Influence of the Backbone Structure on the Release of Bioactive Volatiles from Maleic Acid-Based Polymer Conjugates

Abstract

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.

Controlled Release of Damascone from Poly(styrene-co-maleic anhydride)-based Bioconjugates in Functional Perfumery

“…In a second study, alternating copolymers of maleic anhydride were modified by the ring opening of the reactive anhydride unit with the hydroxyl group of a precursor resulting from the reaction between δ-damascone and 2-mercaptoethanol [27]. Various alternating copolymers of maleic anhydride with other comonomers (e.g., 3, Figure 2) were easily prepared in a one-pot, two-step reaction sequence to afford a series of biocompatible delivery systems [27].…”

“…Various alternating copolymers of maleic anhydride with other comonomers (e.g., 3, Figure 2) were easily prepared in a one-pot, two-step reaction sequence to afford a series of biocompatible delivery systems [27].…”

“…The release of δ-damascone from the polymer conjugates has been measured in buffered aqueous solution as a function of pH and time, as well as after deposition onto a fabric surface in the presence of a cationic surfactant. The most efficient release of δ-damascone was observed for a poly(maleic acid)-based copolymer with a well-adjusted balance between hydrophilicity (giving rise to high release rates) and hydrophobicity (resulting in increased surface deposition) of the polymer backbone [27].…”

“…Reaction conditions allowing covalent bond cleavage and the release of the volatile biomolecule from its precursor comprise changes in temperature or pH, hydrolysis, oxidation and exposure to daylight or enzymes [9][10][11][12][13][14][15]. In addition to small molecular precursors, polymer bioconjugates have been investigated for the slow release of volatile compounds [9][10][11][16][17][18][19][20][21][22][23][24][25][26][27][28]. The ease of structural modulation of polymeric materials was expected to allow the selective influence of the properties of the delivery systems and their adaptation to the particular requirements of the formulations into which they were incorporated.…”

“…The structure of polymers, especially amphiphilic ones, was found to strongly influence the release kinetics of the volatile biomolecules, especially if the formation of self-aggregated structures was possible. The solubility (dispersibility) of the delivery system in aqueous product formulations and the deposition of the conjugates on different surfaces have been identified as important parameters to be considered [23][24][25][26][27].…”