1,721,151 research outputs found
H2O2+ ions in ionized O2/CH4 mixtures: Intermediacy of CH3OOH+ and CH2O+
No full textH2O2+ ions are shown to be formed in ionized O2/CH4 mixtures from the secondary reaction of CH2O+ with O2. By high-resolution mass spectrometric techniques, the peroxide HOOH structure and the H2CO structure of ionized formaldehyde are assigned to the [H2O2](+) ions and the [CH2O](+) reactants, respectively. The [CH4O2](+) intermediate of the reaction between O2(+) and CH4 is characterized as a mixture of the loosely bound [CH4 --O2](+) Complex and the theoretically predicted insertion product CH3OOH+. The CH3OOH+ intermediate, precursor of the most abundant ionic product CH2OOH+, has been characterized for the first time as a long-lived species
Low-energy collisionally activated dissociation of pentose-borate complexes
No full textAbstract: Pentose-borate 1:1 complexes were generated in the ESI source of a triple quadrupole and ion trap mass spectrometer by electrospray ionization of Na2B4O7 and pentose(arabinose, lyxose, ribose,xylose) 2:1 solution in CH3CN/H2O. The study of their low-energy collisionally activated dissociation (CAD) demonstrated that ribose and lyxose are preferentially complexed at the C-2-C-3 cis-diol function whereas arabinose and xylose are esterified at the C-1-C-2 hydroxyl groups. No evidence was found of the stronger affinity for ribose to borate. The ribose probiotic rule can be explained by considering its peculiar capability, among the investigated pentoses, to almost totally complex the borate anion at the C-2-C-3 hydroxyl group, thus enabling the subsequent stages of nucleotide assembly, such as phosphorylation and linkage to the nucleobases. Finally, the differences observed in the pentose-borate complex CAD spectra can be used for the mass spectrometric discrimination of isom..
The mechanism of 2-furaldehyde formation from d-xylose dehydration in the gas phase. A tandem mass spectrometric study
No full textThe mechanism of reactions occurring in solution can be investigated also in the gas phase by suited mass spectrometric techniques, which allow to highlight fundamental mechanistic features independent of the influence of the medium and to clarifying controversial hypotheses proposed in solution studies. In this work, we report a gas-phase study performed by electrospray triple stage quadrupole mass spectrometry (ESI-TSQ/MS) on the dehydration of d-xylose, leading mainly to the formation of 2-furaldehyde (2-FA). It is generally known in carbohydrate chemistry that the thermal acid catalyzed dehydration of pentoses leads to the formation of 2-FA, but several aspects on the solution-phase mechanism are controversial. Here, gaseous reactant ions corresponding to protonated xylose molecules obtained from ESI of a solution containing d-xylose and ammonium acetate as protonating reagent were allowed to undergo collisionally activated decomposition (CAD) into the triple stage quadrupole analyzer. The product ion mass spectra of protonated xylose are characterized by the presence of ionic intermediates arising from xylose dehydration, which were structurally characterized by their fragmentation patterns. As expected, the xylose triple dehydration leads to the formation of the ion at m/z 97, corresponding to protonated 2-FA. On the basis of mass spectrometric evidences, we demonstrated that in the gas phase, the formation of 2-FA involves protonation at the OH group bound to the C1 atom of the sugar, the first ionic intermediate being characterized by a cyclic structure. Finally, energy resolved product ion mass spectra allowed to obtain information on the energetic features of the d-xylose→2-FA conversion. © 2013 American Society for Mass Spectrometry
Gas-Phase Ion Chemistry of BF3/NH3 Mixtures
No full textThe gas-phase ion chemistry of BF3/NH3 mixtures was investigated by the joint application of mass-spectrometric techniques and theoretical methods. The addition of BF2+ to NH3 led to the first observation of [BF2,NH3]+ and [BF,NH2]+ ions. Diamidoboron cation B(NH2)2+ was also detected. Consistent with collisionally activated dissociation (CAD) mass spectrometric results, theoretical calculations performed at the B3LYP and CCSD(T) levels identified the F2B?NH3+, FB?NH2+, and NH2?B?NH2+ ions as the most stable isomers on the corresponding potential energy surfaces. The F2B?NH3+ ion represents the protonated form of aminodifluoroborane, BF2NH2, and consequently behaves as a Brønsted acid under FT-ICR conditions. The FBNH2+ ion is able to add Lewis bases such as water, ammonia, and hydrazoic acid. These species, containing the BN moiety, may represent new promising projectile ions in the boron nitride deposition techniques involving high-energy ion beams
Chemical Investigation and Dose-Response Phytotoxic Effect of Essential Oils from Two Gymnosperm Species (Juniperus communis var. saxatilis Pall. and Larix decidua Mill.)
No full textThe chemical composition of the liquid and vapor phases of leaf essential oils (EOs) obtained from two species of Gymnosperms (Juniperus communis var. saxatilis Willd. and Larix decidua Mill.) was investigated using the SPME-GC-MS technique. The results highlighted a composition characterized by 51 identified volatile compounds (34 in J. communis and 39 in L. decidua). In both bloils, monoterpenes prevailed over the sesquiterpenes, albeit with qualitative and quantitative differences. Sabinene (37.5% and 34.5%, respectively) represented the two most abundant components in the liquid and vapor phases of J. communis, and α-pinene (51.0% and 63.3%) was the main constituent in L. decidua. The phytotoxic activity of the two EOs was assessed in pre-emergence conditions using three concentrations in contact (2, 5, 10 µL/mL) and non-contact (2, 20, 50 µL) tests against Lolium multiflorum Lam. (Poaceae) and Sinapis alba L. (Brassicaceae). Treatments were effective in a dose-dependent manner by significantly reducing the germination (up to 100% and 45–60%, respectively, with filter paper and soil as a substrate) and the seedling development (1.3 to 8 times) of both target species. Moreover, an exploratory survey on the residual presence of volatile compounds in the soil at the end of the tests was carried out
Esential oils extraction: a 24-hour steam distillation systematic methodology
No full textSteam distillation is known to be the most prevalent method of essential oil extraction. Despite many studies on extraction methods, there is no report about the impact of distillation process duration on the yield and oil quality. A new 24-h steam distillation process for extraction of plant essential oils is presented. For improving the total yield, prolonged and continued isolation was used. A selection of plant species from Lamiaceae and Apiaceae families was subjected to direct steam distillation and essential oils were collected at different times (1, 2, 3, 6, 12 and 24 h). The analysis included either annual or perennial species monitored in terms of different harvesting time. From these studies, it is conclusively that there is no rule about appropriate extraction time, and different plants need different periods for the essential oils to achieve the desired quality or quantity of extract. Thus, extraction duration is directly dependent on what the study is conducted for
GC-MS investigation and antiproliferative activities of extracts from male and female flowers of Schinus molle L
No full textThe aim of this study is to define chemical composition and antiproliferative activity of several compounds isolated from Schinus molle male and female flowers on human neuroblastoma (SH-SY5Y) and human leukemia (HL60) cell lines. Three extracts obtained by using solvents with different polarities (petroleum ether, diethyl ether and acetone) were characterized by GC/MS analysis revealing qualitative and quantitative differences in the chemical composition of male and female flowers. Nineteen components were identified and both flower extracts were dominated by the sesquiterpene hydrocarbons fraction, mainly elemol, followed by bicyclic sesquiterpenes and by a smaller amount of monoterpenes. The biological activities of the extracts were evaluated by dose-dependent viability assay on two different cell lines and HL60 cells resulted more sensitive to the treatment. The presence of compounds at low concentration with a well-established cytotoxic activity such as beta-elemene, beta-caryophyllene and gamma-eudesmol could exert a synergistic cytotoxic effect
A mass spectrometric study of the acid-catalysed d-fructose dehydration in the gas phase
No full text5-hydroxymethylfuraldehyde (5-HMF) and simpler compounds, such as levulinic acid (LA) and glyceraldehyde,
are platform molecules produced by the thermal acid-catalyzed dehydration of carbohydrates
coming from biomass. Understanding sugar degradation pathways on a molecular level is necessary to
increase selectivity, reduce degradation by-products yields and optimize catalytic strategies, fundamental
knowledge for the development of a sustainable renewable industry. In this work gaseous protonated
D-fructose ions, generated in the ESI source of a triple quadrupole mass spectrometer, were
allowed to undergo Collisionally Activated Decomposition (CAD) into the quadrupole collision cell. The
ionic intermediates and products derived from protonated D-fructose dehydration were structurally
characterized by their fragmentation patterns and the relative water-loss dehydration energies measured
by energy-resolved CAD mass spectra. The data were compared with those obtained from protonated Dglucose
decomposition in the same experimental conditions. In the gas phase, D-fructose dehydration
leads to the formation of a mixed population of isomeric [C6H6O3]Hþ ions, whose structures do not
correspond exclusively to 5-hydroxymethyl-2-furaldehyde protonated at the more basic aldehydic group
Inside the mechanism of the acid-catalyzed D-Fructose dehydration: a mass spectrometric study.
No full text5-hydroxymethylfuraldehyde (5-HMF) and simpler compounds, such as levulinic acid (LA) and glyceraldehyde, are platform molecules produced by the thermal acid-catalyzed dehydration of carbohydrates coming from biomass.
Understanding sugar degradation pathways on a molecular level is necessary to increase selectivity, reduce degradation by-products yields and optimize catalytic strategies, fundamental knowledge’s for the development of a sustainable renewable industry.
Experimental gas phase studies can play a key role enlightening the more likely route occurring in the absence of solvent molecules.
In this work gaseous protonated D-fructose ions, generated in the ESI source of a triple quadrupole mass spectrometer, were allowed to undergo Collisionally Activated Decomposition (CAD) into the quadrupole collision cell. The ionic intermediates and products derived from protonated D-fructose dehydration were structurally characterized by their fragmentation patterns and the relative water loss dehydration energies measured by energy resolved CAD mass spectra. The data were compared with those obtained from protonated D-glucose decomposition in the same experimental conditions [1].
In the gas phase, D-fructose dehydration leads to the formation of a mixed population of isomeric [C6H6O3]H+ ions, whose structure do not correspond exclusively to 5-hydroxymethyl-2-furaldehyde protonated at the more basic aldehydic group.
The whole experimental data collected compared with the computational results reported in the literature allow the mechanism of D-fructose dehydration in the gas-phase to be hypothesized
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