Synthesis and application of molecular probe for detection of hydroxyl radicals produced by Na¹²⁵I and gamma-rays in aqueous solution

Abstract

Purpose: To synthesize N-(3-(3-aminopropylamino)propyl)-2-oxo-2H-chromene-3-carboxamide (7), a novel DNA-binding, coumarin-based, fluorescent hydroxylradical (^•OH) indicator and to assess its quantum efficiency compared with that of coumarin-3-carboxylic acid (1) and N1,N12-bis[2-oxo-2H-chromene-3-carbonyl]- 1,12-diamine-4,9-diazadodecane (9).

Materials and methods: Using computer-generated molecular modeling, 7 and 9 and their respective 7-hydroxylated derivatives 8 and 10 were docked onto DNA dodecamer d(CGCGAATTCGCG)2, the ligand–DNA complexes were energy minimized, and binding free energies and inhibition constants were calculated. Compound 7 was judged an appropriate target molecule and was synthesized. Compounds 1, 7, and 9 were incubated with Na¹²⁵I or irradiated with ¹³⁷Cs γ-rays, and the influence of pH, dose, type of radiation, and the concentration of indicator on fluorescence yield were determined.

Results: Non-fluorescent 7 and 9 are converted to fluorescent, 7-hydroxylated derivatives 8 and 10 after interaction with ^•OH in aqueous solution. For 1, 7, and 9, hydroxylation yield increases linearly with both Na¹²⁵I dose (0–700×10⁶ decays) and ¹³⁷Cs dose (0–11.0 Gy). Fluorescence induction is significantly reduced at acidic pH and the fluorescent quantum yield of 8 is ∼3 times that of 2 or 10 at pH 7.0. With Na¹²⁵I incubation and γ-ray irradiation, the fluorescence signal of 7 increases linearly with concentration and saturates at ∼50 μM.

Conclusion: Compound 7 quantifies lower concentrations of ^•OH than do 1 and 9. This detector is therefore likely to be a good reporter of ^•OH produced within a few nanometers of DNA.

Keywords:

• Coumarin–polyamine probe
• hydroxyl radical (^•OH)