Photodynamic oxidation of Staphylococcus warneri membrane phospholipids: new insights based on lipidomics

RATIONALE

The photodynamic process involves the combined use of light and a photosensitizer, which, in the presence of oxygen, originates cytotoxic species capable of oxidizing biological molecules, such as lipids. However, the effect of the photodynamic process in the bacterial phospholipid profile by a photosensitizer has never been reported. A lipidomic approach was used to study the photodynamic oxidation of membrane phospholipids of Staphylococcus warneri by a tricationic porphyrin [5,10,15-tris(1-methylpyridinium-4-yl)-20-(pentafluorophenyl)porphyrin triiodide, Tri-Py(+)-Me-PF].

METHODS

S. warneri (10(8) colony forming units mL(-1)) was irradiated with white light (4 mW cm(-2), 21.6 J cm(-2)) in the presence of Tri-Py(+)-Me-PF (5.0 μM). Non-photosensitized bacteria were used as control (irradiated without porphyrin). After irradiation, total lipids were extracted and separated by thin-layer chromatography (TLC). Isolated fractions of lipid classes were quantified by phosphorus assay and analyzed by mass spectrometry (MS): off-line TLC/ESI-MS, hydrophilic interaction (HILIC)-LC/MS and MS/MS.

RESULTS

The most representative classes of S. warneri phospholipids were identified as phosphatidylglycerols (PGs) and cardiolipins (CLs). Lysyl-phosphatidylglycerols (LPGs), phosphatidylethanolamines (PEs), phosphatidylcholines (PCs) and phosphatidic acids (PAs) were also identified. After photodynamic treatment, an overall increase in the relative abundance of PGs was observed as well as the appearance of new oxidized species from CLs, including hydroxy and hydroperoxy derivatives. Formation of high amounts of lipid hydroperoxides was confirmed by FOX2 assay. Photodynamic oxidation of phospholipid standards revealed the formation of hydroperoxy and dihydroperoxy derivatives, confirming the observed CL oxidized species in S. warneri.

CONCLUSIONS

Membrane phospholipids of S. warneri are molecular targets of the photoinactivation process induced by Tri-Py(+) -Me-PF. The overall modification in the relative amount of phospholipids and the formation of lipid hydroxides and hydroperoxides indicate the lethal damage caused to photosensitized bacterial cells.

Electrospray tandem mass spectrometry analysis of methylenedioxy chalcones, flavanones and flavones

RATIONALE

Several methylenedioxy chalcones, flavanones and flavones substituted with mono-, di- and trimethoxy groups have been used in the treatment of proliferative conditions like cancer and inflammatory diseases. The application of these flavonoids in biology requires an analytical method to ensure a detailed knowledge of their structures after drug metabolism.

METHODS

Electrospray ionization mass (ESI-MS) and tandem mass (ESI-MS/MS) spectra were acquired using a Q-TOF 2 instrument. Fragmentation patterns and their pathways were analyzed by CID-MS(2-3) spectra acquired in a LXQ linear ion trap mass spectrometer using standard isolation and excitation procedures (activation q value of 0.25, activation time of 30 ms). ESI-MS and ESI-MS(n) conditions: spray voltage 5 kV, nitrogen 8.00 sheath gas flow rate (arb), heated capillary temperature 275°C, capillary voltage 10.99 V; tube lens voltage 75.01 V.

RESULTS

The ESI-MS/MS spectra of chalcones were nearly identical to their corresponding isomeric flavanones with (0,α)A(+)/(1,3)A(+) and (0,1')B(+)/(1,4)B(+) cleavages. Other common losses are of (•)CH3, H2O, HCHO and C2H2O. The characteristic loss of C2H2O and absence of a (0,α)B(+)/(1,3)B(+) product ion allows to distinguish between the 2- or 4-methoxy-substituted chalcones and flavanones. Common losses of (•)CH3, (•)CH3 and (•)H, and C2H2O2 characteristic for the presence of methylenedioxy groups were observed in flavones.

CONCLUSIONS

The substitution pattern on the B-ring leads to distinct base peak formation in the flavones. In addition, differentiation of isomers with methoxy substituents in ortho and para positions of the B-ring was achieved using MS/MS in chalcones and flavanones. This method will be helpful for identification of these compounds in biological mixtures.

Effects of UV radiation on the lipids and proteins of bacteria studied by mid-infrared spectroscopy

Knowledge of the molecular effects of UV radiation (UVR) on bacteria can contribute to a better understanding of the environmental consequences of enhanced UV levels associated with global climate changes and will help to optimize UV-based disinfection strategies. In the present work, the effects of exposure to UVR in different spectral regions (UVC, 100-280 nm; UVB, 280-320 nm; and UVA, 320-400 nm) on the lipids and proteins of two bacterial strains ( Acinetobacter sp. strain PT5I1.2G and Pseudomonas sp. strain NT5I1.2B) with distinct UV sensitivities were studied by mid-infrared spectroscopy. Exposure to UVR caused an increase in methyl groups associated with lipids, lipid oxidation, and also led to alterations in lipid composition, which were confirmed by gas chromatography. Additionally, mid-infrared spectroscopy revealed the effects of UVR on protein conformation and protein composition, which were confirmed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), oxidative damage to amino acids, and changes in the propionylation, glycosylation and/or phosphorylation status of cell proteins. Differences in the targets of UVR in the two strains tested were identified and may explain their discrepant UV sensitivities. The significance of the results is discussed from an ecological standpoint and with respect to potential improvements in UV-based disinfection technologies.

Liquid chromatography-tandem mass spectrometry of phosphatidylserine advanced glycated end products

Phosphatidylserine (PS) is an aminophospholipid that is prone to glycation. In oxidative conditions, glycated PS may lead to the formation of Amadori compounds and advanced glycated end products (AGEs), which are known to accumulate in diabetic patients. Nevertheless, there have been no studies that identified products from the oxidative reaction of glycated PS. In this study, glycated 1-palmitoyl-2-oleoyl-PS was synthesized and further oxidized by Fenton reagent. The AGES formed were structurally characterized by liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) in negative mode. The oxidation products from glycated PS that we have found include products arising from the oxidation of the fatty acyl chains (hydroperoxides, hydroxides and keto derivatives), and arising from oxidative cleavage of serine polar head and lyso-glycated PS. Oxidation in C6 of glucose lead to the formation of glucuronyl-PS. In addition, new products arising from oxidative cleavage of glucose moiety (between C1C2, C2C3 and C3C4 bonds) were identified as PS-AGES. The current findings add substantially to the best of our knowledge of PS glycoxidation products, opening new perspectives for the detection of these products in complex biological matrices.

Glycophthalocyanines: structural differentiation and isomeric differentiation by matrix-assisted laser desorption/ionization tandem mass spectrometry

RATIONALE

Glycophthalocyanines have a great promising potential in many scientific areas. However, their structural characterization is not an easy task. To overcome this drawback, it is urgent to develop simple and efficient methodologies to characterize this type of compounds. In this work, we describe the use of matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) and MALDI-MS/MS of the [M+H](+) to distinguish between two isomeric glycophatholocyanines bearing four galactose units with protected (1a and 2a) or unprotected hydroxyl groups (1b and 2b).

METHODS

The MALDI-MS and MALDI-MS/MS spectra were acquired using a MALDI-TOF/TOF Applied Biosystems 4800 Proteomics Analyzer instrument equipped with a nitrogen laser and using dithranol as matrix. Computational studies were performed in order to gain insights into the mechanisms underlying the different fragmentation pathways observed for the isomeric species.

RESULTS

The fragmentation pattern observed in MALDI-MS/MS spectra of the [M+H](+) ion was dependent on the peripheral distribution of the sugar units. Phthalocyanines (Pcs) with a sugar unit in each isoindole ring show the typical loss of sugar units (cleavage of C6-O bond) while Pcs with the four sugar units linked to the same isoindole ring show a major and unusual fragmentation pathway corresponding to the cleavage of the C5-C6 bond of the sugar units. This type of fragmentation is not usually observed in the MS/MS of oligosaccharides.

CONCLUSIONS

MALDI-MS is a valuable tool for the structural characterization/differentiation of isomeric glycophthalocyanines.

Photodegradation of the fungicide thiram in aqueous solutions. Kinetic studies and identification of the photodegradation products by HPLC-MS/MS

In this study, the relevance of photodegradation processes on the persistence of the fungicide thiram in waters was investigated. The photodegradation of thiram in Milli-Q water and in aqueous solutions of humic and fulvic acids, as well as the photodegradation in spiked river water were studied. Both pure thiram and one of its commercial formulations were used to prepare the solutions which were irradiated in a solar light simulator. In general, thiram photodegradation follows pseudo-first order kinetics. The half-life time of thiram 2mgL(-1) in Milli-Q water was 28min. However, the degradation rate of thiram was significantly increased (p=0.02) by the inert components of the thiram commercial formulation as well as by commercial humic acids and by fulvic acids isolated from river water (p<0.004). Thus, the half-life time of thiram decreased to 24min in the presence of the inert formulation components, while, in the presence of both humic and fulvic acids (10mgL(-1)) it decreased to 22min. Furthermore, thiram photodegradation in natural river water showed that there is a significant enhancement of the degradation rate constant of thiram relatively to Milli-Q water, corresponding to a decrease of about 38% in its half-life time. This increase of the degradation rate in river water seems to be higher than that observed in the presence of FA, suggesting that beyond organic matter, other natural river components can increase the thiram photodegradation rate. These results allow us to conclude that photodegradation by solar radiation can be an important degradation pathway of thiram in natural waters. HPLC-MS/MS allowed to identify, for the first time, three products of the photodegradation of thiram in aqueous solution. Three compounds were identified and their structure was corroborated by the MS(n) spectra fragmentation profile. Pathways for the formation of the products from thiram photodegradation are proposed and discussed.

Organic-inorganic hybrid materials based on iron(III)-polyoxotungstates and 1-butyl-3-methylimidazolium cations

The iron(III) μ-oxo bridged dimeric polyoxometalate [(PW(11)O(39)Fe)(2)O](10-) was isolated by reacting the transition metal monosubstituted Keggin anion [PW(11)O(39)Fe(H(2)O)](4-) and the ionic liquid 1-butyl-3-methylimidazolium bromide, (Bmim)Br, at pH 5.5. The crystal structure of (Bmim)(10)[(PW(11)O(39)Fe)(2)O]·0.5H(2)O (1) (monoclinic, space group P2(1)/n, Z = 4) was determined by single crystal X-ray diffraction. By changing the reaction conditions, (Bmim)(4)[PW(11)O(39)Fe(H(2)O)]·H(2)O (2) was obtained, whilst the reaction between the Bmim(+) cation and the heteropolyanion [SiW(11)O(39)Fe(H(2)O](5-), in the pH conditions used for 1, afforded (Bmim)(5)[SiW(11)O(39)Fe(H(2)O)]·4H(2)O (3). The compounds were characterized by spectroscopic techniques, thermal analysis, cyclic voltammetry, magnetic measurements and mass spectrometry. This study contributes to the understanding of iron μ-oxo dimer formation in polyoxometalate chemistry and calls attention to the influence of the counter-cations on the stability and formation of compound 1. The combination of the cationic part of ionic liquids and iron-substituted polyoxotungstates is predicted to lead to new materials with interest to catalysis, electrocatalysis and ionic liquid based nanocomposites.

Photooxidation of glycated and non-glycated phosphatidylethanolamines monitored by mass spectrometry

Phosphatidylethanolamines (PE) are one of the major components of cells membranes, namely in skin and in retina, that are continuously exposed to solar UV radiation being major targets of photooxidation damage. In addition, due to the presence of the free amine group, PE can also undergo glycation, in hyperglycemic conditions which may increase the susceptibility to oxidation. The aim of this study is to develop a model, based on mass spectrometry (MS) analysis, to identify photooxidative degradation of selected PE (POPE: PE 16:0/18:1, PLPE: PE 16:0/18:2, PAPE: PE 16:0/20:4) and glycated PEs due to UV irradiation. Photooxidation products were analysed by electrospray ionization MS (ESI-MS) and tandem MS (ESI-MS/MS) in positive and negative mode. Emphasis is placed in the influence of glycation in the generation of distinct photooxidation products. ESI-MS spectra of PE after UV photo-irradiation showed mainly hydroperoxy derivatives, due to oxidation of unsaturated fatty acyl chains. Glycated PE gave rise to several new photooxidation products formed due to oxidative cleavages of the glucose moiety, namely between C1 and C2, C2 and C3, and C5 and C6 of this sugar unit. These new products were identified by ESI-MS/MS in positive mode showing distinct neutral loss depending on the different structure of the polar head group. These new identified advanced glycated photooxidation products may have a deleterious role in the etiology of diabetic retinopathy and in diabetic retinal microvascular complications.

Differentiation of isomeric pentose disaccharides by electrospray ionization tandem mass spectrometry and discriminant analysis

RATIONALE

The structural characterization of unknown oligosaccharides remains a big challenge since a large number of isomeric structures are possible even for disaccharides. In this work, electrospray ionization collision-induced dissociation tandem mass spectrometry (ESI-CID-MS/MS) was used for the differentiation of isomeric pentose disaccharides, α-(1 → 5)-L-arabinobiose (Ara(2)) and β-(1 → 4)-D-xylobiose (Xyl(2)).

METHODS

ESI-MS/MS spectra of [M + Li](+) and [M + Na](+) ions of Ara(2) and Xyl(2), as well as these precursor ions of (18)O-labelled disaccharides, were acquired using two mass spectrometers equipped with different analyzers: LIT (linear ion trap) and Q-TOF (quadrupole time-of-flight).

RESULTS

Product ions observed in MS/MS spectra arise from the cleavage at the nonreducing side of the glycosidic bond (Y(1)(+)) and from cross-ring cleavages (0,1)A(2)(+), (0,2)A(2)(+), and (0,3)A(2)(+) at the reducing residue. Statistically significant differences were observed between the relative abundance of specific product ions, when comparing both disaccharides. These differences allowed discriminant models to be built and to propose a criterion using the relative abundances of selected ions capable of discriminating between the isomers for both adduct ions and spectrometers.

CONCLUSIONS

Isomeric pentose disaccharides can be distinguished based on the fragmentation of both [M + Li](+) and [M + Na](+) ions and using different mass spectrometers. However, LIT instrument has a better discriminant power.

Characterisation of (E)-2-styrylchromones by electrospray ionisation mass spectrometry: singular gas-phase formation of benzoxanthenones

RATIONALE

The electrospray ionisation (ESI) mass spectra (ESI-MS(n) , n = 2 and 3) of six (E)-2-styrylchromones containing electron-donating and electron-withdrawing groups were studied for the first time. The potential application of these compounds as drug candidates brings a need for the development of an analytical method to ensure a detailed knowledge of their structures.

METHODS

ESI-MS, CID-MS(2) and MS(3) spectra of all the studied compounds were acquired using a LXQ linear ion trap mass spectrometer with an electrospray source, operating in the positive ion mode. ESI conditions were: nitrogen 8.00 sheath gas flow rate (arb), spray voltage 5 kV, heated capillary temperature 275 °C, capillary voltage 10.99 V and tube lens voltage 75.01 V. CID-MS(2) and MS(3) experiments were performed on mass-selected precursor ions using standard isolation and excitation procedures (activation q value of 0.25, activation time of 30 ms).

RESULTS

A comparable pattern of product ions was observed for all the studied compounds. Only the product ion ((1,2)(3,4)) A(+) is common to all the studied compounds. Common to compounds 1 (R(2) = H), 1a (R(2) = OMe) and 1c (R(2) = Cl) are the product ions formed by loss of H(2)O, CO, C(6)H(5)OH, and the product ions ((1,2)(2,3))B(+) and ((1,2)(3,4))B(+). Among all compounds, 2-SC 1b (R(2) = NO(2)) shows an obvious differentiation showing the lowest number of product ions under CID-MS(2) conditions.

CONCLUSIONS

The analysed compounds revealed a comparable pattern of product ions formed for each compound only different in what concerns the relative abundance of these formed product ions. A rather interesting and unexpected loss of 2 Da was observed for some compounds. The structure of a benzoxanthenone was proposed for this product ion based on evidence obtained by synthesised benzoxanthenone as a model compound.

Structural characterization of polysaccharides isolated from grape stalks of Vitis vinifera L

The main structural polysaccharides of grape stalks are cellulose, heteroxylan, and glucan. Cellulose contributes 30.3% of grape stalk matter and has an unusually high degree of the crystallinity (75.4%). Among hemicelluloses, xylan was the most abundant one, contributing ∼12% to the weight. The heteroxylan was isolated from the corresponding peracetic holocellulose by DMSO extraction followed by precipitation in ethanol. The M(w) of heteroxylan (19.0 kDa) was assessed by size exclusion chromatography (SEC) and the structure was inferred by methanolysis and methylation linkage analysis, as well as 1D and 2D nuclear magnetic resonance (NMR) spectroscopy. The heteroxylan is a partially acetylated (DS=0.49) glucuronoxylan possessing the main backbone composed by β-(1→4)-linked D-xylopyranosyl units ramified with α-(1→2)-linked 4-O-methyl-α-D-glucuronosyl residues (MeGlcpA) at a molar ratio 25:1. The isolated heteroxylan contained concomitant β-glucan (ca. 15%), whose structure was elucidated by methylation linkage analysis and by NMR spectroscopy. The results obtained revealed mixed β-(1→3; 1→4)-D-glucan with a molar ratio of β-(1→3)- to β-(1→4)-linked glucopyranosyl units of 1:2.

Evaluation of the capacity of oxidized phosphatidylserines to induce the expression of cytokines in monocytes and dendritic cells

Oxidized phospholipids are known to be key signaling molecules in the onset of several diseases involving inflammation. The aim of this study was to evaluate the effect of oxidized phosphatidylserines (oxPS) in modulating the immune system, through cytokine production. Flow cytometry analysis was used to evaluate the oxPS capacity to induce the expression of different cytokines by monocytes, myeloid dendritic cells (mDCs) and DCs CD14(-/low)CD16(+). oxPS were formed during oxidation induced by the hydroxyl radical. Among the four families of oxPS studied, only oxPS modified in the polar head with formation of a terminal hydroperoxyacetaldehyde upregulated the production of cytokines IL-8 and TNF-α by monocytes and DCs subsets (mDCs and CD14(-/low)CD16(+) DCs). This family of oxPS showed the capacity to upregulate the production of IL-1β, IL-6, and MIP-1β from the same type of cells. A significant raise in the percentage of monocytes and dendritic cells producing the studied cytokines was observed, when compared with basal control. Oxidation products modified in the fatty acyl chain did not upregulate TNF and IL-8. oxPS with terminal hydroperoxyacetaldehyde has pro-inflammatory properties. This outcome may help to understand the biological role of phosphatidylserine oxidation products in inflammatory processes and in dysfunctions of immune system.

Recent developments in the structural characterization of substituted meso-tetraarylporphyrins by electrospray tandem mass spectrometry

meso-tetraarylporphyrins with different substituents linked either to an aryl ring or to a β-pyrrolic position were studied by Electrospray (ESI) Tandem Mass Spectrometry (MS/MS). The electrospray mass spectra (ESI-MS) of meso-tetraarylporphyrins show the molecular ions and no significant fragmentation is noted. Structural information can be obtained by inducing fragmentation of the ions generated under ESI conditions. The product ions formed and registered in the tandem mass spectra (ESI-MS/MS) are characteristic of the chemical structure of the groups linked to the porphyrin and depend on their location. Also, the same functional group linked either to the aryl ring or to the β-pyrrolic position yields different product ions that confirm their position. Taking into consideration the Portugal-Spain special issue of the Journal of Porphyrins and Phthalocyanines, in this highlight we analyze the work done at the University of Aveiro related to the use of mass spectrometry in the structural characterization of meso-tetraarylporphyrins with carbohydrate, nitro and amino acid groups.

Profiling changes triggered during maturation of dendritic cells: a lipidomic approach

Lipids are important in several biological processes because they act as signalling and regulating molecules, or, locally, as membrane components that modulate protein function. This paper reports the pattern of lipid composition of dendritic cells (DCs), a cell type of critical importance in inflammatory and immune responses. After activation by antigens, DCs undergo drastic phenotypical and functional transformations, in a process known as maturation. To better characterize this process, changes of lipid profile were evaluated by use of a lipidomic approach. As an experimental model of DCs, we used a foetal skin-derived dendritic cell line (FSDC) induced to mature by treatment with lipopolysaccharide (LPS). The results showed that LPS treatment increased ceramide (Cer) and phosphatidylcholine (PC) levels and reduced sphingomyelin (SM) and phosphatidylinositol (PI) content. Mass spectrometric analysis of a total lipid extract and of each class of lipids revealed that maturation promoted clear changes in ceramide profile. Quantitative analysis enabled identification of an increase in the total ceramide content and enhanced Cer at m/z 646.6, identified as Cer(d18:1/24:1), and at m/z 648.6, identified as Cer(d18:1/24:0). The pattern of change of these lipids give an extremely rich source of data for evaluating modulation of specific lipid species triggered during DC maturation.

Formation of oligomeric alkenylperoxides during the oxidation of unsaturated fatty acids: an electrospray ionization tandem mass spectrometry study

This study reports the identification of oligomeric alkenylperoxides by electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (ESI-MS(2)), during the oxidation of oleic, linoleic and linolenic acids with Fenton's (Fe(2+)/H(2)O(2)) and Fe(2+)/O(2) systems. The reactions were followed by ferrous oxidation-xylenol orange method together with GC-MS and GC-FID, allowing to observe that both oxidation systems are different in terms of hydroperoxide evolution, probably due to the presence of different intermediate reactive species: perferryl ion and OH(·) radical responsible for the decomposition of lipid hydroperoxides and formation of new compounds. The analysis of ESI-MS in the negative mode, obtained after oxidation of each fatty acid, confirmed the presence of the monomeric oxidation products together with other compounds at high mass region above m/z 550. These new ions were attributed to oligomeric structures, identified by the fragmentation pathways observed in the tandem mass spectra.

Photodegradation of psychiatric pharmaceuticals in aquatic environments--kinetics and photodegradation products

Benzodiazepines are widely consumed psychiatric pharmaceuticals which are frequently detected in the environment. The environmental persistence and fate of these pharmaceuticals as well as their degradation products is of high relevance and it is, yet, scarcely elucidated. In this study, the relevance of photodegradation processes on the environmental persistence of four benzodiazepines (oxazepam, diazepam, lorazepam and alprazolam) was investigated. Benzodiazepines were irradiated under simulated solar irradiation and direct and indirect (together with three different fractions of humic substances) photodegradation kinetics were determined. Lorazepam was shown to be quickly photodegradated by direct solar radiation, with a half-life time lower than one summer sunny day. On the contrary, oxazepam, diazepam and alprazolam showed to be highly resistant to photodegradation with half-life times of 4, 7 and 228 summer sunny days, respectively. Apparent indirect and direct photodegradation rates are of the same order of magnitude. However, humic acids were consistently responsible for a decrease in the photodegradation rates while fulvic acids and XAD4 fraction caused an enhancement of the photodegradation. Overall, the results highlight that photodegradation might not be an efficient pathway to prevent the aquatic environmental accumulation of oxazepam, diazepam and alprazolam. Also, nineteen direct photodegradation products were identified by electrospray mass spectrometry, the majority of which are newly identified photoproducts. This identification is crucial to a more complete understanding of the environmental impact of benzodiazepines in aquatic systems.

Tandem mass spectrometry based investigation of cinnamylideneacetophenone derivatives: valuable tool for the differentiation of positional isomers

Cinnamylideneacetophenones have been extensively used as versatile starting materials in numerous different transformations. The structural characterization of this type of compounds is, therefore, of crucial importance since it can give information on the chemistry, reactivity and also the potential biological activity of this type of compounds. Thus, 24 derivatives were systematically studied by tandem mass spectrometry (MS(2)) with electrospray ionization (ESI), in positive ion mode. The protonated molecules, [M + H](+), formed under ESI conditions were induced to dissociate and the fragmentation patterns were studied. The information collected provided important structural information on the type of substituents present and constitute an important database concerning this family of compounds. Overall, it was found that the substitution pattern of the cinnamylideneacetophenone derivatives changes the ESI-MS(2) fragmentation considerably. These results indicate that ESI-MS(2) is a useful technique for distinguishing positional isomers of these cinnamylideneacetophenone derivatives.

Structural characterization of oxidized glycerophosphatidylserine: evidence of polar head oxidation

Non-oxidized phosphatidylserine (PS) is known to play a key role in apoptosis but there is considerable research evidence suggesting that oxidized PS also plays a role in this event, leading to the increasing interest in studying PS oxidative modifications. In this work, different PS (1-palmitoyl-2-linoleoyl-sn-glycero-3-phospho-L-serine (PLPS), 1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-L-serine (POPS), and 1,2-dipalmitoyl-sn-glycero-3-phospho-L-serine (DPPS) were oxidized in vitro by hydroxyl radical, generated under Fenton reaction conditions, and the reactions were monitored by ESI-MS in negative mode. Oxidation products were then fractionated by thin layer chromatography (TLC) and characterized by tandem mass spectrometry (MS/MS). This approach allowed the identification of hydroxyl, peroxy, and keto derivatives due to oxidation of unsaturated fatty acyl chains. Oxidation products due to oxidation of serine polar head were also identified. These products, with lower molecular weight than the non-modified PS, were identified as [M - 29 - H](-) (terminal acetic acid), [M - 30 - H](-) (terminal acetamide), [M - 13 - H](-) (terminal hydroperoxyacetaldehyde), and [M - 13 - H](-) (terminal hydroxyacetaldehyde plus hydroxy fatty acyl chain). Phosphatidic acid was also formed in these conditions. These findings confirm the oxidation of the serine polar head induced by the hydroxyl radical. The identification of these modifications may be a valuable tool to evaluate phosphatidylserine alteration under physiopathologic conditions and also to help understand the biological role of phosphatidylserine oxidation in the apoptotic process and other biological functions.

Evaluation of the effect of roasting on the structure of coffee galactomannans using model oligosaccharides

The roasting process induces structural changes in coffee galactomannans. To know more about the reaction pathways that occur during the roasting of coffee, mannosyl and galactomannosyl oligosaccharides, having a degree of polymerization (DP) between 3 and 4, were used as models for galactomannans. These compounds were dry-heated under air atmosphere from room temperature to 200 °C, being maintained at 200 °C for different periods of time. The roasted materials were analyzed by mass spectrometry (ESI-MS, MALDI-MS, and ESI-MSn) and methylation analysis. In the MS spectra were identified several [M+Na]+ ions belonging to a series from a single hexose to 10 hexose residues ([Hex1-10+Na]+). The ions corresponding to their respective mono- and tridehydrated derivatives ([Hex2-10-H2O+Na]+ and [Hex2-10-3H2O+Na]+, respectively) were also identified. ESI-MSn as well as deuterium-labeling and alditol derivatization experiments showed that the tridehydrations occur at the reducing end of the oligosaccharides. The identification of (1→2)- and (1→6)-linked mannose residues and (1→4)-linked glucose residues by methylation analysis allowed the conclusion that transglycosylation and isomerization reactions occur during dry thermal processing.

Characterization of phenolic components in polar extracts of Eucalyptus globulus Labill. bark by high-performance liquid chromatography-mass spectrometry

High-performance liquid chromatography-electrospray ionization mass spectrometry (HPLC-ESI-MS) and tandem mass spectrometry (MS(n)) were used to investigate the phenolic constituents in methanol, water, and methanol/water extracts of Eucalyptus globulus Labill. bark. Twenty-nine phenolic compounds were identified, 16 of them referenced for the first time as constituents of E. globulus bark, namely, quinic, dihydroxyphenylacetic, and caffeic acids, bis(hexahydroxydiphenoyl (HHDP))-glucose, galloyl-bis(HHDP)-glucose, galloyl-HHDP-glucose, isorhamentin-hexoside, quercetin-hexoside, methylellagic acid (EA)-pentose conjugate, myricetin-rhamnoside, isorhamnetin-rhamnoside, mearnsetin, phloridzin, mearnsetin-hexoside, luteolin, and a proanthocyanidin B-type dimer. Digalloylglucose was identified as the major compound in the methanol and methanol/water extracts, followed by isorhamnetin-rhamnoside in the methanol extract and by catechin in the methanol/water extract, whereas in the water extract catechin and galloyl- HHDP-glucose were identified as the predominant components. The methanol/water extract was shown be the most efficient to isolate phenolic compounds identified in E. globulus bark.