Comprehensive Quantitation Using Two Stable Isotopically Labeled Species and Direct Detection of <Emphasis Type="Italic">N</Emphasis>-Acyl Moiety of Sphingomyelin

Sphingomyelin (ceramide‐phosphocholine, CerPCho) is a common sphingolipid in mammalian cells and is composed of phosphorylcholine and ceramide as polar and hydrophobic components, respectively. In this study, a qualitative liquid chromatography‐electrospray ionization tandem mass spectrometry (LC–ESI–MS/MS/MS) analysis is proposed in which CerPCho structures were assigned based on product ion spectra corresponding to sphingosylphosphorylcholine and N‐acyl moieties. From MS/MS/MS analysis of CerPCho, we observed product ion spectra of the N‐acyl fatty acids as [RCO₂]^? ions as well as sphingosylphosphorylcholine. A calibration curve for CerPCho was constructed using two stable isotopically labeled CerPCho species and then used to quantify the CerPCho species in HeLa cells as a proof‐of‐principle study. The present study proposes an accurate method for quantifying and assigning structures to each CerPCho species in crude biologic samples by LC–ESI–MS/MS/MS analysis.     

Mass Spectrometric Confirmation of γ-Linolenic Acid Ester-Linked Ceramide 1 in the Epidermis of Borage Oil Fed Guinea Pigs

Ceramide 1 (Cer1), a Cer species with eicosasphingenine (d20:1) amide‐linked to two different ω‐hydroxy fatty acids (C30wh:0:C32wh:1), which are, in turn, ester‐linked to linoleic acid (LNA; 18:2n‐6), plays a critical role in maintaining the structural integrity of the epidermal barrier. Prompted by the recovery of a disrupted epidermal barrier with dietary borage oil [BO: 36.5 % LNA and 23.5 % γ‐linolenic acid (GLA; 18:3n‐6)], in essential fatty acid (EFA)‐deficient guinea pigs, we further investigated the effects of BO on the substitution of ester‐linked GLA for LNA in these two epidermal Cer1 species by LC–MS in positive and negative modes. Dietary supplementation of BO for 2 weeks in EFA‐deficient guinea pigs increased LNA ester‐linked to C32wh:1/d20:1 and C30wh:0/d20:1 of Cer1. Moreover, GLA ester‐linked to C32wh:1/d20:1, but not to C30wh:0/d20:1, of Cer1 was detected, which was further confirmed by the product ions of m/z 277.2 for ester‐linked GLA and m/z 802.3 for the deprotonated C32wh:1/d20:1. C20‐Metabolized fatty acids of LNA or GLA were not ester‐linked to these Cer1 species. Dietary BO induced GLA ester‐linked to C32wh:1/d20:1 of epidermal Cer1.     

Electrochemistry-electrospray ionization FT ICR mass spectrometry (EC ESI MS) of guanine–tyrosine and guanine–glutathione crosslinks formed on-line

Crosslinking of guanine with tyrosine and glutathione is studied by on-line electrochemistry electrospray ionization mass spectrometry (EC ESI MS) in the positive ion mode with a high resolution FT ICR mass spectrometer without the use of an external oxidizer in the sample. Dimeric adducts of guanine with tyrosine (m/z 331) and (m/z 333) and a dimer of guanine with glutathione (m/z 459) are detected in the mass spectra of guanine–tyrosine and guanine–glutathione mixtures in addition to dimers of guanine (m/z 303) and tyrosine (m/z 361) and (m/z 363) and glutathione dimers (m/z 613) and (m/z 615). Guanine tetramers (m/z 627) and tetramers of guanine with 1 or 2 tyrosines, but not with three tyrosines, were also identified in the mass spectra of guanine–tyrosine mixtures. Formation of radicals and other oxidation products during positive ion mode ESI can drive the formation of covalent dimer adducts of guanine with tyrosine and glutathione. When low EC cell voltage is applied in on-line EC ESI MS, changes in ion intensities reflect changes in the oxidation conditions and are more apparent for 2e, 2H⁺ than for the 1e, 1H⁺ oxidation processes. Efficient oxidation during ESI is indicated for analytes with low redox potentials.     

A Screening Method to Evaluate Soybean Oil‐Based Biodiesel Oxidative Quality During Its Shelf Life

Biodiesel quality is negatively affected by oxidation, which occurs primarily during the storage and distribution steps. Therefore, the use of suitable analytical methods to assess the oxidation of this biofuel is a fundamental requirement. A direct ambient ionization mass spectrometric technique (EASI‐MS) was tested as a screening method to evaluate the oxidative quality of biodiesel during its shelf life. Using EASI‐MS, the relative abundance of the hydroperoxide ion of m/z 349 was monitored during the induction period (IP) in soybean and a blend of soybean/beef‐tallow (70/30) biodiesel samples. The peroxide value obtained by AOCS Cd 8b‐90 was used as a standard method to evaluate the EASI‐MS data by comparison. The results showed that the peroxide value and EASI‐MS data were highly correlated during the IP for both samples (r > 0.98). Relative abundances of the ion of m/z 349 below 72 % was also found to characterize biodiesel in an initial oxidation stage, whereas abundances exceeding 72 % indicated biodiesel samples nearing the end of their stability. EASI‐MS was therefore found to provide a simple and effective analytical protocol to evaluate the oxidative quality of biodiesel during the IP.     

Plasma sphingolipids in patients with sickle cell disease: Multiple-site vaso-occlusive crises could be associated with lower sphingolipid levels

Although sickle cell disease (SCD) and its manifestations have been associated with various lipid alterations, there are a few studies exploring the impact of sphingolipids in SCD. In this study, we determined plasma ceramide (Cer) and sphingomyelin (CerPCho) species and investigated their association with the crisis in SCD. SCD patients (N = 27) suffering from vaso-occlusive crisis (VOC) or acute chest syndrome (ACS) were involved in this study. Blood samples were drawn at crisis and later at steady state periods. Clinical history, white blood cell count (WBC), C-reactive protein and lactate dehydrogenase (LDH) levels were recorded. 16:0, 18:0, 20:0, 22:0 Cer and 16:0, 18:0, 24:0 CerPCho were measured via LC–MS/MS. All measured Cer and CerPCho levels of SCD patients at crisis and steady-state were found to be similar. Inflammation-related parameters were significantly higher in patients with ACS compared to single-site VOC. Patients with multiple-site VOC were found to have significantly lower sphingolipid levels compared with those with single-site VOC, at crisis (16, 18, 24 CerPCho and 18, 22 Cer) and at steady-state (24:0 CerPCho and 18 Cer). Our results show that sphingolipid levels in SCD patients are similar during crisis and at steady state. However, lower sphingolipid levels appear to be associated with the development of multiple-site VOC. Since the differences were observed at both crisis and steady-state, sphingolipid level could be an underlying factor associated with crisis characteristics in patients with SCD.     

Sphingolipidomics of Thermotolerant Yeasts

Mass spectrometry‐based shotgun lipidomics was applied to the analysis of sphingolipids of 11 yeast strains belonging to four genera, that is Cryptococcus, Saccharomyces, Schizosaccharomyces, and Wickerhamomyces. The analysis yielded comprehensive results on both qualitative and quantitative representation of complex sphingolipids of three classes—phosphoinositol ceramide (PtdInsCer), mannosyl inositol phosphoceramide (MInsPCer), and mannosyl diinositol phosphoceramide (M(InsP)₂Cer). In total, nearly 150 molecular species of complex sphingolipids were identified. Individual strains were cultured at five different temperatures, that is 5, 10, 20, 30, and 40 °C (Wickerhamomyces genus only up to 30 °C), and the change in the culture temperature was found to affect the representation of both the sphingolipid classes and the length of the long‐chain bases (LCB). Individual classes of sphingolipids differing in polar heads differed in the temperature response. The relative content of PtdInsCer increased with increasing temperature, whereas that of M(InsP)₂Cer decreased. Molecular species having C18‐LCB were associated with low cultivation temperature, and a higher proportion of C20‐LCB molecular species was produced at higher temperatures regardless of the type of polar head. On the other hand, the influence of temperature on the representation of very long‐chain fatty acids (VLCFA) was less noticeable, the effect of the taxonomic affiliation of the strains being more pronounced than the cultivation temperature. For example, lignoceric and 2‐hydrocylo‐lignoceric acids were characteristic of the genera Cryptococcus and Schizosaccharomyces, and of Saccharomyces genus cultivated at high temperatures.     

Biosynthesis of 2‐Hydroxy and iso‐Even Fatty Acids is Connected to Sphingolipid Formation in Myxobacteria

2‐Hydroxy fatty acids can be found in several different organisms, including bacteria. In this study, we have studied the biosynthesis of 2‐hydroxy fatty acids in the myxobacteria Myxococcus xanthus and Stigmatella aurantiaca, resulting in the identification of a family of stereospecific fatty acid α‐hydroxylases. Although the stereospecificities of the hydroxylases differ between these two species, they share a common function in supporting fatty acid α‐oxidation; that is, the oxidative shortening of fatty acids. Whereas in S. aurantiaca this process takes place during normal vegetative growth, in M. xanthus it takes place only under developmental conditions. We were also able to identify serine palmitoyltransferase encoding genes involved in sphingolipid biosynthesis as well as sphingolipids themselves in both types of myxobacteria, and were able to show that the α‐hydroxylation reaction is in fact dependent on the presence of fatty acids bound to sphingolipids.     

Structure of Sphingolipids From Sea Cucumber Cucumaria frondosa and Structure-Specific Cytotoxicity Against Human HepG2 Cells

To investigate the relationship between structure and activity, three glucocerebroside series (CFC‐1, CFC‐2 and CFC‐3), ceramides (CF‐Cer) and long‐chain bases (CF‐LCB) of sea cucumber Cucumaria frondosa (C. frondosa) were isolated and evaluated in HepG2 cells. The molecular species of CFC‐1, CFC‐2 and CFC‐3 and CF‐Cer were identified using reversed‐phase liquid chromatography with heated electrospray ionization coupled to high‐resolution mass spectrometry (RPLC‐HESI‐HRMS), and determined on the basis of chemical and spectroscopic evidence: For the three glucocerebroside series, fatty acids (FA) were mainly saturated (18:0 and 22:0), monounsaturated (22:1, 23:1 and 24:1) and 2‐hydroxyl FA (2‐HFA) (23:1 h and 24:1 h), the structure of long‐chain bases (LCB) were dihydroxy (d17:1, d18:1 and d18:2) and trihydroxy (t16:0 and t17:0), and the glycosylation was glucose; For CF‐Cer, FA were primarily saturated (17:0) and monounsaturated (16:1 and 19:1), the structure of LCB were dihydroxy (d17:1 and d18:1), and trihydroxy (t16:0). The results of cell experiment indicated that all of three glucocerebroside series, CF‐Cer and CF‐LCB exhibited an inhibitory effects on cell proliferation. Moreover, CFC‐3 was most effective in three glucocerebrosides to HepG‐2 cell viability. The inhibition effect of CF‐LCB was the strongest, and the inhibition effect of CF‐Cer was much stronger than glucocerebrosides.     

In Situ Formed Bifunctional Primary Amine‐Imine Catalyst: Application to the Construction of Chiral Tertiary Alcohols through Asymmetric Aldol‐Type Reaction

An in situ formation method to obtain chiral bifunctional primary amine‐imine catalysts from the C₂‐symmetric chiral diimines has been developed. The efficiency of this method in the construction of chiral tertiary alcohols which are valuable pharmaceutical intermediates is proved by its application to the asymmetric aldol‐type reaction of cyclic ketones with other activated ketone compounds as the enamine acceptors, i.e., β,γ‐unsaturated α‐keto esters and isatins. In general, good to excellent diastereoselectivities and enantioselectivities (up to 96/4 dr, 96% ee for β,γ‐unsaturated α‐keto esters and up to 91/9 dr, 94% ee for isatins) were obtained. The active primary amine‐imine catalylst and enamine intermediate in the reaction process could be demonstrated by ESI‐MS analysis.     

Isoprenoid Alcohols are Susceptible to Oxidation with Singlet Oxygen and Hydroxyl Radicals

Isoprenoids, as common constituents of all living cells, are exposed to oxidative agents—reactive oxygen species, for example, singlet oxygen or hydroxyl radicals. Despite this fact, products of oxidation of polyisoprenoids have never been characterized. In this study, chemical oxidation of isoprenoid alcohols (Prenol‐2 and ‐10) was performed using singlet oxygen (generated in the presence of hydrogen peroxide/molybdate or upon photochemical reaction in the presence of porphyrin), oxygen (formed upon hydrogen peroxide dismutation) or hydroxyl radical (generated by the hydrogen peroxide/sonication, UV/titanium dioxide or UV/hydrogen peroxide) systems. The structure of the obtained products, hydroxy‐, peroxy‐ and heterocyclic derivatives, was studied with the aid of mass spectrometry (MS) and nuclear magnetic resonance (NMR) methods. Furthermore, mass spectrometry with electrospray ionization appeared to be a useful analytical tool to detect the products of oxidation of isoprenoids (ESI–MS analysis), as well as to establish their structure on the basis of the fragmentation spectra of selected ions (ESI–MS/MS analysis). Taken together, susceptibility of polyisoprenoid alcohols to various oxidizing agents was shown for the first time.     

Plasma Ceramides and Sphingomyelins of Pediatric Patients Increase in Primary Ciliary Dyskinesia but Decrease in Cystic Fibrosis

We investigated plasma sphingomyelin (CerPCho) and ceramide (Cer) levels in pediatric patients with cystic fibrosis (CF) and primary ciliary dyskinesia (PCD). Plasma samples were obtained from CF (n = 19) and PCD (n = 7) patients at exacerbation, discharge, and stable periods. Healthy children (n = 17) of similar age served as control. Levels of 16–24 CerPCho and 16–24 Cer were measured by LC–MS/MS. Concentrations of all CerPCho and Cer species measured at exacerbation were significantly lower in patients with CF than PCD. 16, 18, 24 CerPCho, and 22, 24 Cer in exacerbation; 18, 24 CerPCho, and 18, 20, 22, 24 Cer at discharge; 18, 24 CerPCho and 24 Cer at stable period were significantly lower in CF patients than healthy children (p < 0.001 and p < 0.05). All CerPCho and Cer levels of PCD patients were significantly higher except 24 CerPCho and 24 Cer during exacerbation, 24 CerPCho at discharge, and 18, 22 CerPCho levels at stable period (p < 0.001 and p < 0.05) compared with healthy children. There was no significant difference among exacerbation, discharge, and stable periods in each group for Cer and CerPCho levels. This is the first study measuring plasma Cer and CerPCho levels in PCD and third study in CF patients. The dramatic difference in plasma levels of most CerPCho and Cer species found between two diseases suggest that cilia pathology in PCD and CFTR mutation in CF seem to alter sphingolipid metabolism possibly in opposite directions.     

Analysis of volatile compounds and triacylglycerol composition of fatty seed oil gained from flax and false flax

Linseed (Linum usitatissimum, L.) and camelina (Camelina sativa, L.) are ancient crops containing seed oils with a high potential for nutritional, medicinal, pharmaceutical and technical applications. In the present study, linseed and camelina oils of plant varieties grown under Central European climate conditions were examined with respect to their volatile and triacylglycerol (TAG) components. Solid‐phase microextraction was applied to the study of volatile compounds of several linseed and camelina oils, which have not been described prior to this publication. Hexanol (6.5–20.3% related to the total level of volatiles), trans‐2‐butenal (1.3–5.0%) and acetic acid (3.6–3.8%) could be identified as the main volatile compounds in the linseed oil samples. Trans‐2‐butenal (9.8%) and acetic acid (9.3%), accompanied by trans,trans‐3,5‐octadiene‐2‐one (3.8%) and trans,trans‐2,4‐heptadienal (3.6%), dominated the headspace of the examined camelina oil samples. TAG were analysed by MALDI‐RTOF‐MS and ESI‐IT‐MS, providing information about the total TAG composition of the oils as well as the fatty acid composition of the individual components. More than 20 TAG could be identified directly from whole linseed oil samples, mainly composed of linolenic (18:3), linoleic (18:2) and oleic (18:1) acid, and to a lesser degree of stearic (18:0) and palmitic (16:0) acid. While in linseed these TAG comprise more than 60% of the oils, Camelina sativa exhibited a wider range of more than 50 constituents, with a considerable amount (>35%) of TAG containing gadoleic (20:1) and eicosadienoic (20:2) acid.     

Thermally induced formation of conjugated isomers of linoleic acid

Chemical pathways responsible of the conjugation of linoleic acid during heat treatments such as refining (deodorization), frying or cooking processes have been investigated. For this purpose, methyl linoleate was submitted to oxidative and non‐oxidative thermal conditions. The resulting degradation products were mainly composed of geometrical and conjugated fatty acid isomers. Oxidative conditions were obtained using tert‐butyl hydroperoxide under inert atmosphere, and air. The obtained results from both thermal oxidative conditions were compared to non‐oxidative thermal treatment. Higher levels of conjugated linoleic acid were found when linoleate was heated under oxidative conditions. Two distinct mechanisms responsible for the formation of CLA isomers are proposed and discussed. Evidence of formation of 9,11‐C18:2 and 10,12‐C18:2 acids from 9,12‐C18:2 by a free‐radical chain reaction is provided. The first step consists in the formation of a free radical by abstraction of an active bis‐allylic hydrogen. By delocalization of the initial free radical, two allylic free radicals were stabilized and converted into the corresponding CLA isomers via the abstraction of a hydrogen radical from other linoleic acid or oxygenated species. Kinetic observations confirmed the significance of the bimolecular mechanism. Moreover, the proposed mechanism is supported by several pieces of information from the literature on peroxidation of linoleic acid. Under pure thermal conditions and/or for diluted samples, a second pathway to the formation of CLA from heat‐treated linoleic acid is proposed via an intramolecular rearrangement of the pentadienyl structure. This thermal [1,3]‐sigmatropic rearrangement results in a mixture of 9,11 and 10,12 CLA isomers. The formed cis/trans CLA isomers were readily rearranged by a [1,5]‐sigmatropic shift to yield trans‐8,cis‐10 and cis‐11,trans‐13 CLA isomers, respectively.     

Mass‐Spectrometric and Kinetic Studies on the Mechanism and Degradation Pathways of Titanium Salalen Catalysts for Asymmetric Epoxidation with Aqueous Hydrogen Peroxide

The composition and degradation of a highly active and enantioselective titanium salalen in situ catalyst for the asymmetric epoxidation of olefins with aqueous hydrogen peroxide was investigated. Kinetic data and ESI‐MS studies point to a mononuclear titanium salalen as the catalytically active species. By means of ESI‐MS and selective monodeuteration of the salalen ligand, the oxidative degradation was studied. Upon exposure to aqueous hydrogen peroxide, the amine functionality of the salalen ligand is converted to the hydroxylamine, followed by loss of water and generation of the inactive titanium‐salen complex. This transformation limits the activity of the catalyst in the epoxidation of less electron‐rich olefins, such as 1‐octene.     

Sphingomyelin Deacylase,the Enzyme Involved in the Pathogenesis of Atopic Dermatitis,Is Identical to the β-Subunit of Acid Ceramidase

A ceramide deficiency in the stratum corneum (SC) is an essential etiologic factor for the dry and barrier-disrupted skin of patients with atopic dermatitis (AD). Previously, we reported that sphingomyelin (SM) deacylase, which hydrolyzes SM and glucosylceramide at the acyl site to yield their lysoforms sphingosylphosphorylcholine (SPC) and glucosylsphingosine, respectively, instead of ceramide and/or acylceramide, is over-expressed in AD skin and results in a ceramide deficiency. Although the enzymatic properties of SM deacylase have been clarified, the enzyme itself remains unidentified. In this study, we purified and characterized SM deacylase from rat skin. The activities of SM deacylase and acid ceramidase (aCDase) were measured using SM and ceramide as substrates by tandem mass spectrometry by monitoring the production of SPC and sphingosine, respectively. Levels of SM deacylase activity from various rat organs were higher in the order of skin > lung > heart. By successive chromatography using Phenyl-5PW, Rotofor, SP-Sepharose, Superdex 200 and Shodex RP18-415, SM deacylase was purified to homogeneity with a single band of an apparent molecular mass of 43 kDa with an enrichment of > 14,000-fold. Analysis by MALDI-TOF MS/MS using a protein spot with SM deacylase activity separated by 2D-SDS-PAGE allowed its amino acid sequence to be determined and identified as the β-subunit of aCDase, which consists of α- and β-subunits linked by amino bonds and a single S-S bond. Western blotting of samples treated with 2-mercaptoethanol revealed that, whereas recombinant human aCDase was recognized by antibodies to the α-subunit at ~56 kDa and ~13 kDa and the β-subunit at ~43 kDa, the purified SM deacylase was detectable only by the antibody to the β-subunit at ~43 kDa. Breaking the S-S bond of recombinant human aCDase with dithiothreitol elicited the activity of SM deacylase with ~40 kDa upon gel chromatography. These results provide new insights into the essential role of SM deacylase expressed as an aCDase-degrading β-subunit that evokes the ceramide deficiency in AD skin.     

Electrospray mass spectrometry for characterizing polyglycerols and the effects of adduct ion and cone voltage

Polyglycerol intermediates have been characterized by liquid chromatography-mass spectrometry (LC-MS) with electrospray ionization (ESI). Linear and cyclic components from n=2–23 in a sample of decaglycerol, for example, have been resolved in the second dimension or mass axis. Molecular weight (MW) distributions for tri-, hexa-, and decaglycerol products have been analyzed as a function of cone voltage and adduct ion (H⁺, Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, and NH₄ ⁺). A different combination is required to obtain a reliable MW distribution for each polyglycerol intermediate. The best distribution obtained by ESI/MS is determined by comparing the calculated hydroxyl number and cyclic content to that obtained by wet chemistry and gas chromatography, respectively. Once ESI/MS conditions are established, the distribution can be used, for the first time in polyglycerol analysis, to calculate important parameters such as number average MW, weight average MW, polydispersity, % cyclics, hydroxyl number, wt% above n=6, etc.     

Experimental and computational analysis of thermo‐oxidative‐structural stability of ZrB2–SiC–Ti during arc‐jet testing

The development of new ultra‐high temperature ceramics for thermal protection system (TPS) of hypersonic cruise and re‐entry vehicles requires performance‐qualification testing under simulated flight conditions. The present work, encompassing experiments and computational analysis, critically analyzes the thermo‐oxidative‐structural stability of flat surface disks of spark plasma sintered ZrB₂–18SiC–xTi composites (x=0, 10, 20; composition in wt%) under arc jet flow with heat flux of 2.5 MW/m² for 30 seconds. Such testing conditions effectively simulate the aero‐thermal environment in ground facility, as experienced by hypersonic vehicles. Based on the extensive XRD, SEM‐EDS and electron probe microanalyzer based analysis of the surface/sub‐surface of arc jet exposed ceramics, the oxidation mechanisms are qualitatively discussed. Importantly, thick oxide layers (~400‐950 μm) were found to be adherent, thereby providing good structural stability of such ceramics for reusable TPS. The careful finite element (FE) analysis with high quality structural elements, being generated using HyperMesh, was conducted to understand the underlying reasons for observed oxidation. Such analysis allows us to determine the temporal evolution of through‐thickness temperature distribution. FE‐based calculations were subsequently validated using experimentally measured backwall temperatures. The thermodynamic feasibility of competing oxidation reactions at the analytically computed front wall temperatures was thereafter realistically assessed to support the oxidation mechanisms. Taken together, the present work provides guidelines for better understanding of the thermo‐oxidative‐structural stability of ceramics under arc jet testing and also establishes the good stability of ZrB₂–18SiC–20Ti composites for potential application in TPS of hypersonic space vehicles.     

TEMPO‐Copper(II) Diimine‐Catalysed Oxidation of Benzylic Alcohols in Aqueous Media

In situ generated copper(II)‐diimine complexes combined with TEMPO (2,2,6,6‐tetramethylpiperidinyl‐1‐oxyl radical) were studied in the oxidation of benzylic alcohols, the focus being on enviromentally benign reaction conditions. In this respect, reactions were studied in aqueous alkaline solutions and dioxygen was used as an end oxidant. This simple catalytic system turned out to be highly efficient and selective in the oxidation of primary and secondary benzylic alcohols to their corresponding carbonyl compounds. Under optimised reaction conditions [5 mol % of TEMPO, 3 mol % of copper(II ) diimine, pH 12.6–13.5, 80 °C, 10 bar O₂] benzyl alcohol was quantitatively and selectively oxidised to benzaldehyde. According to ESI‐MS studies, coordination of TEMPO, as well as deprotonated benzyl alcohol to the parent copper‐diimine complex in aqueous solutions is feasible. Supported by these observations a plausible reaction mechanism is proposed for the oxidation reaction.     

Structural and photooxidation studies of poly(styrene oxide) prepared with Maghnite‐H+ as cationic catalyst

The nature of irregularities and end‐groups in poly(styrene oxide) samples prepared using Maghnite‐H⁺ as a cationic catalyst were studied by ¹H‐ and ¹³C‐NMR at 200 MHz. Head‐to‐head (H‐H) and tail‐to‐tail (T‐T) irregularities are detected in all the samples studied. Secondary hydroxyl terminal groups are identified in polymers prepared with Maghnite‐H⁺. Poly(styrene oxide) was found to undergo chain scission by aging at 25°C. It was confirmed that oxidation of this type of polymers results from the important sensitivity of the polyether soft segment to oxidative degradation. For this reason, the scissions due to the oxidation of the material lead to notable quantities of low molecular weight photoproducts. Among the various structures produced by the oxidative degradation process, benzoate and secondary hydroxyl groups are identified by MALDI‐TOF‐MS. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation of chitosan‐bound nitrobenzaldehyde metal complexes and studies on its catalytic oxidative activity and reactive mechanism

Chitosan‐bound nitrobenzaldehyde metal complexes (m‐CNBDM and o‐CNBDM, where M is Mn or Ni) were prepared and characterized by infrared, X‐ray photoelectron spectroscopy, solid‐state ¹³C‐NMR cross‐polarity/magic‐angle spinning, inductively coupled plasma, and elemental analysis. The complexes were found to be catalysts for the oxidation of hydrocarbons with molecular oxygen under mild conditions. o‐CNBDNi has a certain catalytic activity in the oxidation of n‐propylbenzene and isopropylbenzene and has no activity in the oxidation of ethylbenzene. Both o‐CNBDMn and m‐CNBDNi catalyze the oxidation of all the aforementioned hydrocarbons, whereas m‐CNBDMn has no catalytic activity. The main oxidative products of ethylbenzene and n‐propylbenzene are the same as α‐ol and α‐one, but they are 2‐benzyl‐isopropynol and isopropylbenzene peroxide for isopropylbenzene. A mechanism for the catalytic oxidative process is proposed. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2188–2194, 2002