Depending on the temperature, the twofold deprotonation of 1,1′‐methylenebis(3‐methylimidazole‐2‐thione) (1) and the subsequent reaction with 2 equiv. of trimethylsilyl chloride (TMSCl) gives two different bis‐TMS‐functionalized isomers, namely, 1,1′‐methylenebis(3‐methyl‐4‐trimethylsilylimidazole‐2‐thione) (2) and 1,1′‐methylenebis(3‐methyl‐5‐trimethylsilylimidazole‐2‐thione) (3). The cyclic dimethylsilyl‐bridged derivative 1,1′‐methylene‐5,5′‐dimethylsilylenebis(3‐methylimidazole‐2‐thione) (4) can also be obtained, corroborating the 5/5′ addition under certain conditions. All compounds have been examined by multinuclear 1D and 2D NMR experiments (1–4) together with single‐crystal X‐ray diffraction (3 and 4). Additionally, the dilithiated species 5 was synthesized by reacting 1 with 2 equiv. of nBuLi at ambient temperature in solution (THF). 1H and 7Li pulsed field‐gradient spin‐echo (PGSE) NMR, 7Li–1H heteronuclear Overhauser spectroscopy (HOESY), gradient heteronuclear multiple quantum correlation (gHMQC) and gradient heteronuclear multiple bond correlation (gHMBC) experiments showed that 5 exists as a monomeric contact ion pair (CIP) in THF solution. On the contrary, the X‐ray diffraction analysis of 5 revealed a polymeric chain, which can be described as [{5(thf)2}2]∞. Quantum chemical DFT and MP2 calculations were also conducted to determine the energies required for the deprotonation of 1. These results explain the regioselective deprotonation of 1 by CIP formation depending on the temperature and fully support the results of the synthetic and spectroscopic experiments.
Metal tags find application in a multitude of biomedical systems and the combination with laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) offers an opportunity for multiplexing. To lay the foundation for an increase of the signal intensities in such processes, we herein present a general approach for efficient functionalization of a well‐defined metal oxido cluster [Bi6O4(OH)4(SO3CF3)6(CH3CN)6]⋅2 CH3CN (1), which can be realized by selecting 7mer peptide sequences via combinatorial means from large one‐bead one‐compound peptide libraries. Selective cluster‐binding peptide sequences (CBS) for 1 were discriminated from non‐binders by treatment with H2S gas to form the reduction product Bi2S3, clearly visible to the naked eye. Interactions were further confirmed by NMR experiments. Extension of a binding peptide with a maleimide linker (Mal) introduces the possibility to covalently attach thiol‐bearing moieties such as biological probes and for their analysis the presence of the cluster instead of mononuclear entities should lead to an increase of signal intensities in LA‐ICP‐MS measurements. To prove this, CBS‐Mal was covalently bound onto thiol‐presenting glass substrates, which then captured 1 effectively, so that LA‐ICP‐MS measurements demonstrated drastic signal amplification compared to single lanthanide tags.
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