Experimental Correlation between Apparent p 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.

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.

Tunable Oxidized-Chitin Hydrogels with Customizable Mechanical Properties by Metal or Hydrogen Ion Exposure.

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.

Transparent Organogels as a Medium for the Light-Induced Conversion from Spiropyran to Merocyanine.

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.

Valorization Strategies in CO Capture: A New Life for Exhausted Silica-Polyethylenimine.

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 CO 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, H-C-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 CO capture.

Challenges in the Direct Detection of Chirality-induced Spin Selectivity: Investigation of Foldamer-based Donor-acceptor Dyads.

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.

Controlled Lactonization of -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.

Delivery of Active Peptides by Self-Healing, Biocompatible and Supramolecular Hydrogels.

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.

A short oxazolidine-2-one containing peptide forms supramolecular hydrogels under controlled conditions.

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.

Controlled Hydrolysis of Odorants Schiff Bases in Low-Molecular-Weight Gels.

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.

Fluorine Effect in the Gelation Ability of Low Molecular Weight Gelators.

The three gelators presented in this work (Boc-D-Phe-L-Oxd-OH , Boc-D-FPhe-L-Oxd-OH and Boc-D-FPhe-L-Oxd-OH ) share the same scaffold and differ in the number of fluorine atoms linked to the aromatic ring of phenylalanine. They have been applied to the preparation of gels in 0.5% or 1.

L-Dopa in small peptides: an amazing functionality to form supramolecular materials.

l-Dopa (3,4-dihydroxyphenylalanine) is a chiral amino acid generated via biosynthesis from l-tyrosine in plants and some animals. The presence of multiple interacting sites makes l-Dopa a multifunctional building block for the preparation of supramolecular materials. The possibility to form hydrogen bonds and the presence of the aromatic ring allow l-Dopa molecules to interact through a series of non-covalent interactions.

Designing a Transparent and Fluorine Containing Hydrogel.

Physical 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.

Elusive π-helical peptide foldamers spotted by chiroptical studies.

A series of oligomers containing alternate l-Ala and pGlu (pyroglutamic acid) both in the L and D form have been prepared and conformationally investigated by X-ray, NMR, UV/ECD, IR/VCD and molecular modelling. X-ray diffraction analysis was possible for the shortest oligomers LL-1 and LD-1. Molecular dynamics simulations of the oligomers demonstrated that the energy landscapes of the LL-series are broad.

Supramolecular Hydrogels with Properties Tunable by Calcium Ions: A Bio-Inspired Chemical System.

Boc-L-DOPA(OBn)-OH is a simple synthetic molecule that promotes hydrogelation through electrostatic and π-π stacking interactions. Hydrogelation can occur in alkaline conditions by the use of triggers. Four hydrogels were prepared varying the base, NaOH or NaCO, and the trigger, GdL or CaCl.

Tuning Mechanical Properties of Pseudopeptide Supramolecular Hydrogels by Graphene Doping.

Supramolecular hydrogels, obtained from small organic molecules, may be advantageous over polymeric ones for several applications, because these materials have some peculiar properties that differentiate them from the traditional polymeric hydrogels, such as elasticity, thixotropy, self-healing propensity, and biocompatibility. We report here the preparation of strong supramolecular pseudopeptide-based hydrogels that owe their strength to the introduction of graphene in the gelling mixture. These materials proved to be strong, stable, thermoreversible and elastic.

Biocompatible and Light-Penetrating Hydrogels for Water Decontamination.

Solar light-activated photocatalyst nanoparticles (NPs) are promising environment-friendly low cost tools for water decontamination, but their dispersion in the environment must be minimized. Here, we propose the incorporation of TiO-NPs (also in combination with graphene platelets) into highly biocompatible hydrogels as a promising approach for the production of photoactive materials for water treatment. We also propose a convenient fluorescence-based method to investigate the hydrogel photocatalytic activity in real time with a conventional fluorimeter.

Low Molecular Weight Gelators Based on Functionalized l-Dopa Promote Organogels Formation.

We prepared the small pseudopeptide Lau-l-Dopa(OBn)-d-Oxd-OBn (Lau = lauric acid; l-Dopa = l-3,4-dihydroxyphenylalanine; d-Oxd = (4,5)-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)-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.

Synthesis and structure analysis of ferrocene-containing pseudopeptides.

Ferrocene with its aromaticity and facile redox properties is an attractive moiety to be incorporated into functional moieties. Medicinal applications of ferrocene are well known and ferrocene itself shows cytotoxic and antianemic properties. In this article, we will describe the synthesis and the structure analysis of two pseudopeptides containing a ferrocene moiety as N-terminal group.

Peptide-Based Physical Gels Endowed with Thixotropic Behaviour.

Thixotropy is one of the oldest documented rheological phenomenon in colloid science and may be defined as an increase of viscosity in a state of rest and a decrease of viscosity when submitted to a constant shearing stress. This behavior has been exploited in recent years to prepare injectable hydrogels for application in drug delivery systems. Thixotropic hydrogels may be profitably used in the field of regenerative medicine, which promotes tissue healing after injuries and diseases, as the molten hydrogel may be injected by syringe and then self-adapts in the space inside the injection site and recovers the solid form.

The effect of l-DOPA hydroxyl groups on the formation of supramolecular hydrogels.

Fmoc-l-DOPA-d-Oxd-OH was prepared starting from commercially available l-DOPA. Its gelation ability was tested by comparison with Fmoc-l-Tyr-d-Oxd-OH and Fmoc-l-Phe-d-Oxd-OH using ten different triggers. Among them, only GdL, CaCl and ZnCl form strong hydrogels with the three gelators.

Thixotropic Peptide-Based Physical Hydrogels Applied to Three-Dimensional Cell Culture.

Pseudopeptides containing the d-Oxd or the d-pGlu [Oxd = (4,5)-4-methyl-5-carboxyl-oxazolidin-2-one, pGlu = pyroglutamic acid] moiety and selected amino acids were used as low-molecular-weight gelators to prepare strong and thixotropic hydrogels at physiological pH. The addition of calcium chloride to the gelator solutions induces the formation of insoluble salts that get organized in fibers at a pH close to the physiological one. Physical characterization of hydrogels was carried out by morphologic evaluation and rheological measurements and demonstrated that the analyzed hydrogels are thixotropic, as they have the capability to recover their gel-like behavior.