Preparation And Controlled Release Of PH-triggered Pro-fragrances

Fragrances are composed of a variety of aromatic compounds with low molecular weight and high volatility,which are unstable,diffusive and easily lost in a short period of time,so it is important to extend the retention time of fragrances via physical and chemical methods for controlled and/or sustained release.As an chemical method,pro-fragrances can release the fragrance under the influence of moisture,temperature,light and oxygen,while the release rate of aromatic compounds can be changed by the intensity of the stimulus.In this thesis,a series of nicotinoylhydrazone-based pro-fragrance,NTA1～NTA4,have been prepared by reacting nicotinoylhydrazine with a series of aromatic benzaldehydes bearing different electron-donating groups.Their chemical structures and spectroscopy have been confirmed by FT-IR,NMR,HRMS and UV-vis spectroscopies.Controlled release studies of these pro-fragrances in an acidic environment reveal that:(1)these pro-fragrances are p H-triggered and the increase of hydrogen-ion concentration speeds up the release rate,while the reduction has the opposite result;(2)a strong electron-donating substituent accelerates the release rate,while weak electron donor groups favor the deceleration of fragrance release,consistent with the simulation of the molecular electrostatic potential calculation;(3)intramolecular hydrogen bond formation(–OH…N=C–)has an interesting positive impact upon the stability of the hydrazone bridge.These results suggest that both p H value and substituent effect are of paramount importance for the controlled release behavior.(4)In addition,the release kinetics are also investigated and the release rate constant could be estimated with a first-order kinetic model(R~2>0.98).Furthermore,it is demonstrated that fragrance precursors on cotton fabrics could be an efficient controlled release strategy for fragrant aldehydes after exposure to an ambient atmosphere for several days,compared to a reference sample containing the raw aroma chemicals.(5)At the same time,the bacteriostasis experiment results of pro-fragrances showed that the inhibitory effect of the pro-fragrances on Staphylococcus aureus was not obvious,but it showed a certain bacteriostasis effect on Escherichia coli.The results described above can help in the targeted design of fragrance precursors with a hydrazone scaffold aimed at the controlled release of fragrance in fine and functional perfumery systems.