262,200 research outputs found
Deposition of Supercoiled DNA on Mica for Scanning Force Microscopy Imaging
No full textThe deposition of DNA molecules on mica is driven and controlled by the ionic densities around DNA and close to the surface of the substrate. Dramatic improvements in the efficiency and reproducibility of DNA depositions were due to the introduction of divalent cations in the deposition solutions. The ionic distributions on DNA and on mica determine the mobility of adsorbed DNA molecules, thus letting them assume thermodynamically equilibrated conformations, or alternatively trapping them in non-equilibrated conformations upon adsorption.
With these prerequisites, mica does not seem like an inert substrate for DNA deposition for microscopy, and its properties greatly affect the efficiency of DNA deposition and the appearance of the molecules on the substrate. In our laboratory, we have some preliminary evidence that mica could also participate in DNA damage, most likely through its heavy metal impurities
Conformational fluctuations of supercoiled DNA molecules observed in real time with a scanning forcemicroscope
No full textA scanning force microscope operating in a fluid was used to image the dynamics of supercoiled circular DNA molecules adsorbed on mica both under water and buffer. The time scales of the conformational equilibrations of molecules adsorbed on mica are controlled by frictional forces: these are modulated by the strength of adsorption that opposes the molecular mobility. We employ a method that permits the modulation of the adhesion, even to the point of completely immobilizing the molecules on the substrate and afterwards remobilizing them at will, so that their conformational fluctuations can start again. Thismethod was applied to the imaging of the conformational rearrangements that take place in native supercoiled DNA molecules. The motions that were captured in the images could be interpreted in terms of supercoiling tensions that fluctuate locally. © 1998 Springer-Verlag
Molecularly Imprinted solid phase extraction for detection of sudan I in food
No full textSudan I is a synthetic azoic dye employed as an additive in foods, and in particularly in those containing chilli powders, because
of his intense red–orange colour. Now European Community does not allow ‘‘Sudan I’’ as an additive in foods because of its demonstrated
cancerogenity.
Several methods were developed to detect the presence of this compound (HPLC, GC/MS). However when ‘‘Sudan I’’ is mixed
just in traces in foods, very expensive instruments are necessary (LC/MS/MS) to reveal it.
This study describes the synthesis of a molecularly imprinted polymers (MIPs) for solid phase extraction (MISPE) using Sudan I
as template. This procedure allows to concentrate this compound in order to make it detectable by HPLC. Furthermore we investigated
the ability of these MISPE cartridges to absorb selectively Sudan I from food matrices. Considerable differences in the interaction
with ‘‘Sudan I’’ were observed when MIPs were used as stationary phase in SPE compared with the non imprinted polymers
(NIPs)
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
ANALYSIS BY HPLC-MS/MS OF BIOPHENOLIC COMPONENTS IN OLIVE AND OILS
No full textThe aim of this work was to analyze by HPLC-MS-MS natural biophenolic compds. in complex natural samples like olives and olive oils. Eleven benzoic and cinnamic acids, vanillin and other 8 biophenolic compds. were studied by liq. chromatog.-atm. pressure ionization mass spectrometry/mass spectrometry with a Turbo Ion source in the neg. mode. To confirm the specific presence, with great sensitivity, of such compds. in olive samples, in brine samples and in extra virgin olive oil the fragmentation of precursor ions into the product species acquisition was used in Multiple Reaction Monitoring (MRM) mode
N,N’-hexadecanoyl-l-2-diaminomethyl-18-crown-6 Surfactant: Synthesis and Aggregation Properties in Aqueous Solutions.
No full textbolaform-surfactant, self-diffusion, crown ethers, drug carrier
Protecting Animals 36: Author Witi Ihimaera
No full textIn this very special episode of Knowing Animals I am joined by beloved New Zealand author Witi Ihimaera. Witi has written many books featuring nonhuman animals. He offers us a non-colonial lens through which to think about the human/nonhuman relationship
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