulted in the formation of numerous characteristic product ions via a series of dissociative processes. The product ions formed by charge-remote fragmentation (CRF) provided important information for the characterization of acyl chains substituted at the glycerol backbone, and product ions at m/z 84, 97, 113 and 139 were diagnostic for the sodiated glycerol backbone. On the basis of these fragmentation patterns, the structures of five MAGs extracted from marine sponge were elucidated. In addition, high-resolution mass measurement was performed to obtain the elemental compositions of the MAGs.

Compounds inhibitory to nematophagous fungi produced by Bacillus sp. strain H6 isolated from fungistatic soil

Soil fungistasis can cause inconsistent control by nematophagous fungi of plant-pathogenic nematodes in field situations. Recent studies have shown that production of fungistatic compounds by bacteria was the principal explanation for soil fungistasis. The culture filtrate of Bacillus sp. strain H6, a strain representative of the dominant colony types isolated from fungistatic soils, showed strong inhibitory activity against nematophagous fungi by inducing unusual swelling in the conidia and the germ tubes of nematophagous fungi, thereby preventing the fungi from proliferating. This inhibitory mechanism is novel in comparison with other known mechanisms. Antifungal activity of the culture filtrate of strain H6 was maximal after culture in Luria Bertani (LB) broth (pH 7.0) at 36°C for 36 h. The inhibitory effect of the compounds produced by Bacillus sp. strain H6 was not significantly influenced by pH, and the inhibitory compounds in the culture filtrate were thermostable. After being partially purified by thin layer chromatography (TLC) on silica gel plates, characterization by colour reactions and positive fast atom bombardment mass spectrometry indicated that the inhibitory compounds showed similarity to iturin A group compounds.

Selenium-Centered, Undecanuclear Silver Cages Surrounded by Iodo and Dialkyldiselenophosphato Ligands. Syntheses, Structures, and Photophysical Properties

Three clusters [Ag11(mu9-Se)(mu3-I)3{Se2P(OR)2}6] (R = Et, 1; iPr, 2; 2Bu, 3) were isolated from the reaction of [Ag(CH3CN)4](PF6), NH4[Se2P(OR)2], and Bu4NI in a molar ratio of 4:3:1 in CH2Cl2 in 47-55% yield. Compounds 1 and 2 can also be synthesized with high yield from the reaction of Ag10(Se)[Se2P(OR)2]8 with 8 equiv of Bu4NI. In the positive fast atom bombardment mass spectra of 1-3, two major peaks that correspond to the intact molecule with the loss of an iodide ion, [Ag11(mu9-Se)(mu3-I)(2){Se2P(OR)2}6]+, and a diselenophosphate ligand, [Ag11(mu9-Se)(mu3-I)3{Se2P(OR)2}5]+, were identified. Single-crystal X-ray analyses of 2 and 3 reveal an Ag11Se core stabilized by three iodide anions and six diselenophosphato ligands in a tetrametallic tetraconnective (mu2,mu2) coordination mode. The central core adopts the geometry of a 3,3,4,4,4-pentacapped trigonal prism with a selenium atom in the center. In addition, weak intermolecular Se...I interactions exist in 2 and form a one-dimensional polymeric chain structure. Furthermore, all compounds exhibit orange-red luminescence in both the solid state and solution.

Structure-based description of a step-by-step synthesis of homo- and heterodinuclear (4f, 4f ') lanthanide complexes.

The stepwise course of the synthesis of homo- (4f, 4f) and heterodilanthanide (4f, 4f ') complexes has been investigated through structural determination of the intermediate and final products occurring in the process. In the first step, the tripodal ligand H(3)L is reacted with Ln(NO(3))(3) x 5H(2)O to give a complex (H(3)L)Ln(NO(3))(3) in which the ligand does exist in a zwitterionic form. This unexpected feature has been definitely supported by a structural determination performed on a closely related complex (HL')(3)Ln(NO(3))(3) (1). These species are fairly stable and may be isolated. In basic medium, (H(3)L)Ln(NO(3))(3) is deprotonated to yield a neutral LLn complex crystallized as LLnNaClO(4) (2), the lanthanide ion being linked to the inner N(4)O(3) coordination site of the ligand. Finally, addition of Ln'(NO(3))(3) x 5H(2)O (Ln' being similar or different from Ln) to the LLn complex yields the desired homo- or heterodinuclear LLnLn'(NO(3))(3) complex 3, where the Ln' ion is coordinated to the outer O(3)O(3) coordination site of the tripodal ligand. Complex 1 (Ln = La) crystallizes in the triclinic space group P1 (No. 2): a = 11.1883(7) A, b = 11.8993(9) A, c = 16.4197(10) A, alpha = 81.900 (6) degrees, beta = 79.406(5) degrees, gamma = 79.470(6) degrees, V = 2099.5(2) A(3), Z = 2. Complex 2 (Ln = Eu) crystallizes in the monoclinic space group P2(1)/n (No. 14): a = 13.6333(13) A, b = 15.3799(12) A, c = 17.1473(13) A, beta = 111.283(10) degrees, V = 3350.2(5) A(3), Z = 4. Complex 3 (Ln = Ln' = Dy) crystallizes in the trigonal space group R3 (No. 148) with a = b = 23.847(3) A, c = 42.982(2) A, V = 21168(4) A(3), Z = 18. Complex 3 possesses a Dy(O(phenoxo))(3)Dy core, and a nitrato anion has been replaced by a eta(2)-chelated o-vanillin anion. We did not succeed in obtaining crystals of any of the heterodinuclear LLnLn'(NO(3))(3) entities, but their existence was unambiguously confirmed by positive fast atom bombardment mass spectrometry experiments.

Carboxypeptidase A-catalyzed direct conversion of leukotriene C4 to leukotriene F4.

Leukotrienes (LTs) are 5-lipoxygenase (5-LO)-derived arachidonic metabolites that constitute a potent set of lipid mediators produced by inflammatory cells. Leukotriene A(4), a labile allylic epoxide formed from arachidonic acid by dual 5-LO activity, is the precursor for LTB(4) and LTC(4) synthesis. LTC(4) is further transformed enzymatically by the sequential action of gamma-glutamyltranspeptidase and dipeptidase to LTD(4) and LTE(4), respectively. In this report, we present evidence that bovine pancreatic carboxypeptidase A (CPA), which shares significant sequence homology with CPA in mast cell granules, catalyzes the conversion of LTC(4) to LTF(4) via the hydrolysis of an amide bond. The identity of CPA-catalyzed LTC(4) hydrolysis product as LTF(4) was confirmed by several analytical criteria, including enzymatic conversion to conjugated tetraene by soybean LO, conversion to LTE(4) by gamma-glutamyltranspeptidase, cochromatography with the standard LTF(4) and positive-ion fast-atom bombardment mass spectral analysis. Thus, it appears that the physiological significance of this single-step transformation may point toward a major cellular homeostatic mechanism of metabolizing LTC(4), a potent bronco- and vasoconstrictor, to a less potent form of cysteinyl LTs.

Study of structural characteristic features of phenanthriondolizidine alkaloids by fast atom bombardment with tandem mass spectrometry

The mass spectrometric behavior of phenanthroindolizidine alkaloids has been investigated in detail by positive ion fast atom bombardment tandem mass spectrometry (FAB-MS/MS) combined with collision-induced dissociation (CID). The fragmentation has been correlated with the skeleton structure and positions of substituents. The product ions arising from retro-Diels-Alder cleavages differ clearly for compounds with different skeletons. The substituents at C-14 were observed to markedly influence the fragmentation pathway of [M + H](+) ions. A diversity of dissociation behavior initiated by the variation of substituents on the aromatic ring was also observed in the CID spectra. Product ions resulting from loss of CH(4) were obtained for compounds in which both C-6 and C-7 are occupied by methoxy groups. FAB-MS/MS spectra can reflect the connection between the fragmentation behavior and structural features of these phenanthroindolizidine alkaloids rapidly and effectively, and should prove to be a powerful method to determine the structures of related compounds.

Reduction in Desorption Mass Spectrometry: Multiple Protonation on Flavins without Charge Increment.

Three flavin-containing compounds, namely, riboflavin, riboflavin 5′-phosphate (flavin mononucleotide, FMN) and flavin-adenine dinucleotide (FAD, Scheme 1), were studied using matrix-assisted laser desorption ionization (MALDI), fast atom bombardment (FAB) and electrospray ionization (ESI) mass spectrometry. It was found that the isoalloxazine ring (flavin) was reduced in the positive-ion MALDI and FAB ionization processes producing unusual ions [M+2]+· and [M+3]+ in addition to the anticipated [M+1]+, whereas ESI generated only [M+H]+ as the molecular-related ion. The reduction mechanism is hypothesized as the protonation from the matrix with a concomitant electron transfer,*1 rather than the transfer of hydrogen atom(s), H··ESI, in which matrix is not used, did not produce [M+2]+· nor [M+3]+ more than the natural isotope abundance of 13C in the sample molecules. The reduction site expands to N(1)=C(10a)-C(4a)=N(5), a1,4-diaza-1,3-butadiene system, in the isoalloxazine ring, resembling the behavior of prosthetic groups of aerobic dehydrogenases.

Quantification of galactosylsphingosine in the twitcher mouse using electrospray ionization-tandem mass spectrometry

Globoid cell leukodystrophy (Krabbe disease) is an autosomal recessive inherited neurodegenerative disorder caused by the deficiency of the lysosomal enzyme beta-galactosylceramidase. The pathogenesis of the disorder has been proposed to arise from the accumulation of the cytotoxic metabolite galactosylsphingosine (psychosine). The twitcher mouse is a naturally occurring murine model of globoid cell leukodystrophy. We have developed a rapid, sensitive, and specific mass spectrometric method for determining the galactosylsphingosine concentration in the tissues of twitcher mice. Galactosylsphingosine is extracted from the tissues in methanol, isolated using strong cation-exchange and C18 solid-phase extraction chromatography, and then directly analyzed using electrospray ionization-tandem mass spectrometry. A lactosylsphingosine internal standard has been employed for quantification. The assay demonstrated significant accumulation of galactosylsphingosine in the brain, spinal cord, and kidney of twitcher mice. It is anticipated that this method may be of use in the monitoring of experimental therapies for globoid cell leukodystrophy.

Differentiation of Diastereomeric Tertiarybutoxycarbonylprolylproline Ethyl Esters by Collision-Induced Dissociation of Sodium Adduct Ions in Fast Atom Bombardment Mass Spectrometry.

The formation and the fragmentation of the sodium adduct ions for tertiarybutoxycarbonyl-L-prolyl-L-proline ethyl ester (Boc-L-Pro-L-Pro-OEt) were compared with those for Boc-D-Pro-L-Pro-OEt on the addition of sodium chloride in positive-ion fast atom bombardment (FAB) mass spectrometry. The abundance of the [M+Na]+ ion was about 2 times lower than that of the [M+H]′ ion on the addition of sodium chloride in FAB mass spectrum for Boc-L-Pro-L-Pro-OEt, while the former was almost same as the latter in the spectrum for Boc-D-Pro-L-Pro-OEt, suggesting that Boc-D-Pro-L-Pro-OEt has a stronger Na′ ion affinity than Boc-L-Pro-L-Pro-OEt. On the other hand, in the collision-induced dissociation (CID) mass spectra of the [M+Na]′ ions, the abundance of the [M+Na-C(CH3)3+ H]+ ion, which is due to the loss of a tertiarybutyl group from the [M+Na]+ ion for Boc-D-Pro-L-Pro-OEt, was higher than that for Boc-L-Pro-L-Pro-OEt. These results indicate that Boc-L-Pro-L-Pro-OEt was distinguished from Boc-D-Pro-L-Pro-OEt by the CID mass spectra of the [M+Na]+ ions, and the difference of the cleavage patterns between Boc-L-Pro-L-Pro-OEt and Boc-D-Pro-L-Pro-OEt when the carboxyl-terminals were protected with ethyl ester, was smaller than that between tertiarybutoxycarbonyl-L-prolyl-L-proline (Boc-L-Pro-L-Pro) and Boc-D-Pro-L-Pro when they were free reported previously.1)

Mass Spectrometry of Oligosaccharides(I)—Formation of the [M+Nh4]+ Ion of Oligosaccharides in Fast Atom Bombardment Mass Spectrometry

In positive-ion fast atom bombardment (FAB) mass spectrometry, when oligosaccharides are mixed with an appropriate amount of NH4Cl, a highly abundant [M+NH4]+ peak appears in FAB mass spectra. From the adduct ion [M+NH4]+, the molecular weights of oligosaccharides can be determined definitively. This technique may especially be applied to analyze the mixture of oligosaccharides.

Squid nerve sphingomyelin containing an unusual sphingoid base

A new methodology has been developed to determine sphingolipid structures by positive-ion fast atom bombardment tandem mass spectrometry (FAB-MS/MS). The method was verified by application to a structurally known glycosphingolipid, and then used in the structural study of an unusual sphingomyelin isolated from squid (Loligo pealei) nerve. Our previous study of this squid sphingomyelin indicated that the major base had a branched C19 alkyl chain with three double bonds, two of which were conjugated. The positions of the branching as well as the double bonds of this base were unambiguously determined by directly comparing the product ion spectra of the long-chain base ion (LCB+) of two ceramides, one derived from squid nerve sphingomyelin and another, glucosylceramide, obtained from starfish spermatozoa. The latter served as the standard because the structure had already been determined by nuclear magnetic resonance (NMR). The precursor ion here was LCB+, that is, [CH2 − C(NH2) = CHR]+, rather than [M + H]+, where R represents the backbone hydrocarbon chain counting from C-4. The results clearly showed that the squid nerve base is identical to the base derived from starfish (Asterias amurensis), that is, 2-amino-9-methyl-4,8,10-octadecatriene-1,3-diol.This is the first report in which the detailed structure of a branched polyunsaturated sphingoid base was studied by tandem mass spectrometry without derivatization or the aid of NMR. The occurrence of such an unusual sphingoid base in various phyla and tissues suggests the conjugated polyunsaturated branched sphingoid base plays a significant role in animals.

Low-temperature fast atom bombardment mass spectra of frozen nitric acid-water solution

Positive ion low-temperature fast atom bombardment mass spectra of the frozen nitric acid-water system with an initial components ratio which provides preferential formation of the crystalline hydrate of the nitric acid trihydrate, HNO(3).3H(2)O, are reported. A complicated spectral pattern is created by a number of cluster sets which, on the basis of discussion, were attributed to (H(2)O)(n). NO(+) (n = 1-3), (H(2)O)(n).NO(2)(+) (n = 1, 2), (HNO(3))(m). (H(2)O)(n).H(+) (m = 1-5 and n variable) and (H(2)O)(n).H(+) (n = 1-9). Similarities between the size-dependent behavior of hydrate clusters of nitrogen oxides and nitric acid obtained with sputtering from the solid in the present low-temperature experiments and under gas-phase conditions (reported earlier in the literature) were revealed. A suggestion as to possibility of the yield of the cluster ions sputtered due to energetic particle collision with the frozen grains of water ice and nitric acid trihydrate, present in the atmosphere, to the total ionic population of the atmosphere is discussed. Copyright 1999 John Wiley & Sons, Ltd.