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.

Dynamic mixtures generated by reversible aminal formation of fragrance aldehydes with N,N-dibenzyl alkyldiamines in aqueous systems were found to be suitable delivery systems for the controlled release of bioactive volatiles.

Dedicated to Dr. Ferdinand Näf on the occasion of his 65th birthday Amphiphilic polystyrene-and polymethacrylate-based b-acyloxy ketones were investigated as potential delivery systems for the controlled release of damascones by retro-1,4-addition in applications of functional perfumery. A series of random copolymers being composed of the hydrophobic damascone-release unit and a second hydrophilic monomer were obtained by radical polymerization in organic solution by using 2,2'-azobis[2-methylpropanenitrile] (AIBN) as the radical source (Schemes 2 and 3). A first evaluation of the polymer conjugates in acidic or alkaline buffered aqueous solution, and in the presence of a surfactant, showed that polymethacrylates and polystyrenes having a carboxylic acid function as hydrophilic group are particularly interesting for the targeted applications ( Table 2). The release of d-damascone (1) from polymers with poly(methacrylic acid) and poly(vinylbenzoic acid) comonomers in different stoichiometric ratios was thus followed over several days at pH 4, 7, and 9 by comparison of fluorescence probing, solvent extraction, and particle-size measurements (Tables 3 and 4). In acidic media, the polymers were found to be stable, and almost no d-damascone (1) was released. In neutral or alkaline solution, where the carboxylic acid functions are deprotonated, the concentration of 1 increased over time. In the case of the polymethacrylates, the fluorescence probing experiments showed an increasing hydrophilicity of the polymer backbone with increasing fragrance release, whereas in the case of the polystyrene support, the hydrophilicity of the environment remained constant. These results suggest that the nature of the polymer backbone may have a stronger influence on the fragrance release than the ratio of hydrophilic and hydrophobic monomers in the polymer chain.1. Introduction. -The long-lastingness of fragrance perception is often directly associated with the efficiency of perfumed consumer products in body care or household applications. As a consequence of their high volatility, many attempts to control the evaporation of fragrances over time have been undertaken to increase their performance during and after application. As an alternative to encapsulation technologies (see, e.g., [1]), the development of chemical delivery systems for the controlled release of fragrances has become a more and more widely investigated area of research [2]. A series of precursor molecules, so called 'pro-fragrances', have been prepared, and a broad variety of reaction conditions, such as hydrolysis [3] [4] or the change of pH [5] [6], oxidation [7], the action of temperature, light [8] [9], enzymes or microorganisms [10] have been used to trigger the release of perfumery raw materials from their corresponding precursors.Recently, damascones (= 1-(2,6,6-trimethylcyclohexen-1-yl)but-2-en-1-ones) or damascenones (= 1-(2,6,6-trimethylcyclohexadien-1-yl)but-2-en-1-ones), the so-called rose ketones [11], were successfully released from different monomeri...

Poly(maleic acid monoester)-based β-mercapto ketones were synthesized and investigated as potential delivery systems for the controlled release of bioactive, volatile, α,β-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 β-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.

Natural daylight is suitable for controlling the release of volatile compounds, such as fragrances, from different surfaces. Upon UVA irradiation, 2-oxoacetates (α-ketoesters) fragment in a Norrish type II reaction to form aldehydes and ketones. To profit from the stabilising effect of polymers in an aqueous environment, we extended our previous work on 2-oxoacetate profragrances to two alternative polymeric delivery systems. We thus compared the light-induced release of fragrance aldehydes from 2-oxo-2-phenylacetates encapsulated into melamine-formaldehyde core-shell microcapsules, on the one hand, with latex nanoparticle dispersions obtained by radical (co-)polymerisation of fragrance-releasing 2-oxo-2-(4-vinylphenyl)acetate monomers, on the other hand. We could demonstrate that microcapsules prepared with a minimum amount of resin in their shell performed best, while the size of the latex nanoparticles influenced the deposition of the delivery systems from aqueous media onto the target surface. Furthermore, dynamic headspace analysis above cotton showed that both systems are alternative and reliable techniques to control the light-induced delivery of fragrances in practical applications under natural daylight conditions.