FLUORESCENT CHEMOSENSORS FROM BIS(1,4-DIHYDROPYRIDINE) DERIVATIVES WITH OLIGOETHYLENE GLYCOL LINKER

Abstract

To study the possibility of using the 1,4-dihydropyridine (DHP) derivatives as fluorescent sensor and comprehend their allosteric property, novel DHP derivatives (1c and 1d) thus were synthesized from 4-aminophenol via cyclotrimerization reaction of β-amino acrylate intermediate. These compounds offer great fluorescent properties and were easy to linked with various lengths of oligoethylene glycol to gain bis DHPs (5a-d) and mono DHPs (6c, 7 and 8) for the development as fluorescent chemosensor. Glycol chain conceptually did not only enhance its water solubility but also acted as a receptor unit in organic media. The target compounds were studied in terms of absorption and emission properties in both aqueous and organic solutions. In MeOH, all substances reveal the maximum absorption wavelengths at around 360-366 nm, the maximum emission wavelengths at 454-466 nm and fluorescent quantum efficiencies in the value of 0.74-0.32. Moreover, metal ion sensing properties were ascertained and exposed that all compounds selected with gold(III) ion (Au3+) in aqueous media. Their fluorescent signals were quenched as a proportion of time and the probe 5d exhibited the limit of detection of 2.65 µM. These behaviors are expected from the oxidation reaction that converts DHP ring into pyridinium ring by Au3+ specific catalyst. Furthermore, the experiments in surfactant system (Triton X-100) illustrated that there are only a group of bis DHPs (5a-d) that their fluorescent intensities were enhanced, and compound 5d was selectively quenched against iron(II) ion (Fe2+) with the limit of detection of 1.69 µM. In pH buffer, only DHP-4AP probes (1c and 1d) responded by decreasing the fluorescent intensity in base region. Compound 1d exhibited the pKa value of 9.23 ± 0.03 and could be applied as a pH sensor in range of 8.6 to 9.8. Other applications of DHP probes such protein sensor and oxidant sensor were also studied.