Xanthan Exopolysaccharide: Cu2+ Complexes Affected from the pH-Dependent Conformational State; Implications for Environmentally Relevant Biopolymers
Xanthan Exopolysaccharide: Cu2+ Complexes Affected from the pH-Dependent Conformational State; Implications for Environmentally Relevant Biopolymers
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DOI：
10.1021/acs.est.5b03141
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发表时间：
2016-04-05
影响因子：
11.4
通讯作者：
Delolme, Cecile
中科院分区：
文献类型：
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作者：
Causse, Benjamin;Spadini, Lorenzo;Delolme, Cecile
通过黄原胶吸附铜的实验，研究了环境生物高分子的构象对金属吸附的影响。表观Cu 2+络合常数（logK; Cu 2 + + L-Cu L+）从pH 3.5时的2.9 +/- 0.1降低至pH 5.5时的2.5 +/- 0.1（离子强度I = 0.1）。这种行为与基本热力学明显矛盾，因为通常pH值越高，结合的阳离子越多。我们的结合滴定，圆二色谱和动态光散射研究表明，观察到的Cu键强度的变化涉及到黄原胶，在pH 3.5比在pH 5.5产生更多的螯合位点的结构的构象变化。这一假设得到验证的事实，即黄原胶上的Cu吸附常数总是高于那些上测得的混合物的葡糖醛酸和葡糖醛酸（logK = 2.2），这是两个组成的配体存在于黄原胶单体。这项研究显示了天然生物聚合物的结构构象在金属结合强度中的作用。这一发现可能有助于更好地预测铜和其他金属在酸性环境中的命运，如受酸性矿山排水影响的水生介质，以及泥炭和酸性土壤，并更好地确定生物修复过程的最佳条件。
The conformational impact of environmental biopolymers on metal sorption was studied through Cu sorption on xanthan. The apparent Cu2+ complexation constant (logK; Cu2+ + L- CuL+) decreased from 2.9 +/- 0.1 at pH 3.5 to 2.5 +/- 0.1 at pH 5.5 (ionic strength I = 0.1). This behavior is in apparent contradiction with basic thermodynamics, as usually the higher the pH the more cations bind. Our combined titration, circular dichroism and dynamic light scattering study indicated that the change observed in Cu bond strength relates to a conformational change of the structure of xanthan, which generates more chelating sites at pH 3.5 than at pH 5.5. This hypothesis was validated by the fact that the Cu sorption constants on xanthan were always higher than those measured on a mixture of pyruvic and glucuronic acids (logK = 2.2), which are the two constitutive ligands present in the xanthan monomer. This study shows the role of the structural conformation of natural biopolymers in metal bond strength. This finding may help to better predict the fate of Cu and other metals in acidic environmental settings such as aquatic media affected by acid mine drainage, as well as peats and acidic soils, and to better define optimal conditions for bioremediation processes.