1,720,969 research outputs found
Reversible aggregation/deaggregation of gold nanoparticles induced by a cleavable dithiol linker
No full textAqueous solutions of Au colloids (12 +/- 4 nm size) when treated with a blend of mono- and dithiols aggregate forming stable clusters, as evidenced by the shift of their surface plasmon (SP) band from 512 to ca. 600 nm. The presence of carboxylate ester functions on the dithiol allows its cleavage by addition of a cleaving agent, such as hydrazine. The cleavage process results in the breaking down of the clusters of nanoparticles and the shift of the SP band back to lower wavelengths. Further addition of dithiol causes the formation of the clusters again. The aggregation/deaggregation process may be monitored visually by following the color change from pink-red to purple and vice versa in the forward and backward steps, respectively
Reversible aggregation/deaggregation of gold nanoparticles induced by a cleavable dithiol linker
No full textGold nanoparticles-based protease assay
No full textWe describe here a simple assay that allows the visual detection of a protease. The method takes advantage of the high molar absorptivity of the plasmon band of gold colloids and is based on the color change of their solution when treated with dithiols. We used C- and N-terminal cysteinyl derivatives of a peptide substrate exploiting its selective recognition and cleavage by a specific protease. Contrary to the native ones, cleaved peptides are unable to induce nanoparticles aggregation; hence, the color of the solution does not change. The detection of two proteases is reported: thrombin (involved in blood coagulation and thrombosis) and lethal factor (an enzyme component of the toxin produced by Bacillus anthracis). The sensitivity of this nanoparticle-based assay is in the low nanomolar range
Hyaluronic acid auto-crosslinked polymer (ACP): Reaction monitoring, process investigation and hyaluronidase stability
No full textHyaluronic Acid (HA) is a non-sulphated glycosaminoglycan that, despite its high molecular weight, is soluble in water and is not resistant to enzymatic degradation, the latter of which hinders its wider application as a biomedical material. Auto-crosslinked polymer (ACP) gels of HA are fully biocompatible hydrogels that exhibit improved viscoelastic properties and prolonged in vivo residence times compared to the native polymer. Crosslinking is achieved through a base-catalysed reaction consisting of the activation of HA carboxyl groups by 2-chloro-1-methylpyridinium iodide (CMPI) and subsequent nucleophilic acyl substitution by the hydroxyl groups of HA in organic solvent. In this study, a number of ACP hydrogels have been obtained via reactions using varying ratios of CMPI to HA. The crosslinking reaction was monitored by rheological measurements in organic solvents during CMPI addition to the reaction mixture. The ACP intermediates, powders and hydrogels were characterized, helping to elucidate the crosslinking process. A two-step mechanism was proposed to explain the observed trends in viscosity and particle size. Syntheses were carried out by varying the reaction temperature, respectively at 0 °C, 25 °C and 45 °C in N-Methyl-2-Pyrrolidone (NMP), as well as the solvent respectively in NMP, DMSO and DMF at 25 °C. Interestingly, varying these parameters did not substantially affect the degree of crosslinking but likely did influence the intra/inter-molecular crosslinking ratio and, therefore, the viscoelastic properties. A wide range of crosslinking densities was confirmed through ESEM analysis. Finally, a comparative hyaluronidase degradation assay revealed that the ACPs exhibited a higher resistance toward enzymatic cleavage at low elastic modulus compared to other more chemically resistant, crosslinked HAs. These observations demonstrated the importance of crosslinking density of matrix structures on substrate availability
Fully symmetrical functionalization of multivalent scaffold molecules on solid support
No full textA new methodology for the functionalization of scaffold molecules on solid support is described, which does not require (partial) protection of the scaffold or a special functional group arrangement on it, while maintaining scaffold symmetry in the final product. As an illustration of the versatility of this approach, three scaffold molecules (1,3,5-tris(aminomethyl)-2,4,6-triethylbenzene, tris(2-aminoethyl)amine, and triazacyclononane) were functionalized with different functional groups in a moderate to high yield and purity. The developed protocol is a valuable tool for an easy access to multivalent molecules. (c) 2006 Elsevier Ltd. All rights reserve
Functionalization of tripodal scaffold molecules on solid support
No full textA versatile synthetic approach is described for the functionalization of tripodal scaffold molecules on solid support. Intrinsic problems related to the attachment of tripodal scaffolds to a resin (for example mono- vs. polyadducts and intramolecular cyclizations) are studied and solutions are provided. The synthetic approach relies on the use of specific protecting groups in the critical steps of the synthesis. Importantly, however, protecting groups on the scaffold molecule are never used, which significantly facilitates scaffold variation, for instance in combinatorial studies. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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