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Low‐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. [ABSTRACT FROM AUTHOR]

This 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. [ABSTRACT FROM AUTHOR]

Over the past two decades, the chirality‐induced spin selectivity (CISS) effect was reported in several experiments disclosing a unique connection between chirality and electron spin. Recent theoretical works highlighted time‐resolved Electron Paramagnetic Resonance (trEPR) as a powerful tool to directly detect the spin polarization resulting from CISS. Here, we report a first attempt to detect CISS at the molecular level by linking the pyrene electron donor to the fullerene acceptor with chiral peptide bridges of different length and electric dipole moment. The dyads are investigated by an array of techniques, including cyclic voltammetry, steady‐state and transient optical spectroscopies, and trEPR. Despite the promising energy alignment of the electronic levels, our multi‐technique analysis reveals no evidence of electron transfer (ET), highlighting the challenges of spectroscopic detection of CISS. However, the analysis allows the formulation of guidelines for the design of chiral organic model systems suitable to directly probe CISS‐polarized ET. [ABSTRACT FROM AUTHOR]

Low-molecular-weight peptide gelators are a versatile class of compounds able to form gels under a variety of conditions, even via simple ultrasound sonication. In this paper, the ability of Boc-L-Phe-D-Oxd-L-Phe-OBn to gelate three organic solvents (toluene, tert-butyl methyl ether, and ethanol) was evaluated. The rheological behaviour of the materials was assessed via strain sweep analysis, while the fibrous network was analysed via optical microscopy on the wet gels. The gel obtained from toluene is a highly transparent material, and the one from ethanol appears translucent, while the one from tert-butyl methyl ether is opaque. These gels were used to study the reversible light-induced transformation from spyropiran (SP) to merocyanine (MC) and back, as a model system to check the effect of the gel medium onto the rection kinetic. We observed that the solvent used to form the organogels has a crucial effect on the reaction, as gels from aprotic solvents stabilize the SP form, while the ones from protic solvents stabilize the MC form. We thus obtained a solid support to stabilize the two photochromic species just by changing the solvent polarity. Moreover, we could demonstrate that the self-assembled gels do not interfere with the light-driven conversion process, either starting from SP or MC, thus representing a valid and economical photochromic material. [ABSTRACT FROM AUTHOR]

The search for alternative ways to give a second life to materials paved the way for detailed investigation into three silica-polyethylenimine (Si-PEI) materials for the purpose of CO2 adsorption in carbon capture and storage. A solvent extraction procedure was investigated to recover degraded PEIs and silica, and concomitantly, pyrolysis was evaluated to obtain valuable chemicals such as alkylated pyrazines. An array of thermal (TGA, Py-GC-MS), mechanical (rheology), and spectroscopical (ATR-FTIR, 1H-13C-NMR) methods were applied to PEIs extracted with methanol to determine the relevant physico-chemical features of these polymers when subjected to degradation after use in CO2 capture. Proxies of degradation associated with the plausible formation of urea/carbamate moieties were revealed by Py-GC-MS, NMR, and ATR-FTIR. The yield of alkylpyrazines estimated by Py-GC-MS highlighted the potential of exhausted PEIs as possibly valuable materials in other applications. [ABSTRACT FROM AUTHOR]

Low‐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. [ABSTRACT FROM AUTHOR]

Fragrances 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. [ABSTRACT FROM AUTHOR]

Antioxidants 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. [ABSTRACT FROM AUTHOR]

Supramolecular 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. [ABSTRACT FROM AUTHOR]

Three sets of oligomers containing the 4-carboxy-5-methyloxazolidin-2-one (Oxd) moiety were synthesized in a study with the aim of checking whether these molecules are able to fold in ordered structures. A deeper insight into the CD spectra reveals that the secondary structure adopted by one set of oligomers is a beta-bend ribbon spiral, which is a subtype of the 3(sub 10)-helix.

The asymmetric aldol condensation of acetone with isatin, its N-alkylated derivatives, and 5-` is described. A new quaternary stereocenter is obtained with good enantioselectivity, which can easily be enriched by silica flash chromatography and the effect proved to be general for the class of compounds.

The removal of Diclofenac sodium from waste waters has a high relevance since it belongs to the therapeutic group most commonly found in wastes. An aromatic‐free and low‐impact technology that efficiently entraps aqueous pollutants is highly desirable. We synthesised two Boc‐protected and aromatic‐free tripeptides (Boc‐L‐Ala‐Aib‐L‐Val‐OH and Boc‐L‐Val‐Aib‐L‐Val‐OH) and studied their ability to form gels with mixtures of water and alcohols, such as methanol, ethanol and 2‐propanol. Boc‐L‐Ala‐Aib‐L‐Val‐OH forms a strong hydrogel in 2‐propanol/water mixtures able to trap up to 97.8% of Eosin Y model molecule and up to 92.0% of Diclofenac sodium from aqueous solutions. The hydrogel is also thixotropic, thermoreversible and biocompatible. This outcome is very encouraging and paves the way to a new approach for developing new materials using aromatic‐free hydrogels, useful for water remediation. [ABSTRACT FROM AUTHOR]

Imines or Schiff bases (SB) are formed by the condensation of an aldehyde or a ketone with a primary amine, with the removal of a water molecule. Schiff bases are central molecules in several biological processes for their ability to form and cleave by small variation of the medium. We report here the controlled hydrolysis of four SBs that may be applied in the fragrance industry, as they are profragrances all containing odorant molecules: methyl anthranilate as primary amine, and four aldehydes (cyclamal, helional, hydroxycitronellal and triplal) that are very volatile odorants. The SB stability was assessed over time by HPLC-MS in neutral or acidic conditions, both in solution and when trapped in low molecular weight gels. Our results demonstrate that it is possible to control the hydrolysis of the Schiff bases in the gel environment, thus tuning the quantity of aldehyde released and the persistency of the fragrance. [ABSTRACT FROM AUTHOR]

The 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. [ABSTRACT FROM AUTHOR]

The unexpected and facile addition of phenylacetylene to aldehydes and ketones promoted by Me(sub 2)Zn without the employment of specific ligands is described. The substrate itself can become a ligand and catalyze a background reaction, which might result in lowering the enantioselectivity in a desired asymmetric transformation.

Allergic contact dermatitis to braces containing 4,4'-diaminodiphenylmethane, a previously unreported causative agent Keywords: allergic contact dermatitis; brace; case report; diaminodiphenylmethane; orthopedic support EN allergic contact dermatitis brace case report diaminodiphenylmethane orthopedic support 157 159 3 07/27/20 20200801 NES 200801 4,4'-Diaminodiphenylmethane (4,4'-MDA, CAS no. 101-77-9), an aromatic amine, is the degradation product of 4,4'-methylenebis(phenyl isocyanate) (4,4'-MDI). The patient had had a fracture of the fifth right metatarsal bone 20 days prior and had been wearing a leg brace made of polyurethane ever since (Figure 1A). [Extracted from the article]

The formation of fibers through self-assembly is of particular interest, as fibrous proteins (such as collagen, keratin, actin, and so on) are involved in intra- and extracellular functions. To understand aggregation phenomena, oligopeptides may be designed and prepared either to mimic or to interfere with these processes. In this article, we will demonstrate that the introduction of the 4-methyl-5-carboxy-oxazolidin-2-one (Oxd) moiety inside a peptide chain favors the formation of fiber-like materials organized either in β-sheets or in supramolecular helices, provided that it is combined with other factors, like π-stacking interactions and intermolecular NAH…O=C bonds. The presence of the Oxd moiety is essential for the material formation: when Oxd is replaced with Pro, only liquids or amorphous solids are obtained. Remarkably, some of these molecules are low-molecular-weight gelators, as they induce the formation of both organogel and hydrogels that have been used for several applications. [ABSTRACT FROM AUTHOR]