Abstract

Semi-empirical PM3 calculations are made for the electronic absorption spectra of colored forms of nonmethylated anthocyanidins (aurantinidin, pelargonidin, cyanidin, and delphinidin). The position of the absorption band peak is shown to depend on the orientation of hydroxyl groups in the aglycone structure. The observed tendency toward a bathochromic shift after ОН groups are added to the ring generally corresponds to experimental data. The results for the uncharged quinonoid forms of pelargonidin (a hypsochromic shift of absorption bands) do not in this case agree with the prevailing opinion of specialists about the bathochromic shift. While this opinion is confirmed by DFT calculations, there are still no reliable experimental data on their validity. The formation of single-charged (negatively) quinonoid structures is clearly the reason for the bathochromic shift of absorption bands, which is consistent with the experimental data. When the charge multiplicity increases (to −2), a hypsochromic shift of absorption bands to the experimentally observed yellow color of anthocyanins in alkaline solutions is again predicted.

中文翻译：

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某些花青素电子吸收光谱的量子化学计算

摘要

对非甲基化花色素（橙花色素、天竺葵素、花青素和飞燕草素）的有色形式的电子吸收光谱进行了半经验 PM3 计算。显示吸收带峰的位置取决于苷元结构中羟基的取向。在将 ОН 基团添加到环后观察到的红移趋势通常与实验数据相对应。在这种情况下，天竺葵素的不带电荷醌型形式（吸收带的浅色位移）的结果与专家对红色位移的普遍看法不一致。尽管 DFT 计算证实了这一观点，但仍然没有关于其有效性的可靠实验数据。单电荷（负）醌结构的形成显然是吸收带红移的原因，这与实验数据一致。当电荷多重性增加（至 -2）时，再次预测吸收带向实验观察到的碱性溶液中花青素的黄色的低色位移。