Design of Stimuli‐Responsive Dynamic Covalent Delivery Systems for Volatile Compounds (Part 1): Controlled Hydrolysis of Micellar Amphiphilic Imines in Water

Abstract

Despite their intrinsic hydrolysable character, imine bonds can become remarkably stable in water when selfassembled in amphiphilic micellar structures. In this work, we systematically studied some of these structures and the influence of various parameters that can be used to take control of their hydrolysis, including pH, concentration, the position of the imine function in the amphiphilic structure, relative lengths of the linked hydrophilic and hydrophobic moieties. Thermodynamic and kinetic data led us to the rational design of stable imines in water, partly based on the location of the imine function within the hydrophobic part of the amphiphile and on a predictable quantitative term that we define as the total hydrophilic-lipophilic balance (HLB). In addition, we show that such stable systems are also stimuliresponsive and therefore, of potential interest in trapping and releasing micellar components on demand.

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

“…In our preceding publication, [17] we showed that, at initial imine concentrations of ca. 10 mM, the cleavable imine surfactant rapidly hydrolysed in the presence of PEG 25 mono- stearate as the co-surfactant, but then reached stable equilibrium with a constant imine concentration (ca.…”

“…Perfume solubilization and fragrance release from microemulsions: single-surfactant system Cleavable surfactant imines 1-4 have calculated total hydrophilic-lipophilic balance (HLB(T)) values varying between 12.79 (2) and 13.64 (3) (Table 1), which are in the range of noncleavable surfactants commonly used in functional perfumery. [17] As a first proof of concept to use cleavable imines as surfactants in practical applications, we determined the amount of 1-4 required for the solubilization of a typical model perfume in water.…”

“…General: The preparation of cleavable surfactant imines 1-4 has been described in our previous report. [17] Dynamic headspace analysis: Aliquots of the formulations containing the model perfume and surfactant formulations were pipetted onto a watch glass or into a crystallizing dish (in the case of the perfumed shower gel formulations), which were placed inside a homemade headspace sampling cell (ca. 625 mL inner volume).…”

“…We furthermore demonstrated that placing the hydrolytically labile imine group within the hydrophobic part of the micelle, for example by using a linker between the labile imine group and the hydrophilic part of the amphiphile, resulted in relatively stable structures. [17] Similarly, in a different context, Smulders and co-workers [18] recently showed that the presence of polar domains in close proximity to the imine bond considerably accelerated the imine exchange within covalent adaptable networks.…”

“…In our previous work, we have built dynamic imines connecting hydrophobic and hydrophilic moieties in order to generate dynamic covalent amphiphiles, which can protect their imine bonds from fast hydrolysis in water because of their self-assembly in various micellar structures. [14][15][16] In particular, in the preceding paper, [17] we showed that amphiphilic imines (e. g. 1-4, Scheme 1), obtained by condensation of a fragrance aldehyde as the hydrophobic part with an amine derived from a poly(propylene oxide) and poly(ethylene oxide) diblock copolymer of variable length (such as Jeffamines® M1000 and M2070) as the hydrophilic section have surfactant properties and self-assemble into micellar structures in water. We furthermore demonstrated that placing the hydrolytically labile imine group within the hydrophobic part of the micelle, for example by using a linker between the labile imine group and the hydrophilic part of the amphiphile, resulted in relatively stable structures.…”