雌马酚的吸收光谱和荧光光谱研究

Study on the aborption and fluorescence spectra of equol

研究了雌马酚在不同pH条件下的紫外-可见吸收光谱和荧光光谱,从分子结构的角度解释了两种光谱在不同pH条件下发生光谱变化的原因。在中性条件下,雌马酚分子型体的最大吸收峰为280 nm;而在弱碱环境中,7位-OH质子发生电离,电离常数pKa1=10.08±0.05,出现两个吸收峰(240 nm,294 nm),7位-OH质子电离使吸收峰发生红移;当溶液变为强碱性时,4’位-OH质子电离,电离常数为pKa2=13.50±0.22,240 nm吸收峰的强度发生变化。在中性条件下,雌马酚的分子型体具有强荧光,最大激发波长和发射波长λex/λem分别为278 nm/316 nm,荧光量子产率为0.11;在弱碱性溶液中,雌马酚的7位-OH质子电离,荧光光谱没有变化,但荧光强度迅速下降;在强碱性条件下,4’位-OH质子电离,导致雌马酚的荧光几乎消失。雌马酚的紫外-可见吸收光谱和荧光光谱的特征与分子结构中羟基的电离具有直接关系,雌马酚的7位-OH电离后的离子型体具有强吸收,它的分子型体具有强荧光。这些光谱特性可为雌马酚的光谱分析方法研究提供依据。

Theultraviolet-visibleabsorption spectra and fluorescence spectra of equol at different pHs were studied.The reasons for their spectral characteristics at different pHs are explained from the point of view of molecular structure.Under neutral conditions,the maximum absorption peak of the molecular form of equol is 280 nm.Under weak alkaline conditions,the proton of 7-OH is ionized with pKa1=10.08±0.05,so that two absorption peaks(240 nm,294 nm)appear,and the ionization of 7-OH makes the absorption peak to red-shift.When the pH of the solution becomes strongly alkaline,the 4'-OH proton ionization has an ionization constant of pKa2=13.50±0.22,and the intensity of the 240 nm absorption peak changes.The molecular form of equol has strong fluorescenceunder neutral conditions,the maximum excitation wavelength and emission wavelength are 277 nm/316 nm respectively,and the fluorescence quantum yield is 0.11.Under weak alkaline conditions,the proton of 7-OH is ionized,the fluorescence spectra remain unchanged,but the fluorescence intensity decreases rapidly;Under strong alkaline conditions,the proton ionization of 4'-OH causes no fluorescence of equol.The characteristics ofUV-absorption and fluorescence spectra of equol are directly related to the ionization of hydroxyl groups in molecular structure.The 7-OH ionized of equol has strong absorption,and the molecular form of equol has strong fluorescence.These spectral properties providea research basis for the establishment of fluorescence analysis methods.