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1.
Tiffany D. Andras Troy S. Alexander Asiri Gahlena R. Mitchell Parry Facundo M. Fernandez Julia Kubanek May D. Wang Mark E. Hay 《Journal of chemical ecology》2012,38(10):1203-1214
Coral reefs are in global decline, with seaweeds increasing as corals decrease. Although seaweeds inhibit coral growth, recruitment, and survivorship, the mechanism of these interactions is poorly understood. Here, we used field experiments to show that contact with four common seaweeds induces bleaching on natural colonies of Porites rus. Controls in contact with inert, plastic mimics of seaweeds did not bleach, suggesting seaweed effects resulted from allelopathy rather than shading, abrasion, or physical contact. Bioassay-guided fractionation of the hydrophobic extract from the red alga Phacelocarpus neurymenioides revealed a previously characterized antibacterial metabolite, neurymenolide A, as the main allelopathic agent. For allelopathy of lipid-soluble metabolites to be effective, the compounds would need to be deployed on algal surfaces where they could transfer to corals on contact. We used desorption electrospray ionization mass spectrometry (DESI-MS) to visualize and quantify neurymenolide A on the surface of P. neurymenioides, and we found the molecule on all surfaces analyzed, with highest concentrations on basal portions of blades. 相似文献
2.
Santiago A. Pighin Bruno Coco Horacio Troiani Facundo J. Castro Guillermina Urretavizcaya 《International Journal of Hydrogen Energy》2018,43(15):7430-7439
This paper presents a comparative study of H2 absorption and desorption in MgH2 milled with NbF5 or NbH0.9. The addition of NbF5 or NbH0.9 greatly improves hydriding and dehydriding kinetics. After 80 h of milling the mixture of MgH2 with 7 mol.% of NbF5 absorbs 60% of its hydrogen capacity at 250 °C in 30 s, whereas the mixture with 7 mol.% of NbH0.9 takes up 48%, and MgH2 milled without additive only absorbs 2%. At the same temperature, hydrogen desorption in the mixture with NbF5 finishes in 10 min, whereas the mixture with NbH0.9 only desorbs 50% of its hydrogen content, and MgH2 without additive practically does not releases hydrogen. The kinetic improvement is attributed to NbH0.9, a phase observed in the hydrogen cycled MgH2 + NbF5 and MgH2 + NbH0.9 materials, either hydrided or dehydrided. The better kinetic performance of the NbF5-added material is attributed to the combination of smaller size and enhanced distribution of NbH0.9 with more favorable microstructural characteristics. The addition of NbF5 also produces the formation of Mg(HxF1-x)2 solid solutions that limit the practically achievable hydrogen storage capacity of the material. These undesired effects are discussed. 相似文献
3.
Surface-induced dissociation (SID) has been implemented in a matrix-assisted laser desorption/ionization time-of-flight mass spectrometer (MALDI TOF MS), allowing production of tandem mass spectrometric information for peptide ions (MALDI TOF SID TOF). The instrument retains the standard operational modes such as the reflectron monitoring of the MALDI-generated intact ions and postsource decay. We show through ion trajectory simulations and experimental results that implementing SID in a commercial MALDI TOF spectrometer is feasible and that the SID products in this instrument fall in an observation time frame that allows the specific detection of fast-fragmentation channels. The instrument design, pulse timing sequence, and high-voltage electronics together with SID spectra of MALDI-generated peptide ions are presented. Standard peptides such as YGGFLR, angiotensin III, fibrinopeptide A, and des-Arg1-bradykinin were dissociated by means of hyperthermal collisions with a gold surface coated with a self-assembled monolayer of 2-(perfluorodecyl)ethanethiol. With the extraction fields and the short observation times used, the spectra obtained show intense low-mass ion signals such as immonium, b2, b3, and y2 ions. TOF data analysis involved matching simulated and experimental flight times and indicates that the observed fragments are produced at approximately 250 ns after the precursor ion collides with the surface. This submicrosecond gas-phase fragmentation time frame is complementary to the observation time frame of existing SID spectrometers, which are on the order of 10 micros for tandem quadrupoles and are larger than a few milliseconds for SID implemented in Fourier transform ion cyclotron resonance spectrometers. 相似文献
4.
We report the synthesis of superparamagnetic nanoparticles of iron oxide in magnetite phase with diameters of approximately 15 nm. Nanoparticles of magnetite were synthesized by forced hydrolysis method, controlling the oxidation with a nitrogen atmosphere during the synthesis. Nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Mössbauer spectroscopy and vibrating sample magnetometry. Quantitative analysis of crystalline phases was done by performing Rietveld refinement of the XRD profiles. In order to obtain nanometers sizes of magnetite phase solely, the parameters of formation such a pH and molar concentration were analyzed and determined by an equilibrium thermodynamics model with the chemical computer code MINTEQA [Allison Geoscience Consultants, Inc., HydroGeoLogic, Inc., MINTEQA2 for Windows, Equilibrium Speciation Model. Ver 1.5(2003)]. 相似文献
5.
6.
Daniela Domanski Guillermina Urretavizcaya Facundo J. Castro Fabiana C. Gennari 《Journal of the American Ceramic Society》2004,87(11):2020-2024
MgAl2 O4 spinel was successfully synthesized using a mechanochemical route that avoided the formation and calcination of its precursors at high temperatures. The method involved a single step in which γ-Al2 O3 –MgO, AlO(OH)–MgO, and α-Al2 O3 –MgO mixtures were milled at room temperature under air atmosphere. The formation of MgAl2 O4 occurred faster with γ-Al2 O3 than with AlO(OH) or α-Al2 O3 . After 140 h, the mechanochemical treatment of the γ-Al2 O3 –MgO mixture yielded 99% of MgAl2 O4 . 相似文献
7.
Desorption electrospray ionization mass spectrometry (DESI MS) is rapidly becoming accepted as a powerful surface characterization tool for a wide variety of samples in the open air. Besides its well-established high-throughput capabilities, a unique feature of DESI is that chemical reactions between the charged spray microdroplets and surface molecules can be exploited to enhance ionization. Here, we present a rapid screening assay for artesunate antimalarials based on reactive DESI. Artesunate is a vital therapy for Plasmodium falciparum malaria, but artesunate tablets have been counterfeited on a very large scale in SE Asia, and more recently in Africa. For this reason, faster and more sensitive screening tests are urgently needed. The proposed DESI assay is based on the formation of stable noncovalent complexes between linear alkylamines dissolved in the DESI spray solution and artesunate molecules exposed on the tablet surface. We found that, depending on amine type and concentration, a sensitivity gain of up to 170x can be obtained, in comparison to reagent-less DESI. Hexylamine (Hex), dodecylamine (DDA), and octadecylamine (ODA) produced proton-bound noncovalent complexes with gas-phase stabilities, increasing in the order [M + Hex + H]+ < [M + DDA + H]+ < [M + ODA + H]+. Tandem MS experiments revealed that complex formation occurred by hydrogen bonding between the amine nitrogen and the ether-like moieties within the artesunate lactone ring. After the reactive DESI assay was fully characterized, it was applied to a set of recently collected suspicious artesunate tablets purchased in shops and pharmacies in SE Asia. Not only did we find that these samples were counterfeits, but we also detected the presence of several wrong active ingredients. Of particular concern was the positive detection of artesunate traces in the surface of one of the samples, which we quantified with standard chromatographic techniques. 相似文献
8.
Granero D Pérez-Calatayud J Ballester F Bos AJ Venselaar J 《Radiation protection dosimetry》2006,118(1):11-15
The characteristics of the radionuclides (170)Tm and (169)Yb are highly interesting for their use as high dose-rate brachytherapy sources. The introduction of brachytherapy equipment containing these sources will lead to smaller required thicknesses of the materials used in radiation protection barriers compared with the use of conventional sources such as (192)Ir and (137)Cs. The purpose of this study is to determine the required thicknesses of protection material for the design of the protecting walls. Using the Monte Carlo method, transmission data were derived for broad-beam geometries through lead and concrete barriers, from which the first half value layer and tenth value layer are obtained. In addition, the dose reduction in a simulated patient was studied to determine whether transmission in the patient is a relevant factor in radiation protection calculations. 相似文献
9.
Enhanced direct ambient analysis by differential mobility-filtered desorption electrospray ionization-mass spectrometry 总被引:1,自引:0,他引:1
Desorption electrospray ionization (DESI) is rapidly becoming established as one of the most powerful ionization techniques allowing direct surface analysis by mass spectrometry (MS) in the ambient environment. DESI provides a significant number of unique analytical capabilities for a broad range of applications, both quantitative and qualitative in nature including biological tissue imaging, pharmaceutical quality control, in vivo analysis, proteomics, metabolomics, forensics, and explosives detection. Despite its growing adoption as a powerful high throughput analysis tool, DESI-MS analysis at trace levels often suffers from background chemical interferences generated during the electrospray ionization processes. In order to improve sensitivity and selectivity, a differential mobility (DM) ion separation cell was successfully interfaced to a custom-built DESI ion source. This new hybrid platform can be operated in two modes: the "DM-off" mode for standard DESI analysis and "DM-on mode" where DESI-generated ions are detected after discrimination by the differential mobility cell. The performance of the DESI-DM-MS platform was tested with several samples typically amenable to DESI analysis, including counterfeit pharmaceuticals and binary mixtures of isobaric chemicals of importance in the pharmaceutical and food industries. In the DM-on mode, DESI-MS signal-to-noise ratios were improved by 70-190% when compared to the DM-off mode. Also, the addition of the DM cell enabled selective in-source ion activation of specific DESI-generated precursor ions, providing tandem MS-like spectra in a single stage mass spectrometer. 相似文献
10.
Facundo Bigne María C. Puppo Cristina Ferrero 《International Journal of Food Properties》2016,19(2):243-256
Rheological behavior and microstructural characteristics of composite dough with wheat and mesquite flours (from Prosopis alba) were analyzed by response surface methodology. A central composite design was applied varying proportions of water (50 to 80 g each 100 g wheat flour) and mesquite flour (0 to 70 each 100 g wheat flour). Texture profile analysis showed that increasing the amount of mesquite flour and decreasing the amount of water led to less cohesive and more resilient doughs. Stress relaxation curves were fitted with a Maxwell model and relaxation times were obtained. These parameters resulted higher for those formulations low in mesquite content and high water levels. Composite dough showed a typical viscoelastic behavior with higher elastic moduli (G’) when mesquite flour ratio in the mixture was increased. 1H-RMN T2 relaxation assays revealed higher mobility in samples with high amounts of water and minimum level of mesquite. A farinograph was adequate to obtain optimum water amounts and showed that addition of mesquite led to less stable dough respect to control wheat dough. By using confocal laser scanning microscopy with fluorescent probes rhodamine B and fluoresceine isothiocyanate, a poor gluten network development or protein aggregation was observed when water contents were far from optimum. 相似文献