The effects of manganese doping on UVA absorption and free radical generation of micronised titanium dioxide and its consequences for the photostability of UVA absorbing organic sunscreen components

Abstract

The effect of manganese doping on the free radical generation rate, free radical scavenging and UVA absorption properties of micronised sunscreen grade titania has been studied with respect to enhancement of the UVA photostability of test sunscreen formulations containing the organic UVA absorber Parsol 1789. Manganese doping has been shown to increase the UVA:UVB absorption ratio of titania, reduce free radical generation rates by over 90%, and provide free radical scavenging behaviour. Adding manganese-doped titania to a test formulation incorporating Parsol 1789 shows that manganese doping increases UVA attenuation stability by up to 3 times the amount achieved by comparable commercial undoped titania materials. HPLC data shows this to be related to an improved stabilisation of the organic sunscreen components. Manganese doped titania shows improved efficacy over undoped titania in sunscreen formulations containing organic UV absorbers.

Nanosized and Nanoencapsulated Sunscreens

“…The wavelength of maximum absorption of the doped material is 385 nm, compared with 383 nm for the silica-alumina-coated material and 380 nm for the octylsilylated material. The UVA/UVB average absorption ratio is 1.05 for manganese-doped titania, 0.78 for octylsilylated and 0.87 for silica-alumina-coated titania [29]. Most dopants (Al, Mo, Fe, among others) significantly enhance the generation of active species and DNA damage.…”

Effects of undoped and manganese-doped zinc oxide nanoparticles on the colour fading of dyed polyester fabrics

“…The photoactivity of both titanium dioxide [19,20] and zinc oxide [10] has been decreased by doping with manganese. Dyed polyester fabrics were treated with acrylic polymer containing ZnO doped with 3 atomic % of manganese ions.…”

“…When a photoactive material, such as titanium dioxide or zinc oxide nanoparticles, is doped with a transition metal, the dopant ions can be located in the metal oxide lattice [20]. These ions are believed to reduce the photoactivity of nanoparticles by acting as trap centre sites for recombination of the electrons and positive holes produced by UV radiation, before they can migrate onto the particle surface and generate ROS.…”

A review of critical factors for assessing the dermal absorption of metal oxide nanoparticles from sunscreens applied to humans, and a research strategy to address current deficiencies

“…However, the relationship between photocatalytic and physical properties is complex (Chen and Mao 2007;Yin et al 2015). Activity also depends on, and can be controlled by, surface coatings (Carlotti et al 2009;Hong et al 2006) and dopants in the crystalline lattice (Casey et al 2006;Wakefield et al 2004). The free radicals produced by TiO 2 and ZnO nanoparticles in the presence of UV can damage DNA in cells in vitro (Dunford et al 1997;Tiano et al 2010;reviewed by Newman et al (2009) and Osmond and McCall (2010).…”