Natural anthraquinone compounds have emerged as potent anticancer chemotherapeutic agents because of their promising DNA-binding properties. Aloe vera is among one of the very well-known medicinal plants, and the anthraquinone derivatives like aloe emodin (ALM), aloins (ALN), and aloe emodin-8-glucoside (ALMG) are known to have immense biological activities. Here, we have used biophysical methods to elucidate the comparative DNA-binding abilities of these three molecules. Steady-state fluorescence study indicated complexation between calf thymus DNA (ctDNA) and both the molecules ALM and ALMG whereas ALN showed very weak interaction with DNA. Displacement assays with ctDNA-bound intercalator (ethidium bromide) and a groove binder (Hoechst 33258) indicated preferential binding of both ALM and ALMG to minor groove of DNA. Isothermal titration calorimetric (ITC) data suggested spontaneous exothermic single binding mode of both the molecules: ALM and ALMG. Entropy is the most important factor which contributed to the standard molar Gibbs energy associated with relatively small favorable enthalpic contribution. The equilibrium constants of binding to ctDNA were (6.02 ± 0.10) × 104 M-1 and (4.90 ± 0.11) × 104 M-1 at 298.15 K, for ALM and ALMG, respectively. The enthalpy vs temperature plot yielded negative standard molar heat capacity value, and a strong negative correlation between enthalpy and entropy terms was observed which indicates the enthalpy entropy compensation behavior in both systems. All these thermodynamic phenomena indicate that hydrophobic force is the key factor which is involved in the binding process. Moreover, the enhancement of thermal stability of DNA helix by ALM and ALMG fully agreed to the complexation of these molecules with DNA.

中文翻译：

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芦荟活性化合物与小牛胸腺DNA的相互作用。

天然蒽醌化合物因其有希望的DNA结合特性而成为有效的抗癌化学治疗剂。芦荟是非常著名的药用植物之一，而蒽醌衍生物如芦荟大黄素（ALM），芦荟蛋白（ALN）和芦荟大黄素8-葡萄糖苷（ALMG）已知具有巨大的生物活性。在这里，我们已经使用生物物理方法来阐明这三个分子的比较DNA结合能力。稳态荧光研究表明，小牛胸腺DNA（ctDNA）与分子ALM和ALMG之间存在复合，而ALN与DNA的相互作用非常弱。用ctDNA结合的嵌入剂（溴化乙锭）和凹槽结合剂（Hoechst 33258）进行的置换分析表明，ALM和ALMG都优先结合到DNA的微小凹槽上。等温滴定量热法（ITC）数据表明两种分子：ALM和ALMG均自发放热单一结合模式。熵是促成标准摩尔吉布斯能量的最重要因素，而吉卜斯能量与相对较小的有利焓贡献有关。对于ALM和ALMG，与ctDNA结合的平衡常数分别为（6.02±0.10）×104 M-1和（4.90±0.11）×104 M-1（在298.15 K处）。焓与温度的关系图产生负的标准摩尔热容值，并且在焓和熵项之间观察到很强的负相关性，这表明两个系统中的焓熵补偿行为。所有这些热力学现象表明，疏水力是结合过程中涉及的关键因素。此外，