A hexanuclear titanium-oxo cluster with both photoprotection and antioxidant properties

Two hexanuclear titanium-oxo clusters, [Ti₆O₆(OⁱPr)₆L¹₆]·2CH₃CN (1) and [Ti₆O₄(OⁱPr)₁₀(OⁱPrL²)₂L²₂] (2), were synthesized via solvothermal reactions (HL¹ = o-nitrobenzoic acid and H₂L² = 1,3-bisbenzyl-2-oxoimidazolidine-4,5-dicarboxylic acid). Compound 1 is a cluster with an octahedral {Ti₆O₆} core, while compound 2 features as a cluster with chair-shaped {Ti₆O₄} core. Both the compounds show strong UV absorptions, but their activities to radicals including 2,2-diphenylpicrylhydrazyl (DPPH), hydroxyl, and azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) are significantly different. In contrast to the silence of all of the three radicals to compound 1, compound 2 is able to efficiently scavenge all of them. This obvious difference is attributed to that compound 2 shows higher reducibility, which is probably intrinsically related to electronic donating ligands L² and OⁱPrL². The coexistence of strong UV absorption and great antioxidant activity enables compound 2 to protect skin against photoaging and enhance skin health effectively. These results indicate titanium-oxo clusters bearing redox active ligands are potential for next-generation skincare products.