2016 Fiscal Year Research-status Report
N-Heterocyclic Carbene-modified Gold Nanoclusters: Novel Materials with Potential Biological Applications
| Project/Area Number |
16K13962
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| Research Institution | Nagoya University |
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Principal Investigator |
CRUDDEN Cathleen 名古屋大学, トランスフォーマティブ生命分子研究所, 客員教授 (10721029)
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| Project Period (FY) |
2016-04-01 – 2019-03-31
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| Keywords | Gold Nanoclusters / N-Heterocyclic Carbene / Stability / Biological Applications |
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| Outline of Annual Research Achievements |
In this funding year, we have made significant advances. We developed conditions for the synthesis of gold nanoclusters functionalized by up to four N-heterocyclic carbenes. We also developed conditions for the clean preparation of Au clusters substituted by only one NHC. These clusters were extensively characterized by NMR (Nagoya) and mass spec (Tsukuda lab, Tokyo). Four different NHC ligands were examined. In all cases, the ligands were benzannulated, and they differed by the wingtip groups on nitrogen: Me, Et, iPr, Bn. In all cases, the corresponding benzimidazolium hydrogen carbonate was employed since we found that the free carbene led to breakdown/restructuring of the Au core.
The iPr substituted NHC was studied the most extensively. It was found that five equivalents of NHC precursor to Au11 starting material ([Au11(PPh3)8Cl2]Cl) were optimal, with higher equivalents leading to mixtures of products. The amount of water present in the solution was also critical, with clean monosubstitution being observed. We believe this is because of tuning the pKa of the benzimidazolium hydrogen carbonate, with the cation becoming more acidic and the anion more basic as the solution is dehydrated since there are no opportunities for hydration. In the case of the benzyl-substituted NHCs, we always observed multiple products, with up to 4 NHCs observed on the Au core in reasonable amounts. This is the first time we have observed such a high level of substitution.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
Progress this year has been smooth. Identifying the use of mass spectrometry as a key technique and the Tsukuda lab as collaborators was critical for advances this year. All samples are sent there for analysis. The ability to determine reaction parameters for preparing clean monosubstituted clusters or multiply substituted clusters, and preliminary results on purification was also critical. This work is very technically challenging as the clusters need to be prepared on small scales due to the inefficient literature method for the preparation of the starting phosphine cluster. We are planning a bottom-up synthesis that would avoid this problem but we plan to finish this work first before designing a new synthesis.
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| Strategy for Future Research Activity |
In the next year our goals are given below in sections.
A. Complete nanocluster synthesis/purification/characterization (1) Determine optimal reaction conditions for all NHCs examined; (2) separate multiply exchanged clusters; (3) prepare C-13 labeled NHC cluster to identify C-Au signal; (4) obtain X-ray quality single crystals and determine exact structure
B. Nanocluster properties (1) measure stability of other monosubstituted clusters and determine effect of substituent; (2) examine stability of multiply substituted clusters
C. Novel synthetic routes (1) Use the displacement method already employed as described above with different starting clusters; (2) examine bottom-up methods for the preparation of completely novel clusters
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[Journal Article] Simple direct formation of self-assembled N-heterocyclic carbene monolayers on gold and their application in biosensing2016
Author(s)
C. M. Crudden, J. H. Horton, M. R. Narouz, Z. Li, C. A. Smith, K. Munro, C. J. Baddeley, C. R. Larrea, B. Drevniok, B. Thanabalasingam, A. B. McLean, O. V. Zenkina, I. I. Ebralidze, Z. She, H.-B. Kraatz, N. J. Mosey, L. N. Saunders, A. Yagi
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Journal Title
Nature Communications
Volume: 7
Pages: 12654
DOI
Peer Reviewed / Open Access
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