Mechanically Interlocked Profragrances for the Controlled Release of Scents

Formation and Stability of Benzylic Amide [2]- and [3]Rotaxanes: An Intercomponent Interactions Study

One of the most recent focuses in supramolecular chemistry is developing molecules designed to exhibit programmable properties at the molecular level. Rotaxanes, which function as molecular machines with movements controlled by external stimuli, are prime candidates for this purpose. However, the controlled synthesis of rotaxanes, especially amide-benzylic rotaxanes with more than two components, remains an area ripe for exploration. In this study, we aim to elucidate the formation of amide-benzylic [3]rotaxanes using a thread that includes a conventional succinamide station and an innovative triazole-carbonyl station. Including the triazole-carbonyl station introduces new perspectives into the chemistry of rotaxanes, influencing their conformation and dynamics. The synthesis of two-station rotaxanes with varying stoppers demonstrated that the macrocycle consistently occupies the succinamide station, providing greater stability as evidenced by NMR and SC-XRD analyses. The presence of a triazole-carbonyl station facilitated the formation of a second macrocycle exclusively when a secondary amide was employed as the stopper group, presumably due to decreased steric hindrance. Moreover, the second macrocycle directly forms at the triazole-carbonyl station. This investigation reveals that slight modifications in the thread structure can dramatically impact the formation, stability, and interactions between components of rotaxanes.

Light-responsive rotaxane-based materials: inducing motion in the solid state

Light-responsive rotaxane-based solid-state materials are ideal scaffolds in order to develop smart materials due to the properties provided by the mechanical bond, such as control over the dynamics of the components upon application of external stimuli. This perspective aims to highlight the relevance of these materials, by pointing out recent examples of photoresponsive materials prepared from a rotaxanated architecture in which motion of the counterparts and/or macroscopic motion of the interlocked materials are achieved. Although further development is needed, these materials are envisioned as privileged scaffolds which will be used for different advanced applications in the area of molecular machinery.

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.

Recent Advances in the Preparation of Delivery Systems for the Controlled Release of Scents

Scents are volatile compounds highly employed in a wide range of manufactured items, such as fine perfumery, household products, and functional foods. One of the main directions of the research in this area aims to enhance the longevity of scents by designing efficient delivery systems to control the release rate of these volatile molecules and also increase their stability. Several approaches to release scents in a controlled manner have been developed in recent years. Thus, different controlled release systems have been prepared, including polymers, metal-organic frameworks and mechanically interlocked systems, among others. This review is focused on the preparation of different scaffolds to accomplish a slow release of scents, by pointing out examples reported in the last five years. In addition to discuss selected examples, a critical perspective on the state of the art of this research field is provided, comparing the different types of scent delivery systems.

Cyclodextrin-based Schiff base pro-fragrances: Synthesis and release studies

A simple method for the preparation of β-cyclodextrin derivatives containing covalently bonded aldehydes via an imine bond was developed and used to prepare a series of derivatives from 6I-amino-6I-deoxy-β-cyclodextrin and the following volatile aldehydes – cinnamaldehyde, cyclamen aldehyde, lilial, benzaldehyde, anisaldehyde, vanillin, hexanal, heptanal, citral, and 5-methylfurfural. Subsequently, the rate of release of the volatile compound from selected pro-fragrances, as a function of the environment (solvent, pH), was studied by 1H NMR spectroscopy (for benzaldehyde) and static headspace-gas chromatography (for benzaldehyde, heptanal, and 5-methylfurfural). The aldehyde release rate from the imine was shown to depend substantially on the pH from the solution and the air humidity from the solid state.

Photoresponsive Metal-Organic Frameworks as Adjustable Scaffolds in Reticular Chemistry

The easy and remote switching of light makes this stimulus an ideal candidate for a large number of applications, among which the preparation of photoresponsive materials stands out. The interest of several scientists in this area in order to achieve improved functionalities has increase parallel to the growth of the structural complexity of these materials. Thus, metal-organic frameworks (MOFs) turned out to be ideal scaffolds for light-responsive ligands. This review is focused on the integration of photoresponsive organic ligands inside MOF crystalline arrays to prepare enhanced functional materials. Besides the summary of the preparation, properties and applications of these materials, an overview of the future outlook of this research area is provided.

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. 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.