Abstract

Kinetics of the reaction of ninhydrin (Nin) with baclofen (Bac) has been studied spectrophotometrically in an aqueous acidic medium under pseudo order conditions over 30–50°C range, 0.1–0.4 × 10^–4 M of Bac, 0.5–5.0 × 10^–2 M Nin, and ionic strength 0.3–0.9 M. The thermodynamics activation parameters involving ∆H* and ∆S* have been calculated. The UV-visible spectroscopic measurements were carried out to confirm the coupling between Nin and Bac. The reaction is first order with respect to [Nin] and [Bac], decreases as pH increases in the range (3.90–5.06). The experimental rate law is consistent with a mechanism in which the protonated and deprotonated form of Nin are involved in the rate-determining step and the deprotonated species is the more reactive one. The product of the reaction was examined spectroscopically using ¹H-NMR and IR spectra in addition to an ultra-performance liquid chromatograph (UPLC). Density functional theory (DFT) was performed to search the geometries of the final product result from the reaction between Nin and Bac. Also, enthalpy of the reaction was calculated theoretically with DFT. Interaction region indicator (IRI) calculations is used to reveal chemical bonding and weak interaction in the coupled compound of Bac–Nin.

中文翻译：

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巴氯芬与茚三酮在酸性水溶液中的偶联相互作用：动力学和计算研究

摘要

在 30–50°C 范围（0.1–0.4 × 10）的伪级条件下，通过分光光度法研究了茚三酮 (Nin) 与巴氯芬 (Bac) 的反应动力学< a i=1>–4 M Bac，0.5–5.0 × 10^–2 M Nin 和离子强度0.3–0.9 M。热力学活化参数涉及 ΔH* 和 ΔS* 已计算。进行紫外-可见光谱测量以确认 Nin 和 Bac 之间的耦合。该反应相对于 [Nin] 和 [Bac] 为一级反应，随着 pH 值在 (3.90–5.06) 范围内增加而降低。实验速率定律与 Nin 的质子化和去质子化形式参与速率决定步骤并且去质子化物质更具反应性的机制一致。除了超高效液相色谱仪(UPLC)之外，还使用¹H-NMR和IR光谱对反应产物进行光谱检查。采用密度泛函理论 (DFT) 来搜索 Nin 和 Bac 反应最终产物的几何形状。另外，利用DFT从理论上计算了反应的焓。相互作用区域指示符（IRI）计算用于揭示 Bac-Nin 偶联化合物中的化学键合和弱相互作用。