Designing hydrophobic sheet protected Eu(III)-tetracycline complex using long chain unsaturated fatty acid: Efficient 'antenna effect' in aqueous medium

We have designed a novel ternary system consisting of Tetracycline hydrochloride (TC), Eu(III) and unsaturated long chain fatty acid (Oleic acid, α-Linolenic acid) in aqueous buffer at physiological pH of 7.2. The systems exhibit highly efficient 'antenna effect' of Eu(III) compared to that observed in the binary system of TC and Eu(III) [Eu3TC]. Transients of Eu(III) emission in aqueous buffer and D2O buffer show that the number of water molecules, coordinated directly to the Eu(III) ion, decreases from 12 in Eu3TC to 2 in the ternary system using oleic acid. The micelle formed by the bent conformation of the unsaturated oleic acid provides a hydrophobic sheet on all sides of Eu3TC complex protecting Eu(III) from interacting with O-H oscillator. The simple biocompatible system could be used for imaging purpose, and biomedical assay.