1,720,976 research outputs found
Exploring the Self-Assembly of a Fully Protected l-Dopa from Different Organic Solvents and the Relationship Between Gel and Crystal Structures
Full text linkWe report here the self-assembly of a fully protected L-3,4-dihydroxyphenylalanine (Boc-L-Dopa(Bn)2-OMe) under several conditions. Depending on the organic solvent orsolvent mixture, this simple molecule self-assembles into different supramolecular structures, sometimes behaving as a low-molecular-weight gelator. Indeed, we observed the formation of organogels in alcohols, as confirmed by rheological analyses. In contrast, in solvent mixtures, long crystalline fibers were formed, and we could obtain single crystals suitable for X-ray diffraction analysis through a vapor diffusion technique. The deep X-ray diffraction analyses allowed us to determine the structure of the crystals, of the gels, and of the fiber-like aggregates and to deduce that the molecule always self-assembles like antiparallel β-sheets, driven by intermolecular hydrogen bonding and π−π stacking interaction
A short oxazolidine-2-one containing peptide forms supramolecular hydrogels under controlled conditions
Full text linkLow-molecular-weight hydrogels are made of a small percentage of small organic molecules dispersed in an aqueous medium, which may aggregate in several manners using different methods. However, often the organic gelator in water has poor solubility, so the addition of a solubilising agent is required. In the case of acidic gelators, this mainly consists of the addition of a strong base, that is sodium hydroxide, that deprotonates the acidic moiety, so the gelator molecules become more soluble and tend to assemble into micelles, forming a dispersion. Some gelators, however, are sensitive to the harsh pH and get hydrolysed. This is the case of some molecules presenting carbamates in their features, like Fmoc-protected or oxazolidinone-containing peptides. In this paper, we present a valid alternative to sodium hydroxide, by dissolving a tripeptide containing an oxazolidinone moiety in a phosphate buffer (PB) medium at pH 7.4. The results obtained with the NaOH dissolution are compared with the ones with PB, as both methods present advantages and drawbacks. The use of NaOH produces transparent but weak hydrogels, as it exposes the gelator to harsh conditions that end up in its partial hydrolysis, which is more pronounced at high concentrations (≥10 mM). Using PB to dissolve the gelator, this problem is completely avoided as no hydrolysis product has been detected in the hydrogels, which are very stiff although more opaque. By tuning the preparation conditions, we can obtain a wide variety of hydrogels, with the properties required by the final application
Tunable Oxidized-Chitin Hydrogels with Customizable Mechanical Properties by Metal or Hydrogen Ion Exposure
Full text linkThis study focuses on the optimization of chitin oxidation in C6 to carboxylic acid and its use to obtain a hydrogel with tunable resistance. After the optimization, water-soluble crystalline β-chitin fibrils (β-chitOx) with a degree of functionalization of 10% were obtained. Diverse reaction conditions were also tested for α-chitin, which showed a lower reactivity and a slower reaction kinetic. After that, a set of hydrogels was synthesized from β-chitOx 1 wt.% at pH 9, inducing the gelation
by sonication. These hydrogels were exposed to different environments, such as different amounts of Ca2+, Na+ or Mg2+ solutions, buffered environments such as pH 9, PBS, pH 5, and pH 1, and pure water. These hydrogels were characterized using rheology, XRPD, SEM, and FT-IR. The notable feature of these hydrogels is their ability to be strengthened through cation chelation, being metal
cations or hydrogen ions, with a five- to tenfold increase in their storage modulus (G’). The ions were theorized to alter the hydrogen-bonding network of the polymer and intercalate in chitin’s crystal structure along the a-axis. On the other hand, the hydrogel dissolved at pH 9 and pure water. These bio-based tunable hydrogels represent an intriguing material suitable for biomedical applications
Phenylalanine‐Based Amphiphilic Self‐Assembled Materials: Gels or Crystals?
Full text linkWe prepared three simple molecules, that we chose as representative examples of amphiphilic and bolamphiphilic amino acid derivatives: N-lauroyl-L-phenylalanine (Lau-Phe-OH), N-palmitoyl-L-phenylalanine (Pal-Phe-OH), N,N-azeloyl-L-diphenylalanine Az-(Phe-OH)2, to study the influence of the aliphatic side chain on the formation of supramolecular materials. We found that Pal-Phe-OH is a very efficient gelator in contrast with Az-(Phe-OH)2 that efficiently forms crystals, while Lau-Phe-OH forms metastable hydrogels that slowly become crystals. We demonstrated by X-ray diffraction that Lau-Phe-OH and Pal-Phe-OH easily form hetero-intermolecular hydrogen bonds between the carboxylic and amidic groups, while Az-(Phe-OH)2 forms homo-intermolecular hydrogen bonds, i.e., the typical carboxylic ring dimer and chains between the amidic functions, which leads to an extended and robust 2D hydrogen bonding network. Moreover, Lau-Phe-OH is more ordered than Pal-Phe-OH and the comparison of these results clearly indicates that the reduced order of Pal-L-Phe-OH is the main reason for the efficiency of this molecule as supergelator
Low-Molecular-Weight Gels as Smart Materials for the Enhancement of Antioxidants Activity
Full text linkAntioxidants are important substances used in the cosmetic and pharmaceutical fields that are able to block free radicals. These compounds can be incorporated into formulations for many reasons, such as release over time or preservation of the formulation activity and applicability. In the present study, a low-molecular-weight gel made with Boc-L-DOPA(Bn)2-OH was studied as suitable material to host antioxidants and improve their activity. The solvent change (DMSO/H2O) in combination with temperature was the technological procedure for the preparation of the gel. Two different antioxidants were tested: (1) α-tocopherol and (2) postbiotics. The antioxidant activity of α-tocopherol and of the postbiotics in the gel, measured by the (2,2-diphenyl-1-picryl-hydrazyl radical (DPPH) assay, showed higher values than those in the pure solvent. The antioxidant activity of the gel with 0.8 w/v% of gelator and α-tocopherol in the concentration range of 5–100 µM was 2.7–1.1 times higher on average than in the pure solvent. In the case of both postbiotics, the biggest difference was observed at 30% of postbiotics in the gel with 0.5% of a gelator, when the antioxidant activity was 4.4 to 4.7 times higher than that in the pure solvent
Experimental Correlation between Apparent pKa and Gelation Propensity in Amphiphilic Hydrogelators Derived from l-Dopa
Full text linkWe report the gelation propensity of three gelators derived from l-dihydroxyphenylalanine (l-Dopa), where the amino group is derivatized with three different fatty acids (lauric acid, palmitic acid, and azelaic acid). The long aliphatic side chains should introduce additional van der Waals interactions among the molecules, contributing to the self-assembly process. The hydrogels have been prepared with the pH change method, and both the hydrogels and the corresponding aerogels have been analyzed using several techniques. In any case, Lau-Dopa provides stronger hydrogels compared with the other gelators. This property may be ascribed to its tendency to efficiently form supramolecular beta-sheet structures, as outlined by the ECD, IR, and SEM analyses. Moreover, the preliminary measurement of the apparent pK(a) displays for Lau-Dopa two plateaux, as previously observed for, one at about pH 12 and a second one at pH 7.5. Thus, its pK(a) results in two apparent pK(a) shifts of similar to 8.5 and similar to 4 pH units above the theoretical pK(a), as a consequence of a multistep self-assembly pathway that correlates, in the final beta-sheet-based hydrogel, with a high degree of order and stability
Keratin-hydrotalcites hybrid films for drug delivery applications
No full textIn this work novel hybrid materials for drug delivery purposes are obtained by combining keratin with hydrotalcite nanoparticles containing diclofenac. The hybrid films showed a less pronounced swelling, porosity and degradation and a greater thermal stability compared to pure keratin films containing free diclofenac. These results, together with the slight shift towards smaller wavelength numbers of amide I band led to the hypothesis of a probable cross-linking between hydrotalcites and the protein mediated by glutaraldehyde, which results in a total reinforcing action on the hybrid material. In addition, diclofenac release profiles of the hybrid film in physiological conditions were higher than those of the non-hybrid compound. Furthermore, keratin/hydrotalcite were able to support fibroblast cells adhesion and growth suggesting their potential use as drug delivery systems for wound healing and tissue engineering application
Membrane ibride di cheratina-idrotalciti a diversa morfologia per il rilascio controllato di farmaci
No full textNegli ultimi anni, lo sviluppo di materiali a base proteica per il rilascio controllato di farmaci ha ricevuto grande attenzione. Nel presente lavoro sono stati preparati materiali ibridi compositi, sotto forma di film e nanofibre, costituiti da una matrice di cheratina estratta da lana di pecora e nanoparticelle di idrotalciti Zn/Al intercalate con un antinfiammatorio (diclofenac sodico). Tali materiali compositi sono stati caratterizzati dal punto di vista morfologico e strutturale, sono stati testati in vitro come sistemi per il rilascio controllato di farmaci e confrontati con gli stessi materiali contenenti il farmaco libero (senza idrotalciti). Inoltre, è stata valutata la loro eventuale applicazione nell'ingegneria tissutale e nella medicina rigenerativa, analizzando la capacità di supportare l'adesione e la crescita di cellule fibroblastiche. I risultati ottenuti hanno evidenziato un complessivo effetto di rinforzo delle idrotalciti sui materiali ibridi preparati e il rilascio della quasi totalità del farmaco per diffusione in condizioni fisiologiche durante le prime 160 ore. I test biologici sui film hanno mostrato un significativo aumento della crescita di fibroblasti in 72 ore; test di migrazione cellulare sulle nanofibre ibride saranno oggetto di studi futuri
Delivery of Active Peptides by Self-Healing, Biocompatible and Supramolecular Hydrogels
Full text linkSupramolecular and biocompatible hydrogels with a tunable pH ranging from 5.5 to 7.6 lead to a wide variety of formulations useful for many different topical applications compatible with the skin pH. An in vitro viability/cytotoxicity test of the gel components demonstrated that they are non-toxic, as the cells continue to proliferate after 48 h. An analysis of the mechanical properties demonstrates that the hydrogels have moderate strength and an excellent linear viscoelastic range with the absence of a proper breaking point, confirmed with thixotropy experiments. Two cosmetic active peptides (Trifluoroacetyl tripeptide-2 and Palmitoyl tripeptide-5) were successfully added to the hydrogels and their transdermal permeation was analysed with Franz diffusion cells. The liquid chromatography-mass spectrometry (HPLC-MS) analyses of the withdrawn samples from the receiving solutions showed that Trifluoroacetyl tripeptide-2 permeated in a considerable amount while almost no transdermal permeation of Palmitoyl tripeptide-5 was observed
Exploiting and controlling gel-to-crystal transitions in multicomponent supramolecular gels
Full text linkMulticomponent supramolecular gels provide opportunities to form materials that are not accessible when using the single components alone. Different scenarios are possible when mixing multiple components, from complete co-assembly (mixing of the components within the self-assembled structures formed) to complete self-sorting such that each structure contains only one of the components. Most examples of multicomponent gels that currently exist form stable gels. Here, we show that this can be used to control the mechanical properties of the gels, but what is probably most exciting is that we show that we can use a magnetic field to control the shape of the crystals. The gelling component aligns in a magnetic field and so results in anisotropic crystals being formed
- …
