Fitts JP, Persson P, Brown GE, Parks GA
Surface and Aqueous Geochemistry Group, Department of Geological and Environmental Sciences, Stanford University, Stanford, California, 94305-2115
J Colloid Interface Sci. 1999 Dec 1;220(1):133-147. doi: 10.1006/jcis.1999.6521.
Thecomposition and mode of attachment of Cu(II) complexes at the gamma-Al(2)O(3)-water interface in suspensions containing a simple amino acid (glutamate) were characterized with EXAFS and FTIR spectroscopies. The spectroscopic results indicate that two types of Cu(II)-glutamate-alumina interactions are primarily responsible for Cu(II) and glutamate uptake between pH 4 and 9. In acidic suspensions of alumina, glutamate forms a bridge between Cu(II) ions and the (hydr)oxide surface (Type B complex). In this Type B surface complex, Cu(II) is bonded to amino acid headgroups (i.e., (+)H(3)NCHRCOO(-)) of two glutamate molecules. Spectroscopic and ionic strength dependent uptake results are combined to propose that the nonbonded side chain carboxylate groups of this complex are attracted to the oxide surface through long-range forces, leading to enhanced Cu(II) uptake relative to the glutamate-free system. In alkaline suspensions the relative amount of surface-bound Cu(II) complexed by glutamate decreases, and a direct Cu(II)-surface bond becomes the dominant mode of attachment (Type A complex). These surface complexes differ markedly from the species found in the alumina-free Cu(II)-glutamate aqueous system under similar solution conditions, where Cu(H(2)O)(2+)(6) and Cu(glutamate)(2-)(2) are the dominant species in acidic and alkaline solutions, respectively. Based on these spectroscopic results, surface complexation reactions are proposed for the Cu(II) and glutamate ternary interactions with the alumina surface in this system. Similarities between the results of this study and Cu(II) uptake behavior and complexation in the presence of natural organic material (NOM) indicate that Cu(II)-glutamate interactions mimic those in more complex Cu(II)-NOM-mineral-water systems. Copyright 1999 Academic Press.
采用扩展X射线吸收精细结构光谱（EXAFS）和傅里叶变换红外光谱（FTIR）对含有简单氨基酸（谷氨酸）的悬浮液中铜（II）配合物在γ-Al₂O₃-水界面的组成和附着模式进行了表征。光谱结果表明，在pH值为4至9之间，两种类型的铜（II）-谷氨酸-氧化铝相互作用是铜（II）和谷氨酸吸收的主要原因。在氧化铝的酸性悬浮液中，谷氨酸在铜（II）离子和（氢）氧化物表面之间形成桥梁（B型配合物）。在这种B型表面配合物中，铜（II）与两个谷氨酸分子的氨基酸头基（即(+)H₃NCHRCOO(-)）键合。结合光谱和离子强度依赖性吸收结果表明，该配合物的非键合侧链羧酸盐基团通过长程力被吸引到氧化物表面，导致相对于无谷氨酸体系铜（II）吸收增强。在碱性悬浮液中，与谷氨酸络合的表面结合铜（II）的相对量减少，直接的铜（II）-表面键成为主要的附着模式（A型配合物）。这些表面配合物与在类似溶液条件下无氧化铝的铜（II）-谷氨酸水体系中发现的物种明显不同，在该体系中，Cu(H₂O)₆²⁺和Cu(谷氨酸)₂²⁻分别是酸性和碱性溶液中的主要物种。基于这些光谱结果，提出了该体系中铜（II）和谷氨酸与氧化铝表面三元相互作用的表面络合反应。本研究结果与天然有机物质（NOM）存在下铜（II）吸收行为和络合的相似性表明，铜（II）-谷氨酸相互作用模拟了更复杂的铜（II）-NOM-矿物-水体系中的相互作用。版权所有1999年学术出版社。
