Dissociation constants of protonated cysteine species in seawater media
Dissociation constants of protonated cysteine species in seawater media
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海水介质中质子化半胱氨酸的解离常数
DOI：
10.1016/j.marchem.2005.02.005
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发表时间：
2006
期刊：
影响因子：
3
通讯作者：
C. Stefano
中科院分区：
文献类型：
--
作者：
V. Sharma;A. Moulin;F. Millero;C. Stefano
半胱氨酸的解离常数（pK 1 ε、pK 2 ε和pK 3 ε）在海水中作为温度（5至45 °C）和盐度（S=5至35）的函数进行了测量。在相同的离子强度下，海水中的值低于NaCl中的值。为了理解这些差异，我们在25 °C下测量了Na-Mg-Cl溶液中的常数。的测量值进行了比较，从Pitzer离子相互作用模型的计算。Na-Mg-Cl溶液中pK 3的低值归因于Mg 2+与Cys 2 −阴离子形成络合物。在对Mg 2+与H+的相互作用进行校正后，稳定常数已被拟合为。pK 1海水测量表明H3Cys+与SO 42 −相互作用。确定了该相互作用的Pitzer参数β0（H3CysSO 4）、β1（H3CysSO 4）和C（H3CysSO 4）。海水中pK 2和pK 3的形成需要CaCys和MgCys的参与。考虑海水中MgCys和CaCys的形成，产生与测量值一致的pK 1 ε、pK 2 ε和pK 3 ε的模型计算值，其在测量的实验误差内。本研究表明，在考察有机酸的解离时，考虑天然沃茨中所有的离子相互作用是很重要的。
The dissociation constants (pK1⁎, pK2⁎and pK3⁎) for cysteine have been measured in seawater as a function of temperature (5 to 45 °C) and salinity (S=5 to 35). The seawater values were lower than the values in NaCl at the same ionic strength. In an attempt to understand these differences, we have made measurements of the constants in Na–Mg–Cl solutions at 25 °C. The measured values have been compared to those calculated from the Pitzer ionic interaction model. The lower values of pK3⁎in the Na–Mg–Cl solutions have been attributed to the formation of Mg2+complexes with Cys2−anionsThe stability constants have been fitted toafter corrections are made for the interaction of Mg2+with H+. The pK1seawater measurements indicate that H3Cys+interacts with SO42−. The Pitzer parameters β0(H3CysSO4), β1(H3CysSO4) and C(H3CysSO4) have been determined for this interaction. The formation of CaCys as well as MgCys are needed to account for the values of pK2and pK3in seawater. The consideration of the formation of MgCys and CaCys in seawater yields model calculated values of pK1⁎, pK2⁎and pK3⁎that agree with the measured values to within the experimental error of the measurements. This study shows that it is important to consider all of the ionic interactions in natural waters when examining the dissociation of organic acids.