pH-Mediated Single Molecule Conductance of Cucurbit[7]uril

Abstract

Recognition tunneling technique owns the capability for investigating and characterizing molecules at single molecule level. Here, we investigated the conductance value of cucurbit[7]uril (CB[7]) and melphalan@CB[7] (Mel@CB[7]) complex molecular junctions by using recognition tunneling technique. The conductances of CB[7] and Mel@CB[7] with different pH values were studied in aqueous media as well as organic solvent. Both pH value and guest molecule have an impact on the conductance of CB[7] molecular junction. The conductances of CB[7] and Mel@CB[7] both showed slightly difference on the conductance under different measurement systems. This work extends the molecular conductance measurement to aqueous media and provides new insights of pH-responsive host-guest system for single molecule detection through electrical measurements.

pH control of conductance in a pyrazolyl Langmuir–Blodgett monolayer

“…Recently, Ai et al 41 have studied the electrical properties of molecular junctions formed with pH-responsive supramolecular systems. They showed that the conductance of cucurbit [7]uril (host) and melphalan (guest) supramolecular complexes decreased as the pH increased.…”

Recent Advances in Single-Molecule Sensors Based on STM Break Junction Measurements

“…Except the biological molecules, supramolecules [ 27 , 66 , 67 ] have also been proven for the design of single-molecule pH sensors. For example, cucurbit[n]uril (CB[n]) is commonly used due to its unique properties of good biocompatibility.…”

“…For example, cucurbit[n]uril (CB[n]) is commonly used due to its unique properties of good biocompatibility. In 2020, Ai et al used Cucurbit[7]uril (CB[7]) as the host molecule to measure the conductivity properties of CB[7] and its host–guest complex melphalan@CB[7] (Mel@CB[7]) at different pH with STM-BJ technique [ 27 ]. They performed conductance measurements in PB solutions at pH = 1, 4, and 7, respectively, and found that the conductance decreased with increasing pH ( Figure 3 c).…”

“…( c ) Single-molecule conductance of CB[7] in PB buffer solution at pH 1, 4 and 7 (left panel), and molecular structure of CB[7] (right panel). Reprinted with permission from [ 26 , 27 , 65 ]. Copyright 2004 American Chemical Society and 2011 American Chemical Society and 2020 Frontiers.…”

Control of molecular conductance by pH

“…9a). 64 Mel had been reported to form 1 : 1 host-guest complexes with CB [7] at a high equilibrium binding affinity K = 10 6 at pH = 1 through cation-dipole interactions between NH 3 + and CB [7] when the amine group on Mel was protonated under acidic condition. 65 The authors carried out STM fixed junction measurements in phosphate buffer (PB) as well as in organic solvent 1,2,4-trichlorobenzene (TCB) to determine the conductance of CB [7] and Mel@CB [7] complex attached to Au electrodes under different pH values.…”