Chekmeneva Elena, Prohens Rafel, Díaz-Cruz José Manuel, Ariño Cristina, Esteban Miquel
Departament de Química Analítica, Facultat de Química, Universitat de Barcelona, E-08028 Barcelona, Spain.
Anal Biochem. 2008 Apr 1;375(1):82-9. doi: 10.1016/j.ab.2008.01.008. Epub 2008 Jan 12.
Isothermal titration calorimetry (ITC) was used to study the binding of Cd(2+) and Zn(2+) by glutathione (GSH) and phytochelatins (PC(n)), the metal sequestering compounds in plants and algae. The results are compared with those obtained by differential pulse polarography (DPP) assisted by multivariate curve resolution with alternating least squares (MCR-ALS) and by electrospray ionization mass spectrometry (ESI-MS). ITC allows one to determine (i) the stoichiometries of the different complexes (and confirms those found by DPP/MCR-ALS and ESI-MS) and (ii) their binding and thermodynamic parameters. For Cd-PC(4), the sequential binding sites model with two identical sites yields the best fitting of ITC curves and confirms the presence of CdPC(4) and Cd(2)PC(4) complexes. For Zn-PC(4), exothermic formation of ZnPC(4) is reported. Conditional stability and formation constants for Cd-GSH and Zn-GSH are determined from the fitting of the proper model to experimental ITC curves. The effect of different buffers in the complexation processes shows the key role of the choice of the buffer in calorimetric study.
等温滴定量热法（ITC）用于研究谷胱甘肽（GSH）和植物螯合肽（PC(n)）对镉离子（Cd(2+)）和锌离子（Zn(2+)）的结合情况，GSH和PC(n)是植物和藻类中的金属螯合化合物。将这些结果与通过差分脉冲极谱法（DPP）结合交替最小二乘法的多元曲线分辨（MCR-ALS）以及电喷雾电离质谱法（ESI-MS）所获得的结果进行了比较。ITC能够确定：（i）不同络合物的化学计量比（并证实DPP/MCR-ALS和ESI-MS所发现的化学计量比），以及（ii）它们的结合和热力学参数。对于Cd-PC(4)，具有两个相同位点的顺序结合位点模型能给出最佳的ITC曲线拟合结果，并证实了CdPC(4)和Cd(2)PC(4)络合物的存在。对于Zn-PC(4)，有报道称其形成ZnPC(4)的过程是放热的。通过将合适的模型拟合到实验ITC曲线，确定了Cd-GSH和Zn-GSH的条件稳定性和形成常数。络合过程中不同缓冲液的影响表明了缓冲液选择在量热研究中的关键作用。
