Green and Scalable Fractionation of Gold Nanoclusters by Anion Exchange Chromatography: Proof of Principle and Scale-Up

Abstract

The chromatographic separation of atomically precise glutathione-stabilized gold nanocluster (AuNC) mixtures is demonstrated for purely aqueous anion exchange chromatography (AEX) and compared to the results of hydrophilic interaction liquid chromatography (HILIC), which requires mixtures of water and acetonitrile. For isocratic HILIC separations, the influence of the mobile phase composition with respect to ionic strength and acetonitrile content is investigated. Individual AuNCs are identified by their optical properties directly from chromatograms and by comprehensive electrospray ionization differential mobility mass spectrometry. Separations by AEX are performed in aqueous mobile phases and are thus considered as a green and sustainable technique for the efficient fractionation of AuNCs. Henry coefficients are determined, which describe the retention behavior of single AuNCs and thus form the basis for modeling, optimization, and scale-up of the separation. The separation by AEX is optimized by linear salt gradient experiments. The scalability of the separation is demonstrated by increasing the AuNC feed concentration up to 64 g/L. Moreover, we quantify the amounts of individual AuNCs by inductively coupled plasma–optical emission spectroscopy after separation and close the mass balance demonstrating the reversible adsorption from the stationary phase. Our AEX approach is superior to HILIC since it offers a higher resolution, provides access to larger clusters, is readily scalable, and is purely water-based. AEX is considered as a sustainable, scalable, and widely applicable technique for the isolation of all types of water-soluble single cluster species. Therefore, we anticipate applications for instance for highly specialized nanocatalysts, sensors, or in medicine.

Development of an advanced multiwavelength emission detector for the analytical ultracentrifuge

“…The synthesis of glutathione-capped AuNCs was performed as described previously. 21 In brief, a mixture of 5 mM NaAuCl 4 and 20 mM glutathione in 12.5 mL methanol was prepared and stirred for 30 min at room temperature, subsequently cooled to 0 °C and then stirred for another 30 min. An aqueous solution of 150 mM NaBH 4 (3.13 mL, cooled to 0 °C) was then rapidly injected into the methanol solution under vigorous stirring.…”

“…A possible explanation for this phenomenon is the fact that the data was analysed with a fixed frictional ratio and partial specific volume, while both species should have different shapes as well as densities due to the altering gold–glutathione composition. 21 As the contribution of each species to the overall signal is wavelength dependent, this can induce shifts in the sedimentation coefficient distributions. This is supported by the observation that the wavelength shifts can be eliminated when the frictional ratio and partial specific volume are optimised manually instead of using the fixed frictional ratio of 1 and best-fit values for the partial specific volume ( cf.…”

Efficient quenching sheds light on early stages of gold nanoparticle formation

“…To get more information regarding intermediate species, we developed a facile method to freeze the Au NP formation process by adding GSH as a quencher at different time delays aer starting the reaction. GSH is a well-known and highly efficient stabilizer of Au clusters and small Au NPs 46,52 as it binds covalently to the surface of the Au NPs and therefore prevents their further growth. It should be noted, that GSH is able to reduce Au(III) ions to Au(I) ions and forms Au(I) complexes.…”