## 1 Introduction  
The vanadium concentration in the Earth's crust is approximately 160 ppm. Due to its properties, it is an element with a wide range of applications in many industries. Vanadium steel is used, among others, in the manufacture of springs, cutting tools, and parts for the aircraft industry. Vanadium compounds are used as catalysts in many chemical processes [1; 2; 3; 4], e.g., in the production of sulphuric acid and the synthesis of phthalic and maleic anhydrides. They are extensively studied in polymerization reactions, including the coordination polymerization of ethylene and ethylene/1-olefin copolymerization, ring opening polymerization of lactones, and ring opening metathesis polymerization [5; 6; 7; 8]. Vanadium catalysts were applied for the synthesis of ethylene/propylene/diene copolymers (EPDM), which were commercialized as synthetic rubbers and ethylene/cyclic olefin copolymers known under the trade name \"APEL\", which were developed by Mitsui Chemicals, Inc. [6]. For many years, work has been carried out on the application of vanadium compounds in electrochemical processes [9; 10; 11; 12], e.g., for electrical energy storage. The importance of vanadium in highly advanced technologies and the number of vanadium products used in everyday life (e.g., batteries) are constantly increasing. Due to their specific chemical properties, vanadium and its compounds also have a strong effect on living organisms [13]. They inhibit cholesterol synthesis and affect glucose metabolism [14; 15], which gives hope for their therapeutic applications [16; 17; 18] and use in the treatment of diabetes in humans [19]. However, in addition to their desirable therapeutic effects, vanadium compounds also exhibit highly toxic characteristics [20], with destructive effects on living organisms. Vanadium poisoning can lead to disturbances in lipid synthesis, block the action of some enzymes by binding to -SH groups, and cause changes in the composition of proteins and nucleic acids in the blood. One of the effects of vanadium poisoning is a reduction in cysteine levels in the epidermis, dermis, nails, and hair. Contact of the respiratory tract with vanadium oxides can trigger inflammation of the mucous membranes,causing changes in alveolar macrophages and leading to a decrease in the body's immunity, which is an important factor in the light of the COVID-19 pandemic. On the other hand, the toxicity of vanadium compounds offers hope for their use in anticancer therapies [21; 22; 23; 24], involving the development of a new platinum-free preparation. The anticancer activity of vanadium results from its inhibitory effect on the growth of cancer cells [25; 26; 27; 28]. Animal studies indicate strong anti-cancer properties in colorectal malignancies [29; 30], soft tissue tumours (e.g., leiomyosarcoma), and the in vitro destruction of HeLa malignant tumour cells [31]. Vanadium is also an important micronutrient. It is present in trace amounts in the human body but affects the normal functioning of the body. Vanadium deficiency can increase the likelihood of atherosclerosis and diabetes, and stunt adolescent growth. The data shows that vanadium plays a significant role in both technology and living systems. Therefore, it seems that the effects of vanadium compounds on biological systems, and in particular the effects of organic compounds on the lipid bilayer acting as the structural core of all biological membranes, should be further investigated. Liposomes, which are relatively easy to produce in the laboratory, are a good model for the lipid bilayer of natural biological membranes. The production of liposomes often involves natural and synthetic lecithin [32; 33; 34]. The use of the electron paramagnetic resonance (EPR) technique with spin probes makes it possible to track the changes that occur in the membrane across its cross-section under the influence of various physical or chemical stimuli [35; 36; 37; 38].