1,720,976 research outputs found
Synthesis and characterization of fluorescent PAMAM dendrimer modified with 1,8-naphthalimide units and its Cu(II) complex designed for specific biomedical application
No full textA new fluorescent dendrimer was obtained by modifying the periphery of a PAMAM dendrimer from zero generation. The modification involves substitution at the C-4 position with 1,8-naphthalimide units containing N-methylpiperazine and the addition of Cu(II) ions forming the metallodendrimer [Cu2(D)(NO3)2]. The dendrimer ligand and metallodendrimer were subjected to UV-vis, fluorescence spectroscopy, FT-IR, NMR, and SEM investigations to define their precise structure. The photophysical characteristics of the yellow-green fluorescent dendrimer were studied in organic solvents of different polarity. Results show that polar solvents favour a photoinduced electron transfer (PET) process. Experiments on the effect of pH in an ethanol - water solution (1:4 v/v) revealed the fluorescence of the dendrimer to be more than seventeen times higher than that in an acidic medium. Electron paramagnetic resonance (EPR) studies were performed to characterize the complexing ability of the dendrimer towards Cu(II) by varying the [Cu(II)/dendrimer external sites] molar ratio in DMSO solution. The EPR results suggest that Cu(II) formed a Cu-N2O2 square-planar coordination with nitrogen sites (N-CH3 sites of 1,8-methylpiperazine, and amine and amide groups) at the dendrimer internal/external interface, and 2 solvent molecules. The Cu(II) complex was characterized by restricted mobility conditions. Copper (II) ions were distributed between the dendrimer interface and the external surface; saturation of the nitrogen sites at the interface occurred at a 1:2 M ratio between Cu(II) and methylpiperazine units. These results are useful in view of the use of this metallodendrimer as anticancer and antimicrobial drugs. The antimicrobial activity of dendrimer ligand and its Cu(II) complex was tested against several model strains bacteria and yeasts in agar, in liquid medium, and after their deposition onto a cotton fabric. The results showed good antibacterial effect of dendrimer ligand, which was enhanced by its Cu(II) complexation
Fluorescent Hyperbranched Polymers and Cotton Fabrics Treated with Them as Innovative Agents for Antimicrobial Photodynamic Therapy and Self-Disinfecting Textiles
No full textThe results of this study, which involved treating cotton fabrics with three fluorescent hyperbranched polymers modified with 1,8-naphthalamide (P1), acridine (P2), and dansyl (P3) groups, could have applications in the development of antimicrobial textiles with self-disinfecting ability. The polymers, dissolved in DMF/water solution, were deposited on the cotton fabric using the exhaustion method. The fabrics were thoroughly analyzed by reflection spectra, CIEL*a*b* coordinates, and color difference (∆E). The release of the polymers from the cotton surface was studied in a phosphate buffer with pH = 7.4 and an acetate buffer with pH = 4.5 at 37 °C for 10 h. It is shown that at pH = 7.4, the release of the three polymers occurs slowly (about 4–5%). In contrast, in an acidic medium, due to protonation of the tertiary amino group of 1,8-naphthalimide, P1 passes significantly more readily into the aqueous solution (35%). The possibility of singlet oxygen (1O2) generation by the polymers and the cotton fabrics treated with them under sunlight irradiation was followed using an iodometric method. The microbiological activity was investigated against Gram-positive Bacillus cereus and Gram-negative Pseudomonas aeruginosa as model bacterial strains in the dark and after irradiation with sunlight. The antimicrobial activity of the polymers increased after light irradiation, as 1O2 attacks and destroys the bacterial cell membrane. Scanning electron microscopy showed that a stable bacterial biofilm had formed on the untreated cotton surface, but treatment with hyperbranched polymers prevented its formation. However, many bacteria were still observed on the fiber surface when the microbial test was performed in the dark, whereas only a few single bacteria were noticed after the illumination. A virucidal effect against respiratory viruses HRSV-2 and AAdV-5 was observed only after irradiation with sunlight.This study was financed by the European Union Next Generation EU through the National Recovery and Resilience Plan of the Republic of Bulgaria, project № BG-RRP-2.004-0008, and the European Union’s NextGenerationEU package through the National Recovery and Resilience Plan of the Republic of Bulgaria, project № BG-RRP-2.004-0002, and the “BiOrgaMCT” of the European Union (NextGenerationEU) through the CSIC Interdisciplinary Thematic Platform Salud Global+ (PTI-SALUDGLOBAL+).Peer reviewe
Аntimicrobial and anticancer activity of new poly(propyleneamine) metallodendrimers
No full textThe synthesis, EPR characterisation and biological
evaluation of two new metallodendrimers, i.e. a
poly(propyleneamine) dendrimer functionalized at the external
surface with 4-bromo-1,8-naphthalimide and conjugated
with Cu(II) and Zn(II), was performed with the aimto evaluate
their antimicrobial and anticancer activity. The antimicrobial
activity was investigated in meat-peptone broth against bacteria
B. subtilis and P. aeruginosa, and the yeast C. lipolytica.
The results showed that the compounds inhibited effectively
the tested pathogens even after their deposition on a textile
fabric. Anticancer activity was investigated against three human
permanent cell lines from non-small cell lung cancer
(A549), triple negative breast cancer (MDA-MB-231) and
carcinoma of the uterine cervix (HeLa) in the c = 0.01–
30 μM concentration range. The results suggest that these
compounds are promising for application in biomedicine as
anticancer drugs in the design of new effective preparations.
The antimicrobial and anticancer activity may be related to the
peculiar structural and dynamical properties revealed for the
Cu(II) complexes, by a computer aided analysis of the electron
paramagnetic resonance (EPR) spectra. This analysis indicated
the formation, at the lowest Cu(II) concentrations, of a
flexible rhombic Cu-N4 coordination with the internal amino
groups of the dendrimer, which transformed into a Cu2-N4
coordination already at 0.25 equiv. of Cu(II)
Photophysical investigations on the sensor potential of novel, poly(propylenamine) dendrimers modified with 1,8-naphthalimide units
No full textGrabchev, Ivo Staneva, Desislava Chovelon, Jean-MarcNovel poly(propylenamine) first and second generation dendrimers in which the periphery was modified with 1,8-naphthalimide units were synthesized. Acetonitrile solutions of the materials were subjected to photophysical investigation to evaluate their capability to detect metal cations, by monitoring changes in their absorption and fluorescence spectra in the presence of Ag+, Cu2+, Co2+, Ni2+, Fe3+ and Zn2+. The potential of the dendrimers to detect metal ion pollutants was estimated. (C) 2009 Elsevier Ltd. All rights reserved
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
Chromatin organisation and transcription regulation in Trypanosoma brucei
Full text linkIn eukaryotic nuclei, DNA is packaged into chromatin by association with histone proteins.
Specific histone post-translational modifications result in the formation of transcriptionally
active and silent chromatin domains. The aim of this project was to characterise chromatin
organisation and assess the role of transcription regulation in Trypanosoma brucei, the
causative agent of sleeping sickness in Africa. The approach taken was endogenous
fluorescent tagging of putative readers, writers and erasers of histone modifications in T.
brucei and subsequent use of the tags to localise the candidate proteins in the cell and to
identify their genomic associations and protein interaction networks. Chromatin
immunoprecipitation followed by sequencing showed that many of the nuclear proteins
associate with RNAPII transcription start regions (TSRs). Whereas most proteins were
enriched broadly over those regions, Chromo1 and SET27 displayed sharp overlapping peak
profiles. Moreover, co-immunoprecipitation and mass spectrometry revealed that Chromo1
and SET27 are likely part of the same complex together with four uncharacterised proteins
and JBP2, an enzyme involved in the synthesis of the DNA modification base J. Overall, this
work provides the basis for investigating the role of chromatin factors in trypanosome
transcription regulation
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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