Determination of the surface pK of carboxylic- and amine-terminated alkanethiols using surface plasmon resonance spectroscopy
Determination of the surface pK of carboxylic- and amine-terminated alkanethiols using surface plasmon resonance spectroscopy
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DOI：
10.1021/la701760s
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发表时间：
2008-02-05
期刊：
影响因子：
3.9
通讯作者：
Latour, Robert A.
中科院分区：
文献类型：
--
作者：
Fears, Kenan P.;Creager, Stephen E.;Latour, Robert A.
当使用具有可电离官能团（如COOH和NH2）的自组装单层（SAM）时，表面的解离常数（pK（d））是一个重要的属性，因为它定义了给定本体溶液pH值的表面电荷密度。在这项研究中，我们开发了一种使用表面等离子体共振（SPR）光谱直接测量pK（d）的方法，通过结合SPR检测靠近表面的质量浓度的变化和作为表面电荷密度的函数的表面上的离子浓度的偏移的能力，然后应用该方法分别使用CsCl和NaBr盐溶液测量COOH和NH2官能化SAM表面的pK（d）值，其分别提供7.4和6.5的pK（d）值，还进行了分析研究，以通过计算表面上盐离子的过量质量作为SPR曲线的形状。溶液pH和表面pK（d）之间的差异的函数。的分析关系表明，表面电荷的状态也影响局部氢离子浓度，从而导致在一个实质性的局部转移，在表面的pH值相比，本体溶液作为本体溶液的pH值和表面的pK（d）之间的差异的函数。
When using self-assembled monolayers (SAMs) with ionizable functional groups, such as COOH and NH2, the dissociation constant (pK(d)) of the surface is an important property to know, since it defines the charge density of the surface for a given bulk solution pH. In this study, we developed a method using surface plasmon resonance (SPR) spectroscopy for the direct measurement of the pK(d) of a SAM surface by combining the ability of SPR to detect the change in mass concentration close to a surface and the shift in ion concentration over the surface as a function of surface charge density. This method was then applied to measure the pK(d) values of both COOH- and NH2-functionalized SAM surfaces using solutions of CsCl and NaBr salts, respectively, which provided pK(d) values of 7.4 and 6.5, respectively, based on the bulk solution pH. An analytical study was also performed to theoretically predict the shape of the SPR plots by calculating the excess mass of salt ions over a surface as a function of the difference between the solution pH and surface pK(d). The analytical relationships show that the state of surface charge also influences the local hydrogen ion concentration, thus resulting in a substantial local shift in pH at the surface compared to the bulk solution as a function of the difference between the bulk solution pH and the pK(d) of the surface.