56 SUN CARE


#1 Commercial Cosmetic TiO2


Hallstar EZ FLO Protected TiO2


Figure 4: DPPH solutions of different TiO2 samples after sun exposure.


and ZnO absorb UV light because of electrons hopping between the valance band and the conduction band. When excited by UV light, these metal particles become photosensitisers; they transfer their energy to oxygen and generate ROS. Such ROS can then decompose large organic molecules. For example, TiO2


particles


exposed to sunlight or UVR have been used in self-cleaning sprays for glass surfaces and to disinfect contaminated water by killing germs. Therefore, TiO2


particles used for


personal care must be carefully treated to minimise their photosensitivity. We discovered that current commercial treatments for cosmetic grade metal oxides were not thorough enough to eliminate their photosensitivity. Hallstar photostabilisers, on the other hand, can provide further protection to these mineral filters, eliminating photo-generated ROS.


#2 Commercial Cosmetic TiO2


AvoBriteTM


+ Commercial Cosmetic TiO2


Figure 5: DPPH solutions of a commercial TiO2 protection after being exposed to the sun.


To test the efficacy of Hallstar


photostabilisers, we used the DPPH assay to detect ROS. DPPH is the abbreviation for 2,2- diphenyl-1-picrylhydrazyl, a dark-coloured crystalline powder composed of stable free radicals. DPPH is commonly used to monitor chemical reactions involving radicals; most notably, it is a common antioxidant assay. This is because DPPH is both a radical and a trap (‘scavenger’) for other radicals. Due to its strong absorption band centred at about 520 nm, the DPPH radical has a deep violet colour in solution, and it becomes colourless or pale yellow after reacting with another radical or ROS. In other words, as more ROS are generated, more DPPH molecules are neutralised by the ROS, and the solution becomes more yellow than violet in colour. Therefore, the number of initial radicals generated can be counted from the change in the optical absorption at 520 nm.


Es


35000 30000 25000 20000 15000 10000 5000 0


200 0.05 O NC 275nm O 326 nm 0.04 O O RX-14401 0.02 0.01 0.00 250 300 350 λ (nm) 400 450 500 400 500 λ (nm) Figure 6:UV-visible absorption spectrum of a typical Micah compound, RX-14401 Figure 7: Luminescence spectrum of RX-14401. PERSONAL CARE EUROPE November 2018 600 23°C 0.03 C C 77k different TiO2


Commercial Cosmetic TiO2


with and without AvoBrite


Figure 5 displays DPPH solutions of three samples after 10 minutes of


natural sun exposure. Both commercial cosmetic TiO2


samples were obtained from


very reputable ingredient suppliers, and both generated enough free radicals derived from ROS that their DPPH solutions turned pale yellow. The Hallstar EZ-FLO TiO2


samples


were protected with Hallstar photostabilisers, and its DPPH solution remained deep violet, indicating no significant ROS/free radical generation. Hallstar photostabilisers effectively protected TiO2 generating ROS.


, preventing it from


In a subsequent experiment, we added Acrylates Copolymer to one of the commercial cosmetic TiO2


samples. After


sun exposure, we observed that the solutions with Acrylates Copolymer were darker in colour, indicating that Acrylates Copolymer can effectively protect the


~7.25 kcal/mol


Extinction coefficient (M-1 cm-1


)


Normalised intensity


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