1,720,974 research outputs found
Low molecular weight gelators based on functionalized l-dopa promote organogels formation
Get PDFWe prepared the small pseudopeptide Lau-l-Dopa(OBn)2-d-Oxd-OBn (Lau = lauric acid; l-Dopa = l-3,4-dihydroxyphenylalanine; d-Oxd = (4R,5S)-4-methyl-5-carboxyl-oxazolidin-2-one; Bn = benzyl) through a number of coupling reactions between lauric acid, protected l-Dopa and d-Oxd with an excellent overall yield. The ability of the product to form supramolecular organogels has been tested with different organic solvents of increasing polarity and compared with the results obtained with the small pseudopeptide Fmoc-l-Dopa(OBn)2-d-Oxd-OBn. The mechanical and rheological properties of the organogels demonstrated solvent-dependent properties, with a storage modulus of 82 kPa for the ethanol organogel. Finally, to have a preliminary test of the organogels’ ability to adsorb pollutants, we treated a sample of the ethanol organogel with an aqueous solution of Rhodamine B (RhB) for 24 h. The water solution slowly lost its pink color, which became trapped in the organogel
l-Dopa in small peptides: an amazing functionality to form supramolecular materials
Get PDFl-Dopa (3,4-dihydroxyphenylalanine) is a chiral amino acid generatedviabiosynthesis froml-tyrosine in plants and some animals. The presence of multiple interacting sites makesl-Dopa a multifunctional building block for the preparation of supramolecular materials. The possibility to form hydrogen bonds and the presence of the aromatic ring allowl-Dopa molecules to interact through a series of non-covalent interactions. The additional presence of the catechol moiety really makes this compound unique: not only does it have implications in the self-assembly process of Dopa itself and with other substrates, but also it highly increases the number of applications of the final material, since it works as an antioxidant, radical trapper, metal chelator, reducing agent and adhesive.l-Dopa and catechol containing derivatives have been extensively introduced inside both synthetic and natural polymers to obtain amazing functional materials. In this review we report the preparation of small peptides containingl-Dopa, focusing on the supramolecular materials that can be obtained with them, ranging from fibrils to fibres, gels, films and coatings, all having the different applications mentioned above and many others
Low-molecular-weight gels from amino acid and peptide derivatives for controlled release and delivery
Get PDFLow-molecular-weight (LMW) gelators are a versatile class of compounds able to self-assemble and to form supramolecular materials, such as gels. The use of LMW peptides to produce these gels shows many advantages, because of their wide structure tunability, the low-cost and effective synthesis, and the in vivo biocompatibility and biodegradability, which makes them optimal candidates for release and delivery applications. In addition, in these materials, the binding of the hosts may occur through a variety of noncovalent interactions, which are also the main factors responsible for the self-assembly of the gelators, and through specific interactions with the fibers or the pores of the gel matrix. This review aims to report LMW gels based on amino acid and peptide derivatives used for the release of many different species (drugs, fragrances, dyes, proteins, and cells) with a focus on the possible strategies to incorporate the cargo in these materials, and to demonstrate how versatile these self-assembled materials are in several applications.This review reports recent works on low-molecular-weight gels based on amino acid and peptide derivatives used for the release of different species (drugs, fragrances, dyes, proteins, and cells), with a focus on the possible strategies to incorporate the cargo in these versatile supramolecular materials. imag
Controlled Lactonization of o-Coumaric Esters Mediated by Supramolecular Gels
Get PDFFragrances are volatile organic compounds widely used in our daily life. Unfortunately, the high volatility required to reach human receptors reduces their persistency in the air. To contrast this effect, several strategies may be used. Among them, we present here the combination of two techniques: the microencapsulation in supramolecular gels and the use of profragrances. We report a study on the controlled lactonization of four esters derived from o-coumaric acid. The ester lactonization spontaneously occurs after exposure to solar light, releasing coumarin and the corresponding alcohol. To determine the rate of fragrance release, we compared the reaction in solution and in a supramolecular gel and we demonstrated that the lactonization reaction always occurs slower in the gel. We also studied the more suitable gel for this aim, by comparing the properties of two supramolecular gels obtained with the gelator Boc-L-DOPA(Bn)(2)-OH in a 1:1 ethanol/water mixture in different gelator concentration (0.2% and 1% w/v). The gel prepared with 1% w/v gelator concentration is stronger and less transparent than the other and was used for the profragrances encapsulation. In any case, we obtained a significative reduction of lactonization reaction in gel, compared with the same reaction in solution
Designing a transparent and fluorine containing hydrogel
Get PDFPhysical hydrogels are supramolecular materials obtained by self-assembly of small molecules called gelators. Aromatic amino acids and small peptides containing aromatic rings are good candidates as gelators due to their ability to form weak bonds as π-π interactions and hydrogen bonds between NH and CO of the peptide chain. In this paper we show our results in the preparation of a transparent hydrogel that was obtained by self-assembly of a fluorine-containing dipeptide that relies on the additional formation of halogen bonds due to the fluorine atoms contained in the dipeptide. We used Boc-D-F2Phe-L-Oxd-OH (F2Phe = 3,4-difluorophenylalainine; Oxd = 4-methyl-5-carboxy-oxazolidin-2-one) that formed a strong and transparent hydrogel in 0.5% w/w concentration at pH = 4.2. The formation of a hydrogel made of unnatural fluorinated amino acids may be of great interest in the evaluation of patients with parkinsonian syndromes and may be used for controlled release
Boc-Protection on L-DOPA: an Easy Way to Promote Underwater Adhesion
Get PDFThe ability of mussels to adhere to underwater surfaces has attracted a lot of attention from the scientific community. As proteins containing L-DOPA (3,4-dihydroxyphenyl-l-alanine) are involved in their adhesion, a common strategy to synthesize adhesives is the incorporation of this amino acid into other compounds. Herein, we report a study on four compounds of the family of Bocx-(L-DOPA)n-OMe (x = 1–3; n = 1,2), that we prepared through simple synthetic steps. Three of them showed the capability of underwater adhesion: while they are not adhesive in the dry phase, the adhesiveness is triggered when the dried sample is immersed in water or any aqueous solutions. The introduction of protecting groups stabilizes L-DOPA, preventing the oxidation of the catechol moiety, and enhances the hydrophobicity, helping the removal of water from the surface to bind. These molecules show good adhesiveness, with different properties, so they may be all used as adhesives for different purposes. These outcomes pave the way for new applications for these materials as green and biocompatible adhesives
Simple pH-Triggered Control over Hydrogel Formation by Acetyl Valine
No full textThis paper reports on the use of acetyl-L-valine (Ac-Val) as an effective and precise pH modifier for inducing hydrogel formation. Ac-Val offers several advantages: it is fully water-soluble, overcoming dissolution issues, and allows for stock solution preparation to fine-tune trigger volume and final material pH. As a weaker carboxylic acid compared to inorganic acids, Ac-Val enables more controlled pH variation. For comparison, a commercial lactic acid (LA) solution was also evaluated. The reliability of Ac-Val as a pH modifier was tested on three amino acid derivatives-Boc-Dopa(Bn)2-OH, Lau-Dopa(Bn)2-OH, and Pal-Phe-OH, all known to be efficient gelators. These molecules, sharing common structural features, form gels varying in transparency, robustness, and elasticity. Notably, Pal-Phe-OH is a supergelator. A key benefit of Ac-Val lies in its ability to cause an instantaneous pH modification, allowing for precise pH adjustment before the gel network forms. This pH-change approach with Ac-Val demonstrates broad applicability, enabling the creation of gels with tailored pH values for various acidic molecules, which is particularly valuable for applications like drug delivery where specific pH environments are crucial
Understanding gel-to-crystal transitions in supramolecular gels
Get PDFMost supramolecular gels are stable or assumed to be stable over time, and aging effects are often not studied. However, some gels do show clear changes on aging, and a small number of systems exhibit gel-to-crystal transitions. In these cases, crystals form over time, typically at the expense of the network underpinning the gel; this leads to the gel falling apart. These systems are rare, and little is known about how these gel-to-crystal transitions occur. Here, we use a range of techniques to understand in detail a gel-to-crystal transition for a specific functionalised dipeptide based gelator. We show that the gel-to-crystal transition depends on the final pH of the medium which we control by varying the amount of glucon-δ-lactone (GdL) added. In the gel phase, at low concentrations of GdL, and at early time points with high concentrations of GdL, we are able to show the nanometre scale dimensions of the self-assembled fibre using SAXS; however there is no evidence of molecular ordering of the gel fibres in the WAXS. At low concentrations of GdL, these self-assembled fibres stiffen with time but do not crystallise over the timescale of the SAXS experiment. At high concentrations of GdL, the fibres are already stiffened, and then, as the pH drops further, give way to the presence of crystals which appear to grow preferentially along the direction of the fibre axis. We definitively show therefore that the gel and crystal phase are not the same. Our work shows that many assumptions in the literature are incorrect. Finally, we also show that the sample holder geometry is an important parameter for these experiments, with the rate of crystallisation depending on the holder in which the experiment is carried out
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
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