This study elucidated the formation mechanism of calcium-indigo carmine (IC) complex. Parameters of the complex, such as Turbiscan stability index (TSI), yield and stoichiometric ratio (Ca to IC) were investigated. Isothermal titration calorimetry (ITC), UV/Visible spectrophotometry, infrared spectroscopy and Raman spectroscopy were used to explore the interaction between IC and Ca(II) during formation reaction and in the powdered lake. The TSI analysis and yield test suggested pH 7.0 as the most suitable pH to produce this complex. The conjugation between IC and Ca(II) was an exothermal reaction with increase of entropy (ΔH = -0.728 ± 0.11 kJ·mol-1 and ΔS = 66.55 ± 1.89 kJ·mol-1·K-1 at 25 °C). Both ITC and stoichiometric ratio test suggested one Ca atom tended to conjugate five IC molecules at ambient temperature when an adequate amount of Ca(II) appeared. Spectrometry techniques suggested that the sulfonic acid groups in IC formed coordination bonds with the Ca to construct the complex.

中文翻译：

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Ca（II）和靛蓝胭脂红之间形成络合物的机理研究，可作为潜在的食品用作着色剂。

这项研究阐明了钙-靛蓝胭脂红（IC）复合物的形成机理。研究了配合物的参数，如Turbiscan稳定性指数（TSI），收率和化学计量比（Ca与IC的比值）。用等温滴定热法（ITC），紫外/可见光分光光度法，红外光谱和拉曼光谱研究了IC和Ca（II）在形成反应过程中和粉状湖中的相互作用。TSI分析和产率测试表明，pH 7.0是生产该复合物的最合适的pH。IC和Ca（II）之间的共轭反应是伴随熵增加的放热反应（在25°C下ΔH= -0.728±0.11 kJ·mol-1和ΔS= 66.55±1.89 kJ·mol-1·K-1）。ITC和化学计量比测试均表明，在环境温度下，当出现足够量的Ca（II）时，一个Ca原子倾向于共轭五个IC分子。光谱技术表明，IC中的磺酸基团与Ca形成配位键以构建配合物。