1,721,086 research outputs found
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
Antibacterial Activity of Amino Acid-Modified Cationic Dendrimers Loaded with a Mixture of Two Triterpenoid Acids
No full textSearching for new devices capable to counteract the growing bacterial resistance, we
reported the remarkable antimicrobial activity against several Gram-negative species of cationic dendrimers (CD), modified with lysine and histidine, also establishing that their cationic character, due to the lysine content, is essential for their potency. To develop new antibacterial agents, possibly active against Gram-positive species, cationic dendrimer complexes containing arginine and lysine, and trapping ursolic and oleanolic acids (UOACDs), two natural triterpenoids known for their activity against Gram-positive bacteria, were considered here as excellent candidates. Three selected UOACDs were tested unsuccessfully against Gram-negative strains, but successfully against 12 Gram-positive clinical isolates. The preliminary results obtained, in terms of MIC values, established
that the antibacterial activity observed for UOACDs strongly depended on the number of cationic groups and the type of peripheral amino acids present in the CDs, and was attributable only to CDs and not to the presence and release of UOA. Lysine was critical for potency, while arginine redirected activity against Gram-positive species. A high cationic character, associated with the balanced content of lysine/arginine, produced a remarkable antimicrobial effect (MIC = 0.5–8.7 μM). More indepth investigations are underway to better characterize the activity of the developed arginine-containing CDs
Water-soluble Polyester-based Amino Acids-modified Dendrimers loaded with Ursolic and Oleanolic Acids as promising Prodrugs suitable for Intravenous Administration
No full textDendrimers, macromolecules characterized by high controlled size, shape and architecture, presence of inner cavities able to accommodate small molecules and many peripheral functional groups, are of eminent interest for biomedical applications, including gene transfection, tissue engineering, imaging, drug delivery.[1] The well-known pharmacological activities of Ursolic and Oleanolic acids[2] are limited by low water solubility, non-specific cells distribution, poor bioavailability and pharmacokinetics. Thus, the research for new formulations of UA and OA that overcome such drawbacks is very extensive. The strategy most applied concerns the use of carriers, such as liposomes or PAMAM dendrimers which are among the most investigated vectors because endowed with very efficient transfection and delivery activities but also with remarkable cytotoxicity. In this work we described the physical incorporation of the two triterpene acids extracted from Salvia Corrugata inside amino acids-modified polyester-based dendrimers.[3,4] IR, NMR, zeta potential, mean size of particles and buffer capacity of prepared materials were reported.
Figure 1. An eye-catching representation of the prepared complexes
The achieved water soluble complexes harmonize a polycationic character and a buffer capacity which presuppose efficient cells penetration and increased residence time with a biodegradable scaffold thus appearing as a promising team of new non-toxic prodrugs for safe intravenous administration of Ursolic and Oleanolic acids (Figure 1).
[1] S. N. Goonewardena, J. D. Kratz, H. Zong, A. M. Desai, S. Tang, S. Emery, J. R. Jr. Baker, B. Huang, Design considerations for PAMAM dendrimer therapeutics, Biorg. Med. Chem. lett., 23, 2872 (2013).
[2] J. Liu, Pharmacology of oleanolic acid and ursolic acid, J. Ethnopharmacol., 49, 57 (1995).
[3] S. Alfei, S. Castellaro, Synthesis and Characterization of Polyester-Based Dendrimers Containing Peripheral Arginine or Mixed Amino Acids as Potential Vectors for Gene and Drug Delivery, Macromol. Res., DOI 10.1007/s13233-017-5160-3 (2017).
[4] S. Alfei, S. Castellaro, G. B. Taptue, Synthesis and NMR characterization of dendrimers based on 2, 2-bis-(hydroxymethyl)-propanoic acid (bis-HMPA) containing peripheral amino acid residues for gene transfection, Org. Commun., 10, 144 (2017)
Synthesis of a new dendritic anfiphilic polyester with pentaerythritol core and a multifunctional periphery for linking amino acids and for using in gene therapy
No full textDendrimers are synthetic polymers characterized by tree-like branched symmetric structure, globular
shape, low polydispersity and several functions at the periphery which allow further functionalization.
Their cavities can accommodate small drugs molecules protecting them from premature degradation,
increasing their solubility in biological fluids, decreasing their toxicity and favoring their
bioavailability. Dendrimers containing protonable nitrogen atoms can electrostatically bind nucleic
acids. These reasons make dendrimers appealing materials for various biomedical applications such
as drug or gene delivery non viral carriers, biosensors, bioimaging agents and theranostics. Well
known polymeric systems such as bPEI or PAMAM are among the most investigated synthetic
vectors with efficient transfection activity but also affected by high cytotoxicity so chemical
modifications are required to reduce these drawbacks and allow a real use in gene therapy. It is known
that amino acids (1, 2, 3) or peptides (4) were often used for these purposes and arginine is known to
improve siRNA cellular uptake (5), efficiency of transfection and to reduce toxicity (6, 7).
Hydrophobic segments in the dendrimer structure are also important in the internalization process (3)
and may contribute to reduce toxicity caused by high ionic character of vectors. Looking at this
background in this communication we report the step-wise protocol and NMR characterization of a
new hydrolysable polyester-based dendrimer of third generation built on penthaerithritol as core and
with a C-18 saturated alkyl chain as hydrophobic segment.
The peripheral 24 OH groups make this anfiphilic dendritic structure fit to the esterification with
selected amino acids for obtaining polycationic non viral vectors to use in gene delivery.
References: 1. Navath, R. S.; Menjoge, A. R.; Wang, B.; Romero, R.; Kannan, S.; Kannan, R. M. Biomacromolecules
2010, 11, 1544-1536. 2. Park, J.; Park, H.; Park, J-S.; Choi, J. S. Macromol. Res. 2014, 22, 500-508. 3. Wang, F.; Wang,
Y.; Wang, H.; Shao, N.; Chen, Y.; Cheng, Y. Biomaterials 2014, 35, 9187-9198. 4. Lam, S. J.; Sulistio, A.; Ladewig, K.;
Wong, E. H. H.; Blencowe, A.; Qiao, G. G. Austr. J. Chem. 2014, 67, 592-597. 5. Liu, X.; Liu, C.; Zhou, J.; Chen, C.;
Qu, F.; Rossi, J. J.; Rocchi, P.; Peng L. Nanoscale 2015, 7, 3867-3875. 6. Kim, T.; Bai, C. Z.; Nam, K.; Park, J. J. Control.
Release 2009, 136, 132-139. 7. Peng, Q.; Zhu, J.; Yu, Y.; Hoffman, L.; Yang, X. J. Biomater. Sci. Polym. Ed. 2015, 26, 1163-117
Synthesis and Characterization of Polystyrene-Based Cationic Hydrogels Enriched with Antibacterial Pyrazoles
No full textHere, two new topical hydrogel formulations (R1HG-3c and R1HG-4b), promising to treat staphylococcal skin infections, have been developed. To this end, two pyrazoles (3c and 4b) previously reported to possess antibacterial activity against multi drug resistant (MDR) staphylococci, were used as active ingredients, while a polystyrene-based cationic resin (R1) was employed as gelling agent. Particularly, we synthesized and characterized R1, which showed high hydrophilicity, high-level porosity, excellent swelling capabilities, and aptitude to form hydrogel by simple dispersion in water, thus allowing to formulate 3c and 4b as hydrogels, without using any further additive. The obtained R1HG-3c and R1HG-4b showed high equilibrium degrees of swelling (EDS) of 765% and 675%, as well as great equilibrium water contents (EWC) of 88% and 87%, respectively. Chemometric-assisted attenuated total reflectance (ATR) Fourier transform infrared (FTIR) analyses, as well as optical and scanning electronic microscopy were employed to investigate the chemical structure and morphology of both soaked and dried hydrogels. Weight loss studies helped in assessing the water release profiles of hydrogels, whose stability over 4 months was inspected by monitoring their inversion properties and by chemometric-assisted ATR-FTIR spectroscopy. By proper experiments, including amplitude and frequency sweep studies, the flow and dynamic rheological behaviour of the gels was evaluated. Finally, their content in NH3+ groups deriving from R1, and known to promote the antibacterial effects, was determined by potentiometric titrations. Collectively, the favourable physicochemical characteristic of R1HG-3c and R1HG-4b, as well as the demonstrated antibacterial effects of their ingredients (3c and 4b) against MDR staphylococci, possibly further improved by the cationic R1, support the future development of our pyrazole-enriched hydrogels as new weapons to treat severe skin and wound infections sustained by MDR bacteria of Staphylococcus genus
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