Photodecomposition and Phototoxicity of Natural Retinoids
Thermal and Photo Stability
Although RP [retinyl palmitate] is thermally more stable than retinol (6), both compounds are still thermally unstable. As shown in Figure 2, the experimental results from our laboratories indicated that 2% RP in an oil-in-water emulsion (cream) decomposed gradually at 4°C, with about 38% decomposed on day 7. Also, RP, as are retinoids in general, is chemically unstable and its chemical stability is highly dependent on environmental conditions such as solvent, temperature, and availability of oxygen (7). RP is easily thermally-isomerized to the 13-cis isomer. Thermal isomerization is favored in lipophilic solvents and emulsions containing high compositions of oils (7). Anhydroretinol is one of the major decomposition products of RP (8).
Photodecomposition and Phototoxicity of Natural Retinoids
Thermal and Photo Stability
Although RP [retinyl palmitate] is thermally more stable than retinol (6), both compounds are still thermally unstable. As shown in Figure 2, the experimental results from our laboratories indicated that 2% RP in an oil-in-water emulsion (cream) decomposed gradually at 4°C, with about 38% decomposed on day 7. Also, RP, as are retinoids in general, is chemically unstable and its chemical stability is highly dependent on environmental conditions such as solvent, temperature, and availability of oxygen (7). RP is easily thermally-isomerized to the 13-cis isomer. Thermal isomerization is favored in lipophilic solvents and emulsions containing high compositions of oils (7). Anhydroretinol is one of the major decomposition products of RP (8).
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