Effect of Acylation of Flavones with Hydroxycinnamic Acids on their Spectral Characteristics

Abstract

The absorption spectra of twenty-one flavones including glycosides of apigenin, luteolin, chrysoeriol and tricin, nonacylated or acylated with coumaric, ferulic or sinapic acids, were examined to document the influence of acylation on their spectral characteristics. Acylation did not shift the absorption maximum of band II, but the molar absorption coefficients of this band increased 1.3–2.0 fold. Acylation of apigenin and chrysoeriol glycosides did not shift the absorption maximum of band I and the absorption maxima of nonacylated and acylated compounds were at 319–334 nm, but this increased their molar absorption coefficients 1.7–3.0 fold. For luteolin and tricin glycosides, nonacylated compound maxima of absorption of band I were in the range of 342–349 nm. Acylation shifted band I absorption maxima to 329–340 nm and increased their molar absorption coefficient 1.6–1.8 fold. These data document that acylation of flavones leads to significant increase of their absorption in the 280–320 nm region and can be an effective mechanism of protecting plants against UV-B radiation.