| At present,most of the pigments used in the food industry are synthetic pigments,which have almost different degrees of toxicity.Long-term use would endanger people’s health.Therefore,natural pigments have attracted more and more attention in scientific research.Anthocyanins are natural pigments responsible for the majority of the red,purple and blue colors of flowers.They belong to a type of flavonoid group of compounds that show antioxidant effects and can be used for the treatment of free radicals.Additionally,anthocyanins hold anti-diabetic,anti-cancer,anti-inflammatory,anti-microbial,and anti-obesity effects.This thesis includes three research projects in the framework of natural pigments,which will be presented as following.The first project is regarding Hydrangea macrophylla,which is a species of blossoming plant in the family Hydrangeaceae,native to Japan.It is noted for the variation of the color of its sepals from red to blue when they are planted in acidic,aluminum-containing soil.The major anthocyanin present in the colored sepals is 3-O-glucosyl delphinidin and its color change from red to blue is attributed to chelation with Al（III）.The pigment responsible for the blue color may also involve an additional organic copigment such as 5-O-caffeoylquinic acid,forming a 1:1:1 ternary anthocyanin-Al（III）-copigment complex.In this project,we have employed optimized ground state structures and the algebraic diagrammatic construction method to second order（ADC（2））to predict the ab initio excited state energies,oscillator strengths and charge transfer characters in the gas phase and in aqueous solution（via COSMO）of the various species that can potentially contribute to the red and blue colors of Hydrangea sepals.Good agreement is found between the predicted and experimental spectra of the anthocyanin,while those of the binary anthocyanin-copigment complexes are more similar to that of the red sepals.The projected spectra of the binary and ternary Al（III）-containing complexes fall into the same spectral region,slightly displaced to the red relative to blue sepals.Despite these small shifts and other minor spectral differences at shorter wavelengths,when the predicted spectra are converted to color coordinates and plotted on a CIE chromaticity diagram,the species without Al（III）fall into more red-like regions around that of free anthocyanin and the red sepals,while those involving complexation with Al（III）fall into more blue-like regions near to the blue Hydrangea sepals,demonstrating the ability of quantum chemical methods at this level of theory to provide an adequate description of the spectroscopic properties of these relatively complex natural plant pigments.The second project is still with anthocyanin.Metal cation chelation can lead to large changes in the color,primarily from red to blue as for example in Hydrangea,but is limited to anthocyanins with two or more free-OH groups in the B-ring（i.e.,anthocyanins derived from cyanindin,delphinidin and petunidin）.In contrast,copigmentation via complexation with organic molecules results in much smaller red shifts of the absorption,but can increase the p H at which hydration occurs,consistent with steric hindrance to attack of water and charge transfer from the co-pigment to the anthocyanin as an important contributor to the stability of the anthocyanin-co-pigment complex.One limitation of this bimolecular co-pigmentation is the range of stability constants for the complexation,which rarely exceed 104M-1,requiring m M or greater local co-pigment concentrations in order to achieve a substantial percentage of complexation of the anthocyanin.Some plants have overcome the entropic limitations of bimolecular co-pigmentation by covalently attaching one or more co-pigment molecules to the sugar residues of the anthocyanin（e.g.,as acyl ester derivatives）,transforming the co-pigmentation into an entropically much more favorable intramolecular complexation phenomenon.In this project,the quantum chemical methodology ADC（2）,was employed to predict the absorption spectra in vacuum and COSMO/water of a natural anthocyanin containing an ester of coumaric acid（copigment）bound to the sugar residue of a cyanidin chromophore.ADC（2）in a polar environment（water）adequately reproduces the experimental spectra with and without intramolecular copigmentation,pointing to this theoretical technique as a promising approach for predicting the spectroscopic properties of natural（and nature-inspired）dyes and pigments.The color of anthocyanin,can be affected by different aspects such as environment factors and structural features and considering the stability and the color changes,the effect of the acylation has been considered to be a very important piece.CyCoum,which consists of a p-coumaric acid residue covalently attached via an ester linkage to a hydroxyl group of one of the 3-O-sugar residues of a cyanidin-3,5-O-diglycoside chromophore.This study has shown the effect of the acylation between cis and trans configuration of the acylated groups.Most of the time,the anthocyanins are acylated much easier esterified to trans-configured variants of hydroxycinnamic acids（the existence of the trans configuration is broader than the cis one）;but in other hand,there are still some few reports prove that the cis-configured hydroxycinnamic acylated anthocyanins are also available,so we want to find the differences between the cis and trans isomers.The cis acylated anthocyanins are currently occurred when part of the plants can receive much more amount of sunlight naturally.One can modify the structures by cis and trans configuration acylated of the same chromophore,and this can give rise to sole colorimetric properties,which makes the choice of pigment sources or explicit pigments to attain the looked-for colors in food products more complicated.Therefore,a better understanding on how these structural components impact the color of these pigments is of urge need.Therefore,in this project,the goal is to explore how the cis and trans acyl moieties effect on the color appearance of the two kinds of anthocyanin,delphinidin and petunidin.The spectral properties were simulated using the ADC（2）method and helpful results were obtained.Through the above research,the two auxiliary color mechanisms of anthocyanins have been well analyzed,especially the study of the interaction between molecules,and the precise structure of Hydrangea was first discovered,which may have a valuable guiding effect on the experiment. |
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