Acidichromism and Ionochromism of Luteolin and Apigenin, the Main Components of the Naturally Occurring Yellow Weld: A Spectrophotometric and Fluorimetric Study

Abstract

Luteolin and apigenin, extracted from Reseda luteola L., were spectrophotometrically and fluorimetrically studied. The spectra were investigated as a function of pH in methanol/water solutions (1/2, v/v) in the 2-12 pH range. The absorption spectra markedly shifted to the red by increasing the pH. Three acid-base dissociation steps were detected for luteolin (pK (a) = 6.9; 8.6; 10.3) and two for apigenin (pK (a) = 6.6; 9.3). Fluorescence emission was very weak or undetectable (Phi (F) < 10(-4)) in acidic solution, but increased in intensity with increasing the pH. Both molecules exhibited a great propensity towards complex formation with metal ions, with association constants on the order of 10(5)-10(7) for the first complexation step; in the presence of excess Al(3+) ions, multiple equilibria were detected. A marked fluorescence enhancement was observed upon complexation with Al(3+) ions (Phi (F) approximately 1 for luteolin and approximately 10(-2) for apigenin).

Spectroscopic Properties of Flavonoids in Various Aqueous-Organic Solvent Mixtures

“…According to the previous study, the fluorescence emission spectra of API, which was extracted from plant and isolated using preparative HPLC, exhibited a double emission at 430 and 534 nm. 28 This extracted API should be oxidized and aged fully because that material was left in air for a long time at room temperature. It would take a lot of time for extraction from plants and isolation process.…”

Historical organic dyes: a surface‐enhanced Raman scattering (SERS) spectral database on Ag Lee–Meisel colloids aggregated by NaClO4

“…This kind of coordination is also supported by spectrophotometric studies of metal complexes with luteolin and apigenin. [48] As far as SERS spectra of safflower yellow, safflower red (carthamin) and kamala (Fig. 6(e)-(g)) are considered, they show a rather similar pattern, probably due to a preferred interaction between the dye molecule and the metal surface through the 2-hydroxychalcone moiety of the molecule itself, i.e.…”

Use of hollow fiber liquid phase microextraction and HPLC for extraction and determination of apigenin in human urine after consumption of Satureja sahendica Bornm.

“…Apigenin has slightly acidic properties [16], therefore their existing forms (neutral or ionic form) could be changed by changes in pH. In order to reduce the solubility of analyte in water and increase the extraction yield of apigenin into the organic solvent, apigenin in donor phase should be in neutral form, therefore, the pH of donor phase were adjusted in the range of 1.0-6.0 by addition of 1 mol/L HCl.…”