Hicks J F, Templeton A C, Chen S, Sheran K M, Jasti R, Murray R W, Debord J, Schaaff T G, Whetten R L
Kenan Laboratories of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290.
Anal Chem. 1999 Sep 1;71(17):3703-11. doi: 10.1021/ac990432w.
This report describes how the electrochemical double-layer capacitances of nanometer-sized alkanethiolate monolayer-protected Au clusters (MPCs) dissolved in electrolyte solution depend on the alkanethiolate chain length (C4 to C16). The double-layer capacitances of individual MPCs (C(CLU)) are sufficiently small (sub-attoFarad, aF) that their metal core potentials change by >0.1 V increments for single electron transfers at the electrode/solution interface. Thus, the current peaks observed are termed "quantized double layer charging peaks", and their spacing on the potential axis varies with C(CLU). Differential pulse voltammetric measurements of C(CLU) in solutions of core-size-fractionated (i.e., monodisperse) MPCs are compared to a simple theoretical model, which considers the capacitance as governed by the thickness of a dielectric material (the monolayer, whose chain length is varied) between concentric spheres of conductors (the Au core and the electrolyte solution). The experimental results fit the simple model remarkably well. The prominent differential pulse voltammetric charging peaks additionally establish this method, along with high-resolution transmission electron microscopy and laser ionization-desorption mass spectrometry, as a tool for evaluating the degree of monodispersity of MPC preparations. We additionally report on a new tactic for the preparation of monodisperse MPCs with hexanethiolate monolayers.
本报告描述了溶解在电解质溶液中的纳米级链烷硫醇盐单层保护金簇（MPC）的电化学双层电容如何取决于链烷硫醇盐的链长（C4至C16）。单个MPC的双层电容（C(CLU)）足够小（亚阿托法拉，aF），以至于在电极/溶液界面进行单电子转移时，其金属核电位会以>0.1 V的增量变化。因此，观察到的电流峰被称为“量化双层充电峰”，它们在电位轴上的间距随C(CLU)而变化。对核心尺寸分级（即单分散）的MPC溶液中的C(CLU)进行差分脉冲伏安测量，并与一个简单的理论模型进行比较，该模型将电容视为由导体同心球（金核和电解质溶液）之间的介电材料（链长可变的单层）厚度所决定。实验结果与该简单模型拟合得非常好。显著的差分脉冲伏安充电峰还确立了这种方法，连同高分辨率透射电子显微镜和激光电离-解吸质谱法，作为评估MPC制剂单分散程度的一种工具。我们还报告了一种用己硫醇盐单层制备单分散MPC的新策略。
