In this study, we experimentally determined the protonation constants, enthalpy change (ΔHo), change in Gibbs energy (ΔGo), and entropy change (ΔSo) for the deprotonation process of betanin over the temperature range of 298.15 to 318.15 K and at an ionic strength of 0.1 mol·dm−3 (NaClO4) with a combination of spectrophotometric and potentiometric methods. In addition, we theoretically calculated the values of the acidic dissociation constants, the optimized structure, and the thermodynamic properties of betanin in aqueous solutions at various temperatures by ab initio and DFT methods. Density function theory (DFT) methods with the B3LYP/6-31 + G(d) level of theory were applied for calculating the acidic dissociation constants of betanin and also interactions among the solvent and solvated cation, anion, and neutral species of betanin. Thomasi’s method was used to analyze the formation of intermolecular hydrogen bonding between water molecules and various species of betanin. There is a good correlation between the theoretically calculated and experimentally determined values of pKa of betanin.

中文翻译：

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甜菜碱在不同温度水溶液中的酸解离常数和热力学性质的理论计算和实验测量

在这项研究中，我们通过实验确定了甜菜碱去质子化过程在 298.15 至 318.15 K 和离子浓度范围内的质子化常数、焓变 (ΔHo)、吉布斯能变化 (ΔGo) 和熵变 (ΔSo)。 0.1 mol·dm-3 (NaClO4) 的强度，结合分光光度法和电位法。此外，我们通过 ab initio 和 DFT 方法从理论上计算了甜菜碱在各种温度下水溶液中的酸解离常数值、优化结构和热力学性质。具有 B3LYP/6-31 + G(d) 理论水平的密度函数理论 (DFT) 方法被应用于计算甜菜碱的酸性解离常数以及溶剂和溶剂化阳离子、阴离子和甜菜碱的中性物种之间的相互作用。Thomasi 的方法用于分析水分子与各种甜菜碱之间分子间氢键的形成。甜菜碱 pKa 的理论计算值和实验确定值之间存在良好的相关性。