Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, P.O. Box 38, Solomons, Maryland 20688, USA.
Environ Sci Technol. 2010 Mar 1;44(5):1644-9. doi: 10.1021/es9029667.
We performed a series of manual alkalimetric titrations in NaCl solutions (0.01-5.0 M) at T = 25 degrees C on both fresh and dehydrated samples of the marine chlorophyte Ulva lactuca (sea lettuce), a strong metal accumulator holding considerable promise in biosorbent and biomonitor applications. Functional groups were characterized in terms of their number, site densities, and acid dissociation constants (pK(a)s). FITEQL4.0 modeling shows that, at any ionic strength, titration curves for dehydrated biomass in the pH range 2-10 are adequately described by three functional groups with remarkably uniform site densities of about 5 x 10(-4) mol/g. Lower site densities for fresh U. lactuca are consistent with approximately 87% water content. The pK(a)s display pronounced ionic strength dependent behavior obeying an extended Debye-Huckel relation. Extrapolation to I = 0 yields values of 4.26 +/- 0.04, 6.44 +/- 0.02, and 9.56 +/- 0.04. This information by itself is insufficient to unambiguously identify the groups. Similar site densities suggest that all three are linked to major molecular building blocks of the cell material, pointing to carboxylic acids, phosphate esters, and amines as likely candidates. Highly acidic sulfate esters, not detected in our titrations, may also play a role in trace metal adsorption on U. lactuca.
我们在 T = 25°C 下，在 NaCl 溶液（0.01-5.0 M）中对新鲜和脱水的海洋绿藻 Ulva lactuca（海莴苣）进行了一系列手动碱度滴定，这是一种强金属蓄积体，在生物吸附剂和生物监测应用中具有很大的应用前景。根据数量、位置密度和酸离解常数（pK(a)s）来描述官能团。FITEQL4.0 建模表明，在任何离子强度下，脱水生物质在 pH 值 2-10 范围内的滴定曲线可以用三个具有显著均匀位置密度（约 5 x 10(-4) mol/g）的官能团很好地描述。新鲜 U. lactuca 的位置密度较低，与大约 87%的含水量一致。pK(a)s 表现出明显的离子强度依赖性，符合扩展的 Debye-Huckel 关系。外推至 I = 0 得到 4.26 +/- 0.04、6.44 +/- 0.02 和 9.56 +/- 0.04 的值。这些信息本身不足以明确识别这些基团。类似的位置密度表明，所有这三种都与细胞物质的主要分子构建块有关，表明羧酸、磷酸酯和胺可能是候选物质。在我们的滴定中未检测到的高度酸性硫酸酯也可能在 U. lactuca 对痕量金属的吸附中发挥作用。
