Calculation Of Excited States And One-electron Reduction Potentials Of Betalain Natural Plant Pigments

Betalains,known as a class of potential natural plant pigment,is playing a more and more important role in food industry.It not only possesses the excellent properties as a food colorant such as high molar absorption coefficient,consumer safety and compatibility with many kinds of other food products,but also exhibit some significant bioactivities just like anti-oxidation,antiinflammatory and anti-cancer activities,etc.Therefore,betalains have become research emphasis in the last several decades.However,the most reported and published researches and literature are concentrated on the experimental methods and techniques.But some parameters are very hard to determine exactly due to the change of physical conditions.In this case,the theoretical calculation can give a rather accurate result without too much interference in practical conditions.In this project,we proposed quantum chemical calculations to investigate the properties of betalains.Betanin,indicaxanthin and c Beet 120 were taken as the representative betalains for this study.DFT and MP2 approaches were used to perform ground state calculations.The absorption spectra were simulated by ADC(2)and TD-DFT methods,respectively.Compared with the experimental data in the reported researches,ADC(2)results from this work showed a stronger ability to predict the absorption maximum for betalains.ADC(2)and TZVP basis set was proved to be an effective approach for simulating the absorption spectra for betalains in this project.The conical intersection located between the ground state and the first excited state was found for betanin,indicaxanthin and c Beet 120 by SA-2-CASSCF(6,6)/6-31G* method.The result well explained the non-fluorescence or weak fluorescence of these three betalains.Considering the strong anti-oxidation bioactivity of betalains,the one-electron reduction potentials of three molecules at DFT/B3 LYP level were calculated.Although there is no experimental data which can be compared with,the results in this section can be a reference for future experimental measurement of the redox potential of betalains.In conclusion,the quantum chemical methods proposed in this project were proved to be reasonable and effective for theoretical investigation of betalains features.