Polydiacetylene from diacetylene lipids containning oligo(ethylene glycol) as thermal and metal ion sensors

Abstract

Three ethylene glycol esters and one ethanolamide derivatives of 10,12-pentacosadiynoic acid (PCDA) were synthesized and studied as a modulator for poly(PCDA) sensor. Ethylene glycol (EG-PCDA), triethylene glycol (3EG-PCDA) and pentaethylene glycol esters (5EG-PCDA) were synthesized by simple acid catalyzed esterification of PCDA with ethylene glycol and the corresponding oligo(ethylene glycol). The preparation of the amide derivative, NEG-PCDA, was performed via a condensation between the methyl ester of PCDA and ethanolamine. The mixed lipids between PCDA and its derivative can be dispersed in milli-Q water by ultrasonication, giving translucent sol. After being irradiated with UV light, the mixed lipid sols undergo photopolymerization to generate the desired blue polydiacetylene (PDA) sols. The blue to red thermochromic transition of PDA sols were monitored by observing the absorbance of the red phase of PDA at 540 nm in the range of 20-80 C using temperature variable UV-vis spectrometer. The derivative (dA/dT) plot of the PDA sols containing diacetylene esters showed two steps of color transition while the PDA sol containing diacetylene amide exhibited continuous one-stepped color transition. In the two-stepped color transition, the second step observed around 65 °C associated with the color transition temperature of poly(PCDA). The PDA sols containing 30% mole of the diacetylene esters were assessed for colorimetric detection of heavy metal ions such as Cd²⁺, Co²⁺, Cu²⁺, Fe²⁺, Hg²⁺, Ni²⁺, Pb²⁺ and Zn²⁺. At 100 µM, only Pb²⁺ caused a distinct color change of the sol from blue to red for the PDA sol of 5EG-PCDA/PCDA mixed lipid. The sol showed the detection limit of Pb²⁺ as low as 10 µM (~2 ppm).