Controlled release of encapsulated bioactive volatiles by rupture of the capsule wall through the light-induced generation of a gas.

The encapsulation of photolabile 2-oxoacetates in core-shell microcapsules allows the light-induced, controlled release of bioactive compounds. On irradiation with UVA light these compounds degrade to generate an overpressure of gas inside the capsules, which expands or breaks the capsule wall. Headspace measurements confirmed the light-induced formation of CO and CO2 and the successful release of the bioactive compound, while optical microscopy demonstrated the formation of gas bubbles, the cleavage of the capsule wall, and the leakage of the oil phase out of the capsule. The efficiency of the delivery system depends on the structure of the 2-oxoacetate, the quantity used with respect to the thickness of the capsule wall, and the intensity of the irradiating UVA light.

Influence of the backbone structure on the release of bioactive volatiles from maleic acid-based polymer conjugates.

Poly(maleic acid monoester)-based ß-mercapto ketones were synthesized and investigated as potential delivery systems for the controlled release of bioactive, volatile, α,ß-unsaturated enones (such as damascones and damascenones) by retro 1,4-addition. The bioconjugates were prepared in a one-pot synthesis using 2-mercaptoethanol as a linker. The thiol group of 2-mercaptoethanol adds to the double bond of the enone to form a ß-mercapto ketone, which was then grafted via nucleophilic ring-opening of the remaining alcohol function onto a series of alternating copolymers of maleic anhydride and 1-octadecene, ethylene, isobutylene, and methyl vinyl ether. The influence of copolymer backbones on the release of δ-damascone was investigated in buffered aqueous solution as a function of pH and time. In the presence of a cationic surfactant, the polymer conjugates were transferred from an aqueous medium to a cotton surface. The deposition and the release of δ-damascone from the cotton surface as a function of the polymer backbone structure were measured by fluorescence spectroscopy and dynamic headspace analysis, respectively. All polymer conjugates were found to deliver higher amounts of the volatile into the headspace than the reference consisting of unmodified δ-damascone. Polymers with a hydrophobic backbone were generally efficiently deposited on the cotton surface, but released δ-damascone only moderately in solution. Conjugates with a more hydrophilic backbone release the active compound more efficiently in water, but are deposited to a lower extent onto the target surface. A good balance of the hydrophobicity and hydrophilicity of the polymer backbone is the key factor to maximize the deposition of the conjugates on the target surface and to optimize the release of the bioactive volatiles.