1 research outputs found
Triethylamine Solution for the Intractability of Aqueous GoldāThiolate Cluster Anions: How Ion Pairing Enhances ESI-MS and HPLC of <i>aq</i>-Au<sub><i>n</i></sub>(pMBA)<sub><i>p</i></sub>
Herein we disclose
methods that greatly improve the solution- and
gas-phase handling properties of larger aqueous-phase goldāthiolate
clusters, which previously presented extreme technical obstacles to
molecular analysis and size control, even as they have enjoyed ever-wider
applications in materials science and biomedicine. The methods are
based upon an analogy between the polyacidic surface structure of
the pMBA-protected clusters (pMBA = <i>p</i>-mercaptobenzoic
acid) and that of oligonucleotides. A volatile ion-pairing reagent,
TEA = triethylamine, greatly improves solution-phase stability near
neutral pH and thus facilitates both electrospray generation of the
gas-phase ions and the in-line reversed-phase ion-pairing HPLC-ESI-MS
approach to analyzing complex mixtures of Au-pMBA oligomers and clusters.
Previously anticipated but never established compounds, including
Au<sub>36</sub>(pMBA)<sub>24</sub>, are thereby demonstrated. These
results are in accord with recent theoretical simulations of ion pairing
of model Au<sub>144</sub>(pMBA)<sub>60</sub> clusters in aqueous solutions.
This advance complements our recent work on their <i>nonaqueous</i> (hydrophobic) counterparts, in which redox electrochemistry is sufficient
to support the efficient LC-ESI processes, enabling various precise
measurements on the intact molecular ions. Here, we report (i) novel
conditions for enhanced ESI generation of polyanions of the aqueous
clusters and by extension (ii) a notably improved method by which
mixtures of these clusters may be successfully separated and detected
by ion-pair reversed-phase HPLC-MS