Difference between revisions of "Photostable Compounds"
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Departamento de Química/Instituto de Tecnología Química UPV-CSIC, Universitat Politècnica de València, Camino de Vera s/n, 46022 Valencia, Spain. | Departamento de Química/Instituto de Tecnología Química UPV-CSIC, Universitat Politècnica de València, Camino de Vera s/n, 46022 Valencia, Spain. | ||
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| + | Light can change the properties of different materials and products. This is often observed as bleaching of coloured compounds like paint and textiles. Photostability has for many years been a main concern within several fields of industry, e.g. the textile, paint, food, cosmetic and agricultural industries. In the field of pharmacy, the number of drugs found to be photochemically unstable is steadily increasing. In this context, the term photostability is used to describe how a compound responds to light exposure and includes not only degradation reactions but also other processes such as formation of radicals, energy transfer and luminescence. | ||
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| + | Each organism is a product of its response to the pressures of the environment, in order to establish a balance between the organism and its environment. This balance causes changes in the subject, which can be harmful or beneficial to their existence. Therefore, the possibility that several compounds in combination with sunlight may be beneficial or harmful to the patient should be considered. | ||
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| + | ==Photophysical and Photochemical Aspects of Photostability== | ||
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| + | The fact that a substance absorbs radiation in the ultraviolet or visible region of the electromagnetic spectrum means that it is absorbing energy that is sufficient to break a bond in the molecule. Thus the property of absorption is a first indication that the substance may be capable of participating in a photochemical process leading to its own decomposition. According to the Grotthus’ law of photochemistry, no photochemical (or subsequent photobiological) reaction can occur unless electromagnetic radiation is absorbed. The absorption spectrum of a compound is therefore an immediate way of determining the wavelength range to which the substance may be sensitive. | ||
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| + | There are two important factors to ponder in relation to the potential of a compound to be degraded following absorption of electromagnetic radiation. First, the absorption spectrum is normally described by the maximum absorption wavelength and the molar absorptivity at that wavelength, but the spectrum can be broad and any overlap of the absorption spectrum with the output of the photon source impinging upon it has the potential to lead to photochemical change. Second, the decomposition may be initiated by another close compound (for example, in a drug formulation) that has the absorption characteristics that overlap with the incident radiation while the main compound does not. This process is the photosensitization and the absorbing compound is the photosensitizer [1] (see Photosensitization entry). | ||
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| + | Photochemical damage to a substance is initiated by the absorption of energy by the compound itself of by a photosensitizer. Many photochemical reactions are complex, and may involve a series of competing reaction pathways in which oxygen may play a significant role. In fact, the great majority of photoreactions in biological systems involve the consumption of molecular oxygen and are photosensitized oxidation processes.[2] | ||
Revision as of 00:16, 11 December 2017
Under preparation 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.
Light can change the properties of different materials and products. This is often observed as bleaching of coloured compounds like paint and textiles. Photostability has for many years been a main concern within several fields of industry, e.g. the textile, paint, food, cosmetic and agricultural industries. In the field of pharmacy, the number of drugs found to be photochemically unstable is steadily increasing. In this context, the term photostability is used to describe how a compound responds to light exposure and includes not only degradation reactions but also other processes such as formation of radicals, energy transfer and luminescence.
Each organism is a product of its response to the pressures of the environment, in order to establish a balance between the organism and its environment. This balance causes changes in the subject, which can be harmful or beneficial to their existence. Therefore, the possibility that several compounds in combination with sunlight may be beneficial or harmful to the patient should be considered.
Photophysical and Photochemical Aspects of Photostability
The fact that a substance absorbs radiation in the ultraviolet or visible region of the electromagnetic spectrum means that it is absorbing energy that is sufficient to break a bond in the molecule. Thus the property of absorption is a first indication that the substance may be capable of participating in a photochemical process leading to its own decomposition. According to the Grotthus’ law of photochemistry, no photochemical (or subsequent photobiological) reaction can occur unless electromagnetic radiation is absorbed. The absorption spectrum of a compound is therefore an immediate way of determining the wavelength range to which the substance may be sensitive.
There are two important factors to ponder in relation to the potential of a compound to be degraded following absorption of electromagnetic radiation. First, the absorption spectrum is normally described by the maximum absorption wavelength and the molar absorptivity at that wavelength, but the spectrum can be broad and any overlap of the absorption spectrum with the output of the photon source impinging upon it has the potential to lead to photochemical change. Second, the decomposition may be initiated by another close compound (for example, in a drug formulation) that has the absorption characteristics that overlap with the incident radiation while the main compound does not. This process is the photosensitization and the absorbing compound is the photosensitizer [1] (see Photosensitization entry).
Photochemical damage to a substance is initiated by the absorption of energy by the compound itself of by a photosensitizer. Many photochemical reactions are complex, and may involve a series of competing reaction pathways in which oxygen may play a significant role. In fact, the great majority of photoreactions in biological systems involve the consumption of molecular oxygen and are photosensitized oxidation processes.[2]
