Excited state proton transfer in dimethyl-n-dioctadecylammonium chloride and dihexadecyl phosphate vesicles containing the phytohormone indolyl-3-acetic acid

Abstract

Using fluorescence techniques, the excited state proton transfer rate of indolyl-3-acetic acid, a plant growth hormone (auxin) was studied in a reversed micelle consisting of dimethyl-n-dioctadecylammonium chloride and dihexadecyl phosphate (molar ratio 1:1) in cyclohexane in the presence of water. The outstanding finding was the ultra fast proton transfer rate of excited state indolyl-3-acetic acid (kp* = (2.2 ± 0.2) · 10 12 M −1 s −1 and k d * = (2.1 ±0.2) · 1O 7 s −1) in this reversed micelle system. This ultra fast proton transfer rate was between the values obtained for proton transfer in water and that derived from ice. The proximity of the deprotonated carboxyl group of indolyl-3-acetic acid to the inner surface area of the DODAC/DHP micelle is responsible for this fast rate process.