Tandem mass spectrometry of negative ions from choline phospholipid molecular species related to platelet activating factor

Fast atom bombardment mass spectrometry of choline phospholipids produces negative ions characteristic of the intact molecule and tandem mass spectrometry of collision-induced decomposition of M-15 anions characterizes both the identity and substituent position of radyl groups. Certain choline phospholipid molecular species which may be of special interest in the generation of platelet activating factor contain a highly unsaturated fatty acyl substituent atsn-2 and an ether radyl group atsn-1; other choline phospholipid molecular species which contain esterified arachidonic acid are of interest as potential sources of arachidonate for eicosanoid biosynthesis. Collisional activated decomposition of 1-hexadecanoyl-2-arachidonoyl-sn-glycerophosphocholine produce abundant carboxylate anions atm/z 303 (arachidonate) andm/z 255 (hexadecanoate) in a ratio of 3∶1, diagnostic for thesn-2 arachidonoyl position. The ether analog, 1-O-hexadecyl-2-arachidonoyl glycerophosphocholine, produces only one collision-induced dissociation ion atm/z 303 and no product ions corresponding to the ether substituent atsn-1. Molecular weight information from the M-15 ion combined with the CID generated carboxylate anions completely characterize these important phospholipids. Precursor ion studies of M-15 anions from glycerophosphocholine lipids indicate that this ion is derived directly from a unique adduct ion formed by attachment of the molecular species to a matrix alkoxide ion, neutralizing the positive charge of the quaternary choline nitrogen. Decomposition of this adduct ion yields a methylated matrix molecule and the nominal M-15 ion. Based on a paper presented at the Third International Conference on Platelet-Activating Factor and Structurally Related Alkyl Ether Lipids, Tokyo, Japan, May 1989.     

High-resolution mass spectrometric investigation of heteroatom species in coal-carbonization products

High-resolution mass spectrometry is being used to determine the organic species present in coal-carbonization products, airborne particulates, and municipal effluents. Qualitative analysis of an 80–85 °C softening point pitch yielded molecular formulae for 239 compounds which correspond to a minimum of 108 structural types and their alkyl derivatives. Of these, 76 structural types are composed of 8 different combinations of elements; structures containing CH, CHO, and CHN are most numerous while species containing S, N₂, ON, O₂, and O₂N₂ are also present.     

Rapid transesterification and mass spectrometric approach to seed oil analysis

Fatty acid composition of seed oil is determined in less than one hr using a quantitative one-vial technique. The method of analysis requires alcoholic solutions of sodium methoxide mild enough for epoxy and polyunsaturated oils. Separation and characterization of component fatty acids were accomplished by high resolution gas chromatography-mass spectrometry. Using this method,Vernonia galamensis seed oil is shown to contain 79–80% vernolic (cis-12,13-epoxy-cis-9-octadecenoic) acid.Amaranthus cruentus, a West African vegetable crop, is shown to contain 17.3% palmitic acid, 3.2% stearic acid, 22.7% oleic acid, 54.7% linoleic acid and 2.1% linolenic acid.     

A mass spectrometric and molecular modelling study of cisplatin binding to transferrin

A combination of mass spectrometry, UV/Vis spectroscopy and molecular modelling techniques have been used to characterise the interaction of cisplatin with human serum transferrin (Tf). Mass spectrometry indicates that cisplatin binds to the hydroxy functional group of threonine 457, which is located in the iron(III)-binding site on the C-terminal lobe of the protein. UV/Vis spectroscopy confirms the stoichiometry of binding and shows that cisplatin and iron(III) binding are competitive. The binding of cisplatin has been modelled by using molecular dynamic simulations and the results suggest that cisplatin can occupy part of both the iron(III)- and carbonate-binding sites in the C-terminal lobe of the protein. Combined, the studies suggest that cisplatin binding sterically restricts iron(III) binding to the C-terminal lobe binding site, whereas the N-terminal lobe binding site appears to be unaffected by the cisplatin interaction, possibly allowing the iron(III)-induced conformational change necessary for binding to a Tf receptor.     

Variation of coal extract structure with molecular mass

Asphaltenes and benzene-insolubles, and their methylated counterparts, of high-yield supercritical gas (SCG) and hydrogen donor solvent (HDS) extracts have been separated by size exclusíon chromatography (SEC) on cross-linked polystyrene microspheres so as to investigate the variation in coal extract structure with molecular mass (MM). Narrow SEC fractions have been obtained which have been subjected to elemental, molecular mass (MM), functional group, n.m.r. and voltammetric analyses. The analytical results revealed that the M M range of the solvent fractions was 300 to ≈3000. With increasing MM the following trends were observed: aromaticity decreased, but the degree of condensation of aromatic nuclei did not vary significantly; the size of aliphatic substituents increased; and phenolic hydroxyl content decreased for SCG extract fractions but, in contrast, increased for HDS extract fractions. These variations about averages are considerable and demonstrate that caution is necessary in making use of analytical results for gross fractions. Solubility in benzene of coal extracts results from low MM or from low polarity for higher MM materials.     

Electrospray ionization mass spectrometric analyses of changes in tissue phospholipid molecular species during the evolution of hyperlipidemia and hyperglycemia in Zucker diabetic fatty rats

The Zucker diabetic fatty (ZDF) rat is a genetic model of type II diabetes mellitus in which males homozygous for nonfunctional leptin receptors (fa/fa) develop obesity, hyperlipidemia, and hyperglycemia, but rats homozygous for normal receptors (+/+) remain lean and normoglycemic. Insulin resistance develops in young fa/fa rats and is followed by evolution of an insulin secretory defect that triggers hyperglycemia. Because insulin secretion and insulin sensitivity are affected by membrane phospholipid fatty acid composition, we have determined whether metabolic abnormalities in fa/fa rats are associated with changes in tissue phospholipids. Electrospray ionization mass spectrometric analyses of glycerophosphocholine (GPC) and glycerophosphoethanolamine (GPE) molecular species from tissues of prediabetic (6 wk of age) and overtly diabetic (12 wk) fa/fa rats and from +/+ rats of the same ages indicate that arachidonate-containing species from heart, aorta, and liver of prediabetic fa/fa rats made a smaller contribution to GPC total ion current than was the case for +/+ rats. There was a correspondingly larger contribution from species with sn-2 oleate or linoleate substituents in fa/fa heart and aorta. The relative contributions of arachidonate-containing GPC species increased in these tissues as fa/fa rats aged and were equal to or greater than those for +/+ rats by 12 wk. For heart and aorta, relative contributions from GPE species with sn-2 arachidonate or docosahexaenoate substituents to the total ion current increased and those from species with sn-2 oleate or linoleate substituents fell as fa/fa rats aged, but these tissue lipid profiles changed little with age in +/+ rats. GPC and GPE profiles for brain, kidney, sciatic nerve, and red blood cells were similar among fa/fa and +/+ rats at 6 and 12 wk or age, and pancreatic islets from fa/fa and +/+ rats exhibited similar GPC and GPE profiles at 12 wk of age. Under-representation of arachidonate-containing GPC and GPE species in some fa/fa rat tissues at 6 wk could contribute to insulin resistance, but depletion of islet arachidonate-containing GPC and GPE species is unlikely to explain the evolution of the insulin secretory defect that is well-developed by 12 wk of age.     

Influence of phosphine on the diamond growth mechanism: a molecular beam mass spectrometric investigation

We have used a molecular beam mass spectrometer to investigate the effects of addition of phosphine on the growth behaviour of diamond films in a hot filament chemical vapour deposition (CVD) reactor. Films were grown using gas mixtures of 1% CH₄ with increasing amounts of PH₃ (1000–5000 ppm). Gas phase species prevalent during the growth process (e.g. CH₄, CH₃, C₂H₂, PH₃ and HCP) have been monitored quantitatively and compared with the corresponding growth rates, quality and properties of the resulting films. We find that addition of up to 2000 ppm PH₃ increases the film growth rate by a factor of 2–3, and changes the crystal morphology in favour of (100). At higher PH₃ concentrations (3000–5000 ppm) the growth rate decreases again, with predominantly (111) faceted crystals. These observations are discussed in terms of a model of the gas phase chemistry during the growth process.     

Determination of the structure and composition of clinically important polyurethanes by mass spectrometric techniques

Curie-point pyrolysis mass spectrometry (Py-MS) and direct probe pyrolysis high resolution mass spectrometry (Py-HRMS) were used to identify the components and additives used in the synthesis and compounding of Biomer, Lycra Spandex, Tecoflex, and Pellethane. Two types of Biomer were identified (P and Q, our notation) which are composed of poly(tetramethylene glycol) (PTMG) capped with 4,4′-methylenebis(phenylisocyanate) (MDI) and chain-extended with ethylenediamine (EDA). Both forms contain 4,4′-butylidene-bis-(6-t-butyl-m-cresol) antioxidant, and Biomer Q also contains an additive which appears to be a quaternary ammonium chloride salt. Lycra Spandex was found to be identical to Biomer Q, with the exception that a low molecular weight polydimethylsiloxane oil is also present. This silicone oil can be removed by solvent extraction. Tecoflex (type SG80A) is composed of PTMG capped with 4,4′-diisocyanatodicyclohexylmethane and extended with 1,4-butanediol (BD). An industrial grade and a medical grade of Pellethane were analyzed. Both were composed of PTMG capped with MDI and extended with 1,4-butanediol. the industrial grade also contains an antioxidant, possibly butylated diphenylamine.     

Application of thermomechanical mass spectroscopy for analysis of molecular and topological structure of rubber

A novel method was applied to study the topological and molecular structures of multicomponent rubber. This method is based on the thermomechanical analysis of a solid polymer. A diblock amorphous structure was found for the studied rubber network. These blocks differ a great deal in their glass transition temperature. The methodology of how to calculate the crosslink density in each block, the molecular weight distribution of the chains between the junctions of the network, and the shares of low‐temperature (soft) and high‐temperature (hard) blocks in a structure of the rubber network were also shown. Based on these data it is possible to calculate the number‐average and weight‐average molecular weight and the polydispersity coefficients of the chains between the junctions of the network. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 490–501, 1999     

质谱学方法在煤分子结构剖析中的研究进展

为实现“双碳”目标下煤化工行业的转型,以煤分子的禀赋特征为出发点,通过提升其精细转化产物的价值,实现生产过程清洁化及目标产品高端化。基于质谱学方法可以深层探究煤分子的结构特征,以碰撞诱导解离等质谱方法研究煤分子及煤温和转化为主线,评述了煤分子结构的相关研究进展,通过分子水平的探究为认知煤分子结构单元、监控杂原子反应途径、优选催化剂及反应体系提供了方法学借鉴。     

High-resolution mass spectrometric study of weathered road tars

Fractions of road tars of coke-oven and vertical retort origin were examined by high-resolution mass spectrometry before and after exposure to road conditions. Molecular formulae and relative concentrations were determined for eleven series of peaks. A progressive increase in the proportion of components of high molecular weight (> mass 200) was indicated with exposure to road conditions. In the high molecular-weight range, the heterocyclic structures containing oxygen showed larger increases than the polynuclear aromatic hydrocarbons.     

A thermospray mass spectrometric assay for Fe-induced 4-hydroxynonenal in tissues

A method is presented for the determination of 4-hydroxy-nonenal (HNE) in tissue homogenates followingin vitro lipid peroxidation induced by iron (Fe⁺⁺). NHE is measured as the pentafluorobenzyl oxime derivative using liquid chromatography thermospray mass spectrometry.In vitro metabolism of HNEvia the glutathione/glutathione-S-transferase pathway was inhibited using iodoacetic and iodobenzoic acids. The assay has been used as an indicator of the peroxidizability of tissue samples from animals both adequate in and depleted of α-tocopherol. The concentrations of HNE produced in tissues taken from animals depleted of α-tocopherol were found to be up to 8 times higher than those taken from animals supplemented with α-tocopherol.     

Comparison of fast atom bombardment,secondary ion and laser microprobe mass spectrometry as techniques for determining coal structure

Fast atom bombardment, secondary ion and laser microprobe m.s. have the potential advantage of giving information about geologically-related features of coal without the need for preliminary fractionation of the coal. The methods produce spectra which are often highly characteristic of the feature being examined but their interpretation involves an understanding of the mechanism by which the coal substance is ionized. Results obtained by the three techniques are compared and discussed.     

New oxidation pathway of 3,5-di-tert-butyl-4-hydroxytoluene: An ionspray tandem mass spectrometric and gas chromatographic/mass spectrometric study

The autoxidation of 3,5-di-tert-butyl-4-hydroxytoluene (BHT, 1) in bar soap was investigated with ionspray tandem mass spectrometric and on-line gas chromatographic/mass spectrometric methods. The oxidation products of BHT were extracted from the bar soap surface, concentrated, and fractionated with open-column chromatography to remove the impurities. New oxidation products of BHT (BHT phenol-type dimer 7 and others) were identified with the two mass spectrometric methods. The results suggested that oxidation of BHT in bar soap occurred in a way different from that in the previous studies. In the new pathway, oxidation of BHT first generates an excited state of phenol-type dimer 4, and then this species decomposes, due to its high energy, to form dimer 7. The mechanism of oxidation is discussed.     

A new method for determining molecular weight distributions of copolymers

Measurement of the molecular weight distributions of copolymers by size exclusion chromatography (SEC) presents problems because the elution volume of any species may depend on its composition as well as its molecular weight. Also, the response of the usual concentration detectors may also be influenced by the copolymer composition as well as its concentration. These problems arise when the copolymer composition may vary with molecular size. Conventional SEC techniques are suitable for copolymers with invariant compositions. This article describes and illustrates a method for measuring molecular weight distributions of copolymers. In many cases, the variation of copolymer composition with molecular weight can also be determined. The technique uses three detectors: (a) an evaporative detector (ED) to measure the concentration, Δc, of the eluting species; (b) a differential refractive index detector (DRI) to measure the refractive index difference, Δn, between the solution and solvent at any given elution volume; and (c) a low-angle laser light scattering (LALLS) detector that measures the corresponding molecular weight of the eluting solutes. This latter measurement is possible because the appropriate values of Δn/Δc are available from the outputs of the other two detectors. For LALLS measurements of molecular weight all the species in the detector cell at any instant must have the same composition or, at least not have Δn/Δc that varies with composition. The method is illustrated with data from ethylene-propylene and ethylene-propylene-diene copolymers.     

A mass spectrometric survey of some biologically important lipids

The mass spectra of lipids are reviewed with emphasis on characteristic fragmentation patterns of each general class of compounds. Recent developments in the area of field ionization and field desorption mass spectrometry are discussed relative to each class of lipids.     

Study of the CL-20 flame structure using probing molecular beam mass spectrometry

The CL-20 flame structure at pressures of 0.1 and 0.5 MPa was studied using probing molecular beam mass spectrometry. At a pressure of 0.1 MPa, the gaseous products near the surface of the foamy carbonaceous carcass were found to contain eight species: NO, NO₂, CO, CO₂, N₂, H₂O, HCN, and HNCO. At a pressure of 0.5 MPa, NO₂ was not found and the concentration profiles of the remaining seven species were measured versus the distance to the carbonaceous carcass. In the CL-20 flame at a pressure of 0.5 MPa, consumption of N₂ and CO₂ with the formation of NO and HNCO occurred in a zone of width ≈0.8 mm from the surface of the carbonaceous carcass. At a pressure of 0.5 MPa, the composition of the gaseous combustion products of CL-20 at a distance of 3–4 mm differed from the composition at thermodynamic equilibrium. Key words: flame structure, CL-20, probing molecular beam mass spectrometry. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 3, pp. 58–65, May–June, 2009.     

An Insight into molecular structure and properties of flexible amorphous polymers: A molecular dynamics simulation approach

Visualization of polymer molecules by molecular dynamics simulation remains a challenging area in molecular modeling, as it involves a number of factors like type of force field, simulation time, simulation steps, and so forth. In our present study, we have used the condensed-phase optimized molecular potentials for atomistic simulation studies (COMPASS) force field, which is specific for polymers and organic molecules, in order to visualize the macromolecular chains of various flexible amorphous polymers: natural rubber, polybutadiene rubber, styrene–butadiene rubber, nitrile rubber, polychloroprene rubber, and fluoroelastomer. The study covered a wide range from nonpolar rubbers to polar rubbers, and the COMPASS force field was promising to understand the local structure and the packing of the chains inside the simulation box. The distance between different adjacent pairs of carbon atoms within the polymer chains was discussed in detail from intramolecular radial distribution function and represented pictorially in the polymer chains. Various bond angles were also examined for further details. In addition, interchain contacts, glass-transition temperature, and solubility parameter were predicted and compared with the experimental values. The diffusive characteristic of the chains was assessed by mean square displacement which in turn described the polymer chain mobility. In essence, the present study is expected to aid in the vivid conceptualization of molecular orientation of various polymers and would help in predicting various physical properties. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47457     

A mass spectrometric investigation of native and oxidatively inactivated chloroperoxidase

The enzyme chloroperoxidase (CPO) found in Caldariomyces fumago is able to catalyze several stereoselective oxidation reactions by using a clean oxidant, usually hydrogen peroxide (H(2)O(2)), without the need for expensive cofactor generation. CPO's lack of operational stability, however, is a major limitation for its commercial use. In the present study, a capillary-LC on-line trypsin-digestion system combined with reversed-phase chromatography and mass spectrometric detection was optimized for studying the primary sequence of CPO. Samples containing native CPO, CPO treated with H(2)O(2), and CPO oxidatively inactivated by the use of indole and H(2)O(2) were analyzed and compared. Three oxidized peptides were found in the samples treated with H(2)O(2). Two additional oxidized peptides were found in the CPO samples that were completely inactivated, one of which contained an oxidized cysteine residue, Cys50, which is an essential amino acid due to its function as the axial ligand to the iron in the heme--the prosthetic group in CPO. In addition, the heme group was absent in the inactivated samples but was readily detected in other samples.