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Equilibria and Dynamics of Sodium Citrate Aqueous Solutions: The Hydration of Citrate and Formation of the Na3Cit0 Ion Aggregate
The Journal of Physical Chemistry B ( IF 2.8 ) Pub Date : 2020-10-18 , DOI: 10.1021/acs.jpcb.0c06377 Bence Kutus 1, 2 , Csilla Dudás 2 , Sergej Friesen 3 , Gábor Peintler 2 , István Pálinkó 2 , Pál Sipos 2 , Richard Buchner 3
The Journal of Physical Chemistry B ( IF 2.8 ) Pub Date : 2020-10-18 , DOI: 10.1021/acs.jpcb.0c06377 Bence Kutus 1, 2 , Csilla Dudás 2 , Sergej Friesen 3 , Gábor Peintler 2 , István Pálinkó 2 , Pál Sipos 2 , Richard Buchner 3
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Sodium citrate (Na3Cit) has a crucial role in many biological and industrial processes. Yet, quantitative information on its hydration and the ion association between Na+ and Cit3– ions in a broad range of salt concentrations is still lacking. In this work, we study both ion association equilibria and relaxation dynamics of sodium citrate solutions by combining potentiometry, spectrophotometry, and dielectric spectroscopy. From photometric and potentiometric measurements, we detect the formation of the NaCit2– ion-pair and the neutral Na3Cit0 ion aggregate in a wide range of ionic strengths (0.5–4 M). Due to its remarkable stability, the latter becomes the prevailing species at higher salt concentrations. In the dielectric spectra, we observe the dipolar relaxation of Cit3– and NaCit2– and two solvent-related processes, associated with the collective rearrangement of the H-bond network (cooperative water mode) and the H-bond flip of water molecules (fast water mode). Unlike numerous other salt solutions, the relaxation time of the cooperative mode scales with the viscosity indicating that the strongly hydrated anion fits well into the water network. That is, the stabilizing effect of anion–solvent interactions on the H-bond network outweighs the destructive impact of the cations as the latter are only present at low concentration, due to strong ion association. In conclusion, the affinity of citrate toward Na+ binding not only governs solution equilibria but also has a strong impact on water dynamics.
中文翻译：
柠檬酸钠水溶液的平衡和动力学：柠檬酸盐的水合和Na 3 Cit 0离子聚集体的形成
柠檬酸钠（Na 3 Cit）在许多生物和工业过程中都起着至关重要的作用。但是，仍然缺乏有关其水合以及Na +和Cit 3-离子在各种盐浓度下的离子缔合的定量信息。在这项工作中，我们通过结合电位法，分光光度法和介电光谱法研究了柠檬酸钠溶液的离子缔合平衡和弛豫动力学。通过光度和电位测量，我们可以检测到NaCit 2–离子对和中性Na 3 Cit 0的形成。离子在很宽的离子强度（0.5–4 M）中聚集。由于其出色的稳定性，后者在较高的盐浓度下成为主要的物种。在介电谱中，我们观察到Cit 3–和NaCit 2–的偶极弛豫以及两个与溶剂有关的过程，与H键网络的集体重排（协同水模式）和水分子的H键翻转（快速水模式）相关。与许多其他盐溶液不同，协同模式的弛豫时间与粘度成比例，表明强水合阴离子非常适合进入水网络。也就是说，阴离子-溶剂相互作用对氢键网络的稳定作用胜过阳离子的破坏性作用，因为阳离子由于强的离子缔合而仅以低浓度存在。总之，柠檬酸盐对Na +结合的亲和力不仅决定溶液平衡，而且对水动力学有很大影响。
更新日期：2020-10-30
中文翻译：
柠檬酸钠水溶液的平衡和动力学：柠檬酸盐的水合和Na 3 Cit 0离子聚集体的形成
柠檬酸钠（Na 3 Cit）在许多生物和工业过程中都起着至关重要的作用。但是，仍然缺乏有关其水合以及Na +和Cit 3-离子在各种盐浓度下的离子缔合的定量信息。在这项工作中，我们通过结合电位法，分光光度法和介电光谱法研究了柠檬酸钠溶液的离子缔合平衡和弛豫动力学。通过光度和电位测量，我们可以检测到NaCit 2–离子对和中性Na 3 Cit 0的形成。离子在很宽的离子强度（0.5–4 M）中聚集。由于其出色的稳定性，后者在较高的盐浓度下成为主要的物种。在介电谱中，我们观察到Cit 3–和NaCit 2–的偶极弛豫以及两个与溶剂有关的过程，与H键网络的集体重排（协同水模式）和水分子的H键翻转（快速水模式）相关。与许多其他盐溶液不同，协同模式的弛豫时间与粘度成比例，表明强水合阴离子非常适合进入水网络。也就是说，阴离子-溶剂相互作用对氢键网络的稳定作用胜过阳离子的破坏性作用，因为阳离子由于强的离子缔合而仅以低浓度存在。总之，柠檬酸盐对Na +结合的亲和力不仅决定溶液平衡，而且对水动力学有很大影响。
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