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Preparation, Chiroptical and Photoluminescence Studies of Size Selected Gold Nanoclusters |
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PP: 23-31 |
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Author(s) |
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Mostafa Farrag,
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Abstract |
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| Here, we used the methanol-induced precipitation method to prepare and separate two size selected gold clusters protected by two enantiomers and racemic mixture of penicillamine ligand. The clusters materials were obtained by the reduction of HAuCl4∙3H2O salt with NaBH4 in the presence of L-penicillamine (L-pen), D-penicillamine (D-pen) and racemic mixture of penicillamine (rac-pen) as capping ligands. Two fractions were obtained with particles of about 1 nm and 2.6 nm, respectively. The average chemical formula was determined from thermogravimetric analysis (TGA). The optical properties of the samples were studied by three different methods: UV-vis spectroscopy, photoluminescence spectroscopy (PL) and circular dichroism (CD) spectroscopy. PL studies yielded the fluorescent properties of the samples. The main focus of this work, however, lies in the chirality of the particles. The CD spectra for gold clusters capped with one of the two enantiomers (D- or L-form) typical CD spectra were observed, no significant signals were detected for a racemic ligand mixture. Furthermore, gold clusters show quite large asymmetry factors (up to 1.3x10-3) in comparison to most other ligand protected clusters. These large factors and bands in the visible range of the spectrum suggest a strong chiral induction from the ligand to the metal core. |
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