*3.2. The E*ff*ect of Cinnamic Acid and Its Derivatives on the Size of the Phospholipid Liposomes*

The effect of the analyzed phenolic acids on the size of the phospholipid liposome systems is presented in Tables 1–3. The modification of liposome membranes with CinA, FA and p-CoA resulted in variations in the size of the examined systems. Notably, the diameter of the liposomes was also found to be influenced by the applied doses of the phenolic acids (1 and 5 mM/L). These changes are observed in both acidic (pH ~ 2) as well as alkaline (pH ~ 9) pH.


**Table 1.** Effect of cinnamic acid on the diameter of the liposomes at different pH.

**Table 2.** Effect of *p*-coumaric acid on the diameter of the liposomes at different pH.


**Table 3.** Effect of ferulic acid on the diameter of the liposomes at different pH.


Considering the data collected in Table 1, it can be observed that for plain DOPC liposomes as well as for DOPC liposomes treated with cinnamic acid, sizes of the liposomes increase along with increasing pH of the medium. The same tendency was observed for membranes treated with *p*-coumaric and ferulic acids (Tables 2 and 3). However, the opposite trend was noted for negatively charged liposomes (DOPC/PS 9:1, DOPC/PS 8:2, PS). Here, sizes of both plain and modified liposomes decreased together with increasing pH. In acidic pH, the diameter of phospholipid liposomes modified with cinnamic acid did not vary significantly from the diameter of liposomes modified with p-coumaric and ferulic acids. In alkaline pH, phospholipid liposomes treated with ferulic acid exhibited the largest sizes, whereas those treated with cinnamic acid were the smallest.

Figure 5 presents typical pH dependence of the diameter of the liposomes created with pure DOPC and DOPC modified with one of the analyzed phenolic acids, FA. Of note, in pH > 4, the sizes of plain DOPC liposomes and DOPC modified with ferulic acid increased with increasing pH of the medium, whereas in pH ~ 4 (isolectric point of the system), the diameter of analyzed liposomes was the lowest.

■ ■ **Figure 5.** Typical pH dependence of the diameter of the liposomes formed by DOPC ( PC (■) a ■ ) and DOPC modified with 5 mM/L ferulic acid ( ■ id (■). The ). The results represent mean values from three independent experiments run in triplicate.
