Experimental determination of Fe isotope effect for reduction from Fe(III) to Fe(II)

<p>All of the experiments described here begin with Fe(III) bound to the organic ligand ethylenediaminetetraacetic acid (EDTA), and proceed as Fe is reduced to Fe(II). The Fe(II)-specific ligand ferrozine (FZ) is added to the experimental solution in order to capture Fe(II) produced during the experiment, similar to methods previously used to capture Fe(II) produced during biological reduction of Fe(III) (Shaked et al., 2004). Fe(II) in the presence of ferrozine forms an Fe(II)FZ3 complex. This complex has a strong purple color, which made it possible to determine reaction extent visually and by absorbance spectrophotometry. The Fe(II)FZ3 complex is also hydrophobic, allowing us to separate it from the solution by passing the solution through a C18 resin (Waters Sep-Pak C18 Plus Light) with a peristaltic pump. The column was then rinsed with 5 mL of seawater and Fe(II)FZ3 was eluted with 5 mL methanol.</p>本文所述全部实验均以与有机配体乙二胺四乙酸（ethylenediaminetetraacetic acid, EDTA）结合的三价铁（Fe(III)）为起始体系，实验过程中三价铁被还原为二价铁（Fe(II)）。为捕获实验过程中生成的二价铁，我们向实验体系中加入二价铁特异性配体菲洛嗪（ferrozine, FZ），该方法与此前用于捕获生物还原三价铁过程中产生的二价铁的手段一致（Shaked等，2004）。二价铁与菲洛嗪会结合形成Fe(II)FZ3络合物。该络合物呈鲜明紫色，既可通过目视定性判断反应进程，也可借助吸光光度法（absorbance spectrophotometry）进行定量分析。此外，Fe(II)FZ3络合物具有疏水性，因此我们可通过蠕动泵将反应液流经C18树脂（Waters Sep-Pak C18 Plus Light）实现络合物与溶液的分离。随后用5 mL海水冲洗色谱柱，再以5 mL甲醇洗脱得到Fe(II)FZ3络合物。