Gold nanoparticles covered by derivatives of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) with well-defined coverage and narrow size distribution were synthesized and self-assembled on the gold electrode. The TEMPO nanoparticle-coated electrode was characterized using STM and AFM. The kinetics of oxidation of the nitroxide radicals attached to the nanoparticles was evaluated based on cyclic voltammetry measurements. The TEMPO–nanoparticle modified electrode was found more efficient in electrocatalytic oxidation of benzyl alcohol than the electrode modified with a monolayer of TEMPO molecules directly bound to the gold surface.

The influence of the pH of the multicomponent cell medium on the performance of doxorubicin (DOX), an anticancer drug, was studied on the examples of cervical (HeLa) and kidney (A498) cancer cell lines. The change of pH of the cell medium to more acidic led to a decrease of DOX toxicity on both cell lines due to the change of drug permeability across the cell membrane as a result of drug protonation. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) studies and lactate dehydrogenase (LDH) release tests have shown low toxicity of the drug, especially in the case of A498 cells, which are characterized by an extremely high glycolytic metabolism. The behavior was ascribed primarily to the increased proton concentration in the peripheral blood follicle in the presence of products of the acidic glycolytic metabolism. It is not observed in the measurements performed in commercially available media since they usually have a neutral pH. In earlier reports on kidney cancer, several mechanisms were discussed, including the metabolism of DOX to its less toxic derivative, doxorubicinol, overexpression of ATP binding cassette subfamily B member 1 (ABCB1) transporters, that remove DOX from the inside of cells; however, there was no focus on the simple but very important contribution of drug protonation described in the present study. Drug pH-dependent equilibria in the cell medium should be considered since changes in the drug form may be an additional reason for multidrug resistance.

A non-toxic lipoic acid derivative of β cyclodextrin (βCDLip) with an electron-rich aromatic linker was studied as a carrier for the drug doxorubicin with the aim of decreasing the toxic side effects of this drug. The modified cyclodextrin strengthened the drug binding and differentiated the complex-forming ability with dependence on pH. The stability constants of the complexes were evaluated by voltammetry and spectrofluorometry. Molecular modelling provided deeper insight into the nature of the ligand structure itself and the drug–ligand interactions, showing the different contributions of the self-inclusion of the ligand substituent at different pH values. As a result, the modes of interaction of βCDLip with the drug and factors affecting the stabilities of the complex under the pH conditions of healthy and tumour cells could be discovered and explained.