1,720,963 research outputs found
SELF-ASSEMBLY DEI PEPTIDI ETEROCHIRALI IN IDROGEL ANTIMICROBICI
No full textIn questo progetto è stata fatta la sintesi, purificazione e caratterizzazione del tripeptide riportato in letteratura DLeu-LPhe-LPhe e di una serie di nuovi analoghi idrofobici per identificare nuove sequenze con migliore attività antimicrobica, ma anche capaci di formare idrogel supramolecolari. Ogni peptide è stato testato sia in soluzione che come idrogel su colture di E. coli per iniziare a delineare una correlazione tra struttura e attività ed ottenere i primi elementi verso la delucidazione del meccanismo d’azione.
L’attività antimicrobica di DLeu-LPhe-LPhe è stata confermata ed è stata anche riscontrata nel caso del suo enantiomero LLeu-DPhe-DPhe, suggerendo un meccanismo d’azione non mediato da recettore. Tuttavia, l’attività riscontrata risulta molto inferiore rispetto a quella riportata in letteratura. Ciò nonostante, sono state identificate nuove sequenze capaci di autoassemblarsi e formare idrogel, di cui alcuni con proprietà antimicrobiche paragonabili a DLeu-LPhe-LPhe. Da sottolineare che l’attività antimicrobica è stata osservata solo per gli idrogel, e non in soluzione, indicando l’importanza delle strutture supramolecolari per l'attività antimicrobica.This research project focussed on the synthesis, purification, and characterisation of the reported tripeptide DLeu-LPhe-LPhe and a series of analogous short, hydrophobic peptides with the aim of identifying novel sequences with improved antimicrobial activity and possibly also self-assembly ability towards antimicrobial hydrogel biomaterials. Each peptide antimicrobial activity was also evaluated in solution- and gel-based assays on E.coli cultures, with the aim of drawing the first structure-activity correlations and gain the first insights into the potential mechanism of action.
The antimicrobial activity of DLeu-LPhe-LPhe was confirmed and found also for its enantiomer LLeu-DPhe-DPhe, suggesting a mechanism of action that is not mediated by a receptor. However, the antimicrobial activity observed in this work was significantly minor than that reported in the literature.3 Nevertheless, this work led to the identification of new, self-assembling sequences, including examples with comparable antimicrobial activity to DLeu-LPhe-LPhe. Interestingly, such an activity was detected only in the hydrogel-state, and not in solution, indicating a key role played by the supramolecular structures
Tripeptide Self-Assembly into Bioactive Hydrogels: Effects of Terminus Modification on Biocatalysis
Full text linkBioactive hydrogels based on the self-assembly of tripeptides have attracted great interest in recent years. In particular, the search is active for sequences that are able to mimic enzymes when they are self-organized in a nanostructured hydrogel, so as to provide a smart catalytic (bio)material whose activity can be switched on/off with assembly/disassembly. Within the diverse enzymes that have been targeted for mimicry, hydrolases find wide application in biomaterials, ranging from their use to convert prodrugs into active compounds to their ability to work in reverse and catalyze a plethora of reactions. We recently reported the minimalistic l-His-d-Phe-d-Phe for its ability to self-organize into thermoreversible and biocatalytic hydrogels for esterase mimicry. In this work, we analyze the effects of terminus modifications that mimic the inclusion of the tripeptide in a longer sequence. Therefore, three analogues, i.e., N-acetylated, C-amidated, or both, were synthesized, purified, characterized by several techniques, and probed for self-assembly, hydrogelation, and esterase-like biocatalysis. This work provides useful insights into how chemical modifications at the termini affect self-assembly into biocatalytic hydrogels, and these data may become useful for the future design of supramolecular catalysts for enhanced performance
A biocatalytic and thermoreversible hydrogel from a histidine-containing tripeptide
Full text linkWe report the first histidine-containing self-assembling tripeptide devoid of capping groups that forms a thermoreversible hydrogel under physiological conditions and catalyses hydrolysis of an ester, providing a minimalist building block for functional soft materials
Microwave-Assisted Cyclization of Unprotected Dipeptides in Water to 2,5-Piperazinediones and Self-Assembly Study of Products and Reagents
No full textDipeptides and their cyclized 2,5-piperazinedione (or diketopiperazine, DKP) derivatives are attractive building blocks for supramolecular hydrogels. The Phe-Phe, (p-nitro)-Phe-Phe, and Phe-Val dipeptides and their corresponding DKPs are studied for self-assembly in water. The DKPs were obtained in high yields by microwave-assisted cyclization of the dipeptides in water, demonstrating that use of their methyl ester derivatives as reported in the literature is not necessary for successful cyclization. Single-crystal XRD structures are reported for two DKPs as well as stable hydrogels at neutral pH
Luminescent supramolecular hydrogels from a tripeptide and nitrogen-doped carbon nanodots
Full text linkThe combination of different components such as carbon nanostructures and organic gelators into composite nanostructured hydrogels is attracting wide interest for a variety of applications, including sensing and biomaterials. In particular, both supramolecular hydrogels that are formed from unprotected D,L-tripeptides bearing the Phe-Phe motif and nitrogen-doped carbon nanodots (NCNDs) are promising materials for biological use. In this work, they were combined to obtain luminescent, supramolecular hydrogels at physiological conditions. The self-assembly of a tripeptide upon application of a pH trigger was studied in the presence of NCNDs to evaluate effects at the supramolecular level. Luminescent hydrogels were obtained whereby NCND addition allowed the rheological properties to be fine-tuned and led to an overall more homogeneous system composed of thinner fibrils with narrower diameter distributio
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
Assembly of a Tripeptide and Anti-Inflammatory Drugs into Supramolecular Hydrogels for Sustained Release
No full textSupramolecular hydrogels offer interesting opportunities for co-assembly with drugs towards sustained release over time, which could be achieved given that the drug participates in the hydrogel nanostructure, and it is not simply physically entrapped within the gel matrix. dLeu-Phe-Phe is an attractive building block of biomaterials in light of the peptide’s inherent biocompatibility and biodegradability. This study evaluates the assembly of the tripeptide in the presence of either of the anti-inflammatory drugs ketoprofen or naproxen at levels analogous to commercial gel formulations. Fourier-transformed infrared (FT-IR), circular dichroism, Thioflavin T fluorescence, transmission electron microscopy (TEM), and oscillatory rheometry are used. Drug release over time is monitored by means of reverse-phase high performance liquid chromatography, and shows different kinetics for the two drugs
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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