A Method for the Measurement of Site-Specific Tautomeric and Zwitterionic Microspecies Equilibrium Constants
作者:Joseph C. D'Angel、Timothy W. Collette
DOI:10.1021/ac960922d
日期:1997.4.1
We describe a method for the individual measurement of simultaneously occurring, unimolecular, site-specific “microequilibrium” constants as in, for example, prototropic tautomerism and zwitterionic equilibria. Our method represents an elaboration of that of Nygren et al. (Anal. Chem. 1996, 68, 1706−10), which thereby becomes generalized and improves the accuracy. Specifically, by making spectral measurements as a function of temperature, we demonstrate the ability to determine site-specific microenthalpies unambiguously. Analysis proceeds via multivariate nonlinear regression modeling of, for example, the Gibbs−Helmholtz relation. Additional determinations of macroscopic equilibrium constants as a function of temperature, in combination with the previously determined microenthalpies, in turn enables the determination of all remaining site-specific thermodynamic parameters, i.e., microentropies, micro free energies, and/or microequilibrium constants, and moreover allows us to resolve and measure the spectra of tautomeric isocoulombers. To our knowledge, we have hereby devised the first such universally applicable and accurate measurement method on record.
我们介绍了一种单独测量同时发生的、单分子的、特定位点的 "微平衡 "常数的方法,例如在原向同分异构和齐聚平衡中。我们的方法是对 Nygren 等人(Anal. Chem.具体来说,通过光谱测量温度的函数,我们展示了明确测定特定位点微焓的能力。分析是通过吉布斯-赫尔姆霍兹关系等多变量非线性回归模型进行的。结合先前测定的微焓,再测定宏观平衡常数与温度的函数关系,就能测定所有剩余的特定位点热力学参数,即微熵、微自由能和/或微平衡常数,而且还能解析和测量同分异构体的光谱。据我们所知,我们在此设计出了有史以来第一种普遍适用的精确测量方法。