Experimental Correlation between Apparent pKa and Gelation Propensity in Amphiphilic Hydrogelators Derived from l-Dopa.

We 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 ß-sheet structures, as outlined by the ECD, IR, and SEM analyses. Moreover, the preliminary measurement of the apparent pKa 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 pKa results in two apparent pKa shifts of ∼8.5 and ∼4 pH units above the theoretical pKa, as a consequence of a multistep self-assembly pathway that correlates, in the final ß-sheet-based hydrogel, with a high degree of order and stability.

Low-molecular-weight gels from amino acid and peptide derivatives for controlled release and delivery.

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.

Controlled Lactonization of o-Coumaric Esters Mediated by Supramolecular Gels.

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.