Tautomeric equilibrium of pyridoxine in water.: Thermodynamic characterization by 13C and 15N nuclear magnetic resonance
Tautomeric equilibrium of pyridoxine in water.: Thermodynamic characterization by 13C and 15N nuclear magnetic resonance
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DOI：
10.1021/jo991821t
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发表时间：
2000-05-05
影响因子：
3.6
通讯作者：
Muñoz, L
中科院分区：
文献类型：
--
作者：
Llor, J;Muñoz, L
在pH = 7.0的水中，吡哆醇的~（13）C NMR和~（15）N NMR化学位移具有明显的温度依赖性。C-3、C-6和N-1是对温度效应最敏感的核。这种依赖性已被解释的基础上的平衡位移之间的中性和偶极形式的这种分子热诱导。在核磁共振上快速互变的互变异构平衡的热力学特征。时间标度可以从在不同温度（5-90 ℃）下观察到的平均13 C NMR和15 N NMR化学位移进行。我们发展了一种通过将实验数据拟合到理论曲线上来估算给定平衡的热力学参数的新方法。这种新方法使我们能够改进我们以前提出的方法的拟合结果。结果表明，在同一温度下，不同核的平均化学位移之间存在线性相关。这表明纯型的参数在它们之间是相关的。我们已经进行了同时多功能曲线拟合的所有数据从最敏感的信号一起使用这些线性相关性作为限制条件，以减少独立参数的数量来适应。为了测试新的方法，我们研究了吡哆醇在水中的互变异构平衡的热力学。根据所使用的数据集，我们已经获得了该平衡的Δ H度值，范围为-23.6 +/- 1.3至-25.8 +/- 1.7 kJ/mol。这种方法除其他外具有以下优点：它允许在拟合过程中使用来自不同信号的大量实验点，它产生互变异构过程的非常精确和准确的值，并且它允许仅用C-13 NMR数据解决问题，在某些情况下节省NMR时间。
A remarkable temperature dependence on the C-13 NMR and N-15 N NMR chemical shifts of pyridoxine in water (pH = 7.0) has been observed. C-3, C-6, and N-1 were the most sensitive nuclei to the temperature effect. This dependence has been explained on the basis of an equilibrium shift thermally induced between the neutral and the dipolar form of this molecule. The thermodynamic characterization of tautomeric equilibria that interconvert quickly on the NMR. time scale can be carried out from the observed average 13C NMR and 15N NMR chemical shifts at different temperatures (5-90 degrees C). We have developed a new method for the estimation of the thermodynamic parameters of a given equilibrium by fitting the experimental data to a theoretical curve. This new method allows us to improve the fitting results on our previously proposed methodology. We show that there are linear correlations between the average chemical shifts obtained from different nuclei at the same temperature. This indicates that the parameters of the pure forms are related among them. We have carried out a simultaneous multiple function curve fitting of all data obtained from the most sensitive signals together using these linear correlations as restricted conditions in order to diminish the number of independent parameters to fit. To test the new methodology, we have studied the thermodynamics of the tautomeric equilibrium of pyridoxine in water. We have obtained Delta H degrees values ranging from -23.6 +/- 1.3 to -25.8 +/- 1.7 kJ/mol for this equilibrium depending on the used data set, This kind of methodology has, among others, the following advantages: It allows the use of a great number of experimental points from different signals in the fitting process, it yields very precise and accurate values of the tautomeric process, and it allows the resolution of the problem with only C-13 NMR data in some cases saving NMR time.