Thiolate-protected gold cluster
![](http://upload.wikimedia.org/wikipedia/commons/thumb/c/ca/Au25R18_minus_STRUCTURE_CORESHELL_CORE.png/300px-Au25R18_minus_STRUCTURE_CORESHELL_CORE.png)
Thiolate-protected gold clusters are a type of ligand-protected
These clusters can range in size up to hundreds of gold atoms, above which they are classified as passivated gold nanoparticles.
Synthesis
Wet chemical synthesis
The wet chemical synthesis of thiolate-protected gold clusters is achieved by the reduction of gold(III) salt solutions, using a mild reducing agent in the presence of thiol compounds. This method starts with gold ions and synthesizes larger particles from them, therefore this type of synthesis can be regarded as a "bottom-up approach" in nanotechnology to the synthesis of nanoparticles.
The reduction process depends on the equilibrium between different oxidation states of the gold and the oxidized or reduced forms of the reducing agent, or thiols. Gold(I)-thiolate polymers have been identified as important in the initial steps of the reaction.
Template-mediated synthesis
Rather than starting from "naked" gold ions in solution, template reactions can be used for directed synthesis of clusters. The high affinity of the gold ions to electronegative and (partially) charged atoms of functional groups yields potential seeds for cluster formation. The interface between the metal and the template can act as a stabilizer and steer the final size of the cluster. Some potential templates are dendrimers, oligonucleotides, proteins, polyelectrolytes and polymers.
Etching synthesis
Top-down synthesis of the clusters can be achieved by the "etching" of larger metallic
Properties
Electronic and optical properties
The
Magic numbers
Magic numbers are connected with the number of metal atoms in those thiolate-protected clusters which display an outstanding stability. Such clusters can be synthesized monodispersely and are end products of the etching procedure after an addition of excess thiols does not lead to further metal dissolution. Some important clusters with magic numbers are (SG:Glutathione): Au10(SG)10, Au15(SG)13, Au18(SG)14, Au22(SG)16, Au22(SG)17, Au25(SG)18, Au29(SG)20, Au33(SG)22, and Au39(SG)24.[2]
Au20(SCH2Ph)16 is also well-known.[9] It was greater than representatives Au102(p-MBA)44 with the para-mercaptobenzoice (para-mercapto-benzoic acid, p-MBA) produced ligand.[10]
Structure prediction
Worthy of note is that in 2013, a structural prediction of the Au130 (SCH3)50 cluster, based on Density Functional Theory (DFT) was confirmed in 2015.[11] This result represents the maturity of this field where calculations are able to guide the experimental work.[12] The following table features some sizes.
Composition database
Composition | Mass Spec. | Crystal Structure | DFT models | Exp. UV-Vis | Exp. powder XRD |
---|---|---|---|---|---|
Au10(SR)10 | JACS 2005 | JACS 2000 | - | Example | Example |
Au15(SR)13 | JACS 2005 | Not known | JACS 2013, PCCP 2013 | JACS 2005 | |
Au18(SR)14 | Angew. Chem Int. Ed. 2015, Angew. Chem Int. Ed. 2015 | PCCP 2012 | |||
Au24(SR)20 | JPCL 2010 | Nanoscale 2014 | JACS 2012 | JPCL 2010 | |
Au40(SR)24 | JACS 2010 Nano Lett 2015 | Sci Adv 2015 | JACS 2012 Nanoscale 2013 Sci Adv 2015 | Anal. Chem. 2013 Nano Lett 2015 | |
Au130(SR)50 | [1] | J. Phys. Chem. A 2013 | |||
Au187(SR)68 | not known | PCCP 2015 |
Applications
In
References
- ).
- ^ ).
- PMID 15161256.
- ).
- ).
- ).
- ).
- ).
- ).
- ).
- ).
- ).
- ^ Cheng-An J. Lin, Chih-Hsien Lee, Jyun-Tai Hsieh, Hsueh-Hsiao Wang, Jimmy K. Li, Ji-Lin Shen, Wen-Hsiung Chan, Hung-I Yeh, Walter H. Chang: Synthesis of Fluorescent Metallic Nanoclusters toward Biomedical Application: Recent Progress and Present Challenges, Journal of Medical and Biological Engineering, (2009) Vol 29, No 6, (Abstract Archived 2015-06-10 at the Wayback Machine).