To advance the scientific understanding of bacteria-driven mercury (Hg) transformation processes in natural environments, thermodynamics and kinetics of divalent mercury Hg(II) chemical speciation need to be understood. Based on Hg L_III-edge extended X-ray absorption fine structure (EXAFS) spectroscopic information, combined with competitive ligand exchange (CLE) experiments, we determined Hg(II) structures and thermodynamic constants for Hg(II) complexes formed with thiol functional groups in bacterial cell membranes of two extensively studied Hg(II) methylating bacteria: Geobacter sulfurreducens PCA and Desulfovibrio desulfuricans ND132. The Hg EXAFS data suggest that 5% of the total number of membranethiol functionalities (Mem-RS_tot = 380 ± 50 μmol g^–1 C) are situated closely enough to be involved in a 2-coordinated Hg(Mem-RS)₂ structure in Geobacter. The remaining 95% of Mem-RSH is involved in mixed-ligation Hg(II)-complexes, combining either with low molecular mass (LMM) thiols like Cys, Hg(Cys)(Mem-RS), or with neighboring O/N membrane functionalities, Hg(Mem-RSRO). We report log K values for the formation of the structures Hg(Mem-RS)₂, Hg(Cys)(Mem-RS), and Hg(Mem-RSRO) to be 39.1 ± 0.2, 38.1 ± 0.1, and 25.6 ± 0.1, respectively, for Geobacter and 39.2 ± 0.2, 38.2 ± 0.1, and 25.7 ± 0.1, respectively, for ND132. Combined with results obtained from previous studies using the same methodology to determine chemical speciation of Hg(II) in the presence of natural organic matter (NOM; Suwannee River DOM) and 15 LMM thiols, an internally consistent thermodynamic data set is created, which we recommend to be used in studies of Hg transformation processes in bacterium–NOM–LMM thiol systems.

中文翻译：

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建立细菌-天然有机物-低分子量巯基体系中汞（II）化学形态计算的内部一致模型。

为了促进对自然环境中细菌驱动的汞（Hg）转化过程的科学理解，需要了解二价汞Hg（II）化学形态的热力学和动力学。基于Hg L _III边缘扩展X射线吸收精细结构（EXAFS）的光谱信息，结合竞争性配体交换（CLE）实验，我们确定了Hg（II）的结构和由硫醇官能团形成的Hg（II）配合物的热力学常数两个广泛研究的Hg（II）甲基化细菌的细菌细胞膜中的两个基团：还原性土壤细菌PCA和脱硫脱硫弧菌ND132。Hg EXAFS数据表明，膜硫醇官能团总数的5％（Mem-RS _tot= 380±50μmolg ^–1 C）的位置足够近，足以参与Geobacter中2配位的Hg（Mem-RS）₂结构。其余95％的Mem-RSH参与混合连接的Hg（II）-络合物，与低分子量（LMM）硫醇（如Cys，Hg（Cys）（Mem-RS）或与邻域O / N结合）膜功能，汞（Mem-RSRO）。我们报告形成结构Hg（Mem-RS）₂，Hg（Cys）（Mem-RS）和Hg（Mem-RSRO）的log K值分别为39.1±0.2、38.1±0.1和25.6±0.1分别用于Geobacter对于ND132，分别为39.2±0.2、38.2±0.1和25.7±0.1。结合使用相同方法从以前的研究中获得的结果，在存在天然有机物（NOM； Suwannee River DOM）和15个LMM硫醇的情况下确定Hg（II）的化学形态，我们创建了一个内部一致的热力学数据集，建议用于细菌-NOM-LMM硫醇系统中汞转化过程的研究。