Acid-Base Properties and Surface Charge Distribution of the Water-Soluble Au-102(pMBA)(44) Nanocluster

作者：Koivisto Jaakko; Chen Xi; Donnini Serena; Lahtinen Tanja; Hakkinen Hannu; Groenhof Gerrit; Pettersson Mika

来源：Journal of Physical Chemistry C, 2016, 120(18): 10041-10050.

DOI：10.1021/acs.jpcc.6b00922

The pK(a) of the p-mercaptobenzoic acid (pMBA) ligands in the Au-102(pMBA)(44) nanocluster was measured by using acid base and IR titration. The observed macroscopic pK(a) = 6.18 +/- 0.05 is significantly more basic than that of free pMBA (pK(a) = 4.16), and the protonation behavior is anticooperative according to the Hill coefficient n = 0.64 +/- 0.04. The cluster is truly water-soluble when more than 22 and insoluble when fewer than 7 ligands are in the deprotonated state. In order to obtain more insight into the anticooperative character, the cluster was modeled at pH similar to 6.2 using constant pH molecular dynamics simulations. The pK(a) values of the individual pMBAs are in the range of 5.18-7.58, depending on the positions of the ligands, generating a nonuniform charge distribution on the cluster surface. The cluster interactions with inorganic and biological environment depend on the surface charge distribution, stressing the importance of understanding the protonation state of the cluster.

• 出版日期2016-5-12