**3. Results**

*3.1. Specific Capacitance of Lipid Bilayers in the Presence of Simple Carbohydrates* 3.1.1. Free-Standing Lipid Bilayers—Electrodeformation of GUVs

The specific capacitance of POPC bilayers is measured in aqueous solutions of 1 mM NaCl containing different concentrations of glucose, fructose or glucose up to 300 mmol/L. In order to probe for specific effects, we determine the same parameter also for another type of phosphatidylcholine membranes, namely SOPC, at 200 mmol/L of sucrose in the aqueous surroundings. Our choice of synthetic lipids is motivated by their controlled chemical composition combined with the property to mimic well natural lipid extracts, e.g., egg-yolk or soybean phosphatidylcholine extracts. The values obtained for membrane specific capacitance together with the error calculated from the fit of our experimental data for every sugar concentration are summarized in Table 1 and Figure 2.

**Figure 2.** Specific capacitance of (i) POPC bilayers in the presence of 1 mmol/L NaCl and up to 300 mmol/L of glucose, fructose or sucrose; (ii) SOPC membranes in 1 mmol/L NaCl, 200 mmol/L of sucrose obtained from electrodeformation of GUVs.

̅ **λ Λ** ഥ For each sugar concentration, we measure the transition frequency *fcr* (Equation (4)) of 6 to 15 vesicles. The acquired experimental data for *fcr* as a function of the inverse radii of vesicles are fitted for fixed *λin* and Λ. Latter are the same for all recorded and analyzed vesicles in one batch. Membrane capacitance serves as a single fitting parameter. Our results show no alteration of the specific capacitance of POPC bilayers in aqueous

solutions of glucose and fructose at concentrations of up to 300 mmol/L and in the presence of 1 mmol/L NaCl. In glucose solutions, we obtain *<sup>C</sup><sup>m</sup>* <sup>=</sup> 0.52 <sup>±</sup> 0.02 <sup>µ</sup>F/cm<sup>2</sup> with goodness of fit 0.91. The value calculated from the data acquired in fructose solutions is *<sup>C</sup><sup>m</sup>* <sup>=</sup> 0.51 <sup>±</sup> 0.01 <sup>µ</sup>F/cm<sup>2</sup> with goodness of fit 0.55. In sucrose-containing aqueous surroundings we measure 25%-higher values of membrane specific capacitance at 200 and 300 mmol/L sugar concentrations compared to the control value of the same parameter in 1 mmol/L NaCl (Figure 2). Similar increase of *C<sup>m</sup>* is reported also for SOPC bilayers at 200 mmol/L of sucrose in water.

**Table 1.** Specific capacitance of POPC membranes in aqueous solutions containing different concentrations up to 300 mmol/L glucose, fructose or sucrose; data obtained from electrodeformation of GUVs; GF, goodness of fit. The errors in *C<sup>m</sup>* and *C<sup>m</sup>* are standard deviations.

