Deposition of Nanosized Amino Acid Functionalized Bismuth Oxido Clusters on Gold Surfaces

Abstract

Bismuth compounds are of growing interest with regard to potential applications in catalysis, medicine, and electronics, for which their environmentally benign nature is one of the key factors. One thing that currently hampers the further development of bismuth oxido-based materials, however, is the often low solubility of the precursors, which makes targeted immobilisation on substrates challenging. We present an approach towards the solubilisation of bismuth oxido clusters by introducing an amino carboxylate as a functional group. For this purpose, the bismuth oxido cluster [Bi38O45(NO3)20(dmso)28](NO3)4·4dmso (dmso = dimethyl sulfoxide) was reacted with the sodium salt of tert-butyloxycabonyl (Boc)-protected phenylalanine (L-Phe) to obtain the soluble and chiral nanocluster [Bi38O45(Boc–Phe–O)24(dmso)9]. The exchange of the nitrates by the amino carboxylates was proven by nuclear magnetic resonance, Fourier-transform infrared spectroscopy, as well as elemental analysis and X-ray photoemission spectroscopy. The solubility of the bismuth oxido cluster in a protic as well as an aprotic polar organic solvent and the growth mode of the clusters upon spin, dip, and drop coating on gold surfaces were studied by a variety of microscopy, as well as spectroscopic techniques. In all cases, the bismuth oxido clusters form crystalline agglomerations with size, height, and distribution on the substrate that can be controlled by the choice of the solvent and of the deposition method.

Anchoring Atomically Precise Chiral Bismuth Oxido Nanoclusters on Gold: The Role of Amino Acid Linkers

“…The synthesis procedure of BiO-NC 2 in good yields ( ∼ 7 0 % ) i s p e r f o r m e d s t a r t i n g f r o m [Bi 38 O 45 (NO 3 ) 20 (dmso) 28 ](NO 3 ) 4 •4dmso (A) and the sodium salt of Boc-L-Met-OH (C) according to our previous work, 13 which is outlined together with details of the material characterization in the Supporting Information. In order to investigate the chirality transfer from the amino acids to the BiO-NC, CD spectroscopy measurements were performed (cf.…”

“…13 In Figure 3a,b, the growth mode behavior of BiO-NC 1 (di1 120 ) and 2 (di2 120 ) is compared. The SEM images show that the BiO-NC 1 tends to agglomerate according to the Ostwald ripening process 44 and form islands with well-defined terraces, 13 while the agglomeration of BiO-NC 2 is much weaker. Only very small agglomerations can be distinguished, which are explained by a stronger interaction between the BiO-NC 2 and the Au surface via the sulfur atom present in the thioether group (−S−CH 3 ).…”

“…Another approach might be realized using chiral atomically precise metal oxido nanoclusters (MO-NCs) as chiral light absorbers. Especially, we are interested in bismuth-based compounds because this element shows a large pool of accessible MO-NCs, with the option of their targeted optical absorption tuning via a recently developed doping procedure. − In addition, the environmentally benign nature of bismuth compounds offers access to novel sustainable materials and medical applications and led already to developments with potential application, e.g., in catalysis, medicine, and electronics. − Among the bismuth oxido nanoclusters (BiO-NCs), those with a [Bi 38 O 45 ] 24+ core seem to be the most stable ones, as evidenced by studies on various accessible BiO-NCs of this structure type covered with different ligands such as sulfonates, carboxylates, and nitrate. − Furthermore, their physical properties such as the optical band gap can be tuned by doping the cluster core for example with rare earth elements . However, many of the BiO-NCs suffer from either low hydrolytic stability at the ligand periphery, low solubility, low biocompatibility of their ligands, or accessibility on a large scale. , Recently, we were able to prepare a rather stable and highly soluble amino acid-modified BiO-NC of the type [Bi 38 O 45 (Boc- l -Phe-O) 24 (dmso) 9 ] ( 1 ) and studied its deposition behavior using different coating techniques on gold surfaces.…”

“…However, many of the BiO-NCs suffer from either low hydrolytic stability at the ligand periphery, low solubility, low biocompatibility of their ligands, or accessibility on a large scale. , Recently, we were able to prepare a rather stable and highly soluble amino acid-modified BiO-NC of the type [Bi 38 O 45 (Boc- l -Phe-O) 24 (dmso) 9 ] ( 1 ) and studied its deposition behavior using different coating techniques on gold surfaces. Our approach led to microstructured cluster agglomerations on the metal surface due to crystallization processes and strong intermolecular interactions between the clusters . To overcome this challenge, we synthesized the N -( tert -butoxycarbonyl)- l -methionine (Boc- l -Met-OH)-substituted BiO-NC [Bi 38 O 45 (Boc- l -Met-O) 24 ] ( 2 ), which is expected to provide higher affinity to the gold substrate due to its thioether functionality (−S–CH 3 ).…”

“…1 H NMR (ppm, 500.30 MHz, MeOD-d 4 , 298 K): δ 4.15 (s, 1H), 2.66 (s, dmso coord ), 2.60 (m, 2H), 2.18 (m, 1H), 2.14 (s, 3H), 2.01 (m, 1H), 1.48 (s, 9H) 13. C NMR (ppm, 125.80 MHz, MeOD-d 4 , 298 K): 180.7, 157.8, 80.5, 56.3, 33.6, 31.9, 29.2, 16.0.…”