1,354,459 research outputs found
Diketopiperazine gels: New horizons from the self-assembly of cyclic dipeptides
No full textCyclodipeptides (CDPs) or 2, 5-diketopiperazines (DKPs) can exert a variety of biological activities and display pronounced resistance against enzymatic hydrolysis as well as a propensity towards self-assembly into gels, relative to the linear-dipeptide counterparts. They have attracted great interest in a variety of fields spanning from functional materials to drug discovery. This concise review will analyze the latest advancements in their synthesis, self-assembly into gels, and their more innovative applications
Effetti della chiralità su librerie covalenti dinamiche di peptidi
No full textI peptidi sono una classe di biomolecole in grado di attrarre molto interesse in diversi campi scientifici, grazie alla loro biocompatibilità e alla possibilità di assemblare in superstrutture in acqua. In particolare, i ciclopeptidi composti da α-amino acidi sono stati intensivamente studiati per la loro abilità di assemblare in nanotubi supramolecolari, i quali sono tenuti assieme da interazioni di legame idrogeno. L’intensiva ricerca in questa area ha elucidato le regole del design del loro auto-assemblaggio in termini di stereoconfigurazione e composizione amino-acidica. Tuttavia, uno studio estensivo di questa classe di composti richiede uno sforzo sintetico non banale. La chimica dinamica covalente offre quindi un’alternativa interessante alla classica sintesi consentendo di produrre ciclopeptidi da mattoncini lineari molto più semplici da sintetizzare. In questo modo, i reagenti si combinano in una libreria dinamica covalente. Inoltre, la formazione di legami covalenti sotto equilibrio termodinamico in concomitanza all’autoassemblaggio possono essere usati come possibile strada per scoprire nuove suprastrutture, grazie all’effetto di autoreplicazione.
Un set di stereoisomeri tripeptidici Cys-Phe-Cys sono stati sintetizzati per studiare la loro abilità di reagire covalentemente in acqua alcalina attraverso lo scambio tiolo/disolfuro. Lo stereoisomerismo ha influito sulla chimica dinamica portando alla formazione di diversi oligomeri ciclici e ha permesso di fare luce sulle differenze chiave tra la libreria omochirale e quelle eterochirali. Gli oligomeri ciclici sono stati purificati con la cromatografia ad alta prestazione a fase inversa e caratterizzati da RMN e diffrazione a raggi X. Una particolare stereoconfigurazione ha permesso alla libreria di auto assemblarsi in un idrogel composto da un solo macrociclo all’equilibrio termodinamico. L’analisi del materiale supramolecolare da reologia, dicroismo circolare e microscopia a trasmissione elettronica ha rivelato la presenza di una struttura anisotropica allungata compatibile con la presenza di nanotubi, i quali il diametro potrebbe corrispondere alla taglia del mattoncino macrociclico. Questo composto ha conformazioni simili a diversi pH ma è in grado di auto assemblarsi solo quando si trova in forma zwitterionica.
Riassumendo, questo studio dimostra come una scelta appropriata della stereoconfigurazione degli amino acidi su semplici tripeptidi può essere strategica nel progettare diverse strutture cicliche e in casi specifici, ottenere librerie in grado di convergere verso un gel composto da un unico prodotto. Questa ricerca pone quindi le basi per accedere facilmente ad una nuova classe di ciclopeptidi auto assemblanti che possono trovare varie applicazioni nella scienza di materiali e oltre.Peptides are a class of biomolecules that has attracted a lot of interest in different scientific fields, thanks to their biocompatibility and potential to self-assemble into supramolecular structures in water. In particular, cyclopeptides composed of α-amino acids have been intensively studied for their ability to stack into supramolecular nanotubes, which are held together by intermolecular hydrogen bonding. The intense research efforts in this area have unravelled the design rules for self-assembly in terms of stereoconfiguration, and amino-acidic composition. However, an extensive investigation on this class of compounds requires a synthetic effort that is not trivial. Dynamic covalent chemistry (DCC) thus offers an appealing alternative to classical chemical synthesis, to yield cyclopeptides from linear building blocks that are simpler to synthesise. In this way, the reagents can combine into a dynamic covalent library (DCL). Furthermore, the formation of covalent bonds under thermodynamic equilibrium can be used together with the self-assembly process, as a possible route to discover new suprastructures, thanks to the self-templating effect.
A set of Cys-Phe-Cys tripeptide stereoisomers was synthesised to study their ability to undergo DCC in alkaline water, through thiol/disulfide exchange. The stereoisomerism impacted the DCC leading to the formation of diverse cyclic oligomers, and it allowed to shed light on key differences between the homochiral, and the heterochiral DCLs. Cyclic oligomers were purified by reverse-phase HPLC, and characterised by NMR and single-crystal XRD. A particular stereoconfiguration enabled the DCL to self-assemble into a hydrogel composed of only one macrocycle at the thermodynamic equilibrium. The analysis on the supramolecular material by rheology, circular dichroism, and transmission electron microscopy revealed the presence of an anisotropic and elongated supramolecular structure, compatible with the presence of nanotubes whose diameter could correspond to the size of its macrocyclic building block. This compound had a similar conformation in solution at different pH values, but it was able to self-assemble into hydrogels only in the zwitterionic form.
Overall, this study demonstrated how an appropriate choice of amino acid stereoconfiguration on simple tripeptides can be a strategic design tool towards diverse cyclic structures and, in specific cases, to yield DCLs that eventually converge into a main gelator product. This research work thus laid the basis to easily access a new class of self-assembling cyclopeptides that could find various applications in materials science, and beyond
Laboratorios aplicados a las Ciencias Agropecuarias
No full textEn la EEA Reconquista funcionan laboratorios especializados en entomología; suelos, agua y vegetales, fertilidad y sanidad animal; ecofisiología vegetal y biotecnología. Cada uno cuenta con instrumental y equipamiento específico y ofrece servicios para el desarrollo de investigaciones y para la comunidad. En esta nota se detallan las actividades de cada uno de ellos.EEA ReconquistaFil: Vitti Scarel, Daniela. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Reconquista; Argentin
A Molecular Shuttle Driven by Fullerene Radical-Anion Recognition
No full textWe describe a electrochemically driven molecular shuttle, in which shuttling takes place by means of fullerene radical-anion recognition that results in a very low operation potential (E-1/2 = -0.580 V vs. decamethylferrocene). This has been achieved by introducing positive charges on the macrocycle, which strengthen the existing pi-pi interactions between the macrocycle and the electrogenerated fullerene radical anion by means of an electrostatic component. In addition, the synthesis of such a molecular shuttle has been accomplished by developing a new synthetic approach that exploits the controlled translocation of the macrocycle as a selective protecting group
Diverging conformations guide dipeptide self-assembly into crystals or hydrogels
No full textThe prediction of dipeptide assembly into crystals or gels is challenging. This work reveals the diverging conformational landscape that guides self-organization towards different outcomes. In silico and experimental data enabled deciphering of the electronic circular dichroism (ECD) spectra of self-assembling dipeptides to reveal folded or extended conformers as key players
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
High Stereocontrol and Efficiency in CO/Styrene Polyketones Synthesis Promoted by Azabis(oxazoline)-Palladium Complexes
No full textVariations on the Author
No full text“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
No full textWe 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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