Photosensitization
by Dr. Susana Encinas
Departamento de Química/Instituto de Tecnología Química UPV-CSIC, Universitat Politècnica de València, Camino de Vera s/n, 46022 Valencia, Spain.
Photosensitization is the process by which a photochemical or photophysical alteration occurs in one molecular entity as a result of initial absorption of radiation by another molecular entity called aphotosensitizer. In mechanistic photochemistry the term is limited to cases in which the photosensitizer is not consumed in the reaction.[1]
The photosensitization phenomenon can be applied to many fields such as that of photocatalysis where light is used to activate a substance, the photocatalyst, which modifies the rate of a chemical reaction without being involved itself in the chemical transformation.Within the numerous areas in which the concept of photosensitization can be applied, the contents here will be related to the biological subject. Thus, photosensitization is the process whereby a molecule activated by light is able to induce photoreactions in the biomolecules present in its environment (see Figure 1). The process is generally associated with the absorption of normal and harmless doses of light by a "strange" molecule (photosensitizer, PS) in non-harmful concentrations, reaching the absorbed energy to the constituents of tissues and cells. In the absence of this substance, the system is not affected by light provided that direct light absorption is not possible. In humans, the eyes and skin are the main receptors of light. In most cases, photosensitized reactions in the skin give rise to adverse side effects. In fact, the photosensitizing deoxyribonucleic acid (DNA) damage by xenobiotics has attracted considerable attention because it can involve a more extended active fraction of the solar spectrum with carcinogenic potential. In that way, the risk of biomolecules damage is considerably increased. However, photosensitization can also be used for therapeutic purposes, what is called photodynamic therapy (PDT).[2]
