# Assessment of DPPC Liposome Disruption by Embedded
## 1 Introduction  
\(\alpha\)-Tocopherol (Toc) is commonly regarded as a strong lipophilic antioxidant protecting phospholipid membrane in cells against destructive peroxidation. Toc also plays numerousnonantioxidant biological functions in cells [1; 2]. These effects are a result of specific interactions of \(\mathrm{Toc}\) with membranes, the main components of the cells [3]. These in turn depend on the type of phospholipids and the concentration of \(\mathrm{Toc}\)[4; 5]. For a small amount of \(\mathrm{Toc}<4\) mol%, no significant change is observed in the structure of the membrane [6]. Some reports show that \(\mathrm{Toc}\) influences the phase behaviour of phospholipids in a similar way as cholesterol [7]. Due to \(\mathrm{Toc}\) limitations in solubility and bioavailability, some looppherd derivatives containing the oxalate, malonate, and succinate moieties have been formulated based on their antioxidant properties, and it appeared they exhibit biological functions [8; 9]. The malonic acid ester of \(\mathrm{Toc}\), \(\alpha\)-tocopherol malonate (TM), belongs to \(\mathrm{Toc}\) derivatives that cause the apoptosis of cancer cells; such biomimetic actions of malonate have been recognized by [PERSON] [8; 9]. TM action is very close to that detected for \(\mathrm{Toc}\) succinate, which, in preclinical studies performed on animals, inhibited tumor growth (breast, bladder, prostate, and neck) [9; 10; 11; 12; 13]. Liposomes are spherical-shaped vesicles that are composed of one or more phospholipid bilayer, which closely resembles the structure of cell membranes. Thereby, they are an ideal model of a biological membrane used in the studies on the influence of biologically active molecules on its fluidity, stability, or permeability. Due to their amphiphilic properties and capacity to encapsulate hydrophilic drugs in the vesicle interior or lipophilic molecules inside of the bilayer, liposomes are also permitted to be used as drug-delivery systems [14; 15; 16]. Depending on the temperature, water content, and the type of lipid, lipid bilayers can exist in different lamellar forms, like crystal, gel, or the liquid-crystal phase. The structural transition between the two last forms occurs over a melting transition temperature (\(\mathrm{T_{m}}\)), leading to the changes in the membrane properties, like fluidity or permeability. An influence on the membrane transformation can also have different additives, which are incorporated inside the bilayer. A number of investigations have been completed with many different methods have been used to follow those transitions [17; 18], such as differential scanning calorimetry (DSC) [19], fluorescence, and anisotropy methods [8; 20; 21]. The parameters derived from DSC analysis include the onset temperature of the transition (\(\mathrm{T_{p}}\)), the peak maximum of the thermogram correlated to \(\mathrm{T_{m}}\), the width of the main peak at the half-peak height (\(\Delta\mathrm{T_{1/2}}\)), the enthalpy of transition (\(\Delta\mathrm{H_{m}}\)), and the cooperativity unit (CU) [22; 23]. [PERSON] showed that changes in DSC parameters can be applied to characterize interactions between the succinate moiety and phospholipids [24]. 1-anilino-8-naphtalene sulphonate (ANS) is a fluorescence probe commonly used to test the hydrophobicity of proteins [12; 25]. The fluorescence of ANS is very sensitive to the microenvironment and can report conformational changes in the polar head group region of phospholipids induced by ligands. Thus, ANS has also been applied in many studies of the structural changes in liposomes and membranes [26; 27; 28; 29; 30; 31; 32; 33]. Similarly, two other fluorescence probes, 1,6-diphenyl-1,3,5-hexatriene (DPH) and its trimethylammonium derivative (TMA-DPH), are used extensively to examine structural and dynamic properties of lipid bilayers. A steady-state fluorescence anisotropy of DPH indicates lipid order or the viscosity of the acyl chain bilayer interior, which is also called fluidity [34; 35; 36; 37].