Design of Stimuli-Responsive Dynamic Covalent Delivery Systems for Volatile Compounds (Part 2): Fragrance-Releasing Cleavable Surfactants in Functional Perfumery Applications

Molecular Release by the Rotaxane and Pseudorotaxane Approach

The controlled release of target molecules is a relevant application in several areas, such as medicine, fragrance chemistry and catalysis. Systems which pursue this implementation require a fine-tune of the start and rate of the release, among other properties. In this scenario, rotaxane- and pseudorotaxane-based systems are postulated as ideal scaffolds to accomplish a precise cargo release, due to the special features provided by the intertwined arrangement. This short review covers advances towards the controlled release of different molecules using rotaxane- and pseudorotaxane-based systems, both in solution and in the solid state.

Thiadiazole chitosan conjugates as a novel cosmetic ingredient for rinse-off hair conditioners: design, formulation, characterization and in silico-molecular docking studies

Recently, chitosan derivatives, as eco-sustainable and renewable products, have been recorded to be highly effective toward cosmetics with potent biological activity. The main core of this research is to develop an organic hair conditioner (OHC) based on two chitosan-thiadiazole conjugates, chitosan-(ethylthio‑thiadiazole) (CH-ETD) and chitosan-(benzylthio‑thiadiazole) (CH-BTD), with natural fragrances. A series of nine OHC formulae were prepared (CH1-CH3 for chitosan based OHC, E1-E3 for CH-ETD based OHC, and B1-B3 for CH-BTD based OHC) and characterized based on their visual examination, pH, thermal stability, dirt dispersion, moisturizing time, percentage of solid content, hair irritation, rinsing, combing, and the luster. The results showed that the pH values of all OHC formulae were 4.2-4.7 which is considered acceptable to avoid skin irritation. A distinctive film surrounds each individual hair shaft in the CH-ETD and CH-BTD treated groups when compared to control hair without the application of hair conditioner under a scanning electron microscope SEM with a magnification power of 100 μm. Additionally, every single hair shaft is clearly covered, and the control group exhibited noticeable hair issues that were not observed in the treated groups, which showed no signs of tangling. Due to the end-use performance properties of the formulated hair conditioner products, it can be concluded that the formulas of (CH, E2, and B2) were the best efficacy; hair easier to style, detangle the hair, retain moisture, not be very thick, not cause irritation or inflammation, minimize frizz, and create a protective barrier on the hair. These findings collectively validate the potential of CH-ETD and CH-BTD based formulations coupled with natural perfumery as a transformative approach to hair care, aligning with consumer preferences for both efficacy and environmental sustainability. Furthermore, in this work, docking studies have been conducted to provide theoretical proof about the significant roles of chitosan and keratin in hair growth and cosmetic applications (skin).

Dynamic covalent surfactants and their uses in the development of smart materials

Dynamic covalent chemistry, which leverages the dynamic nature of reversible covalent bonds controlled by the conditions of reaction equilibrium, has demonstrated great potential in diverse applications related to both the stability of covalent bonds and the possibility of exchanging building blocks, imparting to the systems the possibility of "error checking" and "proof-reading". By incorporating dynamic covalent bonds into surfactant molecular architectures, combinatorial libraries of surfactants with bespoke functionalities can be readily fabricated through a facile strategy, with minimum effort in organic synthesis. Consequently, a multidisciplinary field of research involving the creation and application of dynamic covalent surfactants has recently emerged, which has aroused great attention in surfactant and colloid science, supramolecular chemistry, self-assembly, smart materials, drug delivery, and nanotechnology. This review reports results in this field published over recent years, discusses the possibilities presented by dynamic covalent surfactants and their applications in developing smart self-assembled materials, and outlines some future perspectives.

Thermal/Redox-triggered release of pyrazinic functional molecules by coordination polymers with luminescence monitoring ability

Storage of volatile active molecules, along with the prolongation of their specific functions, requires the use of regulatable carriers. Pyrazine derivatives are highly volatile compounds with a broad application owing to their flavoring, pharmaceutical, antimicrobial, antiseptic, and insecticidal properties. In this study, pyrazines were stored by coordinating them with cuprous iodide to easily generate a series of luminescent coordination polymer (CP)-based carriers. The CPs could respond to thermal-redox stimuli and manipulate pyrazine release by breaking the labile Cu-N bonds when triggered by the two stimuli. Moreover, the release process could be visualized by decreased luminescence caused by the gradual decomposition of CP structures. The loading efficiencies ranged from 31% to 38%, and the controlled release behaviors accord with the zero-order kinetics. This work is the first to prove that CPs could function as dual stimuli-mediated delivery systems, which hold the potential to control the release and strengthen the usability of functional molecules.

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.

Amphiphilic Graft Copolymers for Time-Delayed Release of Hydrophobic Fragrances

When a controlled or retarded release of perfumes is required such as in cosmetics or cleaning products, polymers can be applied as encapsulation agents. With regard to such applications, we investigated two amphiphilic graft copolymers featuring a polydehydroalanine (PDha) backbone and different hydrophobic side chains. Hereby, grafting of aliphatic octyl side chains (PDha-g-EOct) enabled the adsorption of the aliphatic fragrance tetrahydrolinalool with moderate loads, whereas benzyl side chains (PDha-g-BGE) allowed taking up aromatic fragrances, for example, amylsalicylate-n with exceptionally high loads of up to 8 g g^-1. The side-chain density was studied as well but had no significant influence on the loading. In addition, the characterization and quantification of the load by NMR and thermogravimetric analysis were compared, and it was also possible to load the aromatic model fragrance into the graft copolymer with aliphatic side chains. After 3 months, the load had decreased by 40-50% and, hence, such systems are of interest for a long-term release of perfumes over months. Although this study is a proof-of-concept, we foresee that such polyampholytic graft copolymers can be tailored for the adsorption of a variety of hydrophobic perfumes simply by altering polarity and chemistry of the side chain.

Construction of Supramolecular Systems That Achieve Lifelike Functions

The Nobel Prize in Chemistry was awarded in 1987 and 2016 for research in supramolecular chemistry on the "development and use of molecules with structure-specific interactions of high selectivity" and the "design and production of molecular machines", respectively. This confirmed the explosive development of supramolecular chemistry. In addition, attempts have been made in systems chemistry to embody the complex functions of living organisms as artificial non-equilibrium chemical systems, which have not received much attention in supramolecular chemistry. In this review, we explain recent developments in supramolecular chemistry through four categories: stimuli-responsiveness, time evolution, dissipative self-assembly, and hierarchical expression of functions. We discuss the development of non-equilibrium supramolecular systems, including the use of molecules with precisely designed properties, to achieve functions found in life as a hierarchical chemical system.

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.

Volatile Aroma Surfactants: The Evaluation of the Adsorption-Evaporation Behavior under Dynamic and Equilibrium Conditions

Multicomponent heterogeneous systems containing volatile amphiphiles are relevant to the fields ranging from drug delivery to atmospheric science. Research presented here discloses the individual interfacial activity and adsorption-evaporation behavior of amphiphilic aroma molecules at the liquid-vapor interface. The surface tension of solutions of nonmicellar volatile surfactants linalool and benzyl acetate, fragrances as such, was compared with that of the conventional surfactant sodium dodecyl sulfate (SDS) under equilibrium as well as under no instantaneous equilibrium, including a fast-adsorbing regime. In open systems, the increase in the surface tension on a time scale of ∼10 min is evaluated using a phenomenological model. The derived characteristic mass transfer constant is shown to be specific to both the desorption mechanism and the chemistry of the volatile amphiphile. Fast-adsorbing behavior disclosed here, as well as the synergetic effect in the mixtures with conventional micellar surfactants, justifies the advantages of volatile amphiphiles as cosurfactants in dynamic interfacial processes. The demonstrated approach to derive specific material parameters of fragrance molecules can be used for an application-targeted selection of volatile cosurfactants, e.g., in emulsification and foaming, inkjet printing, microfluidics, spraying, and coating technologies.

Tensiometry as a Simple Analytical Method for Quantification of Solubility and Release of Aroma Molecules in Aqueous Media

Dynamic tensiometry is shown to be a high-potential analytical tool in assessing physico-chemical characteristics of fragrance molecules, such as solubility limit, volatility as well as much rarely assessed interfacial activity of these amphiphilic molecules. Surface tension of aqueous solutions of selected essential oils has been measured as a function of time and fragrance concentration using maximum bubble pressure method. The effect of the temperature and saline solution on the rate of dissolution in water was assessed. Dynamic surface tension turned to be sensitive to the composition of fragrances, as demonstrated on examples of natural and synthetic mixtures. Furthermore, presented work reveals the possibility of maximum bubble pressure tensiometry method to quantify the amount of fragrance compositions in flavored salts, including the artificially aged carrier samples. Suggested here analytical approach can be used for the detection of the purity of essential oils, for the optimization of compositions and of the manufacturing processes of fragrances-containing products, as well as for the assessment of the release/evaporation of fragrances from carrier systems.