Yoshimoto M, Kurosawa S, Tanaka M. Measurement of a Bubble-Free Chemical Oscillator Using QCMs Treated with Self-Assembled Monolayers.
J Phys Chem B 2024;
128:3360-3367. [PMID:
38567983 DOI:
10.1021/acs.jpcb.4c00002]
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Abstract
The oscillation of a 1,4-cyclohexanedione-bromate (CHD-bromate) system was investigated by using a quartz crystal microbalance (QCM) without or with a self-assembled monolayer (SAM), where gold and platinum were used for QCM electrodes and SAMs were composed of HS(CH2)11CH3, HS(CH2CH2O)5H, and HS(CH2CH2O)5CH3. The CHD-bromate system is well-known as a bubble-free oscillator and oscillates without or with a catalyst. In the CHD-bromate system without a catalyst, the oscillation of a resonant frequency shift (ΔF) of the QCM was observed in the Au-electrode QCMs without a SAM or with SAMs formed from HS(CH2)11CH3 and HS(CH2CH2O)5H. On the other hand, the HS(CH2CH2O)5CH3 SAM suppressed the ΔF oscillation. The results revealed that in the CHD-bromate system without a catalyst, hydrophobic CH3 terminal and helical conformation were important to prevent nonspecific adsorption of substances on a gold surface and its dissolution. In the CHD-bromate system with a catalyst (ferroin), the ΔF oscillation was observed in the Au-electrode QCM with the HS(CH2CH2O)5CH3 SAM. The results suggest evidence that the change of the solution viscosity and density led to the ΔF oscillation. These results for Au-electrode QCMs were also corroborated by those for Pt-electrode QCMs.
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