**5. Conclusions**

Currently, in the era of lipidomics, the attention of scientists from many fields has been shifted towards looking at biological membranes from a different perspective. Membranes have been demonstrated to determine certain physiological functions of cells and play important roles in several pathologies such as cancer. In this respect, a great deal of attention is now directed into the understanding of the interactions between anticancer drugs and cellular membranes. Thus, evaluation of drug-membrane dependencies can serve as a useful tool in predicting membrane permeability, bioactivity and cytotoxicity of potential antineoplastic agents in modern oncopharmacology. Regarding the importance of such interactions, the role of biomimetic model membranes and biophysical/electrochemical techniques becomes increasingly significant in chemical and pharmacological studies. As such, based on previous in vitro research conducted on glioblastoma cancer cells, we used electrophoretic light scattering and impedance spectroscopy to study the effects of CinA, *p*-CoA and FA on electrical properties of bilayers formed from DOPC, PS or DOPC-PS

mixture. We demonstrated that after treatment with phenolic acids, the negative charge of membranes increased in alkaline pH solutions, but not in acidic ones. On the other hand, the data from impedance measurements showed elevated values of either the electrical capacitance and the electrical resistance in treated cells. We therefore concluded that at acidic pH, all tested compounds were able to solubilize into the membrane and permeate it. However, at neutral and alkaline pH, the CinA could be partially inserted into the bilayers, whereas *p*-CoA and FA could be anchored at the bilayer surface. Since intracellular penetration seems to be a key determinant of drug functioning, our results imply that electrochemical methods might be employed for predicting pharmacological activity and bioavailability of phenolic acids in the future.

**Author Contributions:** Conceptualization, M.N.; Methodology, J.K. and M.N.; Validation, J.K., M.G. and M.K.; Formal Analysis, J.K., M.Z., M.G. and M.N.; Investigation, M.Z.; Resources, M.N.; Data Curation, J.K. and M.G.; Writing—Original Draft Preparation, M.N.; Writing—Review and Editing, M.Z., J.K., M.K. and M.N.; Visualization, M.N., M.Z. and J.K.; Supervision, M.N.; Project Administration, M.N.; Funding Acquisition, M.N., M.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** This study was funded by the National Science Centre (Poland) on the basis on the decision number 2018/02/X/ST4/02153 (Miniatura 2 call). This research was supported by the Slovak Research and Development Agency under the contract No. APVV-17-0149 and PP-COVID-20-0019. The potentiostat/galvanostat was funded by the European Funds for Regional Development and the National Funds of Ministry of Science and Higher Education as part of the Operational Program Development of Eastern Poland 2007–2013, project: POPW.01.03.00-20-044/11.

**Conflicts of Interest:** The authors declare no conflict of interest.
