Abstract
Root decoctions of anthraquinone-containing plants are often taken as postpartum tonic and aphrodisiac. Anthraquinones are known for their diverse biological activities, especially antioxidant and anticancer. A series of 35 anthraquinones was generated by isolation from Rubiaceae plants and synthesis. Their UV/vis spectrum depends on the nature and relative positions of auxochromic substituents on the basic skeleton. To predict the maximum absorption bands for the current series of anthraquinones, excited sate calculations were performed using TD-DFT, CIS, ZINDO methods. The results showed that the use of PBE0 or its combination with B3LYP and B3P86 hybrid functionals are the most suitable to reproduce accurately the experimental λMAX. The structure–property relationships (SPRs) were established based on structural and electronic properties of the anthraquinones and showed (i) the importance of the number and position of OH groups and (ii) the positive contribution of the electrophilicity and hardness as electronic descriptors on position and amplitude of the maximum absorption bands.
Highlights
Quinones are widely distributed in nature as pigments and intermediates in cellular respiration and photosynthesis (Koyama 2006; Koyama et al 2008)
Methodological approach To determine the adequate methodology for predicting UV/vis spectra of this series of anthraquinone derivatives (Figure 1), EMAX were calculated for two prototypes 1,2-dihydroxyanthraquinone (1) and 1,2-dihydroxy6-methylanthraquinone (21) using different methods and basis sets (Table 1)
EMAX values obtained for 1 using BLYP (0% HF), B3LYP (20% HF), B1LYP (25% HF) and BHandHLYP (50% HF) were 2.47 (502.62), 3.02 (411.08), 3.15 (394.07) and 3.78 eV (328.42 nm) respectively (Table 1a, polarizable continuum model (PCM)-Model column)
Summary
Quinones are widely distributed in nature as pigments and intermediates in cellular respiration and photosynthesis (Koyama 2006; Koyama et al 2008). The latter can be obtained in nature from various types of biological sources, including bacteria, marine sponges, fungi, lichens and higher plants from various families such as Rubiaceae, Gesneriaceae, Scrophulariaceae, Rhamnaceae, Polygonaceae and Leguminosae (Schripsema & Dagnino 1996; Thomson 1971). Anthraquinones attracted attention since the last century due to their applications in medicine and their presence as major constituents in many medicinal plants. They are known for their diverse biological activities especially antioxidant and anticancer properties
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