Electron-Transfer Polymers. XXV. On “Hydrophobic Bonding.” The Effect of Solvent on Quinhydrone

Abstract

An examination of the extent of quinhydrone formation between hydroquinone and p-benzoquinone in 20 dvferent pure and aqueous solvents indicated a reasonable correlation between extent of quinhydrone formation, as judged by the magnitude of the association constant and of the related standard free energy, and the surface tension (surface free energy) of the solvent. This supported the hypothesis of Sinanoglu and Abdulnur that the driving force of "hydrophobic bonding," e.g., in D N A double helix formation, is the decrease in free energy as the total area of solvent cage about the two dissociated entities is decreased in the process of complex formation. Thus the surface of contact between hydroquinone and quinone with solvent is decreased by the order of 20 A. in quinhydrone formation. The energy change f o r water or a high surface tension solvent is large enough to drive complex formation in these solvents as compared with, e.g., tetrahydrofuran, glacial acetic acid, methanol, and n-butyl alcohol.

A kinetic and mechanistic study of the electrochemical oxidation of hydroquinone in 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, [C2mim][NTf2]

“…In this case, when the scan rate is fast enough, since the slow formation of Q and QH 2 , the reduction of QH 2 could be inhibited which explained the disappearance of the corresponding reduction peak [19]. As for the assignment of the new peak, there was no conclusion, but possible processes suggested were the reduction of Q or (QH) 2 .…”

Quinone–hydroquinone complexes as model components of humic acids: Theoretical studies of their structure, stability and Visible–UV spectra

“….H 2 Q? The old experimental data is ambiguous since for the formation of quinhydrone in water Kuboyama and Nagakura (1955) report negative values of DH (by a couple kcal/mol) while Moser and Cassidy (1965) report positive values of DG (by a couple kcal/ mol). Although these values are not necessarily contradictory, since we would expect the free energy change to be more positive than the enthalpy change for a complex formation reaction (we actually calculate a 10 kcal/mol difference, read infra), they do not generate a great deal of confidence.…”

Oxygen supply to immobilized cells: 5. Theoretical calculations and experimental data for the oxidation of glycerol by immobilized Gluconobacter oxydans cells with oxygen or p‐benzoquinone as electron acceptor

“…From the final p values, Dis(p-b) was calculated.The mean value, 7.2 x lo-'' m2/s, was used in the rest of the calculations. For a, the following equation was obtained: = 65,000 ro(15)…”