Photolabile acetals as profragrances: the effect of structural modifications on the light-induced release of volatile aldehydes on cotton.

Because volatile compounds evaporate from surfaces that are usually exposed to daylight, photoresponsive delivery systems are particularly suitable to control their release. In the present study, we investigated 4,4-diphenyl-4H-benzo[d][1,3]dioxins as profragrances for the light-induced delivery of aldehydes in functional perfumery. The efficiency of fragrance release was investigated on cotton after direct and indirect surface deposition from a fabric softening formulation as a function of the substitution pattern of the profragrance structure. Dynamic headspace analysis above the cotton surface demonstrated that the structure of the profragrance had a much larger effect on the fragrance release than did the amount of deposition on the target surface. Although some trends observed for the photolysis in solution also applied to the reaction on cotton, it is not generally possible to predict the photochemical behaviour of structurally different precursors on surfaces from their solution properties. The fact that the present system performed on a dry surface makes it an interesting light-triggered delivery vehicle for other classes of bioactive volatile compounds, such as pheromones or agrochemicals.

Stabilized hemiacetal complexes as precursors for the controlled release of bioactive volatile alcohols.

Hemiacetals of pyridine-2-carbaldehyde derivatives and volatile alcohols can be stabilized in organic solution in the presence of protons or different metal cations. Despite the inherent instability of hemiacetals in H(2) O, stabilizing them with zinc(II) triflate and adding them to a cationic surfactant formulation resulted in the slow release of the alcohol from cotton surfaces being treated with the hemiacetal complex. Stabilized hemiacetals might thus be suitable delivery systems of bioactive volatiles by rapid hydrolysis in H(2) O-based media.

Release of bioactive volatiles from supramolecular hydrogels: influence of reversible acylhydrazone formation on gel stability and volatile compound evaporation.

In the presence of alkali metal cations, guanosine-5'-hydrazide (1) forms stable supramolecular hydrogels by selective self-assembly into a G-quartet structure. Besides being physically trapped inside the gel structure, biologically active aldehydes or ketones can also reversibly react with the free hydrazide functions at the periphery of the G-quartet to form acylhydrazones. This particularity makes the hydrogels interesting as delivery systems for the slow release of bioactive carbonyl derivatives. Hydrogels formed from 1 were found to be significantly more stable than those obtained from guanosine. Both physical inclusion of bioactive volatiles and reversible hydrazone formation could be demonstrated by indirect methods. Gel stabilities were measured by oscillating disk rheology measurements, which showed that thermodynamic equilibration of the gel is slow and requires several cooling and heating cycles. Furthermore, combining the rheology data with dynamic headspace analysis of fragrance evaporation suggested that reversible hydrazone formation of some carbonyl compounds influences the release of volatiles, whereas the absolute stability of the gel seemed to have no influence on the evaporation rates.