Investigating the Thermodynamic Causes Behind the Anomalously Large Shifts in pK_a Values of Benzoic Acid-Modified Graphite and Glassy Carbon Surfaces

Abstract

Figure 4a,b and the values in Tables 1-3 were incorrect as published. The corrected figures, values in tables and conclusion should be as follows:In conclusion, enthalphic contribution was neglected by mistake, but it cannot be neglected, and the different surface pK a values were found to be controlled by both the enthalpic and entropic terms. The ΔH°values for BAcarbon powder and BA-GC are different in sign; both ΔS°values are appreciably different from the values in bulk solution (Tables 1-3). The lateral interactions on the carbon surface and/or hydrogen bond formation are responsible for the enthalpic contribution, whereas the entropic contribution attributed to the ordering of solvent molecules at the interface between the carbon substrate and the solution is likely responsible for the variation in the observed pK a values, reflecting the different hydrophobicity/ hydrophilicity of the graphite and glassy carbon surfaces.

Enhanced electrostatic modulation of ionic diffusion through carbon nanotube membranes by diazonium grafting chemistry

“…As for, e.g. benzoic acid groups on graphitic carbon synthesized by the same diazonium grafting chemistry have shown pKa shifts to pH ∼6.5 [33].…”

Covalently Anchored Carboxyphenyl Monolayer via Aryldiazonium Ion Grafting: A Well-Defined Reactive Tether Layer for On-Surface Chemistry

“…After deprotection, the cyclic voltammogram recorded in 0.1 M HCl is indistinguishable from that obtained at the bare GC electrode; however, in the pH 6.9 solution, although there is an increase in the current for the redox couple after deprotection, the electron transfer rate clearly remains low (ΔE p = 279 mV) relative to that at the polished surface (ΔE p = 65 mV). The pK a of a multilayered Ar-COOH film is in the range of 2.8−3.3, 28 and hence, the deprotected film will be protonated (neutral) in 0.1 M HCl (pH ∼ 1) and deprotonated (negatively charged) at pH 6.9. Although deprotection decreases the film thickness, which accelerates the electron transfer rate, the negative surface charge at pH 6.9 slows the electron transfer rate compared to that at the neutral deprotected surface, because of electrostatic repulsions with the negatively charged redox probe.…”

Carbon Nanotube–Based Sensors and Biosensors

“…In the solution phase 4-carboxybenzene has a pK a of 4.20 at 298 K. On the surface of glassy carbon the pK a was found to shift to 3.25, while on the surface of graphite the pK a was shifted in the opposite direction, to 6.45 [65]. The thermodynamic parameters controlling these shifts were investigated and it was found that the degree and direction of the shift in pK a are dominated by the entropy change upon ionization of the carboxyl groups.…”

“…Finally, Abiman et al studied the shift in pK a of 4-carboxyphenyl groups attached covalently to graphite and glassy carbon surfaces [65]. In the solution phase 4-carboxybenzene has a pK a of 4.20 at 298 K. On the surface of glassy carbon the pK a was found to shift to 3.25, while on the surface of graphite the pK a was shifted in the opposite direction, to 6.45 [65].…”