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121.
A new nitrogenous bromophenol, colensolide A, is isolated from the New Zealand red alga Osmundaria colensoi together with the known bromophenol lanosol and four of its derivatives. In this study, a novel technique is employed to identify potentially new compounds in semi-purified mixtures containing a plethora of structurally similar, known metabolites, using NMR spectroscopy. The structure and relative configuration of colensolide A is determined using standard spectroscopic techniques. Several of the known bromophenols exhibit antibacterial activity and one shows moderate cytotoxicity. 相似文献
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124.
Andrew D. Turner Robert G. Hatfield Andy L. Powell Wendy Higman 《Analytical and bioanalytical chemistry》2010,397(2):743-749
Bivalve shellfish samples containing paralytic shellfish poisoning toxins were subjected to gamma irradiation dosage trials
in order to assess the potential suitability of the technique in the production of toxin reference materials. Two candidate
reference materials of tissue homogenates, mussels (Mytilus sp.) and native oysters (Ostrea edulis), were prepared in-house. Both were subjected to gamma irradiation at four different dose levels, 3.0, 6.0, 13.0 and 18.1 kGy.
Bacterial levels were shown to be eliminated in the mussels and significantly reduced in the oysters following irradiation
at all four dose levels. Paralytic shellfish poisoning (PSP) toxin concentrations were not significantly reduced in any of
the samples indicating the treatment had no adverse affect on the initial stability of any of the PSP toxins monitored. Chromatographic
results showed near-identical profiles for treated and non-treated samples inferring that no fluorescent toxin degradation
products or matrix interferences were produced during the irradiation process. Results therefore proved that gamma irradiation
treatment reduced bacterial levels within paralytic shellfish poisoning reference materials without compromising analyte content,
with the subsequent potential to enhance the stability of future candidate reference materials treated in this manner. 相似文献
125.
Trujillo WA Sorenson WR La Luzerne P Austad JW Sullivan D 《Journal of AOAC International》2006,89(4):942-959
The presence of aristolochic acid in some dietary supplements is a concern to regulators and consumers. A method has been developed, by initially using a reference method as a guide, during single laboratory validation (SLV) for the determination of aristolochic acid I, also known as aristolochic acid A, in botanical species and dietary supplements at concentrations of approximately 2 to 32 microg/g. Higher levels were determined by dilution to fit the standard curve. Through the SLV, the method was optimized for quantification by liquid chromatography with ultraviolet detection (LC-UV) and LC/mass spectrometry (MS) confirmation. The test samples were extracted with organic solvent and water, then injected on a reverse phase LC column. Quantification was achieved with linear regression using a laboratory automation system. The SLV study included systematically optimizing the LC-UV method with regard to test sample size, fine grinding of solids, and solvent extraction efficiency. These parameters were varied in increments (and in separate optimization studies), in order to ensure that each parameter was individually studied; the test results include corresponding tables of parameter variations. In addition, the chromatographic conditions were optimized with respect to injection volume and detection wavelength. Precision studies produced overall relative standard deviation values from 2.44 up to 8.26% for aristolochic acid I. Mean recoveries were between 100 and 103% at the 2 microg/g level, between 102 and 103% at the 10 microg/g level, and 104% at the 30 microg/g level. 相似文献
126.
127.
Zhang X Picariello W Hosein N Towle M Goetzinger W 《Journal of chromatography. A》2006,1119(1-2):147-155
In this paper we report a systematic recovery study based on reversed phase high performance liquid chromatography (RP-HPLC) separation and mass spectrometric (MS) based fractionation. Factors including a compound's physicochemical properties, column mass loading and presence of impurities were investigated through commercially available compounds. Results suggest that the delay time between MS peak detection and fraction collection, fraction detector's signal-to-noise ratio and compound's base peak width in the chromatogram have the biggest impacts on purification recovery. In an effort to assess sample recovery within our high throughput purification process, re-purification was performed on four compound libraries that were synthesized in-house. Reproducible recoveries (>80%) were achieved in all tests. 相似文献
128.
Using high-speed video, we have studied air bubbles detaching from an underwater nozzle. As a bubble distorts, it forms a thin neck which develops a singular shape as it pinches off. As in other singularities, the minimum neck radius scales with the time until the breakup. However, because the air-water interfacial tension does not drive the breakup, even small initial cylindrical asymmetries are preserved throughout the collapse. This novel, nonuniversal singularity retains a memory of the nozzle shape, size, and tilt angle. In the last stages, the air appears to tear instead of pinch. 相似文献
129.
Michelle Dunn Wendy Scott 《International Journal of Mathematical Education in Science & Technology》2018,49(1):31-45
First-year engineering students often struggle to see the relevance of theoretical mathematical concepts for their future studies and professional careers. This is an issue, as students who do not see relevance in fundamental parts of their studies may disengage from these parts and focus their efforts on other subjects they think will be more useful to them. In this study, we surveyed engineering students enrolled in a first-year mathematics subject on their perceptions of the relevance of the individual mathematical topics taught. Surveys were administered at the start of semester when some of these topics were unknown to them, and again at the end of semester when students had not only studied all these topics but also watched a set of animated videos. These videos had been produced by higher-year students to explain where they had seen applications of the mathematical concepts presented in the first year. We notice differences between the perceived relevance of topics for future study and for professional careers, with relevance to study rated higher than relevance to careers. We also find that the animations are seen as helpful in understanding the relevance of first-year mathematics. The majority of students indicated that lecturers with students as partners should work collaboratively to produce future videos. 相似文献
130.
Ysaías J. Alvarado Néstor Cubillán Esker Chacín-Molero Gladys Ferrer-Amado Paola Hernández-Labarca Wendy Velazco José Ojeda-Andara Yovani Marrero-Ponce Federico Arrieta 《Journal of solution chemistry》2010,39(2):277-290
The partial molar volumes of indole(Ind) at infinite dilution (V2¥V_{2}^{\infty}) in carbon tetrachloride (CCl4), acetonitrile (ACN) and tetrahydrofuran (THF) as solvents, were estimated from densitometry measurements at 293.15 K. The
results indicate that $V_{2}^{\infty}\mbox{(ACN)}>V_{2}^{\infty}\mbox{(CCl$V_{2}^{\infty}\mbox{(ACN)}>V_{2}^{\infty}\mbox{(CCl
$\approx V_{2}^{\infty}\mbox{(THF)}$\approx V_{2}^{\infty}\mbox{(THF)}. The values determined in this study are close to the values calculated from reported density for Ind in the solid state.
In order to make a comparison the partial molecular volume of benzimidazole (Bim) and benzothiophene (BT) in solvents with
appropriate solubility were measured too, and the results have revealed that $V_{2}^{\infty}\mbox{(BT)}>V_{2}^{\infty}\mbox{(Ind)}$V_{2}^{\infty}\mbox{(BT)}>V_{2}^{\infty}\mbox{(Ind)} in CCl4 and $V_{2}^{\infty}\mbox{(Ind)}>V_{2}^{\infty}\mbox{(Bim)}$V_{2}^{\infty}\mbox{(Ind)}>V_{2}^{\infty}\mbox{(Bim)} in THF. In this work the role of solvent reorganization around to solute cavity, and specific and nonspecific interactions
on the volumetric behavior of these molecules in solution are discussed using the Terasawa-Itsuki-Arakawa model, the Lee-Graziano
model, molar volumes of solutes calculated at the DFT-B3LYP/cc-pVTZ and aug-cc-pVTZ level in the gas phase and considering solvent presence with the Onsager’s reaction field, and the van der Waals
volume. This analysis suggests that the molecular volumes of solutes are overestimated by the quantum methods employed in
this work and that the volumetric contribution from the van der Waals components to the limiting partial molecular volumes
of solutes is important, with the exception of Ind in CCl4 where the solvent reorganization is the dominant factor. 相似文献